Innate Possibilities

Might modulation of the innate immune
 response turn up the heat on "cold" tumours?

It's been (another) good year for cancer immunotherapy, marked by approval of the first autologous T cell therapies for otherwise untreatable haematological cancers, additional label indications for immune checkpoint inhibitors and even glimmers of hope around personalized cancer vaccines.

All of these advances exploit adaptive immunity- the body's capacity to recognise tumours (and invading pathogens) as "not self" and to programme the immune system to bring exquisitely specific antibodies and effector cells into the attack. A downside to this biological sophistication is that mounting an adaptive immune response takes time and can be deliberately misdirected. We rely on a more primitive and less selective innate immune response as a first defence against rapidly multiplying bacteria and viruses and to prime adaptive immunity.

Bringing the innate immune response into play as a means of increasing the efficacy of cancer immunotherapy is attractive. Non-responsiveness to immune checkpoint inhibitor therapy appears to correlate with tumour inflammation, rather than with immune checkpoint expression or the degree of tumour mutation. Turning “cold” (uninflamed) tumours “hot” (inflamed) might offer patients initially refractory to immunotherapy an additional treatment option.

A signature of tumour inflammation is the presence of IFN-β, a potent cytokine, the production of which is  triggered by STING ("stimulator of interferon genes") in response to molecules ("cyclic dinucleotides"- CDNs) that signal the presence of pathogen or host double-stranded DNA. CDNs produced in response to double-stranded DNA leaking from cancer cells are capable of activating STING and triggering IFN-β production, which in turn, stimulates cancer antigen-specific T cells.

STING activation has attracted the attention of Merck and BMS, rivals in the immune checkpoint inhibitor space. Two investigational STING activators (MK-1454: Merck and ADU-S100: Aduro Biotech/Novartis) are in early clinical evaluation. Both are synthetic CDNs, designed to be more potent than "natural" CDNs but, due to their chemistry, must be delivered directly into the tumour. Spring Bank Pharmaceuticals, BMS (through the acquisition of IFM Therapeutics), iTeos Therapeutics, Invivogen and GSK are also pursuing intratumoral CDN candidates, while Nimbus Therapeutics and CuraDev Pharma are developing small molecules that may allow oral dosing.

Other components of the innate immune system are of interest to immunotherapy developers.  "Toll-like receptors" (TLRs) recognise an array of bacterial and viral debris and are known to be expressed by various cancers. Past clinical studies with TLR-directed agents have been largely disappointing, although a TLR9 agonist, IMO-2125, developed by Idera Pharmaceuticals is under evaluation in combination with immune checkpoint inhibitors in melanoma patients who have previously failed immunotherapy.

"RIG 1 (retinoic acid inducible gene)-like receptors" (RLRs) sense viral infection and can eliminate infected cells, opening the possibility that RLR activation might be exploited to directly kill cancers. RLRs are largely activated by RNA and while perhaps not easily druggable, they offer a promising enough prospect for Merck to have acquired Rigontec, a pioneer in RLR research, for a headline figure of over $500 million.

Inflammasomes are multiprotein complexes of signalling molecules and enzymes that initiate and maintain inflammatory processes in infection and autoimmune disease. Inflammasomes are activated by various "NOD-like receptors" (NLRs), the most widely studied being NLRP3, a trigger sensitive to a wide range of microbial and "damage-associated" molecules, also environmental irritants (silica, asbestos) and amyloid-β, the hallmark protein of Alzheimer's disease. NLRP3 activation may prove to be a practical means of warming up cold tumours and BMS has ambitions to begin clinical studies with an NLRP3 activator in the next 12 months.

Inflammasome activation may not be without risk, being associated with both tumour promotion and suppression in different cancers. Certain tumour-expressed TLRs appears to contribute to development of a benign tumour microenvironment and promotion of metastasis and the STING signalling pathway can contribute to tumour development.  

"Pro-inflammatory" drug development faces the general challenge of achieving an effective degree of tumour inflammation without provoking potentially life-threatening "cytokine storms" or autoimmune adverse events. A better understanding of how the innate immune response might be modulated through the targeting of STING, TLRs, RLRs, inflammasomes or other elements could conceivably lead to novel or improved treatments for a spectrum of conditions that have chronic inflammation at the heart of their pathology. 

