Targeting Cancer Heterogeneity with Immune Responses Driven by Oncolytic Peptides

Synthesis and structural optimization of oncolytic peptide LTX-315

Oncolytic peptides represented potential novel candidates for anticancer treatments especially drug-resistant cancer cell lines. One of the most promising and extensively studied is LTX-315, which is considered as the first in class oncolytic peptide and has entered phase I/II clinical trials. Nevertheless, the shortcomings including poor proteolytic stability, moderate anticancer durability and high synthesis costs may hinder the widespread clinical applications of LTX-315. In order to reduce the synthesis costs, as well as develop derivatives possessing both high protease-stability and durable anticancer efficiency, twenty LTX-315-based derived-peptides were designed and efficiently synthesized. Especially, through solid-phase S-alkylation, as well as the optimized peptide cleavage condition, the derived peptides could be prepared with drastically reduced synthesis cost. The in vitro anticancer efficiency, serum stability, anticancer durability, anti-migration activity, and hemolysis effect were systematically investigated. It was found that derived peptide MS-13 exhibited comparable anticancer efficiency and durability to those of LTX-315. Strikingly, the D-type peptide MS-20, which is the enantiomer of MS-13, was demonstrated to possess significantly high proteolytic stability and sustained anticancer durability. In general, the cost-effective synthesis and stability-guided structural optimizations were conducted on LTX-315, affording the highly hydrolysis resistant MS-20 which possessed durable anticancer activity. Meanwhile, this study also provided a reliable reference for the future optimization of anticancer peptides through the solid-phase S-alkylation and L-type to D-type amino acid substitutions.

Targeting immunogenic cell stress and death for cancer therapy

Immunogenic cell death (ICD), which results from insufficient cellular adaptation to specific stressors, occupies a central position in the development of novel anticancer treatments. Several therapeutic strategies to elicit ICD - either as standalone approaches or as means to convert immunologically cold tumours that are insensitive to immunotherapy into hot and immunotherapy-sensitive lesions - are being actively pursued. However, the development of ICD-inducing treatments is hindered by various obstacles. Some of these relate to the intrinsic complexity of cancer cell biology, whereas others arise from the use of conventional therapeutic strategies that were developed according to immune-agnostic principles. Moreover, current discovery platforms for the development of novel ICD inducers suffer from limitations that must be addressed to improve bench-to-bedside translational efforts. An improved appreciation of the conceptual difference between key factors that discriminate distinct forms of cell death will assist the design of clinically viable ICD inducers.

Immunogenic cell stress and death in the treatment of cancer

The successful treatment of oncological malignancies which results in long-term disease control or the complete eradication of cancerous cells necessitates the onset of adaptive immune responses targeting tumor-specific antigens. Such desirable anticancer immunity can be triggered via the induction of immunogenic cell death (ICD) of cancer cells, thus converting malignant cells into an in situ vaccine that elicits T cell mediated adaptive immune responses and establishes durable immunological memory. The exploration of ICD for cancer treatment has been subject to extensive research. However, functional heterogeneity among ICD activating therapies in many cases requires specific co-medications to achieve full-blown efficacy. Here, we described the hallmarks of ICD and classify ICD activators into three distinct functional categories namely, according to their mode of action: (i) ICD inducers, which increase the immunogenicity of malignant cells, (ii) ICD sensitizers, which prime cellular circuitries for ICD induction by conventional cytotoxic agents, and (iii) ICD enhancers, which improve the perception of ICD signals by antigen presenting dendritic cells. Altogether, ICD induction, sensitization and enhancement offer the possibility to convert well-established conventional anticancer therapies into immunotherapeutic approaches that activate T cell-mediated anticancer immunity.

Three Rounds of Stability-Guided Optimization and Systematical Evaluation of Oncolytic Peptide LTX-315

Oncolytic peptides represent promising novel candidates for anticancer treatments. In our efforts to develop oncolytic peptides possessing both high protease stability and durable anticancer efficiency, three rounds of optimization were conducted on the first-in-class oncolytic peptide LTX-315. The robust synthetic method, in vitro and in vivo anticancer activity, and anticancer mechanism were investigated. The D-type peptides represented by FXY-12 possessed significantly improved proteolytic stability and sustained anticancer efficiency. Strikingly, the novel hybrid peptide FXY-30, containing one FXY-12 and two camptothecin moieties, exhibited the most potent in vitro and in vivo anticancer activities. The mechanism explorations indicated that FXY-30 exhibited rapid membranolytic effects and induced severe DNA double-strand breaks to trigger cell apoptosis. Collectively, this study not only established robust strategies to improve the stability and anticancer potential of oncolytic peptides but also provided valuable references for the future development of D-type peptides-based hybrid anticancer chemotherapeutics.

