LAUSR

SEA-TGT is a human nonfucosylated monoclonal antibody (mAb) targeting the T cell immunoreceptor with immunoglobulin (Ig) and ITIM domains (TIGIT) protein. TIGIT is an immunoregulatory receptor expressed on activated and memory T cells, Tregs, and NK cells. TIGIT binding to CD155 and CD112 on tumor cells drives an inhibitory signal resulting in decreased T cell functionality. TIGIT targeting has been reported to release these inhibitory signals, drive Treg depletion, augment CD8+ T cell generation, and promote anti-tumor responses. SGNTGT-001 (NCT04254107) is a phase 1 clinical trial that evaluated the safety and tolerability of SEA-TGT as monotherapy in solid tumors and lymphomas at doses ranging from 0.01 to 6 mg/kg. Because an MTD was not identified in dose escalation, pharmacokinetic (PK) and pharmacodynamic (PD) endpoints were measured to assess biological activity and inform dose selection. The biological activity of SEA-TGT as monotherapy was compared across different dose levels using a clinical utility index (CUI), which mathematically integrated multiple clinically-meaningful PK and PD endpoints into a single readout. PD endpoints included NK and CD8+ T cell proliferation, maintenance of overall peripheral CD8+ T cell numbers, depletion of peripheral regulatory T cells, and peripheral target engagement. The PK endpoint was pharmacokinetic linearity. Surrogates of predicted tumor efficacy metrics included tumor target engagement and formation of the TIGIT:SEA-TGT:Fc receptor gamma (FcγRIIIa) trimer complexes in the tumor. An increase in the CUI score, representing an increase in biological activity, was observed during dose escalation, with an apparent plateau between the 0.3 and 6.0 mg/kg levels. Based on safety signals at 6 mg/kg and PK variability at lower doses, 1 and 3 mg/kg were of most interest for further evaluation. Both 1 and 3 mg/kg represented biologically active dose levels as they showed PK and PD activity that were within desirable ranges and had similarly high overall CUI scores relative to all doses evaluated. Dose selection for SEA-TGT was based on biological activity as assessed via PK/PD endpoints and integrated into a CUI model. Based on the totality of clinical data and the CUI results from monotherapy dose escalation from SGNTGT-001, the SEA-TGT dose of 1 mg/kg was determined to be the lowest biologically active dose with acceptable safety and tolerability. Citation Format: Gabriela Patilea-Vrana, John Harrold, Joseph A. Ware, Shaparak Lonning, Hun Lee, Lisa Brooks, Haley Neff-LaFord, William D. Hanley, Andres Forero-Torres. Using clinical utility index (CUI) to determine the optimal biological dose of a nonfucosylated anti-TIGIT antibody: A proposed alternative to maximum tolerated dose (MTD). [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5668.