Studies of the pharmacokinetic properties of nimorazole

Activity of Drug Combinations against Mycobacterium abscessus Grown in Aerobic and Hypoxic Conditions

Infections caused by Mycobacterium abscessus (Mab), an environmental non-tuberculous mycobacterium, are difficult to eradicate from patients with pulmonary diseases such as cystic fibrosis and bronchiectasis even after years of antibiotic treatments. In these people, the low oxygen pressure in mucus and biofilm may restrict Mab growth from actively replicating aerobic (A) to non-replicating hypoxic (H) stages, which are known to be extremely drug-tolerant. After the exposure of Mab A and H cells to drugs, killing was monitored by measuring colony-forming units (CFU) and regrowth in liquid medium (MGIT 960) of 1-day-old A cells (A1) and 5-day-old H cells (H5). Mab killing was defined as a lack of regrowth of drug-exposed cells in MGIT tubes after >50 days of incubation. Out of 18 drugs tested, 14-day treatments with bedaquiline-amikacin (BDQ-AMK)-containing three-drug combinations were very active against A1 + H5 cells. However, drug-tolerant cells (persisters) were not killed, as shown by CFU curves with typical bimodal trends. Instead, 56-day treatments with the nitrocompounds containing combinations BDQ-AMK-rifabutin-clarithromycin-nimorazole and BDQ-AMK-rifabutin-clarithromycin-metronidazole-colistin killed all A1 + H5 Mab cells in 42 and 56 days, respectively, as shown by lack of regrowth in agar and MGIT medium. Overall, these data indicated that Mab persisters may be killed by appropriate drug combinations.

Hyperthermia-triggered release of hypoxic cell radiosensitizers from temperature-sensitive liposomes improves radiotherapy efficacy in vitro

Hypoxia is a characteristic feature of solid tumors and an important cause of resistance to radiotherapy. Hypoxic cell radiosensitizers have been shown to increase radiotherapy efficacy, but dose-limiting side effects prevent their widespread use in the clinic. We propose the encapsulation of hypoxic cell radiosensitizers in temperature-sensitive liposomes (TSL) to target the radiosensitizers specifically to tumors and to avoid unwanted accumulation in healthy tissues. The main objective of the present study is to develop and characterize TSL loaded with the radiosensitizer pimonidazole (PMZ) and to evaluate the in vitro efficacy of free PMZ and PMZ encapsulated in TSL in combination with hyperthermia and radiotherapy. PMZ was actively loaded into TSL at different drug/lipid ratios, and the physicochemical characteristics and the stability of the resulting TSL-PMZ were evaluated. PMZ release was determined at 37 °C and 42 °C in HEPES buffer saline and fetal bovine serum. The concentration-dependent radiosensitizing effect of PMZ was investigated by exposing FaDu cells to different PMZ concentrations under hypoxic conditions followed by exposure to ionizing irradiation. The efficacy of TSL-PMZ in combination with hyperthermia and radiotherapy was determined in vitro, assessing cell survival and DNA damage by means of the clonogenic assay and histone H2AX phosphorylation, respectively. All TSL-PMZ formulations showed high encapsulation efficiencies and were stable for 30 d upon storage at 4 °C and 20 °C. Fast PMZ release was observed at 42 °C, regardless of the drug/lipid ratio. Increasing the PMZ concentration significantly enhanced the effect of ionizing irradiation. Pre-heated TSL-PMZ in combination with radiotherapy caused a 14.3-fold increase in cell death as compared to radiotherapy treatment alone. In conclusion, our results indicate that TSL-PMZ in combination with hyperthermia can assist in improving the efficacy of radiotherapy under hypoxic conditions.

Overcoming Radioresistance: Small Molecule Radiosensitisers and Hypoxia-activated Prodrugs

