Modulating radiation resistance by inhibiting ribonucleotide reductase in cancers with virally or mutationally silenced p53 protein

Dose finding, bioavailability, and PK-PD of oral triapine with concurrent chemoradiation for locally advanced cervical cancer and vaginal cancer (ETCTN 9892)

BACKGROUND

The addition of IV triapine to chemoradiation appeared active in phase I and II studies but drug delivery is cumbersome. We examined PO triapine with cisplatin chemoradiation.

METHODS

We implemented a 3 + 3 design for PO triapine dose escalation with expansion, starting at 100 mg, five days a week for five weeks while receiving radiation with weekly IV cisplatin for locally advanced cervical or vaginal cancer. Maximum tolerated dose (MTD), dose limiting toxicity (DLT), adverse events, pharmacokinetics (PK), pharmacodynamics (PD), and metabolic complete response (mCR) were assessed.

RESULTS

19/21 patients were DLT evaluable. DLTs included grade 4 neutropenia (n = 2), leukopenia (n = 2), lymphopenia (n = 2), and hypokalemia (n = 1). Grade 3 toxicities at least possibly related were as expected for cisplatin chemoradiation: lymphopenia (n = 12), anemia (n = 10), neutropenia (n = 4), leukopenia (n = 8), decreased platelets (n = 2), hypertension (n = 1), and hyponatremia (n = 1). MTD and RP2D were established at 100 mg. 8/13 evaluable patients had a mCR. Triapine had a bioavailability of 59%. Methemoglobin levels correlated with triapine exposure. Smoking almost doubled CYP1A2 mediated triapine clearance.

CONCLUSIONS

Oral triapine is safe when given with cisplatin chemoradiation, convenient, bioavailable. Exposure is negatively impacted by smoking, and methemoglobin is a biomarker of exposure.

CLINICAL TRIAL REGISTRATION

NCT02595879.

E2F1-Associated Purine Synthesis Pathway Is a Major Component of the MET-DNA Damage Response Network

Various lines of investigation support a signaling interphase shared by receptor tyrosine kinases and the DNA damage response. However, the underlying network nodes and their contribution to the maintenance of DNA integrity remain unknown. We explored MET-related metabolic pathways in which interruption compromises proper resolution of DNA damage. Discovery metabolomics combined with transcriptomics identified changes in pathways relevant to DNA repair following MET inhibition (METi). METi by tepotinib was associated with the formation of γH2AX foci and with significant alterations in major metabolic circuits such as glycolysis, gluconeogenesis, and purine, pyrimidine, amino acid, and lipid metabolism. 5'-Phosphoribosyl-N-formylglycinamide, a de novo purine synthesis pathway metabolite, was consistently decreased in in vitro and in vivo MET-dependent models, and METi-related depletion of dNTPs was observed. METi instigated the downregulation of critical purine synthesis enzymes including phosphoribosylglycinamide formyltransferase, which catalyzes 5'-phosphoribosyl-N-formylglycinamide synthesis. Genes encoding these enzymes are regulated through E2F1, whose levels decrease upon METi in MET-driven cells and xenografts. Transient E2F1 overexpression prevented dNTP depletion and the concomitant METi-associated DNA damage in MET-driven cells. We conclude that DNA damage following METi results from dNTP reduction via downregulation of E2F1 and a consequent decline of de novo purine synthesis.

SIGNIFICANCE

Maintenance of genome stability prevents disease and affiliates with growth factor receptor tyrosine kinases. We identified de novo purine synthesis as a pathway in which key enzymatic players are regulated through MET receptor and whose depletion via MET targeting explains MET inhibition-associated formation of DNA double-strand breaks. The mechanistic importance of MET inhibition-dependent E2F1 downregulation for interference with DNA integrity has translational implications for MET-targeting-based treatment of malignancies.

Effect of siRNA-mediated silencing of p53R2 gene on sensitivity of T-ALL cellsto Daunorubicin

INTRODUCTION

p53R2 is a p53-inducible protein that, as one of the subunits of ribonucleotide reductase, plays an important role in providing dNTPs for DNA repair. Although p53R2 is associated with cancer progression, its role in T-cell acute lymphoblastic leukemia (T-ALL) cells is unknown. Therefore, in this study, we evaluated the effect of p53R2 silencing on double-stranded DNA breaks, apoptosis and cell cycle of T-ALL cells treated with Daunorubicin.

METHODS

Transfection was performed using Polyethyleneimine (PEI). Gene expression was measured using real-time PCR and protein expression was evaluated using Western blotting. Cell metabolic activity and IC50 were calculated using MTT assay, formation of double-stranded DNA breaks was checked using immunohistochemistry for γH2AX, and cell cycle and apoptosis were evaluated using flow cytometry.

RESULTS

We found that p53 silencing synergistically inhibited the growth of T-ALL cells by Daunorubicin. p53R2 siRNA in combination with Daunorubicin but not alone increases the rate of DNA double-strand breaks in T-ALL cells. In addition, p53R2 siRNA significantly increased Daunorubicin-induced apoptosis. p53R2 siRNA also caused a non-significant increase in cells in G2 phase.

CONCLUSION

The results of the present study showed that silencing of p53R2 using siRNA can significantly increase the antitumor effects of Daunorubicin on T-ALL cells. Therefore, p53R2 siRNA has the potential to be used as an adjuvant therapy in combination with Daunorubicin in T-ALL.

Inhibiting RRM2 to enhance the anticancer activity of chemotherapy

RRM2, the small subunit of ribonucleotide reductase, is identified as a tumor promotor and therapeutic target. It is common to see the overexpression of RRM2 in chemo-resistant cancer cells and patients. RRM2 mediates the resistance of many chemotherapeutic drugs and could become the predictor for chemosensitivity and prognosis. Therefore, inhibition of RRM2 may be an effective means to enhance the anticancer activity of chemotherapy. This review tries to discuss the mechanisms of RRM2 overexpression and the role of RRM2 in resistance to chemotherapy. Additionally, we compile the studies on small interfering RNA targets RRM2, RRM2 inhibitors, kinase inhibitors, and other ways that could overcome the resistance of chemotherapy or exert synergistic anticancer activity with chemotherapy through the expression inhibition or the enzyme inactivation of RRM2.

