Abstract 1897: Preclinical development of MGC028, an ADAM9-targeted, glycan-linked, exatecan-based antibody-drug conjugate for the treatment of solid cancers

Abstract Introduction: Antibody-drug conjugates (ADCs) seek to increase the therapeutic window of potent cytotoxic agents by linking them with monoclonal antibodies (mAbs) to selectively deliver cytotoxic payloads to tumor cells. The effectiveness and safety of ADCs rely on both the mAb specificity, and the linker-payload employed. Several approved ADCs using microtubule inhibitor payloads are impacted by ocular adverse events that have been observed both preclinically and in patients. A class of linker-payloads incorporating topoisomerase 1 inhibitors (TOP1i) has emerged recently as an effective alternative to tubulin inhibitor-based ADCs. To date, TOP1i ADCs have not been associated with dose-limiting ocular toxicity seen with microtubule inhibitor payloads. Here we report the preclinical development of an ADAM9 (a disintegrin and metalloprotease domain 9)-targeted ADC that incorporates a novel glycan-linked TOP1i. ADAM9, a member of the ADAM family of multifunctional type 1 transmembrane proteins, plays a role in tumorigenesis and cancer progression and is overexpressed in multiple cancers, making it an attractive target for cancer treatment. Methods: MGC028 incorporates the cleavable linker-payload, bicyclononyne carbamoyl sulfamide Val-Ala-PABC exatecan (SYNtecan E™), site-specifically conjugated at asparagine 297 of the heavy chain through enzymatic glycan remodeling and metal-free click chemistry using Synaffix’s GlycoConnect™ technology. In vivo efficacy studies were performed in immunodeficient mice with ADAM9-expressing human tumor cell-line (CDX) or patient-derived (PDX) xenografts. A non-human primate toxicology study was conducted in which MGC028 was administered by 15-minute IV infusion every two weeks at dose levels of 22.5 and 55 mg/kg for a total of two doses. Results: MGC028 exhibited specific, dose-dependent in vivo antitumor activity toward ADAM9-positive CDX models representing gastric, lung, pancreatic and colorectal cancer, and head and neck squamous cell carcinoma. Furthermore, MGC028 demonstrated antitumor activity toward ADAM9-positive PDX models of lung and pancreatic cancer, and cholangiocarcinoma. MGC028 was well tolerated in a repeat-dose non-human primate toxicology study, up to 55 mg/kg, the highest dose level tested. Observations were limited to mild, reversible increases in liver enzymes, without microscopic correlates, and decreased lymphoid cellularity in the thymus. In particular, ocular toxicities were not observed. Conclusions: MGC028 exhibited potent antitumor activity in in vivo models representing various solid cancer indications and was well tolerated in non-human primates at exposure levels exceeding those required for antitumor activity. Our findings support continued investigation of MGC028 as an ADC therapeutic for the treatment of ADAM9-expressing solid cancers. Citation Format: Juniper A. Scribner, Jennifer G. Brown, Thomas Son, Linda Jin, Carroll McKenzie, Viktoriya Nam, Curtis Bush, Dienis Quinonez, Delta Ford, Verlene Gonzalez, James Tamura, Sergey Gorlatov, Hua Li, Shelley Butler, Ezio Bonvini, Deryk Loo. Preclinical development of MGC028, an ADAM9-targeted, glycan-linked, exatecan-based antibody-drug conjugate for the treatment of solid cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1897.