One possible explanation is that the Chk1 mediated suppression of origin firing is most significant when extended reproduction could actually create additional Crizotinib clinical trial DNA damage, such as for instance when additional gemcitabine is incorporated into the genome. In contrast, when the damage is pre existing, as with cisplatin, additional beginning firing would not integrate further damage into the genome. This latter point is of particular interest because a recent study indicates that the repair of interstrand cross links is established only once two other replication forks converge on the lesion, thus raising the possibility that the repair of these lesions may depend on the activation of additional replication origins. Chk1, in addition to controlling beginning firing and replication of fork stability, also absolutely regulates DNA repair pathways which can be very important to the repair of interstrand cross-links in a minimum of two ways. First, Chk1 encourages HR, partly by phosphorylating Rad51. Second, Chk1 phosphorylates Meristem FancE, which stimulates the repair of interstrand cross-links through the FA pathway. Because our results demonstrably demonstrate that the HR and FA pathways are essential in HeLa cells treated with cisplatin, the lack of a result on cell survival when Chk1 is reduced suggests that Chk1 doesn’t play a significant regulatory function in these repair pathways in the cell lines examined. We also explored the possibility that Chk1 may possibly only become crucial in cisplatin treated cells when specific DNA repair pathways were disturbed. This is of particular importance since tumors usually have faulty DNA repair pathways, and the defects in these pathways probably contribute to the sensitivity of the tumor to chemotherapy regimens. For example, patients with defects in BRCA1 and BRCA2 have greater overall responses to platinum-based remedies, probably since BRCA1 and BRCA2 play essential roles Icotinib in fixing the cisplatin induced damage. If Chk1 was crucial in such cells, then tumors that harbor these defects might be good candidates for clinical trials that mix a Chk1 inhibitor and cisplatin. We didn’t notice such an result. Alternatively, we found that Chk1 depletion actually reduced the sensitivity of cells with handicapped FA and TLS pathways. Not only do these results further suggest that Chk1 inhibitors might not be beneficial agents to sensitize tumors to platinating agents, they also suggest that the inclusion of the Chk1 chemical to combination therapies containing cisplatin should be undertaken with great caution. The current findings suggest that Chk1 inhibitors might be of limited use to sensitize tumor cells to jewelry induced damage. In fact, given that Chk1 depletion actually reversed the sensitivity of cells with defects in repair pathways that are generally faulty in tumors treated with cisplatin, the utilization of such inhibitors might be counterproductive in a few patients.