Irradiated microparticles suppress prostate cancer by tumor microenvironment reprogramming and ferroptosis.

Immunogenic cell death (ICD) plays a crucial role in triggering the antitumor immune response in the tumor microenvironment (TME). Recently, considerable attention has been dedicated to ferroptosis, a type of ICD that is induced by intracellular iron and has been demonstrated to change the immune desert status of the TME. However, among cancers that are characterized by an immune desert, such as prostate cancer, strategies for inducing high levels of ferroptosis remain limited. Radiated tumor cell-derived microparticles (RMPs) are radiotherapy mimetics that have been shown to activate the cGAS-STING pathway, induce tumor cell ferroptosis, and inhibit M2 macrophage polarization. RMPs can also act as carriers of agents with biocompatibility. In the present study, we designed a therapeutic system wherein the ferroptosis inducer RSL-3 was loaded into RMPs, which were tested in in vitro and in vivo prostate carcinoma models established using RM-1 cells. The apoptosis inducer CT20 peptide (CT20p) was also added to the RMPs to aggravate ferroptosis. Our results showed that RSL-3- and CT20p-loaded RMPs (RC@RMPs) led to ferroptosis and apoptosis of RM-1 cells. Moreover, CT20p had a synergistic effect on ferroptosis by promoting reactive oxygen species (ROS) production, lipid hydroperoxide production, and mitochondrial instability. RC@RMPs elevated dendritic cell (DC) expression of MHCII, CD80, and CD86 and facilitated M1 macrophage polarization. In a subcutaneously transplanted RM-1 tumor model in mice, RC@RMPs inhibited tumor growth and prolonged survival time via DC activation, macrophage reprogramming, enhancement of CD8+ T cell infiltration, and proinflammatory cytokine production in the tumor. Moreover, combination treatment with anti-PD-1 improved RM-1 tumor inhibition. This study provides a strategy for the synergistic enhancement of ferroptosis for prostate cancer immunotherapies.

A broadly applicable protein-polymer adjuvant system for antiviral vaccines.

Although protein subunit vaccines generally have acceptable safety profiles with precise antigenic content, limited immunogenicity can lead to unsatisfactory humoral and cellular immunity and the need for vaccine adjuvants and delivery system. Herein, we assess a vaccine adjuvant system comprising Quillaja Saponaria-21(QS-21) and cobalt porphyrin polymeric micelles that enabling the display of His-tagged antigen on its surface. The nanoscale micelles promote antigen uptake and dendritic cell activation to induce robust cytotoxic T lymphocyte response and germinal center formation. Using the recombinant protein antigens from influenza A and rabies virus, the micelle adjuvant system elicited robust antiviral responses and protected mice from lethal challenge. In addition, this system could be combined with other antigens to induce high titers of neutralizing antibodies in models of three highly pathogenic viral pathogens: Ebola virus, Marburg virus, and Nipah virus. Collectively, our results demonstrate this polymeric micelle adjuvant system can be used as a potent nanoplatform for developing antiviral vaccine countermeasures that promote humoral and cellular immunity.

Applications of Intravital Imaging in Cancer Immunotherapy.

Currently, immunotherapy is one of the most effective treatment strategies for cancer. However, the efficacy of any specific anti-tumor immunotherapy can vary based on the dynamic characteristics of immune cells, such as their rate of migration and cell-to-cell interactions. Therefore, understanding the dynamics among cells involved in the immune response can inform the optimization and improvement of existing immunotherapy strategies. In vivo imaging technologies use optical microscopy techniques to visualize the movement and behavior of cells in vivo, including cells involved in the immune response, thereby showing great potential for application in the field of cancer immunotherapy. In this review, we briefly introduce the technical aspects required for in vivo imaging, such as fluorescent protein labeling, the construction of transgenic mice, and various window chamber models. Then, we discuss the elucidation of new phenomena and mechanisms relating to tumor immunotherapy that has been made possible by the application of in vivo imaging technology. Specifically, in vivo imaging has supported the characterization of the movement of T cells during immune checkpoint inhibitor therapy and the kinetic analysis of dendritic cell migration in tumor vaccine therapy. Finally, we provide a perspective on the challenges and future research directions for the use of in vivo imaging technology in cancer immunotherapy.

