Harpoon Therapeutics, Inc. announced that the first patient has been dosed with HPN328, a delta like ligand 3- (DLL3) targeting TriTAC®, in a Phase 1/2 clinical trial as an investigational treatment of small cell lung cancer (SCLC) and other tumors associated with DLL3 expression. The company has presented preclinical data on HPN328 showing that the drug was well tolerated in cynomolgus monkeys at 1 and 10 mg/kg, and pharmacokinetic data supported the potential for once weekly dosing. When administered to mice bearing human SCLC xenografts and human T cells, HPN328 eradicated tumors. HPN328 is a TriTAC that binds to human and non-human primate DLL3, CD3e, and albumin with similar affinities. The Phase 1/2 trial is an open-label study of HPN328 as monotherapy to assess the safety, tolerability and pharmacokinetics in patients with advanced cancers associated with expression of DLL3. The first part of the trial is designed to determine a dose for additional clinical investigations. The trial plans to enroll patients with SCLC that have relapsed following at least one line of platinum-based chemotherapy. HPN328 will be administered to patients once weekly by intravenous infusion with dose escalation until a therapeutic dose level has been achieved. The primary outcome measure will be to assess safety and tolerability, and to determine a dose for Phase 2.