Neoadjuvant in situ vaccination with cowpea mosaic virus as a novel therapy against canine inflammatory mammary cancer

Preclinical SC and IV repeat-dose toxicology of a cowpea mosaic virus - A cancer immunotherapy candidate

Cancer immunotherapies focus on boosting the immune system to recognize and eliminate tumor cells. Amongst the various biologics under development for cancer immunotherapy, our team has focused on the study of plant viruses in this context. We have shown that intratumoral administration of cowpea mosaic virus (CPMV) relieves the immunosuppressive tumor microenvironment and elicits a potent, systemic and durable anti-tumor immune response. The potency of CPMV has been demonstrated in several tumor mouse models and in companion canine cancer patients. Toward clinical development, we here studied the pharmacology and safety of CPMV. The repeat-dose toxicity of CPMV was evaluated in female Sprague Dawley rats. Rats received three weekly treatments (subcutaneous or intravenous) of a fixed dose (∼20 mg/kg), and complete necropsy was performed either 24 hrs (acute toxicity group) or 14 day (recovery group) post-dose. All animals reached the scheduled euthanasia times, and no clinical abnormalities were noted during the study period. Important clinical chemistry, hematology and histopathology findings included decreased albumin/globulin ratio, leukocytosis, neutrophilia, monocytosis, and lymphoid hyperplasia (Dunnett's test, p<0.05) - these changes support the immunostimulatory mode of action for CPMV. All other changes were considered mild, within historical range for the model, and/or not biologically significant. Neither a maximum tolerated dose (MTD) nor a no-observable adverse effect level (NOAEL) was established in this study. Overall, data indicate a good safety profile for the CPMV cancer immunotherapy candidate.

Pilot Study of Intratumoral Immunotherapy with Cowpea Mosaic Virus Nanoparticles: Safety in Refractory Canine Oral Tumors

Oral tumors (squamous cell carcinoma, malignant melanoma, and fibrosarcoma) represent 6-7% of all canine cancers. Given that these tumors have a high local recurrence rate and metastatic potential, conventional therapies have suboptimal response rates, leading to poor patient outcomes. Here, we report the use of intratumoral virus-like particles from cowpea mosaic virus (CPMV) in four canine patients with recurrent oral malignant tumors and lymph node metastasis. All tumors were nonresponders to chemotherapy and had a mild initial response to CPMV intratumoral immunotherapy without any serious immune-related adverse effects. None of the patients developed pulmonary metastasis during follow-up, although local progression was seen in all the patients. Furthermore, tumor-infiltrated immune T cells increased in number after the intratumoral immunotherapy with CPMV, suggesting activation of the tumor microenvironment. All the patients had a rapid decrease in the tumor-promoting chemokines IL-8 and CXCL1, which could indicate that a decrease in metastatic potential could have been generated by the CPMV immunotherapy. The increased number of infiltrated immune cells, the decrease in some pro-tumoral chemokines, and the absence of adverse effects suggest that CPMV could be a safe treatment and should be further explored as a novel therapy for canine oral tumors.

Metastatic Melanoma Treatment and Prophylaxis with S100A9-Targeting Cowpea Mosaic Virus Nanoparticles

Metastatic cancer continues to be the main cause of cancer-related death, and new therapies must be continuously researched to eradicate these cancers. Immunotherapy aims to stimulate the patient's own immune system to recognize and eliminate tumors and metastatic sites. A particular powerful approach is the use of immunostimulatory agents to reprogram the tumor microenvironment from "cold" to "hot" to prime systemic antitumor immunity. Plant viruses have been investigated for this purpose because their repetitive coat protein structures with encapsidated nucleic acids render them potent immunostimulatory agents. In particular, the cowpea mosaic virus (CPMV) has been found to be a potent anticancer agent when injected intratumorally. However, metastatic cancers cannot be injected in situ, and therefore a systemically administered CPMV prevention and treatment option that is targeted to S100A9 was developed. S100A9 is an immunostimulatory protein that regulates metastatic cancer seeding and growth, thereby making it an attractive target for both prevention and treatment. Protocols for the production and characterization of S100A9-targeted CPMV nanoparticles are described and in vivo experiments that can be carried out to assess the efficacy of the S100A9-targeted CPMV nanoparticles in the prevention and treatment of metastatic melanoma to the lung are detailed. Finally, instructions for flow cytometry analysis of the innate immune cell composition within the lungs following S100A9-targeted CPMV administration are provided.

Plant Virus Intratumoral Immunotherapy with CPMV and PVX Elicits Durable Antitumor Immunity in a Mouse Model of Diffuse Large B-Cell Lymphoma

Plant viruses are naturally occurring nanoparticles and adjuvants that interact with the mammalian immune system. This property can be harnessed in vaccines and immunotherapy. We have previously demonstrated that intratumoral immunotherapy with cowpea mosaic virus (CPMV) stimulates systemic and durable antitumor immunity in mouse tumor models and canine cancer patients. Here we compared the antitumor efficacy of CPMV with potato virus X (PVX) using a mouse model B-cell lymphoma (A20 and BALB/c mice). Despite their diverse morphologies and physiochemical properties, both plant viruses elicited systemic and long-lasting antitumor immune memory, preventing the recurrence of A20 lymphoma in rechallenge experiments. Data indicate differences in the underlying mechanism: CPMV persists longer in the tumor microenvironment (TME) compared to PVX; CPMV is a potent and multivalent toll-like receptor (TLR) agonist (activating TLRs 2, 4 and 7) while PVX may only weakly engage with TLR7. While CPMV and PVX recruit myeloid cells (neutrophils)─CPMV also recruits macrophages. Data further indicate that antiviral T cells may play a role in antitumor efficacy in the case of CPMV immunotherapy, however this may not be the case for PVX. Regardless of the mechanism of action, both CPMV and PVX elicited a durable antitumor response against a B-cell lymphoma tumor model and thus are intratumoral immunotherapy candidates for clinical development.

