Essential Oils Extracted from Boswellia sacra Oleo Gum Resin Loaded into PLGA–PCL Nanoparticles: Enhanced Cytotoxic and Apoptotic Effects against Breast Cancer Cells

[Image: see text] This work aims to develop and optimize blended polylactide-co-glycolide (PLGA) and poly(ε-caprolactone, PCL) loaded with Boswellia sacra oil (BO) to improve BO’s physicochemical properties and anti-breast cancer effects via enhancing apoptosis. In this context, BO was extracted from B. sacra oleo gum resins (BO) via hydrodistillation and chemically characterized by evaluating its essential oil’s composition using gas chromatography–mass spectrometry. Then, BO/PLGA–PCL NPs were formulated using the emulsion (O/W) solvent evaporation technique using a PLGA–PCL mixture at five different ratios (1:1, 2:1, 3:1, 1:2, and 1:3, respectively). The optimized NPs had a spherical morphology with no agglomerations and the lowest hydrodynamic size (230.3 ± 3.7 nm) and polydispersity index (0.13 ± 0.03) and the highest ζ potential (−20.36 ± 4.89 mV), as compared to the rest of the formulas. PLGA–PCL NPs could entrap 80.59 ± 3.37% of the BO and exhibited a controlled, sustained release of BO (83.74 ± 3.34%) over 72 h. Encapsulating BO in the form of BO/PLGA–PCL NPs resulted in a lower IC(50) value as assessed by the MTT assay. Furthermore and upon assessing the apoptotic effect of both BO and BO/PLGA–PCL NPs, there was an increase in the percentage of apoptotic and necrotic cell percentages compared to the control and free BO. Encapsulation of BO in PLGA–PCL NPs doubled the percentage of apoptotic and necrotic cells exerted by free BO. These findings support the potential use of BO/PLGA–PCL NPs in treating breast cancer.