High expression of integrin αvβ3 enables uptake of targeted fluorescent probes into ovarian cancer cells and tumors

Abstract

The cell line OVCAR-4 was recently ranked as one of the most representative cell lines for high grade serous ovarian cancer (HGSOC). However, little work has been done to assess the susceptibility of OVCAR-4 cells and tumors to the more common types of molecular targeting. Proteome profiles suggest OVCAR-4 express high levels of integrin αvβ3 receptors. Using flow cytometry with fluorescent antibodies we determined that OVCAR-4 cells have high number of integrin αvβ3 receptors ([9.8 ± 2.5] × 10⁴/cell) compared to the well-characterized cell line U87-MG ([5.2 ± 1.4] × 10⁴/cell). However, OVCAR-4 cells also have roughly three times the surface area of U87-MG cells, so the average αvβ3 receptor density is actually lower (11 ± 3 versus 18 ± 6 receptors/µm²). A series of new fluorescent molecular probes was prepared with structures comprised of a deep-red squaraine fluorophore (∼680 nm emission) covalently attached to zero, one, or two cyclic pentapeptide cRGD sequences for integrin targeting. Microscopy studies showed that uptake of the divalent probe into cultured OVCAR-4 cells was 2.2 ± 0.4 higher than the monovalent probe, which in turn was 2.2 ± 0.4 higher than the untargeted probe. This probe targeting trend was also seen in OVCAR-4 mouse tumor models. The results suggest that clinically relevant OVCAR-4 cells can be targeted using molecular probes based on αvβ3 integrin receptor antagonists such as the cRGD peptide. Furthermore, deep-red fluorescent cRGD-squaraine probes have potential as targeted stains of cancerous tissue associated with HGSOC in surgery and pathology settings.

Keywords: Cancer; Cyclic peptide; Integrin; OVCAR-4; Squaraine dye.