5844

The vascularization and growth of primary and metastatic lung cancer is influenced by tumor microenvironment. We have previously shown that ZD6474, a selective inhibitor of VEGFR and EGFR tyrosine kinase activity, was effective alone and with paclitaxel (Pac) chemotherapy in an orthotopic model of human lung cancer. The purpose of the current study was to evaluate and characterize therapy against VEGFR and/or EGFR, alone and in combination with Pac, in a human lung cancer bone metastasis model that mimics clinical patterns. To develop the model, human lung adenocarcinoma (PC14) cells were injected into the tibias of nude mice. Digitized radiographic imaging (Faxitron) of the legs was performed weekly. When lytic bone lesions were observed, mice (7-9 per group) were randomized to one of six treatment regimens: ZD6474 (25 mg/kg daily p.o.); gefitinib (50 mg/kg daily p.o.); Pac (200 μg weekly i.p.); concomitant ZD6474 + Pac; concomitant gefitinib + Pac; or vehicle (Table). Therapy was continued until signs of the onset of morbidity were observed in controls. Analysis of tumor (TUNEL) and endothelial (TUNEL/CD31) apoptosis demonstrates that ZD6474 ± Pac induced comparable tumor cell apoptosis, while endothelial cell apoptosis was maximal in ZD6474 (12.6 ± 3.7%) vs ZD6474 + Pac treated tumors (2.9 ± 1.4%, P<0.001). Tumor cells expressed EGFR, but not activated EGFR. Both the tumor and endothelial cells expressed VEGFR-2, and ZD6474 significantly inhibited VEGFR-2 activation (P<0.01). In a repeat experiment, different sequences of ZD6474 and Pac administration (concurrent or ZD6474 before or after Pac for 2 weeks) were compared in the bone metastasis model. The antagonism of the antitumor effect of ZD6474 by Pac was independent of their sequence of administration. In summary, we have developed a murine model to study the biology and therapy of lung cancer bone metastasis, and show that ZD6474 can effectively treat lung cancer bone metastases by targeting both the tumor and its associated vasculature. Surprisingly, our data in this tumor model show that Pac can antagonize these effects of ZD6474 in the bone microenvironment, and that this antagonism is independent of their sequence of administration.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]