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K R Harrap

Publications and source records attributed to K R Harrap.

At least 73 records · Page 4Linked to original sources
PubMed1986

Preclinical toxicology, pharmacokinetics and formulation of N2,N4,N6-trihydroxymethyl-N2,N4,N6-trimethylmelamine (trimelamol), a water-soluble cytotoxic s-triazine which does not require metabolic activation.

N2,N4,N6-Trihydroxymethyl-N2,N4,N6-trimethylmelamine (Trimelamol) is a water-soluble synthetic s-triazine which, unlike hexamethylmelamine (HMM) and pentamethylmelamine (PMM), does not require metabolic activation. The physico-chemical characteristics of Trimelamol were studied with the aim of overcoming the problems of chemical instability, low solubility and polymerisation which had hindered the development of the drug for clinical use. Trimelamol had similar activity to PMM against the murine PC6 plasmacytoma, but enhanced activity with respect to PMM against the Walker 256 carcinosarcoma in the rat, a species which metabolizes PMM less efficiently. Pharmacokinetic studies in mouse, rat and man did not show the major species differences characteristic of PMM. The drug exhibited similar toxicity to PMM against rodents, but had virtually no neurotoxicity. The potential advantages of Trimelamol over previously tested melamines are discussed.

Altretamine↗
PubMed1986

5-Ethyl-2'-deoxyuridine: an explanation for its lack of cytotoxic action in vivo.

The aim of this study was to explain why 5-ethyldeoxyuridine (EUdR) showed cytotoxic activity against Ehrlich ascites tumour (EAT) cells in vitro but not in vivo. In vitro studies showed that EUdR was phosphorylated to nucleotides which inhibit thymidylate synthetase and DNA polymerase. Toxicity in tissue culture appeared to be related to the inhibition of one or both of these enzymes; and could be prevented/reversed by thymidine (TdR). In vivo EAT cells also formed active EUdR nucleotides at levels which in vitro would have been associated with cytotoxicity but these levels were not maintained. EUdR has been shown to compete with TdR for catabolism by pyrimidine nucleoside phosphorylases from mouse liver and gut. In the ascitic fluid it was found that the level of EUdR fell rapidly while that of TdR and 5-ethyl-uracil increased. It is proposed that competition for catabolism in vivo resulted in the rise in TdR which then compromised the antitumour effect of EUdR.

Animals↗
PubMed1986

Quinazoline antifolates inhibiting thymidylate synthase: benzoyl ring modifications.

Four new analogues of the antifolate N10-propargyl-5,8-dideazafolic acid were prepared that were substituted in the benzoyl ring. The 2'-chloro and 2'-methyl analogues were prepared from the appropriately substituted p-nitrobenzoic acids. The route to the 3'-chloro and 3',5'-dichloro analogues was by chlorination of diethyl N10-propargyl-5,8-dideazafolate and diethyl N-[4-(prop-2-ynylamino)benzoyl]-L-glutamate, respectively, using sulfuryl chloride. The compounds were tested for their inhibition of purified L1210 thymidylate synthase (TS), for their inhibition of purified L1210 dihydrofolate reductase (DHFR), and for their inhibition of the growth of L1210 cells in culture. The 2'-chloro substituent reduced the TS inhibition by twofold and the 2'-methyl substituent reduced it by 20-fold; the 3'-chloro and 3',5'-dichloro derivatives were very poor inhibitors. The substituents only slightly affected the DHFR inhibition. None of the compounds improved upon N10-propargyl-5,8-dideazafolic acid in inhibiting the growth of L1210 cells in culture.

Folic Acid↗
PubMed1986

Quinazoline antifolates inhibiting thymidylate synthase: variation of the amino acid.

Five new analogues (1c-g) of the antifolate N10-propargyl-5,8-dideazafolic acid (1a) are described in which the benzoyl-L-glutamate moiety was replaced by benzoic acid (desglutamyl-N10-propargyl-5,8-dideazafolic acid), benzoyl-L-aspartate, 4-phenylbutyrate, benzoylglycine, and benzoyl-L-alanine. The esters of the appropriate 4-aminophenyl (benzoyl) starting materials were sequentially alkylated upon nitrogen, first with a propargyl halide and then with 2-amino-6-(bromomethyl)-4-hydroxyquinazoline hydrobromide. Saponification of the antifolate esters so produced gave the desired analogues. The new derivatives (1c-g) and also the known diethyl ester of 1a (1b) were tested for their inhibition of purified L1210 thymidylate synthase (TS) and for their inhibition of the growth of L1210 cells in culture. The TS inhibition of the analogues 1b-g was estimated by calculating the inverse relative potency, defined as the ratio IC50(compound)/IC50(1a). The results obtained were as follows: greater than 62, 84, 9, 333, 21, and 5, respectively. All were thus less inhibitory than 1a. None of the compounds improved upon 1a in inhibiting the growth of L1210 cells in culture.

