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W Plunkett

Publications and source records attributed to W Plunkett.

At least 163 records · Page 9Linked to original sources
PubMed1987

Variables predicting response to high dose cytosine arabinoside therapy in patients with refractory acute leukemia.

The cytotoxic effect of cytosine arabinoside (ara-C) is presumably mediated by cytosine arabinoside 5'-triphosphate (ara-CTP). We tested for a correlation between intracellular ara-CTP pharmacokinetics and clinical response among 51 patients who received high dose ara-C (3 g/m2 at 12-hr intervals) as therapy for refractory acute leukemia. After accounting for pretreatment clinical variables that correlated with response, measurement of ara-CTP pharmacokinetics added significant prognostic information. This provides a rationale for manipulation of schedules of high dose ara-C administration in those patients whose pharmacokinetic characteristics are inconsistent with response to an every 12-hr schedule.

Acute Disease↗
PubMed1987

Pharmacokinetics of the 5'-triphosphates of arabinosylcytosine and 2',2'-difluorodeoxycytidine in L1210 cells.

The clinical efficacy of ara-C is limited by a rapid elimination of the active triphosphate by target cells. The nucleoside antimetabolite, 2',2'-difluorodeoxycytidine, accumulates in leukemia cells as the respective 5'-triphosphate dFdCTP. In contrast to ara-C triphosphate, dFdCTP is eliminated with biphasic kinetics that exhibit a terminal half-life that approaches the cell cycle time. The cellular pharmacokinetics of dFdCTP may explain the unusual dose schedule and spectrum of efficacy against murine tumors.

Animals↗
PubMed1987

5'-Fluorosulfonylbenzoyl derivatives of therapeutic nucleoside analogs.

Several fluorosulfonylbenzoyl /FSB/ purine and pyrimidine nucleoside analogs of the clinically useful antimetabolites which belong to endo affinity labeling compounds were synthetized. Structures were confirmed by both 1H NMR and UV spectroscopy and by elemental analysis. Procedure for preparation of microamount of [3H] FSB-araC was developed. Bonding of radioactive FSB-araC to nucleotide utilizing enzymes in K562 myeloblasts soluble protein extract was compared with araCTP-degradating activities in this extract after DEAE-cellulose column chromatography. There was found that five major peaks of the radioactivity bound to the protein coincident with peaks of araCTP degradation. Bonding of [3H] FSB-araC in CCRF-CEM lymphoblasts exhibits only 3 major peaks of the bound radioactivity. This result correlates with the higher sensitivity of the CEM cells to araC.

Antimetabolites, Antineoplastic↗
PubMed1986

3-Deazaguanosine is metabolized to the triphosphate derivative in Chinese hamster cells deficient in hypoxanthine-guanine phosphoribosyltransferase.

3-Deazaguanosine containing a 14C label in the ribose moiety was prepared using [U-14C]inosine as the [14C] ribose donor and commercial purine-nucleoside phosphorylase (EC 2.4.2.1) both to degrade the inosine, in the presence of phosphate, and to synthesize [14C-ribosyl]3-deazaguanosine in reduced phosphate and an excess of 3-deazaguanine. Purification was by high-pressure liquid chromatography (HPLC). [14C-ribosyl]3-Deazaguanosine was metabolized by Chinese hamster ovary cells to two metabolites, one major and one minor, eluting in the triphosphate region after HPLC analysis, and appeared to be incorporated into perchloric acid-insoluble material. Cell line TGR-3, deficient in hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8) and resistant to 3-deazaguanine, also formed both metabolites. Line TGR-1/DGRR-9, deficient in hypoxanthine-guanine phosphoribosyltransferase and resistant to both 3-deazaguanine and 3-deazaguanosine, formed greatly reduced levels of the major metabolite. 3-Deazaguanosine 5'-triphosphate, prepared enzymically from authentic 3-deazaguanosine 5'-monophosphate, co-eluted with the major metabolite peak during HPLC analysis. Treatment of a metabolite-containing extract with bacterial alkaline phosphatase (EC 3.1.3.1) resulted in the formation of 3-deazaguanosine. These observations indicate that 3-deazaguanosine can be metabolized, in Chinese hamster ovary cells, to the triphosphate derivative in lieu of the action of hypoxanthine-guanine phosphoribosyltransferase.

Alkaline Phosphatase↗
PubMed1986

9-beta-D-arabinofuranosyl-2-fluoroadenine 5'-monophosphate pharmacokinetics in plasma and tumor cells of patients with relapsed leukemia and lymphoma.

