Author/Editor     Kerr, Martin; Scott, Helen E.; Grošelj, Blaž; Stratford, Michael R. L.; Karaszi, Katalin; Sharma, Naomi L.; Kiltie, Anne E.
Title     Deoxycytidine kinase expression underpins response to gemcitabine in bladder cancer
Type     članek
Vol. and No.     Letnik 20, št. 21
Publication year     2014
Volume     str. 5435-5445
ISSN     1078-0432 - Clinical cancer research : an official journal of the American Association for Cancer Research
Language     eng
Abstract     PURPOSE: In a recent phase II clinical trial, low-dose (100 mg/m(2)) gemcitabine showed promise as a radiosensitizer in bladder cancer, but underlying mechanisms lack elucidation. Here, we investigated the mechanism of radiosensitization by low-dose gemcitabine in bladder cancer cell lines. EXPERIMENTAL DESIGN: Four bladder cancer cell lines were screened for radiosensitization by low-dose gemcitabine using clonogenic assay, and gemcitabine-resistant RT112gem and CALgem cells created by exposure to increasing gemcitabine doses. Four key gemcitabine-regulatory genes were knocked down by transient siRNA. Nude mice carrying CALgem subcutaneous xenografts were exposed to 100 mg/kg gemcitabine % ionizing radiation (IR) and response assessed by tumor growth delay. RESULTS: Gemcitabine was cytotoxic in the low nanomolar range (10-40 nmol/L) in four bladder cancer cell lines and radiosensitized all four lines. Sensitizer enhancement ratios at 10% survival were: RT112 1.42, CAL29 1.55, T24 1.63, and VMCUB1 1.47. Transient siRNA knockdown of deoxycytidine kinase (dCK) significantly reduced radiosensitization by gemcitabine (P = 0.02). RT112gem and CALgem cells displayed robust decreases of dCK mRNA and protein levels; reexpression of dCK restored gemcitabine sensitivity. However, CALgem xenografts responded better to combination gemcitabine/IR than either treatment alone (P < 0.001) with dCK strongly expressed in the tumor vasculature and stroma. CONCLUSIONS: Gemcitabine resistance in bladder cancer cell lines was associated with decreased dCK expression, but gemcitabine-resistant xenografts were responsive to combination low-dose gemcitabine/IR. We propose that dCK activity in tumor vasculature renders it gemcitabine sensitive, which is sufficient to invoke a tumor response and permit tumor cell kill in gemcitabine-resistant tumors.
Keywords     krvni rak
gemicitabin
radiosenzibilnost
klinične študije
bladder cancer
gemicitabine
radiosensitization
clinical trials