Cellular Platinum Accumulation Research Articles

Novel Pt(IV) complexes containing salvigenin ligand reverse cisplatin-induced resistance by inhibiting Rap1b-mediated cancer cell stemness in esophageal squamous cell carcinoma treatments

Esophageal squamous cell carcinoma (ESCC) is a malignant tumor that is highly susceptible to metastasis, recurrence and resistance, and few therapeutic targets have been identified and proven effective. Herein, we demonstrated for the first time that Rap1b can positively regulate ESCC cell stemness, as well as designed and synthesized a novel class of Pt(IV) complexes that can effectively inhibit Raplb. In vitro biological studies showed that complex-1 exhibited stronger cytotoxicity than cisplatin and oxaliplatin against a variety of ESCC cells, and effectively reversed cisplatin-induced resistance of TE6 cells by increasing cellular accumulation of platinum and inhibiting cancer cell stemness. Significantly, complex-1 also exhibited strong ability to reversal cisplatin-induced cancer cell resistance and inhibit tumor growth in TE6/cDDP xenograft mice models, with a tumor growth inhibition rate of 73.3 % at 13 mg/kg and did not show significant systemic toxicity. Overall, Rap1b is a promising target to be developed as an effective treatment for ESCC. Complex-1, as the first Pt(IV) complex that can strongly inhibit Rap1b, is also worthy of further in-depth study.

A nanocomposite competent to overcome cascade drug resistance in ovarian cancer via mitochondria dysfunction and NO gas synergistic therapy

Ovarian cancer (OC) is one of the most common and recurring malignancies in gynecology. Patients with relapsed OC always develop "cascade drug resistance" (CDR) under repeated chemotherapy, leading to subsequent failure of chemotherapy. To overcome this challenge, amphiphiles (P1) carrying a nitric oxide (NO) donor (Isosorbide 5-mononitrate, ISMN) and high-density disulfide are synthesized for encapsulating mitochondria-targeted tetravalent platinum prodrug (TPt) to construct a nanocomposite (INP@TPt). Mechanism studies indicated that INP@TPt significantly inhibited drug-resistant cells by increasing cellular uptake and mitochondrial accumulation of platinum, depleting glutathione, and preventing apoptosis escape through generating highly toxic peroxynitrite anion (ONOO−). To better replicate the microenvironmental and histological characteristics of the drug resistant primary tumor, an OC patient-derived tumor xenograft (PDXOC) model in BALB/c nude mice was established. INP@TPt showed the best therapeutic effects in the PDXOC model. The corresponding tumor tissues contained high ONOO− levels, which were attributed to the simultaneous release of O2•− and NO in tumor tissues. Taken together, INP@TPt-based systematic strategy showed considerable potential and satisfactory biocompatibility in overcoming platinum CDR, providing practical applications for ovarian therapy.

Design, synthesis and biological evaluation of antitumor platinum(II) agents conjugated with non-steroidal anti-inflammatory drug species

As one of the key features of tumor, inflammation attracts much attention of many researchers for antitumor study, in which non-steroidal anti-inflammatory drugs (NSAIDs) have been widely investigated in anti-inflammatory treatments in cancers. Herein, we report a series of novel platinum(II) complexes derived from conjugation of several NSAIDs derivatives with two antitumor platinum(II) agents. The antitumor inhibitory effects of the synthesized compounds on a number of cancer cell lines were estimated. By taking the advantage of two bioactive moieties, these compounds exhibited stronger antitumor activity than their parent platinum agents, and some appeared to have capability of overcoming cisplatin resistance. Among them, IA-1 showed the best cytotoxicity and even exhibited stronger antitumor activity than cisplatin. Further research indicated that IA-1 induced significant DNA damage and ROS generation, accompanied by high cellular platinum accumulation, resulting in a much higher apoptosis rate than cisplatin in A2780 cells. Moreover, IA-1 was found to inhibit metastasis and invasion of A2780 cells by suppressing the COX-2/JAK2/STAT3 axis. All these results revealed that introduction of NSAIDs species efficiently sensitized cancer cells to the synthetic compounds, proving that NSAIDs can enhance the activity of the platinum(II) agents via inhibiting inflammation in cancer cells.

