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PDF file - 841K, Supplementary Figures S1-S6; legends for Supplementary Tables S1-S3; Supplementary Methods describing RNA interference, generation of Ba/F3 cell lines, site-directed mutagenesis, transient transfection, inhibition of cellular ATP production, proliferation assays, enzymatic assays with JAK2 JH1, purification of tyrosine phosporylated peptides and mass-spectrometry; Supplementary References.

PDF file - 11K, Activity of NVP-BBT594 in biochemical and cell-based assays. The IC50 (mean of two experiments) of NVP-BBT594 on the JAK2 kinase was determined in a biochemical kinase assay with the active enzyme. Half-maximal growth inhibition (GI50,) of NVP-BBT594 was determined in SET-2, CMK and K-562 cell lines (mean � SD, n = 4).

The histone 3 lysine 79 (H3K79) methyltransferase (HMT) DOT1L is known to play a critical role for growth and survival of MLL-rearranged leukemia. Serendipitous observations during high-throughput drug screens indicated that the use of DOT1L inhibitors might be expandable to multiple myeloma (MM). Through pharmacologic and genetic experiments, we could validate that DOT1L is essential for growth and viability of a subset of MM cell lines, in line with a recent report from another team. In vivo activity against established MM xenografts was observed with a novel DOT1L inhibitor. In order to understand the molecular mechanism of the dependency in MM, we examined gene expression changes upon DOT1L inhibition in sensitive and insensitive cell lines and discovered that genes belonging to the endoplasmic reticulum (ER) stress pathway and protein synthesis machinery were specifically suppressed in sensitive cells. Whole-genome CRISPR screens in the presence or absence of a DOT1L inhibitor revealed that concomitant targeting of the H3K4me3 methyltransferase SETD1B increases the effect of DOT1L inhibition. Our results provide a strong basis for further investigating DOT1L and SETD1B as targets in MM.

In MLL-rearranged cancer cells, disruptor of telomeric silencing 1-like protein (DOT1L) is aberrantly recruited to ectopic loci leading to local hypermethylation of H3K79 and consequently misexpression of leukemogenic genes. A structure-guided optimization of a HTS hit led to the discovery of DOT1L inhibitors with subnanomolar potency, allowing testing of the therapeutic principle of DOT1L inhibition in a preclinical mouse tumor xenograft model. Compounds displaying good exposure in mouse and nanomolar inhibition of target gene expression in cells were obtained and tested in vivo.

Publisher's Note: There is a Blood Commentary on this article in this issue.

Misdirected catalytic activity of histone methyltransferase Dot1L is believed to be causative for a subset of highly aggressive acute leukemias. Targeting the catalytic domain of Dot1L represents a potential therapeutic approach for these leukemias. In the context of a comprehensive Dot1L hit finding strategy, a knowledge-based virtual screen of the Dot1L SAM binding pocket led to the discovery of 2, a non-nucleoside fragment mimicking key interactions of SAM bound to Dot1L. Fragment linking of 2 and 3, an induced back pocket binder identified in earlier studies, followed by careful ligand optimization led to the identification of 7, a highly potent, selective and structurally novel Dot1L inhibitor.

[Image: see text] In MLL-rearranged cancer cells, disruptor of telomeric silencing 1-like protein (DOT1L) is aberrantly recruited to ectopic loci leading to local hypermethylation of H3K79 and consequently misexpression of leukemogenic genes. A structure-guided optimization of a HTS hit led to the discovery of DOT1L inhibitors with subnanomolar potency, allowing testing of the therapeutic principle of DOT1L inhibition in a preclinical mouse tumor xenograft model. Compounds displaying good exposure in mouse and nanomolar inhibition of target gene expression in cells were obtained and tested in vivo.

Mixed lineage leukemia (MLL) gene rearrangement induces leukemic transformation by ectopic recruitment of disruptor of telomeric silencing 1-like protein (DOT1L), a lysine histone methyltransferase, leading to local hypermethylation of H3K79 and misexpression of genes (including HoxA), which drive the leukemic phenotype. A weak fragment-based screening hit identified by SPR was cocrystallized with DOT1L and optimized using structure-based ligand optimization to yield compound 8 (IC50 = 14 nM). This series of inhibitors is structurally not related to cofactor SAM and is not interacting within the SAM binding pocket but induces a pocket adjacent to the SAM binding site.

