The effects of the EGFr inhibitor Iressa on development of urinary bladder cancers induced by hydroxybutyl(butyl)nitrosamine (OH-BBN) in rats were examined. Iressa treatment (4.5 or 1.5 mg/kg BW/day) beginning one week after the last dose of OH-BBN decreased the occurrence of large (>200 mg) bladder cancers at termination of the study by 75 and 52%, respectively. Treatment with Iressa (10 mg/kg BW/day) beginning one week or three months (delayed initiation) after the last dose of OH-BBN also significantly increased tumor latency and decreased the incidence of palpable bladder cancers. In the delayed initiation study, microscopic cancers already existed when treatment was initiated; implying that the effects of Iressa occur late in tumor progression. Potential pharmacodynamics and/or efficacy biomarkers modulated by short-term exposure (5 day) to Iressa (10 mg/kg BW/day) were determined in palpable bladder lesions by using three different approaches: i) direct immunohistochemical examination of EGFr related proteins; which showed that phosphorylated EGFr, AKT and ERK were significantly decreased; ii) measurement of protein expression by two dimensional gel electrophoresis and tandem mass spectrometry. This showed that the Annexin A2, MAP kinase kinase and nucleolin (all proteins associated with the VEGF pathway) were decreased in treated tumors; and iii) measurement of gene expression determined in gene microarrays demonstrated that numerous pathways were markedly altered by Iressa treatment. In particular, cell cycle genes related to the anaphase protein complex (APC) pathway, including CDC 20, cyclin B1, BUB1 and both of the Aurora kinases, were significantly decreased.

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