[Hepatic stellate cells and oxidative stress]. / Células estrelladas hepáticas y estrés oxidativo.

Hepatic fibrosis is a wound-healing response that takes place during chronic liver injury and is characterized by excessive production and deposition of extracellular matrix (ECM) components, mainly collagen type I. Hepatic stellate cells (HSC) are responsible for the excessive production of scar tissue during liver fibrosis. Activation of HSC, the main step in the development of hepatic fibrosis, is mediated by cytokines and reactive oxygen species (ROS) released by damaged hepatocytes and/or activated Kupffer cells and even HSC themselves. While HSC usually remain quiescent, in response to factors promoting liver injury they undergo activation and become highly proliferative and fibrogenic. Indeed a key feature of HSC activation is uncontrolled production of collagen type I. Collagen is a heterotrimeric protein composed of two a1 chains and one a2 chain forming a triple helix structure. Initiation of HSC activation is largely due to paracrine stimulation, whereas the perpetuation of such activated state involves autocrine as well as paracrine loops. This review focuses on the role of oxidant stress on the activation of stellate cells.

Comparison of prognostic factors and survival among black patients and white patients treated with irradiation for non-small-cell lung cancer.

BACKGROUND: Many studies have reported differences in cancer incidence and survival between populations of Blacks and Whites. A 45% higher death rate from lung cancer for Black men and a survival duration for Black patients with lung cancer that is generally shorter than that for White patients have also been reported. PURPOSE: The purpose of this study was to evaluate whether race affects known prognostic factors for non-small-cell lung cancer in Black versus White patients. This analysis attempts to determine which prognostic factors may contribute to the reported differences in disease outcome. METHODS: We used data from 1565 patients with non-small-cell lung cancer treated in four randomized prospective trials conducted by the Radiation Therapy Oncology Group (RTOG). The data were pooled for a retrospective analysis of survival and prognostic factors by race. RESULTS: Univariate analysis showed significant differences between Blacks and Whites with regard to sex, weight loss, histology, and RTOG T stage (P < .05), but the only clinically significant difference (P < or = .01) was weight loss. Despite these findings, overall survival for Blacks and Whites did not differ significantly (P = .67). Median survival for Blacks and Whites with a Karnofsky performance status (KPS) of 90 or more was 12.1 and 11.3 months, respectively (P = .45). Survival for Blacks and Whites with a KPS of less than 90 was 7.8 and 6.8 months, respectively. Cause of death did not differ between the two races. For both races, KPS, age, sex, weight loss, and RTOG T and N stages were significant prognostic factors for survival (P < .01), but race was not a significant prognostic factor. CONCLUSION: Further studies of the differential in cancer survival for Blacks and Whites may be indicated, but greater impact may be achieved by addressing socioeconomic factors, lifestyle and occupational risk factors, health education, and access to adequate health care.

Relationship between the neurotoxicity of the hypoxic cell radiosensitizer SR 2508 and the pharmacokinetic profile.

Complete pharmacological data from 71 patients treated on the phase I trial of SR 2508 were analyzed to see if the dose-limiting toxicity of peripheral neuropathy is related to the individual patient's pharmacokinetic profile. In a retrospective analysis, the risk of toxicity was best predicted by using the bivariate model of total drug exposure and the time over which the treatment course was given. Drug exposure [area under the curve (AUC)] for a single treatment was calculated by the integral over time of the serum concentration of SR 2508. Since the AUC was constant during the course of a patient's treatment, the total drug exposure (total-AUC) was estimated by the product of the AUC times the number of drug administrations. While the clinical efficacy of hypoxic cell sensitizers remains to be proven, SR 2508 is better tolerated than its predecessors, misonidazole and desmethylmisonidazole, as three times the amount of SR 2508 can be given. If this model is confirmed in the current phase II and III trials, the probability of developing neuropathy would be predictable for an individual patient from measurements made at the time of the first drug dose, allowing for the adjustment of drug schedule to avoid all but minor toxicity.

