RB1 and cancer: Moreover, CA, but not OA, (i) abolished the drug-mediated cleavage of both PARP and caspase 9 thus contrasting the apoptotic process; (ii) maintained the hyperphosphorylated status of RB and down-regulated p21 protein, being these two events that favour rather than oppose cancer cell growth and, lastly, (iii) decreased acetylated levels of histones H3/H4 and α-tubulin (Fig. 7A).