On December 8, 2022 RAPT Therapeutics, Inc. (Nasdaq: RAPT), a clinical-stage, immunology-based biopharmaceutical company focused on discovering, developing and commercializing oral small molecule therapies for patients with significant unmet needs in inflammatory diseases and oncology, reported a poster presentation at the ESMO (Free ESMO Whitepaper) IO Congress covering data from its ongoing Phase 1/2 clinical trial of FLX475 as monotherapy and in combination with pembrolizumab in patients with advanced cancer (NCT03674567) (Press release, RAPT Therapeutics, DEC 8, 2022, https://investors.rapt.com/news-releases/news-release-details/rapt-therapeutics-presents-update-its-phase-12-clinical-trial [SID1234624924]).
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The data showed a confirmed overall response rate of 31% (4/13 patients) in Stage 1 of a Phase 2 expansion cohort of patients with checkpoint-naïve NSCLC, including two responses which are ongoing for over one year. Of the 13 patients treated with 100 mg once-daily FLX475 and a standard regimen of pembrolizumab, eight patients had PD-L1 positive tumors (TPS ≥1%), including two with PD-L1 high tumors (TPS ≥50%), four patients had PD-L1 negative tumors (TPS <1%) and one patient’s PD-L1 status was unknown. The confirmed response rate in the PD-L1 positive tumors was 38% (3/8 patients) and in the PD-L1 negative tumors was 25% (1/4 patients). None of the four responders were PD-L1 high. Most of the patients enrolled in this NSCLC cohort had been previously treated with 1-3 or more prior therapies for advanced disease (10/13 patients).
In a separate Phase 2 expansion cohort of six patients with EBV+ NK/T cell lymphoma treated with FLX475 monotherapy, there were four responses, with two durable complete metabolic responses (CMR), one unconfirmed CMR and one unconfirmed partial metabolic response.
The safety profile for FLX475 was favorable, consistent with that previously seen in healthy volunteers, and there was no evidence of increased severity or frequency of adverse events in combination therapy compared to either FLX475 or pembrolizumab monotherapy.
"These data further support the antitumor activity for FLX475 with clear demonstration as a monotherapy and encouraging activity in a combination regimen with checkpoint inhibition," said Brian Wong, M.D., Ph.D., President and Chief Executive Officer of RAPT Therapeutics. "These data meet our criteria for continued development and based on the promising activity of FLX475 with pembrolizumab in checkpoint-naïve NSCLC patients, we have moved this indication to Stage 2 and are enrolling additional patients into the cohort."
About FLX475
FLX475 is a small molecule CCR4 antagonist designed to block the migration of regulatory T cells (Treg) specifically into tumors, but not healthy tissues. Treg represent a dominant pathway for downregulating the immune response, generally correlate with poor clinical outcomes, and may limit the effectiveness of currently available therapies such as checkpoint inhibitors. RAPT is developing FLX475 in "charged" tumors, which represent cancer types the company believes are most likely to respond to FLX475, where a large quantity of Treg cells are likely to be the cause of immune suppression within the tumor. FLX475 may restore naturally occurring antitumor immunity alone and may synergize with a variety of both conventional and immune-based therapies, such as radiation, chemotherapy, checkpoint inhibitors, immune stimulators, cancer vaccines, and adoptive T cell therapy.