Animals↗
PubMed1986

Increased thymidylate synthase in L1210 cells possessing acquired resistance to N10-propargyl-5,8-dideazafolic acid (CB3717): development, characterization, and cross-resistance studies.

The properties are described of a mutant L1210 cell line (L1210:C15) with acquired resistance (greater than 200-fold) to the thymidylate synthase (TS) inhibitor N10-propargyl-5,8-dideazafolic acid. TS was overproduced 45-fold and was accompanied by a small increase in the activity of dihydrofolate reductase (2.6-fold). Both the level of resistance and enzyme activities were maintained in drug-free medium (greater than 300 generations). Failure of N10-propargyl-5,8-dideazafolic acid to suppress the [3H]-2'-deoxyuridine incorporation into the acid-precipitable material of the resistant line supported the evidence that TS overproduction was the mechanism of resistance; consequently the L1210:C15 cells were largely cross-resistant to another (but weaker) TS inhibitor, 5,8-dideazafolic acid. Minimal cross-resistance was observed to the dihydrofolate reductase inhibitors methotrexate and 5-methyl-5,8-dideazaaminopterin (5- and 2-fold, respectively). L1210 and L1210:C15 cells were, however, equally sensitive to 5-fluorodeoxyuridine (FdUrd), an unexpected finding since a metabolite, 5-fluorodeoxyuridine monophosphate, is a potent TS inhibitor; however, this cytotoxicity against the L1210:C15 cells was antagonized by coincubation with 5 microM folinic acid although folinic acid potentiated the cytotoxicity of FdUrd to the N10-propargyl-5,8-dideazafolic acid-sensitive L1210 line. Thymidine was much less effective as a FdUrd protecting agent in the L1210:C15 when compared with the L1210 cells; however, a combination of thymidine plus hypoxanthine was without any additional effect (compared with thymidine alone) against the sensitive line but effectively protected L1210:C15 cells such that the concentration of FdUrd necessary to reduce the cell count to 50% of control at 48 h was increased greater than 11,000-fold. We propose that the elevated TS levels result in sequestration of the reduced-folate pool (as N5,10-methylene tetrahydrofolic acid) into the TS ternary complex with 5-fluoro-2'-deoxyuridine 5'-monophosphate. Despite "free" TS, the de novo synthesis of thymidylate and purines is inhibited by substrate depletion. The fact that folinic acid is able to reverse the inhibition of [3H]-2'-deoxyuridine incorporation by FdUrd into the resistant cells supports this hypothesis.

Animals↗
PubMed1986

Pharmacokinetics of the thymidylate synthase inhibitor N10-propargyl-5,8-dideazafolic acid (CB3717) in the mouse.

The tissue distribution, excretion, and metabolism of the thymidylate synthase inhibitor N10-propargyl-5,8-dideazafolic acid (CB3717) have been investigated in the mouse. Following 100 mg/kg of 2-14C-CB3717 ip, levels of radioactivity in the brain, testes, muscle, heart, and lung equilibrated slowly with those in the plasma and were no longer significantly lower 5 hours (lung) and 12 hours (brain, testes, muscle, and heart) after administration. In contrast, concentrations of 14C in the liver and kidney were markedly higher than those in the plasma at all time points studied (1.3 hours-23 days). High-performance liquid chromatographic (HPLC) analysis of livers removed 5 hours after drug administration and kidneys excised 24 hours after treatment indicated that, at these time points, greater than 50% of the radioactivity was in the form of unchanged CB3717. Furthermore, HPLC analysis of plasma removed over the period 0.5-6 hours demonstrated that all of the 14C could be accounted for as CB3717. Although the accumulation and retention of radioactivity in the liver and kidney were also apparent following 20 and 200 mg/kg of 14C-CB3717, the effect was less marked at the lower dose, thereby suggesting dose-dependent pharmacokinetics. In excretion studies (0-48 hours), the major route of elimination was found to be via the feces, with 46% of the 14C recovered; 26% of the dose was recovered as unchanged CB3717. Radioactivity excreted in the urine accounted for 20% of the administered 14C, while CB3717 eliminated via this route represented 15% of the dose. In addition to CB3717, a metabolite was detected in the feces which comprised 8% of the dose administered. The metabolite was shown to be 4-(N-((2-amino-4-hydroxy-6-quinazolinyl)methyl)prop-2-ynylamino) benzoic acid (CB3751) by HPLC and mass spectrometry. The formation of CB3751 could be catalyzed in vitro by the contents of the cecum and prevented in vivo by antibiotic pretreatment and is therefore considered to be the result of bacterial metabolism. CB3717 binds extensively to plasma proteins (92%; concentration range, 25-250 microM). These studies have shown that CB3717 does not apparently undergo extensive host metabolism in vivo, and therefore the biological properties of this novel antimetabolite are probably a function of the parent compound. In addition, the accumulation of CB3717 in the liver and kidney may be related to the hepatotoxic and nephrotoxic effects of this drug.

