Heterocyclic complexes of ruthenium(III) induce apoptosis in colorectal carcinoma cells

PURPOSE

The ruthenium complex salt indazolium trans-[tetrachlorobisindazole-ruthenate(III)] (KP1019) and the analogous sodium salt KP1339 are effective tumor-inhibiting drugs in experimental therapy of autochthonous colorectal carcinomas in rats. This paper examines the cell biological mechanisms underlying their antineoplastic effects.

METHODS

Colorectal tumor cell lines were used to analyze uptake of the ruthenium(III) complexes into the cells and the mechanism as well as the efficacy of their cytotoxic effects.

RESULTS

KP1019 and KP1339 are efficiently taken up into the cells: 100 microM ruthenium(III) complex in the growth medium led to the uptake of 120-160 ng ruthenium per 10(6) cells within 30 min. Uptake of KP418 was tenfold lower correlating with its lower cytotoxic efficiency. KP1019 and KP1339 induced apoptosis in SW480 and HT29 cells predominantly by the intrinsic mitochondrial pathway as indicated by loss of mitochondrial membrane potential. Correspondingly sensitivity of the cells paralleled expression of bcl(2) while it was only slightly affected by mutations in Ki-ras.

CONCLUSIONS

Our data demonstrate that trans-[tetrachlorobisindazole-ruthenate(III)] complex salts are promising candidate drugs in the second-line treatment of colorectal cancers resistant to other cytostatic drugs and has been introduced into phase I clinical trials.

Multidrug-resistant cancer cells are preferential targets of the new antineoplastic lanthanum compound KP772 (FFC24)

Recently, we have introduced [tris(1,10-phenanthroline)lanthanum(III)] trithiocyanate (KP772, FFC24) as a new lanthanum compound which has promising anticancer properties in vivo and in vitro. Aim of this study was to investigate the impact of ABC transporter-mediated multidrug resistance (MDR) on the anticancer activity of KP772. Here, we demonstrate that all MDR cell models investigated, overexpressing ABCB1 (P-glycoprotein), ABCC1 (multidrug resistance protein 1), or ABCG2 (breast cancer resistance protein) either due to drug selection or gene transfection, were significantly hypersensitive against KP772. Using ABCB1-overexpressing KBC-1 cells as MDR model, KP772 hypersensitivity was demonstrated to be based on stronger apoptosis induction and/or cell cycle arrest at unaltered cellular drug accumulation. KP772 did neither stimulate ABCB1 ATPase activity nor alter rhodamine 123 accumulation arguing against a direct interaction with ABCB1. Accordingly, several drug resistance modulators did not sensitize but rather protect MDR cells against KP772-induced cytotoxicity. Moreover, long-term KP772 treatment of KBC-1 cells at subtoxic concentrations led within 20 passages to a complete loss of drug resistance based on blocked MDR1 gene expression. When exposing parental KB-3-1 cells to subtoxic, stepwise increasing KP772 concentrations, we observed, in contrast to several other metallo-drugs, no acquisition of KP772 resistance. Summarizing, our data demonstrate that KP772 is hyperactive in MDR cells and might have chemosensitizing properties by blocking ABCB1 expression. Together with the disability of tumor cells to acquire KP772 resistance, our data suggest that KP772 should be especially active against notoriously drug-resistant tumor types and as second line treatment after standard chemotherapy failure.

Anticancer effects of zoledronic acid against human osteosarcoma cells

Based on neoadjuvant chemotherapy, the prognosis of osteosarcoma patients has improved dramatically. However, due to therapy resistance in patient subgroups, the development of new treatment strategies is still of utmost importance. The aim of our study was to test the effects of the nitrogen-containing bisphosphonate zoledronic acid (ZOL) on osteosarcoma cell lines (N = 9). Exposure to ZOL at low micromolar concentrations induced a dose- and time-dependent block of DNA synthesis and cell cycle progression followed by microfilament breakdown and apoptosis induction. The ZOL-induced cell cycle accumulation in S phase was accompanied by significant changes in the expression of cyclins and cyclin-dependent kinase inhibitors with a prominent loss of cyclin E and D1. ZOL not only inhibited growth but also migration of osteosarcoma cells. The mevalonate pathway intermediary geranyl-geraniol (GGOH) but not farnesol (FOH) significantly inhibited the anticancer effects of ZOL against osteosarcoma cells. Correspondingly, ZOL sensitivity correlated with the blockade of protein geranylgeranylation indicated by unprenylated Rap1. Overexpression of even high levels of P-glycoprotein, as frequently present in therapy-resistant osteosarcomas, did not impair the anticancer activity of ZOL. Summarizing, our data suggest that ZOL, which selectively accumulates in the bone, represents a promising agent to improve osteosarcoma therapy.