The pharmacokinetics of 9-beta-D-arabinofuranosyl-2-fluoroadenine (F-ara-A) in plasma and its biologically active 5'-triphosphate (F-ara-ATP) in leukemic cells obtained from the peripheral blood and bone marrow was evaluated in patients with hematologic malignancies subsequent to the first dose of 20-125 mg/m2 per day for 5 days of F-ara-A 5'-monophosphate (F-ara-AMP) administered as an IV bolus over 30 min. The terminal half-lives of elimination of both F-ara-A (8 h) in plasma and intracellular F-ara-ATP (15 h) were not dependent upon the dose of F-ara-AMP. The area under the concentration X time curves for F-ara-A and F-ara-ATP, on the other hand, were increased in proportion to the prodrug dose. There was a high correlation between F-ara-ATP levels in circulating leukemic cells and those in bone marrow cells aspirated at the same time. DNA-synthetic capacity of leukemic cells was inversely related to the associated F-ara-ATP concentration. A linear trend was noted when F-ara-ATP levels in pretreatment peripheral blood leukemic cells incubated with F-ara-A in vitro were compared with the amount of F-ara-A that was incorporated into nucleic acids. Finally, F-ara-ATP concentrations were three times higher in bone marrow cells from patients with lymphomatous bone marrow involvement than from those without evidence of marrow disease.

Antimetabolites, Antineoplastic↗
PubMed1986

Phase I-II clinical and pharmacologic studies of high-dose cytosine arabinoside in refractory leukemia.

Sixty-four patients with refractory acute leukemia were treated with high-dose cytosine arabinoside given at a dosage of 3 g/m2 intravenously over two hours every 12 hours for four to 12 doses, repeated at two- to three-week intervals. Complete remissions were observed in 16 patients (25 percent), and the median duration of remission was three months (range, one to 10 months). Remission rates were similar for patients with acute myelogenous and acute lymphocytic leukemia (24 and 27 percent, respectively). Response rates were significantly higher in patients with initial remission durations of more than six months than in those with shorter remissions or those in whom there was no response to front-line therapy (41 and 9 percent; p less than 0.01). Similarly, patients with disease sensitive to conventional cytosine arabinoside had higher response rates than did those with resistant disease (54 and 17 percent; p = 0.03). Serial in vivo measurements of intracellular concentrations of the active metabolite of cytosine arabinoside in peripheral blasts following the initial dose demonstrated considerable individual variation. Favorable intracellular pharmacology of this active metabolite, manifested by its higher intracellular concentrations 12 hours after the first dose, by longer half-lives of active metabolite levels, and by higher values of the measured area under the curve of its accumulation and retention, was associated with higher response rates. Central nervous system toxicity occurred in 24 percent of patients, and pulmonary toxicity occurred in 22 percent; both were dose-limiting and dose-related. Other toxicities included nausea, vomiting, diarrhea, conjunctivitis, photophobia, cytosine arabinoside fever, skin rashes, and hepatic dysfunction. Response rates were similar for schedules utilizing four to six doses at two-week intervals or nine doses at three-week intervals (27 percent versus 25 percent). The schedule of 12 doses had a more rapid antileukemic effect but resulted in significantly higher toxicity and mortality rates during therapy with a similar overall response rate (21 percent). Thus, high-dose cytosine arabinoside is an effective regimen with substantial toxicity in patients with acute leukemia.

Adolescent↗
PubMed1986

High-dose cytosine arabinoside: treatment and cellular pharmacology of chronic myelogenous leukemia blast crisis.

Twenty-one patients with chronic myelogenous leukemia (CML) in blastic transformation underwent 22 remission induction attempts with high-dose cytosine arabinoside (ara-C), administered as a two-hour infusion of 3 g/m2 for six to 12 doses. Ara-C doses were administered every 12 hours in 15 patients and every six to ten hours in six patients. Median patient age was 35 years (range, 20 to 62). The median duration of benign phase was 25 months (range, 0 to 167). Morphology of blast crisis blast cells was myeloid in 15 patients and lymphoid in six. Five patients achieved complete remission (CR), three had partial remission (PR), and one had hematologic improvement, for an overall response rate of 41%. Median remission duration was 2.5 months (range, 0.5 to 6 months). Survival duration was 6 months for responding patients and 1.5 months for those with resistant disease. The response rate was similar for patients with myeloid and lymphoid blast crisis (31% v 50%, respectively). The response rate was significantly higher for patients whose benign phase was less than 1 year (75% v 21%, P = .05) and who had prolonged marrow aplasia after ara-C (86% v 27%, P = .05). Myelosuppression was the major dose-limiting toxicity, and cerebellar toxicity occurred in two patients. Intracellular ara-C 5'-triphosphate (ara-CTP) levels were similar in blood and bone marrow leukemic cells and were slightly greater in the cells of responding patients compared to those with resistant disease. We conclude that high-dose ara-C is an effective regimen for CML blast crisis, resulting in a substantial response rate but modest remission duration. Its combination with other agents may further improve the prognosis of patients with this resistant disease.

