Meeting report: Cambridge Healthtech Institute’s 4th Annual Immuno-Oncology SUMMIT: Oncolytic Virus Immunotherapy Stream – 2016
Reporter: David Orchard-Webb, PhD
Cambridge Healthtech Institute’s 4th Annual Immuno-Oncology SUMMIT took place August 29-September 2, 2016 at the Marriott Long Wharf Boston, MA. The following is a synthesis of the Oncolytic Virus Immunotherapy stream.
Biomarkers for patient selection in clinical trials is an important consideration for developing cancer therapeutics and immunotherapeutics such as oncolytic viruses in particular. Howard L. Kaufman, M.D., discussed the development of biomarkers for oncolytic virus efficaciousness and patient selection focusing on Imlygic (HSV-1). An important consideration for any viral therapy is the presence or absence of the receptors that the virus uses to gain entry to the cell. For example HSV-1 utilises Nectin and HVEM cell surface receptors and their expression levels on a patient’s tumour will influence whether Imlygic can gain entry and replicate in tumours. In addition he reported that B-RAF mutation facilitates Imlygic infection and that MEK inhibitors sensitise melanoma cell lines to Imlygic. Stephen Russell also presented data on the mathematical modelling of Vesicular Stomatitis Virus (VSV) tumour spread and the development of a companion diagnostic based on gene expression profiling to predict patients whose tumours will be readily infected.
The immune reaction triggered by oncolytic viruses is important to monitor. Howard L. Kaufman discussed immunogenic cell death and stated that oncolytic viruses trigger immunity through the release of pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). He reported that immunosuppressive Tregs, PDL1 and IDO expression were associated with anti-cancer CD8+ T cell infiltration. Imlygic also promoted the tumour infiltration of monocytes which depending on the context may either be immunosuppressive or beneficial through recruiting natural killer (NK) cells. This highlights the importance of combining Imlygic with other immune modulating therapeutics that can modulate the immunosuppressive cells and messengers that are present in the tumour environment. He discussed the finding that high mutation burden is a marker for response to immune checkpoint inhibition (such as CTLA and PD1) and suggested that due to the fact that oncolytic viruses release tumour associated antigens (TAA) during cell lysis this may also be a predictive marker for oncolytic viral therapy immune response. Supporting this notion Stephen Russell reported that a patient that underwent complete remission of multiple myeloma plasmacytomas in response to a measles virus oncotherapy had a very high mutational burden.
Targeting the tumour stroma with adenoviral vectors
“VCN Biosciences SL is a privately-owned company focused in the development of new therapeutic approaches for tumors that lack effective treatment”. Manel Cascalló presented data from an ongoing phase I, multi-center, open-label dose escalation study of intravenous administration of VCN-01 oncolytic adenovirus with or without intravenous gemcitabine and Abraxane® in advanced solid tumors. Patients were selected based on low anti-Ad levels. Manel highlighted the problems of the pancreatic cancer matrix which limit intratumoral virus spread and also reduces chemotherapy uptake and tumour lymphocyte infiltration. VCN-01 expresses hyaluronidase to degrade the extracellular matrix and is administered intravenously. Liver tropism is reduced by replacement of the heparan sulfate glycosaminoglycan putative-binding site KKTK of the fiber shaft with an integrin-binding motif RGDK. VCN-01 replicates only in Rb tumour suppressor pathway dysregulated cancers, achieved through genetic modification of the E1A protein. In previous mouse xenograft studies of pancreatic and melanoma tumours VCN-01 showed efficaciousness in intratumoral spread, degradation of hyaluronan, and evidence of sensitisation to chemotherapy. The mouse models suggested that strategies that further target other major components of the ECM such as collagen and stromal cells may increase VCN-01 efficaciousness further . The phase I trial supported safety and demonstrated that when administered intravenously VCN-01 reached the pancreatic tumour and replicated. In combination with gemcitabine and Abraxane® neutropenia was observed earlier than with chemotherapy alone. This is suggestive of increased efficaciousness of the chemotherapeutics as would be expected if a greater effective concentration reached the tumour. Biopsies suggested that VCN-01 shifted the balance of immune cells towards CD8+ T cells and away from immunosuppressive Treg.
