Sensitization of Pancreatic Cancer Stem Cells to Gemcitabine by Chk1 Inhibition

Abstract

Checkpoint kinase 1 (Chk1) inhibition sensitizes pancreatic cancer cells and tumors to gemcitabine. We hypothesized that Chk1 inhibition would sensitize pancreatic cancer stem cells to gemcitabine. We tested this hypothesis by using two patient-derived xenograft models (designated J and F) and the pancreatic cancer stem cell markers CD24, CD44, and ESA. We determined the percentage of marker-positive cells and their tumor-initiating capacity (by limiting dilution assays) after treatment with gemcitabine and the Chk1 inhibitor, AZD7762. We found that marker-positive cells were significantly reduced by the combination of gemcitabine and AZD7762. In addition, secondary tumor initiation was significantly delayed in response to primary tumor treatment with gemcitabine + AZD7762 compared with control, gemcitabine, or AZD7762 alone. Furthermore, for the same number of stem cells implanted from gemcitabine- versus gemcitabine + AZD7762-treated primary tumors, secondary tumor initiation at 10 weeks was 83% versus 43%, respectively. We also found that pS345 Chk1, which is a measure of DNA damage, was induced in marker-positive cells but not in the marker-negative cells. These data demonstrate that Chk1 inhibition in combination with gemcitabine reduces both the percentage and the tumor-initiating capacity of pancreatic cancer stem cells. Furthermore, the finding that the Chk1-mediated DNA damage response was greater in stem cells than in non-stem cells suggests that Chk1 inhibition may selectively sensitize pancreatic cancer stem cells to gemcitabine, thus making Chk1 a potential therapeutic target for improving pancreatic cancer therapy.

Gemcitabine and CHK1 Inhibition Potentiate EGFR-Directed Radioimmunotherapy against Pancreatic Ductal Adenocarcinoma

“…þ /EpCAM þ pancreatic CSCs after gemcitabine alone or combined treatment with the CHK1i AZD7762 and gemcitabine (34). The discordance with our findings could be due to the specificity of the different inhibitors used; AZD7762 has equal potency in inhibiting CHK1 and CHK2 (35), whereas PF-477736 is 100-fold more specific for CHK1 than CHK2 (7).…”

Depletion of RAD17 sensitizes pancreatic cancer cells to gemcitabine

“…RAD17 is involved in detecting gemcitabine-induced stalled replication forks and acts upstream of checkpoint kinase 1 (CHK1). Knockdown and inhibition of CHK1 has been shown to act in a synthetically lethal manner with gemcitabine in pancreatic cancer cells (Azorsa et al, 2009;Venkatesha et al, 2012), which was also confirmed in this study. Mechanistically, RAD17 in complex with replication factor C (RFC) subunits 2-5 is responsible for loading a DNA clamp composed of RAD9, RAD1 and HUS1 at stalled replication forks, a result of gemcitabine-induced masked chain termination.…”

ATM Mutations in Cancer: Therapeutic Implications

“…Like UCN-01, it enhances the rate of cell death induced by chemotherapy agents. Preclinical studies showed a 20-to 70-fold reduction of the growth-inhibitory (91). AZD7762 also inhibited radiation damage repair and conferred radiosensitivity on p53-mutant breast cancer cell lines, similar to other agents of the class (92).…”