Oncogenic MLL fusion proteins aberrantly recruit Dot1L, a histone methyltransferase, to ectopic loci, leading to local hypermethylation of H3K79 and misexpression of HoxA genes driving MLL-rearranged leukemias. Inhibition of the methyltransferase activity of Dot1L in this setting is predicted to reverse aberrant H3K79 methylation, leading to repression of leukemogenic genes and tumor growth inhibition. In the context of our Dot1L drug discovery program, high-throughput screening led to the identification of 2, a weak Dot1L inhibitor with an unprecedented, induced pocket binding mode. A medicinal chemistry campaign, strongly guided by structure-based consideration and ligand-based morphing, enabled the discovery of 12 and 13, potent, selective, and structurally completely novel Dot1L inhibitors.

Rearrangements in the mixed lineage leukemia (MLL) gene define a distinct, aggressive form of acute leukemia with poor prognosis. The MLL gene encodes for a SET domain histone methyl transferase that catalyzes the methylation of histone 3 lysine 4 (H3K4) at specific gene loci, thus regulating transcription of developmental genes including HOX genes. In disease-linked translocations, the catalytic SET domain is lost and the remaining part fused to a variety of partners, e.g. AF4, AF9, AF10 and ENL. These MLL fusion proteins directly interact with disruptor of telomeric silencing 1-like protein (DOT1L), the only known H3K79 methyltransferase. The H3K79me2 mark is broadly associated with active transcription. Mislocated enzymatic activity of DOT1L causes local H3K79 hypermethylation, misexpression of leukomogenic genes, e.g. HOXA9 and MEIS1, and the aberrant maintenance of a stem cell-like state. Current treatment options of MLL are limited to chemotherapy and allogeneic hematopoietic stem cell transplantation, and outcomes remain poor. The first and only clinical DOT1L inhibitor Pinometostat (EPZ-5676), an S-Adenosyl Methionine (SAM) competitive inhibitor, showed only modest activity and emerging resistance in adult acute leukemia. Pinometostat is no oral drug, but requires administration as continuous infusion to achieve sufficient exposure and sustained target inhibition. So far, there is no approved DOT1L inhibitor and the need remains to develop effective DOT1L inhibitors. We report the identification of new SAM-competitive, structurally SAM-unrelated DOT1L inhibitors with subnanomolar biochemical potency. Compounds with nanomolar cellular activity and good exposure in mouse were tested in tumor xenograft models. Compounds 8 and 9 showed excellent blood exposure after a single dose. However, repeated dosing led to reduced exposure due to cytochrome P450 (Cyp450) 3A4 induction, insufficient pharmacodynamics (PD) and lack of efficacy. Further modification resulted in compound 10 that could be administered orally and was stable upon repeated dosing. A 300 mg/kg dose covered efficacious blood exposure for 24 h, but was not tolerated by tumor-bearing mice. Unfortunately, a 6-fold reduced dose did not achieve sufficient PD modulation and efficacy. Additional activities led to compound 11, which lost its oral bioavailability and had to be administered subcutaneously. Nevertheless, compound 11 achieved tumor growth inhibition in the MV4-11 and Molm-13 xenograft models in mice. In conclusion, we progressed in making DOT1L inhibitors with improved PK properties, but further optimization is required to generate a viable clinical candidate. The limited efficacy obtained with compound 11 and lack of efficacy observed with subcutaneous administration of EPZ-5676 around the maximally tolerated dose illustrate the difficulty to achieve a sustained level of DOT1L inhibitor in vivo to suppress DOT1L activity sufficiently. Furthermore, H3K79me2 and efficacy in vivo seem disconnected. Citation Format: Andreas Weiss, Frederic Stauffer, Clemens Clemens, Henrik Möbitz, Christian Ragot, Kim S. Beyer, Keith Calkins, Claudio Thoma, Daniel Guthy, Michael Kiffe, Bernard Van Eerdenbrugh, William R. Sellers, Francesco Hofmann, Ralph Tiedt, Christoph Gaul. A new DOT1L inhibitor with in vivo activity in mouse models of MLL-translocated leukemia [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1770.

