Category Archives: IBD

Brodalumab for Psoriasis – what a mess

Let’s agree that the headline “Suicide Stunner” – penned by John Carroll for FierceBiotech – can never auger anything but very bad news, and never more so then when it is used to describe clinical trial results. Released on the Friday before the long US holiday weekend, bookended to the announcement of positive news on it’s PSCK9 program, Amgen stated that it was walking away from an expensive co-development program with AstraZeneca, basically washing it’s hands of the anti-IL-17 receptor (IL-17R) antibody brodalumab because of suicidal tendencies and actual suicides that occurred in the Phase 3 psoriasis trials. Brodalumab is under development for the treatment of plaque psoriasis, psoriatic arthritis and axial spondyloarthritis. Amgen stated that they believed that the approval label for brodalumab would contain warning language regarding suicide risk, and this would limit the success of the drug. By using such language while pulling the plug Amgen has essentially put AstraZeneca in the position of having to prove to the FDA that there is no suicide risk.

Holy crap.

Note here that we are not talking about a psychiatric drug, where the risk of suicide might be the consequence of trying to re-align an aberrant central nervous system. Instead we are talking about a drug that targets autoimmune disorders by blocking the action of T cells. This is not a biology linked to psychiatric health, at least not as we understand it today (more on this later).

Backing up: in April 2012, AstraZeneca and Amgen announced a collaboration to jointly develop and commercialize five clinical-stage monoclonal antibodies from Amgen’s inflammation portfolio: AMG 139, AMG 157, AMG 181, AMG 557 and brodalumab (aka AMG 827). The drivers for the collaboration were Amgen’s biologics expertise, the strong respiratory, inflammation and asthma development expertise of MedImmune (AstraZeneca’s biologics division), AstraZeneca’s global commercial reach in respiratory and gastrointestinal diseases, and the shared resources of two experienced R&D organizations

Under the terms of the agreement, AstraZeneca paid Amgen a $50MM upfront payment and the companies shared development costs. The breakout was as follows: AstraZeneca was responsible for approximately 65 percent of costs for the 2012-2014 period, and the companies now split costs equally. Amgen was to book sales globally and retain a low single-digit royalty for brodalumab. Amgen retained a mid single-digit royalty for the rest of the portfolio with remaining profits to be shared equally between the partners.

It gets even more complicated. Amgen was to lead the development and commercialization of brodalumab (and AMG 557, see below). Amgen was to assume promotion responsibility for brodalumab in dermatology indications in North America, and in rheumatology in North America and Europe. AstraZeneca was to assume promotion responsibility in respiratory and dermatology indications ex-North America. AstraZeneca remains responsible for leading the development and commercialization of AMG 139, AMG 157 and AMG 181. We’ll touch on these other antibodies at the very end.

Back to brodalumab. On balance, Amgen was on the hook for the development and commercialization costs, direct, indirect and ongoing, for dermatology indications in the US and also rheumatology, which in this case refers to psoriatic arthritis and axial spondyloarthritis. On the other hand, AstraZeneca was on the hook for commercialization in respiratory indications worldwide, and dermatology ex-US. This is interesting because brodalumab failed in its’ respiratory indication, moderate to severe asthma, and failed late, in a Phase 2b patient subset trial. So, on balance, much of the overall development cost seems to have shifted back onto Amgen over time (this is not to say that the companies would not have changed terms mid-term, they may have).

Two weeks ago I chaired a session on “Biologics for Autoimmune Disease” at the PEGS conference on Boston. In my opening remarks I used psoriasis as an example of an indication in which we were making clear and important progress, including with IL-17-directed therapeutics. Indeed, psoriasis is now a “crowded” indication commercially, with antibodies and receptor fusion proteins targeting the TNFs, IL-6, IL-12, IL-17, and IL-23 pathways all showing at least some activity. Notably, IL-17 and IL-23 targeting drugs appear to offer the greatest benefit in clearing psoriatic plaques. These pathways intersect in myriad ways, not all of which are well understood. This cartoon shows the effector cytokines and the receptors are expressed by diverse cell types, including dendritic cells, macrophages, T cells, and keratinocytes in the dermis.

