Accumulation Of DDP Research Articles

Dual-Targeted Zeolitic Imidazolate Frameworks Drug Delivery System Reversing Cisplatin Resistance to Treat Resistant Ovarian Cancer.

Ovarian cancer cells are prone to acquire tolerance to chemotherapeutic agents, which seriously affects clinical outcomes. The development of novel strategies to enhance the targeting of chemotherapeutic agents to overcome drug resistance and minimize side effects is significant for improving the clinical outcomes of ovarian cancer patients. We employed folic acid (FA)-modified ZIF-90 nanomaterials (FA-ZIF-90) to deliver the chemotherapeutic drug, cisplatin (DDP), via dual targeting to improve its targeting to circumvent cisplatin resistance in ovarian cancer cells, especially by targeting mitochondria. FA-ZIF-90/DDP could rapidly release DDP in response to dual stimulation of acidity and ATP in tumor cells. FA-ZIF-90/DDP showed good blood compatibility. It was efficiently taken up by human ovarian cancer cisplatin-resistant cells A2780/DDP and aggregated in the mitochondrial region. FA-ZIF-90/DDP significantly inhibited the mitochondrial activity and metastatic ability of A2780/DDP cells. In addition, it effectively induced apoptosis in A2780/DDP cells and overcame cisplatin resistance. In vivo experiments showed that FA-ZIF-90/DDP increased the accumulation of DDP in tumor tissues and significantly inhibited tumor growth. FA-modified ZIF-90 nanocarriers can improve the tumor targeting and anti-tumor effects of chemotherapeutic drugs, reduce toxic side effects, and are expected to be a novel therapeutic strategy to reverse drug resistance in ovarian cancer.

CRGD-targeted heparin nanoparticles for effective dual drug treatment of cisplatin-resistant ovarian cancer.

Resistance to the chemotherapeutic agent cisplatin (DDP) is the primary reason for invalid chemotherapy of ovarian cancer. Given the complex mechanisms underlying chemo-resistance, the design of combination therapies based on blocking multiple mechanisms is a rationale to synergistically elevate therapeutic effect for effectively overcoming cancer chemo-resistance. Herein, we demonstrated a multifunctional nanoparticle (DDP-Ola@HR), which could simultaneously co-deliver DDP and Olaparib (Ola, DNA damage repair inhibitor) using targeted ligand cRGD peptide modified with heparin (HR) as nanocarrier, enabling the concurrent tackling of multiple resistance mechanisms to effectively inhibit the growth and metastasis of DDP-resistant ovarian cancer. In combination strategy, heparin could suppress the function of multidrug resistance-associated protein 2 (MRP2) and P-glycoprotein (P-gp) to promote the intracellular accumulation of DDP and Ola by specifically binding with heparanase (HPSE) to down-regulate PI3K/AKT/mTOR signaling pathway, and simultaneously served as a carrier combined with Ola to synergistically enhance the anti-proliferation ability of DDP for resistant ovarian cancer, thus achieving great therapeutic efficacy. Our DDP-Ola@HR could provide a simple and multifunctional combination strategy to trigger an anticipated cascading effect, thus effectively overcoming the chemo-resistance of ovarian cancer.

Combination therapy based on dual-target biomimetic nano-delivery system for overcoming cisplatin resistance in hepatocellular carcinoma

Strategies to overcome toxicity and drug resistance caused by chemotherapeutic drugs for targeted therapy against hepatocellular carcinoma (HCC) are urgently needed. Previous studies revealed that high oxidored-nitro domain-containing protein 1(NOR1) expression in HCC was associated with cisplatin (DDP) resistance. Herein, a novel dual-targeting nanocarrier system AR-NADR was generated for the treatment of DDP resistance in HCC. The core of the nanocarrier system is the metal–organic frameworks (MOF) modified with nuclear location sequence (NLS), which loading with DDP and NOR1 shRNA (R). The shell is an A54 peptide inserted into the erythrocyte membrane (AR). Our results show that AR-NADR efficiently internalized by tumor cells due to its specific binding to the A54 receptors that are abundantly expressed on the surface of HCC cells and NLS peptide-mediated nuclear entry. Additionally, DDP is more likely to be released due to the degradation of Ag-MOF in the acidic tumor microenvironment. Moreover, by acting as a vector for gene delivery, AR-NADR effectively inhibits tumor drug resistance by suppressing the expression of NOR1, which induces intracellular DDP accumulation and makes cells sensitive to DDP. Finally, the anti-HCC efficacy and mechanisms of AR-NADR were systematically elucidated by a HepG2/DDP cell model as well as a tumor model. Therefore, AR-NADR constitutes a key strategy to achieve excellent gene silencing and antitumor efficacy, which provides effective gene therapy and precise treatment strategies for cisplatin resistance in HCC.Graphical

