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Folate is vital for cell development and growth. It is involved in one-carbon transfer reactions essential for the synthesis of purines and pyrimidines. It also acts in conjunction with cobalamin (vitamin B12) as a fundamental cofactor in the remethylation cycle that converts homocysteine to methionine. A deficiency in folate or vitamin B12 can lead to elevated homocysteine level, which has been identified as an independent risk factor in several health-related conditions. Adequate folate levels are essential in women of childbearing age and in pregnant women, and folate deficiency is associated with several congenital malformations. Low folate levels can be caused by dietary deficiencies, a genetic predisposition or treatment with medicines that affect folate concentration. Women who are pregnant or of child-bearing age commonly use medicines, so it is important to identify the basic biochemical mechanisms by which medicines interfere with the folate-homocysteine-methionine pathway. This review focuses on prescription medicines associated with folate disruption. It also summarizes their undesirable/toxic effects. Recommendations regarding folate supplementation during medical therapy are also reviewed. [ABSTRACT FROM AUTHOR]

Pteridine reductase 1 (PTR1) is a trypanosomatid multifunctional enzyme that provides a mechanism for escape of dihydrofolate reductase (DHFR) inhibition. This is because PTR1 can reduce pterins and folates. Trypanosomes require folates and pterins for survival and are unable to synthesize them de novo. Currently there are no anti-folate based Human African Trypanosomiasis (HAT) chemotherapeutics in use. Thus, successful dual inhibition of Trypanosoma brucei dihydrofolate reductase (TbDHFR) and Trypanosoma brucei pteridine reductase 1 (TbPTR1) has implications in the exploitation of anti-folates. We carried out molecular docking of a ligand library of 5742 compounds against TbPTR1 and identified 18 compounds showing promising binding modes. The protein-ligand complexes were subjected to molecular dynamics to characterize their molecular interactions and energetics, followed by in vitro testing. In this study, we identified five compounds which showed low micromolar Trypanosome growth inhibition in in vitro experiments that might be acting by inhibition of TbPTR1. Compounds RUBi004, RUBi007, RUBi014, and RUBi018 displayed moderate to strong antagonism (mutual reduction in potency) when used in combination with the known TbDHFR inhibitor, WR99210. This gave an indication that the compounds might inhibit both TbPTR1 and TbDHFR. RUBi016 showed an additive effect in the isobologram assay. Overall, our results provide a basis for scaffold optimization for further studies in the development of HAT anti-folates.

p16 is a tumor suppressor encoded by the CDKN2A gene whose expression is lost in ~50% of all human cancers. In its canonical role, p16 inhibits the G1-S phase cell cycle progression through suppression of cyclin dependent kinases. Interestingly, p16 also has roles in metabolic reprogramming, and we previously published that loss of p16 promotes nucleotide synthesis via the pentose phosphate pathway. Whether other nucleotide metabolic genes and pathways are affected by p16/ CDKN2A loss and if these can be specifically targeted in p16/ CDKN2A -low tumors has not been previously explored. Using CRISPR KO libraries in multiple isogenic human and mouse melanoma cell lines, we determined that many nucleotide metabolism genes are negatively enriched in p16/ CDKN2A knockdown cells compared to controls. Indeed, many of the genes that are required for survival in the context of low p16/ CDKN2A expression based on our CRISPR screens are upregulated in p16 knockdown melanoma cells and those with endogenously low CDKN2A expression. We determined that cells with low p16/ Cdkn2a expression are sensitive to multiple inhibitors of de novo purine synthesis, including anti-folates. Tumors with p16 knockdown were more sensitive to the anti-folate methotrexate in vivo than control tumors. Together, our data provide evidence to reevaluate the utility of these drugs in patients with p16/ CDKN2A -low tumors as loss of p16/ CDKN2A may provide a therapeutic window for these agents., Competing Interests: Declaration of Interests In the past three years, C.A.L. has consulted for Astellas Pharmaceuticals, Odyssey Therapeutics, Third Rock Ventures, and T-Knife Therapeutics, and is an inventor on patents pertaining to Kras regulated metabolic pathways, redox control pathways in pancreatic cancer, and targeting the GOT1-ME1 pathway as a therapeutic approach (US Patent No: 2015126580-A1, 05/07/2015; US Patent No: 20190136238, 05/09/2019; International Patent No: WO2013177426-A2, 04/23/2015). All other authors declare no competing interests.

