This space represents the ideas, views, opinions, projects and data of researchers within the Aptamer Stream of the Freshman Research Initiative, a program developed at the University of Texas at Austin. These are projects we currently have in the pipeline.
- We're not exclusive...we are SELECTIVE!
Nucleic Acid Aptamer Selection Against
Tie-2 to Limit Tumor Growth
A tumor is a population of cancer cells,
or cells that stop dividing in an orderly manner and start rapidly growing,
dividing, and gaining mutations.
However, due to a lack of nourishment, lone tumors cannot grow past one
or two cubic millimeters (1).
In order to grow larger, tumors require nutrients, which are usually
delivered though blood vessels.
Tie-2, a receptor tyrosine kinase, is an
endothelial cell surface receptor that binds to angiopoietins and mediates cell
signaling through phosphorylation and binding and activation of enzymes (2). An angiopoietin is a protein growth factor
required for angiogenesis, the formation of blood vessels. Angiopoietins function by binding receptor
tyrosine kinases, such as Tie-2, which is mandatory for normal embryonic
vascular development and tumor angiogenesis (3). While angiogenesis is vital in the healing of
wounds, it also serves in the growth and transition of tumors from dormant to
malignant, as well as contributing to metastasis. Tie-2, by mediating the effects of
angiopoietins, is an integral receptor in the pathway of blood vessel formation
As tumors are nourished and led through
metastasis, the process becomes more agonizing for cancer patients and doctors
alike. To manage this there are general
antibody treatments available, but another method of therapy is possible. Such a possibility comes in the form of an
aptamer, which is a short sequence of nucleic acids that binds with great
specificity and strength to a particular target. Isolated in
vitro from vast libraries of sequences, aptamers can fold into tight
binding pockets for nearly any molecule (5). Aptamers are expected to be able to bind
Tie-2; an aptamer that blocks the binding site of angiopoietins would reduce
signaling vital to the growth of tumors by angiogenesis. In this respect, an aptamer would be
beneficial in cancer treatment and therapy by limiting the progression of
tumors in early stages.
Specific Aim 1:
RNA aptamer selection against Tie-2
RNA aptamers are selected through
the SELEX (Systematic Evolution of Ligands by Exponential Enrichment) process (6). Tie-2 proteins are functionalized with 6X
Histidine tags, lending to use of Nickel-NTA magnetic beads in the process of
Specific Aim 2:
Develop an aptamer therapeutic to limit tumor growth
the binding of the angiopoietins, Tie-2 provides the signaling essential to
angiogenesis. Tie-2 also mediates the
actions of angiopoietins in their prevention of apoptosis, further aiding the
growth of blood vessels (7).
An aptamer selected against Tie-2 may inhibit the receptor, thus
suppressing the development and spreading of tumors by depriving the pathway of
the required signaling.
The progression from Tie-2 to tumor growth.
A comparison is shown between an
angiopoietin and an aptamer in binding to Tie-2.
Human Tie-2 with a 6-His tag is available online from R&D Systems
(rndsystems.com). The catalog number is
313-TI-100 and the price is $340 for 100 micrograms. The
protein is 165 kDa and is to be resuspended at 100 ug/mL; this will provide six
rounds of selection at approximately $56 per round, if using 100 pmol per
S.R, Anderson, A.R.A., Chaplain, M.A.J., (2006) “Mathematical modelling of
dynamic adaptive tumour-induced angiogenesis: Clinical implications and
therapeutic targeting strategies.” Journal
of Theoretical Biology. 241.
M., Nelson, D.R. (2008). Lehninger: Principles of Biochemistry (fifth
ed.). W H Freeman & Co.
3. National Library of Medicine – Medical Subject Headings,
(2011). “Receptor, Tie-2.”nlm.nih.gov.
4. Fagiani, E., Christofori, G., (2012).
“Angiopoietins in Angiogenesis.” Cancer Lett. Ahead of print.
5. Famlouk, M., Hartig, J.S., Mayer, G.,
(2007). “Functional aptamers and aptazymes in biotechnology, diagnostics, and
therapy.” Chem Rev. 107:3715-43.
Ellington, A.D. Szostak, J.W., (1990.) “In vitro selection of RNA molecules
that bind specific ligands.” Nature.
7. Milner, C.S., Hansen, T.M., Singh, H.,
Brindle, N.P., (2009). “Roles of the
receptor tyrosine kinases Tie1 and Tie2 in mediating the effects of
angipoietin-1 on endothelial permeability and apoptosis.” Microvasc Res. 77:187-91.