AR-67 (formerly DB-67) represents a rationally engineered drug that possesses improved stability, toxicity, and efficacy compared to current Food and Drug Administration (FDA)-approved camptothecins, based on the extensive research of prior studies. Therefore, the investigators hypothesize that AR-67 (formerly DB-67) will be well-tolerated and efficacious in phase I clinical trials. This initial phase I trial will establish the maximum tolerated dose in humans, establish the toxicity profile, and define the appropriate dose of AR-67 (formerly DB-67) for future phase II and III clinical trials.