Preclinical advance in nanoliposome-mediated photothermal therapy in liver cancer

Abstract

Liver cancer is a highly lethal malignant tumor with a high incidence worldwide. Therefore, its treatment has long been a focus of medical research. Although traditional treatment methods such as surgery, radiotherapy, and chemotherapy have increased the survival rate of patients, their efficacy remains unsatisfactory owing to the nonspecific distribution of drugs, high toxicity, and drug resistance of tumor tissues. In recent years, the application of nanotechnology in the medical field has opened a new avenue for the treatment of liver cancer. Among these treatment methods, photothermal therapy (PTT) based on nanoliposomes has attracted wide attention owing to its unique targeting and high efficiency. This article reviews the latest preclinical research progress of nanoliposome-based PTT for liver cancer and its metastasis, discusses the preclinical challenges in this field, and proposes directions for improvement, with the aim of improving the effectiveness of liver cancer treatment.

Introduction

According to the Global Cancer Statistics Report for 2020, primary liver cancer is the sixth most common type of cancer and third leading cause of cancer-related mortality. Nearly 906,000 new diagnoses and 830,000 fatalities have been linked to primary liver cancer, with hepatocellular carcinoma (HCC) representing 75–85% of these cases [1]. HCC is aggressive in nature and primarily caused by chronic tissue damage [2]. HCC staging is particularly complex because of the various conditions associated with hepatic insufficiency. Common staging criteria include the Barcelona Clinic Liver cancer and Hong Kong Liver Cancer staging systems [3]. Surgery, locally destructive therapies, and liver transplantation have curative potential for patients with early-stage HCC; however, surgery is an invasive treatment that fails to eradicate minimal lesions. Even with surgery at an early stage, the 5-year survival rate is only 47–53% [4, 5]. Most patients with liver cancer are diagnosed at an advanced stage because the clinical manifestations of liver disease are not obvious [6,7,8]. Consequently, systemic therapy for advanced HCC has become a focal point in clinical research [9, 10]. Chemotherapy and radiotherapy can effectively eradicate tumors to some extent; however, these therapies have significant disadvantages including off-target effects, drug or radiation resistance, fatigue, discomfort, hair loss, digestive problems, limited specificity, inflammatory responses, and immune system damage [11, 12]. Thus, further research is necessary for identifying better treatment options for HCC.

Photothermal therapy (PTT) is an innovative method for treating tumors and is rooted in nanomedicine. Among the available treatment options, PTT has attracted considerable attention because of its minimal invasiveness and high selectivity [13, 14]. The basic principle of PTT involves transporting a photothermal agent (PTA) into the tumor tissue and converting light energy into heat using near-infrared (NIR) laser radiation. This process causes local heating in the tumor tissue and kills only the tumor cells [15]. The most commonly used wavelength of light for phototherapy is NIR, which is suitable for the PTT of tumors because of its strong penetration and minimal damage to normal tissues [16, 17]. Under NIR radiation, the PTA captures photon energy and undergoes a process of nonradiative decay known as vibrational relaxation. This process allows it to revert to its ground state via interactions with nearby molecules. The resulting increase in kinetic energy warms the surrounding microenvironment, exerting a thermal effect [18]. The intensity and duration of the temperature increase determine the degree of temperature-induced cellular damage, with different temperatures having different effects on tumor cells [19]. The traditional treatment temperature for PTT is higher than 50 °C [20,21,22,23], which allows the tumor to be rapidly ablated within minutes. However, an excessively high temperature can damage normal tissue surrounding the tumor and cause necrotizing inflammation through thermal diffusion [24]. Compared with conventional PTT, mild-temperature PTT (temperature ≤ 45 °C) can minimize damage to surrounding healthy tissues and the associated side effects [25,26,27]. In recent years, PTT has exhibited broad potential in preclinical studies on various cancers [28,29,30,31]. However, single PTT has drawbacks such as incomplete tumor suppression, which can lead to potential metastasis and recurrence [32,33,34,35]. Therefore, combining PTT with other therapies has attracted considerable research attention as an approach to address these shortcomings and achieve better therapeutic effects.

The use of nanomaterials in medicine has emerged as a significant area of interest among researchers owing to advances in nanotechnology. Nanomedicine-based drug delivery systems with enhanced permeation retention (EPR) can deliver drugs to tumor sites, enhancing their therapeutic effectiveness [36]. This type of drug delivery system focuses on targeted delivery and precise site-specific action and has become increasingly prevalent in nanomedicine [37]. Liposomes were identified as the first nanocarriers, exhibiting remarkable advantages such as targeted delivery, excellent biocompatibility, robust biodegradability, straightforward functionalization, minimal toxicity, and immunogenicity. These qualities significantly enhance the slow release and therapeutic efficacy of drugs [38, 39]. Further, liposomes have attracted considerable interest as potent drug delivery mechanisms because of their remarkable controllability and wide availability [40]. Artificial external stimulation such as PTT can promote drug release from liposomes [41]; thus, liposomes have considerable potential for the treatment of liver cancer [42,43,44]. However, the clinical translation of nanomedicine remains challenging because of the limitations of expensive and time-consuming clinical development [45], limitations of animal models for preclinical testing [46,47,48], uncertainty of nanotherapeutics, and evolving regulatory environment [49].

This review focuses on recent advances in the preclinical application of nanoliposome-mediated PTT in the treatment of liver cancer. By detailing the composition of liposomes and their synergistic mechanism with other therapies such as photodynamic therapy (PDT), immunotherapy and chemotherapy (Fig. 1), this paper not only reveals the key role of liposomes in enhancing the efficacy of PTT but also proposes practical improvement strategies to address the current clinical obstacles. It provides insightful prospects and future research directions for clinical translation.

