Mapping Differential Protein-Protein Interaction Networks using Affinity Purification Mass Spectrometry.

Proteins congregate into complexes to perform fundamental cellular functions. Phenotypic outcomes, in health and disease, are often mechanistically driven by the remodeling of protein complexes by protein-coding mutations or cellular signaling changes in response to molecular cues. Here, we present an affinity purification-mass spectrometry (APMS) proteomics protocol to quantify and visualize global changes in protein-protein interaction (PPI) networks between pairwise conditions. We describe steps for expressing affinity-tagged "bait" proteins in mammalian cells, identifying purified protein complexes, quantifying differential PPIs, and visualizing differential PPI networks. Specifically, this protocol details steps for designing affinity-tagged "bait" gene constructs, transfection, affinity purification, mass spectrometry sample preparation, data acquisition, database search, data quality control, PPI confidence scoring, cross-run normalization, statistical data analysis, and differential PPI visualization. Our protocol discusses caveats and limitations with applicability across cell types and biological areas. For complete details on the use and execution of this protocol, please refer to Bouhaddou et al. 20231.

Parkinsonism-hyperpyrexia, a rare consequence of deep brain stimulator malfunction in advanced Parkinson's disease.

Parkinsonism-hyperpyrexia syndrome (PHS) is a rare neurological emergency that shares clinical features with neuroleptic malignant syndrome. It is usually due to sudden deprivation of dopaminergic treatment, although there are cases related to failure of the deep brain stimulation system.

CRISPR-Cas9 screen of E3 ubiquitin ligases identifies TRAF2 and UHRF1 as regulators of HIV latency in primary human T cells.

During HIV infection of CD4+ T cells, ubiquitin pathways are essential to viral replication and host innate immune response; however, the role of specific E3 ubiquitin ligases is not well understood. Proteomics analyses identified 116 single-subunit E3 ubiquitin ligases expressed in activated primary human CD4+ T cells. Using a CRISPR-based arrayed spreading infectivity assay, we systematically knocked out 116 E3s from activated primary CD4+ T cells and infected them with NL4-3 GFP reporter HIV-1. We found 10 E3s significantly positively or negatively affected HIV infection in activated primary CD4+ T cells, including UHRF1 (pro-viral) and TRAF2 (anti-viral). Furthermore, deletion of either TRAF2 or UHRF1 in three JLat models of latency spontaneously increased HIV transcription. To verify this effect, we developed a CRISPR-compatible resting primary human CD4+ T cell model of latency. Using this system, we found that deletion of TRAF2 or UHRF1 initiated latency reactivation and increased virus production from primary human resting CD4+ T cells, suggesting these two E3s represent promising targets for future HIV latency reversal strategies. IMPORTANCE: HIV, the virus that causes AIDS, heavily relies on the machinery of human cells to infect and replicate. Our study focuses on the host cell's ubiquitination system which is crucial for numerous cellular processes. Many pathogens, including HIV, exploit this system to enhance their own replication and survival. E3 proteins are part of the ubiquitination pathway that are useful drug targets for host-directed therapies. We interrogated the 116 E3s found in human immune cells known as CD4+ T cells, since these are the target cells infected by HIV. Using CRISPR, a gene-editing tool, we individually removed each of these enzymes and observed the impact on HIV infection in human CD4+ T cells isolated from healthy donors. We discovered that 10 of the E3 enzymes had a significant effect on HIV infection. Two of them, TRAF2 and UHRF1, modulated HIV activity within the cells and triggered an increased release of HIV from previously dormant or "latent" cells in a new primary T cell assay. This finding could guide strategies to perturb hidden HIV reservoirs, a major hurdle to curing HIV. Our study offers insights into HIV-host interactions, identifies new factors that influence HIV infection in immune cells, and introduces a novel methodology for studying HIV infection and latency in human immune cells.

