Category Archives: TGFbeta

Fidgeting about TIGIT

Part 1 of 2

Pathways and targets covered: TGF-beta, PD-L1, PD-1, TIGIT

Companies mentioned: Merck KgaA, GSK, Roche, Merck, Mereo, iTeos, BMS, Arcus/Gilead, Compugen, Seagen, Beigene, Innovent, Agenus

Last week we had the bad news that Merck KGaA and GSK had thrown in the towel on bintrafusp alfa therapy for first-line advanced NSCLC.  Bintrafusp alfa is an anti-PD-L1/TGFbR2 TRAP therapeutic designed to selectively antagonize TGF-beta isoforms 1 and 3 while also blocking PD-L1, thereby delivering two-for-one anti-immunosuppression.  Bintrafusp alfa was being tested in a head-to-head trial vs. pembrolizumab and showed no added benefit in a patient population selected for PD-L1-high tumor expression (50%+ of cells in the tumor biopsy sample positive for expression).

This stirred up a fair amount of discussion, as TGF-beta blocking therapies are in vogue for immuno-oncology (IO), with small molecules, biologics, RNA-antagonists and genetic knockouts (in CAR T cells) all in the pipeline. I have high hopes for this space, despite the news out of Darmstadt. And to be fair, the press release stressed the ongoing bintrafusp alfa trials in bladder cancer, cervical cancer, and NSCLC using various drug combinations, and noted new trials in urothelial cancer and TNBC (https://www.emdgroup.com/en/news/bintrafusp-alfa-037-update-20-01-2021.html).  Still, the failure stung, due mainly to the promise of the early (open label) Phase 1 expansion cohort data that had suggested significant benefit from the therapy.

This got me thinking about TIGIT, another hot IO target.  The last time I wrote about TIGIT I ended with this question: “How to select patients who should respond to anti-TIGIT co-therapy (or anti-TIM-3 or anti-LAG-3)…?” (http://www.sugarconebiotech.com/?p=841). This is a question we should ask about any pathway – including TGF-beta of course – particularly as we are now in the post-immune-checkpoint era, that is, in a setting where many patients in the most IO-responsive indications like melanoma and NSCLC will have already been treated with an anti-PD-1 or anti-PD-L1.  So, is there anything known about TIGIT expression that can guide us in patient (or indication) selection?

Roche leads the field with tiragolumab an anti-TIGIT Fc-competent IgG1 that has shown activity in combination with the anti-PD-L1 antibody atezolizumab in first-line NSCLC, and only in patients with PD-L1- expressing tumors (> 1% of cells in the tumor biopsy sample positive for expression).  We can pause here to recall that this is about where we started the discussion above regarding the TGF-beta TRAP/anti-PD-L1 asset from Merck KGaA, being trialed in the PD-L1-high (>50%) setting in NSCLC.

In front-line NSCLC (EGFR and ALK wildtype), Roche reported responses higher than with atezolizumab alone. Data were shown at AACR and then updated at ASCO.  Here are some of the ASCO data:

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The response rate with dual therapy looks rather better than atezo alone, especially in the PD-L1 high cohort (middle panel).  Atezo alone appears to have underperformed, with an ORR = 21% (left panel, all patient data (ITT)).  In the comparable phase 3 trial of atezo vs chemotherapy in front-line NSCLC (also EGFR and ALK wildtype) the ORR = 38.3% in the atezo arm (n=285) and 28.6% in the chemotherapy arm (n=287), see nejm.org/doi/full/10.1056/NEJMoa1917346. Regardless the 66% response rate in the PD-L1-high cohort (middle panel) attracted attention.

The PFS data were also striking when compared to the prior trial.  This is tiragolumab plus atezolizumab / PD-L1 high cohort:

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We can go back and compare this to the atezo alone Phase 3 interim data shown at ESMO in 2019 (I was stuck in the overflow “room” which was a curtained space on the floor of the Barcelona convention center).  This is the PD-L1-high cohort:

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Here the median PFS is 8 months, certainly shorter than what is shown for tiragolumab plus atezolizumab, but again, note the disparity with the atezo alone arm of the study (medPFS for = 4 months).