Fig. 1

Synergistic treatment of PTT with PDT/ chemotherapy/immunotherapy

Structure of nanoliposomes

Liposomes consist of phospholipids, cholesterol, and various auxiliary lipids that function as a lipid vesicle delivery system [50]. Each phospholipid molecule has a hydrophilic head and hydrophobic tail. Cholesterol is the predominant sterol used in the formulation of liposomes because it can prevent the aggregation of liposomes and enhance the stability of their membranes by influencing the fluidity of these synthetic vesicles [51]. The frequently encountered lipid types include cationic, anionic, amphoteric, and polyethylene glycol (PEG)-derived lipids. Liposomes are categorized into small unilamellar vesicles, large unilamellar vesicles, multilamellar vesicles, and multivesicular vesicles according to the number of bilayer structures [52,53,54,55]. Small and large unilamellar vesicles exhibit a greater capacity for encapsulating hydrophilic compounds owing to their single- or double-layer structure and substantial internal aqueous phase, respectively. Multilamellar vesicles consist of several concentric lipid/phospholipid bilayers arranged in an onion-like fashion that can encapsulate lipophilic compounds; however, multi-vesicular vesicles are more suitable for encapsulation of a large amount of hydrophilic drugs owing to the presence of multiple eccentric vesicles, which are encapsulated in the outer bilayer of the single layer [52, 55,56,57]. Liposomes are round vesicles composed of a phospholipid bilayer that exhibit both hydrophilic and hydrophobic traits [58]. Lipophilic medications can be either contained within the phospholipid bilayer or attached to the surfaces of liposomes because of their amphiphilic nature. Hydrophilic drugs can be encased in the watery core of these vesicles, allowing the spontaneous formation of liposomes in an aqueous setting [59]. Liposomes deliver drugs to tumor tissues through two main targeting methods: passive and active targeting. The high vascular density of HCC leads to a significant EPR effect; therefore, passive targeting exploits this effect and tumor characteristics to enrich drugs for liver tumors [60, 61]. However, passive targeting has limitations such as uneven drug distribution in vivo and potential nonspecific uptake [62], which results in a substantial loss of the loaded drug before it reaches the tumor and undesirable side effects from high doses [63]. Compared with free-drug or passively targeted drug delivery systems, active targeting utilizes EPR effects and the specific targeting properties of ligands to facilitate the accumulation of drugs in diseased tissues, increasing the treatment efficiency and limiting side effects, while significantly increasing the amount of drug delivered to target cells and protecting the integrity of the bioactive compound [64, 65]. After drug accumulation at the tumor site, the affinity of the nanocarrier for the cancer-cell surface can be increased through active targeting, enhancing drug penetration and potency [66]. This can be achieved by binding the ligand-modified nanocarrier surface to receptors overexpressed on tumor cells. The phenomenon was initially proposed in 1980 when antibodies were grafted onto the surfaces of liposomes [67], followed by the introduction of various other ligands, including peptides, nucleic acids, and aptamers [68, 69].

The nanoscale version of liposomes is referred to as “nanoliposomes” [56, 70, 71]. Liposomes and nanoliposomes have analogous structures and lysogenicity; however, nanoliposomes possess a larger surface area because of the size reduction to the nanoscale, and their efficiency increases correspondingly [72, 73]. Nanoliposomes are ideal tools for treating HCC and have the advantages of easy preparation, high biocompatibility, and adjustable size. Further, they can respond to stimuli such as high temperature, pH, and ultrasound to release drugs into diseased tissues in a targeted manner [74, 75]. Developing a nanodrug delivery system that excels in both effective delivery and controlled release is crucial considering the current limitations of the delivery efficiency and targeting precision of PTAs and chemotherapeutic drugs. In recent years, scholars have not only loaded chemotherapeutic drugs and targeted drugs onto liposomes but also used liposomes in immunotherapy and programmed them to respond to PTT for achieving better therapeutic effects.

Liposome-loaded photothermal materials

Researchers have combined the use of materials that can absorb NIR light and generate heat in PTT, i.e., PTAs [76, 77], to enhance the depth, range, efficiency and tumor selectivity of PTT. PTAs can absorb NIR light and convert it into thermal energy with high efficiency [78, 79]. An ideal PTA should have low or no toxicity, good biocompatibility, and high efficiency in converting light to the NIR spectrum [80, 81]. Currently, research on PTAs is focused on nanomaterials, and it can be divided into inorganic and organic nano-PTAs [82]. A significant challenge in PTT lies in the systemic spread of PTAs throughout the body coupled with the uneven application of laser exposure, which can lead to considerable adverse effects on healthy tissues adjacent to the tumors [76]. Various nanocarriers have been designed for delivering PTAs to improve biocompatibility and stability, facilitate accumulation at the tumor site, and reduce damage to the surrounding normal tissues [83]. The smaller of these nanoparticles (NPs) can be passively targeted to tumor cells via the EPR effect. The active targeting of NPs can be achieved by binding surface ligands to specific receptors on the surface of tumor cells. Such strategies can realize the accurate delivery of PTAs to the tumor area and increase their accumulated concentration at the site [84, 85]. Among these strategies, the use of liposomes has received considerable attention [86,87,88].

Inorganic PTA

PTAs based on inorganic materials such as metal NPs, nanosheets, transition-metal oxides, carbon-based nanomaterials, and semiconductor materials have been widely developed in biomedicine [89,90,91,92]. These inorganic PTAs exhibit high photothermal conversion efficiency, good photothermal stability, and good inhibitory effects on cancer cells [93,94,95]. More importantly, they are easily surface-modified and can be combined with other functional groups, which can benefit targeted therapies [96, 97]. However, the effective application of inorganic PTAs in cancer therapy is limited by their high cost, non-degradability in vivo, and potential long-term toxicity [98,99,100]. In recent years, there has been growing interest in the use of noble metals and carbon-based nanomaterials for the treatment of HCC [101,102,103]. To reduce the toxicity of these inorganic materials and maintain their photothermal conversion efficiency, researchers have attempted to improve their biocompatibility and reduce their toxicity by changing the size and morphology of inorganic NPs or modifying or doping other metal or non-metal elements to synthesize inorganic NPs [104, 105].

