Platinum(iv) anticancer prodrugs - hypotheses and facts

Novel Nickel(II), Palladium(II), and Platinum(II) Complexes with O,S Bidendate Cinnamic Acid Ester Derivatives: An In Vitro Cytotoxic Comparison to Ruthenium(II) and Osmium(II) Analogues

(1) Background: Since the discovery of cisplatin’s cytotoxic properties, platinum(II) compounds have attracted much interest in the field of anticancer drug development. Over the last few years, classical structure−activity relationships (SAR) have been broken by some promising new compounds based on platinum or other metals. We focus on the synthesis and characterization of 17 different complexes with β-hydroxydithiocinnamic acid esters as O,S bidendate ligands for nickel(II), palladium(II), and platinum(II) complexes. (2) Methods: The bidendate compounds were synthesized and characterized using classical methods including NMR spectroscopy, MS spectrometry, elemental analysis, and X-ray crystallography, and their cytotoxic potential was assessed using in vitro cell culture assays. Data were compared with other recently reported platinum(II), ruthenium(II), and osmium(II) complexes based on the same main ligand system. (3) Results: SAR analyses regarding the metal ion (M), and the alkyl-chain position (P) and length (L), revealed the following order of the effect strength for in vitro activity: M > P > L. The highest activities have Pd complexes and ortho-substituted compounds. Specific palladium(II) complexes show lower IC50 values compared to cisplatin, are able to elude cisplatin resistance mechanisms, and show a higher cancer cell specificity. (4) Conclusion: A promising new palladium(II) candidate (Pd3) should be evaluated in further studies using in vivo model systems, and the identified SARs may help to target platinum-resistant tumors.

Abplatin(IV) inhibited tumor growth on a patient derived cancer model of hepatocellular carcinoma and its comparative multi-omics study with cisplatin

BACKGROUND

Cisplatin, the alkylating agent of platinum(II) (Pt(II)), is the most common antitumor drug in clinic; however, it has many side effects, therefore it is higly desired to develop low toxicity platinum(IV) (Pt(IV)) drugs. Multi-omics analysis, as a powerful tool, has been frequently employed for the mechanism study of a certain therapy at the molecular level, which might be helpful for elucidating the mechanism of platinum drugs and facilitating their clinical application.

METHODS

Strating form cisplatin, a hydrophobic Pt(IV) prodrug (CisPt(IV)) with two hydrophobic aliphatic chains was synthesized, and further encapsulated with a drug carrier, human serum albumin (HSA), to form nanoparticles, namely AbPlatin(IV). The anticancer effect of AbPlatin(IV) was investigated in vitro and in vivo. Moreover, transcriptomics, metabolomics and lipidomics were performed to explore the mechanism of AbPlatin(IV).

RESULTS

Compared with cisplatin, Abplatin(IV) exhibited better tumor-targeting effect and greater tumor inhibition rate. Lipidomics study showed that Abplatin(IV) might induce the changes of BEL-7404 cell membrane, and cause the disorder of glycerophospholipids and sphingolipids. In addition, transcriptomics and metabolomics study showed that Abplatin(IV) significantly disturbed the purine metabolism pathway.

CONCLUSIONS

This research highlighted the development of Abplatin(IV) and the use of multi-omics for the mechanism elucidation of prodrug, which is the key to the clinical translation of prodrug.

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.

Application of Approved Cisplatin Derivatives in Combination Therapy against Different Cancer Diseases

The problems with anticancer therapy are resistance and toxicity. From 3000 Cisplatin derivatives tested as antitumor agents, most of them have been rejected, due to toxicity. The aim of current study is the comparison of therapeutic combinations of the currently applied in clinical practice: Cisplatin, Carboplatin, Oxaliplatin, Nedaplatin, Lobaplatin, Heptaplatin, and Satraplatin. The literature data show that the strategies for the development of platinum anticancer agents and bypassing of resistance to Cisplatin derivatives and their toxicity are: combination therapy, Pt IV prodrugs, the targeted nanocarriers. The very important strategy for the improvement of the antitumor effect against different cancers is synergistic combination of Cisplatin derivatives with: (1) anticancer agents-Fluorouracil, Gemcitabine, Cytarabine, Fludarabine, Pemetrexed, Ifosfamide, Irinotecan, Topotecan, Etoposide, Amrubicin, Doxorubicin, Epirubicin, Vinorelbine, Docetaxel, Paclitaxel, Nab-Paclitaxel; (2) modulators of resistant mechanisms; (3) signaling protein inhibitors-Erlotinib; Bortezomib; Everolimus; (4) and immunotherapeutic drugs-Atezolizumab, Avelumab, Bevacizumab, Cemiplimab, Cetuximab, Durvalumab, Erlotinib, Imatinib, Necitumumab, Nimotuzumab, Nivolumab, Onartuzumab, Panitumumab, Pembrolizumab, Rilotumumab, Trastuzumab, Tremelimumab, and Sintilimab. An important approach for overcoming the drug resistance and reduction of toxicity of Cisplatin derivatives is the application of nanocarriers (polymers and liposomes), which provide improved targeted delivery, increased intracellular penetration, selective accumulation in tumor tissue, and enhanced therapeutic efficacy. The advantages of combination therapy are maximum removal of tumor cells in different phases; prevention of resistance; inhibition of the adaptation of tumor cells and their mutations; and reduction of toxicity.

