Abstract 3909: HDAC inhibition in combination with MEK or BCL-2 inhibition as novel therapeutic strategies in multiple myeloma

Multiple myeloma (MM) is an incurable malignancy of plasma cells. It is the second most common hematologic cancer, affecting nearly 30,000 people in the United States annually. Substantial progress has been made in the past fifteen years in the treatment of MM due to the approval of several new classes of drugs. However, patients inevitably relapse and become refractory to existing therapies. Hence, there is an immediate unmet need to develop novel therapies for MM based on a better understanding of the disease biology. Mutations in RAS have been found to occur in about 40% of newly diagnosed MM patients, with the frequency increasing to around 70% in relapsed/refractory patients. Such mutations are absent in patients with the premalignant conditions monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM). Clearly, RAS mutations contribute to both disease progression and relapse. However, targeting the MEK/ERK pathway has been unsuccessful in MM patients to date. Given the high frequency of RAS mutations in MM, we hypothesized that targeting this pathway could still be a promising strategy when combined with existing agents that have multifaceted mechanisms to promote tumor cell death, such as the recently approved histone deacetylase (HDAC) inhibitor LBH589 (panobinostat). Our results clearly demonstrate that low doses of LBH589 in combination with the MEK inhibitor AZD6244 induce BIM-dependent synergistic cell death in several MM cell lines and patient cells. Our studies also suggest that mutations in RAS/RAF could serve as a predictive biomarker for sensitivity to AZD6244/LBH589. RAS/RAF mutations appear to confer Mcl-1 dependence in MM cells, in part by driving up the phosphorylation of Mcl-1. The AZD6244/LBH589 combination is able to decrease the phosphorylation of Mcl-1 at several sites, which dissociates BIM-Mcl-1 complexes, ultimately leading to activation of the intrinsic apoptosis pathway. Additionally, we identified that wild-type RAS/RAF cells have relatively lower levels of phospho-Mcl-1, as well as higher levels of Bcl-2 and phospho-Bcl-2 when compared to mutated RAS/RAF cells. This seems to confer functional Bcl-2 dependence. Consequently, we found that wild-type RAS/RAF cells are sensitive to the BH3-mimetic ABT199 (venetoclax) when combined with LBH589. Through ongoing experiments, we hope to further confirm the mechanism of action of both these combinations, identify the particular HDAC that is required to be inhibited for the observed synergy, and validate RAS/RAF mutational status as a biomarker for predicting sensitivity to either combination. Our findings have broad therapeutic potential given the prevalence of RAS mutations in MM. Moreover, the ABT199/LBH589 combination could emerge as a targeted therapy for wild-type RAS patients, perhaps broadening the scope and capacity of Bcl-2 inhibition in MM.

Citation Format: Kevin C. Miller, Jessica Haug, Teresa Kimlinger, Sanjay Kumar, Wilson Gonsalves, S. Vincent Rajkumar, Shaji K. Kumar, Vijay Ramakrishnan. HDAC inhibition in combination with MEK or BCL-2 inhibition as novel therapeutic strategies in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3909.

Smac mimetic LCL161 overcomes protective ER stress induced by obatoclax, synergistically causing cell death in multiple myeloma

Bcl2 and IAP families are anti-apoptotic proteins deregulated in multiple myeloma (MM) cells. Pharmacological inhibition of each of these families has shown significant activity only in subgroups of MM patients. Here, we have examined a broad-spectrum Bcl2 family inhibitor Obatoclax (OBX) in combination with a Smac mimetic LCL161 in MM cell lines and patient cells. LCL161/OBX combination induced synergistic cytotoxicity and anti-proliferative effects on a broad range of human MM cell lines. The cytotoxicity was mediated through inhibition of the IAPs, activation of caspases and up regulation of the pro-apoptotic proteins Bid, Bim, Puma and Noxa by the drug combination. In addition, we observed that OBX caused ER stress and activated the Unfolded Protein Response (UPR) leading to drug resistance. LCL161, however inhibited spliced Xbp-1, a pro-survival factor. In addition, we observed that OBX increased GRP78 localization to the cell surface, which then induced PI3K dependent Akt activation and resistance to cell death. LCL161 was able to block OBX induced Akt activation contributing to synergistic cell death. Our results support clinical evaluation of this combination strategy in relapsed refractory MM patients.

PI3K/AKT/mTOR pathway in multiple myeloma: from basic biology to clinical promise

Multiple myeloma (MM), a cancer of terminally differentiated plasma cells, is the second most common hematological malignancy. The disease is characterized by the accumulation of abnormal plasma cells in the bone marrow that remains in close association with other cells in the marrow microenvironment. In addition to the genomic alterations that commonly occur in MM, the interaction with cells in the marrow microenvironment promotes signaling events within the myeloma cells that enhances survival of MM cells. The phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) is such a pathway that is aberrantly activated in a large proportion of MM patients through numerous mechanisms and can play a role in resistance to several existing therapies making this a central pathway in MM pathophysiology. Here, we review the pathway, its role in MM, promising preclinical results obtained thus far and the clinical promise that drugs targeting this pathway have in MM.

