The growth inhibitory effect of p21 adenovirus on human bladder cancer cells

Purpose: To evaluate whether p21 (WAF-1/CIP1) should be considered a potent ial candidate for human bladder cancer gene therapy, we determined: (1) the basal level of p21 expression in bladder cancer cell lines, (2) the respon se of bladder cancer cells to increased p21 expression following p21 adenov irus infection, and (3) the mechanism of growth inhibition produced by p21 overexpression. Materials and Methods: Five established human bladder cancer cell lines and one primary culture derived from an invasive transitional cell carcinoma w ere used in this study. To examine the effect of p21 protein on the growth of human bladder cancer cells, a recombinant adenovirus vector system conta ining p21 cDNA, under the control of cytomegalovirus promoter, was construc ted. A control virus containing p21 in an antisense orientation was used to eliminate potential artifacts caused by viral toxicity. Results: Human bladder cancer cell lines exhibit variable endogenous p21 le vels which correlate with the in vitro growth status. Significant, but high ly variable increases in the steady-state level of p21 were detected in p21 adenovirus infected cells. Human bladder cancer cell lines responded heter ogeneously to p21 adenovirus infection. Growth of the WH cell line was subs tantially inhibited in a dose and time-course dependent fashion. The mechan ism of p21 growth inhibition was found to be due to G(0)/G(1) arrest and no t the induction of apoptosis. In contrast, p21 adenovirus failed to inhibit the growth of T24 bladder cancer cells because T24 cells were resistant to viral infection. The 253J bladder cancer cells exhibited marked sensitivit y to adenovirus; substantial growth inhibition was seen with both sense and antisense p21 very early in the time course of infection. Conclusions: We found significant variation in the basal level of p21 prote in expression in several human bladder cancer cell lines. Increased p21 exp ression as a result of adenoviral infection may be a potent growth suppress or in some human bladder cancer because it elicits cell cycle arrest in G(0 )/G(1) stage, but not the induction of apoptosis. Bladder cancer cells exhi bit a wide spectrum of sensitivity to adenoviral infection that may be caus ed by the presence of viral receptor heterogeneity This wide spectrum of se nsitivity has significant basic scientific and clinical implications and wa rrants further study.