Impact of SARS-CoV-2 ORF6 and its variant polymorphisms on host responses and viral pathogenesis.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) encodes several proteins that inhibit host interferon responses. Among these, ORF6 antagonizes interferon signaling by disrupting nucleocytoplasmic trafficking through interactions with the nuclear pore complex components Nup98-Rae1. However, the roles and contributions of ORF6 during physiological infection remain unexplored. We assessed the role of ORF6 during infection using recombinant viruses carrying a deletion or loss-of-function (LoF) mutation in ORF6. ORF6 plays key roles in interferon antagonism and viral pathogenesis by interfering with nuclear import and specifically the translocation of IRF and STAT transcription factors. Additionally, ORF6 inhibits cellular mRNA export, resulting in the remodeling of the host cell proteome, and regulates viral protein expression. Interestingly, the ORF6:D61L mutation that emerged in the Omicron BA.2 and BA.4 variants exhibits reduced interactions with Nup98-Rae1 and consequently impairs immune evasion. Our findings highlight the role of ORF6 in antagonizing innate immunity and emphasize the importance of studying the immune evasion strategies of SARS-CoV-2.

Proteomic and genetic analyses of influenza A viruses identify pan-viral host targets.

Influenza A Virus (IAV) is a recurring respiratory virus with limited availability of antiviral therapies. Understanding host proteins essential for IAV infection can identify targets for alternative host-directed therapies (HDTs). Using affinity purification-mass spectrometry and global phosphoproteomic and protein abundance analyses using three IAV strains (pH1N1, H3N2, H5N1) in three human cell types (A549, NHBE, THP-1), we map 332 IAV-human protein-protein interactions and identify 13 IAV-modulated kinases. Whole exome sequencing of patients who experienced severe influenza reveals several genes, including scaffold protein AHNAK, with predicted loss-of-function variants that are also identified in our proteomic analyses. Of our identified host factors, 54 significantly alter IAV infection upon siRNA knockdown, and two factors, AHNAK and coatomer subunit COPB1, are also essential for productive infection by SARS-CoV-2. Finally, 16 compounds targeting our identified host factors suppress IAV replication, with two targeting CDK2 and FLT3 showing pan-antiviral activity across influenza and coronavirus families. This study provides a comprehensive network model of IAV infection in human cells, identifying functional host targets for pan-viral HDT.

Network modeling suggests HIV infection phenocopies PI3K-AKT pathway mutations to enhance HPV-associated cervical cancer.

Women coinfected with human immunodeficiency virus type 1 (HIV-1) and human papillomavirus (HPV) are six times as likely to develop invasive cervical carcinoma compared to those without HIV. Unlike other HIV-associated cancers, the risk of cervical cancer development does not change when HPV/HIV coinfected women begin antiretroviral therapy, suggesting HIV-associated immune suppression is not a key driver of cervical cancer development in coinfected women. Here, we investigated whether the persistent secretion of inflammatory factors in HIV-positive patients on antiretroviral therapy could enhance cancer signaling in HPV-infected cervical cells via endocrine mechanisms. We integrated previously reported HIV-induced secreted inflammatory factors (Hi-SIFs), HIV and HPV virus-human protein interactions, and cervical cancer patient genomic data using network propagation to understand the pathways underlying disease development in HPV/HIV coinfection. Our results pinpointed the PI3K-AKT signaling pathway to be enriched at the interface between Hi-SIFs and HPV-host molecular networks, in alignment with PI3K pathway mutations being prominent drivers of HPV-associated, but HIV independent, cervical cancer development. Furthermore, we experimentally stimulated cervical cells with 14 Hi-SIFs to assess their ability to activate PI3K-AKT signaling. Strikingly, we found 8 factors (CD14, CXCL11, CXCL9, CXCL13, CXCL17, AHSG, CCL18, and MMP-1) to significantly upregulate AKT phosphorylation (pAKT-S473) relative to a phosphate buffered saline control. Our findings suggest that Hi-SIFs cooperate with HPV infection in cervical cells to over-activate PI3K-AKT signaling, effectively phenocopying PI3K-AKT pathway mutations, resulting in enhanced cervical cancer development in coinfected women. Our insights could support the design of therapeutic interventions targeting the PI3K-AKT pathway or neutralizing Hi-SIFs in HPV/HIV coinfected cervical cancer patients.