SummaryAlthough clinically tested JAK inhibitors reduce splenomegaly and systemic symptoms, molecular responses are not observed in most myeloproliferative neoplasm (MPN) patients. We previously demonstrated that MPN cells become persistent to type I JAK inhibitors that bind the active conformation of JAK2. We investigated whether CHZ868, a type II JAK inhibitor, would demonstrate activity in JAK inhibitor persistent cells, murine MPN models, and MPN patient samples. JAK2 and MPL mutant cell lines were sensitive to CHZ868, including type I JAK inhibitor persistent cells. CHZ868 showed significant activity in murine MPN models and induced reductions in mutant allele burden not observed with type I JAK inhibitors. These data demonstrate that type II JAK inhibition is a viable therapeutic approach for MPN patients.

A number of N-acryloyl-, N-crotonoyl-, N-(3,3,3-trifluorocrotonoyl)-, N-cinnamoyl-, and N-(3-nitroacryloyl)-4-isopropyl- or -4-phenyl-oxazolidin-2-ones with geminal diphenyl substitution, i.e., 7–15, have been prepared and used for conjugate additions of organocuprate reagents (Me, iPr, Ph, 4-MeOPh) in the β-carbonyl (Table 2) and in the α-carbonyl position (NO2-derivative 11 in Scheme 3). The yields and diastereoselectivities are compared with previously tested enoyl-oxazolidinones (Table 2). Highest diastereoselectivities (>90%) are always observed with the 4-Ph derivatives (Hruby effect). Nitroacryloyl-oxazolidinones and a corresponding phenylmenthol ester undergo less diastereoselective additions (Scheme 3). A 3-(1-methylethyl)-5,5-diphenyloxazolidin-2-one (DIOZ)-derived Li2-enolate-nitronate was also tested for α-carbonyl alkylation (Scheme 4). The X-ray crystal structures of three acryloyl-oxazolidinones and of four adducts are described (Tables 1 and 3), and they serve for configurational assignments and description of the stereochemical courses of the additions and alkylation. Possible applications of the nitro compounds for the preparation of β2-amino acids are discussed (Scheme 2).

Janus kinase (JAK) inhibitors are being developed for the treatment of rheumatoid arthritis, psoriasis, myeloproliferative neoplasms, and leukemias. Most of these drugs target the ATP-binding pocket and stabilize the active conformation of the JAK kinases. This type I binding mode can lead to an increase in JAK activation loop phosphorylation, despite blockade of kinase function. Here we report that stabilizing the inactive state via type II inhibition acts in the opposite manner, leading to a loss of activation loop phosphorylation. We used X-ray crystallography to corroborate the binding mode and report for the first time the crystal structure of the JAK2 kinase domain in an inactive conformation. Importantly, JAK inhibitor–induced activation loop phosphorylation requires receptor interaction, as well as intact kinase and pseudokinase domains. Hence, depending on the respective conformation stabilized by a JAK inhibitor, hyperphosphorylation of the activation loop may or may not be elicited. Significance: This study shows that JAK inhibitors can lead to an increase of activation loop phosphorylation in a manner that is binding mode dependent. Our results highlight the need for detailed understanding of inhibitor mechanism of action, and that it may be possible to devise strategies that avoid target priming using alternative modes of inhibiting JAK kinase activity for the treatment of JAK-dependent diseases. Cancer Discov; 2(6); 512–23. © 2012 AACR. This article is highlighted in the In This Issue feature, p. 473