Photo credit: Rawich at FreeDigitalPhotos.net

Yet more on bugs and cancer

T-cells (red) on the attack

A Research Highlights piece in December’s Nature Reviews Cancer reports on another intriguing aspect of the interplay between our immune systems and the bugs we carry, namely how gut flora might influence the effectiveness of cancer immunotherapy.

Two international research groups set out to determine  whether the composition of the gut microbiome might influence the response to immunotherapy  directed against  PD-1, a so-called “immune checkpoint “ expressed by activated T cells and macrophages and which is exploited by cancer cells to switch off immune attack. Antibody-mediated blockade of the interaction between PD-1 and its ligand, PD-L1 can restore the anti-cancer response. The anti-PD-1 antibodies pembrolizumab and nivolumab (Opdivo® and Keytruda®, respectively) have proved their worth in the treatment of metastatic melanoma and a variety of other solid tumours.

Genetic analysis of faecal bacteria collected from cancer patients before and after anti-PD-1 immunotherapy found a correlation between gut bacteria diversity and the duration of progression-free survival in cancer patient after treatment.

A collaboration between US and French researchers found differences in the abundance of certain gut bacteria, with Faecalibacterium being enriched in melanoma patients responsive to anti‑PD1 therapy: Bacteroidales was enriched in those patients not responsive to immunotherapy. Differences were also found between responders and non-responders in regards to bacterial metabolism and the composition of immune cells found in the tumour microenvironment. Tumour-infiltrating “killer” T cells were more likely to be found in patients carrying an abundance of Faecalibacterium, while  immunosuppresive cells were more common in individuals carrying abundant Bacteroidales.

Another (again, predominantly American and French) research group found that the abundance of the gut bacterium Akkermansia muciniphila in non-small cell lung cancer and renal cancer patients correlated with a positive response to anti-PD-1 immunotherapy.

Both groups looked for possible mechanistic links between gut bacteria abundance and treatment response. When patient-derived gut bacteria were transplanted into germ-free mice, a variety of favourable effects on tumour growth and immune response were observed, including higher numbers of killer T-cells  and other, immune effector cells, along with changes in the expression of  T- cell receptors for key immune signalling molecules (“chemokines”).

The response to immunotherapy is difficult to predict and involves a variety of tumour factors (PD-L1 expression, tumour burden, degree of mutation) and host factors (immune system genetic makeup, T cell infiltration of the tumour). Analysis of the gut microbiome is unlikely to improve prediction of response, but preservation or manipulation of the gut microbiome through avoidance of antibiotic treatment prior to immunotherapy, or probiotic treatment to encourage “good” bacteria could conceivably translate into better and more sustainable response rates for at least some individuals.  

Photo credit : Rita Elena Serda.  National Cancer Institute \ Duncan Comprehensive Cancer Center at Baylor College of Medicine

More on bugs and cancer

A publication in the December issue of Cancer Research points towards another complicated relationship between bacteria and cancer risk.

A group headed by researchers at the Perlmutter Cancer Center (NYU Langone) looked at data gathered from more than 120,000 subjects already enrolled in an ongoing NCI-sponsored study looking at the link between nutrition and certain cancers.

The presence of a mouth-dwelling bacterium, Tannerella forsythia,  was associated with a 21% increase in the risk of oesophageal adenocarcinoma after adjusting for other known risk factors including smoking, drinking and body mass index.

In contrast, the presence of various Streptococcus and Neisseria species was associated with a 24% decrease in cancer risk. The presence of Porphyromonas gingivalis, a bacterium associated with gum disease, appeared to correlate with a higher risk of another form oesophageal cancer, oesophageal squamous cell carcinoma.

How mouth bacteria influence oesophageal cancer risk is not clear. An association between poor oral health and a higher risk of oesophageal cancer has been suggested in epidemiological studies. Neisseria are capable of partially detoxifying tobacco smoke, with lower numbers of Neisseria found in the mouths of smokers than in non-smokers.  Bacterial metabolism analysis hinted at an increase in oesophageal adenocarcinoma risk associated with some pathways but a lower risk with others. Certain metabolites produced by Neisseria sp correlated with the observed protective effect.

While cause and effect remains elusive, it’s possible that analysis of oral flora might eventually serve as a useful marker for oesophageal cancer risk and that manipulation of the oral flora could reduce occurrence in those already at higher risk through other behaviours.  What’s clear is that “local” microbiomes, whether mouth or gut, can have a profound effect on distant organs.