Multifaceted cancer alleviation by cowpea mosaic virus in a bioprinted ovarian cancer peritoneal spheroid model

Ovarian cancer (OvCa) is a leading cause of mortality among gynecological malignancies and usually manifests as intraperitoneal spheroids that generate metastases, ascites, and an immunosuppressive tumor microenvironment. In this study, we explore the immunomodulatory properties of cowpea mosaic virus (CPMV) as an adjuvant immunotherapeutic agent using an in vitro model of OvCa peritoneal spheroids. Previous findings highlighted the potent efficacy of intratumoral CPMV against OvCa in mouse tumor models. Leveraging the precision control over material deposition and cell patterning afforded by digital-light-processing (DLP) based bioprinting, we constructed OvCa-macrophage spheroids to mimic peritoneal spheroids using gelatin methacrylate (GelMA), a collagen-derived photopolymerizable biomaterial to mimic the extracellular matrix. Following CPMV treatment, bioprinted spheroids exhibited inhibited OvCa progression mediated by macrophage activation. Our analysis indicates that CPMV regulates and activates macrophage to both induce OvCa cell killing and restore normal cell-cell junctions. This study deepened our understanding of the mechanism of CPMV intratumoral immunotherapy in the setting of OvCa. This study also highlights the potential of studying immunotherapies using high throughput tissue models via DLP bioprinting.

Virus nanotechnology for intratumoural immunotherapy

Viruses can be designed to be tools and carrier vehicles for intratumoural immunotherapy. Their nanometre-scale size and shape allow for functionalization with or encapsulation of medical cargoes and tissue-specific ligands. Importantly, immunotherapies may particularly benefit from the inherent immunomodulatory properties of viruses. For example, mammalian viruses have already been tested for oncolytic virotherapy, and bacteriophages and plant viruses can be engineered for immunotherapeutic treatment approaches. In this Review, we discuss how viruses - including oncolytic viruses, immunomodulatory plant viruses and bacteriophages - and virus-like particles can be designed for intratumoural immunotherapy to elicit anti-tumour immunity and induce systemic anti-tumour responses at distant non-injected sites. We further highlight the engineering of viruses and virus-like particles as drug-delivery systems, and outline key translational challenges and clinical opportunities.

Cellular fate of a plant virus immunotherapy candidate

Cowpea mosaic virus (CPMV) is a plant virus that is currently being developed for intratumoral immunotherapy. CPMV relieves the immune system from tumor-induced immunosuppression; reprograms the tumor microenvironment to an activated state whereby the treated and distant tumors are recognized and eradicated. Toward translational studies, we investigated the safety of CPMV, specifically addressing whether pathogenicity would be induced in mammalian cells. We show that murine macrophage immune cells recognize CPMV; however, there is no indication of de novo viral protein synthesis or RNA replication. Furthermore, we show that CPMV does not induce hemolysis, platelet aggregation and plasma coagulation amongst other assays in human blood and immune cells. Taken together, we anticipate that these results will reinforce the development of CPMV as an immunotherapeutic platform.

An Abscopal Effect on Lung Metastases in Canine Mammary Cancer Patients Induced by Neoadjuvant Intratumoral Immunotherapy with Cowpea Mosaic Virus Nanoparticles and Anti-Canine PD-1

Neoadjuvant intratumoral (IT) therapy could amplify the weak responses to checkpoint blockade therapy observed in breast cancer (BC). In this study, we administered neoadjuvant IT anti-canine PD-1 therapy (IT acPD-1) alone or combined with IT cowpea mosaic virus therapy (IT CPMV/acPD-1) to companion dogs diagnosed with canine mammary cancer (CMC), a spontaneous tumor resembling human BC. CMC patients treated weekly with acPD-1 (n = 3) or CPMV/acPD-1 (n = 3) for four weeks or with CPMV/acPD-1 (n = 3 patients not candidates for surgery) for up to 11 weeks did not experience immune-related adverse events. We found that acPD-1 and CPMV/acPD-1 injections resulted in tumor control and a reduction in injected tumors in all patients and in noninjected tumors located in the ipsilateral and contralateral mammary chains of treated dogs. In two metastatic CMC patients, CPMV/acPD-1 treatments resulted in the control and reduction of established lung metastases. CPMV/acPD-1 treatments were associated with altered gene expression related to TLR1-4 signaling and complement pathways. These novel therapies could be effective for CMC patients. Owing to the extensive similarities between CMC and human BC, IT CPMV combined with approved anti-PD-1 therapies could be a novel and effective immunotherapy to treat local BC and suppress metastatic BC.

