A view on multi-action Pt(IV) antitumor prodrugs

Coordinative Compounds Based on Unsaturated Carboxylate with Versatile Biological Applications

This review presents an overview of the biological applications of coordinative compounds based on unsaturated carboxylates accompanied by other ligands, usually N-based heterocyclic species. The interest in these compounds arises from the valuable antimicrobial and antitumor activities evidenced by some species, as well as from their ability to generate metal-containing polymers suitable for various medical purposes. Therefore, we describe the recently discovered aspects related to the synthesis, structure, and biological activity of a wide range of unsaturated carboxylate-containing species and metal ions, originating mostly from 3d series. The unsaturated carboxylates encountered in coordinative compounds are acrylate, methacrylate, fumarate, maleate, cinnamate, ferulate, coumarate, and itaconate. Regarding the properties of the investigated compounds, it is worth mentioning the good ability of some to inhibit the development of resistant strains or microbial biofilms on inert surfaces or, even more, exert antitumor activity against resistant cells. The ability of some species to intercalate into DNA strands as well as to scavenge ROS species is also addressed.

Reductive prodrug and AIE copolymer nanoparticle for monitoring and chemotherapy

Polymeric micelle systems for drug delivery, monitor and chemotherapy have gained significant attention, and reductive polymeric micelle systems have become particularly attractive due to their controlled release behavior without additional assistance. However, there are challenges in accurately controlling drug and probe release from the nanoparticles and determining the loading content of drug and probe. To address these issues, we have developed a reduction-responsive Pt(IV) prodrug-based polymeric delivery system that can be dynamically monitored using aggregation-induced emission luminogens (AIE) based bioprobes. These polymeric micelle can self-assemble into nanoparticles and release both bio-active Pt(II) drug and bio-probe upon reduction activation. TPE molecules released in the inner endo/lysosomal microenvironment aggregate and fluoresce upon irradiation, thus allowing real-time tracking of drug biodistribution without additional contrast agents. Advantages of this system include position-specific chemical bond cleavage, control of platinum content, and monitoring of drug reduction and biodistribution.

Oxaliplatin(IV) Prodrugs Functionalized with Gemcitabine and Capecitabine Induce Blockage of Colorectal Cancer Cell Growth-An Investigation of the Activation Mechanism and Their Nanoformulation

The use of platinum-based anticancer drugs, such as cisplatin, oxaliplatin, and carboplatin, is a common frontline option in cancer management, but they have debilitating side effects and can lead to drug resistance. Combination therapy with other chemotherapeutic agents, such as capecitabine and gemcitabine, has been explored. One approach to overcome these limitations is the modification of traditional Pt(II) drugs to obtain new molecules with an improved pharmacological profile, such as Pt(IV) prodrugs. The design, synthesis, and characterization of two novel Pt(IV) prodrugs based on oxaliplatin bearing the anticancer drugs gemcitabine or capecitabine in the axial positions have been reported. These complexes were able to dissociate into their constituents to promote cell death and induce apoptosis and cell cycle blockade in a representative colorectal cancer cell model. Specifically, the complex bearing gemcitabine resulted in being the most active on the HCT116 colorectal cancer cell line with an IC50 value of 0.49 ± 0.04. A pilot study on the encapsulation of these complexes in biocompatible PLGA-PEG nanoparticles is also included to confirm the retention of the pharmacological properties and cellular drug uptake, opening up to the possible delivery of the studied complexes through their nanoformulation.

Disruption of Iron Homeostasis to Induce Ferroptosis with Albumin-Encapsulated Pt(IV) Nanodrug for the Treatment of Non-Small Cell Lung Cancer

Non-small cell lung cancer (NSCLC) is the most common pathological type of lung cancer , accounting for approximately 85% of lung cancers. For more than 40 years, platinum (Pt)-based drugs are still one of the most widely used anticancer drugs even in the era of precision medicine and immunotherapy. However, the clinical limitations of Pt-based drugs, such as serious side effects and drug resistance, have not been well solved. This study constructs a new albumin-encapsulated Pt(IV) nanodrug (HSA@Pt(IV)) based on the Pt(IV) drug and nanodelivery system. The characterization of nanodrug and biological experiments demonstrate its excellent drug delivery and antitumor effects. The multi-omics analysis of the transcriptome and the ionome reveals that nanodrug can activate ferroptosis by affecting intracellular iron homeostasis in NSCLC. This study provides experimental evidence to suggest the potential of HSA@Pt(IV) as a nanodrug with clinical application.

Pyrenebutyrate Pt(IV) Complexes with Nanomolar Anticancer Activity

Research on platinum-based anticancer drugs continuously strives to develop new non-classical platinum complexes. Pt(IV) prodrugs are the most promising, and their activation-by-reduction mechanism of action is being explored as a prospect for higher selectivity and efficiency. Herein, we present the anticancer potency and chemical reactivity of Pt(IV) complexes formed by linking pyrene butyric acid with cisplatin. The results from cytotoxicity screening on 10 types of cancer cell lines and non-malignant cells (HEK-293) indicated IC50 values as low as 50-70 nM for the monosubstituted Pt(IV) complex against leukemia cell lines (HL-60 and SKW3) and a cisplatin-resistant derivative (HL-60/CDDP). Interestingly, the bis-substituted complex is virtually non-toxic to both healthy and cancerous cells of adherent types. Nevertheless, it shows high cytotoxicity against multidrug-resistant derivatives HL-60/CDDP and HL-60/Dox. The reactivity of the complexes with biological reductants was monitored by the NMR method. Furthermore, the platinum uptake by the treated cells was examined on two types of cellular cultures: adherent and suspension growing, and proteome profiling was conducted to track expression changes of key apoptosis-related proteins in HL-60 cells. The general conclusion points to a possible cytoskeletal entrapment of the bulkier bis-pyrene complex that could be limiting its cytotoxicity to adherent cells, both cancerous and healthy ones.

