(T1430-03-13) A Novel Therapeutic Platform for Improved Glioblastoma Treatment

Purpose: Patients diagnosed with glioblastoma multiforme (GBM), a highly aggressive primary brain tumor, face an expected survival of only 15 months post diagnosis [1]. This dismal fate includes those that receive the standard of care treatment:  tumor resection surgery, chemotherapy, and radiation. Approximately 90% of GBM tumors are recurrent and lack efficacious treatment due to the various challenges faced in drug delivery [2]. The blood brain barrier (BBB) restricts the movement of therapeutics out of the systemic circulation and to the site of the tumor. Additionally, the tumors themselves display a high degree of genetic heterogeneity with mutations that allow them to grow rapidly and become therapeutic resistant. Acetelated Dextran (Ace-DEX), a biocompatible and acid sensitive polymer, can be electrospun to encapsulate therapeutics with tunable parameters for optimal drug release kinetics [3]. By using this platform for combinational drug delivery, multiple drugs with different mechanisms of action can act synergistically upon localized release and bypass the BBB. Herein, we describe a novel therapeutic platform for GBM treatment, which addresses these critical drug delivery challenges, through the interstitial delivery of synergistic drug combinations.

Methods: To assess for the potential of synergy between drugs, we curated a GBM drug library which includes 16 chemotherapies and other small molecules that target prominent mutations found in GBM [4]. We first screened these drugs in vitro and in combination against 10 GBM cell lines which covers the phenotypic and genotypic breadth of GBM seen clinically. After a 48-hr treatment at 37°C, fluorescence is used to assess cell viability. Zero Interaction Potency (ZIP) analysis is used to determine the degree of synergy over the increasing dose matrix of the 2-drug combination. A positive ZIP score indicates that the drug combination is synergistic at a given dose ratio. Ace-DEX was synthesized using previously reported methods and electrospun into nanofibrous scaffolds for drug encapsulation. The scaffolds were characterized via scanning electron microscopy and used to perform drug release studies in vitro (pH 7.4 at 37°C). High-performance liquid chromatography was used to determine drug retention over time in the Ace-DEX scaffold. For in vivo translation, fluorescent and bioluminescent GBM cells were implanted in the right frontal lobe of mice and monitored for 8 days. The tumor was then surgically resected, and the drug loaded scaffolds were placed in the tumor cavity. Non-invasive bioluminescent imaging was used to monitor and assess the presence of recurrent tumors.

Results: Of all possible drug combinations screened, most of the cell lines displayed a positive cumulative synergy score with the combination treatment of Paclitaxel (PTX), a microtubule inhibitor, and Everolimus (EVR), an mTOR inhibitor. For the U87-MG GBM cell line, a relevant model used for in vivo studies, the PTX and EVR combination resulted in a synergy score of 3.66 (p < 0.01). PTX and EVR were encapsulated in separate Ace-DEX scaffolds using electrospinning techniques. To ensure that the ratio of drugs was held constant upon release from the scaffolds, the release kinetics were matched by tuning the parameters of Ace-DEX. Medium degrading Ace-DEX was used for PTX (Ace-PTX) and slow degrading Ace-DEX for EVR (Ace-EVR) for 3% drug release per day per scaffold (Figure 1). After tumor development in vivo, resection, and implantation of Ace-DEX scaffolds, the survival of mice treated with Ace-PTX + Ace-EVR was significantly improved when compared to individual scaffolds and the vehicle blank Ace-DEX scaffold control (Figure 2).

Conclusion: This treatment method has the potential to mitigate recurrence of GBM by addressing the heterogeneity native to the tumors while bypassing the BBB through localized delivery. For a proof of concept, we have shown that PTX and EVR Ace-DEX scaffolds act synergistically against a relevant GBM cell line, U87-MG, in vitro and in vivo. These results outline the significance of our approach to improve GBM treatment.

References: [1] Shergalis, A., et al., Pharmacological Reviews 2018. [2] Birzu, C., et al., Cancers 2020. [3] Kauffman, K.J., et al., ACS Appl Mater Interfaces 2012. [4] Mclendon, R., et al., Nature 2008. [5] Graham-Gurysh, E.G., et al., J Control Release 2020.

Acknowledgments: We would like to thank all members of The Ainslie Lab, UNC BRIC, UNC CHANL, and UNC ESOP NMR Core. Funded by the National Institute of Cancer: R01 CA257009.

Figure 1: Drug Release Kinetics from Ace-DEX scaffolds (A) Paclitaxel encapsulated scaffold in medium degrading Ace-DEX (B) Everolimus encapsulated scaffold in slow degrading Ace-DEX.



Figure 2: Kaplan Meier Progression Free Survival Curve Statistical significance by Log-Rank test ** p < 0.001 with respect to Ace-Blank, ## p < 0.001 with respect to Ace-EVR, ‡ p < 0.05 with respect to Ace-PTX. Reproduced with permission from author [5].