Vascular endothelial cell growth factor is an autocrine promoter of abnormal localized immature myeloid precursors and leukemia progenitor formation in myelodysplastic syndromes.

Vascular endothelial growth factor (VEGF) is a potent angiogenic peptide with biologic effects that include regulation of hematopoietic stem cell development, extracellular matrix remodeling, and inflammatory cytokine generation. To delineate the potential role of VEGF in patients with myelodysplastic syndrome (MDS), VEGF protein and receptor expression and its functional significance in MDS bone marrow (BM) were evaluated. In BM clot sections from normal donors, low-intensity cytoplasmic VEGF expression was detected infrequently in isolated myeloid elements. However, monocytoid precursors in chronic myelomonocytic leukemia (CMML) expressed VEGF in an intense cytoplasmic pattern with membranous co-expression of the Flt-1 or KDR receptors, or both. In situ hybridization confirmed the presence of VEGF mRNA in the neoplastic monocytes. In acute myelogenous leukemia (AML) and other MDS subtypes, intense co-expression of VEGF and one or both receptors was detected in myeloblasts and immature myeloid elements, whereas erythroid precursors and lymphoid cells lacked VEGF and receptor expression. Foci of abnormal localized immature myeloid precursors (ALIP) co-expressed VEGF and Flt-1 receptor, suggesting autocrine cytokine interaction. Antibody neutralization of VEGF inhibited colony-forming unit (CFU)-leukemia formation in 9 of 15 CMML and RAEB-t patient specimens, whereas VEGF stimulated leukemia colony formation in 12 patients. Neutralization of VEGF activity suppressed the generation of tumor necrosis factor-alpha and interleukin-1beta from MDS BM-mononuclear cells and BM-stroma and promoted the formation of CFU-GEMM and burst-forming unit-erythroid in methylcellulose cultures. These findings indicate that autocrine production of VEGF may contribute to leukemia progenitor self-renewal and inflammatory cytokine elaboration in CMML and MDS and thus provide a biologic rationale for ALIP and its adverse prognostic relevance in high-risk MDS.

Amifostine stimulates formation of multipotent and erythroid bone marrow progenitors.

Amifostine (WR-2721, Ethyol) is a phosphorylated aminothiol that affords broad cytoprotection from the myelosuppressive effects of antineoplastics. To further characterize its hematopoietic activities, we investigated the effects of amifostine and its dephosphorylated metabolite, WR1065, on the in vitro growth of human bone marrow progenitors. Preincubation exposure to amifostine or WR1065 stimulated the growth of colony-forming units granulocyte, erythroid, macrophage, megakaryocyte (CFU-GEMM) and erythroid bursts (BFU-E) from bone marrow mononuclear cells in a dose-dependent fashion. Over the concentration range tested (0.1-1000 microM), pretreatment with the aminothiols enhanced formation of CFU-GEMM up to five-fold and BFU-E nine-fold, compared to a three-fold increase in myeloid colony recovery. In CD34+ selected cells, preincubation with amifostine increased formation of CFU-GEMM up to 38-fold and produced macroscopic colonies, exceeding colony number in cultures initiated with optimal concentrations of interleukin-1 (IL-1), IL-3, or kit ligand (KL). When compared with recombinant human cytokines, amifostine enhanced IL-1 and IL-3 induced colony formation, although its stimulatory effect was less than additive. In contrast, pretreatment with amifostine antagonized the stimulatory effects of KL, whereas synergy was observed with concurrent exposure. Ex vivo expansion studies showed that amifostine alone supported and augmented the production of myeloid progenitors in secondary cultures. Similarly, under cytokine-deficient conditions, amifostine promoted cell survival and delayed apoptosis as measured by nucleosome generation. These data indicate that amifostine is a novel multipotent hematopoietic stimulant that augments the formation and survival of bone marrow progenitors.

Stimulation of hematopoiesis by amifostine in patients with myelodysplastic syndrome.

