Mechanism Of Protein Synthesis Inhibition Research Articles

Scientific Rationale and Clinical Basis for Clindamycin Use in the Treatment of Dermatologic Disease.

Clindamycin is a highly effective antibiotic of the lincosamide class. It has been widely used for decades to treat a range of skin and soft tissue infections in dermatology and medicine. Clindamycin is commonly prescribed for acne vulgaris, with current practice standards utilizing fixed-combination topicals containing clindamycin that prevent Cutibacterium acnes growth and reduce inflammation associated with acne lesion formation. Certain clinical presentations of folliculitis, rosacea, staphylococcal infections, and hidradenitis suppurativa are also responsive to clindamycin, demonstrating its suitability and versatility as a treatment option. This review describes the use of clindamycin in dermatological practice, the mechanism of protein synthesis inhibition by clindamycin at the level of the bacterial ribosome, and clindamycin's anti-inflammatory properties with a focus on its ability to ameliorate inflammation in acne. A comparison of the dermatologic indications for similarly utilized antibiotics, like the tetracycline class antibiotics, is also presented. Finally, this review addresses both the trends and mechanisms for clindamycin and antibiotic resistance, as well as the current clinical evidence in support of the continued, targeted use of clindamycin in dermatology.

1041 Atomic resolution structure of the cutibacterium acnes ribosome reveals the mechanism of protein synthesis inhibition by the antibiotic sarecycline

1041 Atomic resolution structure of the cutibacterium acnes ribosome reveals the mechanism of protein synthesis inhibition by the antibiotic sarecycline

Structures of proline-rich peptides bound to the ribosome reveal a common mechanism of protein synthesis inhibition.

With bacterial resistance becoming a serious threat to global public health, antimicrobial peptides (AMPs) have become a promising area of focus in antibiotic research. AMPs are derived from a diverse range of species, from prokaryotes to humans, with a mechanism of action that often involves disruption of the bacterial cell membrane. Proline-rich antimicrobial peptides (PrAMPs) are instead actively transported inside the bacterial cell where they bind and inactivate specific targets. Recently, it was reported that some PrAMPs, such as Bac71–35, oncocins and apidaecins, bind and inactivate the bacterial ribosome. Here we report the crystal structures of Bac71–35, Pyrrhocoricin, Metalnikowin and two oncocin derivatives, bound to the Thermus thermophilus 70S ribosome. Each of the PrAMPs blocks the peptide exit tunnel of the ribosome by simultaneously occupying three well characterized antibiotic-binding sites and interferes with the initiation step of translation, thereby revealing a common mechanism of action used by these PrAMPs to inactivate protein synthesis. Our study expands the repertoire of PrAMPs and provides a framework for designing new-generation therapeutics.

Abstract 2663: Idelalisib impacts cell growth through inhibiting translation regulatory mechanisms in mantle cell lymphoma