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).

Synthesis and Antiproliferative Insights of Lipophilic Ru(II)-Hydroxy Stearic Acid Hybrid Species

Metallodrugs represent a combination of multifunctionalities that are present concomitantly and can act differently on diverse biotargets. Their efficacy is often related to the lipophilic features exhibited both by long carbo-chains and the phosphine ligands. Three Ru(II) complexes containing hydroxy stearic acids (HSAs) were successfully synthesized in order to evaluate possible synergistic effects between the known antitumor activity of HSA bio-ligands and the metal center. HSAs were reacted with [Ru(H)₂CO(PPh₃)₃] selectively affording O,O-carboxy bidentate complexes. The organometallic species were fully characterized spectroscopically using ESI-MS, IR, UV-Vis, and NMR techniques. The structure of the compound Ru-12-HSA was also determined using single crystal X-ray diffraction. The biological potency of ruthenium complexes (Ru-7-HSA, Ru-9-HSA, and Ru-12-HSA) was studied on human primary cell lines (HT29, HeLa, and IGROV1). To obtain detailed information about anticancer properties, tests for cytotoxicity, cell proliferation, and DNA damage were performed. The results demonstrate that the new ruthenium complexes, Ru-7-HSA and Ru-9-HSA, possess biological activity. Furthermore, we observed that the Ru-9-HSA complex shows increased antitumor activity on colon cancer cells, HT29.

Synthesis, Characterization and Biological Investigation of the Platinum(IV) Tolfenamato Prodrug–Resolving Cisplatin-Resistance in Ovarian Carcinoma Cell Lines

The research on the anticancer potential of platinum(IV) complexes represents one strategy to circumvent the deficits of approved platinum(II) drugs. Regarding the role of inflammation during carcinogenesis, the effects of non-steroidal anti-inflammatory drug (NSAID) ligands on the cytotoxicity of platinum(IV) complexes is of special interest. The synthesis of cisplatin- and oxaliplatin-based platinum(IV) complexes with four different NSAID ligands is presented in this work. Nine platinum(IV) complexes were synthesized and characterized by use of nuclear magnetic resonance (NMR) spectroscopy (1H, 13C, 195Pt, 19F), high-resolution mass spectrometry, and elemental analysis. The cytotoxic activity of eight compounds was evaluated for two isogenic pairs of cisplatin-sensitive and -resistant ovarian carcinoma cell lines. Platinum(IV) fenamato complexes with a cisplatin core showed especially high in vitro cytotoxicity against the tested cell lines. The most promising complex, 7, was further analyzed for its stability in different buffer solutions and behavior in cell cycle and cell death experiments. Compound 7 induces a strong cytostatic effect and cell line-dependent early apoptotic or late necrotic cell death processes. Gene expression analysis suggests that compound 7 acts through a stress-response pathway integrating p21, CHOP, and ATF3.

Oral Anticancer Heterobimetallic PtIV -AuI Complexes Show High In Vivo Activity and Low Toxicity

Au^I -carbene and Pt^IV -Au^I -carbene prodrugs display low to sub-μM activity against several cancer cell lines and overcome cisplatin (cisPt) resistance. Linking a cisPt-derived Pt^IV (phenylbutyrate) complex to a Au^I -phenylimidazolylidene complex 2, yielded the most potent prodrug. While in vivo tests against Lewis Lung Carcinoma showed that the prodrug Pt^IV (phenylbutyrate)-Au^I -carbene (7) and the 1 : 1 : 1 co-administration of cisPt: phenylbutyrate:2 efficiently inhibited tumor growth (≈95 %), much better than 2 (75 %) or cisPt (84 %), 7 exhibited only 5 % body weight loss compared to 14 % for 2, 20 % for cisPt and >30 % for the co-administration. 7 was much more efficient than 2 at inhibiting TrxR activity in the isolated enzyme, in cells and in the tumor, even though it was much less efficient than 2 at binding to selenocysteine peptides modeling the active site of TrxR. Organ distribution and laser-ablation (LA)-ICP-TOFMS imaging suggest that 7 arrives intact at the tumor and is activated there.

Metal Complexes as Promising Matrix Metalloproteinases Regulators

Nowadays, cancers and dementia, such as Alzheimer's disease, are the most fatal causes of death. Many studies tried to understand the pathogenesis of those diseases clearly and develop a promising way to treat the diseases. Matrix metalloproteinases (MMPs) have been reported to be involved in the pathology of cancers and AD through tumor cell movement and amyloid degradation. Therefore, control of the levels and actions of MMPs, especially MMP-2 and MMP-9, is necessary to care for and/or cure cancer and AD. Various molecules have been examined for their potential application as regulators of MMPs expression and activity. Among the molecules, multiple metal complexes have shown advantages, including simple synthesis, less toxicity and specificity toward MMPs in cancer cells or in the brain. In this review, we summarize the recent studies and knowledge of metal complexes (e.g., Pt-, Ru-, Au-, Fe-, Cu-, Ni-, Zn-, and Sn-complexes) targeting MMPs and their potentials for treating and/or caring the most fatal human diseases, cancers and AD.

