Preparation of Ru(ii)@oligonucleotide nanosized polymers as potential tumor-imaging luminescent probes

Abstract

The development of Ru(ii) complexes as luminescent probes has attracted increasing attention in recent decades. In this study, the nanosized polymers of two Ru(ii) complexes [Ru(phen)₂(dppz)](ClO₄)₂ (1, phen = 1,10-phenanthrolin; dppz = dipyrido[3,2-a:2',3'-c]phenazine) and [Ru(phen)₂(Br-dppz)](ClO₄)₂ (2, Br-dppz = 11-bromodipyrido[3,2-a:2',3'-c]phenazine) with oligonucleotides were prepared and investigated as potential tumor-imaging probes. The formation of the nanosized polymers, which had an average width of 125-438 nm and an average height of 3-6 nm, for 1 and 2@oligonucleotides were observed through atomic force microscopy. The emission spectra indicated that the luminescence of 1 and 2 markedly increased after binding to oligonucleotides and double-strand DNA (calf thymus DNA), respectively. Moreover, further studies indicated that 1@oligonucleotides and 2@oligonucleotides can easily enter into tumor cells and selectively highlight the tumor area in the zebrafish bear xenograft tumor (MDA-MB-231). In summary, this study demonstrated that 1@oligonucleotides and 2@oligonucleotides could be developed as potential tumor-imaging luminescent probes for clinical diagnosis and therapy.

Scheme 1. Molecular structures of 1 and 2.

Fig. 1. (A) AFM images of oligonucleotides after being treated by 1 (in pH 7.2 Tris–HCl KCl buffers). (B) AFM images of oligonucleotides after being treated by 2 (in pH 7.2 Tris–HCl KCl buffers). (C) AFM images of CT-DNA after being treated by 1 (in pH 7.2 Tris–HCl NaCl buffers). (D) AFM images of CT-DNA after being treated by 2 (in pH 7.2 Tris–HCl NaCl buffers). [Ru] = 100 μM, [oligonucleotides] = 100 μM, [CT-DNA] = 100 μM.

Fig. 2. (A) Changes in the luminescence intensities of 1 and 2 in the absence and presence of oligonucleotides. [Ru] = 100 μM, [oligonucleotides] = 0.067n μM, n = 0, 1, 2…, (in pH 7.2 Tris–HCl KCl buffers). (B) Changes in the luminescence intensities of 1 and 2 in the absence and presence of CT-DNA. [Ru] = 100 μM, [CT-DNA] = 0.067n μM, n = 0, 1, 2…, (in pH 7.2 Tris–HCl NaCl buffers).

Fig. 3. (A) The relative intensity (I/I₀) of 1 and 2 with increasing concentration of oligonucleotides or CT-DNA. [Ru] = 20 μM, [oligonucleotides] = 0.067n μM, n = 0, 1, 2…, [CT-DNA] = 0.067n μM, n = 0, 1, 2…, (in pH 7.2 Tris–HCl KCl or NaCl buffers). (B) Hypochromic effect of the changes of 1 and 2 between oligonucleotides and CT-DNA, [Ru] = 20 μM, [oligonucleotides] = 100 μM, [CT-DNA] = 100 μM, (in pH 7.2 Tris–HCl KCl or NaCl buffers).

Fig. 4. (A) Electronic spectra of 1 and 2 in the absence and presence of oligonucleotides in the Tris–HCl KCl buffer (pH 7.2). ([Ru] = 20 μM, [oligonucleotides] = 0.067n μM, n = 0, 1, 2…); (B) electronic spectra of 1 and 2 in the absence and presence of CT-DNA in the Tris–HCl NaCl buffer (pH 7.2). ([Ru] = 20 μM, [CT-DNA] = 0.067n μM, n = 0, 1, 2…).

Fig. 5. (A) CD titration spectra of oligonucleotides with increasing amounts of 1 and 2 in the incubation buffer, [Ru] = 0, 2.660, 5.305, 7.937, 10.554, 13.158, 15.748, 18.325 μM, [oligonucleotides] = 100 μM. (B) CD titration spectra of CT-DNA with increasing amounts of 1 and 2 in the incubation buffer, [Ru] = 0, 2.660, 5.305, 7.937, 10.554, 13.158, 15.748, 18.325 μM, [CT-DNA] = 100 μM.

Fig. 6. Selectively imaging tumor cells by Ru(ii)@oligonucleotide in vitro and in vivo. (A) MDA-MB-231 cells imaging of 1, 1@oligonucleotide and 1@CT-DNA at 37 °C for 24 h. (B) MDA-MB-231 cells imaging of 2, 2@oligonucleotide and 2@CT-DNA at 37 °C for 24 h. (C) Tumor area highlighted by 1@oligonucleotide and 2@oligonucleotide in zebrafish xenografts model. ([Ru] = 2.5 μM, [oligonucleotides] = 2.5 μM).