A phase 1 dose-escalation trial of intratumoral TTI-621, a novel immune checkpoint inhibitor targeting CD47, in subjects with relapsed or refractory percutaneously-accessible solid tumors and mycosis fungoides.

Abstract

TPS3101 Background: CD47 is an immune checkpoint that binds to signal regulatory protein alpha (SIRPα) and delivers a "do not eat" signal to suppress macrophage phagocytosis. Tumor cells frequently overexpress CD47 and exploit this pathway to evade macrophage-mediated destruction. CD47 blockade promotes both innate (macrophage phagocytosis) and adaptive immunity (T cell responses). TTI-621 (SIRPαFc) is an immune checkpoint inhibitor designed to bind human CD47 and block the “do not eat” signal. The IgG1 region of TTI-621 engages Fcγ receptors on macrophages, converting the inhibitory signal to one that activates, thereby enhancing phagocytosis, and antitumor activity. A Phase 1 study is ongoing to evaluate the safety/tolerability and preliminary efficacy of IV administered TTI-621 in subjects with relapsed/refractory hematologic malignancies. It is hypothesized that employing direct intratumoral injections will result in very high local target engagement, promoting the development of innate and adaptive immune responses. Methods: A Phase 1 multicenter, open-label study was initiated to characterize the safety and tolerability of delivering TTI-621 directly into cancer lesions to achieve high local CD47 engagement to increase phagocytosis of tumor cells (NCT02890368). Subjects are being enrolled in sequential cohorts that gradually increase in dose and dosing frequency to characterize the feasibility of intratumoral TTI-621 injections and their safety, PK, pharmacodynamics, and preliminary antitumor activity. Eligible subjects are adults with relapsed or refractory percutaneously-accessible solid tumors or mycosis fungoides (MF), which have progressed on standard anticancer therapy or for which no other approved therapy exists. TTI-621 is delivered by intratumoral injection at protocol-defined doses and dosing regimens starting at 1 mg/injection. Serial biopsies are being collected to characterize local anti-tumor responses and assess the impact of TTI-621 on the tumor microenvironment. Clinical trial information: NCT02890368.