The aminothiol, amifostine (Ethyol; U.S. Bioscience, West Conshohocken, PA), is a cytoprotective agent that ameliorates the toxicities of anticancer therapy. In vitro, amifostine promotes the formation and survival of primitive hematopoietic progenitors derived from myelodysplastic bone marrow (BM) specimens. To evaluate the hematological effects of amifostine, 18 patients with myelodysplastic syndrome (MDS) and one or more refractory cytopenias received treatment with amifostine in a Phase I/II study. Four cohorts received intravenous treatment with 100, 200, or 400 mg/m2 amifostine three times a week, or 740 mg/m2 weekly for three consecutive weeks followed by 2 weeks observation. Nonresponding patients received a second course of therapy at the next higher dose level depending upon drug tolerance. Bone marrow (BM) progenitor growth was assessed before treatment and after day 21. Diagnoses included refractory anemia (7), refractory anemia with ringed sideroblasts (5), refractory anemia with excess blasts (RAEB) (4), and RAEB-in transformation (RAEB-t) (2). Single- or multi-lineage hematologic responses occurred in 15 patients (83%) treated with the three-times-a-week dose schedule. Fourteen patients had a 50% or greater increase in absolute neutrophil count with amifostine treatment (range, 426 to 11,348/microL). Platelet count increased in 6 (43%) of 14 patients with thrombocytopenia (absolute increase, 16, 000 to 110,000/microL), and 5 of 15 red blood cell transfusion-dependent patients had a 50% of greater reduction in transfusion needs. Assayable hematopoietic progenitors increased in 13 of 15 evaluable patients; including CFU-GEMM (12), BFU-E (8), and CFU-GM (6). Amifostine doses less than or equal to 200 mg/m2 were well tolerated, whereas grade II nausea, vomiting, and fatigue was limiting at higher doses. Three patients with excess blasts before enrollment experienced an increase in BM blast percentage and two patients had evolution to acute leukemia that persisted after treatment withdrawal. We conclude that amifostine administered at doses

Amifostine protects primitive hematopoietic progenitors against chemotherapy cytotoxicity.

Controlled clinical trials indicate that amifostine (WR-2721, Ethyol) confers protection from the cumulative hematologic toxicities associated with alkylating agents and organoplatinums. To determine whether amifostine protects primitive hematopoietic progenitors from the cytotoxicity of functionally diverse antineoplastics, formation of the multipotent hematopoietic progenitors colony-forming units-granulocyte-erythroid, macrophage, megakaryocyte (CFU-GEMM) and erythroid burst-forming units (BFU-E) was evaluated using a clonogenic progenitor inhibition assay. Bone marrow mononuclear cells from normal donors were subjected to a 15-minute exposure of medium, amifostine (500 micromol/L), or WR-1065 (100 micromol/L at concentrations approximating peak plasma levels, washed twice, then treated with the antineoplastic for 1 to 6 hours. Colony growth was scored after 14 days of incubation. Amifostine conferred protection against a broader range of antineoplastics than did WR-1065. Amifostine protected CFU-GEMM against cytotoxicity from daunorubicin, mitoxantrone, and paclitaxel (range, 1.29- to 9.57-fold) (P < .05) but did not afford protection against cisplatin, diaziquone, or thiotepa. Similarly, amifostine protected BFU-E against toxicity from doxorubicin, mitoxantrone, paclitaxel, cisplatin, and diaziquone, yielding 3.4- to 65-fold greater colony recovery compared with controls. The high degree of cytoprotection afforded by amifostine derived largely from stimulation of progenitor growth at sublethal chemotherapy concentrations. In the absence of antineoplastic exposure, preincubation with amifostine or WR-1065 enhanced the colony-forming capacity of bone marrow progenitors from six normal donors, increasing recovery of CFU-GEMM and BFU-E up to sevenfold. We conclude that amifostine protects primitive hematopoietic progenitors from a wide range of antineoplastics. This broad hemoprotective effect derives in part from inherent trophic effects on progenitor growth and survival.

Cytogenetics and P-glycoprotein (PGP) are independent predictors of treatment outcome in acute myeloid leukemia (AML).

Clinical and biological features have recognized prognostic significance in acute myeloid leukemia (AML). To evaluate the interaction of these variables and weighted effect on treatment outcome, prognostic variables from 96 previously untreated patients were analyzed for association with expression of the MDR1 gene product P-glycoprotein (Pgp), and effect on response to induction chemotherapy, progression-free survival and overall survival. Multivariate relationships were analyzed using six prognostic variables, including age, cytogenetic pattern, gender, CD34+ surface phenotype, AML type (de novo versus secondary) and Pgp. Univariate comparisons indicate that Pgp (P = 0.0001), cytogenetic pattern (P = 0.0004) and a Cd34+ phenotype (P = 0.0005) are predictive of primary treatment failure, whereas Pgp (P = 0.0001) had the greatest predictive value in multivariate analysis. Only cytogenetic pattern retained prognostic significance (P = 0.0143) for response to induction therapy after adjustment for Pgp. Although all variable except gender were associated with Pgp, specimens harboring the favorable karyotypic abnormalities t(15;17), t(8;21) and inv(16) exclusively lacked Pgp expression. In a multivariate model, both Pgp and cytogenetic pattern predicted response and overall survival, whereas secondary AML and cytogenetic pattern influenced remission duration. These findings indicate that cytogenetic has prognostic relevance that is independent of Pgp, and implies the presence of undefined biological mechanisms affecting chemotherapy resistance.

