Mitochondrial DNA in human malignancy.

Alterations in expression of mitochondrial DNA (mtDNA)-encoded polypeptides required for oxidative phosphorylation and cellular ATP generation may be a general characteristic of cancer cells. Mitochondrial DNA has been proposed to be involved in carcinogenesis because of high susceptibility to mutations and limited repair mechanisms in comparison to nuclear DNA. Since mtDNA lacks introns, it has been suggested that most mutations will occur in coding sequences and subsequent accumulation of mutations may lead to tumor formation. The mitochondrial genome is dependent upon the nuclear genome for transcription, translation, replication and repair, but precise mechanisms for how the two genomes interact and integrate with each other are poorly understood. In solid tumors, elevated expression of mtDNA-encoded subunits of the mitochondrial electron respiratory chain may reflect mitochondrial adaptation to perturbations in cellular energy requirements. In this paper, we review mitochondrial genomic aberrations reported in solid tumors of the breast, colon, stomach, liver, kidney, bladder, head/neck and lung as well as for hematologic diseases such as leukemia, myelodysplastic syndrome and lymphoma. We include data for elevated expression of mtDNA-encoded electron respiratory chain subunits in breast, colon and liver cancers and also the mutations reported in cancers of the colon, stomach, bladder, head/neck and lung. Finally, we examine the role of reactive oxygen species (ROS) generated by mitochondria in the process of carcinogenesis.

Pediatric phase I trial, pharmacokinetic study, and limited sampling strategy for piritrexim administered on a low-dose, intermittent schedule.

Piritrexim, an orally administered, lipid-soluble antifolate, was evaluated in a multi-institutional phase I trial in children. The starting dose was 10 mg/m2/dose administered every 8 h daily for 5 days for 3 consecutive weeks, with dose escalations in increments of 5 mg/m2/dose. Eighteen patients (16 with metastatic sarcoma, 1 with acute lymphoblastic leukemia, and 1 with a brainstem glioma), 3.5-20 years of age, with malignancy refractory to therapy, were entered into the study. The dose-limiting toxicities (DLTs), which were myelosuppression and mucositis, occurred in 4 of 4 patients treated at the 25-mg/m2/dose level but in none of the patients treated at the 15- and 20-mg/m2/dose levels. The recommended dose for phase II trials is 20 mg/m2/dose. Pharmacokinetic monitoring was performed in 15 of the 18 children. The area under the concentration-time curve (AUC) was linearly related to the dose administered. Piritrexim was rapidly absorbed, with the median time to peak level occurring 1.5 h after an oral dose. The terminal half-life of piritrexim ranged from 1.5 to 4.5 h. A limited sampling strategy developed earlier, capable of predicting the AUC based on the plasma concentrations at 3 and 6 h after an oral dose, was prospectively tested in this trial and proved to be highly predictive of the AUC (r = 0.98, P = 0.0001). Pharmacodynamic-pharmacokinetic correlations were obtained after combining data from this and the prior phase I pediatric trial. Trough plasma piritrexim concentration strongly correlated with DLT (P = 0.0016). A trough plasma piritrexim concentration greater than 0.5 microM appeared to be predictive of toxicity. Eleven of 15 patients with trough concentrations exceeding this threshold experienced DLTs. Therapeutic drug monitoring may thus play an important role in adjusting the dose and schedule of piritrexim in future trials.

Choice of starting dose and escalation for phase I studies of antitumor agents.