Splicing regulator SLU7 preserves survival of hepatocellular carcinoma cells and other solid tumors via oncogenic miR-17-92 cluster expression.

Resisting death is a central hallmark of cancer cells. Tumors rely on a number of genetic mechanisms to avoid apoptosis, and alterations in mRNA alternative splicing are increasingly recognized to have a role in tumorigenesis. In this study, we identify the splicing regulator SLU7 as an essential factor for the preservation of hepatocellular carcinoma (HCC) cells viability. Compared with hepatocytes, SLU7 expression is reduced in HCC cells; however, further SLU7 depletion triggered autophagy-related cellular apoptosis in association with the overproduction of reactive oxygen species. Remarkably, these responses were not observed in primary human hepatocytes or in the well-differentiated HepaRG cell line. Mechanistically, we demonstrate that SLU7 binds the C13orf25 primary transcript in which the polycistronic oncomir miR-17-92 cluster is encompassed, and is necessary for its processing and expression. SLU7 knockdown altered the splicing of the C13orf25 primary transcript, and markedly reduced the expression of its miR-17, miR-20 and miR-92a constituents. This led to the upregulation of CDKN1A (P21) and BCL2L11 (BIM) expression, two bona fide targets of the miR-17-92 cluster and recognized mediators of its pro-survival and tumorigenic activity. Interestingly, altered splicing of miR-17-92 and downregulation of miR-17 and miR-20 were not observed upon SLU7 knockdown in non-transformed hepatocytes, but was found in other (HeLa, H358) but not in all (Caco2) non-hepatic tumor cells. The functional relevance of miR-17-92 dysregulation upon SLU7 knockdown was established when oxidative stress, autophagy and apoptosis were reversed by co-transfection of HCC cells with a miR-17 mimic. Together, these findings indicate that SLU7 is co-opted by HCC cells and other tumor cell types to maintain survival, and identify this splicing regulator as a new determinant for the expression of the oncogenic miR-17-92 cluster. This novel mechanism may be exploited for the development of antitumoral strategies in cancers displaying such SLU7-miR-17-92 crosstalk.

Eastern Cooperative Oncology Group: a comparison of adjuvant doxorubicin and observation for patients with localized soft tissue sarcoma.

Forty-seven patients with stage I, II, or III soft tissue sarcoma were entered into a prospective randomized Eastern Cooperative Oncology Group (ECOG) adjuvant protocol. Eligibility included conservative or radical primary treatment for local cure. Patients were then randomized to control or Adriamycin (Adria Laboratories, Columbus, OH). Adriamycin was administered at 70 mg/m2 (slow push, every 3 weeks for seven courses for a maximum of 550 mg/m2). To date, 32 patients, 17 males and 15 females, with an age range of 17 to 75 years (median, 44 years) have been followed sufficiently long to be included in this analysis. Nine patients have died. The median follow-up of the remaining 23 patients is 30 months (range, 2 to 50 months). Survival was not significantly different between Adriamycin or control. However, the disease-free interval was slightly different in favor of observation. This preliminary report does not support the hypothesis that Adriamycin is an effective adjuvant therapy for soft tissue sarcoma. Due to the small numbers, these results must be interpreted in relation to our ability to detect a difference, if in fact one existed. These preliminary data suggest that adjuvant Adriamycin not be used outside the confines of a clinical trial such as the current intergroup adjuvant sarcoma study.

Single-arm, open-label phase II study of intravenously administered tirapazamine and radiation therapy for glioblastoma multiforme.

