thioguanine-anhydrous and Skin-Neoplasms

The thiopurines azathioprine, 6-mercaptopurine and 6-thioguanine (6-TG) are important medications for cancer and inflammatory disorders. They are also widely prescribed as immunosuppressants in organ transplant patients. Their metabolism results in the incorporation of 6-TG into patients' DNA, and this increases skin sensitivity to incident UVA. Unlike the canonical DNA bases, which do not absorb UVA to a significant degree, DNA 6-TG is a strong UVA chromophore. It acts as a Type II UVA photosensitizer, and the combination of 6-TG and UVA treatment induces a synergistic toxicity in cultured human cells. Here, we review some of the damage that this interaction causes. Photochemical activation of DNA 6-TG triggers DNA and protein oxidation; it induces DNA breakage, DNA crosslinking, oxidation of DNA bases and the covalent attachment of proteins to DNA. Many of these photochemical DNA lesions are difficult for cells to deal with, and we review the evidence linking thiopurine immunosuppression with genome instability and the high incidence of skin cancer in organ transplant recipients.

Topics: Azathioprine; Humans; Immunosuppressive Agents; Mercaptopurine; Photosensitizing Agents; Skin Neoplasms; Thioguanine; Ultraviolet Rays

Nucleotide excision repair (NER) protects against sunlight-induced skin cancer. Defective NER is associated with photosensitivity and a high skin cancer incidence. Some clinical treatments that cause photosensitivity can also increase skin cancer risk. Among these, the immunosuppressant azathioprine and the fluoroquinolone antibiotics ciprofloxacin and ofloxacin interact with UVA radiation to generate reactive oxygen species that diminish NER capacity by causing protein damage. The replication protein A (RPA) DNA-binding protein has a pivotal role in DNA metabolism and is an essential component of NER. The relationship between protein oxidation and NER inhibition was investigated in cultured human cells expressing different levels of RPA. We show here that RPA is limiting for NER and that oxidative damage to RPA compromises NER capability. Our findings reveal that cellular RPA is surprisingly vulnerable to oxidation, and we identify oxidized forms of RPA that are associated with impaired NER. The vulnerability of NER to inhibition by oxidation provides a connection between cutaneous photosensitivity, protein damage, and increased skin cancer risk. Our findings emphasize that damage to DNA repair proteins, as well as to DNA itself, is likely to be an important contributor to skin cancer risk.

Topics: Cells, Cultured; DNA Damage; DNA Repair; DNA-Binding Proteins; Enzyme-Linked Immunosorbent Assay; Humans; Immunoblotting; Oxidation-Reduction; Oxidative Stress; Photosensitivity Disorders; Photosensitizing Agents; Replication Protein A; Skin Neoplasms; Thioguanine; Ultraviolet Rays

Damage to skin DNA by solar UV is largely unavoidable, and an optimal cellular response to it requires the coordinated operation of proteins in numerous pathways. A fully functional DNA repair proteome for removing harmful DNA lesions is a prerequisite for an appropriate DNA damage response. Genetically determined failure to repair UV-induced DNA damage is associated with skin photosensitivity and increased skin cancer risk. Patients treated with immunosuppressant/anti-inflammatory thiopurines are also photosensitive and have high rates of sun-related skin cancer. Their DNA contains the base analog 6-thioguanine (6-TG), which acts as a UVA photosensitizer to generate reactive oxygen species (ROS), predominantly singlet oxygen ((1)O2). ROS damage both DNA and proteins. Here we show that UVA irradiation of cultured human cells containing DNA 6-TG causes significant protein oxidation and damages components of the DNA repair proteome, including the Ku, OGG-1, MYH, and RPA proteins. Assays of DNA repair in intact cells or in cell extracts indicate that this protein damage compromises DNA break rejoining and base and nucleotide excision repair. As these experimental conditions simulate those in the skin of patients taking thiopurines, our findings suggest a mechanism whereby UVA in sunlight may contribute to skin carcinogenesis in immunosuppressed patients.

