Synthesis and antitumor activity of 10-alkyl-10-deazaminopterins. A convenient synthesis of 10-deazaminopterin

Further studies on the interaction of nonpolyglutamatable aminopterin analogs with dihydrofolate reductase and the reduced folate carrier as determinants of in vitro antitumor activity

Thirteen structural analogs of the potent nonpolyglutamatable dihydrofolate reductase inhibitor N(alpha)-(4-amino-4-deoxypteroyl)-N(delta)-hemiphthaloyl-L-ornithine (PT523) with modifications in the side chain, the para-aminobenzoyl moiety, or the 9,10-bridge were evaluated for the ability to inhibit human recombinant dihydrofolate reductase (DHFR), to utilize the reduced folate carrier (RFC) for influx, and to inhibit the growth of CCRF-CEM human leukemia cells in culture. In spectrophotometric assays of the kinetics of the reduction of dihydrofolate by DHFR in the presence of NADPH, these compounds had K(i) values ranging from 0.2 to 1.3pM, and thus were not greatly different in potency from the parent drug PT523. By comparison, the K(i) values of aminopterin (AMT), methotrexate (MTX), and 10-ethyl-10-deazaaminopterin (EDX) were 3.7, 4.8, and 11pM. In assays of competitive inhibition of [3H]MTX influx into CCRF-CEM cells, the K(i) values ranged from 0.21 to 7.3 micro M, as compared with 0.71, 5.4, and 1.1 micro M for PT523, AMT, and EDX. The K(t) for MTX was also re-analyzed and found to be 4.7 micro M, in better agreement with the literature than our previously reported value of 7.1 micro M. The IC(50) values of these compounds as inhibitors of the growth of CCRF-CEM cells after 72hr of drug exposure ranged from 0.53 to 55nM, and were qualitatively consistent with the other results.

Synthesis of N-[4-[1-ethyl-2-(2,4-diaminofuro[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamic acid as an antifolate

N-[4-[1-Ethyl-2-(2,4-diaminofuro[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamic acid 3 was designed and synthesized to investigate the effect of homologation of a C9-methyl to an ethyl on dihydrofolate reductase (DHFR) inhibition and on antitumor activity. Compound 3 was obtained via a concise seven step synthesis starting from palladium-catalyzed carbonylation of 4-propionylphenol, followed by a Wittig reaction with 2,4-diamino-5-(chloromethyl)furo[2,3-d]pyrimidine (6), catalytic hydrogenation, hydrolysis, and standard peptide coupling with diethyl L-glutamate. The biological results indicated that extending the C9-methyl group to an ethyl on the C8-C9 bridge region (analogue 3) doubled the inhibitory potency against recombinant human (rh) DHFR (IC(50) = 0.21 microM) as compared to the C9-methyl analogue 1 and was 4-fold more potent than the C9-H analogue 2. As compared to 1, compound 3 demonstrated increased growth inhibitory potency against several human tumor cell lines in culture with GI(50) values < 1.0 x 10(-8) M. Compound 3 was also a weak inhibitor of rh thymidylate synthase. Compounds 1 and 3 were efficient substrates of human folylpolyglutamate synthetase (FPGS). Further evaluation of the cytotoxicity of 3 in methotrexate-resistant CCRF-CEM cell sublines and metabolite protection studies implicated DHFR as the primary intracelluar target. Thus, alkylation of the C9 position in the C8-C9 bridge of the classical 5-substituted 2,4-diaminofuro[2,3-d]pyrimidine is highly conducive to DHFR and tumor inhibitory activity as well as FPGS substrate efficiency.

Synthesis and in vitro antitumor activity of new deaza analogues of the nonpolyglutamatable antifolate N(alpha)-(4-amino-4-deoxypteroyl)-N(delta)-hemiphthaloyl-L-ornithine (PT523)

