A phase I-B trial of the radiosensitizer: etanidazole (SR-2508) with radiosurgery for the treatment of recurrent previously irradiated primary brain tumors or brain metastases (RTOG Study 95-02).

RTOG 95-02 assessed patient tolerance to hypoxic cell radiosensitizer, etanidazole (SR-2508), combined with radiosurgery. Patients had primary or metastatic brain tumors and previously localized or whole brain irradiation. The toxicity is reported in three groups of patients according to the tumor size. Etanidazole doses of 12g/m2 combined with radiosurgery were well tolerated.

Detection of hypoxia in human squamous cell carcinoma by EF5 binding.

Localization and quantitation of 2-nitroimidazole drug binding in low pO2 tumors is a technique that can allow the assessment of hypoxia as a predictive assay. EF5 [2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl) acetamide] is such a drug, and it has been shown to be predictive of radiation response in rodent tumors. Using fluorescence immunohistochemical techniques, we provide data on the presence, distribution, and levels of EF5 binding as a surrogate for hypoxia in human head and neck and uterine cervix squamous cell cancers (SCCs). Six patients with SCC were studied. Four patients had head and neck tumors, and two had uterine cervix cancers. The incubation of fresh tissue cubes in EF3 under hypoxic conditions ("reference binding") demonstrated that all tumors were capable of binding drug, and that this binding varied by a factor of 2.9-fold (174.5-516.1) on an absolute fluorescence scale. In the five patients treated at the lowest drug doses (9 mg/kg), in situ binding was quantitatable. For all six patients, the maximum rate of in situ binding varied by a factor of 6.7 between the lowest and highest binding tumor (24.8-160.3) on an absolute fluorescence scale. In tumors with high binding regions, intratumoral heterogeneity was large, extending from minimal fluorescence (<1%) up to 88.6% of reference binding. In tumors with minimal binding, there was little intratumoral heterogeneity. These studies demonstrate substantial heterogeneity of in situ binding between and within individual squamous cell tumors.

Phase II trial of external beam radiation with etanidazole (SR 2508) for the treatment of locally advanced prostate cancer.

PURPOSE: To evaluate the efficacy and toxicity of the addition of etanidazole (ETA) to external beam radiation. METHODS AND MATERIALS: Fifty eight previously untreated patients with locally advanced adenocarcinoma of the prostate were entered on a Phase II trial of etanidazole (ETA) combined with standard external beam radiation therapy. ETA was given concurrently with irradiation. Four patients received less than 25% of the intended dose of ETA and were ineligible for further analysis. The stage of the remaining patients were T2c-11, T3-39, T4-1, bulky local recurrence after prostatectomy-1, and T3, N1-2. RESULTS: Forty-five of 54 patients (83.3%) achieved a clinical complete response (CCR) in the prostate and seminal vesicles as judged by digital rectal exam (DRE). Responses were rapid with a median time to CCR of 3.4 months, range 0-22.8 months. Local control was maintained in 82% of the patients who achieved a CCR. Fifteen of 32 eligible patients with a normal DRE underwent prostate biopsies from 12-20 months after treatment, seven had negative biopsies (46.6%). Distant metastases occurred in 18 patients (33.3%). Pretreatment prostatic specific antigen (PSA), Gleason score, and stage were not associated with treatment outcome in a univariate analysis. CONCLUSION: While ETA plus radiation was associated with a rapid CCR, the overall treatment outcome of these patients appeared to be similar to published reports of patients receiving RT alone. The rapid response rate may imply biologic activity of the ETA. In future trials, it may be reasonable to focus on patients at lower risk for the subsequent development of distant disease.

A phase I study of etanidazole and radiotherapy in malignant glioma.