IL-17 and friends

In simplistic terms, IL-6 triggers IL-12 and IL-23, and IL-23 triggers IL-17. As mentioned, the IL-17 and IL-23 targeting agents have great efficacy in psoriasis. Amgen and AstraZeneca were preparing an NDA (new drug application) for FDA submission based on results from three large Phase 3 studies. Here are the listed Phase 3 programs for brodalumab:

broda 1

I suppose those Phase 3 studies in psoriatic arthritis will now be tabled or transferred to AstraZeneca. For the sake of completeness here are the earlier studies:

broda 2

Certainly the clinical program was a robust one. So, what went wrong? Amgen R&D head Sean Harper summed up Amgen’s thinking about the suicide issue in the press release: “During our preparation process for regulatory submissions, we came to believe that labeling requirements likely would limit the appropriate patient population for brodalumab.”

The news aggregator and commentary website UpdatesPlus had this to add, questioning whether this result was “bad luck, bad target or victim of brodalumab’s efficacy: Despite high efficacy in Phase 3 studies, whispers of suicidality associated with brodalumab started to emerge at AAD.  At the time Amgen suggested this was related to disease however the company refused to comment on total rates and whether events were seen across arms … The question is whether Amgen is being hyper-cautious or whether the risk of suicidality is especially concerning.  Questions also emerge around the cause of risk – is this a spurious cluster of events unrelated to brodalumab; is suicidality perhaps related to relapse from the excellent efficacy associated with brodalumab after withdrawal (remember most patients exhibited at least PASI 90 on treatment but durability was very poor upon withdrawal); or perhaps suicidality is related to blocking the IL-17RA (note that suicidality has not to our knowledge been reported for the IL-17A ligand mAb Cosentyx) … One final point is whether regulators will now reevaluate suicide risk of IL-17 related molecules as a class – much greater clarity of brodalumab data is required to make a judgement.” That’s quite a nice summary from UpdatesPlus.

FierceBiotech’s report added “AstraZeneca would face some stiff competition if it decides to move forward solo on the drug. Novartis is already well in front with its IL-17 program for secukinumab, approved in January as Cosentyx. Eli Lilly has also been racking up positive late-stage studies for its IL-17-blocking ixekizumab, trailed by Merck’s MK-3222 and Johnson & Johnson’s IL-23 inhibitor guselkumab.”

Still, brodalumab demonstrated remarkable efficacy in psoriasis – Amgen and AstraZeneca went so for as to include a PASI100 score in one of their trials, meaning 100% clearance of psoriatic plaques, and the drug would have shown well against the best of breed, which today is likely Novartis’ anti-IL-17 antibody secukinumab. It is crowded space however, with antagonists targeting multiple nodes in the IL-17/IL-23 axis, alongside the biologics mentioned earlier.

Here is the current landscape from CiteLine (including brodalumab):

CiteLine

All in all, a tough crowd, and one that Amgen likely felt it could not face with a compromised label.

Let’s go back to the question posed above: bad luck, bad target or victim of superior efficacy? “Bad luck” suggests a statistical fluke in the data, potentially caused by the generally higher rates of suicidal tendencies observed in the moderate to severe psoriasis patient population. “Victim of superior efficacy” is in a sense a related issue, since the suggestion is that the loss of responsiveness to the drug, or a relapse, triggers a suicidal response as plaques return. Neither of these statements is really formulated as a hypothesis, and it doesn’t matter, as we don’t have the actual trial data yet with which to perform hypothesis testing.

“Bad target” is the most worrisome suggestion, and this can be formulated as a hypothesis, formally, the null hypothesis is that targeting the IL-17 receptor does not cause suicidal tendencies. Unfortunately, we still can’t test the hypothesis, and it seems likely that having the actual data won’t really help, that is, the study is probably not powered to reject that particular null hypothesis. So, what do we know? A few things, as it turns out.

First is that a link between the immune system and the nervous system is well established, although much of the focus has been on the role of neuronal enervation on immune responses. But clinically at least, the picture is muddier than that. High dose IL-2 can cause neurotoxicity, even hallucinations, according to Dr. Kathleen Mahoney, an oncologist at Beth Israel Deaconess and the Dana Farber. But what is really interesting is what else happens: “Some IL-2 treated patients can have odd dreams, really crazy dreams, and they last for weeks after treatment, long past the time when IL-2 would still be present in the body”, Dr. Mahoney said. Interferon alpha therapy is associated with pathological (severe) fatigue and also depressive symptoms that develop after 4–8 weeks of treatment. Of note, preventive treatment with anti-depressants, in particular serotonin reuptake inhibition attenuates IFN-alpha-associated symptoms of depression, anxiety, and neurotoxicity. Some researchers have suggested (controversially) that anti-TNF antibodies can control depression. Such anecdotal clinical observations suggest that we really do not yet understand the immune system connection to CNS activity.