Mannan-Decorated Lipid Calcium Phosphate Nanoparticle Vaccine Increased the Antitumor Immune Response by Modulating the Tumor Microenvironment

With the rapid development of tumor immunotherapy, nanoparticle vaccines have attracted much attention as potential therapeutic strategies. A systematic review and analysis must be carried out to investigate the effect of mannose modification on the immune response to nanoparticles in regulating the tumor microenvironment, as well as to explore its potential clinical application in tumor therapy. Despite the potential advantages of nanoparticle vaccines in immunotherapy, achieving an effective immune response in the tumor microenvironment remains a challenge. Tumor immune escape and the overexpression of immunosuppressive factors limit its clinical application. Therefore, our review explored how to intervene in the immunosuppressive mechanism in the tumor microenvironment through the use of mannan-decorated lipid calcium phosphate nanoparticle vaccines to improve the efficacy of immunotherapy in patients with tumors and to provide new ideas and strategies for the field of tumor therapy.

Bicalutamide Enhances Conventional Chemotherapy in In Vitro and In Vivo Assays Using Human and Canine Inflammatory Mammary Cancer Cell Lines

Human inflammatory breast cancer (IBC) and canine inflammatory mammary cancer (IMC) are highly aggressive neoplastic diseases that share numerous characteristics. In IBC and IMC, chemotherapy produces a limited pathological response and anti-androgen therapies have been of interest for breast cancer treatment. Therefore, the aim was to evaluate the effect of a therapy based on bicalutamide, a non-steroidal anti-androgen, with doxorubicin and docetaxel chemotherapy on cell proliferation, migration, tumor growth, and steroid-hormone secretion. An IMC-TN cell line, IPC-366, and an IBC-TN cell line, SUM149, were used. In vitro assays revealed that SUM149 exhibited greater sensitivity, reducing cell viability and migration with all tested drugs. In contrast, IPC-366 exhibited only significant in vitro reductions with docetaxel as a single agent or in different combinations. Decreased estrogen levels reduced in vitro tumor growth in both IMC and IBC. Curiously, doxorubicin resulted in low efficacy, especially in IMC. In addition, all drugs reduced the tumor volume in IBC and IMC by increasing intratumoral testosterone (T) levels, which have been related with reduced tumor progression. In conclusion, the addition of bicalutamide to doxorubicin and docetaxel combinations may represent a potential treatment for IMC and IBC.

Intratumoral delivery of immunotherapy to treat breast cancer: current development in clinical and preclinical studies

Breast cancer poses one of the largest threats to women's health. Treatment continues to improve for all the subtypes of breast cancer, but some subtypes, such as triple negative breast cancer, still present a significant treatment challenge. Additionally, metastasis and local recurrence are two prevalent problems in breast cancer treatment. A newer type of therapy, immunotherapy, may offer alternatives to traditional treatments for difficult-to-treat subtypes. Immunotherapy engages the host's immune system to eradicate disease, with the potential to induce long-lasting, durable responses. However, systemic immunotherapy is only approved in a limited number of indications, and it benefits only a minority of patients. Furthermore, immune related toxicities following systemic administration of potent immunomodulators limit dosing and, consequently, efficacy. To address these safety considerations and improve treatment efficacy, interest in local delivery at the site of the tumor has increased. Numerous intratumorally delivered immunotherapeutics have been and are being explored clinically and preclinically, including monoclonal antibodies, cellular therapies, viruses, nucleic acids, cytokines, innate immune agonists, and bacteria. This review summarizes the current and past intratumoral immunotherapy clinical landscape in breast cancer as well as current progress that has been made in preclinical studies, with a focus on delivery parameters and considerations.

Systemic Administration of Cowpea Mosaic Virus Demonstrates Broad Protection Against Metastatic Cancers

The key challenge in cancer treatment is prevention of metastatic disease which is therapeutically resistant and carries poor prognoses necessitating efficacious prophylactic approaches that prevent metastasis and recurrence. It is previously demonstrated that cowpea mosaic virus (CPMV) induces durable antitumor responses when used in situ, i.e., intratumoral injection. As a new direction, it is showed that CPMV demonstrates widespread effectiveness as an immunoprophylactic agent - potent efficacy is demonstrated in four metastatic models of colon, ovarian, melanoma, and breast cancer. Systemic administration of CPMV stimulates the innate immune system, enabling attack of cancer cells; processing of the cancer cells and associated antigens leads to systemic, durable, and adaptive antitumor immunity. Overall, CPMV demonstrated broad efficacy as an immunoprophylactic agent in the rejection of metastatic cancer.

