Alkyne-Tagged PLGA Allows Direct Visualization of Nanoparticles In Vitro and Ex Vivo by Stimulated Raman Scattering Microscopy.

Lida Zoupi,Stefan A Cairns,Sally Vanden-Hehir,Martin Lee,Anna Williams,Alison N Hulme,Michael P Shaver,Valerie G Brunton

doi:10.1021/acs.biomac.9b01092

Abstract

Polymeric nanoparticles (NPs) are attractive candidates for the controlled and targeted delivery of therapeutics in vitro and in vivo. However, detailed understanding of the uptake, location, and ultimate cellular fate of the NPs is necessary to satisfy safety concerns, which is difficult because of the nanoscale size of these carriers. In this work, we show how small chemical labels can be appended to poly(lactic acid-co-glycolic acid) (PLGA) to synthesize NPs that can then be imaged by stimulated Raman scattering microscopy, a vibrational imaging technique that can elucidate bond-specific information in biological environments, such as the identification of alkyne signatures in modified PLGA terpolymers. We show that both deuterium and alkyne labeled NPs can be imaged within primary rat microglia, and the alkyne NPs can also be imaged in ex vivo cortical mouse brain tissue. Immunohistochemical analysis confirms that the NPs localize in microglia in the mouse brain tissue, demonstrating that these NPs have the potential to deliver therapeutics selectively to microglia.

Highlights

The use of polymeric NPs for drug delivery has become increasingly popular to achieve controlled release, targeted delivery, and increased lifetime of therapeutics in vivo
Deuterated poly(lactic acid-co-glycolic acid) (PLGA) (PLGA-D) was synthesized via a direct poly condensation method from lactic acid, lactic acid-d3, and glycolic acid, which produced a polymer with a molecular weight of 4.5 kDa and a dispersity of 1.84 (Scheme 1A).[24,25]
Since Raman is an inherently weak effect, with only approximately 1 in every 108 molecules experiencing Raman scattering,[26] a deuterium group was introduced into the monomer, as opposed to substitution onto a premade polymer, to maximize the Raman signal of the NPs

Summary

Introduction

The use of polymeric NPs for drug delivery has become increasingly popular to achieve controlled release, targeted delivery, and increased lifetime of therapeutics in vivo. NP drug delivery can have wide ranging applications such as the targeting of cancer therapeutics,[1,2] delivery of drugs to the brain,[3,4] and encapsulation of protein therapeutics, which are sensitive to certain biological environments and may degrade to an inactive form in vivo. PLGA micro and nanoparticles have been used extensively in drug delivery research as they are FDA approved, biocompatible, and biodegradable.[5] due to the nanoscale size of these drug carriers, imaging their uptake, biodistribution, and ultimate cellular fate in vitro and in vivo is challenging. Fluorophores are generally unstable in biological environments, and photobleaching can cause signal degradation of the dye (Figure 1).[10]

Methods

Results

Conclusion