The antitumour activity of ZD9331, a non-polyglutamatable quinazoline thymidylate synthase inhibitor

Microwave assisted synthesis of N-arylheterocyclic substituted-4-aminoquinazoline derivatives

A simple, efficient, and general method has been developed for the synthesis of various N-aryl heterocylic substituted-4-aminoquinazoline compounds from 4-chloro- quinazoline and aryl heterocyclic amines under microwave irradiation using 2-propanol as solvent. The advantages of the use of microwave irradiation in relation to the classical method were demonstrated.

A phase I and pharmacokinetic study of the nonpolyglutamatable thymidylate synthase inhibitor ZD9331 plus docetaxel in patients with advanced solid malignancies

PURPOSE

To assess the feasibility of administering ZD9331, a thymidylate synthase (TS) inhibitor that does not undergo polyglutamation and has broad antitumor activity, in combination with docetaxel in patients with advanced solid malignancies. The study also sought to determine the principal toxicities of the regimen and recommend appropriate doses for phase II studies, characterize the pharmacokinetics of the agents, evaluate the possibility of major drug-drug interactions, and seek preliminary evidence of anti-cancer activity.

PATIENTS AND METHODS

Patients with advanced solid malignancies were treated with escalating doses of docetaxel as a 60-minute intravenous (IV) infusion followed 30 minutes later by ZD9331 as a 30-minute IV infusion every 3 weeks. At least three patients were treated at each dose level, and the maximum tolerated dose level was defined as the highest dose level that was not associated with an unacceptably high incidence of severe toxicity. The pharmacokinetics of both ZD9331 and docetaxel were also characterized.

RESULTS

Nineteen patients were treated with 71 cycles of ZD9331 and docetaxel (ZD9331/docetaxel) at dose levels that encompassed dosing iterations of ZD9331 ranging from 65 to 260 mg/m(2) and docetaxel doses in the range of 50 to 75 mg/m(2). Neutropenia was the principal toxicity of the ZD9331/docetaxel regimen. Since five of six patients treated at the ZD9331/docetaxel dose-level of 260/60 mg/m(2) had grade 4 neutropenia that was brief and uncomplicated in the first course, a rigorous exploration of higher dose levels was not undertaken. Nonhematologic toxicities, consisting of malaise, diarrhea, rash, nausea, and vomiting, were also observed, but these effects were rarely severe. No major antitumor responses were observed. The pharmacokinetics of both ZD9331 and docetaxel were similar to those reported in previous studies of each agent administered alone, suggesting the lack of major drug-drug interactions.

CONCLUSION

The combination regimen, consisting of ZD9331 and docetaxel, is feasible and well tolerated at single-agent doses that are clinically-relevant. This ZD9331/docetaxel regimen does not appear to be associated with either major pharmacokinetic or toxicologic drug-drug interactions. A ZD9331/docetaxel dose level of 260/60 mg/m(2) is recommended as an initial dose level in disease-directed studies of the regimen, with further dose escalation of docetaxel to 75 mg/m(2) if the initial treatment is well tolerated. Further studies with this regimen are warranted in tumor types that have demonstrated sensitivity to both agents.

Phase I study of an oral formulation of ZD9331 administered daily for 28 days

PURPOSE

To define the maximum-tolerated dose and dose-limiting toxicities (DLTs) of an oral formulation of ZD9331, a novel thymidylate synthase inhibitor that is not a substrate for folylpolyglutamate synthase.

PATIENTS AND METHODS

Patients had Cancer and Leukemia Group B performance status < or = 2 and refractory solid tumors. Initially, patients received ZD9331 daily for 2 weeks, with the duration of treatment escalated to a maximum of 4 weeks, followed by a 2-week rest period. Once the maximum-tolerated duration of treatment was determined, the dose of ZD9331 was increased until DLT occurred.

