Systemic antitumor virotherapy: Pre-clinical evaluation of tumor targeting, efficacy, and safety of lead candidate (CLD-401).

Abstract

2593 Background: Systemic antitumor virotherapies are a promising modality of cancer immunotherapy. However, challenges include quick virus clearance from the bloodstream and potential off-target toxicity. To overcome these limitations, we have developed a novel strain called RT vaccinia virus which can be enveloped by an extracellular membrane during the manufacturing process and become resistant to human-complement. Our RTNova program, using extracellular enveloped RT (envRT) vaccinia viruses, focuses on generating potent systemic virotherapies with improved survival in circulation, tumor-specific targeting and enhanced therapeutic efficacy. Methods: The RT virus was genetically engineered to improve tumor selectivity and increase resistance to complement-mediated inactivation. The virus's ability to kill cancer cells was tested using the NCI-60 panel. The resistance of envRT vaccinia virus against human humoral immunity and its rapid spread were assessed ex-vivo. Targeting, biodistribution, therapeutic efficacy, and safety profile of selected envRT was evaluated in multiple animal models. Results: Out of several genetically modified RT Vaccinia viruses, we selected the one with three knockouts (3KO): TK (Thymidine kinase), A46R (immunomodulator), and VGF (Vaccinia virus growth factor). These genetic modifications significantly improved tumor-selective amplification and safety profile while maintaining therapeutic efficacy. The 3KO RT virus demonstrated strong oncolytic activity against more than 60 different human cancer cell lines NCI-60. Additionally, the 3KO RT virus was genetically engineered with CD55-domain fused with viral envelope A33R. This chimeric protein is designed to be expressed specifically in the extracellular envelope of the viral particle to robustly protect the envRT and viral progeny from inactivation by human complement. Targeting and biodistribution studies revealed that RT virus targeted all tumors after intravenous administration followed by significant tumor-selective amplification and spreading. In multiple immunocompetent mouse models, including metastatic lung cancer, RT virus demonstrated excellent tumor killing, and expression of selected therapeutic payload. Conclusions: We have developed a new scalable process to manufacture extracellular enveloped antitumor virotherapies and identified the first lead candidate from RTNova Platform, designated as CLD-401. This candidate, CLD-401, demonstrates promising therapeutic efficacy and safety in preclinical models. It effectively addresses the challenge of targeting and treating metastatic lung cancer by delivering Immunotherapeutics directly to disseminated tumors.