In vitro evaluation of flavopiridol, a novel cell cycle inhibitor, in bladder cancer

Purpose: To determine the in vitro effects of flavopiridol on bladder cance r cell lines, immortalized urothelial cell lines, and normal urothelial cel ls well characterized for defects in p53, pRb, and p16. Methods: Growth inh ibition was assessed via an MTT assay and apoptosis via DAPI nuclear staini ng. Cell cycle analysis was performed via propidium iodide staining and flu orescent activated cell sorting (FACS). Multidrug-resistant cells were gene rated by continuous exposure to doxorubicin. Results: Growth inhibition was not correlated with inactivation of p53, pRb, or p16. All cells experience d G2/M arrest within 24 h of flavopiridol exposure. Modest apoptosis was ob served but required 72 h of continuous drug exposure to become evident. The re was no obvious synergistic or antagonistic toxicity when flavopiridol wa s combined with radiotherapy or cisplatin dosed at the IC50 despite the obs ervation that radiotherapy and flavopiridol led to more profound G2/M arres t than either agent alone. Doxorubicin-resistant cells, demonstrated to ove rexpress the MDR1 multidrug-resistance protein were equally as sensitive to flavopiridol as the parental cells. Conclusions: Flavopiridol is a novel c ell cycle inhibitor that may be a useful agent in bladder cancers with tumo r suppressor gene alterations and/or multidrug resistance.