Re: diphtheria toxin-epidermal growth factor fusion protein DAB389EGF for the treatment of bladder cancer.

PURPOSE The novel fusion protein, DAB(389)EGF, is composed of both the catalytic and the translocation domains of diphtheria toxin that are fused to the human EGF, providing a targeting and a toxicity component. We tested DAB(389)EGF for antitumor activity in both in vitro and in vivo urinary bladder cancer models. EXPERIMENTAL DESIGN Human bladder cancer lines were treated with DAB(389)EGF and assessed for growth inhibition and clonogenic suppression. Using 6- to 8-week-old female athymic nude mice implanted orthotopically with HTB9 cells, DAB(389)EGF was administered intravesically twice weekly for 2 weeks. The response of the luciferase-expressing HTB9 cells was monitored via bioluminescence as the primary endpoint. RESULTS Treatment response with DAB(389)EGF was specific and robust, with an IC(50) ranging from 0.5 to 15 ng/mL in eight tested bladder cancer cell lines, but greater than 50 ng/mL in the EGF receptor (EGFR)-negative H520 control cell line. Simulating short-duration intravesical therapy used clinically, a 2-hour treatment exposure of DAB(389)EGF (10 ng/mL) produced clonogenic suppression in three selected bladder cancer cell lines. In vivo, luciferase activity was suppressed in five of six mice treated with DAB(389)EGF [70 μL (1 ng/μL) per mouse], as compared with only one of six mice treated with a control diphtheria toxin (DT) fusion protein. Histologic assessment of tumor clearance correlated with the bioluminescent changes observed with DAB(389)EGF treatment. Immunocompetent mice treated with intravesical DAB(389)EGF did not show any nonspecific systemic toxicity. CONCLUSIONS The intravesical delivery of targeted toxin fusion proteins is a novel treatment approach for non-muscle-invasive urinary bladder cancer. With appropriate targeting, the treatments are effective and well-tolerated in vivo.