RESULTS

Fifty-five patients were enrolled at eight dose levels. The DLTs were thrombocytopenia and neutropenia. At 3 mg/d, two of 19 patients developed DLT; one patient had grade 3 thrombocytopenia and grade 4 neutropenia, and the other patient had grade 3 thrombocytopenia only. Anemia was common, with a median hemoglobin nadir of 75% of baseline, before recovery or transfusion. The apparent oral clearance of ZD9931 was 11.6 +/- 6.3 mL/min. Dose-limiting myelosuppression was associated with both an increased 24-hour ZD9931 concentration and blood urea nitrogen.

CONCLUSION

The recommended phase II dose on this schedule is 3 mg/d for 4 weeks, followed by a 2-week rest period. ZD9331 seems to have a manageable toxicity profile, although it should be used with caution in patients with renal impairment.

Effects of impaired renal function on the pharmacokinetics and toxicity of i.v. ZD9331, a novel non-polyglutamated thymidylate synthase inhibitor, in adult patients with solid tumors

ZD9331 is a potent thymidylate synthase inhibitor. Renal and hepatic clearances were found to be important routes of elimination. The objectives of this pharmacologic trial were to investigate the effect of renal impairment on the pharmacokinetics of ZD9331, to study the toxicity profile and to document any antitumor effects of ZD9331 when administered i.v. to patients with different degrees of renal impairment. Patients were treated with ZD9331 130 mg/m2 given as an i.v. infusion on day 1 of a 4-week cycle to allow full pharmacokinetic assessment. Subsequent cycles involved the administration of ZD9331 on days 1 and 8, every 3 weeks. Patients were stratified according to their renal function assessed by the creatinine clearance: normal renal function (creatinine clearance > or =60 ml/min), mildly impaired renal function (creatinine clearance > or =40 to <60 ml/min) and moderately impaired renal function (creatinine clearance >25 to <40 ml/min). For pharmacokinetic analysis plasma sampling was performed during the first course and assayed using a validated liquid chromatographic tandem mass spectrometry assay. Twenty-three patients were entered on the study, of whom 21 received 130 mg/m2 ZD9331 in the first treatment cycle. No relationship was seen between renal impairment and plasma clearance nor with the area under the concentration-time curve of free ZD9331. Increasing renal impairment was associated with a greater incidence of myelosuppression. No predictive relationship between the clearance of free ZD9331 and the degree of renal impairment as determined by creatinine clearance could be assessed. However, data from this trial indicate that increased renal impairment may be associated with greater ZD9331-induced toxicity, particularly myelosuppression, although this cannot be attributed to any alteration in the plasma pharmacokinetics of ZD9331. Therefore, it may be necessary to administer a reduced dose of ZD9331 to patients with impaired renal function.

Phase I and pharmacologic study of oral ZD9331, a novel nonpolyglutamated thymidylate synthase inhibitor, in adult patients with solid tumors

PURPOSE

To assess the toxicity profile and dose-limiting toxicities (DLTs), to determine the maximum-tolerated dose, and to study the pharmacokinetics of ZD9331 when administered orally to patients with advanced solid tumors.

PATIENTS AND METHODS

Patients were treated with oral ZD9331 given once daily (od) or twice daily (bid) for 5, 7, or 10 days; cycles were repeated every 21 days at doses ranging from 2.5 to 40 mg. For pharmacokinetic analysis, plasma sampling was performed during the first course and assayed using a validated liquid chromatographic-tandem mass spectrometry assay. Plasma levels of 2'-deoxyuridine were measured as a surrogate marker for TS inhibition.

RESULTS

Forty-two patients received a total of 166 courses. The DLTs were myelosuppression and skin rash. Dose escalation of oral ZD9331 from 2.5 to 40 mg, as a single daily dose, resulted in a less than proportional increase in the plasma area under the concentration-time curve of ZD9331. The plasma drug exposure per cycle for the schedules 20 mg od for 5 days, 10 mg od for 10 days, and 10 mg bid for 5 days, all resulting in a total dose per cycle of 100 mg, were comparable. One partial response was noted in a patient with gastric cancer.

CONCLUSION

DLTs in this phase I study of oral ZD9331 were myelosuppression and skin toxicity. The recommended dose for phase II studies of oral ZD9331 is 20 mg od for 5 consecutive days, every 3 weeks.