Novel Radiosensitization Strategies in Uterine Cervix Cancer

The clinical, molecular, and genetic heterogeneity of uterine cervix cancers makes the discovery of effective therapies a challenge. Optimal evaluation of effective radiotherapy-agent combinations requires sophisticated trial strategies from the United States National Cancer Institute and its pharmaceutical collaborators. One strategy involves the phase 0 trial, which falls under the United States Food and Drug Administration Exploratory Investigational New Drug Guidance, or xIND. As currently envisioned for radiotherapy-based trials, the phase 0 trial provides a platform for study of pharmacodynamic effects linked to pharmacokinetic exposures, designed to screen a new experimental agent's dose or schedule, in combination with standard radiotherapy regimens, in a very small number (10-15) of subjects. In the phase 0 trial, radiotherapy-agent combinations are intended to be biologically active, but a new experimental agent's low dose or infrequent schedule is considered nontoxic and nonbeneficial. The phase 0 trial primary endpoint is an individual subject's pharmacodynamic response. Regimens move on from phase 0 trial development if and when a predetermined all-subject pharmacodynamic response rate is crossed. An initial safety experience during and after the radiotherapy-agent combination determines future feasibility. For this article, the clinical example of women with abdominopelvic lymph node-positive uterine cervix cancer is used to elaborate the phase 0 trial approach to the discovery of novel radiosensitizing oncological agents. It is expected that phase 0 radiotherapy-agent trials will become more prevalent in near-term clinical development.

Randomized Phase II Trial of Triapine-Cisplatin-Radiotherapy for Locally Advanced Stage Uterine Cervix or Vaginal Cancers

Uterine cervix or vaginal cancers have inherent overactivity of ribonucleotide reductase (RNR), making these cancers rational targets for therapy based on interruption of cisplatin-radiotherapy-induced DNA damage repair. We conducted a pilot, open-label randomized phase II trial to evaluate the efficacy and safety of cisplatin-radiotherapy with or without triapine, a small molecule with RNR-inhibitory activity, in patients with advanced-stage uterine cervix or vaginal cancers (NCT01835171), as a lead in to a randomized phase III study (NCT02466971). A total of 26 women were randomly assigned to receive 6 weeks of daily radiotherapy followed by brachytherapy (80 Gy) and once-weekly cisplatin (40 mg m⁻²)—with or without three-times weekly intravenous triapine (25 mg m⁻²)—in one 56-days cycle. Primary end points were metabolic complete response by positron emission tomography and safety. Additional end points included the rate of clinical response, rate of methemoglobinemia, and progression-free survival. The addition of triapine to cisplatin-radiotherapy improved the rate of metabolic complete response from 69 to 92% (P = 0.32) and raised the 3-year progression-free survival estimate from 77 to 92% (hazard ratio for progression, 0.30; P = 0.27). The most frequent grade 3 or 4 adverse events in either treatment group included reversible leukopenia, neutropenia, fatigue, or electrolyte abnormalities. No significant differences were seen between the two groups in the rate of adverse events. Symptomatic methemoglobinemia was not encountered after triapine infusion. In conclusion, the addition of triapine to cisplatin-radiotherapy improved the rate of metabolic complete response in patients with advanced-stage uterine cervix or vaginal cancers without significant toxicity. A phase III trial adequately powered to evaluate progression-free and overall survival is underway (NCT02466971).

Radiopharmaceuticals for Persistent or Recurrent Uterine Cervix Cancer

Uterine cervix cancers pose therapeutic challenges because of an overactive ribonucleotide reductase, which provides on-demand deoxyribonucleotides for DNA replication or for a DNA damage repair response. Ribonucleotide reductase overactivity bestows cancer cell resistance to the effects of radiotherapy and chemotherapy used to treat disease; but nevertheless, this same biologic overexpression provides opportune vulnerabilities relatively specific to uterine cervix cancers for new therapeutic strategies to take advantage. The discovery of human epidermal growth factor receptor 2 (ErbB2 or HER2) overexpression on metastatic uterine cervix cancer cells provides an opportunity for clinical trials of targeted radiopharmaceuticals in combination with DNA damage response modifying drugs. The National Cancer Institute's clinical trial infrastructure and its experimental therapeutics portfolio can now offer clinical trial evaluation of molecularly-targeted and tolerated radiopharmaceutical-drug combinations for women with persistent or recurrent metastatic uterine cervix cancer. This article discusses the current thinking of the National Cancer Institute in regard to attractive radiopharmaceutical strategies for this disease and others.

Irradiation of pediatric glioblastoma cells promotes radioresistance and enhances glioma malignancy via genome-wide transcriptome changes

Pediatric glioblastoma (GBM) is a relatively rare brain tumor in children that has a dismal prognosis. Surgery followed by radiotherapy is the main treatment protocol used for older patients. The benefit of adjuvant chemotherapy is still limited due to a poor understanding of the underlying molecular and genetic changes that occur with irradiation of the tumor. In this study, we performed total RNA sequencing on an established stable radioresistant pediatric GBM cell line to identify mRNA expression changes following radiation. The expression of many genes was altered in the radioresistant pediatric GBM model. These genes have never before been reported to be associated with the development of radioresistant GBM. In addition to exhibiting an accelerated growth rate, radioresistant GBM cells also have overexpression of the DNA synthesis-rate-limiting enzyme ribonucleotide reductase, and pro-cathepsin B. These newly identified genes should be concertedly studied to better understand their role in pediatric GBM recurrence and progression after radiation. It was observed that the changes in multiple biological pathways protected GBM cells against radiation and transformed them to a more malignant form. These changes emphasize the importance of developing a treatment regimen that consists of a multiple-agent cocktail that acts on multiple implicated pathways to effectively target irradiated pediatric GBM. An alternative to radiation or a novel therapy that targets differentially expressed genes, such as metalloproteases, growth factors, and oncogenes and aim to minimize oncogenic changes following radiation is necessary to improve recurrent GBM survival.

Triapine Radiochemotherapy in Advanced Stage Cervical Cancer

Clinical ribonucleotide reductase (RNR) inhibitors have reinvigorated enthusiasm for radiochemotherapy treatment of patients with regionally advanced stage cervical cancers. About two-thirds of patients outlive their cervical cancer (1), even though up to half of their tumors retain residual microscopic disease (2). The National Cancer Institute Cancer Therapy Evaluation Program conducted two prospective trials of triapine–cisplatin–radiation to improve upon this finding by precisely targeting cervical cancer’s overactive RNR. Triapine’s potent inactivation of RNR arrests cells at the G1/S cell cycle restriction checkpoint and enhances cisplatin–radiation cytotoxicity. In this article, we provide perspective on challenges encountered in and future potential of clinical development of a triapine–cisplatin–radiation combination for patients with regionally advanced cervical cancer. New trial results and review presented here suggest that a triapine–cisplatin–radiation combination may offer molecular cell cycle target control to maximize damage in cancers and to minimize injury to normal cells. A randomized trial now accrues patients with regionally advanced stage cervical cancer to evaluate triapine’s contribution to clinical benefit after cisplatin–radiation (clinicaltrials.gov, NCT02466971).