Noble-metal nanomaterials

Recently, gold-based nanomaterials have attracted considerable attention as reagents for PTT [106,107,108]. The excellent interaction of gold nanoparticles (AuNPs) with light is attributed to the collective oscillation of conduction electrons on the metal surface when illuminated by light of a particular wavelength, which is referred to as localized surface plasmon resonance [109]. This results in the absorption and scattering intensities of AuNPs being significantly higher than those of non-isomeric exciton NPs of the same size, which are suitable for the diagnosis and PTT of malignant tumors [110,111,112]. The combination of gold with liposomes achieved a controllable localized surface plasmon resonance absorption peak, allowing synergistic photothermal and chemical therapies [113]. Chen et al. developed an all-in-one therapeutic nanoplatform for HCC (FTY720@AM/T7-TL) consisting of gold-manganese dioxide NPs (AM), hybrid liposomes (L), fingolimod (FTY720), tetraphenylethylene (T), and T7 peptides (T7) [114]. This hybrid liposome system (L) exhibited charge reversal, heat sensitivity, pH sensitivity, and tumor-targeting properties. Further, it releases therapeutic agents in response to both endogenous (pH) and exogenous (NIR) triggers, facilitating sustained and controlled release of drugs through a dual-stimulus response mechanism. AM NPs can catalyze H₂O₂ in tumor cells to produce O₂, enhancing the therapeutic effect of PDT. The high temperature generated by PTT further promoted the production of reactive oxygen species (ROS) and accelerates the release of FTY720. This chain reaction significantly enhances the synergistic effect of PTT, PDT and chemotherapy, delivering multiple therapeutic actions to the tumor. In addition, the MnO₂ nanosheet coating of AM NPs releases Mn²⁺ for T1-weighted magnetic resonance imaging. In vivo and in vitro studies indicated that FTY720@AM/T7-TL NPs can play a substantial antitumor role. This provides a new strategy for the diagnosis and treatment of HCC. In a separate investigation, Huang et al. [115] incorporated doxorubicin (DOX) and AM into self-assembled micelles derived from liposomes and subsequently embedded them in a thermosensitive hydrogel (F127) to create a novel hydrogel drug delivery system known as DAML/H. In this study, PTT and chemotherapy were combined with heat-sensitive hydrogels for the diagnosis and treatment of multidrug-resistant HCC. With a single injection into the tumor site and multiple NIR irradiation treatments, the local photothermal effect and sustained release of DOX worked together to kill the tumor cells. The prepared DAML/H can form an in-situ hydrogel when injected into the tumor site and can retain the PTT drug (Au) in the tumor for a long time. The system improves the therapeutic effectiveness of HCC, allowing real-time evaluation via magnetic resonance imaging, while combining chemotherapy and PTT for greater impact. DAML/H has considerable significance for the long-term, sustained-release and on-demand treatment of multidrug-resistant HCC. Qiu et al. [116] designed and fabricated ATO/PFH NP@Au-cRGDs as an innovative nanodrugdelivery platform (Fig. 2a). After centrifugation to obtain arsenic trioxide (ATO)/perfluorohexane (PFH) liposomes, AuNPs were deposited on the surfaces of liposomes to form gold nanoshells. The nanosystem exhibited good stability, with no significant changes in particle size or zeta potential after 7 d of storage in phosphate-buffered saline and serum (5%, pH 7.4) at 4, 25, and 37 °C (Fig. 2b-c). An Ultraviolet–visible spectroscopy revealed that ATO/PFH NPs@Au-cRGD has a unique plasma-coupled absorption peak at 760 nm, while formants at NIR wavelengths are not detected in uncoated liposomes (Fig. 2d). Although ATO offers significant benefits for the palliative management of unresectable primary liver cancer, its toxicity and rapid elimination from the kidney compromise its effectiveness for the treatment of liver cancer [117,118,119,120]. This platform combines cyclic arginylglycylaspartic acid peptide (cRGD) with AuNPs via gold–sulfur bonds to target HCC, NPs with cRGD-SH, and ultrasound-targeted microbubble destruction for reducing toxicity and achieving better targeted delivery of ATO and a nanoultrasound contrast agent (PFH). Compared with free drugs, contrast agents can more effectively achieve ultrasound imaging and ferroptosis via PTT treatment, stimulate systemic immune responses, and inhibit not only liver carcinoma in situ but also lung metastasis. This study provides a new approach for the treatment of HCC using nano-ultrasound contrast agents combined with immunotherapy and chemophotothermal therapy.

Fig. 2

Study on gold nanoshell-encapsulated liposomes for HCC treatment. (a) Schematic of ATO/PFH NPs@Au-cRGD. (b, c) Assessment of the storage stability of ATO/PFH NPs@Au-cRGD. (d) UV–vis spectra for liposome NPs and liposome NPs@Au. The data are presented as mean ± standard deviation. Reproduced from Ref [116]. with permission from Wiley, Copyright 2023

In addition to gold-based nanomaterials, the application of precious-metal nanomaterials such as platinum [121], silver [122], and palladium [123] in the diagnosis and PTT of HCC recently received increasing attention.

Carbon-based nanomaterials

Carbon-based materials have the potential to be highly biocompatible and biodegradable, and graphene-based nanomaterials have broad prospects for PTT because of their exceptional ability to absorb light in the NIR spectrum [124]. Researchers have explored the integration of carbon-based nanomaterials with liposomes to enhance the effectiveness of PTT for HCC. For example, Liu et al. [125] recently employed a reverse-phase evaporation technique to encapsulate graphene quantum dots within liposomes under controlled pressure. The controlled release system has excellent water stability and photothermal treatment properties. Triggered by NIR, it not only leads to the decomposition of the liposome structure but also allows the controlled release of graphene quantum dots, which leads to good PTT performance. This lays a foundation for the manufacture of ultra-small NP-loaded liposomes. In addition, Li et al. [126] studied and prepared a thermosensitive hydrogel containing liposomes loaded with elemene (ELE) and glycyrrhetinic acid (GA)/nano graphene oxide (NGO), which is called ELE-GA/NGO-Lip-gel. Owing to its two-dimensional structure and high photothermal conversion efficiency [127, 128], NGO is used as both a drug carrier and a PTA. The thermosensitive hydrogel has the advantages of a suitable gelling temperature, high embedding rate and drug loading rate, good photothermal conversion efficiency, and time-dependent photothermal conversion characteristics. The liposome-loaded hydrogel system employs liposomes as drug reservoirs and uses the extra diffusion resistance of the hydrogel to prolong drug release, suppress side effects, increase the local drug delivery concentration, and improve drug efficacy [129,130,131]. In this study, the in vitro antitumor activity assay indicated that the new thermosensitive hydrogel had relatively high antitumor efficiency against SMMC-7721 human liver cancer cells under 808 nm laser irradiation. This study provides a promising platform for the application of heat-sensitive hydrogels in cancer therapy. Shehab et al. [132] recently conducted an innovative study in which they successfully embedded a two-dimensional titanium carbide (Ti₃C₂T_x) MXene nanosheet in a zeolite imidazolate frames-8 (ZIF-8) structure, followed by loading the cancer drug sorafenib (SB) onto the MX-ZIF-8 composite. To further improve the performance of the system, researchers modified the lipid bilayer of liposomes to create SB-MX-ZIF-8@LPs nanocomposites. This system holds promise for improving HepG2 cancer cell therapy by combining controlled drug release with enhanced sensitivity to therapeutic approaches. The composite aims to optimize the treatment strategy of HepG2 cancer cells by integrating the precise drug delivery mechanism and enhancing the sensitivity of cancer cells to treatment methods. The introduction of liposomes not only significantly improves the stability and bioavailability of SB, but also realizes the regulation of the drug release process. The combination of SB-MX-ZIF-8 with liposomes, namely SB-MX-ZIF-8@LPs nanocomposites, greatly expands the application range of this system and provides a more accurate targeting and combination therapy strategy for in vivo studies. The results of in vitro experiments showed that the SB-MX-ZIF-8@LPs nanocomposite exhibited excellent tumor cell ablation ability, with a total cell apoptosis rate of up to 95.7%, and minimal impact on normal cells. In vivo results further verified the biocompatibility of SB-MX-ZIF-8@LPs, which was able to significantly reduce cancer volume and maintain body weight stability with minimal toxicity to healthy tissues. Molecular docking analysis revealed that although ZIF-8 showed some interaction with some cancer-related proteins, this did not weaken the strong binding affinity of SB for key targets such as EGFR. In addition, the ADMET (absorption, distribution, metabolism, excretion, and toxicity) analysis also confirmed that MX-ZIF-8@LPs exhibited excellent performance as a drug delivery vehicle, including a high intestinal absorption rate of 96.6% and low toxicity, which further supports its great potential as an efficient drug delivery system in the field of cancer therapy.

