An expanding pipeline for IBD drugs
A number of emerging therapies for inflammatory bowel disease (IBD), as well as new applications of existing drugs, are currently under active investigation or in clinical trials. Unlike existing medications, novel agents are notable for addressing a variety of targets, including:
- Adhesion molecules beta-7 integrin and mucosal addressin cell adhesion molecule-1
- The p40 subunit of interleukin 12/23
- Chemokine receptor 9
- Janus kinase
That diversity is encouraging, says Edward V. Loftus Jr., M.D., of Mayo Clinic in Rochester, Minn. "We used to have this monolithic view that you treat all patients who have Crohn's or ulcerative colitis the same way. With the advent of individual or personalized medicine, we're beginning to appreciate that there is considerable individual variation in response to a particular medication.
"For example, even with the anti-tumor necrosis factor agents, arguably the most effective class of medications for IBD, only 70 to 80 percent of people, at most, respond initially, and many of those patients lose their response over time. So we need multiple drugs with multiple mechanisms of action."
Old drugs, new applications
With that in mind, some older therapies are being re-purposed or reformulated for use in ulcerative colitis (UC), where therapeutic options are particularly limited.
One is the anti-tumor necrosis factor (anti-TNF) monoclonal antibody, adalimumab (Humira), a mainstay of Crohn's disease therapy that is currently approved only for that IBD subtype. But after demonstrating some efficacy for UC in several large studies, Humira is now likely to receive FDA approval for ulcerative colitis, too.
Researchers are also actively studying the arthritis drug golimumab (Simponi), a fully human anti-TNF agent. In preclinical studies, golimumab was more effective at neutralizing TNF-alpha than were other anti-TNF biologics. And unlike other anti-TNFs, golimumab can be administered both intravenously and subcutaneously. The results of a large randomized trial of golimumab in UC will be presented at Digestive Disease Week 2012.
Also under study is a modified corticosteroid, budesonide, currently used for induction therapy in Crohn's disease. The Entocort formulation of the drug is released in the ileum and right colon, but a reworked version using a multimatrix (MMX) formulation that reaches the entire colon may have potential for treating ulcerative colitis. Phase 2 trials were promising, and the drug is now being studied in phase 3 trials. Mayo Clinic in Minnesota will be the site of the Santarus-sponsored trial.
Budesonide has not proved more effective for Crohn's disease than systemic corticosteroids and is not intended for long-term therapy. But because the drug is metabolized quickly in the liver, it causes fewer side effects and less adrenal gland suppression.
Metronidazole (Flagyl) is an antibiotic that is often used as an adjunctive therapy in Crohn's disease patients with perianal fistulas, but the oral formulation is associated with several side effects, such as strong metallic taste, nausea and peripheral neuropathy, which can limit its use in many patients. A metronidazole ointment that is applied topically to the perianal area is currently being assessed in patients with perianal Crohn's disease. Mayo Clinic in Minnesota is currently a site for that study, which is sponsored by Braintree Laboratories.
Adhesion molecule blockers
Novel agents may show the most promise because their targets are more diverse. Among the new therapies are adhesion molecule blockers, which prevent leukocyte migration into the gut mucosa. The drug natalizumab (Tysabri), a humanized monoclonal antibody to alpha-4 integrin, is the existing agent in this class. Natalizumab is currently approved for both multiple sclerosis and Crohn's disease refractory to standard therapy, including anti-TNF therapy.
Although natalizumab has shown efficacy in Crohn's disease, it is rarely prescribed because it increases the risk of progressive multifocal leukoencephalopathy (PML), a viral brain infection that usually results in death or severe disability. The overall rate of PML cases is about 1.16 per 1,000 patients.
"The problem is that natalizumab affects adhesion molecules at the level of the blood-brain barrier system as well as in the gut," Dr. Loftus explains. "So the goal is to develop more gut-specific targets."
