Small-molecule inhibitors targeting Polycomb repressive complex 1 RING domain.

Polycomb repressive complex 1 (PRC1) is an essential chromatin-modifying complex that monoubiquitinates histone H2A and is involved in maintaining the repressed chromatin state. Emerging evidence suggests PRC1 activity in various cancers, rationalizing the need for small-molecule inhibitors with well-defined mechanisms of action. Here, we describe the development of compounds that directly bind to RING1B-BMI1, the heterodimeric complex constituting the E3 ligase activity of PRC1. These compounds block the association of RING1B-BMI1 with chromatin and inhibit H2A ubiquitination. Structural studies demonstrate that these inhibitors bind to RING1B by inducing the formation of a hydrophobic pocket in the RING domain. Our PRC1 inhibitor, RB-3, decreases the global level of H2A ubiquitination and induces differentiation in leukemia cell lines and primary acute myeloid leukemia (AML) samples. In summary, we demonstrate that targeting the PRC1 RING domain with small molecules is feasible, and RB-3 represents a valuable chemical tool to study PRC1 biology.

Structure-Based Design of a Selective Class I Histone Deacetylase (HDAC) Near-Infrared (NIR) Probe for Epigenetic Regulation Detection in Triple-Negative Breast Cancer (TNBC).

Abnormally high levels of class I histone deacetylases (HDACs) are associated with triple-negative breast cancer (TNBC) proliferation, malignant transformation, and poor prognosis of patients. Herein, we report a near-infrared imaging probe for TNBC detection via visualizing class I HDACs. Conjugating Cy5.5 to a cyclic depsipeptide inhibitor, we obtained the probe (20-Cy5.5) that retained desirable class I HDAC affinity and selectivity. Then, this probe could visualize epigenetic changes by class I HDACs in TNBC MDA-MB-231 cells and in xenograft tumor models in real time. Treatment with suberoylanilide hydroxamic acid (SAHA) significantly reduced the uptake of the probe in tumors, suggesting its potential use in evaluation of therapeutic responses of HDACi-mediated therapy. Moreover, 20-Cy5.5 could detect class I HDAC expression in TNBC lung metastasis. This novel NIR probe that achieves tumor class I HDAC imaging not only leads to a better understanding of epigenetic regulation in tumors but also has great potential for improving the TNBC diagnosis and treatment.

Dual nicotinamide phosphoribosyltransferase and epidermal growth factor receptor inhibitors for the treatment of cancer.

Multitarget drugs have emerged as a promising treatment modality in modern anticancer therapy. Taking advantage of the synergy of NAMPT and EGFR inhibition, we have developed the first compounds that serve as dual inhibitors of NAMPT and EGFR. On the basis of CHS828 and erlotinib, a series of hybrid molecules were successfully designed and synthesized by merging of the pharmacophores. Among the compounds that were synthesized, compound 28 showed good NAMPT and EGFR inhibition, and excellent in vitro anti-proliferative activity. Compound 28, which is a new chemotype devoid of a Michael receptor, strongly inhibited the proliferation of several cancer cell lines, including H1975 non-small cell lung cancer cells harboring the EGFRL858R/T790M mutation. More importantly, it imparted significant in vivo antitumor efficacy in a human NSCLC (H1975) xenograft nude mouse model. This study provides promising leads for the development of novel antitumor agents and valuable pharmacological probes for the assessment of dual inhibition in NAMPT and EGFR pathway with a single inhibitor.

Discovery of class I histone deacetylase inhibitors based on romidpesin with promising selectivity for cancer cells.

Aim: Class I histone deacetylases (HDACs) are considered to be promising anticancer targets, but selective inhibition of class I HDAC isoforms remains a challenge. Methods & results: Previously, we obtained a selective class I HDAC inhibitor 9 based on a macrocyclic HDAC inhibitor Romidpesin. As our continuous efforts, a library of novel cyclicdepsipeptides based on 9 was established using a convergent synthesis strategy. The most active compounds 10, 16 and 19 selectively inhibit class I HDACs and exhibit promising nanomolar antiproliferative activities against several cancer cell lines with excellent selectivity toward cancer cells over normal cells. Besides, compound 10 demonstrates excellent antitumor effects in human prostate carcinoma PC3 xenograft models with no observed toxicity. Conclusion: These cyclicdepsipeptides show great therapeutic potential as novel anticancer agents for clinical translation.