Details are disclosed for the synthesis of N(alpha)-[4-[2-(2,4-diaminoquinazolin-6-yl)ethyl]benzoyl]-N(delta)-hemiphthaloyl-L-ornithine (2) and N(alpha)-[4-[5-(2,4-diaminoteridin-6-yl)pent-1-yn-4-yl]benzoyl]-N(delta)-hemiphthaloyl-L-ornithine (6) as analogues of N(alpha)-(4-amino-4-deoxypteroyl)-N(delta)-hemiphthaloyl-L-ornithine (1, PT523), a nonpolyglutamatable antifolate currently in advanced preclinical development. In a 72 h growth inhibition assay against cultures of CCRF-CEM human leukemic lymphoblasts, the IC(50) of 2 and 6 was 0.69 +/- 0.044 nM and 1.3 +/- 0.35 nM, respectively, as compared with previously reported values 4.4 +/- 0.10 nM for aminopterin (AMT) and 1.5 +/- 0.39 nM for PT523. In a spectrophotometric assay of dihydrofolate reductase (DHFR) inhibition using dihydrofolate and NADPH as the cosubstrates, the previously unreported compounds 2 and the mixed 10R and 10S diastereomers of 6 had K(i) values of 0.21 +/- 0.05 pM and 0.60 +/- 0.02 pM, respectively, as compared with previously reported values of 3.70 +/- 0.35 pM for AMT and 0.33 +/- 0.04 pM for PT523. Thus, while they were comparable to 1 and several of its previously studied analogues in their ability to bind to DHFR and inhibit the growth of CCRF-CEM cells, 2 and the mixed diastereomers of 6 were several times more active than AMT despite the fact that they cannot form gamma-polyglutamylated metabolites of the type formed in cells from AMT and other classical antifolates with a glutamate side chain.

Analogues of the potent nonpolyglutamatable antifolate N(alpha)-(4-amino-4-deoxypteroyl)-N(delta)-hemiphthaloyl-L-ornithine (PT523) with modifications in the side chain, p-aminobenzoyl moiety, or 9,10-bridge: synthesis and in vitro antitumor activity

Seven N(alpha)-(4-amino-4-deoxypteroyl)-N(delta)-hemiphthaloyl-L-o rnithine (2, PT523) analogues were synthesized by modifications of the literature synthesis of the corresponding AMT (1) analogues and were tested as inhibitors of tumor cell growth. In growth assays against cultured CCRF-CEM human leukemic cells exposed to drug for 72 h, the IC(50) values of analogues in which N(10) was replaced by CH(2) and CHMe were found to be 0.55 +/- 0.07 and 0.63 +/- 0.08 nM, and thus these analogues are more potent than 1 (IC(50) = 4.4 +/- 1.0 nM) or 2 (IC(50) = 1.5 +/- 0.39 nM). The 10-ethyl-10-deaza analogue of 2 (IC(50) = 1.2 +/- 0.25 nM) was not statistically different from 2 but was more potent than edatrexate, the 10-ethyl-10-deaza analogue of 1, which had an IC(50) of 3.3 +/- 0.36 nM. In contrast, the analogue of 2 with both an ethyl and a CO(2)Me group at the 10-position had an IC(50) of 54 +/- 4.9 nM, showing this modification to be unfavorable. The 4-amino-1-naphthoic acid analogue of 2 had an IC(50) of 1.2 +/- 0.22 nM, indicating that replacement of the p-aminobenzoic acid (pABA) moiety does not diminish cytotoxicity. The analogues in which the (CH(2))(3) side chain was replaced by slightly longer CH(2)SCH(2) and (CH(2))(2)SCH(2) groups gave IC(50) values of 4.4 +/- 1.1 and 5.0 +/- 0.56 nM and thus were somewhat less potent than the parent molecule. However the analogues in which the aromatic COOH group was at the meta and para positions of the phthaloyl ring had IC(50) values of 7.5 +/- 0.47 and 55 +/- 0.07 nM, confirming the low potency we had previously observed with these compounds against other cell lines. Overall, the results in this study support the conclusion that, while the position of the phthaloyl COOH group and the length of the amino acid side chain in 2 are important determinants of cytotoxic potency, changes in the pABA region and 9, 10-bridge are well-tolerated and can even increase potency.

Nonclassical 2,4-diamino-5-aryl-6-ethylpyrimidine antifolates: activity as inhibitors of dihydrofolate reductase from Pneumocystis carinii and Toxoplasma gondii and as antitumor agents