PURPOSE: This phase II study tested the efficacy and safety of tirapazamine (Sanofi Synthelabo Research, Malvern, PA), a bioreductive agent, in glioblastoma multiforme (GBM) patients. The patients were staged according to a model constructed by a recursive partitioning analysis (RPA) of glioma patients in prior Radiation Therapy Oncology Group (RTOG) trials and compared with a matched standard population, as predicted by the model. PATIENTS AND METHODS: A total of 124 patients diagnosed with a GBM were treated with radiation therapy and intravenous tirapazamine between January 27,1995, and April 25,1997. All patients received 60 Gy in 2-Gy fractions. Tirapazamine was delivered three times a week for 12 treatments during radiotherapy. Fifty-five patients received tirapazamine at 159 mg/m(2). A second dose level, 260 mg/m(2), was opened, and 69 patients were entered. RESULTS: There was no significant survival advantage to the drug in any RPA class at either dose level. The median survival time was 10.8 months for the patient population treated with the 159-mg/m(2) dose of tirapazamine and 9.5 months for the group treated with the 260-mg/m (2) dose of tirapazamine. Survival times by RPA class for patients receiving tirapazamine at 159 mg/m(2) were 27.4 months (class III), 10.8 months (class IV), 7.9 months (class V), and 3.8 months (class VI). Survival times by RPA class for patients receiving tirapazamine at 260 mg/m(2) were 16.2 months (class III), 10.3 months (class IV), 5. 1 months (class V), and 1.3 months (class VI). Patients in RPA class III treated in the 159 mg/m(2) dose arm had a notably longer survival than patients in the RTOG database RPA class III, but the difference did not reach statistical significance. There were no fatal toxicities. Grade 3/4 toxicities were more frequent at the higher dose level. CONCLUSION: Survival in the population treated with radiation and tirapazamine was equivalent to the control population. Patients in RPA class III treated with radiation and tirapazamine at the 159-mg/m(2) dose had a longer survival when compared with the historical controls. The improvement in survival did not reach statistical significance. Toxicity was acceptable in both treatment arms, but grade 3/4 toxicities were more frequent in the higher dose regimen.

Abbreviated course of radiation therapy in older patients with glioblastoma multiforme: a prospective randomized clinical trial.

PURPOSE: To prospectively compare standard radiation therapy (RT) with an abbreviated course of RT in older patients with glioblastoma multiforme (GBM). PATIENTS AND METHODS: One hundred patients with GBM, age 60 years or older, were randomly assigned after surgery to receive either standard RT (60 Gy in 30 fractions over 6 weeks) or a shorter course of RT (40 Gy in 15 fractions over 3 weeks). The primary end point was overall survival. The secondary end points were proportionate survival at 6 months, health-related quality of life (HRQoL), and corticosteroid requirement. HRQoL was assessed using the Karnofsky performance status (KPS) and Functional Assessment of Cancer Therapy-Brain (FACT-Br). RESULTS: All patients had died at the time of analysis. Overall survival times measured from randomization were similar at 5.1 months for standard RT versus 5.6 months for the shorter course (log-rank test, P =.57). The survival probabilities at 6 months were also similar at 44.7% for standard RT versus 41.7% for the shorter course (lower-bound 95% CI, -13.7). KPS scores varied markedly but were not significantly different between the two groups (Wilcoxon test, P =.63). Low completion rates of the FACT-Br (45%) precluded meaningful comparisons between the two groups. Of patients completing RT as planned, 49% of patients (standard RT) versus 23% required an increase in posttreatment corticosteroid dosage (chi(2) test, P =.02). CONCLUSION: There is no difference in survival between patients receiving standard RT or short-course RT. In view of the similar KPS scores, decreased increment in corticosteroid requirement, and reduced treatment time, the abbreviated course of RT seems to be a reasonable treatment option for older patients with GBM.

Does improved depth dose characteristics and treatment planning correlate with a gain in therapeutic results? Evidence from past clinical experience using conventional radiation sources.