Depletion of γ-catenin by Histone Deacetylase Inhibition Confers Elimination of CML Stem Cells in Combination with Imatinib.

Quiescent leukemia stem cells (LSCs) that are insensitive to BCR-ABL tyrosine kinase inhibitors confer resistance to imatinib in chronic myelogenous leukemia (CML). Identifying proteins to regulate survival and stemness of LSCs is urgently needed. Although histone deacetylase inhibitors (HDACis) can eliminate quiescent LSCs in CML, little is known about the underlying mechanism that HDACis kill LSCs. By fishing with a biotin-labeled probe, we identified that HDACi JSL-1 bound to the protein γ-catenin. γ-Catenin expression was higher in LSCs from CML patients than normal hematopoietic stem cells. Silencing γ-catenin in human CML CD34(+) bone-marrow (BM) cells sufficiently eliminated LSCs, which suggests that γ-catenin is required for survival of CML LSCs. Pharmacological inhibition of γ-catenin thwarted survival and self-renewal of human CML CD34(+) cells in vitro, and of murine LSCs in BCR-ABL-driven CML mice. γ-Catenin inhibition reduced long-term engraftment of human CML CD34(+) cells in NOD.Cg-Prkdc (scid) II2rg (tm1Sug)/JicCrl (NOG) mice. Silencing γ-catenin by shRNA in human primary CD34(+) cells did not alter ß-catenin, implying a ß-catenin-independent role of γ-catenin in survival and self-renewal of CML LSCs. Taken together, our findings validate that γ-catenin may be a novel therapeutic target of LSCs, and suppression of γ-catenin by HDACi may explain elimination of CML LSCs.

Discovery of Novel Class I Histone Deacetylase Inhibitors with Promising in Vitro and in Vivo Antitumor Activities.

A successful structure-based design of novel cyclic depsipeptides that selectively target class I HDAC isoforms is described. Compound 11 has an IC50 of 2.78 nM for binding to the HDAC1 protein, and the prodrugs 12 and 13 also exhibit promising antiproliferative activities in the nanomolar range against various cancer cell lines. Compounds 12 and 13 show more than 20-fold selectivity toward human cancer cells over human normal cells in comparison with romidepsin (FK228), demonstrating low probability of toxic side effects. In addition, compound 13 exhibits excellent in vivo anticancer activities in a human prostate carcinoma (Du145) xenograft model with no observed toxicity. Thus, prodrug 13 has therapeutic potential as a new class of anticancer agent for further clinical translation.

Unprecedented reactions: from epichlorohydrin to epoxyglycidyl substituted divinyl ether and its conversion into epoxyglycidyl propargyl ether.

The reaction of epichlorohydrin with concentrated sodium hydroxide in hexane under phase transfer conditions has surprisingly led to the formation of the symmetrical di(3-epoxyglycidyl-1-propenyl) ether 1 which contains both nucleophilic and electrophilic moieties. When it was reacted with n-butyllithium, intermediate 1 once again surprisingly generated epoxyglycidyl propargyl ether, which was further reacted in situ with a variety of benzaldehydes to furnish the corresponding substituted propargylic alcohols in good yields. While the reaction is operationally simple, it provides a powerful method for the synthesis of the important products from commodity materials such as epichlorohydrin. Moreover, these reactions may have revealed that some fundamental properties of the hydroxide anion in those once thought straightforward reactions are not well understood. A careful analysis of the experimental data suggests that an unprecedented concerted elimination of the epoxyglycidyl ether with sodium hydroxide may be operative and an alpha deprotonation followed by alpha elimination of the di(3-epoxyglycidyl-1-propenyl) ether with alkyllithium may have been involved.

Design, synthesis, and biological evaluation of 1, 3-disubstituted-pyrazole derivatives as new class I and IIb histone deacetylase inhibitors.

A novel series of HDAC inhibitors demonstrating class I and IIb subtype selectivity have been identified using a scaffold-hopping strategy. Several designed compounds showed better selectivity for class I and IIb over class IIa HDAC isoforms comparing to the FDA approved HDAC targeting drug SAHA. A representative lead compound 22 bearing a biphenyl moiety demonstrated promising class I and IIb HDAC isoforms selectivity and in vitro anticancer activities against several cancer cell lines. This work could serve as a fundamental platform for further exploration of selective HDAC inhibitors using designed molecular scaffold.

