Monthly Archives: September 2014

Hif, Hif, Hif, Hike!

Football season. Except is was 85 degrees here in Massachusetts today and felt more like mid-July. Thankfully there is “fallball” (fall softball season) so we got to enjoy that instead.

We got a good look at the convergence of immune and pathogenic pathways in this week’s issues of Science and Nature. Two papers in Science identify metabolic adjustments made by monocytes and macrophages that may support innate immune memory. The same pathway is hijacked by some tumors to redirect macrophage activity, as described in a very nice Nature paper.

Cheng et al from the Netea lab in The Netherlands used a b-glycan derived from the pathogenic fungus Candida albicans to “educate” monocytes, mimicking an infection event (Cheng et al). C. albicans b-glycan, a carbohydrate moiety, binds the dectin-1 receptor on monocytes, macrophages and other innate immune cells and induces cell activation. This activation response included changes in the epigenetic profile of the cells. The epigenetic signature suggests that monocytes “trained” by exposure to b-glycan alter their metabolic status, in particular by elevating aerobic glycolysis with increased glucose consumption. Key glycolysis enzymes such as hexokinase and pyruvate kinase were epigenetically upregulated, supporting the shift to glycolysis. Aerobic glycolysis produces lactic acid and increased lactate production was also observed: these b-glycan activated monocytes have really committed to this metabolic state.

This metabolic shift was mediated by signaling from dectin-1 to AKT and mTOR. This signaling pathway is responsible for many cellular responses, including induction of HIF-1α (hypoxia-inducible factor–1α). In turn, HIF-1α-dependent signals turn on many genes needed to adapt to the metabolic shift. This is a common tactic in hypoxic conditions for example. Blockade of any steps in the pathway abrogated the metabolic shift and prevented “trained immunity”. The role of epigenetic components in induction of the metabolic shift in monocytes was demonstrated using the epigenetic inhibitors methylthioadenosine, a methyltransferase inhibitor, and givinostat, a class I/II histone deacetylase (HDAC) inhibitor.

A second paper from the same group dives deeper into the monocyte to macrophage differentiation program (Saeed et al). Short-term culture of monocytes with LPS (a TLR4 agonist) or b-glycan yielded distinct macrophage populations. Serum culture (mimicking the homeostatic state) yielded yet a 3rd type. This paper is a technical grind so have at it if you want all the complex details. I was interested in the conclusions. As in the b-glycan study referenced above, LPS and serum culture induced distinct epigenetic signatures. Genome-wide mapping of histone modifications identified epigenetically marked clusters – that is, reactive regions of the genome. Within these clusters we would expect to find transcription regulatory regions, and indeed four such clusters were differentially modulated when monocytes were exposed to LPS or b-glucan. Targets within these clusters include G protein–coupled receptors, protein kinases, and additional epigenetic enzymes. The authors therefore affirm the “trained immunity” state identified in the first paper and now elucidate a macrophage “exhaustion” phenotype induced by short term exposure to LPS. By my reading of the paper it appears both of these induced phenotypes are extensions of the M-CSF/serum induced homeostatic differentiation profile. This makes sense, as monocytes are recruited from circulation so they can differentiate into macrophages at sites of inflammation, a process that optimally requires M-CSF.

In the first paper the production of lactic acid and lactate was noted as a consequence of differentiation to the “trained”, glycolysis-driven phenotype. Turning now to a paper in Nature from Medzhitov and colleagues at Yale, we find ourselves confronting a chicken and egg story (Colegio et al). In this study the crosstalk of tumor-resident macrophages and “client” tumor cells was examined. The premise is that tumor-associated macrophages (TAMs) perform key homeostatic functions that support tumor growth and survival. In this case it appears that the tumor microenvironment subverts macrophage function via production of lactic acid. There are important differences in the study designs – the papers published in Science use short-term culture techniques while the Nature paper relies on in vivo tumor/macrophage development in syngeneic mouse models – but with this caveat in mind the convergence of pathway data is striking. TAMs sorted from implanted lung (LLC) or melanoma (B16-F1) tumors expressed high levels of VEGF and arginase 1 (Arg1) mRNA, accounting for nearly all of the expression of these proteins in tumor samples. Strikingly, tumors induced macrophage expression of VEGF via stabilization of HIF1a in a manner that did not require hypoxia. This is interesting as it identifies a pathway by which tumor cells can stimulate angiogenesis (blood vessel formation) via VEGF and Arg1 prior to a hypoxic challenge. The soluble tumor cell effector capable of turning on this pathway was identified as … lactate. Here it is worth quoting from the paper:

“Warburg observed that cancer cells preferentially perform aerobic glycolysis: that is, they convert most glucose molecules into lactate regardless of the amount of oxygen present. Furthermore, the eponymous Warburg effect is also observed in most cells undergoing rapid proliferation. It has been hypothesized that aerobic glycolysis is conducive to cell proliferation because, despite the consequent reduction in ATP production, aerobic glycolysis produces metabolic precursors, such as lactate, for biosynthetic pathways, and these precursors may be the limiting factor during rapid cell proliferation”

The suggestion here is that tumor cells are going a step further in order to ensure that their supportive microenvironment, which includes TAMs, step in line. Lactate is taken up by TAMs via specific cell surface receptors (the monocarboxylate transporters) and the effect is potentiated by acidic pH (from all the lactic acid) and perhaps requires other mediators such as M-CSF. Once all is said and done the TAMs are surviving and thriving using the same machinery as the tumor cells.

From the drug development perspective it is probably worth asking whether AKT and mTOR inhibitors impact TAM activity in the tumor microenvironment (perhaps someone already has). Conversely, one might speculate on the impact of such inhibitors of macrophage responses to infection. More selectively, I suspect there is a clever way of targeting the epigenetic responses to derail the TAM phenotype and disrupt the tumor-supportive microenvironment while either simultaneously targeting the tumor, as in a combination therapy setting with a therapeutic that targets tumor biology directly. Also, in the era of immune checkpoint therapeutics I wonder if there isn’t some signal to “wake-up” these “trained” macrophages and have them turn on their clients – the tumor cells.

A few other questions:

How is the macrophage glycolysis pathway maintained once initiated by exposure to tumor derived lactate? There must be a feedback mechanism, perhaps similar to the one used by “trained” macrophages?

Do the HIF2-dependent tumors (some renal cell carcinomas for example) also hijack resident TAMs in the same manner, or different?

The tumor microenvironment includes tumor-associated fibroblasts – are these also impacted by exposure to lactic acid?

If there is intimate cross-talk between the macrophage and it’s client (a tumor cell) then disabling that conversation at the level of the macrophage (and other stromal cells) should be therapeutic – or will the tumor (in this case) simply adapt? Remember that in this setting the epigenetic changes are not necessarily addictive (oncogenic).

interesting stuff to consider in this new era of combination therapies….

stay tuned

Rational Immunotherapy Combinations: How’s That Work Again?

I had a very interesting meeting yesterday with a very talented clinical trial physician/researcher and a renowned scientist in the immunotherapy field (I was the dumb tourist, but I’ve played the part before, so no worries). Regardless, the three of us grappled with the question of how to parse the potential immunotherapy combinations that may soon become available, noting that different combinations may prove differentially useful across a wide range of oncology indications.

Lets open the medicine chest and see what target classes are represented (showing just a few examples of each class):

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The perspective of the clinical trial physician/researcher was grounded in the question of what to do with a specific patient – can biomarkers help drive therapy for example. The answer, as we learned at ASCO, is complex. As we heard, biomarkers for PD-1 and PD-L1 are only partly useful, and their use at all may miss patients that would respond despite being negative for the biomarker. This suggests that we will need multiple biomarkers to further subset patients … or that we will need combination therapies to “overrule” the limits PD-1 or PD-L1 biomarkers would impose. The question then becomes which new biomarkers will help us decide which combination of therapies to give to specific patients – and we don’t have this data yet.

The perspective of the immune checkpoint expert was somewhat different and rooted in trying to understand if meshing different biology levers made sense. The obvious one here is pairing inhibitory pathway blockade with immune stimulation, e.g. anti-PD-1 antagonist antibody plus anti-4-1BB agonist antibody. Another approach might be to disable T regulatory cells while boosting T effector cells or targeting myeloid suppressors while stimulating T cells- you can make up your own combinations. The point (and the point of the table) is that this landscape is very complex and it will take time, money, and patients, to sort it out.