Adult↗
PubMed1986

Cellular retention of 9-beta-D-arabinofuranosyladenine 5'-triphosphate and the pattern of recovery of DNA synthesis in Chinese hamster ovary cells.

The factors associated with the recovery of DNA synthesis in Chinese hamster ovary cells after inhibition with 9-beta-D-arabinofuranosyladenine have been investigated. Maintenance of cellular concentrations of the active metabolite 9-beta-D-arabinofuranosyladenine 5'-triphosphate was dependent upon a constant exogenous source of 9-beta-D-arabinofuranosyladenine, without which the triphosphate rapidly degraded. DNA synthesis was inhibited maximally at cellular concentrations of 9-beta-D-arabinofuranosyladenine 5'-triphosphate in excess of 100 microM, but it recovered substantially as the triphosphate concentrations declined below 30 microM. Autoradiographic studies indicated that 9-beta-D-arabinofuranosyladenine had a synchronizing effect on the cells and that recovery of DNA synthesis occurred initially at rates much reduced from those seen in uninhibited cells. A greater portion of an inhibited population recovered DNA synthesis than was able to retain clonogenic potential. These results are consistent with a mechanism of toxicity that postulates recovery of DNA synthesis as a requisite for the loss of viability.

Animals↗
PubMed1986

Regulation of 1-beta-D-arabinofuranosylcytosine 5'-triphosphate accumulation in human leukemia cells by deoxycytidine 5'-triphosphate.

Cell cycle-specific fluctuations in the ability of human leukemic cells to phosphorylate 1-beta-D-arabinofuranosylcytosine (ara-C) to the toxic metabolite 1-beta-D-arabinofuranosylcytosine 5'-triphosphate (ara-CTP) was investigated in whole cells and in cell extracts. Exponentially growing CCRF-CEM cells were fractionated into populations enriched for G1 phase cells and S phase cells by centrifugal elutriation. The accumulation of ara-CTP by S phase-enriched cells was 50% greater than in G1-enriched cells. However, the ability of extracts of S phase-enriched cells to phosphorylate ara-C was twice that of G1 phase-enriched cell extracts. As cells passed from G1 to S phase, this disproportionality was significant. As demonstrated in other cell types, deoxycytidine 5'-triphosphate (dCTP) also potently inhibited ara-C phosphorylation in CCRF-CEM cell extracts (Ki = 5.9 microM). Deoxynucleotide pool levels determined by high pressure liquid chromatography showed a 5 microM dCTP concentration in G1-enriched cells, whereas S phase-enriched cells contained 15 microM dCTP. These findings suggest that the lack of proportionality between the accumulation of ara-CTP in whole cells and the increase of ara-C phosphorylation in extracts during the G1 to S phase transition may be caused by more stringent regulation of ara-C phosphorylation in whole cells by the concomitant increase in cellular dCTP concentrations. Because such regulation is unlikely to be observed in cell extracts, these results indicated that assays of ara-C phosphorylating activity in cell extracts represent upper limits for that function in whole cells. Such determinations may not reflect the regulated nature of the metabolic pathway.

Arabinofuranosylcytosine Triphosphate↗
PubMed1985

Resistance to mutagenesis of cells biochemically transformed by herpesvirus DNA fragments.

LM(TK-) mouse fibroblast cells that were biochemically transformed to the dThd kinase-positive phenotype by restriction nuclease fragments of herpes simplex virus or marmoset herpesvirus DNA, all of which contained the virus dThd kinase coding region, or by HeLa S3 DNA were more resistant to mutagenesis by N-methyl-N'-nitro-N-nitrosoguanidine or 5-bromodeoxyuridine than were dThd kinase-positive LM and LM(TK-) cells. Measurements of dNTP pool sizes did not reveal relative imbalances for representative cell lines under several conditions of growth.

Animals↗
PubMed1985

Nick-translation of metaphase chromosomes: in vitro labeling of nuclease-hypersensitive regions in chromosomes.

