Simultaneous Inhibition of BCR-ABL1 Tyrosine Kinase and PAK1/2 Serine/Threonine Kinase Exerts Synergistic Effect against Chronic Myeloid Leukemia Cells

Abstract

Tyrosine kinase inhibitors (TKIs) revolutionized the treatment of chronic myeloid leukemia in the chronic phase (CML-CP). However, it is unlikely that they can completely “cure” the disease. This might be because some subpopulations of CML-CP cells such as stem and progenitor cells are resistant to chemotherapy, even to the new generation of TKIs. Therefore, it is important to look for new methods of treatment to improve therapeutic outcomes. Previously, we have shown that class I p21-activated serine/threonine kinases (PAKs) remained active in TKI-naive and TKI-treated CML-CP leukemia stem and early progenitor cells. In this study, we aimed to determine if simultaneous inhibition of BCR-ABL1 oncogenic tyrosine kinase and PAK1/2 serine/threonine kinase exert better anti-CML effect than that of individual treatments. PAK1 was inhibited by small-molecule inhibitor IPA-3 (p21-activated kinase inhibitor III), PAK2 was downregulated by specific short hairpin RNA (shRNA), and BCR-ABL1 tyrosine kinase was inhibited by imatinib (IM). The studies were conducted by using (i) primary CML-CP stem/early progenitor cells and normal hematopoietic counterparts isolated from the bone marrow of newly diagnosed patients with CML-CP and from healthy donors, respectively, (ii) CML-blast phase cell lines (K562 and KCL-22), and (iii) from BCR-ABL1-transformed 32Dcl3 cell line. Herein, we show that inhibition of the activity of PAK1 and/or PAK2 enhanced the effect of IM against CML cells without affecting the normal cells. We observed that the combined use of IM with IPA-3 increased the inhibition of growth and apoptosis of leukemia cells. To evaluate the type of interaction between the two drugs, we performed median effect analysis. According to our results, the type and strength of drug interaction depend on the concentration of the drugs tested. Generally, combination of IM with IPA-3 at the 50% of the cell kill level (EC50) generated synergistic effect. Based on our results, we hypothesize that IM, a BCR-ABL1 tyrosine kinase inhibitor, combined with a PAK1/2 inhibitor facilitates eradication of CML-CP cells.

NSC348884 cytotoxicity is not mediated by inhibition of nucleophosmin oligomerization

“…In both adherent cell lines, 293T and HeLa, NSC348884 induced large, dose-dependent changes in the resistance signal, which were similar to those produced by IPA-3 62 , an inhibitor of p21-activated kinases (PAK). PAK are key regulators of adhesion signaling, which have been proposed as therapeutic targets in different kinds of cancer including leukemias 63 , 64 . We thus analyzed possible effect of NSC348884 on expression and activity of PAK1, as well as of Cofilin, which governs actin remodeling during changes of cell shape.…”

“…The rapid onset of changes in the ECIS signal indicated that the cell shrinkage and detachment was not a secondary effect accompanying apoptosis. As the course of the ECIS signal was similar to that induced by the inhibitor of p21-activated kinases, IPA-3 62 , we investigated also activity and expression of PAK1 and Cofilin, a known actin regulator 63 (Fig. 14 ).…”

P21-Activated Kinase 1: Emerging biological functions and potential therapeutic targets in Cancer

“…This is why PAK1 inhibitors can significantly enhance the therapeutic effect of EGFR-TKI inhibitors in EGFR-TKI-resistant non-small cell lung cancer and lung adenocarcinoma 68 , 69 . Furthermore, in chronic myeloid leukemia (CML), PAK1 inhibition displayed synergistic effect with TKIs 70 . In pancreatic ductal adenocarcinoma, PAK1 activation triggers the Wnt/β-catenin signaling cascade that is involved in resistance to Gemcitabine .…”

Coordinated dysregulation of cancer progression by the HER family and p21-activated kinases

“…Targeting PAK2 restores sensitivity in lapatinib-resistant HER2-overexpressing breast cancer cells [153]. Compared with either agents alone, cotargeting PAK1 or PAK2 along with the BCR-ABL1 inhibitor confers superior growth inhibitory effects in chronic myeloid leukemia cells [154] or with Aurora inhibitors in breast cancer cells [155]. PAK4 is upregulated in anaplastic thyroid cancer cells resistant to lenvatinib, a multitarget TKI, and accordingly, co-targeting PAK4 resensitizes these cells to the growth inhibitory effects of lenvatinib [156].…”