Intrinsic and acquired forms of resistance against the anticancer ruthenium compound KP1019 [indazolium trans-[tetrachlorobis(1H-indazole)ruthenate (III)] (FFC14A)

KP1019 [indazolium trans-[tetrachlorobis(1H-indazole)ruthenate (III)] (FFC14A) is a metal complex with promising anticancer activity. Since chemoresistance is a major obstacle in chemotherapy, this study investigated the influence of several drug resistance mechanisms on the anticancer activity of KP1019. Here we demonstrate that the cytotoxic effects of KP1019 are neither substantially hampered by overexpression of the drug resistance proteins multidrug resistance-related protein 1, breast cancer resistance protein, and lung resistance protein nor the transferrin receptor and only marginally by the cellular p53 status. In contrast, P-glycoprotein overexpression weakly but significantly (up to 2-fold) reduced KP1019 activity. P-glycoprotein-related resistance was based on reduced intracellular KP1019 accumulation and reversible by known P-glycoprotein modulators. KP1019 dose dependently inhibited ATPase activity of P-glycoprotein with a K(i) of approximately 31 microM. Furthermore, it potently blocked P-glycoprotein-mediated rhodamine 123 efflux under serum-free conditions (EC(50), approximately 8 microM), however, with reduced activity at increased serum concentrations (EC(50) at 10% serum, approximately 35 microM). Moreover, P-glycoprotein-mediated daunomycin resistance could only be marginally restored by KP1019 in serum-containing medium, also indicating an influence of serum proteins on the interaction between KP1019 and P-glycoprotein. Acquired KP1019 resistance was investigated by selecting KB-3-1 cells against KP1019 for more than 1 year. Only an approximately 2-fold KP1019 resistance could be induced, which unexpectedly was not due to overexpression of P-glycoprotein or other efflux pumps. Accordingly, KP1019-resistant cells did not display reduced drug accumulation. Their unique cross-resistance pattern confirmed an ABC transporter-independent resistance phenotype. In summary, the likeliness of acquiring insensitivity to KP1019 during therapy is expected to be low, and resistance should not be based on overexpression of drug efflux transporters.

Application of C60 Fullerene-Doxorubicin Complex for Tumor Cell Treatment In Vitro and In Vivo

Development of nanocarriers for effective drug delivery to molecular targets in tumor cells is a real problem in modern pharmaceutical chemistry. In the present work we used pristine C60 fullerene as a platform for delivery of anticancer drug doxorubicin (Dox) to its biological targets. The formation of a complex of C60 fullerene with Dox (C60 + Dox) is described and physico-chemical characteristics of such complex are presented. It was found that Dox conjugation with C60 fullerene leads to 1.5-2-fold increase in Dox toxicity towards various human tumor cell lines, compared with such effect when the drug is used alone. Cytotoxic activity of C60 + Dox complex is accompanied by an increased level of cell produced hydrogen peroxide at early time point (3 h) after its addition to cultured cells. At the same time, cellular production of superoxide radicals does not change in comparison with the effect of Dox alone. Cytomorphological studies have demonstrated that C60 + Dox complexes kill tumor cells by apoptosis induction. The results of in vivo experiments using Lewis lung carcinoma in mice confirmed the enhancement of the Dox toxicity towards tumor cells after drug complexation with C60 fullerene. The effect of such complex towards tumor-bearing mice was even more pronounced than that in the in vitro experiment with targeting human tumor cells. The tumor volume decreased by 2.5 times compared with the control, and an average life span of treated animals increased by 63% compared with control. The obtained results suggest a great perspective of application of C60 + Dox complexes for chemotherapy of malignant tumors.

