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DBL%20Hendrix%20small.png College chemistry, 1983

Derek Lowe The 2002 Model

Dbl%20new%20portrait%20B%26W.png After 10 years of blogging. . .

Derek Lowe, an Arkansan by birth, got his BA from Hendrix College and his PhD in organic chemistry from Duke before spending time in Germany on a Humboldt Fellowship on his post-doc. He's worked for several major pharmaceutical companies since 1989 on drug discovery projects against schizophrenia, Alzheimer's, diabetes, osteoporosis and other diseases. To contact Derek email him directly: derekb.lowe@gmail.com Twitter: Dereklowe

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In the Pipeline: Don't miss Derek Lowe's excellent commentary on drug discovery and the pharma industry in general at In the Pipeline

In the Pipeline

August 28, 2014

Drug Repurposing

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Posted by Derek

A reader has sent along the question: "Have any repurposed drugs actually been approved for their new indication?" And initially, I thought, confidently but rather blankly, "Well, certainly, there's. . . and. . .hmm", but then the biggest example hit me: thalidomide. It was, infamously, a sedative and remedy for morning sickness in its original tragic incarnation, but came back into use first for leprosy and then for multiple myeloma. The discovery of its efficacy in leprosy, specifically erythema nodosum laprosum, was a complete and total accident, it should be noted - the story is told in the book Dark Remedy. A physician gave a suffering leprosy patient the only sedative in the hospital's pharmacy that hadn't been tried, and it had a dramatic and unexpected effect on their condition.

That's an example of a total repurposing - a drug that had actually been approved and abandoned (and how) coming back to treat something else. At the other end of the spectrum, you have the normal sort of market expansion that many drugs undergo: kinase inhibitor Insolunib is approved for Cancer X, then later on for Cancer Y, then for Cancer Z. (As a side note, I would almost feel like working for free for a company that would actually propose "insolunib" as a generic name. My mortgage banker might not see things the same way, though). At any rate, that sort of thing doesn't really count as repurposing, in my book - you're using the same effect that the compound was developed for and finding closely related uses for it. When most people think of repurposing, they're thinking about cases where the drug's mechanism is the same, but turns out to be useful for something that no one realized, or those times where the drug has another mechanism that no one appreciated during its first approval.

Eflornithine, an ornithine decarboxylase inhibitor, is a good example - it was originally developed as a possible anticancer agent, but never came close to being submitted for approval. It turned out to be very effective for trypanosomiasis (sleeping sickness). Later, it was approved for slowing the growth of unwanted facial hair. This led, by the way, to an unfortunate and embarrassing period where the compound was available as a cream to improve appearance in several first-world countries, but not as a tablet to save lives in Africa. Aventis, as they were at the time, partnered with the WHO to produce the compound again and donated it to the agency and to Doctors Without Borders. (I should note that with a molecular weight of 182, that eflornithine just barely missed my no-larger-than-aspirin cutoff for the smallest drugs on the market).

Drugs that affect the immune system (cyclosporine, the interferons, anti-TNF antibodies etc.) are in their own category for repurposing, I'd say, They've had particularly broad therapeutic profiles, since that's such a nexus for infectious disease, cancer, inflammation and wound healing, and (naturally) autoimmune diseases of all sorts. Orencia (abatacept) is an example of this. It's approved for rheumatoid arthritis, but has been studied in several other conditions, and there's a report that it's extremely effective against a common kidney condition, focal segmental glomerulosclerosis. Drugs that affect the central or peripheral nervous system also have Swiss-army-knife aspects, since that's another powerful fuse box in a living system. The number of indications that a beta-blocker like propanolol has seen is enough evidence on its own!

C&E News did a drug repurposing story a couple of years ago, and included a table of examples. Some others can be found in this Nature Reviews Drug Discovery paper from 2004. I'm not aware of any new repurposing/repositioning approvals since then, but there's an awful lot of preclinical and clinical activity going on.

