Introduction:

Platinum-based chemotherapies are an important component of standard-of-care regimens for high grade and recurrent low grade transitional cell carcinoma (TCC) of the bladder in both the neoadjuvant and adjuvant settings.  However, these nephrotoxic drugs are often dose-limiting in such regimens.  Cisplatin and carboplatin are most commonly used.  However, dicycloplatin (DCP) has better solubility and stability, giving it comparable efficacy and better tolerability, as well as the possibility of providing an oral platinum option.  Case reports suggest use of DCP as an effective primary treatment for high-grade, non-muscle invasive bladder cancer.  We exposed grade II-IV TCC cell lines to DCP in vitro to assess efficacy in preventing cell proliferation in comparison to other platinum analogs.

Methods:

Our high grade (IV) in vitro bladder TCC cell line (TCCSUP) was exposed to varying concentrations of cisplatin (0-600 ug/mL), carboplatin (0-600 ug/mL), oxaliplatin (0-4.0 ug/mL), and DCP (0-350 ug/mL).  Further, our grade II-IV (II-HTB9, III-T24) cell lines were exposed to varying concentrations of DCP (0-350 ug/mL) to assess growth inhibition at varying times and concentration. We also perfomed a washout assay in which cells were exposed to DCP for two hours then incubated in preferred medium to simulate intravesical use. Percent growth inhibition was determined following exposures of 24, 48, and 72 hours using exposure to MTT, a tetrazolium dye, at the given time intervals to assess mitochondrial dehydrogenase activity with an absorbance assay.  This allows for accurate and comparable assessment of cell viability. Cells grown in their preferred medium with normal saline were used as controls. 

Results:

At the tested concentrations, DCP, cisplatin, and carboplatin were effective in achieving >90% cell-kill rates at 72 hours exposure.  Concentrations of 325 ug/mL DCP, 50 ug/mL cisplatin, and 600 ug/mL carboplatin are sufficient for >90% cell-kill, with cisplatin boasting the highest kill at the lowest concentration and time intervals.  Dose- and time-dependent cell-kill were demonstrated at varying concentrations of DCP in grade II-IV cell lines, including the washout (intravesical simulating) assay. In the washout assay, approximately 30%, 20%, and 40% cell kill was observed in grade II, III, and IV cells at 72 hours, respoectively. (as demonstrated in the below figures).

Conclusion:

Our results show in vitro cell-kill efficacy of DCP in a time and concentration-dependent manner in grade II-IV TCC cell lines, showing promise for its IV, PO, and intravesical use for TCC of the bladder in the primary and adjuvant/neoadjuvant setting. Studies in progress seek to assess bioavailability, efficacy, and safety in vivo in a mouse model prior to moving to early-phase clinical trials. 

Funding: N/A