A Multi-Center, Open-Label Phase 1/1b Dose Finding, Safety, and Pharmacokinetic Study of MBRC-101, an Anth-EphA5 Monomethyl Auristatin (MMAE) Antibody Drug Conjugate, in Advanced Refractory Solid Tumors.

TPS3161 Background: EphA5 receptor is a member of the Ephrin receptor tyrosine kinase family. Several lines of compelling nonclinical evidence indicate EphA5 is a novel and selective target for solid tumor-directed therapy. Expressed only minimally in normal tissues, it is highly expressed in non-small cell lung carcinoma (NSCLC), head and neck squamous cell carcinoma (HNSCC), and breast, colorectal, pancreatic, gastric, and hepatic malignancies. MBRC-101 is a novel antibody drug conjugate (ADC) composed of an anti-EphA5 antibody conjugated to an MMAE payload (drug-to-antibody ratio of 4) through a valine citrulline cleavable linker. In pre-clinical toxicology studies and testing against a variety of cell-derived (CDX) and patient-derived (PDX) xenograft solid tumor models expressing EphA5--including NSCLC, triple negative breast cancer (TNBC), and HNSCC--MBRC-101 demonstrated favorable safety profiles and robust anti-tumor activity. Methods: This first-in-human, Phase 1/1b, multicenter, open-label study is examining the safety and efficacy of MBRC-101 in patients with advanced metastatic solid tumors refractory to standard treatment. Phase 1 will identify potential optimal biologically relevant doses (OBRD) and the maximum tolerated dose (MTD) of MBRC-101 at one or more dosing regimens. Phase 1b will evaluate the safety and preliminary clinical activity of MBRC-101 at potential OBRDs. Phase 1 will enroll patients (n ≈ 30) with advanced or metastatic solid tumors. EphA5 expression will not be required for enrollment into Phase 1 but will be assessed retrospectively. A modified toxicity probability interval (mTPI-2) method will guide dose escalation using a pre-specified decision matrix. The primary endpoints are MTD, dose limiting toxicities (DLTs), treatment emergent adverse events (TEAEs), and clinical laboratory tests. Phase 1b (n ≈ 60 patients) will include 3 expansion cohorts (n ≈ 20 patients per cohort): Cohort A, NSCLC; Cohort B, triple negative or HR+/HER2- breast cancer; and Cohort C, solid tumors irrespective of histologic tissue type (i.e., tumor agnostic) excluding NSCLC and breast cancer. Expression of EphA5 in primary or metastatic tumor tissue will not be required for enrollment into cohorts A and B but will be required for Cohort C. The primary endpoints are TEAEs, clinical laboratory tests, and investigator-assessed objective response rate (ORR) by RECIST v1.1 and clinical evaluation. Secondary endpoints for Ph1 and 1b include PK analytes and EphA5 expression as determined by immunohistochemistry (IHC). A Safety Review Committee will monitor safety at each dose escalation in Phase 1 and at regular intervals throughout Phase 1b. Clinical trial information: NCT06014658 .