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

Purpose: To evaluate whether p21 (WAF-1/CIP1) should be considered a potential candidate for human bladder cancer gene therapy, we determined: (1) the basal level of p21 expression in bladder cancer cell lines, (2) the response of bladder cancer cells to increased p21 expression following p21 adenovirus 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 were used in this study. To examine the effect of p21 protein on the growth of human bladder cancer cells, a recombinant adenovirus vector system containing p21 cDNA, under the control of cytomegalovirus promoter, was constructed. 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 levels which correlate with the in vitro growth status. Significant, but highly variable increases in the steady-state level of p21 were detected in p21 adenovirus infected cells. Human bladder cancer cell lines responded heterogeneously to p21 adenovirus infection. Growth of the WH cell line was substantially inhibited in a dose and time-course dependent fashion. The mechanism of p21 growth inhibition was found to be due to G₀/G₁ arrest and not 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 sensitivity 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 protein expression in several human bladder cancer cell lines. Increased p21 expression as a result of adenoviral infection may be a potent growth suppressor in some human bladder cancer because it elicits cell cycle arrest in G₀/G₁ stage, but not the induction of apoptosis. Bladder cancer cells exhibit a wide spectrum of sensitivity to adenoviral infection that may be caused by the presence of viral receptor heterogeneity. This wide spectrum of sensitivity has significant basic scientific and clinical implications and warrants further study.