Novel CK2-Specific Pt(II) Compound Reverses Cisplatin-Induced Resistance by Inhibiting Cancer Cell Stemness and Suppressing DNA Damage Repair in Non-small Cell Lung Cancer Treatments.

Cancer stem cells (CSCs) have a pivotal impact in drug resistance, tumor metastasis, and progression of various cancer entities, including in non-small cell lung cancer (NSCLC). A CK2 inhibitor HY1 was found to show potent CSC inhibitory effects in A549 cells. By taking advantage of inherent CK2 specificity and CSC inhibition of HY1, a Pt(II) agent (HY1-Pt) was developed by conjugation of HY1 with an active Pt(II) unit to reverse cisplatin-induced resistance in A549/cDDP cell treatment. In vitro biological studies indicated that HY1-Pt can target CK2, suppress DNA damage repair, reinforce cellular accumulation of platinum, and reverse resistance apart from effectively inhibiting CSCs through Wnt/β-catenin signal pathway in A549/cDDP cells. Significantly, HY1-Pt presented an acceptable pharmacokinetic behavior and exhibited higher tumor growth inhibitory efficacy than cisplatin either in A549 or A549/cDDP xenograft models with low toxicity. Overall, HY1-Pt is a promising drug candidate for NSCLC treatment.

Platinum (II)-coordinated Portulaca oleracea polysaccharides as metal-drug based polymers for anticancer study

Novel polysaccharide-platinum conjugated polymers bearing alendronate on Portulaca oleracea polysaccharides (PPS) were designed and synthesized. Their chemical structures and properties were characterized by Fourier transform infrared spectroscopy (FT-IR), 1H NMR and 31P NMR spectroscopy, Thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), UV–vis spectrophotometer (UV–vis) and other analysis methods. The results demonstrated that alendronate can be used as the linker of Portulaca oleracea polysaccharides and platinum compounds. Portulaca oleracea polysaccharides-alendronate (PPS-ALN) conjugates exhibited stronger antioxidant ability than PPS. The cytotoxicity assay to cancer cells was tested in vitro, and the Portulaca oleracea polysaccharides-alendronate-platinum (PPS-ALN-Pt) conjugates strongly inhibited the proliferation of cancer cells than PPS and PPS-ALN. The evaluation of complexes affinity toward supercoiled plasmid DNA, displayed a high DNA interaction. Interestingly, the platinum conjugates displayed immunological competence in HeLa cells by cellular immunofluorescence assay. Besides, the cellular platinum accumulation of PPS-ALN-Pt conjugates was higher than that of cisplatin in HeLa cells, implying that the polysaccharide-platinum conjugated polymers might have a synergistically therapeutic application in metal anticancer drug delivery.

The Drug-Resistance Mechanisms of Five Platinum-Based Antitumor Agents.

Platinum-based anticancer drugs, including cisplatin, carboplatin, oxaliplatin, nedaplatin, and lobaplatin, are heavily applied in chemotherapy regimens. However, the intrinsic or acquired resistance severely limit the clinical application of platinum-based treatment. The underlying mechanisms are incredibly complicated. Multiple transporters participate in the active transport of platinum-based antitumor agents, and the altered expression level, localization, or activity may severely decrease the cellular platinum accumulation. Detoxification components, which are commonly increasing in resistant tumor cells, can efficiently bind to platinum agents and prevent the formation of platinum–DNA adducts, but the adducts production is the determinant step for the cytotoxicity of platinum-based antitumor agents. Even if adequate adducts have formed, tumor cells still manage to survive through increased DNA repair processes or elevated apoptosis threshold. In addition, autophagy has a profound influence on platinum resistance. This review summarizes the critical participators of platinum resistance mechanisms mentioned above and highlights the most potential therapeutic targets or predicted markers. With a deeper understanding of the underlying resistance mechanisms, new solutions would be produced to extend the clinical application of platinum-based antitumor agents largely.