On the other hand, antagonism of cytokine activity, and particularly of the cytokines IL-6, IL-17 and IL-23, has not been associated with neurological symptoms. For example the anti-IL-6 receptor antibody tocilizumab has shown a positive impact in rheumatoid arthritis patients quality of life scoring, which includes fatigue, anxiety, depression and a number of other factors. More to the point, the anti-IL-17 antibody secukinumab, that targets the IL-17 ligand (rather than the receptor), has not shown a link to suicide.

Clearly more data are needed, and it would not be surprising if the FDA began a drug class review if the data in the brodalumab trials warrant. They could cast quite a wide net given the complexity of this pathway, which overlaps with IL-6, IL-12 and IL-23. This casts a pall over the dermatology and particularly the rheumatology landscape, which is really waiting for novel therapeutics to move them successfully into new and important indications such as lupus and Type-1 Diabetes. The IL-17/IL-23 axis was to be that next great hope, and with luck we will still see these drugs moving out of their core indications of psoriasis and inflammatory bowel disease into new indications.

One last thing.

Those other antibodies – where are they now? A quick scorecard:

snapshot

It is readily seen that none of these are beyond early Phase 2, so it’s fair to say that the rest of the Amgen/AstraZeneca partnership has a long way to go. I, for one, wish the ongoing collaboration the very best of luck, particularly in the lupus indications, where we can really use some good news.

stay tuned.

High Fiber, Butyrate, Tregs & Immune Responses – Evaluating Recent Papers in Nature, Nature Medicine and Immunity

Last week I reviewed four recent papers on the impact of gut microbial commensals and pathogens on immune function, focusing on regulatory T cell (Treg) generation and on the role of effector Th17 T cells (Th17s) on disease. See the post here: http://www.sugarconebiotech.com/?p=6.

The other day another paper on the role of dietary fatty acids in the regulation of immune responses appeared (see http://www.nature.com/nm/journal/vaop/ncurrent/full/nm.3444.html). Honestly, the results presented in this new paper are sufficiently distinct from the prior two papers in Nature that a reappraisal makes sense, as there are clearly a whole host of unresolved questions in this body of work. Also, we will touch briefly on an Immunity paper, also just out.

The driver for all of these studies is the extensive observations on the ability of particular fatty acids to modulate the immune response. There are similar observations on the role of fatty acids in regulating metabolism – that work will not be discussed here.

In particular, the investigators are trying to understand if, and how, short-chain fatty acids (SCFAs) produced by gut bacteria, such as butyrate, propionate and acetate, can modulate the immune system. The stakes are high, as there is early clinical work aimed at manipulating the microbiome in order to treat diseases, notably gut diseases such as inflammatory bowel disease (IBD) and severe diarrhea. Also there are the massive supplement and wellness industries already selling such SCFAs, without much understanding of the science.

Suffice to say we are entering the high fiber diet metaverse, cautiously.

Here is a quick recap of the earlier papers, taken one at a time and in a little more detail. I’ll highlight some similarities and differences. The first two studies were published in Nature on 19 December 2013. The key findings are summarized below. Note that this and the other studies discussed here are done in pure strain inbred mice.

  • commensal microbes support Treg development
  • specifically, large bowel (colonic) production of the SCFA butyrate induces Tregs
  • butyrate functions by inhibiting HDAC IIa
  • HDAC inhibition allows more extensive acetylation of FoxP3 and other genes
  • expression of FoxP3 and other genes drives Treg differentiation
  • butyrate blocks the development of IDB in a T-cell dependent mouse colitis model

The first study was led by Hiroshi Ohno from the RIKEN Center in Kanagawa, Japan. The colitis experiment was shown in that paper. Now onto some of the other details – there are 4 figures in the text and 22 supplemental figures so we can’t cover everything.

