Design and synthesis of inhibitors of folate-dependent enzymes as antitumor agents

A Glossary for Chemical Approaches towards Unlocking the Trove of Metabolic Treasures in Actinomycetes

Actinobacterial natural products showed a critical basis for the discovery of new antibiotics as well as other lead secondary metabolites. Varied environmental and physiological signals touch the antibiotic machinery that faced a serious decline in the last decades. The reason was exposed by genomic sequencing data, which revealed that Actinomycetes harbor a large portion of silent biosynthetic gene clusters in their genomes that encrypt for secondary metabolites. These gene clusters are linked with a great reservoir of yet unknown molecules, and arranging them is considered a major challenge for biotechnology approaches. In the present paper, we discuss the recent strategies that have been taken to augment the yield of secondary metabolites via awakening these cryptic genes in Actinomycetes with emphasis on chemical signaling molecules used to induce the antibiotics biosynthesis. The rationale, types, applications and mechanisms are discussed in detail, to reveal the productive path for the unearthing of new metabolites, covering the literature until the end of 2020.

Bioactivity-HiTES Unveils Cryptic Antibiotics Encoded in Actinomycete Bacteria

Bacteria harbor an immense reservoir of potentially new and therapeutic small molecules in the form of "silent" biosynthetic gene clusters (BGCs). These BGCs can be identified bioinformatically but are sparingly expressed under normal laboratory growth conditions, or not at all, and therefore do not produce significant levels of the corresponding small molecule product. Several methods have been developed for activating silent BGCs. A major limitation for nearly all methods is that they require genetic procedures and/or do not report on the bioactivity of the cryptic metabolite. We herein report "Bioactivty-HiTES", an approach that links the bioactivity of cryptic metabolites to their induction while at the same time obviating the need for genetic manipulations. Using this method, we detected induction of cryptic antibiotics in three actinomycete strains that were tested. Follow-up studies in one case allowed us to structurally elucidate two cryptic metabolites, elicited by the β-blocker atenolol in Streptomyces hiroshimensis, with selective growth-inhibitory activity against Gram-negative bacteria, notably Escherichia coli and Acinetobacter baumannii. Atenolol turned out to be a global elicitor of secondary metabolism, and characterization of additional cryptic metabolites led to the discovery of a novel naphthoquinone epoxide. Bioactivity-HiTES is a general, widely applicable procedure that will be useful in identifying cryptic bioactive metabolites in the future.

Pemetrexed combined with paclitaxel in patients with advanced or metastatic non-small-cell lung cancer: A phase I-II trial

Pemetrexed, a novel multi-targeted agent established for the treatment of mesothelioma, has been under investigation for other malignancies, and in recent years particularly for non-small-cell lung cancer (NSCLC). In the present trial we investigated pemetrexed in combination with paclitaxel as front-line treatment in advanced or metastatic NSCLC. Our objectives were to determine the response rate, median and overall survival and toxicity. From April 2005 until May 2006, 51 patients with advanced or metastatic NSCLC were enrolled and 48 were considered evaluable. There were 39 males and nine females, median age 62 years (range 37-81 years), one patient stage IIIA N(2), 23 patients, IIIB and 24, stage IV. All patients had a cytologically- or histologically-confirmed diagnosis. Pemetrexed was administered at a standard dose of 500mg/m(2) and paclitaxel at an escalating dose starting at 135mg/m(2), then 150mg/m(2) and ending at a dose of 175mg/m(2); the level was increased every three patients. Both agents were administered on day 1, repeated every 3 weeks for six courses. A 39.6% partial response rate was observed with a median survival of 14 months. Toxicity was mild with 8.3% grade 3 and 4 neutropenia and other very mild hematologic and non-hematologic adverse reactions. The combination of pemetrexed and paclitaxel at doses of 500mg/m(2) and 175mg/m(2), respectively, has been shown to be an effective combination with very limited toxicity.

Phase II study of pemetrexed in combination with carboplatin in the first-line treatment of advanced nonsmall cell lung cancer

BACKGROUND

The primary objectives of this study were to determine the efficacy and tolerability of a pemetrexed-carboplatin combination as first-line therapy in patients with advanced nonsmall cell lung cancer.

