Induction of apoptosis and autophagy by the small molecule inhibitor VMY-1-103 in cancer cell lines and reduction of tumor growth in vivo
Cancer is a class of diseases in which cells divide uncontrollably and are able to spread throughout the body. In particular, cancer of the prostate and brain, specifically medulloblastoma, are particularly deadly because the early detection methods are not accurate nor are the treatment options adequate in that they often fail, resulting in recurrence and metastasis, or spreading, of the tumor to other organs. In our characterization of both cancers, we identified that these cancer cell lines are highly aggressive. Consequently, we found this state rendered them sensitive to treatment by cyclin dependent kinase (CDK) inhibitors, including a novel CDK inhibitor, VMY-1-103 we developed by adding a unique dansyl side-chain to the 2,6,9-trisubstituted purine compound purvalanol B. We found that VMY was significantly more effective at inducing apoptosis than its parent compound in cancer but not normal immortalized cells. In the current study, we present new data revealing that VMY induces cell death in part through autophagy, an alternative form of cellular death.We also hypothesized that the unique dansyl moiety of VMY could enhance bioavailability and detection in vivo. Using preclinical models, we developed a rapid organic phase extraction technique for quantifying VMY-1-103 and PVB in mouse tissue. Our analyses revealed that VMY-1-103 is widely distributed to the tissues, including prostate and brain at varying concentration while PVB levels were significantly lower. Importantly, we found that VMY-1-103 was detected in the brain cortex and cerebellum of normal mice and in MB tumors, while PVB was undetectable. Analyses of mice treated with 20 mg/kg VMY for an average of 65 days revealed tumor growth volume inhibition compared to untreated mice. MR-spectroscopic analysis found that treated mice show a unique spectroscopic profile in response to VMY. Finally, we confirmed cellular death ex vivo by immunohistochemically staining MB tumors and found a decrease in proliferation markers Cyclin D1 and an increase in apoptosis markers. Taken together, the significance of this study establishes that VMY is a promising anti-cancer agent and that dansylation of compounds could be used to enhance tissue distribution in vivo and detection in both prostate and medulloblastoma.
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