Abstract Idelalisib, also known as CAL-101 and GS1101, was approved in both the US and EU in 2014 to treat relapsed chronic lymphocytic leukemia (CLL), small lymphocytic lymphoma and follicular lymphoma. In CLL, idelalisib mechanism is not yet well-defined; however, it works in part by disrupting signaling from the tumor microenvironment, including from the B-cell receptor, which contributes to the reduction in lymph node size and increase in lymphocytosis in idelalisib-treated patients. Idelalisib selectively targets PI3Kδ, the predominantly expressed PI3K class IA family member in B-cell malignancies. PI3Kα, the more well-studied PI3K isoform is known to regulate translation and we hypothesized that PI3Kδ may similarly target translation in B-cell malignancies, such as in the aggressive and hard-to-treat mantle cell lymphoma (MCL). Treatment with 0.5-5 μM idelalisib over 24-48h resulted in moderate levels of apoptosis (4-10%), and reduction of both cell number (10-20%) and cell size (15-25%) in 3 MCL cell lines (Jeko-1, Mino, Granta 519). However, the cell size reduction was not cell cycle related. Idelalisib treatment also resulted in global protein synthesis inhibition (10-75%) in MCL cell lines and primary cells as detected by leucine incorporation assay. We confirmed that PI3K/AKT pathway is impacted by idelalisib treatment, as both AKT and GSK-3β phosphorylation were blocked by the treatment. To further examine the mechanism of protein synthesis inhibition, we investigated PI3K downstream pathways that regulate translation including the mTOR pathway. We detected decreased p70S6K (T387) and S6 (S235/236) phosphorylation in MCL cell lines, which are both downstream effectors of mTOR. In addition, we observed consistent reduction of PRAS40 (T246) phosphorylation, which is a binding partner and substrate of both AKT and mTOR. Interestingly, there was a concomitant decrease in p90RSK (T359/S363) phosphorylation, a known effector of MAPK/Erk pathway. P90RSK is directly activated by Erk, and also a regulator of mTOR and S6. In contrast, downstream translation regulator 4E-BP1 phosphorylation was unchanged following idelalisib treatment. Since 4E-BP1 activation is regulated by numerous upstream factors, redundant signaling pathways may be compensating for PI3Kδ inhibition. Consistent with effects on protein translation, preliminary results indicate induction of autophagy by idelalisib, which may be a novel mechanism that has not been previously reported in MCL. Our data provided mechanism of idelalisib-mediated effects on cell growth inhibition and suggest inhibition of protein translation as a potential mechanism. Citation Format: Qingshan Yang, Lisa S. Chen, Sattva S. Neelapu, Varsha Gandhi. Idelalisib impacts cell growth through inhibiting translation regulatory mechanisms in mantle cell lymphoma. [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 2663. doi:10.1158/1538-7445.AM2015-2663

Intracellular Expression of a Single Domain Antibody Reduces Cytotoxicity of 15-Acetyldeoxynivalenol in Yeast

15-Acetyldeoxynivalenol (15-AcDON) is a low molecular weight sesquiterpenoid trichothecene mycotoxin associated with Fusarium ear rot of maize and Fusarium head blight of small grain cereals. The accumulation of mycotoxins such as deoxynivalenol (DON) and 15-AcDON within harvested grain is subject to stringent regulation as both toxins pose dietary health risks to humans and animals. These toxins inhibit peptidyltransferase activity, which in turn limits eukaryotic protein synthesis. To assess the ability of intracellular antibodies (intrabodies) to modulate mycotoxin-specific cytotoxocity, a gene encoding a camelid single domain antibody fragment (V(H)H) with specificity and affinity for 15-AcDON was expressed in the methylotropic yeast Pichia pastoris. Cytotoxicity and V(H)H immunomodulation were assessed by continuous measurement of cellular growth. At equivalent doses, 15-AcDON was significantly more toxic to wild-type P. pastoris than was DON. In turn, DON was orders of magnitude more toxic than 3-acetyldeoxynivalenol. Intracellular expression of a mycotoxin-specific V(H)H within P. pastoris conveyed significant (p = 0.01) resistance to 15-AcDON cytotoxicity at doses ranging from 20 to 100 mug.ml(-1). We also documented a biochemical transformation of DON to 15-AcDON to account for the attenuation of DON cytotoxicity at 100 and 200 mug.ml(-1). The proof of concept established within this eukaryotic system suggests that in planta V(H)H expression may lead to enhanced tolerance to mycotoxins and thereby limit Fusarium infection of commercial agricultural crops.

Hypoxia Inhibits Protein Synthesis through a 4E-BP1 and Elongation Factor 2 Kinase Pathway Controlled by mTOR and Uncoupled in Breast Cancer Cells

Hypoxia is a state of low oxygen availability that limits tumor growth. The mechanism of protein synthesis inhibition by hypoxia and its circumvention by transformation are not well understood. Hypoxic breast epithelial cells are shown to downregulate protein synthesis by inhibition of the kinase mTOR, which suppresses mRNA translation through a novel mechanism mitigated in transformed cells: disruption of proteasome-targeted degradation of eukaryotic elongation factor 2 (eEF2) kinase and activation of the regulatory protein 4E-BP1. In transformed breast epithelial cells under hypoxia, the mTOR and S6 kinases are constitutively activated and the mTOR negative regulator tuberous sclerosis complex 2 (TSC2) protein fails to function. Gene silencing of 4E-BP1 and eEF2 kinase or TSC2 confers resistance to hypoxia inhibition of protein synthesis in immortalized breast epithelial cells. Breast cancer cells therefore acquire resistance to hypoxia by uncoupling oxygen-responsive signaling pathways from mTOR function, eliminating inhibition of protein synthesis mediated by 4E-BP1 and eEF2.