Bugs and cancer? The plot thickens...

An item from the New York Times gives me the chance to write about two great interests in the same blog piece: bacteria (once a microbiologist, always a microbiologist) and cancer.

Fusobacterium nucleatum, an
accomplice of colorectal cancer

That bacterial infection might cause or promote cancer was debated for most of the 20^th century, but with little solid evidence emerging to support the notions. During the 1980s, Barry Marshall and Robin Warren (the former famously swigging down a flask of culture broth to prove his hypothesis) established that Helicobacter pylori, a common corkscrew-shaped found in the stomach, was an undisputable cause of gastric inflammation and ulcers.

Epidemiological studies involving British, American and Japanese subjects confirmed that H.pylori carriage was indeed associated with an almost four-fold increase in the likelihood of developing gastric cancer and resulted in the WHO designating H.pylori as a Class I carcinogen.

Continuing research has established that the relationship between  H.pylori and cancer is not a simple one of cause and effect,  with H.pylori infection being a factor in some, but not all, forms of stomach cancer and that H.pylori  strains expressing a particular cytotoxin, “CagA”,  are more strongly associated with an elevated risk of cancer than are non-producing strains. Perversely, H.pylori infection appears to be associated with a lower risk of oesophageal cancer.

A more recently uncovered “smoking gun” is the presence of Fusobacterium nucleatum, a common mouth-dweller, found in higher numbers in around half of colorectal tumours than in the surrounding tissue. F.nucleatum- induced inflammation is cited as a plausible contributor to CRC initiation and progression.

But, as with the Helicobacter story, there is no clear-cut cause and effect between infection and cancer. Bacterial species are rarely solitary and the inhabitants of the local milieu or “microbiome” may be more important with respect to cancer initiation and/or progression than the presence of F.nucleatum alone.

CRC may spread to other organs and give rise to tumours in the liver. According to a recent Science publication, if F.nucleatum and its microbiome buddies are present in the original tumour, then they can accompany the metastasizing cancer and pitch up in the liver. CRC dwelling F.nucleatum remained associated with tumours even after their transplantation into mice. Moreover, dosing of tumour-bearing mice with an F.nucleatum-killing antibiotic slowed tumour growth.

Does this make a case for antibiotic therapy or vaccine development to reduce CRC rates? Well, not yet. Antibiotics therapy tends to ablate both the good and bad and, as is hinted at in immuno-oncology studies, certain gut bacteria might positively influence anti-cancer immune responses. And not all F.nucleatum strains might be bad guys. However, it’s feasible that getting a better handle on the mechanism(s) involved in the bacterial promotion of cancer might identify new interventions to improve outcomes or recurrence rates.

Photo credit: CDC Public Image Library

(Almost) all quiet on the sepsis front

UC Riverside researchers
Meera Nair and Jessica Jang

Sepsis, a massive systemic immune response to infection leading to multiple organ damage and, more often than not, death, has proved resistant to drug development efforts over the last four decades. 

Spectacular late stage clinical study failures in the early 90s of drug candidates developed by some of the then brightest stars of the sector, including Centocor, Xoma, Synergen and Chiron led to sepsis treatment development being tagged as a "biotech graveyard".

Large  pharmaceutical companies have fared no better in sepsis therapy development and commercialisation. Eli Lilly's Xigris®, the first (and only) sepsis treatment to receive regulatory approval was pulled in 2011 after a decade in the market as growing clinical evidence indicated that it was of no significant benefit. In the following year, AstraZeneca abandoned development of the BTG Group's CytoFab®. More recently, Eritoran®, a synthetic lipid developed by Eisai failed to show sufficient efficacy in a pivotal clinical study.

Historically, sepsis treatment development attempts were aimed at blocking events which initiate the inflammatory cascade, such as the binding of bacterial lipid to "toll like" receptors which trigger our first line of defence, the innate immune system, or on neutralizing the cytokines (tumour-necrosis factor, interleukin-1) that ramp up the inflammatory response. Sepsis involves a variety of runaway biological processes, including vascular leakage and activation of the complement and coagulation systems, and, with hindsight, strategies that target any single contributing factor are not likely to element of the storm is likely to have only a minimal effect.

