Oncolytic Reovirus Research Articles

Oral reovirus reshapes the gut microbiome and enhances antitumor immunity in colon cancer

The route of oncolytic virotherapy is pivotal for immunotherapeutic efficacy in advanced cancers. In this preclinical study, an oncolytic reovirus (RC402) is orally administered to induce antitumor immunity. Oral reovirus treatment shows no gross toxicities and effectively suppresses multifocal tumor lesions. Orally administered reovirus interacts with the host immune system in the Peyer’s patch of the terminal ileum, increases IgA+ antibody-secreting cells in the lamina propria through MAdCAM-1+ blood vessels, and reshapes the gut microbiome. Oral reovirus promotes antigen presentation, type I/II interferons, and T cell activation within distant tumors, but does not reach or directly infect tumor cells beyond the gastrointestinal tract. In contrast to intratumoral reovirus injection, the presence of the gut microbiome, Batf3+ dendritic cells, type I interferons, and CD8+ T cells are indispensable for orally administered reovirus-induced antitumor immunity. Oral reovirus treatment is most effective when combined with αPD-1(L1) and/or αCTLA-4, leading to complete colon tumor regression and protective immune memory. Collectively, oral reovirus virotherapy is a feasible and effective immunotherapeutic strategy in preclinical studies.

Oncolytic avian reovirus-sensitized tumor infiltrating CD8+ T cells triggering immunogenic apoptosis in gastric cancer.

Gastric cancer (GC) is a leading malignant disease in numerous countries, including Taiwan with limited therapeutic options. Animal viruses including oncolytic avian reovirus (ARV) have the possibility to avoid pre-existing immunity in humans, while being safe and immunostimulatory. Here, we provide a novel insight into oncolytic ARV and UV-ARV-sensitized patient's peripheral blood mononuclear cells (P-PBMCs) and tumor infiltrating lymphocytes (TILs) killing primary GC (PGC) cells through the surface TLR3 and TRAIL/DR4/DR5 immunogenic apoptosis pathway. We conducted a comprehensive study to reveal whether ARV- or UV-inactivated ARV (UV-ARV)-modulated P-PBMCs or TILs killing ARV- and UV-ARV-sensitized AGS cells and PGC cells derived from clinical patients and to investigate the regulation of surface TLR3 receptor and upstream signaling pathways. Apoptosis analysis by flow cytometry and Western blot, suppression of signal pathway by specific inhibitors, in situ proximity ligation assay (PLA), time-resolved flurometry and lactate dehydrogenase (LDH) cytotoxicity assays, and an in vitro co-culture model were established to study the interplay between ARV- and UV-ARV-sensitized P-PBMCs and TILs to kill PGC cells and their upstream pathways. Our results reveal that increased levels of DR4 and DR5 were observed in ARV and UV-ARV sensitized PGC cells through the TLR3/p38/p53 signaling pathway. Importantly, we found that the σC protein of ARV or UV-ARV interacted with surface TLR3 of CD8+ TILs, thereby triggering the TLR3/NF-κB/IFN-γ/TRAIL signaling pathway which induces immunogenic apoptosis of PGC cells. This study sheds further light on the molecular basis behind ARV oncolysis and facilitates the ARV or UV-ARV as a cancer therapeutic. The study provides novel insights into ARV- or UV-ARV-sensitized P-PBMCs and CD8+ TILs to kill PGC cells through the immunogenic apoptosis pathway. We conclude that P-PBMCs can easily be obtained from GC patients and provide a rich source as TILs to kill PGC cells.

The Oncolytic Avian Reovirus p17 Protein Inhibits Invadopodia Formation in Murine Melanoma Cancer Cells by Suppressing the FAK/Src Pathway and the Formation of theTKs5/NCK1 Complex.

To explore whether the p17 protein of oncolytic avian reovirus (ARV) mediates cell migration and invadopodia formation, we applied several molecular biological approaches for studying the involved cellular factors and signal pathways. We found that ARV p17 activates the p53/phosphatase and tensin homolog (PTEN) pathway to suppress the focal adhesion kinase (FAK)/Src signaling and downstream signal molecules, thus inhibiting cell migration and the formation of invadopodia in murine melanoma cancer cell line (B16-F10). Importantly, p17-induced formation of invadopodia could be reversed in cells transfected with the mutant PTENC124A. p17 protein was found to significantly reduce the expression levels of tyrosine kinase substrate 5 (TKs5), Rab40b, non-catalytic region of tyrosine kinase adaptor protein 1 (NCK1), and matrix metalloproteinases (MMP9), suggesting that TKs5 and Rab40b were transcriptionally downregulated by p17. Furthermore, we found that p17 suppresses the formation of the TKs5/NCK1 complex. Coexpression of TKs5 and Rab40b in B16-F10 cancer cells reversed p17-modulated suppression of the formation of invadopodia. This work provides new insights into p17-modulated suppression of invadopodia formation by activating the p53/PTEN pathway, suppressing the FAK/Src pathway, and inhibiting the formation of the TKs5/NCK1 complex.

