Polymerization of deoxy HbS, although a primary consequence of Val-6(Beta), involves a cooperative participation other intermolecular contact sites. The potential ability to introduce and express genes in appropriate target cells has increased the interest in gene therapy of sickle cell disease. One strategy involves the expression of anti-sickling hemoglobins to perturb the lateral contact sites in the polymer. Design of anti-sickling hemoglobins with super inhibitory potential (compared to the pardigmatic HbF) could realize clinical benefits at low levels of expression. The preliminary studies have demonstrated that non-human alpha-chains of mouse and, in particular, of swine strongly inhibit polymerization by complementary effects of many sequence differences (linked multi-site perturbations). The investigators hypothesize that it is possible to optimize this phenomenon by selecting across species, the best linked multi-site sequence differences. The investigators have generated chimeric HbS containing non-human alpha- chains as well as chimeric alpha-chains exhibiting multiple sequence differences The well as chimeric alpha-chains exhibiting multiple sequence differences (compared with human), designed to map such linked multisite perturbations. The modular construction of alpha-globin chains (using a minimum of two and a maximum of five modules) through protease mediated splicing of the complimentary segments of human and/or non-human alpha- chains will be used as the primary approach to generate chimeric a-chains. The a-chains of monkey, horse, mouse, and swine containing 4, 18, 19 and 22 sequence differences, respectively, have been chosen for the initial studies. These chimeric chains will be used to define the intra- tetrameric functional complementarity of the sequence differences introduced into the cis and trans dimers to increase the inhibition of polymerization. Chimeric hemoglobins will be tested for conformational differences that could alter their function. The super-inhibitory alpha- chains will be hybridized with BetaA chains with sequence differences in the acceptor pocket region and/or the axial contact regions to enhance the inhibitory influence of the anti-sickling Hb. The investigators project that gene constructs of such super-inhibitory hemoglobins could be a welcome addition to the armamentarium for the gene therapy of sickle cell disease.
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