Role of MGMT in protecting against cyclophosphamide-induced toxicity in cells and animals

Protective potential of pterostilbene against cyclophosphamide-induced nephrotoxicity and cystitis in rats

PURPOSE

Cyclophosphamide (CYP) is an antitumor drug. However, in addition to its antitumor affect, CYP can also lead to nephrotoxicity and hemorrhagic cystitis. The purpose of this study was to investigate the potential protective effects of Pterostilbene (Pte), a natural antioxidant as a resveratrol analog against CYP-induced nephrotoxicity and cystitis in rats.

METHODS

Twenty-one male Sprague Dawley rats were divided into 3 equal groups. The control group and the CYP group (CYPG) received 1 ml/kg sunflower oil per day, and the CYP + Pte group (CYP + PteG) 40 mg/kg per day Pte dissolved in sunflower oil once a day via the oral route for 14 days. In addition, on day 9 of the experiment, CYPG and CYP + PteG received a single dose of 200 mg/kg CYP dissolved in saline solution, while the control group received a single dose of 10 ml/kg saline solution, via the intraperitoneal route. Bladder and kidney tissues were collected for histological and biochemical evaluations.

RESULTS

Pte was observed to reduce CYP-derived increases in malondialdehyde level, total oxidant status (TOS), the oxidative stress index (OSI), and apoptosis in kidney tissues and to cause an increase in superoxide dismutase levels. It also reduced CYP-derived increases in TOS, OSI, and apoptosis in bladder tissue. Moreover, Pte also ameliorated histopathological findings associated with CYP-induced tissue damage in both the kidney and bladder.

CONCLUSION

Our study findings show that Pte may exhibit a protective effect against CYP-induced nephrotoxicity and cystitis.

Efflux Capacity and Aldehyde Dehydrogenase Both Contribute to CD8+ T-cell Resistance to Posttransplant Cyclophosphamide

CD8⁺ T cells increase drug effluxing and aldehyde dehydrogenase expression in allogeneic reactions, enhancing resistance to cyclophosphamide.

Common γ-chain cytokines and the proliferative state of the cell modulate these resistance pathways.

Mechanisms of T-cell survival after cytotoxic chemotherapy, including posttransplantation cyclophosphamide (PTCy), are not well understood. Here, we explored the impact of PTCy on human CD8⁺ T-cell survival and reconstitution, including what cellular pathways drive PTCy resistance. In major histocompatibility complex (MHC)-mismatched mixed lymphocyte culture (MLC), treatment with mafosfamide, an in vitro active cyclophosphamide analog, preserved a relatively normal distribution of naïve and memory CD8⁺ T cells, whereas the percentages of mucosal-associated invariant T (MAIT) cells and phenotypically stem cell memory (Tscm) T-cell subsets were increased. Activated (CD25⁺) and proliferating CD8⁺ T cells were derived from both naïve and memory subsets and were reduced but still present after mafosfamide. By contrast, cyclosporine-A (CsA) or rapamycin treatment preferentially maintained nonproliferating CD25⁻ naïve cells. Drug efflux capacity and aldehyde dehydrogenase-1A1 expression were increased in CD8⁺ T cells in allogeneic reactions in vitro and in patients, were modulated by common γ-chain cytokines and the proliferative state of the cell, and contributed to CD8⁺ T-cell survival after mafosfamide. The CD8⁺ T-cell composition early after hematopoietic cell transplantation (HCT) in PTCy-treated patients was dominated by CD25⁺ and phenotypically memory, including Tscm and MAIT, cells, consistent with MLC. Yet, MHC-mismatched murine HCT studies revealed that peripherally expanded, phenotypically memory T cells 1 to 3 months after transplant originated largely from naïve-derived rather than memory-derived T cells surviving PTCy, suggesting that initial resistance and subsequent immune reconstitution are distinct. These studies provide insight into the complex immune mechanisms active in CD8⁺ T-cell survival, differentiation, and reconstitution after cyclophosphamide, with relevance for post-HCT immune recovery, chemotherapy use in autologous settings, and adoptive cellular therapies.

