A new gambit against poxvirus

Oncology's poster-child drug, Gleevec (imatinib), is also effective against poxvirus infections, according to a study in July's Nature Medicine. The drug's new indication came to light with the finding that poxvirus transmission from an infected cell to a neighboring cell depends on host Abl-family tyrosine kinases. Gleevec, developed to treat chronic myelogenous leukemia, inhibits the mutant tyrosine kinase BcrAbl. After pox virions replicate in the cytoplasm of an infected cell, some of them fuse with the cell's plasma membrane to form 'cell-associated enveloped viruses' that subsequently detach outside the cell. Working with vaccinia, the poxvirus used to vaccinate against smallpox, Reeves et al. showed that this detachment step is mediated by host Abl kinases. Although virions are also disseminated by cell lysis, those that exit via plasma-membrane fusion are believed to evade immune surveillance and drive viral spread. Smallpox was declared eradicated in 1980 and routine vaccinations have ceased, but Gleevec may be useful for treating vaccination side effects or, should the need arise, smallpox itself. Compared with anti-viral drugs directed against components of the virus, the present strategy of targeting a host protein is less likely to elicit drug resistance as it does not subject viral mutants to growth selection. (Nat. Med. 11, 731–739, 2005) KA

Virus on demand

Three groups have independently developed similar culture systems for replicating complete hepatitis C virus (HCV) genomes and producing infectious HCV viral particles, whereas a fourth has produced infectious human papillomaviruses (HPV) in cell culture. HCV is the major cause of liver disease in the world, and HPV is the main culprit behind cervical as well as head and neck cancers. Until now, basic research on viral biology and the development of new vaccines and antiviral agents has been hampered by the difficulty of generating sufficiently high numbers of infectious HCV and HPV virions. Using the 2a genotype of the highly virulent JFH1 HCV strain as a starting point, a group headed by Takaji Wakita and teams headed by Charles Rice and Francis Chisari transfected full-length chimeric genomes containing nonstructural regions from related HCV strains or the untransformed JFH1 genome, respectively, into human hepatoma cell lines. The virion particles generated exhibited correct morphologies and immune profiles. Wakita and colleagues went one step further and demonstrated infectivity of the HCV virions in vivo in a chimpanzee model. In a parallel development, Ahlquist and colleagues report on an in vitro system for amplifying another virus, HPV, in human embryonic kidney cells, providing an alternative to existing cumbersome and low yield HPV culture systems, such as artificial skin and human xenografts in mice. (Science, 10.1126/science.1114016, 2005; Nat. Med., 11, 791–796, 2005. Proc. Natl. Acad. Sci. USA 102, 9294–9299, 2005; Proc. Natl. Acad. Sci. USA 102, 9311–9316, 2005) GTO

Less is more in cancer profiling

MicroRNA (miRNA) expression profiling could become an adjunct to mRNA expression profiling in diagnosing cancers. Compared with mRNAs, miRNAs—endogenous ∼21-nucleotide noncoding RNAs involved in cell regulation—were found by Lu et al. not only to be more stable but also to show more diversity of expression in human cancers, enabling fewer to be tracked in diagnosis. Using a bead-based analysis method, the authors profiled the expression of all known mammalian miRNAs in a spectrum of cancer types. The resulting expression patterns revealed that miRNA is downregulated in cancerous compared with normal cells. The approach could distinguish cancers of different lineages (e.g., epithelial versus hematopoietic), different cancers within the same lineage and tumor cells at different stages of differentiation, and could identify tumors of uncertain cellular origin. The authors conclude that tumor classification by miRNA expression patterns, which appear to “encode the developmental history of human cancers,” is more accurate than similar efforts based on mRNA profiling and should lead to improved methods for cancer detection and diagnosis. (Nature 435, 834–838, 2005) MZ

Double-filtered kinase inhibitors

Protein kinases represent an important class of targets for therapeutic intervention, given their pivotal role in many regulatory pathways. Yet, only a few kinase drugs have made it to the clinic—Gleevec, an inhibitor of Abelson kinase being a notable example. Now, Taunton and colleagues describe the rationale design of selective inhibitors of a small cadre of kinases—the ribosome S6 kinases (RSK)—using two filters that uniquely define 3 out of almost 500 kinases that comprise the human kinome. One filter acts as a gatekeeper to the ATP-binding domain, called gatekeeper because the size of the amino acid in this position (whether it is a compact or a large amino acid) determines inhibitor accessibility to the domain. They then defined a second filter, a cysteine in a flexible region of the enzyme, chosen because cysteines can be targeted by electrophilic groups. Searching a human genome database, they found 11 kinases with cysteines in the second filter position, of which only 3 had accessible ATP domains. The scaffold they constructed, an electrophilic flouoromethylketone, was shown both in enzyme assays and in cell extracts to react specifically with RSKs. Furthermore, RSKs with mutations in the two key filter sites showed resistance to the inhibitor. This work illustrates that combining features in inhibitor design provides an avenue to long sought after specific kinase inhibitors. (Science 308, 1319–1321, 2005). LD

FGF-21 tackles diabetes

Type 2 diabetes mellitus is a growing worldwide health problem, with >5% of the US population affected by the disease. Now, Kharitonenkov et al. have demonstrated that a recently identified member of the fibroblast growth factor (FGF) protein family, FGF-21, may be effective in diabetes treatment. FGF proteins are associated with embryonic development and are critical for basic metabolic functions. More recently, FGF proteins have been associated with regulating endocrine-relevant tissues and organs. The authors uncovered FGF-21's ability to modulate glucose by measuring uptake of the sugar in screens of mouse 3T3-L1 and human primary adipocytes. Administration of FGF-21 to diabetic rodents led to significantly lowered blood glucose and triglyceride levels and increased insulin sensitivity and glucose clearance compared with controls, with no evidence of hypoglycemia. In addition, transgenic mice overexpressing FGF-21 in the liver were protected from diet-induced obesity and unaffected by liver tumors or tissue hyperplasia, which have commonly been associated with overexpression of other FGFs. (J. Clin. Invest. 115, 1627–1635, 2005) NC

Research Highlights written by Kathy Aschheim, Nadia Cervoni, Laura DeFrancesco, Gaspar Taroncher-Oldenburg and Mark Zipkin.