Tecovirimat for smallpox infections.

SIGA Technologies, Inc. is a small biotech company committed to developing novel products for the prevention and treatment of serious viral diseases, with an emphasis on products to combat outbreaks that could result from bioterrorism. With government support, SIGA has developed the necessary infrastructure to successfully advance new antiviral drugs from the discovery stage through to licensing. Currently, there is a need to develop safe and effective inhibitors for poxvirus-induced diseases such as smallpox caused by variola, which is a potential biological warfare agent. Likewise emerging zoonotic infections due to cowpox virus and monkeypox virus require the development of effective countermeasures. Tecovirimat, also known as ST-246, has shown efficacy in all small animal and nonhuman primate prophylaxis and therapeutic efficacy models of poxvirus-induced disease tested to date. Phase I clinical trials and new drug application-enabling toxicology studies have been completed with tecovirimat. A phase II clinical study is being run and SIGA has initiated commercial scale-up manufacturing and preparation for the pivotal safety and efficacy studies. SIGA is committed to getting approval for tecovirimat and supplying it to the Strategic National Stockpile, the Department of Defense and global health authorities.

Studies on the genomic organization of recombinant Streptococcus gordonii and the development of a novel intergenic integration site for foreign gene expression.

The methods currently employed to produce recombinant Streptococcus gordonii strains for use as vaccines and/or protein expression vectors result in the insertion of foreign genes into an unknown integration site with no information on the transcriptional context or potential phenotypic consequences. Therefore, the genomic organization surrounding the insertion site of a recombinant strain of S. gordonii (GP1223) containing a portion of the emm6 gene of Streptococcus pyogenes was determined. The nucleotide sequence of chromosomal walks in both directions from the insertion site revealed that the insert was flanked by a duplicated 3061-bp ClaI fragment. A consensus gram-positive promoter and a factor-independent RNA polymerase terminator sequence could be deduced in the fragment immediately upstream of the insertion site. The ClaI fragment also encoded open reading frames (ORFs) with high homology and parallel structural organization to the leucine biosynthesis operon of Lactococcus lactis subsp. lactis. Chromosomal walks downstream of the identified promoter region on the non-recombinant parental strain, GP204, yielded the sequence of two ORFs which would be normal targets of the transcription derived from this promoter. Northern analyses detected a highly expressed M6-specific transcript in recombinant strain GP1223 consistent in size with the proposed transcription unit. Transcripts analogous in length to those observed for the leucine biosynthesis operon of L. lactis subsp. lactis were also detected encompassing the homologous ORFs of S. gordonii. This information has enabled the construction of a recombinant S. gordonii strain in which the emm6 gene from S. pyogenes was targeted to a distinct intergenic locus within the S. gordonii genome. This new recombination site allows for expression of foreign gene products with minimal perturbation of the genomic organization of the wild-type S. gordonii strain and has provided information essential for further optimization of foreign gene expression levels.

Conserved DegP protease in gram-positive bacteria is essential for thermal and oxidative tolerance and full virulence in Streptococcus pyogenes.

The DegP protease, a multifunctional chaperone and protease, has been shown to be essential for virulence in gram-negative pathogens such as Salmonella enterica serovar Typhimurium, Brucella abortus, Yersinia enterocolitica, and Pseudomonas aeruginosa. The function of DegP in pathogenesis appears to be the degradation of damaged proteins that accumulate as a result of the initial host response to infection, which includes the release of reactive oxygen intermediates. Additionally, the DegP protease plays a major role in monitoring and maintaining the Escherichia coli periplasm and influences E. coli pilus biogenesis. We report here the identification of highly homologous enzymes in Streptococcus pyogenes, Streptococcus gordonii, Streptococcus mutans, Staphylococcus aureus, and Enterococcus faecalis. Moreover, the phenotype of an insertionally inactivated degP allele in S. pyogenes is similar to that reported for E. coli, with temperature sensitivity for growth and enhanced sensitivity to reactive oxygen intermediates. Virulence studies in a mouse model of streptococcal infection indicate that a functional DegP protease is required for full virulence. These results suggest DegP as an attractive broad-spectrum target for future anti-infective drug development.

Identification of an intragenic integration site for foreign gene expression in recombinant Streptococcus gordonii strains.

