Abstract 1950: Signature MicroRNAs involved In transition of androgen sensitive prostate cancer cells to androgen-insensitive ones during androgen deprivation therapy

Because of the clinical efficacy, androgen blockade therapy has become the mainstay for advanced prostate cancer. However, prolonged androgen blockade either by androgen deprivation or by the use of androgen receptor antagonists, leads to activation of various adaptive mechanisms, which promotes development of hormone-refractory prostate cancer (HRPC). Microarray analysis revealed an increasingly complex profile of gene expression in prostate cancer with respect to the status of androgen sensitivity or refractoriness but the process of progression to androgen insensitivity is not well understood. Recently, role of MicroRNAs (miRNA) has been demonstrated in regulation of gene expression for cancer progression. Aberrant expression of miRNAs has been correlated with tumor differentiation, metastasis, and resistance to therapeutic strategies. However, the role of miRNAs in progression of androgen sensitive prostate cancer to HRPC has not been clearly defined. In this study, we examined changes in the expression profiles of miRNAs at the genome level during development of HRPC. Androgen sensitive LNCaP prostate cancer cells were subjected to androgen deprivation until a subset of cells remained, which survived in the absence of androgen. Samples were collected at different time points along the treatment and expression of 1,113 miRNAs were monitored through qRT-PCR. Initial analysis identified 140 miRNas that had more than three-fold reduction in expression and 137 miRNAs that had more than three-fold elevated expression compared to untreated samples. Of these, 100 miRNAs were selected for further validation, and finally 41 miRNAs were chosen that displayed the most significant changes with treatment. Using online tools and databases we determined potential mRNA targets of these miRNAs based on sequence homology. MRNA targets with the highest binding scores and especially those that were targeted by multiple miRNAs were further investigated. We found many of these putatively down regulated mRNAs code for transcriptional regulators or were involved in pro-apoptotic signaling. In contrast many of the putatively up regulated mRNAs code for oncoproteins and proteins involved in mitogenic signaling. Western blot analysis confirmed that the expression profiles of these proteins are indeed in correlation with the expression profiles of the miRNAs identified. Our results provide important insight into the development of HRPC and additionally, identify potential biomark