Development of Heterobivalent Small-Molecule Therapeutics for the Treatment of Triple-Negative Breast Cancer

ABSTRACT Breast cancer is the most prevalent cancer in women and the second leading cause of cancer related death. Approximately 20% of breast cancer cases are triple negative breast cancer (TNBC), characterized by tumors negative for three receptors: estrogen, progesterone, and human epidermal growth factor receptor 2 (HER2),

making specific hormone and antibody targeted therapies ineffective due to the lack of their therapeutic targets. Treatment of TNBC involves both local therapies (surgery and radiation), and systemic therapies (chemotherapy). However, compared to other types of breast cancer, TNBC is the most challenging form of

breast cancer to treat, is prone to recurrence and metastasis, and has a poor 5-year survival rate, especially in later stages Notably, advanced BC with distant metastases is currently considered incurable. Mutations in the tumor suppressor gene TP53 gene occur in 80% of cases of TNBC are associated with relapse

to the most aggressive treatments and mortality. Missense mutations in p53 (the protein encoded by this gene) lead to production and accumulation of mutant p53 proteins without tumor suppressor capabilities. Any therapy that could restore tumor suppressor functions to the accumulated p53 proteins would provide an outstanding

therapeutic opportunity to turn even the most aggressive cancers harboring p53 mutations into very treatable ones with good prognosis. There are historic examples of this paradigm. The identification of BCR-Abl in chronic myeloid leukemia or PML-RARA in promyelomonocytic leukemia and their selective therapies (Imatinib/Retinoic

acid), respectively turned the once uncurable cancers into curable diseases. Weatherwax Biotechnologies is developing a novel, proprietary and highly innovative drug-discovery platform to identify bifunctional molecules (BFMs) that reactivate tumor suppressor functions of p53 in the mutant isoforms.

BFMs are a new class of small-molecules with abilities to modulate drug targets that greatly exceed those of traditional therapeutics. This is because BFMs don’t rely on direct binding to modulate drug targets (as standard drugs do). Instead, they recruit endogenous “modifier protein” to bind to and alter the protein of interest. Given

the broad range of post-translational modifications classes of enzymes that catalyze upon other proteins, by co- opting these catalytic capabilities, BFMs can enable mechanisms of action with unprecedented efficacy. The objective of this project is to produce high quality BFM tool compounds with lead-like properties

capable of reactivation of mutant p53. Utilizing Weatherwax’s knowledge gained from the early screening of BFMs, this research will identify hit compounds that selectively induce cell death only in p53 mutant tumor cells. Utilizing parallel chemistry, a library of BFM compounds will be designed and synthesized (Specific Aim 1),

followed by selection of hit modifier proteins showing biological modulation of p53 activity in cellulo (Specific Aim 2). Finally, through structure-activity relationship and ADME, high quality high affinity BFMs will be produced (Specific Aim 3) that (although beyond the scope of this grant) can be then moved to preclinical studies.