Twelve novel 2,4-diamino-5-(4'-benzylamino)- and 2,4-diamino-5[4'-(N-methylbenzylamino)-3'-nitrophenyl]-6-ethylp yrimidines bearing 4-substituents on the benzylamino or N-methylbenzylamino aryl ring were synthesized and evaluated as nonclassical inhibitors of Pneumocystis carinii and Toxoplasma gondii dihydrofolate reductase (DHFR). Compounds were prepared by reaction of 2,4-diamino-5-(4'-chloro-3'-nitrophenyl)- (8) or 2,4-diamino-5-(4'-fluoro-3'-nitrophenyl)-6-ethylpyrimidine (15) with the appropriate 4-substituted (CO2H, CO2Me, SO2NH2, dioxolan-2-yl, CHO, dimethyloxazolin-2-yl) benzylamine or N-methylbenzylamine derivative. Compounds 25-29 were synthesized from 2,4-diamino-5-{4'-[N-(4"-carboxybenzyl)amino]-3'-nitrophenyl}-6- ethylpyrimidine (10) and the corresponding amine (NH3, MeNH2, Me2NH, piperidine, diethyl L-glutamate) via isobutyl mixed anhydride coupling; hydrolysis of the diethyl L-glutamate 29 afforded the L-glutamate analogue 30. The compounds exhibited potent inhibitory activity against T. gondii (IC50 values 0.0018-0.14 microM) and rat liver (IC50 values 0.0029-0.27 microM) DHFR, with a 4-substituent invariably enhancing binding to both enzymes relative to the unsubstituted benzoprim (5) or methylbenzoprim (6). Modest selectivity for T. gondii enzyme was observed with several analogues, whereas all of the compounds were relatively weak inhibitors of P. carinii DHFR and exhibited no selectivity. Selected analogues were evaluated for in vivo antitumor activity against the methotrexate-resistant M5076 murine reticulosarcoma, with 2,4-diamino-5-{4'-[N-[4"-(N"-methylcarbamoyl)benzyl]-N- methylamino]-3'-nitrophenyl}-6-ethylpyrimidine (14) (Ki for rat liver DHFR = 0.00035 +/- 0.00029 nM) combining significant antitumor activity with minimal toxicity.

NMR solution structure of the antitumor compound PT523 and NADPH in the ternary complex with human dihydrofolate reductase

The antitumor compound PT523 [N(alpha)-(4-amino-4-deoxypteroyl)-N(delta)-hemiphthaloyl-L- ornithine] was found to have an inhibition constant (K(i)) of 0.35 +/- 0.10 pM against human dihydrofolate reductase (hDHFR), 15-fold lower than that of the classical antifolate drug methotrexate (MTX). The structure of PT523 bound to hDHFR and hDHFR-NADPH was investigated using multinuclear NMR techniques. NMR data indicate that the binary complex has two distinct conformations in solution which are in slow exchange and that the addition of NADPH stabilizes the ternary complex in a single bound state. Comparison of resonance assignments in the PT523 and MTX ternary complexes revealed that substantial protein chemical shift differences are limited to small regions of hDHFR tertiary structure. A restrained molecular dynamics and energy minimization protocol was performed for the hDHFR-PT523-NADPH complex, using 185 NOE restraints (33 intermolecular) to define the ligand-binding region. The positions of the pteridine and pABA rings of PT523 and the nicotinamide and ribose rings of NADPH are well defined in the solution structures (RMSD = 0.59 A) and are consistent with previously determined structures of DHFR complexes. The N(delta)-hemiphthaloyl-L-ornithine group of PT523 is less well defined, and the calculated model structures suggest the hemiphthaloyl ring may adopt more than one conformation in solution. Contacts between the hemiphthaloyl ring and hDHFR, which are not possible in the hDHFR-MTX-NADPH complex, may explain the greater inhibition potency of PT523.

Analogues of methotrexate in rheumatoid arthritis. 1. Effects of 10-deazaaminopterin analogues on type II collagen-induced arthritis in mice

Carbonation of the dianions (LDA) of 5-methylthiophene-2-carboxylic, 2-methylpyridine-5-carboxylic, and 3-methylpyridine-6-carboxylic acids provided the respective carboxy heteroarylacetic acids. The crude diacids were directly esterified in MeOH-HCl to afford the diesters. Alkylation of the sodio anions with ethyl iodide yielded the appropriate alpha-ethyl diesters. The anions of the various diester substrates were then alkylated by 2,4-diamino-6-(bromomethyl)-pteridine followed by ester saponification at room temperature to afford the respective 2,4-diamino-4-deoxy-10-carboxy-10-deazapteroic acids. The 10-carboxyl group was readily decarboxylated by heating in DMSO at temperatures of 110-135 degrees C to give the diamino 10-deaza heteropteroic acid intermediates. Coupling with diethyl L-glutamate followed by ester hydrolysis afforded the target aminopterins. The analogues were evaluated for antiinflammatory effect in the mouse type II collagen model. The thiophene analogue of 10-ethyl-10-deazaaminopterin was found to be an effective inhibitor in terms of reduced visual evidence of inflammation and swelling as determined by caliper measurement.