Glutamine-derived 2-hydroxyglutarate is associated with disease progression in plasma cell malignancies

The production of the oncometabolite 2-hydroxyglutarate (2-HG) has been associated with c-MYC overexpression. c-MYC also regulates glutamine metabolism and drives progression of asymptomatic precursor plasma cell (PC) malignancies to symptomatic multiple myeloma (MM). However, the presence of 2-HG and its clinical significance in PC malignancies is unknown. By performing 13C stable isotope resolved metabolomics (SIRM) using U[13C6]Glucose and U[13C5]Glutamine in human myeloma cell lines (HMCLs), we show that 2-HG is produced in clonal PCs and is derived predominantly from glutamine anaplerosis into the TCA cycle. Furthermore, the 13C SIRM studies in HMCLs also demonstrate that glutamine is preferentially utilized by the TCA cycle compared with glucose. Finally, measuring the levels of 2-HG in the BM supernatant and peripheral blood plasma from patients with precursor PC malignancies such as smoldering MM (SMM) demonstrates that relatively elevated levels of 2-HG are associated with higher levels of c-MYC expression in the BM clonal PCs and with a subsequent shorter time to progression (TTP) to MM. Thus, measuring 2-HG levels in BM supernatant or peripheral blood plasma of SMM patients offers potential early identification of those patients at high risk of progression to MM, who could benefit from early therapeutic intervention.

The structure of the yeast mitochondrial ribosome

Mitochondria have specialized ribosomes (mitoribosomes) dedicated to the expression of the genetic information encoded by their genomes. Here, using electron cryomicroscopy, we have determined the structure of the 75-component yeast mitoribosome to an overall resolution of 3.3 angstroms. The mitoribosomal small subunit has been built de novo and includes 15S ribosomal RNA (rRNA) and 34 proteins, including 14 without homologs in the evolutionarily related bacterial ribosome. Yeast-specific rRNA and protein elements, including the acquisition of a putatively active enzyme, give the mitoribosome a distinct architecture compared to the mammalian mitoribosome. At an expanded messenger RNA channel exit, there is a binding platform for translational activators that regulate translation in yeast but not mammalian mitochondria. The structure provides insights into the evolution and species-specific specialization of mitochondrial translation.

Signaling Pathways and Emerging Therapies in Multiple Myeloma

Multiple myeloma (MM) is a devastating malignancy of antibody-producing plasma cells. In the absence of a single unifying genetic event contributing to disease manifestation, efforts have focused on understanding signaling events deregulated in myeloma plasma cells. MM cells are dependent on both cellular and non-cellular components of the tumor microenvironment such as bone marrow stromal cells, endothelial cells, and cytokines such as interleukin 6 (IL6), vascular endothelial growth factor (VEGF), and insulin-like growth factor (IGF) for their growth and survival. The cumulative effect of such interactions is the aberrant activation of numerous signal transduction pathways within the MM plasma cells leading to uncontrolled growth and prevention of apoptosis. Here, we will review our current understanding of some of the key signal transduction pathways dysregulated in MM and emerging therapies targeting these pathways in MM.

PSEN1 gene polymorphisms in Caucasian Alzheimer's disease: A meta-analysis

BACKGROUND

A meta-analysis was performed to assess PSEN1 gene polymorphisms (rs1800839 and rs17125721) in Alzheimer's disease (AD) risk.

METHODS

A systematic electronic search was performed across databases to retrieve studies published before 31 January 2017. The association between the selected PSEN1 polymorphisms and AD was based on five genetic models using DerSimonian and Laird's method or Mantel-Haenszel's method.

RESULTS

A total of 14 case-controlled studies were included. Results showed that rs1800839 polymorphism was significantly associated with AD in allelic OR=0.85 (95% CI [0.72-1.00]) and dominant OR=0.82 (95% CI [0.69-0.98]) genetic models, respectively. However, an insignificant association was found for rs17125721 polymorphism in all genetic models.

CONCLUSIONS

Meta-analysis of PSEN1 gene suggests that the rs1800839 polymorphism has potential influence on AD among Caucasians.