The focus on combinations and the need for patients to recruit creates a very dynamic clinical picture. After we saw the compelling data on immunotherapy for NSCLC at ASCO I think it’s fair to say the landscape shifted, and one consequence of this may be that patients who might have been considered for a novel clinical trial therapeutic instead got enrolled into a pembrolizumab cohort (I’m simplifying here, I know). Once pembro was approved for melanoma the landscape shifted again, as physicians, whether clinical trial docs or not, had a novel choice. Quite a lot of ink was spilled (bytes were expended) on whether or not Peregrine Pharmaceuticals (PPHM) for example, would be able to meet its’ clinical trial recruitment timelines in this new landscape (bavituximab is in late stage clinical trials in NSCLC and melanoma). If you listen to the latest earnings call their CEO was asked this very question – are clinical trial enrollments on track – and he very carefully answered that all the sites are activated (which does not answer the question of patient enrollment). It will be very interesting to hear the answer next quarter (I predict it will be positive). Similar questions may soon bedevil other up-and-coming immune checkpoint companies. This begs the question of what data packages new companies will need in their Investigator Brochures in order to attract clinical attention. It’s a critical issue for companies and pipelines.

What about targeted therapeutics, and the combination of these with immune checkpoint therapies? We only know enough to say that the rules have not been established. Small trials and case reports suggest we have to go slowly and test each combo, in each indication, carefully. That’s an awful lot of work yet to be done. In the meantime, the working oncologist, confronted for example with a newly diagnosed NSCLC patient may know that a) the patient carries a known mutation for which there is a targeted drug and b) the patient has a favorable “immune response” profile and has PD-L1+ tumor cells. What to do? We don’t know yet.

There are other consequences in this new landscape. Nearly every oncology vaccine company claims that as soon as they run a combo trial with an anti-PD-1 or anti-CTLA4 antibody their particular vaccine approach will perform beautifully. There are a few problems with this, notably, very few of these companies have a chance in hell of getting an anti-PD-1 antibody via collaboration, and the rest will pay heavily for the privilege. Second we have no idea of how to rationally pair vaccines with immune checkpoint exposure in order to induce optimal responses. Third, there are not enough patients to go around, a simple fact in many indications. So for those investors looking for a renaissance in the oncology vaccine field, I’d say tread carefully.

One way of thinking about this is to ask what a successful combo therapy drug development landscape looks like and happily we don’t have to look far. The hematological malignancies – AML, CML, ALL, NHL, MM etc – have benefitted from having an early bucket of highly efficacious drugs whose tox profile, while perhaps not squeaky clean, is at least well understood. Rituximab (RHHBY, BIIB) is the undisputed leader of the pack here, having been paired in combination with every conceivable therapeutic, followed closely by lenalidomide (CELG) and ibrutinib (JNJ, PCYC). Some combos have worked, some have not, and the whole exercise has taken enormous time and resources, and is ongoing.

Mind you we’ve not touched on the new antibodies, ADCs, bispecifics, CARs, TCRs, TILs and a host of other technologies – it’s just too soon.

In rereading this I realize all I’ve done is ask a bunch of questions: a list of questions I’ll be carrying into the medical conference season as I try to make sense of all the data.

stay tuned.

Upcoming Events

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We are excited to be working with Rob Johnson of Alacrita LLC (alacritaconsulting.com) at the Biopharm America conference in Boston, coming up September 22-24th at the Boston Marriott Copley Place. We’ll be working with Alacrita to facilitate business development and partnerships for nearly 200 companies from around the world. Attendees can connect to Rob or I through the partnership meeting portal, under the Alacrita LLC entry. See the MassBio sponsored page here: Biopharm America.

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As noted the other day, SugarCone Biotech will be attending The CRI Immunotherapy conference at The Grand Hyatt in NYC, October 6-8. The website is here: CRI Immunotherapy.  This year’s theme “Out Of The Gate” reflects the excitement as these novel therapeutics launch, and also the sense we have of a horse race unfolding as companies large and small fight for pole position. We will be there checking on the front-runners but also looking at novel and emerging therapeutics and the companies behind them. Please reach out to me directly at rennertp@sugarconebiotech.com if you would like to meet during this exciting conference.

We’ll have updates soon on the SITC and ASH meetings, later this fall.

SugarCone Biotech will be at CRI Immunotherapy, Oct 6-8, NYC

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Looking forward to meeting friends and colleagues at Cancer Immunotherapy: Out of the Gate, hosted at the New York Grand Hyatt by the Cancer Research Institute. The website is here (link) but dig around a bit and find the agenda – there is an excellent speaker lineup. We see this event as a great chance to get caught up as we head into the medical and scientific conference season. If our blog, work or services interest you please email us and we’ll set up time to talk.