Etoposide (VP-16)

Etoposide inhibits DNA synthesis by forming a complex with topoisomerase II and DNA, which induces breaks in double stranded DNA and prevents repair by topoisomerase II binding. Accumulated breaks in DNA prevent entry into the mitotic phase of cell division, and lead to cell death. Etoposide acts primarily in the G2 and S phases of the cell cycle. ^[1] Etoposide inhibits the growth of murine angiosarcoma cell line (ISOS-1) in a 5 days-period with IC50 of 0.25 μg/mL. Cell growth of normal murine microvascular endothelial cells (mECs) is less sensitive to Etoposide with IC50 of 10 μg/mL). ^[2] Etoposide treated for 6 hr inhibits colonies of tetraploid variant of the human leukemic lymphoblast line CCRF-CEM with IC50 of 0.6 μM. ^[3] Etoposide treated for 2 hr inhibits growth of human pancreatic cancer cell line Y1, Y3, Y5, Y19, YM. YS, and YT with IC50s of 300 μg/mL, 300 μg/mL, 300 μg/mL, 91 μg/mL, 0.68 μg/mL, 300 μg/mL, 300 μg/mL, and 260 μg/mL, respectively. ^[4] Etoposide exposed for 1 hr inhibits growth of human glioma cell lines CL5, G142, G152, G111, and G5 with IC50 of 8, 9, 9.8, 10, and 15.8 μg/mL respectively for 12 days. Under same condition, the IC90 value is attained in cell lines CL5, G152, G142, and G111 at 26, 27, 32, and 33 μg/mL. Etoposide inhibition of topoisomerase II is homogeneous for each cell. The average inhibition rates are 15%, 21.8%, 31.8%, 41.5%, and 49.5% for 1, 2, 4, 8, and 16 μg Etoposide, respectively. ^[5]