Decoding Mammalian Ribosome-mRNA States by Translational GTPase Complexes

In eukaryotes, accurate protein synthesis relies on a family of translational GTPases that pair with specific decoding factors to decipher the mRNA code on ribosomes. We present structures of the mammalian ribosome engaged with decoding factor⋅GTPase complexes representing intermediates of translation elongation (aminoacyl-tRNA⋅eEF1A), termination (eRF1⋅eRF3), and ribosome rescue (Pelota⋅Hbs1l). Comparative analyses reveal that each decoding factor exploits the plasticity of the ribosomal decoding center to differentially remodel ribosomal proteins and rRNA. This leads to varying degrees of large-scale ribosome movements and implies distinct mechanisms for communicating information from the decoding center to each GTPase. Additional structural snapshots of the translation termination pathway reveal the conformational changes that choreograph the accommodation of decoding factors into the peptidyl transferase center. Our results provide a structural framework for how different states of the mammalian ribosome are selectively recognized by the appropriate decoding factor⋅GTPase complex to ensure translational fidelity.

Case Report: Diagnosis of hypogeusia after oral exposure to commercial cleaning agent and considerations for clinical taste testing

Few reports in the literature document acute taste disturbance following exposure to toxic chemicals. We describe the case of a 54-year-old man who presented with primary complaint of tongue numbness and persistent problems with taste 1.5 years following oral exposure to a commercial cleaning agent. A test of olfaction revealed normosmia for age and gender. Lingual tactile two-point discrimination testing showed reduced somatosensation. Taste threshold testing using a 3-drop method demonstrated severe hypogeusia, though the patient was able to discriminate tastants at lower concentrations with a whole mouth swish and spit test. We conclude that clinical evaluation of dysgeusia can be performed using a number of previously published testing methods, however, determining causative factors may be confounded by duration since exposure, lack of knowledge of baseline taste function, and medications. Although many testing options exist, basic taste testing can be performed with minimal expertise or specialized equipment, depending on the patient history and goals of evaluation.

Case Report: Diagnosis of hypogeusia after oral exposure to commercial cleaning agent and considerations for clinical taste testing

Few reports in the literature document acute taste disturbance following exposure to toxic chemicals. We describe the case of a 54-year-old man who presented with primary complaint of tongue numbness and persistent problems with taste 1.5 years following oral exposure to a commercial cleaning agent. A test of olfaction revealed normosmia for age and gender. Lingual tactile two-point discrimination testing showed reduced somatosensation. Taste threshold testing using a 3-drop method demonstrated severe hypogeusia, though the patient was able to discriminate tastants at lower concentrations with a whole mouth swish and spit test. We conclude that clinical evaluation of dysgeusia can be performed using a number of previously published testing methods, however, determining causative factors may be confounded by duration since exposure, lack of knowledge of baseline taste function, and medications. Although many testing options exist, basic taste testing can be performed with minimal expertise or specialized equipment, depending on the patient history and goals of evaluation.

Trapping of excess energy in a nano-layered microenvironment to promote chemical reactions

Nano-layered hybrid compounds composed of a polyfluoroalkyl azobenzene surfactant (abbreviated as C3F-Azo-C6H) and layered inorganic nanosheets undergo three-dimensional morphological changes such as reversible shrinkage and expansion of interlayer spaces, and nanosheet sliding by photo-irradiation. Previously, we have investigated the photoreactivity of C3F-Azo-C6H/clay nano-layered hybrids in various microenvironments and found a remarkable enhancement in the photoreactivity for the cis-trans photo-isomerization reaction (Φ_cis-trans = 1.9). In this paper, nanosecond and microsecond dynamics of trans-C3F-Azo-C6H and its assembly in various microenvironments have been studied by laser flash photolysis to get deeper insight into the extraordinary reactivity of the molecular assembly in the nano-layered microenvironment. In solution, the molecular trans-C3F-Azo-C6H exhibited only a depletion of the trans-form of azobenzene upon the laser pulse excitation. On the other hand, in the case of the C3F-Azo-C6H/clay hybrid film, the depletion of the trans-form was drastically recovered in three steps on nano- and microsecond timescales. This indicates that the once reacted C3F-Azo-C6H molecule (cis-C3F-Azo-C6H) was reverted back to the trans-form after the laser pulse. It is considered that the excess energy provided by the photo-excitation, which is immediately dissipated to the surrounding media through the intermolecular vibrational modes in solution, is trapped in the nano-layered microenvironment to thermally revert the cis-form back to the trans-form. Conversely, in the case of cis-trans isomerization of the C3F-Azo-C6H/clay hybrid film upon photo-irradiation, the reactivity would be much enhanced by the additional contribution of the thermal excess energy efficiently trapped in the nano-layered microenvironment. As compared with the hydrocarbon analogue (C3H-Azo-C6H), the subsequent recovery was very much enhanced in the C3F-Azo-C6H/clay film. The polyfluoroalkyl part of the surfactant layer plays a key role in the retarded dissipation of the excess energy by photo-excitation, which might be coupled with the three-dimensional morphological motion with efficient isomerization reactions.

