Abstract 3933: ORM-5029: A first-in-class targeted protein degradation therapy using antibody neodegrader conjugate (AnDC) for HER2-expressing breast cancer

Abstract Targeted protein degradation (TPD) molecules, including IMiD-based molecular glues and heterobifunctional degraders have expanded the breadth of therapeutic options through both their catalytic mechanism of action and ability to degrade previously “undruggable” target proteins. To increase the efficacy vs. tolerability window of protein degradation and improve drug delivery we combine the catalytic approach of targeted protein degradation with the precision of tumor targeting therapeutic antibodies. Here, we describe the development of ORM-5029, a highly potent and selective GSPT1 degrader targeting HER2-expressing tumor cells. We first screened a panel of cell lines to identify tumors where treatment with a selective, membrane-permeable, molecular glue (SMol007) would exhibit the most potent GSPT1 degradation, integrated stress response, and ultimately apoptosis. HER2+ breast cancer cell lines were more sensitive to GSPT1 degradation than the average IC50 for all cell lines tested. Several of our GSPT1 degrader molecules were tested in HER2-positive tumor models and displayed a consistent pattern of potent cytotoxicity. An unbiased global proteomics evaluation of changes in abundance identified SMol006 as a specific GSPT1 degrader, with no significant depletion of over 6500 other proteins detected. To evaluate whether antibody delivery could provide a potency increase of Smol006 and other GSTP1 degrader payloads, we conjugated these payloads to the HER2-targeting antibodies, trastuzumab and pertuzumab. Given the comparable activity of both antibodies and frequent use of trastuzumab as the antibody domain of several ADCs, we selected pertuzumab as our targeting antibody. Further medicinal chemistry optimization and evaluation of many linker-payloads led to the identification of our first preclinical AnDC candidate ORM-5029, which is composed of SMol006, a highly-potent GSPT1 degrader conjugated to pertuzumab via a clinically-validated Val-Cit PABc linker. ORM-5029 treatment in the HER2-expressing cell lines showed 10-1000 fold superiority in potency compared to SMol006, Kadcyla and/or Enhertu treatment. We evaluated ORM-5029 in several in vivo xenograft models and observed robust efficacy, following a single-dose treatment testing as low as 3 mg/kg. In the BT474 xenograft model, treatment with ORM-5029 demonstrated single-dose activity superior to Kadcyla, and comparable to Enhertu when given at an equivalent dose. In an HCC1569 xenograft model, tumor growth inhibition correlated with the degree and duration of GSPT1 depletion and changes in expression of previously described integrated stress response biomarker genes. ORM-5029 is currently in preclinical development as a potential first-in-class targeted protein degrader therapy with HER2-targeted delivery. Citation Format: James Palacino, Chen Bai, Yong Yi, Anna Skaletskaya, Khuloud Takrouri, Wesley Wong, Min-Soo Kim, Dong-Ki Choi, Da-Young Kim, Yeonhee Yang, Jiae Kook, Pedro Lee, Hangyeol Jeong, Sang-Mi Jee, Jiyun Park, Ki-Hwan Chang, Nathan Fishkin, Peter U. Park. ORM-5029: A first-in-class targeted protein degradation therapy using antibody neodegrader conjugate (AnDC) for HER2-expressing breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3933.