Cisplatin, rather than oxaliplatin, increases paracellular permeability of LLC-PK1 cells via activating protein kinase C

The clinical use of cisplatin is limited by its adverse events, particularly serious nephrotoxicity. It was clarified that cisplatin is transported by a kidney-specific organic cation transporter (OCT2). OCT2 also mediates the uptake of oxaliplatin into renal proximal tubular cells; however, this agent does not lead nephrotoxicity. In the present study, we carried out comparative experiments with cisplatin and oxaliplatin using porcine kidney LLC-PK1 cell monolayers. In the fluorescein-labeled isothiocyanate-dextran flux assay, the basolateral application of cisplatin, but not oxaliplatin, resulted in an increase in the paracellular permeability of cell monolayers. Even though the cellular accumulation of platinum at 50 μM oxaliplatin could reach the same level at 30 μM cisplatin, oxaliplatin did not induce hyper-permeability in cell monolayers. Cisplatin, but not oxaliplatin, significantly activated PKC. In addition, the combination of PKC inhibitors recovered the increase in paracellular permeability. In conclusion, pharmacodynamic mechanisms via PKC could explain the difference in nephrotoxicity between cisplatin and oxaliplatin.

Coexisting Molecular Determinants of Acquired Oxaliplatin Resistance in Human Colorectal and Ovarian Cancer Cell Lines.

Oxaliplatin (OHP) treatment of colorectal cancer (CRC) frequently leads to resistance. OHP resistance was induced in CRC cell lines LoVo-92 and LoVo-Li and a platinum-sensitive ovarian cancer cell line, A2780, and related to cellular platinum accumulation, platinum-DNA adducts, transporter expression, DNA repair genes, gene expression arrays, and array-CGH profiling. Pulse (4 h, 4OHP) and continuous exposure (72 h, cOHP) resulted in 4.0 to 7.9-fold and 5.0 to 11.8-fold drug resistance, respectively. Cellular oxaliplatin accumulation and DNA-adduct formation were decreased and related to OCT1-3 and ATP7A expression. Gene expression profiling and pathway analysis showed significantly altered p53 signaling, xenobiotic metabolism, role of BRCA1 in DNA damage response, and aryl hydrocarbon receptor signaling pathways, were related to decreased ALDH1L2, Bax, and BBC3 (PUMA) and increased aldo-keto reductases C1 and C3. The array-CGH profiles showed focal aberrations. In conclusion, OHP resistance was correlated with total platinum accumulation and OCT1-3 expression, decreased proapoptotic, and increased anti-apoptosis and homologous repair genes.

Synthesis, characterisation and influence of lipophilicity on cellular accumulation and cytotoxicity of unconventional platinum(iv) prodrugs as potent anticancer agents.

Lipophilic platinum(iv) complexes were synthesised of the type [Pt(HL)(AL)(OH)(R)]2+ and [Pt(HL)(AL)(R)2]2+ (HL = 5,6-dimethyl-1,10-phenanthroline or 1,10-phenanthroline; AL = 1S,2S-diaminocyclohexane and R = increasingly lipophilic carboxylate axial ligands (C10-18)) from hydrophilic platinum(ii) precursors that exhibit exceptional anticancer activity. The increased overall lipophilicity of the complexes suggested the formation of spontaneously self-assembled structures in an aqueous environment. The anti-proliferative properties were assessed against one non-cancerous and a panel of cancerous cell lines. Nanomolar levels of activity were observed against several cell lines, with the lowest GI50 of 3.4 nm against the Du145 prostate cancer cell line and over 1100-fold greater activity than cisplatin against HT29 colon carcinoma. RP-HPLC was utilised to establish the relative lipophilicities of each complex. While there seemed to be an increase in cellular accumulation for the lipophilic derivatives in some instances, ICP-MS studies showed no clear correlation between increasing lipophilicity, cellular accumulation and cytotoxicity.

