Small-sized polymeric micelles incorporating docetaxel suppress distant metastases in the clinically-relevant 4T1 mouse breast cancer model

The small size of ultra-small nanoparticles makes them suitable for lymphatic delivery, and many recent studies have examined their role in anti-metastasis therapy. However, the anti-metastatic efficacy of small-sized nanocarriers loaded with taxanes such as docetaxel has not yet been investigated in malignant breast cancer. We encapsulated docetaxel using poly(D,L-lactide)₁₃₀₀-b-(polyethylene glycol-methoxy)₂₀₀₀ (mPEG₂₀₀₀-b-PDLLA₁₃₀₀) to construct polymeric micelles with a mean diameter of 16.76 nm (SPM). Patient-like 4T1/4T1^luc breast cancer models in Balb/c mice, with resected and unresected primary tumors, were used to compare the therapeutic efficacies of SPM and free docetaxel (Duopafei) against breast cancer metastasis using bioluminescent imaging, lung nodule examination, and histological examination. SPM showed similar efficacy to Duopafei in terms of growth suppression of primary tumors, but greater chemotherapeutic efficacy against breast cancer metastasis. In addition, lung tissue inflammation was decreased in the SPM-treated group, while many tumor cells and neutrophils were found in the Duopafei-treated group. Small-sized mPEG₂₀₀₀-b-PDLLA₁₃₀₀ micelles could provide an enhanced method of docetaxel delivery in breast cancer metastasis, and may represent a valid chemotherapeutic strategy in breast cancer patients with resected primary tumors