ATTAINMENT: A phase Ib trial of MDX-124, a first-in-class annexin-A1 targeting antibody, alone and in combination with anti-cancer treatments, in patients with advanced solid tumors.

TPS2671 Background: Annexin-A1 is a Ca 2+ -dependent phospholipid binding protein that is secreted from both cancer and immune cells in response to several physiological stimuli. Secreted annexin-A1 activates formyl peptide receptors driving cancer cell proliferation, angiogenesis, migration, and drug resistance, as well as modulating the tumor microenvironment. Annexin-A1 overexpression is observed in multiple cancers, including pancreatic, triple-negative breast, colorectal, lung and prostate, correlating with poor prognosis and decreased overall survival. MDX-124 is a novel, first-in-class humanised monoclonal antibody that targets annexin-A1. It significantly reduces cancer cell growth via cell cycle arrest, inhibits tumour growth in-vivo, reduces metastasis and induces antibody-dependent cellular cytotoxicity in annexin-A1 expressing cancer cells. Additionally, MDX-124 has synergistic activity when combined with chemotherapy and immunotherapy in pre-clinical models. These data indicate blocking the action of annexin-A1 has anti-cancer and therapeutic activity. Methods: ATTAINMENT is a modular, multi-arm, First-in-Human trial to evaluate the safety and tolerability of MDX-124 alone and in combination with anti-cancer treatments, in participants with locally advanced, unresectable, or metastatic solid malignancies. Module 1 is a single agent dose escalation using a Bayesian optimal interval (BOIN) design with an expansion cohort, followed by Module 2, which will evaluate MDX-124 in combination with standard of care in indication-specific arms by using a traditional 3+3 dose escalation scheme. Adult patients (≥18 years) with ECOG performance score 0-1 and histologically/cytologically confirmed solid tumors believed to overexpress annexin-A1 which are not amenable to or refractory to standard therapy, or for which no standard therapy exists are eligible. The primary objective is to determine the recommended phase 2 dose (RP2D) of MDX-124 both as a single agent and in combination with anti-cancer treatments. Secondary objectives will assess the safety and tolerability of MDX-124 when given as a single agent or in combination with anti-cancer treatments, characterize pharmacokinetic parameters and assess evidence of preliminary anti-tumor activity per RECIST v1.1 criteria. Exploratory objectives will assess host immune response to MDX-124 (immunogenicity and immunophenotyping), circulating levels of annexin-A1 at baseline and after dosing to correlate with response and outcome to MDX-124, and the impact of MDX-124 on blood/tissue biomarkers. The study began enrolling patients at sites in the UK in August 2023. Cohorts at 1, 2.5 and 5 mg/kg have been completed without DLT and enrollment to cohort 4 (10 mg/kg) began in January 2024. Clinical trial information: ISRCTN78740398.