Methotrexate and Ras Methylation: A New Trick for an Old Drug?

Reintroduction of immunosuppressive medications in pediatric rheumatology patients with histoplasmosis: a case series

BACKGROUND

Children with rheumatic diseases (cRD) receiving immunosuppressive medications (IM) are at a higher risk for acquiring potentially lethal pathogens, including Histoplasma capsulatum (histoplasmosis), a fungal infection that can lead to prolonged hospitalization, organ damage, and death. Withholding IM during serious infections is recommended yet poses risk of rheumatic disease flares. Conversely, reinitiating IM increases risk for infection recurrence. Tumor necrosis factor alpha inhibitor (TNFai) biologic therapy carries the highest risk for histoplasmosis infection after epidemiological exposure, so other IM are preferred during active histoplasmosis infection. There is limited guidance as to when and how IM can be reinitiated in cRD with histoplasmosis. This case series chronicles resumption of IM, including non-TNFai biologics, disease-modifying anti-rheumatic drugs (DMARDs), and corticosteroids, following histoplasmosis among cRD.

CASE PRESENTATION

We examine clinical characteristics and outcomes of 9 patients with disseminated or pulmonary histoplasmosis and underlying rheumatic disease [juvenile idiopathic arthritis (JIA), childhood-onset systemic lupus erythematosus (cSLE), and mixed connective tissue disease (MCTD)] after reintroduction of IM. All DMARDs and biologics were halted at histoplasmosis diagnosis, except hydroxychloroquine (HCQ), and patients began antifungals. Following IM discontinuation, all patients required systemic or intra-articular steroids during histoplasmosis treatment, with 4/9 showing Cushingoid features. Four patients began new IM regimens [2 abatacept (ABA), 1 HCQ, and 1 methotrexate (MTX)] while still positive for histoplasmosis, with 3/4 (ABA, MTX, HCQ) later clearing their histoplasmosis and 1 (ABA) showing decreasing antigenemia. Collectively, 8/9 patients initiated or continued DMARDs and/or non-TNFai biologic use (5 ABA, 1 tocilizumab, 1 ustekinumab, 3 MTX, 4 HCQ, 1 leflunomide). No fatalities, exacerbations, or recurrences of histoplasmosis occurred during follow-up (median 33 months).

CONCLUSIONS

In our cohort of cRD, histoplasmosis course following reintroduction of non-TNFai IM was favorable, but additional studies are needed to evaluate optimal IM management during acute histoplasmosis and recovery. In this case series, non-TNFai biologic, DMARD, and steroid treatments did not appear to cause histoplasmosis recurrence. Adverse events from corticosteroid use were common. Further research is needed to implement guidelines for optimal use of non-TNFai (like ABA), DMARDs, and corticosteroids in cRD following histoplasmosis presentation.

Metformin induces a fasting- and antifolate-mimicking modification of systemic host metabolism in breast cancer patients

Certain dietary interventions might improve the therapeutic index of cancer treatments. An alternative to the “drug plus diet” approach is the pharmacological reproduction of the metabolic traits of such diets. Here we explored the impact of adding metformin to an established therapeutic regimen on the systemic host metabolism of cancer patients. A panel of 11 serum metabolites including markers of mitochondrial function and intermediates/products of folate-dependent one-carbon metabolism were measured in paired baseline and post-treatment sera obtained from HER2-positive breast cancer patients randomized to receive either metformin combined with neoadjuvant chemotherapy and trastuzumab or an equivalent regimen without metformin. Metabolite profiles revealed a significant increase of the ketone body β-hydroxybutyrate and of the TCA intermediate α-ketoglutarate in the metformin-containing arm. A significant relationship was found between the follow-up levels of homocysteine and the ability of treatment arms to achieve a pathological complete response (pCR). In the metformin-containing arm, patients with significant elevations of homocysteine tended to have a higher probability of pCR. The addition of metformin to an established anti-cancer therapeutic regimen causes a fasting-mimicking modification of systemic host metabolism. Circulating homocysteine could be explored as a clinical pharmacodynamic biomarker linking the antifolate-like activity of metformin and biological tumor response.