Cytokine-Induced Killer Cells Modulates Resistance to Cisplatin in the A549/DDP Cell Line.

Background Cytokine-induced killer (CIK) cells can potentially enhance the tumor-killing activity of chemotherapy. Objective This study aimed to evaluate the effects of CIK cells on cisplatin (DDP) resistance in the human lung adenocarcinoma cell line A549/DDP. Methods The detect resistance index, drug resistance related-genes and cytokine secretion of A549/DDP co-cultured with CIK cells were assayed in vitro. ResultsAfter A549/DDP co-culture with CIK cells, the DDP resistance of A549/DDP significantly decreased in a time-dependent manner. The DDP resistance of A549/DDP co-cultured with CIK cells for 20 h decreased 4.93-fold compared with that of A549/DDP cells cultured alone (P<0.05). The mRNA and protein expression levels of the glutathione-S-transferase (GST) -π gene in A549/DDP significantly decreased after co-culture with CIK cells (P<0.05). The secretion of interferon (IFN)- γ significantly increased along with the co-culture time of A549/DDP with CIK cells. The expression of GST-π was restored by adding the neutralizing IFN-γ. ConclusionCIK cells can reverse the drug resistance of A549/DDP in a time-dependent manner by reducing GST-π expression to increase the accumulation of DDP. The effect of CIK cells on re-sensitizing lung cancer cells to the chemotherapy drug was partially dependent on the secretion of IFN-γ.

Reversal of multidrug resistance by cisplatin-loaded magnetic Fe3O4 nanoparticles in A549/DDP lung cancer cells in vitro and in vivo

The purpose of this study was to explore whether magnetic Fe3O4 nanoparticles (Fe3O4-MNP) loaded with cisplatin (Fe3O4-MNP-DDP) can reverse DDP resistance in lung cancer cells and to investigate mechanisms of multidrug resistance in vitro and in vivo. MTT assay showed that DDP inhibited both A549 cells and DDP-resistant A549 cells in a time-dependent and dose-dependent manner, and that this inhibition was enhanced by Fe3O4-MNP. An increased rate of apoptosis was detected in the Fe3O4-MNP-DDP group compared with a control group and the Fe3O4-MNP group by flow cytometry, and typical morphologic features of apoptosis were confirmed by confocal microscopy. Accumulation of intracellular DDP in the Fe3O4-MNP-DDP group was greater than that in the DDP group by inductively coupled plasma mass spectrometry. Further, lower levels of multidrug resistance-associated protein-1, lung resistance-related protein, Akt, and Bad, and higher levels of caspase-3 genes and proteins, were demonstrated by reverse transcriptase polymerase chain reaction and Western blotting in the presence of Fe3O4-MNP-DDP. We also demonstrated that Fe3O4-MNP enhanced the effect of DDP on tumor growth in BALB/c nude mice bearing DDP-resistant human A549 xenografts by decreasing localization of lung resistance-related protein and Ki-67 immunoreactivity in cells. There were no apparent signs of toxicity in the animals. Overall, these findings suggest potential clinical application of Fe3O4-MNP-DDP to increase cytotoxicity in lung tumor xenografts.

