rhizoxin and Neoplasms

Although fungi produce highly structurally diverse metabolites, many of which have served as excellent sources of pharmaceuticals, no fungi-derived agent has been approved as a cancer drug so far. This is despite a tremendous amount of research being aimed at the identification of fungal metabolites with promising anticancer activities. This review discusses the results of clinical testing of fungal metabolites and their synthetic derivatives, with the goal to evaluate how far we are from an approved cancer drug of fungal origin. Also, because in vivo studies in animal models are predictive of the efficacy and toxicity of a given compound in a clinical situation, literature describing animal cancer testing of compounds of fungal origin is reviewed as well. Agents showing the potential to advance to clinical trials are also identified. Finally, the technological challenges involved in the exploitation of fungal biodiversity and procurement of sufficient quantities of clinical candidates are discussed, and potential solutions that could be pursued by researchers are highlighted.

Topics: Androstadienes; Animals; Antineoplastic Agents; Aphidicolin; Biological Products; Clinical Trials as Topic; Cyclohexanes; Diketopiperazines; Disease Models, Animal; Drug Design; Drug Resistance, Neoplasm; Fatty Acids, Unsaturated; Female; Fungi; Humans; Macrolides; Male; Mice; Neoplasms; Polycyclic Sesquiterpenes; Sesquiterpenes; Trichothecenes; Wortmannin

The five examples given here illustrate new cytotoxic agents at different stages of evaluation. In all cases, considerable effort has gone into detailed pharmacokinetic studies conducted before and during the clinical phase I studies. Has this effort contributed significantly to the development of these agents? At present, it has to be said that the contribution made in the case of these particular agents has been modest. For the anthrapyrazoles, the availability of the pharmacokinetic data did not permit a pharmacokinetically guided dose escalation to be performed because of non-linear kinetics, and a similar comment can be made for rhizoxin, since the human plasma AUC values at the MTD were much lower than in the mouse. For the camptothecin analogues, a detailed knowledge of the kinetics of the closed and open forms of the various agents did not influence the way in which the studies were conducted, nor did pharmacokinetic information appreciably do so for EO9, although some comfort was gained by clinical investigators when the short half-life seen in preclinical species was also observed in humans. For suramin, therapeutic drug monitoring is clearly essential, although toxicity remains a problem. Of course, a proper understanding of the pharmacokinetics and metabolism of these agents greatly improves the interpretation of the clinical observations made and is often critical in planning the next stages of development. This is more clearly seen with agents that have unusual forms of toxicity, such as flavone acetic acid, for which the achievement of notional target concentrations is a key element in clinical trials (Kerr et al, 1987; Maughan et al, 1992). Moreover, as reviewed elsewhere (Graham and Workman, 1992; see also Graham and Kaye, this volume), there are several other instances where pharmacokinetically guided dose escalation has greatly improved the conduct of a phase I study. Good examples of this are iododoxorubicin (Gianni et al, 1990), mitotic inhibitor CI-980 (Brodfuehrer et al, 1992) and DNA intercalator CI-958 (Whitfield et al, 1992). Not surprisingly then, pharmacokinetics can help guide early clinical studies of some compounds but not others and whether they will be of value can only be determined by carrying out the pharmacokinetic measurements. The real value of the pharmacokinetic studies for the five compounds reviewed may not yet have been seen. Interpatient variations in drug handling can play a major part in determining levels of

Topics: Animals; Anthracyclines; Antibiotics, Antineoplastic; Antineoplastic Agents; Aziridines; Camptothecin; Clinical Trials, Phase I as Topic; Humans; Indolequinones; Indoles; Irinotecan; Lactones; Macrolides; Neoplasms; Suramin; Topotecan

New drug discovery continues to follow the time-honored paths of screening and novel target identification combined with analogue development and serendipity. The agents selected here reflect these various approaches. They include drugs already showing significant antitumor activity, eg, anthrapyrazoles, temozolomide, camptothecin analogues, and taxotere, and updated information is provided on their development. Other drugs just entering or currently in phase I trials include rhizoxin, which seems capable of overcoming multidrug resistance; the novel bioreductive agent EO9 [corrected]; and bryostatin, a highly potent protein kinase C agonist. Sequence specificity could well prove to be an important factor in the development of DNA-interactive agents, and information is provided on the progress with distamycin mustard and the new cyclopropylpyrroloindole analogues carzelesin and adozelesin.

Topics: Antineoplastic Agents; Bryostatins; Camptothecin; Docetaxel; Humans; Lactones; Macrolides; Neoplasms; Paclitaxel; Taxoids

The vinca alkaloids remain among the most useful classes of anticancer agents used in the clinic today. However, previous analogs of these agents have not realized either increased safety or an enhanced antitumor spectrum. Currently, three derivatives are in clinical trial: vinorelbine, vintripol, and vinxaltine. Vinorelbine has shown consistent antitumor activity in patients with breast carcinoma and is in phase III trials in the United States, Europe, and Japan. Vintripol and vinxaltine, vinca alkaloids conjugated to amino acids, are in early clinical trials in Europe. The dose-limiting toxicity of these agents is leukopenia. A similar agent with a different chemical structure, rhizoxin, is in early phase II clinical trials with initial activity noted in breast carcinoma. The ultimate role of these agents in treatment of human malignancy awaits the results of ongoing studies.