Organic PTA

PTAs based on organic materials have broad prospects for the application of PTT to cancer because of their good biocompatibility, biodegradability, and biosafety [133]. Many organic PTAs have been studied, including organic NIR dyes [134], porphyrin liposomes [135, 136], and high-molecular-weight polymers [137]. The use of only PTAs is hampered by limitations such as poor solubility and stability, rapid clearance in vivo, nonspecific distribution in vivo, and limited accumulation at tumor sites. These limitations prevent the application of PTAs in cancer therapy [138, 139]. To solve these problems, NPs such as liposomes have been used to encapsulate materials for the delivery of PTAs [140,141,142,143]. Table 1 presents the liposome-based NIR dyes used in recent HCC treatments.

Table 1 Summary of liposomes based near-infrared dyes for the treatment of HCC in recent years

Indocyanine green (ICG) exhibits high photothermal conversion efficiency when exposed to laser light and has been clinically approved by the U.S. Food and Drug Administration (FDA) for use in NIR fluorescent dyes since 1959 [144, 145]. However, it has shortcomings such as a lack of targeting and poor stability. Researchers have attempted to encapsulate ICG in NPs to overcome these defects, and liposomes have attracted considerable attention as suitable NPs [146]. Studies have indicated that encapsulating ICG in liposomes can improve its stability and prolong its systemic circulation half-life [147,148,149]. Liposome-encapsulated ICG (Lipo-ICG) not only maintains the metabolic pathway of ICG but also has potential for clinical applications [150]. It can passively target tumor regions by enhancing the EPR effect, promoting the accumulation of ICG at tumor sites [151].

Sun et al. [152] designed a drug delivery platform called HepM-TSL for recurrent liver cancer to improve the targeting and stability of drug delivery. HepM-TSL was constructed using an HCC cell membrane as a thermosensitive liposome (TSL) vesicle; therefore, it had a homologous targeting ability. The TSL loaded with PTA (ICG) could effectively convert NIR laser light into heat. When laser irradiation induces TSL decomposition, the encapsulated DOX and ICG can escape from the immune system and be accurately controlled and released in the tumor area, realizing the synergistic treatment of PTT and chemotherapy. This study confirmed that the cumulative DOX release reached > 80% after 6 h at 43 °C, which was significantly higher than that of the control group at 37 °C. This treatment excels in targeting tumors while minimizing adverse effects on the body compared with traditional free drugs [153]. Zhao et al. [154] prepared a phototherapy diagnostic nanoplatform (ICG-ARS@NPs) using liposomes as a carrier to encapsulate ICG and ARS. They found that artesunate (ARS), because of its high bioavailability and hydrophilicity, can trigger the production of ROS when slightly heated in water. Therefore, ICG can exert a photothermal effect after irradiation with an NIR laser, providing a heat source to activate ARS for producing ROS. Once this pH-sensitive liposome nanosystem is in the weakly acidic tumor microenvironment, drugs are released from the liposomes, and the ROS generated by ARS can act on and destroy cancer cells and tumor tissue. This mechanism improves the specificity of tumor targeting and reduces the incidence of side effects. Experiments indicated that ICG-ARS@NPs had an efficient anticancer therapeutic effect in H22 tumor-bearing mice. In another study, Tang et al. [155] designed and fabricated a TSL-based nanocomposite H-TiO₂@PDA@ICG@NPe6@Lipo for HCC treatment. The composite uses H-TiO₂ photocatalysis with a special structure and lattice as the initial nanocrystalline. Polydopamine (PDA), as an NIR absorbent material, has a wide absorption range [156]. After modification with PDA, the absorption range of H-TiO₂ in the NIR region can be expanded, and the photothermal conversion efficiency can be increased. Then, nanoliposomes with heat-sensitive properties can be used as the second carrier to coat H-TiO₂@PDA@ICG@NPe6. The TSL coating used endows the multifunctional material with tumor thermal guidance and controlled release properties. It can prolong the circulation time of the drug in the body and use local heating to stimulate the coating of the drug, so that the drug is released in large quantities at the tumor site [157]. In vivo photothermal and antitumor experiments confirmed that the material can generate large amounts of heat and ROS, leading to apoptosis and tumor-growth restriction. This study provides new ideas for the combination of organic and inorganic materials.

Compared with ICG, the ICG derivative IR780 has better fluorescence intensity and photostability and higher photothermal conversion efficiency [158, 159]. Pluronics F-127 (PF127) has considerable potential for improving the stability of liposomes and reducing their clearance rates in vivo [160]. Therefore, Peng et al. [161] increased the photothermal conversion efficiency and bolstered drug resistance in HCC chemotherapy by developing a PF127-modified TSL where IR-780 and SB were co-loaded into the lipid bilayer to imbue the TSL with photoresponsiveness to NIR irradiation. Since IR-780 has a good photothermal conversion under NIR irradiation, an increase in the internal temperature of the tumor where TSL is located may cause TSL to undergo phase transitions to trigger drug release. Therefore, local application of NIR laser irradiation can trigger rapid release of SB and DOX in tumor tissues, which enables synergistic anti-tumor therapy of DOX and SB to significantly improve anti-cancer outcomes. The cell and animal experiments in this study indicated that PF127-modified TSL co-delivers DOX, SB, and IR-780, exhibiting considerable potential for overcoming chemotherapy resistance in HCC therapy.

However, there are limitations with regard to penetration depth and maximum allowable exposure power density in the first NIR region (660–808 nm, NIR-I). Further, the laser exhibits strong absorption properties and limited tissue penetration, which are not effective for PTT in deep or large tumors [163, 164]. Studies have indicated that the second NIR range (1000–1700 nm, NIR-II) has high-resolution imaging capabilities in deep tissues because of reduced tissue scattering, absorption, and autofluorescence [165,166,167,168]. NIR-II imaging has higher sensitivity for detecting minor tumors and a higher energy security threshold [169,170,171]. Therefore, the early diagnosis of liver tumors and more accurate surgical resection of liver tumors can be achieved via NIR-II imaging [172, 173]. IR1061 exhibited considerable absorbance in the NIR-II range (1064 nm), along with a low fluorescence quantum yield. Compared with the 808-nm laser, the 1064-nm laser has better cell ablation in vitro and a better anticancer ability for deep tissues in vivo [174, 175]. However, its hydrophobic nature poses challenges for its clinical use [176, 177]. To overcome these limitations, Chen et al. [178] developed an innovative lipid NP using IR1061 by incorporating the dye into liposomes modified with DSPE-PEG2000. In vivo experimental studies indicated that this new NP noninvasively and precisely diagnoses HCC while facilitating complete surgical removal of the tumor. Further, the PTT assay indicated an excellent cancer cell-killing ability and light stability. These novel NPs provide new insights into polymethyl dyes, offering novel approaches for the early detection and management of HCC.