Methotrexate and Pralatrexate

This article reviews methotrexate and the more potent, related compound, pralatrexate, for the treatment of cutaneous T-cell lymphomas, including mycosis fungoides, Sézary syndrome, and CD30+ lymphoproliferative disorders. Although these folate antagonists are traditionally viewed as antiproliferative cell cycle inhibitors, it is recognized that they inhibit DNA methylation, providing a rationale for their use as epigenetic regulators and cell proliferation inhibitors. The underlying mechanisms are outlined, key supporting data presented, followed by brief mention of recent mathematical modeling supporting the general superiority of combination therapy. Several novel examples involving folate antagonists are proposed.

Methotrexate inhibits the viability of human melanoma cell lines and enhances Fas/Fas-ligand expression, apoptosis and response to interferon-alpha: rationale for its use in combination therapy

Melanoma, a highly aggressive form of cancer, is notoriously resistant to available therapies. Methotrexate (MTX), an antifolate, competitively inhibits DNA synthesis and is effective for several types of cancer. In cutaneous T-cell lymphoma (CTCL), MTX increases Fas death receptor by decreasing Fas promoter methylation by blocking the synthesis of SAM, the principal methyl donor for DNMTs, resulting in enhanced Fas-mediated apoptosis. The objective of this study was to explore the effects of MTX in human melanoma. MTX variably inhibited the survival of melanoma cells and induced apoptosis as evident by annexin V positivity and senescence associated β-galactosidase activity induction. Furthermore, MTX caused increased transcript and protein levels of extrinsic apoptotic pathway factors Fas and Fas-ligand, albeit at different levels in different cell lines. Our pyrosequencing studies showed that this increased expression of Fas was associated with Fas promoter demethylation. Overall, the ability of MTX to up-regulate Fas/FasL and enhance melanoma apoptosis through extrinsic as well as intrinsic pathways might make it a useful component of novel combination therapies designed to affect multiple melanoma targets simultaneously. In support of this concept, combination therapy with MTX and interferon-alpha (IFNα) induced significantly greater apoptosis in the aggressive A375 cell line than either agent alone.

Targeting the epigenetic machinery of cancer cells

Cancer is characterized by uncontrolled cell growth and the acquisition of metastatic properties. In most cases, the activation of oncogenes and/or deactivation of tumour suppressor genes lead to uncontrolled cell cycle progression and inactivation of apoptotic mechanisms. Although the underlying mechanisms of carcinogenesis remain unknown, increasing evidence links aberrant regulation of methylation to tumourigenesis. In addition to the methylation of DNA and histones, methylation of nonhistone proteins, such as transcription factors, is also implicated in the biology and development of cancer. Because the metabolic cycling of methionine is a key pathway for many of these methylating reactions, strategies to target the epigenetic machinery of cancer cells could result in novel and efficient anticancer therapies. The application of these new epigenetic therapies could be of utility in the promotion of E2F1-dependent apoptosis in cancer cells, in avoiding metastatic pathways and/or in sensitizing tumour cells to radiotherapy.

