Ongoing, first-in-human, phase I dose escalation study of the investigational CD47-blocker TTI-622 in patients with advanced relapsed or refractory lymphoma.

3030 Background: CD47 is an immune checkpoint that binds signal regulatory protein alpha (SIRPα) and delivers a "do not eat" signal to suppress macrophage phagocytosis. Cancer cells frequently overexpress CD47 to escape immune surveillance. TTI-622 is a fusion protein consisting of the CD47-binding domain of human SIRPα linked to the Fc region of human IgG4. TTI-622 acts as a decoy receptor, preventing CD47 from delivering its inhibitory signal and enabling macrophage activation and anti-cancer activity via pro-phagocytic signals present on cancer cells. Unlike many CD47-blocking antibodies, TTI-622 does not bind to human erythrocytes and thus may not cause anemia in patients. Methods: In phase 1A, patients with advanced relapsed or refractory lymphoma received IV TTI-622 once per week with dose increased based on traditional 3+3 escalation. Dosing was on a mg/kg basis with the third and subsequent weekly doses approximately 2-fold higher than the first 2 doses (e.g., 0.05, 0.05, and 0.1 mg/kg for weeks 1, 2 and 3). Blood samples were obtained for PK analysis and assessment of CD47 receptor occupancy (RO) on peripheral T cells. Results: At data cut-off, 19 patients (11 M, 8 F) of median age 62 years (range, 24-86) with the following lymphomas: DLBCL 10; HL 6; and TCL, MCL and FL, 1 each, with a median of 3 prior therapies (range, 1-8) were enrolled. No DLTs have been observed in 5 dose levels (0.05 to 4.0 mg/kg). Grade ≥3 related neutropenia occurred in 2 patients; other related AEs occurring in 2 patients each included abdominal pain, fatigue, and nausea; no patients experienced a related SAE. Acute, post-dose platelet decreases occurred transiently and generally were Grade 1- 2; no related Grade ≥3 thrombocytopenia or anemia AEs have been observed. Preliminary PK data indicate a dose-proportional increase in exposure and a T1/2 of approximately 4-5 days following repeat infusions (Week 6). Preliminary biomarker data reveal approximately 60% RO at the end of the first infusion of 2 mg/kg and more sustained 24-hour RO at 1 and 2 mg/kg vs ≤ 0.8 mg/kg. To date, 1 patient with stage 4 non-GCB DLBCL (5 prior therapies) initially achieved PR by Wk 8 and CR by Wk 36, with response ongoing. Conclusions: TTI-622 is well tolerated at doses up to 4 mg/kg per week. Preliminary data indicate dose-dependent increases in PK exposure and target engagement with 1 DLBCL patient having achieved a durable, ongoing CR. Dose escalation is ongoing and additional safety, PK, biomarker and response data will be available at the time of meeting presentation. Clinical trial information: NCT03530683 .

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