LTX-315 triggers anticancer immunity by inducing MyD88-dependent maturation of dendritic cells

LTX-315 is a synthetic cationic oncolytic peptide with potent anticancer activity but limited toxicity for non-malignant cells. LTX-315 induces both immunogenic tumor cell death and generation of tumor-specific immune responses in multiple experimental tumor models. Given the central role of dendritic cell (DC) maturation in the induction of antigen-specific immunity, we investigated the effect of LTX-315 treatment on the maturation of tumor-infiltrating DCs (TiDCs) and the generation of anti-melanoma immunity. We found that LTX-315 treatment induces the maturation of DCs, both indirectly through the release of cancer cell-derived damage-associated molecular patterns (DAMPs)/alarmins and nucleic acids (DNA and RNA) capable of triggering distinct Toll-like receptor (TLR) signaling, and, directly by activating TLR7. The latter results in the ignition of multiple intracellular signaling pathways that promotes DC maturation, including NF-κB, mitogen activated protein kinases (MAPKs), and inflammasome signaling, as well as increased type 1 interferon production. Critically, the effects of LTX-315 on DCs the consequent promotion of anti-melanoma immunity depend on the cytosolic signal transducer myeloid differentiation response gene 88 (MyD88). These results cast light on the mechanisms by which LTX-315 induces DC maturation and hence elicits anticancer immunity, with important implications for the use of LTX-315 as an anticancer immunotherapeutic.

Design of pH-responsive antimicrobial peptide melittin analog-camptothecin conjugates for tumor therapy

Melittin, a classical antimicrobial peptide, is a highly potent antitumor agent. However, its significant toxicity seriously hampers its application in tumor therapy. In this study, we developed novel melittin analogs with pH-responsive, cell-penetrating and membrane-lytic activities by replacing arginine and lysine with histidine. After conjugation with camptothecin (CPT), CPT-AAM-1 and CPT-AAM-2 were capable of killing tumor cells by releasing CPT at low concentrations and disrupting cell membranes at high concentrations under acidic conditions. Notably, we found that the C-terminus of the melittin analogs was more suitable for drug conjugation than the N-terminus. CPT-AAM-1 significantly suppressed melanoma growth in vivo with relatively low toxicity. Collectively, the present study demonstrates that the development of antitumor drugs based on pH-responsive antimicrobial peptide-drug conjugates is a promising strategy.

Hollow CoFe Nanozymes Integrated with Oncolytic Peptides Designed via Machine-Learning for Tumor Therapy

Developing novel substances to synergize with nanozymes is a challenging yet indispensable task to enable the nanozyme-based therapeutics to tackle individual variations in tumor physicochemical properties. The advancement of machine learning (ML) has provided a useful tool to enhance the accuracy and efficiency in developing synergistic substances. In this study, ML models to mine low-cytotoxicity oncolytic peptides are applied. The filtering Pipeline is constructed using a traversal design and the Autogluon framework. Through the Pipeline, 37 novel peptides with high oncolytic activity against cancer cells and low cytotoxicity to normal cells are identified from a library of 25,740 sequences. Combining dataset testing with cytotoxicity experiments, an 80% accuracy rate is achieved, verifying the reliability of ML predictions. Peptide C2 is proven to possess membranolytic functions specifically for tumor cells as targeted by Pipeline. Then Peptide C2 with CoFe hollow hydroxide nanozyme (H-CF) to form the peptide/H-CF composite is integrated. The new composite exhibited acid-triggered membranolytic function and potent peroxidase-like (POD-like) activity, which induce ferroptosis to tumor cells and inhibits tumor growth. The study suggests that this novel ML-assisted design approach can offer an accurate and efficient paradigm for developing both oncolytic peptides and synergistic peptides for catalytic materials.

Molecular determinants of immunogenic cell death elicited by radiation therapy

Cancer cells undergoing immunogenic cell death (ICD) can initiate adaptive immune responses against dead cell-associated antigens, provided that (1) said antigens are not perfectly covered by central tolerance (antigenicity), (2) cell death occurs along with the emission of immunostimulatory cytokines and damage-associated molecular patterns (DAMPs) that actively engage immune effector mechanisms (adjuvanticity), and (3) the microenvironment of dying cells is permissive for the initiation of adaptive immunity. Finally, ICD-driven immune responses can only operate and exert cytotoxic effector functions if the microenvironment of target cancer cells enables immune cell infiltration and activity. Multiple forms of radiation, including non-ionizing (ultraviolet) and ionizing radiation, elicit bona fide ICD as they increase both the antigenicity and adjuvanticity of dying cancer cells. Here, we review the molecular determinants of ICD as elicited by radiation as we critically discuss strategies to reinforce the immunogenicity of cancer cells succumbing to clinically available radiation strategies.

