Azodyes as markers for tumor hypoxia imaging and therapy: An up-to-date review

Tumor hypoxia is the low tissue oxygen levels seen characteristically in rapidly proliferating and expanding neoplasms. It affects both malignant tumor cells and its microenvironment, resulting in dysfunctional neovascularization. This leads to epithelial-to-mesenchymal transition phenotype, facilitating tumor progression through cell mobility, invasion, and metastasis. The hypoxic condition in solid tumors is thus an indicator of the process of cancer progression towards an aggressive malignant phenotype with an enhanced possibility of metastasis and resistance to treatment. Advancements in the detection of tumor hypoxia and its utilization as a treatment modality in solid tumors are highly imperative. The use of fluorescent probes is an evolving field for detecting hypoxic tumors in biological systems. The present review is an attempt to provide a contextual knowledge on the prominent role of tumor hypoxia in cancer progression and dissemination. The use of azodyes in detecting tumor hypoxia aiding in cancer diagnosis through fluorescence off-on imaging and azodye-based hypoxia selective pro-drugs for assisting cancer therapy are presented. The limitations of fluorescence based hypoxia imaging and further investigations desired for clinical usage of azodye based hypoxic probes for fluorescence imaging are also considered.