Deregulation of kinase activity has emerged as a major mechanism by which cancer cells evade normal physiological constraints on growth and survival. To date, 11 kinase inhibitors have received US Food and Drug Administration approval as cancer treatments, and there are considerable efforts to develop selective small molecule inhibitors for a host of other kinases that are implicated in cancer and other diseases. Herein we discuss the current challenges in the field, such as designing selective inhibitors and developing strategies to overcome resistance mutations. This Review provides a broad overview of some of the approaches currently used to discover and characterize new kinase inhibitors.

Dengue fever (DF) is the most frequent arthropod-borne viral disease of humans, with almost half of the world's population at risk of infection1. The high prevalence, lack of an effective vaccine, and absence of specific treatment conspire to make DF a global public health threat1, 2. Given their compact genomes, dengue viruses (DENV 1-4) and other flaviviruses likely require an extensive number of host factors; however, only a limited number of human, and an even smaller number of insect host factors have been identified3-10. To discover insect host factors required for DENV-2 propagation, we carried out a genome-wide RNA interference screen in Drosophila melanogaster cells using a well-established 22,632 dsRNA library. This screen identified 116 candidate dengue virus host factors (DVHFs) (Supplementary Fig. 1). While some were previously associated with flaviviruses (e.g., V-ATPases and alpha-glucosidases)3-5, 7, 9, 10, most DVHFs were newly implicated in DENV propagation. The dipteran DVHFs had eighty-two readily recognizable human homologues and, using a targeted siRNA screen, we showed that forty-two of these are human DVHFs. This indicates remarkable conservation of required factors between dipteran and human hosts. This work suggests novel approaches to control infection in the insect vector and the mammalian host.

Hepatitis B virus (HBV) is a prototype for liver-specific pathogens in which the failure of the immune system to mount an effective response leads to chronic infection. Our understanding of the immune response to HBV is incomplete, largely due to the narrow host restriction of this pathogen and the limitations of existing experimental models. We have developed a murine model for studying human HBV replication, immunogenicity, and control. After transfection of hepatocytes in vivo with a replicationcompetent, over-length, linear HBV genome, viral antigens and replicative intermediates were synthesized and virus was secreted into the blood. Viral antigens disappeared from the blood as early as 7 days after transfection, coincident with the appearance of antiviral antibodies. HBV transcripts and replicative intermediates disappeared from the liver by day 15, after the appearance of antiviral CD8 ؉ T cells. In contrast, the virus persisted for at least 81 days after transfection of NOD͞Scid mice, which lack functional T cells, B cells, and natural killer (NK) cells. Thus, the outcome of hydrodynamic transfection of HBV depends on the host immune response, as it is during a natural infection. The methods we describe will allow the examination of viral dynamics in a tightly controlled in vivo system, the application of mutagenesis methods to the study of the HBV life cycle in vivo, and the dissection of the immune response to HBV using genetically modified mice whose immunoregulatory and immune effector functions have been deleted or overexpressed. In addition, this methodology represents a prototype for the study of other known and to-be-discovered liver-specific pathogens.H epatitis B virus (HBV) is a human hepadnavirus that causes acute and chronic hepatitis and hepatocellular carcinoma (1). Although an effective vaccine has been available for two decades, an estimated 350 million people worldwide are chronically infected. A significant proportion of chronic infections terminate in hepatocellular carcinoma, leading to more than one million deaths annually (2).A reproducible tissue culture model of HBV infection does not exist, nor is HBV infectious for immunologically well-defined laboratory animals. Much of our current understanding of the viral life cycle after HBV infection is derived from studies of duck HBV (DHBV) (3) and woodchuck HBV (WHV) (4) infection in their natural hosts, HBV-infected chimpanzees (5-7), and HBV transgenic mice (8-10). For various reasons, however, none of these models is ideal. DHBV (11) and WHV (12, 13) are genetically divergent from HBV, and immunological studies in genetically outbred and immunologically uncharacterized ducks and woodchucks are difficult. Chimpanzee experiments are limited by cost, availability, and ethical considerations, whereas transgenic mice are immunologically tolerant to the virus, thereby compromising the greatest potential strength of a mouse model of HBV infection. We present here work describing a recently developed mouse model that alleviates many of thes...