Animals↗
PubMed1985

The clinical pharmacokinetics of the novel antifolate N10-propargyl-5,8-dideazafolic acid (CB 3717).

The pharmacokinetics of the new antifolate CB 3717 were studied in 20 patients during its phase-I clinical evaluation. The drug was administered at doses of 100-550 mg/m2 in 1-h and 12-h infusions, resulting in peak plasma concentrations of CB 3717 of 40-200 microM. There was a linear relationship between the dose and both CB 3717 AUC and peak plasma levels. Following a 1-h infusion, drug levels in the plasma decayed biphasically (t1/2 alpha = 49 +/- 9 min, t1/2 beta = 739 +/- 209 min). 27% +/- 2% of the dose was excreted in urine in the 24-h period after treatment, suggesting that the major route of elimination was via the bile. Furthermore, the parent compound CB 3717 and its desglutamyl metabolite, CB 3751, were found in a faecal collection although the metabolite was not detected in plasma or urine samples. Plasma protein binding of CB 3717 was extensive (97.6% +/- 0.1%). Significant quantities of CB 3717 penetrated into ascitic fluid but not into cerebrospinal fluid. Residual drug was detected in postmortem kidney tissue from a patient who died of progressive disease 8 days after treatment with 330 mg/m2 CB 3717. Thus, dose-limiting renal toxicity (maximum tolerated dose 600 mg/m2) may be due to drug precipitation in the renal tubules. Elevation of liver enzymes, in particular transaminases, occurred frequently as a toxic manifestation of CB 3717 therapy. In 11 patients studied after their first treatment there was a positive correlation between the rise in serum alanine transaminase and peak drug levels (r = 0.69, P = 0.02). These pharmacokinetic studies have shown that, by analogy with experimental systems, cytotoxic plasma levels of CB 3717 are archieved in man. In addition, they have been valuable in interpreting toxicities observed during phase-I clinical studies.

Antineoplastic Agents↗
PubMed1985

Preclinical studies identifying carboplatin as a viable cisplatin alternative.

The claims of eight cisplatin analogues as viable alternatives to the parent drug are discussed in terms of their toxicities, antitumour properties and potential biochemical selectivities. It is concluded that, of the eight, diammine (1,1-cyclobutane dicarboxylato)platinum(II) (carboplatin, CBDCA, JM8) had the features most desirable to merit its clinical evaluation.

Animals↗
PubMed1985

Phase I studies with carboplatin at the Royal Marsden Hospital.

Carboplatin was evaluated in a Phase I and pharmacokinetic study at the Royal Marsden Hospital between April 1981 and November 1981. Sixty patients were entered of whom 16 had impaired renal function. No evidence of ototoxicity or nephrotoxicity was found. Nausea and vomiting were much reduced compared to cisplatin. The dose limiting toxicity was delayed myelosuppression with thrombocytopenia being more severe than leucopenia. A number of clinical responses were seen, particularly in patients with ovarian carcinoma. Pharmacokinetic studies suggested that the dose of JM8 should be adjusted according to the glomerular filtration rate.

Antineoplastic Agents↗
PubMed1984

Modulation of anti-metabolite effects. Effects of thymidine on the efficacy of the quinazoline-based thymidylate synthetase inhibitor, CB3717.

