Final report of the phase I trial of continuous infusion etanidazole (SR 2508): a Radiation Therapy Oncology Group study

Stereotactic radiosurgery of radioresistant glioblastomas. The ways of overcoming radioresistance of hypoxic tumors

Background. Taking into account high degree of resistance of glioblastoma to radiation therapy, and also low overall survival rates of patients, it is necessary to develop improved methods of treating this pathology, in particular, complex combined treatment with radiation therapy and radiosensitizers. Purpose – to assess the effectiveness of radiosensitization of hypoxic tumors in radiosurgical treatment of glioblastomas; to increase non-recurrent and overall survival rate of patients. Materials and methods. Stereotactic radiosurgery (SRS) of glioblastoma was performed in 106 patients (average age – 53 years), 66 males (62,26%) and 40 females (37,73%). The average dose was 18 Gy in a single-fraction SRS, and 32 Gy (7 Gy per fraction) in multi-fraction SRS. The average volume tumor was 29 cm3 . The treatment group consisted of 66 patients who underwent SRS with radiosensitization. 40 patients made up the control group and underwent SRS without radiosensitization. Results. Median overall survival (MOS) was 20 months in the group with radiosensitization, whereas in the control group it was 12 months. 10-month recurrence-free period after radiosurgery was observed in 95,4% of the patients of the group with radiosensitization and in 70,6% of the patients of the control group. MOS after SRS was similar between the patients with wild-type IDH tumors and patients with tumors with IDH mutation (10,0 months and 11,0 months respectively), and also between the patients with MGMT-methylated tumors and patients with MGMT-nonmethylated tumors (11,2 and 10,2 months respectively). Among all the treated patients, in 20 of them (16,6%) side radiation effects after SRS were observed, and in 9 patients (7,5%) radiation necrosis developed in 3 to 16 months after SRS. The signs of moderate toxicity in the form of vomiting were observed in 6,6% of the patients of the subgroup with metronidazole. There were no signs of toxicity in the subgroup with nimorazole. Conclusions. Radiosensitization improves rates of overall survival by 53,3% and recurrence-free survival by 24,8 % in performing SRS of hypoxic radioresistant glioblastomas. Nimorazole and metronidazole are powerful radiosensitizers which increase radiosensitivity of tumor cells through enhancing oxygen saturation of hypoxic cells. In order to determine indications for performing SRS with radiosensitization and periods for performing an SRS session we must take into consideration the result of an oxygen test (level of oxygen saturation of the tumor), the peak of signal intensity in the zone of active tumor growth and the peak of saturation of the whole tumor volume.

The use of radiosensitizing agents in the therapy of glioblastoma multiforme-a comprehensive review

BACKGROUND

Glioblastoma is the most common malignant brain tumor in human adults. Despite several improvements in resective as well as adjuvant therapy over the last decades, its overall prognosis remains poor. As a means of improving patient outcome, the possibility of enhancing radiation response by using radiosensitizing agents has been tested in an array of studies.

METHODS

A comprehensive review of clinical trials involving radiation therapy in combination with radiosensitizing agents on patients diagnosed with glioblastoma was performed in the National Center for Biotechnology Information's PubMed database.

RESULTS

A total of 96 papers addressing this matter were published between 1976 and 2021, of which 63 matched the subject of this paper. All papers were reviewed, and their findings discussed in the context of their underlining mechanisms of radiosensitization.

CONCLUSION

In the history of glioblastoma treatment, several approaches of optimizing radiation-effectiveness using radiosensitizers have been made. Even though several different strategies and agents have been explored, clear evidence of improved patient outcome is still missing. Tissue-selectiveness and penetration of the blood-brain barrier seem to be major roadblocks; nevertheless, modern strategies try to circumvent these obstacles, using novel sensitizers based on preclinical data or alternative ways of delivery.

A phase III randomized study of misonidazole plus radiation vs. radiation alone for cervix cancer

BACKGROUND AND PURPOSE

A randomized-controlled study of radical radiotherapy for cervical cancer with or without the hypoxic sensitizer, misonidazole was conducted from 1981 to 1984 to investigate its therapeutic benefit.

