alvocidib and Leukemia-Lymphoma--Adult-T-Cell

Adult T-cell leukemia/lymphoma (ATL) is an intractable hematological malignancy with extremely poor prognosis. Recent studies have revealed that super-enhancers (SE) play important roles in controlling tumor-specific gene expression and are potential therapeutic targets for neoplastic diseases including ATL. Cyclin-dependent protein kinase (CDK) 9 is a component of a complex comprising transcription factors (TFs) that bind the SE region. Alvocidib is a CDK9 inhibitor that exerts antitumor activity by inhibiting RNA polymerase (Pol) II phosphorylation and suppressing SE-mediated, tumor-specific gene expression. The present study demonstrated that alvocidib inhibited the proliferation of ATL cell lines and tumor cells from patients with ATL. RNA sequencing (RNA-Seq) and chromatin immunoprecipitation sequencing (ChIP-Seq) disclosed that SE regulated IRF4 in the ATL cell lines. Previous studies showed that IRF4 suppression inhibited ATL cell proliferation. Hence, IRF4 is a putative alvocidib target in ATL therapy. The present study revealed that SE-mediated IRF4 downregulation is a possible mechanism by which alvocidib inhibits ATL proliferation. Alvocidib also suppressed ATL in a mouse xenograft model. Hence, the present work demonstrated that alvocidib has therapeutic efficacy against ATL and partially elucidated its mode of action. It also showed that alvocidib is promising for the clinical treatment of ATL and perhaps other malignancies and neoplasms as well.

Topics: Animals; Antineoplastic Agents; Cell Line, Tumor; Cell Proliferation; Cyclin-Dependent Kinases; Enhancer Elements, Genetic; Gene Expression Regulation, Leukemic; Genes, Neoplasm; Humans; Leukemia-Lymphoma, Adult T-Cell; Mice

The in vitro efficacies of three new drugs--clofarabine (CLOF), nelarabine (NEL) and flavopiridol (FP) - were assessed in a panel of acute lymphoblastic leukaemia (ALL) cell lines. The 50% inhibitory concentration (IC50) for CLOF across all lines was 188-fold lower than that of NEL. B-lineage, but not T-lineage lines, were >7-fold more sensitive to CLOF than cytosine arabinoside (ARAC). NEL IC50 was 25-fold and 113-fold higher than ARAC in T- and B-lineage, respectively. T-ALL cells were eightfold more sensitive to NEL than B-lineage but there was considerable overlap. FP was more potent in vitro than glucocorticoids and thiopurines and at doses that recent phase I experience predicts will translate into clinical efficacy. Potential cross-resistance of CLOF, NEL and FP was observed with many front-line ALL therapeutics but not methotrexate or thiopurines. Methotrexate sensitivity was inversely related to that of NEL and FP. Whilst NEL was particularly effective in T-ALL, a subset of patients with B-lineage ALL might also be sensitive. CLOF appeared to be marginally more effective in B-lineage than T-ALL and has a distinct resistance profile that may prove useful in combination with other compounds. FP should be widely effective in ALL if sufficient plasma levels can be achieved clinically.

Topics: Adenine Nucleotides; Antineoplastic Agents; Arabinonucleosides; Burkitt Lymphoma; Child; Clofarabine; Dose-Response Relationship, Drug; Drug Resistance, Neoplasm; Drug Screening Assays, Antitumor; Flavonoids; Humans; Inhibitory Concentration 50; Leukemia-Lymphoma, Adult T-Cell; Piperidines; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Tumor Cells, Cultured

Adult T-cell leukemia (ATL) develops in a small proportion of individuals infected with human T-cell lymphotrophic virus-1. The leukemia consists of an overabundance of activated T cells, which express CD25 on their cell surfaces. Presently, there is no accepted curative therapy for ATL. Flavopiridol, an inhibitor of cyclin-dependent kinases, has potent antiproliferative effects and antitumor activity. We investigated the therapeutic efficacy of flavopiridol alone and in combination with humanized anti-Tac antibody (HAT), which recognizes CD25, in a murine model of human ATL. The ATL model was established by intraperitoneal injection of MET-1 leukemic cells into nonobese diabetic/severe combined immunodeficient mice. Either flavopiridol, given 2.5 mg/kg body weight daily for 5 days, or HAT, given 100 microg weekly for 4 weeks, inhibited tumor growth as monitored by serum levels of human beta-2-microglobulin (beta2mu; P < .01), and prolonged survival of the leukemia-bearing mice (P < .05) as compared with the control group. Combination of the 2 agents dramatically enhanced the antitumor effect, as shown by both beta2mu levels and survival of the mice, when compared with those in the flavopiridol or HAT alone group (P < .01). The significantly improved therapeutic efficacy by combining flavopiridol with HAT provides support for a clinical trial in the treatment of ATL.

Topics: Adult; Animals; Antibodies, Monoclonal; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; beta 2-Microglobulin; Cell Cycle; Cell Division; Cell Line, Tumor; Disease Models, Animal; Flavonoids; Humans; Leukemia-Lymphoma, Adult T-Cell; Mice; Mice, Inbred NOD; Mice, SCID; Piperidines; Receptors, Interleukin-2