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Biochemical Pharmacology Jun 2003To improve the potency of the hypoxic cytotoxin tirapazamine (TPZ), we have constructed an analog, SN26955, with the TPZ moiety attached to an acridine chromophore to...
To improve the potency of the hypoxic cytotoxin tirapazamine (TPZ), we have constructed an analog, SN26955, with the TPZ moiety attached to an acridine chromophore to target the drug to DNA. The underlying reason for this is our previous finding that the hypoxic cytotoxicity of TPZ is a result of its ability to produce DNA double-strand breaks, whereas many of the toxicities of the drug in clinical use are likely the result of its metabolism in the cytoplasm and effects on mitochondria. We found that the DNA-targeted TPZ analog was more potent than TPZ in killing hypoxic cells by 1-2 orders of magnitude, yet it retained the hypoxic selectivity for cell killing of TPZ. We show that SN26955 is only active in producing DNA damage when it is enzymatically reduced while bound to, or in close association with, the DNA. We also show that it has a different cofactor dependence than TPZ for reduction leading to DNA double-strand breaks, suggesting the involvement of a different reductase for production of the lethal lesion than for TPZ. These results show the promise of DNA-targeting of TPZ to produce a DNA compound with greater clinical efficacy than TPZ itself.
Topics: Acridines; Antineoplastic Agents; Cell Survival; DNA Damage; DNA, Neoplasm; Drug Screening Assays, Antitumor; Free Radicals; HeLa Cells; Humans; Hypoxia; Oxygen; Tirapazamine; Triazines; Tumor Cells, Cultured
PubMed: 12781332
DOI: 10.1016/s0006-2952(03)00199-0 -
Journal of Pharmacy & Pharmaceutical... 2020The reduction potentials of bioreductively-activated drugs represent an important design parameter to be accommodated in the course of creating lead compounds and...
The reduction potentials of bioreductively-activated drugs represent an important design parameter to be accommodated in the course of creating lead compounds and improving the efficacy of older generation drugs. Reduction potentials are traditionally reported as single-electron reduction potentials, E(1), measured against reference electrodes under strictly defined experimental conditions. More recently, computational chemists have described redox properties in terms of a molecule's highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), in electron volts (eV). The relative accessibility of HOMO/LUMO data through calculation using today's computer infrastructure and simplified algorithms make the calculated value (LUMO) attractive in comparison to the accepted but rigorous experimental determination of E(1). This paper describes the correlations of eV (LUMO) to E(1) for three series of bioreductively-activated benzotriazine di-N-oxides (BTDOs), ring-substituted BTDOs, ring-added BTDOs and a selection of aromatic nitro compounds. The current computational approach is a closed-shell calculation with a single optimization. Gas phase geometry optimization was followed by a single-point DFT (Density Functional Theory) energy calculation in the gas phase or in the presence of polar solvent. The resulting DFT-derived LUMO energies (eV) calculated for BTDO analogues in gas phase and in presence of polar solvent (water) exhibited very strong linear correlations with high computational efficiency (r2 = 0.9925) and a very high predictive ability (MAD = 7 mV and RMSD = 9 mV) when compared to reported experimentally determined single-electron reduction potentials.
Topics: Density Functional Theory; Electrons; Hypoxia; Oxidation-Reduction; Tirapazamine
PubMed: 32574141
DOI: 10.18433/jpps30602 -
Journal of Clinical Oncology : Official... Jan 2001To determine the maximum-tolerated dose of tirapazamine when combined with cisplatin and radiation in patients with T3/4 and/or N2/3 squamous cell carcinoma of the head... (Clinical Trial)
Clinical Trial
PURPOSE
To determine the maximum-tolerated dose of tirapazamine when combined with cisplatin and radiation in patients with T3/4 and/or N2/3 squamous cell carcinoma of the head and neck.
PATIENTS AND METHODS
The starting schedule was conventionally fractionated radiotherapy (70 Gy in 7 weeks) with concomitant cisplatin 75 mg/m2 and tirapazamine 290 mg/m2 (before cisplatin) in weeks 1, 4, and 7 and tirapazamine alone 160 mg/m2 three times a week in weeks 2, 3, 5, and 6. Positron emission tomography scans for tumor hypoxia (18F misonidazole) were performed before and during radiotherapy.