Large-Scale Movements of IF3 and tRNA during Bacterial Translation Initiation

In bacterial translational initiation, three initiation factors (IFs 1–3) enable the selection of initiator tRNA and the start codon in the P site of the 30S ribosomal subunit. Here, we report 11 single-particle cryo-electron microscopy (cryoEM) reconstructions of the complex of bacterial 30S subunit with initiator tRNA, mRNA, and IFs 1–3, representing different steps along the initiation pathway. IF1 provides key anchoring points for IF2 and IF3, thereby enhancing their activities. IF2 positions a domain in an extended conformation appropriate for capturing the formylmethionyl moiety charged on tRNA. IF3 and tRNA undergo large conformational changes to facilitate the accommodation of the formylmethionyl-tRNA (fMet-tRNA^fMet) into the P site for start codon recognition.

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Structures of the 30S ribosomal subunit with initiation factors, tRNA and mRNA

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IF3 helps to position the correct start codon in the P site before binding of tRNA

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Large-scale conformational changes of IF3 and tRNA are observed

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IF3 movements facilitate the accommodation of initiator tRNA in P site

Translational termination without a stop codon

Ribosomes stall when they encounter the end of messenger RNA (mRNA) without an in-frame stop codon. In bacteria, these "nonstop" complexes can be rescued by alternative ribosome-rescue factor A (ArfA). We used electron cryomicroscopy to determine structures of ArfA bound to the ribosome with 3'-truncated mRNA, at resolutions ranging from 3.0 to 3.4 angstroms. ArfA binds within the ribosomal mRNA channel and substitutes for the absent stop codon in the A site by specifically recruiting release factor 2 (RF2), initially in a compact preaccommodated state. A similar conformation of RF2 may occur on stop codons, suggesting a general mechanism for release-factor-mediated translational termination in which a conformational switch leads to peptide release only when the appropriate signal is present in the A site.

Microbiome of the paranasal sinuses: Update and literature review

BACKGROUND

Our understanding of the resident microbiome of the paranasal sinuses has changed considerably in recent years. Once presumed to be sterile, healthy sinus cavities are now known to harbor a diverse assemblage of microorganisms, and, it is hypothesized that alterations in the kinds and quantities of these microbes may play a role in the pathogenesis of chronic rhinosinusitis (CRS).

OBJECTIVES

To review the current literature regarding the sinus microbiome and collate research findings from relevant studies published to date.

METHODS

A systematic literature review was performed on all molecular studies that investigated the microbial communities of the paranasal sinuses. Methods of detection, microbiome composition, and comparative profiling between patients with and without CRS were explored.

RESULTS

A complex consortium of microorganisms has been demonstrated in the sinuses of both patients with and without CRS. However, the latter generally have been characterized by reduced biodiversity compared with controls, with selective enrichment of particular microbes (e.g., Staphylococcus aureus). Such disruptions in the resident microbiome may contribute to disease pathogenesis by enhancing the virulence of potential pathogens and adversely modulating immune responses.

CONCLUSION

The advent of culture-independent molecular approaches has led to a greater appreciation of the intricate microbial ecology of the paranasal sinuses. Microbiota composition, distribution, and abundance impact mucosal health and influence pathogen growth and function. A deeper understanding of the host-microbiome relationship and its constituents may encourage development of new treatment paradigms for CRS, which target restoration of microbiome homeostasis and cultivation of optimal microbial communities.

Structural characterization of ribosome recruitment and translocation by type IV IRES

Viral mRNA sequences with a type IV IRES are able to initiate translation without any host initiation factors. Initial recruitment of the small ribosomal subunit as well as two translocation steps before the first peptidyl transfer are essential for the initiation of translation by these mRNAs. Using electron cryomicroscopy (cryo-EM) we have structurally characterized at high resolution how the Cricket Paralysis Virus Internal Ribosomal Entry Site (CrPV-IRES) binds the small ribosomal subunit (40S) and the translocation intermediate stabilized by elongation factor 2 (eEF2). The CrPV-IRES restricts the otherwise flexible 40S head to a conformation compatible with binding the large ribosomal subunit (60S). Once the 60S is recruited, the binary CrPV-IRES/80S complex oscillates between canonical and rotated states (Fernández et al., 2014; Koh et al., 2014), as seen for pre-translocation complexes with tRNAs. Elongation factor eEF2 with a GTP analog stabilizes the ribosome-IRES complex in a rotated state with an extra ~3 degrees of rotation. Key residues in domain IV of eEF2 interact with pseudoknot I (PKI) of the CrPV-IRES stabilizing it in a conformation reminiscent of a hybrid tRNA state. The structure explains how diphthamide, a eukaryotic and archaeal specific post-translational modification of a histidine residue of eEF2, is involved in translocation.