A platinum-based fluorescent "turn on" sensor to decipher the reduction of platinum(IV) prodrugs

We report a strategy to use a fluorescence "turn on" sensor to quantify the reduction of platinum(IV) prodrugs in a real-time mode by simply and conveniently monitoring the fluorescence intensity. Proteins with high molecular weights, especially those between 10 and 100 kDa, contribute more to the reduction of the platinum(IV) complex in cell extracts.

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.

Metallodrugs in cancer nanomedicine

Metal complexes are extensively used for cancer therapy. The multiple variables available for tuning (metal, ligand, and metal-ligand interaction) offer unique opportunities for drug design, and have led to a vast portfolio of metallodrugs that can display a higher diversity of functions and mechanisms of action with respect to pure organic structures. Clinically approved metallodrugs, such as cisplatin, carboplatin and oxaliplatin, are used to treat many types of cancer and play prominent roles in combination regimens, including with immunotherapy. However, metallodrugs generally suffer from poor pharmacokinetics, low levels of target site accumulation, metal-mediated off-target reactivity and development of drug resistance, which can all limit their efficacy and clinical translation. Nanomedicine has arisen as a powerful tool to help overcome these shortcomings. Several nanoformulations have already significantly improved the efficacy and reduced the toxicity of (chemo-)therapeutic drugs, including some promising metallodrug-containing nanomedicines currently in clinical trials. In this critical review, we analyse the opportunities and clinical challenges of metallodrugs, and we assess the advantages and limitations of metallodrug delivery, both from a nanocarrier and from a metal-nano interaction perspective. We describe the latest and most relevant nanomedicine formulations developed for metal complexes, and we discuss how the rational combination of coordination chemistry with nanomedicine technology can assist in promoting the clinical translation of metallodrugs.

Flavin-mediated photoactivation of Pt(IV) anticancer complexes: computational insights on the catalytic mechanism

The mechanism for the photocatalytic activation of Pt(IV) anticancer prodrugs by riboflavin in the presence of NADH has been investigated by DFT. In the first step of the reaction, the oxidation kinetics of NADH to afford the catalytically active riboflavin hydroquinone is dramatically favoured by generation of the flavin triplet excited state. In the triplet, formation of a π-π stacked adduct promotes the hydride transfer from NADH to riboflavin with an almost barrierless pathway (2.7 kcal mol^-1). In the singlet channel, conversely, the process is endergonic and requires overcoming a higher activation energy (19.2 kcal mol^-1). In the second half of the reaction, the reduction of the studied Pt(IV) complexes by riboflavin hydroquinone occurs via an inner sphere mechanism, displaying free energy barriers smaller than 10 kcal mol^-1. Pt reduction by bioreductants such as NADH and ascorbate involve instead less stabilized transition states (22.2-38.3 kcal mol^-1), suggesting that riboflavin hydroquinone is an efficient reducing agent for Pt(IV) derivatives in biological settings.

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.

Interactions between mitochondria-damaging platinum(IV) prodrugs and cytochrome c

In this work, we present the first study about the interactions of mitochondria-damaging Pt(IV) prodrugs with cytochrome c. We synthesized a cisplatin-based Pt(IV) prodrug bearing a lipophilic hydrocarbon tail and anionic dansyl head group. The amphiphilic structure facilitates its accumulation in the mitochondria of cancer cells, which was validated using graphite furnace atomic absorption spectroscopy (GFAAS) and fluorescence imaging. Accordingly, this Pt(IV) prodrug is able to trigger mitochondrial damage and apoptosis. Overall, the Pt(IV) prodrug exhibits superior therapeutic effects against a panel of human cancer cells compared to cisplatin. It also overcomes drug resistance in ovarian cancer. Notably, HPLC analysis indicates that cytochrome c accelerates reduction (or activation) of the Pt(IV) prodrug in the presence of the electron donor nicotinamide adenine dinucleotide (NADH). More interestingly, additional studies indicate that cytochrome c was platinated by the reduced product of Pt(IV) prodrugs, and that empowers the proapoptotic peroxidase activity.

Click Pt(IV)-Carbohydrates Pro-Drugs for Treatment of Osteosarcoma

The selectivity vs. cancer cells has always been a major challenge for chemotherapeutic agents and in particular for cisplatin, one of the most important anticancer drugs for the treatment of several types of tumors. One strategy to overtake this challenge is to modify the coordination sphere of the metallic center with specific vectors whose receptors are overexpressed in the tumoral cell membrane, such as monosaccharides. In this paper, we report the synthesis of four novel glyco-modified Pt(IV) pro-drugs, based on cisplatin scaffold, and their biological activity against osteosarcoma (OS), a malignant tumor affecting in particular adolescents and young adults. The sugar moiety and the Pt scaffold are linked exploiting the Copper Azide Alkyne Cycloaddition (CUAAC) reaction, which has become the flagship of click chemistry due to its versatility and mild conditions. Cytotoxicity and drug uptake on three different OS cell lines as well as CSCs (Cancer Stem Cell) are described.

