Modification of cisplatin toxicity with diethyldithiocarbamate

Diethyldithiocarbamate (DDTC), a heavy metal-chelating agent, has been shown to decrease cisplatin (CP) toxicity in preclinical studies. This phase I dose-escalation study was undertaken to investigate DDTC as a chemoprotector in patients with advanced cancer. Thirty-five courses of CP in doses ranging from 120 to 160 mg/m2 were given intravenous (IV) bolus to 19 patients. DDTC at 4 g/m2 was infused over 1 hour, starting 45 minutes after CP. There was minimal nephrotoxicity with a mean creatine clearance of 99 mL/min +/- 4 pretreatment and 86 mL/min +/- 4 on day 21. Two courses were associated with a WBC count less than 2,000/mm3 and one course with a platelet count of 15,000/mm3. Two patients had grade 2 neurotoxicity. Hearing loss occurred in 11 patients: five greater than or equal to 20 dB, five greater than or equal to 40 dB, and one greater than or equal to 60 dB. All patients who received cranial irradiation had ototoxicity compared with 43% of those without radiation (P less than .05). All patients experienced toxicity during the DDTC infusion, including hypertension, flushing, diaphoresis, agitation, and local burning. We conclude that DDTC can protect against CP nephrotoxicity at doses up to 160 mg/m2. Ototoxicity became the dose-limiting factor.

Final report of the phase I trial of the hypoxic cell radiosensitizer SR 2508 (etanidazole) Radiation Therapy Oncology Group 83-03

In a Phase I trial SR 2508 was administered by rapid intravenous infusion to 102 patients receiving radiation therapy. The dose-limiting toxicity was peripheral sensory neuropathy (PN) which was related to the cumulative dose administered. The highest single daily dose, 3.7 g/m2, was tolerated without toxicity. The lowest cumulative toxic dose was 21.6 g/m2, and the highest non-toxic dose was 40.8 g/m2. Grade 1 neuropathies were mild and self-limited; grade 2 neuropathies were long-lasting and debilitating. In a retrospective analysis, the risk of developing neurotoxicity was related to the cumulative drug exposure calculated by the area-under-the-curve (AUC) of plasma concentration versus time. There was an increased incidence of neuropathy in patients with a cumulative AUC of greater than or equal to 36 mM-hr. At a total dose of 34 g/m2 over 6 weeks, the incidence of Grade 1 neuropathy was approximately 30%; no grade 2 neuropathy occurred at this dose and schedule. Additional toxicities observed included nausea and vomiting (6%), skin rash (4%), and transient arthralgias (3%). One patient had transient abnormalities in liver function tests of unknown etiology. (In a more recent Phase II trial neutropenia has been observed which may be related to SR2508). Approximately three times more SR 2508 is tolerable compared to misonidazole, and it appears that severe neuropathy can be avoided by monitoring individual patient pharmacokinetic parameters. Evaluation of the efficacy of this hypoxic cell sensitizer is in progress.

Enhancement of the clinical activity of melphalan by the hypoxic cell sensitizer misonidazole

One hundred patients with non-small cell lung cancer were entered by members of the Northern California Oncology Group into a randomized Phase II trial of i.v. melphalan versus i.v. melphalan with concomitant oral misonidazole. The patients had not received prior chemotherapy. Eighty-five patients were evaluable for assessment of response and 89 were evaluable for toxicity analysis. The melphalan/misonidazole group had a superior response rate (two complete and four partial responses among 42 patients or 14%) compared to the melphalan group in which there were no responses among 43 patients (p = 0.024, two-sided Fisher exact test). Since hematological toxicity was equivalent in the two groups, there was an improvement in therapeutic index. Data from 12 patients undergoing pharmacological studies demonstrated that the plasma concentration of melphalan was 25% higher in the misonidazole group, a difference that is not statistically significant. Although the mechanism of interaction has not been fully established, this randomized trial demonstrates that a chemosensitizer can enhance the clinical antitumor activity of an alkylating agent and suggests that chemosensitizers in combination with alkylating agents should be investigated in further clinical trials.

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.

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.

Initial report of the phase I trial of the hypoxic cell radiosensitizer SR-2508

From March 15, through August 31, 1983, 37 patients have been entered on the RTOG Phase I trial of SR-2508. The drug was given intravenously three times weekly for three weeks. The starting total dose was 11.7 g/m2 and the highest total dose given was 32 g/m2. The lower lipophilicity of SR-2508 has produced the expected decrease in terminal half-life (5.4 hrs) of drug excretion and increase in total drug excreted unchanged in the urine (71%) compared to misonidazole or desmethylmisonidazole. The maximum single dose (3.7 g/m2) administered was well tolerated. With multiple doses peripheral neuropathy is the dose-limiting toxicity. The lowest cumulative dose producing toxicity was 21.6 g/m2, the highest non-toxic dose was 29.7 g/m2. The use of an individual patient's drug exposure as measured by the area under the curve of drug concentration vs time may be an excellent predictor of toxicity. This may eventually permit individualization of dose and prevention of serious toxicity. A single dose of 2 g/m2 will produce a tumor concentration of drug (approx. 100 micrograms/ml) that will yield a sensitizer enhancement ratio of 1.5 to 1.7. Using a starting dose of 2 g/m2 three times weekly, patients are now being studied on a five week drug schedule to further evaluate predictability of drug toxicity in preparation for clinical trials of drug efficacy.