Moving forward with actionable therapeutic targets and opportunities in endometrial cancer: A NCI clinical trials planning meeting report

The incidence of endometrial cancer (EC) in the U.S. has been rising, from an estimated annual incidence of 49,560 in 2013 to 61,380 in 2017. Meanwhile, the SEER-based relative survival of women with EC in the U.S. has remained flat [82.3% from 1987 to 1989, 82.8% from 2007 to 2013] and our recent increased understanding of EC biology and subtypes has not been translated into therapeutic advances. The U.S. National Cancer Institute (NCI) therefore convened a Uterine Clinical Trials Planning Meeting in January 2016 to initiate and accelerate design of molecularly-targeted EC trials. Prior to the meeting a group of experts in this field summarized available data, emphasizing data on human samples, to identify potentially actionable alterations in EC, and the results of their work has been separately published. The Clinical Trials Meeting planners focused on discussion of (1) novel trial designs, including window-of opportunity trials and appropriate control groups for randomized trials, (2) targets specific to serous carcinoma and promises and pitfalls of separate trials for women with tumors of this histology (3) specific recommendations for future randomized trials.

Overexpression of p53R2 is associated with poor prognosis in lung sarcomatoid carcinoma

Background

This study aimmed to evaluate the expression of p53-inducible RR small subunit 2 homologue (p53R2) in Lung sarcomatoid carcinoma (LSC) and its association with clinicopathological parameters and prognosis.

Methods

In this study, clinicopathological factors and prognostic significance of the expression of p53R2 was investigated by immunohistochemistry (IHC) in 100 cases of LSC.

Results

The results showed that the expression of p53R2 was significantly correlated with clinical stage (P<0.05). But there was no statistically correlation with gender, age, smoking, tumor size, pT stage, pN stage, pM stage, therapy and relapse. Kaplan-Meier analysis revealed that the expression of p53R2, clinical stage, pT stage, pN stage, pM stage and tumor size were closely related to patients’ survival, and the analysis also revealed that patients with low expression of p53R2 had a longer overall survival than that with high expression (Mean overall survival: 84.8 months vs. 34.7 months, P<0.05). Further multivariate analysis indicated that the expression of p53R2 was identified as an independent prognostic factor in the prediction of the overall survival for patients with LSC (HR = 3.217, P<0.05).

Conclusions

The expression of p53R2 was inversely associated with the proliferation and progression of LSC, and the results indicated that the high expression of p53R2 was an independent factor for unfavorable prognosis of patients with LSC.

LC-MS/MS assay for the quantitation of the ribonucleotide reductase inhibitor triapine in human plasma

The ribonucleotide reductase inhibitor and radiosensitizer triapine (3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP), NSC 663249) is clinically being evaluated via the intravenous (IV) route for the treatment of cervical and vulvar cancer in combination with primary cisplatin chemoradiation. The need for a 2-h infusion and frequent administration of triapine is logistically challenging, prompting us to pursue oral (PO) administration. In support of the clinical trial investigating oral triapine in combination with chemoradiation, we developed and validated a novel LC-MS/MS assay for the quantification of triapine in 50μL human plasma. After protein precipitation, chromatographic separation of the supernatant was achieved with a Shodex ODP2 column and an isocratic acetonitrile-water mobile phase with 10% ammonium acetate. Detection with an ABI 4000 mass spectrometer utilized electrospray positive mode ionization. The assay was linear from 3 to 3,000ng/mL and proved to be accurate (97.1-103.1%) and precise (<7.4% CV), and met the U.S. FDA guidance for bioanalytical method validation. This LC-MS/MS assay will be an essential tool to further define the pharmacokinetics and oral bioavailability of triapine.

p53R2 overexpression in cervical cancer promotes AKT signaling and EMT, and is correlated with tumor progression, metastasis and poor prognosis

p53R2 is a p53-inducible ribonucleotide reductase subunit involved in deoxyribonucleotide biosynthesis and DNA repair. Although p53R2 has been linked to human cancer, its role in cervical cancer remains unknown. In this study, we investigated the expression and clinical significance of p53R2 in early-stage cervical cancer. p53R2 expression is significantly upregulated at both mRNA and protein levels in cervical cancer cells and tissues, compared with that in matched normal cervical cells and tissues, respectively. p53R2 overexpression is associated with increased risk of pelvic lymph node metastasis (PLNM, p = 0.001) and cancer relapse (p = 0.009). Patients with high p53R2 expression have a shorter overall survival (OS) and disease-free survival (DFS). p53R2 is an independent factor for predicting OS and DFS of cervical cancer patients. We further show that p53R2 is important for oncogenic growth, migration and invasion in cervical cancer cells. Mechanistically, p53R2 promotes Akt signaling and epithelial-mesenchymal transition (EMT). In conclusion, our study demonstrates for the first time that p53R2 protein is overexpressed in early-stage cervical cancer and unravels some unconventional oncogenic functions of p53R2. p53R2 may be a useful prognostic biomarker and therapeutic target for cervical cancer.

Phase I Trial of Triapine-Cisplatin-Paclitaxel Chemotherapy for Advanced Stage or Metastatic Solid Tumor Cancers

Ribonucleotide reductase (RNR) is an enzyme involved in the de novo synthesis of deoxyribonucleotides, which are critical for DNA replication and DNA repair. Triapine is a small-molecule RNR inhibitor. A phase I trial studied the safety of triapine in combination with cisplatin–paclitaxel in patients with advanced stage or metastatic solid tumor cancers in an effort to capitalize on disrupted DNA damage repair. A total of 13 patients with various previously treated cancers were given a 96-h continuous intravenous (i.v.) infusion of triapine (40–120 mg/m²) on day 1, and then 3-h i.v. paclitaxel (80 mg/m²) followed by 1-h i.v. cisplatin (50–75 mg/m²) on day 3. This combination regimen was repeated every 21 days. The maximum tolerated dose (MTD) for each agent was identified to be triapine (80 mg/m²), cisplatin (50 mg/m²), and paclitaxel (80 mg/m²). Common grade 3 or 4 toxicities included reversible anemia, leukopenia, thrombocytopenia, or electrolyte abnormalities. The combination regimen of triapine–cisplatin–paclitaxel resulted in no objective responses; however, five (83%) of six patients treated at the MTD had stable disease between 1 and 8 months duration. This phase I study showed that the combination regimen of triapine–cisplatin–paclitaxel was safe and provides a rational basis for a follow-up phase II trial to evaluate efficacy and progression-free survival in women with metastatic or recurrent uterine cervix cancer.

