Dual-Action Theranostic Nanoparticles Delivering Toll-Like Receptor 2 Inhibitors and Chemotherapy Target Breast Cancer Cells and the Tumor Microenvironment

Purpose: Breast cancer remains the leading cause of cancer-related death in women, largely due to therapy resistance driven by both tumor-intrinsic and tumor microenvironment (TME)-mediated mechanisms. Toll-like receptor 2 (TLR2), which is overexpressed in breast tumors, promotes cancer progression and chemoresistance through both cancer-cell intrinsic and immune-mediated signaling, making it a promising therapeutic target. Methods: We developed a targeted therapy combining two types of nanoparticles (NPs) for targeted drug delivery, hybrid poly (lactic-co-glycolic acid) (PLGA)- lipid NPs loaded with the TLR2 inhibitor CU-CPT22 (PLGA-CU) and liposomes encapsulating doxorubicin (LIPO-DOXO). Both NP types were functionalized with cyclic RGD peptides to target α v β 3 integrins. Their effects were evaluated in vitro on triple-negative and HER2-positive breast cancer cells and in vivo in 4T1 triple negative breast cancer tumor-bearing mice. Results: PLGA-CU effectively inhibited TLR2 signaling. Both PLGA-CU and LIPO-DOXO reduced cell viability and induced apoptosis, with stronger effects observed when used in combination. In vivo imaging confirmed the accumulation of NPs in tumors. While monotherapies reduced tumor growth, the combined treatment targeted both cancer cells and TME, leading to reduced angiogenesis and immunosuppression, as well as enhanced anti-tumor activity. Conclusion: NP-mediated delivery of a TLR2 inhibitor and doxorubicin produces synergistic anti-cancer effects in breast cancer models. This approach may help overcome chemoresistance and improve therapeutic outcomes, offering a promising strategy for the treatment of advanced breast cancer. Keywords: breast cancer, hybrid PLGA-lipid NPs, immunotherapy, liposomes, magnetic resonance imaging, TLR2 inhibitor