PURPOSE: To determine the maximum tolerable total dose (MTD) of etanidazole (ETA) when administered with external beam radiotherapy (XRT) and as a continuous infusion during stereotactic brachytherapy for patients with malignant glioma (anaplastic astrocytoma or glioblastoma multiforme or mixed cell tumors). METHODS AND MATERIALS: Seventy previously untreated patients were entered in a Phase I study. Prior to initiation of treatment, patients were stratified according to whether or not they were candidates for interstitial implantation. The implant patients (IMP, n = 17 pt) received accelerated fractionation XRT 20 Gy BID (6 h apart) to 40 Gy in 2 weeks with ETA 2 gm/m2 x 6 doses, a 2 week break and then interstitial implant to 50 Gy (4-7 days) with a continuous infusion of ETA over 90-96 h. The two sequentially conducted nonimplant arms started with accelerated fractionation XRT 2 Gy BID (6 h apart) to 40 Gy in 2 weeks with ETA 2 gm/m2 x 4-5 doses/week. NonIMP 1 arm (n = 38) received a 2-week break before standard fractionated boost XRT of 20 Gy/day for 2 weeks to a total dose of 60 Gy with ETA. NonIMP 2 arm (n = 14) did not have the 2-week break. All patients had plasma pharmacokinetic monitoring of ETA. RESULTS: The dose-limiting toxicity (DLT) in the IMP group was the cramping/arthralgia syndrome (4) and the cumulative MTD was 26 gm/m2. For both nonIMP 1 and 2 the DLTs were peripheral neuropathy and the cramping-arthralgia syndrome. The MTD for nonIMP 1 was 34 gm/m2 and nonIMP 2, 30 gm/m2. CONCLUSION: The clinical efficacy and radiation-related toxicity of these regimens are being evaluated. The doses of ETA that can be used with accelerated fractionation and with external beam irradiation plus brachytherapy have been established.

Results of a European randomized trial of Etanidazole combined with radiotherapy in head and neck carcinomas.

PURPOSE: The aim of the study was to evaluate the efficacy and toxicity of Etanidazole, a hypoxic cell sensitizer, combined with radiotherapy in the treatment of head and neck squamous cell carcinoma. METHODS AND MATERIALS: A total of 374 patients from 27 European centers were included in this trial between 1987 and 1990. Treatment was either conventional radiotherapy alone (between 66 Gy in 33 fractions and 74 Gy in 37 fractions, 5 fractions per week), or the same radiotherapy dose plus Etanidazole 2 g/m2, three times weekly for 17 doses. A minimization procedure, balancing for center, site, and T stage (T1-T3 vs. T4) was used for randomization. RESULTS: Among the 187 patients in the Etanidazole group, 82% received at least 14 doses of the drug. Compliance to the radiotherapy protocol was 92% in the Etanidazole group and 88% in the control group; the main cause of deviation was acute toxicity, which was observed at an equal rate in the two treatment groups. Fifty-two cases of Grade 1 to 3 peripheral neuropathy were observed in the Etanidazole group vs. 5 cases, all of Grade 1, in the control group (p < 0.001). The 2-year actuarial loco-regional control rates were 53% in the Etanidazole group and 53% in the control group (p = 0.93), and the overall 2-year survival rates were 54% in each group (p = 0.99). CONCLUSION: Adding Etanidazole to conventional radiotherapy did not afford any benefit for patients with head and neck carcinoma. This study failed to confirm the hypothesis of a benefit for patients with N0-N1 disease, which had been suggested by the results of a previous study (10).

Results of an RTOG phase III trial (RTOG 85-27) comparing radiotherapy plus etanidazole with radiotherapy alone for locally advanced head and neck carcinomas.

PURPOSE: The objectives of this study were to determine the efficacy and toxicity of Etanidazole (ETA), a hypoxic cell sensitizer, when combined with conventional radiotherapy (RT) in the management of advanced head and neck carcinomas. METHODS AND MATERIALS: From March 1988 to September 1991, 521 patients who had Stage III or IV head and neck carcinomas were randomized to receive conventional RT alone (66 Gy in 33 fractions to 74 Gy in 37 fractions, 5 fractions per week) or RT+ETA (2.0 g/m2 thrice weekly for 17 doses), of whom 504 were eligible and analyzable. Treatment assignments were stratified before randomization according to the primary site (oral cavity + hypopharynx vs. supraglottic larynx + oropharynx + nasopharynx), T-stage (T1-3 vs. T4), and N-stage (N0-2 vs. N3). Pretreatment characteristics were balanced. In the RT-alone arm, 39% of patients had T3 and 34% had T4 disease, whereas in the RT+ETA arm, 42% of patients had T3 and 33% had T4 disease. Thirty-eight percent of the RT-alone patients and 37% of the RT+ETA patients had N3 disease. The median follow-up of surviving patients was 3.38 years, with a range between 0.96 and 5.63 years. RESULTS: One hundred and ninety-four of the 252 (77%) RT+ETA patients received at least 14 doses of the drug. Overall RT protocol compliance rate was 82% in the RT-alone arm and 86% in the RT+ETA arm. No Grade 3 or 4 central nervous system or peripheral neuropathy was observed in the RT+ETA arm. Eighteen percent of the patients developed Grade 1 and 5% developed Grade 2 peripheral neuropathy. Other drug related toxicities included nausea/vomiting (27%), low blood counts (15%), and allergy (9%). Most of these toxicities were Grade 1 and 2. The incidence of severe acute and late radiation effects were similar between the two arms. The 2-year actuarial local-regional control rate (LCR) was 40% for the RT-alone arm and 40% for the RT+ETA arm. Two-year actuarial survival was 41% for the RT-alone arm and 43% for the RT+ETA arm (p = 0.65). Multivariate analyses were performed to investigate the influence of covariates on treatment effects. A strong treatment interaction with N-stage was revealed: LCR (50% vs. 40% at 2 years), RT+ETA improved for patients with N0-2 disease but not for N3 patients (22% for RT+ETA and 40% for RT). Further analyses showed that RT+ETA was more advantageous in N0-1 patients, with a 2-year LCR of 55% for RT+ETA vs. 37% for RT only (p = 0.03). A similar phenomenon was observed when using survival as the end point. CONCLUSION: The results showed that adding Etanidazole to conventional RT produced no global benefit for patients who had advanced head and neck carcinomas. There was a suggested benefit for patients who had N0-1 disease, and that needs to be confirmed by another study.