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.

Cisplatin-cyclooxygenase inhibitor conjugates, free and immobilised in mesoporous silica SBA-15, prove highly potent against triple-negative MDA-MB-468 breast cancer cell line

For the development of anticancer drugs with higher activity and reduced toxicity, two approaches were combined: preparation of platinum(IV) complexes exhibiting higher stability compared to their platinum(II) counterparts and loading them into mesoporous silica SBA-15 with the aim to utilise the passive enhanced permeability and retention (EPR) effect of nanoparticles for accumulation in tumour tissues. Three conjugates based on a cisplatin scaffold bearing the anti-inflammatory drugs naproxen, ibuprofen or flurbiprofen in the axial positions (1, 2 and 3, respectively) were synthesised and loaded into SBA-15 to afford the mesoporous silica nanoparticles (MSNs) SBA-15|1, SBA-15|2 and SBA-15|3. Superior antiproliferative activity of both free and immobilised conjugates in a panel of four breast cancer cell lines (MDA-MB-468, HCC1937, MCF-7 and BT-474) with markedly increased cytotoxicity with respect to cisplatin was demonstrated. All compounds exhibit highest activity against the triple-negative cell line MDA-MB-468, with conjugate 1 being the most potent. However, against MCF-7 and BT-474 cell lines, the most notable improvement was found, with IC₅₀ values up to 240-fold lower than cisplatin. Flow cytometry assays clearly show that all compounds induce apoptotic cell death elevating the levels of both early and late apoptotic cells. Furthermore, autophagy as well as formation of reactive oxygen species (ROS) and nitric oxide (NO) were elevated to a similar or greater extent than with cisplatin.

19F NMR Allows to Investigate the Fate of Platinum(IV) Prodrugs in Physiological Conditions

Pt(IV) prodrugs can overcome resistance and side effects of conventional Pt(II) anticancer therapies. By 19 F-labeling of a Pt(IV) prodrug (Pt-FBA, FBA = p -fluorobenzoate), the activation under physiological conditions could be investigated. It is found that, unlike single-electron reductants, multi-electron agents can efficiently promote the two electrons reduction of Pt(IV) to Pt(II). Moreover, the activation of Pt-FBA in cell lysate is highly dependent upon the type of cancer cells. When administered to E. coli , Pt-FBA is reduced intracellularly and free FBA can shuttle out of the cell. Interestingly, the reduction rate greatly increases by inducing metallothionein overexpression and is lowered by addition of Zn(II) ions. Finally, when injected into mice, Pt-FBA undergoes fast reduction in the bloodstream accompanied by metabolic degradation of FBA; nevertheless, unreduced Pt-FBA can accumulate to detectable levels in liver and kidneys. The proposed 19 F-NMR approach has the advantage of avoiding the interference of all background signals.

An erythrocyte-delivered photoactivatable oxaliplatin nanoprodrug for enhanced antitumor efficacy and immune response

The outcome of conventional platinum (Pt)-based chemotherapy is limited by reduced circulation, failure to accumulate in the tumor, and dose-limiting toxicity arising from non-controllable activation. To address these limitations, we present an erythrocyte-delivered and near-infrared (NIR) photoactivatable Pt^IV nanoprodrug for advanced cancer treatment. Compared with small molecule Pt^IV prodrugs, this nanoprodrug exhibits significantly enhanced stability, prolonged circulation in the blood, and minimized side effects. The hitchhiking of the nanoprodrug on erythrocytes dramatically increases Pt accumulation in the tumor. Upon irradiation, the nanoprodrug releases oxaliplatin in a controllable manner, resulting in significant antitumor activity against breast tumors in vivo, as evidenced by the complete elimination of tumors from a single-dose injection. Additionally, this nanoprodrug is associated with remarkably enhanced immunopotentiation. Our study highlights an efficient strategy to overcome the shortcomings of traditional Pt-based chemotherapy via the erythrocyte-mediated delivery of an NIR-activatable nanoprodrug of oxaliplatin, a clinically used anticancer drug.

Strategic illustration of an erythrocyte-delivered and near-infrared photoactivatable oxaliplatin nanoprodrug for enhanced antitumor efficacy and immune response.

Effect of chirality on the anticancer activity of Pt(II) and Pt(IV) complexes containing 1R,2R and 1S,2S enantiomers of the trans-1,2-diamino-4-cyclohexene ligand (DACHEX), an analogue of diaminocyclohexane used in oxaliplatin

Six enantiomerically pure, oxaliplatin-like, platinum compounds (two platinum(II) and four platinum(IV)), all containing unsaturated cyclic diamine trans-1,2-diamino-4-cyclohexene (DACHEX) as a substitute for the trans-1,2-diaminocyclohexane used in oxaliplatin, were investigated. The complexes were characterized by elemental analyses, ESI-MS, and 1H-NMR spectroscopy. For the four Pt(IV) complexes the electrochemical redox behaviour, investigated by cyclic voltammetry, showed that all complexes possess reduction potentials suitable for activation in vivo. The antiproliferative activity was assessed in vitro on human cancer cell lines, also selected for resistance to platinum-based drugs or belonging to the MultiDrug-Resistant (MDR) phenotype. All complexes exhibited antiproliferative activity superior to that of cisplatin and almost equivalent to or better than that of oxaliplatin; moreover, most complexes were also capable of overcoming both the cisplatin- and the oxaliplatin-resistance. By comparing the effectiveness of the enantiomerically pure compounds with the racemic one, the R,R enantiomer emerged as the most effective in the case of Pt(II) complexes whereas the S,S enantiomer was the most effective in the case of the Pt(IV) derivatives. From the results obtained also against 3D spheroid tumor models, cis,trans,cis-[Pt(OXA)(OBz)2(1S,2S-DACHEX)] (OBz = benzoate) emerged as the most promising candidate for further preclinical investigation.

