Abstract
Daily vs. weekly dosing with EGFR inhibitors (gefitinib and lapatinib) and an AKT inhibitor (MK2206) were compared in two rodent breast cancer models. Female Sprague-Dawley rats were administered methylnitrosourea (MNU) at 50 days of age, and gefitinib (daily/weekly dosing at 10/70 mg/kg BW) or lapatinib (daily/weekly dosing at 75/525 mg/kg BW) were administered by gavage beginning 5 days after MNU. For the prevention studies, weekly or daily dosing with gefitinib or lapatinib reduced cancer multiplicity >75%, and all treatments reduced tumor weights by >90%. For the therapeutic studies, MNU-treated rats were followed until small palpable mammary cancers developed. The rats were then treated daily or weekly as above for 6 weeks. Either daily or weekly dosing with lapatinib or gefitinib caused regression in >50% of the tumors. Immunohistochemistry biomarker studies in palpable mammary cancers following a weekly dose of gefitinib showed that 1 day (but not 7 days) after treatment, the levels of phosphorylated EGFR1 were significantly decreased. In an ER-negative (ER-) Neu-overexpressing model employing MMTV-Neu/P53KO mice, daily (100 mg/kg BW/day, 5 days each week), or weekly dosing (500 or 250 mg/kg BW) with gefitinib reduced tumor multiplicity 65, 85 and 75%, respectively. In the MNU prevention model, daily dosing (100 mg/kg BW/day) with the allosteric AKT inhibitor MK2206 was ineffective, while weekly dosing (700 mg/kg BW) reduced the final tumor weight >70%. Combining weekly MK2206 with the aromatase inhibitor vorozole (0.12 mg/kg BW/day) showed that each compound alone reduced tumor multiplicity 40-50%. The combination reduced cancer multiplicity ~70%. These studies demonstrate the efficacy of weekly dosing with various protein kinase inhibitors; raising the possibility of employing these agents in a breast cancer preventive setting.