Abstract 4750: Overcoming DDP resistance using folic acid-heparin-DDP nanoparticles

Abstract Cisplatin (DDP) has been widely used in the treatment of different cancers. However, resistance to DDP limits its clinical application. Since reduced intracellular DDP accumulation is one of the main causes for DDP resistance, increasing the accumulation of DDP may overcome drug resistance. The folate receptor (FR) is overexpressed on the surface of many human tumors including breast, ovarian and lung cancer, but is found at low levels in normal tissues. In this study, folic acid (FA) was conjugated to heparin-DDP (FHDDP) nanoparticles to target FR. In vitro cellular uptake experiments showed that the accumulation of FHDDP nanoparticles in FR-expressing DDP-resistant KB-CP.5 cancer cells (selected from KB3-1 cells, and showing a 36-fold increase in resistance to DDP compared with KB3-1) was significantly higher than that of free DDP (9.31±2.2 ng Pt/106 cells vs 0.98±0.25 ng Pt/106 cells, Pt:0.5ug/ml, 4 hrs at 37°C). Further, the level of platinum DNA-adducts in the resistant cells treated with FHDDP nanoparticles was about 4-fold greater than in cells treated with free DDP (24.21±5.32 pg Pt/ug DNA vs 97.9±22.5 pg Pt/ug DNA). Nude mice bearing KB-CP.5 cell tumors receiving FHDDP nanoparticles (2.5mg/kg, tail vein injection, twice weekly, 5 times) showed enhanced antitumor effects as compared with mice treated with free DDP (tumor volume: 823±221mm3 vs 1450±392mm3, 21 days after treatment), while non-targeted heparin-DDP nanoparticles did not show significant difference compared with free DDP. Our results suggest that FHDDP nanoparticles have the potential to be used for overcoming DDP resistance.(This research was supported by the National Cancer Institute award 5 P50 CA128613) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4750. doi:1538-7445.AM2012-4750

Transport of Cisplatin by the Copper Efflux Transporter ATP7B

ATP7B is a P-type ATPase that mediates the efflux of copper. Recent studies have demonstrated that ATP7B regulates the cellular efflux of cisplatin (DDP) and controls sensitivity to the cytotoxic effects of this drug. To determine whether DDP is a substrate for ATP7B, DDP transport was assayed in vesicles isolated from Sf9 cells infected with a baculovirus that expressed either the wild-type ATP7B or a mutant ATP7B that was unable to transport copper as a result of conversion of the transmembrane metal binding CPC motif to CPA. Only the wild-type ATP7B-expressing vesicles exhibited copper-dependent ATPase activity, copper-induced acyl-phosphate formation, and ATP-dependent transport of copper. The amount of DDP that became bound was higher for vesicles expressing either type of ATP7B than for those not expressing either form of ATP7B, but only the vesicles expressing wild-type ATP7B mediated ATP-dependent accumulation of the drug. At pH 4.6, the vesicles expressing the wild-type ATP7B exhibited ATP-dependent accumulation of DDP with an apparent K(m) of 1.2 +/- 0.5 (S.E.M.) muM and V(max) of 0.03 +/- 0.002 (S.E.M.) nmol/mg of protein/min. DDP also induced the acyl-phosphorylation of ATP7B but at a much slower rate than copper. Copper and DDP each inhibited the ATP-dependent transport of the other. These results establish that DDP is a substrate for ATP7B but is transported at a much slower rate than copper.

Modulation of the cellular pharmacology of JM118, the major metabolite of satraplatin, by copper influx and efflux transporters