RESULTS
We treated 16 patients with predominantly oropharyngeal primary tumors, including 10 patients with T4 or N3 disease. Febrile neutropenia occurred toward the end of radiotherapy in three out of six patients treated on the initial dose level. Two of these patients also developed grade 4 acute radiation reactions. Another 10 patients were treated with the same doses, but the week 5 and week 6 tirapazamine doses were omitted. This resulted in less neutropenia and only one dose-limiting toxicity (DLT) (febrile neutropenia), and eight out of 10 patients completed treatment without any dose omissions. In these 10 patients, the acute radiation toxicities were not obviously enhanced compared with chemoradiotherapy regimens using concurrent platinum and fluorouracil. 18F misonidazole scans detected hypoxia in 14 of 15 patients at baseline, with only one patient having detectable hypoxia at the end of treatment. With a median follow-up of 2.7 years, the 3-year failure-free survival rate was 69% (SE, 12%), the 3-year local progression-free rate was 88% (SE, 8%), and the 3-year overall survival rate was 69% (SE, 12%).
CONCLUSION
DLT was due unexpectedly to febrile neutropenia, which could be overcome by omitting tirapazamine in weeks 5 and 6. The combination of tirapazamine, cisplatin, and radiotherapy resulted in remarkably good and durable clinical responses in patients with very advanced head and neck cancers. It warrants further investigation.
Topics: Adult; Aged; Antineoplastic Combined Chemotherapy Protocols; Carcinoma, Squamous Cell; Cell Hypoxia; Cisplatin; Combined Modality Therapy; Dose Fractionation, Radiation; Drug Administration Schedule; Fluorodeoxyglucose F18; Head and Neck Neoplasms; Humans; Middle Aged; Misonidazole; Radiation-Sensitizing Agents; Radiopharmaceuticals; Survival Analysis; Tirapazamine; Tomography, Emission-Computed; Triazines
PubMed: 11208848
DOI: 10.1200/JCO.2001.19.2.535 -
Journal of Biomedical Nanotechnology Feb 2017The efficacy of photodynamic therapy (PDT) in some solid tumors is limited by the poor biodistributive properties of conventional photosensitizers and a natural...
The efficacy of photodynamic therapy (PDT) in some solid tumors is limited by the poor biodistributive properties of conventional photosensitizers and a natural predisposition of tumor cells to survive hypoxia and oxidative stress. This study investigated the therapeutic potential of a third-generation photosensitizer, liposomal zinc phthalocyanine (ZnPC), in combination with the hypoxic cytotoxin tirapazamine (TPZ). TPZ induces DNA double strand breaks (DSBs) under hypoxic conditions and subsequent apoptosis via p53 signaling. Experiments were performed in tumor cells with functional p53 (Sk-Cha1) and dysfunctional p53 (A431). The combination therapy of TPZ and PDT induced DNA DSBs and cell cycle stalling and enhanced the cytotoxicity of PDT by exacerbating apopotic and non-apoptotic tumor cell death. These phenomena occurred regardless of oxygen tension and the mechanism of cell death differed per cell line. Liposomes containing both ZnPC and TPZ exhibited no dark toxicity but were more lethal to both cell types after PDT compared to ZnPC-liposomes lacking TPZ—an effect that was more pronounced under hypoxic conditions. In conclusion, TPZ is a suitable pharmaceutical compound to increase PDT efficacy by exploiting the post-PDT tumor hypoxia. The inclusion of TPZ and ZnPC into a single liposomal delivery system was feasible. The PDT strategy described in this study may be valuable for the treatment of PDT-recalcitrant tumors.