In vivo antitumor efficacy of CW252053, a folate-based thymidylate synthase inhibitor

Previous studies have demonstrated that CW252053, a quinazoline antifolate, exhibits potent inhibitory activity against thymidylate synthase (TS) as well as cytotoxic activity against tumor cell lines in vitro. In this study, we evaluated the in vivo antitumor efficacy of CW252053 in the mouse tumor model. Female B6D2F1 mice were injected with LY3.7.2C TK-/- (thymidine kinase deficient mouse lymphoma) cells into the gastrocnemius muscle. Then, CW252053 was administered twice daily by intraperitoneal injection for 10 days, and tumor growth was monitored daily by leg diameter measurement. All animals in the vehicle, 5-FU, and low dose (30 mg/kg) CW252053 treated groups died between days 12 and 23 because of the tumor burden. In contrast, dosing with 60 mg/kg of CW252053 produced a cure rate against tumor growth of 37.5% and a survival rate of 50%. Even more significantly, a higher dose of CW252053 (120 mg/kg) elicited both a 100% cure rate and a 100% survival rate at the termination of the study, confirming that this compound has very potent in vivo antitumor activity against tumor growth. During the experimental period of this study no signs of toxicity were observed even at the high CW252053 dosage rate of 120 mg/kg.

Phase I study of ZD9331 on short daily intravenous bolus infusion for 5 days every 3 weeks with fixed dosing recommendations

PURPOSE

To conduct a phase I study of ZD9331, a potent, nonpolyglutamatable thymidylate synthase inhibitor using a short daily infusion for 5 consecutive days every 21 days.

PATIENTS AND METHODS

Patients with refractory cancer or cancer for which no standard therapy was available were treated in escalating doses using an accelerated titration design. Plasma and urine samples were collected at timed intervals in the first cycle for pharmacokinetic analysis.

RESULTS

Seventy-four patients were enrolled at 12 dose levels from a starting dose of 0.4 mg/m(2)/d to 16 mg/m(2)/d and 25 mg/d fixed dosing, of which 67 were assessable for toxicity. Maximum-tolerated dose was reached at 16 mg/m(2)/d. Myelosuppression was dose-limiting, consisting of thrombocytopenia associated with neutropenic fever. Body-surface area did not correlate with drug clearance; therefore, fixed daily dosing of 25 mg/d was studied and found to be tolerable, with two of 12 dose-limiting events. Dose-limiting nonhematologic toxicity consisted of grade 3 erythematous maculopapular rash observed in one patient at 12 mg/m(2)/d and one patient at 25 mg/d. Pharmacokinetic analysis showed nonlinearity, with clearance increasing with dose. The mean clearance and terminal half-life of the drug were 6.6 +/- 2.0 mL/min and 71.3 +/- 27.0 hours, respectively. Area-under-the concentration-time curve was a better predictor of toxicity than dose, using multiple linear regression analyses. Minor response (40% shrinkage of tumor) was observed in one patient with colorectal cancer treated at 12 mg/m(2)/d.

CONCLUSION

The recommended dose for ZD9331 on this schedule is 25 mg/d. Neutropenia, thrombocytopenia, and rash were dose-limiting, and efficacy studies in colorectal cancer are indicated.

The use of thymidylate synthase inhibitors in the treatment of advanced colorectal cancer: current status

The combination of 5-fluorouracil (5-FU) and leucovorin has been the unofficial "standard" therapy for patients with colorectal cancer for over a decade. Recently, however, a number of new agents targeted against the enzyme thymidylate synthase have been synthesized and are in various stages of development. The currently available thymidylate synthase inhibitors are discussed. Enormous efforts have been made over the years to improve the efficacy of 5-FU, the most popular of these agents. Biochemical modulation by leucovorin has been the most successful so far. Continuous infusion schedules also appear to be advantageous over bolus administration. However, marked intra- and interpatient variability, combined with nonlinear elimination kinetics and erratic oral bioavailability are relative limitations to further development of 5-FU. New oral 5-FU prodrugs such as UFT, S-1, and Capecitabine may help to overcome some of these difficulties. Eniluracil, a potent inhibitor of the enzyme dihydropyrimidine dehydrogenase, may also help by overcoming potential 5-FU resistance mechanisms, in addition to increasing its bioavailability. Of the antifolate-based inhibitors, Tomudex is in the most advanced stage of development. Similar efficacy with 5-FU and a convenient schedule may suggest a role in future combination regimens. It is quite likely that even the most optimal thymidylate synthase inhibition will have limitations in terms of clinical efficacy. Novel combinations of 5-FU or its analogs with agents that have different mechanisms of action (e.g., oxaliplatin, irinotecan) could provide important new opportunities for improving the outlook of patients with colorectal cancer.