The role of hypoxia in radiation resistance is well established and many approaches to overcome hypoxia in tumours have been explored, with variable success. Two small molecule strategies for targeting hypoxia have dominated preclinical and clinical efforts. One approach has been the use of electron-affinic nitroheterocycles as oxygen-mimetic sensitisers. These agents are best exemplified by the 5-nitroimidazole nimorazole, which has limited use in conjunction with radiotherapy in head and neck squamous cell carcinoma. The second approach seeks to leverage tumour hypoxia as a tumour-specific address for hypoxia-activated prodrugs. These prodrugs are selectively activated by reductases under hypoxia to release cytotoxins, which in some instances may diffuse to kill surrounding oxic tumour tissue. A number of these hypoxia-activated prodrugs have been examined in clinical trial and the merits and shortcomings of recent examples are discussed. There has been an evolution from delivering DNA-interactive cytotoxins to molecularly targeted agents. Efforts to implement these strategies clinically continue today, but success has been elusive. Several issues have been identified that compromised these clinical campaigns. A failure to consider the extravascular transport and the micropharmacokinetic properties of the prodrugs has reduced efficacy. One key element for these 'targeted' approaches is the need to co-develop biomarkers to identify appropriate patients. Hypoxia-activated prodrugs require biomarkers for hypoxia, but also for appropriate activating reductases in tumours, as well as markers of intrinsic sensitivity to the released drug. The field is still evolving and changes in radiation delivery and the impact of immune-oncology will provide fertile ground for future innovation.

Hypoxia-targeted drug delivery

Hypoxia is a state of low oxygen tension found in numerous solid tumours. It is typically associated with abnormal vasculature, which results in a reduced supply of oxygen and nutrients, as well as impaired delivery of drugs. The hypoxic nature of tumours often leads to the development of localized heterogeneous environments characterized by variable oxygen concentrations, relatively low pH, and increased levels of reactive oxygen species (ROS). The hypoxic heterogeneity promotes tumour invasiveness, metastasis, angiogenesis, and an increase in multidrug-resistant proteins. These factors decrease the therapeutic efficacy of anticancer drugs and can provide a barrier to advancing drug leads beyond the early stages of preclinical development. This review highlights various hypoxia-targeted and activated design strategies for the formulation of drugs or prodrugs and their mechanism of action for tumour diagnosis and treatment.

The anti-malarial atovaquone increases radiosensitivity by alleviating tumour hypoxia

Tumour hypoxia renders cancer cells resistant to cancer therapy, resulting in markedly worse clinical outcomes. To find clinical candidate compounds that reduce hypoxia in tumours, we conduct a high-throughput screen for oxygen consumption rate (OCR) reduction and identify a number of drugs with this property. For this study we focus on the anti-malarial, atovaquone. Atovaquone rapidly decreases the OCR by more than 80% in a wide range of cancer cell lines at pharmacological concentrations. In addition, atovaquone eradicates hypoxia in FaDu, HCT116 and H1299 spheroids. Similarly, it reduces hypoxia in FaDu and HCT116 xenografts in nude mice, and causes a significant tumour growth delay when combined with radiation. Atovaquone is a ubiquinone analogue, and decreases the OCR by inhibiting mitochondrial complex III. We are now undertaking clinical studies to assess whether atovaquone reduces tumour hypoxia in patients, thereby increasing the efficacy of radiotherapy.

Targeting tumour hypoxia to improve outcome of stereotactic radiotherapy

BACKGROUND

Hypoxia is a characteristic feature of solid tumours that significantly reduces the efficacy of conventional radiation therapy. In this study we investigated the role of hypoxia in a stereotactic radiation schedule by using a variety of hypoxic modifiers in a preclinical tumour model.

MATERIAL AND METHODS

C3H mammary carcinomas were irradiated with 3 × 15 Gy during a one-week period, followed three days later by a clamped top-up dose to produce a dose response curve; the endpoint was tumour control. The hypoxic modifiers were nimorazole (200 mg/kg), nicotinamide (120 mg/kg) and carbogen (95% O2 + 5% CO2) breathing, OXi4503 (10 mg/kg), and hyperthermia (41.5°C; 1 h).

RESULTS

The radiation dose controlling 50% of clamped tumours (TCD50) following 3 × 15 Gy was 30 Gy. Giving nimorazole or nicotinamide+ carbogen prior to the final 15 Gy fraction non-significantly (χ(2)-test; p < 0.05) reduced this TCD50 to 20-23 Gy; when administered with each 3 × 15 Gy fraction these values were significantly reduced to ≤ 2.5 Gy. Injecting OXi4503 or heating after irradiating significantly reduced the TCD50 to 9-12 Gy regardless of whether administered with one or all three 15 Gy fractions. Combining OXi4503 and heat with the final 15 Gy had a significantly larger effect (TCD50 = 2 Gy).

CONCLUSIONS

Clinically relevant modifiers of hypoxia effectively enhanced an equivalent stereotactic radiation treatment confirming the importance of hypoxia in such schedules.