The cyano dye cypate is another type of ICG derivative. Several studies have demonstrated the potential of cyanine dye-loaded liposomes for tumor diagnosis and targeted therapy [178, 179]. Wang et al. [180] prepared CYP-supported liposomes (Lipo-Cy) for cancer treatment. Owing to the hydrophobic interaction between the lipid bilayer membrane and cypate, cypate molecules are confined to the hydrophobic layer of the liposome; thus, the embedding efficiency of Lipo-Cy can reach 98.1%. This not only enhances the stability of cypate, but also significantly improves its photothermal conversion efficiency, ROS generation ability, and antitumor efficiency. Moreover, Lipo-Cy effectively enters cancer cells in a dose-dependent manner through an energy-dependent pathway, with good tumor accumulation and no dark cell toxicity. At the same time, it produced significant ROS under 785 nm irradiation and hyperthermia, resulting in strong phototoxicity and cancer-cell death. Experiments have indicated that compared with free cypate, Lipo-Cy has better biosafety and stability and a better tumor-targeting ability, giving it broad prospects. In 2023, Li et al. [181] also prepared Cy-lipid to increase the mRNA delivery efficiency by stimulating photothermal accelerated endosomal escape delivery strategy. In an acidic endosomal microenvironment, Cy-lipid is protonated and activates the absorption of IR-II, achieving light-to-heat conversion through 1064-nm laser irradiation. This thermal effect promotes the morphological change of lipid NPs, triggering the rapid escape of lipid NPs from the endosome and enhancing the translation ability of mRNA by a factor of approximately 3 compared with the group without NIR-II light irradiation. The results indicate that the liver is the major organ for the accumulation of lipid NPs in NIR-II, which provides a strategy for improving the photothermal efficiency and the efficiency of delivering therapeutic mRNA drugs, while also paving the way for innovative approaches in the treatment of HCC.

Liu et al. [182] used the second-generation photosensitizer (PS) phthalocyanine (Pc) as the PTA for PTT, integrated ZnPc and DOX for the first time, and designed and prepared a multidrug combined antitumor therapy multifunctional liposome RGD-CuPc: ZnPc(TAP): DOX@LiPOs (RCZDL). This tumor-targeting liposome can encapsulate PTAs in the lipid layer and activate its photoactivity by capturing the quenching drug using intracellular biomolecules. RDZDL exhibited remarkable stability, effective tumor targeting, impressive photothermal properties, and a photocontrolled release mechanism, which allows the synergistic combination of PDT, PTT, and chemotherapy. In vitro experiments indicate that RCZDL may induce apoptosis by interfering with mitochondrial function. In vivo experiments indicate that RCZDL has a good tumor-targeting ability and increases antitumor efficiency. Moreover, very little RCZDL accumulates in the liver, and most of it is rapidly metabolized, reducing the risk of liver toxicity linked to the prolonged retention of Pc.

Synergistic therapy of PTT mediated by nanoliposome

Photothermal/photodynamic synergistic therapy

PTT combined with PDT has been the most important phototherapy method in antitumor research in recent years and has been widely studied [183,184,185,186]. PDT offers several benefits over conventional therapies, including faster recovery, reduced side effects, and a less invasive approach [187]. The cytotoxic ROS produced by PDT relies on PSs to convert light energy into useful forms for surrounding molecules under light exposure [188]. However, this leads to severe hypoxia in the tissue, in which sufficient singlet oxygen is produced to kill tumor cells or destroy the vascular system [189, 190]. PTT is prone to tumor recurrence because of the uneven heat distribution and rapid dissipation. The limited light penetration and low-oxygen environment that occurs when the two therapies are used alone is the reason for the incomplete elimination of the tumor [191, 192]. Therefore, developing a photothermal/photodynamic combination therapy is necessary for overcoming the limitations of the two monotherapies [193, 194].

Lei et al. [195] proposed a groundbreaking approach to leverage the glycolytic inhibitor lonidamine (LND) for improving the photothermal and photodynamic therapies of IR780 cells. Liposomes, because of their minimal toxicity and immunogenic response, were used to encapsulate LND and IR780 (Fig. 3a). In this study, IR780 was utilized as both a PTA and PS to generate ROS and induce a temperature increase under 808-nm laser irradiation. Oxygen is essential for PDT, and the inhibition of glycolysis can lead to increased intracellular oxygen accumulation by reducing oxygen consumption. LND disrupts energy production and hampers glycolysis by selectively attacking hexokinase II, which is a crucial enzyme located in the mitochondria that initiates the glycolytic process. An oxygen consumption rate (OCR) assay kit was used to assess the OCR of LM3 cells under various treatment conditions. As shown in Fig. 3b, incubation with Lip-LND reduced the OCR of LM3 cells, suggesting that LND can significantly inhibit glycolysis, potentially alleviate tumor hypoxia, and improve the therapeutic effect of PDT. Glutathione (GSH) functions as a reducing agent and depletes ROS during PDT. However, this study demonstrated that GSH levels were unaffected by Lip-IR780. Conversely, intracellular GSH levels were significantly reduced after incubation of LM3 cells with Lip-LND or Lip-IR780/LND (Fig. 3c). These results suggest that LND reduces the intracellular GSH levels, which is beneficial for PDT in cancer treatment. DCFH-DA was used as a probe to detect ROS production for investigating the influence of LND on the photodynamic effects of IR780. Interestingly, the cells treated with Lip-IR780/LND exhibited stronger green fluorescence than those treated with Lip-IR780 alone after different treatments (Fig. 3d). This suggests that LND increases intracellular ROS production, implying that it amplifies the photodynamic efficacy of IR780. During PTT for tumor treatment, heat shock proteins (HSPs) play a crucial role as initiators of heat-activated defense responses induced by tumors. As shown in Fig. 3e, incubation with Lip-LND or Lip-IR780/LND significantly reduced HSP90 expression, indicating that LND effectively inhibited HSP90 expression and increased the thermal sensitivity of tumor cells. The potential of LND as a therapeutic agent for phototherapy was explored using a CCK-8 assay. The results indicated that subjecting LM3 cells to Lip-IR780/LND under exposure to 808-nm laser light significantly reduced cancer-cell viability (to ~ 20%) and had robust antitumor effects (Fig. 3f). Furthermore, live/dead staining revealed that nearly all the LM3 cells had died after treatment (Fig. 3g), confirming the ability of LND to enhance the therapeutic outcomes of IR780-induced PTT and PDT. This study further confirmed the diverse effects of LND in decreasing oxygen consumption, lowering intracellular GSH levels, and suppressing the expression of HSPs, as demonstrated through in vivo studies. The antitumor efficacy of Lip-IR780/LND when exposed to laser irradiation in vivo was assessed by monitoring the alterations in tumor size following injection into nude mice implanted with LM3 tumors. Monitoring the tumor volume indicated that only Lip-LND was ineffective in suppressing tumor growth. Laser-irradiated Lip-IR780 inhibited tumor growth to some extent; however, treatment with Lip-IR780/LN combined with laser irradiation yielded the best therapeutic outcomes (Fig. 3h).

