Nanoparticle-Encapsulated NAMPT Inhibitors Administered via Convection Enhanced Delivery as a Novel Glioma Radiosensitization Strategy

Abstract

Mutations of protein phosphatase magnesium-dependent 1D (PPM1D, also known as WIP1) are found in a wide range of brain tumors, including gliomas such as diffuse midline glioma (DMG). PPM1D is a known oncogene, and the phosphatase is involved in pathways crucial for genomic integrity. Recently, we discovered that activating PPM1D mutations induce a silencing of nicotinic acid phosphoribosyltransferase (NAPRT), a key protein involved in nicotinamide adenine dinucleotide (NAD) biosynthesis, leading to decreased NAD levels. This can be exploited with inhibitors of the nicotinamide phosphoribosyltransferase (NAMPT) enzyme (NAMPTi). NAMPTi’s have been tested clinically and have shown promise as chemo- and radio-sensitizers. However, their success has been curbed by factors such as significant dose-limiting toxicities (DLTs) and poor CNS penetration. Administering NAMPTi’s via convection-enhanced delivery (CED) has the potential to obviate these impediments. However, infused drugs rarely persist in the brain beyond 12h. One way to circumvent this limitation is to encapsulate drugs in nanoparticles (NP). NPs have multiple advantages, including sustained release, reduced clearance, and improved stability. This work aims to develop and test NP-encapsulated NAMPTi’s with the intent of treating PPM1D-mutated DMGs in combination with radiation therapy (RT). NP formulations were created with single emulsion and nanoprecipitation techniques using 2 NAMPTi’s and 4 polymers. Formulations were characterized, and stability was tested in artificial cerebrospinal fluid (aCSF). Uptake of NPs was assessed with fluorescence microscopy. Efficacy was evaluated using isogenic cell lines (+/- PPM1D mutation) assayed for NAD levels. Safety, stability, and retention was evaluated in vivo with intracranial CED utilizing a rat model and LC-MS. The NAMPTi GMX-1778 was efficiently encapsulated into NPs (GMX-NP) with multiple polymers (e.g. PLA-PEG, PLA-HPG, and PLGA) with yields of 68-82%. GMX encapsulation ranged from 2-10 ug GMX/mg NP. When compared to single emulsion, the nanoprecipitation method produced significantly smaller NPs with higher drug concentration (up to 50 ug GMX/mg NP). NPs demonstrated near 100% cellular uptake within 24h. GMX-NP is stable for at least 21d in aCSF at 37°C. When exposed to GMX-NP for 24h, NAD was potently depleted in a dose-dependent manner (25, 50, 75 nM GMX). Compared to WT, PPM1D mutants demonstrated 7x higher sensitivity. Finally, GMX-NP was safely and effectively infused intracranially into rats with no adverse events. LC-MS analysis of brain samples demonstrated excellent retention of GMX-NP 24h after CED. This work successfully developed a NP-encapsulated NAMPTi with in vitro efficacy and in vivo safety and stability. Additional studies will continue to refine and characterize these formulations as well as assess in vivo efficacy. These data lay the groundwork for future combinations of NAMPTi NPs with RT.