Mast cell growth factor (c-kit ligand) restores growth of multipotent progenitors in myelodysplastic syndrome.

In vitro growth of primitive hematopoietic progenitors is severely impaired in the myelodysplastic syndromes (MDS). To determine if the c-kit ligand mast cell growth factor (MGF) can improve progenitor growth in MDS, we evaluated in vitro responsiveness of bone marrow progenitors from 25 patients to MGF and/or GM-CSF, interleukin-3 (IL-3) and PIXY 321, and examined the relationship between progenitor response and cellular expression of the c-kit receptor. MGF and erythropoietin gave rise to macroscopic colonies and dose-dependently increased CFU-GEMM and BFU-E up to 27-fold in 15 (60%) and 20 (80%) patients, respectively. Among 17 patients with absent growth in lymphocyte-conditioned media, MGF stimulated CFU-GEMM recovery in 59%, compared to 23% with PIXY 321, 12% with IL-3 and 8% with GM-CSF. Cytokine combinations did not augment recovery of erythropoietin-dependent progenitors above that achieved with MGF alone. MGF and/or IL-3 were comparatively weak stimulants of CFU-GM formation, whereas GM-CSF and PIXY in combination with MGF increased colony number 2- to 15-fold in 60 and 70% of patients, respectively, while preserving maturation competence as evidenced by colony composition and increased colony/cluster ratio. The stimulatory effects of MGF were observed in all morphologic categories of MDS except chronic myelomonocytic leukemia. A mononuclear cell population expressing the c-kit receptor was identified by flow cytometry in 57% of cases. Neither SR-1 reactivity nor cytogenetic pattern predicted progenitor response to MGF. These data indicate that MGF improves the colony-forming capacity of hematopoietic progenitors in MDS and is a potent co-stimulant of multipotent and committed progenitor recovery. The heterogeneity in MGF responsiveness implies an intrinsic defect in growth regulation not explained by cellular loss of c-kit display.

Regulation of transforming growth factor-alpha mRNA expression in T3M4 human pancreatic carcinoma cells.

Cultured human pancreatic cancer cells produce transforming growth factor-alpha (TGF-alpha), a potent mitogenic polypeptide. In the present study, we investigated the regulation of TGF-alpha mRNA expression in T3M4 human pancreatic carcinoma cells. TGF-alpha mRNA levels were quantitated by densitometric analysis of autoradiographs obtained following hybridization of size-fractionated cytoplasmic RNA with 32P-labeled cRNA coding for human TGF-alpha. There was a twofold increase in TGF-alpha mRNA levels at 2 h following addition of either epidermal growth factor (EGF) or TGF-alpha. However, TGF-alpha mRNA levels declined to near basal levels by 10 h. At 2 h, one-half maximal stimulation of TGF-alpha mRNA levels occurred at 1 nM and maximal stimulation at 4 nM of either EGF or TGF-alpha. The transcriptional inhibitor actinomycin D (Act D) and the phorbol ester, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), mimicked the actions of EGF and TGF-alpha. These findings indicate that the regulation of TGF-alpha mRNA expression in T3M4 cells is complex, and is mediated, in part, via the EGF receptor.

cDNA and deduced amino acid sequences of a dog liver cytochrome P-450 of the IIIA gene subfamily.

A 1.96 kbp cDNA encoding a male Beagle dog liver cytochrome P-450 of 503 amino acid residues (Mr 57,636) has been isolated and sequenced. The deduced amino acid sequence is 79.8%, 69.3% and 74.1% identical to the P450IIIA forms human NF25, rat PCN1 and rabbit LM3c, respectively. The amino terminal sequence is identical to the first 28 residues of the dog P450IIIA form PBD-1. Southern blot analysis yields restriction patterns consistent with IIIA gene subfamily multiplicity.