Experience with the use of external beam conventional radiation over a period of several decades has shown that in every instance where there has been a major advance in the physical delivery of radiation to the tumor (beam energy and characteristics and precise tumor dose delivery) there has been a corresponding major improvement in the treatment results. The advent of megavoltage sources following the invention and use of Cobalt 60 and medical linear accelerator units during the late 1940's and early 1950's and their major impact on tumor control and patient survival in solid tumors such as carcinoma of the prostate, Hodgkin's Disease, head and neck tumors and cancer of the cervix are being discussed. Most recently, the use of computerized tomography and computer systems for treatment planning is likely to show a further improvement in the therapeutic results.

Hemibody radiation, an active therapeutic modality for the management of patients with small cell lung cancer.

In a previously published paper, the results of a preliminary clinical trial comparing systemic radiation (upper and lower hemibody technique) versus systemic chemotherapy in the management of all stages of small cell lung cancer (SCLC), suggested that hemibody radiation (HBI) was as efficient as systemic chemotherapy, particularly for patients with early disease. We are now presenting the final results of the above trial. The two year survival has shown that as many patients in the HBI as in the chemotherapy arm have reached this endpoint. However, there is a difference in favor of chemotherapy on both the median and one year survival for those patients with advanced stages. Therefore, as of June 1981, we have initiated a study incorporating HBI as a consolidating-maintenance agent for patients with all stages of the disease who have received a 3 1/2 months induction systemic chemotherapy plus local chest irradiation. Up to date, 65 patients have been entered and our median survival for those who received the complete treatment is 62.5 weeks.

Misonidazole with dexamethasone rescue: an escalating dose toxicity study.

Neurotoxicity induced by misonidazole (MISO) and desmethylmisonidazole (DMM) has become the dose limiting factor in clinical work. In 1981, we reported a preliminary study suggestive that Dexamethasone (DEXA) does have a protective effect against peripheral neuropathies (PN) resulting from toxicity of misonidazole. Furthermore, in that study we have observed that DEXA did not alter the plasma pharmacokinetics of misonidazole. We are presently investigating the use of DEXA (2 mg t.i.d. during treatment), with escalating doses of MISO in an attempt to modify its neurotoxicity. To date, 16 patients have been registered to receive total doses of MISO ranging from 13.5 to 17.5 gm/M2 given in 9 equally divided doses over 3 weeks. DEXA, 2 mg t.i.d. is given 3 days prior to the first dose and continues for the duration of therapy. All patients receive palliative radiation. No toxicity was seen at the total dose of 13.5 gm/M2. One grade I PN occurred in the first four patients receiving 15.5 gm/M2. Six additional patients were entered at this dose level and no further incidence of PN was observed. Patients are being entered at the next step of 17.5 gm/M2.

The effect of radiation on normal human CNS as detected by NMR spectroscopy.

In a prospective study, proton (1H) and phosphorus (31P) nuclear magnetic resonance spectroscopy were used to search for effects of brain tumor radiotherapy on normal human central nervous system. Phosphorus spectroscopy data at 1.5 T seems to suggest that any radiation induced damage that may occur as a result of therapeutic brain irradiation, does not alter the relative concentrations of phosphorus metabolites or the intracellular pH beyond the limits of normal variation (approximately +/- 20%). Proton spectroscopy, on the other hand, detects post radiation changes in the ratios of certain nuclear magnetic resonance visible metabolites following radiotherapy, particularly choline/N-acetylaspartate, and especially in regions of brain receiving high doses of radiation. Such changes may be indicative of the release of membrane bound choline during radiation induced demyelination of brain. Of interest, we have found elevated metabolite ratios of 31P in normal central nervous system prior to radiotherapy, which persisted throughout the time span of the study in both the ipsilateral and contralateral cerebral hemispheres.

A randomized phase III protocol for the evaluation of misonidazole combined with radiation in the treatment of patients with brain metastases (RTOG-7916).

