Protein kinase C (PKC) is an enzyme involved in the regulation of cellular growth and differentiation. Hegemann et al1 tested various PKC inhibitors in an immortalized keratinocyte cell culture. They showed that the degree of inhibition of cell proliferation was proportional to the potency of PKC inhibition. The authors speculated that PKC inhibitors might be effective for treatment of psoriasis.
Hegemann et al showed that polymyxin B is a relatively potent inhibitor of PKC; however, unlike the other PKC inhibitors tested, polymyxin B caused little inhibition of cell proliferation in their culture system. Hegemann et al suspected that the polar polymer structure of polymyxin B prevented its penetration through keratinocyte cell membranes.
Polymyxin B is in common use in over-the-counter preparations with an excellent safety record. Despite its poor inhibition of cell proliferation in culture, we performed a double-blind, randomized, bilateral, vehicle-controlled study comparing the effectiveness of topical polymyxin