Development and in-vitro testing of a urease inhibitor to prevent urinary catheter blockage

Introduction: the clinical problem
In the UK, approximately 15-25% of patients admitted to NHS hospitals each year will require urethral catheterisation. In the community, it is estimated that 3% of people living at home and up to 15% in care homes are catheterised. Foley catheters are often used on a long-term (≥30 days) indwelling basis, as a common management technique for urinary incontinence or retention. These catheters exhibit an approximate 5% per day risk of developing bacterial infections, which can cause catheter blockages resulting in painful distention of the bladder and can lead to serious symptomatic episodes - such as acute pyelonephritis and septicaemia.

Catheter-associated urinary tract infections have been identified as a priority area for the NHS, with healthcare-associated infections costing some £1bn per year . As well as the economic burden and a concern for patient outcomes, the NHS has a commitment to reducing the burden of antimicrobial resistance (AMR), and infection-prevention is a key part of this.

Why do urinary catheters block?
Proteus mirabilis is a Gram negative bacterium which is commonly found in the bladder of patients who are long term catheterised. P. mirablis forms biofilms on the catheter and secretes the enzyme urease. Urease, allows P. mirabilis to exploit urea as a nitrogen source allowing the bacteria to grow. Urea hydrolysis results in the production of carbonic acid and two molecules of ammonia. The physical manifestation of this enzymatic process within the catheterised bladder is the substantial and rapid rise in urinary pH, owing to the net production of ammonia which gradually accumulates within the urine reservoir. Ammonia raises the urinary pH in the bladder to pH 7.5-9, compared to healthy, acidic urine pH of 5.5-6.5. Consequently, local supersaturation and precipitation of struvite MgNH4PO4.6H2O and apatite, Ca10(PO4CO3OH)6(OH)2) into the catheter lumen causes abrasive crystalline deposits to become incorporated onto the catheter lumen external and internal surfaces (figure 1). Total occlusion of the catheter lumen may follow blocking the catheter in as little as 16 hours from placement of catheter into an infected bladder.

The Project
We have recently developed a unique small molecule urease inhibitor. This molecule is cheap and easy to synthesise, but importantly has shown to be more effective at urease enzyme inhibition than any other urease inhibitor used clinically such as Acetohydroxamic acid (AHA), which is marketed as Lithostat in the USA, and Uronefrex in Europe. The principal problem with AHA is that it is intensely toxic and is rarely used in Europe. Initial in-vitro testing of our novel urease inhibitor has shown very promising results, with 2-MA being far more effective than AHA, as well as being less toxic.

Project outline
Part 1: Synthesis of urease inhibitor and analogues

Part 2: Testing of urease inhibitors and analogues in bladder model
Using our established test protocols the compound library made in part 1 will be tested in our in-vitro bladder with inhibition to catheter blockage, reduction in P. mirablis biofilm formation, urinary pH, reduction in P. mirablis viable cells all measured as outcomes. From this work, around 3-4 lead compounds will be taken through for toxicity testing in phase 3.

Part 3: Toxicity testing
Toxicity testing using blood haemolysis and eukaryotic cell viability assays will be used to assess toxicity of lead compounds, benchmarked against the commercial urease inhibitor, AHA.

Part 4: Testing of delivery through the catheter balloon
Urinary catheters are kept in place in the bladder via the ‘inflation’ of a balloon with water. The concept for delivery of our urease inhibitors will be to use the balloon to deliver the drug directly into the bladder. This will rely on the small molecules crossing the ultrathin silicone balloon. We will investigate adding excipients to assist in drug transfer.

Part 5: Preparation for clinical study
Once lead compounds have been identified and tested (above) we will work closely with urologists at the Royal United Hospital in Bath to work up a plan to test the drug on actual patients. This will require full ethical permissions as well as regulatory compliant synthesis of the drugs. We would hope to commence the clinical study in 2023.

More information about the research group: https://smartwound.co.uk