DOI:http://dx.doi.org/10.7554/eLife.13567.001

Ribosome-dependent activation of stringent control

In order to survive, bacteria continually sense, and respond to, environmental fluctuations. Stringent control represents a key bacterial stress response to nutrient starvation1,2 that leads to a rapid and comprehensive reprogramming of metabolic and transcriptional patterns3. In general, transcription of genes for growth and proliferation are down-regulated, while those important for survival and virulence are favored4. Amino acid starvation is sensed by depletion of the aminoacyl-tRNA pools5, which results in accumulation of ribosomes stalled with non-aminoacylated (uncharged) tRNA in the ribosomal A-site6,7. RelA is recruited to stalled ribosomes, and activated to synthesize a hyperphosphorylated guanosine analog, (p)ppGpp8, which acts as a pleiotropic second messenger. However, structural information for how RelA recognizes stalled ribosomes and discriminates against aminoacylated tRNAs is missing. Here, we present the electron cryo-microscopy (cryo-EM) structure of RelA bound to the bacterial ribosome stalled with uncharged tRNA. The structure reveals that RelA utilizes a distinct binding site compared to the translational factors, with a multi-domain architecture that wraps around a highly distorted A-site tRNA. The TGS domain of RelA binds the CCA tail to orient the free 3’ hydroxyl group of the terminal adenosine towards a β-strand, such that an aminoacylated tRNA at this position would be sterically precluded. The structure supports a model where association of RelA with the ribosome suppresses auto-inhibition to activate synthesis of (p)ppGpp and initiate the stringent response. Since stringent control is responsible for the survival of pathogenic bacteria under stress conditions, and contributes to chronic infections and antibiotic tolerance, RelA represents a good target for the development of novel antibacterial therapeutics.

Clinical use and applications of histone deacetylase inhibitors in multiple myeloma

The incorporation of various novel therapies has resulted in a significant survival benefit in newly diagnosed and relapsed patients with multiple myeloma (MM) over the past decade. Despite these advances, resistance to therapy leads to eventual relapse and fatal outcomes in the vast majority of patients. Hence, there is an unmet need for new safe and efficacious therapies for continued improvement in outcomes. Given the role of epigenetic aberrations in the pathogenesis and progression of MM and the success of histone deacetylase inhibitors (HDACi) in other malignancies, many HDACi have been tried in MM. Various preclinical studies helped us to understand the antimyeloma activity of different HDACi in MM as a single agent or in combination with conventional, novel, and immune therapies. The early clinical trials of HDACi depicted only modest single-agent activity, but recent studies have revealed encouraging clinical response rates in combination with other antimyeloma agents, especially proteasome inhibitors. This led to the approval of the combination of panobinostat and bortezomib for the treatment of relapsed/refractory MM patients with two prior lines of treatment by the US Food and Drug Administration. However, it remains yet to be defined how we can incorporate HDACi in the current therapeutic paradigms for MM that will help to achieve longer disease control and significant survival benefits. In addition, isoform-selective and/or class-selective HDAC inhibition to reduce unfavorable side effects needs further evaluation.

Determination of association constant of host-guest supramolecular complex (molecular recognition of carbamazepine, antiseizure drug, with calix(4)arene)

The thermodynamic property of the host-guest, inclusion complex formed between p-t-butyl calix(4)arene which is a supramolecule, and the antiseizure drug, carbamazepine was studied. p-t-Butyl calix(4)arene has been used as a host molecule and carbamazepine as a guest molecule. Optical absorption spectral studies were carried out to investigate the molecular recognition properties of p-t-butyl calix(4)arene with carbamazepine. The stochiometry of the host-guest complexes formed and the association constant were determined. An interesting 1:2 stochiometric host-guest complex was formed. Job's continuous method of variation and Benesi-Hildebrand expression were used for the determination of binding constant and the stochiometry of the host-guest complex formed. Molecular dimension of the host molecule plays a vital role in the formation of the host-guest stochiometric complexes.

Structural basis for stop codon recognition in eukaryotes

Termination of protein synthesis occurs when a translating ribosome encounters one of three universally conserved stop codons: UAA, UAG or UGA. Release factors recognize stop codons in the ribosomal A-site to mediate release of the nascent chain and recycling of the ribosome. Bacteria decode stop codons using two separate release factors with differing specificities for the second and third bases. By contrast, eukaryotes rely on an evolutionarily unrelated omnipotent release factor (eRF1) to recognize all three stop codons. The molecular basis of eRF1 discrimination for stop codons over sense codons is not known. Here we present cryo-electron microscopy (cryo-EM) structures at 3.5-3.8 Å resolution of mammalian ribosomal complexes containing eRF1 interacting with each of the three stop codons in the A-site. Binding of eRF1 flips nucleotide A1825 of 18S ribosomal RNA so that it stacks on the second and third stop codon bases. This configuration pulls the fourth position base into the A-site, where it is stabilized by stacking against G626 of 18S rRNA. Thus, eRF1 exploits two rRNA nucleotides also used during transfer RNA selection to drive messenger RNA compaction. In this compacted mRNA conformation, stop codons are favoured by a hydrogen-bonding network formed between rRNA and essential eRF1 residues that constrains the identity of the bases. These results provide a molecular framework for eukaryotic stop codon recognition and have implications for future studies on the mechanisms of canonical and premature translation termination.