Satraplatin is an orally bioavailable platinum analog that has activity in prostate cancer. JM118 is the most abundant species found in the plasma following the oral ingestion of satraplatin and has anti-tumor activity in vitro against cell lines that are resistant to cisplatin (DDP). The goal of the current study was to determine whether the activity of JM118 in some DDP-resistant cells can be explained by differences in the cellular pharmacology of the two drugs. The effect of each of the Cu transporters CTR1, ATP7A and ATP7B on sensitivity to the growth inhibitory effect of JM118 and its cellular pharmacology was examined to identify the characteristics of JM118 that distinguish it from DDP. These studies were performed using wild type and CTR1-/- homozygous knockout mouse embryo cells, and human Me32a Menkes disease fibroblasts that do not express either ATP7A or ATP7B plus sublines molecularly engineered to express either ATP7A (MeMNK cells) or ATP7B (MeWND cells). Knockout of the Cu influx transporter CTR1 in murine embryo cells increased their resistance to DDP and reduced its cellular accumulation but had no effect on sensitivity to JM118 or its uptake. In the case of DDP, forced expression of either of the two Cu efflux transporters, ATP7A or ATP7B, in Me32a cells rendered them resistant to DDP, increased whole cell accumulation of Pt but reduced the amount of Pt in DNA. In the case of JM118, forced expression of either ATP7A or ATP7B rendered Me32a cells resistant, increased not only whole cell Pt accumulation but also increased rather than decreased the amount of Pt in DNA. These results demonstrate that both ATP7A and ATP7B mediate resistance to JM118 as well as DDP and suggest that they sequester both DDP and JM118 into vesicular compartments within the cell resulting in enhanced whole cell accumulation and reduced cytotoxicity. We conclude that there are two important differences between DDP and JM118 with respect to the effect of Cu transporters on their cellular pharmacology. First, whereas CTR1 is involved in DDP accumulation it does not play a role in the uptake of JM118. Second, ATP7A and ATP7B, while they both mediate resistance, have opposite effects on the accumulation of Pt in DNA following exposure to the two drugs. ATP7A and ATP7B appear to be able to modulate the toxicity of the Pt that accumulates in DNA following exposure to JM118. These results suggest that JM118 will retain activity in cells in which DDP resistance is due to the loss of CTR1, but not in cells in which resistance is due to enhanced expression of ATP7A or ATP7B.

Intracellular Localization and Trafficking of Fluorescein-Labeled Cisplatin in Human Ovarian Carcinoma Cells

We sought to identify the subcellular compartments in which cisplatin [cis-diamminedichloroplatinum (DDP)] accumulates in human ovarian carcinoma cells and define its export pathways. Deconvoluting digital microscopy was used to identify the subcellular location of fluorescein-labeled DDP (F-DDP) in 2008 ovarian carcinoma cells stained with organelle-specific markers. Drugs that block vesicle movement were used to map the traffic pattern. F-DDP accumulated in vesicles and were not detectable in the cytoplasm. F-DDP accumulated in the Golgi, in vesicles belonging to the secretory export pathway, and in lysosomes but not in early endosomes. F-DDP extensively colocalized with vesicles expressing the copper efflux protein, ATP7A, whose expression modulates the cellular pharmacology of DDP. Inhibition of vesicle trafficking with brefeldin A, wortmannin, or H89 increased the F-DDP content of vesicles associated with the pre-Golgi compartments and blocked the loading of F-DDP into vesicles of the secretory pathway. The importance of the secretory pathway was confirmed by showing that wortmannin and H89 increased whole cell accumulation of native DDP. F-DDP is extensively sequestered into vesicular structures of the lysosomal, Golgi, and secretory compartments. Much of the distribution to other compartments occurs via vesicle trafficking. F-DDP detection in the vesicles of the secretory pathway is consistent with a major role for this pathway in the efflux of F-DDP and DDP from the cell.

Cross-resistance to cisplatin in cells with acquired resistance to copper.

Cells selected for resistance to cisplatin (DDP) demonstrate cross-resistance to copper (Cu) suggesting one or more common mechanisms of cellular defense. We sought to determine whether cells selected for resistance to Cu are cross-resistant to DDP. Parental HuH7 human hepatoma cells and the CuR27 Cu-resistant subline were compared for sensitivity to Cu and DDP by clonogenic assay, and with respect to drug uptake and efflux by measuring cellular Cu and Pt content. CuR27 cells were found to be 1.8-fold resistant to Cu and 8.6-fold cross-resistant to DDP. Changes in the cellular pharmacokinetics of Cu in the CuR27 cells were paralleled by changes in the kinetics of DDP. The accumulations of Cu and DDP measured at 1 min were, respectively, 36% and 26% of those in the parental HuH7 cells. The initial rate of efflux from the CuR27 cells was 6.2-fold faster for Cu and 2.5-fold faster for DDP than from the HuH7 cells. Cu reduced the accumulation of DDP in the HuH7 cells in a concentration-dependent manner and vice versa. DDP also reduced the efflux of Cu. Western blot analysis demonstrated that expression of the Cu exporter ATP7B was increased 3.9-fold in the CuR27 cells. In this model system, cross-resistance between Cu and DDP was bidirectional and accompanied by parallel changes in the cellular pharmacokinetics of both compounds. The results are consistent with the idea that transporters and chaperones that normally mediate Cu homeostasis also directly or indirectly modulate the accumulation of DDP.

