Recent advances in tumor microenvironment associated therapeutic strategies and evaluation models

As per a report of the world health organization, an estimated 9.6 million people died due to cancer in 2018, globally. Most of the cancer death attributed to the lack of early detection and effective treatment. In the case of solid tumors, various factors such as leaky vasculature, angiogenesis, interstitial fluid pressure and lymphatic drainage are important in cancer chemotherapy. The poor penetration and retention of the drug/drug delivery system in tumor tissue are most critical issues in the way of effective treatment. In this scenario, the challenges are to design the specific nano-therapeutics with the potential to penetrate inside the adverse condition of tumor microenvironment (TME) including high interstitial pressure region and abnormal vasculature. The modification of nanocarriers surfaces with enzymes, peptides, pH-responsive moieties, antibodies etc. could be a promising strategy to improve the nanocarriers penetration inside the solid tumor. The priming with the drug before the administration of nanotherapeutics may also represents an efficient approach for solid tumor treatment. Further, the growth factors including fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and their pathways could offer potential targeting opportunities for anticancer treatment. Recently, there is a surge in various approaches and formulation design directed towards abnormal TME for more effective cancer therapy. In this review, various factors related to the poor penetration, retention and specific delivery of chemotherapeutics inside tumor cells/tissues are discussed. The emerging formulations strategies directed to the TME and various methodologies for evaluation of their efficacy are also included in this review.