Analogues of methotrexate in rheumatoid arthritis. 2. Effects of 5-deazaaminopterin, 5,10-dideazaaminopterin, and analogues on type II collagen-induced arthritis in mice

Twenty-six compounds derived from the 5-deaza- and 5,10-dideazaaminopterin series of aminopterin analogues were evaluated for antiarthritic activity in the mouse type II collagen model. New compounds in the 5-deaza series were prepared by alkylation of an appropriate N-substituted (4-aminobenzoyl)-L-glutamic acid dialkyl ester or N-(5-amino-2-thenoyl)-L-glutamate diester with a 2,4-diamino-5-alkyl-6-(bromomethyl)-5-deazapteridine. The resultant 5-deazaaminopterin diesters were saponified to provide the target 5-deaza analogues. 5,10-Dideazaaminopterins were synthesized by similar alkylation of the carbanions of appropriate 4-carboxyphenylacetic, (5-carboxy-2-thienyl)acetic, or (5-carboxy-2-pyridyl)acetic acid dimethyl esters. The diesters of the 2,4-diamino-4-deoxy-10-carboxy-5,10-dideazapteroic acid types so obtained were saponified and then readily decarboxylated by heating in Me2SO solution to provide the 2,4-diamino-5,10-dideazapteroic acid-type intermediates. Peptide coupling with diethyl L-glutamate followed by ester hydrolysis at room temperature afforded the new 5,10-dideazaaminopterin analogues. 5-Deazaaminopterins bearing an alkyl substituent at the 5-position were generally quite effective as antiinflammatory agents. Thus 5-propyl-5-deazaaminopterin, 5-methyl-10-propargyl-5-deazaaminopterin, 5-methyl-10-allyl-5-deazaaminopterin, 5-ethyl-5-deazamethotrexate, and 2,5-disubstituted thiophene analogue of 5-methyl-5-deazaaminopterin showed potencies greater than methotrexate by intraperitoneal or oral administration and were active over a considerably broader dose range. Useful activity in the 5,10-dideaza series was only observed for 5,10-dideazaaminopterin and its 10-methyl analogue. Alkyl substitution at C-5 or C-10 was generally detrimental to antiinflammatory activity in this series.

Antifolates: current developments

In summary, the problem of MTX resistance has been approached in a mechanistic fashion, based on the wealth of information generated over the years. To date, these strategies have produced several new classes of anticancer drugs, with a variety of anticipated and unanticipated mechanisms of action. Several of these have shown promising preclinical activity, and these are moving into more stringent testing in the clinic.

Edatrexate in patients with soft tissue sarcoma. Activity in malignant fibrous histiocytoma

BACKGROUND

Chemotherapy has had little impact on the natural history of soft tissue sarcoma, and often is associated with serious toxicity. Edatrexate, an investigational antifolate, is active in patients with lung cancer, and has cytotoxic activity in human sarcoma cell lines.

METHODS

Edatrexate was administered to 36 patients with measurable, advanced soft tissue sarcoma who had not previously received chemotherapy. The drug was given weekly for 5 weeks, then every other week. The initial dose, 80 mg/m2, was escalated by 10 mg/m2 every 2 weeks in the absence of toxicity. Eleven patients had leiomyosarcoma, 7 had malignant fibrous histiocytoma (MFH), and 5 had liposarcoma; the remainder of cell types included hemangiopericytoma (4), angiosarcoma (3), synovial (2), spindle cell (2), extraosseous chondrosarcoma (1), and fibrosarcoma (1).

RESULTS

Thirty-five patients are evaluable. Partial response (PR) was seen in five of the seven patients with MFH; no other major responses occurred. Overall, the response frequency was 14% (two-sided 95% confidence interval, 3% to 26%). Median duration of PR was 6 months (range, 4-18 months). One patient had a minor tumor regression, and six had stable disease. Myelosuppression was generally mild; only three patients had grade 3 hematologic toxicity. Modification of dose or schedule was required in 50% of patients for mucositis. Fatigue was a common toxicity, seen in 66% of patients, but was tolerable in the majority. A rash was seen in 46% of patients; one patient had hepatic toxicity.

