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PDF file - 650K, Figure S1. RSK N-terminal Kinase Directly Phosphorylates YB1 on Ser102. COS7 cells either (A) untransfected or (B) transiently expressing WT RSK2 or T493M RSK2 were placed under serum starvation conditions for 20 hrs, followed by 3 hour treatment with 1microM FMK-PA and subsequently stimulated with 1ng/ml EGF for 10 minutes. The levels of phosphorylated and total RSK2 and YB1 proteins were assessed in total cell lysates using Western Blot. β-actin protein levels were assessed for gel loading control. Figure S2. LJH685 modulates YB1 and BAD phosphorylation in either attached or anchorageindependent setting to similar extent and at similar concentrations of LJH685. MDA-MB-231 cells were treated with the indicated kinase inhibitors for 4 hours. Cell lysates were analyzed by Western blot with indicated antibodies. Figure S3. MDA-MB-231 cells were plated in Matrigel with DMSO or LJH685 for 6 days and colony morphology was examined using phase microscopy. Figure S4. MDA-MB-231 and H358 cells were plated on regular and ultra-low bind tissue culture plates for 5 days in presence of 10 microM LJH685 or DMSO. Cell Cycle distribution was assessed using FACS analysis of propidium iodide stained nuclei.

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PDF file - 28K, Percent Inhibition of MDA-MB-231 or H358 cells when grown as colonies on Scivax plates in the presence of LJI308.

The p90 ribosomal S6 kinase (RSK) family of serine/threonine kinases is expressed in a variety of cancers and its substrate phosphorylation has been implicated in direct regulation of cell survival, proliferation, and cell polarity. This study characterizes and presents the most selective and potent RSK inhibitors known to date, LJH685 and LJI308. Structural analysis confirms binding of LJH685 to the RSK2 N-terminal kinase ATP-binding site and reveals that the inhibitor adopts an unusual nonplanar conformation that explains its excellent selectivity for RSK family kinases. LJH685 and LJI308 efficiently inhibit RSK activity in vitro and in cells. Furthermore, cellular inhibition of RSK and its phosphorylation of YB1 on Ser102 correlate closely with inhibition of cell growth, but only in an anchorage-independent growth setting, and in a subset of examined cell lines. Thus, RSK inhibition reveals dynamic functional responses among the inhibitor-sensitive cell lines, underscoring the heterogeneous nature of RSK dependence in cancer.Implications: Two novel potent and selective RSK inhibitors will now allow a full assessment of the potential of RSK as a therapeutic target for oncology. Mol Cancer Res; 12(5); 803–12. ©2014 AACR.

XLSX file - 27K, Competition binding of LJH685, LJI308, BI-D1870-AE, and FMK-PA at 10 microM concentration to either 96 or 492 kinases.

Supplementary Figure 3. (A) Shown are western blots using antibodies directed against T202/Y204 phosphorylated ERK1/2 following incubation with a range of concentrations of LXH254 over a 4 - 72 hour period. Which individual RAF protein is not expressed in each HCT 116 variant is indicated above the relevant panels. (B) Shown are western blots using Abs directed against the indicated proteins in either whole cell lysates (WCL) or material immuno-precipitated from cell lysates using Abs directed against ARAF (ARAF IP) or BRAF (BRAF IP). Lysates were generated from either parental MIA PaCa-2 cells or a MIA PaCa-2 variant lacking expression of CRAF. (C) Recombinant MEK1 can be phosphorylated by immuno-precipitates from both LXH254 treated and untreated MIA PaCa-2 and MEL-JUSO cells using an anti-body directed against ARAF contains MEK1 kinase activity. Proteins detected in either whole cell lysates (WCL) or ARAF-Ab immuno-precipitates (IP:ARAF) are indicated on the right. (D) IP-kinase activity on recombinant MEK1 in immuno-precipitates from HEK293 cells expressing FLAG-tagged ARAF using Abs directed against FLAG requires ATP and occurs on both wild type (WT) and kinase-dead (K97M) MEK1. (E) Shown are western blots using antibodies directed against T202/Y204 phosphorylated ERK1/2 following incubation with a range of concentrations of LXH254 over a 4-72 hour period. The individual RAF protein expressed in each HCT 116 variant is indicated above the relevant panels. (F) Shown are western blots of phosphorylated MEK1/2 (S218/S221) and ERK1/2 (T202/Y204) following a 4 hr. incubation with a range of LXH254 concentrations in the RAS/RAF wild type cell line PC-9.