From 1979 through July 1983, 859 patients were enrolled in a Phase III RTOG Protocol (7916) evaluating the role of Misonidazole combined with radiation in the treatment of brain metastasis. Patients were randomized to one of four treatment arms (3.0 Gy x 10 fractions with or without 1 g/m2 of Misonidazole [total 10 g/m2] versus 5.0 Gy x 6 fractions with or without 2 g/m2 of Misonidazole) [total 12 g/m2]. Among the 779 analyzable cases, 63% had a lung primary and 12% had breast. Of the histologic types, 43% were adenocarcinoma and 24% were squamous cell. Seventy-eight percent had a Karnofsky of greater than 70. Of the 779 cases, 773 are dead (99%). Median survival is 3.9 months, with 60% alive at 3 months, 35% at 6 months, and 15% at 1 year. Survival was evaluated by treatment arm, Misonidazole status, and fractionation scheme; none showed any statistical significance. Favorable prognostic factors were assessed (age less than 60, Karnofsky of 70-100, controlled primary and brain metastasis only) in each treatment arm and no difference was found. Brain metastasis was cause of death in 1/3, and 19-33% of patients were retreated. Because up to 1/3 of the patients in this study died secondary to uncontrolled brain metastasis, improvement in local control remains an important goal. Until proven otherwise, the treatment of choice for the majority of patients still remains a conventional palliative course of 3.0 Gy x 10 fractions.

Binding of 3H-misonidazole to solid human tumors as a measure of tumor hypoxia.

Treatment-resistant, chronically hypoxic tumor cells have been assumed to exist in some solid human tumors, limiting their curability. To date, six patients with different types of tumors have been studied using radioactive labelled electron affinic compounds that bind to hypoxic cells. Although the gross clinical appearance of the tumors in all six patients was of a large and fixed mass which might on clinical grounds be expected to contain hypoxic cells, we have observed drug binding to hypoxic regions in only two, a rapidly growing small cell lung cancer (SCLC) and a malignant melanoma. The hypoxic fraction of the malignant melanoma was found to be 6% and the SCLC tumor approximately 10%. We have observed that areas of maximum adduct formation can be found in tumor cells immediately adjacent to blood vessels, suggesting that blood flow over the labelling interval was restricted. These preliminary studies suggest that sensitizer adduct formation in human tumor tissue may be a useful measure of tissue pO2 at the cellular level and that tumor hypoxia might be more related to the rate of tumor growth and histological grading than to tumor size.

Heterogeneity in response to treatment with buthionine sulfoximine or interferon in human malignant glioma cells.

Two tumor cell lines were established from each of three human malignant glioma biopsy specimens (M059, M067, M071) and sensitivity to treatment with radiation or chemotherapeutic agents (BCNU, nitrogen mustard) was determined. The effects of recombinant human interferon-alpha (rIFN) on the radiation response and of buthionine sulfoximine (BSO) on the drug response were investigated as well. For tumor M059, two cell lines that differed significantly in radiosensitivity were isolated (surviving fractions at 2 Gy = 0.02 and 0.64). The chemosensitivity and response to chemical modification differed as well. Cell lines established from tumor M071 differed in their response to rIFN only and were not sensitized by BSO. M067 cell lines showed little difference and were not sensitized by either agent. These results suggest that differences may exist both within and among human malignant gliomas with regard to their sensitivity to drugs, radiation, and the ability of chemical agents to modify treatment responses.

Radiosensitivity testing of human primary brain tumor specimens.

The inherent radiosensitivity of early passage cells derived from 22 patients with tumors of glial origin has been determined using a clonogenic assay system. The mean (+/- SD) surviving fraction at 2 Gy was 0.37 +/- 0.22 (range = 0.02-0.87). No correlation between inherent radiosensitivity and tumor cell plating efficiency or intracellular glutathione was observed. Tumor cells that were both resistant to nitrosoureas and expressed the Mer+ phenotype did not differ significantly in their radiosensitivity as compared to cells that were repair deficient (Mer-) and sensitive to nitrosoureas. Initial clinical follow-up suggests that factors in addition to inherent tumor cell radiosensitivity, such as performance status and age, continue to be the most important determinants of the response of patients with primary brain tumors to radiotherapy.