Abstract 2653: Preclinical activity of dual PI3K/mTOR inhibitor SPR965 in multiple myeloma

Introduction: Relapsed and refractory multiple myeloma (MM) remains a significant clinical challenge and drugs with new mechanisms of action to overcome resistance are needed. Constitutive activation of the PI3K/Akt/mTOR pathway in MM promotes tumorigenesis through propagation of the cell cycle, protein synthesis, and inhibition of apoptosis. Anti-MM effects of rapalogs are limited due to feedback activation of the PI3K/Akt signaling pathway. Agents capable of targeting PI3K and mTORC1 or both mTORC1/C2 are able to partially overcome such resistance mechanisms. However, the mTORC2 mediated increase in pAkt (Ser473) after PI3K/mTORC1 inhibition and the activation of PI3K after mTORC1/C2 inhibition could still contribute to resistance to such agents. We sought to investigate the effects of SPR965 (synthesized and provided by Sphaera Pharma, Singapore under an MTA), an orally bioavailable novel small molecule with inhibition of class 1 PI3 kinase and mTORC1/C2 kinases on MM cell lines and patient cells.

Results: SPR965 induced cytotoxicity and inhibited proliferation in all MM cell lines examined with IC50 values between 25-500nM. To understand if SPR965 induced apoptotic cell death, annexin/PI staining followed by flow cytometric assays were performed, which showed a clear increase in cells undergoing apoptosis. Western blots showed increase in caspase-3, -9, and PARP cleavage confirming apoptotic induction by SPR965. Importantly, SPR965 caused potent increase in apoptosis in cytogenetically distinct MM patient cells. Next, we examined the mechanism of action of SPR965. SPR965 caused potent mTORC1 inhibition evidenced by decreased p4E-BP1, p-p70S6K, and pS6 at doses as low as 25nM. SPR965 was able to inhibit PI3K activity as shown by decreased pPDK1 and pBTK at slightly higher concentrations of 75nM. Phosphorylation of Akt S473, a TORC2 substrate, increased at initial low concentrations of SPR965, but was attenuated at concentrations of 100 nM and above, demonstrating dose-dependent inhibition of mTORC2. Such effects were also observed when we performed western blots on MM patient derived primary plasma cells. Increased levels of p27 (KIP1) were observed suggestive of G1 growth arrest, which was confirmed on cell cycle analysis. Since SPR965 caused an increase in pAkt (both T308 and S473) at doses up to 75nM, we examined if SPR965 was able to synergize with an Akt inhibitor MK2206 at doses lower than 75nM. Our results showed potent synergy suggesting that the pAkt up regulation contributes to partial resistance, which is inhibited by SPR965 at doses of 100nM and higher, doses that are still clinically achievable.

Conclusion: Our findings demonstrate SPR965 induces apoptosis of MM cells through the inhibition of PI3K and mTORC1/C2 activity. Further studies are underway to better characterize the mechanism of action of SPR965, all of which will be informative for the drug to be used as a single agent or in combination with other agents in relapsed MM.

Citation Format: Jeremy T. Larsen, Vijay Ramakrishnan, Jessica Haug, Teresa Kimlinger, Somdutta Sen, Dinesh Mahajan, Sundeep Dugar, S. Vincent Rajkumar, Shaji K. Kumar. Preclinical activity of dual PI3K/mTOR inhibitor SPR965 in multiple myeloma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2653. doi:10.1158/1538-7445.AM2015-2653

Conformational Differences between Open and Closed States of the Eukaryotic Translation Initiation Complex

Translation initiation in eukaryotes begins with the formation of a pre-initiation complex (PIC) containing the 40S ribosomal subunit, eIF1, eIF1A, eIF3, ternary complex (eIF2-GTP-Met-tRNA_i), and eIF5. The PIC, in an open conformation, attaches to the 5′ end of the mRNA and scans to locate the start codon, whereupon it closes to arrest scanning. We present single particle cryo-electron microscopy (cryo-EM) reconstructions of 48S PICs from yeast in these open and closed states, at 6.0 Å and 4.9 Å, respectively. These reconstructions show eIF2β as well as a configuration of eIF3 that appears to encircle the 40S, occupying part of the subunit interface. Comparison of the complexes reveals a large conformational change in the 40S head from an open mRNA latch conformation to a closed one that constricts the mRNA entry channel and narrows the P site to enclose tRNA_i, thus elucidating key events in start codon recognition.