Just to be clear, here are the PD-L1-high patient data compared:

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We’re left with the always troubling question of variability between trials and the possibility that the tiragolumab plus atezolizumab results are a fluke.  Unfortunately, we will have to wait and see.

There are two features here worth noting.  One is that TIGIT, the target, is expressed on T cells, along with PD-1.  So far this makes sense – they might very well synergize, particularly given the function of DNAM-1 in the context of T cell signaling (see part 2).  But the anti-TIGIT antibody is an IgG1 isotype, thought to trigger ADCC and CDC-mediated target cell (ie. the T cell) death.  But we want the T cells, that’s the whole point of blocking PD-L1 with atezo.  So what the heck is going on here?

Merck seems to have an answer, but first, some more data.  Merck’s anti-TIGIT antibody, vibostolimab, like Roche’s tiragolumab, is a wildtype IgG1.  Early data on the combination of vibostolimab and pembrolizumab (anti-PD-1), presented at ESMO2020, looked promising in immune checkpoint naïve patients (75% had prior chemotherapy, the rest were treatment naïve):

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We can benchmark these results to monotherapy, just as we did with the Roche data, focusing on the PD-L1-positive subset (here we can see data using a cutoff of >1% or >50% of cells positive in the tumor biopsy):

png6

 

The results compare favorably with pembro-alone using the >1% PD-L1 cutoff and are similar to pembro-alone using the >50% PD-L1 cutoff.  As usual it is difficult to compare between trials, but the signal is encouraging.

Preclinically, Merck has addressed the MOA, stressing the requirement for the intact Fc functionality imparted by the IgG1 antibody isotype.  As mentioned earlier, the mechanistic puzzle is that canonical IgG1 activity includes the triggering of target cell killing via ADCC and CDC mediated cytotoxicity.  Of course, TIGIT is expressed on the very T cells we want to preserve and activate, not kill.  Given this reality we need alternate hypotheses for the action of the IgG1 antibodies.  The predominant hypothesis is that anti-TIGIT antibodies are selectively depleting T-regulatory cells that are TIGIT-bright and immunosuppressive.  This is reminiscent of the now-T-regulatory cells that are TIGIT-bright and immunosuppressive.  It’s an easy hypothesis to advance, similar to the now-debunked arguments made on behalf of anti-CTLA4 and anti-GITR antibodies, and very likely incorrect.

Merck has demonstrated in preclinical models that antagonistic anti-TIGIT antibodies having a  FcgR-engaging isotype induce strong anti-tumor efficacy whereas anti-tumor activity is drastically reduced when using the same anti-TIGIT antibodies that are null for FcgR-engagement (doi: 10.3389/fimmu.2020.573405). These results are consistent with data presented by multiple groups, eg. Mereo and iTeos.  The Merck team further showed shown that FcgR engagement persistently activated myeloid lineage antigen-representing cells APCs, including the induction of proinflammatory cytokines and chemokines while TIGIT blockade simultaneously enhanced T cell activation including elevated secretion of granzyme B and perforin, which synergizes with anti-PD-1 antagonism.  I favor this hypothesis.  Nb. This suggests we’ve a lot to learn still about the best way to engage Fcg receptors, a theme I introduced in the last post (link).

Where does this hypothesis leave everyone else in the TIGIT space?  Let’s line them up:

Png8

A few quick notes: EMD Serono/Merck KGaA and Innovent have anti-TIGIT programs without disclosed isotype information; Arcus has disclosed a second, Fc-competent, anti-TIGIT program (AB308); Agenus is developing both IgG1 and IgG4 anti-TIGIT antibodies.

A question: is Seagen’s hyper-killing IgG1 a step too far?

In summary, we have preliminary data in NSCLC that suggest that anti-TIGIT may synergize with anti-PD-1 or anti-PD-L1 therapies, consistent with the expression of TIGIT on PD-1 positive (ie. activated) T cells.  We have several hypotheses addressing the Fc-end of the therapeutics, and some information on why blocking TIGIT may enhance T cell responses.

