Stiffness of Single Apoptotic Bodies to Inform Brain Cancer Therapeutics

Treatment resistance is a major issue in glioblastoma multiform (GBM) brain cancer management. Predicting and monitoring responses to standard temozolomide (TMZ) treatment will have significant impacts in patient care. We aim to explore the TMZ response of GBM cell lines by correlating apoptotic body (AB) stiffness with TMZ treatment or resistance and protein content. ABs are large 1-5-µm extracellular vesicles shed during cellular apoptosis. ABs were isolated via centrifugation from GBM cell line supernatants (wild-type, 3-day TMZ treatment, TMZ resistance by chronic exposure). Protein concentration was measured by NanoDrop. Non-contact stiffness measurements of single ABs were performed by gently stretching ABs in extensional flow. Our microfluidic AB stiffness technique discriminated between GBM cell lines (5% sig. level) and TMZ-treated vs wild-type cells within a cell line (10% sig. level). Wild-type GBM cells with contrasting phenotypes showed different AB stiffnesses and protein content. AB stiffnesses were not significantly different between wild-type and TMZ-resistant cells, though protein content was moderately changed. Our data indicate that AB stiffness could be a sensitive indicator of short-term TMZ treatment with applications in personalized cancer treatment.