Correction for Huang et al., "p17-Modulated Hsp90/Cdc37 Complex Governs Oncolytic Avian Reovirus Replication by Chaperoning p17, Which Promotes Viral Protein Synthesis and Accumulation of Viral Proteins σC and σA in Viral Factories".

Correction for Huang et al., "p17-Modulated Hsp90/Cdc37 Complex Governs Oncolytic Avian Reovirus Replication by Chaperoning p17, Which Promotes Viral Protein Synthesis and Accumulation of Viral Proteins σC and σA in Viral Factories".

Abstract PO1-02-01: T Cell Receptor Sequencing to Monitor Pelareorep-Induced Expansion of Tumor Infiltrating Lymphocytes

Abstract Background: Tumor infiltrating lymphocytes (TILs) represent a major immunological tumor control mechanism that is associated with better prognosis in breast cancer. We have previously reported the effect of pelareorep (pela), an intravenously delivered, non-engineered oncolytic reovirus, on a composite measurement of TILs and tumor cellularity (CelTIL) from the AWARE-1 window-of-opportunity study in patients with early breast cancer (eBC). These results showed treatment increased in CelTIL scores especially in the atezolizumab group. To confirm and extend these findings we applied T cell receptor sequencing of matched tumor tissue and whole blood pre and post-treatment from the AWARE-1 study to further explore the effects of pela therapy on TILs. Methods: Newly diagnosed HR+/HER2- eBC patients were enrolled into two cohorts: Cohort 1: pela + letrozole (n=10); and Cohort 2: pela + letrozole + atezolizumab (n=10). Pela was administered on days 1, 2 and 8, 9, and atezolizumab was given on day 3. Tumor biopsies (FFPE samples) collected pre-treatment (~D-23) and on day ~21 when tumors were surgically removed. T cell fraction analysis and T cell receptor sequencing were performed by Adaptive Biotechnology (Seattle, Washington) Immunoseq protocol. Results: As was shown for the CelTIL scores, an increase in the tumor T cell fraction, a direct measurement of TILs, was observed at 1-month post-treatment in both cohorts with a mean percent increase of 21% for Cohort 1 and 67% for Cohort 2. Through TCR-sequencing of tumor tissue, we identified TIL clones and tracked their differential abundance in tumor tissue and blood post-treatment. The results of this analysis at Day 21 showed a mean post-treatment expansion of 10 tumor specific clones in the blood for Cohort 1, and a mean post-treatment increase of 40 tumor specific clones for Cohort 2. Conclusions: These results confirm the previously reported CelTIL results from AWARE-1 on pela-induced increases in TILs and demonstrate the expansion of these clones in both tumor and blood as a consequence of pela therapy for HR+/HER2- breast cancer. Citation Format: Richard Trauger, Houra Loghmani, Matt Coffey, Fernando Salvador, Joaquín Gavilá, Luis Manso, Tomás Pascual, Aleix Prat, Thomas Heineman. T Cell Receptor Sequencing to Monitor Pelareorep-Induced Expansion of Tumor Infiltrating Lymphocytes [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-02-01.

Abstract CT186: A first-in-human phase 1 dose-escalation and expansion study of intratumoral oncolytic reovirus (RC402) as a monotherapy or in combination with pembrolizumab in advanced solid tumors

