- Systemic amyloidosis and serum amyloid P component (SAP).
The tissue damage that causes disease and death in systemic amyloidosis is produced by accumulation of amyloid deposits in the extracellular space. There are currently no clinical treatments which directly target amyloid deposits for elimination. The Pepys team first identified and validated human serum amyloid P component (SAP) as a therapeutic target in amyloidosis in the mid 1990s. In vitro, SAP both enhances amyloid fibril formation and protects amyloid fibrils from proteolytic degradation by macrophages. In collaboration with Roche they developed the novel palindromic bis-D-proline compound (R)-1-[6-[(R)-2-Carboxy-Pyrrolidin-1-yl]-6-oxo-Hexanoyl]Pyrrolidine-2-Carboxylic acid (CPHPC), which was intended to prevent SAP from binding to amyloid fibrils in vivo and dissociate bound SAP from amyloid deposits (Nature 2002). Pentraxin acquired full ownership of CPHPC from Roche in December 2008.
CPHPC is avidly bound by human SAP in a complex composed of two native pentameric SAP molecules cross linked by 5 bivalent CPHPC molecules. The complex is perceived as abnormal by the liver and instantly cleared, leading to profound depletion of SAP from the circulation which persists for as long as the drug is administered (PNAS 2009). Targeted depletion of a pathogenic protein by a small molecule drug constitutes a potent, novel pharmacological mechanism. The depletion of plasma SAP also clears most of the SAP from amyloid deposits but the affinity of SAP for CPHPC is insufficient to produce complete dissociation of all SAP from systemic amyloid deposits, due to the avid binding of SAP to amyloid fibrils and the continuous production of 50-100 mg of new SAP per day. About 10% of the amyloid‑associated SAP remains in major visceral amyloid deposits even after months of continuous CPHPC treatment and we have not detected any amyloid regression in patients receiving the drug. Thus, although CPHPC and sustained SAP depletion are well tolerated by patients with no adverse effects other than transient stinging and occasional erythema at the sites of subcutaneous injection of the drug. CPHPC does not itself promote elimination of amyloid deposits.
The capacity of CPHPC to clear essentially all SAP from the circulation, while leaving significant amounts of SAP specifically bound in the amyloid deposits, suggested the possibility of using the residual SAP as an amyloid-specific target for antibodies which can invoke physiological clearance of amyloid from the tissues. Depletion of circulating SAP crucially allows such antibodies to be administered safely and effectively. This approach is unrelated to the function of SAP itself and simply uses SAP as a passive amyloid-specific target. It has been remarkably successful in experimental models (Nature 2010) and should be applicable to all forms of amyloidosis. In February 2009, GlaxoSmithKline licensed from Pentraxin Pepys’s invention of this first in class combination of a small molecule drug and a monoclonal antibody. They fully humanised one of our optimal mouse monoclonal anti‑human SAP antibodies and clinical development is in progress.
In 2012 GSK conducted a phase I, open label, dose characteristic study to investigate the pharmacokinetics, pharmacodynamics, safety, and tolerability of intravenous and subcutaneous doses of CPHPC in patients with systemic amyloidosis (http://www.clinicaltrials.gov/ct2/show/NCT01406314?term=amyloid+gsk&rank=4), enabling progression to the single dose first in human study of anti-SAP antibodies co‑administered with CPHPC in patients with systemic amyloidosis (http://www.clinicaltrials.gov/ct2/show/NCT01777243?term=amyloid+gsk&rank=2). The initial results in the first 15 subjects to be treated were reported in the New England Journal of Medicine online in July 2015 and in print in September 2015 (373: 1106-1114). The treatment was safe and well tolerated and produced unequivocal and unprecedented, swift and dramatic reduction in amyloid load, documented so far in the liver, spleen, kidneys and lymph node, with associated clinical benefit. Subsequent results of repeat dosing in the phase 1 study confirmed efficacy and were initially reported at the 2015 annual meeting of the American Society for Hematology. The full report of the whole phase 1 trial is published in Science Translational Medicine on 3 January 2018, showing progressive removal of visceral amyloid with serial doses of CPHPC followed by anti-SAP antibody. Meanwhile, early in 2017, the official WHO International Nonproprietary Names assigned to the two drugs were published: miridesap for CPHPC and dezamizumab for the humanised monoclonal anti-SAP antibody.
Cardiac amyloidosis was excluded from the first part of the phase 1 study but subjects with cardiac involvement were treated in the second part of the trial without any drug related adverse effects and are reported in the recent paper. GSK’s phase 2 clinical trial of miridesap plus dezamizumab, focussed on cardiac amyloidosis, is currently in progress.
- Targeting SAP in Alzheimer’s disease.