To better define the mechanism(s) likely responsible for viral clearance during hepatitis B virus (HBV) infection, viral clearance was studied in a panel of immunodeficient mouse strains that were hydrodynamically transfected with a plasmid containing a replication-competent copy of the HBV genome. Neither B cells nor perforin were required to clear the viral DNA transcriptional template from the liver. In contrast, the template persisted for at least 60 days at high levels in NOD/Scid mice and at lower levels in the absence of CD4 + and CD8 + T cells, NK cells, Fas, IFN-gamma (IFN-γ), IFN-alpha/beta receptor (IFN-α/βR1), and TNF receptor 1 (TNFR1), indicating that each of these effectors was required to eliminate the transcriptional template from the liver. Interestingly, viral replication was ultimately terminated in all lineages except the NOD/Scid mice, suggesting the existence of redundant pathways that inhibit HBV replication. Finally, induction of a CD8 + T cell response in these animals depended on the presence of CD4 + T cells. These results are consistent with a model in which CD4 + T cells serve as master regulators of the adaptive immune response to HBV; CD8 + T cells are the key cellular effectors mediating HBV clearance from the liver, apparently by a Fas-dependent, perforinindependent process in which NK cells, IFN-γ, TNFR1, and IFN-α/βR play supporting roles. These results provide insight into the complexity of the systems involved in HBV clearance, and they suggest unique directions for analysis of the mechanism(s) responsible for HBV persistence.H epatitis B virus (HBV) is a noncytopathic human hepadnavirus that causes acute and chronic hepatitis and hepatocellular carcinoma (1). Approximately 350 million people worldwide are chronically infected by HBV, which greatly increases the risk of hepatocellular carcinoma (HCC) and causes more than 1 million deaths annually (2). Because HBV is not infectious in small animal or tissue culture models, systematic examination of the host-virus interactions during HBV infection has been difficult. The full spectrum of immunological requirements for HBV clearance is not completely defined.Our current understanding is based to a large extent on comparison of the immune responses mounted against HBV in patients who clear and who fail to clear HBV (3), experiments in which potential effectors of clearance (e.g., HBsAg-specific CD8 + T cells, recombinant IFN-γ and TNF-α) have been adoptively transferred to or induced in HBV transgenic mice (4-8), and a limited number of experiments conducted in HBVinfected chimpanzees (9, 10, 18). Collectively, these studies have led to the current model for clearance of acute HBV infection, namely (i) that viral clearance during HBV infection is associated with entry of CD8 + T cells into the liver, the production of IFN-γ, and the induction of inflammatory liver disease (reviewed in ref.3); (ii) that IFN-γ production, viral clearance, and liver disease are all impaired in the absence of CD8 + T cells (11); and (iii) that noncy...

The germline genes used by the mouse to generate the esterolytic antibody 48G7 were cloned and expressed in an effort to increase our understanding of the detailed molecular mechanisms by which the immune system evolves catalytic function. The nine replacement mutations that were fixed during affinity maturation increased affinity for the transition state analogue by a factor of 10 4 , primarily the result of a decrease in the dissociation rate of the hapten-antibody complex. There was a corresponding increase in the rate of reaction of antibody with substrate, k cat / K m , from 1.7 × 10 2 M −1 min −1 to 1.4 × 10 4 M −1 min −1 . The three-dimensional crystal structure of the 48G7-transition state analogue complex at 2.0 angstroms resolution indicates that none of the nine residues in which somatic mutations have been fixed directly contact the hapten. Thus, in the case of 48G7, affinity maturation appears to play a conformational role, either in reorganizing the active site geometry or limiting side-chain and backbone flexibility of the germline antibody. The crystal structure and analysis of somatic and directed active site mutants underscore the role of transition state stabilization in the evolution of this catalytic antibody.

The outbreak of COVID-19, the pandemic disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spurred an intense search for treatments by the scientific community. In the absence of a vaccine, the goal is to target the viral life cycle and alleviate the lung-damaging symptoms of infection, which can be lifethreatening. There are numerous protein kinases associated with these processes that can be inhibited by FDA-approved drugs, the repurposing of which presents an alluring option as they have been thoroughly vetted for safety and are more readily available for treatment of patients and testing in clinical trials. Here, we characterize more than 30 approved kinase inhibitors in terms of their antiviral potential, due to their measured potency against key kinases required for viral entry, metabolism, or reproduction. We also highlight inhibitors with potential to reverse pulmonary insufficiency because of their anti-inflammatory activity, cytokine suppression, or antifibrotic activity. Certain agents are projected to be dualpurpose drugs in terms of antiviral activity and alleviation of disease symptoms, however drug combination is also an option for inhibitors with optimal pharmacokinetic properties that allow safe and efficacious co-administration with other drugs, such as antiviral agents, IL-6 blocking agents, or other kinase inhibitors.

