Platinum coordination complexes which circumvent cisplatin resistance

Oxidation of the Platinum(II) Anticancer Agent [Pt{(p-BrC6F4)NCH2CH2NEt2}Cl(py)] to Platinum(IV) Complexes by Hydrogen Peroxide

PtIV coordination complexes are of interest as prodrugs of PtII anticancer agents, as they can avoid deactivation pathways owing to their inert nature. Here, we report the oxidation of the antitumor agent [PtII(p-BrC6F4)NCH2CH2NEt2}Cl(py)], 1 (py = pyridine) to dihydroxidoplatinum(IV) solvate complexes [PtIV{(p-BrC6F4)NCH2CH2NEt2}Cl(OH)2(py)].H2O, 2·H2O with hydrogen peroxide (H2O2) at room temperature. To optimize the yield, 1 was oxidized in the presence of added lithium chloride with H2O2 in a 1:2 ratio of Pt: H2O2, in CH2Cl2 producing complex 2·H2O in higher yields in both gold and red forms. Despite the color difference, red and yellow 2·H2O have the same structure as determined by single-crystal and X-ray powder diffraction, namely, an octahedral ligand array with a chelating organoamide, pyridine and chloride ligands in the equatorial plane, and axial hydroxido ligands. When tetrabutylammonium chloride was used as a chloride source, in CH2Cl2, another solvate, [PtIV{(p-BrC6F4)NCH2CH2NEt2}Cl(OH)2(py)].0.5CH2Cl2,3·0.5CH2Cl2, was obtained. These PtIV compounds show reductive dehydration into PtII [Pt{(p-BrC6F4)NCH=CHNEt2}Cl(py)], 1H over time in the solid state, as determined by X-ray powder diffraction, and in solution, as determined by 1H and 19F NMR spectroscopy and mass spectrometry. 1H contains an oxidized coordinating ligand and was previously obtained by oxidation of 1 under more vigorous conditions. Experimental data suggest that oxidation of the ligand is favored in the presence of excess H2O2 and elevated temperatures. In contrast, a smaller amount (1Pt:2H2O2) of H2O2 at room temperature favors the oxidation of the metal and yields platinum(IV) complexes.

Development of Novel Pt(IV)-Carbohydrate Derivatives as Targeted Anticancer Agents against Osteosarcoma

Despite the enormous importance of cisplatin as a chemotherapeutic agent, its application is impacted by dose-limiting side effects and lack of selectivity for cancer cells. Researchers can overcome these issues by taking advantage of the pro-drug nature of the platinum(IV) oxidation state, and by modifying the coordination sphere of the metal centre with specific vectors whose receptors are overexpressed in tumour cell membranes (e.g., carbohydrates). In this paper we report the synthesis of four novel carbohydrate-modified Pt(IV) pro-drugs, based on the cisplatin scaffold, and their biological activity against osteosarcoma (OS), a malignant tumour which is most common in adolescents and young adults. The carbohydrate-targeting vectors and Pt scaffold are linked using copper-catalysed azide-alkyne cycloaddition (CuAAC) chemistry, which is synonymous with mild and robust reaction conditions. The novel complexes are characterised using multinuclear 1D-2D NMR (¹H, ¹³C and ¹⁹⁵Pt), IR, HR-MS, Elem. Analyses, and CV. Cytotoxicity on 2D and 3D and cell morphology studies on OS cell lines, as well as non-cancerous human foetal osteoblasts (hFOBs), are discussed.

Effective Oral Administration of an Antitumorigenic Nanoformulated Titanium Complex

Orally administered anticancer drugs facilitate treatment, but the acidic conditions in the stomach often challenge their availability. PhenolaTi is a Ti^IV -based nontoxic anticancer drug with marked in-vivo efficacy. We report that nanoformulation protects phenolaTi from decomposition in stomach-like conditions. This is evidenced by similar NMR characteristics and similar in-vitro cytotoxicity toward murine (CT-26) and human (HT-29) colon cancer cells before and after incubation of nanoformulated phenolaTi (phenolaTi-F) at pH 2, unlike results with the unformulated form of the complex. Furthermore, administration of phenolaTi-F in animal drinking water revealed a notable inhibition of tumor growth in Balb/c and immune-deficient (Nude) mice inoculated with CT-26 and HT-29 cells, respectively. In-vivo efficacy was at least similar to that of the corresponding intraperitoneal treatment with phenolaTi-F and the clinically employed oral drug, capecitabine. No body weight loss or clinical signs of toxicity were evident in the phenolaTi-F-treated animals. These findings demonstrate a new convenient mode of cancer treatment through oral administration by safe titanium-based drugs.