Combined cytokinesis-block micronucleus and chromosomal aberration assay for the evaluation of radiosensitizers at low radiation doses.

PURPOSE: Several methods have been tried for evaluating the efficacy of hypoxic cell radiosensitizers at clinically relevant low radiation doses (1-4 Gy). The cytokinesis-block micronucleus assay is known to be useful for both the in vitro and in vivo evaluation of radiosensitizers, while the chromosomal aberration assay has been commonly used to assess the mutagenicity of various agents. In the present study, the chromosomal aberration assay and the cytokinesis-block micronucleus assay were performed simultaneously to assess the radiosensitizing effect of etanidazole and KU-2285 at low radiation doses. The correlation between the two assays was also evaluated. METHODS AND MATERIALS: In vitro study: EMT-6 cells were irradiated at a dose of 1-3 Gy under hypoxic conditions with or without the drugs at 1 mM. In vivo-in vitro study: EMT-6 tumor-bearing BALB/c mice received 2-4 Gy of radiation with or without administration of the drugs at 200 mg/kg. Single-cell suspensions were then obtained in both studies and were used for the cytokinesis-block micronucleus assay and the chromosomal aberration assay. The micronucleus frequency in binucleate cells was evaluated in the former assay, and the frequency of chromosomal aberrations in metaphase cells was evaluated in the latter assay. RESULTS: In vitro study: the sensitizer enhancement ratios of etanidazole and KU-2285 were 1.73 and 2.21, respectively, in the micronucleus assay, and 1.41 and 1.79 in the chromosomal aberration assay. In vivo-in vitro study: the sensitizer enhancement ratios of etanidazole and KU-2285 were 1.18 and 1.31, respectively, in the micronucleus assay, and 1.16 and 1.42 in the chromosomal aberration assay. In both studies, a linear correlation was observed between the micronucleus frequency and the chromosomal aberration frequency. The background (i.e., the frequency at 0 Gy) of the latter assay was considerably lower than that of the former assay, especially in the vivo study. CONCLUSIONS: The chromosomal aberration assay has not yet been established as a method for evaluating the effect of radiosensitizers. However, a combination of the cytokinesis-block micronucleus assay and the chromosomal aberration assay seems to be useful for assessing radiosensitizers at low radiation doses for the following reasons: a) the chromosomal aberration assay is as sensitive as the micronucleus assay and possibly more specific, because chromosomal aberrations can be observed before cells pass through the first metaphase after irradiation and, thus, reflect quite acute damage, even though they reflect only a part of the total damage; b) the combined assay provides relatively more information for the time and labor required.

The hypoxic cytotoxin SR 4233 increases the effectiveness of radioimmunotherapy in mice with human non-Hodgkin's lymphoma xenografts.

