High-risk B-cell acute lymphoblastic leukemia (B-ALL) is an aggressive disease, often characterized by resistance to chemotherapy. A frequent feature of high-risk B-ALL is loss of function of the IKAROS (encoded by the IKZF1 gene) tumor suppressor. Here, we report that IKAROS regulates expression of the BCL2L1 gene (encodes the BCL-XL protein) in human B-ALL. Gain-of-function and loss-of-function experiments demonstrate that IKAROS binds to the BCL2L1 promoter, recruits histone deacetylase HDAC1, and represses BCL2L1 expression via chromatin remodeling. In leukemia, IKAROS' function is impaired by oncogenic Casein Kinase II (CK2), which is overexpressed in B-ALL. Phosphorylation by CK2 reduces IKAROS binding and recruitment of HDAC1 to the BCL2L1 promoter. This results in a loss of IKAROS-mediated repression of BCL2L1 and increased expression of BCL-XL. Increased expression of BCL-XL and/or CK2, as well as reduced IKAROS expression, are associated with resistance to doxorubicin treatment. Molecular and pharmacological inhibition of CK2 with a specific inhibitor CX-4945, increases binding of IKAROS to the BCL2L1 promoter and enhances IKAROS-mediated repression of BCL2L1 in B-ALL. Treatment with CX-4945 increases sensitivity to doxorubicin in B-ALL, and reverses resistance to doxorubicin in multi-drug resistant B-ALL. Combination treatment with CX-4945 and doxorubicin show synergistic therapeutic effects in vitro and in preclinical models of high-risk B-ALL. Results reveal a novel signaling network that regulates chemoresistance in leukemia. These data lay the groundwork for clinical testing of a rationally-designed, targeted therapy that combines the CK2 inhibitor, CX-4945, with doxorubicin for the treatment of hematopoietic malignancies.

BackgroundApproximately 5-10% of breast cancers are hereditary. Among hereditary syndromes, Hereditary Breast and Ovarian Cancer Syndrome (HBOC) and Li-Fraumeni Syndrome (LFS) have received the most attention. HBOC is due to mutations in the BRCA1 and BRCA2 genes and is characterized by breast adenocarcinoma and/or epithelial ovarian carcinoma. LFS is associated with germline mutations in TP53; the most frequent cancer types associated with this syndrome are sarcoma, breast cancer, leukemia, brain tumors and adrenocortical carcinomas. Other cancers related to LFS are found at lower frequencies. In Brazil, especially in the southern part of the country, a specific mutation in the TP53 gene, TP53 p.R337H, occurs at a high frequency in childhood adrenocortical tumors. It has been proposed that this mutation increases breast cancer risk in southern Brazilian women.MethodsWe carried out a case-control study to determine the prevalence of the TP53 p.R337H mutation in 28 female cancer patients attended at the Cancer Genetic Counseling Service of the General Hospital of the University of São Paulo Medical School of Ribeirão Preto who fulfilled Hereditary Breast and Ovary Cancer Syndrome genetic test criteria compared to healthy woman (controls). TP53 p.R337H mutation status was determined using the High Resolution Melting (HRM) method, followed by DNA sequencing. Fisher’s test was used to compare the prevalence of TP53 p.R337H in the patient and control groups.ResultsTwo of the breast cancer cases (7.1%) and none of the controls carried the TP53 p.R337H mutation. At the time of the investigation, both cases fulfilled testing criteria for Hereditary Breast and Ovary Cancer Syndrome but not Li-Fraumeni or Li-Fraumeni-like Syndrome, based on genetic testing criteria of NCCN Clinical Practice Guidelines in Oncology (v.1.2010).ConclusionsWe suggest that genetic screening of Brazilian breast cancer patients who fulfill Hereditary Breast and Ovary Cancer Syndrome criteria and have a family history that includes other tumors of the LFS/LFL spectrum be tested for the TP53 p.R337H mutation.