Fig. 3

A new study of photothermal/photodynamic synergy therapy for HCC. (a) Lip-IR780/LND co-loaded liposomes were prepared by thin-film hydration method. (b) The inhibition of intracellular oxygen consumptionin in LM3 cells treated with different concentrations of Lip-IR780 or Lip-LND. (c) The intracellular GSH concentrations in LM3 cells after treatment with PBS, Lip-IR780, Lip-LND, and Lip-IR780/LND. (d) The ROS production detected by DCFH-DA in LM3 cells. The cells were treated with PBS, Lip-IR780, Lip-LND + L, and Lip-IR780/LND + L. Scale bar: 100 μm. (n = 5). (e) With PBS, laser Lip - IR780 (Lip - IR780 + L), Lip LND and laser Lip - IR780 / LND (Lip - IR780 / LND + L) receiving LM3 cell, Intracellular HSP90 levels were determined by Western blot. (f) Relative viability of LM3 cells treated with Lip-IR780, Lip-LND, Lip-IR780 + L, and Lip-IR780/LND + L. (g) The cytotoxicity of different treatments (PBS, PBS + L, Lip-IR780, Lip-LND, Lip-IR780 + L and Lip-IR780/LND + L) on LM3 cells in vitro was measured by live/dead double staining. Lip - IR780 and Lip - LND concentrations were 7.5 µg mL^− 1 and 15 µg mL^− 1. Scale bar: 100 μm. (n = 5). (h) Different groups during treatment LM3 tumor-burdened mice tumor growth curve. Data were represented as means ± SD. p < 0.05, p < 0.01, p < 0.001******. Reproduced from ref [195]. with permission from Creative Commons, copyright 2023

In another study, Yu et al. [196] designed photoactivated liposomes combined with PS chlorine e6 (Ce6) and the chemotherapeutic drug triptolide (TP) to overcome the drawbacks of TP for treating HCC, such as its low solubility in vivo, high toxicity, and fast clearance. This not only stops the progression of HCC but also suppresses the toxic effects of TP and is a new potential treatment option for HCC. Zeng et al. used hybrid tumor cell membranes and TSLs as oxygen carriers combined with PS Ce6, PFH, and the IR-II dye IR1048 to establish a bionic oxygen delivery system referred to as BLICP@O₂ [197]. This system exhibited excellent photothermal and photodynamic effects and enhanced the efficacy of PDT by alleviating tumor hypoxia. Liposomes have good biocompatibility and are excellent carriers of PS.

Photothermal/immune synergistic therapy

Immunotherapy has been incorporated into the fourth pillar of clinical cancer treatment [198]. Immunotherapy for cancer treatment includes immune checkpoint inhibitors (ICIs), cancer vaccines, lymphocyte activating factors, lysosomal viruses and bispecific antibodies, and induction of immunogenic cell death [199]. It has led to major advances in the treatment of HCC and provides promising strategies for patients with advanced HCC [200,201,202]. However, immunotherapy still has limited response rates, unpredictable clinical efficacy, and potential side effects, such as autoimmune reactions or cytokine release syndrome [203]. Studies have indicated that PTT can trigger immune responses by activating immune cells, promoting the release of exosomes (EXOs) from tumor cells and upregulating the expression of inflammatory cytokines and HSPs [204, 205]. This mechanism can induce apoptosis or necrosis of tumor cells, releasing tumor-associated antigens that can be taken up and presented by antigen-presenting cells and then activate the immune system to produce anticancer responses [206]. When PTT is combined with immunotherapy, the two can complement each other to improve the therapeutic efficacy of primary and metastatic tumor cells. This approach not only enhances antitumor immunity but also achieves better efficacy in a shorter time than either treatment alone and reduces the amount of invasive damage to the body during the treatment [207].

Yang et al. [208] designed and established phenylboronic acid (PBA) group-modified polydopamine (PBA-PDA) as a photothermal material and an active targeted delivery carrier loaded with the immunostimulants CpG-ODN and DOX. DOX induces the release of associated antigens from tumor cells while exerting a direct cytotoxic effect on the tumor. CpG-ODN is a synthetic DNA molecule that can stimulate tumor-specific CD8 + T cell immunity and the Th1 cell immune response [209]. Further, it significantly enhances the immunogenicity of tumor cell lysate vaccines [210, 211]. PBA binds to sialic acid residues on tumor cells, allowing effective enrichment and deep penetration into tumors and thereby improving uptake by cancer cells [212, 213]. Concurrently, the specific interaction between PBA and lysosomal membrane proteins facilitates the escape of encapsulated drugs from lysosomes. This mechanism ultimately enables the formation of an in situ tumor vaccine comprising tumor antigens generated through PTT combined with chemotherapy alongside the adjuvant CpG-ODN [214, 215]. The present study demonstrates that loading DOX and CpG-ODNs onto PBA-PDA carriers mitigates systemic toxicity associated with free drug administration and holds promise for clinical applications. This system combines PTT, chemotherapy, and immunotherapy to treat HCC, rapidly killing cancer cells while stimulating strong antitumor immune memory effects and preventing tumor recurrence. More recently, Xie et al. [216] developed a novel “integrated” and controllable system, i.e., CD105/CD3 Nb-LipoICG, by integrating NIR laser-induced PTT and specific Nbs target-binding capabilities into the Lipo platform (Fig. 4a). The platform exhibited an excellent ability to target tumor and T cells, as well as low ICG leakage, good stability, and low toxicity. In an in vivo experiment, five groups of different materials were injected into Bel7404 tumor-bearing mice, which were euthanized within 12 h to collect major organs. The CD105/CD3 Nb-LipoICG treatment group had the highest fluorescence intensity in tumor tissues among all treatments, indicating the good tumor-targeting and EPR effects (Fig. 4b-c). To explore the influence of CD105/CD3 Nb-LipoICG on the antitumor effect of T cells, an experiment was designed in which CD105/CD3 Nb-LipoICG was combined with human T cells to treat tumors (Fig. 4d). The results indicated that in Bel7404 tumor-bearing mouse models, treatment of CD105/CD3 Nb-LipoICG with T cells or NIR significantly inhibited tumor growth and extended survival compared with the control group. CD105/CD3 Nb-LipoICG, T cell, and NIR laser irradiation even almost completely suppressed tumor growth (Fig. 4e) and prolonged survival in mice (Fig. 4f). In this study, CD105/CD3 Nb-LipoICG provided photothermal effects and dynamic visibility through ICG, while engaging T cells and tumor cells through dual Nbs specificity and stability, achieving synergistic PTT and immunotherapy. In addition, tumor progression can be monitored through in situ visualization, which provides a new option for T-cell immunotherapy to treat solid tumors in clinical practice.

Fig. 4

A novel study of photothermal/ immune synergistic therapy. (a) Synthesis and design of CD105/CD3 Nb-LipoICG. (b) Anatomy and imaging of major organs and subcutaneous tumors 12 h after injection of the specified material. (c) Fluorescence intensity of major organs and subcutaneous tumors in each group. (d) Schematic diagram of in vivo mouse tumor modeling and therapeutic trials. (e) The growth curve of NON/SCID mouse Bel7404 xenograft tumor was plotted based on periodic measurements of tumor volume. (f) The survival rate of Bel7404 tumor-bearing mice was analyzed using Kaplan-Meier method, expressed as the average percentage of surviving mice in each group. Data were represented as means ± SD. *** P < 0.001, **** P < 0.0001

Photothermal/ chemotherapy synergistic therapy

Long-term use of chemotherapy drugs can induce multidrug resistance phenomenon in tumor cells, which is a key factor leading to chemotherapy failure, and involves the complex defense mechanism of tumor cells against chemotherapy drugs [217]. Although PTT can completely kill the primary tumor but cannot eradicate metastatic tumor cells, whereas chemotherapy can improve the effectiveness of anticancer drugs, killing both primary and metastatic tumor cells [218]. In addition to generating heat for tumor ablation, PTT accelerates the release of chemotherapy drugs from delivery platforms [219]. Therefore, the synergy between PTT and chemotherapy has attracted increasing attention and is widely used in the treatment of HCC [220,221,222,223].

