**6.4. Bcl-2**

The proteins Bcl-2 family members are anti-apoptotic molecules known to be overexpressed in most cancers, and are associated directly with the CSCs [231]. Therefore, recent studies are aimed to target these proteins. A representative example is found in pancreatic cancer, against which the most potent and clinically acceptable Bcl-2 inhibitor AT-101 is currently in 20 different clinical trials around the world [232]. In glioblastoma, high expression levels of the anti-apoptoticc Bcl-2 protein, Mcl-1, were associated with resistance to treatment with Bcl-2 inhibitor ABT-737 in glioma stem cells [233]. In hematopoietic malignances, it has been showed that despite the over-expression of Bcl-2 this is not the critical point for the generation, selection and maintenance of leukemia stem cells [234].