DNA methylation regulates cocaine-induced behavioral sensitization in mice

The behavioral sensitization produced by repeated cocaine treatment represents the neural adaptations underlying some of the features of addiction in humans. Cocaine administrations induce neural adaptations through regulation of gene expression. Several studies suggest that epigenetic modifications, including DNA methylation, are the critical regulators of gene expression in the adult central nervous system. DNA methylation is catalyzed by DNA methyltransferases (DNMTs) and consequent promoter region hypermethylation is associated with transcriptional silencing. In this study a potential role for DNA methylation in a cocaine-induced behavioral sensitization model in mice was explored. We report that acute cocaine treatment caused an upregulation of DNMT3A and DNMT3B gene expression in the nucleus accumbens (NAc). Using methylated DNA immunoprecipitation, DNA bisulfite modification, and chromatin immunoprecipitation assays, we observed that cocaine treatment resulted in DNA hypermethylation and increased binding of methyl CpG binding protein 2 (MeCP2) at the protein phosphatase-1 catalytic subunit (PP1c) promoter. These changes are associated with transcriptional downregulation of PP1c in NAc. In contrast, acute and repeated cocaine administrations induced hypomethylation and decreased binding of MeCP2 at the fosB promoter, and these are associated with transcriptional upregulation of fosB in NAc. We also found that pharmacological inhibition of DNMT by zebularine treatment decreased cocaine-induced DNA hypermethylation at the PP1c promoter and attenuated PP1c mRNA downregulation in NAc. Finally, zebularine and cocaine co-treatment delayed the development of cocaine-induced behavioral sensitization. Together, these results suggest that dynamic changes of DNA methylation may be an important gene regulation mechanism underlying cocaine-induced behavioral sensitization.

DNA methylation-mediated nucleosome dynamics and oncogenic Ras signaling: insights from FAS, FAS ligand and RASSF1A

Cytosine methylation at the 5-carbon position is the only known stable base modification found in the mammalian genome. The organization and modification of chromatin is a key factor in programming gene expression patterns. Recent findings suggest that DNA methylation at the junction of transcription initiation and elongation plays a critical role in suppression of transcription. This effect is mechanistically mediated by the state of chromatin modification. DNA methylation attracts binding of methyl-CpG-binding domain proteins that trigger repression of transcription, whereas DNA demethylation facilitates transcription activation. Understanding the rules that guide differential gene expression, as well as transcription dynamics and transcript abundance, has proven to be a taxing problem for molecular biologists and oncologists alike. The use of novel molecular modeling methods is providing exciting insights into the challenging problem of how methylation mediates chromatin dynamics. New data implicate lipid rafts as the coordinators of signals emanating from the cell membrane and are converging on the mechanisms linking DNA methylation and chromatin dynamics. This review focuses on some of these recent advances and uses lipid-raft-facilitated Ras signaling as a paradigm for understanding DNA methylation, chromatin dynamics and apoptosis.

Ras regulation of DNA-methylation and cancer

Genome wide hypomethylation and regional hypermethylation of cancer cells and tissues remain a paradox, though it has received a convincing confirmation that epigenetic switching systems, including DNA-methylation represent a fundamental regulatory mechanism that has an impact on genome maintenance and gene transcription. Methylated cytosine residues of vertebrate DNA are transmitted by clonal inheritance through the strong preference of DNA methyltransferase, DNMT1, for hemimethylated-DNA. Maintenance of methylation patterns is necessary for normal development of mice, and aberrant methylation patterns are associated with many human tumours. DNMT1 interacts with many proteins during cell cycle progression, including PCNA, p53, EZH2 and HP1. Ras family of GTPases promotes cell proliferation by its oncogenic nature, which transmits signals by multiple pathways in both lipid raft dependent and independent fashion. DNA-methylation-mediated repression of DNA-repair protein O6-methylguanine DNA methyltransferase (MGMT) gene and increased rate of K-Ras mutation at codon for amino acids 12 and 13 have been correlated with a secondary role for Ras-effector homologues (RASSFs) in tumourigenesis. Lines of evidence suggest that DNA-methylation associated repression of tumour suppressors and apoptotic genes and ceaseless proliferation of tumour cells are regulated in part by Ras-signaling. Control of Ras GTPase signaling might reduce the aberrant methylation and accordingly may reduce the risk of cancer development.

