Optimizing docetaxel bladder penetration following gemcitabine pretreatment: An analysis of concentration and timing protocols.

Abstract

785 Background: Shortage and suboptimal efficacy of BCG has spurred the development of novel treatments for patients with intermediate- and high-risk non-muscle-invasive bladder cancer (NMIBC). Sequential intravesical gemcitabine and docetaxel (Gem/Doce) has emerged as a promising and widely utilized treatment for NMIBC. Furthermore, there are numerous other sequential combination approaches of gemcitabine with other agents in development. There is a need to better understand tissue penetration profiles of sequential intravesical therapies. Herein, we aimed to understand the impact of gemcitabine concentration and duration on subsequent tissue penetration of docetaxel. Methods: IRB approval was obtained at the University of Iowa. Rabbit bladders were obtained and samples were cut into 38 mm diameter sections. Samples were incubated at 37°C and pre-treated with 20 mg/mL gemcitabine (MedChem Express) in artificial urine (Aldon Corporation) at varied incubation times (1x concentration at 0, 1, or 2 hours) and concentrations (0x, 0.5x, 0.75x, and 1x for 2 hours). Next, 0.75 mg/mL docetaxel (MedChem Express) was applied to the tissue for 2 hours. Tissues were flash frozen in liquid nitrogen and stored at -80°C. Each sample was cryosectioned into 50 μm slices, and 200 μg of tissue was weighed and extracted with five times its mass of ethyl acetate (Macron), and docetaxel concentration was determined. Results: There was a statistically significant increase in docetaxel penetration with gemcitabine pre-treatment. With no gemcitabine pre-treatment, the docetaxel concentration decreased to < 0.1 mg/mL after 2 hours. Gemcitabine concentration did not have a major impact on docetaxel penetration. There was similar docetaxel penetration with 1-3 hour gemcitabine pre-treatment. The tissue that was treated with gemcitabine for 4 hours maintained a 0.2 mg/mL concentration of docetaxel after two hours. Conclusions: Our preclinical study has implications for Gem/Doce optimization as well as for other sequential combination therapies. We found that gemcitabine pre-treatment was necessary for sufficient docetaxel penetration. One and two hour gemcitabine incubation times had similar effects. Additional studies are needed to continue to optimize sequential therapy combinations in NMIBC.