Modulating the DNA Damage Response to Improve Treatment Response in Cervical Cancer

Cervical cancer is the fourth most common cause of cancer-related death in women worldwide and new therapeutic approaches are needed to improve clinical outcomes for this group of patients. Current treatment protocols for locally advanced and metastatic disease consist of ionising radiation and chemotherapy. Chemoradiation induces cytotoxic levels of DNA double-strand breaks, which activates programmed cell death via the DNA damage response (DDR). Cervical cancers are unique given an almost exclusive association with human papillomavirus (HPV) infection; a potent manipulator of the DDR, with the potential to alter tumour sensitivity to DNA-damaging agents and influence treatment response. This review highlights the wide range of therapeutic strategies in development that have the potential to modulate DDR and sensitise cervical tumours to DNA-damaging agents in the context of HPV oncogenesis.

Phase I trial of daily triapine in combination with cisplatin chemotherapy for advanced-stage malignancies

PURPOSE

Advanced-stage malignancies have increased deoxyribonucleotide demands in DNA replication and repair, making deoxyribonucleotide supply a potential exploitable target for therapy based on ribonucleotide reductase (RNR) inhibition.

METHODS

A dose-finding phase I trial was conducted of intravenous (i.v.) triapine, a small-molecule RNR inhibitor, and cisplatin chemotherapy in patients with advanced-stage solid tumor malignancies. Patients received dose-finding levels of i.v. triapine (48-96 mg/m²) and i.v. cisplatin (20-75 mg/m²) on 1 of 3 different schedules. The primary endpoint was to identify the maximum tolerated dose of a triapine-cisplatin combination. Secondary endpoints included the rate of triapine-cisplatin objective response and the pharmacokinetics and bioavailability of a single oral triapine dose. (Clinicaltrials.gov number, NCT00024323).

RESULTS

The MTD was 96 mg/m² triapine daily days 1-4 and 75 mg/m² cisplatin split over day 2 and day 3. Frequent grade 3 or 4 adverse events included fatigue, dyspnea, leukopenia, thrombocytopenia, and electrolyte abnormalities. No objective responses were observed; 5 (50%) of 10 patients treated at the MTD had stable disease. Pharmacokinetics indicated an oral triapine bioavailability of 88%.

CONCLUSIONS

The triapine-cisplatin combination may be given safely in patients with advanced-stage solid tumor malignancies. On the basis of these results, a phase I trial adequately powered to evaluate oral triapine bioavailability in women with advanced-stage uterine cervix or vulvar cancers is underway.

Radiation-Therapeutic Agent Clinical Trials: Leveraging Advantages of a National Cancer Institute Programmatic Collaboration

A number of oncology phase II radiochemotherapy trials with promising results have been conducted late in the overall experimental therapeutic agent development process. Accelerated development and approval of experimental therapeutic agents have stimulated further interest in much earlier radiation-agent studies to increase the likelihood of success in phase III trials. To sustain this interest, more forward-thinking preclinical radiobiology experimental designs are needed to improve discovery of promising radiochemotherapy plus agent combinations for clinical trial testing. These experimental designs should better inform next-step radiation-agent clinical trial dose, schedule, exposure, and therapeutic effect. Recognizing the need for a better strategy to develop preclinical data supporting radiation-agent phase I or II trials, the National Cancer Institute (NCI)-Cancer Therapy Evaluation Program (CTEP) and the NCI-Molecular Radiation Therapeutics Branch of the Radiation Research Program have partnered to promote earlier radiobiology studies of CTEP portfolio agents. In this Seminars in Radiation Oncology article, four key components of this effort are discussed. First, we outline steps for accessing CTEP agents for preclinical testing. Second, we propose radiobiology studies that facilitate transition from preclinical testing to early phase trial activation. Third, we navigate steps that walk through CTEP agent strategic development paths available for radiation-agent testing. Fourth, we highlight a new NCI-sponsored cooperative agreement grant supporting in vitro and in vivo radiation-CTEP agent testing that informs early phase trial designs. Throughout the article, we include contemporary examples of successful radiation-agent development initiatives.

A phase I-II evaluation of veliparib (NSC #737664), topotecan, and filgrastim or pegfilgrastim in the treatment of persistent or recurrent carcinoma of the uterine cervix: an NRG Oncology/Gynecologic Oncology Group study

PURPOSE

The aim of this study was to evaluate the tolerability and efficacy of poly(ADP-ribose) polymerase (PARP) inhibition by veliparib during cytotoxic topotecan administration with filgrastim or pegfilgrastim neutrophil support in women with persistent or recurrent uterine cervix cancer.

EXPERIMENTAL DESIGN

This phase I-II trial examined twice-daily oral veliparib (10 mg) given during once-daily intravenous topotecan (0.6 mg/m²) on days 1 to 5 of each treatment cycle. Cycles were repeated every 21 days until disease progression or until toxicity prohibited further therapy. Toxicity and objective response rate were primary endpoints.

RESULTS

Twenty-seven women were enrolled. Frequently reported grade 3 or higher treatment-related toxicities were anemia (59%), thrombocytopenia (44%), leukopenia (22%), and neutropenia (19%). There were 2 partial responses (7% [90% confidence interval, 1%-22%]). Four patients had a disease progression date more than 6 months after the start of veliparib-topotecan therapy. Patients with low immunohistochemical expression (0-1+) of PARP-1 in their primary uterine cervix cancer were more likely to have a longer progression-free interval (hazard ratio, 0.25; P = 0.02) and survival (hazard ratio, 0.12; P = 0.005) after veliparib-topotecan therapy.

CONCLUSIONS

Clinical activity of a veliparib-topotecan combination was minimal in women with persistent or recurrent uterine cervix cancer. Women whose uterine cervix cancers express PARP-1 at low levels may benefit preferentially from PARP inhibitors combined with cytotoxic therapies, suggesting further study of PARP expression as an integral triage biomarker.