Enhancer of zeste homolog 2 promotes cisplatin resistance by reducing cellular platinum accumulation.

Enhancer of zeste homolog 2 (EZH2), which is overexpressed in a wide range of tumors, contributes to ovarian cancer malignancy in several different ways. We aimed to illustrate the role of EZH2 in ovarian cancer cisplatin resistance and to identify possible underlying mechanisms of this role that may provide a rationale for targeting EZH2 in cancer treatment. Here, we present data indicating that EZH2 overexpression is associated with cisplatin resistance and intracellular platinum drug accumulation. Measurements of EZH2 in 84 ovarian cancer patients suggested that patients with high EZH2 levels tend to have poor responses to cisplatin. The EZH2 level progressively increased in cells receiving repeated cisplatin exposure. Downregulation of EZH2 not only sensitized cellular reactions to cisplatin and increased cellular platinum accumulation when cells were exposed to both cisplatin and BODIPY‐Pt (a fluorescent cisplatin complex) but also protected copper transporter 1, a high‐affinity copper transporter closely related to cisplatin resistance, from cisplatin‐induced proteasomal degradation. Overall, these findings identify a new mechanism that expands the unrecognized role of EZH2 in ovarian cancer cisplatin resistance.

Cisplatin resistance in non-small cell lung cancer cells is associated with an abrogation of cisplatin-induced G2/M cell cycle arrest.

The efficacy of cisplatin-based chemotherapy in cancer is limited by the occurrence of innate and acquired drug resistance. In order to better understand the mechanisms underlying acquired cisplatin resistance, we have compared the adenocarcinoma-derived non-small cell lung cancer (NSCLC) cell line A549 and its cisplatin-resistant sub-line A549rCDDP2000 with regard to cisplatin resistance mechanisms including cellular platinum accumulation, DNA-adduct formation, cell cycle alterations, apoptosis induction and activation of key players of DNA damage response. In A549rCDDP2000 cells, a cisplatin-induced G2/M cell cycle arrest was lacking and apoptosis was reduced compared to A549 cells, although equitoxic cisplatin concentrations resulted in comparable platinum-DNA adduct levels. These differences were accompanied by changes in the expression of proteins involved in DNA damage response. In A549 cells, cisplatin exposure led to a significantly higher expression of genes coding for proteins mediating G2/M arrest and apoptosis (mouse double minute 2 homolog (MDM2), xeroderma pigmentosum complementation group C (XPC), stress inducible protein (SIP) and p21) compared to resistant cells. This was underlined by significantly higher protein levels of phosphorylated Ataxia telangiectasia mutated (pAtm) and p53 in A549 cells compared to their respective untreated control. The results were compiled in a preliminary model of resistance-associated signaling alterations. In conclusion, these findings suggest that acquired resistance of NSCLC cells against cisplatin is the consequence of altered signaling leading to reduced G2/M cell cycle arrest and apoptosis.

Abstract 4212: Natural compounds alone and in combination with platinum drugs found to show significant anti-tumour activity against ovarian cancer cell lines

