CDK Inhibitors Induce Mitochondria-mediated Apoptosis Through the Activation of Polyamine Catabolic Pathway in LNCaP, DU145 and PC3 Prostate Cancer Cells

Abstract

Androgen signaling is critical in prostate cancer development and progression. The co-existence of hormone responsive and irresponsive cells due to functional androgen receptor (AR) in prostate gland is the major obstacle in prostate cancer therapy models. Targeting aberrant cell cycle by novel cell cycle blocking agents is a promising strategy to treat various types of malignancies. Purvalanol and roscovitine are cyclin dependent kinase (CDK) inhibitors able to activate apoptotic cell death by inducing cell cycle arrest at G1/S and G2/M phases in cancer cells. Polyamines are unique cationic amine derivatives involved in the regulation of cell proliferation. Although the elevated intracellular level of polyamines (putrescine, spermidine and spermine) is typical for prostate gland, abnormal regulation of polyamine metabolism might result in rapid cell proliferation and, thus in prostate cancer progression. Therefore, treatment with drug-induced depletion of intracellular polyamine levels through the activated polyamine catabolism is critical to achieve successful strategies for prostate cancer. In this study we aimed to investigate the apoptotic efficiency of CDK inhibitors in three prostate cancer cell lines (LNCaP, DU145 and PC3), showing different AR expression profile. We found that both purvalanol and roscovitine were able to induce apoptosis at moderate cytotoxic concentrations by decreasing mitochondria membrane potential. The apoptotic effect of both CDK inhibitors was due to activation of caspases by modulating Bcl-2 family members. The efficiency of drugs was quite similar on the three prostate cell lines used in this study. However, DU145 cells were found the least sensitive against CDK inhibitors while purvalanol was more potent than roscovitine. Similarly to classical chemotherapeutic agents, both drugs could up-regulate polyamine catabolic enzymes (SSAT, SMO and PAO) in cell type dependent manner. Transient silencing of SSAT and/or inhibition of PAO/ SMO with MDL72527 prevented CDK inhibitors- induced apoptotic cell death in DU145 and PC3 cells. Although roscovitine was less effective in DU145 cells, pre-treatment with α-difluoromethylornithine (DFMO), an inhibitor of ODC, enhanced the roscovitine-induced apoptotic cell death through the cleavage of caspase-9 and caspase-3. Therefore, we conclude that polyamine catabolism might have essential role in the cellular responses against CDK inhibitors in different androgen-responsive or irresponsive prostate cancer cells.

Inhibition of autophagy by 3-MA potentiates purvalanol-induced apoptosis in Bax deficient HCT 116 colon cancer cells

“…It was reported that CDK inhibitors could activate caspasedependent apoptosis by altering mitochondria membrane functions in various cancer cell lines such as breast, prostate, lung, and colon cancer cells [6,8,28]. Bax is an essential key molecule in the caspasedependent mitochondrial activated apoptotic cell death.…”

“…Roscovitine and purvalanol, novel CDK inhibitors, are referred as strong apoptotic inducers, which prevent the binding efficiency of CDKs to their cyclin partners. Therefore, these drugs effectively induced cell cycle arrest and apoptosis in prostate [8], breast [9], lung [10], cervix [11] and colon cancer [12,13] cell lines.…”

Anti-cancer effects of torulene, isolated from Sporidiobolus pararoseus, on human prostate cancer LNCaP and PC-3 cells via a mitochondrial signal pathway and the down-regulation of AR expression

“…Moreover, according to WST-1 assay, PC-3 cells were more sensitive against torulene treatment compared to LNCaP cells. 18,27 Cell morphology plays vital roles in diverse cellular processes, including cell growth, motility, proliferation, and division. 21 To investigate the mechanism induced by the carotenoids, the changes in cell morphology were also observed and the observation results were consistent with that of viability analysis.…”

“…27,28 The decrease in MMP is the earliest intracellular event before the apoptosis caused by the mitochondria-mediated death pathway, so the decline of MMP is considered as a symbolic event of early cellular apoptosis. 16 In this assay, both groups showed a significant (p < 0.05) decrease in MMP when treated with carotenoids compared to the control group.…”

Prostate Cancer and Aspirin Use: Synopsis of the Proposed Molecular Mechanisms

“…Another proposed mechanism of control—as suggested by epidemiological studies in colorectal cancer patients (Seiler, 2003; Laukaitis and Gerner, 2011)—is the induction of polyamine catabolism and subsequent regulation of cell proliferation and cancer progression (Arisan et al, 2014). Polyamines are small cationic molecules, formed from the decarboxylation products of ornithine and S-adenosyl-methionine.…”