Glypican-3 (GPC3) is a 60-kDa protein located on the cell surface and a member of the phosphatidylinositol proteoglycan family. Numerous reports have indicated high GPC3 expression in various tumors—particularly in HCC [224,225,226]. Therefore, in recent years, GPC3 has been considered an important therapeutic target for HCC [227], and its immune reactivity in HCC cells has been widely studied [228, 229]. Mu et al. [230] developed a GPC3-specific targeted therapy diagnostic NP that modified liposomes (GSI-Lip) with the GPC3-targeting peptide G12, co-loaded with SB and IR780 iodide, to facilitate early detection and precise chemo-photothermal treatment of HCC. Compared with FA-modified liposomes, they have better antitumor effects and promote the specificity and sensitivity of the early diagnosis of HCC.

Huang et al. [231] recently designed GPC3-EXOs in combination with IR780 and Lenvartinib (IL@GPC3-EXOs) as a drug delivery system for the combined treatment of HCC. As lipid membrane nanostructures, EXO are natural liposomes and ideal carriers for the delivery of various drugs or biomaterials in vitro and in vivo [232]. In their experiment, the GPC3 scFv antibody was genetically engineered onto the surfaces of the EXOs, followed by ultracentrifugation (Fig. 5a). This allowed the EXO to target GPC3-positive tumors, including HCC. The CCK-8 assay indicated that IL@GPC4-EXOs + NIR had potent tumor suppressor activity (Fig. 5b), which was confirmed by the clone formation assay (Fig. 5c). Furthermore, both wound-healing and transwell assays illustrated that IL@GPC3-EXOs combined with NIR significantly inhibited the migration and invasion of cancer cells (Fig. 5d). The tumor-growth curves after various treatments in the in vivo experiments revealed that the combined treatment had a stronger inhibitory effect on tumor growth than heating or chemotherapy alone (Fig. 5e). Experimental observations confirmed that the combination treatment significantly prolonged the survival of mice (Fig. 5f). In this study, the GPC3 scFv antibody, which was modified for display on the surface of EXOs, exhibited enhanced targeting of HCC both in vitro and in vivo. As an innovative nanodelivery system for PTT, it allows a single administration, offering a novel approach for the combined treatment of HCC.

Fig. 5

A novel study of exosome-based photothermal/chemical synergistic therapy. (a) Schematic representation of the separation of GPC3 engineered EXOs. (b) The viability of cells after different treatments. (c) Assay of colony formation of HCC cells after various treatments. (d) Cell migration and invasion after different treatments. (e) The tumour growth curves after different treatments. (f) The survival rates of mice in various groups. **p < 0.01. Reproduced from ref [231]. with permission from National Institutes of Health, copyright 2023

In addition, targeting YTHDF2 has the potential to suppress cancer and enhance the effectiveness of anticancer treatments [233, 234]. Wen et al. [235] found that YTHDF2 expression is enhanced in HCC by initiating the acetylation of trimethylated histone H3 at lysine 4 and lysine 27. They effectively curtailed the growth and spread of HCC using liposomes designed to target YTHDF2. In another study, Zhao et al. [236] developed a novel DOX delivery agent (HCSP4/Lipo-DOX/miR125a-5p) for the targeted chemotherapy of HCC. This advancement opens new avenues for both treatment approaches and drug development in the context of HCC resistant to conventional therapies. Zhang et al. [237] developed an innovative multifunctional drug delivery system utilizing MnAs and human serum albumin (HSA) called MnAs/ICG/HSA-RGD. This was a pioneering effort to integrate chemotherapeutic and photothermal therapies with single-albumin nanomedicine for the treatment of HCC. In experiments, treatment with MnAs/ICG/HSA-RGD effectively suppressed the levels of HSP90, vimentin, and MMP-9 in tumor cells. This suggests that MnAs/ICG/HSA-RGD is effective for curtailing tumor growth, recurrence, and metastasis in living organisms. Further, its remarkable therapeutic efficacy, coupled with minimal side effects, serves as a catalyst for advancing innovative treatments for HCC.

Numerous studies have indicated a connection between high cholesterol levels and the development of several types of cancer—particularly those impacting the liver, breast, prostate, and colon [238,239,240,241]. In addition, cholesterol is easily oxidized, leading to the production of impurities that affect the safety and quality of liposomes. Zhang et al. [242] designed a novel thermosensitive multifunctional liposome system consisting of temoxaponin AIII (TAIII) and lipids. IIn this system, TAIII has a structure similar to that of cholesterol, and it simultaneously acts as a membrane stabilizer and chemotherapeutic agent. This not only solves the problem of easy oxidation of cholesterol in conventional liposomes but also enhances DOX uptake by HCC cells. The innovative use of TAIII holds significant promise for developing a more stable and multifunctional liposome delivery system for the combined treatment of HCC.

Chemotherapy also has considerable immunotherapeutic effects, which can help the immune eliminate cancer cells and establish durable tumoricidal immunity via mechanisms distinct from immunotherapy [243]. Some chemotherapeutic agents can induce the release of relevant antigens from tumor cells while directly killing tumors, but chemotherapy alone can only produce weak immune effects [244, 245]. As a rapid tumor-killing method, PTT can induce tumor cells to produce tumor-associated antigens, increasing the efficiency of chemotherapy-induced immune responses [20, 246,247,248]. Recently, Yang et al. [249] proposed a novel approach to improve the therapeutic effect of HCC by combining multiple immune escape with antiangiogenic therapy to achieve optimal ICIs treatment. To this end, they designed and prepared a triple combination photothermal-boosted nanoBike composed of black phosphorus tandem-augmented anti-PD-L1 mAb and SB, which were then loaded onto liposomes. Black phosphorus, as the most promising two-dimensional layered inorganic material, has a high photothermal conversion efficiency, good biocompatibility, and a high drug loading efficiency [250,251,252]. In this study, black phosphorus was used both as self-delivering drug nanocellulators for embedding SB and anti-PD-L1 mAb and as a PTA. PTT can both kill tumor cells and remodel the extracellular matrix by reducing collagen I expression, thereby promoting the deep penetration of immune cells [253]. Furthermore, PTT induces ICD to strongly trigger antitumor immune responses required to rebalance the tumor immunosuppressive microenvironment. This nanoBike can kill tumor cells while inhibiting tumor angiogenesis and effectively eliminate immune escape, thus providing good conditions for immunotherapy. Significant tumor-growth inhibition was observed in both subcutaneous and orthotopic HCC models. This provides a promising avenue for combining chemotherapy with PTT and immunotherapy, along with insights for the treatment of other types of cancer.