Abstract Acquired drug resistance remains major problem in platinum based chemotherapy against ovarian cancer. It is believed that elevated expression of NF-kB and AKT/PKB is one of the prime reasons for acquired drug resistance. Since tumour active natural compounds can dampen NF-kB and AKT/PKB expression, it is thought that platinum drugs in combination with the natural compounds may produce synergism in killing tumor cells. The present study aimed to apply combinations of platinum drugs cisplatin, oxaliplatin, and carboplatin with natural compounds mycophenolic acid, honokiol, cholecalciferol and 6-shogaol to four ovarian cancer cell lines: A2780, A2780CisR, A2780ZD0473R and SKOV-3 towards overcoming drug resistance. IC50 values of single compounds were determined followed by administration of binary combinations. Studies on DNA damage, cellular platinum accumulation, and platinum-DNA binding levels were carried out. Proteomic studies will be done to explore the key proteins involve with drug resistance. Mycophenolic acid (IC50: 1.34-7.83 μM) from Penicillium brevicompactum and 6-shogaol (IC50: 6.79-10.20 μM) from Zingiber officinale showed significant activity against ovarian cancer cell lines. Ginger derived pure compound 6-shogaol showed prominent synergism in combination with platinums when administered as a bolus (0/0h) and with 0/4 h sequence. Honokiol from Magnolia virginia alone and in combination with cisplatin showed significant DNA damage in A2780 cell line whereas cholecalciferol did the same to A2780cisR cell line. Bolus combination of cisplatin and 6-shogoal produced increased cellular platinum accumulation and 3 times more Pt-DNA binding than cisplatin alone treated A2780 cells. Though honokiol and cisplatin (0/0 h) combination have half cellular platinum accumulation in compare to cisplatin alone treated A2780 cells but showed 9 times higher Pt-DNA binding. Cholecalciferol and 6-shogaol in combination with cisplatin also showed promising Pt-DNA in A2780CisR cell line. In conclusion, 6-shogaol, cholecalciferol and honokiol showed significant activity alone and in combination with cisplatin and oxaliplatin against ovarian cancer tumour models. Note: This abstract was not presented at the meeting. Citation Format: Md Sheikh Anwar, Jun Qing Yu, Philip Beale, Fazlul Huq. Natural compounds alone and in combination with platinum drugs found to show significant anti-tumour activity against ovarian cancer cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4212. doi:10.1158/1538-7445.AM2017-4212

Changes in the in vitro activity of platinum drugs when administered in two aliquots.

BackgroundThe management of ovarian cancer remains a challenge. Because of the lack of early symptoms, it is often diagnosed at a late stage when it is likely to have metastasized beyond ovaries. Currently, platinum based chemotherapy is the primary treatment for the disease. However acquired drug resistance remains an on-going problem. As cisplatin brings about apoptosis by intrinsic and extrinsic pathways, this study aimed to determine changes in activity of platinum drugs when administered in two aliquots as against a bolus and sought to determine association with changes in GSH, speciation of platinum drugs and changes in protein expression.MethodsThe efficacy of administering cisplatin, carboplatin and oxaliplatin in two aliquots with a time gap was investigated in ovarian A2780, A2780cisR, A2780ZD0473R and SKOV-3 cell lines. The cellular accumulation of platinum, level of platinum − DNA binding and cellular glutathione level were determined, and proteomic studies were carried out to identify key proteins associated with platinum resistance in ovarian A2780cisR cancer cell line.ResultsMuch greater cell kill was observed with solutions left standing at room temperature than with freshly prepared solutions, indicating that the increase in activity on ageing was related to speciation of the drug in solution. Proteomic studies identified 72 proteins that were differentially expressed in A2780 and A2780cisR cell lines; 22 of them were restored back to normal levels as a result of synergistic treatments, indicating their relevance in enhanced drug action.ConclusionsThe proteins identified are relevant to several different cellular functions including invasion and metastasis, cell cycle regulation and proliferation, metabolic and biosynthesis processes, stress-related proteins and molecular chaperones, mRNA processing, cellular organization/cytoskeleton, cellular communication and signal transduction. This highlights the multifactorial nature of platinum resistance in which many different proteins with diverse functions play key roles. This means multiple strategies can be harnessed to overcome platinum resistance in ovarian cancer. The results of the studies can be significant both from fundamental and clinical view points.

