guanosine-triphosphate and Leukemia-Lymphoma--Adult-T-Cell

Adult T-cell leukemia/lymphoma (ATLL) is a distinct form of peripheral T-cell lymphoma with poor prognosis, which is caused by the human T-lymphotropic virus type 1 (HTLV-1). In contrast to the unequivocal importance of HTLV-1 infection in the pathogenesis of ATLL, the role of acquired mutations in HTLV-1 infected T cells has not been fully elucidated, with a handful of genes known to be recurrently mutated. In this study, we identified unique RHOA mutations in ATLL through whole genome sequencing of an index case, followed by deep sequencing of 203 ATLL samples. RHOA mutations showed distinct distribution and function from those found in other cancers. Involving 15% (30/203) of ATLL cases, RHOA mutations were widely distributed across the entire coding sequence but almost invariably located at the guanosine triphosphate (GTP)-binding pocket, with Cys16Arg being most frequently observed. Unexpectedly, depending on mutation types and positions, these RHOA mutants showed different or even opposite functional consequences in terms of GTP/guanosine diphosphate (GDP)-binding kinetics, regulation of actin fibers, and transcriptional activation. The Gly17Val mutant did not bind GTP/GDP and act as a dominant negative molecule, whereas other mutants (Cys16Arg and Ala161Pro) showed fast GTP/GDP cycling with enhanced transcriptional activation. These findings suggest that both loss- and gain-of-RHOA functions could be involved in ATLL leukemogenesis. In summary, our study not only provides a novel insight into the molecular pathogenesis of ATLL but also highlights a unique role of variegation of heterologous RHOA mutations in human cancers.

Topics: Adult; Amino Acid Sequence; Binding Sites; DNA Mutational Analysis; Guanosine Diphosphate; Guanosine Triphosphate; High-Throughput Nucleotide Sequencing; Humans; Leukemia-Lymphoma, Adult T-Cell; Models, Molecular; Molecular Sequence Data; Mutation; Protein Structure, Tertiary; rhoA GTP-Binding Protein

The 9-beta-D-arabinofuranosylguanine (ara-G), an active compound of nelarabine, demonstrates potent cytotoxicity specifically on T-cell malignancies. In cells, ara-G is phosphorylated to ara-G triphosphate (ara-GTP), which is subsequently incorporated into DNA, thereby inhibiting DNA synthesis. Because ara-GTP is crucial to ara-G's cytotoxicity, the determination of ara-GTP production in cancer cells is informative for optimizing nelarabine administration. Here, we developed a new, sensitive isocratic-elution HPLC method for quantifying ara-GTP. Samples were eluted isocratically by using phosphate buffer at a constant flow rate. Ara-GTP was clearly separated from other nucleotides by using an anion-exchange column and it was quantitated by its peak area at 254 nm. The standard curve was linear with low variability and a sensitive detection limit (10 pmol). Furthermore, due to ara-G's specificity to T-cells we hypothesized that nelarabine might be effective against adult T-cell leukemia (ATL). The ara-GTP production was compared between T-lymphoblastic leukemia CCRF-CEM and ATL cell lines in vitro. When CEM cells were incubated with ara-G, the ara-GTP production increased in a concentration- and time-dependent manner. In contrast, 5 ATL cell lines accumulated lower ara-GTP in the same condition. While ara-G inhibited the growth of CEM cells with a 50% growth inhibition concentration of 2 microM, the inhibitory-concentration values were >1 mM in 8 of the 12 ATL cell lines. This ineffectiveness appeared to correspond with the low ara-GTP production. The present study is the first to evaluate the potential of ara-G against ATL cells; our results suggest that nelarabine would not be effective against ATL.

Topics: Antineoplastic Agents; Arabinonucleosides; Arabinonucleotides; Biomarkers; Cell Proliferation; Chemical Fractionation; Chromatography, High Pressure Liquid; Guanosine Triphosphate; Humans; Leukemia-Lymphoma, Adult T-Cell; Prodrugs; Reference Standards; Sensitivity and Specificity; Treatment Outcome; Tumor Cells, Cultured

