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Dong J, Huang C, Guo S, Xia Y, Hou Y, Yang C, Zhang X, Jie J, Zhu BZ, Su H. Free-Radical-Mediated Photoinduced Electron Transfer between 6-Thioguanine and Tryptophan Leading to DNA-Protein-Like Cross-Link. J Phys Chem B 2021; 126:14-22. [PMID: 34951313 DOI: 10.1021/acs.jpcb.1c03380] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The nucleobase analog 6-thioguanine (6-TG) has emerged as important immunosuppressant, anti-inflammatory, and anticancer drug in the past few decades, but its unique photosensitivity of absorbing strongly ultraviolet UVA light elicits photochemical hazards in many ways. The particularly intriguing yet unresolved question is whether the direct photoreaction of 6-TG can promote DNA-protein cross-links (DPCs) formation, which are large DNA adducts blocking DNA replication and physically impede DNA-related processes. Herein, by real-time observation of radical intermediates using time-resolved UV-vis absorption spectroscopy in conjunction with product analysis by HPLC-MS, we discover that UVA excitation of 6-TG triggers direct covalent cross-linking with tryptophan (TrpH) via an exquisite radical mechanism of electron transfer. The photoexcitation prepares the redox-active triplet 36-TG*, which initiates electron transfer with TrpH, creating TrpH•+ and 6-TG•- in the first step. The deprotonated Trp• undergoes radical-recombination with its geminate partner 6-TG•- and eliminates a H2S, leading to the cross-linking product 6-TG-Trp. The photoadduct structures (two chiral isomers and one constitutional isomer) are identified unambiguously, validating further the mechanism. These findings pinpoint the exact amino acid that is vulnerable to photo-cross-linking with 6-TG and establish a mechanistic framework for understanding mutagenic DPCs formation and developing photoprobes based on this new type of photo-cross-linking.
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Affiliation(s)
- Junjie Dong
- College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
| | - Chunhua Huang
- State Key Lab of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085, P. R. China
| | - Shaoshi Guo
- College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
| | - Ye Xia
- College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
| | - Yue Hou
- College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
| | - Chunfan Yang
- College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
| | - Xianwang Zhang
- College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
| | - Jialong Jie
- College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
| | - Ben-Zhan Zhu
- State Key Lab of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085, P. R. China
| | - Hongmei Su
- College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
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2
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Euceda N, Jahnke J, Espinal A, Louis MF, Bashkin E, Roccanova P, Espaillat A, Fuentes GV, Nieto F, Gao R. Thioguanine restoration through type I photosensitization-superoxide oxidation-glutathione reduction cycles. Phys Chem Chem Phys 2021; 23:5069-5073. [PMID: 33655288 DOI: 10.1039/d1cp00101a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
UVA-induced deleterious effect of thiopurine prodrugs including azathioprine, 6-mercaptopurine and 6-thioguanine (6-TG) increases the risk of cancer development due to the incorporation of 6-TG in patients' DNA. The catalytic mechanism by which thiobases act as a sustained oxidant producer has yet to be explored, especially through the Type I electron transfer pathway that produces superoxide radicals (O2˙-). Under Fenton-like conditions O2˙- radicals convert to extremely reactive hydroxyl radicals (˙OH), thus carrying even higher risk of biological damage than that induced by the well-studied type II reaction. By monitoring 6-TG/UVA-induced photochemistry in mass spectra and superoxide radicals (O2˙-) via nitro blue tetrazolium (NBT) reduction, this work provides two new findings: (1) in the presence of reduced glutathione (GSH), the production of O2˙-via the type I reaction is enhanced 10-fold. 6-TG thiyl radicals are identified as the primary intermediate formed in the reaction of 6-TG with O2˙-. The restoration of 6-TG and concurrent generation of O2˙- occur via a 3-step-cycle: 6-TG type I photosensitization, O2˙- oxidation and GSH reduction. (2) In the absence of GSH, 6-TG thiyl radicals undergo oxygen addition and sulfur dioxide removal to form carbon radicals (C6) which further convert to thioether by reacting with 6-TG molecules. These findings help explain not only thiol-regulation in a biological system but chemoprevention of cancer.
