The influence of a Grb2 inhibitor on K562 cell growth

Abstract

Objective To analyze the effects of an inhibitor of the SH3 (Src homology) domains of Grb2 on the growth and proliferation of K562 cells. Methods The peptidimer [(VPPPVPPRRR)2-K], penetratin (RQIKIWFQNRRMKWKK) and peptidimer-c [poptidimer linked to penetratin: (VPPPVPPRRR)2-K-Aha-RQIKIWFQNRRMKWKK] were synthesized by solid-phase synthesis using Fmoc chemistry, and purified by high performance liquid chromatography (HPLC) on a C18 column. Purity was evaluated by HPLC, and the identity of the peptides was checked by electrospray mass spectroscopy (MS). A pull-down assay was used to observe the specific binding of peptidimer-c to the Grb2 of K562 cell lysates. The inhibition of peptidimer-c on K562 cell proliferation was evaluated by trypan blue exclusion assay, the cytostatic effect was tested by clonogenic assay, and the cytotoxicity was examined by WST-1 method. A further experiment was performed with clonogenic assay to analyze the co-effect of peptidimer-c respectively combined with Gleevec, Hydroxyurea and Cytarabine by Jing's method. Results The HPLC analysis showed only a simple peak, which means that the peptide is in high purity. MS analysis showed the peptides were coincided with the design. The molecular weight of peptidimer-c was of 4794.0 and that of the penetratin 2246.7. Pull-down assay demonstrated that the peptidimer-c, not the penetratin, could bind to Grb2 specifically. The trypan blue assay showed that the peptidimer-c could inhibit the proliferation of K562 significantly in a dose-dependent manner, even 3～6 h after the cells were exposed to the drug, and penetratin alone did not influence the cell proliferation. Gleevec inhibited the growth of K562 not only in a dose-dependent manner, but also in a time-dependent manner. WST-1 test showed the cytotoxieity of peptidimer-c or Gleevec on K562 cells, the IC50 of peptidimer-c was (17±2) μmol/L and the IC50 of Gleevec was (0.25±0.05) μmol/L. In the methylcellulose semi-solid medium system, the colony formation of K562 was greatly decreased by peptidimer-c as compared to the penetratin, and the colony number decreased as the dose of peptidimer-c increased. The IC50 value ofpeptidimer-c on K562 colony formation was (3.9±0.9) μmol/L, IC50 of Gleevec was (0.03±0.02) μmol/L, IC50 of Hydroxyurea was (15±7) μmol/L, and that of cytarabine was (0.014±0.012) μmol/L. There were synergistic effects of peptidimer-c with Gleevec, Hydroxyurea or Cytarabine on K562 by colonogenic assay. Combination of 1.5 μmol/L peptidimer-c and 0.05 μmol/L Gleevec showed synergistic effect on K562, as well as the combination of 1.5 μmol/L peptidimer-c and 0.006 μmol/L or 0.01 μmol/L Cytarabine. Conclusion These results suggested that peptidimer-c had an inhibitory effect on K562 cells and combination of peptidimer-c with other drugs would increase the anti-cancer effects. Key words: Grb2; SH3 domain; Inhibitor, K562