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

Glutathione Depletion and Stalwart Anticancer Activity of Metallotherapeutics Inducing Programmed Cell Death: Opening a New Window for Cancer Therapy

The cellular defense system against exogenous substances makes therapeutics inefficient as intracellular glutathione (GSH) exhibits an astounding antioxidant activity in scavenging reactive oxygen species (ROS) or reactive nitrogen species (RNS) or other free radicals produced by the therapeutics. In the cancer cell microenvironment, the intracellular GSH level becomes exceptionally high to fight against oxidative stress created by the production of ROS/RNS or any free radicals, which are the byproducts of intracellular redox reactions or cellular respiration processes. Thus, in order to maintain redox homeostasis for survival of cancer cells and their rapid proliferation, the GSH level starts to escalate. In this circumstance, the administration of anticancer therapeutics is in vain, as the elevated GSH level reduces their potential by reduction or by scavenging the ROS/RNS they produce. Therefore, in order to augment the therapeutic potential of anticancer agents against elevated GSH condition, the GSH level must be depleted by hook or by crook. Hence, this Review aims to compile precisely the role of GSH in cancer cells, the importance of its depletion for cancer therapy and examples of anticancer activity of a few selected metal complexes which are able to trigger cancer cell death by depleting the GSH level.

Platinum(IV) combo prodrugs containing cyclohexane-1R,2R-diamine, valproic acid, and perillic acid as a multiaction chemotherapeutic platform for colon cancer

The complex [PtCl2(cyclohexane-1R,2R-diamine)] has been combined in a Pt(IV) molecule with two different bioactive molecules (i.e., the histone deacetylase inhibitor 2-propylpentanoic acid or valproic acid, VPA, and the potential antimetastatic molecule 4-isopropenylcyclohexene-1-carboxylic acid or perillic acid, PA) in order to obtain a set of multiaction or multitarget antiproliferative agents. In addition to traditional thermal synthetic procedures, microwave-assisted heating was used to speed up their preparation. All Pt(IV) complexes showed antiproliferative activity on four human colon cancer cell lines (namely HCT116, HCT8, RKO and HT29) in the nanomolar range, considerably better than those of [PtCl2(cyclohexane-1R,2R-diamine)], VPA, PA, and the reference drug oxaliplatin. The synthesized complexes showed pro-apoptotic and pro-necrotic effects and the ability to induce cell cycle alterations. Moreover, the downregulation of histone deacetylase activity, leading to an increase in histone H3 and H4 levels, and the antimigratory activity, indicated by the reduction of the levels of matrix metalloproteinases MMP2 and MMP9, demonstrated the multiaction nature of the complexes, which showed biological properties similar to or better than those of VPA and PA, but at lower concentrations, probably due to the lipophilicity of the combo molecule that increases the intracellular concentration of the single components (i.e., [PtCl2(cyclohexane-1R,2R-diamine)], VPA and PA).

From the Discovery of Targets to Delivery Systems: How to Decipher and Improve the Metallodrugs' Actions at a Molecular Level

Metals are indispensable for the life of all organisms, and their dysregulation leads to various disorders due to the disruption of their homeostasis. Nowadays, various transition metals are used in pharmaceutical products as diagnostic and therapeutic agents because their electronic structure allows them to adjust the properties of molecules differently from organic molecules. Therefore, interest in the study of metal-drug complexes from different aspects has been aroused, and numerous approaches have been developed to characterize, activate, deliver, and clarify molecular mechanisms. The integration of these different approaches, ranging from chemoproteomics to nanoparticle systems and various activation strategies, enables the understanding of the cellular responses to metal drugs, which may form the basis for the development of new drugs and/or the modification of currently used drugs. The purpose of this review is to briefly summarize the recent advances in this field by describing the technological platforms and their potential applications for identifying protein targets for discovering the mechanisms of action of metallodrugs and improving their efficiency during delivery.

The Strange Case: The Unsymmetric Cisplatin-Based Pt(IV) Prodrug [Pt(CH3COO)Cl2(NH3)2(OH)] Exhibits Higher Cytotoxic Activity with respect to Its Symmetric Congeners due to Carrier-Mediated Cellular Uptake

The biological behavior of the axially unsymmetric antitumor prodrug (OC-6-44)-acetatodiamminedichloridohydroxidoplatinum(IV), 2, was deeply investigated and compared with that of analogous symmetric Pt(IV) complexes, namely, dihydroxido 1 and diacetato 3, which have a similar structure. The complexes were tested on a panel of human tumor cell lines. Complex 2 showed an anomalous higher cytotoxicity (similar to that of cisplatin) with respect to their analogues 1 and 3. Their reduction potentials, reduction kinetics, lipophilicity, and membrane affinity are compared. Cellular uptake and DNA platination of Pt(IV) complexes were deeply investigated in the sensitive A2780 human ovarian cancer cell line and in the corresponding resistant A2780cisR subline. The unexpected activity of 2 appears to be related to its peculiar cellular accumulation and not to a different rate of reduction or a different efficacy in DNA platination and/or efficiency in apoptosis induction. Although the exact mechanism of cell uptake is not fully deciphered, a series of naïve experiments indicates an energy-dependent, carrier-mediated transport: the organic cation transporters (OCTs) are the likely proteins involved.