Synthesis, Characterization and Photoactivation Studies on the Novel Pt(IV)-Based [Pt(OCOCH3)3(phterpy)] Complex

Photoactivatable Pt(IV) prodrugs represent nowadays an intriguing class of potential metal-based drugs, endowed with more chemical inertness in their oxidized form and better selectivity for the target with respect to the clinically established Pt(II) compounds. In fact, they have the possibility to be reduced by light irradiation directly at the site of interest. For this reason, we synthesized a new Pt(IV) complex, [Pt(OCOCH₃)₃(4'-phenyl-2,2':6',2''-terpyridine)][CF₃SO₃] (1), that is well soluble in aqueous medium and totally unreactive towards selected model biomolecules until its reduction. The highlight of this work is the rapid and efficient photoreduction of 1 with visible light (460 nm), which leads to its reactive Pt(II) analogue. This behavior was made possible by taking advantage of an efficient catalytic system based on flavin and NADH, which is naturally present in the cellular environment. As a comparison, the reduction of 1 was also studied with simple UV irradiation, but both UV-Vis spectrophotometry and ¹H-NMR spectrometry showed that the flavin-catalyzed reduction with visible light was faster. Lastly, the reactivity against two representative biological targets, i.e., human serum albumin and one monofilament oligonucleotide fragment, was evaluated by high-resolution mass spectrometry. The results clearly pointed out that the prodrug 1 did not interact with these targets until its photoreduction to the Pt(II) analogue.

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.

Recent Advances in Light-Controlled Activation of Pt(IV) Prodrugs

Pt(IV) prodrugs remain one of the most promising alternatives to conventional Pt(II) therapy due to their versatility in axial ligand choice and delayed mode of action. Selective activation from an external source is especially attractive due to the opportunity to control the activity of an antitumor drug in space and time and avoid damage to normal tissues. In this review, we discuss recent advances in photoabsorber-mediated photocontrollable activation of Pt(IV) prodrugs. Two main approaches developed are the focus of the review. The first one is the photocatalytic strategy based on the flavin derivatives that are not covalently bound to the Pt(IV) substrate. The second one is the conjugation of photoactive molecules with the Pt(II) drug via axial position, yielding dual-action Pt(IV) molecules capable of the controllable release of Pt(II) cytotoxic agents. Thus, Pt(IV) prodrugs with a light-controlled mode of activation are non-toxic in the absence of light, but show high antiproliferative activity when irradiated. The susceptibility of Pt(IV) prodrugs to photoreduction, photoactivation mechanisms, and biological activity is considered in this review.

Platinum(IV) Complexes of the 1,3,5-Triamino Analogue of the Biomolecule Cis-Inositol Designed as Innovative Antineoplastic Drug Candidates

Metal complexes occupy a special place in the field of treatment and diagnostics. Their main advantages stem from the possibility of fine-tuning their thermodynamic properties and kinetic behavior in the biological milieu by applying different approaches such as properly constructed inner coordination sphere, appropriate choice of ligands, metal oxidation state, redox potential, etc., which are specific to these compounds. Here we discuss the design and synthesis of two octahedral cationic Pt(IV) complexes of the tridentate ligand all-cis-2,4,6-triaminocyclohexane-1,3,5-triol (taci) with composition, fac-[Pt(taci)I₃]⁺, 1 and bis-[Pt(taci)₂]⁴⁺, 2 as well as the potential for their application as antineoplastic agents. The complexes have been isolated in a solid state as: fac-[Pt(taci)I₃]I·3H₂O (1A), fac-[Pt(taci)I₃]I (1B), fac-[Pt(taci)I₃]I·2DMF (1C), bis-[Pt(taci)₂](CO₃)₂·6H₂O (2A) by changing the acidity of the reaction systems, the molar ratios of the reagents and the counterions, and by re-crystallization. The ligand taci is coordinated through the NH₂-groups, each molecule occupying three coordination places in the inner coordination sphere of Pt(IV). Monitoring of the hydrolysis processes of 1A and 2A at different acidity showed that while 2A remained stable over the study period, the I⁻-ions in 1A were successively substituted, with the main product under physiologically mimetic conditions being fac,cis-[Pt(taci)I(OH)₂]⁺ (h2). The antiproliferative tests involved eight cancer cell models, among which chemosensitive (derived from leukemias and solid tumors) and chemoresistant human Acute myeloid leukemia lines (HL-60/Dox, HL-60/CDDP), as well as the non-malignant kidney’ cells HEK-293T showed that the complexes 1A and 2A are characterized by a fundamentally different profile of chemosensitivity and spectrum of cytotoxic activity compared to cisplatin. The new Pt(IV) complexes were shown to be more effective in selectively inhibiting the proliferation of human malignant cells compared to cisplatin. Remarkable activity was recorded for 1A, which showed an effect (IC₅₀ = 8.9 ± 2.4) at more than 16-fold lower concentration than cisplatin (IC₅₀ = 144.4 ± 9.8) against the resistant cell line HL-60/CDDP. In parallel, 1A exhibited virtually the same cytotoxic effect against the parental HL-60 cells (IC₅₀ = 9.0 ± 1.2), where cisplatin displays comparable chemosensitivity (IC₅₀ = 8.3 ± 0.8). The determined resistance indices (RI~1) show unequivocally that the resistant lines are sensitive to both compounds tested; therefore, they are capable of overcoming the mechanisms of cisplatin resistance. The structural features of these compounds and their promising pharmacological properties justify their inclusion in the group of “non-classical metal-based antitumor compounds” and are a prerequisite for the admission of alternative mechanisms of action.

Potent Chlorambucil-Platinum(IV) Prodrugs

The DNA-alkylating derivative chlorambucil was coordinated in the axial position to atypical cytotoxic, heterocyclic, and non-DNA coordinating platinum(IV) complexes of type, [Pt^IV(H_L)(A_L)(OH)₂](NO₃)₂ (where H_L is 1,10-phenanthroline, 5-methyl-1,10-phenanthroline or 5,6-dimethyl-1,10-phenanthroline, A_L is 1S,2S-diaminocyclohexane). The resultant platinum(IV)-chlorambucil prodrugs, PCLB, 5CLB, and 56CLB, were characterized using high-performance liquid chromatography, nuclear magnetic resonance, ultraviolet-visible, circular dichroism spectroscopy, and electrospray ionization mass spectrometry. The prodrugs displayed remarkable antitumor potential across multiple human cancer cell lines compared to chlorambucil, cisplatin, oxaliplatin, and carboplatin, as well as their platinum(II) precursors, PHENSS, 5MESS, and 56MESS. Notably, 56CLB was exceptionally potent in HT29 colon, Du145 prostate, MCF10A breast, MIA pancreas, H460 lung, A2780, and ADDP ovarian cell lines, with GI₅₀ values ranging between 2.7 and 21 nM. Moreover, significant production of reactive oxygen species was detected in HT29 cells after treatment with PCLB, 5CLB, and 56CLB up to 72 h compared to chlorambucil and the platinum(II) and (IV) precursors.