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Structures of eukaryotic translation initiation complexes in open and closed states

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In the open complex the 40S head moves upward to open the mRNA entry channel latch

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Transition to closed state locks initiator tRNA in the P site base-paired with AUG

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The structures show how eIF3 contacts eIF2 and eIF1 on the 40S subunit interface

A multidisciplinary team approach minimises prophylactic mastectomy rates

BACKGROUND

Prophylactic mastectomy (PM) has become increasingly common but is not without complications especially if accompanied by reconstructive surgery. In patients with sporadic unilateral breast cancer, contralateral PM offers no survival advantage. Multidisciplinary team (MDT) communication and interaction may facilitate shared decision-making and curtail PM rates. The aim of this study was investigate the effect of a regional MDT meeting on PM decision-making.

METHODS

We conducted an observational study involving retrospective review of prospectively recorded MDT meeting records for a 151 patient requests for PM from 2011 to 2014. Final MDT decisions were recorded as PM 'accepted', 'declined' or 'pending'. For MDT sanctioned requests, the factors justifying PM were recorded. Where PM was declined, justification for MDT refusal was sought and recorded.

RESULTS

Approximately half of all requests for PM have been upheld (53.0%) and 1/3 of requests have been declined (32.5%). Of those declined, low risk of contralateral breast cancer versus relatively high risk of systemic relapse were commonly cited as justification for PM refusal (45.7%). A proportion of patients who initiated PM discussion subsequently changed their minds (19.6%), or failed to attend clinic appointments (6.5%). Some patients were deemed medically unfit for complex reconstructive surgery (13%), or were declined on the basis of an apparent cosmetic drive for surgery (6.5%), concerns regarding depression or anxiety (2.2%) and/or if family history could not be substantiated (6.5%).

DISCUSSION

MDT meetings facilitate cross-specialty interrogation of requests for PM, minimise unnecessary surgery and restrict PM to those likely to derive maximum benefit.

Ribosome. The structure of the human mitochondrial ribosome

The highly divergent ribosomes of human mitochondria (mitoribosomes) synthesize 13 essential proteins of oxidative phosphorylation complexes. We have determined the structure of the intact mitoribosome to 3.5 angstrom resolution by means of single-particle electron cryogenic microscopy. It reveals 80 extensively interconnected proteins, 36 of which are specific to mitochondria, and three ribosomal RNA molecules. The head domain of the small subunit, particularly the messenger (mRNA) channel, is highly remodeled. Many intersubunit bridges are specific to the mitoribosome, which adopts conformations involving ratcheting or rolling of the small subunit that are distinct from those seen in bacteria or eukaryotes. An intrinsic guanosine triphosphatase mediates a contact between the head and central protuberance. The structure provides a reference for analysis of mutations that cause severe pathologies and for future drug design.

The ribosome emerges from a black box

Although the basic facts about the ribosome were already known 40 years ago, elucidating its atomic structure and molecular mechanisms required sheer persistence and the innovative use of new technology and methods. These advances have transformed our understanding of translation in the cell.

The Diamond Light Source and the challenges ahead for structural biology: some informal remarks

The remarkable advances in structural biology in the past three decades have led to the determination of increasingly complex structures that lie at the heart of many important biological processes. Many of these advances have been made possible by the use of X-ray crystallography using synchrotron radiation. In this short article, some of the challenges and prospects that lie ahead will be summarized.

Bactobolin A binds to a site on the 70S ribosome distinct from previously seen antibiotics

The ribosome is the target of a large number of antibiotics. Here, we report a 3.4-Å-resolution crystal structure of bactobolin A bound to 70S ribosome-tRNA complex. The antibiotic binds at a previously unseen site in the 50S subunit and displaces tRNA bound at the P-site. It thus likely has a similar mechanism of action as blasticidin S despite binding to a different site. The structure also rationalizes previously identified resistance mutations.

Photoinduced interaction studies on N-(2-methylthiophenyl)-2-hydroxy-1-naphthadiamine with TiO2 nanoparticles: a combined experimental and theoretical (DFT and spectroscopic) approach

Schiff base derivative synthesized by the reaction of 2-(methylthio) aniline and 2-hydroxy-1-naphthaldehyde exhibits keto-amine tautomerism in methanol solvent. The fluorescence quenching of N-(2-methyl thiophenyl)-2-hydroxy-1-naphthadiamine (NMTHN) by TiO2 nanoparticles in methanol has been studied. The excitation and emission peaks have been observed at 439 and 509nm respectively. The apparent association constant has been deduced from the absorption spectral changes of NMTHN-TiO2 nanoparticles using Bensi-Hildebrand equation. The number of binding sites and the binding constant have been calculated from the relevant fluorescence data. Quenching of fluorescence of NMTHN by TiO2 could be due to a dynamic mode. Density Functional Theory (DFT) calculations also have been performed to study the charge distribution of NMTHN-TiO2 both in ground and excited states. The HOMO-LUMO analysis of NMTHN-TiO2 in the ground state has been made.