From oncolytic peptides to oncolytic polymers: A new paradigm for oncotherapy

Traditional cancer therapy methods, especially those directed against specific intracellular targets or signaling pathways, are not powerful enough to overcome tumor heterogeneity and therapeutic resistance. Oncolytic peptides that can induce membrane lysis-mediated cancer cell death and subsequent anticancer immune responses, has provided a new paradigm for cancer therapy. However, the clinical application of oncolytic peptides is always limited by some factors such as unsatisfactory bio-distribution, poor stability, and off-target toxicity. To overcome these limitations, oncolytic polymers stand out as prospective therapeutic materials owing to their high stability, chemical versatility, and scalable production capacity, which has the potential to drive a revolution in cancer treatment. This review provides an overview of the mechanism and structure-activity relationship of oncolytic peptides. Then the oncolytic peptides-mediated combination therapy and the nano-delivery strategies for oncolytic peptides are summarized. Emphatically, the current research progress of oncolytic polymers has been highlighted. Lastly, the challenges and prospects in the development of oncolytic polymers are discussed.

Systemic Administration with Bacteria-Inspired Nanosystems for Targeted Oncolytic Therapy and Antitumor Immunomodulation

Malignant tumors represent a formidable global health challenge, compelling the pursuit of innovative treatment modalities. Oncolytic therapy has emerged as a promising frontier in antitumor strategies. However, both natural agents (such as oncolytic bacteria or viruses) and synthetic oncolytic peptides confront formidable obstacles in clinical trials, which include the delicate equilibrium between safety and efficacy, the imperative for systemic administration with targeted therapy, and the need to counteract oncolysis-induced immunosuppression. To overcome these dilemmas, we have developed biomimetic nanoengineering to create oncolytic bacteria-inspired nanosystems (OBNs), spanning from hierarchical structural biomimicry to advanced bioactive biomimicry. Our OBNs harbor inherent oncolytic potential, including functionalized oligosaccharides mimicking bacterial cell walls for optimal blood circulation and tumor targeting, tumor acidity-switchable decoration for tumor-specific oncolysis, stereospecific tryptophan-rich peptides for robust oncolytic activity, encapsulated tumor immunomodulators for enhanced immunotherapy, and innate multimodal imaging potential for biological tracing. This work elucidates the efficacy and mechanisms of OBNs, encompassing primary tumor suppression, metastasis prevention, and recurrence inhibition. Systemic administration of d-chiral OBNs has demonstrated superior oncolytic efficacy, surpassing intratumoral injections of clinical-grade oncolytic peptides. This work heralds an era in biomimetic engineering on oncolytic agents, promising the revolutionization of contemporary oncolytic therapy paradigms for clinical translation.

Immunotherapies inducing immunogenic cell death in cancer: insight of the innate immune system

Cancer immunotherapies include monoclonal antibodies, cytokines, oncolytic viruses, cellular therapies, and other biological and synthetic immunomodulators. These are traditionally studied for their effect on the immune system's role in eliminating cancer cells. However, some of these therapies have the unique ability to directly induce cytotoxicity in cancer cells by inducing immunogenic cell death (ICD). Unlike general immune stimulation, ICD triggers specific therapy-induced cell death pathways, based on the release of damage-associated molecular patterns (DAMPs) from dying tumour cells. These activate innate pattern recognition receptors (PRRs) and subsequent adaptive immune responses, offering the promise of sustained anticancer drug efficacy and durable antitumour immune memory. Exploring how onco-immunotherapies can trigger ICD, enhances our understanding of their mechanisms and potential for combination strategies. This review explores the complexities of these immunotherapeutic approaches that induce ICD, highlighting their implications for the innate immune system, addressing challenges in cancer treatment, and emphasising the pivotal role of ICD in contemporary cancer research.

Enantiomeric Virus-Inspired Oncolytic Particles for Efficient Antitumor Immunotherapy

Synthesizing biomimetic systems with stereospecific architectures and advanced bioactivity remains an enormous challenge in modern science. To fundamentally eliminate biosafety issues of natural oncolytic viruses, the development of synthetic virus-inspired particles with high oncolytic activity is urgently needed for clinical antitumor treatments. Here, we describe the design and synthesis of enantiomeric virus-inspired particles for efficient oncolytic therapy from homochiral building blocks to stereospecific supramolecular constructions. The L-virus-inspired oncolytic particles (L-VOPs) and D-VOPs possess similar biomimetic nanostructures but mirror-imaged enantiomeric forms. It is important that both L-VOPs and D-VOPs successfully mimic the pharmacological activity of oncolytic viruses, including direct tumor lysis and antitumor immune activation. D-VOPs provide quite better oncolytic efficacy than that of clinical-grade oncolytic agents (LTX-315, IC50 = 53.00 μg mL-1) with more than 5-fold decrease in IC50 value (10.93 μg mL-1) and close to 100% tumor suppression (98.79%) against 4T1 tumor-bearing mice, attributed to the chirality-dependent tumor recognition, interaction, antidegradation, and immunotherapy. This work provides a strategy for the synthesis of stereospecific biomimetic material systems as well as develops an advanced candidate for biomimetic oncolytic agents without biosafety risks.

