Abrogation of the radiation-induced G2 checkpoint by the staurosporine derivative UCN-01 is associated with radiosensitisation in a subset of colorectal tumour cell lines

Abstract

Ionising radiation is commonly used in the treatment of colorectal cancer. Tumour cells with mutant p53 undergo cell cycle arrest at G2/M after ionising radiation and evidence suggests that abrogation of this G2 arrest can lead to a premature, aberrant mitosis, thus enhancing ionising radiation-induced cell killing. The G2 checkpoint inhibitor UCN-01 was thus investigated to determine whether it would abrogate the G2 checkpoint induced by 5 Gy ionising radiation in a range of colorectal tumour cell lines. Data presented show that, at doses that are alone non-toxic to the cells, UCN-01 inhibits the ionising radiation-induced G2 checkpoint in five colorectal tumour cell lines with mutant p53. The ability of UCN-01 to sensitise cells to ionising radiation-induced growth inhibition and apoptosis was also investigated and UCN-01 was found to radiosensitise two out of five cell lines. These results were confirmed by long-term colony forming efficiency studies. These results demonstrate that abrogation of the ionising radiation-induced G2 checkpoint is not necessarily associated with sensitisation to ionising radiation, however, some colorectal tumour cell lines can be radiosensitised by UCN-01. Although the mechanism of radiosensitisation is not clear, this may still be an important treatment strategy.

Radiation-induced apoptosis in developing mouse retina exhibits dose-dependent requirement for ATM phosphorylation of p53

“…UCN-01 can abolish IR-induced G2/M checkpoint and this may account for its ability to enhance IR-induced apoptosis. [32][33][34] We observed a strong induction of p21Cip1 by IR in the developing retinas (not shown). However, Cdkn1a (p21Cip1) knockout did not affect IR-induced apoptosis in the developing retinas (Figure 4e).…”

The oncogenic phosphatase PPM1D confers cisplatin resistance in ovarian carcinoma cells by attenuating checkpoint kinase 1 and p53 activation

“…Chk1 could have both pro-and anti-apoptotic roles in resistant cancer cells, depending on their p53 status (Bunch and Eastman, 1996;Shao et al, 1997;Sugiyama et al, 2000;Playle et al, 2002;Carrassa et al, 2004;Chen et al, 2006;Reinhardt et al, 2007;Wagner and Karnitz, 2009;Pan et al, 2009). Our working hypothesis assumes Chk1 is pro-apoptotic and acts in a p53-dependent manner.…”

“…The dimorphic nature of Chk1 (proor anti-apoptotic) depends primarily on the presence of a functional p53 signaling pathway, a key mediator of its pro-apoptotic activity. However, in the studies where Chk1 inhibition lead to sensitization to several cytotoxic agents, the cell lines used had aberrant p53 signaling due to deficiency or mutation (Bunch and Eastman, 1996;Shao et al, 1997;Sugiyama et al, 2000;Playle et al, 2002;Carrassa et al, 2004;Chen et al, 2006;Reinhardt et al, 2007;Wagner and Karnitz, 2009;Pan et al, 2009). Our data suggest that the delay in Chk1 activation PPM1D knockdown did not sensitize A2780cp (p53 mutant), OCC-1 (p53 mutant), OVCAR-3 (p53 mutant) and SKOV3 (p53 null) cells to CDDP-induced apoptosis.…”

Knockdown of Chk1 sensitizes human colon carcinoma HCT116 cells in a p53-dependent manner to lidamycin through abrogation of a G2/M checkpoint and induction of apoptosis

“…[10][11][12][13][14] However, the effect of Chk1 inhibition on DNA-damage agents is dependent on the cell line and cytotoxic agent. [15][16][17][18][19][20] It has been reported that inhibition of Chk1 hyperactivated ataxia telangectasia mutated gene (ATM), Rad 3 related gene (ATR), and caspase-2 after γ-radiation and trigger a caspase-2-dependent apoptotic program in human tumor cells. 21 Our previous studies have showed that LDM induced alterations of Chk1 and Chk2 in various cancer cells, 22,23 but the potential effects of cell cycle checkpoint kinases on LDM cytotoxicity remain elusive.…”