Topics: Animals; Anti-Inflammatory Agents; Antimetabolites, Antineoplastic; Cricetinae; DNA End-Joining Repair; DNA Glycosylases; DNA Helicases; DNA Repair; Fibroblasts; HeLa Cells; Humans; Immunosuppressive Agents; Ku Autoantigen; Leukemia; Oxidation-Reduction; Photosensitivity Disorders; Proteome; Risk Factors; Skin Neoplasms; Thioguanine; Ultraviolet Rays

Congenital leukemia is infrequent, occurring in <1% of pediatric leukemia patients, and mainly of myeloid lineage. Twenty-five to 30% of congenital leukemia cases present with cutaneous leukemic infiltrates. Rarely, infants will have aleukemic leukemia cutis, presenting with leukemic skin lesions but without systemic symptoms or bone marrow involvement. Few cases of congenital aleukemic leukemia cutis have been reported in the literature. The course of disease is variable as cases of spontaneous resolution have been described. Here we present the first report of siblings with progressive congenital aleukemic leukemia cutis, both treated successfully with myeloid leukemia chemotherapy.

Topics: Antineoplastic Combined Chemotherapy Protocols; Cytarabine; Daunorubicin; Dexamethasone; Etoposide; Female; Humans; Infant, Newborn; Leukemia, Myeloid, Acute; Male; Siblings; Skin Neoplasms; Thioguanine

Azathioprine is used to treat a variety of conditions and to prevent graft rejection in organ transplant recipients (OTRs).. To investigate clinically our previous finding that azathioprine metabolites interact with ultraviolet (UV) A radiation to form promutagenic oxidative DNA damage and to determine whether this may be causal or contributory to the development of excess skin cancers post-transplantation.. The clinical corollary of these data were investigated. Five patients were recruited and the minimal erythema dose (MED) for UVB, UVA and solar-simulated radiation (SSR) was determined for each person before, and at least 12 weeks after, starting azathioprine therapy.. In all five patients azathioprine treatment was associated with an increased UVA and SSR sensitivity of the skin and a significant reduction in MEDs for UVA and SSR. We found no change in UVB-induced erythema or MED. In addition, we found that DNA from the skin of patients on azathioprine contains 6-thioguanine (6-TG).. Our findings confirm the presence of DNA 6-TG in the skin of those taking therapeutic doses of azathioprine and provide support for the hypothesis that DNA damage occurs when DNA 6-TG interacts with UVA, resulting in abnormal cutaneous photosensitivity.

Topics: Adult; Azathioprine; Case-Control Studies; DNA Damage; Dose-Response Relationship, Radiation; Epidermis; Female; Graft Rejection; Humans; Immunosuppressive Agents; Male; Middle Aged; Photosensitivity Disorders; Skin Neoplasms; Thioguanine; Treatment Outcome; Ultraviolet Therapy

Topics: Azathioprine; Carcinoma, Squamous Cell; DNA Damage; Humans; Immunosuppression Therapy; Immunosuppressive Agents; Mutagenesis; Oxidative Stress; Radiography; Risk Factors; Skin; Skin Neoplasms; Thioguanine; Ultraviolet Rays

Xeroderma pigmentosum group A gene (XPA)-deficient mice are defective in nucleotide excision repair (NER) and are therefore highly sensitive to ultraviolet (UV)-induced skin carcinogenesis. We established cell lines from skin cancers of UVB-irradiated XPA-deficient mice to investigate the phenotypic changes occurring during skin carcinogenesis. As anticipated, the skin cancer cell lines were devoid of NER activity but were less sensitive to killing by UV-irradiation than the XPA(-/-) fibroblast cell line. The lines were also more resistant to 6-thioguanine (6-TG) than XPA(-/-) and XPA(+/+) fibroblasts, which was suggestive of a mismatch repair (MMR) defect. Indeed, in vitro mismatch binding and MMR activity were impaired in several of these cell lines. Moreover, these cell lines displayed cell cycle checkpoint derangements following UV-irradiation and 6-TG exposure. The above findings suggest that MMR downregulation may help cells escape killing by UVB, as was seen previously for methylating agents and cisplatin, and thus that MMR deficient clones are selected for during the tumorigenic transformation of XPA(-/-) cells.

