Disclosed herein is a method of facilitating the delivery of an agent across blood-brain barrier (BBB) of a subject. The method includes administering to the subject in sequence or concomitantly, an effective amount of a growth factor selected from the group consisting of, vascular endothelial growth factor (VEGF), insulin-like growth factor I (IGF-1), IGF-II, a portion thereof and a combination thereof； and an agent that is any of a therapeutic agent or an imaging agent. The administered amount of the growth factor is capable of transiently increasing BBB permeability of the subject and thereby allowing the agent to be delivered across BBB. Also disclosed herein is a method of treating a subject suffering from a brain tumor, a brain stroke, a neuropsychiatric disorder and/or a neurodegenerative disease.