Arabinosylguanine (araG) is a nucleoside analogue that is rapidly converted by cells of the T lymphoid lineage to its corresponding arabinosylguanine nucleotide triphosphate (araGTP), resulting in inhibition of DNA synthesis and selective in vitro toxicity to T lymphoblastoid cell lines as well as to freshly isolated leukemia cells from patients with T cell acute lymphoblastic leukemia (ALL). We have previously demonstrated that araG is an effective agent to use for chemoseparation of malignant T lymphoblasts from human bone marrow. When freshly isolated human T leukemia cells or T lymphoblastoid cells were treated with 100 microM araG for 18 hours, up to 6 logs of clonogenic T cells are eliminated without appreciable toxicity to the normal myeloid, erythroid, and megakaryocytoid clonal progenitor cells. We subsequently described studies in a murine model of T cell acute lymphoblastic leukemia (ALL) in which we tested whether bone marrow contaminated with malignant T cells and purged ex vivo with araG, could reconstitute both the lymphoid and myeloerythroid lineages in the absence of leukemic relapse. The model utilized 6C3HED tumor cells, derived from a Thy 1.2+ malignant murine T cell line, which were shown to cause lethal leukemia in C3H/HeN mice. Intravenous injection of 10(6) 6C3HED cells resulted in 100 percent mortality within 18 days, with autopsy revealing tumor infiltration of multiple organs. Evidence of araG's ability to purge bone marrow of malignant tumor cells without causing significant toxicity to normal marrow-derived hematopoietic progenitor cells was documented in experiments in which 75 percent of lethally irradiated mice receiving transplants of syngeneic bone marrow contaminated with 6C3HED tumor cells and treated ex vivo with 100 mM araG for 18 hours survived for 250 to > 400 days. Reconstitution of the lymphoid, myeloid, and erythroid lineages with donor cells in surviving mice was documented. The data presented indicate that araG may effectively purge bone marrow of malignant T cells without irreversible toxicity to hematopoietic stem cells. This purging regimen is recommended for consideration for clinical trials in patients with T cell malignancies undergoing autologous bone marrow transplantation and may also be a viable option for T cell depletion as a strategy to prevent graft versus host disease.

Topics: Animals; Antineoplastic Agents; Arabinonucleosides; Arabinonucleotides; Bone Marrow Purging; Bone Marrow Transplantation; Cell Division; Dose-Response Relationship, Drug; Female; Guanosine Triphosphate; Hematopoietic Stem Cells; Humans; Leukemia-Lymphoma, Adult T-Cell; Male; Mice; Mice, Inbred C3H; T-Lymphocytes; Tumor Cells, Cultured

(6R)-5,10-Dideaza-5,6,7,8-tetrahydrofolic acid [(6R)DDATHF] is a folate antimetabolite with activity specifically directed against de novo purine synthesis, primarily through inhibition of glycinamide ribonucleotide transformylase. This inhibition resulted in major changes in the size of the nucleotide pools in CCRF-CEM cells. After a 4-h incubation with 1 microM (6R)DDATHF, dramatic reductions in the ATP and GTP pools were observed, with almost no effect on CTP, UTP, and deoxyribonucleotide pools. When the incubation was continued in drug-free medium, recovery of ATP and GTP pools was protracted. ATP did not return to normal until 24-36 h, and GTP pools were only partially repleted by 48 h. The ATP and GTP pools were not affected when the initial 4-h incubation with (6R)DDATHF was conducted in the presence of 100 microM hypoxanthine. Addition of hypoxanthine to the medium after a 4-h incubation with (6R)DDATHF caused rapid recovery of the ATP and GTP pools. Similar effects were seen when the purine precursor aminoimidazole carboxamide was used in place of hypoxanthine. The effect of (6R)DDATHF on nucleotide pools and the capability of hypoxanthine or aminoimidazole carboxamide to prevent or reverse this phenomenon correlated directly with the inhibition of cell growth. Presumably as a consequence of the decrease in purine nucleotide triphosphate levels, the conversion of exogenously added uridine, thymidine, and deoxyuridine to nucleotides was markedly decreased. These effects were protracted for almost 48 h and were also reversed by hypoxanthine. Differential repletion of ATP and GTP pools after (6R)DDATHF pre-treatment demonstrated that diminished precursor phosphorylation is primarily a consequence of GTP rather than ATP starvation.

Topics: Adenosine Triphosphate; Aminoimidazole Carboxamide; Cytidine Triphosphate; DNA; Folic Acid Antagonists; Guanosine Triphosphate; Humans; Hypoxanthine; Hypoxanthines; Leukemia-Lymphoma, Adult T-Cell; RNA; Tetrahydrofolates; Thymidylate Synthase; Time Factors; Tumor Cells, Cultured; Uridine Triphosphate

Arabinosylguanine (araG) is a nucleoside analog that is rapidly converted by cells of the T lymphoid lineage to its corresponding arabinosylguanine nucleotide triphosphate, resulting in inhibition of DNA synthesis and selective in vitro toxicity to T lymphoblastoid cell lines as well as to freshly isolated leukemia cells from patients with T cell acute lymphoblastic leukemia. In this report, we demonstrate that araG is an effective agent to use for chemoseparation of malignant T lymphoblasts from human bone marrow. When freshly isolated human T leukemia cells or T lymphoblastoid cells were treated with 100 microM araG for 18 hr, up to 6 logs of clonogenic T cells could be eliminated without appreciable toxicity to the normal myeloid, erythroid, and megakaryocytoid clonal progenitor cells. We discuss the use of this agent in ex vivo elimination of residual malignant T cells from marrow of patients requiring myeloablative chemotherapy with autologous bone marrow rescue.

Topics: Antineoplastic Agents; Arabinonucleosides; Arabinonucleotides; Bone Marrow Purging; Cell Death; Cell Division; Cell Separation; Clone Cells; Erythroid Precursor Cells; Guanosine Triphosphate; Humans; Leukemia-Lymphoma, Adult T-Cell; Pentostatin; Precursor Cell Lymphoblastic Leukemia-Lymphoma; T-Lymphocytes; Tumor Cells, Cultured