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Affiliation(s)
- Nelson Euceda
- Chemistry and Physics Department, SUNY College at Old Westbury, Old Westbury, NY 11568, USA.
| | - Joyce Jahnke
- Chemistry and Physics Department, SUNY College at Old Westbury, Old Westbury, NY 11568, USA.
| | - Aileen Espinal
- Chemistry and Physics Department, SUNY College at Old Westbury, Old Westbury, NY 11568, USA.
| | - Monique F Louis
- Chemistry and Physics Department, SUNY College at Old Westbury, Old Westbury, NY 11568, USA.
| | - Edan Bashkin
- Chemistry and Physics Department, SUNY College at Old Westbury, Old Westbury, NY 11568, USA.
| | - Patricia Roccanova
- Biological Sciences Department, SUNY College at Old Westbury, Old Westbury, NY 11568, USA
| | - Abraham Espaillat
- Chemistry and Physics Department, SUNY College at Old Westbury, Old Westbury, NY 11568, USA.
| | - German V Fuentes
- Chemistry and Physics Department, SUNY College at Old Westbury, Old Westbury, NY 11568, USA.
| | - Fernando Nieto
- Biological Sciences Department, SUNY College at Old Westbury, Old Westbury, NY 11568, USA
| | - Ruomei Gao
- Chemistry and Physics Department, SUNY College at Old Westbury, Old Westbury, NY 11568, USA.
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3
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Yamada M, Mohammed Y, Prow TW. Advances and controversies in studying sunscreen delivery and toxicity. Adv Drug Deliv Rev 2020; 153:72-86. [PMID: 32084432 DOI: 10.1016/j.addr.2020.02.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Revised: 01/02/2020] [Accepted: 02/10/2020] [Indexed: 02/04/2023]
Abstract
This review critically evaluates the sunscreen delivery and toxicity field. We chose to focus on approved sunscreens in this review. Optimal sunscreen use prevents skin cancer and photoageing but there is an important knowledge gap in sunscreen/skin interactions. Sunscreen delivery is a key for efficacy, but studying sunscreen delivery is not straightforward. We review the strengths and weaknesses of in vitro, excised skin and clinical approaches. Understanding positive and negative sunscreen effects on skin homeostasis is also challenging. The results in this field, especially in vitro testing, are controversial and experimental design varies widely which further supports disparities between some findings. We hypothesize that bias towards showing sunscreen toxicity to increase impact could be problematic. We explore that perception through a detailed review of experimental design, especially in cell culture models. Our conclusion is that emerging, non- and minimally invasive technologies are enabling new approaches to volunteer studies that could significantly improve knowledge of sunscreen delivery and interactions.
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4
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Puza CJ, Beasley GM, Barbas AS, Mosca PJ. Type of Organ Transplanted Impacts the Risk and Presentation of Cutaneous Squamous Cell Carcinoma in Transplant Recipients. EXP CLIN TRANSPLANT 2019; 18:93-97. [PMID: 30968759 DOI: 10.6002/ect.2018.0238] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
OBJECTIVES Transplant immunosuppression increases the risk of cutaneous squamous cell carcinoma by 65- to 200-fold. Our objective was to investigate the impact of the type of organ transplanted on the risk and presentation of cutaneous squamous cell carcinoma. MATERIALS AND METHODS The retrospective database of the Duke University Health System was queried to identify patients who underwent an organ transplant from 1996 to 2016. Data regarding transplant outcomes, cutaneous squamous cell carcinoma, immunosuppressive regimens, and survival were recorded. We used chi-square tests, analysis of variance, and unpaired t tests to compare the incidence and presentation of cutaneous squamous cell carcinoma among organ types. RESULTS Of 3652 renal, hepatic, and cardiothoracic transplant patients identified, 142 patients developed at least 1 cutaneous squamous cell carcinoma. The incidence of cutaneous squamous cell carcinoma varied by type of organ transplanted, with 46 of 1684 (2.7%) renal transplant patients developing cutaneous squamous cell carcinoma, 33 of 804 (4.1%) hepatic transplant patients, and 63 of 1164 (5.4%) cardiothoracic transplant patients over the median follow-up time of 6.5 years. Incidence in the renal transplant versus the cardiothoracic transplant group was significantly different (P < .001). The time to presentation of cutaneous squamous cell carcinoma varied significantly by group, with the renal cohort presenting at 3.8 years compared with at 2.4 years in the cardiothoracic group and 2.1 years in the hepatic group (P < .001). CONCLUSIONS The type of organ transplanted confers a unique risk and presentation of cutaneous squamous cell carcinoma.