Long-Term Disease Control with Triapine-Based Radiochemotherapy for Patients with Stage IB2-IIIB Cervical Cancer

Background: National Cancer Institute phase I #7336 and phase II #8327 clinical trials explored the safety and efficacy of triapine (NSC #663249) added to cisplatin radiochemotherapy in untreated patients with advanced-stage cervical cancer. Triapine inhibits ribonucleotide reductase, the rate-limiting enzyme responsible for DNA-building deoxyribonucleotides, and thereby, enhances radiochemosensitivity by prolonging DNA repair time. Here, we report 3-year efficacy endpoints of pelvic locoregional relapse rate, disease-free, and overall survivals.

Methods: Eligible patients with bulky IB–IIIB cervical cancer underwent three-times weekly triapine (25 or 50 mg/m²), once-weekly cisplatin (40 mg/m²), and conventional daily pelvic radiation followed by brachytherapy. A cumulative incidence method estimated pelvic locoregional relapse rates. Disease-free survival was measured from radiochemotherapy start date to the date of first relapse or cancer-related death. Overall survival was measured from radiochemotherapy start date to the date of any-cause death. The Kaplan–Meier method estimated survivals.

Findings: Between 2006 and 2011, 24 untreated patients with cervical cancer met criteria for reporting in this study. A median 3.4 years of follow-up time (range, 0.3–7.6 years) has been observed. All had squamous cancers and the majority had either node-positive stage IB–IIA (33%) or stage IIIB (42%) disease. The 3-year pelvic locoregional relapse rate, disease-free survival, and overall survival were 4% [95% confidence interval (CI), 0–20%], 80% (95% CI: 71–89%), and 82% (95% CI: 74–90%), respectively.

Interpretation: Triapine radiochemotherapy was safe, active, and effective in patients with untreated advanced-stage cervical cancer, worthy of randomized clinical trial study.

Ribonucleotide reductase expression in cervical cancer: a radiation therapy oncology group translational science analysis

OBJECTIVE

To evaluate pretherapy ribonucleotide reductase (RNR) expression and its effect on radiochemotherapeutic outcome in women with cervical cancer.

METHODS/MATERIALS

Pretherapy RNR M1, M2, and M2b immunohistochemistry was done on cervical cancer specimens retrieved from women treated on Radiation Therapy Oncology Group (RTOG) 0116 and 0128 clinical trials. Enrollees of RTOG 0116 (node-positive stages IA-IVA) received weekly cisplatin (40 mg/m(2)) with amifostine (500 mg) and extended-field radiation then brachytherapy (85 Gy). Enrollees of RTOG 0128 (node-positive or bulky ≥5 cm, stages IB-IIA or stages IIB-IVA) received cisplatin (75 mg/m(2)) on days 1, 23, and 43 and 5-FU (1 g/m(2) for 4 days) during pelvic radiation then brachytherapy (85 Gy), plus celecoxib (400 mg twice daily, day 1 through 1 year). Disease-free survival (DFS) was estimated univariately by the Kaplan-Meier method. Cox proportional hazards models evaluated the impact of RNR immunoreactivity on DFS.

RESULTS

Fifty-one tissue samples were analyzed: 13 from RTOG 0116 and 38 from RTOG 0128. M1, M2, and M2b overexpression (3+) frequencies were 2%, 80%, and 47%, respectively. Low-level (0-1+, n = 44/51) expression of the regulatory subunit M1 did not associate with DFS (P = 0.38). High (3+) M2 expression occurred in most (n = 41/51) but without impact alone on DFS (hazard ratio, 0.54; 95% confidence interval, 0.2-1.4; P = 0.20). After adjusting for M2b status, pelvic node-positive women had increased hazard for relapse or death (hazard ratio, 5.5; 95% confidence interval, 2.2-13.8; P = 0.0003).

CONCLUSIONS

These results suggest that RNR subunit expression may discriminate cervical cancer phenotype and radiochemotherapy outcome. Future RNR biomarker studies are warranted.

Targeting ribonucleotide reductase for cancer therapy

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.

Radiochemotherapy plus 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP, NSC #663249) in advanced-stage cervical and vaginal cancers

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 3× weekly 2-hour intravenous 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP, 25 mg/m(2)) co-administered with 1× weekly intravenous cisplatin (40 mg/m(2)) and daily pelvic radiation (45 Gy) in women with stage I(B2)-IV(B) 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.

Inhibition of Poly(ADP-Ribose) Polymerase Enhances Radiochemosensitivity in Cancers Proficient in DNA Double-Strand Break Repair

Pharmacologic inhibitors of poly(ADP-ribose) polymerase (PARP) putatively enhance radiation toxicity in cancer cells. Although there is considerable information on the molecular interactions of PARP and BRCA1- and BRCA2-deficient cancers, very little is known of the PARP inhibition effect upon cancers proficient in DNA double-strand break repair after ionizing radiation or after stalled replication forks. In this work, we investigate whether PARP inhibition by ABT-888 (veliparib) augments death-provoking effects of ionizing radiation, or of the topoisomerase I poison topotecan, within uterine cervix cancers cells harboring an unfettered, overactive ribonucleotide reductase facilitating DNA double-strand break repair and contrast these findings with ovarian cancer cells whose regulation of ribonucleotide reductase is relatively intact. Cell lethality of a radiation-ABT-888 combination is radiation and drug dose dependent. Data particularly highlight an enhanced topotecan-ABT-888 cytotoxicity, and corresponds to an increased number of unrepaired DNA double-strand breaks. Overall, our findings support enhanced radiochemotherapy toxicity in cancers proficient in DNA double-strand break repair when PARP is inhibited by ABT-888.

Elevated ribonucleotide reductase levels associate with suppressed radiochemotherapy response in human cervical cancers

OBJECTIVE

Ribonucleotide reductase (RNR) supplies deoxyribonucleotide diphosphates demanded by cells to repair radiation-induced DNA damage. Here, we investigate the impact of pretherapy RNR M1, M2, and M2b (p53R3) subunit level upon human cervical cancer radiochemosensitivity.

MATERIALS/METHODS

Immunohistochemistry was performed on a tissue array comprised of 18 paired benign uterine cervix and stage IB2 cervical cancers to evaluate the relationship between cytosolic RNR M1, M2, and M2b staining intensity and radiochemotherapy cancer response. Patients underwent surgical hysterectomy (n = 8), or daily radiation (45 Gy), coadministered once-weekly cisplatin (40 mg/m), then low-dose rate brachytherapy (30 Gy) followed by adjuvant hysterectomy (n = 10). Radiochemotherapy response was determined by Response Evaluation Criteria In Solid Tumors version 1.0 criteria during brachytherapy. Cancer relapse rates and disease-free survival were calculated.