Enhancement of sensitivity to cisplatin by orobol is associatedwith increased mitochondrial cytochrome c releasein human ovarian carcinoma cells

Objectives Based on our previous report showing that orobol, a potent phosphatidylinositol 4-kinase (PI4K) inhibitor, produced cisplatin (DDP) sensitivity, we have determined the mechanism of orobol-sensitization effect. Methods and results Orobol produced >2-fold DDP sensitivity in human ovarian carcinoma 2008 cells and its DDP-resistant variant 2008/C13*5.25 cells (C13). Because orobol had no effect on conventional mechanisms such as DDP accumulation or cellular metallothionein and glutathione content, we have focused on the apoptotic signaling pathway. Orobol induced a significant increase in apoptosis in DDP-treated cells, as estimated by frequency of condensed nuclear chromatin with Hoechst 33342 stain, although orobol alone did not have any effect on apoptotic potential. The caspase-3-inhibiting peptide Ac-DEVD-CHO completely inhibited the orobol sensitization effect but did not block DDP cell cytotoxicity per se. Orobol rendered both of these cells resistant to rhodamine 123 (Rh) by more than 2.5-fold, indicating significant decrease of mitochondrial membrane potential (ΔΨm). Confocal laser microscopy of cells stained with the mitochondria (MT)-specific dye Rh revealed that orobol decreased Rh-fluorescent intensity. Electron microscopy of these cells showed that orobol induced swelling and condensation of MT. Orobol suppressed both naturally expressed and the DDP-induced Bcl-2 expression significantly. Orobol and DDP treatment reduced cytochrome c level in MT determined by Western blot analysis, indicating increased amount of cytochrome c release from MT, whereas orobol alone did not alter the amount of cytochrome c in MT. Conclusions These results indicate that orobol produced DDP sensitivity in human ovarian carcinoma cells by inducing apoptosis through the MT-dependent signaling pathway.

The copper transporter CTR1 regulates cisplatin uptake in Saccharomyces cerevisiae.

Resistance to cisplatin (DDP) is often accompanied by impaired accumulation in mammalian cells. The mechanism of impaired DDP accumulation is unknown, but copper uptake is diminished as well. We investigated the ability of the copper transporter CTR1 to control the accumulation of DDP in Saccharomyces cerevisiae. Parallel studies of copper and DDP cellular pharmacokinetics were carried out using an isogenic pair of wild-type CTR1 and ctr1 knockout S. cerevisiae strains. Both copper and platinum accumulation increased linearly as a function of time and drug concentration in the parental cells. Deletion of CTR1 resulted in a 16-fold reduction in the uptake of copper and an 8-fold reduction in the uptake of DDP measured at 1 h. The CTR1-deficient cells accumulated 2.3-fold (p < 0.05) less platinum in their DNA and were 1.9-fold more resistant to the cytotoxic effect of DDP than the CTR1-replete cells. The kinetics of cellular copper accumulation were similar to those of DDP. Based on measurements of accumulation at 1 h, the K(m) for copper influx was 128.8 microM, and the V(max) was 169.5 ng/mg of protein/min; for DDP, the K(m) was 140.2 microM and the V(max) was 76.9 ng/mg of protein/min. DDP blocked the uptake of copper into the parental cells but not ctr1-deficient cells. CTR1-deficient cells also demonstrated impaired accumulation of the DDP analogs carboplatin, oxaliplatin, and ZD0473 [cis-amminedichloro(2-methylpyridine) platinum (II)]. These results indicate that CTR1 function markedly influences the uptake of all of the clinically used platinum-containing drugs and suggest that this copper transporter may also transport DDP.