Abstract Background: RC402 is an oncolytic reovirus that selectively infects and destroys cancer cells. Preclinical studies have shown that RC402 remodels the tumor immune microenvironments and elicits potent anti-tumor immunity, thereby enhancing immune checkpoint inhibitors. Methods: This Phase I clinical trial (ACTRN12620000777998) was designed to evaluate the safety profiles and antitumor efficacy of intratumoral (IT) RC402 in patients with advanced solid tumors refractory to standard therapy and with accessible tumor lesions for IT injection of RC402. For the dose-escalation part (Phase 1a), the RC402 monotherapy dose was evaluated at 3 dose levels in Part A and the RC402 combination therapy dose with pembrolizumab was evaluated at 2 dose levels in part B using an accelerated titration method followed by a standard 3+3 dose escalation. In the dose-expansion part (Phase 1b), patients were treated with IT RC402 in combination with pembrolizumab at the recommended dose selected from the dose escalation part. RC402 was IT injected on day 1 of each treatment cycle. Fixed-dose pembrolizumab (200mg Q3W) was intravenously administered on day 8 of each treatment cycle for Phase 1a Part B and Phase 1b. Viral shedding was assessed serially in serum, urine, sputum, and stool samples, and neutralizing antibodies to Reovirus Type 3 Dearing were analyzed in serum samples. Results: Nine patients (2 gastric cancer and 1 cutaneous squamous cell carcinoma [cSCC] in Phase 1a Part A, 1 cSCC and 1 colorectal cancer [CRC] in Phase 1a Part B, and 1 cSCC and 3 CRC in Phase 1b) were enrolled and treated with at least two doses of RC402. IT administration of RC402 was generally well tolerated with no dose-limiting toxicities at all dose levels (1.6 × 108, 1.4 × 109, and 1.4 ×1010 PFU) as a monotherapy or in combination with pembrolizumab. The maximum tolerated dose was not reached. There were no treatment-emergent adverse events (TEAEs) leading to treatment discontinuation and no RC402-related serious TEAEs. The most common AEs were chills, fatigue, injection site reactions (erythema and pain) and nausea. Response evaluation showed two complete responses (one patients with cSCC in Phase 1a Part A and another patient with cSCC in the dose expansion part) lasting longer than 90 weeks and 36 weeks, respectively. No viral shedding was detected in any serum, urine, sputum, and stool samples on days 1, 2, and 15 of cycle 1, on day 2 of subsequent cycles and at the end of treatment. All patients showed an initial increase in antireoviral antibody titers on day 1 of cycle 2, followed by a decrease in subsequent cycles. Conclusion: This first-in-human study demonstrated IT RC402 is well tolerated and has a manageable safety profile with preliminary clinical activity as a monotherapy and in combination with pembrolizumab. These results warrant further clinical development of RC402. Citation Format: Mark Voskoboynik, Jia Liu, Ki-Hoon Song, Dong-Guk Park, Min-Hee Ryu, Hong Jae Chon, Chan Kim. A first-in-human phase 1 dose-escalation and expansion study of intratumoral oncolytic reovirus (RC402) as a monotherapy or in combination with pembrolizumab in advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT186.

Abstract 2025: Zeb1 downregulation sensitizes pancreatic cancer-associated fibroblasts to killing by oncolytic reovirus through upregulation of the reovirus receptor junction adhesion molecule A

Abstract Pancreatic tumors display an abundance of cancer-associated fibroblasts (CAFs), which negatively affect prognosis and therapy response. Oncolytic virotherapy exploits viruses that preferentially lyse epithelial cancer cells as opposed to normal cells. Interestingly, we have observed that oncolytic reoviruses are able to infect and lyse CAFs, in addition to epithelial cancer cells. Targeting CAFs, in addition to cancer cells, could be advantageous to increase therapy effectiveness. It could serve as a conduit for viral spread and simultaneously disrupt the desmoplastic barrier around tumors, thereby also accelerating the influx of other therapeutics and immune cells. We previously found that the proneness of CAFs to lysis by oncolytic reovirus correlates with the cell surface expression levels of the reovirus entry receptor junction adhesion molecule A (JAM-A). However, most pancreatic CAFs do not express JAM-A. Therefore, a genome-wide CRISPR/Cas9 screen was employed to identify the genes regulating JAM-A expression on fibroblasts, which can subsequently be targeted to sensitize CAFs to reovirus. Pancreatic stellate cells with a moderate JAM-A expression level were transduced with a gRNA library making a knockout of one gene per cell. The highest and lowest JAM-A expressing cells were sorted and sequenced to identify the gRNAs that regulate JAM-A expression. Clonal CRISPR/Cas9-generated knockouts of a top negative regulator were generated and infected with reovirus, followed by cell viability assays to quantify their susceptibilities to reovirus-induced cell death. F11R, the gene encoding JAM-A, was identified as the top positive regulator of JAM-A expression in the CRISPR/Cas9 screen, verifying the validity of the screen. The top negative regulators identified were Fibroblast Growth Factor Receptor 1 (FGFR1) and Zinc finger E-box Binding homeobox 1 (Zeb1), thereby serving as potential therapeutic targets to sensitize CAFs to reovirus treatment. Using clonal Zeb1 knock-outs, Zeb1 was confirmed as a strong regulator of JAM-A expression. Zeb1 knockout in JAM-A negative pancreatic fibroblasts caused a robust upregulation of JAM-A and sensitized these inherently resistant fibroblasts to reovirus-directed cytolysis. Additionally, the clinically approved drug Mocetinostat, previously described to inhibit Zeb1, upregulated JAM-A expression on CAFs and increased cell lysis by reovirus. Altogether, our data show that Zeb1 is a strong negative regulator of JAM-A expression on fibroblasts and that Zeb1 inhibition can sensitize CAFs to reovirus-induced cell death. This research provides a rationale for combining Zeb1 inhibitory drugs with oncolytic reovirus treatment to improve killing of CAFs, which in turn could boost overall tumor eradication. Citation Format: Nicole Dam, Tom J. Harryvan, Bernhard Schmierer, Lukas J.A.C. Hawinkels, Vera Kemp. Zeb1 downregulation sensitizes pancreatic cancer-associated fibroblasts to killing by oncolytic reovirus through upregulation of the reovirus receptor junction adhesion molecule A [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2025.

