In vitro selection of RNA aptamer and specific targeting of ErbB2 in breast cancer cells.

The ErbB family (also referred to as HER/neu or HER) of receptor tyrosine kinases plays major roles in the formation and progression of human tumors. Amplification and/or overexpression of ErbB2 have been reported in numerous cancers, including breast, ovarian, stomach, bladder, salivary, and lung cancers. As ErbB2 has been used as a target for the treatment of advanced cancer, RNA aptamers for the extracellular domain of the ErbB2 were selected from a RNA library consisting of 2'-fluorine-modified RNA transcripts. After 15 cycles of selection, high-affinity RNA aptamer was isolated. Binding patterns of the selected RNA aptamer clones were evaluated to choose RNA aptamers that were specific to the extracellular domain of ErbB2 protein. RNA aptamer 15-8 was the best candidate and its minimal version (mini-aptamer) was chemically synthesized. Surface plasmon resonance measurement showed that the mini-aptamer specifically bound to the ErbB2 protein with high affinity and specificity. To evaluate its potential as an ErbB2-targeting molecule in breast cancer cells, specific recognition of the mini-aptamer was confirmed with various breast cancer cell lines. We propose that the selected RNA aptamer is a potential cancer imaging agent by targeting malignant cells overexpressing the ErbB2 receptor.