The nuclear export protein XPO1 is overexpressed in cancer, leading to the cytoplasmic mislocalization of multiple tumor suppressor proteins. Existing XPO1-targeting agents lack selectivity and have been associated with significant toxicity. Small molecule selective inhibitors of nuclear export (SINEs) were designed that specifically inhibit XPO1. Genetic experiments and X-ray structures demonstrate that SINE covalently bind to a cysteine residue in the cargo-binding groove of

The polyketide natural product Leptomycin B inhibits nuclear export mediated by the karyopherin protein chromosomal region maintenance 1 (CRM1). Here, we present 1.8-to 2.0-Å-resolution crystal structures of CRM1 bound to Leptomycin B and related inhibitors Anguinomycin A and Ratjadone A. Structural and complementary chemical analyses reveal an unexpected mechanism of inhibition involving covalent conjugation and CRM1-mediated hydrolysis of the natural products' lactone rings. Furthermore, mutagenesis reveals the mechanism of hydrolysis by CRM1. The nuclear export signal (NES)-binding groove of CRM1 is able to drive a chemical reaction in addition to binding protein cargos for transport through the nuclear pore complex.exportin-1 | Xpo-1 | lactone hydrolysis | Michael addition | KPT inhibitor

Drugs that target the chief mediator of nuclear export, chromosome region maintenance 1 protein (CRM1) have potential as therapeutics for leukemia, but existing CRM1 inhibitors show variable potencies and a broad range of cytotoxic effects. Here, we report the structural analysis and antileukemic activity of a new generation of small-molecule inhibitors of CRM1. Designated selective inhibitors of nuclear export (SINE), these compounds were developed using molecular modeling to screen a small virtual library of compounds against the nuclear export signal (NES) groove of CRM1. The 2.2-Å crystal structure of the CRM1-Ran-RanBP1 complex bound to KPT-251, a representative molecule of this class of inhibitors, shows that the drug occupies part of the groove in CRM1 that is usually occupied by the NES, but penetrates much deeper into the groove and blocks CRM1-directed protein export. SINE inhibitors exhibit potent antileukemic activity, inducing apoptosis at nanomolar concentrations in a panel of 14 human acute myeloid leukemia (AML) cell lines representing different molecular subtypes of the disease. When administered orally to immunodeficient mice engrafted with human AML cells, KPT-251 had potent antileukemic activity with negligible toxicity to normal hematopoietic cells. Thus, KPT-SINE CRM1 antagonists represent a novel class of drugs that warrant further testing in AML patients.

Impairment of the formation or action of hydrogen sulfide (H 2 S), an endogenous gasotransmitter, is associated with various diseases, such as hypertension, diabetes mellitus, septic and hemorrhagic shock, and pancreatitis. Cystathionine ␤-synthase and cystathionine ␥-lyase (CSE) are two pyridoxal-5-phosphate (PLP)-dependent enzymes largely responsible for the production of H 2 S in mammals. Inhibition of CSE by DL-propargylglycine (PAG) has been shown to alleviate disease symptoms. Here we report crystal structures of human CSE (hCSE), in apo form, and in complex with PLP and PLP⅐PAG. Structural characterization, combined with biophysical and biochemical studies, provides new insights into the inhibition mechanism of hCSEmediated production of H 2 S. Transition from the open form of apo-hCSE to the closed PLP-bound form reveals large conformational changes hitherto not reported. In addition, PAG binds hCSE via a unique binding mode, not observed in PAG-enzyme complexes previously. The interaction of PAG-hCSE was not predicted based on existing information from known PAG complexes. The structure of hCSE⅐PLP⅐PAG complex highlights the particular importance of Tyr 114 in hCSE and the mechanism of PAG-dependent inhibition of hCSE. These results provide significant insights, which will facilitate the structure-based design of novel inhibitors of hCSE to aid in the development of therapies for diseases involving disorders of sulfur metabolism.

Treating cancer through inhibition of nuclear export is one of the best examples of basic research translation into clinical application. Nuclear export factor chromosomal region maintenance 1 (CRM1; Xpo1 and exportin-1) controls cellular localization and function of numerous proteins that are critical for the development of many cancer hallmarks. The diverse actions of CRM1 are likely to explain the broad ranging anti-cancer potency of CRM1 inhibitors observed in pre-clinical studies and/or clinical trials (phase I–III) on both advanced-stage solid and hematological tumors. In this review, we compare and contrast the mechanisms of action of different CRM1 inhibitors, and discuss the potential benefit of unexplored non-covalent CRM1 inhibitors. This emerging field has uncovered that nuclear export inhibition is well poised as an attractive target towards low-toxicity broad-spectrum potent anti-cancer therapy.