A comparative study of pharmacokinetics, urinary excretion and tissue distribution of platinum in rats following a single-dose oral administration of two platinum(IV) complexes LA-12 (OC-6-43)-bis(acetato)(1-adamantylamine)amminedichloroplatinum(IV) and satraplatin (OC-6-43)-bis(acetato)amminedichloro(cyclohexylamine)platinum(IV)

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.

Platinum, palladium, gold and ruthenium complexes as anticancer agents: Current clinical uses, cytotoxicity studies and future perspectives

Metallodrugs offer potential for unique mechanism of drug action based on the choice of the metal, its oxidation state, the types and number of coordinated ligands and the coordination geometry. This review illustrates notable recent progress in the field of medicinal bioinorganic chemistry as many new approaches to the design of innovative metal-based anticancer drugs are emerging. Current research addressing the problems associated with platinum drugs has focused on other metal-based therapeutics that have different modes of action and on prodrug and targeting strategies in an effort to diminish the side-effects of cisplatin chemotherapy. Examples of metal compounds and chelating agents currently in clinical use, clinical trials or preclinical development are highlighted.

Comparative in vitro and in vivo pharmacological investigation of platinum(IV) complexes as novel anticancer drug candidates for oral application

Platinum(IV) complexes are promising candidates as prodrugs for oral application in anticancer chemotherapy. However, only a few Pt(IV) compounds entered (pre)clinical trials, e.g. satraplatin, while most of the others were only tested in vitro. Aim of the study was investigation of the in vivo pharmacological behavior as well as the anticancer activity of two novel platinum(IV) complexes vs. satraplatin. The drugs were selected due to significantly different in vitro cytotoxicity while sharing some physicochemical properties (e.g. lipophilicity). Initial experiments indicated that the highly in vitro cytotoxic compound 1 ((OC-6-33)-dichloridobis((4-ethoxy)-4-oxobutanoato)-bis(ethylamine)platinum(IV)) was also characterized by high drug absorption and tissue platinum levels after oral application. Interestingly, analysis of serum samples using SEC-ICP-MS revealed that the administered drugs have completely been metabolized and/or bound to proteins in serum within 2 h after treatment. With regard to the activity in vivo, the outcomes were rather unexpected: although potent anticancer effect of 1 was observed in cell culture, the effects in vivo were rather minor. Nevertheless, 1 was superior to 2 ((OC-6-33)-diammine(cyclobutane-1,1-dicarboxylato)-bis((4-cyclopentylamino)-4-oxobutanoato)platinum(IV)) after i.p. administration, which was, at least to some extent, in accordance to the cell culture experiments. After oral gavage, both compounds exhibited comparable activity. This is remarkable considering the distinctly lower activity of 2 in cell culture as well as the low platinum levels detected both in serum and tissues after oral application. Consequently, our data indicate that the prediction of in vivo anticancer activity by cell culture experiments is not trivial, especially for orally applied drugs.

A novel class of bis- and tris-chelate diam(m)inebis(dicarboxylato)platinum(IV) complexes as potential anticancer prodrugs

A novel class of platinum(IV) complexes of the type [Pt(Am)(R(COO)2)2], where Am is a chelating diamine or two monodentate am(m)ine ligands and R(COO)2 is a chelating dicarboxylato moiety, was synthesized. For this purpose, the reaction between the corresponding tetrahydroxidoplatinum(IV) precursors and various dicarboxylic acids, such as oxalic, malonic, 3-methylmalonic, and cyclobutanedicarboxylic acid, was utilized. All new compounds were characterized in detail, using 1D and 2D NMR techniques, ESI-MS, FTIR spectroscopy, elemental analysis, TGA, and X-ray diffraction. Their in vitro cytotoxicity was determined in a panel of human tumor cell lines (CH1, SW480 and A549) by means of the MTT colorimetric assay. Furthermore, the lipophilicity and redox properties of the novel complexes were evaluated in order to better understand their pharmacological behavior. The most promising drug candidate, 4b (Pt(DACH)(mal)2), demonstrated low in vivo toxicity but profound anticancer activity against both the L1210 leukemia and CT-26 colon carcinoma models.

Synthesis and characterization of Pt(IV) fluorescein conjugates to investigate Pt(IV) intracellular transformations

Pt(IV) anticancer compounds typically operate as prodrugs that are reduced in the hypoxic environment of cancer cells, losing two axial ligands in the process to generate active Pt(II) species. Here we report the synthesis of two fluorescent Pt(IV) prodrugs of cisplatin in order to image and evaluate the Pt(IV) reduction process in simulated and real biological environments. Treatment of the complexes dissolved in PBS buffer with reducing agents typically encountered in cells, glutathione or ascorbate, afforded a 3- to 5-fold fluorescence turn-on owing to reduction and loss of their fluorescein-based axial ligands, which are quenched when bound to platinum. Both Pt(IV) conjugates displayed moderate cytotoxicity against human cancer cell lines, with IC50 values higher than that of cisplatin. Immunoblotting and DNA flow cytometry analyses of one of the complexes, Pt(IV)FL2, revealed that it damages DNA, causes cell cycle arrest in S or G2/M depending on exposure time, and ultimately triggers apoptotic cell death. Fluorescence microscopic studies prove that Pt(IV)FL2 enters cells intact and undergoes reduction intracellularly. The results are best interpreted in terms of a model in which the axial fluorescein ligands are expelled through lysosomes, with the platinum(II) moiety generated in the process binding to genomic DNA, which results in cell death.