The Tregs under discussion in this paper are peripherally generated (i.e. not thymic in origin) and are identified in flow cytometry (FACS) experiments as FoxP3+/neuropilin-/Helios-. About half the high-fiber diet (HFD) induced Tregs were activated and therefore CD103+. Critically, Ohno and colleagues show that this Treg population in restricted to the local (colonic lamina propria) environment. There are plenty of Tregs in the lymphoid organs – mesenteric lymph nodes and spleen – but the percentage of FoxP3+/neuropilin-/Helios- cellsdoes not change in these organs in response to the HFD. The investigators then demonstrate that the microbes responsible for fermenting the HFD into beneficial SCFAs are bacteria of the class Clostridiales and that the potentially beneficial SCFAs include the very potent butyrate and the less potent propionate. Acetate had no effect.

Now this is where is starts to get a little complicated. Having demonstrated that the gut SCFAs induce Treg differentiation only in the colonic lamina propria, the authors next show that T cells isolated from the mouse spleen can be differentiated into Tregs using stimulation conditions that include TGFbeta and butyrate plus stimulatory antibodies to CD3 and CD28. This might indicate that there is some barrier that prevents butyrate reaching sites other than the gut wall, and that this accounts for the local aspect of the Treg response to butyrate. However, while most of these SCFAs are passively and actively taken up by intestinal cells, SCFAs can also be detected in circulation. The absorption of SCFAs can be saturating, i.e. above some concentration SCFA uptake into the circulation is maxed out. These observations suggest that there is a requirement for locally high concentrations of SCFAs in order to induce Treg differentiation – this would explain why these induced Tregs were only found in colonic tissue and not in spleen or LN. I can’t find the relevant concentration data nor is there any dose response data – this is disconcerting. They also report that butyrate can drive naive T cells to a Treg phenotype irrespective of pro-inflammatory Th1, Th2 or Th17 inducing conditions. This is a very dramatic result but suffers from the same lack of critical experimental detail.

The observations made using butyrate stimulation of T cell are followed up in vivo using SCFA supplemented diets. As noted earlier the MOA here is the antagonism of the deacetylase HDAC IIa, thereby allowing increased acetylation and activation of the FoxP3 gene. Finally, using an activated CD4+ T cell transfer colitis model (a model in which Tregs are specifically excluded from the transferred cells) the investigators show protection from disease when the mice are fed diets containing butyrate.

OK, we still have no idea how this is mediated, but the observation is in line with other papers that have examined to ability of butyrate to control colitis (its a large body of work). So, we are not criticizing this whole story, but just suggesting that more experimental detail would be useful, especially in a world where one can buy butyrate capsules or arrange for butyrate enema treatment. A more general critique is offered at the end of this post.

The second Nature paper is by Alexander Rudensky and colleagues from Memorial Sloan-Kettering in NY and reaches broadly similar conclusions as the Ohno paper. Their naive T cell culture conditions are a little different, substituting dendritic cells and Il-2 for the anti-CD28 antibody signal, and they do show dose response data. The latter results indicate a sharp rise in Treg induction above 30uM butyrate. To manipulate the system in vivo these investigators used antibiotics to clear the SCFA producing bacteria. Thus the model is rigged to show an increase above an artificially low background. That’s OK, but let us just be clear about it.

Using sodium butyrate in the drinking water, the investigators induced Treg differentiation in the peripheral LN and spleen. The serum concentration achieved with the drinking water regimen was 500pg/ul which is ~ 4.5uM, a physiological concentration in wildtype, untreated mice. In other words, they brought the SCFA level back to normal, and that induced T regs. In order to induce Tregs in the colonic lamina propria they used either butyrate-enriched food, or a butyrate enema.

The conclusion of all that work is that systemic exposure (drinking water) can induce Tregs in the periphery (spleen, LN) but that local exposure (food, enema) is required to induce Tregs in the gut. Note that this latter conclusion echoes the Ohno paper. Turning to propionate and acetate, they next show that propionate in the drinking water can induce peripheral Tregs in the spleen and LN, and that both propionate and acetate can induce local Tregs in the colon. However, these latter cells are possibly thymic-derived, not extrathymic Tregs, as shown by independence from the CNSI gene (required for extrathymic Treg differentiation). The other option is that these cells are preferentially recruited from the circulation. Note that the acetate result is at odds with this prior paper.

So this has now gotten very complicated, with three abundant starch-derived fatty acids being endowed with both unique and overlapping abilities to induce different types of Tregs in different geographies. Just to make this even more complicated, the Rudensky team next shows that this biology is not just T cell specific, but that butyrate can also endow dendritic cells (DCs) with the ability to preferentially induce Tregs. Lets not go into detail except to say that this effect on DCs did not depend on GPR109a, the niacin and butyrate specific G-protein-coupled receptor (GPCR). More on GPCRs later. The rest of the story – HDAC inhibition and FoxP3 induction – is familiar from the Ohno paper (and many others, the HDAC mechanism is pretty well known).