Photochemistry and in vitro anticancer activity of Pt(IV)Re(I) conjugates

The photophysical and photochemical properties of two Pt(IV)Re(I) conjugates were studied via both experimental and computational methods. Both conjugates exhibit modest photocytotoxicity against ovarian cancer cells. X-ray fluorescence microscopy showed that Pt and Re colocalize in cells whether they had been irradiated or not. This work demonstrates the potential of photoactivated multilimetallic agents for combating cancer.

Novel recognition mechanism based on oxidative addition of Pt(II) complex-based luminescent probes for hypochlorite ion detection

Platinum(II) complexes are the most commonly used anticancer drugs and potential optical materials, but the detectability of Pt(II) complex-based probes is seldom reported. In our previous work, a tetradentate Pt(II) complex Pt-CHO was utilised as a 'turn-off' probe to detect ClO^- and image cancer cells. However, the recognition mechanism has not been completely clarified and there are still doubts. In this work, three Pt(II) complexes, Pt-H, Pt-CHO and Pt-COOH, were developed to elucidate the mechanism of this class of complexes and refine their property studies. As a result, the UV-visible absorption and luminescence emission experiments, as well as the mass spectrum, proved that the oxidation of Pt(II) to Pt(IV) was the real reason for luminescence quenching, which has nothing to do with aldehyde groups. This first reported mechanism introduces a new type of ClO^- probe based on Pt(II) complexes, thereby expanding the application fields of platinum complexes. Moreover, the quantum yield measurements, the effect of biomolecules and reversibility were studied to improve the properties of the probes. Theoretical calculations were used to gain an in-depth understanding of optical characteristics and related mechanisms. The cell imaging of RAW264.7 cells under endogenous ClO^- proved the potential of the probes in bioimaging.

Structure-Activity Relationships of Triple-Action Platinum(IV) Prodrugs with Albumin-Binding Properties and Immunomodulating Ligands

Chemotherapy with platinum complexes is essential for clinical anticancer therapy. However, due to side effects and drug resistance, further drug improvement is urgently needed. Herein, we report on triple-action platinum(IV) prodrugs, which, in addition to tumor targeting via maleimide-mediated albumin binding, release the immunomodulatory ligand 1-methyl-d-tryptophan (1-MDT). Unexpectedly, structure-activity relationship analysis showed that the mode of 1-MDT conjugation distinctly impacts the reducibility and thus activation of the prodrugs. This in turn affected ligand release, pharmacokinetic properties, efficiency of immunomodulation, and the anticancer activity in vitro and in a mouse model in vivo. Moreover, we could demonstrate that the design of albumin-targeted multi-modal prodrugs using platinum(IV) is a promising strategy to enhance the cellular uptake of bioactive ligands with low cell permeability (1-MDT) and to improve their selective delivery into the malignant tissue. This will allow tumor-specific anticancer therapy supported by a favorably tuned immune microenvironment.

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.

Platinum-based chemotherapy via nanocarriers and co-delivery of multiple drugs

Platinum-based anticancer drugs can inhibit the growth of cancer cells by disrupting DNA replication, which makes them widely applicable in clinics for treating tumors and cancers. However, owing to the intrinsic or acquired drug resistance and severe side effects caused in the treatment, their successful clinical applications have been limited. Various strategies have been used to address these challenges. Nanocarriers have been used for platinum drug delivery because they can be effectively deposited in tumor tissues to reduce the damage to normal organs for an enhanced permeability and retention (EPR) effect. Furthermore, for synergizing the function of platinum-based drugs with different mechanisms to decrease the toxicities, multicomponent chemotherapy has become an imperative strategy in clinical cancer treatments. This review aims to introduce the mechanisms of action and limitations of platinum-based drugs in clinics, followed by providing the current advancement of nanocarriers including lipids, polymers, dendrimers, micelles and albumin for platinum drug delivery in cancer treatments. In addition, multicomponent chemotherapy based on platinum drugs is introduced in detail. Finally, the prospects of multicomponent chemotherapy for cancer treatment are discussed as well.