METHODS

Eligibility criteria included Zubrod performance status of 0 or 1, Stage IIIB (malignant effusion) or IV disease, and no prior chemotherapy. Treatment was pemetrexed 500 mg/m2 given intravenously and carboplatin area under the serum concentration-time curve = 6 given intravenously on Day 1 every 3 weeks for six cycles; patients could receive additional cycles at the discretion of the treating physician and patient. All patients received folic acid, vitamin B12, and dexamethasone prophylaxis.

RESULTS

Fifty patients (31 men and 19 women) were treated. The median age was 62 years. Ninety-six percent of patients had Stage IV disease, and 88% had a performance status of 1. The median number of cycles was 6; 15 patients received 8 or more cycles. There was Grade 3/4 neutropenia in 11 (22%) and 2 (4%) patients, respectively; Grade 3/4 thrombocytopenia in 1 (2%) and 0 patients, respectively. Three patients (6%) experienced Grade 3 nonhematologic side effects (diarrhea, neutropenic pneumonia, and fatigue). No patients had sensory neuropathy or alopecia >Grade 1. The partial response rate was 24%, median time to progression 5.4 months, 1-year survival 56.0%, and median survival 13.5 months.

CONCLUSIONS

This is an active, very well-tolerated regimen. Trials focused on how to integrate this doublet with novel agents are warranted.

The role of Pemetrexed (Alimta , LY231514) in lung cancer therapy

Pemetrexed (Alimta , LY231514) is a new multitargeted antifolate that inhibits several enzymes involved in the folate pathway. Pemetrexed is a potent inhibitor of thymidylate synthase, dihydrofolate reductase, and glycinamide ribonucleotide formyltransferase. Pemetrexed has demonstrated clinical activity in non-small-cell lung cancer (NSCLC) as well as in a broad array of other solid tumors including mesothelioma and breast, colorectal, bladder, cervical, gastric, and pancreatic cancer. In NSCLC, single-agent activity has been documented in the first- and second-line settings. Promising activity has also been demonstrated when pemetrexed is combined with cisplatin, vinorelbine, oxaliplatin, carboplatin, and gemcitabine. Low-level dietary supplement of folic acid and vitamin B12 has significantly improved the safety profile of pemetrexed without compromising its antitumor effect. In this review, the pharmacology and clinical activity of pemetrexed in NSCLC cancer is discussed.

Design, synthesis and biological evaluation of 10-CF3CO-DDACTHF analogues and derivatives as inhibitors of GAR Tfase and the de novo purine biosynthetic pathway

The synthesis and evaluation of analogues and key derivatives of 10-CF3CO-DDACTHF as inhibitors of glycinamide ribonucleotide transformylase (GAR Tfase) and aminoimidazole carboxamide transformylase (AICAR Tfase) are reported. Polyglutamate analogues of 1 were evaluated as inhibitors of Escherichia coli and recombinant human (rh) GAR Tfase, and AICAR Tfase. Although the pentaglutamate 6 was found to be the most active inhibitor of the series tested against rhGAR Tfase (Ki=0.004 microM), little distinction between the mono-pentaglutamate derivatives was observed (Ki=0.02-0.004 microM), suggesting that the principal role of the required polyglutamation of 1 is intracellular retention. In contrast, 1 and its defined polyglutamates 3-6 were much less inactive when tested against rhAICAR Tfase (Ki=65-0.120 microM) and very selective (> or =100-fold) for rh versus E. coli GAR Tfase. Additional key analogues of 1 were examined (7 and 8) and found to be much less active (1000-fold) highlighting the exceptional characteristics of 1.

Design, synthesis, and biological evaluation of simplified alpha-keto heterocycle, trifluoromethyl ketone, and formyl substituted folate analogues as potential inhibitors of GAR transformylase and AICAR transformylase

A series of simplified alpha-keto heterocycle, trifluoromethyl ketone, and formyl substituted folate analogues lacking the benzoylglutamate subunit were prepared and examined as potential inhibitors of glycinamide ribonucleotide transformylase (GAR Tfase) and aminoimidazole carboxamide transformylase (AICAR Tfase).

