AGX101: A TM4SF1-directed tubulin inhibitor conjugate in ongoing first-in-human trial including GI cancers.

829 Background: TM4SF1 (Transmembrane-4 L-Six-Family-Member-1) is an endothelial marker with critical roles in angiogenesis, as well as a tumor cell antigen that contributes significantly to invasion and metastasis. TM4SF1 is upregulated 20-fold in angiogenic tumor vascular endothelium compared to normal vasculature endothelium and exhibits a unique nuclear internalization pathway. AGX101 is a novel tubulin inhibitor conjugate specifically directed against TM4SF1, delivering a potent maytansinoid payload directly to the nucleus of cells within the tumor microenvironment. Delivery to both the vascular and tumor cell compartments of the tumor results in three mechanisms of action (MoAs): (1) activation of tumor immune surveillance, (2) tumor blood supply deprivation, and (3) direct tumor cell killing. Methods: TM4SF1 expression was assessed using immunohistochemistry. Safety and pharmacokinetics of AGX101 were evaluated in non-human primates (NHP), with escalating doses to determine the highest non-severely toxic dose (HNSTD). Efficacy studies were also conducted in mouse models, enabling assessment of the minimum effective dose (MED) needed to engage each of the three MoAs. The combination of HNSTD and MED enables calculation of a therapeutic index (TI). The potential for synergy with immune checkpoint inhibitors (ICIs) was also investigated. A first-in-human study of AGX101 in patients with advanced solid tumors with the primary objective of safety and dose-limiting toxicities (DLTs) has initiated. Results: Notable cancers with high TM4SF1 scoring intensity include pancreatic adenocarcinoma, hepatocellular carcinoma, cholangiocarcinoma, and gastric cancer. In esophageal cancer, 20% of patients have a TM4SF1 copy number amplification, and these have worse prognosis. In NHP, AGX101 exhibited a favorable safety profile. In preclinical efficacy studies, monotherapy demonstrated robust efficacy through each of the three MoAs in syngeneic models in mice including CT26 colon carcinoma, and human tumor xenograft models including MIA PaCa-2 pancreatic cancer. Measured by exposure, TI was large. In syngeneic mouse models including CT26, the effects of ICIs were potentiated, suggesting a potential synergistic approach in cancer therapy. The first two dose levels of AGX101 monotherapy in humans has cleared without DLTs. Three patients with pancreatic adenocarcinoma have been treated thus far. Conclusions: AGX101, targeting the TM4SF1 antigen, represents a promising new approach in cancer therapy. The preclinical data suggest that AGX101 could provide a significant therapeutic benefit by novel and differentiated mechanisms of action, namely selectively targeting the tumor vasculature and potentiating immune-based therapies. Further clinical development of AGX101 is ongoing and initial outcome data will become available by the conference. Clinical trial information: NCT06440005 .