TWiV 412: WO, open the borders and rig the infection

The TWiVome reveal the first eukaryotic genes found in a bacteriophage of Wolbachia, and how DNA tumor virus oncogenes antagonize sensing of cytoplasmic DNA by the cell.

You can find TWiV #412 at microbe.tv/twiv, or listen below.

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TWiV 344: Glasgwegians go viral

Episode #344 of the science show This Week in Virology was recorded at the Glasgow Science Festival microTALKS, where Vincent spoke with Ruth, Glen, and Esther about their research on viruses and Hodgkin lymphoma, adenovirus structure and entry into cells, and interactions between arthropod borne viruses and their hosts.

You can find TWiV #344 at www.microbe.tv/twiv.

Designer viruses for killing tumor cells

Rb and E2fA major goal of viral oncotherapy – the use of viruses to destroy tumors –  is to design viruses that kill tumor cells but not normal cells. Two adenoviruses provide perfect examples of how this specificity can be achieved.

Adenovirus CG0070, designed to treat bladder cancer, and adenovirus Oncorine, for head and neck tumors, replicate only in tumor cells. The selectivity is caused by mutations introduced into the viral genomes.

When adenovirus infects a cell, the first event is synthesis of mRNA that encodes the E1 proteins. These proteins are needed to start cellular DNA synthesis. Most cells in our bodies are not dividing, an environment not conducive to viral replication. The adenovirus E1 proteins solve this problem. The E1A protein binds the cellular Rb (retinoblastoma) protein, which is normally bound to members of the E2f family of transcription factors (illustrated, upper left). Binding of E1A to Rb frees E2f which goes on to induce the transcription of cell genes needed for DNA synthesis and cell division.

The genome of CG0070 (illustrated below) has been modified so that the promoter for mRNA synthesis of the E1 proteins is replaced by the viral E2f promoter. This promoter requires E2f transcription factors for activity; hence the promoter does not function in non-dividing cells in which Rb is bound to E2f. However, many tumors lack Rb, and E2f is always available. CG0070 will replicate in such tumor cells.

GC0070 adenovirus

The genome of adenovirus Oncorine lacks the early region protein E1b-55K. The function of this viral protein is to bind the cellular protein p53, which would otherwise halt division and induce death of the infected cell. Binding to p53 leads to its degradation, allowing the virus to execute its 24 hour reproductive cycle. Adenovirus lacking the E1b-55K protein will not replicate in normal cells. However, the virus will replicate in p53 deficient tumors.

E1b-55k

Oncorine has been licensed in China for the treatment of head and neck tumors, while CG0070 is in phase III clinical studies for the treatment of bladder cancer. Both oncolytic adenoviruses were developed by using knowledge of fundamental aspects of viral replication, yet another illustration of how basic research can lead to clinical applications.

Treatment of Ebola virus infection with brincidofovir

brincidofovirThe Liberian man who was diagnosed with Ebola virus infection after traveling to Dallas, Texas, was treated with an antiviral drug called brincidofovir. This drug had originally been developed to treat infections with DNA-containing viruses. Why was it used to treat an Ebola virus infection?

Brincidofovir (illustrated) is a modified version of an antiviral drug called cidofovir, which inhibits replication of a variety of DNA viruses including poxviruses and herpesviruses. When cidofovir enters a cell, two phosphates are added to the compound by a cellular enzyme, producing cidofovir diphosphate. Cidofovir is used by viral DNA polymerases because it looks very much like a normal building block of DNA, cytidine. For reasons that are not known, incorporation of phosphorylated cidofovir causes inefficient viral DNA synthesis. As a result, viral replication is inhibited.

Cidofovir was modified by the addition of a lipid chain to produce brincidofovir. This compound (pictured) is more potent, can be given orally, and does not have kidney toxicity, a problem with cidofovir. When brincidofovir enters a cell, the lipid is removed, giving rise to cidofovir. Brincidofovir inhibits poxviruses, herpesviruses, and adenoviruses, and has been tested in phase 2 and 3 clinical trials. The antiviral drug is being stockpiled by the US for use in the event of a bioterrorism attack with smallpox virus.

Ebola virus is an RNA virus, so why was brincidofovir used to treat the Dallas patient? According to the drug’s manufacturer, Chimerix,  with the onset of the Ebola virus outbreak in early 2014, the company provided brincidofovir, and other compounds, to the CDC and NIH to determine if they could inhibit virus replication. Apparently brincidofovir was found to be a potent inhibitor of Ebola virus replication in cell culture. Based on this finding, and the fact that the compound had been tested for safety in humans, the US FDA authorized its emergency use in the Dallas patient.

Unfortunately the Dallas patient passed away on 8 October. Even if he had survived, we would not have known if the compound had any effect. Furthermore, the drug is not without side effects and these might not be tolerated in Ebola virus-infected patients. It seems likely that the drug will also be used if other individuals in the US are infected.

Looking at the compound, one could not predict that it would inhibit Ebola virus, which has an RNA genome. RNA polymerases use different substrates than DNA polymerases – NTPs versus dNTPs. NTPs have two hydroxyls on the ribose sugar, while dNTPs have just one (pictured). The ribose is not present in cidofovir, although several hydroxyls are available for chain extension. I suspect that the company was simply taking a chance on whether any of its antiviral compounds in development, which had gone through clinical trials, would be effective. This procedure is standard in emergency situations, and might financially benefit the company.

Update: The NBC news cameraman is being treated with brincidofovir in Nebraska.

TWiV 291: Ft. Collins abuzz with virologists

Vincent, Rich, and Kathy and their guests Clodagh and Ron recorded episode #291 of the science show This Week in Virology at the 33rd annual meeting of the American Society for Virology at Colorado State University in Ft. Collins, Colorado.

You can find TWiV #291 at www.microbe.tv/twiv.

TWiV 244: Back in the CVVR

Episode #244 of the science show This Week in Virology was recorded before an audience at the Beth Israel Deaconess Medical Center, where Vincent and Alan spoke with Dan and Jeff about AIDS vaccines.

You can find TWiV #244 at www.microbe.tv/twiv.

TWiV 214: This is your brain on polyomavirus

On episode #214 of the science show This Week in Virology, Vincent, Alan, and Kathy discuss how coagulation factor X binding to adenovirus activates the innate immune system, and a novel polyomavirus associated with brain tumors in raccoons.

You can find TWiV #214 at www.microbe.tv/twiv.

TWiV 204: M m m my corona

On episode #204 of the science show This Week in Virology, Vincent, Alan, Matt and Kathy review isolation of a new coronavirus from two patients in the Middle East, and expansion of the enteric virome during simian AIDS.

You can find TWiV #204 at www.microbe.tv/twiv.

TWiV 203: Mark Challberg, a cold room kind of guy

On episode #203 of the science show This Week in Virology, Vincent and Rich meet up with Mark Challberg to talk about his scientific career studying viral DNA replication, and his transition to an NIH Program Officer.

You can find TWiV #203 at www.microbe.tv/twiv.

TWiV 201: Rabid about viruses

On episode #201 of the science show This Week in Virology, Vincent, Alan, Rich, Dickson, and Kathy answer reader email about rabies, xenotransplantation, poliovirus, Ph.D. programs, mosquitoes, and much more.

You can find TWiV #201 at www.microbe.tv/twiv.