The role of the equatorial ligands for the redox behavior, mode of cellular accumulation and cytotoxicity of platinum(IV) prodrugs

The current study aims to elucidate the possible reasons for the significantly different pharmacological behavior of platinum(IV) complexes with cisplatin-, carboplatin- or nedaplatin-like cores and how this difference can be related to their main physicochemical properties. Chlorido-containing complexes are reduced fast (within hours) by ascorbate and are able to unwind plasmid DNA in the presence of ascorbate, while their tri- and tetracarboxylato analogs are generally inert under the same conditions. Comparison of the lipophilicity, cellular accumulation and cytotoxicity of the investigated platinum compounds revealed the necessity to define new structure-property/activity relationships (SPRs and SARs). The higher activity and improved accumulation of platinum(IV) complexes bearing Cl− in equatorial position cannot only be attributed to passive diffusion facilitated by their lipophilicity. Therefore, further platinum accumulation experiments under conditions where active/facilitated transport mechanisms are suppressed were performed. Under hypothermic conditions (4°C), accumulation of dichloridoplatinum(IV) complexes is reduced down to 10% of the amount determined at 37°C. These findings suggest the involvement of active and/or facilitated transport in cellular uptake of platinum(IV) complexes with a cisplatin-like core. Studies with ATP depletion mediated by oligomycin and low glucose partially confirmed these observations, but their feasibility was severely limited in the adherent cell culture setting.

Abstract 2534: Sequenced combinations of platinum drugs and phytochemicals towards overcoming drug resistance in ovarian cancer

Abstract Background and aims Resistance to platinum-based chemotherapy remains a major obstacle in the treatment against human ovarian cancer. In this study, binary combinations of platinum compounds: cisplatin, carboplatin and oxaliplatin with phytochemicals: artemisinin, thymoquinone, curcumin, lupeol and oleanolic acid have been applied to human ovarian cancer cell lines: A2780, A2780cisR, and A2780ZD0473R using three different sequences of administration (0/0h, 0/4h and 4/0h) where 0/0h means both the drugs added at the same time, 0/4h means platinum added first followed phytochemical 4 h later and 4/0h means the converse. Methods Cytotoxicity was determined based on MTT reduction MTT assay. Median effect analysis was done to characterize combined drug action and combination Index (CI) was used as a measure of synergism or antagonism whereas cellular accumulation of platinum, platinum to DNA binding levels and proteomic studies were done to provide insight into drug resistance and synergism from combined drug action. Results The combinations of platinum and the phytochemicals produced sequence- and concentration-dependent synergism in the ovarian tumour models. The degree of synergism was greater in the resistant cell lines than the parent cell line. It was found that combination with phytochemicals also increased intracellular accumulation of platinum and the level of platinum binding with DNA. Proteomic study identified a number of proteins believed to be associated with cisplatin resistance in ovarian cancer cells A2780 and A2780cisR. The expression of the proteins were either down- or up-regulated in A2780cisR cell line as compared to A2780 cell line but fully or partially restored after treatment with synergistic combinations. Conclusion The results of the study indicate that appropriately sequenced combinations of platinum drugs and phytochemicals can provide a means of overcoming drug resistance in ovarian cancer. Citation Format: Safiah I. Althurwi, Jun Qing Yu,, Philip Beale, Charles Chan, Fazlul Huq. Sequenced combinations of platinum drugs and phytochemicals towards overcoming drug resistance in ovarian cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2534. doi:10.1158/1538-7445.AM2015-2534

Cellular accumulation, lipophilicity and photocytotoxicity of diazido platinum(IV) anticancer complexes.