PURPOSE: To determine if either the hypoxic cell radiosensitizer etanidazole (SR 2508) or the hypoxic cytotoxin SR 4233 could improve the effectiveness of radioimmunotherapy. METHODS AND MATERIALS: LC4 (an IgG1 monoclonal antibody directed toward malignant T cells) and MB-1 (an irrelevant isotype-matched control antibody) were injected intraperitoneally into severe combined immunodeficient phenotype mice with human cutaneous T cell lymphoma xenografts in order to determine the distribution of the antibodies in the tumors and normal tissues as a function of time. Computerized-pO2-histography was used to measure the median oxygen tension in the tumors. Tumor-bearing mice were treated with: (a) LC4; (b) 90Y-LC4; (c) 90Y-MB-1; (d) whole body irradiation delivered via an external 137Cs source; (e) etanidazole and 90Y-LC4; (f) SR 4233 and 90Y-LC4; (g) etanidazole; and (h) SR 4233. An additional group of mice received no treatment and served as controls. A tumor growth delay assay was used to assess the effectiveness of the different treatment regimens. RESULTS: LC4 accumulated in the tumors to a significantly greater extent than MB-1 (p < 0.001) and reached a peak concentration in the tumors 5 days post-injection. The human cutaneous T cell lymphoma xenografts had a relatively low median oxygen tension. LC4 by itself was able to produce a minor decrease in tumor size (control vs. LC4; p = 0.001). 90Y-LC4 produced greater tumor growth delay than LC4 alone (LC4 vs. 90Y-LC4; p = 0.01); however, the Yttrium-90 caused neutropenia and weight loss. The 90Y-labeled tumor-specific and non-specific antibodies both exerted greater tumor growth delay than externally delivered whole body irradiation (p < or = 0.03) due to preferential uptake of the antibodies in the tumors. Etanidazole and SR 4233 by themselves did not significantly inhibit the growth of the tumors. Etanidazole did not significantly enhance the tumor growth delay produced by 90Y-LC4 (90Y-LC4 vs etanidazole and 90Y-LC4, p = 0.13). SR 4233, on the other hand, did enhance the tumor growth delay produced by 90Y-LC4 (90Y-LC4 vs. SR 4233 and 90Y-LC4, p = 0.046). The neutropenia and weight loss caused by 90Y-LC4 were exacerbated slightly (< 10%) by the administration of SR 4233. CONCLUSIONS: A first generation hypoxic cytotoxin, SR 4233, was able to enhance the tumor growth delay produced by radioimmunotherapy in severe combined immunodeficient phenotype mice with human cutaneous T cell lymphoma xenografts.

In vivo radiosensitization efficacy of KU-2285 and etanidazole at clinically relevant low radiation doses.

PURPOSE: The in vivo radiosensitization efficacy of KU-2285 at clinically relevant low radiation doses (2-4 Gy) was compared with that of etanidazole using four types of assays with EMT6, SCCVII, and C3H mammary tumors. METHODS AND MATERIALS: The in vivo-in vitro cytokinesis-block micronucleus assay and the chromosomal aberration assay were used to assess the sensitizing effect at single doses of 2-4 Gy. After in vivo treatment for tumors, tumor cells were cultured in the presence of cytochalasin B for the former assay or demecolcine for the latter assay, and the micronucleus frequency in binucleate cells and the chromosomal frequency in metaphase cells were evaluated after 42 hr and 3 hr of culture. In addition, an in vivo-in vitro colony assay and a growth delay assay were performed using fractionated irradiation regimens (4 Gy x 5). RESULTS: The sensitizer enhancement ratio for 100-400 mg/kg of KU-2285 was between 1.12 and 1.42. KU-2285 was a more efficient sensitizer than etanidazole in 3 of 9 experiments and as efficient as etanidazole in the remaining six experiments. CONCLUSION: Both the micronucleus assay and the chromosomal aberration assay appeared to be very useful in evaluating the in vivo sensitizing effect at low radiation doses. KU-2285 had a definite radiosensitizing effect even at low radiation doses, and clinical trials of KU-2285 may be warranted.

RTOG's first quality of life study--RTOG 90-20: a phase II trial of external beam radiation with etanidazole for locally advanced prostate cancer.

