Abstract 1661: Development of lipid-based nanosuspension formulation of first-in-class PLK2 inhibitor GBO-006 to treat triple-negative breast cancer
Authors: Tirunagaru Vijaya G. , Roy Chowdhury Arnab , Duraiswamy Jeyaraj Athisayamani , Maddi Srinivasa Rao , Mitra Sayan , Deb Chandra , Adluri Ram Sudheer , Gupta Jang B. 
Published: August 2015

Abstract
Introduction: The highly selective, ATP competitive PLK2 inhibitor GBO-006 was previously shown by us to arrest growth of triple negative breast cancer (TNBC) at 30mg/kg dose (mpk) in MDAMB-231 xenograft model. However, the maximum formulation strength was 20mg/ml and was not adequate for toxicology studies. GBO-006 was found to be crystalline and poorly soluble (&lt;1 mg/mL) in organic solvents/co-solvents and non-aqueous media including lipids & oils, even in the presence of complexing agents. Degradation at very high temperatures (∼346 °C) limited the use of amorphous based strategies. Efforts to dissolve GBO-006 using one solvation strategy (co-solvency, complexation, micellar solubilization) were unsuccessful. The study described herein focused on particle engineering efforts to develop a 50mg/ml nanosuspension formulation of GBO-006 stabilized by ionic, non-ionic, and polymeric and lipid stabilizers alone or in combination.
Experimental procedures: Nanosizing of GBO-006 by ‘bottom-up’ and ‘combination of bottom-up and top-down’ technologies did not yield particles in the desirable nanosize range. Nanosizing GBO-006 to less than 400 nm (d0.9) particle sizes was feasible by top-down technology using bead milling and a high shear microfluidics processor. During initial trials, lower strength formulations (5 to 25 mg/mL) were nanosized and stabilized using bead milling with non-ionic surfactant(s), Tween 80 & poloxamer 188, in addition to polymers such as PVP K12. Microfluidization was not pursued further due to clogging of the interaction chamber at higher concentrations (50 mg/mL).
Results: A crystalline, lipid nanoparticle of GBO-006 was feasible by bead milling and further assessed for pharmacokinetic evaluation and efficacy studies. Intraperitoneal dose escalation studies in mice showed a dose-dependent linear increase in plasma exposure of GBO-006. Fifty percent reduction in MDAMB-231 xenograft tumor volume was observed with 1.5 mpk of GBO-006 after qd dosing. Significant accumulation of GBO-006 was observed in spleen and liver upon chronic dosing (21 days). We hypothesized that accumulation was likely due to reticulo-endothelial system (RES) mediated uptake, which was further proven by in vitro experiments with differentiated macrophages.
Conclusion: We have successfully developed a nanosuspension formulation for GBO-006. Notably, this nanosuspension showed similar efficacy to previous formulations at much lower doses (1.5 mpk), however particle size of 260 nm accentuated RES uptake. Ongoing studies are focused on decreasing particle size below 150 nm and incorporating a negative zeta potential to bypass RES uptake and minimize tissue distribution.
Citation Format: Vijaya G. Tirunagaru, Arnab Roy Chowdhury, Jeyaraj Athisayamani Duraiswamy, Srinivasa Rao Maddi, Sayan Mitra, Chandra Deb, Ram Sudheer Adluri, Jang B. Gupta. Development of lipid-based nanosuspension formulation of first-in-class PLK2 inhibitor GBO-006 to treat triple-negative breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1661. doi:10.1158/1538-7445.AM2015-1661