A rapid and sensitive determination of hypoxic radiosensitizer agent nimorazole in rat plasma by LC-MS/MS and its application to a pharmacokinetic study

A highly sensitive, accurate and robust LC-MS/MS method was developed and validated for determination of nimorazole (NMZ) in rat plasma using metronidazole (MNZ) as internal standard (IS). The analyte and IS were extracted from plasma by precipitating protein with acetonitrile and were chromatographed using an Agilent Poroshell 120, EC-C18 column. The mobile phase was composed of a mixture of acetonitrile and 0.1 % formic acid (85:15 v/v). The total run time was 1.5 min and injection volume was 5 μL. Multiple reaction monitoring mode using the transitions of m/z 227.1 → m/z 114.0 for MNZ and m/z 172.10 → m/z 128.1 for IS were monitored on a triple quadrupole mass spectrometer, operating in positive ion mode. The calibration curve was linear in the range of 0.25-200 ng/mL (r(2)  > 0.9996) and the lower limit of quantification was 0.25 ng/mL in the rat plasma samples. Recoveries of NMZ ranged between 88.05 and 95.25%. The precision (intra-day and inter-day) and accuracy of the quality control samples were 1.25-8.20% and -2.50-3.10, respectively. The analyte and IS were found to be stable during all sample storage and analysis procedures. The LC-MS/MS method described here was validated and successfully applied to pharmacokinetic study in rats.

Study of the population pharmacokinetic characteristics of nimorazole in head and neck cancer patients treated in the DAHANCA-5 trial

AIMS

To study the pharmacokinetic characteristics of the hypoxic radiosensitiser nimorazole in patients with head and neck squamous cell carcinoma.

MATERIALS AND METHODS

The pharmacokinetics of the hypoxic radiosensitiser nimorazole were studied in 63 patients treated in the DAHANCA-5 trial. After the first day of treatment, serial venous blood samples were taken and plasma concentrations of nimorazole measured by high pressure liquid chromatography (HPLC). Plasma concentration profiles were subjected to non-compartmental pharmacokinetic analysis using validated PC-based software. The different pharmacokinetic parameters were calculated and correlated with the different patient- and treatment-related variables.

RESULTS

HPLC measurements showed a linear relationship between peak plasma concentration and administered dose. The mean peak concentration adjusted for dose (in g/m(2)) was 32.2 ± 0.9 μg/ml. The time of peak concentration ranged between 30 and 180 min (median 60 min). Plasma elimination occurred with a mean half-life of 3.35 ± 0.09 h and was not significantly altered as a function of dose. There was a well-established linear-linear relationship between area under the concentration-time curve (AUC; mean 191 ± 6 μg·h/ml) and administered dose, especially when expressed as g/m(2). The mean apparent volume of distribution was 0.77 ± 0.02 l/kg. A statistically significant longer elimination half-life in men relative to women (mean difference 0.40 h; 95% confidence interval 0.77-0.03; P 0.03) was detected. Nimorazole was well tolerated; with 67% of patients reporting no toxicity; nausea/vomiting was the most reported toxicity in the remaining patients.

CONCLUSION

The study supports the current nimorazole dose scheduling in patients.

Compliance and toxicity of the hypoxic radiosensitizer nimorazole in the treatment of patients with head and neck squamous cell carcinoma (HNSCC)

PURPOSE

To evaluate the compliance and toxicity of the hypoxic radiosensitizer nimorazole in head and neck cancer patients.

METHODS

A retrospective study of patients with head and neck squamous cell carcinoma (HNSCC), treated in Denmark between 1990 and 2013. All patients treated with radical radiotherapy (± chemotherapy) [66-70 Gy; 33-35 fractions; 2 Gy/fraction; 5-6 fractions/week] concomitant with the hypoxic radiosensitizer nimorazole. Nimorazole was administered as oral tablets in doses of approximately 1.2 g/m(2) body surface area in connection with the first of each daily radiation treatment. A second daily dose of 1 g was given in connection with the second radiotherapy fraction in the accelerated fractionation regimen. The compliance was estimated as the percentage of the initially prescribed dose, which was received by each patient. The main side effects were recorded.

RESULTS

A total of 1049 patients were investigated. The tolerance to nimorazole was fair: 58% of patients received the full prescribed total dose. Nausea and vomiting were the major complaints: among the 260 patients with dose reductions due to known side effects, (87%) were due to nausea/vomiting. All side effects ceased when treatment was interrupted, and neither severe nor long lasting side effects were observed. Female patients were significantly more likely to have dose reduction (OR 2.02; 95% CI 1.50-2.70), and nausea/vomiting. Patients aged more than 70 years were significantly more likely to have dose reduction. Patients who received less than 1100 mg/m(2) were significantly less likely to have dose reduction (OR 0.58; CI 0.44-0.78), and nausea/vomiting, compared to those who received 1100-1300 mg/m(2). The tolerance was also less in the group of patients received accelerated chemoradiotherapy (OR 1.70; CI 1.20-2.50) with more association with nausea/vomiting (OR 2.09; CI 1.40-3.10).

