Serum Free or Not: Two Distinct Recycling Mechanisms Mediated by Alpha v Beta 3 Integrin

Background: Among the many researches on cellular uptake and intracellular trafficking pathways of αvβ3-targeted nanomedicines, a large number of studies utilize serum-free medium to evaluate drug effects and cellular mechanisms in vitro whether the medium is serum free or not has not been paid much attention. Methods: The aim of this study was to assess the impact of serum on αvβ3-mediated endocytosis and intracellular trafficking pathways. cRGDfK conjugated with Alexa Fluor® 555 was used to recognize αvβ3 integrins specifically. Transferrin-Alexa Fluor® 488 conjugates were selected as the intracellular trafficking pathway markers by real-time confocal analysis method using confocal laser-scanning microscope. Results: The results showed that after internalization, cRGDfK showed perfect colocalization with transferrin (Tfn) when the cells were cultured in serum-free medium, but manifested obvious separation from Tfn to recycle back to the plasma membrane when the cells were cultured in complete medium. cRGDfK travels two quite different pathways under different culture conditions. Conclusion: We strongly recommended that when the intracellular mechanisms or pharmacodynamics of αvβ3-targeted nanomedicines was investigated, serum free medium or medium with serum should be taken into consideration. We hope this paper will provide helpful suggestions for studies on αvβ3- targeted drug delivery system.