A novel class of lipophilic quinazoline-based folic acid analogues: cytotoxic agents with a folate-independent locus

Three lipophilic quinazoline-based aminomethyl pyridine compounds, which differ only in the position of the nitrogen in their pyridine ring, are described. CB300179 (2-pyridine), CB300189 (4-pyridine) and CB30865 (3-pyridine) all inhibited isolated mammalian TS with IC50 values of 508, 250 and 156 nM respectively. CB30865 was the most potent growth inhibitory agent (IC50 values in the range 1-100 nM for several mouse and human cell types). CB300179 and CB300189 were active in the micromolar range. Against W1L2 cells, CB300179 and CB300189 demonstrated reduced potency in the presence of exogenous thymidine (dThd), and against a W1L2:C1 TS overproducing cell line. In contrast, CB30865 retained activity in these systems. Furthermore, combinations of precursors and end products of folate metabolism, e.g. dThd/hypoxanthine (HX) or leucovorin (LV), did not prevent activity. CB30865 did not interfere with the incorporation of tritiated dThd, uridine or leucine after 4 h. A cell line was raised with acquired resistance to CB30865 (W1L2:R865; > 200-fold), which was not cross-resistant to CB300179 or CB300189. In addition, W1L2:R865 cells were as sensitive as parental cells to agents from all the major chemotherapeutic drug classes. CB300179 and CB300189 induced an S phase accumulation (preventable by co-administration of dThd). No cell cycle redistribution was observed following exposure (4-48 h) to an equitoxic concentration of CB30865. In the NCI anticancer drug-discovery screen, CB30865 displayed a pattern of activity which was not consistent with known anti-tumour agents. These data suggest that CB30865 represents a class of potent potential anti-tumour agents with a novel mechanism of action.

New antimetabolites in cancer chemotherapy and their clinical impact

It is almost 50 years since antimetabolites were first found to have clinical antitumour activity, with Farber's discovery that aminopterin could cause remission in acute leukaemia. In the following 10 years, methotrexate, 6-mercaptopurine and 5-fluorouracil (5-FU) found their way into clinical practice. Subsequently, cytosine arabinoside was found to have activity in acute leukaemia, but, until recently, other significant developments have involved optimizing the efficacy of existing antimetabolites, including the use of leucovorin with methotrexate or 5-FU. Recently, new antimetabolites have become a fertile area for anti-cancer drug research. Gemcitabine (GEMZAR) has emerged as an important new agent in several tumour types, including pancreatic, non-small-cell lung, bladder, breast and ovarian cancers. Capecitabine is an intriguing new prodrug, offering tumour selectivity and prolonged tumour exposure to 5-FU. More potent thymidylate synthase inhibitors have also emerged; raltitrexed is now commercially available for the treatment of colorectal cancer. Others under development include LY231514, which has other sites of action, hence the acronym MTA (multi-targeted antifolate). A novel target is glycinamide ribonucleotide formyltransferase (GARFT) and LY309887 and AG2034 are undergoing clinical investigation as GARFT inhibitors. A critical element with LY309887 appears to be co-administration of folate. It seems entirely possible that several novel antimetabolites will establish themselves in clinical practice in future for the treatment of solid tumours.

