"Breast cancer (BCa) is the most common cancer amongst women worldwide and the leading cause of cancer related death. The triple negative BCa (TNBCa) subtype is associated with a particularly aggressive clinical behavior including an early peak of fatal distant metastasis, predominantly to bone. Routine systemic chemotherapeutic treatment with doxorubicin (DOX) is limited due to its severe side effects, especially cardiotoxicity. Novel (targeted) nanotherapies are a promising breakthrough to enhance treatment efficacy and specificity of known chemotherapeutics while at the same time decreasing their systemic toxicity. Therefore, we studied the therapeutic effect of non-targeted and targeted DOX-containing nanoparticles as a novel treatment approach against TNBCa bone metastases using a humanized tissue-engineered mouse model.
A humanized bone microenvironment was created in NSG mice by subcutaneous implantation of humanized tissue-engineered bone constructs (hTEBCs) consisting of tubular biodegradable medical grade polycaprolactone scaffolds seeded with human osteoblasts and an inner vascular bone marrow niche. After 13 weeks of in vivo bone formation, TNBCa primary tumor was induced by injecting MDA-MB-231BO-Luc cells into the mammary fat pad and the tumor was allowed to grow and metastasize to humanized bone. Subsequently, treatment with DOX-loaded hyper branched methoxy polyethylene glycol (mPEG) (HBP) nanoparticles was performed. The DOX-HBP nanoparticles were either non-targeted or targeted with a Thomsen-Friedenreich (TF)-mPEG bispecific antibody (BsAb) and administered once per week over a duration of 3 weeks.
Implantation of the hTEBCs resulted in the formation of a chimeric bone organ in vivo containing human-derived extracellular matrix, bone marrow and showing evidence of ongoing complex bone formation through endochondral ossification. HBP nanoparticles predominantly accumulated at the primary tumor and hTEBCs. The non-targeted HBP-DOX nanoparticles were able to slow primary tumor growth and reduce metastasis compared to the targeted HBP-DOX nanoparticles and non-DOX containing control groups. Additionally, the non-targeted nanoparticles reduced systemic toxicity effects (cardiotoxicity, hepatotoxicity, hematological toxicity) and prolonged survival compared to free DOX treatment. Further targeting with the BsAb did not improve treatment outcome, most likely because of enhanced clearance (accumulation in liver and spleen). However, the targeted HBP-DOX nanoparticles lead to increased lung metastases and tended to increase metastasis to the liver and hTEBCs compared to the saline control.
In conclusion, this study is an exciting example of complex pre-clinical disease modelling including a humanized bone niche in the mouse. Furthermore, it highlights the great potential of nanomedicines in cancer therapy, but also demonstrates how changed nanoparticle properties can alter their treatment efficacy in vivo."