Aminoglycoside-Induced Reduction in Nucleotide Mobility at the Ribosomal RNA A-Site as a Potentially Key Determinant of Antibacterial Activity

Steady-state and time-resolved fluorescence techniques have been used to characterize the energetics and dynamics associated with the interaction of an E. coli 16 S rRNA A-site model oligonucleotide and four aminoglycoside antibiotics that exhibit a broad range of antibacterial activity. The results of these characterizations suggest that aminoglycoside-induced reduction in the mobility of an adenine residue at position 1492 of the rRNA A-site is a more important determinant of antibacterial activity than drug affinity for the A-site. This observation is consistent with a recently proposed model for the mechanism of protein synthesis inhibition by aminoglycosides that invokes a drug-induced alteration in the conformational equilibrium of the rRNA A-site (centered around the conserved adenine residues at positions 1492 and 1493), which, in turn, promotes an enhanced interaction between the rRNA and the minihelix formed by the tRNA anticodon and the mRNA codon, even when the anticodon is noncognate. Regarded as a whole, the results reported here indicate that the rational design of antibiotics that target the 16 S rRNA A-site requires consideration of not only the structure and energetics of the drug-RNA complex but also the dynamics associated with that complex.

Effects of moxifloxacin in zymogen A or S. aureus stimulated human THP-1 monocytes on the inflammatory process and the spread of infection

Antimicrobial agents have been reported to exhibit immunomodulatory and anti-inflammatory activities, both in vivo and in vitro (e.g., in human lymphocytes, macrophages and monocytes). The effects of moxifloxacin on cytokine immunomodulatory mediators, free radical generation and hydrolytic enzyme activities in zymogen A-stimulated human THP-1 monocytes were evaluated. An increase in c-AMP levels, protein kinase C activity, and the release of nitric oxide and hydrogen peroxide with a decrease in pH occurred within the first hour. Further, the effects of moxifloxacin were reduced by agents which blocked the oxygen burst, lysosome-phagosome fusion, and the energy generation within the cell. After 4 h, there was a decrease in NAG and cathepsin D activities, lipid peroxidation and the release of pro-inflammatory cytokines. These data indicate that moxifloxacin may modify the acute-phase inflammatory responses through inhibition of cytokine release in monocytes. Moxifloxacin inhibited the release of TNFα, IL-1, IL-6, and IL-8 in a concentration-dependent manner across a range of 0.004 to 4 μg/mL. After 4 h, there was a decrease in the release of these cytokines, thus interfering with the inflammation process to reduce infection and its spread. The effects of moxifloxacin appear initially to activate monocytes to kill bacteria through the innate immune process by releasing ROS and lysosomal hydrolytic enzymes as well as phagocytosis of the organism. At a later time the bacteria are killed through a Bacterialstatic mechanism of protein synthesis inhibition and there is a reversal of the effects of moxifloxacin on cytokine release, free radical generation and hydrolytic enzymes so that lipid peroxidation and tissue destruction by the infection process is suppressed.

The oxazolidinones as a new family of antimicrobial agent

The oxazolidinones are a new chemical class of synthetic antmicrobials characterized by a unique mechanism of protein synthesis inhibition. Linezolid is the first compound of this class and has recently received approval for the treatment of community- and hospital-acquired pneumonia and skin and skin structure infections. In vitro tests demonstrate that linezolid possesses a significant activity against Gram-positive pathogens including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), vancomycin-intermediate strains (VISA) and penicillin-resistant pneumococci (PRPN). Combined with other drugs linezolid interacts favourably against many important pathogens and it is able to affect some bacterial virulence factors as well as produce a postantibiotic effect. Results from experimental models of infection reveal linezolid to be highly active in vivo against infections due to Gram-positive pathogens. Linezolid may be administered either intravenously or orally with oral bioavailability of approximately 100% and limited adverse effects. The clinical efficacy of linezolid has been investigated in several phase II and III trials. Linezolid has been proved to be useful in severe infections sustained by multiresistant Gram-positive micro-organisms. Synthesis of the second-generation oxazolidinones with improved potency against Gram-positive and negative bacteria is currently under way.