Polymeric Nanosystems Applied for Metal-Based Drugs and Photosensitizers Delivery: The State of the Art and Recent Advancements

Nanotechnology-based approaches for targeting the delivery and controlled release of metal-based therapeutic agents have revealed significant potential as tools for enhancing the therapeutic effect of metal-based agents and minimizing their systemic toxicities. In this context, a series of polymer-based nanosized systems designed to physically load or covalently conjugate metal-based therapeutic agents have been remarkably improving their bioavailability and anticancer efficacy. Initially, the polymeric nanocarriers were applied for platinum-based chemotherapeutic agents resulting in some nanoformulations currently in clinical tests and even in medical applications. At present, these nanoassemblies have been slowly expanding for nonplatinum-containing metal-based chemotherapeutic agents. Interestingly, for metal-based photosensitizers (PS) applied in photodynamic therapy (PDT), especially for cancer treatment, strategies employing polymeric nanocarriers have been investigated for almost 30 years. In this review, we address the polymeric nanocarrier-assisted metal-based therapeutics agent delivery systems with a specific focus on non-platinum systems; we explore some biological and physicochemical aspects of the polymer–metallodrug assembly. Finally, we summarize some recent advances in polymeric nanosystems coupled with metal-based compounds that present potential for successful clinical applications as chemotherapeutic or photosensitizing agents. We hope this review can provide a fertile ground for the innovative design of polymeric nanosystems for targeting the delivery and controlled release of metal-containing therapeutic agents.

Ligand Evolution in the Photoactivatable Platinum(IV) Anticancer Prodrugs

Photoactivatable Pt(IV) anticancer prodrugs with the structure of [Pt^IV(N₁)(N₂)(L₁)(L₂)(A₁)(A₂)], where N₁ and N₂ are non-leaving nitrogen donor ligands, L₁ and L₂ are leaving ligands, and A₁ and A₂ are axial ligands, have attracted increasing attention due to their promising photo-cytotoxicity even to cisplatin-resistant cancer cells. These photochemotherapeutic prodrugs have high dark-stability under physiological conditions, while they can be activated by visible light restrained at the disease areas, as a consequence showing higher spatial and temporal controllability and much more safety than conventional chemotherapy. The coordinated ligands to the Pt center have been proved to be pivotal in determining the function and activity of the photoactivatable Pt(IV) prodrugs. In this review, we will focus on the development of the coordinated ligands in such Pt(IV) prodrugs and discuss the effects of diverse ligands on their photochemistry and photoactivity as well as the future evolution directions of the ligands. We hope this review can help to facilitate the design and development of novel photoactivatable Pt(IV) anticancer prodrugs.

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.

Synthesis and characterization of thiocarbonato-linked platinum(IV) complexes

Herein we show the formation of new oxaliplatin-based platinum(IV) complexes by reaction with DSC-activated thiols via thiocarbonate linkage. Three model complexes based on aliphatic and aromatic thiols, as well as one complex with N-acetylcysteine as biologically active thiol were synthesized. This synthetic strategy affords the expansion of biologically active compounds other than those containing carboxylic, amine or hydroxy groups for coupling to the platinum(IV) center. The complexes were characterized by high-resolution mass spectrometry, NMR spectroscopy (¹H, ¹³C, ¹⁹⁵Pt) and elemental analysis. Their biological behavior was evaluated against two ovarian carcinoma cell lines and their cisplatin-resistant analogues. Remarkably, the platinum(IV) samples show modest in vitro cytotoxicity against A2780 cells and comparable effects against A2780cis cells. Two complexes in particular demonstrate improved activity against SKOV3cis cells. The reduction experiment of complex 8, investigated by UHPLC-HRMS, provides evidence of interesting platinum-species formed during reaction with ascorbic acid.

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.

Ketoprofen and Loxoprofen Platinum(IV) Complexes Displaying Antimetastatic Activities by Inducing DNA Damage, Inflammation Suppression, and Enhanced Immune Response

Metastasis is a major contributor of death in cancer patients, and there is an urgent need for effective treatments of metastatic malignancies. Herein, ketoprofen (KP) and loxoprofen (LP) platinum(IV) complexes with antiproliferative and antimetastatic properties were designed and prepared by integrating chemotherapy and immunotherapy targeting cyclooxygenase-2 (COX-2), matrix metalloproteinase-9 (MMP-9), and programmed death ligand 1 (PD-L1), besides DNA. A mono-KP platinum(IV) complex with a cisplatin core is screened out as a candidate possessing potent anti-proliferative and anti-metastasis activities both in vitro and in vivo. It induces serious DNA damage and further leads to high expression of γ-H2AX and p53. Moreover, it promotes apoptosis of tumor cells through mitochondrial apoptotic pathway Bcl-2/Bax/caspase3. Then, COX-2, MMP-9, NLRP3, and caspase1 as pivotal enzymes igniting inflammation and metastasis are obviously inhibited. Notably, it significantly improves immune response through restraining the expression of PD-L1 to increase CD3⁺ and CD8⁺ T infiltrating cells in tumor tissues.

