Effects of concomitant inactivation of p53 and pRb on response to doxorubicin treatment in breast cancer cell lines.

Loss of and function have both been linked to poor response to DNA damaging drugs in breast cancer patients. We inactivated and/or by siRNA mediated knockdown in breast cancer cell lines varying with respect to ER/PgR and Her-2 status as well as and mutation status (MCF-7, T47D, HTB-122 and CRL2324) and determined effects on cell cycle arrest, apoptosis and senescence with or without concomitant treatment with doxorubicin. In T47D cells, we found the cell cycle phase distribution to be altered when inactivating (=0.0003) or and concomitantly (≤0.001). No similar changes were observed in MCF-7, HTB-122 or CRL2324 cells. While no significant change was observed for the CRL2324 cells upon doxorubicin treatment, MCF-7, T47D as well as HTB-122 cells responded to knockdown of and in concert, with a decrease in the fraction of cells in G1/G0-phase (=0.042, 0.021 and 0.027, respectively). Inactivation of and/or caused no change in induction of apoptosis. Upon doxorubicin treatment, inactivation of or separately caused no induction of apoptosis in MCF-7 and HTB-122 cells; however, concomitant inactivation leads to a slightly reduced activation of apoptosis. Interestingly, upon doxorubicin treatment, concomitant inactivation of and caused a decrease in senescence in MCF-7 cells (=0.027). Comparing the effects of concomitant knockdown on apoptosis and senescence, we observed a strong interaction (=0.001). We found concomitant inactivation of and to affect various routes of response to doxorubicin treatment in breast cancer cells.