CONCLUSION

The compliance to nimorazole is fair, with tolerable acute, but neither persistent nor late, toxicity. It can be administered with chemotherapy and different radiotherapy fractionation schedules.

Hypoxia as a target for combined modality treatments

There is overwhelming evidence that solid human tumours grow within a unique micro-environment. This environment is characterised by an abnormal vasculature, which leads to an insufficient supply of oxygen and nutrients to the tumour cells. These characteristics of the environment limit the effectiveness of both radiotherapy and chemotherapy. Measurement of the oxygenation status of human tumours has unequivocally demonstrated the importance of this parameter on patient prognosis. Tumour hypoxia has been shown to be an independent prognostic indicator of poor outcome in prostate, head and neck and cervical cancers. Recent laboratory and clinical data have shown that hypoxia is also associated with a more malignant phenotype, affecting genomic stability, apoptosis, angiogenesis and metastasis. Several years ago, scientists realised that the unique properties within the tumour micro-environment could provide the basis for tumour-specific therapies. Efforts that are underway to develop therapies that exploit the tumour micro-environment can be categorised into three groups. The first includes agents that exploit the environmental changes that occur within the micro-environment such as hypoxia and reduced pH. This includes bioreductive drugs that are specifically toxic to hypoxic cells, as well as hypoxia-specific gene delivery systems. The second category includes therapies designed to exploit the unique properties of the tumour vasculature and include both angiogenesis inhibitors and vascular targeting agents. The final category includes agents that exploit the molecular and cellular responses to hypoxia. For example, many genes are induced by hypoxia and promoter elements from these genes can be used for the selective expression of therapeutic proteins in hypoxic tumour cells. An overview of the various properties ascribed to tumour hypoxia and the current efforts underway to exploit hypoxia for improving cancer treatment will be discussed.

Pilot study of nimorazole as a hypoxic-cell sensitizer with the "chart" regimen in head and neck cancer

PURPOSE

A potential disadvantage of accelerated fractionation in radiotherapy is the lack of time for reoxygenation, so that hypoxia becomes a more potent cause of failure. Accordingly, we have combined nimorazole, the only hypoxic radiosensitizer shown to significantly improve local control in head and neck cancer, with continuous hyperfractionated accelerated radiation therapy (CHART).

METHODS AND MATERIALS

Twenty-two patients with locally advanced (stage IV) squamous cell carcinoma of the head and neck were treated with escalating doses of nimorazole given concomitantly with CHART (three fractions of 1.5 Gy per day, spaced 5 1/2 hours apart, on 12 consecutive days). All patients received 1.2 g/m2 nimorazole 90 minutes before each first daily fraction. Seventeen patients received a further 0.6 g/m2 before each second daily fraction and six of these patients received an additional dose of 0.6 g/m2 before each third fraction.

RESULTS

The three times daily schedule yielded mean plasma drug concentrations at the time of irradiation of 37.7 microg/ml with the morning fractions, 31.2 microg/ml with the afternoon fractions, and 30.4 microg/ml with the evening fractions. In view of these results the midday dose was increased to 0.9 microg/m2 in an ongoing Phase II study. Drug toxicity was limited to nausea and vomiting apart from two cases of mild paraesthesia at the highest dose level.

CONCLUSIONS

Comparison with a historical group of patients, treated with the CHART regimen alone and matched for irradiation volume and technique, showed that nimorazole did not increase the severity of acute normal tissue radiation effects. Encouraging tumor responses have been seen in the patients receiving nimorazole with every radiotherapy fraction.

A randomized double-blind phase III study of nimorazole as a hypoxic radiosensitizer of primary radiotherapy in supraglottic larynx and pharynx carcinoma. Results of the Danish Head and Neck Cancer Study (DAHANCA) Protocol 5-85

PURPOSE

A multicenter randomized and balanced double-blind trial with the objective of assessing the efficacy and tolerance of nimorazole given as a hypoxic radiosensitizer in conjunction with primary radiotherapy of invasive carcinoma of the supraglottic larynx and pharynx.