Image reconstruction algorithm for laser-induced ultrasonic imaging: The single sensor scanning synthetic aperture focusing technique.

This paper aims to implement a laser-induced ultrasound imaging reconstruction method based on the delay-and-sum beamforming through the synthetic aperture focusing technique (SAFT) for a circular scanning, performed with a tomograph that had one acoustic sensor and a system that rotates the sample around a fixed axis. The proposed method, called the Single-sensor Scanning Synthetic Aperture Focusing Technique, considers the size of the sensor and the detection procedure inside the SAFT's algebra. This image reconstruction method was evaluated numerically, using the Green function for the laser-induced ultrasound wave equation to generate a forward problem, and experimentally, using a solid object of polylactic acid, and a Sprague-Dawley rat heart located in a tissue-mimicking phantom. The resulting images were compared to those obtained from the time reversal and the conventional delay-and-sum reconstruction algorithms. The presented method removes the sidelobe artifacts and the comet tail sign, which produces a more distinguishable target on the image. In addition, the proposed method has a faster performance and lower computational load. The implementation of this method in photoacoustic microscopy techniques for image reconstruction is discussed.

A virological view of tenascin-C in infection.

Tenascin-C is a large extracellular matrix glycoprotein with complex, not yet fully unveiled roles. Its context- and structure-dependent modus operandi renders tenascin-C a puzzling protein. Since its discovery ∼40 years ago, research into tenascin-C biology continues to reveal novel functions, the most recent of all being its immunomodulatory activity, especially its role in infection, which is just now beginning to emerge. Here, we explore the role of tenascin-C in the immune response to viruses, including SARS-CoV-2 and HIV-1. Recently, tenascin-C has emerged as a biomarker of disease severity during COVID-19 and other viral infections, and we highlight relevant RNA sequencing and proteomic analyses that suggest a correlation between tenascin-C levels and disease severity. Finally, we ask what the function of this protein during viral replication is and propose tenascin-C as an intercellular signal of inflammation shuttled to distal sites via exosomes, a player in the repair and remodeling of infected and damaged tissues during severe infectious disease, as well as a ligand for specific pathogens with distinct implications for the host.

Evasion of cGAS and TRIM5 defines pandemic HIV.

Of the 13 known independent zoonoses of simian immunodeficiency viruses to humans, only one, leading to human immunodeficiency virus (HIV) type 1(M) has become pandemic, causing over 80 million human infections. To understand the specific features associated with pandemic human-to-human HIV spread, we compared replication of HIV-1(M) with non-pandemic HIV-(O) and HIV-2 strains in myeloid cell models. We found that non-pandemic HIV lineages replicate less well than HIV-1(M) owing to activation of cGAS and TRIM5-mediated antiviral responses. We applied phylogenetic and X-ray crystallography structural analyses to identify differences between pandemic and non-pandemic HIV capsids. We found that genetic reversal of two specific amino acid adaptations in HIV-1(M) enables activation of TRIM5, cGAS and innate immune responses. We propose a model in which the parental lineage of pandemic HIV-1(M) evolved a capsid that prevents cGAS and TRIM5 triggering, thereby allowing silent replication in myeloid cells. We hypothesize that this capsid adaptation promotes human-to-human spread through avoidance of innate immune response activation.

Impact of SARS-CoV-2 ORF6 and its variant polymorphisms on host responses and viral pathogenesis.

