Theodosia Teo

MAP kinase-interacting kinases--emerging targets against cancer.

Mitogen-activated protein kinase (MAPK)-interacting kinases (Mnks) regulate the initiation of translation through phosphorylation of eukaryotic initiation factor 4E (eIF4E). Mnk-mediated eIF4E activation promotes cancer development and progression. While the phosphorylation of eIF4E is necessary for oncogenic transformation, the kinase activity of Mnks seems dispensable for normal development. For this reason, pharmacological inhibition of Mnks could represent an ideal mechanism-based and nontoxic therapeutic strategy for cancer treatment. In this review, we discuss the current understanding of Mnk biological roles, structures, and functions, as well as clinical implications. Importantly, we propose different strategies for identification of highly selective small molecule inhibitors of Mnks, including exploring a structural feature of their kinase domain, DFD motif, which is unique within the human kinome. We also argue that a combined targeting of Mnks and other pathways should be considered given the complexity of cancer.

Discovery of 5‐(2‐(Phenylamino)pyrimidin‐4‐yl)thiazol‐2(3H)‐one Derivatives as Potent Mnk2 Inhibitors: Synthesis, SAR Analysis and Biological Evaluation

Phosphorylation of eIF4E by human mitogen‐activated protein kinase (MAPK)‐interacting kinases (Mnks) is crucial for human tumourigenesis and development. Targeting Mnks may provide a novel anticancer therapeutic strategy. However, the lack of selective Mnk inhibitors has so far hampered pharmacological target validation and clinical drug development. Herein, we report, for the first time, the discovery of a series of 5‐(2‐(phenylamino)pyrimidin‐4‐yl)thiazole‐2(3H)‐one derivatives as Mnk inhibitors. Several derivatives demonstrate very potent Mnk2 inhibitory activity. The most active and selective compounds were tested against a panel of cancer cell lines, and the results confirm the cell‐type‐specific effect of these Mnk inhibitors. Detailed cellular mechanistic studies reveal that Mnk inhibitors are capable of reducing the expression level of anti‐apoptotic protein Mcl‐1, and of promoting apoptosis in MV4‐11 acute myeloid leukaemia cells.

Pharmacologic co-inhibition of Mnks and mTORC1 synergistically suppresses proliferation and perturbs cell cycle progression in blast crisis-chronic myeloid leukemia cells

The Ras/Raf/MAPK and PI3K/Akt/mTORC1 cascades are two most aberrantly regulated pathways in cancers. As MAPK-interacting kinases (Mnks) are part of the convergent node of these two pathways, and play a pivotal role in cellular transformation, targeting Mnks has emerged as a potential therapeutic strategy. Herein, a dual-specific Mnk1/2 inhibitor MNKI-57 and a potent Mnk2-specific inhibitor MNKI-4 were selected for a panel screen against 28 human cancer cell lines. The study reveals that MNKI-57 and MNKI-4 are most potent against leukemia cells KYO-1 (i.e. BC-CML) and KG-1 (i.e. AML). Interestingly, we found that sensitivity of selected leukemia cells to Mnk inhibitors is correlated with the level of phosphorylated 4E-BP1 at Thr70. The anti-proliferative effects of Mnk inhibitors are cytostatic in the sensitive KYO-1 cells, inducing significant G1 arrest via down-regulation of cyclin D1 expression. In KYO-1 cells where Akt is not constitutively active, Mnk inhibitors increase the sensitivity of cells to rapamycin, resulting in a more pronounced anti-proliferative activity. Remarkably, the synergistic anti-proliferative effects are associated with a marked de-phosphorylation of 4E-BP1 at Thr70. Collectively, these data highlight the importance of 4E-BP1 as a key integrator in the MAPK and mTORC1 cascades, and suggest that a combined pharmacologic inhibition of mTORC1 and Mnk kinases offers an innovative therapeutic opportunity in BC-CML.

Identification of a Novel Oligomerization Disrupting Mutation in CRYΑA Associated with Congenital Cataract in a South Australian Family

Congenital cataract is a heterogeneous disorder causing severe visual impairment in affected children. We screened four South Australian families with autosomal dominant congenital cataract for mutations in 10 crystallin genes known to cause congenital cataract. We identified a novel segregating heterozygous mutation, c.62G>A (p.R21Q), in the CRYΑA gene in one family. Western blotting of proteins freshly extracted from cataractous lens material of the proband demonstrated a marked reduction in the amount of the high‐molecular‐weight oligomers seen in the lens material of an unaffected individual. We conclude that the p.R21Q mutation, which is located in the highly conserved and structurally significant N‐terminal region of the protein, is responsible for the cataract phenotype observed in the family as this mutation likely reduces the formation of the functional oligomeric alpha‐crystallin.

Discovery of 4-(dihydropyridinon-3-yl)amino-5-methylthieno[2,3-d]pyrimidine derivatives as potent Mnk inhibitors: synthesis, structure-activity relationship analysis and biological evaluation.

Phosphorylation of the eukaryotic initiation factor 4E (eIF4E) by mitogen-activated protein kinase (MAPK)-interacting kinases (Mnks) is essential for oncogenesis but unnecessary for normal development. Thus, pharmacological inhibition of Mnks may offer an effective and non-toxic anti-cancer therapeutic strategy. Herein, we report the discovery of 4-(dihydropyridinon-3-yl)amino-5-methylthieno[2,3-d]pyrimidine derivatives as potent Mnk inhibitors. Docking study of 7a in Mnk2 suggests that the compound is stabilised in the ATP binding site through multiple hydrogen bonds and hydrophobic interaction. Cellular mechanistic studies on MV-4-11 cells with leads 7a, 8e and 8f reveal that they are able to down-regulate the phosphorylated eIF4E, Mcl-1 and cyclin D1, and induce apoptosis.

