Objective      To explore the stabilities of 2 tumor targeted peptides (QKRKRKKSRKKH and RKRKRKKSRYIVLS) after modification (N-terminal acetylation

C-terminal amidation) and study their targets preliminarily.       Methods      The effect of the peptides before and after modification on inhibiting

proliferation of A549 cells was tested by

3

H-TdR incorporation

and the cell vitality was explored by CCK-8 assay. The remaining peptides were tested by high-performance liquid chromatography (HPLC) in 10% serum at different time points (12 and 24 h)

and then the stability of peptides after modification could be evaluated. The expression vectors of GST-tagged peptides were constructed

and GST-peptide fused proteins were over-expressed in Escherichia coli and purified. Co-immunoprecipitation assay was used to confirm the interactions between GST-peptide fused proteins and interest receptors (VEGFR-1 and VEGFR-2).       Results      After modification

the inhibition ratio of RKRKRKKSRYIVLS peptide on A549 cell proliferation was increased to (48.50±7.14)% from (2.63±6.19)% (P0.01)

and the cell vitality inhibition ratio was changed to (20.80±5.90)% from (1.30±7.90)% (P0.01) in 10% serum. The remaining peptides were increased to (64.64±0.30)% from (56.04±1.81)% (P0.01) at 24 h after modification. Before and after modification

the inhibitory ratios of QKRKRKKSRKKH peptide on A549 cell proliferation were (28.38±5.63)% and (34.25±10.90)%

respectively (P0.05)

and the cell vitality inhibitory ratio were (8.09±5.84)% and (15.07±8.09)%

respectively

in 10% serum (P0.05). The remaining peptides were increased to (77.43%±1.78)% from (72.72±2.60)% (P0.05) at 24 h after modification. Co-immunoprecipitation assay confirmed that the 2 peptides could bind to VEGFR-1 and VEGFR-2.       Conclusion      VEGFR-1and VEGFR-2 are the targets of the 2 tumor targeted peptides. In serum

the stability of both RKRKRKKSRYIVLS peptide and QKRKRKKSRKKH peptide is enhanced significantly after modification. The inhibitory effect of RKRKRKKSRYIVLS peptide after modification on the proliferation and vitality of A549 cells is enhanced.