Abstract PO3-18-12: Results from a first-in-human study of DAN-222, a novel high-capacity drug conjugate in metastatic breast cancer as monotherapy and in combination with a PARPi [NCT05261269]

Abstract

Abstract Background: Topoisomerase I inhibitors (Topo I) have been shown to be highly effective across a broad range of tumors including breast cancer. Poly (ADP-ribose) polymerase inhibitors (PARPi) have been shown to be effective in BRCAm breast cancers. The combination of Topo I plus PARPi is known to be synergistic beyond the BRCAm subtype but overlapping myelotoxicities have prohibited successful clinical combinations. DAN-222 is a novel therapeutic HDC (High-capacity drug conjugate) whose payload is the topoisomerase 1 inhibitor camptothecin (CPT). Our previously published preclinical data demonstrates synergy of DAN-222 plus a PARPi regardless of BRCA or HRD status. Furthermore, DAN-222 demonstrates reduced bone marrow exposure enabling clinical combinations. Herein we present data for the first-in-human study of DAN-222 as mono- and combination therapy with a PARPi. The expectation is clinical benefit with this complimentary combination for patients with HRD+ and HRD- tumors, and not restricted to BRCAm, while minimizing overlapping myelotoxicities. Methods: A phase 1 study of DAN-222 as monotherapy and in combination with niraparib is being conducted in heavily pretreated patients with metastatic breast cancer. The objectives are to evaluate the safety, tolerability, and pharmacokinetics of DAN-222, and initial clinical activity based on RECIST v1.1 criteria to determine the recommended phase 2 dose. PK will be characterized for the total conjugated and the unconjugated CPT. Adults (≥18 years) with HER2-negative metastatic breast cancer that progressed on standard therapies were enrolled, without restriction on BRCA or HRD status. Results: As of June 2023, 30 patients had enrolled in dose escalation of monotherapy (2-16 mg/m2) or combination therapy with niraparib (100 mg). The median age was 61.5 years old (range, 36-75). The median number of prior treatment lines was 6. All patients were PARPi naïve and BRCAwt. In the monotherapy cohorts, the hematological adverse events (AEs) were neutropenia (28%; grade [Gr] ≥3: 17%), thrombocytopenia (22%; Gr ≥3: 6%) anemia (17%; Gr ≥3: 0%), and lymphopenia (11%; Gr ≥3: 0%), the non-hematologic adverse events Gr ≥3 was one case of cystitis. In the combination cohorts, the hematological AEs were anemia (25%; Gr ≥3: 17%), thrombocytopenia (17%; Gr ≥3: 8%), neutropenia (8%; grade Gr ≥3: 8%), and lymphopenia 8%; Gr ≥3: 0%) and there was no Gr ≥3 non-hematologic adverse events. The exposure of DAN-222 was linear and increased in a dose-proportional manner. The mean half-life ranged from 25.2 to 33.5 hours across all cohorts. Clinical activity during dose escalation was demonstrated with stable disease in 28% of patients with monotherapy and 67% of patients with combination therapy across all dose levels. Conclusions: No DLTs were observed in monotherapy or combination therapy in the dose escalation phase of this study. This study demonstrates the feasibility for DAN-222 to be combined with a PARPi at clinically relevant doses. The reduced myelotoxicity of DAN-222 will also enable combination with other therapies to treat patients with other types of cancer. The promising antitumor activity seen with DAN-222 in combination with PARPi in BRCAwt, supports continued clinical development. Citation Format: Sara Hurvitz, Erika Hamilton, Timothy Pluard, Aki Morikawa, Hatem Soliman, Kay Yeung, Adam Brufsky, Amy Tiersten, Wajeeha Razaq, Kristen Foye, Timothy Hagerty. Results from a first-in-human study of DAN-222, a novel high-capacity drug conjugate in metastatic breast cancer as monotherapy and in combination with a PARPi [NCT05261269] [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-18-12.