SAP is an attractive therapeutic target in Alzheimer’s disease because of its role in amyloid, which is always present in the brain in this condition, and also because there is evidence that SAP itself may be directly neurocytotoxic. In a first clinical study of CPHPC in Alzheimer’s disease we showed that the drug safely and completely depletes SAP from the cerebrospinal fluid (PNAS 2009). Furthermore, we have shown that, in contrast to systemic amyloid deposits, CPHPC completely removes all detectable SAP from the microscopic cerebral and cerebrovascular amyloid deposits in an experimental model of human Alzheimer’s disease (Open Biol 2016). In collaboration with Professor Martin Rossor, Professor of Clinical Neurology, Founder of the Dementia Research Centre at the UCL Institute of Neurology, and now NIHR National Director for Dementia, we have designed a comprehensive clinical trial of CPHPC in Alzheimer’s disease, seeking evidence of disease modification and clinical efficacy. Preparation for and conduct of the ‘DEpletion of Serum amyloid P component In Alzheimer’s Disease (DESPIAD) trial’ is receiving substantial logistical and expert support from GSK and is funded exclusively by the National Institute for Health Research (NIHR) via the UCL/UCLH Biomedical Research Centre. After unfortunately very prolonged logistical delays, the 3 year study is now expected to start in 2018.
- Inhibition of C-reactive protein (CRP) for treatment of cardiovascular and inflammatory disease.
We have shown that human CRP, the classical acute phase plasma protein that increases greatly in concentration in response to most forms of tissue damage, infection and inflammation, can exacerbate pre-existing tissue injury by binding to the damaged cells, activating complement and thus provoking additional inflammation. In particular, in ischaemic injury to the heart and brain, in heart attacks and strokes respectively, CRP is likely to make a significant contribution to the eventual scale of the damage. Inhibition of CRP binding is thus a valid therapeutic target.
Pepys and his team designed de novo a family of compounds which were the first potential CRP inhibitor drugs (Nature 2006). The optimal molecule, bis(phosphocholine)-octane (BPC8), inhibits binding of CRP to other ligands in vitro and in vivo and also promotes accelerated clearance and thus plasma depletion of CRP. Treatment with BPC8 completely abrogates the adverse effect of human CRP in experimental models of acute myocardial infarction. The Medical Research Council awarded £3.84 million to Professor Pepys in 2010, as the first grant given under their then new Developmental Clinical Studies scheme, to support development of this drug up to and including human phase I studies.
After extensive evaluation, BPC8 was found not to possess properties suitable for development into a drug. Using the knowledge gained during the evaluation of this molecule Pepys and his team have continued working on new leads for development, in studies funded by part of the MRC grant, a special project grant from the British Heart Foundation and lately PoC funds from UCL Business PLC.
- SAP depletion and DNA vaccination.
Successful immunisation induces a protective immune response against particular component(s) of the target pathogen, the so-called immunogen(s). For some diseases the immunogens are not known and for others they are difficult and expensive to produce, transport and administer, for example influenza vaccine must be produced in millions of chicken eggs. A very attractive potential solution is to inject the DNA gene encoding the immunogen rather than the immunogen itself. In this process, known as DNA vaccination, the DNA enters cells, predominantly at the site of injection, and causes them to produce the immunogen locally within the body. DNA vaccination works well and stimulates excellent protective immunity against a variety of different infections, and even some cancers, in mice, horses, dogs, rabbits and pigs. But in humans and other primates, and in cows and sheep, the immune response to DNA vaccination is very feeble. Despite enormous academic and pharmaceutical industry efforts, the reasons for this failure have not been understood or overcome. We previously discovered, in work funded by the MRC, that a protein in human plasma, known as serum amyloid P component (SAP), is the only normal plasma protein which binds avidly to DNA. We have now found that, in each of the animal species in which DNA vaccination is effective, this protein is either absent or, if it is present, it binds only weakly to DNA. In contrast, non-human primates, cows and sheep share with humans the presence of SAP proteins which strongly bind to DNA. We believe that binding of DNA by SAP may be responsible for blocking induction of immune responses by DNA and that removal of SAP may overcome this inhibition. SAP contributes to important human diseases, amyloidosis and Alzheimer’s disease, and, in MRC funded work towards treatment for these conditions, we have previously developed a drug, CPHPC, which safely removes almost all SAP from the blood in humans. Another laboratory has recently reported that the presence of human SAP inhibits DNA vaccination in mice and that this effect is reversed by our drug, CPHPC. These observations confirm our hypothesis. We have therefore conducted the first human clinical study of DNA vaccination after SAP depletion, in collaboration with Professor Tomas Hanke at the University of Oxford and funded by an MRC DCS award. We measured the immune responses to HIV‑1 in normal adult male volunteers, comparing a group in whom circulating SAP had been depleted at the time of DNA vaccination against HIV-1 and a control group vaccinated without SAP depletion. However, the only significant difference observed in a comprehensive assessment of the immune responses in the test and control groups was the recognition of a broader range of epitopes in the test group. The full report of the trial has just been submitted for publication.
Although the outcome of the study was generally negative, the observations and evidence supporting our hypothesis remain compelling. It is not possible to measure the SAP concentration in the extracellular tissue fluid into which the DNA immunogen is injected and we therefore do not know whether adequate depletion of SAP had been achieved in the trial protocol. Additional studies, using more sustained SAP depletion and possibly other immunogens, the responses to which are more tractably and robustly measured, will be required to rigorously exclude or confirm our hypothesis.