Combination of 7-hydroxycoumarin in a platinum(IV) complex derived from cisplatin enhanced cytotoxicity with multiple mechanisms of action

A novel compound, Cou-platin, composed of 7-hydroxycoumarin and a platinum(IV) moiety derived from cisplatin was designed and synthesized. Significantly, Cou-platin exhibited more potent in vitro antitumor activity against all tested cancer cell lines than that of cisplatin, which was mainly attributed to the liberation of cisplatin and 7-hydroxycoumarin upon reduction with a biomolecular agent. Besides, cellular accumulation of Cou-platin was dramatically increased among several cancer cells in contrast to cisplatin. Flow cytometry study revealed that Cou-platin arrested cell cycle at G2 phase and induced cell apoptosis. Western blots results indicated that it not only activated cell apoptosis pathway, but also inhibited extracellular regulated protein kinases/mitogen-activated protein kinase pathway. In vivo tests showed that Cou-platin, at equimolar dose to cisplatin, could inhibit tumor growth in nude mouse HCT116 tumor xenograft models almost as cisplatin and oxaliplatin, but with less toxicity.

New oral chemotherapeutic agents for lung cancer

Anticancer treatment has recently shifted to include a broad range of antineoplastic therapies. Old agents are continuously being re-evaluated, and new mechanisms of treatment are rapidly being explored and developed. At the same time, the patient's perceived quality of life, adverse effects of therapy, time demands, and healthcare costs have become paramount in the treatment process. Lung cancer is the most common cause of cancer death in the USA, and because many of the patients are older or debilitated, these issues become all the more important. The oral administration of anticancer therapy offers both quality-of-life and healthcare cost advantages. Oral forms of 3 new cytotoxic agents and 2 novel oral therapies are discussed. Vinorelbine, a vinca alkaloid, has well documented activity in non-small cell lung cancer. Myelosuppression is dose limiting; neurotoxicity is rare. Satraplatin (JM-216), an oral platinum derivative, shows activity in lung cancer with a favourable adverse effect profile, with no neurotoxicity or nephrotoxicity. The oral topoisomerase I inhibitor topotecan may be ideal for obtaining long term low plasma drug concentrations, which appears to maximise efficacy. LGD-1069 is a retinoid X receptor agonist that modulates cell proliferation, and BAY-129566, a matrix metalloproteinase inhibitor, appears to interrupt both the processes of angiogenesis and metastasis. LGD-1069 and BAY-129566 are nontraditional anticancer agents which may be used in conjunction with chemotherapy, other modalities, or in prevention. These 5 agents will be discussed with particular reference to recent developments in the treatment of lung cancer.

Ammine/amine platinum (II) complexes effective in vivo against murine tumors sensitive or resistant to cisplatin and tetraplatin

Three homologous series, each differing from the other in the coordinated amine ligand class, namely alicyclic, heterocyclic or isoaliphatic, were highly effective against wild-type murine leukemia L1210/0 cells in vivo (T/C = 171%-426% at optimal doses). Of the 13 complexes comprising the three series, 3 were inactive in the cisplatin-resistant L1210/DDP model, but the other 10 maintained good efficacy (T/C = 131%-167%). Long-term survivors, frequently observed with these complexes in the L1210/0 model, were also seen in the L1210/DDP model but to a lesser extent. In the homologous alicyclic series, which contained six analogs, as the alicyclic ring size increased, potency against L1210/0 and L1210/DDP cells also increased up to cyclohexylamine, and then declined. Four ammine/alicyclic amine analogs were evaluated against L1210/DACH cells, which are cross-resistant to tetraplatin, and the clinically predictive M5076 reticulosarcoma. Although the congeners were ineffective or minimally effective in prolonging the survival time of L1210/DACH-bearing mice (T/C = 111%-134%), 20%-40% cure rate was consistently observed and suggested that the compounds possessed a low inherent ability to circumvent resistance in these tumor cells also. In the solid M5076 model, activity was greatest (tumor growth delays of about 25 days) for the alicyclic homologs containing the ammine/cyclobutylamine or ammine/cyclopentylamine carrier ligand combination. In summary, ammine/amine platinum (II) analogs have demonstrated promise at the preclinical level in their ability to circumvent acquired resistance, which is a major drawback of cisplatin use in treating cancer.