Pharmacologic Inhibition of MNKs in Acute Myeloid Leukemia

The Ras/Raf/MAPK and PI3K/Akt/mTOR pathways are key signaling cascades involved in the regulation of cell proliferation and survival, and have been implicated in the pathogenesis of several types of cancers, including acute myeloid leukemia (AML). The oncogenic activity of eIF4E driven by the Mnk kinases is a convergent determinant of the two cascades, suggesting that targeting the Mnk/eIF4E axis may provide therapeutic opportunity for the treatment of cancer. Herein, a potent and selective Mnk2 inhibitor (MNKI-85) and a dual-specific Mnk1 and Mnk2 inhibitor (MNKI-19), both derived from a thienopyrimidinyl chemotype, were selected to explore their antileukemic properties. MNKI-19 and MNKI-85 are effective in inhibiting the growth of AML cells that possess an M5 subtype with FLT3-internal tandem duplication mutation. Further mechanistic studies show that the downstream effects with respect to the selective Mnk1/2 kinase inhibition in AML cells causes G1 cell cycle arrest followed by induction of apoptosis. MNKI-19 and MNKI-85 demonstrate similar Mnk2 kinase activity and cellular antiproliferative activity but exhibit different time-dependent effects on cell cycle progression and apoptosis. Collectively, this study shows that pharmacologic inhibition of both Mnk1 and Mnk2 can result in a more pronounced cellular response than targeting Mnk2 alone. However, MNKI-85, a first-in-class inhibitor of Mnk2, can be used as a powerful pharmacologic tool in studying the Mnk2/eIF4E-mediated tumorigenic mechanism. In conclusion, this study provides a better understanding of the mechanism underlying the inhibition of AML cell growth by Mnk inhibitors and suggests their potential utility as a therapeutic agent for AML.

An integrated approach for discovery of highly potent and selective Mnk inhibitors: Screening, synthesis and SAR analysis.

Deregulation of protein synthesis is a common event in cancer. As MAPK-interacting kinases (Mnks) play critical roles in regulation of protein synthesis, they have emerged as novel anti-cancer targets. Mnks phosphorylate eukaryotic initiation factor 4E (eIF4E) and promote eIF4E-mediated oncogenic activity. Given that the kinase activity of Mnks is essential for oncogenesis but is dispensable for normal development, the discovery of potent and selective pharmacological Mnk inhibitors provides pharmacological target validation and offers a new strategy for cancer treatment. Herein, comprehensive in silico screening approaches were deployed, and three thieno[2,3-d]pyrimidine and pyrazolo[3,4-d]pyrimidine derivatives were identified as hit compounds. Further chemical modification of thieno[2,3-d]pyrimidine derivative 3 has given rise to a series of highly potent Mnk2 inhibitors that could be potential leads for the treatment of acute myeloid leukemia.

Discovery of (E)-3-((styrylsulfonyl)methyl)pyridine and (E)-2-((styrylsulfonyl)methyl)pyridine derivatives as anticancer agents: synthesis, structure-activity relationships, and biological activities.

ON01910.Na is a highly effective anticancer agent that induces mitotic arrest and apoptosis. Clinical studies with ON01910 in cancer patients have shown efficacy along with an impressive safety profile. While ON01910 is highly active against cancer cells, it has a low oral availability and requires continuous intravenous infusion or multiple gram doses to ensure sufficient drug exposure for biological activity in patients. We have identified two novel series of styrylsulfonyl-methylpyridines. Lead compounds 8, 9a, 18 and 19a are highly potent mitotic inhibitors and selectively cytotoxic to cancer cells. Impressively, these compounds possess excellent pharmaceutical properties and two lead drug candidates 9a and 18 demonstrated antitumor activities in animal models.

Insights into the Importance of DFD-Motif and Insertion I1 in Stabilizing the DFD-Out Conformation of Mnk2 Kinase.

Human mitogen-activated protein kinases (MAPK)-interacting kinases 1 and 2 (Mnk1/2) are promising anticancer targets. Mnks possess special insertions and a DFD-motif that are distinct from other kinases. Crystallographic studies of Mnk1/2 have revealed that the DFD-motif adopts the DFG/D-out conformation in which residue F227 flips into the ATP binding pocket. This is rarely observed in other kinases. Although the DFG-out conformation has attracted great interest for designing selective inhibitors, structural requirements for binding and the mechanism governing the DFG-out conformation remain unclear. This work presents for the first time the applicability of 3D models of Mnk2 protein in studying conformational changes by utilizing homology modeling and molecular dynamics simulations. The study reveals that the interactions between residue K234 of insertion I1 and D226 of the DFD motif play a key role in inducing and stabilizing the DFD-out conformation. The structural features will aid in the rational design of Mnk2 inhibitors.

Highly Potent, Selective, and Orally Bioavailable 4-Thiazol-N-(pyridin-2-yl)pyrimidin-2-amine Cyclin-Dependent Kinases 4 and 6 Inhibitors as Anticancer Drug Candidates: Design, Synthesis, and Evaluation

Cyclin D dependent kinases (CDK4 and CDK6) regulate entry into S phase of the cell cycle and are validated targets for anticancer drug discovery. Herein we detail the discovery of a novel series of 4-thiazol-N-(pyridin-2-yl)pyrimidin-2-amine derivatives as highly potent and selective inhibitors of CDK4 and CDK6. Medicinal chemistry optimization resulted in 83, an orally bioavailable inhibitor molecule with remarkable selectivity. Repeated oral administration of 83 caused marked inhibition of tumor growth in MV4-11 acute myeloid leukemia mouse xenografts without having a negative effect on body weight and showing any sign of clinical toxicity. The data merit 83 as a clinical development candidate.