Finally, I mentioned at the top the Nature Medicine paper that triggered this reappraisal (http://www.nature.com/nm/journal/vaop/ncurrent/full/nm.3444.html). Using a mouse model of house dust mite (HDM) antigen allergic asthma, Benjamin Marsland and colleagues from the University of Lausanne, Switzerland, demonstrate that the susceptibility to and severity of HDM-induced asthma was worsened on a low fiber diet and improved on a high fiber diet. They traced the change in asthmatic response to a change in the gut microbiota supported by the different diets, bringing us again to the SCFAs produced. Higher concentrations of the usual suspects (butyrate, propionate, acetate) were produced when the microbiome was dominated by the Phylum Bacteroidetes, to which the class Clostridiales belongs. Note that the differences in the composition of the microbiome on the low and high fat diets were not significant. This is an issue we will revisit.

The asthma paper is strikingly different from the two Treg papers. In this paper the focus in on propionate, not butyrate, and on systemic effects, not local effects. The premise is that the dietary changes impact the bone marrow, not the local lung tissue. Indeed SCFAs could not be detected in the lung. Propionate treatment reduced Th2 immune responses to HDM in a manner that was dependent on GPR41, a SCFA receptor. This receptor is expressed at high levels in the colon where it mediates a variety of responses to SCFAs, however, in this paper the impact of propionate was traced to the CD11bhisubset of DC in the lung-training LN. How this impacts the allergic-asthmatic response is hypothesized to be (and I’m quoting the paper here) “after inflammation, the lung DC compartment is replenished with inflammatory monocyte-derived DCs that have been exposed to SCFAs in the bone marrow and circu­lation, leading to a maturation profile that is ineffective at driving Th2 cell responses.”

Therefore the authors conclude that they have elucidated a “gut-lung axis for the formation of the airway microbiota” and therefore I suppose, lung immune responses.

Really?

What we have here are three reductionist tales, necessary to help us understand the rules of the system but perhaps not sufficient in themselves to draw sweeping biological and pathological conclusions. It’s very clear from the disparate results obtained that we are still working out the rules. Also, one cautionary note, a recent study in human subjects showed that plasma butyrate concentration remained very close to 2uM under a variety of high fiber meal and fasting conditions, suggesting that this SCFA may not be as variable in concentration as is seen in mice (http://jn.nutrition.org/content/140/11/1932.full).

A somewhat more straightforward study just published last week in Immunity (http://download.cell.com/immunity/pdf/PIIS1074761313005645.pdf?intermediate=true). Vadivel Ganapathy and colleagues from the Georgia Regents University in Augusta show that GPR109 signaling is required to maintain IL-10 dependent Treg activity in the colon, and they trace this function to DC and macrophage responses. Butyrate (or niacin, the nominate ligand for Niacr1 aka GPR109a) treatment of DCs and macrophages induced a phenotype that supported Treg differentiation. Note that this result contradicts the Rudensky paper, in which GPR109a was ruled out as the causative receptor, at least on DCs.

GPR109a gene-deficient mice were then shown to be more susceptible to colitis and inflammation induced colon carcinogenesis, and this effect was shown to be dependent on both the hematopoietic compartment and colonic tissue cells. This final study is satisfying, as now we are seeing pharmacological manipulation of a defined receptor, albeit with a molecule (niacin) that has a pretty checkered history as a therapeutic.

Where does this leave us? I think the take home message is that these systems are very complex, and by trying to simplify them we have the benefit of gaining some insight but the risk of over-interpretation. The human microbiome is incredibly variable, over time and between individuals. The fact that we are seeing different results from manipulation of highly inbred strains of mice on very carefully defined diets should give us pause, especially when some studies can’t statistically distinguish between components of the microbiota they are describing. However, at the very least these studies support the belief that high fiber diets that producing lots of butyrate and propionate should be beneficial, and we have identified some targetable GPCRs, which should drive further research. Finally, we are perhaps a step or two closer to understanding how to manipulate Treg cell populations in human disease. This last goal, the ability to regulate immune responses via regulatory T cell modulation, has proved to be an elusive one so far.