Abstract
INTRODUCTION: Enadenotucirev (EnAd) and successor transgene-armed Tumor-Specific Immuno-Gene (T-SIGn) vectors are replication-competent, blood-stable viral vectors that traffic to tumor sites following intravenous (IV) administration. Following initial proof of mechanism for this immunotherapy modality, there is a need to identify a safe dosing approach, understand whether transgenes affect tolerability, and determine how to measure exposure and pharmacodynamic effects. METHODS: Safety data from multiple phase 1 trials were aggregated to assess various dosing regimens and toxicities, including those that may be associated with transgene arming. Viral delivery to tumors, peripheral viral persistence, transgene expression, and cytokine responses were also assessed and compared between the unarmed EnAd and armed T-SIGn vectors. RESULTS: IV administration of EnAd and the armed T-SIGn vectors led to virus detection in epithelial tumors and prolonged peripheral virus persistence. Despite the short half-life of the viruses and cell-free nucleic acids, viral DNA or transgene messenger RNA (mRNA) remained detectable in blood at higher dose levels for at least 56 days, indicating sustained release of these molecules likely driven by ongoing viral replication and concomitant transcription of the transgene in tumors. Safety, predominantly defined by the effects of IV administration and associated viremia, was managed by a well-tolerated dosing regimen. To date, no transgene-related or off-target toxicities have been observed. Transient monocyte chemoattractant protein 1 (MCP-1) and interleukin (IL)-6 elevations were associated with viremia. A second phase of elevations of proinflammatory cytokines such as IL-12p70, interferon (IFN) α2, IL-17A, and IFNγ without clinical symptoms started around day 12, suggesting that release of these cytokines was driven by localized pharmacodynamic effects within the tumor microenvironment (TME). CONCLUSION: Armed T-SIGn vectors exhibit the same high tumor selectivity and replicative activity as the unarmed parent EnAd and achieve consistent viral delivery to a broad range of epithelial tumor tissues. The aggregated safety analysis revealed that safety and tolerability are defined by systemic viremia but not off-target or transgene-related toxicities. Nucleic acid and cytokine release from tumors and changes in the TME (e.g., CD8+ T cells), indicative of the mechanism of action of replication-competent viral vectors, constitute potentially valuable data to support the definition of a recommended phase 2 dose and the assessment of the benefit of multicycle administration.