Abstract LB082: A high-throughput immune-oncology screen identifies immunostimulatory properties of low dose chemotherapy in triple negative breast cancer

Abstract Triple-negative breast cancer (TNBC) is a heterogeneous subtype broadly characterized by the lack of hormone receptor (HR) and HER2 expression. Compared to HR+ breast cancers, TNBCs typically have a greater immune cell infiltrate and are more likely to respond to immune checkpoint inhibition (ICI). The results from KEYNOTE-355 and KEYNOTE-522 trials led to the approvals of anti-PD-1 in combination with physician’s choice chemotherapy for the treatment of TNBC in adjuvant and neoadjuvant settings. However, few patients achieve a durable response, and there remains a need to optimize combination strategies to enhance the benefits of ICI in TNBC. Therefore, we developed a high-throughput co-culture screening assay to identify compounds enhancing T-cell-mediated cytotoxicity. Co-cultures included three cell types: mKate2-labeled PyMT tumor cells expressing the OVA antigen, BPF-labeled PyMT cells, and CD8+ OT-1 T-cells. The screening library included over 400 FDA-approved compounds or agents under investigation for oncology indications. Each compound was evaluated at five concentrations (3µM-12nM) and across three-time points (24hr, 48hr, and 72hr) to provide insight into the kinetics. Cell viability was assessed via image analysis at each time point, and enhanced cell death in the PyMT-OVA cells compared to the non-OVA PyMT cells was considered evidence of enhanced T-cell mediated cytotoxicity. Five chemotherapy agents were chosen as priority hits for mechanistic follow-up due to their ability to enhance T-cell mediated cytotoxicity at multiple doses and multiple timepoints: paclitaxel, bleomycin sulfate, kinesin-inhibitor, ABT-751, and etoposide. We are exploring the dose dependency of MHC-I and MHC-II induction, as well as the minimum dose required to cause immunogenic cell death. We further found that low doses of these agents do not negativity affect CD8+ T-cell proliferation, whereas high doses may have deleterious effects on CD8+ T-cell functioning. The results of these studies provide mechanistic insight into potential new chemotherapy partners to enhance anti-PD-1 efficacy in TNBC patients and suggest benefit to further investigating the immunostimulatory potential of low dose chemotherapy. Citation Format: Kennady K. Bullock, Thomas Hasaka, Emily Days, Joshua Bauer, Ann Richmond. A high-throughput immune-oncology screen identifies immunostimulatory properties of low dose chemotherapy in triple negative breast cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr LB082.