Dutasteride and Metformin Reduce the Growth of LNCaP Cells and Alter the SREBP-1 Pathway

Prostate cancer (PCa) is the second most prevalent cancer in men after lung cancer. Prostate cancer development and progression is associated with the dysregulation of a number of molecular pathways; hence, therapeutic strategies targeting such pathways bring great promise. Recently we have shown that metformin, the anti-diabetic drug, can inhibit tumor progression when combined with dutasteride, a 5-alpha-reductase inhibitor (5ARI). Interestingly, both metformin and dutasteride have been reported to alter the Sterol Regulatory Element Binding Proteins (SREBP) Fatty Acid Synthase (FASN) pathway. The SREBP pathway is involved with lipid and energy homeostasis. In our present study, we investigated if dutasteride in combination with metformin can reduce the proliferation of LNCaP PCa cells, and whether this is mediated through the SREBP-1/FASN pathway. Human PCa cells were treated with either dutasteride (0-100 μM) or metformin (0-50 mM) alone or in combination. The treated cells were then incubated for up to 24 hours, and proliferation assessed using the MTS 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay. Western blot analysis was performed on cell lysates to assess alterations in key signaling molecules including cleaved SREBP-1, FASN, AR, PSA, pAMPK and apoptotic markers. Results revealed that there was a significant (p<0.05) decrease in cellular proliferation of LNCaP cells treated with a combination of metformin and dutasteride, this effect being greater than either treatment alone. Treating LNCaP cells with both metformin and dutasteride reduced the expression of FASN, cleaved SREBP-1 and pro-caspase-3 with expression of cleaved PARP; suggesting a possible interaction between FASN and apoptosis. All treatments resulted in reductions in AR, PSA and an upregulation of pAMPK, with the highest expression seen in combination treatment. We report for the first time that metformin and dutasteride in combination can reduce the proliferation of androgen-sensitive cell line through the activation of p-AMPK, and SREBP1/FASN pathway and highlight the importance of targeting the SREBP-1 pathway, for improving future therapeutic strategies for prostate cancer.