The Rho family of Ras superfamily small GTPases regulates a broad range of biological
processes such as migration, differentiation, cell growth and cell survival. Therefore, the
availability of small molecule modulators as tool compounds could greatly enhance research on
these proteins and their biological function. To this end, we designed a biochemical, high
throughput screening assay with complementary follow-up assays to identify small molecule
compounds inhibiting MgcRacGAP, a Rho family GTPase activating protein involved in
cytokinesis and transcriptionally upregulated in many cancers. We first performed an in-house
screen of 20,480 compounds, and later we tested the assay against 342,046 compounds from the
NIH Molecular Libraries Small Molecule Repository. Primary screening hit rates were about 1%
with the majority of those affecting the primary readout, an enzyme-coupled GDP detection assay.
After orthogonal and counter screens, we identified two hits with high selectivity towards MgcRacGAP, compared with
other RhoGAPs, and potencies in the low micromolar range. The most promising hit, termed MINC1, was then examined
with cell-based testing where it was observed to induce an increased rate of cytokinetic failure and multinucleation in
addition to other cell division defects, suggesting that it may act as an MgcRacGAP inhibitor also in cells.