Research 

  A Harmless Viral Protein to Treat Atopic Dermatitis
And Related Conditions David A.Paslin, M.D.

david.paslin@ucsf.edu

         

Background

By serendipitous observation, a harmless skin virus, Molluscum contagiosum virus (MCV), was seen to block the expression of atopic dermatitis (AD) induced exfoliative erythroderma. Available data suggest that MCV was able to suppress the dermatitis by delivering an anti-inflammatory protein (MC148p) into the inflamed skin surrounding MCV papules that infected the index case. MC148p consists of 104 amino acids, weighs 8984 daltons and carries a positive charge. The presence of culture proven Staphylococcus aureus infection, superimposed upon the AD, did not prevent MC148p induced inhibition of the dermatitis. The inhibitory effect was sustained over a period of many years. Despite the delivery of MC148p and other MCV proteins into the skin, MCV and its secreted products did not cause any objective or subjective adverse effects.

Mechanism of the Effect

The human body is protected from invasive foreign matter, including infectious organisms, by the immune system. Among the many components of this system are proteins called chemokines. Chemokines are constructed in such a manner as to attract inflammatory cells which control or destroy the invading infectious organisms. The inflammatory cells have receptor proteins in their surface membranes which allow these cells to respond to and move toward the chemokine signals. MC148p structurally resembles some of these chemokines, called cc-chemokines. One of these cc-chemokines is called CCL1 (I-309). CCL1 attracts inflammatory cells whose surface membranes carry the receptor protein called CCR8. During certain kinds of skin inflammation, including AD, cells in the skin make and release CCL1. Indeed CCL1 is elevated in the peripheral blood of patients with AD. As a result of CCL1 release, inflammatory cells expressing CCR8 move toward the CCL1 signaling in the inflamed skin. MC148p, by mimicking CCL1, acts by binding to the CCR8 receptor protein with higher affinity than CCL1 in such a manner as to block the movement of inflammatory cells expressing CCR8 toward the inflamed atopic skin. This results in a striking reduction of several types of inflammatory cells in the atopic skin and a marked improvement of the dermatitis, leaving the appearance of normal skin both by clinical and microscopic assessment.

Therapeutic Applications

Similar to biologics used to treat such diseases as psoriasis, rheumatoid arthritis and Crohn’s disease, MC148p may be administered by subcutaneous injections. (“Biologics” are extracts of products of living cells.) MC148p may be used to treat conditions such as moderate to severe atopic dermatitis as well as other diseases in which the CCR8 pathway is involved. Such other diseases may include prurigo nodularis, nummular dermatitis, forms of asthma, multiple sclerosis, and arteriosclerotic cardiovascular disease. This is because macrophages expressing CCR8 may be involved in the pathogenesis of these diseases.

Although MC148p may be administered by injection, it cannot be delivered topically. As an unmodified protein, MC148p does not penetrate intact skin. However, as the fusion protein MC148fp, MC148p retains its capacity to block migration of inflammatory cells specific to those expressing the chemokine receptor CCR8 while also being able to penetrate human neonatal foreskin. The experimental model of human neonatal foreskin was chosen because neonatal skin shares crucial characteristics of atopic dermatitis skin. MC148pf consists of MC148p to which is added a small chain of mostly basic amino acids called the TAT sequence toward the carboxyl terminal of MC148p. (“Basic” means that these amino acids carry a positive charge.) Attached to the 11 amino acid TAT sequence and ending the fusion protein is a string of 6 histidines which enables the localization of MC148fp in the skin. In addition there is evidence that the histidines may add to the therapeutic effect. In brief the structure of MC148fp is MC148p-TAT-6xHis.

Current Status

The serendipitous observation has been made. The MCV from the index case has been harvested, its DNA separated and the MC148 gene amplified and isolated. Using the baculovirus SF9 insect cell expression system, recombinant MC148p (rMC148p) has been prepared. [Note non-recombinant/synthetic MC148p and segments of MC148p have been tested and are functionally ineffective.] The inhibitory activity of rMC148p has been proven using chemotaxis assays of cells expressing CCR8. Continuing the use of the baculovirus SF9 insect cell expression system, codons for the transcription of TAT and 6xHistidine for attachment to the carboxyl terminus of rMC148p were added into the polymerase chain reaction primers to generate recombinant MC148fp (rMC148fp). This fusion protein also showed significant inhibitory activity in that it too blocks the migration of cells expressing CCR8 in chemotaxis assays. In conclusion, functional effectiveness of both rMC148p and rMC148fp have been shown in chemotaxis assays. Furthermore penetration of rMC148fp into neonatal foreskin has been shown. For proof of concept, MC148fp will be rubbed into the surface of atopic dermatitis skin in human volunteers. Penetration and therapeutic effect are expected. No adverse effects from this fusion protein are anticipated.

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