Total synthesis of securinega alkaloids (-)-norsecurinine, (-)-niruroidine and (-)-flueggine A.

A consecutive synthetic strategy was developed toward the total synthesis of securinega alkaloids. (-)-Norsecurinine was concisely assembled by addition of a methoxyallene to a ketone for efficient side-chain installation. Ring-closing metathesis was also utilized as a key step. The first total synthesis of (-)-niruroidine was achieved from (-)-norsecurinine in three steps, while the route to (-)-flueggine A featured a 1,3-dipolar cycloaddition to forge the core structure.

PQJS380: a novel lead compound to induce apoptosis in acute lymphoblastic leukemia cells.

Acute lymphoblastic leukemia (ALL) is a malignant disorder of lymphoid progenitor cells that are committed to the B- or the T-cell lineage. The pathogenesis of ALL is heterogeneous and may be at least in part caused by genetic alterations. Although the modern sequencing technologies make it possible to rapidly discover novel genetic and epigenetic alterations and molecular targets for therapeutic intervention for ALL, conventional chemotherapy is still the most important therapeutic approach. Relapses and high morbidity and mortality remain major challenges particularly in adult patients with ALL. Therefore, development of novel chemotherapeutic agents remains in demand for ALL patients. In the course of seeking novel agents against ALL, we screened a library of small molecules and identified that PQJS380, a S-(E)-4-([7S,10S]-4-ethyl-7-isopropyl-2,5,8,12-tetraoxo-9-oxa-3,6,13,18-tetraaza-bicycle[13,2,1] octadec-1-en-10-yl)but-3-enyl octanethioate, showed potent anti-leukemia activity. PQJS380 inhibited the proliferation with IC 50 values of 14.25 nM and 5 nM in REH and NALM-6 cells, respectively. PQJS380 had 10-fold higher molar potency than the front-line ALL drugs Ara-C and VP-16. The median IC 50 value for leukemia blast cells from 17 patients with ALL was 52 nM. PQJS380 induced G 1-phase arrest in REH cells, and S-phase in NALM-6 cells, respectively. Treatment of PQJS380 led to apoptosis in ALL cell lines (REH and NALM-6) and primary ALL cells. Our data supported that PQJS380 may be a promising lead compound for ALL treatment even though the precise targets remain to be elucidated.

Design, synthesis, and biological evaluation of novel histone deacetylase 1 inhibitors through click chemistry.

We report the design, synthesis, and biological evaluation of a new series of HDAC1 inhibitors using click chemistry. Compound 17 bearing a phenyl ring at meta-position was identified to show much better selectivity for HDAC1 over HDAC7 than SAHA. The compond 17 also showed better in vitro anticancer activities against several cancer cell lines than that of SAHA. This work could serve as a foundation for further exploration of selective HDAC inhibitors using the compound 17 molecular scaffold.

Biological evaluation of new largazole analogues: alteration of macrocyclic scaffold with click chemistry.

We report the design, synthesis, and biological evaluation of a new series of largazole analogues in which a 4-methylthiazoline moiety was replaced with a triazole and tetrazole ring, respectively. Compound 7 bearing a tetrazole ring was identified to show much better selectivity for HDAC1 over HDAC9 than largazole (10-fold). This work could serve as a foundation for further exploration of selective HDAC inhibitors using a largazole molecular scaffold.

Practical access to four stereoisomers of naftidrofuryl and their binding affinity towards 5-hydroxytryptamine 2A receptor.

Naftidrofuryl oxalate (Praxilene®, 1) has been used for the treatment of intermittent claudication for more than 30 years. It selectively blocks vascular and platelet 5-hydroxytryptamine 2 (5-HT(2)) receptors. This drug is marketed as a mixture of four stereoisomers, and so far there is no individual biological evaluation on the single isomers. The purpose of this study is to provide an improved method for the preparation of all four stereoisomers of naftidrofuryl, and more importantly, to distinguish them in terms of their binding affinity to 5-hydroxytryptamine 2A (5-HT(2A)) receptor. The bioassay results revealed that the C-2S configuration of naftidrofuryl was crucial for the binding affinity with 5-HT(2A) receptor, and the C-2' configuration was less important for binding. In conclusion, our study may pave the way to develop single naftidrofuryl isomers with C-2S configuration as inhibitors of 5-HT(2A) receptor that have clinical significance as vasodilators and CNS agents.