Abstract 4566: OncoVEXmGM-CSF (HSV-1 modified similarly to Talimogene Laherparepvec) in combination with CTLA-4 blockade leads to both local and systemic efficacy in a murine syngeneic model of metastatic melanoma
Authors: Cooke Keegan , Estrada Juan , Zhan Jinghui , Hill David , Boden Andrea , Werner Jon , Beltran Pedro J. 
Published: July 2017

Talimogene laherparepvec is an oncolytic immunotherapy based on a modified herpes simplex virus type 1 (HSV-1) designed to kill cancer cells through two mechanisms: a) direct viral-mediated lysis and b) stimulation of a tumor antigen-specific adaptive immune response. We developed a mouse model of metastatic melanoma using the B16F10 cell line to study local and systemic responses following treatment with talimogene laherparepvec alone or in combination with CTLA-4 blockade. OncoVEXmGM-CSF, an HSV-1 modified similarly to talimogene laherparepvec (murine GM-CSF is expressed instead of human GM-CSF) was used in these studies.

B16F10 cells have been reported to be resistant to HSV-1 infection due to a lack of requisite entry receptors. To overcome resistance, we transduced B16F10 cells with a lentiviral vector expressing mouse nectin1 (mNectin1) or eGFP as a control. Expression was confirmed by ddPCR and sensitivity to OncoVEXmGM-CSF evaluated in an in vitro viability assay. B16F10-mNectin1 cells were highly sensitive to OncoVEXmGM-CSF with a multiplicity of infection (MOI) IC50 of 0.001 (B16F10-eGFP were insensitive at MOI of 100). In vivo, B16F10-mNectin1 and B16F10-eGFP cells showed similar growth when injected subcutaneously. OncoVEXmGM-CSF treatment of B16F10-mNectin1 tumors (intratumoral, 5x106 PFU/dose, 3X) caused a significant (p&lt;0.0001) inhibition of tumor growth and prolonged median overall survival compared to control animals. To assess the local and systemic effect of OncoVEXmGM-CSF in combination with CTLA-4 blockade, we developed a model of experimental metastatic melanoma by delivering the B16F10-eGFP cells intravenously (systemic, non-injectable tumors) on day 0 and implanting the B16F10-mNectin1 cells SC (local, injectable tumors) on day 2. Mice were dosed with OncoVEXmGM-CSF and anti-CTLA-4 antibody 9D9 (100ug/dose) every 3 days between days 12 and 19. Subcutaneous tumor growth inhibition was assessed and lung metastasis were quantified on day 28. Both OncoVEXmGM-CSF and CTLA-4 treatment significantly inhibited subcutaneous tumor growth and lung metastasis. The combination of both therapeutics resulted in significantly greater local and systemic efficacy than either agent alone. The strong local and systemic anti-tumor activity of the combination resulted in a significant increase in median overall survival (p&lt;0.0001) compared to control mice that received intravenous B16F10-eGFP cells only.

In conclusion, OncoVEXmGM-CSF in combination with CTLA-4 blockade significantly reduced systemic tumor burden and prolonged median overall survival in a B16F10 mouse model of metastatic melanoma. These data support the proposed MOA by which OncoVEXmGM-CSF treatment can cause direct tumor lysis along with potentiation of an adaptive, systemic anti-tumor immune response.

Citation Format: Keegan Cooke, Juan Estrada, Jinghui Zhan, David Hill, Andrea Boden, Jon Werner, Pedro J. Beltran. OncoVEXmGM-CSF (HSV-1 modified similarly to Talimogene Laherparepvec) in combination with CTLA-4 blockade leads to both local and systemic efficacy in a murine syngeneic model of metastatic melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4566. doi:10.1158/1538-7445.AM2017-4566