CXCL12-loaded poly(lactic-co-glycolic) acid microspheres for the chemotactic recruitment of glioblastoma stem cells

INTRODUCTION
Glioblastoma (GBM) stem cells (GSC) have been found to specifically migrate in response to a gradient of CXCL12 in a CXCR4-dependent manner1. This enables the escape of GSCs from the tumor mass, potentially evading treatment and initiating metastases. We seek to take advantage of this mechanism for GBM therapy. By encapsulating CXCL12 in poly(lactic-co-glycolic) acid (PLGA) microspheres, we aim to create a polymeric platform capable of recruiting and directing migratory GSCs, thereby influencing GBM progression and metastasis formation.

METHODS
Human CXCL12 was initially complexated with heparin and poloxamine (Tetronic 1107)2. Resulting nanocomplexes were encapsulated in PLGA via emulsion solvent evaporation/extraction to form microspheres. Microspheres were characterized for morphology, encapsulation efficiency, and in vitro release characteristics. To verify promigratory activity, media preconditioned with blank and CXCL12-loaded microspheres were evaluated for chemotactic activity on U87MG GBM cells using a transwell migration assay.

RESULTS AND DISCUSSION
CXCL12-heparin nanocomplexes were successfully encapsulated in PLGA microspheres with diameter of 81.9±58.3 µm. The formulation had low initial burst release in vitro at <8%, and released >40% of the payload over a period of up to 90 days. Furthermore, media preconditioned with CXCL12-loaded microspheres for 1 to 8 weeks displayed promigratory activity towards GSCs. The number of migrating cells were 1.8- to 2.8-fold higher as compared to media preconditioned with blank microspheres. Treatment with AMD3100, a CXCR4 antagonist, abrogated this promigratory effect, indicating CXCR4 involvement.
CONCLUSION
The obtained results point to the potential of CXCL12-loaded microspheres for long-term recruitment of GSCs. These chemotactic microspheres, in combination with conventional and/or novel therapies, present a promising strategy for tackling GBM and its recurrence.