Therapy Analysis - Psoriasis and Skin Cancer
Psoriasis
Chronic plaque psoriasis, an inflammatory skin disease that affects 1-3% of the population, causes red scaly patches to appear on the skin, due to excess cell proliferation and inflammation. One percent of sufferers develop acute generalised pustular psoriasis, a severe condition made famous in the TV series "The Singing Detective", in which Michael Gambon plays a novelist who is hospitalized with a severe case of psoriasis. It is not known what the exact causes of the condition are, and being unpredictable in nature, it waxes and wanes, with wide variations in course progression and severity from person-to-person.
In Turkey, doctor fish, which live in the outdoor pools of spas, are encouraged to feed on the affected areas of psoriatic skin..Despite the fact that the occurrence of psoriasis has been recorded since biblical times, treatment did not show any real improvement until the second half of the 20th century. As yet, there is no cure, but there is now a range of topical, systemic and ultraviolet light-based therapies that can alleviate symptoms and are administered based on the type, location and severity of psoriasis. Topical treatments clear lesions relatively quickly, are usually well tolerated and are effective initial and adjunctive treatments. However, they have to be used repeatedly as they rarely maintain remission, and they do not successfully treat large areas of skin. Dithranol, a DNA replication inhibitor derived from the bark of the araroba tree, has been used to treat psoriasis for over a century, as has salicyclic acid, which is a keratolytic that helps shedding of excess skin to reduce thickening and scaling of the plaques. Topical vitamin D derivatives were introduced in the 1990s and can be more effective than dithranol, while steroids, administered topically and orally, have been prescribed for psoriasis since the 1950s. Corticosteroids are the most commonly-prescribed short-term treatments for psoriasis in many parts of the world, and act by decelerating the growth of skin cells and decreasing lesion inflammation.
Photochemotherapy such as psoralen combined with UVA therapy was introduced in the 1970s, and can be a very efficacious; however, there is an associated risk of photoageing and skin cancer. Psoriasis which is resistant to topical treatment and phototherapy can benefit from systemic medications such as the anticancer treatment methotrexate, which inhibits folic acid metabolism, and has been used for the treatment of psoriasis since the 1980s, and the immunosuppressant ciclosporin has similar efficacy in clearing lesions and maintaining remission. However, it too carries the risk of serious adverse events.
The 21st century has seen the introduction of laser treatment and biological therapies as new classes of psoriasis treatment. Biologicals include the cytokineblocking agents etanercept, a recombinant human soluble TNFα receptor, and infliximab, the first chimeric monoclonal antibody against TNFα to be marketed for clinical use. Alternatively, T cell-targeted therapies alefacept, an immunosuppressant approved in Australia, Canada and the US, and efalizumab, a humanized monoclonal antibody, can improve lesion clearance; however, their long term effects are as yet unknown.
Alternative therapy has also been exploited. In Turkey, doctor fish, which live in the outdoor pools of spas, are encouraged to feed on the affected areas of psoriatic skin. This treatment can provide temporary relief of symptoms, but it can become quite costly, as a revisit to the spas every few months is often required!
According to our data, for an 8 year period there were around 30 to 35 drugs in development for psoriasis per year, a figure which has steadily increased since 2003, exceeding 50 in 2006 (Graph 1). Overall, our research has found 173 compounds currently launched or in active development for the treatment of psoriasis, many of which are biological therapies (Graph 2).