Topics: Animals; Cell Cycle; Cell Survival; Cell Transformation, Neoplastic; DNA Repair; DNA-Binding Proteins; Drug Resistance; Gene Deletion; Mice; Phenotype; Radiation Tolerance; Skin Neoplasms; Thioguanine; Tumor Cells, Cultured; Ultraviolet Rays; Xeroderma Pigmentosum; Xeroderma Pigmentosum Group A Protein

A 67-year-old woman with acute myelomonocytic leukemia had a clinical course characterized by the initial appearance of leukemia cutis without bone marrow involvement. When marrow involvement subsequently occurred, induction chemotherapy cleared all manifestations of the illness. Shortly thereafter, while blood and bone marrow remained in remission, the skin lesions reappeared. The introduction of 6-thioguanine, as part of the maintenance treatment protocol, resulted in the rapid and permanent disappearance of the leukemic skin infiltrates.

Topics: Aged; Bone Marrow; Female; Humans; Leukemia; Leukemia, Myeloid, Acute; Skin Neoplasms; Thioguanine

Topics: Cell Division; Cell Line; Cell Transformation, Neoplastic; Drug Resistance; Humans; Lesch-Nyhan Syndrome; Mutation; Skin Neoplasms; Skin Physiological Phenomena; Sodium-Potassium-Exchanging ATPase; Thioguanine

The ubiquitous polycyclic aromatic hydrocarbon (PAH), cyclopenta[c,d]pyrene (CPP), was tested to determine its mutagenicity for 6-thioguanine and ouabain resistance in Chinese hamster V79 cells and its tumor-initiating activity in the skin of the tumor susceptible Sencar mice. The potent carcinogen/mutagen, benzo[a]pyrene (BP), was included for comparison. Inasmuch as V79 cells do not metabolize PAHs, mutagenesis was tested both in the presence and in the absence of X-irradiated golden hamster embryo fibroblasts capable of metabolizing PAH. Neither CPP nor BP showed mutagenicity for V79 cells in the absence of the embryo cells. In the presence of these cells (in the cell-mediated assay) both PAHs elicited, in a dose dependent manner, a cytotoxic and mutagenic response in V79 cells. CPP was however less active than BP in inducing both of these responses. At the optimal expression time and at the dose range of 0.1-1 microgram/ml, CPP induced 2-8 6-thioguanine resistant mutants per 10(5) colony forming cells compared to 9-50 mutants induced by BP. Similarly, these doses of CPP induced 1-9 ouabain resistant mutants per 10(6) colony forming cells compared to 7-75 mutants induced by BP. CPP was also active in initiating skin tumors in approximately 60% of the mice at 200 micrograms, the highest dose tested. BP was more efficient in tumor initiation and yielded a similar response with 10 micrograms. These results indicate that CPP and BP elicit, in the cell mediated assay, a mutagenic response similar to the activity of these PAH in the skin of Sencar mice.

Topics: Animals; Carcinogens; Cells, Cultured; Cricetinae; Drug Resistance; Mesocricetus; Mutagens; Neoplasms, Experimental; Ouabain; Pyrenes; Skin Neoplasms; Thioguanine

The results obtained with very intensive treatment in previously untreated patients early in the disease are encouraging, and we hope will change the philosophy of most investigators that even in far advanced disease such as those with marrow metastases or multiple primary sites, one can still obtain complete regression at all tumour sites within 1 to 1 1/2 months from onset of therapy by combined treatment with multiple chemotherapeutic agents and radiation therapy to one or more sites.

Topics: Adolescent; Antineoplastic Agents; Asparaginase; Bone Neoplasms; Child; Child, Preschool; Cyclophosphamide; Cytarabine; Daunorubicin; Drug Therapy, Combination; Female; Humans; Hydroxyurea; Leukemia; Leukemia, Lymphoid; Lymph Nodes; Lymphoma; Male; Mediastinal Neoplasms; Methotrexate; Nasopharyngeal Neoplasms; Ovarian Neoplasms; Skin Neoplasms; Stomach Neoplasms; Thioguanine; Vincristine

Topics: Aged; Antineoplastic Agents; Blood Coagulation; Carcinoma; Carcinoma, Bronchogenic; Carcinoma, Small Cell; Carcinoma, Squamous Cell; Cyclophosphamide; Drug Therapy, Combination; Fibrinogen; Fluorouracil; Heparin; Humans; Infusions, Parenteral; Lung Neoplasms; Male; Methotrexate; Middle Aged; Neoplasm Metastasis; Radiography; Skin Neoplasms; Thioguanine; Vincristine