| Description |
The occurrence of treatment refractory tumors contributes significantly to the morbidity of cancer. Clinical treatment with chemotherapeutics frequently results in robust initial responses but the majority of patients relapse with drug-insensitive forms of the disease. Considering the lack of therapies available to these patients, our labs implemented a chemical biology approach towards understanding and defining molecular processes of drug-insensitive cancer cells. A small molecule screen was developed with the goal of identifying new molecular tools to characterize vulnerabilities of drug refractory tumor cells. The screen employed malignant pleural effusion cells derived from treatment refractory breast cancer patients in addition to untransformed mammary epithelial cells; the incorporation of untransformed cells in the screen permitted for the identification of small molecules with cancer-specific phenotypes. Fourteen novel small molecules were identified and two of these molecules, C-6 and zinaamidole (ZNA), were chosen for detailed follow-up studies. The first molecule, C-6, was found to be cytotoxic against multiple patient-derived malignant cell types in addition to a variety of breast cancer cell lines, but did not significantly affect to viability of untransformed cells. Next-generation RNA sequencing revealed that C-6 induced endoplasmic reticulum stress and blocked mitochondrial genome transcription. Cells treated with C-6 with disruptions in mitochondrial energy production as assessed by oxygen consumption measurements. Cancer-specific increases in the oxidation of 2',7'-dichlorodihydrofluorescein diacetate were also observed, indicating that cellular redox states were altered by treatment with C-6. Finally, C-6 was found to induce cancer cell death via a caspase independent mechanism. The second molecule identified, ZNA, contains a cyclic guanidine core and was found to induce metal trafficking gene expression and disrupt Zn2+ homeostasis. CuSO4 strongly potentiated ZNA's cytotoxic effects and treatment with ZNA/CuSO4 promoted rapid cell death in both malignant and untransformed cell types. ZnSO4 also potentiated ZNA's cytotoxicity, however, ZNA/ZnSO4 only resulted in cell death in malignant cell types. ZNA and ZNA/ZnSO4 were both found to induce caspase independent cell death selectively in cancer cells. Collectively, these investigations revealed a common theme of caspase independent cell death, suggesting a new strategy for the development of treatments targeting drug insensitive cancers. |
