Different cell cycle modulation following treatment of human ovarian carcinoma cells with a new platinum(IV) complex vs cisplatin

Summary Platinum (IV) derivative with adamantylamine—LA-12—represents a new generation of highly efficient anti-cancer drug derived from cisplatin and is currently in the final stage of phase I clinical trials. Understanding the specific mechanisms of its effects on cell cycle is necessary for defining the mode of action of LA-12. In this study, we characterized the ability of LA-12 to induce cell cycle perturbations in ovarian cancer cell line A2780 as compared to equitoxic cisplatin treatment. LA-12 induced a permanent accumulation of A2780 cells in S phase while cisplatin caused G₂/M arrest at 24-h time point, where we also detected an increased expression of Gadd45α protein. Although both derivatives induced a rapid increase of p53 expression, this was not associated with a down-regulation of Mdm2 protein. Increased expression of p21^Cip1/WAF1 protein and its association with cyclins A and B1 suggested that this cyclin-dependent kinase inhibitor might contribute significantly to the observed perturbations of cell cycle. The results of this study provide insight into the mechanism of action of platinum-based derivative with adamantylamine on cell cycle in ovarian cancer cells. The differences between effects of LA-12 and cisplatin suggest that more attention should be paid to elucidation of modes of action of novel platinum(IV) complexes at cellular level.     

DNA strand breaks and apoptosis induced by oxaliplatin in cancer cells

Platinum anticancer drugs, such as cisplatin, are thought to exert their activity by DNA damage. Oxaliplatin, a clinically active diaminocyclohexane platinum compound, however, requires fewer DNA-Pt adducts than cisplatin to achieve cell growth inhibition. Here we investigated whether secondary DNA damage and apoptotic responses to oxaliplatin compensate for the reduced formation of DNA adducts. Oxaliplatin treatment of leukemic CEM and ovarian A2780 cancer cells resulted in early (4 hr) induction of DNA single-strand breaks measured by nucleoid sedimentation. These infrequent early lesions progress with time into massive double-stranded DNA fragmentation (fragments >50k bp) paralleled by characteristic apoptotic changes revealed by cell morphology and multivariate flow cytometry. Profound oxaliplatin-induced apoptotic DNA fragmentation was detectable following a 24 hr treatment of A2780 and CEM cells with 2 and 10 microM oxaliplatin, respectively. This DNA fragmentation was inhibited completely by the broad-spectrum caspase inhibitor Z-VAD-fmk. Cisplatin, which forms markedly more DNA-Pt adducts in CEM and A2780 cells than equimolar oxaliplatin, was similarly potent as oxaliplatin in terms of early strand breaks and later apoptotic responses. Oxaliplatin was also profoundly apoptotic in several other tumor cell lines of prostate origin but had only a marginal effect in normal prostate PrEC cells. Collectively, the results demonstrate that, relative to the magnitude of the primary DNA-Pt lesions, oxaliplatin is disproportionately more potent than cisplatin in the induction of apoptosis. Apoptosis induction, possibly enhanced by a contribution of targets other than DNA, seems to be an important factor in the mechanism of action of oxaliplatin.     

Comparative anti-tumor efficacy of two orally administered platinum(IV) drugs in nude mice bearing human tumor xenografts

The oral anti-tumor activity of a novel platinum(IV) complex, coded as LA-12, with a bulky adamantylamine ligand was evaluated and compared with another platinum(IV) complex satraplatin. The human carcinoma xenografts of colon HCT116, prostate PC3, and ovarian A2780 and A2780/cisR (resistant to cisplatin) were used to evaluate the in-vivo anti-tumor activity. The daily x 5 repeated dose regimen in equimolar doses of LA-12 and satraplatin, administered in 2 cycles, was selected for this evaluation. All doses of LA-12 and satraplatin were significantly effective in comparison with the control. The activities of LA-12 in all doses and all used tumor xenografts were higher than equimolar doses of satraplatin. The highest effect was reached with LA-12 at a dose of 60 mg/kg. The shapes of growth curves of ovarian carcinoma A2780 and its subline resistant to cisplatin after therapy with LA-12 were very similar. This shows that LA-12 is able to overcome resistance to cisplatin.     