Adenovirus tumor-specific immunogene (T-SIGn) Therapy
“PsiOxus Therapeutics Ltd develops novel therapeutics for serious diseases with a particular focus upon cancer”. Brian Champion discussed the application EnAd a chimeric Ad11p/Ad3 adenovirus which retains the Ad11 receptor usage (CD46 and DSG2). PsiOxus are developing Membrane-integrated T-cell Engagers (MiTe) proteins delivered via EnAd. These MiTe proteins are expressed at the cancer cell surface and engage with and activate T-cells. Their lead candidate NG-348 showed promising T-cell activation in vitro.
Vaccinia virus – overcoming the immunosuppressive cancer microenvironment
David Kirn provided a recent history of the oncolytic virus field and provided an overview of the validation of vaccinia virus over the period 2007-14 stating that it can produce cancer oncolysis, induce an immune response, and result in angiogenic ablation.
“Western Oncolytics develops novel therapies for cancer”. Steve Thorne discussed strategies to mitigate the immunosupressive environment encountered by oncolytic viruses. He presented data from models of tumours resistant to vaccinia oncolytic virus that Treg, and myeloid-derived suppressor cell (MDSC) numbers were higher whereas CD8+ T-cell levels were lower than in a sensitive model. He elaborated on a strategy of targeting the PGE2 pathway in order to reduce MDSC numbers entering the tumour microenvironment. He demonstrated that vaccinia virus expressing HPGD has reduced levels of MDSC in target tumours.
“Transgene (Euronext: TNG), part of Institut Mérieux, is a publicly traded French biopharmaceutical company focused on discovering and developing targeted immunotherapies for the treatment of cancer and infectious diseases”. Eric Quéméneur presented preclinical data on Transgene’s oncolytic vaccinia virus TG6002 which expresses a chimeric bifunctional enzyme which converts the nontoxic prodrug 5‐FC into the toxic metabolites 5‐FU and 5‐FUMP. This allows systemic delivery of the non-toxic prodrug chemotherapy with activation at tumours infected with the Vaccinia oncolytic virus. The virus plus prodrug combination was effective against all of the solid tumour cell lines tested. In addition the combination was effective against glioblastoma cancer stem-like cells. In pancreatic and colorectal cancer cell line models the vaccinia prodrug combination was synergistic or additive when combined with additional chemotherapeutics. In immunocompetent mouse models TG6002 increased the Tumour Teff/Treg ratio indicative of a shift from an immunosuppressive to an immunocompetent microenvironment. Furthermore in mouse models TG6002 induced an abscopal response.
Vesicular Stomatitis Virus (VSV) – A single shot cure for cancer?
“Vyriad strives to develop potent, safe and cost-effective cancer therapies in areas of unmet need”. Stephen Russell presented his position that oncolytic viruses could be a single shot cure for cancer. He emphasised the point that in oncolytic viral therapy the initial dose will be the most effective due to the relatively low levels of neutralising antibodies present and therefore defining the optimal dose is critical. The trend is for increased initial dose. Two IND’s have been accepted by the FDA, one for measles virus and the other for VSV.
John Bell described using VSV to deliver Artificial microRNAs (amiRNAs) to tumours. It was demonstrate that a VSV delivering ARID1A amiRNA was synthetic lethal when combined with EZH2 (methyl transferase) inhibition. He postulated that oncolytic viruses can be used to create factories of therapeutic amiRNAs transmitted throughout the tumour by exosomes.