Expression of Concern: Cytokine-induced killer cell delivery enhances the antitumor activity of oncolytic reovirus.

Expression of Concern: Cytokine-induced killer cell delivery enhances the antitumor activity of oncolytic reovirus.

Abstract B033: Multiplex analysis of the tumor immune microenvironment during treatment with atezolizumab/pelareorep/letrozole reveals novel immune-tumor interactions

Abstract Background: Pelareorep (pela) is a non-modified intravenously administered oncolytic reovirus exhibiting effective tumor suppression through both innate and adaptive immune responses, as well as direct tumor lysis. Findings from the AWARE-1 window of opportunity study previously demonstrated the synergistic potential of combining pela with atezolizumab (atezo), showcasing promising immunological reactions within tumors of early breast cancer (eBC) patients. To gain deeper insights into the complex tumor immune microenvironment (TiME) pre- and post-treatment, we employed imaging mass cytometry (IMC) to conduct high-dimensional, single-cell analysis of tissue samples. Methods: Patients (n=10) received pela (days 1, 2 and 8, 9), atezolizumab (day 3), and letrozole (day 1 to 21). Tumor biopsies (FFPE samples) were collected pre-treatment on day 3 (prior to atezolizumab administration) and on day ~21 (surgical excision). Samples from 8 out of 10 patients were subjected to IMC with a comprehensive panel of 37 antibodies for single cell investigation of TiME changes. Tumor, proliferation, T cell, macrophage, NK, and immunoregulatory markers were included in the panel. Results: Our first pass analysis of IMC images, showed an increase in proliferating (Ki67+) cytotoxic T cells adjacent to apoptotic (caspase 3+) tumor cells post-treatment (both D3 and D21) samples indicating immunogenic cell death. Conversely, we observed a decrease in Ki67+ and ER-positive tumor cells after treatment indicating decreased tumor cell proliferation and hormone expression. In 3 out of 8 patients, treatment was associated with a shift in monocyte/macrophages from an M1 (CD68+/CD163-) to M2 (CD68+/CD163+) phenotype associated with significant tumor infiltration. Surprisingly, in these patients we also noted a significant increase in apoptotic M2 macrophages on D21. Consistent with the known immune priming effects of pela, both PD-1 and PD-L1 increased on D3. Subsequently, on day 21, post atezo, tumor PD-L1 decreased on tumor cells while PD-1 expression persisted. Pela induced IDO expression on both tumor and monocyte/macrophage cells. Unlike its effect on PD-L1, atezo did not appear to attenuate IDO expression on day 21. We were also able to detect a treatment related increase in immune cell perivascular localization on D3 providing further evidence of TiME priming. Conclusions: The immune system plays a crucial role in regulating cancer progression; however, our understanding of immune interactions with tumors remains limited. Our study utilizing IMC revealed complex immune-tumor interactions changes during treatment with atezo/pela/letrozole. These findings provide valuable insights into the intricate dynamics of the TiME and may inform new therapeutic combination approaches in breast cancer treatment. Citation Format: Homa Dadrastoussi, Julian Olea, Eduardo Fernandez Hernandez, Hugo Lara Martinez, Kaijin Wu, Houra Loghmani, Thomas Heineman, Richard Trauger, Matt Coffey, Akil Merchant, Kevin Kelly. Multiplex analysis of the tumor immune microenvironment during treatment with atezolizumab/pelareorep/letrozole reveals novel immune-tumor interactions [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2023 Oct 1-4; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Immunol Res 2023;11(12 Suppl):Abstract nr B033.

The efficacy and safety assessment of oncolytic virotherapies in the treatment of advanced melanoma: a systematic review and meta-analysis