Hsp90 inhibition in B cell acute lymphoblastic leukemia overcomes resistance to JAK2 inhibitors., Enzymatic inhibitors of Janus kinase 2 (JAK2) are in clinical development for the treatment of myeloproliferative neoplasms (MPNs), B cell acute lymphoblastic leukemia (B-ALL) with rearrangements of the cytokine receptor subunit cytokine receptor–like factor 2 (CRLF2), and other tumors with constitutive JAK2 signaling. In this study, we identify G935R, Y931C, and E864K mutations within the JAK2 kinase domain that confer resistance across a panel of JAK inhibitors, whether present in cis with JAK2 V617F (observed in MPNs) or JAK2 R683G (observed in B-ALL). G935R, Y931C, and E864K do not reduce the sensitivity of JAK2-dependent cells to inhibitors of heat shock protein 90 (HSP90), which promote the degradation of both wild-type and mutant JAK2. HSP90 inhibitors were 100–1,000-fold more potent against CRLF2-rearranged B-ALL cells, which correlated with JAK2 degradation and more extensive blockade of JAK2/STAT5, MAP kinase, and AKT signaling. In addition, the HSP90 inhibitor AUY922 prolonged survival of mice xenografted with primary human CRLF2-rearranged B-ALL further than an enzymatic JAK2 inhibitor. Thus, HSP90 is a promising therapeutic target in JAK2-driven cancers, including those with genetic resistance to JAK enzymatic inhibitors.

Tumor metastasis is the most common cause of death in cancer patients. Here, we show that two, fully synthetic migrastatin analogues, core macroketone and core macrolactam, are potent inhibitors of metastasis in a murine breast tumor model. Administration of these readily accessible compounds nearly completely inhibits lung metastasis of highly metastatic mammary carcinoma cells. Treatment of tumor cells with core macroketone and core macrolactam blocks Rac activation, lamellipodia formation, and cell migration, suggesting that these chemical compounds interfere with the invasion step of the metastatic process. These compounds also inhibit the migration of human metastatic breast cancer cells, prostate cancer cells, and colon cancer cells but not normal mammary-gland epithelial cells, fibroblasts, and leukocytes. These data demonstrate that the macroketone and macrolactam core structures are specific small-molecule inhibitors of tumor metastasis. These compounds or their analogues could potentially be used in cancer-therapy strategies.

We have previously used trisubstituted cyclopropanes as peptide replacements to induce conformational constraints in known pseudopeptide inhibitors of a number of important enzymes. Cyclopropane-derived peptide mimics are novel in that they are among the few replacements that locally orient the peptide backbone and the amino acid side chain in a predefined manner. Although these dipeptide isosteres have been employed to orient amino acid side chains mimicking the gauche(-) conformation of chi(1)-space, their ability to project the side chains into an anti orientation has not been evaluated. As a first step toward this goal, the conformationally constrained pseudopeptides 8 and 10 and their corresponding flexible analogues 9 and 11 were prepared and tested as inhibitors of matrix metalloproteinases (MMPs). These compounds are analogues of 4 and 5, which were known to be potent MMP inhibitors. The anti orientations of the isopropyl side chain in 8 and the aromatic ring in 10 relative to the peptide backbone substituents on the cyclopropane were predicted to correspond to the known orientations of the P1' and P2' side chains of 5 when bound to MMPs. Hence, 8 and 10 were designed explicitly to probe topological features of the S1' or the S2' binding pockets of the MMPs. They were also designed to explore the importance of the P1'-P2' amide group, which is known to form highly conserved hydrogen bonds in several MMP-inhibitor complexes, and the viability of introducing a retro amide linkage between P2' and P3'. Pseudopeptides 8 and 9 were found to be weak competitive inhibitors of a series of MMPs. Any entropically favorable conformational constraints that were induced by the cyclopropane in 8 were thus overwhelmed by the loss of the hydrogen bonding capability associated with the P1'-P2' amide group. On the other hand, compounds 10 and 11, which contain a P2'-P3' retro amide group, were modest competitive inhibitors of a series of MMPs. The results obtained for 10 and 11 suggest that there may be a loss of hydrogen bonding capability associated with introducing the P2'-P3' retro amide group. However, because the conformationally constrained pseudopeptide 10 was significantly more potent than its flexible analogue 11, trisubstituted cyclopropanes related to 3 may serve as useful rigid dipeptide replacements in some biologically active pseudopeptides.