CONCLUSIONS

Overall, the activity of edatrexate in this study, dominated by patients with either visceral or vascular sarcoma, was poor. However, the responses observed in patients with metastatic MFH suggests that further evaluation of edatrexate in patients with soft tissue sarcoma is warranted.

Edatrexate, an antifolate with antitumor activity: a review

Edatrexate (10-ethyl, 10-deaza-aminopterin; 10-EdAM) is one of a group of compounds developed by substitutions at the N10-position of 4-aminofolate. In phase I and II trials, activity has been seen against non-small-cell lung cancer, breast cancer, non-Hodgkin's lymphoma, and cancer of the head and neck. In preclinical studies, a synergistic effect has been reported when edatrexate is combined with other antineoplastic drugs, and enhanced activity has been seen in two combination-chemotherapy phase II studies in patients with non-small-cell lung cancer. In in vivo preclinical studies, edatrexate has demonstrated antitumor activity against mouse solid and ascites tumors as well as human tumor xenografts. The activity is superior to that of methotrexate and the other antifolates tested. The improved therapeutic index of edatrexate appears to be related to its increased entry into, and polyglutamylation within, tumor cells, and its relative exclusion and rapid elimination from sensitive host tissues, compared to methotrexate. Edatrexate is metabolized in the liver and then excreted mainly in the bile. In clinical trials in cancer patients, the dose-limiting and most frequent toxicity is mucositis. Other side effects are generally mild and include myelosuppression, nausea, vomiting, elevations in SGOT, and macular rash. The responses seen in clinical trials along with preclinical data suggest that edatrexate may be a valuable agent in the treatment of cancer. Studies currently underway include the evaluation of edatrexate in small-cell lung cancer and edatrexate in combination with leucovorin, new vinca alkaloids, and cisplatin.

Phase II study of Edatrexate in stage III and IV non-small-cell lung cancer

A total of 49 patients with advanced, previously untreated non-small-cell lung cancer (NSCLC) were treated with a new antifolate, Edatrexate (10-ethyl-10-deaza-aminopterin; 10-EdAM). Patients received 80 mg/m2 weekly for 12 weeks, and responders received a further 6 cycles at 2-week intervals. Dose reductions were carried out for haematological toxicity and mucositis. Response was assessed prior to each treatment according to WHO criteria. Among the 45 evaluable patients, 6 [13.3%; 95% confidence interval (CI), 6%-26%] achieved a partial response (PR) and 9 (20%; 95% CI, 11%-34%) showed a minor response (MR; 25%-50% reduction in the sum of 2 perpendicular tumour diameters). In those receiving four or more cycles of treatment, the PR and MR rates were 17.6% and 26.4%, respectively. The resultant toxicity mainly constituted skin rash, mucositis and myelosuppression. Edatrexate is active against NSCLC and produces toxicity profile similar to that of methotrexate.

Long-term treatment of the MRL/lpr mouse with methotrexate and 10-deazaaminopterin

Female MRL/lpr mice were treated with I.P. doses of methotrexate (MTX) and 10-deazaaminopterin (DAAM) in the range of 1 to 100 mg/kg body weight/week, in two equally divided doses. Treatment began at 7 weeks of age and continued to 30 weeks of age. Joint histopathology scores were tightly correlated with skin lesion-proteinuria scores at 30 weeks of age. MTX at levels of 5, 25, and 100 mg/kg body weight/week and DAAM at a level of 25 mg/kg body weight/week significantly reduced skin lesion-proteinuria scores below controls in a dose dependent manner. Animals receiving MTX at 25 mg/kg body weight/week had a significantly longer median life span and animals receiving MTX at 100 mg/kg body weight/week had a greater than 15% suppression of growth when compared with controls. Longevity and skin lesion-proteinuria scores appeared to be good indicators of drug efficacy while growth suppression appeared to be a good indicator of drug toxicity.

Inhibition of the neutrophil NADPH oxidase by folic acid and antagonists of the folic acid metabolism

The influence of folic acid and several antagonists of the folic acid metabolism on neutrophil superoxide generation was investigated with the cytochrome c reduction assay. The compounds were found to be partial competitive inhibitors of the NADPH oxidase, their activity apparently increasing with larger substituents at the 10 position. There is evidence that compounds with a 4-oxo substituent are taken up more slowly by neutrophils than those with a 4-amino functionality. Scavenging properties could be excluded from control measurements with the xanthine/xanthine oxidase assay.