Enhanced Photodynamic Therapy Synergizing with Inhibition of Tumor Neutrophil Ferroptosis Boosts Anti-PD-1 Therapy of Gastric Cancer

For tumor treatment, the ultimate goal in tumor therapy is to eliminate the primary tumor, manage potential metastases, and trigger an antitumor immune response, resulting in the complete clearance of all malignant cells. Tumor microenvironment (TME) refers to the local biological environment of solid tumors and has increasingly become an attractive target for cancer therapy. Neutrophils within TME of gastric cancer (GC) spontaneously undergo ferroptosis, and this process releases oxidized lipids that limit T cell activity. Enhanced photodynamic therapy (PDT) mediated by di-iodinated IR780 (Icy7) significantly increases the production of reactive oxygen species (ROS). Meanwhile, neutrophil ferroptosis can be triggered by increased ROS generation in the TME. In this study, a liposome encapsulating both ferroptosis inhibitor Liproxstatin-1 and modified photosensitizer Icy7, denoted LLI, significantly inhibits tumor growth of GC. LLI internalizes into MFC cells to generate ROS causing immunogenic cell death (ICD). Simultaneously, liposome-deliver Liproxstatin-1 effectively inhibits the ferroptosis of tumor neutrophils. LLI-based immunogenic PDT and neutrophil-targeting immunotherapy synergistically boost the anti-PD-1 treatment to elicit potent TME and systemic antitumor immune response with abscopal effects. In conclusion, LLI holds great potential for GC immunotherapy.

3D bioprinting cowpea mosaic virus as an immunotherapy depot for ovarian cancer prevention in a preclinical mouse model

Implantable polymeric hydrogels loaded with immunostimulatory cowpea mosaic virus (CPMV) were fabricated using digital light processing (DLP) printing technology. The CPMV-laden hydrogels were surgically implanted into the peritoneal cavity to serve as depots for cancer slow-release immunotherapy. Sustained release of CPMV within the intraperitoneal space alleviates the need for repeated dosing and we demonstrated efficacy against ovarian cancer in a metastatic mouse model.

Melanoma immunotherapy enabled by M2 macrophage targeted immunomodulatory cowpea mosaic virus

We have developed nanoparticle formulations targeting M2 macrophages for cancer immunotherapy by conjugating high-affinity binding peptides to cowpea mosaic virus as an immunostimulatory adjuvant. We confirmed the targeting of and uptake by M2 macrophages in vitro and the therapeutic efficacy of the nanoparticles against murine melanoma in vivo.

Exosome lncRNA IFNG-AS1 derived from mesenchymal stem cells of human adipose ameliorates neurogenesis and ASD-like behavior in BTBR mice

BACKGROUND

The transplantation of exosomes derived from human adipose-derived mesenchymal stem cells (hADSCs) has emerged as a prospective cellular-free therapeutic intervention for the treatment of neurodevelopmental disorders (NDDs), as well as autism spectrum disorder (ASD). Nevertheless, the efficacy of hADSC exosome transplantation for ASD treatment remains to be verified, and the underlying mechanism of action remains unclear.

RESULTS

The exosomal long non-coding RNAs (lncRNAs) from hADSC and human umbilical cord mesenchymal stem cells (hUCMSC) were sequenced and 13,915 and 729 lncRNAs were obtained, respectively. The lncRNAs present in hADSC-Exos encompass those found in hUCMSC-Exos and are associated with neurogenesis. The biodistribution of hADSC-Exos in mouse brain ventricles and organoids was tracked, and the cellular uptake of hADSC-Exos was evaluated both in vivo and in vitro. hADSC-Exos promote neurogenesis in brain organoid and ameliorate social deficits in ASD mouse model BTBR T + tf/J (BTBR). Fluorescence in situ hybridization (FISH) confirmed lncRNA Ifngas1 significantly increased in the prefrontal cortex (PFC) of adult mice after hADSC-Exos intraventricular injection. The lncRNA Ifngas1 can act as a molecular sponge for miR-21a-3p to play a regulatory role and promote neurogenesis through the miR-21a-3p/PI3K/AKT axis.

CONCLUSION

We demonstrated hADSC-Exos have the ability to confer neuroprotection through functional restoration, attenuation of neuroinflammation, inhibition of neuronal apoptosis, and promotion of neurogenesis both in vitro and in vivo. The hADSC-Exos-derived lncRNA IFNG-AS1 acts as a molecular sponge and facilitates neurogenesis via the miR-21a-3p/PI3K/AKT signaling pathway, thereby exerting a regulatory effect. Our findings suggest a potential therapeutic avenue for individuals with ASD.

Pharmacology of a Plant Virus Immunotherapy Candidate for Peritoneal Metastatic Ovarian Cancer

Due to the increasing incidence of cancer, there is a need to develop new platforms that can combat this disease. Cancer immunotherapy is a platform that takes advantage of the immune system to recognize and eradicate tumors and metastases. Our lab has identified a plant virus nanoparticle, cowpea mosaic virus (CPMV) as a promising approach for cancer immunotherapy. When administered intratumorally, CPMV relieves the immune system of tumor-induced immunosuppression and reprograms the tumor microenvironment into an activated state to launch systemic antitumor immunity. The efficacy of CPMV has been tested in many tumor models and in canine cancer patients with promising results: tumor shrinkage, systemic efficacy (abscopal effect), and immune memory to prevent recurrence. To translate this drug candidate from the bench to the clinic, studies that investigate the safety, pharmacology, and toxicity are needed. In this work, we describe the efficacy of CPMV against a metastatic ovarian tumor model and investigate the biodistribution of CPMV after single or repeated intraperitoneal administration in tumor-bearing and healthy mice. CPMV shows good retention in the tumor nodules and broad bioavailability with no apparent organ toxicity based on histopathology. Data indicate persistence of the viral RNA, which remains detectable 2 weeks post final administration, a phenomenon also observed with some mammalian viral infections. Lastly, while protein was not detected in stool or urine, RNA was shed through excretion from mice; however, there was no evidence that RNA was infectious to plants. Taken together, the data indicate that systemic administration results in broad bioavailability with no apparent toxicity. While RNA is shed from the subjects, data suggest agronomical safety. This data is consistent with prior reports and provides support for translational efforts.