Reinforcing the immunogenic cell death to enhance cancer immunotherapy efficacy

Immunogenic cell death (ICD) has been a revolutionary modality in cancer treatment since it kills primary tumors and prevents recurrent malignancy simultaneously. ICD represents a particular form of cancer cell death accompanied by production of damage-associated molecular patterns (DAMPs) that can be recognized by pattern recognition receptors (PRRs), which enhances infiltration of effector T cells and potentiates antitumor immune responses. Various treatment methods can elicit ICD involving chemo- and radio-therapy, phototherapy and nanotechnology to efficiently convert dead cancer cells into vaccines and trigger the antigen-specific immune responses. Nevertheless, the efficacy of ICD-induced therapies is restrained due to low accumulation in the tumor sites and damage of normal tissues. Thus, researchers have been devoted to overcoming these problems with novel materials and strategies. In this review, current knowledge on different ICD modalities, various ICD inducers, development and application of novel ICD-inducing strategies are summarized. Moreover, the prospects and challenges are briefly outlined to provide reference for future design of novel immunotherapy based on ICD effect.

Design, synthesis and anticancer evaluation of novel oncolytic peptide-chlorambucil conjugates

Nitrogen mustards (NMs) are an important class of chemotherapeutic drugs and have been widely employed for the treatment of various cancers. However, due to the high reactivity of nitrogen mustard, most NMs react with proteins and phospholipids within the cell membrane. Therefore, only a very small fraction of NMs can reach the reach nucleus, alkylating and cross-linking DNA. To efficiently penetrate the cell membrane barrier, the hybridization of NMs with a membranolytic agent may be an effective strategy. Herein, the chlorambucil (CLB, a kind of NM) hybrids were first designed by conjugation with membranolytic peptide LTX-315. However, although LTX-315 could help large amounts of CLB penetrate the cytomembrane and enter the cytoplasm, CLB still did not readily reach the nucleus. Our previous work demonstrated that the hybrid peptide NTP-385 obtained by covalent conjugation of rhodamine B with LTX-315 could accumulate in the nucleus. Hence, the NTP-385-CLB conjugate, named FXY-3, was then designed and systematically evaluated both in vitro and in vivo. FXY-3 displayed prominent localization in the cancer cell nucleus and induced severe DNA double-strand breaks (DSBs) to trigger cell apoptosis. Especially, compared with CLB and LTX-315, FXY-3 exhibited significantly increased in vitro cytotoxicity against a panel of cancer cell lines. Moreover, FXY-3 showed superior in vivo anticancer efficiency in the mouse cancer model. Collectively, this study established an effective strategy to increase the anticancer activity and the nuclear accumulation of NMs, which will provide a valuable reference for future nucleus-targeting modification of nitrogen mustards.

Curvature-sensing peptide inhibits tumour-derived exosomes for enhanced cancer immunotherapy

Tumour-derived exosomes (T-EXOs) impede immune checkpoint blockade therapies, motivating pharmacological efforts to inhibit them. Inspired by how antiviral curvature-sensing peptides disrupt membrane-enveloped virus particles in the exosome size range, we devised a broadly useful strategy that repurposes an engineered antiviral peptide to disrupt membrane-enveloped T-EXOs for synergistic cancer immunotherapy. The membrane-targeting peptide inhibits T-EXOs from various cancer types and exhibits pH-enhanced membrane disruption relevant to the tumour microenvironment. The combination of T-EXO-disrupting peptide and programmed cell death protein-1 antibody-based immune checkpoint blockade therapy improves treatment outcomes in tumour-bearing mice. Peptide-mediated disruption of T-EXOs not only reduces levels of circulating exosomal programmed death-ligand 1, but also restores CD8⁺ T cell effector function, prevents premetastatic niche formation and reshapes the tumour microenvironment in vivo. Our findings demonstrate that peptide-induced T-EXO depletion can enhance cancer immunotherapy and support the potential of peptide engineering for exosome-targeting applications.

Combining in situ vaccination and immunogenic apoptosis to treat cancer

Immunization approaches are designed to stimulate the immune system and eliminate the tumor. Studies indicate that cancer immunization combined with certain chemotherapeutics and immunostimulatory agents can improve outcomes. Chemotherapeutics-based immunogenic cell death makes the tumor more recognizable by the immune system. In situ vaccination (ISV) utilizes established tumors as antigen sources and directly applies an immune adjuvant to the tumor to reverse a cold tumor microenvironment to a hot one. Immunogenic cell death and ISV highlight for the immune system the tumor antigens that are recognizable by immune cells and support a T-cell attack of the tumor cells. This review presents the concept of immunogenic apoptosis and ISV as a powerful platform for cancer immunization.

