A Star-PEGylation Strategy to Improve Testosterone Pharmacokinetics

Testosterone, an androgenic steroid hormone, regulates primary sexual characteristics and influences mood, cognition, social behavior, and sexual function. Deficiency, caused by factors such as aging and genetics, is linked to multiple disease conditions. However, current testosterone therapies are limited by extensive metabolism, poor solubility, and undesirable side effects. To address these limitations, we synthesized a four-armed star PEG-OH-linked testosterone (PEG-T). The in vitro release of testosterone from PEG-T was evaluated in buffer (pH 7.4) and mouse plasma. PEG-T was stable in the buffer, but released testosterone in plasma via esterase-mediated hydrolysis. Pharmacokinetics of testosterone and PEG-T were compared following intraperitoneal (IP) and subcutaneous (SC) administration. Following IP dosing, PEG-T exhibited a ~6-fold improvement in half-life compared to testosterone (1.18 h vs. 0.21 h), and a 54-fold increase in exposure (AUC0-t = 36.0 μM·h vs. 0.67 μM·h) at equimolar doses; furthermore, following SC dosing, PEG-T showed a 4-fold improvement in both half-life (3.57 h vs. 0.91 h) and plasma exposure (11.5 μM·h vs. 3.1 μM·h). Additionally, PEG-T showed lower liver and kidney to plasma ratios, which could potentially result in reduced hepatotoxicity and nephrotoxicity. Overall, PEG-T provides sustained release pharmacokinetics, representing a promising candidate for safer testosterone replacement therapy.