Oxazolidinones

The oxazolidinones represent a novel chemical class of synthetic antimicrobial agents. They exhibit an unique mechanism of protein synthesis inhibition and generally display bacteriostatic activity against many important human pathogens, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and penicillin- and cephalosporin-resistant Streptococcus pneumoniae. Linezolid, the oxazolidinone which has been selected for clinical development, has near complete oral bioavailability plus favourable pharmacokinetic and toxicity profiles. Results from experimental models of infection and phase II trials reveal linezolid to be highly active in vivo against infections due to many common gram-positive pathogens. The role of linezolid remains to be determined in phase III clinical trials, but it shows great promise as an alternative to glycopeptides and streptogramins to treat serious infections due to resistant gram-positive organisms. Further modification of the oxazolidinone nucleus may yield agents with even greater potency and with novel spectra of activity.

Reducing Agents Mitigate Protein Synthesis Inhibition Mediated by Vanadate and Vanadyl Compounds in Reticulocyte Lysates

Recently, we synthesized and characterized vanadyl saccharides to evaluate the effects of various vanadate and vanadyl complexes, which differ in their oxidation states on various biomacromolecules and cellular activities (1, 2). Here, we report that both vanadate (+V oxidation state) and different vanadyl species (+IV oxidation state) such as vanadyld-glucose, vanadyl diascorbate, and vanadyl sulfate, impair the formation of polysomes and inhibit the initiation of protein synthesis in hemin-supplemented rabbit reticulocyte lysates. Vanadate inhibits protein synthesis more severely than vanadyl species and is consistent with the idea that vanadate is reduced to vanadyl state intracellularly. The inhibition of protein synthesis caused by low concentrations (10–20 μM) of vanadate and vanadyl species is effectively mitigated by reducing agents such as dithiothreitol, reduced glutathione (GSH), or reduced pyridine dinucleotide. A significant decrease in the protein synthesis inhibition in vanadate-treated lysates by GSH suggests that the mechanism of protein synthesis inhibition by vanadate is different than the action of other oxidants such as heavy metal ions and oxidized glutathione. This suggestion is also consistent with the findings that vanadium compounds do not stimulate phosphorylation of the alpha (α) subunit of initiation factor 2 (eIF2) or decrease the guanine nucleotide exchange activity of eIF2B, which is required to exchange GDP for GTP in eIF2·GDP binary complex. The reduction of vanadate to vanadyl state and the subsequent complex formation of vanadyl species with the endogenous reducing compounds or with the -SH groups of certain proteins may be the cause for protein synthesis inhibition in lysates.

Mechanism of protein synthesis inhibition by didemnin B in vitro.

The cytotoxic and immunosuppressive marine depsipeptide didemnin B is a potent inhibitor of protein biosynthesis in intact cells. Here, didemnin B is shown to inhibit protein synthesis in vitro during the elongation cycle, by preventing eukaryotic elongation factor 2-(eEF-2-) dependent translocation. No inhibition of aminoacyl-tRNA delivery or of peptidyltransferase activity is observed. Didemnin B stimulates eEF-1 alpha-dependent aminoacyl-tRNA binding to rabbit reticulocyte ribosomes, and eEF-1 alpha is required for inhibition of the subsequent translocation of phenylalanyl-tRNA(Phe) from the A- to the P-site. These observations suggest that didemnin B prevents translocation by stabilizing aminoacyl-tRNA bound to the ribosomal A-site, similar to the antibiotic kirromycin, and consistent with the known affinity of didemnins for elongation factor eEF-1 alpha [Crews et al. (1994) J. Biol. Chem. 269, 15411]. Unlike kirromycin, didemnin B does not prevent peptide bond formation, so inhibition is observed only at the translocation step. Inhibition of translocation by didemnin B is attenuated by increasing concentrations of eEF-2.