Irradiated engineered tumor cell-derived microparticles remodel the tumor immune microenvironment and enhance antitumor immunity.

Radiotherapy (RT), administered to roughly half of all cancer patients, occupies a crucial role in the landscape of cancer treatment. However, expanding the clinical indications of RT remains challenging. Inspired by the radiation-induced bystander effect (RIBE), we used the mediators of RIBE to mimic RT. Specifically, we discovered that irradiated tumor cell-released microparticles (RT-MPs) mediated the RIBE and had immune activation effects. To further boost the immune activation effect of RT-MPs to achieve cancer remission, even in advanced stages, we engineered RT-MPs with different cytokine and chemokine combinations by modifying their production method. After comparing the therapeutic effect of the engineered RT-MPs in vitro and in vivo, we demonstrated that tIL-15/tCCL19-RT-MPs effectively activated antitumor immune responses, significantly prolonged the survival of mice with malignant pleural effusion (MPE), and even achieved complete cancer remission. When tIL-15/tCCL19-RT-MPs were combined with PD-1 monoclonal antibody (mAb), a cure rate of up to 60% was achieved. This combination therapy relied on the activation of CD8+ T cells and macrophages, resulting in the inhibition of tumor growth and the establishment of immunological memory against tumor cells. Hence, our research may provide an alternative and promising strategy for cancers that are not amenable to conventional RT.

Engineering irradiated tumor-derived microparticles as personalized vaccines to enhance anti-tumor immunity.

The inadequate activation of antigen-presenting cells, the entanglement of T cells, and the highly immunosuppressive conditions in the tumor microenvironment (TME) are important factors that limit the effectiveness of cancer vaccines. Studies show that a personalized and broad antigen repertoire fully activates anti-tumor immunity and that inhibiting the function of transforming growth factor (TGF)-ß facilitates T cell migration. In our study, we introduce a vaccine strategy by engineering irradiated tumor cell-derived microparticles (RT-MPs), which have both personalized and broad antigen repertoire, to induce comprehensive anti-tumor effects. Encouraged by the proinflammatory effects of the spike protein from the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the high affinity between TGF-ß receptor 2 (TGFBR2) and TGF-ß, we develop RT-MPs with the SARS-CoV-2 spike protein and TGFBR2. This spike protein and high TGFBR2 expression induce the innate immune response and ameliorate the immunosuppressive TME, thereby promoting T cell activation and infiltration and ultimately inhibiting tumor growth. Our study provides a strategy for producing an effective personalized anti-tumor vaccine.

HSF1 protects cells from cadmium toxicity by governing proteome integrity.

BACKGROUND: Cadmium toxicity has been associated with disruption of protein homeostasis by interfering with protein folding processes. Heat shock factor 1 (HSF1) coordinates the rapid and extensive cellular response to maintain proteomic balance facing the challenges from many environmental stressors. Thus, we suspect that HSF1 may shield cells from cadmium toxicity by conserving proteome integrity. RESULTS: Here, we demonstrate that cadmium, a highly poisonous metal, induces aggregation of cytosolic proteins in human cells, which disrupts protein homeostasis and activates HSF1. Cadmium exposure increases HSF1's phosphorylation, nuclear translocation and DNA bindings. Aside from this, HSF1 goes through liquid-liquid phase separation to form small nuclear condensates upon cadmium exposure. A specific regulatory domain of HSF1 is critical for HSF1's phase separation capability. Most importantly, human cells with impaired HSF1 are sensitized to cadmium, however, cells with overexpressed HSF1 are protected from cadmium toxicity. Overexpression of HSF1 in human cells reduces protein aggregates, amyloid fibrils and DNA damages to antagonize cadmium toxicity. CONCLUSIONS: HSF1 protects cells from cadmium toxicity by governing the integrity of both proteome and genome. Similar mechanisms may enable HSF1 to alleviate cellular toxicity caused by other heavy metals. HSF1's role in cadmium exposure may provide important insights into the toxic effects of heavy metals on human cells and body organs, allowing us to better manage heavy metal poisoning.