Higher anti-tumour efficacy of platinum(IV) complex LA-12 is associated with its ability to bypass M-phase entry block induced in oxaliplatin-treated human colon cancer cells

OBJECTIVES

Therapeutic potential of conventionally used platinum-based drugs in treatment of colorectal tumours has been limited due to high incidence of tumour resistance to them and to their severe side effects. This evokes a search for more suitable anti-cancer drugs. We have compared ability of oxaliplatin and a novel platinum(IV) complex, LA-12, to modulate the cell cycle and induce apoptosis in human colon adenocarcinoma HCT116 wt and p53/p21 null cells, and have investigated molecular mechanisms involved.

MATERIALS AND METHODS

Cell cycle-related changes were analysed by flow cytometry (bromodeoxyuridine/propidium iodide staining, histone H3 phosphorylation). Apoptosis was detected using flow cytometry (assays monitoring caspase activity) and fluorescence microscopy (nuclear morphology). Changes in levels of genes/proteins involved in cell cycle and apoptosis regulation were examined by RT-PCR and western blotting.

RESULTS

Our results highlight the outstanding ability of LA-12 to induce effective elimination of colon cancer cells independently of p53/p21, and in significantly lower doses compared to oxaliplatin. While oxaliplatin induced p53- and p21-dependent G2 -phase arrest associated with downregulation of cyclin B1 and Cdk1, LA-12 allowed cells to enter M-phase of the cell cycle regardless of p53/p21 status.

CONCLUSIONS

Higher malignant cell toxicity and ability to bypass cell cycle arrest important for the cell damage repair suggest LA-12 to be a more effective candidate for elimination of colon tumours from a variety of genetic backgrounds, compared with oxaliplatin.

Pharmacokinetics, tissue distribution, and plasma protein binding study of platinum originating from dicycloplatin, a novel antitumor supramolecule, in rats and dogs by ICP-MS

Dicycloplatin, as a new antitumor supramolecule, was considered to have higher solubility and higher stability compared with carboplatin. The aim of the present study was to evaluate the pharmacokinetic characteristics of platinum originating from dicycloplatin. A rapid, sensitive, and specific method with inductively coupled plasma mass spectrometry (ICP-MS) has been developed for the determination of platinum in bio-samples. The study was performed in male rats and dogs at a single dose of 10 and 5 mg kg(-1) separately by intravenous injection. Pharmacokinetic parameters were calculated by non-compartmental method, and the dose of platinum was used in the calculation of these parameters. Results showed that plasma concentrations of platinum began to decrease rapidly initially but decline slowly with a long terminal phase. The mean half-life was 27.39 and 100.98 and clearance was 0.77 and 0.08 L/h/kg for rats and dogs separately. Tissue distribution showed that platinum originating from dicycloplatin had a certain distribution in testis and prostate. Plasma protein binding proportion of platinum was increased with time. In conclusion, this research investigated the pharmacokinetic characteristics including plasma kinetics, tissue distribution, and plasma protein binding of platinum originating from dicycloplatin in rats and dogs in detail for the first time by ICP-MS.

Clinical and pharmacokinetic evaluation of satraplatin

INTRODUCTION

The toxicities of cisplatin, that is, nephrotoxicity, neurotoxicity and emesis, provided the impetus for the development of more tolerable platinum analogs. Satraplatin is an investigational third-generation orally available lipophilic platinum, which has demonstrated safety and antitumor activity in multiple settings.

AREAS COVERED

The clinical activity of satraplatin in metastatic castrate-resistant prostate cancer (mCRPC), breast, lung and other advanced solid tumors is discussed with a focus on its pharmacokinetic properties. The article was formulated using publications found through PubMed search in addition to presentations given at major conferences.

EXPERT OPINION

Satraplatin was associated with dose-limiting myelosuppression, but no significant ototoxicity, neurotoxicity or nephrotoxicity. Despite the activity of satraplatin in mCRPC, survival was not extended in an unselected population included in a Phase III trial. While further development of satraplatin in large Phase III trials is not planned at this time, efforts are ongoing to develop tailored therapy in mCRPC based on excision repair cross-complementing group 1 expression or BRCAness. Moreover, based on potentially better central nervous system penetration due to lipophilicity, evaluation in patients with brain tumors is ongoing. Given the favorable toxicity profile and convenient oral administration, satraplatin may warrant development in settings that preclude cisplatin, for example, underlying renal dysfunction, elderly age and poor performance status.

The new platinum-based anticancer agent LA-12 induces retinol binding protein 4 in vivo

BACKGROUND

The initial pharmacokinetic study of a new anticancer agent (OC-6-43)-bis(acetato)(1-adamantylamine)amminedichloroplatinum (IV) (LA-12) was complemented by proteomic screening of rat plasma. The objective of the study was to identify new LA-12 target proteins that serve as markers of LA-12 treatment, response and therapy monitoring.

METHODS

Proteomic profiles were measured by surface-enhanced laser desorption-ionization time-of-flight mass spectrometry (SELDI-TOF MS) in 72 samples of rat plasma randomized according to LA-12 dose and time from administration. Correlation of 92 peak clusters with platinum concentration was evaluated using Spearman correlation analysis.

RESULTS

We identified Retinol-binding protein 4 (RBP4) whose level correlated with LA-12 level in treated rats. Similar results were observed in randomly selected patients involved in Phase I clinical trials.

CONCLUSIONS

RBP4 induction is in agreement with known RBP4 regulation by amantadine and cisplatin. Since retinol metabolism is disrupted in many cancers and inversely associates with malignancy, these data identify a potential novel mechanism for the action of LA-12 and other similar anti-cancer drugs.