Characterization of the Mechanism of Cellular and Cell Free Protein Synthesis Inhibition by an Anti-tumor Ribonuclease

Onconase, a protein with anti-tumor activity, causes potent inhibition of protein synthesis in the rabbit reticulocyte lysate (IC5010−11M) and when microinjected into Xenopus oocytes (IC5010−10M). Onconase is a member of the RNase A superfamily; however, unlike RNase A, the mechanism of protein synthesis inhibition does not involve apparent degradation of lysate or cellular ribosomal RNAs. Rather, reticulocyte and oocyte tRNA is hydrolyzed after Onconase treatment. Furthermore, re-addition of tRNA to Onconase pretreated lysates or oocytes restores the translational capacity of the system. Taken together these results suggest that Onconase causes potent protein synthesis inhibition by a mechanism involving inactivation of cellular tRNA.

Mechanism of protein synthesis inhibition by vaccinia viral core and reversal of this inhibition by reticulocyte peptide chain initiation factors

Vaccinia viral core inhibits protein synthesis in heme-supplemented reticulocyte lysate. A reticulocyte cell suPernatant factor, which reversed Protein synthesis inhibition in heme-deficient reticulocyte lysate also reversed vaccinia viral core induced Protein synthesis inhibition in heme-suPPlemented reticulocyte lysate. Significant inhibition reversal activity was also observed with a partially purified eukaryotic initiation factor-2 PreParation and this activity was lost uPon further Purification of eukaryotic initiation factor-2.The ribosomal salt-wash factor Co-eukaryotic initiation factor-2 which like reticulocyte suPernatant factor contains guanine nucleotide exchange factor activity, was comPletely inactive. Vaccinia viral core induced detectable level of eukaryotic initiation factor-2 α-subunit phosphorylation when incubated in the heme-supplemented reticulocyte lysate. This lysate preparation contains guanine nucleotide exchange factor activity. However, when the same reticulocyte lysate was previously incubated with the vaccinia viral core, the guanine nucleotide exchange factor activity during subsequent incubation was almost comPletely inhibited.

Roles of Eukaryotic Initiation Factor 2 Ancillary Factors in the Regulation of Eukaryotic Protein Synthesis Initiation

This chapter discusses a possible mechanism of protein synthesis inhibition by eukaryotic initiation factor-2 (eIF-2) kinases, heme-regulated protein synthesis inhibitor, and double-stranded RNA-activated inhibitor; it discusses the roles of four eIF-2 ancillary protein factors in the complex regulation of protein synthesis initiation in animal cells. The loss of interaction of eIF-2α(P) with Co-eIF-2B and Co-eIF-2C has been suggested as the mechanism of protein synthesis inhibition by eIF-2 kinases. However, a direct evidence that the formation of eIF-2α(P) and consequent loss of interaction of eIF-2α(P) with Co-eIF-2B and Co-eIF-2C are the sole cause of protein synthesis inhibition in heme-deficient reticulocyte lysates is still lacking. The four eIF-2 ancillary factors, Co-eIF-2A, Co-eIF-2B, Co-eIF-2C, and reversal factor, have been characterized by their effects on eIF-2 activity in vitro . The requirement for Co-eIF-2A for protein synthesis in reticulocyte lysates is shown by using antibodies. It has not yet been possible to reconstitute from purified components an efficient protein-synthesizing system with which to examine the requirements for specific factors in overall peptide chain initiation.

Mechanism of protein synthesis inhibition during stationary phase in Bacillus stearothermophilus.

The appearance of a protein (association factor I) in ribosomes from Bacillus stearothermophilus at stationary phase of growth is described. Association factor I is present on 30S subunits and 30S-50S ribosomal couples, but not on 50S subunits. This protein is responsible for the low levels of polyphenylalanine synthesis shown by stationary phase ribosomes. Association factor I is able to bind to free 30S-50S ribonsomal couples but not to polysomes, and exerts its effect by inhibiting the initiation step of protein synthesis. Ribonsomes preincubated with association factor I have a decreased ability for polypeptide synthesis directed page mRNA or poly(U).

Inhibition of cell-free protein synthesis by low-molecular-weight nuclear polyadenylate-containing ribonucleic acid species isolated from the lactating guinea pig.

