Oral Fluids-Derived Exosomes from Oral Cancer Patients as delivering Vehicles of Natural Anti-Cancer Substances to the Tumor Microenvironment

Oral cancer (OC) has a low 5-year survival rate of ~50% despite advances in molecular biology and improvements in treatment. The tumor microenvironment (TME) contributes to the poor prognosis in OC. Curcumin, a natural product with proved anti-tumor potential, showed encouraging results in OC preclinical studies; however poor bioavailability limits its clinical efficacy. Exosomes, especially tumor-derived, can be absorbed by neoplastic or TME–related cells, and therefore can be utilized as a new strategy for curcumin delivery. Aim: to load curcumin into oral fluids (OF)-derived exosomes and compare between healthy individuals (HI) and OC patients. Methods: 1ml aliquots of pooled OF from OC patients (n=36) or HI (n=25) were incubated with 40/80µM curcumin. Exosomal pellets were isolated by ExoQuick-TC™ or ultracentrifugation (120,000g, 90min X2). Supernatants were separated from the pellets, which were submitted for sonication. The concentrations of curcumin from the supernatants and that released from the exosomal pellets were spectrophotometrically assessed (420nm). Pooled OF from OC was assessed by nanoparticle tracking analysis (NTA) before/after incubation with 50µM curcumin. Results: Curcumin-loaded pellets could not be obtained from microvesicles/exosome-free supernatants. The hydrophobic ExoQuick-TC™ competed with the exosomes for binding curcumin, therefore results were inconsistent. OC-pellets were constantly larger than HI-pellets. OC-pellets bound more curcumin than HI-pellets at 80µM (p<0.05). Simultaneously, supernatants of OC-pellets contained less curcumin than HI-pellets at 80µM (p<0.05). NTA showed larger nanoparticles in OC-OF incubated with curcumin than without (p<0.05). Conclusions: Exosomes bound curcumin from a hydrophilic medium such as OF. OC-OF-derived exosomes were able to load more curcumin than HI-OF-derived exosomes, thus creating a novel platform to combat both OC and TME cells.