The identification of JAK2 mutations in patients with myeloproliferative neoplasms (MPN) led to the clinical development of JAK2 inhibitors, and the JAK1/2 inhibitor ruxolitinib has been approved for the treatment of myelofibrosis (MF). Although clinically tested JAK inhibitors improve MPN-associated splenomegaly and systemic symptoms, they do not significantly reduce the MPN clone in most MPN patients.We previously demonstrated that MPN cells can acquire persistence to ruxolitinib and other type I JAK inhibitors which bind the active conformation of JAK2, and that JAK2 inhibitor persistence is associated with reactivation of JAK-STAT signaling and with heterodimerization between activated JAK2 and JAK1/TYK2, consistent with activation of JAK2 in trans by other JAK kinases. We have now extended our studies to other type I JAK inhibitors in clinical development, including CYT387, BMS911543 and SAR302503. In each case we see the same mechanism of persistence as observed with ruxolitinib, with transactivation of JAK2 by other JAK kinases. Most importantly, we found that MPN cells which were persistent to one JAK inhibitor were insensitive to the other JAK inhibitors, suggesting that the mechanisms which limit overall efficacy of ruxolitinib will limit the efficacy of other JAK inhibitors in clinical development. All JAK inhibitors in clinical development are type I inhibitors that interact with and inhibit the active confirmation of the JAK2 kinase. We hypothesized that novel, type II JAK inhibitors that interact with and inhibit JAK2 in the inactive conformation might retain activity in JAK inhibitor persistent cells and show increased efficacy in murine MPN models. We therefore characterized the efficacy of NVP-CHZ868, a novel type II JAK inhibitor, in MPN cells and in murine MPN models. CHZ868 potently inhibited proliferation of cells expressing the JAK2V617F mutation or the TEL-JAK2 fusion. We found that JAK2/MPL-mutant cell lines were universally sensitive to NVP-CHZ868. CHZ868 treatment of JAK2-mutant SET2 cells induced a higher degree of apoptosis compared to ruxolitinib. Signaling studies demonstrated that CHZ868 more potently attenuated JAK-STAT signaling in JAK2/MPL-mutant cells, with suppression of JAK2 phosphorylation consistent with a type II mechanism of kinase inhibition. We next investigated the ability of CHZ868 to inhibit the proliferation and signaling of MPN cells that had acquired persistence to type I JAK inhibitors. Type II inhibition with CHZ868 completely suppressed JAK-STAT signaling in type I JAK inhibitor-persistent cells, and prevented heterodimeric activation of JAK2 by JAK1 and TYK2. Most importantly, JAK2/MPL-mutant cells which were insensitive to type I JAK inhibitors remained highly sensitive to CHZ868, demonstrating that type I JAK inhibitor persistence does not confer resistance to type II inhibitors. We next evaluated the efficacy of CHZ868 in murine models of JAK2/MPL-mutant MPN. CHZ868 showed significant activity in conditional knock-in and bone marrow transplant (BMT) models of Jak2V617F-induced polycythemia vera, with normalization of hematocrit, reversal of stem/progenitor expansion, normalization of splenomegaly/splenic architecture, and reversal of bone marrow fibrosis. CHZ868 demonstrated similar activity in the MPLW515L BMT model of MF, with normalization of blood counts, stem/progenitor expansion, spleen weights, and extramedullary hematopoiesis in vivo. Most importantly, CHZ868 resulted in significant reductions of mutant allele burden (mean allele burden reduction 49%) in the Jak2V617F model. We observed analogous reductions in allele burden in the Jak2V617F and MPLW515L BMT models, consistent with disease modifying activity. Taken together, our data demonstrate that a spectrum of type I JAK inhibitors induce JAK inhibitor persistence, by a similar mechanism of JAK2 transactivation as observed with ruxolitinib. By contrast, type II JAK inhibition with CHZ868 remains highly active in JAK inhibitor persistent cells, and shows increased activity in murine MPN models. These data demonstrate that novel JAK inhibitors can increase target inhibition and therapeutic efficacy and should be pursued as an approach to improve outcomes for MPN patients. Figure 1 Figure 1. Figure 2 Figure 2. Disclosures Koppikar: Amgen: Employment. Sellers:Novartis: Employment. Hofmann:Novartis: Employment. Baffert:Novartis: Employment. Gaul:Novartis: Employment. Radimerski:Novartis: Employment. Levine:Novartis: Consultancy, Grant support Other.