We and others have previously shown that the SARS-CoV-2 accessory protein ORF6 is a powerful antagonist of the interferon (IFN) signaling pathway by directly interacting with Nup98-Rae1 at the nuclear pore complex (NPC) and disrupting bidirectional nucleo-cytoplasmic trafficking. In this study, we further assessed the role of ORF6 during infection using recombinant SARS-CoV-2 viruses carrying either a deletion or a well characterized M58R loss-of-function mutation in ORF6. We show that ORF6 plays a key role in the antagonism of IFN signaling and in viral pathogenesis by interfering with karyopherin(importin)-mediated nuclear import during SARS-CoV-2 infection both in vitro , and in the Syrian golden hamster model in vivo . In addition, we found that ORF6-Nup98 interaction also contributes to inhibition of cellular mRNA export during SARS-CoV-2 infection. As a result, ORF6 expression significantly remodels the host cell proteome upon infection. Importantly, we also unravel a previously unrecognized function of ORF6 in the modulation of viral protein expression, which is independent of its function at the nuclear pore. Lastly, we characterized the ORF6 D61L mutation that recently emerged in Omicron BA.2 and BA.4 and demonstrated that it is able to disrupt ORF6 protein functions at the NPC and to impair SARS-CoV-2 innate immune evasion strategies. Importantly, the now more abundant Omicron BA.5 lacks this loss-of-function polymorphism in ORF6. Altogether, our findings not only further highlight the key role of ORF6 in the antagonism of the antiviral innate immune response, but also emphasize the importance of studying the role of non-spike mutations to better understand the mechanisms governing differential pathogenicity and immune evasion strategies of SARS-CoV-2 and its evolving variants. ONE SENTENCE SUMMARY: SARS-CoV-2 ORF6 subverts bidirectional nucleo-cytoplasmic trafficking to inhibit host gene expression and contribute to viral pathogenesis.

SARS-CoV-2 vaccination patterns in a private hematology and internal medicine outpatient clinic.

OBJECTIVE: Determine the proportion of vaccinated patients in a private hematology and internal medicine outpatient clinic and potential factors in adherence in at-risk patients (due to onco-hematological diseases). MATERIALS AND METHODS: This is a cross-sectional study of outpatients from a private clinic. We applied a non-validated instrument to all patients attending the outpatient clinic from May to October 2021. According to the primary diagnosis, we classified patients into onco-hematological and non-onco-hematological patients. Since national authorities exclusively executed and planned the rollout of vaccines, the order and eligibility defined by authorities of vaccination was considered when conducting the analysis and patients were classified according to the their corresponding group. RESULTS: 397 participants were accrued, 269 (68%) had an onco-hematological condition. In the whole group, 73 (18.3%) had a history of infection. Vaccination history was present in 286 persons (72%); 82% had two doses. In the subset of 269 persons with an onco-hematological condition, 191 (71%) were vaccinated, whereas 95 participants with non-hematological conditions (73%) had received the vaccine. Vaccination status was associated with age (OR 1.07, 95%CI: 1.03,1.10, p<0.0001) and body mass index (OR 1.11, 95%CI: 1.04,1.17, p<0.0001). CONCLUSIONS: According to our study, vaccination adherence at our center is significantly different from the nationwide proportion of vaccines.

Long-term results of the treatment of adolescents and adults with acute lymphoblastic leukemia with a pediatric-inspired regimen delivered on an outpatient basis: A single institution experience.

