Abstract 7007: Identifying novel non-allosteric PIM1 degraders to overcome treatment resistance in triple negative breast cancer

Abstract Background: Breast cancer (BC) is the most common cancer among women, with triple-negative breast cancers (TNBC) being the most aggressive type. Resistance to current mainline therapies is one of the major reasons for increased mortality. PIM1 oncoprotein has been implicated in causing treatment resistance, and therefore, associated with the development and progression of this disease. Several attempts have been made to develop inhibitors of PIM1. However, these inhibitors are not specific and can lead to toxicity by inhibiting the activity of other kinases. Therefore, there is an unmet need to develop a non-orthosteric inhibitor or non-allosteric degrader, which would be more specific and could help in effective treatment of TNBC. Methods: We synthesized a novel class of PIM1 degraders and confirmed their non-allostatic mode of action experimentally in vitro, in silico and in vivo. Results: Our lab has designed indole-based compounds and identified initial hits on their PIM1 inhibition properties in a luciferase reporter assay. Further optimization improved the PIM1 inhibition up to 80-90%. However, the in silico analysis suggested that the compounds do not interact with the orthosteric center of the protein. This was confirmed by a kinase assay, which revealed that the new compounds do not interfere with PIM1 kinase activity. On the other hand, Bio-layer interferometry (BLI) studies confirmed the physical interaction of our compounds with the PIM1 protein, concluding non-allosteric interaction. The top three compounds were tested further in vitro. Treatment with our top candidate(s) inhibits cell proliferation and arrests the cells in G1 phase. This was followed by apoptotic cell death. These findings suggest that our newly designed compounds can indeed interact with PIM1 and hinder its protein function while leaving its kinase activity unaffected. Furthermore, in vivo study in the EMT6 orthotopic mice model of the top three compounds suggest that treatment inhibits tumor progression and lung metastasis. Conclusion: Preliminary results merit the optimization of ‘Hit-to-Lead’ and development of a suitable candidate to treat TNBC, where PIM1 is the cause of treatment resistance. Successful completion of the proposed work will enable a new combination therapy to reverse chemoresistance. Citation Format: Sanjay V. Malhotra, Benedikt W. Grau, Dhanir Tailor, Abel Bermudez, Fernando Jose Garcia Marques, Juliana Geppert, Sharon Pitteri. Identifying novel non-allosteric PIM1 degraders to overcome treatment resistance in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 7007.