Correlation of total and interstrand DNA adducts in tumor and kidney with antitumor efficacies and differential nephrotoxicities of cis-ammine/cyclohexylamine-dichloroplatinum(II) and cisplatin

Mixed amine platinum complexes have been identified as a new class of antitumor agents with activity in some cisplatin-resistant tumor models. cis-Ammine/cyclohexylamine-dichloroplatinum(II) is one such analog that we have evaluated in vivo and found it to have antitumor activity that was comparable to that of cisplatin in a solid murine fibrosarcoma tumor model. In contrast to the nephrotoxicity observed with cisplatin, the analog was free from inducing this side-effect. Pharmacokinetics of the two compounds administered i.v. at equitoxic dose levels to tumor-bearing mice indicated similar decay kinetics of total platinum in plasma, kidney and the tumor. Furthermore, DNA-platinum adducts of the two agents were similar in the tumor. Total adduct levels in the kidney, on the other hand, were significantly greater (P < 0.5) by up to 4-fold for cisplatin compared with the mixed amine analog. Likewise, the levels of interstrand cross-links of the two platinum complexes were comparable in the tumor, but significantly greater (P < 0.05) in the kidney for cisplatin. The data indicate that the greater renal levels of total and interstrand DNA-platinum adducts formed by cisplatin correlate with renal damage associated with this agent, and suggest that adduct levels, and not total tissue platinum levels, provide a more useful correlation with pharmacodynamic observations.

Kinetics of tissue disposition of cis-ammine/cyclohexylamine-dichloroplatinum(II) and cisplatin in mice bearing FSaIIC tumors

The clinical potential of mixed amine platinum(IV) complexes has been identified, and interest in this new class of antitumor agents has been heightened by demonstration of their activity in cisplatin-resistant neoplasms. These tetravalent platinum agents are expected to undergo a reductive reaction to form the corresponding platinum(II) drug prior to eliciting biological activity. cis-Ammine/cyclohexylamine-dichloroplatinum(II) is one such product that we evaluated with cisplatin in vivo, and we found the two complexes given i.v. or i.p. to have comparable activities against a solid murine fibrosarcoma. Following i.v. administration of the two compounds at equitoxic dose levels (20 mg/kg) to tumor-bearing mice, platinum levels in the plasma were consistently higher for cisplatin. Tissue platinum levels, in contrast, were comparable between the agents or higher for the mixed amine analog at the earliest (3-h) time point. The temporal profiles determined for the concentrations over 48 h were tissue- and/or drug-specific and could be described by terminal-phase constants or half-lives of platinum in most tissues. In the plasma, kidney, lung, and jejunum, platinum levels arising from both compounds decayed with half-lives of 24-92 h. The terminal-phase constants of platinum determined in the heart for the two complexes were not significantly different from zero, indicative of levels remaining steady, whereas the constants were negative in the spleen, indicative of an increase in tissue drug concentration. In the tumor, liver, and testes, positive values for the decay-phase constants corresponding to half-lives of 47, 256, and 79 h, respectively, were seen with the mixed amine complex; this pattern contrasted with that found for cisplatin, for which the terminal-phase constant was either zero or negative. In vitro binding studies demonstrated the mixed amine complex to be more reactive. Thus, the presence of one ammine and one cyclohexylamine carrier ligand in the mixed amine complex, as opposed to the diammine ligands in cisplatin, leads to an increase in drug distribution and an alteration in the kinetics of tissue binding and removal of platinum.

New platinum antitumor complexes

Over the past two decades, platinum-based drugs (cisplatin and, latterly, the less toxic analogue carboplatin) have conferred significant therapeutic benefit to a large number of cancer sufferers. However, there remains scope for substantial improvement in the clinical utility of metal coordination complexes through the discovery of additional platinum-based complexes (or possibly alternative metals). Future drug discovery strategies should focus on tumor resistance and its circumvention. To date, only one series of compounds, those containing a 1,2-diaminocyclohexane carrier ligand (e.g., oxaliplatin, tetraplatin), has entered clinical trial based on their circumvention of acquired cisplatin resistance in some (mainly murine) preclinical tumor models. At present these agents are in early clinical trial and thus their true clinical utility in cisplatin/carboplatin refractory disease is not yet determinable (and may not be due to dose-limiting neurotoxicity). Over the past few years, our understanding of mechanisms of resistance to cisplatin and its interaction with DNA has vastly increased. This new information will undoubtedly guide the development of new strategies aimed at the circumvention of intrinsic and acquired tumor resistance to cisplatin. Approaches to circumvent resistance will probably involve not only the rational development of a new generation of platinum-based drugs (e.g., compounds designed to overcome reduced cisplatin accumulation or enhanced removal of cisplatin-induced DNA adducts) but also non-platinum drugs which are capable of modulating resistance (e.g., modulators of signal transduction pathways, ras and myc oncogene expression and glutathione biosynthesis). One may look forward with a great deal of optimism that these promising new approaches will result in clinical benefit by the end of the century. Nevertheless, cisplatin and carboplatin remain the standard anticancer drugs to which novel platinum-based complexes must be compared.

