NLG919/cyclodextrin complexation and anti-cancer therapeutic benefit as a potential immunotherapy in combination with paclitaxel

Abstract NLG919 is an effective small molecule inhibitor of indoleamine 2, 3-dioxygenase-1 (IDO-1) in anti-tumour immunotherapy, but the poor aqueous solubility limits its application for effective intravenous dosing. In this study a cyclodextrin (CD) complexation strategy has been systematically evaluated to achieve a simple and feasible method to prepare a NLG919 injectable formulation. From a series of CDs, HP-β-CD proved to be the most conducive for NLG919 solubilization (approx 800-fold increase). Characterization studies using DSC, 1H NMR, XRPD and molecular simulation demonstrated that the NLG919/HP-β-CD loading mechanism involved an increasing pH-dependent binding affinity. Importantly cell-based studies in vitro and anti-tumour activity in vivo demonstrated that the pharmacological activity of NLG919 as an IDO-1 inhibitor was not influenced by HP-β-CD complexation. Furthermore, the combination of NLG919/HP-β-CD with paclitaxel (PTX) significantly improved anti-tumour chemotherapy compared to PTX alone. In summary, NLG919/HP-β-CD is shown to highly enhance the aqueous solubility of NLG919 with activity unaffected, greatly facilitating the intravenous use of this small molecule immunotherapeutic to improve the efficacy of PTX.