Paclitaxel and SN-38 overcome cisplatin resistance of ovarian cancer cell lines by down-regulating the influx and efflux system of cisplatin.

Cisplatin (DDP) is one of the key drugs used to treat patients with ovarian cancer, although resistance to DDP can occur. Paclitaxel and SN‐38 (an active metabolite of irinotecan (CPT‐11)) are two drugs that are effective in patients with DDP‐resistant ovarian cancer. To study how these drugs may overcome the intrinsic and/or acquired resistance of cancer cells to DDP, we investigated the effect of a combination of DDP with paclitaxel and a combination of DDP with SN‐38 on three ovarian cancer cell lines, RTSG (intrinsically resistant cell line), KF (DDP‐sensitive cell line), and KFra (acquired resistant cell line obtained from KF). We found that these combinations showed additive to synergistic antitumor activity. A time‐dependent platinum (Pt) accumulation was observed in the DDP‐sensitive KF cell line, while a decrease occurred in the KFra cell line. Little accumulation was observed in RTSG. Intracellular Pt accumulation was increased in all three cell lines by exposure to paclitaxel or SN‐38. Ouabain, a Na+,K+‐ATPase inhibitor, decreased Pt accumulation in KF and KFra cell lines and inhibited the paclitaxel‐ and SN‐38‐induced increases in Pt accumulation in these cell lines. When we assessed the mRNA levels of the multidrug resistance‐associated protein (MRP), which may be an efflux pump for DDP, the combination of paclitaxel or SN‐38 with DDP down‐regulated these levels, which are up‐regulated by DDP alone. These results suggest that paclitaxel and SN‐38 overcome DDP resistance of ovarian cell lines by controlling intracellular accumulation of DDP via both the influx and efflux systems

Differential sensitization by orobol in proliferating and quiescent human ovarian carcinoma cells.

The object of this study was to determine how phosphatidylinositol (PI) signaling pathway is involved in the regulation of cisplatin (DDP) sensitivity. Clonogenic survival assay was used to determine the effect of orobol, a potent PI4-kinase inhibitor, on DDP sensitivity in human ovarian carcinoma 2008 cells. Orobol enhanced sensitivity to DDP in 2008 cells by a factor of 2.1+/-0.4 (SD)-fold (N=3; P<0.01). Sensitization was specific for proliferating cells. Orobol did not alter DDP sensitivity in quiescent cells. Orobol also produced a 2-fold increase in sensitivity to DDP in proliferating 2008/C13*5.25 DDP-resistant variants. Our studies indicated that orobol-induced sensitization depended on the presence of proliferating cells in G2+M phase of the cell cycle. Orobol did not modulate the cellular accumulation of DDP nor did it alter the CdCl2 sensitivity, suggesting that the amount of platinated-DNA was not changed by orobol treatment. However, orobol rendered 2008 cells resistant to rhodamin 123 by 5.7+/-1.7 (SD)-fold (N=3, P<0.01). Since sensitivity to rhodamin 123 is indicative of mitochondrial membrane potential, these results imply that mitochondrial alterations may be an important component of the orobol sensitization effect in these cells.

Depletion of protein kinase C (PKC) by 12-O-tetradecanoylphorbol-13-acetate (TPA) enhances platinum drug sensitivity in human ovarian carcinoma cells.

