PLK1 and cancer: For example, in a continuation of a previous study about tumor apoptosis, delayed tumor growth and prolonged survival of human lung xenograft-bearing mice after intratumoral administration of small interfering RNA (siRNA)-functionalized MWCNTs complexes [156], Guo et al. functionalized MWCNTs with a proper siRNA, whose effect is the inhibition of polo-like kinase 1 (PLK1) that is predicted to block the reproduction of cancer cells (lung cancer in this case).