The present invention relates to the use of an antisecretory factor (AF) protein, peptide, derivative, homologue, and/or fragment thereof, having equivalent functional activity, and/or a pharmaceutically active salt thereof, for optimizing delivery and cellular uptake of a pharmaceutical substance and/or formulation, or a gene delivery. Typically, said pharmaceutical substance and/or formulation comprises an anticancer drug, radiation therapy, an antibiotic substance, an antiviral substance or a drug targeting posttraumatic injury, neurodegeneration, a parasite, or an inflammatory condition.