PATIENTS AND TREATMENT

Between January 1986 and September 1990, 422 patients (414 eligible) with pharynx and supraglottic larynx carcinoma were double-blind randomized to receive the hypoxic cell radiosensitizer nimorazole, or placebo, in association with conventional primary radiotherapy (62-68 Gy, 2 Gy per fraction, five fractions per week). The median observation time was 112 months.

RESULTS

Univariate analysis showed that the outcome (5-year actuarial loco-regional tumor control) was significantly related to T-classification (T1-T2 48% versus T3-T4 36%, P = 0.0008), neck-nodes (N- 53% versus N+ 33%), pre-irradiation hemoglobin (Hb) concentration (high 46% versus low 37%, P = 0.02) and sex (females 51% versus males 38%, P = 0.03). Overall the nimorazole group showed a significantly better loco-regional control rate than the placebo group (49 versus 33%, P = 0.002). A similar significant benefit of nimorazole was observed for the end-points of final loco-regional control (including surgical salvage) and cancer-related deaths (52 versus 41%, P = 0.002). This trend was also found in the overall survival but to a lesser, non-significant extent (26 versus 16%, 10-year actuarial values, P = 0.32). Cox multivariate regression analysis showed the most important prognostic parameters for loco-regional control to be positive neck nodes (relative risk 1.84 (1.38-2.45)), T3-T4 tumor (relative risk 1.65 (1.25-2.17)) and nimorazole (relative risk 0.69 (0.52-0.90)). The same parameters were also significantly related to the probability of dying from cancer. The compliance to radiotherapy was good and 98% of the patients received the planned dose. Late radiation-related morbidity was observed in 10% of the patients, irrespective of nimorazole treatment. Drug-related side-effects were minor and tolerable with transient nausea and vomiting being the most frequent complications.

CONCLUSION

Nimorazole significantly improves the effect of radiotherapeutic management of supraglottic and pharynx tumors and can be given without major side-effects.

Clinical pharmacokinetics of metronidazole and other nitroimidazole anti-infectives

Metronidazole was first introduced for the treatment of trichomoniasis. Its therapeutic use has subsequently been expanded to include amoebiasis, giardiasis and, more recently, anaerobic infections. Most of the early pharmacokinetic studies employed nonspecific assays such as microbiological and chemical assays. These assays were not able to differentiate the parent drug from the metabolites or other interfering substances. Pharmacokinetic data obtained through the use of specific chromatographic techniques provide the basis for this review of recent pharmacokinetic findings concerning metronidazole and other nitroimidazole antibiotics. When given intravenously or orally at usual recommended doses, metronidazole attains concentrations well above the minimum inhibitory concentrations for most susceptible micro-organisms. The drug has an oral bioavailability approaching 100%. Rectal and vaginal administration results in a smaller amount of drug absorption and lower serum concentrations. Metronidazole has limited plasma protein binding but can attain very favourable tissue distribution, including into the central nervous system. The drug is extensively metabolised by the liver to form 2 primary oxidative metabolites: the hydroxy and acetic acid metabolites. The kidney is responsible for the elimination of only a small amount of the parent drug; however, normal excretion of the 2 metabolites is dependent on the integrity of kidney function. The metabolism of metronidazole was found to vary among patient groups. Preterm and term infants have lower total body clearance (CL) and prolonged elimination half-lives. However, children older than 4 years old were observed to have pharmacokinetic parameters similar to those in adults. Reduced CL was also observed in children who are malnourished. Elderly patients have reduced renal excretion of both the parent drug and hydroxy metabolite. Pharmacokinetic parameters in pregnant patients were not significantly different from those in nonpregnant women; however, the drug is distributed into breastmilk and the infant will be exposed to the drug through the nursing mother. Patients undergoing gastrointestinal surgery or having enteric diseases and those who are hospitalised or critically ill also have altered pharmacokinetics. Metabolism of the drug is reduced in patients with liver dysfunction, giving delayed production of metabolites. In contrast, renal failure has little effect on the elimination of the parent drug, but affects the excretion of the metabolites more significantly. Haemodialysis was found to remove a substantial amount of the metronidazole while the effect of peritoneal dialysis was more limited. Energy and protein deficient diets as well as occupational exposure to gasoline did not alter metronidazole pharmacokinetics. However, the effect of alcohol consumption on metronidazole CL requires further study.(ABSTRACT TRUNCATED AT 400 WORDS)