BackgroundThe efficacy and safety of oncolytic virotherapies in the treatment of advanced melanoma still remains controversal. It is necessary to conduct quantitative evaluation on the basis of preclinical trial reports.MethodsPublicly available databases (PubMed, Embase, Medline, Web of Science and Cochrane Library.) and register (Clinicaltrials.gov) were searched to collect treatment outcomes of oncolytic virotherapies (including herpes simplex virus type 1 (HSV), coxsackievirus A21 (CVA21), adenovirus, poxvirus and reovirus) for advanced/unresectable melanoma. Comparisons of treatment response, adverse events (AEs) and survival analyses for different virotherapies were performed by R software based on the extracted data from eligible studies.ResultsFinally, thirty-four eligible studies were analysed and HSV virotherapy had the highest average complete response (CR, 24.8%) and HSV had a slightly higher average overall response rate (ORR) than CVA21 (43.8% vs 42.6%). In the pooled results of comparing talimogene laherparepve (T-VEC) with or without GM-CSF/ICIs (immune checkpoint inhibitors) to GM-CSF/ICIs monotherapy suggested virotherapy was more efficient in subgroups CR (RR = 1.80, 95% CI [1.30; 2.51], P < 0.01), ORR (RR = 1.17, 95% CI [1.02; 1.34], P < 0.05), and DCR (RR = 1.27, 95% CI [1.15; 1.40], P < 0.01). In patients treated with T-VEC+ICIs, 2-year overall survival (12.1 ± 6.9 months) and progression-free survival (9.9 ± 6.9) were significantly longer than those treated with T-VEC alone. Furthermore, we found that AEs occurred frequently in virotherapy but decreased in a large cohort of enrolled patients, some of which, such as abdominal distension/pain, injection site pain and pruritus, were found to be positively associated with disease progression in patients treated with T-VEC monotherapy.ConclusionGiven the relative safety and tolerability of oncolytic viruses, and the lack of reports of dose-limiting-dependent toxicities, more patients treated with T-VEC with or without ICIs should be added to future assessment analyses. There is still a long way to go before it can be used as a first-line therapy for patients with advanced or unresectable melanoma.

Noncoding RNA Profile in Reovirus Treated KRAS-Mutated Colorectal Cancer Patients.

To investigate the alterations in the expression of noncoding, micro, and small RNA expression during treatment with oncolytic reovirus in KRAS-mutated colorectal cancer. Oncolytic reovirus treatment was administered in phase 1 clinical trial (NCT01274624) for 5 days every 28 days, and blood samples were collected before the administration of the reovirus and 48 h, 8 days, and 15 days after its administration on day 1. Data from the blood samples were sorted using Transcriptome Analysis Software (TAC) 4.0, where a two-tailed t-test and a fold change filter were used to ascertain which sample signals had a statistically significant relative fold change of greater than 2 at multiple timepoints before or after oncolytic reovirus administration. The long noncoding RNA's RP11-332M2.1 (-6.1 x), LINC01506 (-16.18 x), and LINC00534 (-1.94 x) were downregulated at 48 h after reovirus administration [p < 0.05]. ncRNA's EPB41L4A-AS1 (-6.34 x, 48 h; 11.99 x, day 8), JAK2 (2.2 x, 48 h; -2.23 x, day 8), ANXA4 (20.47 x, day 8; -7.54 x, day 15), and PCDH9 (-2.09, day 8; 1.82 x, day 15) were affected by the reovirus treatment and reflected the progress of the treatment [p < 0.05]. The small RNA SNORA26 (-1.59 x, day 8) was downregulated 48 h after the reovirus administration [p < 0.05]. The microRNA MIR-4461 (6.18 x, day 8; -3.76 x, day 15) was also affected by the reovirus administration [p < 0.05]. The administration of oncolytic reovirus to treat KRAS-mutated colorectal cancer is reflected in a noncoding RNA profile, and expression levels of the ncRNAs in that profile may thus be able to be used as a potential predictive marker for reovirus-treated colorectal cancer.

UP14 - Exploring the efficacy of oncolytic reovirus jin-3 in a preclinical orthotopic prostate cancer model

UP14 - Exploring the efficacy of oncolytic reovirus jin-3 in a preclinical orthotopic prostate cancer model

Reovirus combined with a STING agonist enhances anti-tumor immunity in a mouse model of colorectal cancer.

Reovirus, a naturally occurring oncolytic virus, initiates the lysis of tumor cells while simultaneously releasing tumor antigens or proapoptotic cytokines in the tumor microenvironment to augment anticancer immunity. However, reovirus has developed a strategy to evade antiviral immunity via its inhibitory effect on interferon production, which negatively affects the induction of antitumor immune responses. The mammalian adaptor protein Stimulator of Interferon Genes (STING) was identified as a key regulator that orchestrates immune responses by sensing cytosolic DNA derived from pathogens or tumors, resulting in the production of type I interferon. Recent studies reported the role of STING in innate immune responses to RNA viruses leading to the restriction of RNA virus replication. In the current study, we found that reovirus had a reciprocal reaction with a STING agonist regarding type I interferon responses in vitro; however, we found that the combination of reovirus and STING agonist enhanced anti-tumor immunity by enhancing cytotoxic T cell trafficking into tumors, leading to significant tumor regression and survival benefit in a syngeneic colorectal cancer model. Our data indicate the combination of reovirus and a STING agonist to enhance inflammation in the tumor microenvironment might be a strategy to improve oncolytic reovirus immunotherapy.

Modulation of Reoviral Cytolysis (I): Combination Therapeutics.

