Category Archives: TAMs

The Tumor Microenvironment “Big Tent” series continues (part 4)


The Tumor Microenvironment (TME) series to date is assembled here containing parts 1-3

I’m happy to point you to the most recent content, posted on Slideshare:

In this deck I review the challenges of the TME particularly with reference to Pancreatic and Ovarian cancers. A few targets are shown below.

Feedback most welcome.

Screen Shot 2015-08-27 at 7.20.21 AM


“Combination Cancer Immunotherapy and New Immunomodulatory Targets” published in Nature Reviews Drug Discovery

Part of the Article Series from Nature Reviews Drug Discovery, our paper hit the press today

Combination cancer immunotherapy and new immunomodulatory targets. Nature Reviews Drug Discovery 14, 561–584. 2015.  doi:10.1038/nrd4591

by Kathleen Mahoney, Paul Rennert, Gordon Freeman.

a prepublication version is available here: nrd4591 (1)

The Big Tent: Tumor Microenvironment Targets Heat Up – part 2 of an occasional series

I recently asked folks for their favorite hot targets in the tumor microenvironment space. Among a flurry of responses I got these two related answers:

mcbio CSF-1R

 Screen Shot 2014-11-23 at 6.36.37 PM

These responses from @mcbio316 and @Festivus159 were very timely, given what happened 4 days later (and a big shout-out to mcbio, whose post had preceded this):

Bristol-Myers Squibb and Five Prime Therapeutics Announce Exclusive Clinical Collaboration to Evaluate the Combination of Investigational Immunotherapies Opdivo (nivolumab) and FPA008 in Six Tumor Types

Five Prime Therapeutics, Inc. November 24, 2014 8:59 AM GlobeNewswire

  • NEW YORK and SOUTH SAN FRANCISCO, Calif., Nov. 24, 2014 (GLOBE NEWSWIRE) – Bristol-Myers Squibb Company (BMY) and Five Prime Therapeutics, Inc. (FPRX) today announced that they have entered into an exclusive clinical collaboration agreement to evaluate the safety, tolerability and preliminary efficacy of combining Opdivo (nivolumab), Bristol-Myers Squibb’s investigational PD-1 (programmed death-1) immune checkpoint inhibitor, with FPA008, Five Prime’s monoclonal antibody that inhibits colony stimulating factor-1 receptor (CSF1R). The Phase 1a/1b study will evaluate the combination of Opdivo and FPA008 as a potential treatment option for patients with non-small cell lung cancer (NSCLC), melanoma, head and neck cancer, pancreatic cancer, colorectal cancer and malignant glioma. Bristol-Myers Squibb has proposed the name Opdivo, which, if approved by health authorities, will serve as the trademark for nivolumab.

So BMS will immediately move FPA008, but all measures an early stage and largely unproven therapeutic, into combination therapy trials with nivolumab for the treatment of solid tumors. Not to be outdone, Roche has already positioned it’s CSF1R targeted therapeutic, as noted by @jq1234t:

 JQ screen shot

There are a number of interesting questions to answer here: What does CSF1R do, why is it so interesting, how does it impact the tumor microenvironment, how are these trials being done and (a favorite of mine), who else has assets in development?

CSF1R is the receptor for macrophage-colony-stimulating factor (aka M-CSF or CSF-1). The receptor is a control node for macrophage differentiation. CSF1R also serves as a receptor for the monocyte survival factor IL-34. Although the ultimate outcome depends on many factors, signaling through CSF1R is necessary for myeloid lineage precursor cell differentiation into macrophages, and it is this feature that interests us in the tumor microenvironment setting. We cannot gloss over the fact that this is a pleiotropic and complex biological system but it is safe to say that by the time we are confronted by an immunosuppressed tumor (as in the case of combo therapy with anti-PD-1/PD-L1 therapeutics), our pathway focus is on tumor associated macrophages (TAM), their impact on the tumor microenvironment and their susceptibility to CSF1R-targeted therapy.

Roche poached this figure that I’m now borrowing (with fair reference to Chen and Mellman, 2013).

Roche version Cancer Immunity Cycle

In the original figure (see Immunity 39: – an open access article), Chen and Mellman placed the PD-1 pathway inhibitors with a variety of microenvironmental modulators (IDO1, Arginase, TGFb) that together prevent, in distinct ways, cancer cell death. The Roche version of the figure, reproduced above, has been modified to include CSF1R among other targets in the “killing cancer cells” category.