The tumour-promoting role of protein homeostasis: Implications for cancer immunotherapy.

Protein homeostasis, an important aspect of cellular fitness that encompasses the balance of production, folding and degradation of proteins, has been linked to several diseases of the human body. Multiple interconnected pathways coordinate to maintain protein homeostasis within the cell. Recently, the role of the protein homeostasis network in tumorigenesis and tumour progression has gradually come to light. Here, we summarize the involvement of the most prominent components of the protein quality control mechanisms (HSR, UPS, autophagy, UPR and ERAD) in tumour development and cancer immunity. In addition, evidence for protein quality control mechanisms and targeted drugs is outlined, and attempts to combine these drugs with cancer immunotherapy are discussed. Altogether, combination therapy represents a promising direction for future investigations, and this exciting insight will be further illuminated by the development of drugs that can reach a balance between the benefits and hazards associated with protein homeostasis interference.

The roles of inflammasomes in cancer.

Inflammation is a key characteristic of all stages of tumor development, including tumor initiation, progression, malignant transformation, invasion, and metastasis. Inflammasomes are an important component of the inflammatory response and an indispensable part of the innate immune system. Inflammasomes regulate the nature of infiltrating immune cells by signaling the secretion of different cytokines and chemokines, thus regulating the anti-tumor immunity of the body. Inflammasome expression patterns vary across different tumor types and stages, playing different roles during tumor progression. The complex diversity of the inflammasomes is determined by both internal and external factors relating to tumor establishment and progression. Therefore, elucidating the specific effects of different inflammasomes in anti-tumor immunity is critical for promoting the discovery of inflammasome-targeting drugs. This review focuses on the structure, activation pathway, and identification methods of the NLRP3, NLRC4, NLRP1 and AIM2 inflammasomes. Herein, we also explore the role of inflammasomes in different cancers and their complex regulatory mechanisms, and discuss current and future directions for targeting inflammasomes in cancer therapy. A detailed knowledge of inflammasome function and regulation may lead to novel therapies that target the activation of inflammasomes as well as the discovery of new drug targets.

Ferroptosis-Enhanced Immunotherapy with an Injectable Dextran-Chitosan Hydrogel for the Treatment of Malignant Ascites in Hepatocellular Carcinoma.

Malignant ascites in advanced hepatocellular carcinoma (HCC) is a complex clinical problem that lacks effective treatments. Due to the insensitivity of advanced HCC cells to traditional chemotherapies, low drug accumulation, and limited drug residence time in the peritoneal cavity, the therapeutic effects of malignant ascites in HCC are not satisfactory. In this study, an injectable hydrogel drug delivery system based on chitosan hydrochloride and oxidized dextran (CH-OD) is designed to load sulfasalazine (SSZ), an FDA-approved drug with ferroptosis-inducing ability, for effective tumor-killing and activation of anti-tumor immunity. Compared to free SSZ, SSZ-loaded CH-OD (CH-OD-SSZ) hydrogel exhibits greater cytotoxicity and induces higher levels of immunogenic ferroptosis. In the preclinical model of hepatoma ascites, intraperitoneal administration of CH-OD-SSZ hydrogel can significantly suppress tumor progression and improve the immune landscape. Both in vitro and in vivo, CH-OD-SSZ hydrogel induces the repolarization of macrophages to an M1-like phenotype and promotes the maturation and activation of dendritic cells. Combination treatment with CH-OD-SSZ hydrogel and anti-programmed cell death protein 1 (PD-1) immunotherapy achieves more than 50% ascites regression and generates long-term immune memory. Collectively, CH-OD-SSZ hydrogel exhibits promising therapeutic potential in the treatment of peritoneal dissemination and malignant ascites in advanced HCC, especially when combined with anti-PD-1 immunotherapy.

