Selecting an Aptamer Against the RCAS1 Biomarker for a Novel Tool in the Diagnosis and Treatment of Cancer

Daniel Liaou

          RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is a protein expressed by the EBAG9 (estrogen receptor-binding fragment-associated gene 9) gene¹. Overexpression of this biomarker has been identified to be present in nearly all gastric cancers­² and the degree of overexpression has been shown to be indicative of the prognosis in 14 different types of cancer. In addition to this, levels of RCAS1 have been linked to "clinicopathological parameters including the histological type of cancer, its differentiation, tumor size, clinical stage, [and] the depth of invasion..."³ RCAS1 is also a biologically active molecule. For example, in gastric cancers, it has been implicated to facilitate tumor cell evasion of the immune system via growth-inhibition and apoptosis-induction in lymphocytes expressing the receptor for the antigen³. Another role that has been associated with RCAS1 is remodeling of connective tissue⁴. The capability of remodeling connective tissue is an essential factor contributing to tumor malignancy and eventual metastasis - the ultimate cause of death in over 90% of cancers⁵.

            Aptamers, short sequences of RNA or DNA, provide a double-faceted approach to utilizing the RCAS1 protein. First, because of the high affinity and specificity of aptamers as well as their relative ease of production, an aptamer selected against RCAS1 could provide a high-yield method of detecting RCAS1 levels and a novel test for diagnosing cancers associated with its overexpression. If a cancer is found to be present, additional qualitative information could be revealed relating to the disease progression. Second, because of the innate specificity which is required for antigens to trigger a response, a selected aptamer that can bind uniquely to and alter the surface of RCAS1 holds the potential to suppress key mechanisms in cancer development by targeting key steps in the disease pathway dependent on the biological role RCAS1. With its close association and implicated roles in a number of different cancers, an aptamer against RCAS1 would provide medically-relevant tools in a number of clinical contexts.

Specific Aim 1: Select an RNA aptamer against the RCAS1 protein using Systematic Evolution of Ligands by Exponential Enrichment (SELEX).

Specific Aim 2: Modify the aptamer for use in diagnostic tests for RCAS1-associated cancers. Once an aptamer is isolated that can discriminately identify RCAS1 in a complex fluid, it can be used to detect RCAS1 levels that would implicate the presence of cancer (Figure 1).

Specific Aim 3: Modify the aptamer to be an inhibitor of RCAS1. If RCAS1 plays a key biological role in the pathogenesis of the cancer, aptamer-inhibition could be used therapeutically to impede the progression of the disease (Figure 2).

             The RCAS1 protein will be ordered from Creative Biomart at a cost of $265.00 per 100 ug, which corresponds to a cost of $12.40 per round. The catalog number is EBAG9-26510TH at the http://www.creativebiomart.net/ website. The contact phone number is 1-631-559-9269.



References

1. Nakashima, Manabu, Kenzo Sonoda, and Takeshi Watanabe. "Inhibition of cell growth and induction of apoptotic cell death by the human tumor-associated antigen RCAS1." Nature Medicine. 5.8 (1999): 940. Web. 29 Aug. 2013.

2. Bohunicky, Brian, and Shaker Mousa. "Biosensors: the new wave in cancer diagnosis." Nanotechnology, Science and Applications. 2011.4 (2010): 4. Web. 29 Aug. 2013

3. Sonoda, Kenzo, Shingo Miyamoto, Manabu Nakashima, Norio Wake. "The Biological Role of the Unique Molecule RCAS1: A Bioactive Marker that Induces Connective Tissue Remodeling and Lymphocyte Apoptosis." Frontiers in Bioscience. 13 (2008): 1106-16. Web. 29 Aug. 2013.

4. Nakamura, Yuichi, Koichi Yamazaki, Satoshi Oizumi, Manabu Nakashima,Takeshi Watanabe, Hirotoshi Dosaka-Akita, and Masaharu Nishimura. "Expression of RCAS1 in human gastric carcinoma: A potential mechanism of immune escape." Cancer Science. 95.3 (2004): 260–265. Web. 29 Aug. 2013.

5. Cox, Thomas, and Janine Erler. "Remodeling and homeostasis of the extracellular matrix: implications for fibrotic diseases and cancer." Disease Models and Mechanisms. 4.2 (2011): 165-178. Web. 29 Aug. 2013.


Click here to view full target proposal.
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Click here to view Progress Report 1.
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Click here to view Final Report.
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