Other than selecting patients with PD-L1-positive tumors, can we gate on TIGIT expression?  Apparently not, at least not in NSCLC, as just reported at the World Conference on Lung Cancer (abstract P77.02 – Efficacy of Tiragolumab + Atezolizumab in PD-L1 IHC and TIGIT Subgroups in the Phase II CITYSCAPE Study in First-Line NSCLC).

Here’s their text:

“Among the 135 enrolled patients with PD-L1-positive NSCLC (intent-to-treat [ITT] population), 113 had results from the SP263 assay and 105 had results from the TIGIT assay. The biomarker-evaluable populations (BEP) for both of these assays were similar to the ITT population. Comparable PFS improvement with tira + atezo relative to atezo monotherapy was seen in PD-L1–high (≥50% TC) subgroups defined by SP263 (PFS HR 0.23, 95% CI: 0.10–0.53) when compared with PD-L1-high subgroups defined by 22C3. However, for patients whose tumors were defined as TIGIT-high (≥5% IC), no strong association with PFS improvement was observed.

Biomarker subgroup Subgroup, n (BEP, N) PFS HR (CI) relative to atezo monotherapy arm
ITT (PD-L1 IHC 22C3 >1% TPS) 135 (135) 0.58 (0.39–0.88)
PD-L1 IHC 22C3 (≥50% TPS) 58 (135) 0.30* (0.15–0.61)
PD-L1 IHC SP263 (≥50% TC) 45 (113) 0.23* (0.10–0.53)
TIGIT IHC (≥5% IC) 49 (105) 0.62* (0.30–1.32)
*Unstratified HR

Prevalence of PD-L1 subgroups in the BEP was comparable with previous reports for both IHC assays. The PFS benefit observed with tira + atezo in patients with tumors defined as PD-L1-high by 22C3 was also observed using the SP263 IHC assay, but not in tumors classified as TIGIT-high using an exploratory TIGIT IHC assay. Our results suggest that PD-L1 expression, assessed by 22C3 or SP263, may be a biomarker for tira + atezo combination therapy in metastatic PD-L1-positive untreated NSCLC.”

So that the answer to the question we started with, can we pick patients, is ‘no’ for TIGIT expression, at least in this indication.

Regardless, to actually understand what blocking TIGIT does, we need to better understand the pathway.

That will be discussed in Part 2, coming soon.

Stay tuned.

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

 

The Tumor Microenvironment (TME) series to date is assembled here http://www.sugarconebiotech.com/?s=big+tent containing parts 1-3

I’m happy to point you to the most recent content, posted on Slideshare: http://www.slideshare.net/PaulDRennert/im-vacs-2015-rennert-v2

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)

ICI15 presentation is now available

Over 100 slides on immune checkpoint combination therapy, novel targets and drug development in immuno-oncology, created for a 3 hour workshop at ICI15 (link).

As always we work from indications to discovery and back again, keeping one eye on the rapid evolution of clinical practice in oncology and the other on novel targets and therapeutics.

on SlideShare now:

Creating a New Therapeutic Focus

In 2012 we were engaged by a large local biotech company to evaluate a new therapeutic area. This effort was driven by the desire of the client to move aggressively into a new suite of diseases. We began by doing a deep dive into the client’s existing portfolio in order to identify assets already in development that could be directed to novel diseases. Concurrently we began a comprehensive review of preclinical and clinical stage assets available for partnering or in-licensing. Finally we engaged in pathological pathway analysis to identify novel targets for discovery programs. This effort, initiated and completed within two quarters, led to the eventual acquisition of a private company and its Phase 2 clinical stage assets, for nearly 100MM $USD. Based on our analyses the client also started several new discovery and preclinical development programs to complement the clinical stage acquisition.