The influence of different carbonate ligands on the hydrolytic stability and reduction of platinum(IV) prodrugs

Pt(IV) complexes bearing axial carbonate linkages have drawn much attention recently. A synthetic method behind this allows the hydroxyl group of bioactive ligands to be attached to the available hydroxyl group of Pt(IV) complexes, and the rapid release of free drugs is achieved after the reduction of carbonate-linked Pt(IV) complexes. Further understanding on the properties of Pt(IV) carbonates such as hydrolytic stability and reduction profiles, however, is hindered by limited research. Herein, six mono-carbonated Pt(IV) complexes in which the carbonate axial ligands possess various electron-withdrawing powers were synthesized, and the corresponding mono-carboxylated analogues were also prepared as references to highlight the different properties. The influence of the coordination environment towards the hydrolysis and reduction rate of Pt(IV) carbonates and carboxylates was explored. The mono-carbonated Pt(IV) complexes are both less stable and reduced faster than the corresponding mono-carboxylated ones. Moreover, the hydrolysis and reduction profiles are dependent not only on the electron-withdrawing ability of the carbonates but also on the nature of the opposite axial ligands. Besides, the exploration of the hydrolytic pathway for Pt(IV) carbonates suggests that the process proceeds by an attack of OH^- on the carbonyl carbon, followed by elimination, which is different from that of Pt(IV) carboxylates. This study provides some information on the influence of axial carbonate ligands with different electron-withdrawing abilities on the properties of the Pt(IV) center, which may inspire new thoughts on the design of "multi-action" Pt(IV) prodrugs.

Ultrasound-Triggered Delivery of Iproplatin from Microbubble-Conjugated Liposomes

The PtIV prodrug iproplatin has been actively loaded into liposomes using a calcium acetate gradient, achieving a 3-fold enhancement in drug concentration compared to passive loading strategies. A strain-promoted cycloaddition reaction (azide- dibenzocyclooctyne) was used to attach iproplatin-loaded liposomes L(Pt) to gas-filled microbubbles (M), forming an ultrasound-responsive drug delivery vehicle [M-L(Pt)]. Ultrasound-triggered release of iproplatin from the microbubble-liposome construct was evaluated in cellulo. Breast cancer (MCF-7) cells treated with both free iproplatin and iproplatin-loaded liposome-microbubbles [M-L(Pt)] demonstrated an increase in platinum concentration when exposed to ultrasound. No appreciable platinum uptake was observed in MCF-7 cells following treatment with L(Pt) only or L(Pt)+ultrasound, suggesting that microbubble-mediated ultrasonic release of platinum-based drugs from liposomal carriers enables greater control over drug delivery.

Investigation on Optical and Biological Properties of 2-(4-Dimethylaminophenyl)benzothiazole Based Cycloplatinated Complexes

The optical and biological properties of 2-(4-dimethylaminophenyl)benzothiazole cycloplatinated complexes featuring bioactive ligands ([{Pt(Me 2 N-pbt)(C 6 F 5 )}L] [L = Me 2 N-pbtH 1 , p -dpbH (4-(diphenylphosphino)benzoic acid) 2 , o -dpbH (2-(diphenylphosphino)benzoic acid) 3) , [Pt(Me 2 N-pbt)( o -dpb)] 4 ,  [{Pt(Me 2 N-pbt)(C 6 F 5 )} 2 (µ-PR n P)] [PR 4 P = O(CH 2 CH 2 OC(O)C 6 H 4 PPh 2 ) 2 5 , PR 12 P = O{(CH 2 CH 2 O) 3 C(O)C 6 H 4 PPh 2 } 2 6 ] are presented. Complexes 1-6 display 1 ILCT and metal perturbed 3 ILCT dual emissions. The ratio between both bands is excitation dependent, accomplishing warm-white emissions for 2 , 5 and 6 .  The phosphorescent emission is lost in aerated solutions owing to photoinduced electron transfer to 3 O 2 and formation of 1 O 2 , as confirmed in complexes 2 and 4 . They also exhibit photoinduced phosphorescence enhancement in non-degassed DMSO, due to local oxidation of DMSO by sensitized 1 O 2 , which causes a local degassing. Me 2 N-pbtH and the complexes exhibit specific accumulation in the Golgi apparatus although only 2 , 3 and 6 were active against A549 and HeLa cancer cell lines, being 6 highly selective respect to nontumoral cells. The potential photodynamic property of these complexes was demonstrated with complex 4 .

Recent Progresses in Conjugation with Bioactive Ligands to Improve the Anticancer Activity of Platinum Compounds

Platinum (Pt) drugs, including cisplatin, are widely used for the treatment of solid tumors. Despite the clinical success, side effects and occurrence of resistance represent major limitations to the use of clinically available Pt drugs. To overcome these problems, a variety of derivatives have been designed and synthetized. Here, we summarize the recent progress in the development of Pt(II) and Pt(IV) complexes with bioactive ligands. The development of Pt(II) and Pt(IV) complexes with targeting molecules, clinically available agents, and other bioactive molecules is an active field of research. Even if none of the reported Pt derivatives has been yet approved for clinical use, many of these compounds exhibit promising anticancer activities with an improved pharmacological profile. Thus, planning hybrid compounds can be considered as a promising approach to improve the available Pt-based anticancer agents and to obtain new molecular tools to deepen the knowledge of cancer progression and drug resistance mechanisms.

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.

ctc-[Pt(NH3)2(cinnamate)(valproate)Cl2] is a highly potent and low-toxic triple action anticancer prodrug

Pt(iv) prodrugs have gained tremendous attention due to their indisputable advantages compared to cisplatin. Herein, new Pt(iv) derivatives with cinnamic acid at the first axial position, and inhibitor of matrix metalloproteinases-2 and -9, histone deacetylase, cyclooxygenase or pyruvate dehydrogenase at the second axial position are constructed to develop multi-action prodrugs. We demonstrate that Pt(iv) prodrugs are reducible and have superior antiproliferative activity with IC₅₀ values at submicromolar concentrations. Notably, Pt(iv) prodrugs exhibit highly potent anti-tumour activity in an in vivo breast cancer model. Our results support the view that a triple-action Pt(iv) prodrug acts via a synergistic mechanism, which involves the effects of CDDP and the effects of axial moieties, thus jointly leading to the death of tumour cells. These findings provide a practical strategy for the rational design of more effective Pt(iv) prodrugs to efficiently kill tumour cells by enhancing their cellular accumulation and tuning their canonical mechanism.

