In Vitro and In Vivo Investigations into the Carbene Silver Acetate Anticancer Drug Candidate SBC1

Iduna      Fichtner; Jindrich      Cinatl; Martin      Michaelis; Lara      C. Sanders; Ralf      Hilger; Breandan      N. Kennedy; Alison      L. Reynolds; Frauke      Hackenberg; Grainne      Lally; Susan      J. Quinn; Ian      McRae; Matthias      Tacke

Abstract

The anticancer drug candidate (1-methyl-3-(p-cyanobenzyl)benzimidazole-2-ylidene)silver(I)acetate (SBC1) was tested in vitro against human neuroblastoma cells, UKF-NB-3 and UKF-NB-6, delivering IC50 values of 29 +/- 5 and 29 +/- 4 μM, while further testing against cisplatin-, carboplatin- and oxaliplatin-resistant UKF-NB-3/6 sub-lines showed no cross-resistance with respect to SBC1. A similar trend was found for SBC1 against the human colon carcinoma cell line HCT8 with an IC50 value of 3.1 +/- 0.9 μM; SBC1 was again able to break cisplatin- and carboplatin-resistance in the corresponding sub-lines. SBC1 was also tested against the prostate cancer cell line PC-3 and its paclitaxel-resistant sub-line, which gave IC50 values of 14.1 +/- 0.9 and 14.5 +/- 0.8 μM, which indicated no cross-resistance with paclitaxel. In order to test the possible transport of SBC1 via albumin the binding of SBC1 against this transport protein was measured using a fluorescence titration, which gave an ΔG value of 28 +/- 3 kJ/mol. In circular dichroism and DNA denaturation assays SBC1 proved to be a strongly DNA-binding drug candidate. SBC1 was then given at 25 and 50 mg/kg/d, in four injections to two cohorts of eight CAKI-1 tumor-bearing NMRI:nu/nu mice, while a further cohort was treated with solvent only. At these two dosages SBC1 showed a borderline toxicity leading to mortality and body weight loss, while no significant tumor growth reduction or influence on blood parameter with respect to the solvent-treated control group was observed. Further in vivo testing against zebrafish larvae revealed significant toxicity of SBC1 at micromolar concentrations; no useable anti-angiogenic dosage was observed.

Keywords: Anticancer drug, Anti-angiogenic drug, Carbene-silver complex, Renal cell cancer, Albumin-binding assay, DNAbinding assay, Xenograft mouse model, Zebrafish intersegmental vessel assay