The Florida-based company said it has found the conditions for maintaining long-term stability and optimisation of the formulation of RiVax.
RiVax contains a recombinant subunit of the A chain of ricin toxin and has been shown to induce antibodies in humans that neutralise the ricin toxin, in Phase I clinical trials.
The ricin A chain is very fragile and difficult to maintain structurally in water-based solutions that are commonly used for human vaccines, so the company said it has added compounds to solutions of protein to stabilise the structure, by preventing the unfolding of protein during stress conditions such as heat.
The vaccine that is being developed contains an adjuvant system which is necessary to increase the level of ricin neutralising antibodies and also to lengthen the period of immunity to ricin exposure.
The development of an adjuvant formulation has centered on the need for protein stabilisation.
"We have taken a fundamental approach to understanding the structure of the ricin A chain and its relationship to generating effective immune responses in animals and humans," said Robert Brey, chief scientific officer of Dor.
"Long-term stability is the key factor for the further clinical development of RiVax and for potential US government vaccine stockpiling purposes."
These studies also identified conditions to optimise the interaction of the protein with adjuvants containing aluminum salts, which are immune-enhancing agents with a long history of use in human vaccines licensed by the regulator.
The urgency for protective countermeasures against ricin has been heightened by its recent and continued use as a biological weapon in both the United States and Europe.
Ricin, which is extracted from castor beans, has a highly lethal toxicity in small doses, causing fever, nausea abdominal pain or lung damage, followed by death within a few days of exposure.
Because castor beans are readily available, ricin is easily manufactured and it is also easily aerosolised - making it all the more dangerous - however currently there is no prevention or cure for the deadly substance.
"The successful development of an effective vaccine against ricin toxin may actually reduce the threat of its use as a bioterror weapon," said Brey.
The firm tested the vaccine in clinical trials to examine the influence of an immunological adjuvant formulation and vaccination regimen on the human immune response and it said it could have gathered the evidence it needed to gain US Food & Drug Administration (FDA) approval of the vaccine.
Dor and its manufacturing partner, Cambrex BioSciences, had previously developed a robust and reproducible manufacturing process for the large-scale production of RiVax and reached a crucial manufacturing milestone under a $6.4m (€5m) grant awarded in 2004 to make the vaccine by the National Institutes of Health (NIH).
Recent grant funding of approximately $5m has broadened the development capabilities of the program in further animal testing and formulation.
Dor, through its BioDefense Division is active in developing biomedical countermeasures as part of the US government's "Project BioShield," enacted in 2004 to encourage the development of effective drugs and vaccines to protect against attack by biological and chemical weapons or other dangerous pathogens.
The firm has already developed a vaccine against the deadly botulinum toxin and is in the process of developing a treatment for botulism exposure in conjunction with contract manufacturer, Dowpharma.