Comments (11) + TrackBacks (0) | Category: Clinical Trials | Drug Development | Drug Industry History | Regulatory Affairs

August 27, 2014

The Smallest Drugs

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Posted by Derek

Here is the updated version of the "smallest drugs" collection that I did the other day. Here are the criteria I used: the molecular weight cutoff was set, arbitrarily, at aspirin's 180. I excluded the inhaled anaesthetics, only allowing things that are oils or solids in their form of use. As a small-molecule organic chemist, I only allowed organic compounds - lithium and so on are for another category. And the hardest one was "Must be in current use across several countries". That's another arbitrary cutoff, but it excludes pemoline (176), for example, which has basically been removed from the market. It also gets rid of a lot of historical things like aminorex. That's not to say that there aren't some old drugs on the remaining list, but they're still in there pitching (even sulfanilamide, interestingly). I'm sure I've still missed a few.

What can be learned from this exercise? Well, take a look at those structures. There sure are a lot of carboxylic acids and phenols, and a lot more sulfur than we're used to seeing. And pretty much everything is polar, very polar, which makes sense: if you're down in this fragment-sized space, you've got to be making some strong interactions with biological targets. These are fragments that are also drugs, so fragment-based drug discovery people may find this interesting as the bedrock layer of the whole field.

Some of these are pretty specialized and obscure - you're only going to see pralidoxime if you have the misfortune to be exposed to nerve gas, for example. But there are some huge, huge compounds on the list, too, gigantic sellers that have changed their whole therapeutic areas and are still in constant use. Metformin alone is a constant rebuke to a lot of our med-chem prejudices: who among us, had we never heard of it, would not have crossed it off our lists of screening hits? So give these small things a chance, and keep an open mind. They're real, and they can really be drugs.
Smallest%20drugs%20final%20set2.jpg

Comments (14) + TrackBacks (0) | Category: Chemical News | Drug Industry History

Life Is Too Short For Some Journal Feeds

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Posted by Derek

What scientific journals can you not be bothered to keep up with? I know, sometimes it's tempting to answer "all of them", but a well-informed chemist really should watch what comes out in the better ones. But how about the not-so-better ones? The "Life's too short" ones? Reading journals by RSS gives a person some perspective on signal-to-noise.

One problem is that Elsevier's RSS feeds are sort of perpetually hosed. Are they working now? I haven't checked in a while, because I finally gave up on them. And that means that I don't regularly look at Tetrahedron Letters or Bioorganic and Medicinal Chemistry Letters, even though (once in a while) something interesting turns up there. I look at ACS Medicinal Chemistry Letters more often, just because it has a working RSS feed (and I should note that I've rotated off their editorial board, by the way). Overall, though, I can't say that I miss either of those Elsevier journals, because you have to scroll through an awful lot of. . .stuff. . .to see something worth noting.

The same goes, I'm afraid, for Chemical Communications, and that makes me wonder if it's possible to keep up with the Letters/Communications style journals usefully at all. There are just so many papers pouring through them, and since Chem Comm takes them in from every sort of chemistry there is, vast numbers of them are of little interest to any particular reader. Their mini-review articles are perhaps an attempt to counteract this problem, and the journal also seems to have a slant towards "hot" topics. It's still in my RSS feed, but I look at the numbers of papers that pile up in it, and wonder if I should just delete and get it over with.

Organic Letters, on the other hand, I seem to be able to stay on top of, perhaps because it's focused down to at least organic chemistry (as opposed to Chem Comm). And I find a higher percentage of papers worth looking at than I do in Tet Lett (do others feel the same way?) And as for the other short-communications organic chemistry journals, I don't have them in the feed. Synthesis, Syn Comm, Synlett - writing this prompts me to go in and add them, but we'll see over the next couple of months if I regret it.

What it comes down to is that there's room for only a certain number of titles that can be followed as the papers publish. (The rest of them turn up in literature searches, responses to directed queries). And there are only a certain number of titles that are worth following in real time. So to get back to the question at the start of the post, which well-known journals do you find to be not worth the trouble?

Comments (16) + TrackBacks (0) | Category: The Scientific Literature

August 26, 2014

A New Look at Phenotypic Screening

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Posted by Derek

There have been several analyses that have suggested that phenotypic drug discovery was unusually effective in delivering "first in class" drugs. Now comes a reworking of that question, and these authors (Jörg Eder, Richard Sedrani, and Christian Wiesmann of Novartis) find plenty of room to question that conclusion.

What they've done is to deliberately focus on the first-in-class drug approvals from 1999 to 2013, and take a detailed look at their origins. There have been 113 such drugs, and they find that 78 of them (45 small molecules and 33 biologics) come from target-based approaches, and 35 from "systems-based" approaches. They further divide the latter into "chemocentric" discovery, based around known pharmacophores, and so on, versus pure from-the-ground-up phenotypic screening, and the 33 systems compounds then split out 25 to 8.