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Affiliation(s)
- Charles J Puza
- From the Duke University School of Medicine, Duke University Health System, Durham, North Carolina, USA
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5
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Miyata S, Tanabe S, Isozaki T, Xu YZ, Suzuki T. Characteristics of the excited triplet states of thiolated guanosine derivatives and singlet oxygen generation. Photochem Photobiol Sci 2018; 17:1469-1476. [PMID: 30280174 DOI: 10.1039/c8pp00240a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Thioguanine is sensitive to UVA light and generates singlet molecular oxygen (1O2*) when exposed to UVA. Three thioguanosine derivatives, 2',3',5'-tri-O-acetyl-6-thioguanosine (ta6TGuo), 2',3',5'-tri-O-acetyl-8-thioguanosine (ta8TGuo), and 2',3',5'-tri-O-acetyl-6,8-dithioguanosine (taDTGuo) were explored photophysically and photochemically. Nanosecond transient absorption and time-resolved near-infrared emission measurements were carried out to investigate the characteristics of their excited triplet states in acetonitrile solution. The quantum yield of intersystem crossing (ΦISC), the intrinsic decay rate constant (k0), the quenching rate constant by 3O2 (kq) and the self-quenching rate constant (kSQ) of their triplet states were all determined. From the precise analysis of the quantum yield of 1O2* generation (ΦΔ) against the concentration of dissolved molecular oxygen, the fraction of the triplet states quenched by dissolved oxygen which gives rise to 1O2* formation (SΔ) was successfully obtained with high accuracy. The ΦΔ values at low oxygen concentrations reveal that these thioguanosines, particularly taDTGuo, can still effectively generate 1O2* at low molecular oxygen concentrations like carcinomatous microenvironments. These findings indicate that taDTGuo would perform well as a potential agent for photo-induced cancer therapies.
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Affiliation(s)
- Shoma Miyata
- Department of Chemistry and Biological Science, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.
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6
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Cutaneous Complications in Recipients of Lung Transplants: A Pictorial Review. Chest 2018; 155:178-193. [PMID: 30201407 DOI: 10.1016/j.chest.2018.08.1060] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 08/16/2018] [Indexed: 12/26/2022] Open
Abstract
Lung transplant is now an established modality for a broad spectrum of end-stage pulmonary diseases. According to the International Society for Heart and Lung Transplantation Registry, more than 50,000 lung transplants have been performed worldwide, with nearly 11,000 recipients of lung transplants alive in the United States. With the increasing use of lung transplant, pulmonologists must be cognizant of the common as well as the unique posttransplant dermatologic complications. Immunosuppression, infections, and a variety of medications and environmental exposures can contribute to these complications. This review aims to provide representative pictures and describe the pathogenesis, epidemiologic characteristics, and clinical manifestations of dermatologic complications encountered among recipients of lung transplants.
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7
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Puza CJ, Myers SA, Cardones AR, Beasley GM, Mosca PJ. The impact of transplant rejection on cutaneous squamous cell carcinoma in renal transplant recipients. Clin Exp Dermatol 2018; 44:265-269. [PMID: 29952022 DOI: 10.1111/ced.13699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/14/2018] [Indexed: 11/27/2022]
Abstract
BACKGROUND The incidence of cutaneous squamous cell carcinoma (cSCC) is markedly increased in renal transplant recipients compared with that of the nontransplant population. AIM To investigate whether there is a relationship between transplant rejection and cSCC. METHODS The Duke Enterprise Data Unified Content Explorer historical database was used to identify patients who had undergone a renal transplant at Duke University Hospital during a 20-year period. Data on patient demographics, transplant dates, first rejection episodes, first cSCC development, medication, laboratory results and survival were recorded. RESULTS In total, 1684 patients were identified, of whom 126 (7.5%) experienced an episode of rejection and 46 (4.0%) developed a cSCC after transplant. The incidence of cSCC was significantly greater in the rejection group, with 8.7% of patients developing cSCC compared with 2.2% in the no-rejection group (P < 0.001). Median lag time to cSCC was shorter in the rejection group (2.5 years; age 0.4-9.0 years) than the no-rejection group (4.2 years; range 1.3-20.4 years) (P < 0.03). CONCLUSIONS Transplant rejection is associated with both a higher incidence and an accelerated time course for development of cSCC following renal transplantation. Close dermatological surveillance should be considered following an episode of rejection in this patient population.
