Reversal of hypoxia-induced chemoresistance using hemoglobin-loaded polycaprolactone nanoparticles.

Cancer is a multifactorial and complex disease, typically managed through a combination of therapies including surgery, chemotherapy, and radiation; however, it remains a leading cause of mortality worldwide, with solid tumors such as lung, breast, and pancreatic cancers continuing to pose significant therapeutic challenges. A key contributor to treatment failure in these malignancies is tumor hypoxia, an oxygen-deficient microenvironment that reprograms cancer cell metabolism, promotes immune evasion, and fosters drug resistance. Although hemoglobin (Hb) is a natural oxygen carrier, its therapeutic application is limited due to structural instability, oxidative degradation, and dose-dependent cytotoxicity, as well as its tendency to elicit inflammatory responses when administered in free form. To address this, we develop hemoglobin-loaded polycaprolactone nanoparticles (PCL-Hb NPs) for targeted oxygen delivery within hypoxic tumors. Hemoglobin is encapsulated in a stable core-shell structure, retaining its oxygen-binding capacity and structural integrity as confirmed by biophysical and spectroscopic analysis. Oxygen release assays confirm sustained and reversible oxygen diffusion. In vitro studies demonstrated that PCL-Hb nanoparticles are biocompatible, showing no cytotoxicity in HFL1 normal lung fibroblast and A549 lung cancer cells and no inflammatory activation in THP-1 macrophages. Flow cytometry and confocal microscopy revealed efficient cellular uptake both under normoxic and hypoxic conditions. Under hypoxic conditions, PCL-Hb reduced the expression of hypoxia-responsive genes and effectively reverses resistance to paclitaxel. Simultaneous treatment of PCL-Hb with paclitaxel significantly enhances drug efficacy in 2D hypoxic cells and 3D spheroids, restoring sensitivity and improving therapeutic response. These findings underscore the potential of PCL-Hb nanoparticles as an oxygen delivery system to alleviate tumor hypoxia and overcome hypoxia-induced chemotherapy resistance in solid tumors.