Topics: Antineoplastic Agents; Cell Death; Cell Line, Tumor; Cell Survival; DNA Damage; Humans; Indoles; Isoindoles; Liposomes; Neoplasms; Organometallic Compounds; Oxidative Stress; Photochemotherapy; Photosensitizing Agents; Reactive Oxygen Species; Tirapazamine; Triazines; Zinc Compounds
PubMed: 29377650
DOI: 10.1166/jbn.2017.2327 -
Cancer Research Jul 2001Tirapazamine (TPZ) is a hypoxia-selective cytotoxin that is currently being examined in Phase II and III clinical trials in combination with radiotherapy and... (Comparative Study)
Comparative Study
Tirapazamine (TPZ) is a hypoxia-selective cytotoxin that is currently being examined in Phase II and III clinical trials in combination with radiotherapy and cisplatin-based chemotherapy. Reductases convert TPZ to a cytotoxic radical that produces DNA damage under hypoxic conditions. Because one or more of the enzymes responsible for the bioactivation of TPZ is/are thought to be at or near the nuclear matrix, we hypothesized that TPZ may have a major affect on DNA replication, a process that is known to occur predominantly at the nuclear matrix. To assess the effect of TPZ on DNA replication, we measured the incorporation of radioactive thymidine into DNA of HCT116 human colon cancer cells and HeLa cells. We show that incorporation of radioactive thymidine is dramatically inhibited in cells that are pretreated with TPZ under hypoxic conditions. TPZ-induced inhibition of DNA synthesis was much greater than that produced by more toxic doses of ionizing radiation. We used the SV40-based in vitro DNA replication assay to study the mechanism of inhibition of DNA synthesis in cells treated with TPZ. Using this assay, we show that extracts prepared from cells treated with TPZ under hypoxic conditions had only 25-50% of the DNA replication activity measured in control cells. This reduction in DNA replication activity was associated with a reduction in levels of replication protein A (RPA) in cytoplasmic extracts used for the in vitro DNA replication assay and could be overcome by addition of recombinant human RPA. Furthermore, we show by indirect immunofluorescence that TPZ leads to a localization of the p34 subunit of RPA (RPA2) to small subnuclear foci. These results show that TPZ dramatically inhibits DNA replication and that the mechanism of inhibition, at least in part, involves changes in RPA that alter its cellular localization.
Topics: Antineoplastic Agents; DNA Replication; DNA, Neoplasm; Dose-Response Relationship, Drug; Dose-Response Relationship, Radiation; HeLa Cells; Humans; Oxygen; Tirapazamine; Triazines; Tumor Cells, Cultured
PubMed: 11454687
DOI: No ID Found -
Clinical Oncology (Royal College of... Aug 2007One of the key issues for radiobiologists is the importance of hypoxia to the radiotherapy response. This review addresses the reasons for this and primarily focuses on... (Review)
Review
One of the key issues for radiobiologists is the importance of hypoxia to the radiotherapy response. This review addresses the reasons for this and primarily focuses on one aspect, the development of bioreductive drugs that are specifically designed to target hypoxic tumour cells. Four classes of compound have been developed since this concept was first proposed: quinones, nitroaromatics, aliphatic and heteroaromatic N-oxides. All share two characteristics: (1) they require hypoxia for activation and (2) this activation is dependent on the presence of specific reductases. The most effective compounds have shown the ability to enhance the anti-tumour efficacy of agents that kill better-oxygenated cells, i.e. radiation and standard cytotoxic chemotherapy agents such as cisplatin and cyclophosphamide. Tirapazamine (TPZ) is the most widely studied of the lead compounds. After successful pre-clinical in vivo combination studies it entered clinical trial; over 20 trials have now been reported. Although TPZ has enhanced some standard regimens, the results are variable and in some combinations toxicity was enhanced. Banoxantrone (AQ4N) is another agent that is showing promise in early phase I/II clinical trials; the drug is well tolerated, is known to locate in the tumour and can be given in high doses without major toxicities. Mitomycin C (MMC), which shows some bioreductive activation in vitro, has been tested in combination trials. However, it is difficult to assign the enhancement of its effects to targeting of the hypoxic cells because of the significant level of its hypoxia-independent toxicity. More specific analogues of MMC, e.g. porfiromycin and apaziquone (EO9), have had variable success in the clinic. Other new drugs that have good pre-clinical profiles are PR 104 and NLCQ-1; data on their clinical safety/efficacy are not yet available. This paper reviews the pre-clinical data and discusses the clinical studies that have been reported.