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. [ABSTRACT FROM AUTHOR]

Abstract: The tri-functional enzyme of Saccharomyces cerevisiae dihydroneopterin aldolase (DHNA)¿dihydropterin pyrophosphokinase (PPPK)¿dihydropteroate synthase (DHPS) catalyzes three sequential steps in folate biosynthesis. A cDNA encoding the PPPK and DHPS domains of the tri-functional enzyme has been cloned. This bi-functional enzyme was expressed as a His6 fusion protein in Escherichia coli and the protein was purified to apparent homogeneity. The purified protein possesses both PPPK and DHPS activities as measured by the incorporation of [3H]p-ABA into the appropriate substrate. The pH optimum of the DHPS activity was determined to be 8.5. Gel filtration measurement indicates that the protein exists as a dimer in solution. A robotic screening method was used to identify crystallization conditions. Bi-pyramidal crystals of the enzyme formed with the protein in the presence of a pterin substrate analog in phosphate buffer (pH 6.3) and these diffracted to 2.3Å. Structural information from these crystals could be used to design novel drugs to inhibit folate biosynthesis. [Copyright &y& Elsevier]

Pteridine reductase 1 (PTR1) is a trypanosomatid multifunctional enzyme that provides a mechanism for escape of dihydrofolate reductase (DHFR) inhibition. This is because PTR1 can reduce pterins and folates. Trypanosomes require folates and pterins for survival and are unable to synthesize them de novo. Currently there are no anti-folate based Human African Trypanosomiasis (HAT) chemotherapeutics in use. Thus, successful dual inhibition of Trypanosoma brucei dihydrofolate reductase (TbDHFR) and Trypanosoma brucei pteridine reductase 1 (TbPTR1) has implications in the exploitation of anti-folates. We carried out molecular docking of a ligand library of 5742 compounds against TbPTR1 and identified 18 compounds showing promising binding modes. The protein-ligand complexes were subjected to molecular dynamics to characterize their molecular interactions and energetics, followed by in vitro testing. In this study, we identified five compounds which showed low micromolar Trypanosome growth inhibition in in vitro experiments that might be acting by inhibition of TbPTR1. Compounds RUBi004, RUBi007, RUBi014, and RUBi018 displayed moderate to strong antagonism (mutual reduction in potency) when used in combination with the known TbDHFR inhibitor, WR99210. This gave an indication that the compounds might inhibit both TbPTR1 and TbDHFR. RUBi016 showed an additive effect in the isobologram assay. Overall, our results provide a basis for scaffold optimization for further studies in the development of HAT anti-folates. [ABSTRACT FROM AUTHOR]

Background: Pemetrexed (Alimta(®)) is a new-generation antifolate used to treat malignant pleural mesothelioma and non-small cell lung cancer (NSCLC). We report two cases of a new toxicity induced by pemetrexed: scleroderma-like induration of the lower extremities., Patients and Methods: The first case concerned a 66-year-old man diagnosed with pulmonary adenocarcinoma metastatic from the outset and in whom maintenance treatment comprised pemetrexed after first-line therapy comprising six courses of cisplatin-pemetrexed. After the fourth cycle of pemetrexed, he presented an erythematous oedema of the left leg, which was subsequently bilateral. Clinically, there was painful cellulitis associated with areas of bruising. The lesions had an appearance of erysipeloid-like infection, and there was no fever. The second case concerned a 70-year-old woman diagnosed with metastatic NSCLC. From the first course of pemetrexed, given as maintenance therapy, she presented erythematous oedema of both legs, without fever. After the second course, we observed the recurrence of the lesions consisting of erythemato-violaceous plaques on both legs, with severe bilateral indurated and painful oedema, associated with major functional disability. A diagnosis of bilateral erysipelas was made, and antibiotic treatment with cloxacillin was given. In both cases, pemetrexed was discontinued and the local outcome was very slowly favourable, with persistence of scleroderma., Discussion: This cutaneous adverse effect is unrecognized, resulting in delayed diagnosis. It is often initially confused with bilateral erysipelas, despite absence of fever. According to some studies, the severity of the cutaneous toxicity may be connected with patients' folate status. Thus folate and vitamin B12 supplementation combined with dexamethasone could decrease the incidence of this side effect. There was no recurrence and no worsening with taxanes, chemotherapy agents known to induce scleroderma. We feel that this cutaneous toxicity must be recognised on account of its potential severity., (Copyright © 2014 Elsevier Masson SAS. All rights reserved.)