Metformin: what a weird compound it is. Very small, very polar, the sort of thing you'd probably cross off your list of screening hits. But it's been taken by untold millions of diabetics (and made untold billions of dollars in the process), because it really does reduce glucose levels. It does so though mechanisms that are still the subject of vigorous debate and which (I might add) were completely unknown when the drug was approved. (I keep running into people who think that mechanism-of-action is some sort of FDA requirement, but it most certainly is not. Not saying that it wouldn't help, but what the regulatory agencies want are efficacy and safety. As they should).
And evidence has been piling up that the compound does many other things besides. The situation is murky. There was a report in 2009 that suggested that it might exacerbate the pathology of Alzheimer's. But last summer there was a rodent study that showed (in obese mice) that the compound seemed to improve neurogenerative effects seen in the hippocampus. (Whether this operates in animals, or humans, who are not metabolically impaired is an open question, although metformin is right in the middle of the whole "Type III diabetes" debate about Alzheimer's, which I'm going to cover in another post at some point soon). Meanwhile, human studies (in the large populations taking the drug) are not saying one way or another just yet. This British analysis suggested that there might be an association, but it's not for sure.
Then there's oncology. In 2010 I wrote about the evidence linking metformin use with lower incidence of some types of cancer, and one proposal for the mechanism. Now another paper is out suggesting that the compound works in this regard through modifying the inflammatory cascade. (Note that James Watson also highlighted this lab's previous work in his recent paper, blogged about here). The summary:
. . .Taken together, our observations suggest that metformin inhibits the inflammatory pathway necessary for transformation and CSC formation. To link our results with previous work on metformin in the diabetic context, we speculate that metformin may block a metabolic stress response that stimulates the inflammatory pathway associated with a wide variety of cancers. . .
. . .We suspect that this glucose- and metabolism-mediated pathway operates in many different cell types, and hence might explain why metformin reduces incidence of different human cancers and why the combination of metformin and chemotherapy is effective on many cell types in the xenograft context. While this pathway is hypothetical and has not been described in molecular terms, our results suggest that components in this pathway might be potential targets for cancer therapy.
The pathway referred to is through Src and IkappaB (of the NF-kB pathway), among others; the paper goes into more detail for those who are interested. There's a lot of stuff going on in the clinic with metformin added to different chemotherapy regimes, and I very much look forward to seeing the results. On the molecular level, I'd agree with the statement above - there's a lot to dig into here. The whole intersection of metabolism and cancer is a very large, very complex (and very tricky) area, but you'd have to think that there's a lot of really useful stuff to be found in it.