Multi-scale imaging of anticancer platinum(iv) compounds in murine tumor and kidney

Nano-scale secondary ion mass spectrometry (NanoSIMS) enables trace element and isotope analyses with high spatial resolution. This unique capability has recently been exploited in several studies analyzing the subcellular distribution of Au and Pt anticancer compounds. However, these studies were restricted to cell culture systems. To explore the applicability to the in vivo setting, we developed a combined imaging approach consisting of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), NanoSIMS and transmission electron microscopy (TEM) suitable for multi-scale detection of the platinum distribution in tissues. Applying this approach to kidney and tumor samples upon administration of selected platinum(iv) anticancer prodrugs revealed uneven platinum distributions on both the organ and subcellular scales. Spatial platinum accumulation patterns were quantitatively assessed by LA-ICP-MS in histologically heterogeneous organs (e.g., higher platinum accumulation in kidney cortex than in medulla) and used to select regions of interest for subcellular-scale imaging with NanoSIMS. These analyses revealed cytoplasmic sulfur-rich organelles accumulating platinum in both kidney and malignant cells. Those in the tumor were subsequently identified as organelles of lysosomal origin, demonstrating the potential of the combinatorial approach for investigating therapeutically relevant drug concentrations on a submicrometer scale.

Nanoformulation improves activity of the (pre)clinical anticancer ruthenium complex KP1019

Ruthenium anticancer drugs belong to the most promising non-platinum anticancer metal compounds in clinical evaluation. However, although the clinical results are promising regarding both activity and very low adverse effects, the clinical application is currently hampered by the limited solubility and stability of the drug in aqueous solution. Here, we present a new nanoparticle formulation based on polymer-based micelles loaded with the anticancer lead ruthenium compound KP1019. Nanoprepared KP1019 was characterised by enhanced stability in aqueous solutions. Moreover, the nanoparticle formulation facilitated cellular accumulation of KP1019 (determined by ICP-MS measurements) resulting in significantly lowered IC50 values. With regard to the mode of action, increased cell cycle arrest in G2/M phase (PI-staining), DNA damage (Comet assay) as well as enhanced levels of apoptotic cell death (caspase 7 and PARP cleavage) were found in HCT116 cells treated with the new nanoformulation of KP1019. Summarizing, we present for the first time evidence that nanoformulation is a feasible strategy for improving the stability as well as activity of experimental anticancer ruthenium compounds.

Destruxins: fungal-derived cyclohexadepsipeptides with multifaceted anticancer and antiangiogenic activities

Destruxins (Dtx) are secondary metabolites of the entomopathogenic fungus Metarhizium anisopliae. Recently, Dtx came into focus of interest as anticancer therapeutics. However, data on human and especially on cancer cells are fragmentary. In order to successfully establish novel anticancer therapeutics, a broad knowledge on the cellular and molecular mechanisms underlying their activity is essential. Consequently, this study aimed to investigate the impact of the most common Dtx derivatives A, B and E on human cancer cell growth and survival with a focus on colon cancer cell models. Summarizing, the experimental data showed that (i) Dtx A and B exert potent antiproliferative activity in the micromolar and Dtx E in the nanomolar range in KB-3-1, A549, CaCo-2, and especially in HCT116 colon cancer cells, (ii) all three Dtx derivatives cause imbalance of cell cycle distribution, (iii) their cytostatic/cytotoxic effects are widely p53-independent but reduced by p21- and bax-deletion, respectively, (iv) cytotoxicity is based on intrinsic apoptosis induction and associated with phosphoinositide-3-kinase (PI3K)/Akt pathway inhibition, (v) anticancer activity of Dtx E but not Dtx A and B involves disturbance of the intracellular redox balance, (vi) Dtx inhibit the migration and tube formation of human endothelial cells indicating antiangiogenic potential, and (vii) all three Dtx derivatives possess ionophoric properties not differing in conductivity, ion selectivity and single channel kinetics. Thus, Dtx represent feasible, multifunctional anticancer drug candidates for preclinical development especially against colorectal cancer.