1. Poly(A)-containing RNA was isolated from the nuclei of mammary gland, liver and brain of lactating guinea pigs. 2. Total nuclear poly(A)-containing RNA from mammary gland inhibited mRNA-directed protein synthesis by a wheat-germ cell-free system. It also inhibited the endogenous activity of the wheat-germ and other cell-free systems. It did not inhibit a wheat-germ cell-free system directed by poly(U). 3. Total nuclear poly(A)-containing RNA from liver and brain did not inhibit the mRNA-directed wheat-germ system. 4. Fractionation of the nuclear poly(A)-containing RNA revealed inhibitory activity in the less than 10 S fraction from mammary gland as well as that from liver and brain. 5. The mechanism of protein-synthesis inhibition appeared to be at the level of elongation. 6. The inhibitory activity could be reversed in a wheat-germ system by increasing the amount of S-30 supernatant. 7. The mechanism of inhibition of protein synthesis is discussed in relation to other RNA species known to inhibit such systems.

Protein synthesis in rabbit reticulocytes: mechanism of protein synthesis inhibition by heme-regulated inhibitor.

Partially purified Met-tRNAf binding factor, eIF-2, was phosphorylated by using heme-regulated inhibitor (HRI). Phosphorylated eIF-2 was freed from HRI by phosphocellulose column chromatography. Analysis by isoelectric focusing showed 100% phosphorylation of the 38,000-dalton subunit of eIF-2. Both eIF-2 and eIF-2(P) formed ternary complexes with Met-tRNAf and GTP with almost the same efficiency, and in both cases the ternary complex formation was drastically inhibited by prior addition of Mg2+. However, whereas the ternary complexes formed with eIF-2 could be stimulated by Co-eIF-2C at 1 mM Mg2+ and dissociated by Co-eIF-2B at 5 mM Mg2+, the ternary complexes formed with eIF-2(P) were unresponsive to both Co-eIF-2B and Co-e-IF-2C. Also, under conditions of eIF-2 phosphorylation, HRI drastically inhibited AUG-dependent Met-tRNAf binding to 40S ribosomes. However, HRI (in the presence of ATP) had no effect on the joining of preformed Met-tRNAf . 40S . AUG complex to the 60S ribosomal subunit to form Met-tRNAf-80S . AUG complex. These studies suggest that HRI inhibits protein synthesis initiation by phosphorylation of the 38,000-dalton subunit of eIF-2. HRI-phosphorylated eIF-2 does not interact with at least two other protein factors, Co-eIF-2B and Co-eIF-2C, and is thus inactive in protein synthesis initiation.

On the mechanism of protein-synthesis inhibition by abrin and ricin. Inhibition of the GTP-hydrolysis site on the 60-S ribosomal subunit.

The mechanism of protein synthesis inhibition by the toxic lectins, abrin and ricin, has been studied in crude and in purified cell-free systems from rabbit reticulocytes and Krebs II ascites cells. In crude systems abrin and ricin strongly inhibited protein synthesis from added aminoacyl-tRNA, demonstrating that the toxins act at some point after the charging of tRNA. Supernatant factors and polysomes washed free of elongation factors were treated separately with the toxins and then neutralizing amounts of anti-toxins were added. Recombination experiments between toxin-treated ribosomes and untreated supernatant factors and vice versa showed that the toxin-treated ribosomes had lost most of their ability to support polyphenylalanine synthesis, whereas treatment of the supernatant factors with the toxins did not inhibit polypeptide synthesis. Recombination experiments between toxin-treated isolated 40-S subunits and untreated 60-S subunits and vice versa showed that only when the 60-S subunits had been treated with the toxins was protein synthesis inhibited in the reconstituted system. The incorporation of [3H]puromycin into nascent peptide chains was unaffected by the toxins, indicating that the peptidyl transferase is not inhibited. Both the EF-1-catalyzed and the EF-2-catalyzed ability of the ribosomes to hydrolyze [gamma-32P]GTP was inhibited by abrin and ricin. An 8-S complex released from the 60-S subunit by EDTA treatment possessed both GTPase and ATPase activity, while the particle remaining after the EDTA treatment had lost most of its GTPase activity. Both enzyme activities of the 8-S complex were inhibited by abrin and ricin. The present data indicate that there is a common site on the 60-S subunits for EF-1- and EF-2- stimulated GTPase activity and they suggest that abrin and ricin inhibit protein synthesis by modifying this site.

Mechanism of protein synthesis inhibition by fusidic acid and related antibiotics

Mechanism of protein synthesis inhibition by fusidic acid and related antibiotics