High-throughput drug screen to identify compounds working selectively and synergistically with CQ to inhibit proliferation of TSC-2 deficient cells
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Tuberous sclerosis complex (TSC) is a multisystem genetic disease that is caused by a germ line mutation in the genes TSC1 and TSC2. Patients with the disease tend to suffer from benign tumors of the brain, heart, kidneys, skin, and other organs that contain giant cells. Although mTORC1 inhibitors (rapamycin and rapalogs) are often used to treat TSC because of their efficacy in promoting tumor shrinkage, clinical studies in the past have shown that when treatment is taken away, the tumor size returns to its original state. The objective of this study was to identify compounds that selectively inhibit proliferation of TSC2-deficient cells. A high-throughput screen of about 4000 compounds was performed using a lysosomal inhibitor (chloroquine [CQ], 5 μM) and a “repurposing” library of compounds. Through some yet to be determined mechanism, the combination of ritanserin (a selective serotonin reuptake inhibitor [SSRI]) and chloroquine was found to synergize to selectively inhibit the cell viability of DJK MEFs and TSC2-/-KO cells (TFFs) starting at 48 hours after treatment. The effects of this combination treatment were confirmed in a second cell line (TFFs) exhibiting similar reduction in proliferation. Interestingly, treatment with CQ (5 μM) and ritanserin (20 μM) showed synergistic action (combination index [CI] = 0.6) against TSC2-deficient cells. This combination treatment induced apoptosis (41%) in TSC2-deficient cells but not in TSC2-expressing cells. These results suggest a novel treatment approach in tuberous sclerosis complex and provide an incentive for further investigation of the mechanisms contributing to the vulnerability of TSC2-deficient cells. Moreover, the use of an already Food and Drug Administration (FDA)-approved compound can lead to a more rapid pharmacologic approach for TSC patients.