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Affiliation(s)
- C J Puza
- Duke University School of Medicine, Durham, NC, USA
| | - S A Myers
- Department of Dermatology, Duke Medical Center, Durham, NC, USA
| | - A R Cardones
- Department of Dermatology, Duke Medical Center, Durham, NC, USA
| | - G M Beasley
- Department of Surgery, Duke Medical Center, Durham, NC, USA
| | - P J Mosca
- Department of Surgery, Duke Medical Center, Durham, NC, USA
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8
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Miyata S, Hoshino M, Isozaki T, Yamada T, Sugimura H, Xu YZ, Suzuki T. Acid Dissociation Equilibrium and Singlet Molecular Oxygen Quantum Yield of Acetylated 6,8-Dithioguanosine in Aqueous Buffer Solution. J Phys Chem B 2018; 122:2912-2921. [DOI: 10.1021/acs.jpcb.8b00517] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- Shoma Miyata
- Department of Chemistry and Biological Science, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan
| | - Mina Hoshino
- Department of Chemistry and Biological Science, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan
| | - Tasuku Isozaki
- Department of Chemistry and Biological Science, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan
| | - Takeshi Yamada
- Department of Chemistry and Biological Science, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan
| | - Hideyuki Sugimura
- Department of Chemistry and Biological Science, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan
| | - Yao-Zhong Xu
- School of Life, Health and Chemical Sciences, The Open University, Milton Keynes MK7 6AA, U.K
| | - Tadashi Suzuki
- Department of Chemistry and Biological Science, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan
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9
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Martínez-Rojas F, Del Valle MA, Isaacs M, Ramírez G, Armijo F. Electrochemical Behaviour Study and Determination of Guanine, 6-Thioguanine, Acyclovir and Gancyclovir on Fluorine-doped SnO2
Electrode. Application in Pharmaceutical Preparations. ELECTROANAL 2017. [DOI: 10.1002/elan.201700516] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- F. Martínez-Rojas
- Pontificia Universidad Católica de Chile, Facultad de Química, Departamento de Química Inorgánica; Laboratorio de Bioelectroquímica; Av. Vicuña Mackenna 4860 7820436 Macul Santiago Chile
| | - M. A. Del Valle
- Pontificia Universidad Católica de Chile, Facultad de Química, Departamento de Química Inorgánica; Laboratorio de Bioelectroquímica; Av. Vicuña Mackenna 4860 7820436 Macul Santiago Chile
| | - M. Isaacs
- Pontificia Universidad Católica de Chile, Facultad de Química, Departamento de Química Inorgánica; Laboratorio de Bioelectroquímica; Av. Vicuña Mackenna 4860 7820436 Macul Santiago Chile
| | - Galo Ramírez
- Pontificia Universidad Católica de Chile, Facultad de Química, Departamento de Química Inorgánica; Laboratorio de Bioelectroquímica; Av. Vicuña Mackenna 4860 7820436 Macul Santiago Chile
| | - F. Armijo
- Pontificia Universidad Católica de Chile, Facultad de Química, Departamento de Química Inorgánica; Laboratorio de Bioelectroquímica; Av. Vicuña Mackenna 4860 7820436 Macul Santiago Chile
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10
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Mittal A, Colegio OR. Skin Cancers in Organ Transplant Recipients. Am J Transplant 2017; 17:2509-2530. [PMID: 28556451 DOI: 10.1111/ajt.14382] [Citation(s) in RCA: 115] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2016] [Revised: 05/05/2017] [Accepted: 05/19/2017] [Indexed: 02/06/2023]
Abstract
Long-term utilization of immunosuppression in organ transplant recipients (OTRs) leads to decreased immune-mediated tumor surveillance and development of malignant tumors. A delicate balance needs to be maintained in the intensity of immunosuppression to keep the risk of malignancy low without jeopardizing life-saving graft function. OTRs are prone to developing skin cancers that exhibit unique epidemiologic, pathophysiologic, and prognostic characteristics. In this review, we discuss the most commonly reported skin cancers in OTRs: squamous cell carcinoma (SCC), basal cell carcinoma (BCC), Kaposi sarcoma, Merkel cell carcinoma, and malignant melanoma (MM). Tumors in this high-risk population are aggressive and may respond poorly to standard therapies; however, new targeted therapies are promising. Checkpoint inhibitor antibodies have been used for treatment of cutaneous SCC, Merkel cell carcinoma, and MM; epidermal growth factor receptor inhibitors have been used for cutaneous SCC; hedgehog pathway inhibitors have been used for BCC; and BRAF and MEK inhibitors are being used increasingly in the management of MM. Guidelines for dermatologic screening are variable and primarily based on expert opinion. Prospective evidence-based trials by multidisciplinary groups are needed to better define surveillance schedules for pre- and posttransplant cutaneous malignancies.