PURPOSE: To assess institutional and patient compliance with quality of life (QL) instruments in RTOG clinical trials. To assess feasibility of using the Functional Assessment Cancer Therapy (FACT), Sexual Adjustment Questionnaire (SAQ), and Changes in Urinary Function (CUF) QL instruments in a prostate clinical trial and to compare patient self-report of symptoms to medical professional ratings of the same symptoms using the RTOG acute toxicity rating scales. METHODS AND MATERIALS: Three self-assessment QL instruments, the FACT, the SAQ, and CUF, were to be administered to patients on a Phase II locally advanced prostate trial at specified time points. Specific instructions for both data managers and for patients on when, how, and why to fill out the questionnaires were included. RESULTS: Sixty-seven percent (24 out of 36) of patients accrued to RTOG 90-20 completed both the initial FACT and SAQ. Eighty-five percent completed FACT at end of RT and 73% at 3 months. Eighty-one percent completed SAQ at end of treatment, while 69% completed this form at 3 months. Compliance drops off thereafter. Seventy-five percent of patients who had their symptom of dysuria rated by a medical professional as 0 on the RTOG toxicity rating scale self-reported the same. Only 56% of patient self-reports on FACT regarding diarrhea were in agreement with the medical professional's RTOG rating of 0 toxicity. The measures were determined to be in moderate agreement when the patient evaluated a symptom as a 1 on the FACT and the medical professional rated the same symptom as a 0 on the RTOG toxicity rating scale. There was moderate agreement in 13% of patients with dysuria and 31% of patients with diarrhea. Low agreement occurred when the patient evaluated a symptom as a 2 or 3 on the FACT and the medical professional rated the same symptom as a 0 on the RTOG scale. Low agreement occurred in 13% of both patients reporting dysuria and diarrhea. Differences between how medical professionals and patients were able to rate erectile function make direct comparisons difficult, but the trend towards significant discrepancies is still noteworthy. CONCLUSIONS: Quality of life assessments are necessary and attainable in RTOG clinical trials. Compliance rates for both institutional and patient participation were acceptable at initial and 3 month follow-up. Reasons for noncompliance were predominantly institution related and not patient related. Strategies to address both institution and patient compliance have been developed and implemented within the RTOG. Serious disagreement between patient self-reports of symptoms on the FACT QL scale and medical professional ratings on the RTOG acute toxicity rating scales of the same symptoms was 13% at 3 months follow-up. This warrants continued use of QL self-assessments in clinical trials.

RTOG #89-06: a phase I study to evaluate intraoperative radiation therapy and the hypoxic cell sensitizer etanidazole in locally advanced malignancies.

PURPOSE: To identify the maximum tolerated dose of the oxygen mimetic radiation sensitizer Etanidazole in the setting of surgery and intraoperative radiation therapy. 12 grams/meter2 was the maximum chosen target dose based on tolerance from other trials. METHODS AND MATERIALS: 42 patients were entered in an escalating dose scheme, 5.5, 7.5, 9, 10.5, and 12.0 grams/meter2. Etanidazole was given via intravenous infusion over 15 minutes, followed within 20 to 30 minutes by intraoperative radiation therapy. Multiple tissue samples from tumor, tumor bed, and/or normal tissue were obtained with simultaneous plasma samples. Etanidazole concentrations in tissue and serum were determined in 33 of the 42 patients. RESULTS: The median time to maximum serum concentration was 25 minutes. Median time to maximum tissue concentration was 40 minutes. Tissue concentrations began falling approximately one hour after infusion. Acute drug toxicities were minimal. Toxicities reported during follow-up related to surgery and/or radiation, not to drug. The concentration of sensitizer in tumor/tumor bed tissues was ten-fold greater than in previous trials. A sensitizer enhancement ratio for the hypoxic cells of 2 to 2.5 is projected. CONCLUSION: On the basis of tissue biopsy information, intraoperative radiation therapy will be given 40 minutes after the start of the 15 minute infusion allowing time for maximum intracellular uptake into tumor cells. In view of these findings, a Phase III trial testing etanidazole with intraoperative radiation therapy will be conducted. The tolerable single dose level of 12 grams/meter2 has potential with other high-dose radiation settings such as brachytherapy or stereotactic radiosurgery.

Anemia is associated with decreased survival and increased locoregional failure in patients with locally advanced head and neck carcinoma: a secondary analysis of RTOG 85-27.