Of selective adhesion molecule blockers currently in development, the most prominent is vedolizumab, a humanized monoclonal antibody to the adhesion molecule α4β7-integrin that theoretically inhibits leukocyte migration in the gut without affecting the blood-brain barrier. Vedolizumab has been studied for both Crohn's disease and UC.
In late February, drugmaker Takeda announced that vedolizumab had met all its primary endpoints in a pivotal phase 3 trial for ulcerative colitis. Trial results will be presented in detail at Digestive Disease Week 2012. To date, more than 1,000 patients have received the drug, with no known cases of PML.
"It's looking good in terms of safety, but we're waiting for the results of the big trials," Dr. Loftus says. "Vedolizumab might be a year-and-a-half to two years away from release."
Other monoclonal antibodies affecting the adhesion molecule pathway are several years behind. Genentech's ulcerative colitis drug etrolizumab
— formerly known as rhuMAb Beta 7 or RG7413 — is selective for the β7 subunit, which is gut-specific and should help eliminate the risk of PML.
Etrolizumab is currently under study in a phase 2 trial of patients with moderate to severe UC who are refractory to anti-TNF therapy. Mayo Clinic in Minnesota is one of the sites for the study. Pfizer is developing PF-00547659, a monoclonal antibody to mucosal addressin cell adhesion molecule-1 (MAdCAM-1). The drug is being assessed in a phase 2 trial of patients with moderate to severe Crohn's disease at several sites, including Mayo Clinic in Minnesota and Florida.
Certain chemokines are proinflammatory receptors that attract leukocytes — in a sense, second cousins to adhesion molecules. Chemokine receptor 9 (CCR9) is integral to the migration of immune cells into the intestine, and several drugs that block this receptor are in development. One, GSK-1605786, is an oral agent that may inhibit B and T cell entry into the small gut while maintaining normal immune function. Small, preliminary trials of GSK-1605786 were promising, and a larger trial for treatment of moderate to severe Crohn's disease is now under way. Mayo Clinic in Minnesota is one of the sites of the GlaxoSmithKline-sponsored study.
Janus kinase (JAK) inhibitors modulate signaling for a number of important proinflammatory cytokines. Tofacitinib is a novel oral JAK inhibitor originally developed for the treatment of rheumatoid arthritis that also appears to have some benefit for ulcerative colitis. A multicenter, phase 2 study of 200 patients with UC presented at Digestive Disease Week 2011 showed significant differences in response rates and mean Mayo scores for tofacitinib compared with placebo.
Although there was little difference in adverse events between tofacitinib and placebo at eight weeks — the length of the study — long-term safety will need to be assessed because of the potential for immunosuppression and perhaps for dyslipidemia. A phase 3 trial of tofacitinib for moderate to severe UC has recently gotten underway, with Mayo Clinic in Minnesota as one of the study sites.
Ustekinumab (Stelara) is a human monoclonal antibody that binds to the p40 subunit shared by the interleukin (IL)-12 and IL-23 cytokines. Both cytokines are involved in inflammatory and immune responses. Ustekinumab is approved for the treatment of plaque psoriasis and has performed well in phase 2 studies for Crohn's disease. Additional clinical trials for patients with active Crohn's disease are ongoing, including one at Mayo Clinic in Minnesota sponsored by Janssen Biotech.
Clinical trials at Mayo
Dr. Loftus says, "I want to make it clear that we are always happy to see people on short notice if a referring physician has a patient who seems to be interested in a clinical trial. Ordinarily, we have a waiting list, but will work in potential clinical trial patients as soon as possible."
He adds, "The fundamental difficulty in treating IBD is that we don't understand what triggers the inflammatory process. We're not getting at the root cause; we're simply targeting nodes in the inflammatory pathways that seem important and blocking inflammation at those points. It stands to reason that not all patients will respond to drug A, so the more drugs with different mechanisms of action, the better. (After all), this isn't a disease that lasts 26 weeks. It waxes and wanes over the course of a lifetime, and we need to have different ways to treat it."