The standard approaches to initial dose selection and dose escalation in phase I trials may be inappropriately conservative. These approaches mandate accrual of large numbers of patients, most of whom are treated at low and potentially ineffective doses. We compared the clinically determined maximum tolerable dose (MTD) with the starting dose of 45 drugs that had undergone phase I studies during the period 1977-1989. We also examined the number of dose-escalation steps required to achieve the MTD in relation to nonhematologic and hematologic dose-limiting toxicity. The median ratio of MTD to starting dose for all drugs was 20 (range, < 1-433) and the median number of dose levels studied to reach the MTD was 8 (range, 0-23). For drugs with nonhematologic dose-limiting toxicity, the median ratio of MTD to starting dose was 30 (range, 3-385) as compared with 12.8 (range, < 1-433) for those with hematologic dose-limiting toxicity (P = 0.023). The median number of dose-escalation steps required to reach the MTD was 9 (range, 2-18) for drugs with nonhematologic dose-limiting toxicity as compared with 5.5 (range, 0-23) for those with hematologic dose-limiting toxicity (P = 0.038). We also examined the response rate for 1,110 patients treated with 21 phase-I-study drugs for which response information was available. Responses were reported for 29 patients (2.6%). Among the 476 patients treated at the 3 highest dose steps, 17 responded (3.6%), which is double the response rate obtained at the lower doses (P = 0.08). It is suggested that although the usual methods for choosing starting doses and dose-escalation schemes for phase I studies are safe, they are overly conservative and delay opportunities for therapeutic benefit in phase I and subsequent phase II trials.

Pediatric phase I trial and pharmacokinetic study of piritrexim administered orally on a five-day schedule.

Piritrexim, a new nonclassical antifolate, was evaluated in a multiinstitutional phase I trial in children. The starting dose was 290 mg/m2/day, administered p.o. every 12 h for 5 consecutive days, with courses repeated every 21 days. Dose reduction, initially to 200 mg/m2/day and subsequently to 140 mg/m2/day, was required because dose limiting myelosuppression and mucositis were encountered at the 290- and 200-mg/m2/day dose levels. Non-dose limiting toxicities included transient elevations in liver function tests, mild nausea, and skin rashes. The maximum tolerated dose was 140 mg/m2/day for 5 days. Pharmacokinetic monitoring was performed at steady state during the first course. For the 140-, 200-, and 290-mg/m2/day dose groups, the mean +/- SE peak plasma concentrations were 5.3 +/- 0.84, 9.3 +/- 1.7, and 10.2 +/- 2.3 microM, respectively, and occurred at a median of 1.5 h following the p.o. dose. The mean area under the plasma concentration-time curves were 18.1 +/- 2.3, 45.4 +/- 8.9, and 56.9 +/- 16.3 microM.h, respectively. Absolute bioavailability in two patients who were also monitored following a single i.v. dose of 140 and 200 mg/m2/day of piritrexim was 35 and 93%, respectively. Dose limiting toxicities were observed in 9 of 10 patients with 12-h trough piritrexim concentrations greater than 0.5 microM, whereas only 2 of 7 patients with trough concentrations less than 0.5 microM experienced dose limiting toxicities. A limited pharmacokinetic sampling strategy that allowed the area under the plasma concentration-time curve to be accurately predicted from the 3- and 6-h plasma drug concentration was developed. The recommended dose for future phase II trials is 140 mg/m2/day administered p.o. every 12 h for 5 consecutive days. Pharmacokinetic monitoring at 3, 6, and 12 h postdose may be useful for estimating bioavailability and for predicting which patients are at greatest risk for developing toxicity.

Current status of chemotherapy, hormonal therapy, and immunotherapy in the treatment of renal cell carcinoma.

Renal cell carcinoma is an uncommon but lethal disease. Since many patients initially present with metastatic disease and/or fail primary local therapy, therapeutic alternatives are needed. In our review of single agents none emerge as uniformly effective, although a number of chemotherapeutic agents are somewhat active, as is the hormonal agent, medroxyprogesterone. Combination chemotherapy, with and without hormonal agents and immunotherapeutics, appears to be somewhat more active, with several reports of CRs. Immunotherapeutic agents alone show promise in the limited studies reported to date. Several studies are now in progress, attempting to study new agents and combinations in this disease. Physicians are urged to participate in these studies.

PCNU: a new nitrosourea in clinical oncology.