As you might expect, a lot of these conclusions depend on what you classify as "phenotypic". The earlier paper stopped at the target-based/not target-based distinction, but this one is more strict: phenotypic screening is the evaluation of a large number of compounds (likely a random assortment) against a biological system, where you look for a desired phenotype without knowing what the target might be. And that's why this paper comes up with the term "chemocentric drug discovery", to encompass isolation of natural products, modification of known active structures, and so on.

Such conclusions also depend on knowing what approach was used in the original screening, and as everyone who's written about these things admits, this isn't always public information. The many readers of this site who've seen a drug project go from start to finish will appreciate how hard it is to find an accurate retelling of any given effort. Stuff gets left out, forgotten, is un- (or over-)appreciated, swept under the rug, etc. (And besides, an absolutely faithful retelling, with every single wrong turn left in, would be pretty difficult to sit through, wouldn't it?) At any rate, by the time a drug reaches FDA approval, many of the people who were present at the project's birth have probably scattered to other organizations entirely, have retired or been retired against their will, and so on.

But against all these obstacles, the authors seem to have done as thorough a job as anyone could possibly do. So looking further at their numbers, here are some more detailed breakdowns. Of those 45 first-in-class small molecules, 21 were from screening (18 of those high-throughput screening, 1 fragment-based, 1 in silico, and one low-throughput/directed screening). 18 came from chemocentric approaches, and 6 from modeling off of a known compound.

Of the 33 systems-based drugs, those 8 that were "pure phenotypic" feature one antibody (alemtuzumab) which was raised without knowledge of its target, and seven small molecules: sirolimus, fingolimod, eribulin, daptomycin, artemether–lumefantrine, bedaquiline and trametinib. The first three of those are natural products, or derived from natural products. Outside of fingolimod, all of them are anti-infectives or antiproliferatives, which I'd bet reflects the comparative ease of running pure phenotypic assays with those readouts.

Here are the authors on the discrepancies between their paper and the earlier one:

At first glance, the results of our analysis appear to sig­nificantly deviate from the numbers previously pub­lished for first­-in­-class drugs, which reported that of the 75 first-­in-­class drugs discovered between 1999 and 2008, 28 (37%) were discovered through phenotypic screening, 17 (23%) through target-­based approaches, 25 (33%) were biologics and five (7%) came from other approaches. This discrepancy occurs for two reasons. First, we consider biologics to be target­-based drugs, as there is little philosophical distinction in the hypothesis­ driven approach to drug discovery for small­-molecule drugs versus biologics. Second, the past 5 years of our analysis time frame have seen a significant increase in the approval of first-­in-­class drugs, most of which were discovered in a target­-based fashion.

Fair enough, and it may well be that many of us have been too optimistic about the evidence for the straight phenotypic approach. But the figure we don't have (and aren't going to get) is the overall success rate for both techniques. The number of target-based and phenotypic-based screening efforts that have been quietly abandoned - that's what we'd need to have to know which one has the better delivery percentage. If 78/113 drugs, 69% of the first-in-class approvals from the last 25 years, have come from target-based approaches how does that compare with the total number of first-in-class drug projects? My own suspicion is that target-based drug discovery has accounted for more than 70% of the industry's efforts over that span, which would mean that systems-based approaches have been relatively over-performing. But there's no way to know this for sure, and I may just be coming up with something that I want to hear.

That might especially be true when you consider that there are many therapeutic areas where phenotypic screening basically impossible (Alzheimer's, anyone?) But there's a flip side to that argument: it means that there's no special phenotypic sauce that you can spread around, either. The fact that so many of those pure-phenotypic drugs are in areas with such clear cellular readouts is suggestive. Even if phenotypic screeningwere to have some statistical advantage, you can't just go around telling people to be "more phenotypic" and expect increased success, especially outside anti-infectives or antiproliferatives.

The authors have another interesting point to make. As part of their analysis of these 113 first-in-class drugs, they've tried to see what the timeline is from the first efforts in the area to an approved drug. That's not easy, and there are some arbitrary decisions to be made. One example they give is anti-angiogenesis. The first report of tumors being able to stimulate blood vessel growth was in 1945. The presence of soluble tumor-derived growth factors was confirmed in 1968. VEGF, the outstanding example of these, was purified in 1983, and was cloned in 1989. So when did the starting pistol fire for drug discovery in this area? The authors choose 1983, which seems reasonable, but it's a judgment call.

