Chemosensitization of androgen-independent prostate cancer with neutral endopeptidase.
OBJECTIVE
We investigated whether neutral endopeptidase (NEP) could augment chemosensitivity to anticancer drugs by promoting protein kinase C (PKC)delta-mediated mitochondrial apoptosis in prostate cancer (PC) cells.


METHODS
Human PC cell lines LNCaP and PC-3, and a normal prostate epithelial cell line (PrEC) were used. The protein expression was detected by Western blot analysis, and the protein turnover was determined by pulse-chase assay. Apoptotic ratio was measured by annexin V staining.


RESULTS
Western blot analyses and pulse-chase assays showed that the specific NEP inhibitor CGS24592 decreased PKCdelta protein expression by promoting PKCdelta protein degradation in NEP-expressing LNCaP cells. Conversely, recombinant NEP (rNEP) increased PKCdelta protein expression by delaying PKCdelta protein degradation in NEP-negative PC-3 cells. Apoptosis assays showed that rNEP promoted anticancer drug-induced apoptosis in PC-3 cells specifically through PKCdelta activity that mediated anticancer drug-induced mitochondrial change such as cytochrome-c release and caspase-9 activation. Of note, rNEP was able to increase PKCdelta protein expression predominantly in PC-3 cells rather than in PrEC cells. Treatment with rNEP before subtoxic concentrations of etoposide (0.1 micro M) significantly promoted mitochondrial apoptosis compared with only etoposide in PC-3 cells (P < 0.01) but not in PrEC cells.


CONCLUSIONS
These results suggest that NEP enzyme activity contributes to anticancer drug-induced PC cell apoptosis dependent on PKCdelta-mediated mitochondrial events. More importantly, the combination of NEP with anticancer drugs may be a promising therapeutic modality because rNEP is able to augment chemosensitivity in androgen-independent PC with minimal toxicity in normal tissues.
Sumitomo
Makoto
M
Department of Urology, National Defense Medical College, Tokorozawa, Saitama, Japan.
Asano
Tomohiko
T
Asakuma
Junichi
J
Asano
Takako
T
Nanus
David M
DM
Hayakawa
Masamichi
M
D000728:Androgens / Q000494:pharmacology*; D017304:Annexin A5 / Q000378:metabolism; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D002478:Cells, Cultured / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009376:Neoplasms, Hormone-Dependent / Q000201:enzymology / Q000473:pathology; D015260:Neprilysin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D063065:Organophosphonates / Q000494:pharmacology; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D011467:Prostate / Q000378:metabolism / Q000473:pathology; D011471:Prostatic Neoplasms / Q000201:enzymology* / Q000473:pathology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051745:Protein Kinase C-delta; D011994:Recombinant Proteins / Q000494:pharmacology
D000728:Androgens; D017304:Annexin A5; D000972:Antineoplastic Agents, Phytogenic; C086164:CGS 24592; D063065:Organophosphonates; D011994:Recombinant Proteins; D010649:Phenylalanine; D005047:Etoposide; C497258:PRKCD protein, human; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; D015260:Neprilysin