Purpose:Targeting RAF for antitumor therapy in RAS-mutant tumors holds promise. Herein, we describe in detail novel properties of the type II RAF inhibitor, LXH254.Experimental Design:LXH254 was profiled in biochemical, in vitro, and in vivo assays, including examining the activities of the drug in a large panel of cancer-derived cell lines and a comprehensive set of in vivo models. In addition, activity of LXH254 was assessed in cells where different sets of RAF paralogs were ablated, or that expressed kinase-impaired and dimer-deficient variants of ARAF.Results:We describe an unexpected paralog selectivity of LXH254, which is able to potently inhibit BRAF and CRAF, but has less activity against ARAF. LXH254 was active in models harboring BRAF alterations, including atypical BRAF alterations coexpressed with mutant K/NRAS, and NRAS mutants, but had only modest activity in KRAS mutants. In RAS-mutant lines, loss of ARAF, but not BRAF or CRAF, sensitized cells to LXH254. ARAF-mediated resistance to LXH254 required both kinase function and dimerization. Higher concentrations of LXH254 were required to inhibit signaling in RAS-mutant cells expressing only ARAF relative to BRAF or CRAF. Moreover, specifically in cells expressing only ARAF, LXH254 caused paradoxical activation of MAPK signaling in a manner similar to dabrafenib. Finally, in vivo, LXH254 drove complete regressions of isogenic variants of RAS-mutant cells lacking ARAF expression, while parental lines were only modestly sensitive.Conclusions:LXH254 is a novel RAF inhibitor, which is able to inhibit dimerized BRAF and CRAF, as well as monomeric BRAF, while largely sparing ARAF.

Supplementary Legend

Proliferation IC50 values for various cell lines and cell line derivatives

Purpose: Targeting RAF for antitumor therapy in RAS-mutant tumors holds promise. Herein, we describe in detail novel properties of the type II RAF inhibitor, LXH254. Experimental Design: LXH254 was profiled in biochemical, in vitro, and in vivo assays, including examining the activities of the drug in a large panel of cancer-derived cell lines and a comprehensive set of in vivo models. In addition, activity of LXH254 was assessed in cells where different sets of RAF paralogs were ablated, or that expressed kinase-impaired and dimer-deficient variants of ARAF. Results: We describe an unexpected paralog selectivity of LXH254, which is able to potently inhibit BRAF and CRAF, but has less activity against ARAF. LXH254 was active in models harboring BRAF alterations, including atypical BRAF alterations coexpressed with mutant K/NRAS, and NRAS mutants, but had only modest activity in KRAS mutants. In RAS-mutant lines, loss of ARAF, but not BRAF or CRAF, sensitized cells to LXH254. ARAF-mediated resistance to LXH254 required both kinase function and dimerization. Higher concentrations of LXH254 were required to inhibit signaling in RAS-mutant cells expressing only ARAF relative to BRAF or CRAF. Moreover, specifically in cells expressing only ARAF, LXH254 caused paradoxical activation of MAPK signaling in a manner similar to dabrafenib. Finally, in vivo, LXH254 drove complete regressions of isogenic variants of RAS-mutant cells lacking ARAF expression, while parental lines were only modestly sensitive. Conclusions: LXH254 is a novel RAF inhibitor, which is able to inhibit dimerized BRAF and CRAF, as well as monomeric BRAF, while largely sparing ARAF.

Tumors put in a vulnerable position Cancer cells often display alterations in metabolism that help fuel their growth. Such metabolic “rewiring” may also work against the cancer cells, however, by creating new vulnerabilities that can be exploited therapeutically. A variety of human tumors show changes in methionine metabolism caused by loss of the gene coding for 5-methylthioadenosine phosphorylase (MTAP). Mavrakis et al. and Kryukov et al. found that the loss of MTAP renders cancer cell lines sensitive to growth inhibition by compounds that suppress the activity of a specific arginine methyltransferase called PRMT5. Conceivably, drugs that inhibit PRMT5 activity could be developed into a tailored therapy for MTAP-deficient tumors. Science , this issue pp. 1208 and 1214

Extracellular signal-regulated kinase 2 (ERK2) is a serine/threonine protein kinase involved in many cellular programs, such as cell proliferation, differentiation, motility and programed cell-death. It is therefore considered an important target in the treatment of cancer. In an effort to support biochemical screening and small molecule drug discovery, we established a robust system to generate both inactive and active forms of ERK2 using insect expression system. We report here, for the first time, that inactive ERK2 can be expressed and purified with 100% homogeneity in the unphosphorylated form using insect system. This resulted in a significant 20-fold yield improvement compared to that previously reported using bacterial expression system. We also report a newly developed system to generate active ERK2 in insect cells through in vivo co-expression with a constitutively active MEK1 (S218D S222D). Isolated active ERK2 was confirmed to be doubly phosphorylated at the correct sites, T185 and Y187, in the activation loop of ERK2. Both ERK2 forms, inactive and active, were well characterized by biochemical activity assay for their kinase function. Inactive and active ERK2 were the two key reagents that enabled successful high through-put biochemical assay screen and structural drug discovery studies.

