A phase I study of the lipophilic thymidylate synthase inhibitor Thymitaq (nolatrexed dihydrochloride) given by 10-day oral administration

4-(3H)-quinazolinones N-3 substituted with a five membered heterocycle: A promising scaffold towards bioactive molecules

The quinazolinone nucleus represents, among the class of fused heterocycles, a very important scaffold to obtain molecules with biological activities. A review of literature revealed how such kind of fused heterocycles, coming from natural or synthetic source, are associated with a wide range of biological activities. This review is mainly directed towards the 4-(3H)-quinazolinones N-3 substituted with a five membered heterocycle in which all the possible combinations of nitrogen, sulfur and oxygen atoms are present.

Cancer Research UK Centre for Drug Development: translating 21st-century science into the cancer medicines of tomorrow

The Cancer Research UK Centre (CRUK) for Drug Development (CDD) can trace its origins back to the Cancer Research Campaign Phase I/II Committee (created in 1980) and to date has tested over 120 potential cancer medicines in early-phase clinical trials. Five drugs are now registered, providing benefit to thousands of patients with cancer as part of their routine standard of care. In recent years, the CDD has established several different business and operating models that provide it with access to the pipelines of pharmaceutical and biotechnology companies. This has enabled potential new treatments to be taken into clinical development that might have otherwise languished on companies' shelves and has increased the number of drug combinations being explored in early-phase clinical trials.

Pemetrexed pharmacokinetics and pharmacodynamics in a phase I/II study of doublet chemotherapy with vinorelbine: implications for further optimisation of pemetrexed schedules

The purpose of this study was to investigate the utility of plasma pharmacokinetic and pharmacodynamic measures including plasma deoxynucleosides, homocysteine and methylmalonic acid concentrations in understanding the time course and extent of the inhibition of thymidylate synthase (TS) by pemetrexed in the context of a phase I/II combination study with vinorelbine. Eighteen patients received supplementation with folic acid and Vitamin B₁₂ 1 week before beginning treatment with pemetrexed and vinorelbine administered in a dose-escalating manner on a 21-day cycle. Heparinised blood samples were collected from consenting patients in the first cycle for pharmacokinetic analyses and in the first two cycles for determination of plasma thymidine, deoxyuridine, homocysteine and methylmalonic acid concentrations. These values were correlated with response and toxicity. Plasma deoxyuridine was used as a measure of TS inhibition, and concentrations of deoxyuridine were significantly elevated relative to baseline on days 1 (P<0.01), 2 (P<0.001) and 3 (P<0.05) after treatment at all pemetrexed dose levels (400–700 mg m⁻²). The magnitude of deoxyuridine elevation correlated with pemetrexed area under the plasma concentration–time curve (AUC) (r²=0.23, P<0.05). However, deoxyuridine concentrations returned to baseline between 8 and 15 days after treatment with pemetrexed, suggesting that inhibition of TS was not durable. Pemetrexed AUC correlated with the percentage decline (relative to baseline) in both platelets (r²=0.58, P<0.001) and leucocytes (r²=0.26, P<0.05) at day 8. Baseline homocysteine was also significantly correlated with these measures of haematological toxicity (r²=0.37, P<0.01 and r²=0.39, P<0.01, respectively). In addition, there was a significant reduction of plasma homocysteine on days 8 (P<0.005) and 15 (P<0.05) in cycle 1 compared to baseline values. The results suggest that the TS inhibitory effects of pemetrexed are short-lived and make the case for a more frequent schedule of administration such as every 2 weeks. The lack of protracted TS inhibition may be due to concomitant vitamin administration, and this may be the mechanism by which vitamins prevent life-threatening toxicity from pemetrexed. Baseline homocysteine concentration remains a predictive marker for haematological toxicity even following folate supplementation.

Altered deoxyuridine and thymidine in plasma following capecitabine treatment in colorectal cancer patients

AIMS

To investigate the relationship between changes in plasma deoxynucleoside concentrations and response and toxicity in patients treated with capecitabine.

METHODS

Twenty-six patients received 2 g capecitabine twice daily orally for 2 weeks of a 3-week cycle. Blood samples were collected on day 0 (baseline), day 8, day 15 and day 22 of the first cycle for the determination of plasma thymidine (TdR) and deoxyuridine (UdR) concentrations. Patients were reviewed weekly during the first cycle, then 3-weekly for toxicity assessment. Response was assessed according to Response Evaluation Criteria in Solid Tumours (RECIST) criteria.

RESULTS

The plasma UdR and UdR/TdR ratios were significantly elevated (P < 0.001) compared with baseline (49.3 +/- 20.8 nmol l(-1)) for the entire 3-week treatment period. In contrast, the plasma TdR concentrations of these patients were significantly reduced only on day 8 (P < 0.01) compared with baseline (12.1 +/- 3.83 nmol l(-1)), but returned gradually to basal levels by day 15. There were no significant correlations demonstrated between pretreatment or maximal post-treatment plasma nucleoside ratio and either toxicity or response. The TSER genotype frequencies of homozygous TSER*2, TSER*3 and heterozygous TSER*2/*3 were 7.7%, 42.3% and 50%, respectively. These preliminary data also indicate no direct relationship between thymidylate synthase (TS) genotype and plasma nucleoside levels.