Annotation of 1350 Common Genetic Variants of the 19 ALDH Multigene Family from Global Human Genome Aggregation Database (gnomAD)

Human aldehyde dehydrogenase (ALDH) is a multigene family with 19 functional members encoding a class of diverse but important enzymes for detoxification or biotransformation of different endogenous and exogenous aldehyde substrates. Genetic mutations in the ALDH genes can cause the accumulation of toxic aldehydes and abnormal carbonyl metabolism and serious human pathologies. However, the physiological functions and substrate specificity of many ALDH genes are still unknown. Although many genetic variants of the ALDH gene family exist in human populations, their phenotype or clinical consequences have not been determined. Using the most comprehensive global human Genome Aggregation Database, gnomAD, we annotated here 1350 common variants in the 19 ALDH genes. These 1350 common variants represent all known genetic polymorphisms with a variant allele frequency of ≥0.1% (or an expected occurrence of ≥1 carrier per 500 individuals) in any of the seven major ethnic groups recorded by gnomAD. We detailed 13 types of DNA sequence variants, their genomic positions, SNP ID numbers, and allele frequencies among the seven major ethnic groups worldwide for each of the 19 ALDH genes. For the 313 missense variants identified in the gnomAD, we used two software algorithms, Polymorphism Phenotyping (PolyPhen) and Sorting Intolerant From Tolerant (SIFT), to predict the consequences of the variants on the structure and function of the enzyme. Finally, gene constraint analysis was used to predict how well genetic mutations were tolerated by selection forces for each of the ALDH genes in humans. Based on the ratio of observed and expected variant numbers in gnomAD, the three ALDH1A gene members, ALDH1A1, ALDH1A2, and ALDH1A3, appeared to have the lowest tolerance for loss-of-function mutations as compared to the other ALDH genes (# observed/# expected ratio 0.15–0.26). These analyses suggest that the ALDH1A1, ALDH1A2, and ALDH1A3 enzymes may serve a more essential function as compared with the other ALDH enzymes; functional loss mutations are much less common in healthy human populations than expected. This informatic analysis may assist the research community in determining the physiological function of ALDH isozymes and associate common variants with clinical phenotypes.

Acrolein measurement and degradation in Dulbecco's Modified Eagle Medium: an examination of in-vitro exposure metrics

Acrolein is a reactive α,β-unsaturated aldehyde known for its adduction to endogenous biomolecules, resulting in initiation or exacerbation of several disease pathways. In-vitro systems are routinely used to elucidate the cytotoxic or mechanistic role(s) of acrolein in pathogenesis. Nevertheless, the half-life of acrolein in biological or in-vitro systems, e.g. blood or culture media, has not been well characterized. Since in-vitro cytotoxic and mechanistic investigations routinely expose cultures to acrolein from 1 hour to 72 hours, we aimed to characterize the half-life of acrolein in culture medium to ascertain the plausible exposure window. Half-life determinations were conducted in low-serum DMEM at room temperature and 37 °C, both with and without H9c2 cells. For quantitative assessment, acrolein was derivatized to a fluorescent 7-hydroxyquinoline method validated in-house and assessed via fluorescent spectroscopy. In closed vessel experiments at room temperature, acrolein in DMEM was reduced by more than 40% at 24 hours, irrespective of the initial concentration. Expectedly, open vessel experiments demonstrated accelerated depletion over time at room temperature, and faster still at 37 °C. The presence of cells tended to further accelerate degradation by an additional 15-30%, depending on temperature. These results undermine described experimental exposure conditions stated in most in-vitro experiments. Recognition of this discrepancy between stated and actual exposure metrics warrant examination of novel alternative objective and representative exposure characterization for in-vitro studies to facilitate translation to in-vivo and in-silico methods.

New insights into estrogenic regulation of O6-methylguanine DNA-methyltransferase (MGMT) in human breast cancer cells: Co-degradation of ER-α and MGMT proteins by fulvestrant or O6-benzylguanine indicates fresh avenues for therapy