JM216-, JM118-, and cisplatin-induced cytotoxicity in relation to platinum-DNA adduct formation,glutathione levels and p53 status in human tumour cell lines with different sensitivities to cisplatin

The aim of this study is to establish anti-tumour potency of the new oral platinum drug JM216 and its metabolite JM118 in relation to the platinum (Pt)-DNA adduct formation, glutathione (GSH)-levels, and p53 status in human cancer cell lines with different sensitivities to cisplatin (CDDP). These parameters were studied in the CDDP sensitive human germ cell cancer cell line Tera and the small-cell lung cancer cell line GLC4 and their sublines with in vitro acquired CDDP resistance, Tera-CP and GLC4-CDDP, in a human ovarian cancer cell line transfected with mutant p53 (A2780/mt273) and with an empty vector as control (A2780/cmv), and in the intrinsic CDDP resistant human non-small-cell lung cancer cell line SW1573/S1 and colon carcinoma cell line Caco-2. Cytotoxicity was tested with the microculture tetrazolium (MTT)-assay. Pt-DNA adduct levels were assessed immunocytochemically. Quantitative analysis was performed by double fluorescence video microscopy. Results were correlated with GSH levels and p53 status of the cell lines. This study showed that both JM216 and JM118 can partially circumvent intrinsic and acquired resistance to CDDP. Drug-induced cytotoxicity only correlated negatively with GSH levels for JM216 and CDDP in the tested unselected cell lines. At equimolar basis, JM216 induced lower levels of Pt-DNA adducts in the various cell lines than JM118 and CDDP, whereas the JM118-induced amount and pattern of Pt-DNA adducts was comparable to CDDP. No difference in initial Pt-DNA adducts levels was observed between cell lines sensitive, acquired or intrinsic resistant to CDDP suggesting a Pt-resistance mechanism based on tolerance or increased repair, rather than decreased initial Pt-DNA adduct formation.     

New platinum(IV) complex with adamantylamine ligand as a promising anti-cancer drug: comparison of in vitro cytotoxic potential towards A2780/cisR cisplatin-resistant cell line within homologous series of platinum(IV) complexes

The aim of this study was to compare anti-tumor potency of platinum(IV) complexes with increasing hydrophobicity of their ligands. Cytotoxic potential of the new platinum(IV) complex, coded as LA-12 [(OC-6-43)-bis(acetato)(1-adamantylamine)amminedichloroplatinum(IV)], was compared within the series of complexes of the general formula (OC-6-43)-bis(acetato)(alkylamine)amminedichloroplatinum(IV). Alkylamine ligands with increasing hydrophobicity were: isopropylamine, cyclohexylamine, 1-adamantylamine and 3,5-dimethyl-1-adamantylamine. Particular platinum(IV) complexes were coded as LA-4, LA-2 (known as JM-216), LA-12 and LA-15, respectively. Cytotoxicity was tested with the microplate tetrazolium (MTT) assay on the panel of cancer cell lines and the results were verified by microscopy. HPLC was used to measure hydrophobicity, stability of complexes in various buffers and velocity constants for their reactivity with glutathione. Platinum(IV) complexes with bulky hydrophobic ligands (LA-12 and LA-15) demonstrated about one order higher velocity constant for pseudo-first-order reaction with glutathione in comparison to cisplatin, LA-4 and LA-2, whose velocity constants were close to those measured for cisplatin and related platinum(II) complexes. Cytotoxicities of LA-12 and LA-15 towards cisplatin-resistant epithelial carcinoma A2780/cisR were superior to cisplatin, LA-4 and LA-2 in both 24- and 72-h continuous exposure MTT tests. Rapid induction of apoptosis in the treated cancer cell lines and no cisplatin cross-resistance were found for LA-12, which is a candidate for clinical testing.     