Sustained release of tumor cell lysate and CpG from an injectable, cytotoxic hydrogel for melanoma immunotherapy.

Many basic research studies have shown the potential of autologous cancer vaccines in the treatment of melanoma. However, some clinical trials showed that simplex whole tumor cell vaccines can only elicit weak CD8+ T cell-mediated antitumor responses which were not enough for effective tumor elimination. So efficient cancer vaccine delivery strategies with improved immunogenicity are needed. Herein, we described a novel hybrid vaccine "MCL" (Melittin-RADA32-CpG-Lysate) which was composed of melittin, RADA32, CpG and tumor lysate. In this hybrid vaccine, antitumor peptide melittin and self-assembling fusion peptide RADA32 were assembled to form the hydrogel framework melittin-RADA32(MR). Then, whole tumor cell lysate and immune adjuvant CpG-ODN were loaded into MR to develop an injectable and cytotoxic hydrogel MCL. MCL showed excellent ability for sustained drug release, to activate dendritic cells and directly kill melanoma cells in vitro. In vivo, MCL not only exerted direct antitumor activity, but also had robust immune initiation effects including the activation of dendritic cells in draining lymph nodes and the infiltration of cytotoxic T lymphocytes (CTLs) in tumor microenvironment. In addition, MCL can efficiently inhibit melanoma growth in B16-F10 tumor bearing mice, which suggested that MCL is a potential cancer vaccine strategy for melanoma treatment.

Cupric-ion-promoted fabrication of oxygen-replenishing nanotherapeutics for synergistic chemo and photodynamic therapy against tumor hypoxia.

Mixing a glutathione (GSH)-responsive carboxy zinc(II) phthalocyanine (ZnPc*) and CuSO4·5H2O in water with or without the presence of the anticancer drug SN38 resulted in the formation of self-assembled nanotherapeutics labeled as ZnPc*/Cu/SN38@NP and ZnPc*/Cu@NP, respectively. The Cu2+ ions not only promoted the self-assembly of the carboxy phthalocyanine through metal complexation, but also catalyzed the transformation of H2O2 to oxygen via a catalase-like reaction, rendering an oxygen-replenishing property to the nanosystems. Both nanosystems exhibited high stability in aqueous media, but the nanoparticles disassembled gradually in an acidic or GSH-enriched environment and inside human colorectal adenocarcinoma HT29 cells, releasing the encapsulated therapeutic components. The disassembly process together with the activation by the intracellular GSH led to relaxation of the intrinsic quenching of the nanophotosensitizers and restoration of the photoactivities of ZnPc*. Under a hypoxic condition, ZnPc*/Cu/SN38@NP could attenuate the intracellular hypoxia level and maintain the photodynamic activity due to its Cu2+-promoted oxygen-replenishing ability. The photodynamic effect of ZnPc* and the anticancer effect of SN38 worked cooperatively, causing substantial apoptotic cell death. The dual therapeutic actions could also effectively inhibit the tumor growth in HT29 tumor-bearing nude mice without initiating notable adverse effects to the mice. STATEMENT OF SIGNIFICANCE: The oxygen-dependent nature of photodynamic therapy generally reduces its efficacy against tumor hypoxia, which is a common characteristic of advanced solid tumors and usually leads to resistance toward various anticancer therapies. We report herein a facile approach to assemble a glutathione-responsive carboxy phthalocyanine-based photosensitizer and an anticancer drug in aqueous media, in which Cu(II) ions were used to promote the self-assembly through metal complexation and catalyze the conversion of H2O2 to oxygen through a catalase-like reaction, making the resulting nanoparticles possessing an oxygen-replenishing property that could promote the photodynamic effect against hypoxic cancer cells and tumors. The use of Cu(II) ions to achieve the aforementioned dual functions in the fabrication of advanced nano-photosensitizing systems has not been reported.