Quality of life and neuropsychological evaluation for patients with malignant astrocytomas: RTOG 91-14. Radiation Therapy Oncology Group.

UNLABELLED: With increasingly aggressive neurosurgical and radiation therapy modalities (gamma knife, external beam stereotactic radiation and interstitial brachytherapy with or without hyperthermia) offered to patients with malignant astrocytomas (MA), increasing national demand for medical outcome studies and rising health care costs amidst public, business, and governmental debate to cut spending, we as physicians are obligated to continue our research to find effective treatments for malignant astrocytoma (MA) and a cost-effective means to study their impact upon the patient's quality of life (QOL). PURPOSE: We report data that was collected within the Radiation Therapy Oncology Group (RTOG) on 126 patients with MA who were enrolled in RTOG 91-14. This study was undertaken to prospectively test the feasibility of performing quality of life (QOL) and neuropsychological evaluation (NPE) and collecting this data within the RTOG. RESULTS: The NPE and QOL parameters that were used in this study are cost effective. They are not only much cheaper than formal cognitive and memory testing, but also provide additional information regarding the patients' day to day functional abilities that are not provided by the current routinely used means, such as KPS. The Mini-Mental Status Exam (MMSE) provides greater sensitivity to patients' differences in neurological status and may be preferable to NFS as an eligibility criteria.

Intervention with the hypoxic tumor cell sensitizer etanidazole in the combined modality treatment of limited stage small-cell lung cancer. A one-institution study.

PURPOSE: We report the toxicity, patterns of failure and survival of a cohort of patients with limited disease (LD) small-cell lung cancer (SCLC) treated with combined radiation and chemotherapy. During the course of thoracic irradiation, we added intravenous (i.v.) etanidazole (SR-2508, a third-generation 2-nitroimidazole) as a hypoxic cell sensitizer in an attempt to reduce the primary local failure rate and improve survival. METHODS AND MATERIALS: Between July 1988 and August 1990, 30 consecutive patients with limited disease SCLC were enrolled and treated on a Phase II protocol receiving a standard combination chemotherapy regimen utilizing i.v. cisplatin 25 mg/m2/day x 3 days, i.v. etoposide 100 mg/m2/day x 3 days alternating with intravenous cyclophosphamide 1000 mg/m2/day, intravenous doxorubicin 15 mg/m2, and intravenous vincristine 2 mg (CAV) to a total of six cycles every 3 weeks. Radiotherapy and etanidazole were started after the first cycle of chemotherapy. Etanidazole was administered intravenously at a dose of 2 g/m2 three times per week for a total of 30 g/m2 during the course of thoracic radiation that delivered 50.00 Gy tumor dose in 25 fractions in an overall time of 6 weeks. RESULTS: The overall response rate of the primary lesion in the thorax was 96% (CR + PR), with 64% complete responses. The median time to treatment failure was 18 months. Of the patients that have relapsed, only 18% failed in the thorax (alone or concomitant with other sites). This is a marked improvement compared to the 40-50% rate reported in the literature. The 2-year crude survival was 46%. The 3- and 5-year crude survival rate with no evidence of disease was 33 and 30%, respectively. We have observed a 10% increase in the incidence of transient etanidazole related peripheral neuropathies compared to previous etanidazole studies not utilizing systemic chemotherapy. There was no increased incidence of radiation esophagitis, pulmonary toxicity, or nephro- or myelotoxicity over and above what has been routinely observed with this radio/chemotherapy regimen. There were no treatment related deaths. CONCLUSION: The moderate increase in etanidazole-related transient peripheral neuropathies could have been related to the concomitant use of etanidazole with vincristine and cisplatin. Although the almost 50% improvement in the incidence of tumor failure rate in the thorax in this small group of patients did not correlate with an equal marked improvement in their survival, the 5-year survival outcome in our series is at least equal or better than the best reports in the literature of larger clinical trials. We believe there is sufficient data from this study, particularly the improvement of local tumor control, to warrant a large randomized controlled clinical trial, using the most current systemic chemotherapy with concomitant thoracic irradiation with or without the most effective available hypoxic cell cytotoxic/sensitizer.