RESULTS

M1, M2, and M2b antibody staining intensity was low (0-1+) in benign uterine cervical tissue. M1 and M2b immunoreactivity was 2+ or 3+ in most (13/18) cervical cancers. M2 immunoreactivity was 3+ in nearly all (16/18) cervical cancers. Cervical cancers overexpressing M1 and M2b had an increased hazard for incomplete radiochemotherapy response, relapse, and shortened disease-free survival.

CONCLUSIONS

Ribonucleotide reductase subunit levels may predict human cervical cancer radiochemosensitivity and subsequent posttherapy cancer outcome. Further validation testing of RNR subunits as biomarkers for radiochemotherapy response is warranted.

A dose escalation and pharmacodynamic study of triapine and radiation in patients with locally advanced pancreas cancer

PURPOSE

Triapine, a novel inhibitor of the M2 subunit of ribonucleotide reductase (RR), is a potent radiosensitizer. This phase 1 study, sponsored by the National Cancer Institute Cancer Therapy Evaluation Program, assessed the safety and tolerability of triapine in combination with radiation (RT) in patients with locally advanced pancreas cancer (LAPCA).

METHODS AND MATERIALS

We evaluated 3 dosage levels of triapine (24 mg/m2, 48 mg/m2, 72 mg/m2) administered with 50.4 Gy of RT in 28 fractions. Patients with LAPCA received triapine thrice weekly, every other week during the course of RT. Dose-limiting toxicity (DLT) was assessed during RT and for 4 weeks after its completion. Dynamic contrast-enhanced magnetic resonance imaging and serum RR levels were evaluated as potential predictors for early response.

RESULTS

Twelve patients were treated. Four patients (1 nonevaluable) were enrolled at dosage level 1 (DL1), 3 patients at DL2, and 5 patients (2 nonevaluable) at DL3. No DLTs were observed, and the maximum tolerated dose was not reached. Two patients (17%) achieved partial response, and 6 patients (50%) had stable disease. One patient underwent R0 resection after therapy. Ninety-two percent of patients (100% at DL3) experienced freedom from local tumor progression. In 75% of patients who eventually experienced progression, metastases developed without local progression. RR levels did not seem to predict outcome. In 4 patients with available data, dynamic contrast-enhanced magnetic resonance imaging may predict early response or resistance to therapy.

CONCLUSION

The combination of triapine at 72 mg/m2 3 times weekly every other week and standard RT is tolerable with interesting activity in patients with LAPCA.

γ-H2AX kinetics as a novel approach to high content screening for small molecule radiosensitizers

BACKGROUND

Persistence of γ-H2AX after ionizing radiation (IR) or drug therapy is a robust reporter of unrepaired DNA double strand breaks in treated cells.

METHODS

DU-145 prostate cancer cells were treated with a chemical library ±IR and assayed for persistence of γ-H2AX using an automated 96-well immunocytochemistry assay at 4 hours after treatment. Hits that resulted in persistence of γ-H2AX foci were tested for effects on cell survival. The molecular targets of hits were validated by molecular, genetic and biochemical assays and in vivo activity was tested in a validated Drosophila cancer model.

RESULTS

We identified 2 compounds, MS0019266 and MS0017509, which markedly increased persistence of γ-H2AX, apoptosis and radiosensitization in DU-145 cells. Chemical evaluation demonstrated that both compounds exhibited structurally similar and biochemical assays confirmed that these compounds inhibit ribonucleotide reductase. DNA microarray analysis and immunoblotting demonstrates that MS0019266 significantly decreased polo-like kinase 1 gene and protein expression. MS0019266 demonstrated in vivo antitumor activity without significant whole organism toxicity.

CONCLUSIONS

MS0019266 and MS0017509 are promising compounds that may be candidates for further development as radiosensitizing compounds as inhibitors of ribonucleotide reductase.

Management of 3-aminopyridine-2-carboxaldehyde thiosemicarbazone-induced methemoglobinemia

The anticancer agent 3-aminopyridine-2-carboxaldehyde thiosemicarbazone is a ribonucleotide reductase inhibitor. It inactivates ribonucleotide reductase by disrupting an iron-stabilized radical in ribonucleotide reductase's small subunits, M2 and M2b (p53R2). Unfortunately, 3-aminopyridine-2-carboxaldehyde thiosemicarbazone also alters iron II (Fe(2+)) in hemoglobin. This creates Fe(3+) methemoglobin that does not deliver oxygen. Fe(2+) in hemoglobin normally auto-oxidizes to inactive Fe(3+) methemoglobin at a rate of nearly 3% per day and this is counterbalanced by a reductase system that normally limits methemoglobin concentrations to less than 1% of hemoglobin. This balance may be perturbed by symptomatic toxicity levels during 3-aminopyridine-2-carboxaldehyde thiosemicarbazone therapy. Indications of 3-aminopyridine-2-carboxaldehyde thiosemicarbazone sequelae attributable to methemoglobinemia include resting dyspnea, headaches and altered cognition. Management of methemoglobinemia includes supplemental oxygen, ascorbate and, most importantly, intravenously administered methylene blue as a therapeutic antidote.

Ribonucleotide reductase inhibition restores platinum-sensitivity in platinum-resistant ovarian cancer: a Gynecologic Oncology Group Study

Background

The potent ribonucleotide reductase (RNR) inhibitor 3-aminopyridine-2-carboxyaldehyde-thiosemicarbazone (3-AP) was tested as a chemosensitizer for restored cisplatin-mediated cytotoxicity in platinum-resistant ovarian cancer.

Methods

Preclinical in vitro platinum-resistant ovarian cancer cell survival, RNR activity, and DNA damage assays were done after cisplatin or cisplatin plus 3-AP treatments. Six women with platinum-resistant ovarian cancer underwent four-day 3-AP (96 mg/m², day one to four) and cisplatin (25 mg/m², day two and three) infusions every 21 days until disease progression or adverse effects prohibited further therapy. Pre-therapy ovarian cancer tissues were analyzed by immunohistochemistry for RNR subunit expression as an indicator of cisplatin plus 3-AP treatment response.

Results

3-AP preceding cisplatin exposure in platinum-resistant ovarian cancer cells was not as effective as sequencing cisplatin plus 3-AP together in cell survival assays. Platinum-mediated DNA damage (i.e., γH2AX foci) resolved quickly after cisplatin-alone or 3-AP preceding cisplatin exposure, but persisted after a cisplatin plus 3-AP sequence. On trial, 25 four-day overlapping 3-AP and cisplatin cycles were administered to six women (median 4.2 cycles per patient). 3-AP-related methemoglobinemia (range seven to 10%) occurred in two (33%) of six women, halting trial accrual.

