Cancer nanomedicine: Recent developments in drug delivery systems and strategies to overcome eventual barriers to achieve a better outcome

Cancer has been a global challenge given the number of limitations of current therapies, such as multi-drug resistance, high levels of toxicity, side effects, the tumor microenvironment, and the lack of cell-targeted approaches. Over the past decades, several strategies using nanotechnological structures for drug delivery systems have been developed to provide targeted and controlled release of drugs for in situ anticancer therapies. These nanostructures are made of different types of biocompatible materials, ranging from polymeric to organic and inorganic nanoparticles, thus allowing them to interact with different cells, membranes, and receptors, as well as to conjugate molecules with the most diverse physicochemical characteristics. Moreover, these structures can potentially overcome the drawbacks of systemic therapy, taking advantage of the organism's biological mechanisms to increase therapeutic efficacy while reducing systemic toxicity. In this review, we focus on nanostructures as drug delivery systems for cancer treatment, how they can reach tumor cells and improve in situ toxicity, and the barriers they may face to achieve a positive outcome. Overall, several nanoproducts have been developed to treat different types of cancers, and most of the current nanomedical approaches focus on the ability to target tumor cells by improving drug delivery rates and combining different molecules, therefore potentially reducing side effects. On the other hand, concerns regarding individual characteristics of patients, tumor barrier mechanisms, and the potential toxicity of non-biological materials are still challenges to be addressed. Nonetheless, the rapid development of nanomedicine and the constant improvement of related techniques point to a promising future in the treatment of cancer and in improving the quality of life of patients.