Oxford, UK – Vaccitech Limited and the University of Oxford today announce initial efficacy and safety data for ADVANCE, a Phase 2a study testing VTP-800, an immunotherapeutic product candidate in patients with metastatic castration resistant prostate cancer (mCRPC). The study demonstrated that VTP-800 is safe and showed an encouraging efficacy trend in patients with mCRPC.

ADVANCE (NCT03815942) is an open-label, non-randomized study sponsored and conducted by the University of Oxford and funded by the European Commission FP7 programme and Vaccitech. The objectives of the study are to measure the safety of the immunotherapeutic VTP-800 when combined with an anti-PD-1 agent, and the reduction in serum prostate-specific antigen (PSA) levels as a surrogate biomarker used to evaluate the efficacy of prostate cancer treatments.

VTP-800 is comprised of Vaccitech’s Chimpanzee Adenovirus Oxford 1 vector (PRIME) encoding the oncofetal antigen 5T4 (ChAdOx.5T4), followed by a Modified Vaccinia Ankara vector (BOOST) encoding the same antigen (MVA.5T4) administered in a heterologous prime-boost regimen.

In the 23 mCRPC patients who received VTP-800 in conjunction with an anti-PD-1, 5 patients (22%) had a >50% reduction in PSA level at any timepoint compared to baseline (median of 88 ng/ml). This compares favourably to the 9% response rate reported from a previous anti-PD-1 monotherapy study, KEYNOTE-199, which evaluated 243 mCRPC patients with similar baseline PSA levels. Additionally, four of the five ADVANCE patients (17.4%) maintained their response when tested three weeks later versus 5.8% in the KEYNOTE-199 study. One ADVANCE patient had a response with a PSA level of 0 at 24 weeks.

Whilst full analysis is still pending, initial safety data is comparable to that seen from dosing anti-PD-1 alone and there are no serious adverse events attributable to VTP-800.

ADVANCE patients received two cycles of VTP-800 four weeks apart and 480 mg of an anti-PD-1 agent on weeks 4, 8 and 12 of treatment. KEYNOTE-199 patients received 200 mg of anti-PD-1 every three weeks for up to 35 weeks.

“We are encouraged by these data and we believe they validate the application of our platform in other oncology indications using different antigens,” stated Bill Enright, Vaccitech CEO. “We look forward to continuing to work with Oxford University to explore options for future clinical studies to evaluate the added patient benefit VTP-800 can provide when combined with checkpoint inhibitors.”

”We have seen promising clinical activity of VTP-800 in conjunction with an anti-PD-1, including responses in patients with advanced hormone resistant prostate cancer that are resistant to standard treatments. These encouraging data will hopefully lead to the initiation of a larger phase 2 clinical trial in patients with advanced prostate cancer,” commented Dr Mark Tuthill, Chief Investigator of ADVANCE.

Previous VTP-800 studies

Phase 1 study (VANCE) in pre-surgical, early-stage prostate cancer patients. Data presented at ASCO 2018: https://www.vaccitech.co.uk/phase-1-data-vaccitech-prostate-cancer-vaccine-presented-asco-2018/