The mechanism of membrane fusion by “class II” viral fusion proteins follows a pathway that involves large-scale domain rearrangements of the envelope glycoprotein (E) and a transition from dimers to trimers. The rearrangement is believed to proceed by an outward rotation of the E ectodomain after loss of the dimer interface, followed by a reassociation into extended trimers. The ∼55-aa-residue, membrane proximal “stem” can then zip up along domain II, bringing together the transmembrane segments of the C-terminus and the fusion loops at the tip of domain II. We find that peptides derived from the stem of dengue-virus E bind stem-less E trimer, which models a conformational intermediate. In vitro assays demonstrate that these peptides specifically block viral fusion. The peptides inhibit infectivity with potency proportional to their affinity for the conformational intermediate, even when free peptide is removed from a preincubated inoculum before infecting cells. We conclude that peptides bind virions before attachment and are carried with virions into endosomes, the compartment in which acidification initiates fusion. Binding depends on particle dynamics, as there is no inhibition of infectivity if preincubation and separation are at 4°C rather than 37°C. We propose a two-step model for the mechanism of fusion inhibition. Targeting a viral entry pathway can be an effective way to block infection. Our data, which support and extend proposed mechanisms for how the E conformational change promotes membrane fusion, suggest strategies for inhibiting flavivirus entry.

Dengue virus is a mosquito-borne flavivirus that represents an important emerging infectious disease and is an international health concern. Currently, there is no vaccine or effective antiviral therapy to prevent or to treat dengue virus infection. The slow progress in developing antiviral agents might be alleviated by the availability of efficient high-throughput anti-dengue virus screening assays. In this study, we report an immunofluorescence imagebased assay suitable for identification of small molecule inhibitors of dengue virus infection and replication. Using this assay, we have discovered that inhibitors of the c-Src protein kinase exhibit a potent inhibitory effect on dengue virus (serotypes 1-4) and murine flavivirus Modoc. Mechanism of action studies demonstrated that the c-Src protein kinase inhibitor dasatinib prevents the assembly of dengue virions within the virus-induced membranous replication complex. These results demonstrate that this cell-based screen may provide a powerful means to identify new potential targets for anti-dengue drug development while simultaneously providing pharmacological probes to investigate dengue virus-host cell interactions at the biochemical level. gen that causes dengue fever (DF) and a severe lifethreatening illness, dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) (1). DENV is a small, enveloped, positive-stranded RNA virus that belongs to the Flavivirus genus of the Flaviviridae family. Four distinct serotypes (DENV1 to -4) of dengue viruses are transmitted to humans through the bites of the mosquito species, Aedes aegypti and Aedes albopictus (2). It has been estimated that Ϸ50-100 million cases of DF, and Ϸ250,000-500,000 cases of DHF occur every year (3). Furthermore, 2.5 billion of people are at risk for infection in subtropical and tropical regions of the world (4) in the absence of effective intervention. The intracellular life cycle of DENV begins with receptor-mediated endocytosis of the virus into cells, followed by fusion of the viral envelope protein with the late endosomal membrane, which results in the release of the viral genome into the cytoplasm for replication. Replication of the viral RNA genome occurs within membrane-bound complexes formed from the endoplasmic reticulum membrane. Subsequently, virus particles are assembled and released via the host cell secretory machinery (5). Although replication of DENV involves complex interaction between viral proteins and cellular factors, many of these interactions remain unidentified and uncharacterized. Small molecules that specifically target different steps in the viral replication cycle could potentially be used as ''tool compounds'' to facilitate biochemical characterization of these host-virus interactions and might also be used to identify pharmacological intervention points for treatment of DENV infection. Although extensive studies have been carried out over the years to understand the pathogenicity of DENV infection, little progress has been made in the development of specific anti-DE...