Transcriptomics of Canine Inflammatory Mammary Cancer Treated with Empty Cowpea Mosaic Virus Implicates Neutrophils in Anti-Tumor Immunity

Canine inflammatory mammary cancer (IMC) is a highly aggressive and lethal cancer in dogs serving as a valuable animal model for its human counterpart, inflammatory breast cancer (IBC), both lacking effective therapies. Intratumoral immunotherapy (IT-IT) with empty cowpea mosaic virus (eCPMV) nanoparticles has shown promising results, demonstrating a reduction in tumor size, longer survival rates, and improved quality of life. This study compares the transcriptomic profiles of tumor samples from female dogs with IMC receiving eCPMV IT-IT and medical therapy (MT) versus MT alone. Transcriptomic analyses, gene expression profiles, signaling pathways, and cell type profiling of immune cell populations in samples from four eCPMV-treated dogs with IMC and four dogs with IMC treated with MT were evaluated using NanoString Technologies using a canine immune-oncology panel. Comparative analyses revealed 34 differentially expressed genes between treated and untreated samples. Five genes (CXCL8, S100A9, CCL20, IL6, and PTGS2) involved in neutrophil recruitment and activation were upregulated in the treated samples, linked to the IL17-signaling pathway. Cell type profiling showed a significant increase in neutrophil populations in the tumor microenvironment after eCPMV treatment. These findings highlight the role of neutrophils in the anti-tumor response mediated by eCPMV IT-IT and suggest eCPMV as a novel therapeutic approach for IBC/IMC.

Neoadjuvant Intratumoral Immunotherapy with Cowpea Mosaic Virus Induces Local and Systemic Antitumor Efficacy in Canine Mammary Cancer Patients

The lack of optimal models to evaluate novel agents is delaying the development of effective immunotherapies against human breast cancer (BC). In this prospective open label study, we applied neoadjuvant intratumoral immunotherapy with empty cowpea mosaic virus-like particles (eCPMV) to 11 companion dogs diagnosed with canine mammary cancer (CMC), a spontaneous tumor resembling human BC. We found that two neoadjuvant intratumoral eCPMV injections resulted in tumor reduction in injected tumors in all patients and in noninjected tumors located in the ipsilateral and contralateral mammary chains of injected dogs. Tumor reduction was independent of clinical stage, tumor size, histopathologic grade, and tumor molecular subtype. RNA-seq-based analysis of injected tumors indicated a decrease in DNA replication activity and an increase in activated dendritic cell infiltration in the tumor microenvironment. Immunohistochemistry analysis demonstrated significant intratumoral increases in neutrophils, T and B lymphocytes, and plasma cells. eCPMV intratumoral immunotherapy demonstrated antitumor efficacy without any adverse effects. This novel immunotherapy has the potential for improving outcomes for human BC patients.

The Potency of Cowpea Mosaic Virus Particles for Cancer In Situ Vaccination Is Unaffected by the Specific Encapsidated Viral RNA

Plant virus nanoparticles can be used as drug carriers, imaging reagents, vaccine carriers, and immune adjuvants in the formulation of intratumoral in situ cancer vaccines. One example is the cowpea mosaic virus (CPMV), a nonenveloped virus with a bipartite positive-strand RNA genome with each RNA packaged separately into identical protein capsids. Based on differences in their densities, the components carrying RNA-1 (6 kb) denoted as the bottom (B) component or carrying RNA-2 (3.5 kb) denoted as the middle (M) component can be separated from each other and from a top (T) component, which is devoid of any RNA. Previous preclinical mouse studies and canine cancer trials used mixed populations of CPMV (containing B, M, and T components), so it is unclear whether the particle types differ in their efficacies. It is known that the CPMV RNA genome contributes to immunostimulation by activation of TLR7. To determine whether the two RNA genomes that have different sizes and unrelated sequences cause different immune stimulation, we compared the therapeutic efficacies of B and M components and unfractionated CPMV in vitro and in mouse cancer models. We found that separated B and M particles behaved similarly to the mixed CPMV, activating innate immune cells to induce the secretion of pro-inflammatory cytokines such as IFNα, IFNγ, IL-6, and IL-12, while inhibiting immunosuppressive cytokines such as TGF-β and IL-10. In murine models of melanoma and colon cancer, the mixed and separated CPMV particles all significantly reduced tumor growth and prolonged survival with no significant difference. This shows that the specific RNA genomes similarly stimulate the immune system even though B particles have 40% more RNA than M particles; each CPMV particle type can be used as an effective adjuvant against cancer with the same efficacy as native mixed CPMV. From a translational point of view, the use of either B or M component vs the mixed CPMV formulation offers the advantage that separated B or M alone is noninfectious toward plants and thus provides agronomic safety.