The effect of vitamin B6 on the neurotoxicity and pharmacology of desmethylmisonidazole and misonidazole: clinical and laboratory studies

The clinical usefulness of misonidazole (MISO) and desmethylmisonidazole (DMM) is severely limited by neurotoxicity. Based on theoretical considerations and on laboratory data suggesting that pyridoxine (PN) decreased MISO toxicity in mice, we attempted to ameliorate the clinical neuropathy of DMM using oral PN. Pharmacokinetic analysis suggested interaction of PN and DMM but no protection against neuropathy was observed. Serial experiments with C3H and BALB/c mice were done using various forms of vitamin B6 (PN, pyridoxal, pyridoxal phosphate) administered orally and i.p. and the nonspecific adsorbing agent activated charcoal. No consistent protection was observed. A slower rate of drug delivery (dose/day) allowed a larger cumulative dose of MISO to be given, a result paradoxical to that seen in the clinic. Dexamethasone did not alter MISO toxicity in mice, contrary to the clinical findings. We conclude that vitamin B6 is not useful in preventing clinical neurotoxicity of MISO or DMM. Furthermore, this mouse model of neurotoxicity assessment has produced results inconsistent with those seen clinically.

The current status of drug development of hypoxic cell radiosensitizers and their potential role in gynecologic oncology

Both laboratory and clinical data suggest that hypoxia contributes to the failure of radiotherapy to achieve local control of bulky gynecologic tumors. As part of a Phase I trial of hypoxic cell radiosensitizers, 19 women at Stanford University with advanced (n = 6) or recurrent (n = 13) pelvic neoplasms were treated with radiotherapy plus desmethylmisonidazole. Complete or partial response occurred in 42% of patients with some patients achieving local control for over 1 year. It is unknown if the sensitizer added to the results of radiotherapy alone. A Phase I trial of a theoretically superior sensitizer, SR-2508, is soon to begin. It is anticipated that the dose-limiting neurotoxicity seen with misonidazole and desmethylmisonidazole will either be eliminated or will occur at a much higher total dose of drug. Many patients with gynecologic tumors could potentially benefit from participation in the new drug trials.

Phase I trial of intravenous L-phenylalanine mustard plus the sensitizer misonidazole

Misonidazole (MISO), a hypoxic cell radiosensitizer, has been shown in vivo to enhance tumor cell killing by melphalan (LPAM) with little or no enhancement of normal tissue injury. A Phase I trial was conducted using MISO p.o. 2 hr before i.v. LPAM. The highest doses used were the single maximum tolerated doses of MISO, 4 g/sq m, and LPAM, 0.6 mg/kg. Thirty-five patients were entered; 30 were evaluable for assessment of hematological toxicity, which was predicted to be the dose-limiting toxicity. The median age was 60 years (range, 28 to 72 years). Mild to moderate nausea and vomiting occurred in 80% of patients. Five developed serious hematological toxicity defined as nadir white blood cell count less than 1000/cu mm, platelets less than 20,000/cu mm or 4-week posttreatment white blood cell count less than 2000/cu mm, platelets less than 50,000/cu mm. Four of the toxicities occurred at the LPAM dose of 0.6 mg/kg but were independent of MISO dose. One patient died of infection. Two patients whose tumor demonstrated an objective response to therapy and 10 others with disease stabilization received additional courses. Four patients developed mild MISO neuropathy. Pharmacokinetic studies demonstrated that MISO did not appear to affect the pharmacokinetics of LPAM in plasma. Both LPAM and MISO can be given safely at their individual maximum tolerated dose. This combination will proceed to Phase II trials.

Conversion from daily to alternate daily corticosteroids in rheumatoid arthritis

An attempt was made to convert 24 patients on corticosteroid treatment from a daily to an alternate daily regimen. Ten patients were successfully converted, 11 failed to convert, and 3 had to be withdrawn for irrelevant reasons. A simple tetracosactrin stimulation test gave some indication of which patients were more likely to convert successfully. Success was not influenced by severity or duration of disease, nor by dose of duration of steroid therapy. Conversion did not influence various clinical and laboratory measures of undesirable steroid side effects, but the follow-up period was probably too short to judge this. The evidence of others suggests that conversion is worth attempting.

Calorimetric studies of the interaction of magnesium and phosphate with Na+, K+) ATPase: evidence for a ligand-induced conformational change in the enzyme

The phosphorylation of (Na+, K+)ATPase from the electric organ of the electric eel is dependent on Mg2+. The amount of phosphoenzyme formed was increased by K+ and decreased by Na+. Kinetic analyses indicate that a ternary complex of ATPase, Pi and Mg2+ is formed prior to phosphorylation of the protein. Calorimetric studies revealed extraordinarily large enthalpy changes associated with the binding of Mg2+ (-49 kcal/mol) and of Pi (-42 kcal/mol), indicating a thermodynamically significant conformational change in the enzyme. The dissociation constant for the binding of Mg2+ and Pi derived from calorimetric measurements is in good agreement with the value obtained from the kinetic studies. These results indicate that ion binding induces a conformational change in the enzyme which is a prerequisite for phosphorylation by Pi.