Nanoparticulate drugs and vaccines: Breakthroughs and bottlenecks of repurposing in breast cancer

Breast cancer (BC) is a highly diagnosed and topmost cause of death in females worldwide. Drug repurposing (DR) has shown great potential against BC by overcoming major shortcomings of approved anticancer thera-peutics. However, poor physicochemical properties, pharmacokinetic performance, stability, non-selectivity to tumors, and side effects are severe hurdles in repurposed drug delivery against BC. The variety of nanocarriers (NCs) has shown great promise in delivering repurposed therapeutics for effective treatment of BC via improving solubility, stability, tumor selectivity and reducing toxicity. Besides, delivering repurposed cargos via theranostic NCs can be helpful in the quick diagnosis and treatment of BC. Localized delivery of repurposed candidates through apt NCs can diminish the systemic side effects and improve anti-tumor effectiveness. However, breast tumor variability and tumor microenvironment have created several challenges to nanoparticulate delivery of repurposed cargos. This review focuses on DR as an ingenious strategy to treat BC and circumvent the drawbacks of approved anticancer therapeutics. Various nanoparticulate avenues delivering repurposed therapeutics, including non-oncology cargos and vaccines to target BC effectively, are discussed along with case studies. Moreover, clinical trial information on repurposed medications and vaccines for the treatment of BC is covered along with various obstacles in nanoparticulate drug delivery against cancer that have been so far identified. In a nutshell, DR and drug delivery of repurposed drugs via NCs appears to be a propitious approach in devastating BC.