Targeting ROS-AMPK pathway by multiaction Platinum(IV) prodrugs containing hypolipidemic drug bezafibrate

Alterations in lipid metabolism, commonly disregarded in the past, have been accepted as a hallmark for cancer. Exploring cancer therapeutics that interrupt the lipid metabolic pathways by monotherapy or combination with conventional chemotherapy or immunotherapy is of great importance. Here we modified cisplatin with an FDA-approved hypolipidemic drug, bezafibrate (BEZ), via the well-established Pt(IV) strategy, affording two multi-functional Pt(IV) anticancer agents cis,cis,trans-[Pt(NH₃)₂Cl₂(BEZ)(OH)] (CB) and cis,cis,trans-[Pt(NH₃)₂Cl₂(BEZ)₂] (CP) (BEZ = bezafibrate). The Pt(IV) prodrug CB exhibited an enhanced anticancer activity up to 187-fold greater than the clinical anticancer drug cisplatin. Both CB and CP had less toxicity to normal cells, showing higher efficacies and superior therapeutic indexes than cisplatin. Mechanism studies revealed that the bezafibrate-conjugated Pt(IV) complex CB, as a representative, could massively accumulate in A549 cells and genomic DNA, induce DNA damage, elevate intracellular ROS levels, perturb mitochondrial transmembrane potentials, activate the cellular metabolic sensor AMPK, and result in profound proliferation inhibition and apoptosis. Further cellular data also provided evidence that phosphorylation of AMPK, as a metabolic sensor, could suppress the downstream HMGB1, NF-κB, and VEGFA, which may contribute to the inhibition of angiogenesis and metastasis. Our study suggests that the antitumor action of CB and CP mechanistically distinct from the conventional platinum drugs and that functionalizing platinum-based agents with lipid-modulating agents may represent a novel practical strategy for cancer treatment.

Oxoplatin-B, a cisplatin-based platinum(IV) complex with photoactive BODIPY for mitochondria specific "chemo-PDT" activity

Oxoplatin-B, a platinum(IV) complex [Pt(NH₃)₂Cl₂(L¹)(OH)] (1) of 4-methylbenzoic acid (HL¹) functionalized with 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) was prepared, characterized and its antitumor activity studied. [Pt(NH₃)₂Cl₂(L²)(OH)] (2) of 4-methylbenzoic acid (HL²) was studied as a control. Complex 1 showed an absorption band at 500 nm (ɛ = 4.34 × 10⁴ M^-1 cm^-1) and an emission band at 515 nm (λ_ex = 488 nm, Φ_F = 0.64) in 1% dimethyl sulfoxide/Dulbecco's Modified Eagle's Medium (pH = 7.2). Visible light-induced (400-700 nm) generation of singlet oxygen was evidenced from 1,3-diphenylisobenzofuran titration study. Complex 1 showed photo-induced cytotoxicity in visible light (400-700 nm, 10 J cm^-2) against human breast cancer (MCF-7), cervical cancer (HeLa) and lung cancer (A549) cells (IC₅₀: 1.1-3.8 μM) while being less toxic in normal cells. Confocal imaging showed mitochondrial localization with additional evidence from platinum content from isolated mitochondria and 5,5,6,6'-tetrachloro-1,1',3,3' tetraethylbenzimi-dazoylcarbocyanine iodide (JC-1) assay. Cellular apoptosis was observed from Annexin-V-FITC (fluorescein isothiocyanate)/propidium iodide assay.

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.

Alternative mechanism of action of the DNP PtIV prodrug: intracellular cisplatin release and the mitochondria-mediated apoptotic pathway

In a recent research paper Dr. Suxing Jin et al. reported two multispecific PtIV complexes DNP and NP with non-steroidal anti-inflammatory drug naproxen (NPX) as the axial ligand(s). Herein, we clarify the mechanism of action of DNP, its therapeutic target and intracellular redox-status.

New Oxaliplatin-Pyrophosphato Analogs with Improved In Vitro Cytotoxicity

Two new Pt(II)-pyrophosphato complexes containing the carrier ligands cis-1,3-diaminocyclohexane (cis-1,3-DACH) and trans-1,2-diamine-4-cyclohexene (1,2-DACHEX), variants of the 1R,2R-diaminocyclohexane ligand present in the clinically used Pt-drug oxaliplatin, have been synthesized with the aim of developing new potential antitumor drugs with high bone tropism. The complexes are more stable at physiological pH than in acid conditions, with Na2[Pt(pyrophosphato)(cis-1,3-DACH)] (1) slightly more stable than [Pt(dihydrogenpyrophosphato)(1,2-DACHEX)] (2). The greater reactivity at acidic pH ensures a greater efficacy at the tumor site. Preliminary NMR studies indicate that 1 and 2 react slowly with 5'-GMP (used as a model of nucleic acids), releasing the pyrophosphate ligand and affording the bis 5'-GMP adduct. In vitro cytotoxicity assays performed against a panel of four human cancer cell lines have shown that both compounds are more active than oxaliplatin. Flow cytometry studies on HCT116 cells showed that the pyrophosphato compounds with the non-classical 1,3- and 1,4-diaminocyclohexane ligands (1 and 4) are the most capable to induce cells' death by apoptosis and necrosis.

