Metallo-drugs in the treatment of malignant pleural mesothelioma

Pt(IV) antitumor prodrugs: dogmas, paradigms, and realities

Platinum(II)-based drugs are widely used for the treatment of solid tumors, especially in combination protocols. Severe side effects and occurrence of resistance are the major limitations to their clinical use. To overcome these drawbacks, a plethora of Pt(IV) derivatives, acting as anticancer prodrugs, have been designed, synthesized and preclinically (often only in vitro) tested. Here, we summarize the recent progress in the development and understanding of the chemical properties and biochemical features of these Pt(IV) prodrugs, especially those containing bioactive molecules as axial ligands, acting as multi-functional agents. Even though no such prodrugs have been yet approved for clinical use, many show encouraging pharmacological profiles. Thus, a better understanding of their features is a promising approach towards improving the available Pt-based anticancer agents.

Unsymmetric Cisplatin-Based Pt(IV) Conjugates Containing a PARP-1 Inhibitor Pharmacophore Tested on Malignant Pleural Mesothelioma Cell Lines

Cisplatin is widely employed as a first-line chemotherapeutic agent for many solid tumors, including malignant pleural mesothelioma (MPM). However, its clinical use is limited by heavy side effects and acquired resistance, the latter being mainly related to enhanced DNA repair. Many clinical trials using combinations of platinum drugs and PARP-1 inhibitors (PARPis) have been carried out, with the hope that such combinations might lead to improved therapeutic efficacy against tumors. Here, the synthesis and efficacy in reducing MPM cell viability of four cisplatin-based Pt(IV) prodrugs containing the PARPi 3-aminobenzamide (3-ABA) fragment are described. The most promising conjugate is more effective than cisplatin or cisplatin/3-ABA combination, administered in equimolar doses, in inhibiting PARP-1 activity and inducing apoptosis in BRCA1/2 wild type MPM cells, grown as monolayer or as multicellular spheroids.

Cis,cis,trans-[PtIVCl2(NH3)2(perillato)2], a dual-action prodrug with excellent cytotoxic and antimetastatic activity

Two Pt(iv) conjugates containing one or two molecules of perillic acid (4-isopropenylcyclohexene-1-carboxylic acid), an active metabolite of limonene, were synthesized both with traditional and microwave-assisted methods and characterized. Their antiproliferative activity was tested on a panel of human tumor cell lines. In particular, cis,cis,trans-[Pt^IVCl₂(NH₃)₂(perillato)₂] exhibited excellent antiproliferative and antimetastatic activity on A-549 lung tumor cells at nanomolar concentrations. A number of in vitro biological tests were performed to decipher some aspects of its mechanism of action, including transwell migration and invasion as well as wound healing assay.

Uptake-release by MSCs of a cationic platinum(II) complex active in vitro on human malignant cancer cell lines

In this study, the in vitro stability of cisplatin (CisPt) and cationic platinum(II)-complex (caPt(II)-complex) and their in vitro activity (antiproliferative and anti-angiogenic properties) were investigated against three aggressive human tumor cell lines. caPt(II)-complex shown a high stability until 9 days of treatment and displayed a significant and higher activity than CisPt against both NCI-H28 mesothelioma (19.37 ± 9.57 μM versus 34.66 ± 7.65 μM for CisPt) and U87 MG glioblastoma (19.85 ± 0.97 μM versus 54.14 ± 3.19 for CisPt). Mesenchymal Stromal Cells (AT-MSCs) showed a significant different sensitivity (IC₅₀ = 71.9 ± 15.1 μM for caPt(II)-complex and 8.7 ± 4.5 μM for CisPt) to the antiproliferative activity of caPt(II)-complex and CisPt. The ability of MSCs to uptake both the drugs in a similar amount of 2.49 pM /cell, suggested a possible development of new therapies based on cell mediated drug delivery.

Cisplatin and valproate released from the bifunctional [Pt(IV)Cl2(NH3)2(valproato)2] antitumor prodrug or from liposome formulations: who does what?

Comparison between the antiproliferative properties of a Pt(iv)-valproato complex and its metabolites indicates that the former is more active because it is unremoved from cells.

