For example, manganese dioxide (MnO2) NPs synthesized by chemical (Lim et al., 2021) or biological methods (Liu et al., 2021) can catalyze the conversion of endogenous hydrogen peroxide (H2O2) in tumor region into O2 due to its catalase-like activity, thereby alleviating tumor hypoxia. The gene discussed is CAT; the disease is neoplasm.