PCNU is a new nitrosourea compound which has recently entered clinical trials. Preclinically it has been found to be effective against a variety of tumor models. Biochemically, PCNU was found to have optimal lipophilic, alkylating, and carbamoylating properties as compared to other nitrosourea agents. PCNU is able to diffuse into the CSF as demonstrated by pharmacokinetic studies. Clinical phase I studies indicate that the main toxicity is myelosuppression; nausea and vomiting were less frequently observed with PCNU than with other nitrosourea compounds. Human antitumor activity has been reported in a number of tumors, but most consistently in brain tumors. Phase II studies are now underway to confirm the antitumor activity of PCNU.

Clinical trials with antiemetic agents in cancer patients receiving chemotherapy.

Vomiting accompanied by nausea is a serious acute toxicity which occurs after chemotherapy with virtually every class of cancer chemotherapeutic agents. The inability to adequately alleviate this toxicity may lead to serious complications such as general malaise, weight loss, and electrolyte imbalance. We have reviewed 34 studies in which more than 2200 cancer patients were administered 25 different antiemetics for treatment of chemotherapy-induced vomiting. All patients received a variety of cancer chemotherapeutic agents given either as single agents or in combination. The antiemetic agents included phenothiazines, antihistamines, anticholinergics, benzoquinolizines, barbiturates, butyrophenones, procainamides, cannabinoids, steroids, and benzodiazepines. It is apparent from these studies that the use of conventional antiemetic agents for treating cancer chemotherapy-induced vomiting is of marginal value, and the use of investigational antiemetic agents show conflicting results as to efficacy. More quantitative measures for evaluating emesis need to be defined, and the implications that a particular antiemetic therapy may be efficacious for some but not all classes of cancer chemotherapeutic agents need to be evaluated.

delta 9-tetrahydrocannabinol in clinical oncology.

After anecdotal reports of marijuana's providing antiemetic activity in cancer chemotherapy patients refractory to standard agents, orally administered delta 9-tetrahydrocannabinol (THC) was formally studied by a number of investigators. In six of seven well-controlled studies, orally administered THC was a superior antiemetic agent compared with control agents. The THC toxic effects are notable but manageable. Patients rarely require hospitalization after the development of THC-induced dysphorias. However, serious toxic effects are uncommon and the most frequently noted effects are somnolence, conjunctivitis, and tachycardias. Because certain subgroups of patients are more prone to have toxicities develop, careful selection of the candidates to receive this agent is mandatory. Overall, the benefits of orally administered THC use represent a major advance in antiemetic therapy.

Animal toxicology for early clinical trials with anticancer agents.

This analysis was carried out to assess quantitative and qualitative relationships between animal and human toxicology data with anticancer drugs. Among 21 chemotherapeutic agents, one-sixth LD10 in the mouse or one-third toxic dose low (TDL) in the dog corresponded to acceptable doses in man when experimental and clinical data were obtained at identical schedules and compared on a mg/m2 basis. The mouse and the dog largely differed in their tolerance to individual drugs. One-tenth LD10 in the mouse seemed always tolerated in the dog. On the average, these species were equally relevant for establishing the initial dose in man. A similar number of dose escalation steps would have been required in phase I clinical trials if the starting dose had been based on one-tenth LD10 in the mouse or the lowest value of one-sixth LD10 in the mouse and one-third TDL in the dog. These observations indicate that the starting dose in phase I clinical trials could be safely and efficiently based on one-tenth LD10 in the mouse. Prior verification that the resulting dose is not lethal or life-threatening in the dog could add further safety to this procedure. The predictive value (PV+) in man of organ system toxicity in animals depends upon the prevalence of this toxicity in man. In our study, PV+ was high (greater than 0.85) for common toxic effects in man, i.e., gastrointestinal intolerance and myelosuppression. PV+ declined dramatically (0.05 to 0.54) with rarer toxic manifestations. There was no clear superiority of animal findings over the mere knowledge of the prevalence of these findings in man. Thus, it would appear that routine and undiscerned investigation of organ system toxicity in animals is of questionable usefulness for the clinician experienced in early clinical trials with chemotherapeutic agents.

ICRF-187 in clinical oncology.

