Carrier effect of cyclodextrins vs CNTs for tumour cells grown in vitro using a trithiacyclononane ruthenium complex as model guest
Susana S. Braga,* Joana Marques, Elena Heister, Cátia V. Diogo, Paulo J. Oliveira, Filipe A. Almeida Paz, Teresa M. Santos, Maria Paula M. Marques
Electronic Supplementary Information
S1. Interaction of compound 1 with CNTs , UV-Vis spectrometry
S1.1. Optical properties of the Ruthenium compounds
Absorption spectra were recorded using a Helios Alpha UV/Vis spectrophotometer (Thermo Scientific).
A dilution series of the two compounds was prepared at concentrations ranging from 20 to 80 µM. Figure S1 shows the optical absorption spectra of the complexes, recorded at wavelengths between 190 and 600 nm. The spectrum of [Ru[9]aneS3(dppz)Cl]Cl presents absorption maxima at 206, 277, and 355 nm, as well as a shoulder around 430 nm. The spectrum of [Ru[9]aneS3(pdon)Cl]Cl (1) features peaks at 205, 296, and 415 nm.
Figure S1. UV/vis absorption spectra of a) [Ru[9]aneS3(dppz)Cl]Cl, featuring maxima at 206, 277, and 355 nm and b) [Ru[9]aneS3(pdon)Cl]Cl (1), featuring maxima at 205, 296, and 415 nm.
The absorbance values at the three peak maxima of each compound were plotted against the concentration to determine the molar extinction coefficients at these wavelengths. In the case of [Ru[9]aneS3(dppz)Cl]Cl, the obtained molar extinction coefficients were about 34,000 Lmol-1cm-1 (206 nm), 29,000 Lmol-1cm-1 (277 nm), and 8,000 Lmol-1cm-1 (355 nm) and in the case of the complex 1, about 34,000 Lmol-1cm-1 (205 nm), 11,000 Lmol-1cm-1 (296 nm), and 3,000 Lmol-1cm-1 (415 nm)
S2. Loading of the complexes 1 and [Ru([9]aneS3)(dppz)Cl]Cl onto oxCNTs
Figure S2 shows the results of the binding tests carried for the complex 1 (denoted here as Rupdon) and its analogue with a more extended conjugated π-π system, [Ru([9]aneS3)(dppz)Cl]Cl (denoted here as Ru-dppz). Aside from the points corresponding to weight ratios of CNT to the Ru complex within acceptable therapeutic values (region marked with a red arrow), other rations were also tested, with lower amounts of Ru complex and therefore excess of CNT, making them lie outside effective therapeutic concentrations.
Fig. S2 - Binding of 1 and Ru-dppz to oxCNTs at different weight ratios of Ru-complex/CNT (n=3). The Ru complexes are designated using the term “drug” in the chart. Binding is only observed for low drug/CNT ratios, but not for therapeutic concentrations (starting at ratios of 20:1).
The lower the ration of Ru-complex/CNT , that is, the higher the percentage of CNTs in the mix, the higher the drug binding. In the case of Ru-dppz, almost 100% binds to the nanotubes at a ratio of 1:2, whereas at the same ratio, only 60% binding is achieved for Ru-pdon. This is likely due to Ru-pdon’s structure, which has a less extended conjugated p-electron system than Ru-dppz and is thus less likely to participate in p-p interactions with the CNT surface. A binding of 100% for Ru-pdon could possibly be achieved at even lower Ru-pdon/CNT ratios.
A major issue is, however, that the cytotoxic concentrations of both the Ru complexes are in the range of 200 – 1000 µM or 100 – 500 µg/mL, respectively, whereas CNT concentrations commonly used in cell viability assays are app. 10 µg/mL in order to avoid material-related cytotoxicity. This would correlate with ratios of about 10:1 – 50:1 or higher. However, as Figure S2 shows, the percentage of binding of the Ru complexes to the carbon nanotubes at these ratios is zero. To obtain higher drug binding, one would have to increase the CNT concentration - however, in order to obtain > 80% drug binding, CNT concentrations of 2,000-5,000 µg/mL would be required, which is far out of the suitable range for biological applications due to CNT-related cytotoxicity. All in all, this indicates that carbon nanotubes are not a suitable delivery system for the two drugs investigated in this report.