PURPOSE: The purpose of the present study is to investigate the strength of association between anemia and overall survival, locoregional failure, and late radiation therapy (RT) complications in a large prospective study of patients with advanced head and neck cancer treated with conventional radiotherapy with or without a hypoxic cell sensitizer. METHODS AND MATERIALS: Between March 1988 and September 1991, 521 patients with Stage III or IV squamous cell carcinoma of the head and neck were entered into a randomized trial examining the addition of etanidazole (SR 2508) to conventional radiation therapy (RT) (66-74 Gy in 33-37 fractions, 5 days a week). Patients with hemoglobin (Hgb) levels measured and recorded prior to the second week of RT were included in this secondary analysis. Hemoglobin levels were stratified as normal (> or = 14.5 gm% for men, > or = 13 gm% for women) or anemic (< 14.5 gm% for men, < 13 gm% for women). Locoregional failure rates were calculated using the cumulative incidence approach. Overall survival was estimated according to the Kaplan-Meier method. Late RT toxicity was scored according to the RTOG morbidity scale. Differences in rates of overall survival, locoregional failure, and late complications were tested by the Cox proportional hazard model. RESULTS: Of 504 eligible patients, 451 had a Hgb level measured and recorded prior to the second week of RT. One hundred sixty-two patients (35.9%) were considered to have a normal Hgb level and 289 patients (64.1%) were considered to be anemic. The estimated survival rate is 35.7% at 5 years in patients with a normal Hgb, versus 21.7% in anemic patients (p = 0.0016). The estimated locoregional failure rate is 51.6% at 5 years in patients with a normal Hgb, versus 67.8% in anemic patients (p = 0.00028). The estimated rate of grade 3 or greater toxicity is 19.8% at 5 years in patients with a normal Hgb, versus 12.7% in anemic patients (p = 0.063). On multivariate analysis, several variables were found to be independent predictors of survival including: T stage, Karnofsky performance status, N stage, age, total radiation dose to the primary, and Hgb level. Independent predictors of locoregional control included T stage, Karnofsky performance status, N stage, radiation dose, and Hgb level. The only variables which predicted for the development of late RT complications were gender (p = 0.0109) and age (p = 0.0167). These findings were consistent regardless of whether Hgb level was considered a dichotomous or continuous variable. CONCLUSION: Low Hgb levels are associated with a statistically significant reduction in survival and an increase in locoregional failure in this large prospective study of patients with advanced head and neck cancer. Hgb level should be considered as a stratification variable in subsequent studies of head and neck cancer. Strategies to increase Hgb prior to RT in patients with head and neck cancer may lead to improved survival and loco-regional control.

Results of a phase II trial of external beam radiation with etanidazole (SR 2508) for the treatment of locally advanced prostate cancer (RTOG Protocol 90-20).

PURPOSE: RTOG Protocol 90-20 was designed to evaluate the effect of the hypoxic cell sensitizer Etanidazole (SR-2508) on locally advanced adenocarcinoma of the prostate treated with concurrent external beam irradiation. METHODS AND MATERIALS: Patients with biopsy-proven adenocarcinoma of the prostate with locally advanced T2b, T3, and T4 tumors were eligible for this study. No patients with disease beyond the pelvis were eligible. Serum prostate specific antigen (PSA) was mandatory. All patients received definitive external beam irradiation using standard four-field whole pelvis treatment to 45-50 Gy, followed by a cone down with a minimum total dose to the prostate of 66 Gy at 1.8-2.0 Gy/fraction over 6.5-7.5 weeks. Etanidazole was delivered 1.8 g/m2 given 3 times a week to a total of 34.2 g/m2 or 19 doses. RESULTS: Thirty-nine patients were entered onto the study. Three patients refused treatment; therefore, 36 patients were eligible for further evaluation. Median follow-up was 36.9 months from treatment end. All patients had elevated initial PSA levels, and 18 patients had PSAs of > 20 ng/ml. Tumor classification was T2, 12 patients (33.3%); T3, 22 patients (61.1%); and T4, 2 patients (5.6%). Complete clinical response, defined as PSA < 4 ng/ml and complete clinical disappearance, was attained in 17.9% of (5/28 pts) with information at 90 days and 56% of patients by 12 months following treatment. Relapse-free survival was 13% at 3 years with PSA < 4 ng/ml. There were no Grade 4 or 5 toxicities, either acute (during treatment) or in follow-up. CONCLUSIONS: Results of this trial regarding PSA response and clinical disappearance of disease are similar to historical controls and do not warrant further investigation of etanidazole as was done in this trial. Drug toxicity that, in the past, has been unacceptably high with other hypoxic cell sensitizers does not appear to be a significant problem with this drug.

Radiosensitization by a new potent nucleoside analog: 1-(1',3',4'-trihydroxy-2'-butoxy)methyl-2-nitroimidazole(RP-343).

