Endoplasmic reticulum Ca(2+) content decrease by PKA-dependent hyperphosphorylation of type 1 IP3 receptor contributes to prostate cancer cell resistance to androgen deprivation.

Reference treatment of advanced prostate cancer (PCa) relies on pharmacological or surgical androgen deprivation therapy. However, it is only temporarily efficient as tumor cells inevitably adapt to the low testosterone environment and become hormone-refractory (HRPCa). We observed that androgen removal in HRPCa-derived LNCaP cells causes different alterations in their Ca(2+) homeostasis among which a reduction of ER Ca(2+) content. We show that the decrease in [Ca(2+)]ER is due to a modest overexpression of type 1 IP3R and a threefold increased phosphorylation of IP3R1 on Ser-1716, a protein kinase A (PKA) consensus site, both implicated in ER Ca(2+) leak. Accordingly, ER Ca(2+) content was restored by siRNA-mediated down-regulation of IP3R1 or by inhibition of its phosphorylation by competition with a permeant TAT-peptide containing the Ser-1716 consensus phosphorylation sequence or by treatment with the PKA inhibitor H89. Moreover, inhibition of the IP3R1 phosphorylation by both methods sensitized the LNCaP cells to androgen deprivation-induced apoptosis. In addition, SERCA2b overexpression precluded the effect of androgen deprivation on ER Ca(2+) store content and reduced resistance to androgen deprivation. Taken together, these results indicate that lowering the ER Ca(2+)-store content by increasing IP3R1 levels and IP3R1 phosphorylation by PKA is a protective mechanism by which HRPCa-derived cells escape cell death in the absence of androgenic stimulation.

Androgen deprivation and androgen receptor competition by bicalutamide induce autophagy of hormone-resistant prostate cancer cells and confer resistance to apoptosis.

BACKGROUND: Treatment of advanced prostate cancer (PCa) relies on pharmacological or surgical androgen deprivation. However, it is only temporarily efficient. After a few months or years, the tumor relapses despite the absence of androgenic stimulation: a state referred to as hormone-refractory prostate cancer (HRPCa). Although autophagy confers chemoresistance in some cancers, its role in the development of HRPCa remains unknown. METHODS: Autophagic flux was assayed by GFP-LC3 clustering, by LC3-I to LC3-II conversion and transmission electron microscopy. Cell death was detected by sub-G1 quantification and concomitant measurement of transmembrane mitochondrial potential and plasma membrane permeabilization. Inhibition of autophagy was achieved by siRNAs and pharmacological inhibitors. RESULTS: Androgen deprivation or treatment with the anti-androgen bicalutamide promoted autophagy in HRPCa-derived LNCaP cells. This effect was dramatically reduced after depletion of Atg5 and Beclin-1, two canonical autophagy genes, and was associated with an inhibition of the androgen-induced mTOR pathway. The depletion of Atg5 and Beclin-1 significantly increased the level of cell death induced by androgen deprivation or bicalutamide. Finally, the safe anti-malarial drug chloroquine, an inhibitor of autophagy, dramatically increased cell death after androgen deprivation or bicalutamide treatment. CONCLUSION: Taken together, our data suggest that autophagy is a protective mechanism against androgen deprivation in HRPCa cells and that chloroquine could restore hormone dependence. This set of data could lead to the development of new therapeutic strategy against HRPCa.

Vaccination with epigenetically treated mesothelioma cells induces immunisation and blocks tumour growth.

Malignant mesothelioma (MM) is an aggressive tumour associated with poor outcome in patients. Current treatments for MM are of limited efficacy. Our recent findings suggest that epigenetic drugs may induce both cytotoxicity and an immune response against MM cells. Thus, we used a mouse model of MM (AK7) to analyse how epigenetic drugs could modulate MM development in vivo. The treatment of tumour-bearing mice with an epigenetic drug already tested in clinical MM treatments (SAHA/Vorinostat) reduced the tumour mass and induced a moderate lymphocytic infiltration. However, the treatment did not stop tumour development. In order to show the potential effect of this epigenetic drug on tumour immunogenicity, in addition to cell cytotoxicity, we immunised mice either with AK7 cells pre-treated with SAHA, or with one of two cytotoxic drugs (curcumin or selenite), prior to transplantation of live AK7 cells. A specific immune response was observed only in mice immunised with AK7 cells pre-treated with the epigenetic drug (SAHA) and the tumour growth was arrested. An increase in the proportion of CD3+ CD8+ lymphocytes occurred in the peritoneal cavity. We also observed large conglomerates of immune cells in the omentum with clusters of CD8+ T cells, together with lymphocytes directed against residual AK7 cells in the interlobular connective tissue of the pancreas. Our data demonstrate that epigenetic drugs, such as SAHA, can stimulate tumour immunogenicity and improve the recognition of aggressive MM cells by the immune system in vivo.