The specific aim of this study was to investigate the potential efficacy and safety of topically administered alicaforsen in ulcerative colitis. We found that administration of alicaforsen in patients with mild to moderate ulcerative colitis caused a significant dose dependent reduction in disease activity. The 4 mg/ml dose of alicaforsen enema showed a statistically significant acute (day 29) improvement in DAI status. The 2 and 4 mg/ml doses of alicaforsen showed statistically significant long term (month 3) improvement in DAI status as well as a trend towards improvement in CAI. At the highest dose, DAI status on day 29 improved by 70% from baseline, from 6.3 to 2.2 (p
0.03); 2/8 patients in the 2 mg/kg group and 3/8 patients in the 4 mg/kg group had complete endoscopic remission on day 29. At three months, complete endoscopic remission was found in 4/8 and 5/8 patients (2 mg and 4 mg/kg dose groups, respectively). Total treatment duration was four weeks. As this was an exploratory study with a small sample size, adjustments for multiple comparisons were not made. While the statistically significant results must be viewed cautiously because of the small sample size, they suggest drug activity in patients with mild to moderately active distal ulcerative colitis.
Consistent with the improvement in DAI, more patients completed the study through to month 6 in the 2 and 4 mg/ml treatment groups than in the 0.1 and 0.5 mg/ml, and placebo treatment groups. None of the patients in the 4 mg/ml treatment group and only two patients in the 2 mg/ml treatment group (2/8) required additional medical or surgical intervention for ulcerative colitis during the treatment period through to month 6. Patients who did not complete the study to month 6 generally did so because their colitis failed to respond or even worsened (15/16 cases), providing a correlation between the more objective DAI parameter and the clinical behaviour of patients and the physicians treating them. ISIS 2302 had a marked effect on DAI status and a lesser effect on CAI status. The reason for this difference is not entirely clear but a practical explanation is that DAI may provide a more objective and accurate measure of efficacy than CAI. The DAI score includes an objective endoscopic assessment of the colonic mucosa and also carries less subjectivity in its patient questionnaire components. By comparison, the CAI contains a number of subjective questions in its patient questionnaire and these questions also carry a great degree of subjectivity in their grading. In addition, while the results of the DAI and CAI differed, both showed positive trends.
Alicaforsen enema was well tolerated and there were no safety issues. Adverse events reported were consistent with those commonly seen in this patient population. There was no obvious or consistent relationship between alicaforsen enema and any adverse event.
Infiltration of neutrophils into the colonic mucosa is a principal event in the pathophysiology of ulcerative colitis. A variety of observations support a pivotal role for ICAM-1 in this process. Sonicated colonic tissue from ulcerative colitis patients contains higher concentrations of ICAM-1 relative to controls. ICAM-1 significantly increases during active ulcerative colitis compared with ulcerative colitis in remission and increasing ICAM-1 concentration correlates with increasing disease activity.17
Ultrastructural studies of colonic biopsies from ulcerative colitis patients and control patients have demonstrated ICAM labelling on basal endothelial cell membranes, on macrophages, and on plasma cells in active ulcerative colitis, suggesting that ICAM-1 is involved in the entire leucocyte infiltration process and not simply in the early extravasation phase.18
Therefore, cell adhesion molecules, and ICAM-1 in particular, appear to play a critical role in the migration of leucocytes into the inflamed colon and the overall pathophysiology of ulcerative colitis.
Alicaforsen is a 20 base phosphorothioate oligodeoxynucleotide designed to specifically hybridise to a sequence in the 3′-untranslated region of human ICAM-1 (CD54) messenger RNA. RNase-H, a ubiquitous family of nucleases, uniquely recognises oligodeoxynucleotide-RNA heterodimers and will destroy the RNA strand of such heterodimers by enzymatic cleavage.19
A highly specific reduction in ICAM-1 mRNA, and consequently ICAM-1 expression, follows and has been demonstrated in human endothelial cell culture models, in mouse heterotopic heart transplant models, in mouse pancreatic islet transplant models, in rat heart and kidney transplants, and in mouse models of colitis.20,21
A previous study of ISIS 2302 administered intravenously21
failed to show a treatment effect in patients with active steroid dependent Crohn’s disease. Post hoc pharmacokinetics and population analysis of these results suggested a correlation between drug exposure and response to ISIS 2302. This hypothesis is being further explored in additional randomised controlled clinical trials in Crohn’s patients. In the current study, ISIS 2302 was administered topically. It may be that topical administration is a more effective way of administering antisense to the target tissue in inflammatory bowel disease.
The alicaforsen enema doses used in this study (60 ml of 0.1, 0.5, 2, or 4 mg/ml) were selected based on the safety and efficacy demonstrated with comparable doses in murine models of colitis (data on file at Isis Pharmaceuticals). As alicaforsen bioavailability from inflamed colon in humans was not known, a conservative dose escalation protocol was used. Dose duration (daily evening dose for 28 consecutive days) was selected to evaluate duration of therapy comparable with other anti-inflammatory therapies for ulcerative colitis.
Retention enemas are an effective way of achieving therapeutic concentrations within the mucosa of the distal and left colon. Meta-analyses of mesalamine therapy in ulcerative colitis have reported that topical mesalamine therapy is superior to oral therapy for induction and maintenance of remission.1,2
Enema therapy is well tolerated by patients with ulcerative colitis and has become an accepted route of drug administration.22
In this study, all four alicaforsen dosing regimens resulted in high, dose dependent, tissue concentrations in mucosal biopsy samples of colon obtained on day 29. Median tissue concentrations ranged from 0.48 to 5.49 μg/g, and patient compliance with administration of the retention enemas for 28 consecutive days was excellent (only one patient received less than 27 doses).
In conclusion, alicaforsen enema demonstrated acute and long term improvement in DAI and resulted in complete endoscopic remissions in a significant percentage of patients treated with drug concentrations of 2 mg/kg or 4 mg/kg. The drug was well tolerated with no major safety issues identified. These early findings should be validated in additional larger, prospective, randomised, controlled, clinical trials.