Can the Self-Assembling of Dicarboxylate Pt(IV) Prodrugs Influence Their Cell Uptake?

The possibility of spontaneous self-assembly of dicarboxylato Pt(IV) prodrugs and the consequences on their uptake in cancer cells have been evaluated in different aqueous solutions. Four Pt(IV) complexes, namely, (OC-6-33)-diacetatodiamminedichloridoplatinum(IV), Ace, (OC-6-33)-diamminedibutanoatodichloridoplatinum(IV), But, (OC-6-33)-diamminedichloridodihexanoatoplatinum(IV), Hex, and (OC-6-33)-diamminedichloridodioctanoatoplatinum(IV), Oct, have been dispersed in i) milliQ water, ii) phosphate buffered saline, and iii) complete cell culture media (RPMI 1640 or DMEM) containing fetal bovine serum (FBS). The samples have been analyzed by dynamic light scattering (DLS) to measure the size and distribution of the nanoparticles possibly present. The zeta potential offered an indication of the stability of the resulting aggregates. In the case of the most lipophilic compounds of the series, namely, Oct and to a lesser extent Hex, the formation of nanosized aggregates has been observed, in particular at the highest concentration tested (10 μM). The cell culture media had the effect to disaggregate these nanoparticles, mainly by virtue of their albumin content, able to interact with the organic chains via noncovalent (hydrophobic) interactions. For Oct, at the highest concentration employed for the uptake tests (10 μM), the combination between passive diffusion and endocytosis of the self-assembled nanoparticles makes the cellular uptake higher than in the presence of passive diffusion only. During the study of cellular uptake on A2780 ovarian cancer cells pretreated with cytochalasin D, a statistically significant inhibition of endocytosis was observed for Oct. In these experimental conditions, the relationship between uptake and lipophilicity becomes almost linear instead of exponential. Since Oct anticancer prodrug is active at nanomolar concentrations, where the aggregation in culture media is almost abolished, this phenomenon should not significantly impact its antiproliferative activity.

Pt(IV) Anticancer Prodrugs - A Tale of Mice and Men

We would like to be able to design Pt(IV) prodrugs that can overcome resistance and minimize side effects. Unlike with the early exploration of Pt(II) anticancer agents where clear structure-activity relationships were defined, even after more than two decades of research on Pt(IV) prodrugs, there is no roadmap that can point us to the holy grail. Despite many excellent rational endeavors, we still have not found the "right" two axial ligands to append to the Pt(IV) derivatives of platinum(II) drugs that will "make platinum great again". So far this proved elusive, indicating that the design of Pt(IV) prodrugs is a difficult and frustrating task. Despite our better understanding of the biological processes and availability of advanced technologies, even our sophisticated rational plans often leave us disappointed and frustrated because at the end of the day, we are not able to outsmart the cancer cells or the mice, and just like Rosenberg, we might need to be rescued by serendipity.

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.

Platinum(IV) anticancer agents; are we en route to the holy grail or to a dead end?

Pt(IV) complexes are designed as prodrugs that are intended to overcome resistance. Pt(IV) prodrugs are activated inside cancer cells releasing cytotoxic Pt(II) drugs as well as two axial ligands that can be used to confer favorable pharmacological properties to the prodrug. The ligands can be innocent spectators, cancer targeting agents or bioactive moieties. The choice of axial ligands determines the chemical and pharmacological properties of the prodrugs. Over the years, several approaches were employed in attempts to increase the selectivity of the prodrugs to cancer cells and to utilize multi-action prodrugs to overcome resistance. In this review, we critically examine several of these approaches in order to evaluate the validity of some of the working hypotheses that are driving the current research.

Fluorescence, DNA Interaction and Cytotoxicity Studies of 4,5-Dihydro-1H-Pyrazol-1-Yl Moiety Based Os(IV) Compounds: Synthesis, Characterization and Biological Evaluation

Osmium(IV) pyrazole compounds and ligands were synthesized and well characterised. Ligands were characterized by heteronuclear NMR spectroscopy (¹H & ¹³C), elemental analysis, IR spectroscopy and liquid crystal mass spectroscopy. Os(IV) complexes were characterized by ESI-MS, ICP-OES, IR spectroscopy, conductance measurements, magnetic measurements and electronic spectroscopy. Binding of compounds with HS-DNA were evaluated using viscosity measurements, absorption titration, fluorescence quenching, and molecular docking, which show effective intercalation mode exhibited by compounds. Binding constant of Os(IV) complexes are found to be 8.1 to 9.2 × 10⁴ M^-1. Bacteriostatic and cytotoxic activities were carried out to evaluate MIC, LC₅₀, and IC₅₀. The compounds have been undergone bacteriostatic screening using three sets of Gram^+ve and two sets of Gram^-ve bacteria. MIC of complexes are found to be 72.5-100 μM, whereas that of ligands fall at about 122.5-150 μM.. LC₅₀ count of ligands fall in the range of 16.22-17.28 μg/mL whereas that of complexes of Os(IV) fall in the range of 4.87-5.87 μg/mL. IC₅₀ of osmium compounds were evaluated using HCT-116 cell line. All the Os(IV) compounds show moderate IC₅₀.