Phase III study of pemetrexed in combination with cisplatin versus cisplatin alone in patients with malignant pleural mesothelioma

PURPOSE

Patients with malignant pleural mesothelioma, a rapidly progressing malignancy with a median survival time of 6 to 9 months, have previously responded poorly to chemotherapy. We conducted a phase III trial to determine whether treatment with pemetrexed and cisplatin results in survival time superior to that achieved with cisplatin alone.

PATIENTS AND METHODS

Chemotherapy-naive patients who were not eligible for curative surgery were randomly assigned to receive pemetrexed 500 mg/m2 and cisplatin 75 mg/m2 on day 1, or cisplatin 75 mg/m2 on day 1. Both regimens were given intravenously every 21 days.

RESULTS

A total of 456 patients were assigned: 226 received pemetrexed and cisplatin, 222 received cisplatin alone, and eight never received therapy. Median survival time in the pemetrexed/cisplatin arm was 12.1 months versus 9.3 months in the control arm (P =.020, two-sided log-rank test). The hazard ratio for death of patients in the pemetrexed/cisplatin arm versus those in the control arm was 0.77. Median time to progression was significantly longer in the pemetrexed/cisplatin arm: 5.7 months versus 3.9 months (P =.001). Response rates were 41.3% in the pemetrexed/cisplatin arm versus 16.7% in the control arm (P <.0001). After 117 patients had enrolled, folic acid and vitamin B12 were added to reduce toxicity, resulting in a significant reduction in toxicities in the pemetrexed/cisplatin arm.

CONCLUSION

Treatment with pemetrexed plus cisplatin and vitamin supplementation resulted in superior survival time, time to progression, and response rates compared with treatment with cisplatin alone in patients with malignant pleural mesothelioma. Addition of folic acid and vitamin B12 significantly reduced toxicity without adversely affecting survival time.

10-Formyl-5,10-dideaza-acyclic-5,6,7,8-tetrahydrofolic acid (10-formyl-DDACTHF): a potent cytotoxic agent acting by selective inhibition of human GAR Tfase and the de novo purine biosynthetic pathway

The synthesis of 10-formyl-DDACTHF (3) as a potential inhibitor of glycinamide ribonucleotide transformylase (GAR Tfase) and aminoimidazole carboxamide ribonucleotide transformylase (AICAR Tfase) is reported. Aldehyde 3, the corresponding gamma- and alpha-pentaglutamates 21 and 25 and related agents were evaluated for inhibition of folate-dependent enzymes including GAR Tfase and AICAR Tfase. The inhibitors were found to exhibit potent cytotoxic activity (CCRF-CEM IC(50) for 3=60nM) that exceeded their enzyme inhibition potency [K(i) (3)=6 and 1 microM for Escherichia coli GAR and human AICAR Tfase, respectively]. Cytotoxicity rescue by medium purines, but not pyrimidines, indicated that the potent cytotoxic activity is derived from selective purine biosynthesis inhibition and rescue by AICAR monophosphate established that the activity is derived preferentially from GAR versus AICAR Tfase inhibition. The potent cytotoxic compounds including aldehyde 3 lost activity against CCRF-CEM cell lines deficient in the reduced folate carrier (CCRF-CEM/MTX) or folylpolyglutamate synthase (CCRF-CEM/FPGS(-)) establishing that their potent activity requires both reduced folate carrier transport and polyglutamation. Unexpectedly, the pentaglutamates displayed surprisingly similar K(i)'s versus E. coli GAR Tfase and only modestly enhanced K(i)'s versus human AICAR Tfase. On the surface this initially suggested that the potent cytotoxic activity of 3 and related compounds might be due simply to preferential intracellular accumulation of the inhibitors derived from effective transport and polyglutamation (i.e., ca. 100-fold higher intracellular concentrations). However, a subsequent examination of the inhibitors against recombinant human GAR Tfase revealed they and the corresponding gamma-pentaglutamates were unexpectedly much more potent against the human versus E. coli enzyme (K(i) for 3, 14nM against rhGAR Tfase versus 6 microM against E. coli GAR Tfase) which also accounts for their exceptional cytotoxic potency.

