Aberrant activation of p21-activated kinase 1 (PAK1) is associated with tumour progression, and PAK1 has been recognized as a promising target for anticancer drug discovery. However, the development of potent PAK1 inhibitors with satisfactory kinase selectivity and favourable physicochemical properties remains a daunting challenge. Herein, we identified the 1H-indazole-3-carboxamide derivatives as potential PAK1 inhibitors using a fragment-based screening approach. The representative compound 30l exhibited excellent enzyme inhibition (PAK1 IC₅₀ = 9.8 nM) and high PAK1 selectivity toward a panel of 29 kinases. The Structure-activity relationship (SAR) analysis showed that substituting of an appropriate hydrophobic ring in the deep back pocket and introducing a hydrophilic group in the bulk solvent region were critical for PAK1 inhibitory activity and selectivity. Additionally, the hERG channel activity of 30l demonstrated its low risk of hERG toxicity. Furthermore, it significantly suppressed the migration and invasion of MDA-MB-231 cells by downregulating Snail expression without affecting the tumour growth. These results provide a new type of chemical scaffolds targeting PAK1 and suggested that 1H-indazole-3-carboxamide derivatives may serve as lead compounds for the development of potential and selective PAK1 inhibitors.

p21活化的激酶1（PAK1）的异常激活与肿瘤的进展有关，并且PAK1被公认为是抗癌药物发现的有希望的靶标。然而，开发具有令人满意的激酶选择性和良好的理化性质的有效PAK1抑制剂仍然是一项艰巨的挑战。在本文中，我们使用基于片段的筛选方法确定了1 H-吲唑-3-羧酰胺衍生物为潜在的PAK1抑制剂。代表性化合物30l表现出优异的酶抑制作用（PAK1 IC ₅₀＝ 9.8nM）和对一组29种激酶的高PAK1选择性。结构-活性关系（SAR）分析表明，在深后袋中适当的疏水环取代并在本体溶剂区域引入亲水基团对于PAK1抑制活性和选择性至关重要。此外，30l的hERG通道活性证明其hERG毒性的低风险。此外，它通过下调Snail表达而显着抑制MDA-MB-231细胞的迁移和侵袭，而不会影响肿瘤的生长。这些结果提供了一种新型的靶向PAK1的化学支架，并表明1 H-吲唑-3-羧酰胺衍生物可作为潜在化合物和选择性PAK1抑制剂开发的先导化合物。