trans-Dichloro(triphenylarsino)(N, N-dialkylamino)platinum(II) Complexes: In Search of New Scaffolds to Circumvent Cisplatin Resistance

Abstract

The high incidence of the resistance phenomenon represents one of the most important limitations to the clinical usefulness of cisplatin as an anticancer drug. Notwithstanding the considerable efforts to solve this problem, the circumvention of cisplatin resistance remains a challenge in the treatment of cancer. In this work, the synthesis and characterization of two trans-dichloro(triphenylarsino)(N,N-dialkylamino)platinum(II) complexes (1 and 2) were described. The trypan blue exclusion assay demonstrated an interesting antiproliferative effect for complex 1 in ovarian carcinoma-resistant cells, A2780cis. Quantitative analysis performed by ICP-AES demonstrated a scarce ability to platinate DNA, and a significant intracellular accumulation. The investigation of the mechanism of action highlighted the ability of 1 to inhibit the relaxation of supercoiled plasmid DNA mediated by topoisomerase II and to stabilize the cleavable complex. Cytofluorimetric analyses indicated the activation of the apoptotic pathway and the mitochondrial membrane depolarization. Therefore, topoisomerase II and mitochondria could represent possible intracellular targets. The biological properties of 1 and 2 were compared to those of the related trans-dichloro(triphenylphosphino)(N,N-dialkylamino)platinum(II) complexes in order to draw structure-activity relationships useful to face the resistance phenotype.

Keywords: antiproliferative activity; drug resistance; organometallic complexes; platinum.

Scheme 1

Complexes 1 and 2 and previously studied triphenylphosphine analogues 3 [18] and 4 [22].

Figure 1

View of the molecular structure of cis-[PtCl₂(AsPh₃)(NCMe)]. Thermal ellipsoids are at 30% probability.

Figure 2

Quantitative analysis of platinum (triangles) and phosphorus (circles) bound to DNA performed by ICP-AES. Salmon testes DNA (9 × 10⁻⁴ M) was incubated with 1 for different durations (0–48 h) at [DNA]/[complex] = 10. Mean values ± SD of three experiments in duplicate are reported.

Figure 3

Effect of complex 1 on (a) relaxation of supercoiled DNA by topoisomerase II and (b) stabilization of covalent DNA-topoisomerase II complex. Supercoiled plasmid pBR322 (DNA) was incubated with topoisomerase II in the absence (Topo II) and in the presence of complex 1 at indicated concentrations. 20 μM m-AMSA was used as a poison reference drug.

Figure 4

Platinum (ppb)/Phosphorus (ppb) ratio ([Pt]/[P]) in A2780 (a) and A2780cis (b) cells incubated with 100 μM 1 for 60 and 120 min. Cisplatin is shown as a reference. Mean values ± SD of at least three experiments in duplicate are reported.

Figure 5

Cytofluorimetric analyses in A2780cis cells (3 × 10⁵) incubated for 40 h with complex 1 or cisplatin (cisPt) at indicated concentrations. (a) Mitochondrial transmembrane potential (ΔΨ) in cells loaded with JC-1 (5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolcarbocyanine iodide). (b) Percentage of viable, apoptotic and necrotic cells loaded with Annexin V-FITC and propidium iodide. Values are the mean ± SD of four independent experiments.