Harnessing the Power of Nanocarriers to Exploit the Tumor Microenvironment for Enhanced Cancer Therapy.

The tumor microenvironment (TME) has a major role in malignancy and its complex nature can mediate tumor survival, metastasis, immune evasion, and drug resistance. Thus, reprogramming or regulating the immunosuppressive TME has a significant contribution to make in cancer therapy. Targeting TME with nanocarriers (NCs) has been widely used to directly deliver anticancer drugs to control TME, which has revealed auspicious outcomes. TME can be reprogrammed by using a range of NCs to regulate immunosuppressive factors and activate immunostimulatory cells. Moreover, TME can be ameliorated via regulating the redox environment, oxygen content, and pH value of the tumor site. NCs have the capacity to provide site-specific delivery of therapeutic agents, controlled release, enhanced solubility and stability, decreased toxicities, and enhanced pharmacokinetics as well as biodistribution. Numerous NCs have demonstrated their potential by inducing distinct anticancer mechanisms by delivering a range of anticancer drugs in various preclinical studies, including metal NCs, liposomal NCs, solid lipid NCs, micelles, nanoemulsions, polymer-based NCs, dendrimers, nanoclays, nanocrystals, and many more. Some of them have already received US Food and Drug Administration approval, and some have entered different clinical phases. However, there are several challenges in NC-mediated TME targeting, including scale-up of NC-based cancer therapy, rapid clearance of NCs by the mononuclear phagocyte system, and TME heterogeneity. In order to harness the full potential of NCs in tumor treatment, there are several factors that need to be carefully studied, including optimization of drug loading into NCs, NC-associated immunogenicity, and biocompatibility for the successful translation of NC-based anticancer therapies into clinical practice. In this review, a range of NCs and their applications in drug delivery to remodel TME for cancer therapy are extensively discussed. Moreover, findings from numerous preclinical and clinical studies with these NCs are also highlighted.