Sepsis remains a major problem, with a mortality rate somewhere in the 30% to 50% range and is the cause of around 37,000 deaths each year in the UK alone. It goes without saying that better interventions are required, but the combination of biological complexity, the challenges in designing and executing meaningful clinical studies and a history of high profile failures means that the pipeline is slender.

Work on new therapies is more or less confined to a handful of small-cap biopharmas, although several once promising although candidates with novel modes of action, such as Altor Biosciences’s anti-tissue factor antibody ALT-836 and InflaRx's anti-complement antibody, IFX-1, appear to have been quietly ditched. AM Pharma is currently evaluating a recombinant version of alkaline phosphatase in sepsis patient with acute kidney failure, although the reason for the apparent protective effect of the enzyme remains a mystery.

The lack of anything newsworthy in the sepsis field made two recent articles stand out. Critical Pressure Ltd, a UK start-up received funds to evaluate a small molecule selective inhibitor of nitric oxide (NO) synthesis. Nitric oxide is a potent vasodilator and contributes to vascular collapse. At the same time, NO also protects against the effects of infection, chiefly through macrophage and cardiomyocyte activation. Critical Pressure is banking on the selectivity of its candidate enzyme inhibitor to reduce the unwanted consequence of NO production.

A research paper from a group at the University of California (Riverside) suggests that resistin, a hormone associated with insulin resistance in diabetes and the accumulation of “bad” (low-density lipoprotein) cholesterol might actually have a protective effect in sepsis through binding to a toll-like receptor and preventing cytokine release. Resistin was shown to provide 100% protection from mortality in an animal model of sepsis. A synthetic analogue of resistin, “Retn N-Pep” is undergoing laboratory development as a possible sepsis treatment.

Photo credit:  Ross French, UC Riverside.

Roche’s lampalizumab disappoints- is the "dry" AMD pipeline about to dry up?

Ageing has many biological consequences, ranging from the merely annoying through to conditions that profoundly affect everyday living. The eye is a complex organ and susceptible to a variety of age-related conditions, including cataract formation, glaucoma, dry eye syndrome and loss of retinal function. 

Age-related macular degeneration (AMD) is a progressive loss of function of the macula, the central portion of the retina responsible for precise vision.  The condition starts with the accumulation of fat and protein waste- "drusen" in the subretinal space, causing a loss of essential pigmentation in the retina. The majority of individuals with AMD experience a slow decline in visual acuity- "dry" AMD, but around 10-20% experience acute and catastrophic loss of vision through the formation of new, leaky blood vessels below the retina- neovascular or "wet" AMD.

New blood vessel formation in AMD (and in several types of solid tumours) is stimulated by vascular endothelial growth factor (VEGF). Anti-VEGF drugs have proved reasonably effective over the last decade in slowing the progress of wet AMD when injected into the eye . A variety of other agents targeting VEGF are in clinical development, including brolucizumab (Novartis); RG7716 (Genentech) and abicipar (Allergan).

Unfortunately, no single point of attack is established for dry AMD. Nutritional supplements can slow AMD progression, presumably through reducing oxidative stress (diet, smoking and cardiovascular disease are all implicated as risk factors for drusen formation), but, being an inflammatory condition, a variety of immune mechanisms are likely to contribute to macular damage. 

The alternative complement pathway serves as a first line defence against infection and kicks in before the body mounts a specific immune response. On the back of a strong correlation between AMD and genetic changes in complement regulatory proteins, targeting various complement proteins provides a rational basis for AMD therapy development.

A clinical study with eculizumab, an antibody approved for another complement-mediated condition, failed to show benefit but some progress has been made with other complement-directed agents. Until last week, lampalizumab (Roche) was widely regarded as the first drug to be approved for late-stage dry AMD; unfortunately, treatment for 48 weeks did not show any improvement over placebo. A second Phase III study in ongoing but further development (and a marketing approval submission) will depend on establishing beneficial effects on visual acuity. 

Lampalizumab acts by targeting complement factor D, while other investigational agents are specific for other complement proteins. Opthotech's Zimura (a non-antibody drug) binds to C5, as does tesidolumab (Novartis) while APL-2 (Apellis Pharmaceuticals) targets C3. These other complement directed therapies might yet prove to be effective in AMD, although the decline in Opthotech's share price suggests investor nervousness over the approach.