Edatrexate improves the antitumor effects of cyclophosphamide and cisplatin against non-small cell lung cancer

The authors treated 32 patients with Stage IIIB or IV non-small cell lung cancer (NSCLC) with an outpatient regimen of edatrexate (10-ethyl-10-deaza-aminopterin) (10-EdAM) on days 1 and 8, cyclophosphamide on day 1, and cisplatin on day 1, repeated every 3 weeks with dose modification. The 22 men and 10 women (median age, 57 years of age) had no prior chemotherapy and a Zubrod performance status less than or equal to 2. A schedule with initial doses of 80 mg/m2, 800 mg/m2, and 80 mg/m2, respectively, yielded a 47% major response rate with two complete responses (95% confidence interval [CI], 25% to 70%), but it also yielded significant stomatitis and myelosuppression. A schedule with reduced starting doses (70 mg/m2, 700 mg/m2, and 70 mg/m2) was better tolerated, but dropped the major response rate to 27% with no complete responses (95% CI, 11% to 52%). Median survival time was 39 weeks for all 30 evaluable patients without a significant difference between the treatment groups (which were comparable in patient characteristics). Major response, however, was associated with longer survival time than minor response or no change (P = 0.024) or progressive disease (P = 0.001) (median survival times, 55, 39, and 27 weeks, respectively). When the doses delivered were compared, patients treated with the reduced dose schedule received less mean 10-EdAM per course (P = 0.01), although the doses of cyclophosphamide and cisplatin were comparable to the original dose schedule for the second course and thereafter. These results suggest that this three-drug regimen may have synergistic antitumor effects, with a steep dose-response relationship, particularly with 10-EdAM. With amelioration of the dose-limiting stomatitis of 10-EdAM, it seems possible to maximize the antitumor effects of this regimen.

The antifolate 10-deazaaminopterin inhibits neutrophil chemotaxis and superoxide generation

The effect of the dihydrofolate reductase inhibitor 10-deazaaminopterin on several neutrophil functions was tested in vitro. At 100 uM it inhibited chemotaxis by 50% and reduced the generation of superoxide by 30%. It had no influence on phagocytosis and did not significantly change the secretion of beta-D-glucuronidase, a marker enzyme of degranulation. After preincubation of white cells with various concentrations of 10-deazaaminopterin, followed by resuspension in drug-free medium, no inhibition of chemotaxis or superoxide generation was seen. Therefore, the effects on chemotaxis and NADPH oxidase appear to be reversible and not due to metabolic transformation of the dihydrofolate reductase inhibitor.

Alleviation by leucovorin of the dose-limiting toxicity of edatrexate: potential for improved therapeutic efficacy

Edatrexate (10-ethyl-10-deaza-aminopterin; CGP 30 694) is a methotrexate (MTX) analogue that shows promise against non-small-cell lung cancer (NSCLC) and other tumors. Since edatrexate's mechanism of action is the same as that of MTX, we used leucovorin in an attempt to alleviate its dose-limiting toxicity, stomatitis. In four patients with NSCLC who had experienced significant stomatitis after treatment with edatrexate, cyclophosphamide, and cisplatin, we observed a remarkable reduction in stomatitis following the administration of low-dose leucovorin. On the basis of the results obtained in these individuals, we treated 15 additional patients with this three-drug regimen plus leucovorin rescue. These subjects could tolerate the treatment with lesser degrees of stomatitis and received higher edatrexate doses in subsequent courses as compared with the patients who previously received this regimen without leucovorin rescue. This approach is expected to improve the therapeutic indices of edatrexate and edatrexate-containing chemotherapy regimens by modifying the dose-limiting toxicity of this antineoplastic agent.

Comparative study of the sensitivity of head and neck cell lines to methotrexate (MTX) and the analog 10-ethyl, 10-deazaaminopterin (10-EdAM)

Squamous cell lines cultured in vitro provide a potential test system for the selection of analogs that have an improved therapeutic index. The growth inhibitory effects of methotrexate and the new folate analog 10-ethyl, 10-deazaaminopterin were compared in three in vitro-cultured human head and neck squamous cell carcinoma cell lines. The inhibitory concentrations of the new analog were 10- to 100-fold lower than the inhibitory concentrations of methotrexate. The sensitivity of these three head and neck squamous cell carcinoma cell lines to both drugs was essentially the same as the sensitivity of a rhabdomyosarcoma cell line known to be very sensitive to methotrexate when the cell line is grown as a xenograft in athymic nude mice. These data indicate that 10-ethyl, 10-deazaaminopterin may be a new and effective agent against head and neck squamous cell carcinoma.