A helical oncolytic polypeptide with potent membranolytic activity for cancer therapy

Oncolytic peptides (OLPs) with membranolytic activity show great potential to combat multidrug-resistant cancer cells. Herein, we report a cationic helical oncolytic polypeptide (OLPP) with potent membranolytic activity for cancer therapy. The OLPP was synthesized by ring-opening polymerization of N-carboxyanhydrides (NCAs) and thiol-ene reaction. The OLPP was resistant to protease, showed high cytotoxicity to a series of cancer cells and caused cancer cell necrosis by quickly lysing cancer cell membrane independent of classic death-related intracellular pathways. Intra-tumoral injection of the OLPP effectively suppressed tumor growth in mice through the direct oncolytic effect. The OLPP represents a potential oncolytic chemotherapeutics for cancer therapy.

Hybrid peptide NTP-217 triggers ROS-mediated rapid necrosis in liver cancer cells by induction of mitochondrial leakage

Liver cancer is the third leading cause of cancer-associated mortality globally, and >830,000 patients with liver cancer undergoing treatment succumbed to the disease in 2020, which indicates the urgent need to develop a more effective anti-liver cancer drug. In our previous study, nucleus-targeting hybrid peptides obtained from the fusion of LTX-315 and the rhodamine B group possessed potent anti-adherent cancer cell activity. Hybrid peptides accumulated in the cell nucleus and damaged the nuclear membrane, resulting in the transfer of reactive oxygen species (ROS) from the cytoplasm to the nucleus and the induction of apoptosis. However, the source of the high concentration of ROS within the cytoplasm is unclear. Moreover, although our previous study demonstrated that hybrid peptides possessed potent anticancer activity against adherent cancer cells, their efficacy on liver cancer remained unexplored. The current study found that the hybrid peptide NTP-217 killed liver cancer cells after 4-h treatment with a half-maximal inhibitory concentration of 14.6-45.7 μM. NTP-217 could stably accumulate in the liver tumor tissue and markedly inhibited liver tumor growth in mice. Furthermore, NTP-217 destroyed mitochondria and induced the leakage of mitochondrial contents, resulting in the generation of a substantial quantity of ROS. Unlike the apoptosis induced by 24 h of treatment by NTP-217, 4 h of treatment caused ROS-mediated necrotic cell death. These findings suggested that short-time treatment with hybrid peptides could trigger ROS-mediated rapid necrosis in liver cancer cells, and provided a basis for the future development of hybrid peptides as anti-liver cancer agents.

The hybrid oncolytic peptide NTP-385 potently inhibits adherent cancer cells by targeting the nucleus

The use of oncolytic peptides with activity against a wide range of cancer entities as a new and promising cancer therapeutic strategy has drawn increasing attention. The oncolytic peptide LTX-315 derived from bovine lactoferricin (LfcinB) was found to be highly effective against suspension cancer cells, but not adherent cancer cells. In this study, we tactically fused LTX-315 with rhodamine B through a hybridization strategy to design and synthesize a series of nucleus-targeting hybrid peptides and evaluated their activity against adherent cancer cells. Thus, four hybrid peptides, NTP-212, NTP-217, NTP-223 and NTP-385, were synthesized. These hybrid peptides enhanced the anticancer activity of LTX-315 in a panel of adherent cancer cell lines by 2.4- to 37.5-fold. In model mice bearing B16-F10 melanoma xenografts, injection of NTP-385 (0.5 mg per mouse for 3 consecutive days) induced almost complete regression of melanoma, prolonged the median survival time and increased the overall survival. Notably, the administered dose of NTP-385 was only half the effective dose of LTX-315. We further revealed that unlike LTX-315, which targets the mitochondria, NTP-385 disrupted the nuclear membrane and accumulated in the nucleus, resulting in the transfer of a substantial amount of reactive oxygen species (ROS) from the cytoplasm to the nucleus through the fragmented nuclear membrane. This ultimately led to DNA double-strand break (DSB)-mediated intrinsic apoptosis. In conclusion, this study demonstrates that hybrid peptides obtained from the fusion of LTX-315 and rhodamine B enhance anti-adherent cancer cell activity by targeting the nucleus and triggering DNA DSB-mediated intrinsic apoptosis. This study also provides an advantageous reference for nucleus-targeting peptide modification.

Evaluation of immunotherapy efficacy in gynecologic cancer

Various immunotherapies have demonstrated remarkable success over the past few decades, and have been approved for the treatment of different cancer types. However, patient responses to immunotherapy are variable, and approximately 50% of cases are refractory to these agents. Tumor biomarker-based stratification of cases may therefore help identify subpopulations that are sensitive/resistant to immunotherapy; it may also improve prediction of response in various cancers including gynecologic cancer. These biomarkers include the tumor mutational burden, microsatellite instability, mismatch repair deficiency, T cell-inflamed gene expression profile, programmed cell death protein 1 ligand 1, tumor-infiltrating lymphocytes, and numerous other genomic alterations. Future directions in the treatment of gynecologic cancer include the utilization of these biomarkers to select ideal candidates. This review focused on recent advances in the predictive ability of molecular biomarkers in patients with gynecologic cancer who undergo immunotherapy. The most recent developments in combined immunotherapy and targeted therapy strategies and novel immune interventions against gynecologic cancers have also been discussed.

