Login to Access Video or Poster Abstract: MP65-13
Sources of Funding: NIH intramural support

Introduction

Bladder cancer (CaB) is the 4th most common cancer among men in the US. It is among the most expensive malignancies to treat from diagnosis to death. There is an urgent need for the development of new treatment therapies. We utilized a quantitative high throughput screening (qHTS) technique to identify new therapies in two primary bladder cancer cell lines (T24 and UMUC3) and their metastatic lines (T24T, SLT3 and FL3 of T24 and LUL-2 for UMUC3) and further characterized one novel inhibitor: flavopiridol.

Methods

We screened 7 bladder cancer cell lines (including RT4, T24, and UMUC3) against 1,912 oncology drugs using a 48-hour cell proliferation assay with an ATP?based readout (CellTiterGlo) to determine activity and potency of compounds in a dose response manner. One of the candidate drugs inhibitory in all cell lines tested was flavopiridol, a pan-CDK inhibitor. We further characterized the mechanism of action and in vivo effects of flavopiridol using various cell based assays and mouse xenograft studies.

Results

The initial screen identified 95 compounds active in 7 cell lines. The top 50 compounds were further analyzed for molecular size of >200 g/mol and TPSA<90. This identified mitomycin C and 8 novel compounds. One of these compounds was flavopiridol which had an IC50 of 100-300nM in additional cell lines. Flavopiridol induces G2/M arrest; however, very little apoptosis was seen suggesting cytostatic rather than cytotoxic mechanism of action. Flavopiridol demonstrated dose dependent inhibition of migration, invasion and colony formation in CaB cell lines tested. Xenograft studies in rapidly growing UMUC-3 cells showed slowing of tumor growth but not complete reduction indicating cytostatic mechanism of flavopiridol. However, in slow growing cells, 5637, 5/8 treated mice showed complete tumor reduction.

Conclusions

qHTS can identify novel compounds. Flavopiridol seems to be a very effective inhibitor both in vitro and in vivo. Physical properties of Flavopiridol are most suited for intravesical use which may lead to it being an effective inhibitor of CaB in the bladder at higher doses without any/few systemic toxicities. Studies are underway to elucidate the use of flavopiridol as a single intravesical agent. Finally, combination therapy with intravesical chemotherapeutics shown to be effective in bladder cancer (e.g. paclitaxel, gemcitabine) can also be considered if intravesical therapy of flavopiridol is feasible.

Funding

NIH intramural support