Long-term exposure of immortalized keratinocytes to arsenic induces EMT, impairs differentiation in organotypic skin models and mimics aspects of human skin derangements

Arsenic is one of the most important human carcinogens and environmental pollutants. However, the evaluation of the underlying carcinogenic mechanisms is challenging due to the lack of suitable in vivo and in vitro models, as distinct interspecies differences in arsenic metabolism exist. Thus, it is of high interest to develop new experimental models of arsenic-induced skin tumorigenesis in humans. Consequently, aim of this study was to establish an advanced 3D model for the investigation of arsenic-induced skin derangements, namely skin equivalents, built from immortalized human keratinocytes (NHEK/SVTERT3-5). In contrast to spontaneously immortalized HACAT cells, NHEK/SVTERT3-5 cells more closely resembled the differentiation pattern of primary keratinocytes. With regard to arsenic, our results showed that while our new cell model was widely unaffected by short-time treatment (72 h) with low, non-toxic doses of ATO (0.05-0.25 µM), chronic exposure (6 months) resulted in distinct changes of several cell characteristics. Thus, we observed an increase in the G2 fraction of the cell cycle accompanied by increased nucleus size and uneven tubulin distribution. Moreover, cells showed strong signs of de-differentiation and upregulation of several epithelial-to-mesenchymal transition markers. In line with these effects, chronic contact to arsenic resulted in impaired skin-forming capacities as well as localization of ki67-positive (proliferating) cells at the upper layers of the epidermis; a condition termed Bowen's disease. Finally, chronically arsenic-exposed cells were characterized by an increased tumorigenicity in SCID mice. Taken together, our study presents a new model system for the investigation of mechanisms underlying the tumor-promoting effects of chronic arsenic exposure.

Triapine-mediated ABCB1 induction via PKC induces widespread therapy unresponsiveness but is not underlying acquired triapine resistance

Although triapine is promising for treatment of advanced leukemia, it failed against solid tumors due to widely unknown reasons. To address this issue, a new triapine-resistant cell line (SW480/tria) was generated by drug selection and investigated in this study. Notably, SW480/tria cells displayed broad cross-resistance against several known ABCB1 substrates due to high ABCB1 levels (induced by promoter hypomethylation). However, ABCB1 inhibition did not re-sensitize SW480/tria cells to triapine and subsequent analysis revealed that triapine is only a weak ABCB1 substrate without significant interaction with the ABCB1 transport function. Interestingly, in chemo-naive, parental SW480 cells short-time (24 h) treatment with triapine stimulated ABCB1 expression. These effects were based on activation of protein kinase C (PKC), a known response to cellular stress. In accordance, SW480/tria cells were characterized by elevated levels of PKC. Together, this led to the conclusion that increased ABCB1 expression is not the major mechanism of triapine resistance in SW480/tria cells. In contrast, increased ABCB1 expression was found to be a consequence of triapine stress-induced PKC activation. These data are especially of importance when considering the choice of chemotherapeutics for combination with triapine.

Ribonucleotide reductase as one important target of [Tris(1,10-phenanthroline)lanthanum(III)] trithiocyanate (KP772)

KP772 is a new lanthanum complex containing three 1,10-phenathroline molecules. Recently, we have demonstrated that the promising in vitro and in vivo anticancer properties of KP772 are based on p53-independent G(0)G(1) arrest and apoptosis induction. A National Cancer Institute (NCI) screen revealed significant correlation of KP772 activity with that of the ribonucleotide reductase (RR) inhibitor hydroxyurea (HU). Consequently, this study aimed to investigate whether KP772 targets DNA synthesis in tumor cells by RR inhibition. Indeed, KP772 treatment led to significant reduction of cytidine incorporation paralleled by a decrease of deoxynucleoside triphosphate (dNTP) pools. This strongly indicates disruption of RR activity. Moreover, KP772 protected against oxidative stress, suggesting that this drug might interfere with RR by interaction with the tyrosyl radical in subunit R2. Additionally, several observations (e.g. increase of transferrin receptor expression and protective effect of iron preloading) indicate that KP772 interferes with cellular iron homeostasis. Accordingly, co-incubation of Fe(II) with KP772 led to generation of a coloured iron complex (Fe-KP772) in cell free systems. In electron paramagnetic resonance (EPR) measurements of mouse R2 subunits, KP772 disrupted the tyrosyl radical while Fe-KP772 had no significant effects. Moreover, coincubation of KP772 with iron-loaded R2 led to formation of Fe-KP772 suggesting chelation of RR-bound Fe(II). Summarizing, our data prove that KP772 inhibits RR by targeting the iron centre of the R2 subunit. As also Fe-KP772 as well as free lanthanum exert significant -though less pronounced- cytotoxic/static activities, additional mechanisms are likely to synergise with RR inhibition in the promising anticancer activity of KP772.

