DPP-IV is short for “dipeptidylpeptidase IV”, understandably, and we need a good abbreviation for it. It’s an important enzyme target for diabetes therapy, since under normal conditions it breaks down glucagon-like-peptide 1. Longer-circulating GLP-1 would actually do a lot of diabetics good, and people have actually made such proteins as separate drugs, so inhibiting an enzyme that clears it out looks like a good bet. Of such reasoning are drug targets made.
A lot of companies have bought into this reasoning, for sure. For quite a while, Novartis looked like the leader in the area, with the most advanced clinical candidate and a lot of publications in the literature from their development work. But Merck turned out to be running a big effort of their own, and actually got to market first with Januvia (sitagliptin). Novartis’s drug (Galvus, vildagliptin) looks as if it will never make it at all here in the US.
They had to slow down development due to some troubling side effects, giving Merck the edge. There are several DPP subtypes, and you need to be pretty selective, as it turns out – at least some of the problems stem from that consideration. This wasn’t fully appreciated in the first wave of development in this area – the pioneers had to figure it out the hard and expensive way. But a number of companies have come up behind, trying to get a piece of the market, and they now have a clearer idea of what they need to accomplish.
Or do they? Takeda recently heard from the FDA that their DPP-IV inhibitor alogliptin has been turned down for now. What’s more, the agency wants more cardiovascular safety data from them and from anyone else who comes in with a drug in that category. Cardiovascular problems have always been the weak point for Type II diabetes drugs, to be sure. The patient population tends to be older and overweight, often with elevated blood pressure, so you really don’t have much room to work in when it comes to side effects. That’s led to a lot of attempts to come up with therapies that address the CV side of things at the same time as glucose levels (such as the ill-fated disaster of the PPAR alpha-gamma compounds, all of when went most expensively down in flames). DPP-IV inhibitors wouldn’t be expected to have any direct CV benefits, but they do have to avoid making things any worse.
So Merck looks to have the market to itself for a while longer, but as the only DPP-IV drug on the market, they’re going to be under a good deal of scrutiny. The company has already had its share of post-launch cardiovascular nightmares; you’d think that they’re going to work hard to avoid any more. And now all we have to do is assure ourselves that the actions of the DPP-IV inhibitors are all through making GLP-1 last longer. Because even if you're selective for that one enzyme, it has a lot of other substrates. So the story may well swing back to the biochemical mechanism again before we're through.