Subcellular distribution and mechanism of action of AL906, a novel and potent EGFR inhibitor rationally designed to be green fluorescent.

To enhance the potency of EGFR inhibitors, we developed a novel strategy that seeks to conjugate EGFR to a bioactive moiety leading to a molecule termed "combi-molecule". In order to mimic the penetration of this type of molecules, based upon previously reported structure activity relationship studies, we designed a new molecule containing a quinazoline moiety tethered to a p-nitrobenzoxadiazole (NBD) moiety [molecular weight (MW) 700]. Despite its size, AL906 growth inhibitory activity was superior to that of the clinical drug gefitinib. Furthermore, AL906 retained significant EGFR inhibitory activity and good cellular penetration with abundant distribution in the perinuclear region of the cells. In an isogenic NIH3T3 transfected cell panel, it selectively inhibited the growth  of the NIH3T3-EGFR and HER2 transfectants. Confocal microscopy analysis revealed that it was capable of penetrating multilayer aggregates although to a lesser extent than FD105, a small inhibitor of EGFR inhibitor of the same class (MW 300). Its ability to inhibit EGFR auto-phosphorylation in monolayer culture was stronger than in the aggregates. The results suggest that our strategy did not negatively affect EGFR inhibitory potency, EGFR selectivity and growth inhibition. However, its molecular size may account for its decreased aggregate penetration when compared with a smaller EGFR inhibitor of the quinazoline class.