Login to Access Video or Poster Abstract: MP65-07
Sources of Funding: None

Introduction

HDACs constitute a family of enzymes that deacetylate histones and cellular proteins resulting in regulation of transcription and cellular processes. HDAC inhibition has been shown to induce genes coding for MHC class I and class II molecules and immunologic activation molecules. Tissue microarray analysis of bladder cancer cell lines has demonstrated high HDAC expression in 40-60% of urothelial tumors. _x000D_ Our objective was to investigate the use of HDAC inhibitors on bladder tumors to stimulate immune mediated tumor cell destruction.

Methods

In vitro human bladder cancer cell lines were cultured with exposure to various HDAC inhibitors and HLA matched human T cells. The murine urothelial cell line, MB49 was also cultured with HDAC inhibitors and activated murine splenocytes. MTT assay was performed to measure cell viability. _x000D_ We transduced the murine tumor line to carry Firefly luciferase to allow for bioluminescence monitoring post implantation and then implanted the cells intra-vesically using a 24Fr angiocatheter delivery method. Following implantation bioluminescence signals were monitored using IVIS Lumina imaging system. _x000D_ Our treatment arm consisted of a single intra-vesical instillation of CI-994 for 60 minutes on post-implantation Day 6 with intraperitoneal injection of PD-1 blockade, appropriate controls were also performed. Total flux was monitored by IVIS in the treatment and control arms. _x000D_

Results

In Vitro analysis showed a statistically significant decrease in viable tumor cells when treated with a short course of CI-994 and then exposed to activated human T cells (p 0.0025). There was an even greater response when the T cells had received PD-1 blockade (p 0.0003). MTT assay analysis of MB49 yielded similar positive results with CI-994 treatment and T cell exposure. _x000D_ In vivo mice who received intravesical CI-994 in combination with intraperitoneal PD-1 blockade showed a more immediate and durable response than mice in the control arms. The average bioluminescence signal for our combination treatment arm indicates minimal to no retained tumor burden._x000D_

Conclusions

HDACs are widely expressed in urothelial cancer and inhibition of the selective HDAC inhibitor CI-994 has shown promising results in vitro and in an in vivo orthotopic model at reducing tumor burden.

Funding

None