So with all that in mind, they find that the average lead time (from discovery to drug) for a target-based project is 20 years, and for a systems-based drug it's been 25 years. They suggest that since target-based drug discovery has only been around since the late 1980s or so, that its impact is only recently beginning to show up in the figures, and that it's in much better shape than some would suppose.

The data also suggest that target-­based drug discovery might have helped reduce the median time for drug discovery and development. Closer examination of the differences in median times between systems­-based approaches and target­-based approaches revealed that the 5-­year median difference in overall approval time is largely due to statistically significant differences in the period from patent publication to FDA approval, where target-­based approaches (taking 8 years) took only half the time as systems­-based approaches (taking 16 years). . .

The pharmaceutical industry has often been criticized for not being sufficiently innovative. We think that our analysis indicates otherwise and perhaps even suggests that the best is yet to come as, owing to the length of time between project initiation and launch, new technologies such as high­-throughput screening and the sequencing of the human genome may only be starting to have a major impact on drug approvals. . .

Now that's an optimistic point of view, I have to say. The genome certainly still has plenty of time to deliver, but you probably won't find too many other people saying in 2014 that HTS is only now starting to have an impact on drug approvals. My own take on this is that they're covering too wide a band of technologies with such statements, lumping together things that have come in at different times during this period and which would be expected to have differently-timed impacts on the rate of drug discovery. On the other hand, I would like this glass-half-full view to be correct, since it implies that things should be steadily improving in the business, and we could use it.

But the authors take pains to show, in the last part of their paper, that they're not putting down phenotypic drug discovery. In fact, they're calling for it to be strengthened as its own discipline, and not (as they put it) just as a falling back to the older "chemocentric" methods of the 1980s and before:

Perhaps we are in a phase today similar to the one in the mid­-1980s, when systems-­based chemocentric drug discovery was largely replaced by target­-based approaches. This allowed the field to greatly expand beyond the relatively limited number of scaffolds that had been studied for decades and to gain access to many more pharmacologically active compound classes, pro­viding a boost to innovation. Now, with an increased chemical space, the time might be right to further broaden the target space and open up new avenues. This could well be achieved by investing in phenotypic screening using the compound libraries that have been established in the context of target-­based approaches. We therefore consider phenotypic screening not as a neoclassical approach that reverts to a supposedly more successful systems­-based method of the past, but instead as a logical evolution of the current target­-based activi­ties in drug discovery. Moreover, phenotypic screening is not just dependent on the use of many tools that have been established for target-­based approaches; it also requires further technological advancements.

That seems to me to be right on target: we probably are in a period just like the mid-to-late 1980s. In that case, though, a promising new technology was taking over because it seemed to offer so much more. Today, it's more driven by disillusionment with the current methods - but that means, even more, that we have to dig in and come up with some new ones and make them work.

Comments (5) + TrackBacks (0) | Category: Drug Assays | Drug Development | Drug Industry History

August 25, 2014

Small Molecules - Really, Really Small

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Posted by Derek

Mentioning such a small compound as pirfenidone prompts me to put up the graphic shown below: these are the smallest commonly used drugs that I can think of. (OK, there's cocaine as a nasal anaesthetic - no, really - but that's where I draw the line at "commonly used". Nominations for ones that I've missed are welcome, and I'll update the list as needed. Note: four more have been added since the initial post, with more to come. This sort of thing really makes a chemist think, though - some of these compounds are very good indeed at what they do, and have been wildly successful. We need to keep an open mind about small molecules, that's for sure, no matter how small they are.

Update: see this follow-up post for the latest version of the graphic.

Comments (50) + TrackBacks (0) | Category: Drug Industry History

InterMune Bought

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Posted by Derek

It has been a bizarre ride for InterMune, its employees, and its investors. But now it ends with Roche buying them for $8.3 billion dollars, a sum that would have brought incredulous stares a few years ago. The deal makes sense for Roche, and it will provide investors a rationale for years as they buy into small biopharma companies - trying to pick the next InterMune, you know.

Comments (7) + TrackBacks (0) | Category: Business and Markets