Escalating doses of WR 6026 will be studied in successive patient cohorts. Four patients will be randomized to active drug or placebo in a 3:1 ratio at each dose level until moderate toxicity is demonstrated. If one patient at a given dose level experiences WR 6026-related moderate or worse toxicity, the sample size for all subsequent dose levels will be doubled. If two or more patients at a given dose level experience moderate or dose-limiting toxicity, an additional four patients (randomized in the same 3:1 ratio) will be entered at that level, and sample size at all subsequent dose levels will be doubled. Dose escalation will continue until three of six patients receiving active drug at a given dose level experience dose-limiting or worse toxicity, or until two of six patients at a given dose level experience life-threatening toxicity. The MTD will be defined as the dose immediately below the highest dose studied. Eight additional patients will be studied at the presumed MTD to confirm tolerance.