PATIENTS AND METHODS

Seventy-three patients were accrued from the Princess Margaret Hospital, and St John Regional Cancer Centre and randomized to either misonidazole (MISO, n = 39) or placebo (P, n = 34) in addition to radiotherapy. MISO was given orally each day 4 h prior to external beam radiation treatment (45Gy to midplane in 20 daily fractions) at a dose of 0.45 g/m(2), as well as during intra-uterine brachytherapy (40Gy).

RESULTS

The 10-year overall survival (OS) for the entire group was 46%, and the disease-free survival (DFS) was 39%. The 10-year OS for patients in the MISO arm was 45%, compared to 49% for the P arm (P = 0.89). The corresponding DFS figures were 36 and 43%, respectively, (P = 0.6). Ten patients (14%) developed severe late complications (grade 3 or 4). The 10-year serious late complication rate was 14% for MISO and 12% for P (P = 0.51).

CONCLUSIONS

Misonidazole failed to improve the outcome of patients with cervix cancer treated with radiotherapy.

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.

Radiation Therapy Oncology Group clinical trials for carcinoma of the cervix

Grigsby PW. Radiation Therapy Oncology Group clinical trials for carcinoma of the cervix. The purpose of this paper is to review the primary data of the clinical trials performed by the Radiation Therapy Oncology Group (RTOG) for patients with carcinoma of the uterine cervix. The trials, their strengths, limitations, and the implications of the results are discussed. During the past 25 years there have been several clinical trials performed by the RTOG to test various hypotheses for improving local control and survival for patients with carcinoma of the uterine cervix. The major research themes that have been appraised are the use of hyperbaric oxygen, altered fractionation radiotherapy, hypoxic cell sensitization, chemo-sensitization, prophylactic paraaortic irradiation, and neutron radiotherapy. There are two general research themes. The initial RTOG trials for cervical cancer attempted to address the issues of tumor volume and hypoxic cells while the latter studies addressed these issues and the issue of micrometastatic disease. The phase III clinical trials performed by the RTOG have not demonstrated a local control or survival advantage in the experimental arm with the use of hyperbaric oxygen, split-course radiotherapy, hypoxic cell sensitization, or neutron radiotherapy. Acceptable toxicity and efficacy results were shown in phase II studies evaluating twice-daily irradiation and chemo-sensitization. The positive phase III trials were RTOG 79-20 which evaluated prophylactic paraaortic irradiation in patients with bulky stages IB, IIA, and IIB disease, and RTOG 90-01 which evaluated concurrent chemotherapy. Results of more recent clinical trials are pending their completion.

Radiosensitization of a mouse tumor model by sustained intra-tumoral release of etanidazole and tirapazamine using a biodegradable polymer implant device

BACKGROUND AND PURPOSE

Drug toxicities are often a limiting factor in long term treatment regimes used in conjunction with radiotherapy. If the drug could be localized to the tumor site and released slowly, then optimal, intra-tumoral drug concentrations could be achieved without the cumulative toxicity associated with repeated systemic drug dosage. In this paper we describe the use of a biodegradable polymer implant for sustained intra-tumoral release of high concentrations of drugs targeting hypoxic cells.

MATERIALS AND METHODS

The RIF-1 tumor was implanted subcutaneously or intramuscularly in C3H mice and irradiated with 60Co gamma rays. The drug delivery device was the co-polymer CPP-SA;20:80 into which the drug was homogeneously incorporated. The hypoxic radiosensitizer Etanidazole or the bioreductive drug Tirapazamine were delivered intra-tumorally by means of implanted polymer rods containing the drugs. Tumor growth delay (TGD) was used as the end point in these experiments.

RESULTS

Both Etanidazole and Tirapazamine potentiated the effects of acute and fractionated radiation in the intra-muscular tumors but neither drug was effective in sub-cutaneous tumors. Since both drugs target hypoxic cells we hypothesized that the lack of effect in the subcutaneous tumor was attributable to the smaller size of the hypoxic fraction in this tumor model. This was confirmed using the hypoxia marker EF5.