Endocrine therapy using estrogen receptor-α (ER-α) antagonists for attenuating horm2one-driven cell proliferation is a major treatment modality for breast cancers. To exploit any DNA repair deficiencies associated with endocrine therapy, we investigated the functional and physical interactions of ER-α with O6-methylguanine DNA methyltransferase (MGMT), a unique DNA repair protein that confers tumor resistance to various anticancer alkylating agents. The ER-α -positive breast cancer cell lines (MCF-7, T47D) and ER- negative cell lines (MDAMB-468, MDAMB-231), and established inhibitors of ER-α and MGMT, namely, ICI-182,780 (Faslodex) and O6-benzylguanine, respectively, were used to study MGMT- ER interactions. The MGMT gene promoter was found to harbor one full and two half estrogen-responsive elements (EREs) and two antioxidant-responsive elements (AREs). MGMT expression was upregulated by estrogen, downregulated by tamoxifen in Western blot and promoter-linked reporter assays. Similarly, both transient and stable transfections of Nrf-2 (nuclear factor-erythroid 2-related factor-2) increased the levels of MGMT protein and activity 3 to 4-fold reflecting novel regulatory nodes for this drug-resistance determinant. Of the different ER-α antagonists tested, the pure anti-estrogen fulvestrant was most potent in inhibiting the MGMT activity in a dose, time and ER-α dependent manner, similar to O6-benzylguanine. Interestingly, fulvestrant exposure led to a degradation of both ER-α and MGMT proteins and O6-benzylguanine also induced a specific loss of ER-α and MGMT proteins in MCF-7 and T47D breast cancer cells with similar kinetics. Immunoprecipitation revealed a specific association of ER-α and MGMT proteins in breast cancer cells. Furthermore, silencing of MGMT gene expression triggered a decrease in the levels of both MGMT and ER-α proteins. The involvement of proteasome in the drug-induced degradation of both proteins was also demonstrated. Fulvestrant enhanced the cytotoxicity of MGMT-targeted alkylating agents, namely, temozolomide and BCNU by 3 to 4-fold in ER-α positive cells, but not in ER-negative cells. We conclude that MGMT and ER-α proteins exist as a complex and are co-targeted for ubiquitin-conjugation and subsequent proteasomal degradation. The findings offer a clear rationale for combining alkylating agents with endocrine therapy.

Protective effect of mirtazapine and hesperidin on cyclophosphamide-induced oxidative damage and infertility in rat ovaries

Cyclophosphamide (CP) causes infertility due to ovarian toxicity. The toxicity mechanism suggests oxidative stress. We assessed whether mirtazapine (MTZ) and hesperidin (HSP) could promote ovarian protection against damage due to CP chemotherapy. Female Wistar rats aged 14 weeks were used. Animals were divided into four groups: control vehicle group (n = 8); CP group (n = 8, rats received 150 mg/kg of CP, single intraperitoneal [i.p.] injection); CP + MTZ group (n = 8, rats received same dose of CP + 30 mg/kg of MTZ, orally, daily); and HSP + CP group (n = 8, rats received same dose of CP + 100 mg/kg of HSP, orally, daily). After eight days of medication, ovaries were removed and ovarian toxicity was assessed by counting follicles and corpora lutea. Nitric oxide (NO) and malondialdehyde (MDA) levels, myeloperoxidase (MPO), glutathione peroxidase (GPx), and superoxide dismutase (SOD) activities were estimated in ovarian tissue. NO level, MDA level, and MPO activity were increased (P < 0.001), while, GPx and SOD activities were lowered significantly (P < 0.001) in CP-treated group compared with control vehicle. In addition, ovulation, number of follicles, and ovarian weight were reduced by CP treatment. On the contrary, rats pretreated with MTZ and HSP showed significant decrease in NO, MDA levels, and MPO activity, while, activities of SOD and GPx were increased (P < 0.001). Oxidative stress induced by CP in the rat ovary causes infertility in the female rats. HSP and MTZ could reverse this effect and provide protection of fertility against CP-induced toxicity.

O6-methylguanine-DNA methyltransferase as a prognostic and predictive marker for basal-like breast cancer treated with cyclophosphamide-based chemotherapy

