Background Systemic antitumor virotherapy holds promise for treating both local and metastatic diseases. However, rapid immune system inactivation of virotherapeutics has led to disappointing clinical efficacy. To overcome this challenge, we established the RT-Nova program, which focuses on developing a cellular-based technology to protect oncolytic virotherapy. This approach enables precise targeting of therapy to tumor sites, effectively addressing clinical obstacles.

Our strategy involves leveraging a newly engineered, tumor-selective strain of vaccinia virus (RT-01). This strain produces abundant extracellular enveloped virions (EEVs) containing a second human cell-derived membrane. By preserving this crucial membrane during manufacturing, we enhance protection against systemic elimination.

Methods We assessed the resistance of the manufactured enveloped RT-01 (EnvRT-01) virus against human humoral immunity and its rapid spread using a plaque assay and the xCELLigence label-free system. In various xenograft and syngeneic models, we evaluated envRT-01’s specificity in targeting tumors and its therapeutic efficacy, both alone and in combination with cell therapies. The amplification of virus-encoded red fluorescent potein (RFP) was monitored using the amiHT Spectral imaging system. Additionally, flow cytometry and immunohistochemistry (IHC) were employed to analyze immune infiltration in localized subQ tumors or metastases. The virus’s toxicology was evaluated in multiple immune-compromised and immunocompetent mouse models.

Results EnvRT-01 demonstrated an impressive 80% survival rate in the presence of active complement, along with resistance to neutralizing antibodies and rapid viral expansion. In animal studies, a single systemic dose of EnvRT-01 selectively targeted three distinct human cancer indications (lung, melanoma, head&neck), resulting in tumor growth suppression across all three cases. Additionally, in an immunocompetent syngeneic model, EnvRT-01 effectively reduced multiple murine lung tumors. EnvRT-01 not only targeted and expressed viral-encoded proteins in all tumor sites but also significantly modified the tumor immune microenvironment, facilitating other innate-based cell therapies and chemotherapies. In metastasis models, EnvRT-01 specifically targeted tumors, reducing metastatic tumor sites not only in the lungs but also in the metastasized liver, while drastically transforming the immune microenvironments from ‘cold’ to ‘hot’.

Conclusions The development of this innovative systemic antitumor enveloped virotherapeutic, along with advancements in its manufacturing methods, unlocks new possibilities in cancer therapy. It directly tackles the challenges posed by untargetable and untreatable metastatic diseases, offering a transformative solution with wide-ranging implications for the field.