Our work has showed that schistosome cercariae are aided in invasion of host skin by a secreted protease. Transcription of the gene coding for this protease is developmentally regulated to the sporocyst stage when cercariae are differentiating. Newly synthesized protease is a proenzyme stored in the acetabular cells of cercariae until cercariae are stimulated to invade the host by lipid on the surface of host skin. Immunolocalization studies show that the enzyme is then slowly released during the course of cercarial migration through host skin. We have concentrated on two of our major aims. First, we have continued to test the effect of specific inhibitors, designed by computer graphics analysis of the enzyme active site, for their ability to inhibit cercariae from invading human skin. In previous work, we had confirmed that inhibitors of the enzyme will in fact inhibit cercarial penetration. Our more recent work has concentrated on optimizing a formulation that will allow inhibitors to remain on the surface of skin while it is immersed in water. This would lead to a lotion, not unlike water-resistant sunblocks, that could be used in association with other control measures in endemic areas, or by tourist and military personnel. Two types of formulations were tested. The first is an isopropyl alcohol/propylene glycol-based formulation designed by Professor Richard Guy of the Department of Dermatology and Pharmaceutical Chemistry at UCSF. We have been analyzing variations in the formulation to maximize aqueous stability, while at the same time ensuring that the inhibitor remains at the surface of skin and cannot enter the bloodstream, minimizing any toxicity. We have been successful in blocking cercarial penetration utilizing the inhibitor 2-(4-methoxy benzoyl)-4-naphthoic acid). Our next goals are to assay a group of the most effective inhibitors in this formulation to determine what is the optimal coupling of inhibitor and lotion. At the same time, we have recently entered into a collaboration with Penederm, Inc.; Penederm used formulations with our group of inhibitors as we have done previously with the isopropyl/propylene glycol lotions. Another goal of our research has been to clone the homologues of the Schistosoma mansoni cercarial protease from cDNA or genomic DNA of S. haematobium, S. japonicum, and Schistosomatium doutthiti. Over the past year we have been successful in this endeavor. We have isolated gene fragments corresponding to the cercarial protease of each of these species, and we made one unexpected discovery. S. haematobium has two genes coding for the cercarial protease, whereas S. mansoni has only one. We are now in the process of utilizing these gene fragments as probes of both cDNA and genomic libraries for these organisms. We have produced cDNA libraries from sporocysts of S. doutthiti and S. haematobium. We have genomic libraries for S. haematobium and S. japonicum. One of our next goals will be to isolate the full length genes or c DNAs coding for these homologous proteases and then compare them biochemically to their S. mansoni homologue following expression of recombinant protease in bacteria or yeast. During the past year we have also produced monospecific antisera to a synthetic peptide representing the proenzyme domain of the cercarial protease. This reagent will be used in our proposed studies to try to identify the site of zymogen activation during cercarial invasion.
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