Variation in the kinetics of caspase-3 activation, Bcl-2 phosphorylation and apoptotic morphology in unselected human ovarian cancer cell lines as a response to docetaxel

Paclitaxel is able to cause cell death through the induction of apoptosis. Cell death characteristics for docetaxel have not yet been described in detail. We investigated four unselected human ovarian cancer cell lines for the sensitivity to a 1hr exposure to docetaxel and calculated the concentrations inhibiting 50% (IC(50)) and 90% (IC(90)) of cell growth. Of the cell lines A2780, H134, IGROV-1 (all wild-type p53) and OVCAR-3 (mutant, mt p53) A2780 was most sensitive and OVCAR-3 least sensitive. Equitoxic drug concentrations representing IC(90) values (25-510nM) were applied for 1hr to measure cell cycle distribution, DNA degradation, and to count apoptotic cell bodies and cells with multifragmented nuclei at various time-points after drug exposure. H134, IGROV-1 and OVCAR-3 showed a continued mitotic block up to at least 72hr and prolonged presence of cells with multifragmented nuclei. High percentages of apoptosis were calculated at 48hr and at later time-points. In contrast, A2780 cells accumulated in the S-phase of the cell cycle and apoptosis was hardly present. The changes in the expression levels of p53, p21/WAF1, Bax and Bcl-2, were not predictive for docetaxel-induced apoptosis. Caspase-3 activation occurred only in cells with accumulation in the G2/M phase starting as early as 8hr in OVCAR-3. Prolonged Bcl-2 phosphorylation was evident in OVCAR-3, visible at 24hr in H134 and IGROV-1, while this phenomenon did not occur in A2780. The mitogen-activated protein kinase pathway (JNKs/SAPKs or c-Jun N-terminal kinases/stress-activated protein kinases, JNK1/2; extracellular response kinase, ERK1/2; p38) did not seem to be directly involved in Bcl-2 phosphorylation or apoptosis. We conclude that docetaxel is able to activate caspase-3, induce Bcl-2 phosphorylation and apoptosis in cells that show a prolonged G2/M arrest, but cells may also die by a caspase-3-independent cell death mechanism.     

Synthesis and biological evaluation of 2'-methyl taxoids derived from baccatin III and 14beta-OH-baccatin III 1,14-carbonate

A series of 2'-methyl taxoids were synthesized and essayed for growth inhibition experiments conducted in human ovarian cancer cell line A2780wt and its counterparts A2780cis, A2780tax, and A2780adr, resistant to cisplatin, paclitaxel, and doxorubicin, respectively, to test the effect of this substituent on the antitumor activity. Additional experiments were performed on MCF-7 human breast cancer cell line and MCF7-R resistant to doxorubicin. In several cases these taxoids were more active than paclitaxel showing subnanomolar IC(50) values.     

Quantitative relationship between guanine O-alkyl lesions produced by Onrigin™ and tumor resistance by O-alkylguanine-DNA alkyltransferase

O⁶-Alkylguanine-DNA alkyltransferase (AGT) mediates tumor resistance to alkylating agents that generate guanine O⁶-chloroethyl (Onrigin™ and carmustine) and O⁶-methyl (temozolomide) lesions; however, the relative efficiency of AGT protection against these lesions and the degree of resistance to these agents that a given number of AGT molecules produces are unclear. Measured from differential cytotoxicity in AGT-ablated and AGT-intact HL-60 cells containing 17,000 AGT molecules/cell, AGT produced 12- and 24-fold resistance to chloroethylating (90CE) and methylating (KS90) analogs of Onrigin™, respectively. For 50% growth inhibition, KS90 and 90CE generated 5,600 O⁶-methylguanines/cell and ∼300 O⁶-chloroethylguanines/cell, respectively. AGT repaired O⁶-methylguanines until the AGT pool was exhausted, while its repair of O⁶-chloroethylguanines was incomplete due to progression of the lesions to AGT-irreparable interstrand DNA cross-links. Thus, the smaller number of O⁶-chloroethylguanine lesions needed for cytotoxicity accounted for the marked degree of resistance (12-fold) to 90CE produced by AGT. Transfection of human or murine AGT into AGT deficient transplantable tumor cells (i.e., EMT6, M109 and U251) generated transfectants expressing AGT ranging from 4,000 to 700,000 molecules/cell. In vitro growth inhibition assays using these transfectants treated with 90CE revealed that AGT caused a concentration dependent resistance up to a level of ∼10,000 AGT molecules/cell. This finding was corroborated by in vivo studies where expression of 4,000 and 10,000 murine AGT molecules/cell rendered EMT6 tumors partially and completely resistant to Onrigin™, respectively. These studies imply that the antitumor activity of Onrigin™ stems from guanine O⁶-chloroethylation and define the threshold concentration of AGT that negates its antineoplastic activity.     