Exploitation of folate and antifolate polyglutamylation to achieve selective anticancer chemotherapy

Synthesis of poly(gamma-glutamate) metabolites of natural folates and antifolates is a critical process. Folypolyglutamates are essential for cell proliferation. Polyglutamates of glutamate (Glu)-containing antifolates are often critical for their cytotoxic action and are relevant to antifolate resistance. However, the role of polyglutamate synthesis in selectivity is less clear. We have undertaken a research program to further define the significance of polyglutamate metabolism and to devise ways to exploit this metabolism to achieve greater therapeutic selectivity in cancer chemotherapy. This article briefly reviews several approaches tested thus far. Inhibition of folypolyglutamate synthesis should lead to cell death. Current ornithine (Orn)-containing folate-based inhibitors of the enzyme responsible for their synthesis, folypolyglutamate synthetase (FPGS), are poorly transported, apparently because of interference by the protonated delta-amine. Replacement of Orn with 4, 4-difluoroOrn, the delta-amine of which has a much lower pKa and is thus less protonated at physiological pH, was explored. Since it is unclear how polyglutamylation contributes to selectivity, we explored generic means either to eliminate or to enhance polyglutamylation. The data indicate that substitution for Glu in an antifolate by some Glu analogs in which the gamma-COOH is either altered or replaced (e.g., gamma-tetrazole-Glu) leads to loss of both FPGS substrate activity and binding; antifolate target specificity is unchanged, while uptake is actually enhanced. Substitution of 3,3-difluoroGlu for Glu leads to enhanced polyglutamylation (although probably only to the diglutamate), retention of target specificity, and at least equal uptake. Comparative studies of the same antifolate containing different replacements for Glu, such as gamma-tetrazole-Glu (no polyglutamylation) or 3,3-difluoroGlu (enhanced polyglutamylation), will be useful in exploring the role and significance of polyglutamylation.

Folate-based thymidylate synthase inhibitors as anticancer drugs

The enzyme, thymidylate synthase (TS) is considered an important target for the development of new anticancer agents. Moreover, the folate-binding site in TS is believed to offer better opportunities for the design of highly specific inhibitors than the pyrimidine (dUMP) binding site. This belief led to the design of N10-propargyl-5,8-dideazafolic acid (CB3717), a quinazoline-based drug which had antitumour activity in clinical studies. Occasional, but serious nephrotoxicity led to the withdrawal of CB3717 from further clinical study. More water-soluble and non-nephrotoxic analogues were developed with an interesting diversity in biochemical profile, particularly with respect to interactions with the reduced-folate cell membrane carrier (RFC) and folylpolyglutamate synthetase (FPGS). An example of a compound that uses both of these processes well is the quinazoline, ZD1694 (Tomudex), a drug which is about to complete phase III evaluation for colorectal cancer. High chain length polyglutamates are formed that are up to 70-fold more potent TS inhibitors than the parent drug (Ki tetraglutamate = 1 nM). Furthermore they are retained in cells/tissues for a prolonged period. A number of other novel folate-based TS inhibitors are currently in pre-clinical or clinical study. For example, LY231514 is a pyrrolopyrimidine analogue in phase I study and, although less potent as a TS inhibitor, has biochemical properties similar to ZD1694. Another compound in phase I study is the benzoquinazoline, BW1843U89 which has somewhat different properties. It is a very potent TS inhibitor (Ki = 0.09 nM) and an excellent substrate for the RFC (human) and FPGS, but polyglutamation proceeds to diglutamate only and is not accompanied by increased TS inhibition. Another highly water-soluble compound in pre-clinical development is ZD9331 which was specifically designed to use the RFC but not be a substrate for FPGS. Potent TS inhibition (Ki = 0.4 nM) was achieved through a rational programme of computerised molecular modelling of the active site of TS and a large database of structure-activity relationships. Two lipophilic compounds were designed to be devoid of interactions with either the RFC or FPGS. High resolutions crystal complexes of E. coli TS were central to obtaining potent TS inhibitors and both AG337 (Ki human recombinant TS = 16 nM) and AG331 (Ki = 12 nM) are in clinical studies. This portfolio of novel compounds therefore comprehensively addresses the potential of TS as a target for cancer chemotherapy.