Amphipathic barbiturates as marine product mimics with cytolytic and immunogenic effects on head and neck squamous cell carcinoma cell lines

The incidence of head and neck squamous cell carcinoma (HNSCC) is increasing and the conventional treatments for this form of cancer can be tough. Despite the success of existing immunotherapies in some HNSCC patients, many do not respond to this type of treatment. Thus, the development of novel anti-cancer therapies should be prioritized. In the current study, the anticancer activity of a panel of novel compounds, herein termed marine product mimics (MPMs), against HNSCC cell lines is explored. The previously reported compound MPM-1, which is structurally related to the novel MPMs, was shown to have promising effects on the HNSCC cell line HSC-3. The results from the current study indicate that the novel MPMs are more potent than MPM-1 but cause a similar type of cell death. The results indicated that the MPMs must cross through the cell membrane to exert their action and that they are lysosomotropic. Further experiments showed that some of the MPMs could induce phosphorylation of eukaryotic initiation factor 2α (eIF2α) in HSC-3 and UT-SCC-24A cells, which indicates that they can activate the integrated stress response that is strongly associated with immunogenic cell death. Cell surface expression of calreticulin and release of HMGB1 and ATP, which are all hallmarks of immunogenic cell death, was also demonstrated in HSC-3 and UT-SCC-24A cells treated with MPMs. This suggests that the MPMs are interesting candidates for future HNSCC cancer therapies.

The marine natural product mimic MPM-1 is cytolytic and induces DAMP release from human cancer cell lines

Bioprospecting contributes to the discovery of new molecules with anticancer properties. Compounds with cytolytic activity and the ability to induce immunogenic cell death can be administered as intratumoral injections with the aim to activate anti-tumor immune responses by causing the release of tumor antigens as well as damage-associated molecular patterns (DAMPs) from dying cancer cells. In the present study, we report the cytolytic and DAMP-releasing effects of a new natural product mimic termed MPM-1 that was inspired by the marine Eusynstyelamides. We found that MPM-1 rapidly killed cancer cells in vitro by inducing a necrosis-like death, which was accompanied by lysosomal swelling and perturbation of autophagy in HSC-3 (human oral squamous cell carcinoma) cells. MPM-1 also induced release of the DAMPs adenosine triphosphate (ATP) and high mobility group box 1 (HMGB1) from Ramos (B-cell lymphoma) and HSC-3 cells, as well as cell surface expression of calreticulin in HSC-3 cells. This indicates that MPM-1 has the ability to induce immunogenic cell death, further suggesting that it may have potential as a novel anticancer compound.

Biophysical Characterization of LTX-315 Anticancer Peptide Interactions with Model Membrane Platforms: Effect of Membrane Surface Charge

LTX-315 is a clinical-stage, anticancer peptide therapeutic that disrupts cancer cell membranes. Existing mechanistic knowledge about LTX-315 has been obtained from cell-based biological assays, and there is an outstanding need to directly characterize the corresponding membrane-peptide interactions from a biophysical perspective. Herein, we investigated the membrane-disruptive properties of the LTX-315 peptide using three cell-membrane-mimicking membrane platforms on solid supports, namely the supported lipid bilayer, intact vesicle adlayer, and tethered lipid bilayer, in combination with quartz crystal microbalance-dissipation (QCM-D) and electrochemical impedance spectroscopy (EIS) measurements. The results showed that the cationic LTX-315 peptide selectively disrupted negatively charged phospholipid membranes to a greater extent than zwitterionic or positively charged phospholipid membranes, whereby electrostatic interactions were the main factor to influence peptide attachment and membrane curvature was a secondary factor. Of note, the EIS measurements showed that the LTX-315 peptide extensively and irreversibly permeabilized negatively charged, tethered lipid bilayers that contained high phosphatidylserine lipid levels representative of the outer leaflet of cancer cell membranes, while circular dichroism (CD) spectroscopy experiments indicated that the LTX-315 peptide was structureless and the corresponding membrane-disruptive interactions did not involve peptide conformational changes. Dynamic light scattering (DLS) measurements further verified that the LTX-315 peptide selectively caused irreversible disruption of negatively charged lipid vesicles. Together, our findings demonstrate that the LTX-315 peptide preferentially disrupts negatively charged phospholipid membranes in an irreversible manner, which reinforces its potential as an emerging cancer immunotherapy and offers a biophysical framework to guide future peptide engineering efforts.

