The Targeting of MRE11 or RAD51 Sensitizes Colorectal Cancer Stem Cells to CHK1 Inhibition

Abstract

Cancer stem cells (CSCs) drive not only tumor initiation and expansion, but also therapeutic resistance and tumor relapse. Therefore, CSC eradication is required for effective cancer therapy. In preclinical models, CSCs demonstrated high capability to tolerate even extensive genotoxic stress, including replication stress, because they are endowed with a very robust DNA damage response (DDR). This favors the survival of DNA-damaged CSCs instead of their inhibition via apoptosis or senescence. The DDR represents a unique CSC vulnerability, but the abrogation of the DDR through the inhibition of the ATR-CHK1 axis is effective only against some subtypes of CSCs, and resistance often emerges. Here, we analyzed the impact of druggable DDR players in the response of patient-derived colorectal CSCs (CRC-SCs) to CHK1/2 inhibitor prexasertib, identifying RAD51 and MRE11 as sensitizing targets enhancing prexasertib efficacy. We showed that combined inhibition of RAD51 and CHK1 (via B02+prexasertib) or MRE11 and CHK1 (via mirin+prexasertib) kills CSCs by affecting multiple genoprotective processes. In more detail, these two prexasertib-based regimens promote CSC eradication through a sequential mechanism involving the induction of elevated replication stress in a context in which cell cycle checkpoints usually activated during the replication stress response are abrogated. This leads to uncontrolled proliferation and premature entry into mitosis of replication-stressed cells, followed by the induction of mitotic catastrophe. CRC-SCs subjected to RAD51+CHK1 inhibitors or MRE11+CHK1 inhibitors are eventually eliminated, and CRC-SC tumorspheres inhibited or disaggregated, via a caspase-dependent apoptosis. These results support further clinical development of these prexasertib-based regimens in colorectal cancer patients.

HELQ suppresses migration and proliferation of non‐small cell lung cancer cells by repairing DNA damage and inducing necrosis

“…RAD51, ATR and its substrate CHK1 are key molecules involved in the regulation of DNA damage repair, cell cycle checkpoint and apoptosis (Foster et al, 2012; Hjorth‐Jensen et al, 2018; Mattiello et al, 2021). HELQ is reportedly associated with these three DNA damage‐responsive factors thereby contributing to ICL repair (Anand et al, 2022; Takata et al, 2013).…”

“…DNA damage can enhance the ability of tumor cells to be aggressive, which is associated with chromosomal instability (Morris et al, 2021). It is well-documented that the comet assay, also known as the single-cell gel electrophoresis assay, is a highly RAD51, ATR and its substrate CHK1 are key molecules involved in the regulation of DNA damage repair, cell cycle checkpoint and apoptosis (Foster et al, 2012;Hjorth-Jensen et al, 2018;Mattiello et al, 2021). HELQ is reportedly associated with these three DNA damage-responsive factors thereby contributing to ICL repair (Anand et al, 2022;Takata et al, 2013).…”

Fanconi Anemia Pathway in Colorectal Cancer: A Novel Opportunity for Diagnosis, Prognosis and Therapy

“…However, some CRC stem cells display resistance to ATR or CHK1 inhibitors. In such context, one study revealed that RAD51 targeting improves the vulnerability of CRC stem cells to the CHK1/2 inhibitor prexasertib and annihilates them through triggering mitotic catastrophe by the caspase-dependent mechanism [ 131 ]. Likewise, Manic et al [ 129 ] have demonstrated that the RAD51 inhibitor B02, along with the MRE11 inhibitor mirin, selectively kills the PARP1-upregulated CRC stem cells via mitotic catastrophe without the need for exposing cells to ATR/CHK1 inhibitors [ 129 ].…”

Analyzing the Opportunities to Target DNA Double-Strand Breaks Repair and Replicative Stress Responses to Improve Therapeutic Index of Colorectal Cancer

“…CRC-SC with these markers depend on CHK1 activity, so LY2606368 treatment by inhibiting CHK1 impaired cell cycle checkpoint resulting in lethal replication catastrophe [145]. Interestingly, the inhibition of RAD51 (B02) or MRE11 (Mirin) was able to sensitized resistant CRC-SC to prexasertib by induction of replication stress, while others inhibitors of DDR proteins ATM, ATR, or DNA-PK were ineffective [243]. RAD51 and MRE11 are HR factors, the main pathway activated for resolving DSB during replication, and CRC-SC are tolerable to high replication stress level due to modulation of DNA damage response [156].…”