Nimorazole as a hypoxic radiosensitizer in the treatment of supraglottic larynx and pharynx carcinoma. First report from the Danish Head and Neck Cancer Study (DAHANCA) protocol 5-85

Between January 1986 and September 1990, 442 patients with pharynx and supraglottic larynx carcinoma were randomized to receive the hypoxic cell radiosensitizer nimorazole (NIM) or placebo in association with a course of conventional primary radiotherapy. A preliminary analysis including the first 288 patients showed that the stratification parameters were significant (3-year actuarial local-regional tumor control, p less than 0.05) for sex (females 52% vs males 34%), tumor size (T1-T2 47% vs T3-T4 32%) and pre-irradiation hemoglobin (Hb) concentration (high 41% vs low 34%). Overall, the NIM group showed a significantly better local-regional control rate than the placebo group (46% vs 32%). There was an apparent additive effect of Hb concentration and NIM. Thus, in the male group, placebo patients with low Hb had a 23% control rate compared to 46% in NIM treated patients with Hb above 9 mmol/l (p less than 0.05). The similar effect in females could not be evaluated due to the small number of women with this disease. NIM was well tolerated and drug-related side effects were minor and tolerable, with transient nausea and vomiting as the most frequent complication. A final conclusion of the study must await an evaluation including all patients and a longer observation time.

Misonidazole neuropathy. A prospective study

The frequency with which polyneuropathy developed was investigated in patients with cancer of the larynx and pharynx who participated in a double-blind trial of the radiosensitizing drug misonidazole. Fourteen of 36 patients receiving misonidazole (total dose of about 11 g/m2) developed neuropathy, while this occurred in only 2 of 34 patients in the placebo group. Vibration perception threshold increased in all patients who developed neuropathy, but also in 12 (5 misonidazole and 7 placebo treated) without other symptoms or signs of neuropathy. Pharmacokinetic studies of misonidazole revealed a correlation between development of neuropathy and a high 'peak plasma concentration/g misonidazole in each fraction' and especially a high 'area under plasma concentration curve/g misonidazole in each fraction'.

Interactions of radiation, cyclophosphamide and nimorazole in a C3H mammary carcinoma in vivo

The combined effect of adjuvant Cyclophosphamide (CTX) and the hypoxic radiosensitizer, Nimorazole (NIM), on the radiation response was studied in a C3H mammary carcinoma in CDF1 mice. The effect of NIM and CTX alone or in combination without radiation was assessed by tumor growth delay measured by tumor growth time (TGT). Administration of CTX (100 mg/kg) increased the TGT from 5.2 days in untreated controls to 18.8 days. NIM (1000 mg/kg) had no effect on the TGT. The combined treatment with NIM given 4 hrs before CTX did not increase the TGT compared with CTX alone, which suggests that NIM does not potentiate CTX. The possible effect of an interaction between the therapeutic parameters was determined by administration of NIM, CTX, and radiation in different sequences to C3H mammary tumor bearing mice. The drugs were administered as single doses before or after graded single doses of irradiation. The end point was the radiation dose required to achieve local tumor control in 50% of the mice (TCD50). The enhancement ratio (ER)--defined as TCD50 for radiation alone relative to TCD50 for radiation combined with drug--was 1.2 for CTX given either 15 min before or 4 hrs after radiation. NIM given 30 min before radiation showed an ER of 1.6, but no enhancement was obtained when NIM was given after radiation. When NIM was given immediately after radiation, followed 4 hrs later by CTX, the ER was 1.2. However, applying NIM 30 min before radiation and CTX 3.5 hrs after radiation, the ER increased to 1.6. NIM given 30 min before, together with CTX given 15 min before radiation, showed an ER of 1.8. Our data suggest that: an improved tumor response may be expected when CTX is added to a radiation and hypoxic radiosensitizer treatment; this improvement is attributable to an additive effect based on the chemotherapy response alone rather than to chemopotentiation by the hypoxic radiosensitizer.

A phase I clinical study of Nimorazole as a hypoxic radiosensitizer

Nimorazole, a 5-Nitromidazole compound has been shown in animal studies to have similar radiosensitizing properties to misonidazole at clinically acceptable dose levels. The drug is well absorbed in humans after oral administration with peak plasma levels occurring around 90 min after ingestion (range 35-135 min) and a plasma half life between 2 and 4.8 hours. Total doses of Nimorazole up to 60 grams given in daily doses with conventional radiation therapy have demonstrated a significant lack of side effects, in particular no demonstrable neurotoxicity.