Renovation as innovation: Repurposing human antibacterial peptide LL-37 for cancer therapy

In many organisms, antimicrobial peptides (AMPs) display wide activities in innate host defense against microbial pathogens. Mammalian AMPs include the cathelicidin and defensin families. LL37 is the only one member of the cathelicidin family of host defense peptides expressed in humans. Since its discovery, it has become clear that they have pleiotropic effects. In addition to its antibacterial properties, many studies have shown that LL37 is also involved in a wide variety of biological activities, including tissue repair, inflammatory responses, hemotaxis, and chemokine induction. Moreover, recent studies suggest that LL37 exhibits the intricate and contradictory effects in promoting or inhibiting tumor growth. Indeed, an increasing amount of evidence suggests that human LL37 including its fragments and analogs shows anticancer effects on many kinds of cancer cell lines, although LL37 is also involved in cancer progression. Focusing on recent information, in this review, we explore and summarize how LL37 contributes to anticancer effect as well as discuss the strategies to enhance delivery of this peptide and selectivity for cancer cells.

Oncolytic immunotherapy: multiple mechanisms of oncolytic peptides to confer anticancer immunity

Oncolytic peptides are highly effective on remodeling the tumor microenvironment and potentiating the anticancer immunity through multiple mechanisms, particularly by inducing immunogenic cell death. Intriguingly, a recent study demonstrates that LTX-315, one of the most promising and extensively studied oncolytic peptides, inhibits PD-L1 expression via ATP11B, thus enhancing the effectiveness of cancer immunotherapy by targeting the PD-1/PD-L1 axis. Therefore, this commentary discusses the broad effects and perspectives of oncolytic peptides on anticancer immunity, further highlighting the potential issues and directions of oncolytic peptides in cancer immunotherapy.

Influence of chain length on the anticancer activity of the antimicrobial peptide CAMEL with fatty acid modification

Antimicrobial peptides (AMPs) display promising potential in cancer therapy. Modification with fatty acids is a simple and effective approach to improve the activity of AMPs. In the present study, we investigated the effects of fatty acid chain lengths on the anticancer activity, self-assembly and mechanism of action of CAMEL (CM15, KWKLFKKIGAVLKVL-NH₂), an amphipathic AMP with 15 amino acids. Conjugation of fatty acids could obviously improve the in vitro anticancer activity of CAMEL. Among the tested peptides, C12-CAMEL showed the highest anticancer activity, while C16-CAMEL killed cancer cells with the slowest kinetics. This may be related to the self-assembly of C12-CAMEL and C16-CAMEL, which could form spherical nanoparticles and tightened nanofibers, respectively. In addition, necrosis and necroptosis rather than apoptosis were the major mechanisms underlying the anticancer activity of CAMEL, C12-CAMEL and C16-CAMEL, implying that modification with fatty acids did not obviously alter the mechanism of action of CAMEL. Notably, C12-CAMEL, with high and rapid cell-killing activity, exhibited significantly stronger in vivo anticancer activity than CAMEL and C16-CAMEL. Overall, the present work suggests that the choice of a suitable fatty acid for structural modification is necessary for improving the anticancer activity of AMPs.

Oncolytic peptide LTX-315 induces anti-pancreatic cancer immunity by targeting the ATP11B-PD-L1 axis

Background

LTX-315 is an oncolytic peptide deriving from bovine lactoferrin, with the ability to induce cancer immunogenic cell death. However, the mechanism used by LTX-315 to trigger the antitumor immune response is still poorly understood. The expression of programmed cell death ligand 1 (PD-L1) largely determines the efficacy and effectiveness of cancer immunotherapies targeting this specific immune checkpoint. This study aimed to demonstrate the potential effect and mechanism of LTX-315 in PD-L1 inhibition-induced anti-pancreatic cancer immunity.

Methods

Both immunodeficient and immunocompetent mouse models were used to evaluate the therapeutic efficacy of monotherapy and combination therapy. Flow cytometry and immunohistochemistry were used to assess the immune microenvironment. Multiomic analysis was used to identify the potential target and down-streaming signaling pathway. Both in-house tissue microarray and open accessed The Cancer Genome Atlas data sets were used to evaluate the clinical relevance in pancreatic cancer prognosis.

Results

LTX-315 treatment inhibited PD-L1 expression and enhanced lymphocyte infiltration in pancreatic tumors. ATP11B was identified as a potential target of LTX-315 and a critical regulator in maintaining PD-L1 expression in pancreatic cancer cells. As regards the mechanism, ATP11B interacted with PD-L1 in a CKLF-like MARVEL transmembrane domain containing 6 (CMTM6)-dependent manner. The depletion of ATP11B promoted CMTM6-mediated lysosomal degradation of PD-L1, thus reactivating the immune microenvironment and inducing an antitumor immune response. The significant correlation among ATP11B, CMTM6, and PD-L1 was confirmed in clinical samples of pancreatic cancer.

Conclusions

LTX-315 was first identified as a peptide drug inducing PD-L1 downregulation via ATP11B. Therefore, LTX-315, or the development of ATP11B-targeting drugs, might improve the efficacy of cancer immunotherapy.

