DAB389 EGF for the treatment of superficial urothelial cancer.

Abstract

255 Background: Intravesical BCG has remained the standard treatment for superficial bladder cancer for decades, despite frequent recurrences after its use. Toxic fusion proteins are a novel class of agents containing both a targeting and a treatment component; correspondingly, DAB389EGF contains an EGF and a diphtheria element, thereby targeting any cell expressing EGFR. Notably, the normal urothelium has little or no luminal EGFR expression in contrast to urothelial cancers, which frequently overexpress EGFR. Methods: DAB389EGF was tested in vitro to determine the effect of DAB389EGF on cell viability in culture. Tests of clonogenicity were performed by treating plated cells for 2 hours and following colony counts over 14 days. DAB389EGF was tested in an orthotopic murine model of bladder cancer with implanted HTB9 cells modified to express luciferase. DAB389EGF was administered intravesically via catheterization of the murine bladder and held in place for 2 hours with a temporary suture to close the urethra. Treatments were continued twice weekly for 2 weeks, with DT-GMCSF used as a control. Results: Treatment with DAB389EGF yielded IC50's ranging from 0.5 to 15.7 ng/ml in 8 tested bladder cancer cell lines, but the IC50 was > 500ng/ml in the EGFR- negative H520 control cell line. A single 2-hour exposure to DAB389EGF (50ng/ml) decreased colony formation in all of the bladder cancer cell lines, with complete suppression in HT1376 and T24 cells. In the animal model, luciferase activity was lost in 5 of 6 mice treated with DAB389EGF, versus 1 of 6 mice treated with control. After the 2 week treatment period, histological assessment of the treated mice was undertaken and was consistent with the luciferase findings. FISH was used to detect human or murine-originated cells in order to confirm the presence or absence of xenograft tissue histologically. Conclusions: Targeted-toxin fusion proteins represent a novel treatment approach for superficial bladder cancer. By capitalizing on the differential expression of EGFR between cancerous and normal urothelium, DAB389EGF selectively targets bladder cancer cells. Preliminary animal studies support the efficacy and tolerability of this approach with additionally animal work currently underway. No significant financial relationships to disclose.