The results of treatment of adolescents and adults with acute lymphoblastic leukemia (ALL) remain unsatisfactory. Pediatric-inspired treatments seem to be related with better outcomes. 126 adolescent and adult patients with ALL were treated in a 37-year period with a pediatric inspired combined chemotherapy (PICC) schedule, delivered on an outpatient basis and based on the St. Jude´s TOTAL XI pediatric protocol employing vincristine, prednisone, asparaginase, daunorubicin, etoposide, cytarabine, methotrexate, mercaptopurine and triple intrathecal therapy. 80 % of patients were able to receive the initial seven-week period of induction / consolidation fully as outpatients and 77 % achieved a complete remission. In adolescents and young adults (AYAs) the median probability of overall survival (OS) was 44 months, whereas the 5-year OS was 48 %. In adults, the median probability of OS was 24 months, and the 5-year OS was 32 %. Patients with T-cell ALL did significantly worse than those with a B cell phenotype (OS at 5 years 17 versus 40 %, respectively). These figures are better than those informed in our country employing more aggressive, in-hospital schedules such as the hyper-CVAD. We found that, in AYAs and adult patients with ALL, the use of an asparaginase-containing PICC delivered on an outpatient basis renders acceptable results, better than those obtained in similar socioeconomic circumstances employing adult-oriented schedules. Additional studies are needed to assess the usefulness of these PICC treatments in adult individuals with ALL treated in underprivileged circumstances, such as those prevailing in LMIC.

Families of doctors at Academia Nacional de Medicina de México.

INTRODUCTION: The decision to get involved in the study and practice of medicine is not easy. Within the scientific environment, achieving both professional and personal success requires a strict discipline, where effort becomes an essential part of daily life; in addition, having family support becomes crucial in order for not to lose hope when confronting the different adversities that arise during medical training. OBJECTIVE: To identify families where at least two members belong to the Academia Nacional de Medicina de México (ANMM). METHODS: A cross-sectional study was carried out to identify families of Mexican doctors where at least two members, consanguineous or in-laws, have been or are ANMM members through a review of 2017 ANMM Directory and personal contact with the different academics. RESULTS: Information on 45 families belonging to the ANMM was collected. CONCLUSIONS: From this study, it is possible to show the great influence that some doctors have in their family environment, which makes the study of medicine attractive as a life project.

INTRODUCCIÓN: La decisión de involucrarse en el estudio y la práctica de la medicina no es fácil. Dentro del ambiente científico, alcanzar el éxito tanto profesional como personal requiere de una disciplina estricta en donde el esfuerzo se vuelve parte esencial de la vida diaria, además, el tener el apoyo familiar se vuelve un pilar para no perder la ilusión ante las distintas adversidades que se presentan en la formación médica. OBJETIVO: Identificar a las familias donde mínimo dos miembros pertenecen a la Academia Nacional de Medicina. MÉTODOS: Se llevó a cabo un estudio transversal para analizar las familias de médicos mexicanos en las que por lo menos dos miembros, consanguíneos o políticos, han sido o son miembros de la Academia Nacional de Medicina de México por medio de la consulta del Directorio de la Academia Nacional de Medicina del año 2017 y el contacto de manera personal con los distintos académicos. RESULTADOS: Se recolectó información de 45 familias pertenecientes a la Academia Nacional de Medicina de México. CONCLUSIONES: A partir de este estudio es posible evidenciar la gran influencia que emiten algunos médicos en su entorno familiar, que hace que el estudio de la medicina sea atractivo como proyecto de vida.

Familias de médicos en la Academia Nacional de Medicina de México / Families of doctors at Academia Nacional de Medicina de México

Resumen Introducción: La decisión de involucrarse en el estudio y la práctica de la medicina no es fácil. Dentro del ambiente científico, alcanzar el éxito tanto profesional como personal requiere de una disciplina estricta en donde el esfuerzo se vuelve parte esencial de la vida diaria, además, el tener el apoyo familiar se vuelve un pilar para no perder la ilusión ante las distintas adversidades que se presentan en la formación médica. Objetivo: Identificar a las familias donde mínimo dos miembros pertenecen a la Academia Nacional de Medicina. Métodos: Se llevó a cabo un estudio transversal para analizar las familias de médicos mexicanos en las que por lo menos dos miembros, consanguíneos o políticos, han sido o son miembros de la Academia Nacional de Medicina de México por medio de la consulta del Directorio de la Academia Nacional de Medicina del año 2017 y el contacto de manera personal con los distintos académicos. Resultados: Se recolectó información de 45 familias pertenecientes a la Academia Nacional de Medicina de México. Conclusiones: A partir de este estudio es posible evidenciar la gran influencia que emiten algunos médicos en su entorno familiar, que hace que el estudio de la medicina sea atractivo como proyecto de vida.

