Human Aspartyl (Asparaginyl) Beta Hydroxylase (HAAH) is an overexpressed cell surface enzyme in tumor cells that is closely associated with cancer etiologyincluding cell proliferation, motility, and invasiveness. In keeping with this correlation, we have pursued HAAH as a target for both diagnostic and therapeutic applications. Our monoclonal sandwich ELISA detecting HAAH in serum performs with a clinical specificity and sensitivity greater than 90% to distinguish the presence of cancer. However, we have encountered occasional assay interference by some samples that result in under-detection of HAAH. Trouble shooting and follow-up resulted in the discovery that detectable HAAH resides in the exosomal fraction of serum. Isolation of cancer patient serum exosomes and reconstitution into normal serum or serum-free buffer, results in quantitative recovery of HAAH compared to the original intact serum for most cancer patients. When this exosomal reconstitution is done on false negative cancer patient samples, HAAH detection is restored. The HAAH signal is lost when the exosomal fraction is reconstituted in serum that contains the interfering substance(s). The nature of the interfering substance(s) is yet to be determined but the extraction of HAAH signal producing exosomes from serum improves assay performance. Since exosomes are produced by cells and released into the tumor microenvironment, studying this association with HAAH will help in the understanding of exosomal role in elimination, distribution and other functions in the body. This, in turn, is expected to greatly enhance and expand our development of diagnostic and therapeutic programs targeting HAAH.
Citation Format: Mark A. Semenuk, Eleanor B. Ghanbari, Michael S. Lebowitz, Hossein A. Ghanbari. Quantitative recovery of aspartyl (asparaginyl) beta hydroxylase (HAAH) from an exosomal fraction of human sera from cancer patients. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr B83.
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