New insights into the molecular and epigenetic effects of antitumor Pt(IV)-valproic acid conjugates in human ovarian cancer cells

Substitutionally inert Pt(IV) prodrugs, combining bioactive axial ligands with Pt(IV) derivatives of antitumor Pt(II) compounds, represent a new generation of anticancer drugs. The rationale behind these prodrugs is to release, by reductive elimination inside the cancer cell, an active Pt(II) drug which binds nuclear DNA as well as bioactive ligands that may potentiate toxic effects of the Pt(II) drugs by an independent pathway. Platinum prodrugs, such as Pt(IV) derivatives of cisplatin containing axial valproic acid (VPA) ligands, destroy cancer cells with greater efficacy than conventional cisplatin. These axial ligands were chosen because VPA inhibits histone deacetylase (HDAC) activity, thereby decondensing chromatin and subsequently increasing the accessibility of DNA within chromatin to DNA-binding agents. We examined the mechanism of cytotoxic activity of Pt(IV) derivatives of cisplatin with VPA axial ligands. Particular attention was paid to the role of the VPA ligand in these Pt(IV) prodrugs in the mechanism underlying their toxic effects in human ovarian tumor cells. We demonstrate that (i) treatment of the cells with these prodrugs resulted in enhanced histone H3 acetylation and decondensation of heterochromatin markedly more effectively than free VPA; (ii) of the total Pt inside the cells, a considerably higher fraction of Pt from the Pt(IV)-VPA conjugates is bound to DNA than from the conjugates with biologically inactive ligands. The results indicate that the enhanced cytotoxicity of the Pt(IV)-VPA conjugates is a consequence of several processes involving enhanced cellular accumulation, downregulation of HDACs and yet other biochemical processes (not involving HDACs) which may potentiate antitumor effects.

Biological activity of a series of cisplatin-based aliphatic bis(carboxylato) Pt(IV) prodrugs: how long the organic chain should be?

The biological properties of a series of cisplatin-based Pt(IV) prodrug candidates, namely trans,cis,cis-[Pt(carboxylato)2Cl2(NH3)2], where carboxylato=CH3(CH2)nCOO(-) [(1), n=0; (2), n=2; (3), n=4; (4), n=6] having a large interval of lipophilicity are discussed. The stability of the complexes was tested in different pH conditions (i.e. from 1.0 to 9.0) to simulate the hypothetical conditions for an oral route of administration, showing a high stability (>90%). The transformation into their active Pt(II) metabolites was demonstrated in the presence of ascorbic acid, with a pseudo-first order kinetics, the half-time of which smoothly decreases as the chain length of carboxylic acid increases. Their antiproliferative activity has been evaluated in vitro on a large panel of human cancer cell lines. As expected, the potency increases with the chain length: 3 and 4 resulted by far more active than cisplatin on all cell lines of about one or two orders of magnitude, respectively. Both complexes retained their activity also on cisplatin-resistant cell line, and exhibited a progressive increase of the selectivity compared with non-tumor cells. These results were confirmed with more prolonged treatment (up to 14days) studied on multicellular tumor spheroids (MCTSs). In this case the Pt(IV) complexes exert a protracted antiproliferative action, even if the drug is removed from the culture medium. Finally, in a time-course experiment of the total platinum evaluation in mice blood (after a single oral administration of the title complexes), 2 gave the best results, representing a good compromise between lipophilicity and water solubility, that increase and decrease respectively on passing from 1 to 4.

Antitumor platinum(IV) derivatives of oxaliplatin with axial valproato ligands

We report new anticancer prodrugs, platinum(IV) derivatives of oxaliplatin conjugated with valproic acid (VPA), a well-known drug having histone deacetylase inhibitory activity. Like most platinum(IV) derivatives, the cytotoxicity of the conjugates was lower in cell culture than that of oxaliplatin, but greater than those of its Pt(IV) derivative containing biologically inactive axial ligands in several cancer cell lines. Notably, these conjugates display activity in both cisplatin sensitive- and resistant tumor cells capable of both markedly enhanced accumulation in tumor cells and acting in a dual threat manner, concurrently targeting histone deacetylase and genomic DNA. These results demonstrate the dual targeting strategy to be a valuable route to pursue in the design of platinum agents which may be more effective in cancer types that are typically resistant to therapy by conventional cisplatin. Moreover, platinum(IV) derivatives containing VPA axial ligands seem to be promising dual-targeting candidates for additional preclinical studies.

Pros and cons of bifunctional platinum(IV) antitumor prodrugs: two are (not always) better than one

This article evaluates the efficacy and applicability of bifunctional prodrugs consisting of a six-coordinate Pt(iv) octahedral core and one or more bioactive molecules. The platinum(iv) complexes release upon reduction the corresponding cytotoxic Pt(ii) agents and the bioactive molecules, able to inhibit some biochemical mechanisms of cancer growth and/or prevent the deactivation of the Pt(ii) metabolites.