Although the mechanism of action of ICRF-159 and 187 has not been clearly defined, it is evident from both preclinical and early clinical studies that these compounds are of interest. There are three distinct characteristics of these ICRF compounds that deserve careful clinical evaluation. First, these drugs are apparently alkylating agents with modest, predictable and noncumulative bone marrow toxicity that makes them good potential candidates for combination chemotherapy regimens. The second characteristic that should be investigated is the suggestion that combination of ICRF-187 with an anthracycline may ameliorate the cardiac toxicity of the latter. The third factor in the preclinical evaluation of the bis-diketopiperazines that may have clinical application is the evidence that suggests that these drugs have an antimetastatic effect.

2'-deoxycoformycin. A new anticancer agent.

2'-deoxycoformycin (2'-dCF) is a powerful inhibitor of adenosine deaminase (ADA), an enzyme found in high concentrations in lymphoid tissue. Although inactive in preclinical tumor models, 2'-dCF has shown clinical antitumor activity as a single agent in lymphoid malignancies. This drug has the added potential of being useful as a potentiator of other antitumor agents which are deactivated by ADA. It is also possible that the drug has potential as an immunosuppressive agent. Phase I studies are ongoing and phase II trials are planned to define the antitumor spectrum of this agent.

Selected anticancer drugs in Phase I trials in the United States (1979--1980).

Phase I trials in 1979 include some drugs representing totally new structures, new schedules of old compounds undergoing reevaluation, and second generation compounds. The rational development of analogs based on structure-activity relationships and on overcoming pharmacologic or toxicologic problems of parent compounds requires much future emphasis; two such examples (pentamethylmelamine and AZQ) are cited here. For all drugs, a plan of clinical development should ensure a more thorough initial evaluation as well as validation of concepts and systems that have prompted their introduction into the clinic. Establishment of clinical usefulness for the new structures, and particularly for three compounds herein reintroduced after a long period of oblivion, would constitute tangible proof of methodological and technological advances that have taken place in the development and clinical evaluation of anticancer drugs.

Adequacies and inadequacies in assessing murine toxicity data with antineoplastic agents.

Previous retrospective analyses have suggested a very positive correlation in toxic doses of antineoplastic agents between mice and humans. Additional toxicological information has now been accumulated and reveals a noticeable variability in the existing data base. Nevertheless, it is likely that mouse toxicological studies will become a principal determinant for estimating initial doses to be used in humans. Recognition of the factors responsible for differences in determinations of toxic dose levels in mice will enhance the proper utilization of this approach.

The hypoxic cell sensitizer programme in the United States.

The initial results of a Phase I evaluation of misonidazole in the U.S.A. are described, as well as the U.S. National Cancer Institute programme for radiosensitizer development. A total of 12 patients have been given 1--6 doses of 1--2 g/m2. Serum levels ranged from 25--87 microgram/ml at 4--6 h. One patient has developed mild peripheral neuropathy. Urinary excretion was chiefly of a demethylated metabolite as measured by HPLC assay.

Whatever happened to NSC--? An analysis of clinical results of discontinued anticancer agents.

Twenty-six investigational anticancer drugs formerly supplied by the National Cancer Institute are no longer available due to the lack of requests for their use in clinical trials. This report examines the data on these drugs to determine how well they were clinically evaluated. Generally, the studies are incomplete, and 34% of the compounds have not been studied beyond phase I trials. Clinical pharmacology data were not obtained for most of the drugs. In addition, the information available for drugs that did undergo phase II trials is grossly inadequate and does not permit a confident decision to withdraw them from investigational use. Instances of "hints" of activity and interesting drug properties are cited to stimulate further study. Finally, a list of compounds scheduled for future termination is given within the framework of this analysis to provoke thought toward obtaining more phase II data before these drugs fall into disuse.

Incidence of drug-related deaths secondary to high-dose methotrexate and citrovorum factor administration.

A review of 498 patients treated with high-dose methotrexate (MTX) with citrovorum factor rescue revealed 29 drug-related deaths. Until the important factors in those deaths are identified, the use of high-dose MTX should be limited to institutions that possess the necessary supportive facilities and the ability to measure serum levels of the drug.