Engineered Microparticles for Treatment of Murine Brain Metastasis by Reprograming Tumor Microenvironment and Inhibiting MAPK Pathway.

Brain metastases (BRM) are common in advanced lung cancer. However, their treatment is challenging due to the blood-brain barrier (BBB) and the immunosuppressive tumor microenvironment (ITME). Microparticles (MPs), a type of extracellular vesicle, can serve as biocompatible drug delivery vehicles that can be further modulated with genetic engineering techniques. MPs prepared from cells induced with different insults are compared and it is found that radiation-treated cell-released microparticles (RMPs) achieve optimal targeting and macrophage activation. The enzyme ubiquitin-specific protease 7 (USP7), which simultaneously regulates tumor growth and reprograms M2 macrophages (M2Φ), is found to be expressed in BRM. Engineered RMPs are then constructed that comprise: 1) the RMP carrier that targets and reprograms M2Φ; 2) a genetically expressed SR-B1-targeting peptide for improved BBB permeability; and 3) a USP7 inhibitor to kill tumor cells and reprogram M2Φ. These RMPs successfully cross the BBB and target M2Φ in vitro and in vivo in mice, effectively reprogramming M2Φ and improving survival in a murine BRM model. Therapeutic effects are further augmented when combined with immune checkpoint blockade. This study provides proof-of-concept for the use of genetically engineered MPs for the treatment of BRM.

Hierarchical Supramolecular Self-Assembly: Fabrication and Visualization of Multiblock Microstructures.

Due to the fast dynamics and re-equilibration of supramolecular self-assembly, bottom-up molecular strategies to fabricate well-defined and controllable multiblock structures are rare. Herein, we propose a new concept for fabrication of fluorescent multiblock microcolumns containing 1 to 7 blocks via hierarchical supramolecular self-assembly based on cucurbit[8]uril (CB[8]), NaBr and an AIEgen guest. Through the complexation between CB[8] and different numbers of AIEgen guests (2, 1, 0), the competitive displacement caused by the binding of the sodium cation to the CB[8] portal, and the reversible assembly of positively charged guests in salt solutions, one-pot hierarchical supramolecular self-assembly is realized. The molecular structure of each block is analyzed by single-crystal X-ray diffraction. The AIEgen enables the self-assembly of multiblocks to be visualized, understood, and regulated.

Ionizing Radiation-Induced Tumor Cell-Derived Microparticles Prevent Lung Metastasis by Remodeling the Pulmonary Immune Microenvironment.

PURPOSE: The majority of cancer-related deaths are attributed to metastasis rather than localized primary tumor progression. However, the factors that regulate the premetastatic niche (PMN) and metastasis have not yet been clearly elucidated. We investigated the antimetastatic effects of irradiated tumor cell-derived microparticles (RT-MPs) and highlighted the role of innate immune cells in PMN formation. METHODS AND MATERIALS: Mice were treated 3 times with isolated RT-MPs, followed by tumor cell injection via the tail vein. The hematoxylin and eosin staining was performed to assess the number of tumor nodules in the lungs, and in vivo luciferase-based noninvasive bioluminescence imaging was conducted to detected tumor burden. The mechanisms of RT-MPs mediated PMN formation was evaluated using flow cytometry, transwell assay, and reverse transcription-polymerase chain reaction. RESULTS: RT-MPs inhibited tumor cell colonization in the lungs. Neutrophils phagocytosed RT-MPs and secreted CCL3 and CCL4, which induced monocytes chemotaxis and maturation into macrophages. RT-MPs promoted the transition of neutrophils and macrophages into antitumor phenotypes, hence inhibiting cancer cell colonization and proliferation. CONCLUSIONS: RT-MPs inhibited PMN formation and lung metastasis in a neutrophil- and macrophage-dependent but T cell-independent manner.

Self-adjuvanting cancer nanovaccines.