Abstract Introduction: The decision to get involved in the study and practice of medicine is not easy. Within the scientific environment, achieving both professional and personal success requires a strict discipline, where effort becomes an essential part of daily life; in addition, having family support becomes crucial in order for not to lose hope when confronting the different adversities that arise during medical training. Objective: To identify members where at least two members belong to the Academia Nacional de Medicina de México" (ANMM). Methods: A cross-sectional study was carried out to identify families of Mexican doctors where at least two members, consanguineous or in-laws, have been or are ANMM members of the through a review of 2017 ANMM Directory personal contact with the different academics. Results: Information on 45 families belonging to the ANMM was collected. Conclusions: From this study, it is possible to show the great influence that some doctors have in their family environment, wich makes the study of medicine attractive as a life project.

miRNAs in multiple sclerosis: A clinical approach.

Micro-RNAs (miRNAs) are noncoding, single stranded segments of RNA measuring 19 to 25 nucleotides in length. They play an active role in autoimmune diseases, including multiple sclerosis (MS). These structures have been studied given their implication in the process of diagnosis, disease development, treatment and prognosis of MS. Given the progressive and neurodegenerative nature of MS, miRNAs have been identified as critical mediators and molecular pinpoints of the disease, which poses them as excellent candidates for the obtention of suitable biomarkers and treatment targets. This review condenses recent findings on the role of miRNAs in multiple sclerosis, including their role in MS etiology and molecular mechanisms of the disease, exploitation of miRNAs as diagnostic tools and biomarkers, miRNAs as treatment option or target for MS, and their significance as predictors of disease prognosis.

High dose melphalan is an adequate preparative regimen for autologous hematopoietic stem cell transplantation in relapsed/refractory lymphoma.

INTRODUCTION: High-dose melphalan (HD-Mel) has been successfully employed in autografting patients with multiple myeloma. An advantage of this regimen is that the total dose of Mel can be delivered in a single day, being particularly useful when non-frozen hematopoietic stem cells are employed in the autograft. MATERIAL AND METHODS: All consecutive patients with R/R lymphomas, both HL and NHL studied and treated at two different centers were prospectively included in a study of ASCT employing a single dose of HD-Mel (200 mg/m2). A group of R/R HL or NHL autografted employing BEAM-like preparative regimens was constructed matched by diagnosis and age. The primary endpoint of the study was overall survival (OS), the secondary endpoint was event-free survival (EFS). RESULTS: Twenty-five R/R HL/NHL patients were prospectively accrued in the study. There were 8 (32%) females, 13 (52%) patients had at least 1 adverse effect: 7 (28%) developed mucositis, 5 (20%) neutropenic fever, and 6 (24%) grade IV nausea. In the HD-Mel group, median overall survival (OS) was not achieved and OS at 36 months was 71%, the transplant-related mortality being 0%. In the control group, median OS was not achieved and the 36-month OS was 76%, results not statistically significant (p 0.5). The EFS was also similar in both groups (p 0.5). CONCLUSION: HD-Mel alone is non-inferior to a BEAM-like regimen as a preparative regimen for autografting patients with R/R HL and NHL. The regimen is adequate to graft persons with non-frozen stem cells.

Mutations in SARS-CoV-2 variants of concern link to increased spike cleavage and virus transmission.

