Y-mAbs Therapeutics, Inc. (the “Company” or “Y-mAbs”) (Nasdaq: YMAB) a commercial-stage biopharmaceutical company focused on the development and commercialization of novel, antibody-based therapeutic products for the treatment of cancer, today announced that the first patient has been dosed with both the protein dose and the 177Lu-DOTA imaging dose in its Phase 1 clinical trial, evaluating the Company’s pre-targeted radioimmunotherapy Self-Assembly and Disassembly-Bispecific (“SADA”) technology platform for the treatment of certain GD2-positive solid tumors, including small cell lung cancer, sarcoma and malignant melanoma. The two-step approach separating the administration of SADA protein (“pre-targeting”) from the administration of radioactive ligand is believed to differentiate SADA constructs from most other radioimmunotherapy approaches.

“We are excited to advance our SADA platform into the clinic for the first time with the initiation of patient dosing in this trial. This is a significant milestone for Y-mAbs in our efforts to potentially build a global franchise of radiotherapeutic assets,” said Thomas Gad, Founder, President, and Interim CEO. “SADA can potentially generate the clinical data to further unlock the potential of radiolabeled therapeutics in tumors that have not historically demonstrated meaningful responses. Further, during the first part of the study, Part A, we plan to collect imaging data to assess tumor targeting and assess the PK profile of GD2-SADA, as this could potentially allow for early evaluation of the program and more informed development decisions.”

The Phase 1 dose-escalation, single-arm, open-label, non-randomized, multicenter trial (NCT05130255) targets malignant melanoma, sarcoma and small cell lung cancer. The trial will have three parts: Part A will explore dose-finding for the SADA molecule and testing of dosing intervals between the protein and the 177Lu-DOTA payload; Part B will determine the optimal dose of 177Lu-DOTA; and Part C will be evaluating safety and initial signals of efficacy using repeated dosing. The Company expects a total of approximately 60 patients to be enrolled in the trial across 6-10 U.S. sites.

The GD2-SADA construct was created using the Company’s SADA platform, which was licensed by the Company from Memorial Sloan Kettering Cancer Center (“MSK”) and Massachusetts Institute of Technology (“MIT”). SADA utilizes a pre-targeted payload delivery method where antibody constructs assemble in tetramers and bind to the tumor target. In prior nonclinical studies unbound constructs predictably disassembled into smaller antibody fragments and were taken up by the liver or excreted through the kidneys within a few days after administration. In a second infusion, a radioactive payload designed specifically to target the SADA molecules attached to the tumor target. We believe this approach provides the possibility of targeting tumors with precision while minimizing radiation of normal tissues. We believe the SADA platform has the potential to deliver a variety of payloads and be developed against multiple tumor targets, as well as for theragnostic purposes.