Abstract
The prolyl isomerase PIN1, a critical modifier of multiple signalling pathways, is overexpressed in the majority of cancers and its activity strongly contributes to tumour initiation and progression. Inactivation of PIN1 function conversely curbs tumour growth and cancer stem cell expansion, restores chemosensitivity and blocks metastatic spread, thus providing the rationale for a therapeutic strategy based on PIN1 inhibition. Notwithstanding, potent PIN1 inhibitors are still missing from the arsenal of anti-cancer drugs. By a mechanism-based screening, we have identified a novel covalent PIN1 inhibitor, KPT-6566, able to selectively inhibit PIN1 and target it for degradation. We demonstrate that KPT-6566 covalently binds to the catalytic site of PIN1. This interaction results in the release of a quinone-mimicking drug that generates reactive oxygen species and DNA damage, inducing cell death specifically in cancer cells. Accordingly, KPT-6566 treatment impairs PIN1-dependent cancer phenotypes in vitro and growth of lung metastasis in vivo.
Highlights
The prolyl isomerase PIN1, a critical modifier of multiple signalling pathways, is overexpressed in the majority of cancers and its activity strongly contributes to tumour initiation and progression
Phosphorylation of proteins at serine or threonine residues followed by proline (S/T-P) represents a common and central signal transduction mechanism in many oncogenic pathways and it is executed by a repertoire of proline-directed kinases, for example, Cyclin-dependent kinases, and Mitogen activated protein kinases, that fulfil key roles in controlling signal transduction
Among peptidyl-prolyl cis/trans isomerase (PPIase), PIN1 is the only enzyme able to efficiently bind proteins containing phosphorylated S/T-P sites[1]. Targeting of these motifs occurs in a modular fashion: PIN1 firstly binds them through its WW domain, and catalyses their cis/trans isomerization through its catalytic PPIase domain
Summary
Structure- and mechanism-based screening for PIN1 inhibitors. With the intent of isolating covalent inhibitors targeting the cysteine C113 residue of PIN1 catalytic core, we screened a drug like collection of 200,000 commercial compounds obtained from several drug repositories (Fig. 1a). The results show that, out of nine tested compounds, only KPT-6566 (1) inhibited the PPIase activity of PIN1 (Fig. 1b) and turned out to have an IC50 of 0.64 mM (Supplementary Table 2). RT-qPCR analyses of MDA-MB-231 cells treated with increasing concentrations of KPT-6566 showed a dose-dependent decrease in their expression levels (Fig. 3b). This effect was comparable to that observed upon PIN1 silencing (Supplementary Fig. 2d). Superimposable results were obtained with the prostate cancer cell line PC3 (Supplementary Fig. 3d–f) These data suggest that KPT-6566 impairs colony formation through specific PIN1 inhibition.
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