Discovery and characterization of small molecule Rac1 inhibitors

Abstract

Aberrant activation of Rho GTPase Rac1 has been observed in various tumor types, including pancreatic cancer. Rac1 activates multiple signaling pathways that lead to uncontrolled proliferation, invasion and metastasis. Thus, inhibition of Rac1 activity is a viable therapeutic strategy for proliferative disorders such as cancer. Here we identified small molecule inhibitors that target the nucleotide-binding site of Rac1 through in silico screening. Follow up in vitro studies demonstrated that two compounds blocked active Rac1 from binding to its effector PAK1. Fluorescence polarization studies indicate that these compounds target the nucleotide-binding site of Rac1. In cells, both compounds blocked Rac1 binding to its effector PAK1 following EGF-induced Rac1 activation in a dose-dependent manner, while showing no inhibition of the closely related Cdc42 and RhoA activity. Furthermore, functional studies indicate that both compounds reduced cell proliferation and migration in a dose-dependent manner in multiple pancreatic cancer cell lines. Additionally, the two compounds suppressed the clonogenic survival of pancreatic cancer cells, while they had no effect on the survival of normal pancreatic ductal cells. These compounds do not share the core structure of the known Rac1 inhibitors and could serve as additional lead compounds to target pancreatic cancers with high Rac1 activity.

Small Molecule Inhibitors Targeting Gαi2 Protein Attenuate Migration of Cancer Cells

“…These compounds impair the activation of Gα i 2 by inhibiting the conversion of GDP-to GTP-state of the Gα i 2 subunit. A similar inhibition of GDP-GTP exchange by small molecules targeting Rho GTPases has been shown by others to impair cancer progression and invasion [28,29]. Among all the compounds that we investigated, 13 and 14, at the concentration of 10 µM, were able to significantly reduce the migratory capability of prostate cancer cells (Figure 3).…”

“…The epidermal growth factor (EGF) is one of the most common inducer of migration of normal and cancer cells [28,32,33]. We also know that cell migration elicited by tyrosine kinase receptors is not mediated by G-proteins.…”

Small Ones to Fight a Big Problem—Intervention of Cancer Metastasis by Small Molecules

“…Therefore, PAK1 as a major executor of Rac1-mediated migration, was targeted in an extensive in silico screen. Two compounds structurally unrelated to NSC23766 emerged as potent targeting pancreatic cancer cell migration while non-toxic towards normal pancreatic cells [130].…”

Rho GTPases as therapeutic targets in cancer (Review)

“…Recently, Arnst et al ( 102 ) demonstrated two new compounds, referred in their publication as #1 and #6, that were design to target the nucleotide-binding site of Rac1 although, were able to block active Rac1 from binding to its effector PAK1, following EGF-induced Rac1 activation in a dose-dependent manner, they showed no inhibition of Cdc42 or RhoA. Functional studies indicated that both compounds reduced cell proliferation and migration in a dose-dependent manner in multiple pancreatic cancer cell lines at micromolar concentrations.…”