Patients with stage IV gastric cancer suffer from dismal outcomes, a challenge especially in many Asian populations and for which new therapeutic options are needed. To explore this issue, we used oncolytic reovirus in combination with currently used chemotherapeutic drugs (irinotecan, paclitaxel, and docetaxel) for the treatment of gastric and other gastrointestinal cancer cells in vitro and in a mouse model. Cell viability in vitro was quantified by WST-1 assays in human cancer cell lines treated with reovirus and/or chemotherapeutic agents. The expression of reovirus protein and caspase activity was determined by flow cytometry. For in vivo studies, athymic mice received intratumoral injections of reovirus in combination with irinotecan or paclitaxel, after which tumor size was monitored. In contrast to expectations, we found that reoviral oncolysis was only poorly correlated with Ras pathway activation. Even so, the combination of reovirus with chemotherapeutic agents showed synergistic cytopathic effects in vitro, plus enhanced reovirus replication and apoptosis. In vivo experiments showed that reovirus alone can reduce tumor size and that the combination of reovirus with chemotherapeutic agents enhances this effect. Thus, we find that oncolytic reovirus therapy is effective against gastric cancer. Moreover, the combination of reovirus and chemotherapeutic agents synergistically enhanced cytotoxicity in human gastric cancer cell lines in vitro and in vivo. Our data support the use of reovirus in combination with chemotherapy in further clinical trials, and highlight the need for better biomarkers for reoviral oncolytic responsiveness.

BRACELET-1 (PrE0113): Inducing an inflammatory phenotype in metastatic HR+/HER2- breast cancer with the oncolytic reovirus pelareorep in combination with paclitaxel and avelumab.

1012 Background: In preclinical studies, the oncolytic reovirus pelareorep promoted an inflammatory tumor microenvironment (TME) by promoting greater infiltration of tumor infiltrating lymphocytes and upregulating PD-1/PD-L1 expression, potentially increasing the efficacy of immune checkpoint blockade. The addition of pelareorep to paclitaxel (PTX) was associated with improved survival (10.4 vs. 17.4 mos., HR = 0.65, p = 0.1) in a prior trial, with the greatest benefit in patients (pts) with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) disease (N = 57; 10.8 vs. 21.0 mos., HR 0.60, p = 0.1). Methods: This is a randomized phase 2 study in pts with HR+/HER2- metastatic breast cancer. Patients must have progressed on at least one hormone therapy with a CDK4/6 inhibitor. After a safety run-in for Cohort 3, patients were randomized 1:1:1 to PTX-alone (Cohort 1), PTX + pelareorep (Cohort 2), or PTX + pelareorep + avelumab (Cohort 3). The primary endpoint was overall response rate (ORR) at week 16 according to RECIST v1.1 without formal comparison across groups. Toxicity, progression-free survival (PFS) and overall survival were secondary endpoints. Blood samples were collected at cycle 1-day 1 (C1D1), C2D1 and C4D1, and T-cell receptor sequencing was performed. Results: Forty-eight pts were enrolled between June 2020 and June 2022. Median age was 55.5 yrs, range 37-74. Forty pts (83%) had visceral disease. Six pts (12%) previously received everolimus, and 3 alpelisib. Thirteen pts (27%) received prior taxanes in the neo/adjuvant setting. Three pts who withdrew consent prior to starting therapy and 2 pts who discontinued treatment after week 1 were considered non-responders and were censored for PFS. The most common pelareorep-associated toxicities were fever, chills, and flu-like infusion reactions, which were occasionally severe enough to require hospitalization in 5 (15%) pts despite acetaminophen prophylaxis. Nine pts (33%) discontinued pelareorep and 6 (35%) discontinued avelumab due to toxicity. Pelareorep increased T-cell repertoire turnover, with identification and expansion of new and pre-existing T-cell clones by C2D1. Conclusions: The addition of pelareorep to PTX is an active regimen with a high 6-month PFS rate worthy of further study. One third of patients discontinued either pelareorep or avelumab due to toxicity, highlighting the need for attentive supportive care. Survival data is maturing. Clinical trial information: NCT04215146 . [Table: see text]

Intravesical oncolytic virotherapy and immunotherapy for non-muscle-invasive bladder cancer mouse model.

