Use of pharmacologic data and computer simulations to design an efficacy trial of intravesical mitomycin C therapy for superficial bladder cancer

Summary

Treatment of superficial bladder cancers by intravesical mitomycin C (MMC) chemotherapy gives a varying and incomplete response. Our recent pharmacokinetics and pharmacodynamics studies have shown that treatment effectiveness is limited by drug degradation in acidic urine and by drug dilution due to residual urine volume and urine production. A model was developed to predict drug exposure in tumors in the bladder wall and to correlate drug exposure with antitumor effect. The model is based on the known pharmacokinetic data in patients treated with intravesical chemotherapy, drug-penetration data in the bladder wall of patients undergoing radical cystectomy, and pharmacodynamic data on patient's bladder-tumor chemosensitivity. Computer simulations based on the model were generated. The simulations predicted that changes in treatment parameters would affect the therapeutic outcome in the following rank order: dose>residual volume>urine production>dosing volume>urine pH>dwell time. Tissue exposure could be enhanced by increased dose, complete bladder emptying, reduced fluid intake, use of the minimal dosing volume, and alkalinization of the urine to a neutral pH. Increasing the dwell time from 2 to 4 h gave an insignificant improvement and posed a compliance problem. The selected optimized regimen of a 40-mg dose, no residual volume, 0.62-ml/min urine production, a 20-ml dosing volume, and alkaline urine pH yielded a calculated 8.5-fold increase in tissue exposure over that achieved by the standard regimen, which consisted of a 20-mg dose, 32-ml residual volume, 1.5-ml/min urine production, a 20-ml dosing volume, and acidic urine pH. On the basis of previously established pharmacodynamic data, we hypothesize that the increase in tissue exposure in the optimized treatment would result in a 20% improvement over the standard therapy along with an increase in the recurrence-free rate from 56% to 76% of patients. A phase III efficacy trial comparing the optimized and standard regimens is proposed.