Venetoclax, a specific inhibitor of the pro-survival protein BCL2, has gained success in treating patients with chronic lymphocytic leukemia (CLL). However, the activity of venetoclax is often limited by the co-dependence, to varying degrees, of the tumor cells on MCL1 and other pro-survival proteins related to BCL2. The aim of this study is to identify rational new strategies to enhance the action of venetoclax in cancers where MCL1 limits its activity.
We are focused on NOXA, a BH3-only protein that binds selectively to MCL1. We hypothesize that increased NOXA expression could prime cancer cells to venetoclax killing since this should reduce their co-dependence on MCL1. In order to find such new targets that act to modulate NOXAexpression, we generated and validated a number of cell lines that report on NOXAtranscription and then carried out CRISPR/Cas9-based genetic screens in such NOXAreporter cell lines.
In one such the screen using a library focused on the NOXA promoter region, we found that a small hypermethylated region on NOXApromoter is important for the repressing NOXAexpression across diverse cell lines derived from blood cancers. Disrupting this region leads to NOXAinduction. Potentially, our findings could explain, at least in part, the action of hypomethylating agents driving NOXAupregulation in myeloid neoplasms. Moreover, our results could provide a rational basis of combining hypomethylating agents with venetoclax in a range of hematological malignancies, an avenue we are actively pursuing.