Antitumor Effects of Esculetin, a Natural Coumarin Derivative, against Canine Mammary Gland Tumor Cells by Inducing Cell Cycle Arrest and Apoptosis

Mammary gland tumors are the most common neoplasms in female dogs, of which 50% are malignant. Esculetin, a coumarin derivative, reportedly induces death in different types of cancer cells. In this study, we explore the anticancer effects of esculetin against CMT-U27 and CF41.mg canine mammary gland tumor cells. Esculetin significantly inhibited the viability and migration of both CMT-U27 and CF41.mg cells in a dose- and time-dependent manner. Flow cytometric analysis and terminal deoxynucleotidyl transferase dUTP nick-end labeling assay revealed increased numbers of annexin-V-positive cells and DNA fragmentation. Furthermore, a cell cycle analysis demonstrated that esculetin blocked the cell progression at the G0/G1 phase and the S phase in CMT-U27 and CF41.mg cells. These results were supported by a Western blot analysis, which revealed upregulated protein expression of cleaved caspase-3, a marker of apoptosis, and downregulated cyclin-dependent kinase 4 and cyclin D1 protein, the cell cycle regulators. In conclusion, this novel study proves that esculetin exerts in vitro antitumor effects by inducing apoptosis and cell cycle arrest in canine mammary gland tumors.

Inactivated Cowpea Mosaic Virus for In Situ Vaccination: Differential Efficacy of Formalin vs UV-Inactivated Formulations

Cowpea mosaic virus (CPMV) has been developed as a promising nanoplatform technology for cancer immunotherapy; when applied as in situ vaccine, CPMV exhibits potent, systemic, and durable efficacy. While CPMV is not infectious to mammals, it is infectious to legumes; therefore, agronomic safety needs to be addressed to broaden the translational application of CPMV. RNA-containing formulations are preferred over RNA-free virus-like particles because the RNA and protein, each, contribute to CPMV's potent antitumor efficacy. We have previously optimized inactivation methods to develop CPMV that contains RNA but is not infectious to plants. We established that inactivated CPMV has reduced efficacy compared to untreated, native CPMV. However, a systematic comparison between native CPMV and different inactivated forms of CPMV was not done. Therefore, in this study, we directly compared the therapeutic efficacies and mechanisms of immune activation of CPMV, ultraviolet- (UV-), and formalin (Form)-inactivated CPMV to explain the differential efficacies. In a B16F10 melanoma mouse tumor model, Form-CPMV suppressed the tumor growth with prolonged survival (there were no statistical differences comparing CPMV and Form-CPMV). In comparison, UV-CPMV inhibited tumor growth significantly but not as well as Form-CPMV or CPMV. The reduced therapeutic efficacy of UV-CPMV is explained by the degree of cross-linking and aggregated state of the RNA, which renders it inaccessible for sensing by Toll-like receptor (TLR) 7/8 to activate immune responses. The mechanistic studies showed that the highly aggregated state of UV-CPMV inhibited TLR7 signaling more so than for the Form-CPMV formulation, reducing the secretion of interleukin-6 (IL-6) and interferon-α (IFN-α), cytokines associated with TLR7 signaling. These findings support the translational development of Form-CPMV as a noninfectious immunotherapeutic agent.

Systemic cellular viroimmunotherapy for canine high-grade gliomas

BACKGROUND

Oncolytic viruses constitute a growing field of interest, both in human and veterinary oncology, given that they are particularly helpful for treating non-surgical tumors and disseminated cancer, such as high-grade gliomas. Companion dogs present malignant gliomas with biological, genetic, phenotypic, immunological, and clinical similarities to human gliomas. These features favor comparative approaches, leading to the treatment of canine oncological patients to achieve translational applications to the human clinic. The systemic administration of oncolytic viruses presents a challenge due to their limitations in effectively targeting tumors and metastases. Therefore, the aim of this study is to evaluate the safety and antitumor activity of a virotherapy used in spontaneous canine tumors.

METHODS

Ten dogs with high-grade rostrotentorial gliomas underwent weekly systemic endovenous cellular virotherapy with dCelyvir (canine mesenchymal stem cells infected with the canine oncolytic adenovirus ICOCAV17) for 8 weeks. Efficacy was determined in seven dogs according to the Response Assessment in Veterinary Neuro-Oncology criteria considering clinical status and MRI measurements. Medical history, physical and neurological examinations, and vaccination status were evaluated prior to and during follow-up. Safety was evaluated by physical examinations and hematological and biochemical changes in peripheral blood. Immune populations were analyzed by flow cytometry in peripheral blood and by gene expression and immunohistochemistry in the tumor microenvironment.

RESULTS

The treatment was well tolerated and major adverse effects were not observed. Two dogs had partial responses (76% and 86% reduction in tumor size), and 3/7 showed stable disease. ICOCAV17 was detected in peripheral blood in nine dogs, and a correlation between the ICOCAV17 particles and anti-canine adenovirus (CAV) antibodies was observed. ICOCAV17 was detected in 3/9 tumor tissues after necropsies. Regarding tumor-infiltrating lymphocytes, the dogs with disease stabilization and partial response tended to have reduced memory B-cell infiltration and increased monocyte/macrophage lineage cells.

CONCLUSIONS

These findings indicate that dCelyvir is safe and presents efficacy in canine rostrotentorial high-grade gliomas. These data are relevant to the ongoing phase Ib regulated human clinical trial that is administering this virotherapy to children, adolescents, and young adults with diffuse pontine glioma. Celyvir should be further explored as a treatment in veterinary and human neuro-oncology.