Cool Science: Pathways Driving Fibrosis and Related Drug Development

December 10, 2013, by P.D. Rennert
Some recent interesting papers reveal new mechanisms for the regulation of fibrotic pathways, and suggest drug discovery opportunities.
Fibrosis is a huge medical problem and encompasses many different diseases across most organs and tissues: lung, kidney, liver, gut, vasculature, skin, ocular, cardiac, etc. Lets just assume upfront that we recognize that TGFbeta (TGFb) signaling is a critical pathologic pathway in the induction and persistence of the fibrotic state. I want to take that as a given. TGFb is also showing up more and more often in the context of tumor genetics, as befits a critical growth factor. From the drug development perspective, TGFb antagonism not yet been successful due to the toxicities encountered: TGFb is very pleiotropic and controls many normal functions as well. As a result several alternative means to target the TGFb pathway are under development for the treatment of fibrosis.
A very clever strategy for targeting TGFb was developed by researchers at Biogen, along with a top notch group of outside collaborators (see for example Horan et al. 2008). It was determined that activation of TGFb at sites of inflammation and injury, which are sites for the initiation or promotion of fibrosis, depended on an integrin, namely alphavbeta6 (avb6). Biogen developed a monoclonal antibody (mAb) to avb6 and subsequently outlicensed this mAb to Stromedix. I helped bring that mAb back into Biogen 5 years later (early 2012). By then the mAb, now called STX-100, was Phase 2 ready, a testament to the strength of the Stromedix team. Stromedix was acquired for 75MM upfront, plus milestones: a good deal for both companies. 
On the science side, how avb6 activated TGFb was not well understood, but this was thought to involve a conformational change in the beta6 strand of the integrin.
So lets jump ahead, or sideways anyway.
A parallel basic research and drug discovery effort had uncovered an interesting role for the bioactive lipid lysophosphatidic acid (LPA), and for the LPA receptors, in fibrosis. LPA receptor gene-deficient mice (LPAR knock-out or KO) were resistant to the development of fibrosis in a variety of models, and across diseases in different organ systems. This was interesting since it suggested that somehow LPA and the LPARs were regulating the TGFb pathway (see here, and here). How this occurred was not known, and the available data were correlative: when LPARs were blocked, disease was lessened and there was less TGFb, but was this specific to the LPA pathway or was it due to reduced disease activity? It turned out that the LPA/LPAR pathway interacted with integrin biology, in a couple of interesting ways. The first concerned signaling through one of the LPARs, LPAR2. LPARs are G-protein-coupled receptors, that is, they signal using G proteins. We won’t go into these, but its enough to say that signaling from LPAR2 through a specific G-protein induced a conformational change in the beta chain of avb6, and that this conformational change was associated with the ability of avb6 to activate TGFb. The second way has to do with the manner in which LPA is produced by the enzyme autotaxin, and we’ll come back to that later. This is not the only manner in which LPA impacts fibrosis, as was demonstrated by the Amira drugs that are selective antagonists for LPAR1 and perhaps also LPAR3 (see for example, here). This drug also blocked the development of fibrosis in multiple models, and showed activity in early clinical development for idiopathic pulmonary fibrosis (IPF). The data were suggestive enough that Bristol-Myers Squibb bought the company for $325MM upfront in 2011.
Now lets jump ahead.
In 2011 Tim Springer’s lab published a remarkable paper (Shi et al). What this paper explored, using structural biochemical and biophysical techniques, was how TGFb was kept in an inactive state by its own protein structure (called the “straightjacket”). Breaking this inactive state required distinct and critical interactions, one in which TGFb was embedded into the cell membrane in complex with latent TGFb binding proteins (LTBP), which in turn bound to the extracellular matrix, and the other by which TGFb interacted with the avb6 integrin. Productive binding of the integrin required interaction with cell’s the actin filaments, the protein fibers that hold the cell together and also rearrange themselves in order to allow the cell to move. We should note here that integrin:actin interaction is most often mediated by talins, the proteins that sort of cross link the actin filaments (think of rungs on a ladder as a simple picture). This complex interaction of TGFb, avb6, the cell membrane and the actin fibers imposed enough force on TGFb to break its lock, and free it for activation and release from the cell surface. Its as if you had to rearrange the walls of your house in order to open a window. This is a highly regulated system. So, how did avb6 accomplish this trick? Spinger’s lab didn’t give an answer – they were intently focused on the TGFb structure. But a recent paper on a different integrin provides a clue, and maybe brings us back to the LPAR pathway.
