Ultrasensitive <i>In Vitro</i> and <i>Ex Vivo</i> Tracking of <sup>13</sup>C‑Labeled PEG–PLA\nDegradation Products by MALDI-TOF Mass Spectrometry

Copolymers of poly(lactic acid) (PLA) and poly(ethylene\nglycol)\n(PEG) are widely used in biomedical applications. As inactive ingredients\nin formulations, tracking their degradation byproducts <i>in\nvivo</i> stands as a major challenge but is a pivotal endeavor\nto ensure safety and further progress in clinical stages. Current\nbioanalytical methods used to monitor this degradation lack sensitivity\nand quantification precision. This study introduces a cost-effective\nsynthetic route for <sup>13</sup>C-labeled PEG–PLA copolymers,\ncombined with matrix-assisted laser desorption/ionization time-of-flight\nmass spectrometry (MALDI-TOF MS), to monitor their <i>in vitro</i> and <i>ex vivo</i> degradation. Incorporating <sup>13</sup>C isotopes into copolymers significantly enhances MALDI-TOF sensitivity,\nallowing for precise detection of degradation products at exceedingly\nlow concentrations. We demonstrate the ability to trace <sup>13</sup>C-labeled PEG–PLA in complex biological media (urine, plasma)\nat concentrations 100 times lower than labeled PEG–PLA. Our\nresults pave the way toward ultrasensitive <i>in vivo</i> tracking and elucidation of <i>in vivo</i> fate of this\nwidely investigated polymer family.