Chinese hamster metaphase chromosomes were labeled by nick-translation, which involved pretreatment of metaphase chromosomes with low levels of DNase I followed by incubation with DNA polymerase I and radioactively labeled nucleotides. The labeled DNA was located on nuclease-hypersensitive regions of the chromosomes, as suggested by the following observations. (i) The labeled DNA was hypersensitive to the subsequent DNase I digestion. (ii) The labeled DNA contained no nucleosomes. DNA reassociation kinetic analysis suggested that the labeled DNA was enriched in repetitive DNA sequences. Base composition analyses showed that the labeled DNA was highly enriched in guanine and adenine residues, suggesting that the nick-translation reaction was asymmetrical and the strand enriched in purine was preferentially translated. Autoradiographic analysis revealed that the label was distributed on every chromosome, but there was a lower grain density on the Y chromosome, which is heterochromatic and exhibits a relatively low level of gene activity. The locations of silver grains on the Y chromosomes were generally consistent with that revealed by the in situ hybridization using [3H]cDNA synthesized from the total Chinese hamster messenger RNA. These observations suggest that a specific subset of genomic DNA on active chromatin is the preferred site of the nick-translation.

Animals↗
PubMed1985

Pharmacologically directed ara-C therapy for refractory leukemia.

During a two-year experience treating patients with refractory acute leukemia with a fixed 12-hour schedule of high-dose ara-C, cellular ara-CTP pharmacodynamics were ascertained in circulating blasts of these patients. A strong correlation was found between achievement of complete remission and cellular ara-CTP levels. We therefore, attempted to improve the complete remission rate in patients with low ara-CTP levels by decreasing the intermittent ara-C dosing interval, thereby raising the minimum ara-CTP level in leukemic cells between doses. This initial attempt at pharmacologic direction of chemotherapy was successful in elevating minimum ara-CTP levels but did not produce an increase in response rate, probably because the total duration of ara-CTP exposure was decreased when the dose intervals were shortened. Currently we are engaged in a new approach based on the knowledge accumulated over the past three years. Patients receive a test ara-C dose from which data on ara-CTP cellular metabolism is derived, followed by a CI of ara-C at a dose calculated individually for each patient. Preliminary results of this approach thus far indicate an increased response rate and a different spectrum of toxicity than that observed with intermittent dose ara-C. Further clinical trials will determine the true effectiveness of this approach.

Arabinofuranosylcytosine Triphosphate↗
PubMed1985

Relationship of 1-beta-D-arabinofuranosylcytosine in plasma to 1-beta-D-arabinofuranosylcytosine 5'-triphosphate levels in leukemic cells during treatment with high-dose 1-beta-D-arabinofuranosylcytosine.

The pharmacokinetic values of 1-beta-D-arabinofuranosylcytosine (ara-C) in plasma and its active metabolite 1-beta-D-arabinofuranosylcytosine 5'-triphosphate (ara-CTP) in circulating blast cells were studied in 11 patients with acute leukemia. ara-C was administered as a 2-h infusion (3 g/m2) followed in 12 to 24 h by a continuous infusion for 4 days in 10 patients and for 7 days in one. A steady-state concentration of ara-C in plasma (94 +/- 32 microM) was reached by the end of the 2-h infusion. Its elimination was biphasic with an initial and terminal t1/2 of 0.44 +/- 0.10 h and 2.8 +/- 0.9 h, respectively. The accumulation of ara-CTP in leukemic cells was linear and continued for up to 2 h after the bolus infusion. ara-CTP elimination was monophasic with a median t1/2 of 3.4 h (range, 1.25 to 18.9 h). The disposition of ara-C and 1-beta-D-arabinofuranosyluracil during continuous infusion was linear with dose rate over the dose range of 70 to 3000 mg/m2/day. The area under the concentration versus time curve for ara-CTP in leukemic cells was not related to the dose infused, but rather appeared to be intrinsic to the cells of each individual. As a general finding, the pharmacokinetic values of ara-CTP in circulating blasts were more heterogeneous than those of ara-C in plasma. There were marked differences in the absolute concentrations of ara-C in plasma and ara-CTP in leukemic cells at different times after the bolus infusion and also during continuous infusion. No correlation was evident between the determinants of ara-C pharmacokinetic values and those of ara-CTP. Thus, it is concluded that the pharmacokinetics of ara-C in plasma cannot predict for the metabolism of ara-CTP in leukemic cells.

Arabinofuranosylcytosine Triphosphate↗