Pharmacological inactivation of CDK2 inhibits MYC/BCL-XL-driven leukemia in vivo through induction of cellular senescence.

Deregulated expression of the MYC oncogene is a frequent event during tumorigenesis and generally correlates with aggressive disease and poor prognosis. While MYC is a potent inducer of apoptosis, it often suppresses cellular senescence, which together with apoptosis is an important barrier against tumor development. For this latter function, MYC is dependent on cyclin-dependent kinase 2 (CDK2). Here, we utilized a MYC/BCL-X-driven mouse model of acute myeloblastic leukemia (AML) to investigate whether pharmacological inhibition of CDK2 can inhibit MYC-driven tumorigenesis through induction of senescence. Purified mouse hematopoietic stem cells transduced with MYC and BCL-X were transplanted into lethally irradiated mice, leading to the development of massive leukemia and subsequent death 15-17 days after transplantation. Upon disease onset, mice were treated with the selective CDK2 inhibitor CVT2584 or vehicle either by daily intraperitoneal injections or continuous delivery via mini-pumps. CVT2584 treatment delayed disease onset and moderately but significantly improved survival of mice. Flow cytometry revealed a significant decrease in tumor load in the spleen, liver and bone marrow of CVT2584-treated compared to vehicle-treated mice. This was correlated with induced senescence evidenced by reduced cell proliferation, increased senescence-associated β-galactosidase activity and heterochromatin foci, expression of p19 and p21, and reduced phosphorylation (activation) of pRb, while very few apoptotic cells were observed. In addition, phosphorylation of MYC at Ser-62 was decreased. In summary, inhibition of CDK2 delayed MYC/BCL-X-driven AML linked to senescence induction. Our results suggest that CDK2 is a promising target for pro-senescence cancer therapy, in particular for MYC-driven tumors, including leukemia.