Approximately 10% of B-ALLs harbor CRLF2 rearrangements, which may portend a poor prognosis. Although these leukemias are addicted to JAK2 signaling, ATP-competitive type I JAK2 inhibitors have limited activity in vitro or in vivo (Weigert et al. J Exp Med 2012). This may result from heterodimerization of JAK2 with other JAK family members (Koppikar et al. Nature 2012). Type II inhibitors bind JAK2 in the inactive conformation, which may overcome this resistance. When assayed in MHH-CALL4 cells harboring a CRLF2/IGH rearrangement and JAK2 I682F mutation, the type II JAK2 inhibitors NVP-BBT594 and NVP-CHZ868 were 10-35-fold more potent than the type I JAK2 inhibitors NVP-BSK805 and NVP-BVB808. Similarly, in Ba/F3 cells dependent on CRLF2 and the gain-of-function allele JAK2 R683G, the IC50 for CHZ868 was 5-20-fold lower than the IC50s for BSK805 and BVB808. Unlike type I inhibitors, which induce paradoxical hyperphosphorylation of JAK2, CHZ868 completely blocks JAK2 and STAT5 phosphorylation. In addition, the JAK2 Y931C allele that confers 4-6-fold resistance to BSK805 and BVB808 did not alter sensitivity to CHZ868. CHZ868 abrogates STAT5 phosphorylation in Ba/F3 cells expressing CRLF2 with JAK2 R683G/Y931C while BVB808 does not. CHZ868 is the first type II JAK2 inhibitor amenable to in vivo use. We assessed its efficacy in mice transplanted with transgenic (CRLF2/JAK2 R683G/Cdkn2a-/- or CRLF2/JAK2 R683G/Pax5+/-/Ts1Rhr) or primary human CRLF2-rearranged B-ALLs. Splenocytes from patient-derived xenografts (PDXs) treated with CHZ868 in vivo for 3 days are more primed for apoptosis as demonstrated by a 2-6-fold EC50 reduction for PUMA permeabilizing activity compared to vehicle. Transcriptional profiling of splenocytes from CHZ868-treated PDXs revealed downregulation of critical survival pathways including E2F1, STAT3, and AKT-mediated signaling. Of note, 2 of the most downregulated genes are STAT targets, PIM1 and Myc. Mice treated for 5-6 days with CHZ868 had significant reductions in spleen size and complete loss of phospho-STAT5 in residual leukemia cells. In both murine leukemias and human xenografts, CHZ868 prolonged survival compared to controls (p30 clones sequenced harbored the same JAK2 L884P mutation. Ba/F3 cells expressing CRLF2 with JAK2 R683G/L884P displayed cross-resistance to CHZ868, while sensitivity to type I inhibitors was not affected. Structural modeling of the JAK2 JH1 domain suggested that L884P alters the binding pocket for type II inhibitors. JAK2 L884P is homologous to an EGFR L747P activating mutation, which destabilizes the P-loop and C-helix portion of the kinase domain (He et al. Clin Cancer Res 2012). The fact that L884P was reported in two B-ALL patients lacking additional JAK2 mutations (Torra et al. Blood (ASH Annual Meeting Abstracts) 2010) raised the possibility it was also an activating mutation. We confirmed L884P is an activating allele, as Ba/F3 cells expressing CRLF2, IL7R, and JAK2 L884P proliferated in the absence of TSLP ligand. To improve CHZ868 efficacy, we tested for synergy with multiple chemotherapy agents currently used in B-ALL treatment. Dexamethasone was the most highly synergistic with CHZ868 in MHH-CALL4 cells. To assess the combination in vivo, we treated mice transplanted with CRLF2/JAK2 R683G/Pax5+/-/Ts1Rhr murine B-ALL with vehicle, CHZ868, dexamethasone, or CHZ868 + dexamethasone for 14 days post engraftment. CHZ868 treatment prolonged survival compared to vehicle (p Disclosures Hofmann: Novartis Institutes for BioMedical Research: Employment. Baffert:Novartis: Employment. Vangrevelinghe:Novartis Institutes for BioMedical Research: Employment. Gaul:Novartis: Employment. Radimerski:Novartis: Employment. Weinstock:Novartis: Consultancy, Research Funding.