CB3717 (N-(4-(N-((2-amino-4- hydroxy-6-quinazolinyl)methyl)prop-2-ynylamino ) benzoyl)-L-glutamic acid) is an antitumour agent that inhibits thymidylate synthetase (TS). A dose-dependent fall in plasma thymidine (dThd) (1.43 microM to 0.47 microM) occurred in non-tumour-bearing mice following the administration of CB3717. Further, in mice carrying the L1210/CBRI tumour, the drug's antitumour properties were ablated by co-administration of dThd, an effect consistent with TS being the cytotoxic locus. In vitro studies of protection by dThd against CB3717 cytotoxicity were carried out in an attempt to quantify this reversal. The metabolism of [14C]-dThd was measured in cultures of L1210 cells (10(4)/ml) exposed to a completely cytotoxic dose of CB3717 (50 microM). The cytotoxicity of the drug was only expressed when the dThd concentration (0.5-2 microM) had fallen to less than 0.1 microM in the media. This reduction was due to: (1) dThd incorporation into DNA, (2) catabolism of dThd to thymine. By reducing the initial cell concentration to 10(3)/ml the depletion of dThd was substantially reduced and consequently cells continued to grow for a longer period. The critical concentration of dThd, below which growth in the presence of CB3717 could not be supported was estimated to be between 0.026 and 0.1 microM. Thus even the minimum level of dThd achieved in vivo was still in excess of that required for protection from CB3717 toxicity in vitro. There was a small accumulation of deoxyuridine (dUrd) (approximately 2-fold) in mouse plasma 24 hr after completion of a 5-day course of CB3717 (200 mg/kg) but in vitro studies demonstrated that this was unlikely to modulate CB3717 toxicity in the presence of dThd. We caution against the use of rodent tumour models (or human tumour xenografts) for antitumour or toxicity testing of compounds designed to inhibit the de novo synthesis of thymidylate; they may be misleading because the high dThd levels found in these animals compared with man may mask the cytotoxic effects of these drugs.

Animals↗
PubMed1984

A reappraisal of the effect upon thymidine kinase of thymidine derivatives carrying large groups at the 5'-position.

Several thymidine derivatives with hydrophobic 5'-substituents, linked by chemically stable amide and ether links, were synthesized as potential thymidine kinase inhibitors. None of these was active nor were several derivatives of thymidine 5'-acetate, which were previously reported to be inhibitors. It was shown that the apparent inhibition by the latter compounds was due to their facile hydrolysis in aqueous solution with release of thymidine. These results must cast doubt on any conclusions drawn from biological studies with 5'-esters of thymidine.

Animals↗
PubMed1984

Pharmacokinetics of cis-diammine-1,1-cyclobutane dicarboxylate platinum(II) in patients with normal and impaired renal function.

cis-Diammine-1,1-cyclobutane dicarboxylate platinum(II) (CBDCA, JM8) is a nonnephrotoxic analogue of cisplatin currently undergoing clinical evaluation. Pharmacokinetic studies have been performed in patients receiving CBDCA (20 to 520 mg/sq m) as a 1-hr infusion without hydration or diuresis. Following the end of the infusion, plasma levels of total platinum and ultrafilterable (Mr less than 50,000) platinum (free platinum) decayed biphasically with first-order kinetics (total platinum t alpha 1/2 = 98 min; t beta 1/2 range, 399 to greater than 1440 min; free platinum t alpha 1/2 = 87 min; t beta 1/2 = 354 min). During the first four hr, binding of platinum to plasma protein was limited (24%), with most of the free platinum in the form of unchanged CBDCA (94%). However, by 24 hr, the majority of platinum was protein bound (87%). The major route of elimination was renal, 65% of the platinum administered being excreted in the urine within 24 hr, with 32% of the dose excreted as unchanged CBDCA. No evidence was found from studies on the renal clearance of free platinum to indicate renal tubular secretion (mean free platinum renal clearance, 69 ml/min). However, the plasma clearance of free platinum did correlate positively with glomerular filtration rates (p = 0.005). None of the pharmacokinetic parameters determined were dose dependent. In vitro studies with plasma and urine demonstrated that, in contrast to cisplatin, CBDCA is a stable complex [t 1/2 - 37 degrees; plasma, 30 hr, and urine (range), 20 to 460 hr]. The differences in the pharmacokinetics of cisplatin and CBDCA may explain why the latter complex is not nephrotoxic.

Antineoplastic Agents↗
PubMed1983

Pentamethylmelamine (PMM): Phase I clinical and pharmacokinetic studies.

PMM is a water-soluble alternative to HMM. PMM has been administered as an intravenous infusion to 17 patients in a Phase I clinical trial. The dose-limiting toxicities were nausea and vomiting which were observed in all patients at 500 mg m-2 and above. The dose was not escalated above 1300 mg m-2 where nausea and vomiting were severe, prolonged (greater than 24 h) and poorly controlled by anti-emetics. Haematological, hepatic and renal toxicities were not observed. Neurological toxicity was not observed at low doses (less than 500 mg/m2) but could not be determined at higher doses due to intensive anti-emetic therapy. Pharmacokinetic studies (100-500 mg m-2) indicated that PMM plasma levels are dose-dependent and that the PMM disposition-phase half-life is prolonged in patients with abnormal liver function. It is concluded that the severe toxicity of PMM will limit the clinical utility of this compound and hence Phase II trials are not recommended.

Adult↗