Abstract P059: Exploiting mutant PPM1D-induced metabolic defects with nanoparticle-encapsulated NAMPT inhibitors
Authors: Murray Matthew A. , Wang Yazhe , Sundaram Ranjini , Beckta Jason , Saltzman Mark , Bindra Ranjit 
Published: December 2021

Abstract
Diffuse Intrinsic Pontine Glioma (DIPG) is a leading cause of death in pediatric cancer, with an abysmal &lt;1% 5-year survival rate due to lack of effective treatment options. A significant effort is needed to understand the genetic landscape of this disease to develop novel therapeutic strategies and modalities. Recently, the Bindra laboratory found that a truncation mutation in the gene PPM1D, found in ~30% of DIPG cases, causes global epigenetic alterations that lead to therapeutic vulnerabilities. They found that mutant PPM1D activity results in loss of the NAD+ biogenesis protein NAPRT that can be therapeutically targeted by inhibitors of another protein in the NAD+ biogenesis pathway NAMPT (NAMPTi), providing a viable therapeutic strategy for these cancers. Some NAMPTis have been FDA-approved for clinical usage, but present with systemic and retinal toxicity. Moreover, while there are few NAMPTis that can pass the blood brain barrier through systemic delivery, studies show diminished concentrations at the target site. Together, current studies show that the use of NAMPTis for precision targeting of CNS cancers such as DIPG with mutant PPM1D status is a promising therapeutic strategy, but impractical given the limitations of these drugs. However, recent developments in drug delivery systems offer a chance to overcome these issues. Tools such as nanoparticle (NP) drug delivery and unique injection set-ups such as convection-enhanced delivery (CED) allow for drugs such as NAMPTis to be reconsidered for clinical usage. To circumvent the challenges presented by these drugs, we have developed and characterized nanoparticles that encapsulate NAMPTis (NAMPTi-NP) and use CED for sustained intratumoral delivery. Thus far, we have fabricated and optimized PLA-PEG copolymeric nanoparticles capable of encapsulating the NAMPTi, GMX-1778. We characterized these nanoparticles based on (1) hydrodynamic diameter, (2) zeta potential, and (3) stability within an artificial cerebrospinal fluid solution. We have performed both in vitro and in vivo assays to determine the functionality of the NAMPTi-NPs through (1) cellular uptake studies via immunofluorescence, (2) functional analysis via NAD+ quantification, (3) short- and long-term cell viability assays to determine sensitivity to the NAMPTi-NP, and (4) in vivo biodistribution studies to assess sustained retention of NAMPTi-NP with CED intracranial injections. We find that NAMPTi-NPs have immediate and sustained cellular uptake, loss of NAD+ post-treatment indicating effective targeting, and enhanced sensitivity in long-term viability studies in mutant PPM1D models. Lastly, these NAMPTi-NP display prolonged retention in brain tissue compared to free drug injection over time. With further in vivo validation, this NP-based strategy will be a powerful tool for targeting mutant PPM1D DIPG and other cancers.
Citation Format: Matthew A. Murray, Yazhe Wang, Ranjini Sundaram, Jason Beckta, Mark Saltzman, Ranjit Bindra. Exploiting mutant PPM1D-induced metabolic defects with nanoparticle-encapsulated NAMPT inhibitors [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P059.