Figure 12.3 Immune system/anti‐inflammatory strategies. Inflammation in AP may result directly from cell death‐dependent or ‐independent pathways. Acinar cell injury can result in direct cytokine and chemokine release that is then amplified by immune cells: interleukin (IL)‐1, IL‐2, IL‐6, IL‐8, IL‐12, IL‐18; platelet‐activating factor (PAF); tumor necrosis factor (TNF‐α). Cell death pathways resulting in cell membrane permeabilization or rupture (predominantly necrosis) of acinar cells, but also potentially neutrophils (NETosis), with the subsequent release of both mitochondrial and nuclear damage‐associated molecular patterns (DAMPs) also drives inflammation. Strategies inhibiting DAMPS (TLR‐9 with IRS‐954, monoclonal antibodies directed towards HMGB1 and histones), immune cell modulation such as by inhibiting NETosis (Cl‐amidine, chloroquine), or direct cytokine inhibition (infliximab, CytoSorb) all hold promise for AP. mtDNA, mitochondrial DNA; nDNA, nuclear DNA; TLR, toll‐like receptor; HSPs, heat shock proteins; HMGB1, high mobility group box 1.
Whereas release of DAMPs is thought to be primarily a passive process, pancreatic acinar cells also actively synthesize and release cytokines [70] and chemokines [84] and upregulate intercellular adhesion molecule (ICAM)‐1 [85] to promote neutrophil and monocyte infiltration [86,87]. Infiltrating inflammatory cells act together with activated peritoneal macrophages and hepatic Kupffer cells to amplify proinflammatory cytokines in the systemic circulation [88–90], manifesting clinically as the systemic inflammatory response syndrome (SIRS). Early intervention to reduce local and systemic AP injury is the basis of an ongoing randomized clinical trial of infliximab, a monoclonal anti‐tumor necrosis factor (TNF)‐α antibody, in early AP that is currently recruiting (RAPID‐I, ISRCTN16935761) as well as a pan‐cytokine absorption trial (PACIFIC [91]). With the exception of the use of nonsteroidal anti‐inflammatory agents in the prevention of pancreatitis post endoscopic retrograde cholangiopancreatography [92,93], these are the first trials in AP to directly target the inflammatory cascade since the lexipafant (platelet activating factor inhibitor) trials of the early 1990s [94], which despite promising preclinical results failed to demonstrate a benefit in human AP.
Neutrophils are among the earliest cellular responders to acinar cell injury and can be observed within the pancreas as early as one hour after initiation of experimental AP and after three hours in the lung [95]. Antibody‐mediated depletion of neutrophils ameliorates disease in experimental models [96–98], in particular with respect to associated lung injury. Knockout and/or inhibition of chemokines or their receptors can reduce inflammatory cell migration and has been shown to ameliorate AP in a variety of ways, including by inhibition of CXCR2 [99–101], CXCR4 [102], CXCL4 [103], and CXCL16 [104], but no human trials have been published to date. More recently, a novel mechanism of neutrophil toxicity has been described where neutrophils actively release nuclear chromatin, laced with proteases, in the form of web‐like structures termed neutrophil extracellular traps (NETs). NETs have been shown to promote the pathogenesis in experimental AP [105,106] and inhibition of NET release (NETosis) has been found to ameliorate AP by deletion of protein arginine deiminase type IV (PAD4), or through pharmacological inhibition with Cl‐amidine [107] or chloroquine [108]. Because of their highly regulated release and their effect on both pancreas and lung, NETs present a fantastic opportunity for the development of novel therapeutic agents.
Targeting immune‐based mechanisms has yet to be proven to be effective in the treatment of human AP, but the results of ongoing trials, notably RAPID‐I and PACIFIC, are awaited. The complex interactions and redundancies of immune pathways remain problematic, but the continuing discovery of new mechanisms, availability of novel investigative technologies, and a drive towards personalized medicine presents opportunities for yet untested strategies in this vital area.
CFTR
Cystic fibrosis transmembrane conductance regulator (CFTR) is a membrane protein and chloride channel in vertebrates that is essential for ductal fluid and HCO3 – secretion [109] (see Figure 12.2). CFTR dysfunction due to either reduced expression or reduced activity has been increasingly recognized as a critical risk factor for AP and chronic pancreatitis and is also associated with hereditary pancreatitis [110–112]. Defects of the CFTR gene have been reported to be present in up to 34% of paediatric cohorts with recurrent AP [113]. Pancreatic fluid and bicarbonate secretion appear to be protective in AP, as suggested by CFTR −/− mice that have more severe pancreatitis in experimental mouse models [114]. Furthermore, common pancreatic toxins not only damage acinar cells but also decrease fluid and HCO3 – secretion by ductal cells [111]. Recently, experimental mouse models of autoimmune pancreatitis have been identified with decreased CFTR levels [115]. The CFTR corrector C18 and potentiator VX770 as well as VX‐809 (lumacaftor) rescued CFTR expression and localization with decreased inflammation and reduced tissue damage in experimental pancreatitis models [116]. These studies indicate the possible utility of CFTR correctors already approved by the FDA, with potential in recurrent pancreatitis, hereditary pancreatitis, and chronic pancreatitis.
Design of Future Clinical Trials
Previous systematic reviews of clinical trials in AP have provided disappointing results [64]. Initial poor risk stratification and inappropriate outcome measures have been inhibitory to progress. Common primary outcome measures previously used have been mortality, organ failure, pancreatic infections, and SIRS [1]. Looking to the future, study end points in AP should be determined based on the context of the proposed intervention. Traditional approaches for the development of novel therapeutics in AP have focused on prevention or reduction of severe forms of illness, with expectations that may have been too high. These studies incorporated initial risk stratification to identify higher‐risk subgroups of patients, which takes time for amelioration in outcomes such as persistent organ failure or mortality. These strategies have been accompanied by recruitment within 72–96 hours of admission, despite the emergency nature of the condition. An alternative approach would be to include all AP patients as early as possible after disease onset. In parallel with this, improvement in patient‐reported outcomes (as sought by regulatory agencies) related to pain, nutritional deficit, and quality of life alongside inclusion of surrogate outcomes of severity, such as C‐reactive protein, albumin and neutrophil count, offer the potential for enhanced and more rapid recruitment with greater generalizability of results. However, it remains important that all surrogates closely parallel severe outcomes, which would themselves preferably be included in trials at least as secondary outcome measures. However, this approach has yet to be validated [1,2]. Realistically, as acute pancreatitis has proven a tough disease to solve with any drug treatment, it is desirable to establish a pipeline of interventional trials to achieve regulatory approval for any treatment that improves outcomes from AP. This will require increased input from major funding agencies as well as investment through, and commitment from, Pharma. Nor will the quest stop once this is achieved, since there will continue to be a drive to improve AP outcomes further with effective, personalized treatments.
Conclusion
The demand for targeted pharmacological treatment in AP remains a high priority since none are currently available. Recent and ongoing determination of critical pathogenic mechanisms continues to support effective drug target evaluation. New molecular entities that inhibit calcium toxicity and repositioned drugs that block inflammatory pathways have progressed into clinical trials, the results of which are eagerly awaited. In addition, strategies targeting mitochondrial dysfunction