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Affiliation(s)
- A Mittal
- Departments of Dermatology, Yale University School of Medicine, New Haven, CT
| | - O R Colegio
- Departments of Dermatology, Yale University School of Medicine, New Haven, CT.,Departments of Pathology, Yale University School of Medicine, New Haven, CT.,Departments of Surgery, Yale University School of Medicine, New Haven, CT.,Yale Cancer Center, Yale University School of Medicine, New Haven, CT.,Yale-New Haven Transplantation Center, Yale University School of Medicine, New Haven, CT
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11
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Gueranger Q, Li F, Peacock M, Larnicol-Fery A, Brem R, Macpherson P, Egly JM, Karran P. Response to Emanuele. J Invest Dermatol 2014; 134:2053-2055. [PMID: 24492241 DOI: 10.1038/jid.2014.67] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Quentin Gueranger
- Clare Hall Laboratories, Cancer Research UK London Research Institute, South Mimms, UK
| | - Feng Li
- Clare Hall Laboratories, Cancer Research UK London Research Institute, South Mimms, UK
| | - Matthew Peacock
- Clare Hall Laboratories, Cancer Research UK London Research Institute, South Mimms, UK
| | - Annabel Larnicol-Fery
- Institut de Genetique et de Biologie Moleculaire et Cellulaire, CNRS/Inserm/ULP, Strasbourg, France
| | - Reto Brem
- Clare Hall Laboratories, Cancer Research UK London Research Institute, South Mimms, UK
| | - Peter Macpherson
- Clare Hall Laboratories, Cancer Research UK London Research Institute, South Mimms, UK
| | - Jean-Marc Egly
- Institut de Genetique et de Biologie Moleculaire et Cellulaire, CNRS/Inserm/ULP, Strasbourg, France
| | - Peter Karran
- Clare Hall Laboratories, Cancer Research UK London Research Institute, South Mimms, UK.
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12
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Kalra S, Knatko EV, Zhang Y, Honda T, Yamamoto M, Dinkova-Kostova AT. Highly potent activation of Nrf2 by topical tricyclic bis(cyano enone): implications for protection against UV radiation during thiopurine therapy. Cancer Prev Res (Phila) 2012; 5:973-81. [PMID: 22659146 DOI: 10.1158/1940-6207.capr-12-0041] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Chronic treatment with azathioprine, a highly effective anti-inflammatory and immunosuppressive agent, profoundly increases the risk for development of unusually aggressive cutaneous squamous cell carcinoma. Its ultimate metabolite, 6-thioguanine (6-TG) nucleotide, is incorporated in DNA of skin cells, and upon exposure to UVA radiation, causes oxidative stress, followed by damage of DNA and associated proteins. The acetylenic tricyclic bis(cyano enone) TBE-31 is a strong inhibitor of inflammation and a potent inducer of the Keap1/Nrf2/ARE pathway, which orchestrates the expression of a large network of cytoprotective genes. We now report that long-term (five days per week for four weeks) topical daily applications of small (200 nmol) quantities of TBE-31 cause a robust systemic induction of the Keap1/Nrf2/ARE pathway and decreases the 6-TG incorporation in DNA of skin, blood, and liver of azathioprine-treated mice, indicating extraordinary bioavailability and efficacy. In addition, TBE-31, at nanomolar concentrations, protects cells with 6-TG in their genomic DNA against oxidative stress caused by UVA radiation through induction of the Keap1/Nrf2/ARE pathway. At the same 6-TG DNA levels, Keap1-knockout cells, in which the pathway is constitutively upregulated, are highly resistant to UVA radiation-induced oxidative stress. The protective effects of both the Keap1-knockout genotype and TBE-31 are completely lost in the absence of transcription factor Nrf2. Our findings suggest that compounds of this kind are excellent candidates for mechanism-based chemoprotective agents against conditions in which oxidative stress and inflammation underlie disease pathogenesis. Moreover, their potential skin patch incorporation for transdermal delivery is an exciting possibility.