Stimuli-responsive platinum and ruthenium complexes for lung cancer therapy

Lung cancer is the most common cause of cancer-related deaths worldwide. More efficient treatments are desperately needed. For decades, the success of platinum-based anticancer drugs has promoted the exploration of metal-based agents. Four ruthenium-based complexes have also entered clinical trials as candidates of anticancer metallodrugs. However, systemic toxicity, severe side effects and drug-resistance impeded their applications and efficacy. Stimuli-responsiveness of Pt- and Ru-based complexes provide a great chance to weaken the side effects and strengthen the clinical efficacy in drug design. This review provides an overview on the stimuli-responsive Pt- and Ru-based metallic anticancer drugs for lung cancer. They are categorized as endo-stimuli-responsive, exo-stimuli-responsive, and dual-stimuli-responsive prodrugs based on the nature of stimuli. We describe various representative examples of structure, response mechanism, and potential medical applications in lung cancer. In the end, we discuss the future opportunities and challenges in this field.

Microwave-Assisted Synthesis: Can Transition Metal Complexes Take Advantage of This “Green” Method?

Microwave-assisted synthesis is considered environmental-friendly and, therefore, in agreement with the principles of green chemistry. This form of energy has been employed extensively and successfully in organic synthesis also in the case of metal-catalyzed synthetic procedures. However, it has been less widely exploited in the synthesis of metal complexes. As microwave irradiation has been proving its utility as both a time-saving procedure and an alternative way to carry on tricky transformations, its use can help inorganic chemists, too. This review focuses on the use of microwave irradiation in the preparation of transition metal complexes and organometallic compounds and also includes new, unpublished results. The syntheses of the compounds are described following the group of the periodic table to which the contained metal belongs. A general overview of the results from over 150 papers points out that microwaves can be a useful synthetic tool for inorganic chemists, reducing dramatically the reaction times with respect to traditional heating. This is often accompanied by a more limited risk of decomposition of reagents or products by an increase in yield, purity, and (sometimes) selectivity. In any case, thermal control is operative, whereas nonthermal or specific microwave effects seem to be absent.

Synthesis and anticancer activity of two highly water-soluble and ionic Pt(iv) complexes as prodrugs for Pt(ii) anticancer drugs

Two new Pt(iv) complexes featuring mesylate as the outer sphere anion, cis,trans,cis-[PtCl₂(OH₂)₂(NH₃)₂](CH₃SO₃)₂ (SPt-1) and cis,trans,cis-[PtCl₂(OH₂)₂(1R,2R-DACH)](CH₃SO₃)₂ (SPt-2), were synthesized and characterized by elemental analysis, ¹H and ¹³C NMR, IR, and ESI-MS. Both complexes have excellent water-solubility, high molar conductivity and good water stability. They exhibit an irreversible two-electron reduction event with the peak potentials (E _p) for the processes being -0.40 V for SPt-1 and -0.52 V for SPt-2. The biological tests reveal that SPt-2 possesses high in vitro anticancer activity against three human cancer cell lines (HCT-116, A549 and MKN-1) and its overall anticancer activity is slightly greater than that of oxaliplatin, whereas SPt-1 is less active than cisplatin. Moreover, the antitumor efficacy of SPt-2 on human colon carcinoma HCT-116 xenografts in nude mice is also greater than that of oxaliplatin, suggesting that SPt-2 deserves further evaluation as a prodrug for oxaliplatin.

Application of the anthraquinone drug rhein as an axial ligand in bifunctional Pt(IV) complexes to obtain antiproliferative agents against human glioblastoma cells

Octahedral Pt(IV) prodrugs are an effective way to combine cisplatin-like moieties and a second drug to obtain selective and stimuli responsive bifunctional antiproliferative compounds. Recently, two bifunctional Pt(IV) complexes have shown interesting in vitro and in vivo effects in glioblastoma, the most aggressive primary brain tumor. An interesting observation indicates that 4,5-dihydroxy-9,10-dioxo-9,10-dihydroanthracene-2-carboxylic acid (rhein) can inhibit in vivo glioma tumor progression. Furthermore, a prodrug in which cisplatin was combined with two molecules of rhein showed a potency higher than that of cisplatin toward cisplatin-resistant lung carcinoma cells. However, the high lipophilicity of this type of complex affects their solubility and bioavailability. To overcome these limits, in the present work, three Pt(IV) derivatives were obtained by differently linking one molecule of rhein and one acetato ligand at the axial position to a cisplatin core. The complexes proved to be similar to or more potent than the parent cisplatin and rhein, and the reference drug temozolomide on two human glioblastoma cell lines (U87-MG and T98G). They retained their activity under hypoxia and caused a significant reduction in the motility of both cell lines, which can be related to their ability to inhibit MMP2 and MMP9 matrix metalloproteinases. Finally, physicochemical and computational studies indicated that these Pt(IV) derivatives are more prone than rhein to cross the blood-brain barrier.

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.