Nanovaccines, a new generation of vaccines that use nanoparticles as carriers and/or adjuvants, have been widely used in the prevention and treatment of various diseases, including cancer. Nanovaccines have sparked considerable interest in cancer therapy due to a variety of advantages, including improved access to lymph nodes (LN), optimal packing and presentation of antigens, and induction of a persistent anti-tumor immune response. As a delivery system for cancer vaccines, various types of nanoparticles have been designed to facilitate the delivery of antigens and adjuvants to lymphoid organs and antigen-presenting cells (APCs). Particularly, some types of nanoparticles are able to confer an immune-enhancing capability and can themselves be utilized for adjuvant-like effect for vaccines, suggesting a direction for a better use of nanomaterials and the optimization of cancer vaccines. However, this role of nanoparticles in vaccines has not been well studied. To further elucidate the role of self-adjuvanting nanovaccines in cancer therapy, we review the mechanisms of antitumor vaccine adjuvants with respect to nanovaccines with self-adjuvanting properties, including enhancing cross-presentation, targeting signaling pathways, biomimicking of the natural invasion process of pathogens, and further unknown mechanisms. We surveyed self-adjuvanting cancer nanovaccines in clinical research and discussed their advantages and challenges. In this review, we classified self-adjuvanting cancer nanovaccines according to the underlying immunomodulatory mechanism, which may provide mechanistic insights into the design of nanovaccines in the future.

Microparticles: biogenesis, characteristics and intervention therapy for cancers in preclinical and clinical research.

Extracellular vesicles (EVs), spherical biological vesicles, mainly contain nucleic acids, proteins, lipids and metabolites for biological information transfer between cells. Microparticles (MPs), a subtype of EVs, directly emerge from plasma membranes, and have gained interest in recent years. Specific cell stimulation conditions, such as ultraviolet and X-rays irradiation, can induce the release of MPs, which are endowed with unique antitumor functionalities, either for therapeutic vaccines or as direct antitumor agents. Moreover, the size of MPs (100-1000 nm) and their spherical structures surrounded by a lipid bilayer membrane allow MPs to function as delivery vectors for bioactive antitumor compounds, with favorable phamacokinetic behavior, immunostimulatory activity and biological function, without inherent carrier-specific toxic side effects. In this review, the mechanisms underlying MP biogenesis, factors that influence MP production, properties of MP membranes, size, composition and isolation methods of MPs are discussed. Additionally, the applications and mechanisms of action of MPs, as well as the main hurdles for their applications in cancer management, are introduced.

Secretions from hypochlorous acid-treated tumor cells delivered in a melittin hydrogel potentiate cancer immunotherapy.

Autologous tumor cells and cell-derived secretions (CDS) can induce antitumor immune responses. The conditions in which cells are cultured and treated impact CDS, and cellular insults alter their composition and function. In this study, we generated CDS from tumor cells exposed to normal culture conditions, hypoxia, cisplatin, radiotherapy, photodynamic therapy, or hypochlorous acid (HOCl). In vitro HOCl-CDS showed the strongest stimulatory effects on dendritic cells and macrophages compared to CDS generated by hypoxia, cisplatin, radiotherapy or photodynamic therapy. To improve HOCl-CDS activity at the tumor site, we loaded HOCl-CDS into a melittin-encapsulated hydrogel scaffold. When injected intratumorally, the HOCl-CDS hydrogel promoted tumor cell death, cytotoxic T lymphocyte infiltration, and tumor-associated macrophage reprogramming towards an M1 phenotype. The hydrogel inhibited tumor growth and prolonged the survival of mice bearing B16-F10 melanoma. Furthermore, hydrogel-delivered HOCl-CDS augmented the antitumor effects of immune checkpoint blockade. These results underscore the importance of the CDS generation method and delivery approach for improving cancer immunotherapy.

Targeting senescence-like fibroblasts radiosensitizes non-small cell lung cancer and reduces radiation-induced pulmonary fibrosis.

