In vitro selection of DNA aptamers against human osteosarcoma.

BACKGROUND: Osteosarcoma is a highly malignant bone tumor, most frequently occurring in the rapid bone growth phase. Effective treatment of this disease is hindered by the lack of specific probes for early diagnosis and the fast cancer widespread. METHODS: To find such probes, the cell-Systematic Evolution of Ligands by EXponential enrichment (cell-SELEX) methodology was implemented against the human osteosarcoma MG-63 cell line towards the selection of new specific aptamers. After 10 rounds of selection, the aptamer DNA pool was Sanger sequenced and the sequences were subjected to a bioinformatic analysis that included sequence alignment, phylogenetic relationship, and secondary structure prediction. RESULTS: A DNA aptamer (OS-7.9), with a dissociation constant (Kd) value in the nanomolar range (12.8 ± 0.9 nM), revealed high affinity against the target cells at the physiological temperature. Furthermore, the selected aptamer also recognized lung carcinoma and colon colorectal adenocarcinoma cell lines, which are reported as common metastasis sites of osteosarcoma. CONCLUSIONS: These results suggest that OS-7.9 could recognize a common protein expressed in these cancer cells, possibly becoming a potential molecular probe for early diagnosis and targeted therapies for metastatic disease. Moreover, to the best of our knowledge, this was the first attempt to generate a DNA aptamer (OS-7.9 aptamer) against the MG-63-cell line by cell-SELEX.

Microfluidic immobilized metal affinity chromatography based on Ti(IV)-decorated silica microspheres for purification of phosphoproteins.

A silica-based immobilized metal affinity chromatography (IMAC) sorbent with the morphological properties suitable for purification of large phosphorylated biomolecules was synthesized. The sorbent was designed in the form of monodisperse-porous silica microspheres, 5.3 µm in size, having bimodal pore size distribution with a large median pore size (40 nm) and high surface area (163 m2/g) decorated with Ti(IV) cations (i.e. Ti(IV)@THSPMP@SiO2 microspheres). The decoration of silica microspheres with Ti(IV) cations was made by using 3-(trihydroxysilyl)propyl methylphosphonate (THSPMP) as a bifunctiontional linker, by preserving their bimodal pore size distribution. The mesopores provided a large surface area for parking of adsorbed phosphoproteins as large phosphorylated biomolecules while the intraparticular transport of phosphoproteins was facilitated by the macropores providing a large median pore size. High equilibrium adsorption capacity and high desorption yield in the purification of phosphoproteins were obtained using Ti(IV)@THSPMP@SiO2 microspheres as the sorbent in batch- and microfluidic-IMAC systems. The phosphoproteins, α-casein and ß-casein were isolated from milk and human serum with almost quantitative yields and high purity in the batch IMAC system. The appropriate microcolumn permeability (3.66 × 10-14 m2) originating from its appropriate average diameter (5.3 µm), high porosity (0.948 cm3/g) and high surface area (163 m2/g) of Ti(IV)@THSPMP@SiO2 microspheres makes the synthesized sorbent a promising stationary phase for dynamic chromatography. Hence, a new phosphoprotein enrichment format, a microfluidic IMAC system was constructed and successfully operated for highly selective purification of phosphoproteins from non-fat milk as a complex sample. The microfluidic-IMAC system is a promising tool particularly for phosphoproteomic applications performed using samples in microliter or nanoliter scale, also involving an on-line connection of purification unit to LC-MS for the identification of large phosphorylated biomolecules enriched.