Venetoclax, sold under the brand names Venclexta and Venclyxto, is a medication used to treat adults with chronic lymphocytic leukemia (CLL), small lymphocytic lymphoma (SLL), or acute myeloid leukemia (AML). The most common side effects are low levels of neutrophils (a type of white blood cell), diarrhea, nausea, anemia (low red blood cell counts), nose and throat infection and tiredness. Venetoclax attaches to a protein called Bcl-2. This protein is present in high amounts in CLL cancer cells, where it helps the cells survive for longer in the body and makes them resistant to cancer medicines. By attaching to Bcl-2 and blocking its actions, venetoclax causes the death of cancer cells and thereby slows down progression of the disease.

Reference
Wiki: CPT-resistant leukemia