Impact of Oral Disulfiram on Aldehyde Dehydrogenase (ALDH) Mediated Ocular Fibrosis in Mucous Membrane Pemphigoid (OcMMP)

Conjunctival scarring results from many diseases. These include trachoma, an infection that is known to be the largest cause of preventable blindness worldwide. It causes irreversible sight-loss in both eyes in 1.9 million worldwide. In the UK, the most common cause is a rare autoimmune driven disorder called Ocular Mucous Membrane Pemphigoid (OcMMP) that occurs in 0.8 people in a million population each year. OcMMP creates chronic inflammation and scarring of the conjunctiva which lines the inside of the eyelids and covers the white of the eye. Scarring of the inside lining of the eyelid can cause the lashes to turn inwards and scratch the cornea (trichiasis). This and inflammation, lead to debilitating symptoms of constant irritation, pain, and dryness. Treatments involve immunosuppression but this has little effect on scarring. For half of patients, scar formation continues; 20% become irreversibly blind.

Our research on conjunctival tissue taken from patients with OcMMP whilst undergoing diagnostic conjunctival biopsies as part of their routine clinical care, and in our ocular pemphigoid-like mouse model, has shown that the enzyme, aldehyde dehydrogenase (ALDH), controls conjunctival scarring both in OcMMP human tissue and in the pemphigoid mouse. Disulfiram (DSF; a drug used as a tablet given by mouth for alcohol-abuse treatment) permanently blocks ALDH action. We have found that DSF has anti-inflammatory and anti-scarring properties and when given to the pemphigoid-like mouse in an eyedrop form (once daily for one week), DSF reverses inflammation and scarring.

We would like to understand whether disulfiram has the same mechanism of action if given to patients with OcMMP. As there is no licensed disulfiram eyedrop formulation, we would like to give tablets by mouth at the UK licensed safe dose, to patients with OcMMP for two weeks and examine how it effects the scarring signals in the conjunctiva. We will do this by taking swabs, tear and blood samples from patients before starting treatment, one week into treatment, at the end of treatment and two weeks after coming off treatment.

Previously, we have taken conjunctival swabs from patients with and without OcMMP and have shown that we can detect key players in the mechanisms of conjunctival scarring at a genetic level using a technique called nanostring. Nanostring allows us to detect a large number of genes from one swab. We have identified a cluster of genes known to be part of the scarring pathway that are abnormal in OcMMP patient conjunctiva.

Importantly, using a sensitive assay optimised by us, we have been able to quantify ALDH levels in tears and have shown ALDH activity to be around 10 times higher in patients with OcMMP compared to those who do not have the disease.

What this means is that we can test whether giving disulfiram tablets to patients with OcMMP switches off ALDH action in the conjunctiva (determined using tear samples) and whether this modifies the scarring process (assessed using conjunctival swabs). As inflammation drives scarring, and we know that the disulfiram eyedrop in the pemphigoid-like mouse reduced conjunctival inflammation, we will analyse the presence of inflammatory biomarkers both on the surface of the eye (using tears) and the bloodstream (using a blood sample) to see if taking disulfiram tablets can also reduce the associated inflammatory signals.

In this way, we anticipate we will generate sufficient information to support our hypothesis that ALDH is pivotal to the human conjunctival scarring pathway. As indefinite use of oral disulfiram should be avoided, this finding will encourage development of a novel disulfiram anti-scarring eyedrop to test as a treatment in clinical trials. Our goal is to improve the patient experience of living with OcMMP, and to transform patient care on a global scale by reducing the burden of sight-loss for this and other conjunctival scarring disorders.

OcMMP is an orphan disease characterised by chronic autoimmune-driven conjunctival inflammation leading to progressive scarring, debilitating symptoms and blinding sequelae. Systemic immunotherapy modifies inflammation but does not limit progression of fibrosis either in inflamed eyes, or in 50% of clinically quiescent eyes, leading to blindness in 20%. Understanding the pathogenic mechanism underpinning progressive conjunctival fibrosis will facilitate development of therapies for which there is a clear unmet clinical need.

Using gene expression in human OcMMP conjunctival tissue, we have shown that inhibition of the ALDH1A3 isoform is a candidate anti-fibrotic mechanism. This is supported by (i) structural and functional abnormalities of human OcMMP conjunctival fibroblasts that were normalised by ALDH inhibition in vitro, and (ii) prevention of conjunctival scarring and inflammation in a surrogate OcMMP mouse model.

Building on this, we aim to repurpose oral disulfiram (DSF) as a tool drug to interrogate the ALDH-mediated conjunctival fibrosis signalling pathway in patients with OcMMP. DSF is a non-sleective aldehyde dehydrogenase (ALDH) inhibitor with an established safety profile licensed for treatment of alcohol-abuse, yet would present clinical issues if used as a chronic oral therapy. Patients will receive DSF for just 2 weeks and ocular samples (tears, swabs) and peripheral blood analysed pre-, during and post-DSF with mechanistic outcomes assessed (including (i) ALDH inhibition in the tears as a readout of pharmacological engagement and, (ii) normalisation of pivotal profibrotic factors such as Collagen Type 1 as a biomarker predictive of efficacy).

Arising supporting data will provide confidence in our hypothesis that ocular ALDH inhibition can deliver local anti-fibrotic efficacy and hence encourage our development of a topical DSF formulation predicted to deliver clinical efficacy without systemic issues arising from chronic oral DSF.