Broad strokes, what does this mean? TAM, the tumor associated macrophages mentioned above, are dependent on CSF1R signaling. TAM are myeloid lineage-derived cells that are co-opted by the resident tumor as part of it’s microenvironmental support system. TAM are potently angiogenic, remodel the stroma (extracellular matrix and related components) and are immunosuppressive. Among the plethora of critical factors produced by TAM we find the hypoxia response proteins and growth factors that drive angiogenesis, tissue remodeling and immunosuppression, i.e. HIF2a, MMP-9, EGF, VEGF and TGFbeta, cytokines that can maintain this response in a chronic state (IL-10, IL-4) and chemokines that attract myeloid cells and regulatory T cells (CCL22, CCXL8). The TAM population can be directly regulated by tumor cell secretion of CSF-1, thus the importance of the CSF1R target. Multiple labs have produced preclinical data showing that anti-CSF1R antibody therapy can rapidly and effectively deplete tumors of the TAM population, and that this depletion has an impact on tumor growth and survival.

Clinical development to date is scattered. The FPRX program began with a Phase 1 trial in healthy volunteers and rheumatoid arthritis patients (NCT01962337) reflecting the role of diverse macrophage populations in inflammation and autoimmunity. Indeed the FPRX website states “we are currently conducting nonclinical research in areas such as idiopathic pulmonary fibrosis, lupus nephritis and other inflammatory disorders to identify a second target indication by the end of 2014″ although this may be trumped by the BMS deal. That trial reported safety and pharmacodynamic endpoints at AACR earlier this year. FPA008 was well-tolerated at all dose levels tested and the drug impacted inflammatory macrophage numbers and, interestingly, bone turnover (this latter effect due to the control of osteoclast differentiation by CSF1R, an important feature in bone metastasis settings perhaps).

In contrast Roche has been testing it’s antibody in a rare disease (a form of giant cell tumor) that is caused by a  t(1;2) translocation resulting in fusion of COL6A3 and M-CSF genes encoding for CSF1. The tumor is characterized by CSF1R+ cells. Roche reported that RG7155 had the following activities (Reis et al. 2014. Cell 25: 846–859):

- Anti-CSF-1R antibody depletes tumor-associated macrophages in cancer patients

- CSF-1R inhibitor shows clinical activity in diffuse-type giant cell tumor patients

- CSF-1R signaling inhibition increases lymphocyte infiltration in cancer patients

That last highlight referring to an effect on immunosuppression and refers to a relative increase of CD8+ T cells versus CD4+ FoxP3+ T regulatory cells, thus feeding the enthusiasm for combination therapy with anti-PD-1/PD-L1 therapeutics. More data is available in their ASCO abstract (

Other clinical stage antibodies include IMC-CS4 from Eli Lilly, in Phase 1 for advanced solid tumors (NCT01346358), ARRY-282 from Array BioPharma and Celgene, which had completed a Phase 1 trial in advanced solid tumors (NCT01316822) before the program was terminated, AMG 820 from Amgen with a completed Phase 1 study in advanced malignancies (NCT01444404), and others. Preclinical programs are visible at many small companies, both private and public, and include small molecule inhibitors of the receptor, e.g the Ambit and Plexxikon programs.

While the enthusiasm seems warranted by the preclinical modeling data and the (to date) apparent tolerability of the antibody therapies, I did receive this one note of caution from @Boston_Biotech:

Bos Biotech screenshot

Nuances, indeed. It is important to consider a few possible issues. First, blockade of CSF1R in mice led to the pronounced and sustained upregulation of CSF-1, and drug doses had to be kept high in order to “drug-through” this level of ligand to block the receptor. Rebound activity at trough or upon drug cessation could be a big problem, as has been described for other systems, including CCL2 blockade in breast cancer models (leading to abundant metastasis). Sticking with breast cancer, it has been reported that blocking CSF1R leads to upregulation of GM-CSF signaling, changing the composition perhaps (but not the stability) of the tumor microenvironment. Finally, as always, we cannot yet see what efficacy drugs will have as monotherapies (its too early) while we race ahead to combo therapies. While its all hands on deck to get these assets into patients, they won’t all work and certainly can’t be sure they will do no harm. However, that said, I think targeting components of the tumor microenvironment, including TAM, is our next best step forward, and I certainly will enjoy watching the data unfold.

next time … what wraps pancreatic cancer up so tight that you can’t treat it until it explodes in a deadly metastasis fireball?

cool stuff.

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