Aldehyde dehydrogenase isoform 1A1 (ALDH1A1) activity has been reported in numerous cancers to have a role in chemoresistance. However, the previously proposed resistant mechanism of protecting DNA via free radical scavenger and thus promoting cell survival within a chemically hostile environment has yet to be elicited in cancer. Considering the heterogeneity of cancer, we propose an alternative mechanism of ALDH-mediated platinum-resistance in ovarian cancer must exist.
Isogenic ovarian cancer cell lines (A2780: platinum sensitive & A2780/CP70: platinum resistant) were evaluated for potential mechanisms of platinum resistance. ALDEFLUOR kit was utilized to measure ALDH activity as well as sort cell lines into ALDH(+) & ALDH(-) phenotypes for experiments. An ALDH1A1 shRNA knockdown model was established to determine its effect on cancer stem cell properties, downstream signaling, and platinum resistance. RTQ, Western blot and PCR microarrays were utilized to evaluate potential mechanisms of ALDH-mediated platinum resistance, with select downstream siRNA mediated downregulation of KLF4.
Compared to Platinum-sensitive A2780 cells, platinum-resistant CP70 cells demonstrated a 100-fold increase in ALDH1A1 activity (0.2 vs. 24%, respectively (p< 0.001). ALDH(+) cells demonstrated enhanced malignant characteristics of 2-fold increase of tumorigenicity and invasion. A 3-fold increase in cancer stem cell transcriptional factor Kruppel-like factor-4 (KFL4) was shown in ALDH(+) cells (p=0.007). Increased KFL4, upregulated cell-cycle regulator p21, thereby causing G1 arrest and allows for cancer cell repair and survival. Compared to control, shRNA-ALDH knockdown demonstrated expected decreases in KFL4, with subsequent 5-fold decrease in p21 levels and its associated mediator CDK4. Cell cycle kinetics demonstrated a significant decrease in G1-associated cell cycle arrest with decreases in apoptotic threshold, which allows DNA damage to induce apoptosis confirmed with 4-fold increase in apoptotic factor BAX and cell death. Platinum sensitivity was restored in shRNA-ALDH cells, with significant increases in response rates to carboplatin with a 60% reduction of carboplatin dose needed to achieve IC50.
ALDH mediates platinum resistance via a specific KFL4/p21 cell cycle arrest pathway. Inhibition of this pathway resulted in reversal of platinum resistant ovarian cancer cells and could be utilized for possible targeting for inducing platinum sensitivity.
Citation Format: Erhong Meng, Aparna Mitra, Steven McClelan, Lalita Shevde, Rodney P. Rocconi. Aldehyde dehydrogenase isoform 1A1 mediates platinum resistance in ovarian cancer through the KLF4/p21 cell cycle arrest pathway. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 957. doi:10.1158/1538-7445.AM2013-957
Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.