A few weeks ago Shen et al (in Nature) elucidated differential signaling by the integrin alphaIIb-beta3 (aIIb-b3), focusing on the interaction of the b3 subunit with talin and with a G-protein, Galpha13 (Ga13). They found a specific amino acid motif – EXE – mediated binding to the G-protein. This motif is found in many beta subunits, including b6. The protein domain in which this motif is found is within a region known to mediate binding to talin, and Shen et al. go on to show that the two binding phenomena are mutually exclusive. Importantly, interaction with the G-protein required binding to fibrinogen, a ligand for the aIIb-b3 integrin. Integrins transmit signals bidirectionally. Inside-out signalling, the process by which an integrin undergoes conformational change in response to ligand binding, is a talin-dependent mechanism. aIIb-b3 integrin ligation mediates platelet aggregation and triggers outside-in signalling, which requires Ga13 and greatly expands thrombus formation. Switching back to interaction with the G-protein corresponds to clot retraction. So this model proposes waves of signaling controlled in part by which component of the cellular machinery – talin or G-protein – is engaged.
It has been demonstrated in lung and kidney fibrosis models that avb6-mediated activation of TGFb can be triggered by the LPAR2 signaling through Galphaq (Gaq) to the Rho/Rac kinase pathway (see here, and here). The connecting dots from Rho/Rac kinase to avb6 activation are not yet described, by may work by regulating the interaction of avb6 with a G-protein (eg. Ga13) v talin or actin. In KO mouse experiments, Ga12/13 were shown to be required for basal TGFb activation in embryonic fibroblasts (MEFs), but not in LPAR2 transfected MEFs. The relevance of this data to the fibrotic condition however is unclear, and I think it remains worth exploring this link further.
There is an independent link between the LPA/LPAR2/avb6/TGFb pathway and integrin biology. The production of LPA is controlled by the enzyme autotaxin. In settings of tissue injury and inflammation, autotaxin and the LPARs are upregulated by various cells. In this way the LPA production machinery (autotaxin) and the responding receptors are operating in tandem. More remarkably, autotaxin is carried into the inflamed or injured tissue by activated cells – platelets, T cells, and likely other cells types. The manner in which autotaxin is transported is by binding to integrins with b1 or b3 subunits, carried on the cell surface and maneuvered into place by the coordinated action of the activated cell (see a review here). This has likely evolved to maximize the production of LPA at sites where it is required – the half life of LPA in circulation is very short, minutes only. Indeed the half-life of TGFb is even shorter, less than one minute.

So, this is a highly coordinated and highly regulated system, as might be expected when dealing with a potent growth factor like TGFb. The implications of the model for drug development are several. First it seems clear that LPA receptor antagonists that can target LPAR2 would be therapeutic and differentiated from the Amira assets now owned by BMS. The benefit of targeting avb6 was discussed earlier in the context of the Stromedix/Biogen deal. Another target that appears here is autotaxin, and several companies are pursuing autotaxin antagonists – I developed a beautiful compound series at X-Rx Discovery, as one example. Finally, there is the very exciting prospect of using the new structural information about TGFb and related proteins (its a big family) to design drugs that selectively block TGFb activation in the context of an activated cell response. This may be one of the things that Scholar Rock Therapeutics, a venture-company founded by Tim Springer and colleagues, is up to now. We’ll have to wait and see.
Bottom line: we are learning a lot about fibrosis pathophysiology, only a little of which is touched on here. With that knowledge will come a new wave of drug development, and ultimately we hope to provide relief for patients suffering from these chronic and very serious diseases.
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