Clinical trials with hypoxic cell sensitizers: time to retrench or time to push forward?

Results of world-wide clinical trials with misonidazole are discussed. An attempt is made to assess the reasons for the lack of positive results and the cost-benefit analysis is critically reviewed. The data on the clinical investigations of the second generation misonidazole analogues SR-2508 and RO-03-8799 are presented. Emphasis is placed on future work such as tumor selection for clinical trials, reduction of drug toxicity and methods to increase the drug radiosensitizing properties. Because of the large amount of knowledge, experience, productivity and good scientific clinical data accummulated with nitroimidazoles over the past five years, it is recommended that this is the time to push forward with the work on the newest, more efficient compounds.

High dose misonidazole with dexamethasone rescue: a possible approach to circumvent neurotoxicity.

With a view to modifying misonidazole (MISO) neurotoxicity, we initiated a randomized clinical study to assess a possible drug interaction and toxicity protection when dexamethasone (DXM) is administered concomittantly with MISO. The ongoing study consists of: 1. Pharmacokinetic evaluation; 2. Assessment of toxicity. Fourteen patients undergoing radiation therapy for different types of malignant neoplasia (excluding brain tumors) have been randomized to receive either MISO alone, or DXM one week prior and during treatment with MISO. Five of seven patients receiving MISO alone developed peripheral neuropathies while only one out of 7 patients that received MISO with DXM coverage developed a transient and mild neuropathy. Pharmacokinetic evaluation of MISO in plasma and urine of those patients receiving DXM has shown no evidence of drug interaction. It is postulated that the mechanism of action of DXM is at the nerve cell membrane level, restoring and stabilizing cell surface properties. In future studies we will investigate the use of DXM with increasing doses of MISO above the recommended maximum dose of 12 gm/m2, hoping to achieve a higher tumor tissue level of MISO while avoiding unacceptable toxicity. The effect of Allopurinol on the plasma kinetics of MISO was studied in four additional patients, observing also no evidence of drug interaction.

Phase I trial of the hypoxic cell radiosensitizer SR-2508: the results of the five to six week drug schedule.

Sixty-five patients were entered on the long schedule of the Phase I trial of SR-2508. The planned total doses ranged from 30 to 40.8 g/m2 using various treatment schema including daily, split course, and every-other-day schedules. The individual dose size was 2 g/m2 for 56 patients and 1.7 g/m2 for nine. In contrast to misonidazole and desmethylmisonidazole, more SR-2508 can be administered as the duration of therapy is lengthened. All six patients on the 30 g/m2 step tolerated the drug without toxicity. This total dose was not achievable in the three week schedule. Additionally, a number of patients did not develop neuropathy at a cumulative dose of 40.8 g/m2. Although the analysis is not yet complete, a given patient's drug exposure as measured by their total AUC (mMxhr), defined as the area-under-the-curve of serum concentration of SR-2508 vs. time for a single dose times the number of doses given, is useful in predicting toxicity for that patient. The recommended starting schedule for the Phase II and III trials is 34 g/m2 over a 6 week period (2 g/m2 every other day). A total AUC of approximately 39 mMxhr should be tolerable. The drug regimen must be altered for patients who have a high AUC. Therefore, it is mandatory to have an accurate and rapid pharmacokinetic analysis for each patient. The clinical efficacy of the hypoxic cell sensitizers remains to be proven. However, using the guidelines derived from the Phase I trial, SR-2508 should be a relatively safe drug, producing minor or no toxicity.