Topics: Animals; Anthraquinones; Antineoplastic Agents; Cell Hypoxia; Genetic Therapy; Humans; Mitomycin; Neoplasms; Polycyclic Aromatic Hydrocarbons; Quinones; Radiation-Sensitizing Agents; Tirapazamine; Triazines
PubMed: 17482438
DOI: 10.1016/j.clon.2007.03.006 -
Seminars in Radiation Oncology Jul 2004Hypoxic modification has been the subject of investigations in clinical radiation oncology since the early 60s. To date, this has not yet resulted in a treatment that... (Review)
Review
Hypoxic modification has been the subject of investigations in clinical radiation oncology since the early 60s. To date, this has not yet resulted in a treatment that has been widely accepted. Logistics and technical difficulties limit the routine use of hyperbaric oxygen in radiotherapy. The nitroimidazoles have not gained general acceptance, initially because of their toxicity and later because of doubts about the effectiveness of the newer generation of less toxic drugs. Nevertheless, there is good evidence from these studies that improving clinical outcome by hypoxic modulation is an achievable goal. Newer approaches including combinations of radiotherapy with tirapazamine, erythropoietin, and carbogen and nicotinamide (ARCON) are currently in phase III trial. For these new strategies to be successful, it is important that the proper patient categories are selected. Various methods to assess tumor oxygenation are now becoming available in the clinic. These potential predictive assays must be incorporated and validated in current and future large-scale clinical trials. Modifiers that target other aspects of tumor biology may also have indirect effects on tumor oxygenation. These aspects require further study in preclinical and early clinical settings.
Topics: Antineoplastic Agents; Cell Hypoxia; Clinical Trials, Phase III as Topic; Dose Fractionation, Radiation; Erythropoietin; Humans; Hyperbaric Oxygenation; Neoplasms; Patient Selection; Tirapazamine; Triazines
PubMed: 15254866
DOI: 10.1016/j.semradonc.2004.04.002 -
Oncology (Williston Park, N.Y.) Oct 1999That hypoxic tissues are more resistant to the effects of radiation than well-oxygenated tissues has been known for many decades, and repeated in vitro demonstrations... (Review)
Review
That hypoxic tissues are more resistant to the effects of radiation than well-oxygenated tissues has been known for many decades, and repeated in vitro demonstrations have confirmed that to achieve the same degree of cytotoxicity, hypoxic cells require about three times the radiation dose that well-oxygenated cells need. Hypoxic cell sensitizers enhance the tissue response to standard radiation, generally by mimicking the effects of oxygen, which induces the formation and stabilization of toxic DNA radicals. Although many hypoxic cell sensitizers like the nitroimidazoles have been evaluated in combination with radiation, these agents have had no or only minimal therapeutic impact due to either their limited potency or their toxicity at biologically relevant concentrations. This article reviews several new modalities that either increase oxygen delivery or sensitize hypoxic tissues. These modalities, all currently in early clinical evaluations, include: (1) tirapazamine, a bioreductive agent; (2) gadolinium texaphyrin, a hypoxic cell sensitizer with biolocalization properties using magnetic resonance imaging; (3) RSR13, an allosteric modifier of hemoglobin; and (4) bovine hemoglobin modified by the attachment of polyethylene glycol polymers.
Topics: Animals; Antineoplastic Agents; Cell Hypoxia; Clinical Trials as Topic; Combined Modality Therapy; DNA Damage; Hemoglobins; Humans; Metalloporphyrins; Neoplasms; Radiation-Sensitizing Agents; Tirapazamine; Triazines
PubMed: 10550828
DOI: No ID Found -
International Journal of Nanomedicine 2016Reductive drug-functionalized gold nanoparticles (AuNPs) have been proposed to enhance the damage of X-rays to cells through improving hydroxyl radical production by...