The novel platinum(IV) complex LA-12 induces p53 and p53/47 responses that differ from the related drug, cisplatin

The platinum(II)-based complex cisplatin is one of the most frequently used antitumour agents; however, a high incidence of harmful side effects and the frequent emergence of acquired resistance are the major clinical problems. The novel platinum(IV)-based complex LA-12 exhibits a high efficacy against cancer cell lines, including cisplatin-insensitive cells, but the mechanisms by which LA-12 perturbs cell growth are unclear. We tested the effects of LA-12 on the p53 response and demonstrate that LA-12 induces unique changes in the profile of gene expression compared with cisplatin and doxorubicin. Furthermore, the ability of LA-12 to disrupt cellular proliferation is greatly enhanced by the expression of p53 and p53/47 indicating both p53-dependent and p53-independent effects of LA-12. Exposure of the human cancer cell lines H1299, A2780, BT549 and BT474 to LA-12 alters the expression of p53 and p53/47 in both a time-dependent and dose-dependent manner. Treatment of cells with a low concentration of the drug results in accumulation of p53 and p53/47 concomitant with their posttranslational modification, whereas a high dose results in the disappearance of both the forms of p53. The distinct p53 activation profile of LA-12 compared with cisplatin and doxorubicin provides a molecular explanation for the ability of this drug to treat cisplatin-resistant cells and indicates its potential usefulness as an alternative antitumour agent in first-line therapy or as a second-line therapy in patients with acquired cisplatin resistance.     

DNA interactions of new antitumor platinum complexes with trans geometry activated by a 2-metylbutylamine or sec-butylamine ligand

The global modification of mammalian and plasmid DNAs by novel platinum compounds, trans-[PtCl(2)(NH(3))(Am)], where Am=2 -methylbutylamine or sec-butylamine was investigated in cell-free media using various biochemical and biophysical methods. These modifications were analyzed in the context of the activity of these new compounds in several tumor cell lines including those resistant to antitumor cis-diamminedichloroplatinum(II) (cisplatin). The results showed that the replacement of one amine group by 2-methylbutylamine or sec-butylamine ligand in clinically ineffective trans-diamminedichloroplatinum(II) (transplatin) resulted in a radical enhancement of its activity in tumor cell lines so that they are more cytotoxic than cisplatin and exhibited significant antitumor activity including activity in cisplatin-resistant tumor cells. Importantly, this replacement also markedly altered DNA binding mode of transplatin and reduced the efficiency of repair systems to remove the adducts of the new analogues from DNA. The results support the view that one strategy to activate trans geometry in bifunctional platinum(II) compounds including circumvention of resistance to cisplatin may consist in a chemical modification of the ineffective transplatin which results in an increased efficiency to form DNA interstrand cross-links.     

Identification of potent anticancer activity in Ximenia americana aqueous extracts used by African traditional medicine

The antineoplastic activity of a plant powder used in African traditional medicine for treating cancer was investigated by analyzing the activity of various extracts in vitro. The most active, aqueous extract was subsequently subjected to a detailed investigation in a panel of 17 tumor cell lines, showing an average IC50 of 49 mg raw powder/ml medium. The sensitivity of the cell lines varied by two orders of magnitude, from 1.7 mg/ml in MCF7 breast cancer cells to 170 mg/ml in AR230 chronic-myeloid leukemia cells. Immortalized, non-tumorigenic cell lines showed a marginal sensitivity. In addition, kinetic and recovery experiments performed in MCF7 and U87-MG cells and a comparison with the antineoplastic activity of miltefosine, gemcitabine, and cisplatinum in MCF7, U87-MG, HEp2, and SAOS2 cells revealed no obvious similarity between the sensitivity profiles of the extract and the three standard agents, suggesting a different mechanism of cytotoxicity. The in vivo antitumor activity was determined in the CC531 colorectal cancer rat model. Significant anticancer activity was found following administration of equitoxic doses of 100 (perorally) and 5 (intraperitoneally) mg raw powder/kg, indicating a 95% reduced activity following intestinal absorption. By sequencing the mitochondrial gene for the large subunit of the ribulose bis-phosphate carboxylase (rbcL) in DNA from the plant material, the source plant was identified as Ximenia americana. A physicochemical characterization showed that the active antineoplastic component(s) of the plant material are proteins with galactose affinity. Moreover, by mass spectrometry, one of these proteins was shown to contain a stretch of 11 amino acids identical to a tryptic peptide from the ribosome-inactivating protein ricin.     