A new intragenic chromosomal integration site within the lacG gene of the lac operon has been identified in Streptococcus gordonii for use in the expression of foreign genes. Introduction of a portion of the Streptococcus pyogenes emm6 gene into the lacG locus resulted in the lactose-inducible surface expression of the S. pyogenes M6 protein. This result demonstrates the ability to modulate the in vitro or in vivo expression of a foreign gene in a S. gordonii recombinant using a biosynthetic metabolite.

Inactivation of the srtA gene in Streptococcus gordonii inhibits cell wall anchoring of surface proteins and decreases in vitro and in vivo adhesion.

The srtA gene product, SrtA, has been shown to be required for cell wall anchoring of protein A as well as virulence in the pathogenic bacterium Staphylococcus aureus. There are five major mechanisms for displaying proteins at the surface of gram-positive bacteria (P. Cossart and R. Jonquieres, Proc. Natl. Acad. Sci. USA 97:5013-5015, 2000). However, since many of the known surface proteins of gram-positive bacteria are believed to be exported and anchored via the sortase pathway, it was of interest to determine if srtA plays a similar role in other gram-positive bacteria. To that end, the srtA gene in the human oral commensal organism Streptococcus gordonii was insertionally inactivated. The srtA mutant S. gordonii exhibited a marked reduction in quantity of a specific anchored surface protein. Furthermore, the srtA mutant had reduced binding to immobilized human fibronectin and had a decreased ability to colonize the oral mucosa of mice. Taken together, these results suggest that the activity of SrtA plays an important role in the biology of nonpathogenic as well as pathogenic gram-positive cocci.

Expression and purification of histidine-tagged proteins from the gram-positive Streptococcus gordonii SPEX system.

Streptococcus gordonii (S. gordonii) has been used as a gram-positive bacterial expression vector for secreted or surface-anchored recombinant proteins. Fusion of the gram-positive bacterial N-terminal signal sequence to the target protein is all that is required for efficient export. This system is termed SPEX for Surface Protein EXpression and has been used to express proteins for a variety of uses. In this study, the SPEX system has been further developed by the construction of vectors that express polyhistidine-tagged fusion proteins. SPEX vectors were constructed with an N-terminal or C-terminal histidine tag. The C-repeat region (CRR) from Streptococcus pyogenes M6 protein and the Staphylococcus aureus nuclease A (NucA) enzyme were tested for expression. The fusion proteins were purified using metal affinity chromatography (MAC). Results show that the fusion proteins were expressed and secreted from S. gordonii with the His tag at either the N- or C-terminal position and could be purified using MAC. The M6 fusions retained immunoreactivity after expression and purification as determined by immunoblots and ELISA analyses. In addition, NucA fusions retained functional activity after MAC purification. The M6-His and NucA-His fusions were purified approximately 15- and 10-fold respectively with approximately 30% recovery of protein using MAC. This study shows that the polyhistidine tag in either the N- or C-terminal position is a viable way to purify secreted heterologous proteins from the supernatant of recombinant S. gordonii cultures. This study further illustrates the value of the SPEX system for secreted expression and purification of proteins.

Expression of active monomeric and dimeric nuclease A from the gram-positive Streptococcus gordonii surface protein expression system.

We used the surface protein expression (SPEX) system to express an anchored and a secreted form of staphylococcal nuclease A (NucA) from gram-positive bacteria. NucA is a small ( approximately 18 kDa), extracellular, monomeric enzyme from Staphylococcus aureus. A deletion of amino acids 114-119 causes monomeric NucA to form homodimers. The DNA sequence encoding either wild-type or deletion mutant NucA was cloned via homologous recombination into Streptococcus gordonii. S. gordonii strains expressing either anchored or secreted, monomeric or dimeric NucA were isolated and tested for enzymatic activity using a novel fluorescence enzyme assay. We show that active monomeric and dimeric NucA enzyme can be expressed either anchored on the cell surface or secreted into the culture medium. The activity of the dimer NucA was approximately 100-fold less than the monomer. Secreted and anchored, monomeric NucA migrated on SDS-polyacrylamide gels at approximately 18 or approximately 30 kDa, respectively. In addition, similar to S. aureus NucA, the S. gordonii recombinant NucA enzyme was dependent on CaCl(2) and was heat stable. In contrast, however, the recombinant NucA activity was maximal at pH 7.0-7.5 whereas S. aureus NucA was maximal at pH 9.0. These results show, for the first time, expression of active enzyme and polymeric protein in secreted and anchored forms using SPEX. This further demonstrates the utility of this gram-positive surface protein expression system as a potential commensal bacterial delivery system for active, therapeutic enzymes, biopharmaceuticals, or vaccines.