Preclinical antitumor activity of orally administered platinum (IV) complexes

Several novel platinum (IV) mixed ammine/amine dicarboxylate dichlorides of general structure [Pt(IV)Cl2(OCOY)2NH3(XNH2)], where Y is aliphatic or aromatic and X is alicyclic or aliphatic, known to be particularly well absorbed following oral administration, were evaluated by that route for their antitumor activity. Testing of the Pt(IV) derivatives took place concomitantly with i.v. administered cisplatin and carboplatin in two s.c. staged tumor models, the murine M5076 sarcoma and human A2780 ovarian carcinoma. Based upon repetitive experiments which included an evaluation of different vehicles and treatment schedules, each of the orally administered Pt(IV) dicarboxylates was reproducibly active in the M5076 tumor, producing mean maximum gross log cell kill (LCK) values of between 1.5 and 2.0, and lifespan increases, reflected by mean maximum treated/control median survival (T/C) values, of 139-151%. Cisplatin and carboplatin given i.v. yielded mean maximum LCK of 3.5 and 2.5, respectively, as well as mean maximum T/C values of 166% and 164%, respectively, in the same tumor model. The best of the derivatives in the M5076 experiments, JM-216 [ammine/cyclohexylamine diacetato dichloride Pt(IV)], produced LCK values that averaged only 0.5 lower than that of carboplatin, and increases in lifespan not significantly different than that of carboplatin. Against the A2780 tumor, the Pt(IV) dicarboxylates produced individual best effects of between 0.8-1.1 LCK, based on data from two or three experiments. The mean maximum LCK values for cisplatin and carboplatin were 1.8 and 2.2 LCK, respectively. JM-225, ammine/cyclopentylamine diacetato dichloride Pt(IV), was active in two of three experiments, including one result comparable to that of carboplatin. The Pt(IV) mixed ammine/amine dicarboxylate dichlorides represent a novel class of Pt derivative capable of expressing oral antitumor activity in both murine and human tumor models.

Human ovarian-carcinoma cell lines and companion xenografts: a disease-oriented approach to new platinum anticancer drug discovery

A disease-oriented approach to the discovery of novel platinum anticancer drugs has been established through the setting up of parallel human ovarian-carcinoma cell lines and xenografts. The correlation between in vitro and in vivo antitumour activity was determined for four reference platinum agents (cisplatin, carboplatin, iproplatin and tetraplatin) in eight companion lines. Two methods of assessing antitumour effect were used in vitro (tritiated thymidine incorporation and sulforhodamine B staining) and three were applied in vivo [28-day treated/control (T/C) ratio, growth delay and specific growth delay]. In vitro, large differences in cytotoxicity across the cell lines were observed for each drug. This was also reflected in the xenografts for cisplatin and carboplatin and, to a lesser extent, for iproplatin. A correlation analysis of in vitro vs in vivo data revealed a high, statistically significant positive correlation for cisplatin and a strong positive correlation for carboplatin. However, for the two platinum(IV) drugs, the correlation was less good. In particular, tetraplatin was markedly less active in vivo (showing a general lack of activity against all of the tumour lines) than its in vitro potency against the cell lines predicted, resulting in poor correlation coefficients. These human tumour panels may be valuable for the elucidation of both cellular/molecular and corresponding in vivo pharmacological mechanisms of platinum drug resistance. Moreover, the HX/62 and SKOV-3 tumour lines, which exhibit a level of intrinsic resistance to the four reference agents both in vitro and in vivo (and which were derived from patients who had not received prior platinum therapy), represent particularly useful evaluation models for the discovery of novel broad-spectrum platinum drugs.