Reductive drug-functionalized gold nanoparticles (AuNPs) have been proposed to enhance the damage of X-rays to cells through improving hydroxyl radical production by secondary electrons. In this work, polyethylene glycol-capped AuNPs were conjugated with tirapazamine (TPZ) moiety, and then thioctyl TPZ (TPZs)-modified AuNPs (TPZs-AuNPs) were synthesized. The TPZs-AuNPs were characterized by transmission electron microscopy, ultraviolet-visible spectra, dynamic light scattering, and inductively coupled plasma mass spectrometry to have a size of 16.6±2.1 nm in diameter and a TPZs/AuNPs ratio of ~700:1. In contrast with PEGylated AuNPs, the as-synthesized TPZs-AuNPs exhibited 20% increment in hydroxyl radical production in water at 2.0 Gy, and 19% increase in sensitizer enhancement ratio at 10% survival fraction for human hepatoma HepG2 cells under X-ray irradiation. The production of reactive oxygen species in HepG2 cells exposed to X-rays in vitro demonstrated a synergistic radiosensitizing effect of AuNPs and TPZ moiety. Thus, the reductive drug-conjugated TPZs-AuNPs as a kind of AuNP radiosensitizer with low gold loading provide a new strategy for enhancing the efficacy of radiation therapy.
Topics: Gold; Hep G2 Cells; Humans; Hydroxyl Radical; Metal Nanoparticles; Microscopy, Electron, Transmission; Polyethylene Glycols; Radiation-Sensitizing Agents; Tirapazamine; Triazines; Tumor Microenvironment; X-Rays
PubMed: 27555772
DOI: 10.2147/IJN.S105348 -
Journal of Clinical Oncology : Official... Apr 2004To determine the dose limiting toxicity (DLT), maximum-tolerated dose (MTD), and pharmacokinetic profile of tirapazamine (Sanofi Synthelabo Research, Malvern, PA)... (Clinical Trial)
Clinical Trial
PURPOSE
To determine the dose limiting toxicity (DLT), maximum-tolerated dose (MTD), and pharmacokinetic profile of tirapazamine (Sanofi Synthelabo Research, Malvern, PA) combined with cyclophosphamide in children with recurrent solid tumors.
PATIENTS AND METHODS
Patients received a 2-hour infusion of tirapazamine, followed by 1,500 mg/m(2) cyclophosphamide, and mesna once every 3 weeks. Dose escalation of tirapazamine began at 250 mg/m(2) and was increased by 30% in subsequent cohorts. If DLT was hematologic, less-heavily pretreated patients were to be enrolled until their DLTs were encountered, and MTDs defined. Pharmacokinetic profiles were also characterized.
RESULTS
Twenty-three patients were enrolled onto the study. Pharmacokinetic data were calculated for 22 patients. Prolonged neutropenia was the DLT at 420 mg/m(2) in heavily pretreated patients. Grade 3, reversible ototoxicity was the DLT in less-heavily pretreated patients at 420 mg/m(2). Two (one with neuroblastoma and one with rhabdomyosarcoma) had partial responses. One child with neuroblastoma had prolonged stable disease (10 cycles) at a dose of 250 mg/m(2). This patient had disease detectable in the bone marrow only and all evidence of bone marrow involvement resolved for 17 cycles of therapy. Four other patients had stable disease. An apparent dose-proportional increase in tirapazamine maximal concentration and area under the curve(last) was observed. Tirapazamine clearance, volume of distribution at steady-state, and terminal half-life did not appear to be dose-dependent.
CONCLUSION
The recommended dose of tirapazamine given with 1,500 mg/m(2) of cyclophosphamide once every 3 weeks is 325 mg/m(2). Neutropenia and ototoxicity were dose-limiting. Based on early evidence of antitumor activity, additional studies appear warranted.
Topics: Adolescent; Adult; Antineoplastic Combined Chemotherapy Protocols; Child; Child, Preschool; Cyclophosphamide; Female; Humans; Male; Neoplasm Recurrence, Local; Neoplasms; Neutropenia; Tirapazamine; Triazines
PubMed: 15084615
DOI: 10.1200/JCO.2004.07.111