SARS-CoV-2 lineages have diverged into highly prevalent variants termed "variants of concern" (VOCs). Here, we characterized emerging SARS-CoV-2 spike polymorphisms in vitro and in vivo to understand their impact on transmissibility and virus pathogenicity and fitness. We demonstrate that the substitution S:655Y, represented in the gamma and omicron VOCs, enhances viral replication and spike protein cleavage. The S:655Y substitution was transmitted more efficiently than its ancestor S:655H in the hamster infection model and was able to outcompete S:655H in the hamster model and in a human primary airway system. Finally, we analyzed a set of emerging SARS-CoV-2 variants to investigate how different sets of mutations may impact spike processing. All VOCs tested exhibited increased spike cleavage and fusogenic capacity. Taken together, our study demonstrates that the spike mutations present in VOCs that become epidemiologically prevalent in humans are linked to an increase in spike processing and virus transmission.

Preclinical evidence for mitochondrial DNA as a potential blood biomarker for chemotherapy-induced peripheral neuropathy.

Chemotherapy-induced peripheral neuropathy (CIPN) is a serious dose-limiting side effect of several first-line chemotherapeutic agents including paclitaxel, oxaliplatin and bortezomib, for which no predictive marker is currently available. We have previously shown that mitochondrial dysfunction is associated with the development and maintenance of CIPN. The aim of this study was to evaluate the potential use of mitochondrial DNA (mtDNA) levels and complex I enzyme activity as blood biomarkers for CIPN. Real-time qPCR was used to measure mtDNA levels in whole blood collected from chemotherapy- and vehicle-treated rats at three key time-points of pain-like behaviour: prior to pain development, at the peak of mechanical hypersensitivity and at resolution of pain-like behaviour. Systemic oxaliplatin significantly increased mtDNA levels in whole blood prior to pain development. Furthermore, paclitaxel- and bortezomib-treated animals displayed significantly higher levels of mtDNA at the peak of mechanical hypersensitivity. Mitochondrial complex I activity in whole blood was assessed with an ELISA-based Complex I Enzyme Activity Dipstick Assay. Complex I activity was not altered by any of the three chemotherapeutic agents, either prior to or during pain-like behaviour. These data demonstrate that blood levels of mtDNA are altered after systemic administration of chemotherapy. Oxaliplatin, in particular, is associated with higher mtDNA levels before animals show any pain-like behaviour, thus suggesting a potential role for circulating mtDNA levels as non-invasive predictive biomarker for CIPN.

Preclinical and randomized phase I studies of plitidepsin in adults hospitalized with COVID-19.

Plitidepsin, a marine-derived cyclic-peptide, inhibits SARS-CoV-2 replication at nanomolar concentrations by targeting the host protein eukaryotic translation elongation factor 1A. Here, we show that plitidepsin distributes preferentially to lung over plasma, with similar potency against across several SARS-CoV-2 variants in preclinical studies. Simultaneously, in this randomized, parallel, open-label, proof-of-concept study (NCT04382066) conducted in 10 Spanish hospitals between May and November 2020, 46 adult hospitalized patients with confirmed SARS-CoV-2 infection received either 1.5 mg (n = 15), 2.0 mg (n = 16), or 2.5 mg (n = 15) plitidepsin once daily for 3 d. The primary objective was safety; viral load kinetics, mortality, need for increased respiratory support, and dose selection were secondary end points. One patient withdrew consent before starting procedures; 45 initiated treatment; one withdrew because of hypersensitivity. Two Grade 3 treatment-related adverse events were observed (hypersensitivity and diarrhea). Treatment-related adverse events affecting more than 5% of patients were nausea (42.2%), vomiting (15.6%), and diarrhea (6.7%). Mean viral load reductions from baseline were 1.35, 2.35, 3.25, and 3.85 log10 at days 4, 7, 15, and 31. Nonmechanical invasive ventilation was required in 8 of 44 evaluable patients (16.0%); six patients required intensive care support (13.6%), and three patients (6.7%) died (COVID-19-related). Plitidepsin has a favorable safety profile in patients with COVID-19.