In 2009, it was shown that cidofovir impairs Vaccinia DNA encapsidation and, consequently, affects viral morphogenesis (Jesus et al., 2009). In humans, cidofovir has been used successfully against Molluscum contagiosum virus and ORF virus, however renal toxicity is a known side effect caused by this drug (De Clercq, 2002). Importantly, cidofovir-resistant strains of camelpox, cowpox, monkeypox and vaccinia viruses have

also been isolated (Smee et al., 2002). To overcome nephrotoxicity, a derivative form of CDV has been generated and tested. CMX001 is a lipid conjugate of the acyclic nucleotide phosphonate and is currently in Phase II clinical trials for the prophylaxis of human cytomegalovirus infection and under development using the Animal Rule Selleckchem Etoposide for smallpox infection. MDV3100 research buy CMX001 has demonstrated in vitro and in vivo efficacy against orthopoxvirus infections, and no evidence of nephrotoxicity in either

animals or humans was found. Both drugs target the viral DNA polymerase, and VACV strains have been shown to be cross resistant to CMX001 as well. A new class of anti-poxvirus drugs, which affects both viral spread and dissemination, has also emerged. One of them, ST-246, has been intensely tested against a number of Orthopoxvirus species in animal studies (Yang et al., 2005a, Yang et al., 2005b, Sbrana et al., 2007 and Quenelle et al., 2007). ST-246 specifically inhibits the viral Pregnenolone protein F13, which is required for the formation of enveloped virus forms. Similar to CDV in which viral resistance is conferred by point mutations in the DNA polymerase

gene (Becker et al., 2008), it has also been described that a single point mutation in F13 conferred resistance to ST-246 (Yang et al., 2005a and Yang et al., 2005b). ST-246 was recently tested in a Phase I clinical trial and found to be well tolerated and safe in healthy humans (Jordan et al., 2008 and Jordan et al., 2010). An additional approach to inhibit viral multiplication is targeting cellular signaling pathways stimulated and required for successful replication and dissemination. In the past years, we and others have shown the ability of the Orthopoxviruses VACV and CPXV to induce protein kinases pathways to provide an adequate environment to favor their viral replication cycles (de Magalhães et al., 2001, Andrade et al., 2004, da Silva et al., 2006, Mercer and Helenius, 2008, Soares et al., 2009 and McNulty et al., 2010). It is also known that poxviruses use the Src and Abl family kinase activities to modulate intracellular spread and release (Frischknecht et al., 1999, Reeves et al., 2005 and Reeves et al., 2011) but only the Abl family of kinases mediate release of CEV to form EEV (Reeves et al., 2005).