Structural changes enable start codon recognition by the eukaryotic translation initiation complex

During eukaryotic translation initiation, initiator tRNA does not insert fully into the P decoding site on the 40S ribosomal subunit. This conformation (POUT) is compatible with scanning mRNA for the AUG start codon. Base pairing with AUG is thought to promote isomerization to a more stable conformation (PIN) that arrests scanning and promotes dissociation of eIF1 from the 40S subunit. Here, we present a cryoEM reconstruction of a yeast preinitiation complex at 4.0 Å resolution with initiator tRNA in the PIN state, prior to eIF1 release. The structure reveals stabilization of the codon-anticodon duplex by the N-terminal tail of eIF1A, changes in the structure of eIF1 likely instrumental in its subsequent release, and changes in the conformation of eIF2. The mRNA traverses the entire mRNA cleft and makes connections to the regulatory domain of eIF2?, eIF1A, and ribosomal elements that allow recognition of context nucleotides surrounding the AUG codon.

Structure of the large ribosomal subunit from human mitochondria

Human mitochondrial ribosomes are highly divergent from all other known ribosomes and are specialized to exclusively translate membrane proteins. They are linked with hereditary mitochondrial diseases and are often the unintended targets of various clinically useful antibiotics. Using single-particle cryogenic electron microscopy, we have determined the structure of its large subunit to 3.4 angstrom resolution, revealing 48 proteins, 21 of which are specific to mitochondria. The structure unveils an adaptation of the exit tunnel for hydrophobic nascent peptides, extensive remodeling of the central protuberance, including recruitment of mitochondrial valine transfer RNA (tRNA(Val)) to play an integral structural role, and changes in the tRNA binding sites related to the unusual characteristics of mitochondrial tRNAs.

Molecular recognition of curcumin (Indian Ayurvedic medicine) by the supramolecular probe, p-t-butyl calix(8)arene

The thermodynamic property of the host-guest complexes formed between the curcumin, component of Indian Ayurvedic medicine turmeric, a drug molecule, with the supra molecule, p-t-butyl calix(8)arene was studied. p-t-Butyl calix(8)arene has been used as a host molecule and curcumin as a guest molecule. Optical absorption spectral studies were carried out to investigate the molecular recognition properties of p-t-butyl calix(8)arene with curcumin. The stochiometry of the host-guest complexes formed and the binding constant were determined. An interesting 1:1 and 4:1 stochiometric host-guest complexes were formed. Job's continuous method of variation and Benesi-Hildebrand expression were used for the determination of binding constant and the stochiometry of the host-guest complex formed.

Initiation of translation by cricket paralysis virus IRES requires its translocation in the ribosome

The cricket paralysis virus internal ribosome entry site (CrPV-IRES) is a folded structure in a viral mRNA that allows initiation of translation in the absence of any host initiation factors. By using recent advances in single-particle electron cryomicroscopy, we have solved the structure of CrPV-IRES bound to the ribosome of the yeast Kluyveromyces lactis in both the canonical and rotated states at overall resolutions of 3.7 and 3.8 Å, respectively. In both states, the pseudoknot PKI of the CrPV-IRES mimics a tRNA/mRNA interaction in the decoding center of the A site of the 40S ribosomal subunit. The structure and accompanying factor-binding data show that CrPV-IRES binding mimics a pretranslocation rather than initiation state of the ribosome. Translocation of the IRES by elongation factor 2 (eEF2) is required to bring the first codon of the mRNA into the A site and to allow the start of translation.

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The high-resolution structure of CrPV-IRES bound to the ribosome was solved by cryoEM

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Pseudoknot I of CrPV-IRES binds in the decoding center, thus blocking the A site

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CrPV-IRES mimics a pretranslocation rather than initiation complex of the ribosome

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Translocation of CrPV-IRES by eEF2 is required for the start of translation

Structure of the yeast mitochondrial large ribosomal subunit

Mitochondria have specialized ribosomes that have diverged from their bacterial and cytoplasmic counterparts. We have solved the structure of the yeast mitoribosomal large subunit using single-particle cryo-electron microscopy. The resolution of 3.2 angstroms enabled a nearly complete atomic model to be built de novo and refined, including 39 proteins, 13 of which are unique to mitochondria, as well as expansion segments of mitoribosomal RNA. The structure reveals a new exit tunnel path and architecture, unique elements of the E site, and a putative membrane docking site.

Molecular recognition study of Carbamazepine, antiseizure drug, by p-t-butyl calix(8)arene

The formation of inclusion complex of Carbamazepine, a antiseizure drug molecule, with the supra molecule, p-t-butyl calix(8)arene was studied. p-t-Butyl calix(8)arene was the host molecule and Carbamazepine was the guest molecule. Optical absorption spectral studies were carried out to study the molecular recognition properties of p-t-butyl calix(8)arene with Carbamazepine. The stochiometry of the host-guest complex and the binding constant were determined.