This story has been updated from a previous version to include comments from Tacere's CEO.
By Doug Macron
Pfizer has exercised its option to develop and commercialize Tacere Therapeutics' expressed RNAi-based hepatitis C treatment, triggering the payment of an undisclosed option fee, Tacere said last week.
And while privately held Tacere is weighing the possible expansion of its pipeline, having met this milestone in its flagship drug-development program, its management has set its sights on exiting the field through the sale of the company to a bigger player, CEO Sara Hall told RNAi News this week.
"This is a good time to look around [for a buyer], especially [considering the number of RNAi] players that don't have a robust pipeline and don't have a partnered drug, which is basically everybody in RNAi," she said.
Tacere acquired its HCV program from Australia's Benitec in late 2006 after that company underwent a sweeping corporate reorganization that included the shuttering of its US operations (see RNAi News, 10/12/2006). As part of that deal, Benitec holds an undisclosed stake in Tacere and stands to receive milestones and royalties related to the drug's clinical development and commercialization.
Less than two years later, Tacere inked a deal granting Pfizer the option to license the worldwide rights outside of Asia to the program and its lead candidate, TT-033, following a period of joint preclinical development (see RNAi News, 1/10/2008).
According to the company, TT-033 contains shRNAs against three different sites of the hepatitis C virus, and is encapsulated in an adeno-associated virus protein coat. Hall noted that preclinical work conducted with Pfizer showed the drug to be safer than had been expected.
In cynomolgus monkey and mouse experiments, "we've seen no maximum tolerated dose and no safety signals at all," she said. Meanwhile, the companies observed 100 percent viral inhibition in in vitro HCV replication models, as well as 100 percent penetration of human hepatocytes "at a very clinically relevant dose."
"If you can show that you are getting it into the liver, that's the main thing," Hall explained.
"Making sure you have enough coverage … has always been the issue with macromolecules going into the liver," she said. "Hepatocytes, which are the only site of HCV replication, don't take up things like liposomes very well because the [cellular] pore size is very small. That's always been the limitation.
But with AAV delivery, "the receptor distribution on hepatocytes is very good. And it is a receptor-mediated infection, so you can totally bypass all of the toll-like receptors [and] all of the interferon responses."
Hall noted that the deal with Pfizer calls for Tacere to continue to support the program though phase I trials. She added that an investigational new drug application is expected to be filed with US regulators before the end of the year, with human studies beginning in the first quarter of 2011.
Now, with the HCV program on track to enter human studies, Tacere is looking around for what to do next.
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"From a scientific standpoint, we are starting to look to see what [other indications] are out there … and we'll focus on our strength, which is AAV-delivered shRNA," Hall explained. "We know that inside and out, we know exactly what to expect, and from a molecule-development standpoint, we understand the entire battery of tests we'd need to do."
But of greater interest to the company is finding an acquirer — be it "either a large biotech or pharma, or Pfizer," she said, adding that discussions related to all of those options "are going on simultaneously."
"We're in a fantastic position" when it comes to putting Tacere on the block, Hall said. "We have a significant amount of money in the bank, we've cleared the major milestone with Pfizer … and we're a small team with just eight people so we've probably got four or five years of burn in the bank, if not more," given Pfizer's handling of virtually all costs associated with the HCV program.
She said it was difficult to predict when a deal might be consummated, noting that "until you've got term sheets on the table, it's hard to speculate how quickly things would go." And in the end, Tacere may not even choose to go the M&A route, she added.
A sale of the company "is not a 'need to do' by any means," Hall said. "We can keep going for years and continue to develop the pipeline."