Novel taxane-site tubulin ligands with a dual apoptosis and senescence-inducing mechanism of action

PROJECT SUMMARY Senescence, like apoptosis, is an established tumor suppressive mechanism that protects against cancer development by inducing sustained proliferative arrest. Apoptosis and senescence are common fates of cancer therapy and both contribute to clinical response. When cancer cells receive a lethal dose of a cancer therapeutic, they typically execute apoptosis. Conversely, cellular damage that results from sub-lethal doses induces a senescent fate. Although therapies that trigger stable senescence (pro-senescent) are beneficial because they suppress proliferation, senescent cancer cells can resume proliferation, often with more biologically aggressive features, therefore the durability of senescence is an important pharmacologic property. We have designed and synthesized congeners of the taxane-site tubulin molecule (+)-discodermolide (DDM), that potently induce cell death AND senescence in taxane-refractory triple negative breast cancer models. Pleasingly, the senescent phenotype induced by these analogs is significantly more durable than the parent molecule, Taxol or other cytotoxic drugs, thereby improving the potential for prolonged anti-tumor efficacy. Using X-ray crystallography, we will continue to evolve the chemistry of DDM to better engage underexplored residues of the taxane pharmacophore to address whether differential occupation of DDM congeners impacts pharmacology, cell fate and metabolic stability. We will also generate fluorescent DDM molecules to track the distribution and longevity of DDM-stabilized microtubules using time-lapse imaging. Multiplexed, dose- response modeling in taxane-refractory cancer cell lines will primarily guide the selection of lead DDM molecules for in vivo analyses. In Aim 2, we will use X-ray crystallography and Cryo-EM to decipher DDM-tubulin and DDM-microtubule interactions, of lead DDM congeners. These results will feed back to Aim 1 to guide more efficient chemical optimization and potentially provide mechanistic insight for the durable senescence of DDM molecules. In Aim 3 we will evaluate the optimal dosing and in vivo safety of lead DDM molecules in C57BL/6 mice, focusing on hematologic, neuropathic and behavioral metrics, as well as histopathologic analyses. Anti-tumor efficacy in models of Taxol-resistance using patient-derived breast cancer xenografts will also be evaluated. This interdisciplinary, collaborative program will employ chemical synthesis, structural biology and phenotypic screening tactics to develop highly efficacious and metabolically stable DDM analogs that mobilize both apoptosis and senescence cell fates to maximize tumor suppressive capabilities.