Therapeutic application of genetic association results: CF lung disease modifiers as a model

Case Western Reserve University, Cleveland OH

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Abstract

Project Summary/Abstract Despite recent therapeutic advances, patients with cystic fibrosis (CF) have an average lifespan of less than 40 years. The major cause of morbidity and mortality in CF patients is progressive pulmonary disease. Thus, there remains a strong clinical need for improved CF therapies particularly in regards to CF pulmonary disease. In a GWAS surveying over 6,000 CF patients, we found that alleles of the type-2 angiotensin II receptor gene, AGTR2, and alleles of a microtubule regulating protein, tubulin polymerization promoting protein (TPPP), significantly associate with CF pulmonary function (p<1.7x10-7). TPPP promotes tubulin polymerization and also enhances tubulin acetylation through inhibition of histone deacetylase 6 (HDAC6), a deacetylase that targets microtubules. This proposal explores the clinical potential of these two distinct candidate targets (AGTR2 and HDAC6). Our preliminary data indicate that loss of Agtr2 in the CF mouse (CF/Agtr2 double knockouts) results in a reversal of the impaired pulmonary mechanics detected in CF mouse models. In addition, loss of Hdac6 in the CF mouse (CF/Hdac6 double knockouts) results in improved growth and survival, and attenuation of the inflammatory response characteristic of CF mice. The therapeutic potential of these two targets is apparent: null alleles of Agtr2 and Hdac6 each prevent different aspects of CF mouse airway and other CF-associated phenotypes independently, but it is currently unclear how they impart their beneficial effects, or whether these benefits are achievable pharmacologically. These proteins and their pathways not only represent new therapeutic targets, but ones that may act additively or synergistically with each other. Our secondary analysis of the GWAS data has revealed that CF patients carrying the adverse allele at both of these loci (AGTR2 and TPPP) have significantly reduced pulmonary function compared to patients carrying only one adverse genotype, indicating an additive effect of these two pathways on clinical outcomes. Finally, other CF therapies exist, such as small molecule drugs that improve cystic fibrosis transmembrane conductance regulator (CFTR) processing and activity. While beneficial, these new therapies are by no means curative, and often limited to patients carrying specific CFTR mutations. Therefore, additional therapies, designed to benefit CF patients regardless of CFTR genotype, are warranted. The hypothesis of this study is that targeting both GWAS identified pathways, AGTR2 and HDAC6, with small molecule antagonists will have complementary benefits to multiple CF phenotypes independent of CFTR genotype. The potential benefits of these antagonists in combination with CFTR modulating compounds will also be explored. These results could inform the development of a clinical trial designed to translate this genetic information to therapeutic benefit for CF patients.