Abstract 4370: GSK3α/β inhibition as a drug target in prostate cancer
Authors: Ali Husnain , Burke Amy , O'Connell Enda , Sullivan Frank , Giles Frank , Glynn Sharon 
Published: August 2015

Despite what its namesake suggests, Glycogen Synthase Kinase 3 (GSK3) is a kinase that is implicated in a myriad of signalling pathways and has recently received considerable interest due to its conflicting roles oncogenesis. Though GSK3 has classically been regarded as a tumour suppressor due to in role in supressing WNT signalling, emerging evidence suggests that GSK3 also functions as a tumor promoter by facilitating tumor cell survival and conferring drug resistance in cancer. These tumor promoting effects have been partly linked to the expression of certain NFκB target genes, whose expression in some cancers are influenced by direct GSK3 phosphorylation of NFκB's p65 subunit. Given the complex interplay between GSK3 and the androgen receptor in prostate cancer (PCa), and the inverse correlation between the androgen receptor status and NFκB, we investigate the potential of GSK3 inhibitors to treat and overcome drug resistance in PCa.

A kinase inhibitor screen for 80 compounds and additional chemical inhibitors for GSK3 was carried out using the JANUS Automated Workstation at the robotics facility at NUI Galway, Ireland. The cellular fractions for treated cells were separated and assessed for differences in expression between the cytoplasmic and nuclear compartments using western blotting. Flow cytometry and western blotting using antibodies for markers of apoptosis were used to assess for mode of cell death. Differences in gene expression of NFκB target genes were assessed using gene specific primers for SYBR green RT-PCR. RNAi using siRNA directed against each of the GSK3 isoforms, α and β, was utilised for target validation

The kinase inhibitor screen demonstrated significant growth inhibition among all the tested PCa cell lines to the GSK3 inhibitor, BIO. This result was validated using two additional chemical GSK3 inhibitors, LiCl and CHIR99021. Expression analysis demonstrated aberrant NFκB and GSK3 expression in the cytoplasmic and nuclear compartments of the cell lines that varied upon treatment with GSK3 inhibitors. siRNA directed against GSK3 confirmed that the effects of the inhibitors were GSK3 specific and demonstrated that both isoforms distinguished between the effects of each of the two isoforms.

Our results suggest that GSK3 has a role in the pathogenesis of PCa. This notion is supported by the findings that GSK3 inhibition reduces the viability of PCa cells via a mechanism that is consistent with apoptosis. Furthermore, both NFκB and GSK3 are shown to be active and aberrantly co-expressed in our PCa model. Collectively, these results suggest that GSK3 has an effect on NFκB that may be independent of WNT signalling.

Citation Format: Husnain Ali, Amy Burke, Enda O'Connell, Frank Sullivan, Frank Giles, Sharon Glynn. GSK3α/β inhibition as a drug target in prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4370. doi:10.1158/1538-7445.AM2015-4370