Conclusions and future directions

The unique circular structure of liposomes results in excellent drug-loading efficiency, biocompatibility, stability in biological environments, and controllable release kinetics [254]. Thus, liposomes are superior to many other carriers with regard to pharmacokinetics and the biological distribution of therapeutic drugs [255]. Since Doxil was approved by the FDA for clinical use in 1995 as a liposomal formulation of anticancer drugs [256], more than a dozen liposomal drug delivery systems have been approved for clinical use [257]. Many liposome drugs, such as liposome irinotecan, have entered clinical trials in combination therapy for pancreatic cancer, esophageal cancer, small cell lung cancer, and other cancers [258,259,260]. For example, Cui et al. [261] recently conducted a randomized Phase III trial (NCT05074589) to evaluate the efficacy and safety of liposome irinotecan HR070803 in combination with 5-fluorouracil and leucovorin in a population of patients with unresectable, locally advanced, or metastatic pancreatic ductal adenocarcinoma who had previously received gemcitabine-based therapy. This study is indeed a milestone as the first Phase III clinical trial of pancreatic cancer to include the entire Chinese population and obtain expected positive results. Given the development of nanotechnology, liposomes have become the main delivery mechanism for the diagnosis and treatment of various diseases and have considerable potential for targeting, diagnosis, and therapeutic diagnosis [262, 263]. As effective carriers, liposomes can deliver drugs to the tumor site with reduced toxicity to healthy tissues. Sensing elements in liposomes can control the release of the therapeutic payload in response to stimuli such as light, temperature, and ultrasound, destabilizing the liposomes and leading to controlled release of liposome-encapsulated drugs [264]. Among the stimuli, light is particularly attractive for on-demand drug delivery owing to its advantages of easy application, noninvasiveness, and fine spatiotemporal control [265]. Drug release can be adjusted by changing the intensity, wavelength, and duration of light, which is conducive to meeting different therapeutic needs. PTAs absorb NIR energy at specific wavelengths and convert it into thermal energy by nonradiative decay, rapidly increasing the local temperature of the tumor to a threshold lethal to its cells [266]. As a highly effective, noninvasive therapy with low toxicity and minimal side effects, PTT is promising for the treatment of cancer [267, 268]. Excellent tissue penetration depth and ideal PTAs are important factors affecting its efficacy [269]. In recent years, in order to improve the effectiveness of PTT, studies on ultra-deep PTT strategies, PTAs with excellent performance, and PTT combined with other therapies have been performed, which has further developed the clinical transformation of PTT [81, 270,271,272,273,274].

Nevertheless, despite its promising potential, there are numerous challenges that need to be addressed in order to fully harness the clinical benefits of nanoliposome-mediated PTT. First, liposomes with long circulation times may cause drug leakage in unexpected places. The common chemotherapeutic drug PEGylated liposomal DOX can cause hand-foot syndrome [275]. These toxic effects can be addressed via strategies to change the schedule and dose of therapeutic agents [275]. Additionally, the cytotoxicity of liposomes should be considered; cationic lipids can cause cellular changes such as cell shrinkage, reduced mitosis, and cytoplasmic vacuolization [276]. Therefore, to mitigate the lipid toxicity problem, the lipid components used in clinically approved preparations should be preferentially selected for the preparation of liposomes in practical applications. In addition, the stability, targeting, and controllability of drug release from nanoliposomes in vivo require further optimization. The size, composition, and surface modification of liposomes affect their stability, which is important for ensuring the stability of the transport process and is an important factor influencing the therapeutic effect. Liposomes are modified by targeting substances so that they can transport the substances more precisely. However, the efficacy of targeted therapy using nanocarriers may be compromised by the emergence of drug resistance mechanisms and tumor heterogeneity. The combination of nanocarrier-based therapies with other forms of treatment or the development of strategies to address drug resistance may help overcome this limitation [277, 278]. It should be mentioned that the potential biotoxicity and immune rejection of PTA are significant problems. For example, despite their excellent photothermal conversion ability, it has been shown that complexes of carbon nanotubes frequently accumulate in the liver and kidneys, and when introduced into the abdominal cavities of mice, they exhibit carcinogenic potential similar to that of asbestos [279, 280]. In contrast, liposomes have good biocompatibility and biodegradability [281]. Therefore, many researchers have focused on the application of inorganic photothermal materials combined with liposomes, as it has been observed that liposomes can overcome the disadvantages of inorganic photothermal materials [282,283,284]. Hence, strategies such as accurate assessment of their in vivo biotoxicity, encapsulation with biocompatible nanocapsules, or surface coating with PEG are needed to enhance biocompatibility and reduce cytotoxicity while maintaining good photothermal conversion ability before liposomes can be used as PTAs. It should not be ignored that although PTT has been shown to be effective in the treatment of HCC in preclinical mouse models, the follow-up of metastasis and recurrence in HCC models is an important issue that needs attention. In addition, subcutaneous implantation is generally used for tumors in mouse models, but since liver tumors are located in the deep abdominal cavity of humans, there are challenges in the clinical translation of PTT for the treatment of liver cancer considering the limited tissue penetration depth.

In addition to these PTT synergistic therapies, PTT synergistic gene therapy, PTT synergistic gas therapy and other synergistic therapies are also very promising in the treatment of liver cancer. Phototherapy can quickly remove primary tumor tissue, while gene therapy can effectively remove residual metastatic tumor cells, and the synergistic combination of the two can achieve rapid and thorough cancer treatment [285]. Studies have indicated that coupling gene therapy with mild PTT is an excellent option for inhibiting heat resistance and minimizing side effects to improve overall treatment outcomes [286,287,288]. However, owing to the inevitably strong cell-membrane repulsion of negatively charged gene molecules and their inherent vulnerability to nuclease degradation, efficient delivery vectors are needed to compensate for the limitations of free gene molecules and allow them to successfully complete their tasks in the cell [289, 290]. Scholars have proposed that nano liposomes are considered to be the most effective non-viral nucleic acid (DNA/RNA) delivery platform at present [291, 292]. Gas therapy was found to be a good adjunct to other treatment shortcomings [293, 294]. It has been reported that small gaseous molecules such as CO and NO can effectively inhibit HSP70 in tumor cells [295]. Therefore, if a small-molecule gas can be produced while PTAs exert their PTT effect, HSPs can be synchronously regulated, and the PTT effect can be enhanced [296].

Future research should focus on developing more stable, efficient, and well-targeted nanoliposome carriers; studying PTAs with better photothermal effects, biocompatibility, tumor tissue specific accumulation abilities, and safety; exploring the combined application strategy of PTT and other therapeutic methods; constructing some in situ models closer to the clinical stage; conducting larger, multicenter clinical trials to verify their efficacy and safety; and assessing the acute and long-term toxicity in the body.