Pharmacodynamic analysis of receptor tyrosine kinase (RTK) activity reveals differential target inhibition in skin and tumor in a phase I study of advanced colorectal cancer patients treated with AEE788

3601 Background: AEE788 (AEE) is an oral inhibitor against tyrosine kinases and has an IC50 of < 100 nM against EGFR and VEGFR-2. This PD study investigated the effects of AEE on its targets in vitro and in biopsies from advanced colorectal cancer patients. Methods: HUVECs and HT-29 cells were incubated with AEE for 4h at 0–1 mM. 22 pts were treated at doses of 25 (n=4), 50 (n=3), 100 (n=4), 250 (n=1), 300 (n=4), and 400 mg (n=6) mg/day in 28-day cycles. No major clinical respones were observed. Wound-induced paired skin biopsies were performed on days -8, -1, 22, 29. Tumor biopsies were obtained before and 28 days post-treatment. Evaluable paired skin and tumor samples were available in 18 and 14 patients respectively. The effects of AEE on pKDR, pEGFR, AKT, Ki67, and apoptosis were analyzed by laser scanning cytometry (LSC). Wilcoxon signed rank test and Spearman correlation were used to compare biomarker changes post-treatment and correlation with dose, respectively. Results: In vitro, AEE treatment resulted in a dose-dependent inhibition of pKDR and pEGFR with inhibition of 65% and 63% at 1 mM in HUVECs and HT-29 cells, respectively. pKDR levels increased in response to AEE treatment in HT-29 cells. In skin, AEE increased basal levels of pKDR (p=0.03) post-treatment. AEE increased AKT (p=0.02) and EGFR (p=0.01) in a dose-dependent manner. In wound-induced skin pairs, AEE significantly inhibited endothelial cell pKDR/KDR (ratio) in a dose-dependent manner (p=0.02). In tumors, AEE increased pKDR expression (p=0.05) and was dose-dependent (p=0.06). Tumor endothelial cell pKDR levels decreased (avg. 47%) after AEE treatment (p=0.08). Furthermore, levels of Ki67 increased (p=0.08) and no significant effects were observed on pEGFR or apoptosis at any dose level in post-treatment samples. Conclusions: LSC quantitative analysis confirmed the target inhibition of AEE in vitro and in wound-induced skin pairs. The lack of significant target inhibition in tumors is consistent with the lack of clinical activity of AEE in this cohort of patients. Quantifying pKDR/KDR in wound-induced skin pairs may serve as a surrogate for assessing the activity of an angiogenesis inhibitor such as AEE. [Table: see text]