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241 Cdk1-cyclin B complex: A potential target for counteracting everolimus-induced resistance in prostate cancer
241 - Cdk1-cyclin B complex: A potential target for counteracting everolimus-induced re... Page 1 of 1
e241 Cdk1-cyclin B complex: A potential target for counteracting everolimus-induced resistance in prostate cancer Tsaur I., Makarevic J., Reiter M., Kurosch M., Bartsch G., Wiesner C., Haferkamp A., Blaheta R. University Medical Center, Dept. of Urology and Pediatric Urology, Frankfurt, Germany Since the phosphatidyl-inositol-3-kinase INTRODUCTION & OBJECTIVES: (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway is aberrantly activated in various tumor types, mTOR targeting is a promising strategy for cancer therapy. Unfortunately, not all patients benefit equally from an mTOR based regimen and disease progression unavoidably occurs during treatment. Based on clinical data, it has been argued that chronic drug exposure provokes the development of resistance, ultimately limiting the utility of mTOR-inhibitors. As no published studies previously dealt with this issue, a prostate cancer subline resistant to the mTOR–inhibitor everolimus was established and the consequences of drug resistance on the proliferative potential of the tumor cells and molecular characteristics of cell growth regulation were analyzed. MATERIAL & METHODS: The growth and proliferation properties of PC3 prostate cancer cells, sensible (PC3par) or resistant (PC3res) to the mTOR inhibitor everolimus, were investigated. Knock-down models were established by transfection of cells with cdk1 or cyclin B siRNA. RESULTS: Cell growth and proliferation rates of PC3res and PC3par were comparable. Removal of everolimus from the culture medium of PC3res cells followed by low-dosed treatment with everolimus resulted in no growth inhibiting effect. Similar basal apoptosis rate was observed in PC3par and PC3res cells. However, late apoptosis increased in PC3par but decreased in PC3res following treatment with low-dosed everolimus. Accordingly, the number of vital cells was reduced in PC3par but elevated in PC3res cells following everolimus treatment. PC3res accumulated in the G2/M-phase, accompanied by a significant loss of PC3res in G0/G1, compared to PC3par cells. Particularly, cdk1 and cyclin B were strongly upregulated in PC3res. Incubation of the prostate cancer cells with siRNA against cdk1 or cyclin B distinctly diminished the protein content in both PC3par and PC3res. The specific knockdown was accompanied by a significant growth blockade of PC3par and, most importantly, of the everolimus resistant subline PC3res. Interestingly, incubation of PC3res cells with cyclin B siRNA restored the sensitivity of tumor cells to everolimus. Cell growth attenuation was now induced in this cell line by treatment with the drug. CONCLUSIONS: The data indicate that cdk1-cyclin B overexpression is related to resistance development in PC3 cells under chronic treatment with everolimus, leading to enhanced progression towards G2/M. Down-regulation of the cdk1-cyclin B complex may prolong the efficacy of a therapeutic regimen based on mTOR-inhibition in prostate cancer.
file://F:\RamShankar\April\04-05-12\Cip\Sour\241.html
4/6/2012
e241 Cdk1-cyclin B complex: A potential target for counteracting everolimus-induced resistance in prostate cancer Tsaur I., Makarevic J., Reiter M., Kurosch M., Bartsch G., Wiesner C., Haferkamp A., Blaheta R. University Medical Center, Dept. of Urology and Pediatric Urology, Frankfurt, Germany Since the phosphatidyl-inositol-3-kinase INTRODUCTION & OBJECTIVES: (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway is aberrantly activated in various tumor types, mTOR targeting is a promising strategy for cancer therapy. Unfortunately, not all patients benefit equally from an mTOR based regimen and disease progression unavoidably occurs during treatment. Based on clinical data, it has been argued that chronic drug exposure provokes the development of resistance, ultimately limiting the utility of mTOR-inhibitors. As no published studies previously dealt with this issue, a prostate cancer subline resistant to the mTOR–inhibitor everolimus was established and the consequences of drug resistance on the proliferative potential of the tumor cells and molecular characteristics of cell growth regulation were analyzed. MATERIAL & METHODS: The growth and proliferation properties of PC3 prostate cancer cells, sensible (PC3par) or resistant (PC3res) to the mTOR inhibitor everolimus, were investigated. Knock-down models were established by transfection of cells with cdk1 or cyclin B siRNA. RESULTS: Cell growth and proliferation rates of PC3res and PC3par were comparable. Removal of everolimus from the culture medium of PC3res cells followed by low-dosed treatment with everolimus resulted in no growth inhibiting effect. Similar basal apoptosis rate was observed in PC3par and PC3res cells. However, late apoptosis increased in PC3par but decreased in PC3res following treatment with low-dosed everolimus. Accordingly, the number of vital cells was reduced in PC3par but elevated in PC3res cells following everolimus treatment. PC3res accumulated in the G2/M-phase, accompanied by a significant loss of PC3res in G0/G1, compared to PC3par cells. Particularly, cdk1 and cyclin B were strongly upregulated in PC3res. Incubation of the prostate cancer cells with siRNA against cdk1 or cyclin B distinctly diminished the protein content in both PC3par and PC3res. The specific knockdown was accompanied by a significant growth blockade of PC3par and, most importantly, of the everolimus resistant subline PC3res. Interestingly, incubation of PC3res cells with cyclin B siRNA restored the sensitivity of tumor cells to everolimus. Cell growth attenuation was now induced in this cell line by treatment with the drug. CONCLUSIONS: The data indicate that cdk1-cyclin B overexpression is related to resistance development in PC3 cells under chronic treatment with everolimus, leading to enhanced progression towards G2/M. Down-regulation of the cdk1-cyclin B complex may prolong the efficacy of a therapeutic regimen based on mTOR-inhibition in prostate cancer.
file://F:\RamShankar\April\04-05-12\Cip\Sour\241.html
4/6/2012