Discontinuation of lampalizumab development could effectively dry up the AMD clinical (and pre-clinical) pipeline should it take the other complement inhibitors with it.  A few AMD studies with repurposed drugs are ongoing and stem cell implantation might eventually prove capable of restoring some degree of vision to a handful of fortunate individuals, but there is little in the late stage development pipeline that offers any cheer for the three million or so individuals in Europe and the US handicapped by late-stage AMD. 

A new generation of AMD candidates awaits better understanding of the retinal microenvironment in disease, particularly an unravelling of the role of macrophages in the inflammatory process, alongside the contribution made by genetic and environmental factors.   

Photo credit: National Eye Institute, National Institutes of Health

Safety concerns put the brakes on checkpoint inhibitor studies in multiple myeloma

While CAR-T therapy development has regularly been in the spotlight due to an association with lethal adverse events (AEs), immune checkpoint inhibitor therapies, with the exception of some combinations, have so far proved to be comparatively benign.

Severe AEs do occur with current PD-1/PD-L1 antibodies, most commonly with the CTLA-4 antibody ipilimumab (Yervoy®). Immune checkpoint inhibitors act by restoring the immune system’s ability to identify tumours as being “not self”: since the same mechanisms also serve to prevent unwanted immune responses to normal tissue, it’s not surprising that checkpoint inhibitor therapy can result in autoimmune-disease like effects involving the gut, liver, skin and thyroid gland. Severe immune related AEs can require intensive management with steroid and/or other anti-inflammatories, but fortunately occur in a minority of patients.

Studies leading to the approval of checkpoint inhibitors in melanoma, non-small cell lung cancer, classical Hodgkin lymphoma, head and neck cancer and bladder cancer progressed without the red flag of safety concerns, so it’s all the more surprising that a slew of multiple myeloma studies involving checkpoint inhibitor combinations have been brought to a halt by the FDA.

Three Merck studies involving anti-PD-L1 (Keytruda®: pembrolizumab) in combination with drugs already used in multiple myeloma treatment (pomalidomide or lenalidomide with dexamethasone) were placed on clinical hold as of early July following a higher number of deaths in the treatment arms. The FDA have since halted enrolment (although not dosing of enrolled subjects in similar studies involving combination with Bristol Myer Squibb’s anti-PD-1 checkpoint inhibitor, Opdivo® (nivolumab) plus either of two antibodies approved for multiple myeloma treatment.

The FDA’s caution also extend to six combination studies sponsored by Celgene, all involving AstraZeneca’s anti-PD-L1 antibody, Infinzi® (durvalumab),with one study being placed on full hold.

Lenalidomide (Revlimid®) and pomalidomide (Pomalyst®), chemical descendant of thalidomide, are approved for the treatment of multiple myeloma.  Lenalidomide and pomalidomide are potent immunomodulators but also act through a variety of other, non-immune mechanisms. It’s tempting to consider excessive up (or down) regulation of cytokines as a likely  smoking gun, but the combination of effects on tumour/immune system interaction with PD-1/PD-L1 may prove hard to unravel.

No approved cancer treatment is effective (or necessarily safe) for all tumour types: clinical experience with checkpoint inhibitors is still at a early stage, so perhaps safety (or efficacy) issues arising with one or more form of malignancy and/or with a number of the various checkpoint inhibitor combinations under study should perhaps not be unexpected and will not derail the advance of immuno-oncology.

The current generation of checkpoint inhibitors might never make for better multiple myeloma treatment but each setback represents an opportunity to gain better insight into what might work, and what’s to be avoided in the ongoing development and deployment of cancer immunotherapy.

Image courtesy of sheelamohan at FreeDigitalPhotos.net

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First flagged in:  UPDATED: Safety fears spur FDA to pause checkpoint combo studies by Bristol-Myers, Celgene. John Carroll. Endpoints News, online 7^th September 2017. http://tinyurl.com/ybekxrzl

Bristol-Myers Squibb Provides an Update on Three Opdivo-based Combination Clinical Studies in Multiple Myeloma. Company press release online 6^th September 2017. http://tinyurl.com/y9wv3h3g

Merck Provides Further Update on Three Multiple Myeloma Studies Evaluating KEYTRUDA® (pembrolizumab) in Combination with Pomalidomide or Lenalidomide. Company press release online 5^th July 2017. http://tinyurl.com/ya9z2tfs