HORIZON (OP-106): Melflufen Plus Dexamethasone (dex) in Patients (pts) with Relapsed/Refractory Multiple Myeloma (RRMM) Exposed to Prior Alkylator Therapy-Subgroup Analysis

Background:Current treatments for MM consist of multidrug regimens combining a variety of drug classes including IMiDs, proteasome inhibitors (PIs), monoclonal antibodies (mAbs), alkylators, XP01 inhibitors, histone deacetylase inhibitors, and corticosteroids. Despite advances in therapy, outcomes remain poor for pts with RRMM. Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate (PDC) that targets aminopeptidases and rapidly releases alkylating agents into tumor cells. In the pivotal, phase 2 HORIZON study (NCT02963493), melflufen plus dex showed meaningful efficacy and a safety profile characterized primarily by clinically manageable hematologic adverse events (AEs) in heavily pretreated and poor-risk pts with RRMM (Richardson et al. EHA 2020. Abs. EP945). Preclinical data show that melflufen is 50-fold more potent than melphalan against MM cells due to an increased intracellular alkylator concentration (Wickstrom et al. Oncotarget.2017;8:666641). Melflufen has a mechanism of action distinct from alkylators, with cytotoxicity independent of p53 activity (Slipicevic et al. AACR 2020. Abs. 1843). In this analysis, the clinical activity of melflufen is examined in a subset of pts exposed to prior alkylator therapy.