A New Route to 7-Substituted Derivatives of N-{4-[2-(2-Amino-3,4-dihydro-4-oxo-7H-pyrrolo[2,3-d]pyrimidin-5-yl)- ethyl]benzoyl}-l-glutamic Acid [ALIMTA (LY231514, MTA)]1

Alkylation of various primary amines with crotyl bromide, followed by DMAP-promoted acylation with methyl malonyl chloride to 4 and then manganic triacetate dihydrate/cupric acetate induced radical cyclization, gave 1-substituted-4-vinyl-3-carbomethoxy-2-pyrrolidinones (5). Thiation to the thiolactams 6 and guanidine cyclization then gave a series of 2-amino-3,4-dihydro-4-oxo-5-vinyl-7-substituted pyrrolo[2,3-d]pyrimidines (7). Palladium-catalyzed C-C coupling with diethyl 4-iodobenzoylglutamate led in one step via an unexpected redox reaction to the diethyl esters 9 of a series of 7-substituted derivatives of ALIMTA (LY231514, MTA), from which the target analogues 10 were readily prepared by saponification. Attempted deprotection at position 7 was successful in only one case (9d, R = CH(2)C(6)H(3)(OMe)(2)(-3',4'), which resulted in a known pentultimate precursor (9, R = H) of ALIMTA. The 7-substituted derivatives 10 proved to be inactive in vitro as inhibitors of cell division.

Multitargeted antifolate LY231514 as first-line chemotherapy for patients with advanced non-small-cell lung cancer: A phase II study. National Cancer Institute of Canada Clinical Trials Group

PURPOSE

To evaluate the efficacy and safety of the multitargeted antifolate LY231514 (MTA) in patients receiving initial chemotherapy for unresectable, advanced non-small-cell lung cancer (NSCLC).

PATIENTS AND METHODS

Patients with measurable, advanced NSCLC who had not received previous chemotherapy for advanced disease were considered for this study. Eligible patients who gave written informed consent initially received MTA 600 mg/m(2) intravenously (IV) for 10 minutes every 3 weeks. After three patients received treatment at this dose, the dose was reduced to 500 mg/m(2) IV at the same infusion time and frequency because of toxicity seen in this study and another Canadian MTA trial in colorectal cancer. Patients received up to four cycles after complete or partial remission or six cycles after stable disease was documented.

RESULTS

Thirty-three patients were accrued onto the study. All were assessable for toxicity, and 30 patients were assessable for response. All but one patient had an Eastern Cooperative Oncology Group performance status score of 0 or 1, 18 patients (55%) had adenocarcinoma, and nine patients (27%) had squamous cell carcinoma. Twenty-five patients (76%) had stage IV disease, and the remainder had stage IIIB disease at trial entry. Seven patients experienced a confirmed partial response and no complete responses were seen; thus, the overall response rate was 23.3% (95% confidence interval, 9.9% to 42.3%). The median duration of response was 3.1 months (range, 2. 3 to 13.5 months) after a median follow-up period of 7.9 months. Four (67%) of six patients with stage IIIB disease and three (12.5%) of 24 with stage IV disease responded to treatment. Four patients (13.3%) experienced febrile neutropenia and 13 (39%) experienced grade 3 or 4 neutropenia, whereas only one patient (3%) developed grade 4 thrombocytopenia. Nonhematologic toxicity was generally mild or moderate, but 39% of patients developed a grade 3 skin rash. Most other toxicities comprised grade 1 or 2 stomatitis, diarrhea, lethargy, and anorexia. Ten patients stopped protocol therapy because of toxicity.

CONCLUSION

MTA seems to have clinically meaningful activity as a single agent against advanced NSCLC. Toxicity is generally mild and tolerable. Further study of this agent in combination with cisplatin and other active drugs is warranted in this disease.

A simplified and efficient synthesis of 5,10-dideaza-5,6,7,8-tetrahydrofolic acid (DDATHF)

A new and extremely efficient synthesis of DDATHF from 4-vinylbenzoic acid and bromomalondialdehyde as precursors has been developed which proceeds in 48% overall yield.