The lipophilicity of ten photoactivatable platinum(IV) diazido prodrugs of formula trans,trans,trans-[Pt(N3 )2 (OH)2 (R)(R')] (where R and R' are NH3 , methylamine, ethylamine, pyridine, 2-picoline, 3-picoline or thiazole) has been determined by their retention times on reversed-phase HPLC. The lipophilicity of the complexes shows a linear dependence on the lipophilicity (partition coefficient) of the ligands. Accumulation of platinum in A2780 human ovarian cancer cells after one hour drug exposure in the dark is compared with their cytotoxic potency on activation with UVA (365 nm) and to their lipophilicity. No correlation between lipophilicity and intracellular accumulation of platinum was observed, perhaps suggesting involvement of active transport and favoured influx of selected structures. Furthermore, no correlation between platinum accumulation and photocytotoxicity was observed in A2780 cancer cells, implying that the type of intracellular damage induced by these complexes plays a key role in their cytotoxic effects.

Synthesis and activity of three new trinuclear platinums with cis-geometry for terminal metal centres.

BackgroundAs compared to cisplatin, trinuclear platinum compounds such as BBR3464 and DH6Cl have an altered spectrum of activity possibly because they form long-range adducts with DNA as against mainly intrastrand 1,2-bifunctional adducts formed by cisplatin and its analogues. Because of the labilizing effect associated with the trans-geometry, the compounds are expected to break down inside the cell thus serving to reduce the number of long-range adducts formed. In contrast, trinuclear platinum complexes with cis-geometry for the terminal metal centres would be less subject to such breakdown and hence may produce a greater number of long-range inter- and intrastrand adducts with the DNA. This paper describes the synthesis and activity against human ovarian tumour models of of three new trinuclear platinum complexes with cis-geometry for terminal platinum centres, coded as QH4, QH7 and QH8. The paper also describes cellular accumulation of platinum, level of drug−DNA binding, and nature of interaction of the compounds with pBR322 plasmid DNA.ResultsMethods of synthesis, elemental analysis, spectral studies and molar conductivity measurements provide support to the suggested structures of the compounds. QH4 and QH8 are found to be more cytotoxic than cisplatin against the parental A2780 cell line; QH8 is more active than cisplatin against the resistant A2780cisR and A2780ZD0473R cell lines as well. The least compound QH7 shows a greater activity against the resistant cell lines than the parental cell line; it is most damaging to pBR322 plasmid DNA and most able to induce changes in DNA conformation. The variations in activity of the compounds, changes in intracellular drug accumulation and levels of Pt−DNA binding with the changes in number of planaramine ligands bound to central platinum and the length of the linking diamines, can be seen (1) to illustrate structure-activity relationships and (2) to highlight that the relationship between antitumour activity and interaction with cellular platinophiles including DNA can be quite complex as the cell death is carried out by downstream processes in the cell cycle where many proteins are involved.ConclusionAmong the three designed trinuclear platinum complexes with cis-geometry for the terminal metal centres, the most active compound QH8 is found to be more active than cisplatin against the parental A2780 and the resistant A2780cisR and A2780ZD0473R cell lines.

Carboplatin and oxaliplatin in sequenced combination with bortezomib in ovarian tumour models

BackgroundOvarian cancer remains an on-going challenge mainly due to the development of drug resistance and also because the cancer is likely to have metastasized at the time of diagnosis. Currently, chemotherapy based on platinum drugs such as cisplatin is the primary treatment for the disease. Copper transporter 1 is involved in the transport of cisplatin into the cell, but is also down-regulated by the drug. Bortezomib, a proteasome inhibitor, has been reported to block this platinum-induced down-regulation of CTR1, so that in the presence of bortezomib, the cellular uptake of platinum drugs may be increased. Increased platinum accumulation may result in increased platinum − DNA binding so that the platinum drug in combination with bortezomib may produce enhanced cell kill.MethodsIn this study the efficacy of the sequential combinations of carboplatin, oxaliplatin and a trans-platinum compound coded as CH1 with BORT on the human ovarian A2780, A2780cisR, A2780ZD0473R and SKOV-3 cancer cell lines was evaluated. The levels of cellular platinum accumulation and platinum-DNA binding were determined following the treatment with these combinations. In order to investigate the effect of the combinations of the formation of ROS, the total and oxidized glutathione levels were also determined.ResultsPrevention of copper transporter 1 degradation by bortezomib is found to enhance the cellular accumulation of platinum, the level of Platinum − DNA binding and increases oxidative stress especially in the resistant cell lines.ConclusionsThe results suggest that the prevention of CTR1 degradation by bortezomib may be playing a major role in increasing the cellular uptake of platinum drugs and platinum-DNA binding level. Furthermore, the generation of oxidative stress appears to be a major contributor to the enhanced cell kill.