Development of Monoclonal Antibodies Targeting Canine PD-L1 and PD-1 and Their Clinical Relevance in Canine Apocrine Gland Anal Sac Adenocarcinoma

Canine apocrine gland anal sac adenocarcinoma (AGASACA) is an aggressive canine tumor originating from the anal sac glands. Surgical resection, with or without adjuvant chemotherapy, represents the standard of care for this tumor, but the outcome is generally poor, particularly for tumors diagnosed at an advanced stage. For this reason, novel treatment options are warranted, and a few recent reports have suggested the activation of the immune checkpoint axis in canine AGASACA. In our study, we developed canine-specific monoclonal antibodies targeting PD-1 and PD-L1. A total of 41 AGASACAs with complete clinical and follow-up information were then analyzed by immunohistochemistry for the expression of the two checkpoint molecules (PD-L1 and PD-1) and the presence of tumor-infiltrating lymphocytes (CD3 and CD20), which were evaluated within the tumor bulk (intratumor) and in the surrounding stroma (peritumor). Seventeen AGASACAs (42%) expressed PD-L1 in a range between 5% and 95%. The intratumor lymphocytes were predominantly CD3+ T-cells and were positively correlated with the number of PD-1+ intratumor lymphocytes (ρ = 0.36; p = 0.02). The peritumor lymphocytes were a mixture of CD3+ and CD20+ cells with variable PD-1 expression (range 0-50%). PD-L1 expression negatively affected survival only in the subgroup of dogs treated with surgery alone (n = 14; 576 vs. 235 days). The presence of a heterogeneous lymphocytic infiltrate and the expression of PD-1 and PD-L1 molecules support the relevance of the immune microenvironment in canine AGASACAs and the potential value of immune checkpoints as promising therapeutic targets.

Metastatic Colon Cancer Treatment Using S100A9-Targeted Cowpea Mosaic Virus Nanoparticles

Peritoneal metastases (PMs) occur due to the metastasis of gynecological and gastrointestinal cancers such as ovarian, colon, pancreatic, or gastric tumors. PM outgrowth is often fatal, and patients with PMs have a median survival of 6 months. Cowpea mosaic virus (CPMV) has been shown, when injected intratumorally, to act as an immunomodulator reversing the immunosuppressive tumor microenvironment, therefore turning cold tumors hot and priming systemic antitumor immunity. However, not all tumors are injectable, and PMs especially will require targeted treatments to direct CPMV toward the disseminated tumor nodules. Toward this goal, we designed and tested a CPMV nanoparticle targeted to S100A9, a key immune mediator for many cancer types indicated in cancer growth, invasiveness, and metastasis. Here, we chose to use an intraperitoneal (IP) colon cancer model, and analysis of IP gavage fluid demonstrates that S100A9 is upregulated following IP challenge. S100A9-targeted CPMV particles displaying peptide ligands specific for S100A9 homed to IP-disseminated tumors, and treatment led to improved survival and decreased tumor burden. Targeting CPMV to S100A9 improves preclinical outcomes and harbors the potential of utilizing CPMV for the treatment of IP-disseminated diseases.

In situ vaccination with cowpea mosaic virus elicits systemic antitumor immunity and potentiates immune checkpoint blockade

BACKGROUND

In situ vaccination (ISV) is a cancer immunotherapy strategy in which immunostimulatory reagents are introduced directly into a tumor to stimulate antitumor immunity both against the treated tumor and systemically against untreated tumors. Recently, we showed that cowpea mosaic virus (CPMV) is a potent multi-toll-like receptor (TLR) agonist with potent efficacy for treating tumors in mice and dogs by ISV. However, ISV with CPMV alone does not uniformly treat all mouse tumor models tested, however this can be overcome through strategic combinations. More insight is needed to delineate potency and mechanism of systemic antitumor immunity and abscopal effect.

METHOD

We investigated the systemic efficacy (abscopal effect) of CPMV ISV with a two-tumor mouse model using murine tumor lines B16F10, 4T1, CT26 and MC38. Flow cytometry identified changes in cell populations responsible for systemic efficacy of CPMV. Transgenic knockout mice and depleting antibodies validated the role of relevant candidate cell populations and cytokines. We evaluated these findings and engineered a multicomponent combination therapy to specifically target the candidate cell population and investigated its systemic efficacy, acquired resistance and immunological memory in mouse models.

RESULTS

ISV with CPMV induces systemic antitumor T-cell-mediated immunity that inhibits growth of untreated tumors and requires conventional type-1 dendritic cells (cDC1s). Furthermore, using multiple tumor mouse models resistant to anti-programmed death 1 (PD-1) therapy, we tested the hypothesis that CPMV along with local activation of antigen-presenting cells with agonistic anti-CD40 can synergize and strengthen antitumor efficacy. Indeed, this combination ISV strategy induces an influx of CD8+ T cells, triggers regression in both treated local and untreated distant tumors and potentiates tumor responses to anti-PD-1 therapy. Moreover, serial ISV overcomes resistance to anti-PD-1 therapy and establishes tumor-specific immunological memory.

