Hybrid Temozolomide Nanoconjugates: A polymer–drug strategy for enhanced stability and glioblastoma therapy

Glioblastoma multiforme (GBM) is one of the most aggressive and deadly brain cancers, and current therapies offer limited survival benefits. Temozolomide (TMZ) is the standard chemotherapeutic agent used for treatment; however, its effectiveness is hampered by rapid hydrolysis, a short plasma half-life, poor brain bioavailability, and dose-dependent systemic toxicities.  This study aimed to improve the in vivo stability and therapeutic efficacy of TMZ through a hybrid nanoconjugate strategy. TMZ was covalently linked to an amphiphilic copolymer, mPEG-b-P(CB-{g-COOH}), resulting in stable polymer-drug conjugates with varying TMZ loading capacities. Among these, mPEG-b-P(CB-{g-COOH; g-TMZ40}) showed optimal size, stability, and drug incorporation. A hybrid nanoconjugate system was then created by combining this conjugate with mPEG-polylactic acid (mPEG-PLA) using thin-film hydration. The resulting hybrid nanoconjugates had a mean particle size of 105.7 nm, a narrow polydispersity index (PDI < 0.2), and a drug loading of 21.6%. Stability studies demonstrated a significantly longer half-life (~194 hours) compared to free TMZ (1.8 hours).  In vitro assays conducted on C6 and U87MG glioma cell lines confirmed superior cellular uptake, enhanced apoptosis, and reduced IC50 values compared to the free drug. Furthermore, in vivo evaluation using a C6 cell-induced orthotopic glioma rat model showed significant reductions in brain weight and hemispherical width ratio, improved survival rates, and minimal toxicity to vital organs, as demonstrated by histopathological examinations.