Reactions of a photoactivatable diazido Pt(iv) anticancer complex with a single-stranded oligodeoxynucleotide

Platinum based anticancer agents are widely applied in clinic and their major target is believed to be DNA. Herein, the interaction of a photoactivatable diazido Pt(iv) anticancer prodrug trans,trans,trans-[Pt(N3)2(OH)2(py)2] (py = pyridine; 1) with a 15-mer single-G-containing oligodeoxynucleotide (ODN I: 5'-CT2CTCTTG8T9CT11TCTC-3') was investigated by mass spectrometric methods. Up to penta-platinated ODN I adducts were identified from primary mass spectra while the mono- and di-platinated adducts had the highest intensity. Fragmentation of mono-, di- and tri-platinated I adducts in tandem MS revealed that T2, G8, T11 and T9 are binding sites. No cytosine sites were identified which may be due to the facile loss of Pt adducts from cytosine during CID. The intensity of {Pt(py)2}-bound adducts was comparable to that of {Pt(N3)(py)2}-bound adducts, indicating that the photo-reduction pathway of complex 1 from Pt(iv) to Pt(ii) through two one-electron donations from two azides was substantial. Moreover, no transformation of N3 to NH3 on the {Pt(N3)(py)2}-bound adducts was observed, whereas it is very popular during the reactions of complexes with short ODNs or mono-nucleotides. The oxidation on I induced by the reactive oxygen species (ROS) formed by the photodecomposition of complex 1 was significant, and the oxidation of G8 to 8-hydroxyguanine (8-OH-G), spiroiminodihydantoin (Sp) and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyG) was discovered. These results unambiguously revealed a sequence-length-dependent photochemical reactivity of complex 1 when it interacted with different ODNs, providing deeper understanding in the reactivity of photoactivatable diazido anticancer Pt(iv) prodrugs to DNA.

Biodistribution and efficacy of the anticancer drug, oxaliplatin palmitate acetate, in mice

Oxaliplatin palmitate acetate (OPA), a platinum (IV) oxaliplatin derivative, was previously designed with the aim to improve the platinum-based anti-cancer therapy. In this work, we further explore the potential of OPA in extensive in vitro and in vivo studies. OPA in pancreatic (BxPC3-luc), lung (NCI-H1993) and liver (Hep3B) cancer cell lines showed a higher toxicity in comparison to oxaliplatin. The in vitro release kinetic experiments of OPA from the nanoparticles (NPs) under sink conditions exhibited a very rapid profile. Furthermore, OPA cannot be considered a prodrug of oxaliplatin, based on the OPA intact molecule pharmacokinetic profile study in rats. The formation of oxaliplatin from the biodegradation of OPA ranges only from 5% to 7% and both drugs were rapidly eliminated from the plasma. Pharmacokinetics of OPA PLGA nanoparticles in mice showed that nanoparticles failed to prolong the release of OPA in the plasma and did not add any therapeutic benefit over OPA solution, as suggested by the rapid in vitro release of OPA from nanoparticles. In pancreatic xenograft BxPC3-luc cancer model, both OPA in solution and OPA nanoparticles inhibited the tumor growth, equally and significantly, as compared to oxaliplatin. In liver xenograft Hep3B cancer model, OPA solution and cisplatin demonstrated good and similar antitumor efficacy. In lung xenograft NCI-H1993 cancer model, OPA solution, with a significant antitumor efficacy, was superior to cisplatin, which did not differ from the vehicle. In conclusion, OPA may offer a promising advance in platinum-based chemotherapy against various forms of cancers in an adequate dose and schedule.

Multifunctional Pt(iv) prodrug candidates featuring the carboplatin core and deferoxamine

The synergistic combination of the anticancer drug carboplatin and the iron chelator deferoxamine (DFO) served as a foundation for the development of novel multifunctional prodrugs. Hence, five platinum(iv) complexes, featuring the equatorial coordination sphere of carboplatin, and one or two DFO units incorporated at axial positions, were synthesized and characterized using ESI-HRMS, multinuclear (¹H, ¹³C, ¹⁵N, ¹⁹⁵Pt) NMR spectroscopy and elemental analysis. Analytical studies demonstrated that the chelating properties of the DFO moiety were not compromised after coupling to the platinum(iv) core. The cytotoxic activity of the compounds was evaluated in monolayer (2D) and spheroid (3D) cancer cell models, derived from ovarian teratocarcinoma (CH1/PA-1), colon carcinoma (SW480) and non-small cell lung cancer (A549). The platinum(iv)-DFO prodrugs demonstrated moderate in vitro cytotoxicity (a consequence of their slow activation kinetics) but with less pronounced differences between intrinsically chemoresistant and chemosensitive cell lines as well as between 2D and 3D models than the clinically used platinum(ii) drug carboplatin.

Multifunctional polymeric micellar nanomedicine in the diagnosis and treatment of cancer

Polymeric micelles are a prevalent topic of research for the past decade, especially concerning their fitting ability to deliver drug and diagnostic agents. This delivery system offers outstanding advantages, such as biocompatibility, high loading efficiency, water-solubility, and good stability in biological fluids, to name a few. The multifunctional polymeric micellar architect offers the added capability to adapt its surface to meet the looked-for clinical needs. This review cross-talks the recent reports, proof-of-concept studies, patents, and clinical trials that utilize polymeric micellar family architectures concerning cancer targeted delivery of anticancer drugs, gene therapeutics, and diagnostic agents. The manuscript also expounds on the underlying opportunities, allied challenges, and ways to resolve their bench-to-bedside translation for allied clinical applications.

