Mechanistic rationale for MCL1 inhibition during androgen deprivation therapy.

Androgen deprivation therapy induces apoptosis or cell cycle arrest in prostate cancer (PCa) cells. Here we set out to analyze whether MCL1, a known mediator of chemotherapy resistance regulates the cellular response to androgen withdrawal. Analysis of MCL1 protein and mRNA expression in PCa tissue and primary cell culture specimens of luminal and basal origin, respectively, reveals higher expression in cancerous tissue compared to benign origin. Using PCa cellular models in vitro and in vivo we show that MCL1 expression is upregulated in androgen-deprived PCa cells. Regulation of MCL1 through the AR signaling axis is indirectly mediated via a cell cycle-dependent mechanism. Using constructs downregulating or overexpressing MCL1 we demonstrate that expression of MCL1 prevents induction of apoptosis when PCa cells are grown under steroid-deprived conditions. The BH3-mimetic Obatoclax induces apoptosis and decreases MCL1 expression in androgen-sensitive PCa cells, while castration-resistant PCa cells are less sensitive and react with an upregulation of MCL1 expression. Synergistic effects of Obatoclax with androgen receptor inactivation can be observed. Moreover, clonogenicity of primary basal PCa cells is efficiently inhibited by Obatoclax. Altogether, our results suggest that MCL1 is a key molecule deciding over the fate of PCa cells upon inactivation of androgen receptor signaling.

Enhanced inhibition of prostate tumor growth by dual targeting the androgen receptor and the regulatory subunit type iα of protein kinase a in vivo.

Progression to castration resistance is a major problem in the treatment of advanced prostate cancer and is likely to be driven by activation of several molecular pathways, including androgen receptor (AR) and cyclic AMP-dependent protein kinase A (PKA). In this study, we examined the therapeutic efficacy of a combined inhibition of the AR and the regulatory subunit type Iα (RIα) of protein kinase A with second generation antisense oligonucleotides (ODNs) in androgen-sensitive LNCaP and castration-resistant LNCaPabl tumors in vivo. We found that targeting the AR alone inhibited LNCaP, as well as LNCaPabl tumors. Combined inhibition resulted in an improved response over single targeting and even a complete tumor remission in LNCaPabl. Western blot analysis revealed that both ODNs were effective in reducing their target proteins when administered alone or in combination. In addition, treatment with the ODNs was associated with an induction of apoptosis. Our data suggest that dual targeting of the AR and PKARIα is more effective in inhibiting LNCaP and LNCaPabl tumor growth than single treatment and may give a treatment benefit, especially in castration-resistant prostate cancers.

Lovastatin causes diminished PSA secretion by inhibiting AR expression and function in LNCaP prostate cancer cells.

OBJECTIVES: To investigate why statin users display a noticeable decline in prostate specific antigen (PSA) as revealed in recent clinical trials, we tested the effects of lovastatin on the androgen signaling cascade in lymph node carcinoma of the prostate (LNCaP) prostate cancer cells. METHODS: Effects of lovastatin alone or in combination with a small interference RNA to inhibit AR expression on cell proliferation and induction of apoptosis were assessed by [(3)H] thymidine incorporation and caspase-3 activity assay. PSA levels were measured in the cell culture supernatant by immunoassay. In addition, expression and activity of AR and Akt/protein kinase B (Akt) were determined by Western blotting and real-time polymerase chain reaction as well as by luciferase reporter gene assay. RESULTS: Our results show that lovastatin significantly reduces AR expression and activity, resulting in decreased PSA levels. These effects were associated with inhibition of cell proliferation and induction of apoptosis. In addition, we observed that the Akt signaling pathway plays a pivotal role in lovastatin-mediated regulation of AR signaling. CONCLUSIONS: Our data suggest that the regular use of statins may have beneficial effects in statin users by preventing prostate cancer growth through inhibition of androgen activation and expression, resulting in diminished PSA levels.