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

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

ASCO 2017 Annual Report again picks immunotherapy as “Advance of the Year “

ASCO, the American Society of Clinical Oncology, is probably best known to followers of the pharma and biotech industries for its high profile annual conference, always the subject of intense sector analyst scrutiny.  ASCO also publishes a highly-readable annual report highlighting clinical advances in cancer therapy and the shape of future research.

Once again, immunotherapy (dubbed “Immunotherapy 2.0” by ASCO) takes the honours as “Advance of the Year”, underscoring the breakthrough nature of this approach to cancer treatment and its expanding role across a growing number of cancer indications.

Put very simply, immunotherapy utilises the patient’s own immune system to combat cancer. Tumours thrive by deploying a variety of countermeasures which are highly effective in subverting the immune response.  A mechanism common to several tumour types is surface expression of proteins that lock onto receptors (“immune checkpoints”) present on T cells,  resulting in their deactivation. By deliberately blocking this interaction, T-cell “seek and destroy” functions can be restored.

Immune checkpoint inhibitors were first approved on the basis of their efficacy in metastatic melanoma, with the first being Yervoy® (ipilimumab: Bristol Myers Squibb) in 2011, followed by Keytruda® (pembrolizumab: Merck) and Opdivo® (nivolumab: Bristol Myers Squibb) in 2014 and,  most recently, Tecentriq® (atezolizumab: Roche) for the treatment of some forms of lung cancer. A number of other biologic immune checkpoint inhibitors are in late stage clinical evaluation.

From the outset, checkpoint inhibitor treatment has been notable for impressive increases in patient survival, although not across the board. Reliable identification of those patients most likely to benefit from checkpoint inhibitor therapy remains a frustration. Optimum duration of therapy also remains to be established. Given the cost of checkpoint inhibitor treatment (around £30,000 before an undisclosed discount in the UK and around $150,000 in the US), patient selection and length of treatment are of key importance to healthcare systems already struggling with soaring cancer therapy expenditure.

Recent checkpoint inhibitor approvals include treatment of head and neck, bladder and renal cancers and Hodgkin’s lymphoma, and evaluation is progressing in liver, breast, gastric and other cancers. The need to attain market dominance is a major driver of clinical trial activity: at the end of 2016, Merck’s Keytruda® was being trialled against 30 tumour type in more than 350 registered studies, of which around 100 studies will evaluate treatment combinations.

Hundreds of micro and mid-cap companies are looking to stake a claim in the immunotherapy (aka “immuno-oncology) space. Some are hopeful that repurposed drugs can modify the tumour microenvironment to favour the immune system, while others believe that combination with checkpoint inhibitors and other agents can boost the so far disappointing efficacy of cancer vaccines.

Tumour immunology remains poorly understood. Potential big winners in next generation immunotherapy are those companies engaged in the unravelling of tumour defence mechanisms to find exploitable vulnerabilities.

Who knows, but given the rate of progress, the 2027 ASCO “Advance of the Year” could well be “Immunotherapy 12.0”.

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ASCO 12^th Annual Report on Progress Against Cancer. 2017 Clinical Advances. Online 1^st February 2017    http://tinyurl.com/zwzv5vg