To test if intravesical instillation of both an anti-programmed cell death protein 1 (PD-1) inhibitor and an oncolytic reovirus would demonstrate a greater effect than either treatment alone, as non-muscle-invasive bladder cancer that is refractory to intravesical bacillus Calmette-Guérin can be treated by systemic anti-PD-1 immunotherapy and we previously demonstrated improved overall survival (OS) with six once-weekly instillations of intravesical anti-PD-1 in a murine model. Using an orthotopic syngeneic C3H murine model of MBT2 urothelial bladder cancer, groups of 10 mice were compared between no treatment, intravesical anti-PD-1, intravesical oncolytic reovirus, or intravesical reovirus + anti-PD-1. A single intravesical treatment session was given. The primary outcome was OS, and the secondary outcomes included long-term immunity and tumour-immune profile. With a median follow-up of 9 months, all mice that received no treatment died with a median survival of 41 days, while the comparison median OS was not reached for reovirus (hazard ratio [HR] 14.4, 95% confidence interval [CI] 3.9-32.6; P < 0.001), anti-PD-1 (HR 28.4, 95% CI 7.0-115.9; P < 0.001), and reovirus + anti-PD-1 (HR 28.4, 95% CI 7.0-115.9; P < 0.001). Monotherapy with anti-PD-1 or reovirus demonstrated no significant differences in survival (P = 0.067). Mass cytometry showed that reovirus + anti-PD-1 treatment enriched monocytes and decreased myeloid-derived suppressor cells, generating an immuno-responsive tumour microenvironment. Depletion of CD8+ T cells eliminated the survival advantage provided by the intravesical treatment. Treatment of murine orthotopic bladder tumours with a single instillation of intravesical reovirus, anti-PD-1 antibody, or the combination confers superior survival compared to controls. Tumour-immune microenvironment differences indicated myeloid-derived suppressor cells and CD8+ T cells mediate the treatment response.

Abstract PD4-03: PD4-03 Pelareorep primes the tumor for checkpoint inhibition therapy by activating the interferon-gamma signaling pathway and tumor inflammation signature in early breast cancer patients - results of the AWARE-1 trial

Abstract Background The status of the tumor microenvironment (TME) can profoundly affect the response to immune-based therapies for the treatment of cancer. Results previously reported from the AWARE-1 study in early breast cancer patients demonstrated that pelareorep (pela, an oncolytic reovirus), alone or in combination with checkpoint inhibitor (CPI) therapy, modified the inflammatory state of the TME. We also showed that many of pela’s effects on the TME were enhanced by the addition of checkpoint blockade. Here, we report the effect of treatment with pela on selected molecular markers associated with enhanced anti-tumor immunity. Methods Newly diagnosed HR+/HER2- early BC patients were enrolled into two cohorts: Cohort 1 (C1): pela + letrozole (n=10); and Cohort 2 (C2): pela + letrozole + atezolizumab (n=10). Pela was intravenously administered on days 1, 2 and 8, 9, and atezolizumab was given on day 3. For this analysis, tumor biopsies (FFPE samples) collected pre-treatment (D1) and on days 3 (D3, prior to the atezolizumab administration) were examined by GeoMx digital spatial profiling (DSP, using Nanostring’s Cancer Transcriptome Atlas [CTA]). Moreover, the expression of 770 immune-related genes was analyzed using a specific immune panel (n=20). Gene Set Enrichment Analysis (GSEA) (version 4.1.0) was used to assess pela-induced activation pathways. Results GeoMx DSP showed that pela therapy significantly activated IFN-gamma signaling and associated interferon response genes from D1 to D3 (Normalized Enrichment Score [NES] = 3.3, p-values &amp;lt; 0.02) in the cytokeratin-positive subset of the tumor samples. GSEA of the immune dataset (730 immune genes + 30 housekeeping genes) from the whole tissue also showed a significant upregulation of IFN-gamma signaling pathway genes (FDR &amp;lt; 25%, p-value&amp;lt; 0.001). Increases were also observed in genes reported to be associated with an enhanced tumor inflammatory signal (TIS) including PD-L1, IDO1, HLA-E and STAT1 (p-values &amp;lt; 0.005). Conclusions These results demonstrate that treatment with pela alters the TME to induce and enhance anti-tumor immunity. This enhancement of anti-tumor immunity may potentiate the TME for CPI therapy. Citation Format: Houra Loghmani, Joaquín Gavilá, Luis Manso, Matt Coffey, Richard Trauger, Fernando Salvador, Tomás Pascual, Aleix Prat, Thomas Heineman. PD4-03 Pelareorep primes the tumor for checkpoint inhibition therapy by activating the interferon-gamma signaling pathway and tumor inflammation signature in early breast cancer patients - results of the AWARE-1 trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD4-03.

Oncolytic Avian Reovirus σA-Modulated Upregulation of the HIF-1α/C-myc/glut1 Pathway to Produce More Energy in Different Cancer Cell Lines Benefiting Virus Replication.