HSV-1 an update on immune checkpoint combinations
Amgen was the first company to launch an FDA approved (October 2015) oncolytic virus, trade name Imlygic, which was developed by the UK based company Biovex. Jennifer Gansert gave a background on Imlygic and presented new data on combination with the CTLA4 inhibitor Ipilimumab. In mouse models abscopal response in contralateral tumours was 100% when a single tumour was treated with Imlygic combined with systemic delivery of anti-CTLA4. A Phase 1b clinical trial to test the combination in unresectable melanoma patients was completed and published in 2016. Fifty percent of the patients had durable response for greater than 6 months and 20% of the patients had ongoing complete response after a year of follow-up. Overall 72% of patients has controlled disease (no progression). In addition Amgen is recruiting for a phase III trial of the anti-PD1 Pembrolizumab in combination with Imlygic for unresectable stage IIIB to IVM1c melanoma.
“Virttu is a privately held biotechnology company, which has pioneered the development of oncolytic viruses for treating cancer”. Joe Connor discussed Seprehvir an oncolyic virus based on HSV-1 like Imlygic which is in clinical trials for which 100 patients have been treated to date. The trial data indicate that Seprehvir induces CD8+ T cell infiltration and activity as well as a novel anti-tumour immune response against select antigens such as Mage A8/9. Preclinical investigations focus on combination with checkpoint inhibitor antibodies, CAR-T targeted to GD2, and synergies with targeted therapies on the mTOR/VEGFR signalling axes.
Reovirus – an update
“Oncolytics Biotech Inc. is a clinical-stage oncology company focused on the development of oncolytic viruses for use as cancer therapeutics in some of the most prevalent forms of the disease”. Brad Thompson provided an update on REOLYSIN®, Oncolytics Biotech’s proprietary T3D reovirus. Highlights included concluding the first checkpoint inhibitor and REOLYSIN® study in patients with pancreatic cancer and preparing for registration study in multiple myeloma.
Maraba virus – privileged antigen presentation in splenic B cell follicles
Turnstone Biologics is developing “a first-in-class oncolytic viral immunotherapy that combines a bioselected and engineered oncolytic virus to directly lyse tumors with a potent vaccine technology to drive tumor-antigen specific T-cell responses of unprecedented magnitude”. Caroline Breitbach described Maraba MG1 Oncolytic Virus which was isolated from Brazilian sand flies. Their lead candidate is an MG1 virus expressing the tumour antigen MAGE-A3. In mouse models a combination of adenovirus-MAGE-A3 and MG1-MAGE-A3 in a prime-boost regimen produced extremely robust CD8+ T cell responses. It is thought that a privileged antigen presentation in splenic B cell follicles maximizes the T cell responses. A phase I/II trial is enrolling patients to test the adenovirus-MAGE-A3 and MG1-MAGE-A3 prime-boost regimen in patients with MAGE‐A3 positive solid tumours for which there is no life prolonging standard therapy.
Oncolytic virus manufacturing
Anthony Davies of Dark Horse Consulting Inc. reviewed the manufacturing hurdles facing oncolytic viruses and pointed out that thus far adenovirus is the gold standard. He discussed isoelectric focusing for virus manufacturing, process flow and the procurement of key raw materials. He emphasized the importance of codifying analytical methods, and the statistical design of experiments (DOE) for optimal use of finite resources.
Mark Federspiel described the difficulties associated with measles virus manufacturing which include the large pleomorphic size (100-300nm) which cannot be filter sterilized efficiently due to shear stress. As a result aseptic conditions must be maintained throughout the manufacturing process. There are also issues with genomic contamination from infected cells. He described improved manufacturing bioprocesses to overcome these limitations using the HeLa S3 cell line. Using this cell line resulted in less residual genomic DNA than the standard however it was still relatively high compared to vaccine production. There is still much room for improvement.
Rodríguez-García A, Giménez-Alejandre M, Rojas JJ, Moreno R, Bazan-Peregrino M, Cascalló M, Alemany R. Safety and efficacy of VCN-01, an oncolytic adenovirus combining fiber HSG-binding domain replacement with RGD and hyaluronidase expression. Clin Cancer Res. 2015 Mar 15;21(6):1406-18. Doi: 10.1158/1078-0432.CCR-14-2213. Epub 2014 Nov 12. PubMed PMID: 25391696.
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