PURPOSE: A new hypoxic cell sensitizer has been synthesized; this is a 2-nitroimidazole nucleoside analog having erythritol as a sugar moiety at the N-1 position of the imidazole ring (RP-343). Its possibility as a potent hypoxic cell sensitizer was compared with those of RP-170 and etanidazole. METHODS AND MATERIALS: Radiosensitization was tested in two murine tumors, EMT6 using in vitro and in vivo-in vitro assays and SCCVII using growth delay and TCD50 assays. Pharmacokinetic study was performed in Balb/c mice bearing EMT6 tumors and in Beagle dogs. LD50 of each sensitizer was obtained with ICR mice. RESULTS: As might be expected from the almost identical electron affinities of the three sensitizers, they were equally effective against hypoxic EMT6 cells in vitro. While having the lowest partition coefficient (0.035), RP-343 exhibited almost equally effective distribution to tumors and sensitizing radiation activity. An intravenous (i.v.) injection of 100 mg/kg of RP-343, RP-170 and etanidazole showed an almost equal sensitizer enhancement ratio (SER) of about 1.4 to solid EMT6 tumor under in vivo-in vitro assay and a virtually equal SER of 1.33-1.44 to solid SCCVII tumor under both tumor growth delay assay and TCD50 assay. A great advantage of RP-343 over RP-170 and etanidazole is its very much lower toxicity; their LD50 in mice were > 6.0, 4.3 and 4.8 g/kg, respectively, on i.v. injection. The lower toxicity of RP-343 was supported by its lower concentrations in the brain; the RP-343 AUC for brain was 0.43 times that of RP-170. Three indices were selected to compare the three nitroimidazoles. SER at 5% LD50 doses of RP-343, RP-170 and etanidazole was 1.66, 1.59 and 1.56. At the same toxicity levels, RP-343 was found to have better sensitization of solid tumors over both etanidazole and RP-170. The maximum tumor concentration/AUC for brain (Cmax,tumor/AUCbrain) ratios for RP-343 and RP-170 were 9.62 and 3.98. CONCLUSIONS: This extremely high ratio of RP-343 could explain its lower toxicity than RP-170 or etanidazole. The therapeutic risk index defined as D1.5/LD50 (D1.5 is the sensitizer dose to obtain the SER of 1.5 in vivo) for RP-343, RP-170 and etanidazole were 0.022, 0.033 and 0.036, respectively. Especially, the effectively lower therapeutic risk index for RP-343 presents the possibility of clinical advantage over etanidazole.

A phase I trial of etanidazole and hyperfractionated radiotherapy in children with diffuse brainstem glioma.

PURPOSE: To determine the toxicity and maximum tolerated dose of etanidazole administered concurrently with hyperfractionated radiation therapy (HRT) for children with brainstem glioma. METHODS AND MATERIALS: Eighteen patients with brainstem glioma were treated with etanidazole and HRT on a dose escalation protocol (Phase I trial) between 1990 and 1996. All patients had MRI confirmation of diffuse pontine glioma and signs/symptoms of cranial nerve deficit, ataxia, or long tract signs of <6 months' duration. Cervicomedullary tumors were excluded. Patients (median age: 8.5 years; 11 males, 7 females) received HRT to the tumor volume plus a 2-cm margin with parallel-opposed 6-15-MV photons. The total dose was 66 Gy in 44 fractions (1.5 Gy b.i.d., with at least 6 h between fractions) for the first 3 patients and 63 Gy in 42 fractions for the subsequent 15 patients. Etanidazole was administered as a rapid i.v. infusion 30 min before the morning fraction of HRT. Planned doses of etanidazole were 1.8 g/m(2) x 17 doses (30.6 g/m(2)) at Step 1 to a maximum of 2.4 g/m(2) x 21 doses (50.4 g/m(2)) at Step 8. Dose escalation was planned with 3 patients at each of the 8 levels. RESULTS: Three patients were treated at each dose level except Level 2, on which only 1 patient was treated. The highest dose level achieved was Level 7, which delivered a total etanidazole dose of 46.2 g/m(2). Two patients were treated at this level, and both patients experienced Grade 3 toxicity in the form of a diffuse cutaneous rash. Three patients received a lower dose of 42 g/m(2) (dose Level 6) without significant toxicity, and this represents the maximum tolerated dose (MTD). There were 23 cases of Grade 1 toxicity (10 vomiting, 5 peripheral neuropathy, 2 rash, 2 constipation, 1 weight loss, 3 others), 11 cases of Grade 2 toxicity (4 vomiting, 2 skin erythema, 2 constipation, 1 arthralgia, 1 urinary retention, 1 hematologic), and 4 Grade 3 toxicities (2 rash, 1 vomiting, 1 skin desquamation). Grade 2 or 3 peripheral neuropathy was not seen at any dose level. The median survival from the start of treatment was 8.5 months (range: 3-58 months). CONCLUSION: The MTD of etanidazole in children receiving HRT for brainstem glioma is 42 g/m(2), with cutaneous rash as the dose-limiting toxicity. This is in contrast to the adult experience, which demonstrates a 24% lower MTD of 34 g/m(2) limited by peripheral neuropathy.