CONCLUSIONS

These findings provide new insights into in situ TLR activation and cDC1 recruitment as effective strategies to overcome resistance to immunotherapy in treated and untreated tumors.

In Vivo Fate of Cowpea Mosaic Virus In Situ Vaccine: Biodistribution and Clearance

Cowpea mosaic virus (CPMV) is a nucleoprotein nanoparticle that functions as a highly potent immunomodulator when administered intratumorally and is used as an in situ vaccine. CPMV in situ vaccination remodels the tumor microenvironment and primes a highly potent, systemic, and durable antitumor immune response against the treated and untreated, distant metastatic sites (abscopal effect). Potent efficacy was demonstrated in multiple tumor mouse models and, most importantly, in canine cancer patients with spontaneous tumors. Data indicate that presence of anti-CPMV antibodies are not neutralizing and that in fact opsonization leads to enhanced efficacy. Plant viruses are part of the food chain, but to date, there is no information on human exposure to CPMV. Therefore, patient sera were tested for the presence of immunoglobulins against CPMV, and indeed, >50% of deidentified patient samples tested positive for CPMV antibodies. To get a broader sense of plant virus exposure and immunogenicity in humans, we also tested sera for antibodies against tobacco mosaic virus (>90% patients tested positive), potato virus X (<20% patients tested positive), and cowpea chlorotic mottle virus (no antibodies were detected). Further, patient sera were analyzed for the presence of antibodies against the coliphage Qβ, a platform technology currently undergoing clinical trials for in situ vaccination; we found that 60% of patients present with anti-Qβ antibodies. Thus, data indicate human exposure to CPMV and other plant viruses and phages. Next, we thought to address agronomical safety; i.e., we examined the fate of CPMV after intratumoral treatment and oral gavage (to mimic consumption by food). Because live CPMV is used, an important question is whether there is any evidence of shedding of infectious particles from mice or patients. CPMV is noninfectious toward mammals; however, it is infectious toward plants including black-eyed peas and other legumes. Biodistribution data in tumor-bearing and healthy mice indicate little leaching from tumors and clearance via the reticuloendothelial system followed by biliary excretion. While there was evidence of shedding of RNA in stool, there was no evidence of infectious particles when plants were challenged with stool extracts, thus indicating agronomical safety. Together these data aid the translational development of CPMV as a drug candidate for cancer immunotherapy.

Comparative Evaluation of Tumor-Infiltrating Lymphocytes in Companion Animals: Immuno-Oncology as a Relevant Translational Model for Cancer Therapy

Despite the important role of preclinical experiments to characterize tumor biology and molecular pathways, there are ongoing challenges to model the tumor microenvironment, specifically the dynamic interactions between tumor cells and immune infiltrates. Comprehensive models of host-tumor immune interactions will enhance the development of emerging treatment strategies, such as immunotherapies. Although in vitro and murine models are important for the early modelling of cancer and treatment-response mechanisms, comparative research studies involving veterinary oncology may bridge the translational pathway to human studies. The natural progression of several malignancies in animals exhibits similar pathogenesis to human cancers, and previous studies have shown a relevant and evaluable immune system. Veterinary oncologists working alongside oncologists and cancer researchers have the potential to advance discovery. Understanding the host-tumor-immune interactions can accelerate drug and biomarker discovery in a clinically relevant setting. This review presents discoveries in comparative immuno-oncology and implications to cancer therapy.

Proactive Immunotherapeutic Approaches against Inflammatory Breast Cancer May Improve Patient Outcomes

Inflammatory breast cancer (IBC) is highly metastatic at the onset of the disease with no IBC-specific treatments, resulting in dismal patient survival. IBC treatment is a clear unmet clinical need. This commentary highlights findings from a recent seminal approach in which pembrolizumab, a checkpoint inhibitor against programmed cell death protein 1 (PD-1), was provided to a triple-negative IBC patient as a neoadjuvant immune therapy combined with anthracycline-taxane-based chemotherapy. We highlight the findings of the case report and offer a perspective on taking a proactive approach to deploy approved immune checkpoint inhibitors. On the basis of our recently published research study, we propose in situ vaccination with direct injection of immunostimulatory agents into the tumor as an option to improve outcomes safely, effectively, and economically for IBC patients.

Cowpea Mosaic Virus and Natural Killer Cell Agonism for In Situ Cancer Vaccination

We have previously shown the plant virus Cowpea mosaic virus (CPMV) to be an efficacious in situ cancer vaccine, providing elimination of tumors and tumor-specific immune memory. Additionally, we have shown that CPMV recruits Natural Killer (NK) cells within the tumor microenvironment. Here we aimed to determine whether a combination of CPMV and anti-4-1BB monoclonal antibody agonist to stimulate tumor-resident and CPMV-recruited NK cells is an effective dual therapy approach to improve NK cell function and in situ cancer vaccination efficacy. Using murine models of metastatic colon carcinomatosis and intradermal melanoma, intratumorally administered CPMV + anti-4-1BB dual therapy provided a robust antitumor response, improved elimination of primary tumors, and reduced mortality compared to CPMV and anti-4-1BB monotherapies. Additionally, on tumor rechallenge there was significant delay/prevention of tumor development and improved survival, highlighting that the CPMV + anti-4-1BB dual therapy enables potent and durable antitumor efficacy.