Abstract NT-089: TRAIL-EXPRESSING ONCOLYTIC VACCINIA VIRUS COMBINED WITH SMALL-MOLECULE DRUG PAC1 IS A POTENTIALLY EFFECTIVE TREATMENT ALTERNATIVE FOR OVARIAN CANCERS

INTRODUCTION: Procaspase activating compound-1 (PAC1) is a small-molecule drug shown in vitro to sequester inhibitory zinc ions from caspase-3. TNF-related apoptosis-inducing ligand (TRAIL) is a pro-apoptotic ligand that binds membrane-bound death receptors, triggering the extrinsic apoptotic pathway. Both agents display low toxicity in humans. Vaccinia virus (VACV) is a double-stranded DNA virus that has shown therapeutic efficacy in clinical trials and has an established safety profile in humans due to its use as the smallpox vaccine.

First-line standard of care for ovarian cancer is combination taxane and carboplatin, which has significant potential toxicity and 70% of women who receive it suffer relapse. Clinical trials involving TRAIL, both alone and combined with other drugs, have shown that while it is well-tolerated it is ineffective partly due to insufficient dosing at the tumour site.

In an effort to uncover a safer, more effective therapeutic for ovarian cancer we report here on the successful construction of a recombinant oncolytic vaccinia virus expressing TRAIL (VACV^TRAIL). Secretion of TRAIL by VACV-infected cancer cells will result in localized administration of TRAIL at higher dosages and minimize potential side-effects. We posit that treatment with PAC1 and VACV^TRAIL represents a potentially safe, effective treatment for ovarian cancers.

RESULTS: Testing in cell line models of granulosa cell tumour (GCT) have shown that recombinant human (rh)TRAIL is effective in combination with PAC1. Dose-response assays established that combination of PAC1 (20 μM) with rhTRAIL (10 ng/mL) dramatically reduced viability of cancer cells while being substantially less toxic to normal cells. Replication of those assays on patient-derived primary and recurrent GCT cells confirmed PAC1 combined with rhTRAIL was dramatically more cytotoxic than treatment with rhTRAIL or PAC1 alone.

To optimize delivery of TRAIL to tumour cells, we constructed a recombinant VACV^TRAIL virus that secretes TRAIL in the range of 70–80 ng/mL. Dose-response curves showed VACV^TRAIL to be strongly cytotoxic with an ED₅₀ of 0.1 plaque forming unit (PFU) per cell. Comparing toxicity of VACV^TRAIL to a non-TRAIL-expressing VACV established that secretion of TRAIL is the basis for VACV^TRAIL superiority in killing GCT cells, and supernatant collected from infected cells is more effective at reducing cell viability when combined with PAC1 than is rhTRAIL combined with PAC1.

CONCLUSION: We have successfully constructed a TRAIL-expressing oncolytic VACV which produces effective levels of active TRAIL from infected cells. Results in vitro suggest combining PAC1 with oncolytic VACV^TRAIL will allow localized delivery of TRAIL resulting in a safe, synergistic, self-amplifying therapy.

Citation Format: Powel Crosley, Kate Agopsowicz, Kyle Potts, Ryan Noyce, Marjut Pihlajoki, Markku Heikinheimo, Anniina Färkkilä, David Evans, Mary Hitt. TRAIL-EXPRESSING ONCOLYTIC VACCINIA VIRUS COMBINED WITH SMALL-MOLECULE DRUG PAC1 IS A POTENTIALLY EFFECTIVE TREATMENT ALTERNATIVE FOR OVARIAN CANCERS [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr NT-089.