Platinum(IV)-Estramustine Multiaction Prodrugs Are Effective Antiproliferative Agents against Prostate Cancer Cells

Herein, we describe the synthesis, characterization, and biological properties of Pt(IV) derivatives of cisplatin with estramustine at the first axial position, which is known to disrupt the microtubule assembly and act as an androgen antagonist, and varying the second axial position using an innocent ligand (acetate or hydroxyl) to prepare dual-action and triple-action prodrugs with known inhibitors of histone deacetylase, cyclooxygenase, and pyruvate dehydrogenase kinase. We demonstrate superior antiproliferative activity at submicromolar concentrations of the prodrugs against a panel of cancer cell lines, particularly against prostate cancer cell lines. The results obtained in this study exemplify the complex mode of action of "multiaction" Pt(IV) prodrugs. Interestingly, changing the second axial ligand in the Pt-estramustine complex has a significant effect on the mode of action, suggesting that all three components of the Pt(IV) prodrugs (platinum moiety and axial ligands) contribute to the killing of cells and not just one dominant component.

A Multi-action PtIV Conjugate with Oleate and Cinnamate Ligands Targets Human Epithelial Growth Factor Receptor HER2 in Aggressive Breast Cancer Cells

HER2-positive breast cancer is an aggressive subtype that typically responds poorly to standard chemotherapy. To design an anticancer drug selective for HER2-expressing breast cancer, a Pt^IV prodrug with axial oleate and cinnamate ligands was synthesized. We demonstrate its superior antiproliferative activity in monolayer and 3D spheroid models; the antiproliferative efficiency increases gradually with increasing expression of HER2. The results also suggest that the released Pt^II compound inhibits the proliferation of cancer cells by a DNA-damage-mediated mechanism. Simultaneously, the released oleic and cinnamic acid can effectively inhibit HER2 expression. To our knowledge, this is the first platinum-based complex inhibiting HER2 expression that does not contain protein or peptide. Moreover, this Pt^IV prodrug is capable of overcoming the resistance of cancer stem cells (CSCs), inducing death in both CSCs and differentiated cancer cells. Thus, the results substantiate our design strategy and demonstrate the potential of this approach for the development of new, therapeutically relevant compounds.

Oxidation of cis-Diamminediacetato PtII with Hydrogen Peroxide Can Give Rise to Two Isomeric PtIV Products

The oxidation of cis-[Pt(NH₃ )₂ (OAc)₂ ] with H₂ O₂ yields a mixture of two isomers: ctc-[Pt(NH₃ )₂ (OH)₂ (OAc)₂ ] and ctc-[Pt(NH₃ )₂ (OH)(OAc)(OH)(OAc)]. Following modification with 4-phenylbutyric (PhB) anhydride, two isomers were separated and characterized; the symmetric ctc-[Pt(NH₃ )₂ (PhB)₂ (OAc)₂ ] (1) and the nonsymmetric ctc-[Pt(NH₃ )₂ (PhB)(OAc)(PhB)(OAc)] (2). They differ in their log P values and despite having similar cellular uptake and similar DNA platination levels, the symmetric ctc-[Pt(NH₃ )₂ (OH)₂ (OAc)₂ ] is more than 4-fold more potent than the nonsymmetric isomer in a panel of 4 cancer cell lines.

Stability, Reduction, and Cytotoxicity of Platinum(IV) Anticancer Prodrugs Bearing Carbamate Axial Ligands: Comparison with Their Carboxylate Analogues

Platinum(IV) complexes containing carboxylate and carbamate ligands at the axial position have been reported previously. A better understanding of the similarity and difference between the two types of ligands will provide us with new insights and more choices to design novel Pt(IV) complexes. In this study, we systematically investigated and compared the properties of Pt(IV) complexes bearing the two types of ligands. Ten pairs of unsymmetric Pt(IV) complexes bearing axial carbamate or carboxylate ligands were synthesized and characterized. The stability of these Pt(IV) complexes in a PBS buffer with or without a reducing agent was investigated, and most of these complexes exhibited good stability. Besides, most Pt(IV) prodrugs with carbamate axial ligands were reduced faster than the corresponding ones with carboxylate ligands. Furthermore, the aqueous solubilities and lipophilicities of these Pt(IV) complexes were tested. All the carbamate complexes showed better aqueous solubility and decreased lipophilicity as compared to those of the corresponding carboxylate complexes, due to the increased polarity of carbamate ligands. Biological properties of these complexes were also evaluated. Many carbamate complexes showed cytotoxicity similar to that of the carboxylate complexes, which may derive from the lower cellular accumulation but faster reduction of the former. Our research highlights the differences between the Pt(IV) prodrugs containing carbamate and carboxylate axial ligands and may contribute to the future rational design of Pt-based anticancer prodrugs.

Anticancer Melatplatin Prodrugs: High Effect and Low Toxicity, MT1-ER-Target and Immune Response In Vivo

Multitargeted therapy could rectify various oncogenic pathways to block tumorigenesis and progression. The combination of endocrine-, immune-, and chemotherapy might exert a highly synergistic effect against certain tumors. Herein, a series of smart Pt(IV) prodrugs 3-6, named Melatplatin, were rationally designed not only to multitarget DNA, MT1, and estrogen receptor (ER) but also to activate immune response. Melatplatin, conjugating first-line chemotherapeutic Pt drugs with human endogenous melatonin (MT), significantly enhanced drug efficacy especially in ER high-expression (ER⁺) cells, among which 3 presented the most potent cytotoxicity toward ER⁺ MCF-7 with nanomolar IC₅₀ values 100-fold lower than cisplatin. Melatplatin could bind well to melatonin receptor (MT1) according to molecular docking. Besides, 3 evidently increased intracellular accumulation and DNA damage, upregulated γH2AX and P53, and silenced NF-κB to induce massive apoptosis. Most strikingly, 3 effectively inhibited tumor growth and attenuated systemic toxicity compared to cisplatin in vivo, promoting lymphocyte proliferation in spleen to achieve immune modulation.