Single pre-treatment with hypericin,a St. John’s wort secondary metabolite,attenuates cisplatin- and mitoxantrone-induced cell death in A2780, A2780cis and HL-60 cells

St. John’s wort (SJW, Hypericum perforatum L.) is a commonly used natural antidepressant responsible for the altered toxicity of some anticancer agents. These interactions have been primarily attributed to the hyperforin-mediated induction of some pharmacokinetic mechanisms. However, as previously demonstrated by our group, hypericin induces the expression of two ABC transporters: multidrug resistance-associated protein 1 (MRP1) and breast cancer resistance protein (BCRP). Because cisplatin (CDDP) and mitoxantrone (MTX) are potential substrates of ABC transporters, we investigated the effect of 24 h hypericin pre-treatment on the cytotoxicity of CDDP and MTX in human cancer cell lines. CDDP-sensitive and -resistant ovarian adenocarcinoma cell lines A2780/A2780cis, together with HL-60 promyelocytic leukemia cells and ABCG2-over-expressing cBCRP subclone, were used in our experiments. We present CDDP cytotoxicity attenuated by hypericin pre-treatment in both A2780 and A2780cis cells and MTX cytotoxicity in HL-60 cells. In contrast, hypericin potentiated MTX-induced death in cBCRP cells. Interestingly, hypericin did not restore cell proliferation in rescued cells. Nevertheless, hypericin did increase the expression of MRP1 transporter in A2780 and A2780cis cells indicating the impact of hypericin on certain resistance mechanisms. Additionally, our results indicate that hypericin may be the potential substrate of BCRP transporter. In conclusion, for the first time, we report the ability of hypericin to affect the onset and/or progress of CDDP- and MTX-induced cell death, despite strong cell cycle arrest. Thus, hypericin represents another SJW metabolite that might be able to affect the effectiveness of anti-cancer drugs and that could interact with ABC transporters, particularly with BCRP.     

Relevance of drug uptake and efflux for cisplatin sensitivity of tumor cells

Platinum sensitivity and platinum resistance may involve altered activity of transport proteins. In order to assess the role of drug uptake and efflux in this phenomenon, we compared the expression of three copper transporters, intracellular platinum accumulation, DNA platination and cytotoxicity of cisplatin in two cisplatin-sensitive and -resistant tumor cell line pairs (ovarian A2780/A2780cis and cervical HeLa/HeLaCK cells). Gene expression of importer CTR1, and ATP7A and ATP7B efflux transporters (with and without cisplatin treatment) was investigated using quantitative real-time PCR and platinum concentrations were determined by flameless atomic absorption spectrometry. After incubation with cisplatin, DNA platination was significantly lower in the resistant variants compared to the respective sensitive cell lines, whereas no obvious difference in DNA repair was found. Accordingly, the resistant variants exhibited lower intracellular platinum concentrations than their respective parental cells (2.5- and 2.9-fold lower in A2780cis and HeLaCK cells, respectively). No differences in efflux were observed. Resistant cells expressed lower levels of CTR1 (1.5-1.8-fold) than their sensitive counterparts. Expression differences of ATP7A and ATP7B between resistant and sensitive cells were cell type-specific. The results highlight the relevance of CTR1 for cisplatin sensitivity as there is a clear relationship between lower CTR1 expression, intracellular concentration, DNA platination and cytotoxicity of cisplatin in both resistant cell lines. Our data provide the basis for a quantitative understanding of alterations in uptake and efflux processes leading to cisplatin resistance and might hence facilitate the development of ex vivo assays that can predict cisplatin sensitivity in tumor specimens of patients.     