CONCLUSIONS

These results indicate that the biodegradable polymer implant is an effective vehicle for the intra-tumoral delivery of Etanidazole and Tirapazamine and that, in conjunction with radiation, this approach could improve treatment outcome in tumors which contain a sub-population of hypoxic, radioresistant cells.

Long term results of stereotactic brachytherapy used in the initial treatment of patients with glioblastomas

BACKGROUND

Despite optimal therapy with surgery and radiotherapy, the prognosis of patients with glioblastomas remains poor. Stereotactic brachytherapy involves the accurate placement of radioactive isotopes within brain tumors, significantly increasing the dose of radiation that can be delivered to the tumor bed without substantial risk to surrounding normal tissue, potentially improving local tumor control and patient survival.

METHODS

Between February 1987 and July 1993, the authors treated 56 patients with glioblastomas with stereotactic brachytherapy as part of their initial therapy. Patients underwent surgery, limited field external beam radiotherapy, and brachytherapy with temporary high-activity iodine 125 sources, giving an additional 50 Gy to the tumor bed.

RESULTS

Median survival for patients undergoing brachytherapy was 18 months compared with 11 months for a matched brachytherapy control group with similar clinical and radiologic features (P < 0.0007). Survival rates at 1, 2, and 3 years after diagnosis of 83%, 34%, and 27%, respectively, for patients receiving brachytherapy were significantly increased compared with survival rates of 40%, 12.5%, and 9%, respectively, for control subjects. Thirty-six patients (64%) underwent reoperation for symptomatic radiation necrosis from 3 to 42 months (median, 11 months) after brachytherapy. The median survival of patients undergoing reoperation was 22 months compared with 13 months for those who did not have further surgery (P < 0.02). Thirty-five percent of patients relapsed locally within the brachytherapy target volume, whereas 65% had marginal or distant relapses.

CONCLUSIONS

Brachytherapy may improve local tumor control and prolong survival when used in the initial treatment of selected patients with glioblastomas.

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.

Bioreductive metabolism of SR-4233 (WIN 59075) by whole cell suspensions under aerobic and hypoxic conditions: role of the pentose cycle and implications for the mechanism of cytotoxicity observed in air

PURPOSE

Measurement of pentose cycle (PC) activity is shown to be a noninvasive means for monitoring the reduction of SR-4233 in whole cells. Comparing these measurements to the actual measurements of drug loss under aerobic and hypoxic conditions helps to define the mechanism for the associated aerobic toxicity.

METHODS AND MATERIALS

SR-4233 is activated to a toxic species by bioreductive metabolism. NADPH is required for the activation of the drug by purified enzymes, cell homogenates and whole cells. In vivo the NADPH:NADP+ ratio is maintained by the oxidation of glucose via the oxidative limb of the pentose cycle. By measuring radiolabeled 14CO2 released as a product of this oxidation one can get an accurate measurement of the rate of drug metabolism in whole cells. These results are compared to measurements of drug consumption under aerobic and hypoxic conditions using an HPLC assay.

RESULTS

SR-4233 stimulates pentose cycle activity to a greater extent in air then under hypoxia, however, in the presence of added catalase, pentose cycle activity is stimulated to a similar extent under both conditions. The higher levels of PC activity observed in air are due to the production of hydrogen peroxide by the nitroxide free radical undergoing futile redox cycling. The contribution of H2O2 to the observed aerobic cytotoxicity of SR-4233 is minimal however, since toxicity is only slightly reduced in the presence of exogenous catalase and antioxidants such as vitamin E. The level of PC stimulation by SR-4233 suggests that the rate of electron addition to the drug is independent of O2 concentration. The loss of drug from the incubation medium, i.e., conversion to a stable intermediate species, occurs approximately five times faster under nitrogen than in air for A549 cells. It is the rate of drug loss from the cell and not the rate of reduction which best correlates with the observed aerobic and hypoxic toxicity.

CONCLUSION

Toxicity in air and in nitrogen is directly related to the rate of drug reduction, i.e., at equivalent levels of drug loss we observe equal levels of cytotoxicity.

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.

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.