Topics: Animals; Antineoplastic Agents; Chemistry, Pharmaceutical; Clinical Trials as Topic; Drugs, Investigational; Humans; Lactones; Macrolides; Neoplasms; Vinblastine; Vinca Alkaloids; Vinorelbine

Rhizoxin (NSC 332598) is a novel macrolide antitumor antibiotic that inhibits microtubule assembly and also depolymerizes preformed microtubules. In preclinical evaluations, rhizoxin demonstrated broad antitumor activity in vitro and in vivo including both vincristine- and vindesine-resistant human lung cancers. Prolonged exposure schedules in xenograft models demonstrated optimal efficacy indicating schedule-dependent antitumor activity. The early phase I and II evaluations a five-minute bolus infusion schedule was studied, however, only modest anti-tumor activity was noted, possibly due to rapid systemic clearance. To overcome these limitations and to exploit the potential for schedule-dependent behavior of rhizoxin, the feasibility of administering rhizoxin as a 72-hour continuous intravenous (i.v.) infusion was evaluated.. Patients with advanced solid malignancies were entered into this phase I study, in which both the infusion duration and dose of rhizoxin were increased. The starting dose was 0.2 mg/m2 over 12 hours administered every 3 weeks. In each successive dose level, the dose and infusion duration were incrementally increased in a stepwise fashion. Once a 72-hour i.v. infusion duration was reached, rhizoxin dose-escalations alone continued until a maximum tolerated dose (MTD) was determined.. Nineteen patients were entered into the study. Rhizoxin was administered at doses ranging from 0.2 mg/m2 i.v. over 12 hours to 2.4 mg/m2 i.v. over 72 hours every 3 weeks. The principal dose-limiting toxicities (DLT) were severe neutropenia and mucositis, and the incidence of DLT was unacceptably high at rhizoxin doses above 1.2 mg/m2, which was determined to be the MTD and dose recommended for phase II studies. At these dose levels, rhizoxin could not be detected in the plasma by a previously validated and sensitive high-performance liquid chromatography assay with a lower limit of detection of 1 ng/ml. No antitumor responses were observed.. Rhizoxin can be safely administered using a 72-hour i.v. infusion schedule. The toxicity profile is similar to that observed previously using brief infusion schedules. Using this protracted i.v. infusion schedule the maximum tolerated dose is 1.2 mg/m2/72 hours.

Topics: Adult; Aged; Antibiotics, Antineoplastic; Humans; In Vitro Techniques; Lactones; Macrolides; Middle Aged; Neoplasms; Neutropenia

New drug discovery continues to follow the time-honored paths of screening and novel target identification combined with analogue development and serendipity. The agents selected here reflect these various approaches. They include drugs already showing significant antitumor activity, eg, anthrapyrazoles, temozolomide, camptothecin analogues, and taxotere, and updated information is provided on their development. Other drugs just entering or currently in phase I trials include rhizoxin, which seems capable of overcoming multidrug resistance; the novel bioreductive agent EO9 [corrected]; and bryostatin, a highly potent protein kinase C agonist. Sequence specificity could well prove to be an important factor in the development of DNA-interactive agents, and information is provided on the progress with distamycin mustard and the new cyclopropylpyrroloindole analogues carzelesin and adozelesin.

Topics: Antineoplastic Agents; Bryostatins; Camptothecin; Docetaxel; Humans; Lactones; Macrolides; Neoplasms; Paclitaxel; Taxoids

Rhizoxin is a tubulin-binding cytotoxic compound, isolated from the fungus Rhizopus chinensis, with significant antineoplastic activity in several murine and human tumor models. In this Phase I study, the drug was administered by i.v. bolus injection at 3-wk intervals. Twenty-four patients with refractory solid tumors were treated; 60 courses of rhizoxin were given, at doses ranging from 0.8 to 2.6 mg/m2. Grade 3 mucositis, Grade 4 leukopenia, and Grade 3 diarrhea were dose limiting but reversible at 2.6 mg/m2, the maximum tolerated dose for both previously untreated and heavily pretreated patients. Alopecia and moderate discomfort at the injection site occurred at all doses. Other sequelae, including peripheral neuropathy, phlebitis, and nausea and vomiting, were sporadic and mild. Two heavily pretreated patients with recurrent breast cancer had minor responses to rhizoxin, one at 1.6 mg/m2 and the other at 2.6 mg/m2. Plasma concentrations of rhizoxin were measured by high-performance liquid chromatography. The drug was not detectable (less than 5 ng/ml) at doses of 0.8 mg/m2 and 1.6 mg/m2 and was not measurable 10 min after injection at 2.0 mg/m2. At 2.6 mg/m2, there was considerable intersubject variation in the plasma concentration-time profiles; the area under the curve ranged from 0.29 to 0.96 microgram/ml.min. Rhizoxin has shown some clinical activity in this Phase I study, and a dose of 2.0 mg/m2 is recommended for Phase II studies using this schedule.

Topics: Adult; Aged; Animals; Antibiotics, Antineoplastic; Body Weight; Diarrhea; Drug Administration Schedule; Drug Evaluation; Female; Hindlimb; Humans; Injections, Intraperitoneal; Lactones; Leukopenia; Macrolides; Male; Middle Aged; Neoplasms; Paralysis