Overcoming doxorubicin resistance in triple-negative breast cancer with novel mPEG-PCL-DOX nanoparticles

Triple-negative breast cancer (TNBC) is an aggressive subtype characterised by the absence of estrogen, progesterone, and human epidermal growth factor receptors, limiting the use of targeted therapies clocking these proteins. Chemotherapy is still the first line treatment for TNBC and Doxorubicin (DOX) is a commonly used drug, but its effectiveness is limited by dose-dependent cardiotoxicity and multidrug resistance (MDR), often mediated by P-glycoprotein (PgP) efflux. This thesis focused on developing novel pH-responsive methoxy-poly(ethylene glycol)-poly(ε-caprolactone) (mPEG-PCL) nanoparticles conjugated with doxorubicin (mPEG-PCL-DOX) via azide–alkyne click chemistry as a new drug delivery system to overcome resistances. The nanoparticles synthesis showed stability at physiological pH with accelerated drug release under acidic conditions. In MDA-MB-231 TNBC cells and resistant derivatives (acquired DOX-resistant and PgP-overexpressing models), mPEG-PCL-DOX showed slower but sustained cytotoxicity compared with free DOX, with improved intracellular accumulation. Importantly, in 3D spheroid models incorporating basement membrane extract to mimic tumour hypoxia, acidosis, and ECM barriers, mPEG-PCL-DOX showed superior penetration compared with free DOX, particularly in resistant spheroids. These findings demonstrate the ability of pH-responsive polymer– drug conjugates to use the acidic TME, overcome efflux-based resistance, and enhance therapeutic performance in physiologically relevant models Overall, this work highlights mPEG-PCL-DOX nanoparticles as a promising strategy to improve the efficacy and safety of DOX in TNBC. While current results are based on in vitro studies, they provide a strong ground for in vivo evaluation of biodistribution, pharmacokinetics, therapeutic efficacy, and toxicity. This platform may also be adapted to the use of alternative drugs in breast cancer subtypes where DOX is not standard treatment, supporting its broader application in precision nanomedicine.