10 Genetic approaches to understanding the physiologic importance of the carboxyl methylation of isoprenylated proteins

This chapter examines recent studies on the physiologic importance of the carboxyl methylation of isoprenylated proteins, focusing largely on what has been learned from cells lacking the Icmt methyltransferase. Proteins terminating with a CaaX motif (e.g., the nuclear lamins, the Ras family of proteins) undergo posttranslational modification of a carboxyl-terminal cysteine with an isoprenyl lipid (a process generally called protein isoprenylation or protein prenylation). Following this lipidation step, CaaX proteins generally undergo two additional processing steps: endoproteolytic release of the last three residues of the protein (i.e., the -aaX of the CaaX motif) and methylesterification of the newly exposed isoprenylcysteine a-carboxyl group. The CaaX proteins are not, however, the only prenylated proteins that undergo carboxyl methylation. A subset of the Rab family of proteins, those terminating with a CXC motif, undergo methylesterification of a carboxyl-terminal geranylgeranylcysteine. The methylation of CaaX proteins and the CXC Rab proteins is carried out by a single membrane methyltransferase of the endoplasmic reticulum, Icmt (for isoprenylcysteine carboxyl methyltransferase). Many studies have shown that protein prenylation is essential for the proper intracellular targeting and function of numerous intracellular proteins, but the physiologic importance of the carboxyl methylation step has remained less certain. Here, we review recent studies that have shed light on the importance of carboxyl methylation of prenylated proteins.

Therapeutic intervention based on protein prenylation and associated modifications

In eukaryotic cells, a specific set of proteins are modified by C-terminal attachment of 15-carbon farnesyl groups or 20-carbon geranylgeranyl groups that function both as anchors for fixing proteins to membranes and as molecular handles for facilitating binding of these lipidated proteins to other proteins. Additional modification of these prenylated proteins includes C-terminal proteolysis and methylation, and attachment of a 16-carbon palmitoyl group; these modifications augment membrane anchoring and alter the dynamics of movement of proteins between different cellular membrane compartments. The enzymes in the protein prenylation pathway have been isolated and characterized. Blocking protein prenylation is proving to be therapeutically useful for the treatment of certain cancers, infection by protozoan parasites and the rare genetic disease Hutchinson-Gilford progeria syndrome.

Farnesyltransferase inhibitors and human malignant pleural mesothelioma: a first-step comparative translational study

It is known that the potential clinical use of farnesyltransferase inhibitors (FTI) could be expanded to include cancers harboring activated receptor tyrosine kinases. Approximately 70% of malignant pleural mesotheliomas (MPM) overexpress epidermal growth factor receptors (EGFR) and a subset express both EGFR and transforming growth factor alpha (TGF-alpha), suggesting an autocrine role for EGFR in MPM. We checked on MPM cells (10 human cell lines, 11 primary cultures obtained by human biopsies, and 7 short-term normal mesothelial cell cultures) concerning the following: (a) the relative overexpression of EGFR (Western blotting, flow cytometry, immunohistochemistry), (b) the relative expression of EGFR ligands (EGF, amphiregulin, TGF-alpha, ELISA), (c) the relative increase of the activated form of Ras (Ras-bound GTP) after EGF stimulation (Ras activation assay), (d) the efficacy of five different FTIs (HDJ2 prenylation, cell cytotoxicity, and apoptosis using ApopTag and gel ladder). EGFR was overexpressed in MPM cells compared with normal pleural mesothelial cells in equivalent levels as in non-small cell lung cancer cells A459. MPM cells constitutively expressed EGFR ligands; however, Ras activation was attenuated at high EGF concentrations (100 ng/mL). Growth of MPM cells was substantially not affected by treatment with different FTIs (SCH66336, BMS-214662, R115777, RPR-115135, and Manumycin). Among these, BMS-214662 was the only one moderately active. BMS-214662 triggered apoptosis in a small fraction of cells (not higher than 30%) that was paralleled by a slight decrease in the levels of TGF-alpha secreted by treated MPM cells. Our data highlighted the concept that the same signaling pathway can be regulated in different ways and these regulations can differ between different cells of different origin.