Enhanced anticancer activity and circumvention of resistance mechanisms by novel polymeric/ phospholipidic nanocarriers of doxorubicin

Severe toxic side effects and drug resistance are the major limitations of doxorubicin (Dox), one of the most potent anticancer agents in clinical use. Nanocarrier preparations offer the opportunity to overcome these drawbacks, which is reflected in the clinical approval of two liposomal Dox preparations. Additionally, there are many attempts to enhance the activity of Dox against multi-drug resistant (MDR) cancer cells. However, most of these strategies resulted in the increased uptake of Dox in resistant cells, only, while it remained unchanged in chemo-sensitive cells. Here, we present a new polymeric-phospholipidic hybrid delivery system which distinctly enhanced the accumulation and activity of Dox in all tested cancer cell lines including several MDR cell models. Notably, the resistance levels against Dox were reduced from about 6-fold to about 2-fold. Moreover, the new nanocarriers were shown to rapidly (within 10 min) and effectively transport Dox into resistant as well as sensitive cancer cells. Consequently, treatment with the new Dox-containing nanocarriers resulted in effective cell cycle arrest in G2/M phase and ROS-induced cell death induction. Finally, the new nanocarriers were tested against NK/Ly lymphoma and L1210 leukemia cells in vivo. In both cell models, the nanoformulation of Dox resulted in 100% cured animals already at low concentrations (0.1 mg/kg), while free Dox solely extended survival time. This indicates that the incorporation of phospholipids into PEGylated polymeric nanocarriers is a promising strategy to enhance efficacy and reduce toxicity of Dox treatment against both sensitive and resistant cancer models in vitro and in vivo.

[Effect of free and polymer carrier encapsulated doxorubicin towards HCT116 cells of human colorectal carcinoma]

Development of novel nanoscale functionalized carriers is nowadays one of the most urgent problems in cancer treatment. The aim of our study was to compare the antineoplastic effect of free doxorubicin and its complex with a nanoscale polymeric carrier towards HTC116 colorectal carcinoma cells. It was established that application of the complex of poly(5-tret-butylperoxy)-5-methyl-1-hexene-3-in-co-glycydyl metacrylat)-graft-polyethyleneglycol (poly(VEP-GMA-PEG)-graft-PEG), where VEP--5-tret-butylperoxy)-5-methyl-1-hexene-3-in; GMA--glycydyl metacrylat; graft-PEG--graft-polyethyleneglycol accordingly, functionalized with phosphatidylcholine for doxorubicin delivery increased 10 times the efficiency of cytotoxic action of this drug, as compared wich such efficiency in case of the action of free doxorubicin. The encapsulated form of doxorubicin caused more intensive cleavage of the reparation enzyme PARP and longer delay in G2/M cell cycle arrest, compared to such effects of free doxorubicin. The developed carrier itself is non-toxic to the used mammalian cells and does not cause impairment in their cell cycle. A deletion in both alleles of p53 gene did not affect the antineoplastic action of doxorubicin that was immobilized on the nanoscale carrier. Thus, p53-dependent signaling pathways are not involved in the cytotoxic action of doxorubicin-carrier complex. It is suggested that novel nanoscale polymeric carrier poly(VEP-GMA-PEG)-graft-PEG functionalized with phosphatidylcholine could be a promising carrier for targeted delivery of anticancer drugs.