Oxaliplatin and [Pt(R,R-DACH)(panobinostat-2H)] show nanomolar cytotoxicity towards diffuse intrinsic pontine glioma (DIPG)

We report the synthesis of two novel platinum(ii) complexes which incorporate histone deacetylase (HDAC) inhibitors: [Pt^II(R,R-DACH)(Sub_-H)] (1), [Pt^II(R,R-DACH)(panobinostat_-2H)] (2), where SubH = suberoyl-bis-hydroxamic acid; DACH = (1R,2R)-(-)-1,2-diaminocyclohexane and panobinostat = (E)-N-hydroxy-3-[4-[[2-(2-methyl-1H-indol-3-yl)ethylamino]methyl]phenyl]prop-2-enamide. Complexes 1 and 2 were characterised by ¹H, ¹³C, ¹⁹⁵Pt NMR spectroscopy and ESI-MS. Whilst oxaliplatin demonstrated considerable cytotoxicity in two patient-derived low-passage paediatric glioma DIPG cell lines (IC₅₀ values of 0.333 μM in SU-DIPG-IV, and 0.135 μM in SU-DIPG-XXI), complex 2 showed even greater cytotoxicities, with IC₅₀ values of 0.021 μM (SU-DIPG-IV), 0.067 μM (BIOMEDE 194) and 0.009 μM (SU-DIPG-XXI). Complex 2 also demonstrated superior aqueous solubility in comparison to panobinostat. Complex 2 released free intact panobinostat under HPLC conditions, as determined by ESI-MS. Incubation of solutions of oxaliplatin (H₂O) and panobinostat (DMF) resulted in instantaneous reactivity and precipitation of a panobinostat derivative which was not a platinum complex; the same reactivity was not observed between carboplatin and panobinostat.

Multiaction Pt(IV) Carbamate Complexes Can Codeliver Pt(II) Drugs and Amine Containing Bioactive Molecules

Multiaction Pt(IV) prodrugs can overcome resistance associated with the FDA approved Pt(II) drugs like cisplatin. Intracellular reduction of the octahedral Pt(IV) derivatives of cisplatin releases cisplatin and the two axial ligands. When the released axial ligands act synergistically with cisplatin to kill the cancer cells, we have multiaction prodrugs. Most Pt(IV) multiaction prodrugs have bioactive ligands possessing a carboxylate that is conjugated to the Pt(IV) because breaking the Pt(IV)-ligand bond releases the active moiety. As many drugs that act synergistically with cisplatin do not have carboxylates, a major challenge is to prepare multiaction Pt(IV) complexes with drugs that have amino groups or hydroxyl groups such that following reduction, the drugs are released in their active form. Our objective was to prepare multiaction Pt(IV) prodrugs that release bioactive molecules having amino groups. Because we cannot conjugate amino groups to the axial position of Pt(IV), we developed a novel and efficient approach for the synthesis of Pt(IV)-carbamato complexes and demonstrated that following reduction of the Pt(IV), the released carbamates undergo rapid decarboxylation, releasing the free amine, as in the case of the PARP-1 inhibitor 3-aminobenzamide and the amino derivative of the HDAC inhibitor SAHA. Pt(IV)-carbamato complexes are stable in cell culture medium and are reduced by ascorbate. They are reduced slower than their carboxylato and carbonato analogues. We believe that this approach paves the way for preparing novel classes of multiaction Pt(IV) prodrugs with amino containing bioactive molecules that up to now were not accessible.

Pt(II) versus Pt(IV) in Carbene Glycoconjugate Antitumor Agents: Minimal Structural Variations and Great Performance Changes

Octahedral Pt(IV) complexes (2Pt-R) containing a glycoconjugate carbene ligand were prepared and fully characterized. These complexes are structural analogues to the trigonal bipyramidal Pt(II) species (1Pt-R) recently described. Thus, an unprecedented direct comparison between the biological properties of Pt compounds with different oxidation states and almost indistinguishable structural features was performed. The stability profile of the novel Pt(IV) compounds in reference solvents was determined and compared to that of the analogous Pt(II) complexes. The uptake and antiproliferative activities of 2Pt-R and 1Pt-R were evaluated on the same panel of cell lines. DNA and protein binding properties were assessed using human serum albumin, the model protein hen egg white lysozyme, and double stranded DNA model systems by a variety of experimental techniques, including UV-vis absorption spectroscopy, fluorescence, circular dichroism, and electrospray ionization mass spectrometry. Although the compounds present similar structures, their in-solution stability, cellular uptake, and DNA binding properties are diverse. These differences may represent the basis of their different cytotoxicity and biological activity.

Metallothionein isoforms as double agents - Their roles in carcinogenesis, cancer progression and chemoresistance

Metallothioneins (MTs) are small cysteine-rich intracellular proteins with four major isoforms identified in mammals, designated MT-1 through MT-4. The best known biological functions of MTs are their ability to bind and sequester metal ions as well as their active role in redox homeostasis. Despite these protective roles, numerous studies have demonstrated that changes in MT expression could be associated with the process of carcinogenesis and participation in cell differentiation, proliferation, migration, and angiogenesis. Hence, MTs have the role of double agents, i.e., working with and against cancer. In view of their rich biochemical properties, it is not surprising that MTs participate in the emergence of chemoresistance in tumor cells. Many studies have demonstrated that MT overexpression is involved in the acquisition of resistance to anticancer drugs including cisplatin, anthracyclines, tyrosine kinase inhibitors and mitomycin. The evidence is gradually increasing for a cellular switch in MT functions, showing that they indeed have two faces: protector and saboteur. Initially, MTs display anti-oncogenic and protective roles; however, once the oncogenic process was launched, MTs are utilized by cancer cells for progression, survival, and contribution to chemoresistance. The duality of MTs can serve as a potential prognostic/diagnostic biomarker and can therefore pave the way towards the development of new cancer treatment strategies. Herein, we review and discuss MTs as tumor disease markers and describe their role in chemoresistance to distinct anticancer drugs.