Conclusions

When sequenced cisplatin plus 3-AP, RNR inhibition restored platinum-sensitivity in platinum-resistant ovarian cancers. 3-AP (96 mg/m²) infusions produced modest methemoglobinemia, the expected consequence of ribonucleotide reductase inhibitors disrupting collateral proteins containing iron.

Trial registry

ClinicalTrials.gov NCT00081276

Ribonucleotide reductase inhibitors: a new look at an old target for radiosensitization

Ribonucleotide reductase (RR), the rate limiting enzyme in the synthesis and repair of DNA, has been studied as a target for inhibition in the treatment of cancer for many years. While some researchers have focused on RR inhibitors as chemotherapeutic agents, particularly in hematologic malignancies, some of the most promising data has been generated in the field of radiosensitization. Early pre-clinical studies demonstrated that the addition of the first of these drugs, hydroxyurea, to ionizing radiation (IR) produced a synergistic effect in vitro, leading to a large number of clinical studies in the 1970–1980s. These studies, mainly in cervical cancer, initially produced a great deal of interest, leading to the incorporation of hydroxyurea in the treatment protocols of many institutions. However, over time, the conclusions from these studies have been called into question and hydroxyurea has been replaced in the standard of care of cervical cancer. Over the last 10 years, a number of well-done pre-clinical studies have greatly advanced our understanding of RR as a target. Those advances include the elucidation of the role of p53R2 and our understanding of the temporal relationship between the delivery of IR and the response of RR. At the same time, new inhibitors with increased potency and improved binding characteristics have been discovered, and pre-clinical and early clinical data look promising. Here we present a comprehensive review of the pre-clinical and clinical data in the field to date and provide some discussion of future areas of research.

Therapeutic Mechanisms of Treatment in Cervical and Vaginal Cancer

Cervical and vaginal cancers remain serious health problems. Worldwide, more than 530,000 women annually are diagnosed with these diseases, with most new incident cases occurring in nations with limited health resources and underdeveloped screening programs. For women whose disease is too bulky or widespread for surgery, radiochemotherapy should be looked upon as the standard of care. Randomized clinical trials have indicated that radiochemotherapy strategies that disrupt the repair of damaged DNA are key to the management of advanced stage cervical and vaginal cancers. Here, from a viewpoint of cancer cell molecular biology, treatments for advanced stage cervical and vaginal cancers are discussed.

Molecular Strategies of Deoxynucleotide Triphosphate Supply Inhibition Used in the Treatment of Gynecologic Malignancies

Chemotherapies targeting deoxynucleotide triphosphate synthesis are of high medical interest in the treatment of gynecologic malignancies. In this article, we focus on targeted inhibitors of ribonucleotide reductase, an enzyme in charge of ribonucleotide reduction to their corresponding deoxyribonucleotide to be used as the building blocks of DNA. We also discuss human clinical trials have utilized ribonucleotide reductase subunit-specific inhibitors, particularly trials for women with cervical cancer.

A phase I and pharmacokinetic study of oral 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP, NSC #663249) in the treatment of advanced-stage solid cancers: a California Cancer Consortium Study

BACKGROUND

3-Aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP) is a novel small-molecule ribonucleotide reductase inhibitor. This study was designed to estimate the maximum tolerated dose (MTD) and oral bioavailability of 3-AP in patients with advanced-stage solid tumors.

METHODS

Twenty patients received one dose of intravenous and subsequent cycles of oral 3-AP following a 3 + 3 patient dose escalation. Intravenous 3-AP was administered to every patient at a fixed dose of 100 mg over a 2-h infusion 1 week prior to the first oral cycle. Oral 3-AP was administered every 12 h for 5 consecutive doses on days 1-3, days 8-10, and days 15-17 of every 28-day cycle. 3-AP was started at 50 mg with a planned dose escalation to 100, 150, and 200 mg. Dose-limiting toxicities (DLT) and bioavailability were evaluated.

RESULTS

Twenty patients were enrolled. For dose level 1 (50 mg), the second of three treated patients had a DLT of grade 3 hypertension. In the dose level 1 expansion cohort, three patients had no DLTs. No further DLTs were encountered during escalation until the 200-mg dose was reached. At the 200 mg 3-AP dose level, two treated patients had DLTs of grade 3 hypoxia. One additional DLT of grade 4 febrile neutropenia was subsequently observed at the de-escalated 150 mg dose. One DLT in 6 evaluable patients established the MTD as 150 mg per dose on this dosing schedule. Responses in the form of stable disease occurred in 5 (25%) of 20 patients. The oral bioavailability of 3-AP was 67 ± 29% and was consistent with the finding that the MTD by the oral route was 33% higher than by the intravenous route.

CONCLUSIONS

Oral 3-AP is well tolerated and has an MTD similar to its intravenous form after accounting for the oral bioavailability. Oral 3-AP is associated with a modest clinical benefit rate of 25% in our treated patient population with advanced solid tumors.

Deoxynucleoside salvage facilitates DNA repair during ribonucleotide reductase blockade in human cervical cancers

Cells generate 2'-deoxyribonucleoside triphosphates (dNTPs) for both replication and repair of damaged DNA predominantly through de novo reduction of intracellular ribonucleotides by ribonucleotide reductase (RNR). Cells can also salvage deoxynucleosides by deoxycytidine kinase/thymidine kinase 1 in the cytosol or by deoxyguanosine kinase/thymidine kinase 2 in mitochondria. In this study we investigated whether the salvage dNTP supply pathway facilitates DNA damage repair, promoting cell survival, when pharmacological inhibition of RNR by 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP, NSC no. 663249) impairs the de novo pathway. Human cervical cancer cells were subjected to radiation with or without 3-AP under medium deoxynucleoside concentrations of 0, 0.05, 0.5 and 5.0 µM. Efficacy of DNA damage repair was assessed by γ-H2AX flow cytometry and focus counts, by single cell electrophoresis (Comet assay), and by caspase 3 cleavage assay as a marker of treatment-induced apoptosis. Cell survival was assessed by colony formation. We found that deoxyribonucleotide salvage facilitates DNA repair during RNR inhibition by 3-AP and that salvage reduces the radiochemosensitivity of human cervical cancer cells.