Hypoxic sensitizer and cytotoxin for head and neck cancer.

Tumour hypoxia is well recognised as a major factor contributing to radioresistance. This article examines the role of hypoxia in influencing the treatment outcome following radiotherapy (RT), and reviews the rationale and results of clinical trials that utilise hypoxic sensitizers or cytotoxins in the treatment of head and neck carcinoma. Histologic evidence for tumour hypoxia in human neoplasms was first reported in 1955. Since then, direct measurement by microelectrodes has revealed heterogeneity in intratumoural oxygen concentrations, and low oxygen concentrations are associated with poor local-regional control by RT. These findings coupled with the result of nuclear imaging studies employing radiolabelled imidazoles, provide strong evidence for the existence of tumour hypoxia which influences RT treatment outcome. Hyperbaric oxygen (HBO) trials for head and neck cancer, conducted in the early 1970s, demonstrated that HBO improved local control and survival rates in patients with head and neck cancer receiving radiotherapy (RT). Since the mid-1970s, clinical research in overcoming tumour hypoxia was mainly centred on the use of nitro-imidazoles as hypoxic cell sensitizers. However, the results from several major clinical trials remain inconclusive. Specifically, the Radiation Therapy Oncology Group (RTOG) misonidazole head and neck trial (298 patients) showed no benefit. The Danish misonidazole trial (626 patients) showed no overall benefit, however positive results were observed in a subgroup (304 pharyngeal cancer patients). Although the European Organisation for Research and Teaching of Cancer (EORTC) misonidazole trial with hyperfractionated RT showed no benefit, the Danish nimorazole trial demonstrated an overall benefit in survival as well as local control. The European etanidazole (ETA) trial (374 patients) showed no advantage of adding the drug to RT. The RTOG ETA trial (504 patients) showed no global benefit. However, positive results were observed in a subset of patients with early nodal disease (197 patients). In addition, a recent meta-analysis by Overgaard, utilising pooled results in the literature demonstrated that modification of tumour hypoxia significantly improved local-regional control in head and neck cancers with an odds ratio of 1.23 (95% confidence limits 1.09 to 1.37). Hypoxic cytotoxins, such as tirapazamine, represent a novel approach in overcoming radioresistant hypoxic cells. Tirapazamine is a bioreductive agent which, by undergoing one electron reduction in hypoxic conditions, forms cytotoxic free radicals that produce DNA strand breaks causing cell death. In vitro and in vivo laboratory studies demonstrate that tirapazamine is 40 to 150 times more toxic to cells under hypoxic conditions as compared to oxygenated conditions and that tirapazamine is superior to ETA in enhancing fractionated irradiation in mouse SCCVII and other tumour types with an enhancement ratio of 1.5 to 3.0. Phase I studies demonstrated that therapeutic doses of tirapazamine can be given safely. A multi-institutional phase II trial using tirapazamine with concurrent RT for head and neck cancer is now in progress.

Stereotactic ablative radiotherapy should be combined with a hypoxic cell radiosensitizer.

PURPOSE: To evaluate the effect of tumor hypoxia on the expected level of cell killing by regimens of stereotactic ablative radiotherapy (SABR) and to determine the extent to which the negative effect of hypoxia could be prevented using a clinically available hypoxic cell radiosensitizer. RESULTS AND DISCUSSION: We have calculated the expected level of tumor cell killing from regimens of SABR, both with and without the assumption that 20% of the tumor cells are hypoxic, using the standard linear quadratic model and the universal survival curve modification. We compare the results obtained with our own clinical data for lung tumors of different sizes and with published data from other studies. We also have calculated the expected effect on cell survival of adding the hypoxic cell sensitizer etanidazole at clinically achievable drug concentrations. Modeling tumor cell killing with any of the currently used regimens of SABR produces results that are inconsistent with the majority of clinical findings if tumor hypoxia is not considered. However, with the assumption of tumor hypoxia, the expected level of cell killing is consistent with clinical data. For only some of the smallest tumors are the clinical data consistent with no tumor hypoxia, but there could be other reasons for the sensitivity of these tumors. The addition of etanidazole at clinically achievable tumor concentrations produces a large increase in the expected level of tumor cell killing from the large radiation doses used in SABR. CONCLUSIONS: The presence of tumor hypoxia is a major negative factor in limiting the curability of tumors by SABR at radiation doses that are tolerable to surrounding normal tissues. However, this negative effect of hypoxia could be overcome by the addition of clinically tolerable doses of the hypoxic cell radiosensitizer etanidazole.