The O⁶-methylguanine-DNA methyltransferase (MGMT) protein protects cells from alkylating agents by removing alkyl groups from the O⁶-position of guanine. However, its effect on DNA damage induced by cyclophosphamide (CPM) is unclear. The present study investigated whether MGMT expression was correlated with prognosis in patients with breast cancer that was managed according to a common therapeutic protocol or treated with CPM-based chemotherapy. The intrinsic subtypes and MGMT protein expression levels were assessed in 635 consecutive patients with breast cancer using immunohistochemistry. In total, 425 (67%) luminal A, 95 (15%) luminal B, 47 (7%) human epidermal growth factor receptor-2⁺/estrogen receptor^- (HER2⁺/ER^-) and 48 (8%) basal-like subtypes were identified. Of these, MGMT positivity was identified in 398 (63%) of 635 breast cancers; 68% of luminal A, 67% of luminal B, 30% of HER2⁺/ER^- and 46% of basal-like subtypes were positive. The overall survival (OS) and disease-free survival (DFS) rates did not significantly differ according to the MGMT status among patients with luminal A, luminal B or HER2⁺/ER^- subtypes, and patients with MGMT-negative basal-like cancers tended to have a longer DFS, but not a significantly longer OS time. CPM-containing chemotherapy was administered to 26%, 40%, 47% and 31% of patients with luminal A, luminal B, HER2⁺/ER^- and basal-like tumors, respectively. Although the MGMT status and clinical outcomes of patients with the luminal A, luminal B or HER2⁺/ER^- subtypes treated with CPM were not significantly correlated, the patients with MGMT-negative basal-like tumors who received CPM exhibited significantly improved DFS and OS compared with the CPM-treated patients with MGMT-positive tumors. MGMT may be a useful prognostic and predictive marker for CPM-containing chemotherapy in basal-like breast cancer.

Labeled oxazaphosphorines for applications in mass spectrometry studies. 2. Synthesis of deuterium-labeled 2-dechloroethylcyclophosphamides and 2- and 3-dechloroethylifosfamides

The prodrugs cyclophosphamide (CP) and ifosfamide (IF) each metabolize to an active alkylating agent through a cytochrome P450-mediated oxidation at the C-4 position. Competing with this activation pathway are enzymatic oxidations at the exocyclic α and α' carbons, which result in dechloroethylation of CP and IF. The incidence of oxidation at one position relative to another is believed to be at least one factor underlying the high degree of interpatient variability in both CP and IF pharmacokinetics. As standards for the mass spectrometry quantification of dechloroethylation, the following were synthesized: (1) [4,4,5,5-(2) H4 ]-2-dechloroethylcyclophosphamide (equivalent to [4,4,5,5-(2) H4 ]-3-dechloroethylifosfamide); (2) [α,α,4,4,5,5-(2) H6 ]-2-dechloroethylcyclophosphamide (equivalent to [α,α,4,4,5,5-(2) H6 ]-3-dechloroethylifosfamide); and (3) [α,α,4,4,5,5-(2) H6 ]-2-dechloroethylifosfamide. The common precursor to all of the target compounds was [2,2,3,3-(2) H4 ]-3-aminopropanol. A one-pot reaction of this compound with POCl3 and unlabeled or labeled 2-chloroethylamine hydrochloride gave the d4 and d6 labeled 2-dechloroethylcyclophosphamides. The construction of the 2-dechloroethylifosfamide from the aminopropanol required five discreet steps. Optimization of the synthetic pathways and stability studies are discussed.

The cytogenetic action of ifosfamide, mesna, and their combination on peripheral rabbit lymphocytes: an in vivo/in vitro cytogenetic study

Ifosfamide (IFO) is an alkylating nitrogen mustard, administrated as an antineoplasmic agent. It is characterized by its intense urotoxic action, leading to hemorrhagic cystitis. This side effect of IFO raises the requirement for the co-administration with sodium 2-sulfanylethanesulfonate (Mesna) aiming to avoid or minimize this effect. IFO and Mesna were administrated separately on rabbit's lymphocytes in vivo, which were later developed in vitro. Cytogenetic markers for sister chromatid exchanges (SCEs), proliferation rate index (PRI) and Mitotic Index were recorded. Mesna's action, in conjunction with IFO reduces the frequency of SCEs, in comparison with the SCEs recordings obtained when IFO is administered alone. In addition to this, when high concentrations of Mesna were administered alone significant reductions of the PRI were noted, than with IFO acting at the same concentration on the lymphocytes. Mesna significantly reduces IFO's genotoxicity, while when administered in high concentrations it acts in an inhibitory fashion on the cytostatic action of the drug.