Radiosensitization of human cervical cancer cells by inhibiting ribonucleotide reductase: enhanced radiation response at low-dose rates

PURPOSE

To test whether pharmacologic inhibition of ribonucleotide reductase (RNR) by 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP, NSC #663249) enhances radiation sensitivity during low-dose-rate ionizing radiation provided by a novel purpose-built iridium-192 cell irradiator.

METHODS AND MATERIALS

The cells were exposed to low-dose-rate radiation (11, 23, 37, 67 cGy/h) using a custom-fabricated cell irradiator or to high-dose-rate radiation (330 cGy/min) using a conventional cell irradiator. The radiation sensitivity of human cervical (CaSki, C33-a) cancer cells with or without RNR inhibition by 3-AP was evaluated using a clonogenic survival and an RNR activity assay. Alteration in the cell cycle distribution was monitored using flow cytometry.

RESULTS

Increasing radiation sensitivity of both CaSki and C33-a cells was observed with the incremental increase in radiation dose rates. 3-AP treatment led to enhanced radiation sensitivity in both cell lines, eliminating differences in cell cytotoxicity from the radiation dose rate. RNR blockade by 3-AP during low-dose-rate irradiation was associated with low RNR activity and extended G(1)-phase cell cycle arrest.

CONCLUSIONS

We conclude that RNR inhibition by 3-AP impedes DNA damage repair mechanisms that rely on deoxyribonucleotide production and thereby increases radiation sensitivity of human cervical cancers to low-dose-rate radiation.

Cytotoxic Evaluation of 3-Aminopyridine-2-Carboxaldehyde Thiosemicarbazone, 3-AP, in Peripheral Blood Lymphocytes of Patients with Refractory Solid Tumors using Electron Paramagnetic Resonance

PURPOSE: 3-AP (3-aminopyridine-2-carboxaldehyde thiosemicarbazone, 3-AP) is a metal chelator that potently inhibits the enzyme ribonucleotide reductase, RR, which plays a key role in cell division and tumor progression. A sub-unit of RR has a non-heme iron and a tyrosine free radical, which are required for the enzymatic reduction of ribonucleotides to deoxyribonucleotides. The objective of the study was to determine whether 3-AP affects its targeted action by measuring EPR signals formed either directly or indirectly from low molecular weight ferric-3-AP chelates. METHODS: Peripheral blood lymphocytes were collected from patients with refractory solid tumors at baseline and at 2, 4.5 and 22 hours after 3-AP administration. EPR spectra were used to identify signals from high-spin Fe-transferrin, high-spin heme and low-spin iron or copper ions. RESULTS: An increase in Fe-transferrin signal was observed, suggesting blockage of Fe uptake. It is hypothesized that formation of reactive oxygen species by FeT(2) or CuT damage transferrin or the transferrin receptor. An increase in heme signal was also observed, which is a probable source of cytochrome c release from the mitochondria and potential apoptosis. In addition, increased levels of Fe and Cu were identified. CONCLUSION: These results, which were consistent with our earlier study validating 3-AP-mediated signals by EPR, provide valuable insights into the in vivo mechanism of action of 3-AP.

Posttherapy residual disease associates with long-term survival after chemoradiation for bulky stage 1B cervical carcinoma: a Gynecologic Oncology Group study

OBJECTIVE

The objective of the study was to study posttherapy chemoradiation hysterectomy histology with long-term survival in bulky stage 1(B) cervical cancer patients.

STUDY DESIGN

Gynecologic Oncology Group protocols 71 and 123 enrolled 464 patients randomly allocated to pelvic radiation (75 Gy, n = 291) plus hysterectomy (RTH) or to pelvic radiation (75 Gy) and cisplatin (40 mg/m(2), n = 176) plus hysterectomy (RTCH). Risk of progression and death were evaluated by posttherapy hysterectomy response (good: <10% viable; poor: ≥10% viable).

RESULTS

Median survivor follow-up was 112 months. Relative risks of disease progression and death were 0.656 (95% confidence interval, 0.472-0.912) and 0.638 (95% confidence interval, 0.449-0.908), favoring RTCH. Good response patients (345; 74%) had similar 10 year overall survival (OS) and progression-free survival (PFS) after RTH or RTCH (P > .47). Poor response patients after RTCH had superior OS (P = .046) and PFS (P = .084). Extrapelvic recurrences occurred more often in poor response patients.

CONCLUSION

Posttherapy viable residual disease less than 10% was associated with reduced risk of progression and cancer-related death.

Ribonucleotide reductase inhibition enhances chemoradiosensitivity of human cervical cancers

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.

Phase I trial of pelvic radiation, weekly cisplatin, and 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP, NSC #663249) for locally advanced cervical cancer

PURPOSE

This study assessed the safety/tolerability, pharmacokinetics, and clinical activity of three times weekly i.v. 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP, NSC #663249) in combination with once-weekly i.v. cisplatin and daily pelvic radiation in patients with gynecologic malignancies. 3-AP is a novel small-molecule inhibitor of ribonucleotide reductase (RNR) and is being tested as a potential radiosensitizer and chemosensitizer.

EXPERIMENTAL DESIGN

Patients with stage IB2 to IVB cervical cancer (n = 10) or recurrent uterine sarcoma (n = 1) were assigned to dose-finding cohorts of 2-hour 3-AP infusions during 5 weeks of cisplatin chemoradiation. Pharmacokinetic and methemoglobin samples and tumor biopsy for RNR activity were obtained on day 1 and day 10. Clinical response was assessed.

RESULTS

The maximum tolerated 3-AP dose was 25 mg/m(2) given three times weekly during cisplatin and pelvic radiation. Two patients experienced manageable 3-AP-related grade 3 or 4 electrolyte abnormalities. 3-AP pharmacokinetics showed a 2-hour half-life, with median peak plasma concentrations of 277 ng/mL (25 mg/m(2)) and 467 ng/mL (50 mg/m(2)). Median methemoglobin levels peaked at 1% (25 mg/m(2)) and 6% (50 mg/m(2)) at 4 hours after initiating 3-AP infusions. No change in RNR activity was found on day 1 versus day 10 in six early complete responders, whereas elevated RNR activity was seen on day 10 as compared with day 1 in four late complete responders (P = 0.02). Ten (100%) patients with stage IB2 to IVB cervical cancer achieved complete clinical response and remained without disease relapse with a median 18 months of follow-up (6-32 months).

CONCLUSIONS

3-AP was well tolerated at a three times weekly i.v. 25 mg/m(2) dose during cisplatin and pelvic radiation. Clin Cancer Res; 16(4); 1298-306.