Strategies for the Improvement of Metal-Based Chemotherapeutic Treatments

This article provides an overview of the various research approaches we have explored in recent years to improve metal-based agents for cancer or infection treatments. Although cisplatin, carboplatin, and oxaliplatin remain the cornerstones in tumor chemotherapy, the discovery and approval of novel inorganic anticancer drugs is a very slow process. Analogously, although a few promising inorganic drugs have found clinical application against parasitic or bacterial infections, their use remains relatively limited. Moreover, the discovery process is often affected by small therapeutic enhancements that are not attractive for the pharmaceutical industry. However, the availability of increasing mechanistic information for the modes of action of established inorganic drugs is fueling the exploration of various approaches for developing effective inorganic chemotherapy agents. Through a series of examples, some from our own research experience, we focus our attention on a number of promising strategies, including (1) drug repurposing, (2) the simple modification of the chemical structures of approved metal-based drugs, (3) testing novel drug combinations, and (4) newly synthesized complexes coupling different anticancer drugs. Accordingly, we aim to suggest and summarize a series of reliable approaches that are exploitable for the development of improved and innovative treatments.

Maloplatin-B, a Cisplatin-Based BODIPY-Tagged Mito-Specific "Chemo-PDT" Agent Active in Red Light

Maloplatin-B, a cisplatin-based complex, namely [Pt(A-BOD)(NH₃)₂](NO₃) (Pt-A-BOD) with a pendant boron-dipyrromethene (BODIPY) moiety, where HA-BOD is a methyl malonyl chloride derived monostyryl BODIPY ligand, was designed and developed as near-IR light (600-720 nm) organelle-targeting photodynamic therapy agent. The complex [Pt(acac)(NH₃)₂](NO₃) (Pt-Ac) was used as a control. Pt-A-BOD displayed an absorption band at 616 nm (ε = 2.9 × 10⁴ M^-1 cm^-1) in 10% dimethyl sulfoxide/Dulbecco's Modified Eagle's Medium (DMSO/DMEM, pH 7.2). This complex displayed a broad emission band within 650-850 nm with a λ_em value of 720 nm in 10% DMSO-DMEM (pH 7.2) upon excitation (λ_ex) at 615 nm with a large Stokes shift. The fluorescence quantum yield (Φ_F) value for Pt-A-BOD is 0.032 and for the ligand HA-BOD is 0.24. The BODIPY complex and ligand showed the formation of singlet oxygen as the ROS (reactive oxygen species) on irradiation with near-IR red light of 660 nm, as evidenced from a 1,3-diphenylisobenzofuran (DPBF) assay. The complex displayed remarkable apoptotic NIR light-induced PDT activity with half-maximum inhibitory concentration values (IC₅₀) of 1.6-2.4 μM in A549 lung and HeLa cervical cancer cells, while it was less active in the dark. The cellular ROS generation by the complex in red light was ascertained by a DCFDA (2',7'-dichlorofluorescein diacetate) assay. Cellular imaging showed its localization primarily in the mitochondria of A549 cancer cells. The JC1 and Annexin-V FITC/PI assays carried out for A549 cancer cells treated with the BODIPY complex showed the alteration of mitochondrial membrane potential and apoptotic cell death on near-IR red light (600-720 nm) irradiation, respectively.

Effect of the aniline fragment in Pt(II) and Pt(IV) complexes as anti-proliferative agents. Standard reduction potential as a more reliable parameter for Pt(IV) compounds than peak reduction potential

The problems of resistance and side effects associated with cisplatin and other chemotherapeutic drugs have boosted research aimed at finding new compounds with improved properties. The use of platinum(IV) prodrugs is one alternative, although there is some controversy regarding the predictive ability of the peak reduction potentials. In the work described here a series of fourteen chloride Pt(II) and Pt(IV) compounds was synthesised and fully characterised. The compounds contain different bidentate arylazole heterocyclic ligands. Their cytotoxic properties against human lung carcinoma (A549), human breast carcinoma (MCF7) and human colon carcinoma (HCT116 and HT29) cell lines were studied. A clear relationship between the type of ligand and the anti-proliferative properties was found, with the best results obtained for the Pt(II) compound that contains an aniline fragment, (13), thus evidencing a positive effect of the NH₂ group. Stability and aquation studies in DMSO, DMF and DMSO/water mixtures were carried out on the active complexes and an in-depth analysis of the two aquation processes, including DFT analysis, of 13 was undertaken. It was verified that DNA was the target and that cell death occurred by apoptosis in the case of 13. Furthermore, the cytotoxic derivatives did not exhibit haemolytic activity. The reduction of the Pt(IV) compounds whose Pt(II) congeners were active was studied by several techniques. It was concluded that the peak reduction potential was not useful to predict the ability for reduction. However, a correlation between the cytotoxic activity and the standard reduction potential was found.

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.

