Cell is a complex system whose components change with time and space,and heterogeneity is a widespread event existing in all cells [1].Most previous studies are based on bulk analysis which lead to the losing of key information about the distribution within one cell.Single cell analysis gives us a more accurate result,offering comprehensive information on the fundamental mechanism of biological system.Arsenic have long been used as therapeutic agents.Understanding the mechanism of action of arsenic-based drugs enables more effective arsenic drugs to be developed.Cell cycle has been known to play a critical role for cell division and growth.Herein,we establish a methodology to evaluate the uptake of two arsenic-based drugs(ATO and ZIO-101)across the cell cycle in single leukemia cells,i.e.,NB4 and HL60,using a double thymidine block combined with time-resolved ICP-MS [2,3].We show that cells absorb maximal amounts of both ATO and ZIO-101 in G2/M phase and minimum in S phase,and such variation is less apparent for ZIO-101 than ATO(NB4-G2/M: S=2.5:1 for ATO and 1.6:1 for ZIO-101).We subsequently demonstrate that AQP9,an ATO transporter,is highly expressed in G1 phase(50.2%-46.9%)and least expressed in S phase(27.6%-24.6%); while xCT,a ZIO-101 transporter,is mostly expressed in G2/M phase(74.8%-76.1%),and least expressed in G1 phases(55.4-59.8%).Furthermore,we show that the cytotoxicity of ATO and ZIO-101 on NB4 cells is also cell cycle dependent,with the highest cytotoxicity at S+G2/M phase and the lowest at G1+S phase.Our studies provide the first evidence on cell cycle dependent uptake and cytotoxicity of arsenic-based drugs at single cell levels,may have general implications for precise evaluation of other anticancer drugs by considering cell cycle phase.