AK4 and neoplasm: When CDDP was administered into mice, the inhibition of tumor growth was greater for AK4 knockdown cells (62.0 % of the volume of untreated AK4 knockdown cells) than for control cells (86.3 % of the volume of untreated control shRNA cells), indicating that down-regulation of AK4 expression increased the sensitivity of these cells to CDDP (Fig. 2e and f).