Synthesis of the 7-hydroxy metabolites of methotrexate and 10-ethyl-10-deazaaminopterin

The potent folate antagonists methotrexate and 10-ethyl-10-deazaaminopterin are oxidized in vivo to their 7-hydroxy derivatives. A specific cyanation at the C-7 position of the pteridine ring system using diethyl phosphorocyanidate converted the dimethyl esters of methotrexate and 10-ethyl-10-deazaaminopterin to the corresponding 7-cyano dimethyl ester derivatives, which were hydrolyzed to the 7-hydroxy metabolites.

Biological and biochemical properties of new anticancer folate antagonists

We review the biology and biochemical pharmacology of four antifolates that were recently introduced into clinical trial as anticancer agents, and one compound in preclinical development. Toxicology and clinical data are not discussed. 10-Ethyl-10-deazaaminopterin (10-EdAM) is a classical antifolate, structurally related to methotrexate (MTX) but with greater activity against murine tumors. 10-EdAM has more efficient membrane transport, and relatively greater polyglutamylation in murine tumors than in normal mouse tissues, and these differential effects are greater for 10-EdAM than for other 10-deaza antifolates or for MTX. Trimetrexate and piritrexim are nonclassical antifolates, lacking a glutamate substitution. They are lipophilic, cross cell membranes more rapidly than does MTX, and retain activity against tumors resistant to MTX because of impaired drug transport. These nonclassical antifolates are active against several MTX-insensitive murine tumors, and both have demonstrated clinical anticancer activity. 10-EdAM, trimetrexate and piritrexim all inhibit dihydrofolate reductase (DHFR) as their primary site of action. As such, they deplete cellular thymidylate and purine pools, and inhibit DNA replication. N10-Propargyl-5,8-dideazafolic acid (CB3717) differs from the first three compounds in acting primarily on thymidylate synthase. Like DHFR inhibitors, it blocks DNA replication through depletion of dTTP, but it does not exert an antipurine effect. CB3717 retains activity against transport-defective MTX-resistant cells, and also against cells that overproduce DHFR. 5,10-Dideazatetrahydrofolic acid (DDATHF) is a selective inhibitor of glycinamide ribotide transformylase, and its biochemical pharmacology may differ appreciably from that of the other antifolates under study. DDATHF has strong antitumor activity in several murine systems.

Fluorometric high-performance liquid chromatographic analysis of 10-deazaaminopterin, 10-ethyl-10-deazaaminopterin, and known metabolites

The antifolate compounds 10-deazaaminopterin (10-dAM) and 10-ethyl-10-deazaaminopterin (10-EdAM) are therapeutically superior to methotrexate in transplanted murine tumor systems and in human tumor xenografts growing in immunodeficient "nude" mice. The increased therapeutic index of these analogs correlates with their selective uptake, retention, and polyglutamation within neoplastic cells. We have developed a fluorescence high-performance liquid chromatographic assay applicable to 10-dAM, 10-EdAM, their polyglutamate anabolites, and their 7-hydroxy (7-OH) and deglutamate catabolites. The assay is based upon the high native fluorescence of pteridine-containing compounds which contain carbon in the 10 position. The assay employs a reverse-phase C-18 column and an ascending acetonitrile gradient in 50 mM phosphate, pH 7.0. The compounds are extracted from plasma and urine with 95 +/- 7% and 98 +/- 2% recoveries, respectively, using C-18 Sep-Paks. The linear range of the assay is, for 10-dAM, 2-100 nM, and for 10-EdAM, 1-100 nM. Polyglutamated metabolites of [3H]10-EdAM isolated from L1210 cells have been separated by HPLC with identification of five derivatives (Glu 1-5) confirmed by enzymatic peak shift using serum conjugase and by quantitative correlation of fluorescence intensity, radioactivity, and titration inhibition of dihydrofolate reductase. The assay has been used successfully in pharmacokinetic analyses of plasma and urine samples from patients receiving 10-dAM and 10-EdAM. In patients who had received 10-EdAM, 7-OH-10-EdAM, and the deglutamate catabolite were also detected. This HPLC fluorescence assay is superior to the dihydrofolate reductase inhibition and binding assays with regard to specificity and precision; moreover, it can provide a means for simultaneous assay of the physiologically important anabolites and catabolites of these new antifolates.