Mass spectrometry techniques for imaging and detection of metallodrugs

Undoubtedly, metallomic approaches based on mass spectrometry have evolved into essential tools supporting the drug development of novel metal-based anticancer drugs. This article will comment on the state-of-the-art instrumentation and highlight some of the recent analytical advances beyond routine, especially focusing on the latest developments in inductively coupled plasma-mass spectrometry (ICP-MS). Mass spectrometry-based bioimaging and single-cell methods will be presented, paving the way to exciting investigations of metal-based anticancer drugs in heterogeneous and structurally, as well as functionally complex solid tumor tissues.

Design, synthesis and biological evaluation of dihydro-2-quinolone platinum(iv) hybrids as antitumor agents displaying mitochondria injury and DNA damage mechanism

The design of novel platinum(iv) complexes with mitochondria injury competence, besides the DNA damage mechanism, is a promising way to develop new platinum drugs. Herein, dihydro-2-quinolone (DHQLO) as a mitocan was incorporated into the platinum(iv) system for the first time to prepare a new series of DHQLO platinum(iv) compounds. Complex 1b could effectively inhibit the proliferation of tumor cells in vitro and in vivo. It accumulated at higher levels in both whole cells and DNA, and easily underwent intercellular reduction to release platinum(ii) and DHQLO moieties. The released platinum(ii) complex caused serious DNA damage by covalent conjunction with the DNA duplex, and remarkably increased the expression of the γ-H2AX protein. Moreover, 1b also caused serious mitochondria injury to induce mitochondrial membrane depolarization and increase ROS generation. Such actions upon DNA and mitochondria activate the p53 apoptotic pathway synergetically in tumor cells by upregulating the protein p53 and apoptotic proteins caspase9 and caspase3, which efficiently promoted the apoptotic death of tumor cells. Compound 1b with such synergic mechanism exhibited great potential in reversing cisplatin resistance and improving antitumor efficacies.

On the hydrolytic stability of unsymmetric platinum(iv) anticancer prodrugs containing axial halogens

The hydrolytic stability of Pt(iv) complexes is determined by all the six ligands that coordinate to the Pt(iv) center. By appropriately choosing all the ligands during the design of Pt(iv) prodrugs, the stability of Pt(iv) prodrugs can be improved.

Mitochondria as a Novel Target for Cancer Chemoprevention: Emergence of Mitochondrial-targeting Agents

Cancer chemoprevention is the most effective approach to control cancer in the population. Despite significant progress, chemoprevention has not been widely adopted because agents that are safe tend to be less effective and those that are highly effective tend to be toxic. Thus, there is an urgent need to develop novel and effective chemopreventive agents, such as mitochondria-targeted agents, that can prevent cancer and prolong survival. Mitochondria, the central site for cellular energy production, have important functions in cell survival and death. Several studies have revealed a significant role for mitochondrial metabolism in promoting cancer development and progression, making mitochondria a promising new target for cancer prevention. Conjugating delocalized lipophilic cations, such as triphenylphosphonium cation (TPP+), to compounds of interest is an effective approach for mitochondrial targeting. The hyperpolarized tumor cell membrane and mitochondrial membrane potential allow for selective accumulation of TPP⁺ conjugates in tumor cell mitochondria versus those in normal cells. This could enhance direct killing of precancerous, dysplastic, and tumor cells while minimizing potential toxicities to normal cells.

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.

Photoactivatable Platinum-Based Anticancer Drugs: Mode of Photoactivation and Mechanism of Action

Platinum-based anticancer drugs are a class of widely used agents in clinical cancer treatment. However, their efficacy was greatly limited by their severe side effects and the arising drug resistance. The selective activation of inert platinum-based drugs in the tumor site by light irradiation is able to reduce side effects, and the novel mechanism of action of photoactivatable platinum drugs might also conquer the resistance. In this review, the recent advances in the design of photoactivatable platinum-based drugs were summarized. The complexes are classified according to their mode of action, including photoreduction, photo-uncaging, and photodissociation. The rationale of drug design, dark stability, photoactivation process, cytotoxicity, and mechanism of action of typical photoactivatable platinum drugs were reviewed. Finally, the challenges and opportunities for designing more potent photoactivatable platinum drugs were discussed.

Inhibition of histone deacetylases, topoisomerases and epidermal growth factor receptor by metal-based anticancer agents: Design & synthetic strategies and their medicinal attributes

Metal-based inhibitors of histone deacetylases (HDAC), DNA topoisomerases (Topos) and Epidermal Growth Factor Receptor (EGFR) have demonstrated their cytotoxic potential against various cancer types such as breast, lung, uterus, colon, etc. Additionally, these have proven their role in resolving the resistance issues, enhancing the affinity, lipophilicity, stability, and biocompatibility and therefore, emerged as potential candidates for molecularly targeted therapeutics. This review focusses on nature and role of metals and organic ligands in tuning the anticancer activity in multiple modes of inhibition considering HDACs, Topos or EGFR as one of the primary targets. The conceptual design and synthetic approaches of platinum and non-platinum metal complexes comprising of chiefly ruthenium, rhodium, palladium, copper, iron, nickel, cobalt, zinc metals coordinated with organic scaffolds, along with their biological activity profiles, structure-activity relationships (SARs), docking studies, possible modes of action, and their scope and limitations are discussed in detail.