The heterocyclic compound specified in the title (and readily prepared from commercial precursors) has a sterically protected C==O group, so that direct lithiation by BuLi at the exocyclic CH(2) group is possible (3 --Li-3). The lithiated N,S-acetal derivative (Li-3) adds diastereoselectively to aldehydes (Table 2), unsymmetrical ketones (Table 3), chalcone (1,4-addition, Scheme 2), and N-phosphinoyl- and N-sulfonylimines (Table 4). Protection of the newly formed OH groups (Scheme 3) and/or MeS/OH displacement by Hg(O(2)CCF(3))(2) in aqueous THF/acetonitrile converts the N,S-acetals into hemiaminals (--20) which, in turn, are readily cleaved to aldehydes, with recovery of the chiral auxiliary (1, Scheme 4). The aldehydes (especially those lacking alpha-carbonyl hydrogens) may be isolated, or they are trapped in situ by reduction to (selectively protected) diols or amino alcohols, by addition of Grignard or Li reagents, which provides diols with two stereogenic centers, by oxidation to give 2-hydroxy esters, or by olefination to provide 4-hydroxy-2-alkenoates (Scheme 5). The scope and limitations of the new, overall enantioselective transformation are determined, and the readily recovered chiral auxiliary used is compared with oxazolidinones of other substitution patterns (Scheme 7). The configuration of a number of products has been assigned by single-crystal X-ray diffraction (cf. Figure 5). These structures and similarities of NMR data led to configurational assignment of the other products (see formulas in the schemes and tables) by analogy. A simple mechanistic model for the stereochemical course of the addition of Li-3 to aldehydes and ketones is presented (Figure 6).

The first total synthesis of (+)-migrastatin, a macrolide natural product with interesting antimetastatic properties, has been accomplished. Our concise and flexible approach utilizes a Lewis acid-catalyzed diene aldehyde condensation to install the three contiguous stereocenters and the trisubstituted (Z)-alkene of migrastatin. Construction of the two remaining stereocenters and incorporation of the glutarimide-containing side chain have been achieved via an anti-selective aldol reaction, followed by a Horner-Wadsworth-Emmons olefination. Finally, the assembly of the macrocycle has been realized by a highly (E)-selective ring-closing metathesis.