CONCLUSIONS

Capecitabine mimics continuous infusion of 5-FU to achieve sustained cellular TS inhibitory effects and suggests the antiproliferative mechanism of capectabine is at least partly due to TS inhibition through its active metabolite FdUMP. Although plasma UdR and TdR concentrations and the UdR/TdR ratio can provide some pharmacodynamic indication of TS inhibition, they are unlikely to predict therapeutic response or toxicity accurately following capecitabine treatment in cancer patients.

2-[11C]thymidine positron emission tomography as an indicator of thymidylate synthase inhibition in patients treated with AG337

BACKGROUND

Some anticancer drugs inhibit thymidylate synthase (TS), a key enzyme for thymidine nucleotide biosynthesis. Cells can compensate for depleted thymidine levels by taking up extracellular thymidine via a salvage pathway. We investigated the use of 2-[11C]thymidine positron emission tomography (PET) to measure thymidine salvage kinetics in vivo in humans.

METHODS

Five patients with advanced gastrointestinal cancer were PET scanned both before and 1 hour after oral administration of the TS inhibitor AG337 (THYMITAQ [nolatrexed]); seven control patients were scanned twice but not treated with AG337. Thymidine salvage kinetics were measured in vivo using 2-[11C]thymidine PET and spectral analysis to obtain the standardized uptake values (SUV), the area under the time-activity curve (AUC), and the fractional retention of thymidine (FRT). Changes in PET parameters between scans in the AG337-treated and control groups were compared using the Mann-Whitney U test. The relationship between AG337 exposure and AG337-induced changes in tumor FRT and in plasma deoxyuridine levels (a conventional pharmacodynamic systemic measure of TS inhibition) was examined using Spearman's regression analysis. Statistical tests were two-sided.

RESULTS

The between-scan change in FRT in patients treated with AG337 (38% increase, 95% confidence interval [CI] = 8% to 68%) was higher than that in control patients (3% increase, 95% CI = -11% to 17%) (P =.028). The level of AG337-induced increase in both 2-[11C]thymidine FRT and plasma deoxyuridine levels was statistically significantly correlated with AG337 exposure (r = 1.00, P =.01 for both).

CONCLUSIONS

AG337 administration was associated with increased tumor tracer retention that was consistent with tumor cell uptake of exogenous 2-[11C]thymidine as a result of TS inhibition. 2-[11C]Thymidine PET can be used to measure thymidine salvage kinetics directly in the tissue of interest.

Design, synthesis, and X-ray crystal structure of a potent dual inhibitor of thymidylate synthase and dihydrofolate reductase as an antitumor agent

A novel N-¿2-amino-4-methyl[(pyrrolo[2, 3-d]pyrimidin-5-yl)ethyl]benzoyl¿-L-glutamic acid (3a) was designed and synthesized as a potent dual inhibitor of thymidylate synthase (TS) and dihydrofolate reductase (DHFR) and as an antitumor agent. Compound 3b, the N7-benzylated analogue of 3a, was also synthesized as an antitumor agent. The synthesis of 3a was accomplished via a 12-step sequence which involved the synthesis of 2-amino-4-methylpyrrolo[2,3-d]pyrimidine (10) in 5 steps from 2-acetylbutyrolactone. Protection of the 2-amino group of 10 and regioselective iodination at the 5-position followed by palladium-catalyzed coupling afforded intermediate 14 which was converted to 3a by reduction and saponification. Similar synthetic methodology was used for 3b. X-ray crystal structure of the ternary complex of 3a, DHFR, and NADPH showed that the pyrrolo[2, 3-d]pyrimidine ring binds in a "2,4-diamino mode" in which the pyrrole nitrogen mimics the 4-amino moiety of 2,4-diaminopyrimidines. This is the first example of a classical pyrrolo[2,3-d]pyrimidine antifolate shown to have this alternate mode of binding to DHFR. Compounds 3a and 3b were more inhibitory than LY231514 against TS from Lactobacillus casei and Escherichia coli. Analogue 3a was also more inhibitory against DHFR from human, Toxoplasma gondii, and Pneumocystis carinii. Evaluation of 3a against methotrexate (MTX)-resistant cell lines with defined mechanisms indicated that cross-resistance of 3a was much lower than that of MTX. Metabolite protection studies and folylpoly-gamma-glutamate synthetase studies suggest that the antitumor activity of 3a against the growth of tumor cells in culture is a result of dual inhibition of TS and DHFR. Compound 3a inhibited the growth of CCRF-CEM and FaDu cells in culture at ED(50) values of 12.5 and 7.0 nM, respectively, and was more active against FaDu cells than MTX. In contrast, compound 3b was inactive against both cell lines. Compound 3a was evaluated in the National Cancer Institute in vitro preclinical antitumor screening program and afforded IG(50) values in the nanomolar range against a number of tumor cell lines.