Ribonucleotide reductase inhibition enhances chemoradiosensitivity of human cervical cancers.
ABSTRACT For repair of damaged DNA, cells increase de novo synthesis of deoxyribonucleotide triphosphates through the rate-limiting, p53-regulated ribonucleotide reductase (RNR) enzyme. In this study we investigated whether pharmacological inhibition of RNR by 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP, NSC #663249) enhanced chemoradiation sensitivity through a mechanism involving sustained DNA damage. RNR inactivation by 3-AP and resulting chemoradiosensitization were evaluated in human cervical (CaSki, C33-a) cancer cells through study of DNA damage (γ-H2AX signal) by flow cytometry, RNR subunit p53R2 and p21 protein steady-state levels by Western blot analysis and laser scanning imaging cytometry, and cell survival by colony formation assays. 3-AP treatment led to sustained radiation- and cisplatin-induced DNA damage (i.e. increased γ-H2AX signal) in both cell lines through a mechanism of inhibited RNR activity. Radiation, cisplatin and 3-AP exposure resulted in significantly elevated numbers and persistence of γ-H2AX foci that were associated with reduced clonogenic survival. DNA damage was associated with a rise in p53R2 but not p21 protein levels 6 h after treatment with radiation and/or cisplatin plus 3-AP. We conclude that blockage of RNR activity by 3-AP impairs DNA damage responses that rely on deoxyribonucleotide production and thereby may substantially increase chemoradiosensitivity of human cervical cancers.
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ABSTRACT: OBJECTIVE: Cervical and vaginal cancers have virally-mediated or mutated defects in DNA damage repair responses, making these cancers sensible targets for ribonucleotide reductase inhibition during radiochemotherapy. METHODS: We conducted a phase II study evaluating 3x weekly 2-hour intravenous 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP, 25 mg/m(2)) co-administered with 1x weekly intravenous cisplatin (40 mg/m(2)) and daily pelvic radiation (45 Gy) in women with stage IB2-IVB cervical (n = 22) or stage II-IV vaginal (n = 3) cancers. Brachytherapy followed (40 Gy). Toxicity was monitored by common terminology criteria for adverse events (version 3.0). The primary end point of response was assessed by 3-month posttherapy 2-[(18)F] fluoro-2-deoxy-D-glucose positron emission tomography (PET/CT) and clinical examination. RESULTS: 3-AP radiochemotherapy achieved clinical responses in 24 (96% [95% confidence interval: 80-99%]) of 25 patients (median follow-up 20 months, range 2-35 months). 23 (96% [95% confidence interval: 80-99%]) of 24 patients had 3-month posttherapy PET/CT scans that recorded metabolic activity in the cervix or vagina equal or less than that of the cardiac blood pool, suggesting complete metabolic responses. The most frequent 3-AP radiochemotherapy-related adverse events included fatigue, nausea, diarrhea, and reversible hematological and electrolyte abnormalities. CONCLUSIONS: The addition of 3-AP to cisplatin radiochemotherapy was tolerable and produced high rates of clinical and metabolic responses in women with cervical and vaginal cancers. Future randomized phase II and III clinical trials of 3-AP radiochemotherapy are warranted.Gynecologic Oncology 04/2013; · 3.93 Impact Factor
Article: Emerging drugs for cervical cancer.[Show abstract] [Hide abstract]
ABSTRACT: INTRODUCTION: There is a shortage of therapeutical agents for invasive cervical cancer in late stages of development; however, a number of promising molecules are currently in early phases of development. AREAS COVERED: This review briefly discusses the current achievements in treating cervical cancer with an emphasis in emerging agents based on a literature search on pubmed and related sites for cervical cancer information. This is not a systematic review. EXPERT OPINION: In advanced disease, modest survival gains have been achieved with cisplatin doublets. Contrariwise, chemoradiation has increased survival rates in locally advanced disease, but there is still room for improvement. Anti-vascular endothelial growth factor and anti-epidermal growth factor receptor monoclonal antibodies are promising molecules that are at present in late-phase development, but a high number of miscellaneous agents are in early development. Strong experimental bases support that the 'Achilles' heel' of cervical cancer are the HPV-E6/E7 oncogenes. Unfortunately, agents aimed at targeting these cervical cancer-driven players are found in very early development; hence, major research efforts must be focused on developing technological strategies for their effective targeting using nucleic acid-based vehicles for safe and effective delivery to cancer cells as well as accelerating the search for small-molecule inhibitors of E6/E7 themselves or their interacting cellular proteins.Expert Opinion on Emerging Drugs 04/2012; 17(2):203-18. · 2.48 Impact Factor
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ABSTRACT: Introduction: Ribonucleotide reductase (RR) is a unique enzyme, because it is responsible for reducing ribonucleotides to their corresponding deoxyribonucleotides, which are the building blocks required for DNA replication and repair. Dysregulated RR activity is associated with genomic instability, malignant transformation and cancer development. The use of RR inhibitors, either as a single agent or combined with other therapies, has proven to be a promising approach for treating solid tumors and hematological malignancies. Areas covered: This review covers recent publications in the area of RR, which include: i) the structure, function and regulation of RR; ii) the roles of RR in cancer development; iii) the classification, mechanisms and clinical application of RR inhibitors for cancer therapy and iv) strategies for developing novel RR inhibitors in the future. Expert opinion: Exploring the possible nonenzymatic roles of RR subunit proteins in carcinogenesis may lead to new rationales for developing novel anticancer drugs. Updated information about the structure and holoenzyme models of RR will help in identifying potential sites in the protein that could be targets for novel RR inhibitors. Determining RR activity and subunit levels in clinical samples will provide a rational platform for developing personalized cancer therapies that use RR inhibitors.Expert Opinion on Therapeutic Targets 10/2013; · 4.90 Impact Factor