Abstract 970: Probing the expression and function of aldehyde dehydrogenases in prostate cancer using ALDH-affinic compounds and siRNA
Authors: Sadiq Maria , Ibrahim Ali I. , Frame Fiona , Allison Simon J. , Sutherland Mark , Phillips Roger M. , Maitland Norman J. , Pors Klaus 
Published: July 2017

The human aldehyde dehydrogenases (ALDHs) play a major role in detoxifying highly reactive aldehydes into carboxylic acids. Deregulation of ALDHs have implications in a number of cancers including prostate cancer. They play an important role as a cancer stem cell (CSC) marker due to high activity found in CSCs while high expression is also known to lead to resistance to drugs including docetaxel. Although the exact role of ALDHs is not fully understood, emerging information indicates several isoforms including ALDH1A3 and ALDH7A1 play a key role in cancer. To further elucidate the role of ALDHs in prostate cancer, we here report on the perturbation of ALDH expression and function using chemical probes and siRNA.

Primary prostate epithelial cells cultured from patient tissue were used for this study. Cancer samples were obtained from radical prostatectomies and benign samples from transurethral resection of the prostate.

qPCR analysis showed ALDH1A3 to be more highly expressed than ALDH7A1 in the primary prostate epithelial cultures in 18 patient samples. Expression of ALDH1A3 was 3-fold higher in the cancer samples compared to the benign samples. The RNA data correlates with protein expression in 6 patient samples by immunofluorescence. qPCR analysis also showed that knockdown of ALDH7A1 resulted in an increase in the expression of ALDH1A3 suggesting a compensatory mechanism. Trypan blue exclusion assay showed that knockdown of ALDH1A3, ALDH7A1 or a combination of both resulted in a reduction in cell numbers. Flow cytometry was used to study cell differentiation upon knockdown of ALDH1A3, ALDH7A1 or both. In all 7 samples studied there was a reduction in CD49b expression indicating cell differentiation. ALDH7A1 knockdown showed a higher level of cell differentiation in all cases. The colony forming ability of primary cells was also investigated post-transfection of siRNAs against ALDH1A3, ALDH7A1 or both using the colony formation assay which resulted in a lower number of colonies in all 7 samples tested. The effect was more pronounced in benign prostatic hyperplasia (BPH) than in malignant cancer samples and patient variability was observed. ALDH-affinic probe compounds (DEAB and three derivatives, Ali-9, Ali-14 & Ali-18) were tested against 5 patient samples to investigate if they have an effect on cell viability. All four compounds showed reduction in cell viability at the highest concentration while Ali-14 and Ali-18 showed a synergistic effect in combination treatment with docetaxel.

In conclusion, knockdown of ALDH1A3 and ALDH7A1 reduce cell number, induce cells to differentiate and reduce their colony forming ability. Novel ALDH-affinic probe compounds reduced cell viability alone and in combination with docetaxel, therefore these compounds may be of value both as single treatments and to provide a strategy to enhance taxane-based therapy such as docetaxel.

Citation Format: Maria Sadiq, Ali I. Ibrahim, Fiona Frame, Simon J. Allison, Mark Sutherland, Roger M. Phillips, Norman J. Maitland, Klaus Pors. Probing the expression and function of aldehyde dehydrogenases in prostate cancer using ALDH-affinic compounds and siRNA [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 970. doi:10.1158/1538-7445.AM2017-970