Cancer cell radioresistance is the primary cause of the decreased curability of non-small cell lung cancer (NSCLC) observed in patients receiving definitive radiotherapy (RT). Following RT, a set of microenvironmental stress responses is triggered, including cell senescence. However, cell senescence is often ignored in designing effective strategies to resolve cancer cell radioresistance. Herein, we identify the senescence-like characteristics of cancer-associated fibroblasts (CAFs) after RT and clarify the formidable ability of senescence-like CAFs in promoting NSCLC cell proliferation and radioresistance through the JAK/STAT pathway. Specific induction of senescence-like CAF apoptosis using FOXO4-DRI, a FOXO4-p53-interfering peptide, resulted in remarkable effects on radiosensitizing NSCLC cells in vitro and in vivo. In addition, in this study, we also uncovered an obvious therapeutic effect of FOXO4-DRI on alleviating radiation-induced pulmonary fibrosis (RIPF) by targeting senescence-like fibroblasts in vivo. In conclusion, by targeting senescence, we offer a strategy that simultaneously decreases radioresistance of NSCLC and the incidence of RIPF.

Local biomaterial-assisted antitumour immunotherapy for effusions in the pleural and peritoneal cavities caused by malignancies.

Malignant pleural effusion (MPE) and malignant ascites (MA), which are common but serious conditions caused by malignancies, are related to poor quality of life and high mortality. Current treatments, including therapeutic thoracentesis and indwelling pleural catheters or paracentesis and catheter drainage, are largely palliative. An effective treatment is urgently needed. MPE and MA are excellent candidates for intratumoural injections that have direct contact with tumour cells and kill tumour cells more effectively and efficiently with fewer side effects, and the fluid environment of MPE and MA can provide a homogeneous area for drug distribution. The immunosuppressive environments within the pleural and peritoneal cavities suggest the feasibility of local immunotherapy. In this review, we introduce the current management of MPE and MA, discuss the latest advances and challenges in utilizing local biomaterial-assisted antitumour therapies for the treatment of MPE and MA, and discuss further opportunities in this field.

Encapsulating an acid-activatable phthalocyanine-doxorubicin conjugate and the hypoxia-sensitive tirapazamine in polymeric micelles for multimodal cancer therapy.

A zinc(ii) phthalocyanine (ZnPc) was conjugated to doxorubicin (Dox) via an acid-labile hydrazone linker. The resulting ZnPc-Dox conjugate was then encapsulated into polymeric micelles formed through self-assembly of a block copolymer of poly(ethylene glycol) and poly(d,l-lactide) both in the absence and presence of the hypoxia-activated prodrug tirapazamine (TPZ) to give ZnPc-Dox@micelles and ZnPc-Dox/TPZ@micelles respectively. These polymeric micelles exhibited an excellent stability in aqueous media, but underwent disassembly in an acidic environment. Upon internalisation into HT29 human colorectal carcinoma cells, fluorescence due to ZnPc and Dox could be observed in the cytoplasm and nucleus respectively for both nanosystems. This observation suggested the disassembly of the polymeric micelles and the cleavage of the hydrazone linker in ZnPc-Dox in the acidic intracellular compartments. These micelles were slightly cytotoxic against HT29 cells in the dark due to the chemotherapeutic effect of Dox and/or TPZ. Upon light irradiation, ZnPc-Dox@micelles showed higher cytotoxicity. The IC50 value under a normoxic condition (0.35 µM based on ZnPc-Dox) was significantly lower than that under hypoxia (>1 µM). With an additional therapeutic component, ZnPc-Dox/TPZ@micelles exhibited higher photocytotoxicity with IC50 values of 0.20 µM and 0.78 µM under normoxia and hypoxia respectively. It is believed that the photodynamic action of this nanosystem consumed the intracellular oxygen and hence triggered the hypoxia-mediated chemotherapeutic action of TPZ. The multimodal antitumor effects of these polymeric micelles were also validated on HT29 tumour-bearing nude mice.