Platinum(IV)-Gold(I) Agents with Promising Anticancer Activity: Selected Studies in 2D and 3D Triple-Negative Breast Cancer Models

Abstract

New heterometallic binuclear and trinuclear platinum(IV)-gold(I) compounds of the type [Pt(L)_n Cl₂ (OH){(OOC-4-C₆ H₄ -PPh₂ )AuCl}_x ] (L=NH₃ , n=2; x=1, 2; L=diaminocyclohexane, DACH, n=1; x=2) are described. These compounds are cytotoxic and selective against a small panel of renal, bladder, ovarian, and breast cancer cell lines. We selected a trinuclear PtAu₂ compound containing the Pt^IV core based on oxaliplatin, to further investigate its cell-death pathway, cell and organelle uptake and anticancer effects against the triple-negative breast cancer (TNBC) MDA-MB-231 cell line. This compound induces apoptosis and accumulates mainly in the nucleus and mitochondria. It also exerts remarkable antimigratory and antiangiogenic properties, and has a potent cytotoxic effect against TNBC 3D spheroids. Trinuclear compounds do not seem to display relevant interactions with calf thymus (CT) DNA and plasmid (pBR322) even in the presence of reducing agents, but inhibit pro-angiogenic enzyme thioredoxin reductase (TrxR) in TNBC cells.

Keywords: Chemotherapeutics; TNBC; gold; heterometallic phosphanes; platinum.

Figure 1.

FDA-approved Pt(II)-based square-planar drugs for the treatment of cancer (a-c). Pt(IV) octahedral compound (d), and Au(I) derivative (e) approved for the treatment of rheumatoid arthritis.

Figure 2.

Energy-minimized (DFT) models for heterometallic (PtAu-3) and PtAu₂ compounds (PtAu₂-4 and PtAu₂-5). Color code: white, hydrogen; grey, carbon; red, oxygen; blue; nitrogen; orange, phosphorus; green, chlorine; yellow, gold; metallic grey, platinum.

Figure 3.

Apoptotic cell death quantitation of oxaliplatin, monometallic starting materials oxo-oxaliplatin and Au-1, and heterometallic PtAu₂-5 in MDA-MB-231 cell line using AnnexinV with propidium iodide (PI) labeling analyzed after 72 h of incubation with IC₅₀ using flow cytometry. The data reported in the graphs, and standard deviation of the sample mean, from three independent trials.

Figure 4.

Platinum and gold organelle uptake quantitation of monometallic Au-1, oxo-oxaliplatin and oxaliplatin and heterometallic PtAu₂-5 in MDA-MB-231 cell line using fractionation buffer and centrifugation and analyzed by Atomic Absorption Spectrometry (AAS) after 72 h of incubation with IC₅₀. The data reported in the graphs, and standard deviation of the sample mean, result from three independent trials.

Figure 5.

Cell Migration and Endothelial Tube Formation Assays for heterometallic PtAu₂-5 and monometallic Au-1, oxo-oxaliplatin and oxaliplatin compounds. A) 2D wound-healing scratch assay showing MDA-MB-231 migration interference images captured at 0 h (top) and 24 h (bottom) post dosing and B) migration inhibition quantitation of all compounds after 72 h IC₂₀ concentration was added. C) Vascular endothelial reorganization images captured at 4h (top) and 16 h (bottom) post dosing and D) vascular disruption quantitation in seeded Human Umbilical Vein Endothelial Cells (HUVEC) after 72 h IC₁₀ concentration of all compounds was added. The data reported in the graphs, and standard deviation of the sample mean, result from three independent trials averaging quantitation from four fields of view per trial. All images were capture at 5x magnification. 90% confluency was confirmed prior to dosing in each well.

Figure 6.

Electrophoresis mobility shift assays for monometallic platinum(II) (cisplatin and oxaliplatin), platinum(IV) (oxo-cisplatin and oxo-oxaliplatin), gold(I) Au-1, and heterometallic compounds PtAu-3,PtAu₂ −4 and PtAu₂-5. Plasmid refers to untreated control of DNA plasmid pBR322. (a, b, c, d and e) correspond to metal/DNAbp ratios of 0.2, 0.4, 0.6, 0.8 and 1.0.

Figure 7.

Inhibition of pro-angiogenic protein in MDA-MB-231 TNBC cells. A) Inhibition of mitochondrial protein TrxR at IC₅₀ concentration by monometallic Au(I), Pt(II) and Pt(IV) compounds and heterometallic compounds PtAu-3, PtAu₂-4, and PtAu₂-5, and auranofin at 72 h. B) Inhibition of TrxR enzyme by oxo-oxaliplatin, PtAu₂-5 and auranofin (1μM) at 72 h. The values indicate concentration per milliliter of TrxR activity inhibition relative to the control (DMSO 0.1%). (*= enzyme activity completely inhibited at the concentration tested).

Scheme 1.

Preparation of monometallic gold(I) compound Au-2 and heterometallic binuclear PtAu (PtAu-3) and trinuclear PtAu₂ compounds (PtAu₂-4 and PtAu₂-5) via coupling reaction between gold(I) and platinum (IV) precursors.