RAPT Therapeutics to Present Biomarker Data Corroborating Demonstrated Clinical Activity and Mechanism of Action of FLX475 in Advanced Cancers

-FLX475-treated patients exhibited significant changes in immune pathways likely to enhance an antitumor response

-FLX475 modifies the tumor microenvironment (TME) to resemble those of responders to anti-PD(L)1 monotherapy

-Data to be presented at the 2023 American Society of Clinical Oncology (ASCO) Annual Meeting  

SOUTH SAN FRANCISCO, Calif., May 25, 2023 (GLOBE NEWSWIRE) -- RAPT Therapeutics, Inc. (Nasdaq: RAPT), a clinical-stage, immunology-based therapeutics company focused on discovering, developing and commercializing oral small molecule therapies for patients with significant unmet needs in inflammatory diseases and oncology, today announced biomarker data for FLX475 from its ongoing FLX475-02 Phase 1/2 clinical trial which corroborate the clinical activity of FLX475 reported in Epstein-Barr virus-positive (EBV+) lymphoma, EBV+ gastric cancer and non-small cell lung cancer (NSCLC), as well as the mechanism of this novel CCR4 antagonist. These data will be presented in a poster at the 2023 American Society of Clinical Oncology (ASCO) annual meeting taking place next week at the McCormick Place Convention Center in Chicago, IL.

FLX475 is a potent and selective CCR4 antagonist, designed to block the recruitment of immunosuppressive regulatory T cells (T_reg) into tumors without affecting healthy tissues. In December 2022 at ESMO-IO, a clinical update from the Phase 1/2 trial reported evidence of monotherapy and combination activity. FLX475 monotherapy induced confirmed complete metabolic responses in two of the six evaluable patients with EBV+ NK/T cell lymphoma. In patients with checkpoint inhibitor naïve NSCLC, the overall confirmed objective response rate was 31% (4/13 patients), and the confirmed objective response rate in PD-L1+ tumors was 38% (3/8 patients) following treatment with FLX475 plus pembrolizumab.

As part of the clinical trial protocol, the company analyzed peripheral blood and tumor tissue biomarker data from patients with a broad range of tumor types treated with FLX475 monotherapy. These data substantiate the mechanism of action and support the combination of FLX475 with pembrolizumab. In peripheral blood, FLX475 monotherapy resulted in a small, but significant, increase in the proportion of circulating T_reg, consistent with blocking the migration of T_reg into the TME. In tumor tissues, changes in the TME conducive to anti-PD(L)1 response were observed. First, FLX475 monotherapy resulted in a decrease in T_reg cell populations and an increase in the distance between CD8+ effector T cells and T_reg in the TME. Second, transcriptomic profiles from tumors after FLX475 monotherapy exhibited significant changes known to be correlated with an enhanced response to checkpoint inhibitor therapy.