Synthesis and In Vitro Pharmacological Behavior of Platinum(II) Complexes Containing 1,2-Diamino-1-(4-fluorophenyl)-2-alkanol Ligands

In continuation of our effort to optimize the pharmacological profile of [1,2-diamino-1,2-bis(4-fluorophenyl)ethane]dichloridoplatinum(II) complexes, we synthesized [1,2-diamino-1-(4-fluorophenyl)alkanol]dichloridoplatinum(II) analogs. The aim of this study was to evaluate the influence of hydroxyl groups at the C2 moiety on aqueous solubility, lipophilicity, cellular platinum accumulation, and cytotoxicity against MDA-MB-231, U-937, RAJI, and SC-1 cells as well as against cisplatin-sensitive and cisplatin-resistant A2780 and A2780cisR ovarian carcinoma cells. As expected, the OH groups improved the water solubility and decreased the lipophilicity of the neutral ligands, resulting in complexes with favorable pharmacokinetic properties. The cellular uptake of the compounds in MDA-MB-231 and U-937 cells proved to depend on the configuration and showed only a slight correlation with lipophilicity. The most active complexes were R,R/S,S configured, which points to a carrier-mediated mode of action. [threo-1,2-Diamino-1-(4-fluorophenyl)propan]dichloridoplatinum(II) and [threo-2,3-diamino-3-(4-fluorophenyl)propan-1-ol]dichloridoplatinum(II) possessed only low cross-resistance to cisplatin and were up to 10-fold more active in lymphoma cell lines.

Contribution of intracellular ATP to cisplatin resistance of tumor cells.

Decreased cellular accumulation of cisplatin is a frequently observed mechanism of resistance to the drug. Beside passive diffusion, several cellular proteins using ATP hydrolysis as an energy source are assumed to be involved in cisplatin transport in and out of the cell. This investigation aimed at clarifying the contribution of intracellular ATP as an indicator of energy-dependent transport to cisplatin resistance using the A2780 human ovarian adenocarcinoma cell line and its cisplatin-resistant variant A2780cis. Depletion of intracellular ATP with oligomycin significantly decreased cellular platinum accumulation (measured by flameless atomic absorption spectrometry) in sensitive but not in resistant cells, and did not affect cisplatin efflux in both cell lines. Inhibition of Na(+),K(+)-ATPase with ouabain reduced platinum accumulation in A2780 cells but to a lesser extent compared with oligomycin. Western blot analysis revealed lower expression of Na(+),K(+)-ATPase α(1) subunit in resistant cells compared with sensitive counterparts. The basal intracellular ATP level (determined using a bioluminescence-based assay) was significantly higher in A2780cis cells than in A2780 cells. Our results highlight the importance of ATP-dependent transport, among other processes mediated by Na(+),K(+)-ATPase, for cisplatin influx in sensitive cells. Cellular platinum accumulation in resistant cells is reduced and less dependent on energy sources, which may partly result from Na(+),K(+)-ATPase downregulation. Our data suggest the involvement of other ATP-dependent processes beside those regulated by Na(+),K(+)-ATPase. Higher basal ATP level in cisplatin-resistant cells, which appears to be a consequence of enhanced mitochondrial ATP production, may represent a survival mechanism established during development of resistance.