Combination treatment of glioblastoma multiforme cell lines with the anti-malarial artesunate and the epidermal growth factor receptor tyrosine kinase inhibitor OSI-774

New drugs and combination modalities for otherwise non-responsive brain tumors are urgently required. The anti-malarial artesunate (ART) and the EGFR tyrosine kinase inhibitor OSI-774 reveal profound cytotoxic activity. The effectiveness of a combination treatment and the underlying molecular determinants of cellular response are unknown. In the present investigation, we studied ART and OSI-774 in glioblastoma multiforme (GBM) cell lines. Supra-additive inhibition of cell growth was observed in U-87MG.DeltaEGFR cells transduced with a deletion-mutant constitutively active EGFR gene, while additive effects were present in cells transduced with wild-type EGFR (U-87MG.WT-2N), kinase-deficient EGFR (U-87MG.DK-2N), mock vector controls (U-87MG.LUX), or non-transduced parental U-87MG cells. Among nine other non-transduced GBM cell lines, supra-additive effects were found in two cell lines (G-210GM, G-599GM), while ART and OSI-774 acted in an additive manner in the other seven cell lines (G-211GM, G-750GM, G-1163GM, G-1187GM, G-1265GM, G-1301GM, and G-1408GM). Sub-additive or antagonistic effects were not observed. Genomic gains and losses of genetic material in the non-transduced cell lines as assessed by comparative genomic hybridization were correlated with the IC(50) values for ART and OSI-774 and subsequently subjected to hierarchical cluster analysis and cluster image mapping. A genomic profile of imbalances was detected that predicted cellular response to ART and OSI-774. The genes located at the genomic imbalances of interest may serve as candidate resistance genes of GBM cells towards ART and OSI-774. In conclusion, the combination treatment of ART and OSI-774 resulted in an increased growth inhibition of GBM cell lines as compared to each drug alone.     

Growth Inhibitory Effect of (E)-2,4-bis(p-hydroxyphenyl)-2-Butenal Diacetate through Induction of Apoptotic Cell Death by Increasing DR3 Expression in Human Lung Cancer Cells

The Maillard Reaction Products (MRPs) are chemical compounds which have been known to be effective in chemoprevention. Death receptors (DR) play a central role in directing apoptosis in several cancer cells. In our previous study, we demonstrated that (E)-2,4-bis(p-hydroxyphenyl)-2-butenal, a MRP product, inhibited human colon cancer cell growth by inducing apoptosis via nuclear factor-κB (NF-κB) inactivation and G₂/M phase cell cycle arrest. In this study, (E)-2,4-bis(p-hydroxyphenyl)-2-butenal diacetate, a new (E)-2,4-bis(p-hydroxyphenyl)-2-butenal derivative, was synthesized to improve their solubility and stability in water and then evaluated against NCI-H460 and A549 human lung cancer cells. (E)-2,4-bis(p-hydroxyphenyl)-2-butenal diacetate reduced the viability in both cell lines in a time and dose-dependent manner. We also found that (E)-2,4-bis(p-hydroxyphenyl)-2-butenal diacetate increased apoptotic cell death through the upregulation of the expression of death receptor (DR)-3 and DR6 in both lung cancer cell lines. In addition to this, the transfection of DR3 siRNA diminished the growth inhibitory and apoptosis inducing effect of (E)-2,4-bis(p-hydroxyphenyl)-2-butenal diacetate on lung cancer cells, however these effects of (E)-2,4-bis(p-hydroxyphenyl)-2-butenal diacetate was not changed by DR6 siRNA. These results indicated that (E)-2,4-bis(p-hydroxyphenyl)-2-butenal diacetate inhibits human lung cancer cell growth via increasing apoptotic cell death by upregulation of the expression of DR3.     

Enhanced DNA excision repair in CCRF-CEM cells resistant to 1,3-bis(2-chloroethyl)-1-nitrosourea,quantitated using the single cell gel electrophoresis (Comet) assay

