Comparative Studies to Evaluate Relative in vitro Potency ofLuteolin in Inducing Cell Cycle Arrest and Apoptosis in HaCaTand A375 Cells

Luteolin is a naturally occurring flavonoid present in many plants with diverse applications in pharmacology.Despite several studies elucidating its significant anti-cancer activity against various cancer cells, the mechanismof action in skin cancer is not well addressed. Hence, we investigated the effects of luteolin in HaCaT (humanimmortalized keratinocytes) and A375 (human melanoma) cells. The radical scavenging abilities of luteolin weredetermined spectrophotometrically, prior to a cytotoxic study (XTT assay). Inhibitory effects were assessedby colony formation assay. Further, the capability of luteolin to induce cell cycle arrest and apoptosis weredemonstrated by flow cytometry and cellular DNA fragmentation ELISA, respectively. The results revealedthat luteolin possesses considerable cytotoxicity against both HaCaT and A375 cells with IC50 values of 37.1μM and 115.1 μM, respectively. Luteolin also inhibited colony formation and induced apoptosis in a dose andtime-dependent manner by disturbing cellular integrity as evident from morphological evaluation by Wright-Giemsa staining. Accumulation of cells in G2/M (0.83-8.14%) phase for HaCaT cells and G0/G1 (60.4-72.6%)phase for A375 cells after 24 h treatment indicated cell cycle arresting potential of this flavonoid. These datasuggest that luteolin inhibits cell proliferation and promotes cell cycle arrest and apoptosis in skin cancer cellswith possible involvement of programmed cell death, providing a substantial basis for it to be developed into apotent chemopreventive template for skin cancer.