Abstract 62 Mutation within the kinase domain of tyrosine kinases is a common mechanisms of resistance to enzymatic inhibitors. Inhibitors of janus kinase 2 (JAK2) are under evaluation in patients with myeloproliferative neoplasms (MPNs), B-cell acute lymphoblastic leukemia (B-ALL) with rearrangements of the cytokine receptor subunit CRLF2, and other tumors with constitutive JAK2 signaling. To identify resistance mutations in JAK2, we randomly mutagenized human JAK2 R683G, which is observed in approximately half of CRLF2-rearranged B-ALL. We transduced the mutagenized JAK2 cDNA library into murine Ba/F3 cells that express CRLF2. Expression of CRLF2 and JAK2 R683G confers IL3 independent growth in Ba/F3 cells. The transduced population was selected in the JAK2-selective inhibitor NVP-BVB808 in the absence of IL3. Multiple BVB808-resistant clones were recovered that harbored either E864K, Y931C or G935R mutations in JAK2. Alignment of homologous regions of the JAK2 kinase domain (JH1) with ABL1 demonstrated that the three mutations are located in regions homologous to imatinib resistance hotspots in ABL1. Codons Y931 and G935 are within the hinge region of the kinase domain. Based on structural modeling, Y931C is likely to inhibit substrate binding. E864K is located in the middle of b3 following the P-loop in the N-lobe and may modify the structure and flexibility of the preceding P-loop, thus destabilizing the conformation required for inhibitor binding. We expressed JAK2 V617F alleles harboring Y931C, G935R or E864K in Ba/F3-EPOR cells and exposed the cells to the JAK2 enzymatic inhibitors JAK inhibitor-1, NVP-BSK805, TG101348, tofacitinib (formerly tasocitnib), ruxolitinib (formerly INCB18424) and BVB808. All three mutations conferred 2- to >10-fold resistance against BVB808, NVP-BSK805, TG101348, ruxolitinib and JAK inhibitor-1. Y931C and E864K but not G935R conferred resistance to tofactinib. Modeling of G935R indicated that a 935R side-chain would occlude the hydrophobic channel of the ATP-binding pocket. As a consequence, this mutation would decrease the binding affinity of compounds occupying the hydrophobic channel like JAK inhibitor-1 or BSK805, but not affect the potency of tofactinib, which does not bind in this region. Mutation of G935 to arginine, histidine or glutamine reduced the inhibitory effects of JAK inhibitor-1, but not tofacitinib, on JAK2 kinase domain activity. None of the codon 935 mutations had significant effects on Km or Vmaxin vitro. BVB808 treatment partially reduced activation state-specific phosphorylation of STAT5 in Ba/F3-EPOR/JAK2 V617F cells but not in Ba/F3-EPOR/JAK2 V617F/G935R or G935H cells. JAK2 is a known client of HSP90, and HSP90 inhibitors promote the degradation of both wild-type and mutant JAK2. We hypothesized that resistance mutations within the JAK2 kinase domain would not affect JAK2 degradation induced by HSP90 inhibitors. We assayed the cytotoxicity of the resorcinylic isoxazole amide NVP-AUY922 and the benzoquinone ansamycin 17-AAG in Ba/F3 cells that express the erythropoietin receptor (EPOR) and JAK2 V617F, which is observed in more than half of MPNs. Mutation of JAK2 V617F to include E864K, Y931C or G935R did not affect sensitivity to either AUY922 or 17-AAG. In fact, AUY922 was more active against cells harboring G935R (GI50, 3.87 nM) or E864K (GI50, 6.14 nM) compared to cells with no resistance mutation (GI50, 14.7 nM; p Disclosures: Gaul: Novartis: Employment. Vangrevelinghe:Novartis: Employment. De Pover:Novartis: Employment. Regnier:Novartis: Employment. Erdmann:Novartis: Employment. Hofmann:Novartis: Employment. Eck:Novartis: Consultancy, Research Funding. Kung:Novartis Pharmaceuticals: Consultancy, Research Funding. Radimerski:Novartis Pharma AG: Employment. Weinstock:Novartis: Consultancy, Research Funding.

The research activities of our group are demonstrated by examples in the following fields: (i) TADDOL auxiliary system (combinatorial synthesis, a chiral hydroperoxide, immobilization on controlled-pore glass silica gel); (ii) a geminally diphenyl-substituted 4-isopropyl-1,3-oxazolidinone as a superior Evans-type auxiliary (for enantioselective enolate alkylation, aldol addition, Michael addition, and Diels-Alder reactions); (iii) enantioselective reactivity umpolung (with a lithiated methylthiomethyl derivative of an oxazolidinone), and (iv) chemical and biological investigations of γ-peptides (folding to helices and turns, stability against peptidases). The impact of biology on the projects of a synthetic organic group is discussed.

SummaryA variety of cancers depend on JAK2 signaling, including the high-risk subset of B cell acute lymphoblastic leukemias (B-ALLs) with CRLF2 rearrangements. Type I JAK2 inhibitors induce paradoxical JAK2 hyperphosphorylation in these leukemias and have limited activity. To improve the efficacy of JAK2 inhibition in B-ALL, we developed the type II inhibitor CHZ868, which stabilizes JAK2 in an inactive conformation. CHZ868 potently suppressed the growth of CRLF2-rearranged human B-ALL cells, abrogated JAK2 signaling, and improved survival in mice with human or murine B-ALL. CHZ868 and dexamethasone synergistically induced apoptosis in JAK2-dependent B-ALLs and further improved in vivo survival compared to CHZ868 alone. These data support the testing of type II JAK2 inhibition in patients with JAK2-dependent leukemias and other disorders.