Role of pharmacogenetics in busulfan/cyclophosphamide conditioning therapy prior to hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) is a curative treatment for several malignant and nonmalignant disorders. Busulfan (Bu) and cyclophosphamide (Cy) are the most commonly used alkylators in high-dose pretransplant conditioning for HSCT; a treatment that is correlated with drug-related toxicity and relapse. Pharmacogenetic investigations have shown that CYP450, as well as aldehyde dehydrogenase, are clearly involved with Cy metabolism and are associated with altered treatment response, Cy metabolism and the unique stem-cell sparing capacity. Moreover, glutathione-S-transferase isoenzymes have been associated with cellular outward transport of various alkylating agents, including Cy metabolites, melphalan, Bu and chlorambucil. A shift from genetic-based studies to whole-genome-based investigations of Cy- and Bu-associated markers may contribute to personalizing the conditioning therapy and enhancing the clinical outcome of HSCT.

Acrolein induced DNA damage, mutagenicity and effect on DNA repair

Acrolein (Acr) is a ubiquitous environmental contaminant; it also can be generated endogenously by lipid peroxidation. Acr contains a carbonyl group and an olefinic double bond; it can react with many cellular molecules including amino acids, proteins and nucleic acids. In this review article we focus on updating information regarding: (i) Acr-induced DNA damage and methods of detection, (ii) repair of Acr-DNA damage, (iii) mutagenicity of Acr-DNA adducts, (iv) sequence specificity and methylation effect on Acr-DNA adduct formation and (v) the role of Acr in human cancer. We have found that Acr can inhibit DNA repair and induces mutagenic Acr-dG adducts and that the binding spectrum of Acr in the p53 gene in normal human bronchial epithelial cells is similar to the p53 mutational spectrum in lung cancer. Since Acr-DNA adduct has been identified in human lung tissue and Acr causes bladder cancer in human and rat models, we conclude that Acr is a major lung and bladder carcinogen, and its carcinogenicity arises via induction of DNA damage and inhibition of DNA repair.

Cross-linking of the DNA repair protein Omicron6-alkylguanine DNA alkyltransferase to DNA in the presence of antitumor nitrogen mustards

The antitumor activity of chemotherapeutic nitrogen mustards including chlorambucil, cyclophosphamide, and melphalan is commonly attributed to their ability to induce DNA-DNA cross-links by consecutive alkylation of two nucleophilic sites within the DNA duplex. DNA-protein cross-linking by nitrogen mustards is not well characterized, probably because of its inherent complexity and the insufficient sensitivity of previous methodologies. If formed, DNA-protein conjugates are likely to contribute to both target and off-target cytotoxicity of nitrogen mustard drugs. Here, we show that the DNA repair protein, O (6)-alkylguanine DNA alkyltransferase (AGT), can be readily cross-linked to DNA in the presence of nitrogen mustards. Both chlorambucil and mechlorethamine induced the formation of covalent conjugates between (32)P-labeled double-stranded oligodeoxynucleotides and recombinant human AGT protein, which were detected by SDS-PAGE. Capillary HPLC-electrospray ionization mass spectrometry (ESI-MS) analysis of AGT that had been treated with the guanine half-mustards of chlorambucil or mechlorethamine revealed the ability of the protein to form either one or two cross-links to guanine. C145A AGT (a variant containing a single point mutation in the protein's active site) was found capable of forming a single guanine conjugate, while cross-linking was virtually abolished upon treatment of the C145A/C150S AGT double mutant with the guanine half-mustards. HPLC-ESI (+)-MS/MS sequencing of tryptic peptides obtained from the wild-type AGT protein that had been treated with nitrogen mustards in the presence of DNA confirmed that the cross-linking took place between the N7 position of guanine in DNA and two active site residues within the AGT protein (Cys (145) and Cys (150)). The exact chemical structures of AGT-DNA cross-links induced by chlorambucil and mechlorethamine were identified as N-(2-[ S-cysteinyl]ethyl)- N-(2-[guan-7-yl]ethyl)- p-aminophenylbuyric acid and N-(2-[ S-cysteinyl]ethyl)- N-(2-[guan-7-yl]ethyl)methylamine, respectively, based upon HPLC-MS/MS analysis of protein hydrolysates in parallel with the corresponding amino acid conjugates prepared synthetically. Mechlorethamine-induced AGT-DNA conjugates were isolated from protein extracts of AGT-expressing CHO cells but not control cells, demonstrating that nitrogen mustards can cross-link the AGT protein to DNA in the presence of other nuclear proteins. Because AGT is overexpressed in many tumor types, further investigations of the potential role of AGT-DNA cross-linking in the antitumor and mutagenic activity of antitumor nitrogen mustards are warranted.