Enhanced DNA repair activity is important for the development of cellular resistance to alkylating agents. Here, we quantitated the kinetics of DNA excision repairs initiated by 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in human leukemia CCRF-CEM cells. CEM cells that had been established resistant to BCNU (CEM-R) were evaluated in comparison with parental CEM cells (CEM-S). The excision repair kinetics were quantitated as the amount of DNA single strand breaks, which were generated from the incision/excision of the damaged DNA and were diminished by the rejoining of renewed DNA, using the single cell gel electrophoresis (Comet) assay. CEM-R cells were 10-fold more resistant to BCNU than CEM-S cells, and also showed cross-resistance to melphalan and cisplatin. In response to the treatment with BCNU, both CEM-S and CEM-R cells initiated an incision/excision reaction at the end of the incubation period, and completed the rejoining process within 4 hr. While CEM-S cells could not repair the damage induced by the high concentration of BCNU, CEM-R cells completed the repair process regardless of BCNU concentrations, suggesting enhanced excision repairs in CEM-R cells. The excision repair activity of CEM-R cells was increased with regard to the incision reaction and to the rate of the repair. Similar results were obtained using ultraviolet C, suggesting enhanced nucleotide excision repair in CEM-R cells. Thus, the enhanced DNA excision repairs were successfully quantitated in the resistant leukemic cell line using the Comet assay. The evaluation of the repair activity may predict the sensitivity of cancer cells to chemotherapy and provide a clue to overcome the resistance.     

Cytotoxic activity and cellular processing in human ovarian carcinoma cell lines of a new platinum(II) compound containing a fluorescent substituted propylene diamine ligand

A new fluorescent platinum(II) compound containing the N,N′-bis-(anthracen-9-ylmethyl)propane-1,3-diamine as a carrier ligand has been designed, synthesized and characterized. High cytotoxic activity of cis-[Pt(bapda)Cl₂] is observed in A2780 and A2780R cells (human ovarian carcinoma sensitive and cisplatin-resistant, respectively). Nevertheless, cross-resistance to platinum from cis-[Pt(bapda)Cl₂] in the A2780R cells was found. To study the role of GSH towards inactivation of cis-[Pt(bapda)Cl₂], GSH-depleted and non-depleted A2780R cells were used in several in vitro studies. The results suggest that cis-[Pt(bapda)Cl₂] is not susceptible to the inactivation by GSH. Cellular processing of bapda and cis-[Pt(bapda)Cl₂] was followed using fluorescence microscopy in the A2780, the A2780R and GSH-depleted A2780R cells. Interestingly, differences in the cellular processing followed by fluorescence microscopy between normal and GSH-depleted A2780R cells have been observed for the carrier ligand. Sequestration of these compounds in acidic lysosomes is visible after incubation in most cases, and no fluorescence was observed in the nucleus. Interaction of cis-[Pt(bapda)Cl₂] with calf thymus DNA strongly suggests that the this new platinum(II) compound intercalates between the DNA base pairs. Additionally, the reaction of cis-[Pt(bapda)Cl₂] with 9-ethylguanine appears to be very slow, as studied by ¹H and ¹⁹⁵Pt NMR spectroscopy.     

Cationic nonsymmetric transplatinum complexes with piperidinopiperidine ligands. Preparation, characterization, in vitro cytotoxicity, in vivo toxicity, and anticancer efficacy studies

A series of complexes of the general formula trans-[PtCl2(Am)(pip-pip)] x HCl where pip-pip is 4-piperidinopiperidine and Am is NH3, methylamine (MA), dimethylamine (DMA), n-propylamine (NPA), isopropylamine (IPA), n-butylamine (NBA), or cyclohexylamine (CHA) were prepared and characterized, and their cytotoxic properties against ovarian and colon cancer cells were evaluated. The trans-[PtCl2(NH3)(pip-pip)] x HCl was significantly more potent than cisplatin in all the cisplatin-resistant ovarian cancer cell lines and was nearly as cytotoxic as cisplatin against colon cancer cells. In vivo studies in mice showed that the pip-pip complexes are significantly less toxic than cisplatin. Cisplatin was more efficacious than both trans-[PtCl2(NH3)(pip-pip)] x HCl and trans-[PtCl2(NBA)(pip-pip)] x HCl in the A2780 and A2780cisR tumor xenograft models, consistent with its lower IC50 values in A2780 cells but contrary to the higher IC50 values in A2780cisR cells. In the colon cancer cell studies, trans-[PtCl2(NH3)(pip-pip)] x HCl was slightly less potent than cisplatin in the in vitro studies but had efficacy comparable to that of cisplatin in the in vivo xenograft model.