ATR, a protein kinase in the PIKK family, plays a critical role in the cell DNA-damage response and is an attractive anticancer drug target. Several potent and selective inhibitors of ATR have been reported showing significant antitumor efficacy, with most advanced ones entering clinical trials. However, due to the absence of an experimental ATR structure, the determinants contributing to ATR inhibitors' potency and specificity are not well understood. Here we present the mutations in the ATP-binding site of PI3Kα to progressively transform the pocket to mimic that of ATR. The generated PI3Kα mutants exhibit significantly improved affinity for selective ATR inhibitors in multiple chemical classes. Furthermore, we obtained the X-ray structures of the PI3Kα mutants in complex with the ATR inhibitors. The crystal structures together with the analysis on the inhibitor affinity profile elucidate the roles of individual amino acid residues in the binding of ATR inhibitors, offering key insights for the binding mechanism and revealing the structure features important for the specificity of ATR inhibitors. The ability to obtain structural and binding data for these PI3Kα mutants, together with their ATR-like inhibitor binding profiles, makes these chimeric PI3Kα proteins valuable model systems for structure-based inhibitor design.

RAS mutations lead to a constitutively active oncogenic protein that signals through multiple effector pathways. In this chemical biology study, we describe a novel coupled biochemical assay that measures activation of the effector BRAF by prenylated KRASG12V in a lipid-dependent manner. Using this assay, we discovered compounds that block biochemical and cellular functions of KRASG12V with low single-digit micromolar potency. We characterized the structural basis for inhibition using NMR methods and showed that the compounds stabilized the inactive conformation of KRASG12V. Determination of the biophysical affinity of binding using biolayer interferometry demonstrated that the potency of inhibition matches the affinity of binding only when KRAS is in its native state, namely post-translationally modified and in a lipid environment. The assays we describe here provide a first-time alignment across biochemical, biophysical, and cellular KRAS assays through incorporation of key physiological factors regulating RAS biology, namely a negatively charged lipid environment and prenylation, into the in vitro assays. These assays and the ligands we discovered are valuable tools for further study of KRAS inhibition and drug discovery., PLoS ONE, 12 (4), ISSN:1932-6203

Phosphoinositide-3-kinases (PI3Ks) are important oncology targets due to the deregulation of this signaling pathway in a wide variety of human cancers. Herein we describe the structure guided optimization of a series of 2-morpholino, 4-substituted, 6-heterocyclic pyrimidines where the pharmacokinetic properties were improved by modulating the electronics of the 6-position heterocycle, and the overall druglike properties were fine-tuned further by modification of the 4-position substituent. The resulting 2,4-bismorpholino 6-heterocyclic pyrimidines are potent class I PI3K inhibitors showing mechanism modulation in PI3K dependent cell lines and in vivo efficacy in tumor xenograft models with PI3K pathway deregulation (A2780 ovarian and U87MG glioma). These efforts culminated in the discovery of 15 (NVP-BKM120), currently in Phase II clinical trials for the treatment of cancer.

The p90 ribosomal S6 kinase (RSK) family of serine/threonine kinases is expressed in a variety of cancers and its substrate phosphorylation has been implicated in direct regulation of cell survival, proliferation, and cell polarity. This study characterizes and presents the most selective and potent RSK inhibitors known to date, LJH685 and LJI308. Structural analysis confirms binding of LJH685 to the RSK2 N-terminal kinase ATP-binding site and reveals that the inhibitor adopts an unusual nonplanar conformation that explains its excellent selectivity for RSK family kinases. LJH685 and LJI308 efficiently inhibit RSK activity in vitro and in cells. Furthermore, cellular inhibition of RSK and its phosphorylation of YB1 on Ser102 correlate closely with inhibition of cell growth, but only in an anchorage-independent growth setting, and in a subset of examined cell lines. Thus, RSK inhibition reveals dynamic functional responses among the inhibitor-sensitive cell lines, underscoring the heterogeneous nature of RSK dependence in cancer. Implications: Two novel potent and selective RSK inhibitors will now allow a full assessment of the potential of RSK as a therapeutic target for oncology. Mol Cancer Res; 12(5); 803–12. ©2014 AACR.

We report an all-fiber depolarizer that uses high-birefringence fibers with birefringence modulation. The device can be used to depolarize coherent light from sources such as single-mode and multimode lasers. Experiments with a He–Ne laser demonstrated a reduction in the degree of polarization from 1 (0 dB) to −12 dB.

In fiber optic interferometric sensors, polarization noise and fading may occur due to environmental induced birefringence fluctuations. One way to overcome this problem is to depolarize the source light. For broadband sources such as light emitting diodes, the light can be easily depolarized by utilizing fiber implementations of conventional Lyot depolarizes. However, for highly coherent lasers, this approach is not viable. Several techniques for producing a depolarized source from coherent light have been demonstrated. However, they are only suitable for certain input polarization states, and often involve bulk optical components which may not be ideal for certain applications. In this paper, we report a simple all fiber depolarizer for coherent light which is suitable for any input polarization states.