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Affiliation(s)
- Sukirti Kalra
- Division of Cancer Research, Medical Research Institute, University of Dundee, Dundee, Scotland, UK
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13
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Abstract
Thiopurines are prescribed frequently as medication for cancer and for inflammatory disorders. One of them, azathioprine, has been the immunosuppressant of choice for organ transplant recipients for many years. Thiopurine use is associated with elevated sun sensitivity and skin cancer risk. Skin sensitization is selective for UVA. 6-TG integrates into DNA and unlike the canonical DNA bases, it is a strong UVA chromophore with an absorbance maximum at 342 nm. DNA 6-TG is a photosensitizer and a source of reactive oxygen species. Reactive oxygen that is generated from the photochemical activation of DNA 6-TG causes extensive damage to DNA and proteins. This damage is mutagenic and extremely toxic to cultured human cells. Here we describe some of the lesions that are known to be generated from UVA irradiation of DNA 6-TG. We discuss how this photochemical damage might contribute to the toxic effect of thiopurine/UVA treatment on cultured cells and to the high risk of skin cancer in thiopurine-treated patients.
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Affiliation(s)
- Reto Brem
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Herts, UK.
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14
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Attard NR, Karran P. UVA photosensitization of thiopurines and skin cancer in organ transplant recipients. Photochem Photobiol Sci 2012; 11:62-8. [PMID: 21860872 DOI: 10.1039/c1pp05194f] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2011] [Accepted: 07/21/2011] [Indexed: 01/31/2023]
Abstract
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.
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Affiliation(s)
- Natalie R Attard
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Hertfordshire EN6 3LD, UK
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15
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Abstract
This review of Photochemistry and Photobiology summarizes articles published in 2010, and highlights progress in the area of photosensitization. The synthesis of conjugated photosensitizers is an area of interest where increasing water solubility has been a goal. Targeting infrared sensitizer absorption has been another goal, and relates to the practical need of deep tissue absorption of light. Photodynamic techniques for inactivating microbes and destroying tumors have been particularly successful. Biologically, singlet oxygen [(1)O(2)((1)Δ(g))] is an integral species in many of these reactions, although photosensitized oxidations tuned to electron and hydrogen transfer (Type I) give rise to other reactive species, such as superoxide and hydrogen peroxide. How photoprotection against yellowing, oxygenation and degradation occurs was also an area of topical interest.
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Affiliation(s)
- Bonnie I Kruft
- Department of Chemistry, Graduate Center & The City University of New York (CUNY), Brooklyn College, Brooklyn, NY, USA
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16
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Kalra S, Zhang Y, Knatko EV, Finlayson S, Yamamoto M, Dinkova-Kostova AT. Oral azathioprine leads to higher incorporation of 6-thioguanine in DNA of skin than liver: the protective role of the Keap1/Nrf2/ARE pathway. Cancer Prev Res (Phila) 2011; 4:1665-74. [PMID: 21803983 DOI: 10.1158/1940-6207.capr-11-0137] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Azathioprine is a widely used anti-inflammatory, immunosuppressive, and anticancer agent. However, chronic treatment with this drug is associated with a profoundly increased risk (in certain cases by more than 100-fold) of developing squamous cell carcinoma of the skin. Incorporation of its ultimate metabolite, thio-dGTP, in DNA results in partial substitution of guanine with 6-thioguanine which, combined with exposure to UVA radiation, creates a source of synergistic mutagenic damage to DNA. We now report that oral treatment with azathioprine leads to a much greater incorporation of 6-thioguanine in DNA of mouse skin than liver. These higher levels of 6-thioguanine, together with the fact that the skin is constantly exposed to UV radiation from the sun, may be responsible, at least in part, for the increased susceptibility of this organ to tumor development. Genetic upregulation of the Keap1/Nrf2/ARE pathway, a major cellular regulator of the expression of a network of cytoprotective genes, reduces the incorporation of 6-thioguanine in DNA of both skin and liver following treatment with azathioprine. Similarly, pharmacologic activation of the pathway by the potent inducer sulforaphane results in lower 6-thioguanine incorporation in DNA and protects 6-thioguanine-treated cells against oxidative stress following exposure to UVA radiation. Protection is accompanied by increased levels of glutathione and induction of multidrug resistance-associated protein 4, an organic anion efflux pump that also exports nucleoside monophosphate analogues. Our findings suggest that activation of the Keap1/Nrf2/ARE pathway could reduce the risk for skin cancer in patients receiving long-term azathioprine therapy.
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Affiliation(s)
- Sukirti Kalra
- Biomedical Research Institute, University of Dundee, Scotland, United Kingdom
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