Natural Peptides Inducing Cancer Cell Death: Mechanisms and Properties of Specific Candidates for Cancer Therapeutics

Nowadays, cancer has become the second highest leading cause of death, and it is expected to continue to affect the population in forthcoming years. Additionally, treatment options will become less accessible to the public as cases continue to grow and disease mechanisms expand. Hence, specific candidates with confirmed anticancer effects are required to develop new drugs. Among the novel therapeutic options, proteins are considered a relevant source, given that they have bioactive peptides encrypted within their sequences. These bioactive peptides, which are molecules consisting of 2–50 amino acids, have specific activities when administered, producing anticancer effects. Current databases report the effects of peptides. However, uncertainty is found when their molecular mechanisms are investigated. Furthermore, analyses addressing their interaction networks or their directly implicated mechanisms are needed to elucidate their effects on cancer cells entirely. Therefore, relevant peptides considered as candidates for cancer therapeutics with specific sequences and known anticancer mechanisms were accurately reviewed. Likewise, those features which turn certain peptides into candidates and the mechanisms by which peptides mediate tumor cell death were highlighted. This information will make robust the knowledge of these candidate peptides with recognized mechanisms and enhance their non-toxic capacity in relation to healthy cells and further avoid cell resistance.

Natural Peptides Inducing Cancer Cell Death: Mechanisms and Properties of Specific Candidates for Cancer Therapeutics

Nowadays, cancer has become the second highest leading cause of death, and it is expected to continue to affect the population in forthcoming years. Additionally, treatment options will become less accessible to the public as cases continue to grow and disease mechanisms expand. Hence, specific candidates with confirmed anticancer effects are required to develop new drugs. Among the novel therapeutic options, proteins are considered a relevant source, given that they have bioactive peptides encrypted within their sequences. These bioactive peptides, which are molecules consisting of 2–50 amino acids, have specific activities when administered, producing anticancer effects. Current databases report the effects of peptides. However, uncertainty is found when their molecular mechanisms are investigated. Furthermore, analyses addressing their interaction networks or their directly implicated mechanisms are needed to elucidate their effects on cancer cells entirely. Therefore, relevant peptides considered as candidates for cancer therapeutics with specific sequences and known anticancer mechanisms were accurately reviewed. Likewise, those features which turn certain peptides into candidates and the mechanisms by which peptides mediate tumor cell death were highlighted. This information will make robust the knowledge of these candidate peptides with recognized mechanisms and enhance their non-toxic capacity in relation to healthy cells and further avoid cell resistance.

LTX-315-enabled, radiotherapy-boosted immunotherapeutic control of breast cancer by NK cells

LTX-315 is a nonameric oncolytic peptide in early clinical development for the treatment of solid malignancies. Preclinical and clinical evidence indicates that the anticancer properties of LTX-315 originate not only from its ability to selectively kill cancer cells, but also from its capacity to promote tumor-targeting immune responses. Here, we investigated the therapeutic activity and immunological correlates of intratumoral LTX-315 administration in three syngeneic mouse models of breast carcinoma, with a focus on the identification of possible combinatorial partners. We found that breast cancer control by LTX-315 is accompanied by a reconfiguration of the immunological tumor microenvironment that supports the activation of anticancer immunity and can be boosted by radiation therapy. Mechanistically, depletion of natural killer (NK) cells compromised the capacity of LTX-315 to limit local and systemic disease progression in a mouse model of triple-negative breast cancer, and to extend the survival of mice bearing hormone-accelerated, carcinogen-driven endogenous mammary carcinomas. Altogether, our data suggest that LTX-315 controls breast cancer progression by engaging NK cell-dependent immunity.

Stapled Wasp Venom-Derived Oncolytic Peptides with Side Chains Induce Rapid Membrane Lysis and Prolonged Immune Responses in Melanoma

Peptide stapling chemistry represents an attractive strategy to promote the clinical translation of protein epitope mimetics, but its use has not been applied to natural cytotoxic peptides (NCPs) to produce new oncolytic peptides. Based on a wasp venom peptide, a series of stapled anoplin peptides (StAnos) were prepared. The optimized stapled Ano-3/3s were shown to be protease-resistant and exerted superior tumor cell-selective cytotoxicity by rapid membrane disruption. In addition, Ano-3/3s induced tumor ablation in mice through the direct oncolytic effect and subsequent stimulation of immunogenic cell death. This synergistic oncolytic-immunotherapy effect is more remarkable on melanoma than on triple-negative breast cancer in vivo. The efficacies exerted by Ano-3/3s on melanoma were further characterized by CD8+ T cell infiltration, and the addition of anti-CD8 antibodies diminished the long-term antitumor effects. In summary, these results support stapled peptide chemistry as an advantageous method to enhance the NCP potency for oncolytic therapy.