A dual-targeting, p53-independent, apoptosis-inducing platinum(II) anticancer complex, [Pt(BDI(QQ))]Cl

Abstract

The therapeutic index and cellular mechanism of action of [Pt(BDI(QQ))]Cl, a monocationic, square-planar platinum(II) complex, are reported. [Pt(BDI(QQ))]Cl was used to treat several cell lines, including wild type and cisplatin-resistant ovarian carcinoma cells (A2780 and A2780CP70) and non-proliferating lung carcinoma cells (A549). [Pt(BDI(QQ))]Cl selectively kills cancer cells over healthy cells and exhibits no cross-resistance with cisplatin. The mechanism of cell killing was established through detailed cell-based assays. [Pt(BDI(QQ))]Cl exhibits dual-threat capabilities, targeting nuclear DNA and mitochondria simultaneously. [Pt(BDI(QQ))]Cl induces DNA damage, leading to p53 enrichment, mitochondrial membrane potential depolarisation, and caspase-mediated apoptosis. [Pt(BDI(QQ))]Cl also accumulates in the mitochondria, resulting in direct mitochondrial damage. Flow cytometric studies demonstrated that [Pt(BDI(QQ))]Cl has no significant effect on cell cycle progression. Remarkably, p53-status is a not a determinant of [Pt(BDI(QQ))]Cl activity. In p53-null cells, [Pt(BDI(QQ))]Cl induces cell death through mitochondrial dysfunction. Cancers with p53-null status could therefore be targeted using [Pt(BDI(QQ))]Cl.

Figure 1

Cellular uptake following [Pt(BDI^QQ)]Cl treatment (10 μM for 12 h). The amount of platinum (ng) per million A549 lung carcinoma and A2780 ovarian carcinoma cells is shown for the cytoplasmic, nuclear, membrane, and mitochondrial fractions. The errors represent standard deviations.

Figure 2

(a) Immunoblotting analysis of proteins related to the DNA damage response and p53 induction pathways. Protein expression in A549 cells was observed following treatment with [Pt(BDI^QQ)]Cl (1–5 μM for 72 h). Whole cell lysates were resolved by SDS-PAGE and analysed by immunoblotting against γH2AX, p53, phosp53, p21, and β-actin (loading control). (b) Platinum content in genomic DNA extracted from A549 and A2780 cells dosed with [Pt(BDI^QQ)]Cl and cisplatin (10 μM for 12 h).

Figure 3

(a) The mean intensity of red fluorescence emitted by JC-1 stained A549 and A2780 cells in the absence and presence of [Pt(BDI^QQ)]Cl (5 μM for 48 h) or carbonyl cyanide m-chlorophenyl hydrazone (CCCP) (1 μM for 48 h). The errors represent standard deviations. (b) Histogram displaying red fluorescence emitted by JC-1 stained A549 and A2780 cells prior to (red line) and upon treatment with [Pt(BDI^QQ)]Cl (5 μM for 48 h) (blue line). (c) Fluorescence microscopy images of A549 cells untreated and treated with [Pt(BDI^QQ)]Cl (0.5 μM for 24 h), and then stained with Hoechst 33258 and MitoTracker Green. Scale bar = 21 μm.