Our previous reports proved that the structural protein σA of avian reovirus (ARV) is an energy activator which can regulate cellular metabolism that is essential for virus replication. This study has further demonstrated that the ARV protein σA is able to upregulate the HIF-1α/myc/glut1 pathway in three cancer cell lines (A549, B16-F10, and HeLa) to alter the metabolic pathway of host cells. Quantitative real-time RT-PCR and Western blotting results have revealed that σA protein could enhance both mRNA and the protein levels of HIF-1α, c-myc, and glut1 in these cancer cell lines. In this work, ATeam immunofluorescence staining was used to reveal that knockdown of HIF-1α, c-myc, and glut1 by shRNAs decreased cellular ATP levels. Our data reveal that the ARV σA protein can downregulate lactate fermentation and upregulate glutaminolysis. The σA protein upregulates glutaminase, which converts glutamate into the TCA cycle intermediate α-ketoglutarate, activating the TCA cycle. In the lactate fermentation pathway, ARV σA protein suppresses lactate dehydrogenase A (LDHA), implying the Warburg effect does not occur in these cancer cell lines. This study provides a novel finding revealing that ARV σA protein upregulates glycolysis and glutaminolysis to produce energy using the HIF-1α/c-myc/glut1 pathway to benefit virus replication in these cancer cell lines.

P38 Mitogen-Activated Protein Kinase Signaling Enhances Reovirus Replication by Facilitating Efficient Virus Entry, Capsid Uncoating, and Postuncoating Steps.

Mammalian orthoreovirus serotype 3 Dearing is an oncolytic virus currently undergoing multiple clinical trials as a potential cancer therapy. Previous clinical trials have emphasized the importance of prescreening patients for prognostic markers to improve therapeutic success. However, only generic cancer markers such as epidermal growth factor receptor (EGFR), Hras, Kras, Nras, Braf, and p53 are currently utilized, with limited benefit in predicting therapeutic efficacy. This study aimed to investigate the role of p38 mitogen-activated protein kinase (MAPK) signaling during reovirus infection. Using a panel of specific p38 MAPK inhibitors and an inactive inhibitor analogue, p38 MAPK signaling was found to be essential for establishment of reovirus infection by enhancing reovirus endocytosis, facilitating efficient reovirus uncoating at the endo-lysosomal stage, and augmenting postuncoating replication steps. Using a broad panel of human breast cancer cell lines, susceptibility to reovirus infection corresponded with virus binding and uncoating efficiency, which strongly correlated with status of the p38β isoform. Together, results suggest p38β isoform as a potential prognostic marker for early stages of reovirus infection that are crucial to successful reovirus infection. IMPORTANCE The use of Pelareorep (mammalian orthoreovirus) as a therapy for metastatic breast cancer has shown promising results in recent clinical trials. However, the selection of prognostic markers to stratify patients has had limited success due to the fact that these markers are upstream receptors and signaling pathways that are present in a high percentage of cancers. This study demonstrates that the mechanism of action of p38 MAPK signaling plays a key role in establishment of reovirus infection at both early entry and late replication steps. Using a panel of breast cancer cell lines, we found that the expression levels of the MAPK11 (p38β) isoform are a strong determinant of reovirus uncoating and infection establishment. Our findings suggest that selecting prognostic markers that target key steps in reovirus replication may improve patient stratification during oncolytic reovirus therapy.

Pre-treatment of oncolytic reovirus improves tumor accumulation and intratumoral distribution of PEG-liposomes.

PEGylated liposomes (PEG-liposomes) are a promising drug delivery vehicle for tumor targeting because of their efficient tumor disposition profiles via the enhanced permeability and retention (EPR) effect. However, tumor targeting of PEG-liposomes, particularly their delivery inside the tumors, is often disturbed by physical barriers in the tumor, including tumor cells themselves, extracellular matrices, and interstitial pressures. In this study, B16 melanoma tumor-bearing mice were injected intravenously with oncolytic reovirus before administration of PEG-liposomes to enhance PEG-liposomes' tumor disposition. Three days after reovirus administration, significant expression of reovirus sigma 3 protein, elevation of apoptosis-related gene expression, and activation of caspase 3 in the tumors were found. Apoptotic cells were found inside the tumors. These data indicated that reovirus efficiently replicated in the tumors and induced apoptosis of tumor cells. The tumor disposition levels of PEG-liposomes were approximately doubled by reovirus pre-administration, compared with a PBS-pretreated group. PEG-liposomes were widely distributed in the tumors of reovirus-pretreated mice, whereas in the PBS-pretreated group, PEG-liposomes were found mainly around or inside the blood vessels in the tumors. Pre-treatment with reovirus also improved the tumor accumulation of PEG-liposomes in human pancreatic BxPC-3 tumors. 3D imaging analysis of whole BxPC-3 tumors demonstrated that pretreatment with reovirus led to the enhancement of PEG-liposome accumulation inside the tumors. Combination treatment with reovirus and paclitaxel-loaded PEG-liposomes (PTX-PEG-liposomes) significantly suppressed B16 tumor growth. These results provide important information for clinical use of combination therapy of reovirus and nanoparticle-based drug delivery system (DDS).