Down-regulation of protein kinase C (PKC) by 12- O -tetradecanoylphorbol-13-acetate (TPA) enhances the sensitivity of human ovarian carcinoma 2008 cells to various types of platinum compounds such as cisplatin (DDP), carboplatin and (–)-(R)-2-aminomethylpyrrolidine (1,1-cyclobutanedicarboxylato)-platinum(II) monohydrate (DWA) by a factor of two- to threefold. TPA enhanced the sensitivity of the DDP-resistant 2008/C13*5.25 subline to each of these three drugs to the same extent as for the 2008 cells. The extent of PKC down-regulation and drug sensitization depended on the duration of TPA exposure; maximum effect was achieved with a 48 h pretreatment. Sensitization was TPA concentration-dependent and was maximal at 0.05 μM TPA. 2008 cells expressed only the PKCα and PKCζ isoforms. Western blot analysis revealed that whereas the expression of PKCα was reduced by TPA the level of PKCζ was not affected. These results suggest that PKCα is the isotype responsive to TPA in these cells and that platinum drug sensitivity can be modulated by this isoform alone. In parallel to its effect on PKCα, TPA decreased cellular glutathione content by 30 ± 3 (standard deviation (s.d.) % in 2008 cells and by 41 ± 3 (s.d.) % in 2008/C13*5.25 cells. TPA also increased accumulation of DDP and DWA by 70%, although this effect was limited to the 2008/C13*5.25 cells. TPA rendered 2008 and 2008/C13*5.25 cells resistant to cadmium chloride by a factor of 3.7 and 3.6-fold respectively, suggesting a significant increase in cellular metallothionein content. Although the mechanism of TPA induced sensitization is not yet fully understood, this study points to a central role for PKCα in modulating platinum drug sensitivity. © 2000 Cancer Research Campaign

Cisplatin efflux, binding and intracellular pH in the HTB56 human lung adenocarcinoma cell line and the E-8/0.7 cisplatin-resistant variant

Many cell lines resistant to cisplatin (DDP) have reduced DDP accumulation. We postulated that reduced accumulation of DDP in resistant cells might be due to decreased intracellular DDP binding, leading to increased passive efflux. The total cellular ([T-DDP]), intracellular ultrafiltrable ([F-DDP]) and precipitable cellular bound ([B-DDP]) DDP concentrations were all compared in the HTB56 human lung adenocarcinoma cell line and its E-8/0.7 variant that has acquired DDP resistance. Cells were exposed to 509 microM DDP for 20 min. Ultrafiltration with a 500 molecular weight cut-off separated cellular free from bound cisplatin. Fragmentation by sonication and microcentrifugal spinning precipitated cellular bound cisplatin. Flow cytometry was used to measure the intracellular pH (pHi) of the HTB56 cell line, the E-8/0.7 cell line, as well as of the OV2008 cell line and its C13 resistant variant. The DNA-bound DDP and protein-bound DDP ([P-DDP]) were also compared when equal [T-DDP] was achieved for both sensitive and resistant cells by exposing them for 1 h to two pairs of DDP concentrations, i.e. 509 vs 911 microM DDP, and 111 vs 666 microM DDP, respectively. Platinum was assayed by flameless atomic absorption spectrophotometry. At time 0 (end of cisplatin exposure), [T-DDP] and [B-DDP] were significantly higher in the sensitive HTB56 parent cell line (P < 0.02 and P < 0.001, respectively), whereas [F-DDP] did not differ significantly (P = 0.62). Two distinct phases of T-DDP efflux were observed. In the first 10 s after DDP exposure, the rate constant for resistant cells (KR1) was 0.17 s(-1), whereas that for sensitive cells (KS1) was 0.14 s(-1). From 10 s to 50 s, however, KR2 and KS2 became 0.005 s(-1) and 0.004 s, respectively. [T-DDP] remained lower in resistant cells than in sensitive cells at 10, 30 and 50 s (all P < 0.0001). For 1 h drug exposure to 509 vs 911 microM cisplatin concentrations designed to give comparable [T-DDP] in the sensitive and resistant cell lines, only [DNA-bound DDP] was found to be significantly higher in sensitive cells (P = 0.002), whereas both [F-DDP] and [P-DDP] did not differ significantly (P = 0.18, P = 0.75, respectively). On the other hand, there were no significant differences found in [F-DDP], [P-DDP] and [DNA-bound DDP] between the two cell lines when 111 vs 666 microM DDP was used. Flow cytometry data indicated that the pHi was significantly higher in the E-8/0.7 (P < 0.0186) and C13 (P < 0.0169) resistant variants than in the sensitive parent cell lines. DDP binds more slowly in resistant than in sensitive lung cancer cells, despite comparable amounts of free drug. Early efflux is higher in the resistant variant. Differences between the lines with respect to DNA binding may be DDP concentration-dependent. We speculate that the reduced early binding and increased early efflux in the resistant line may be related to the higher pH in this line. A higher pH is supposed to favor production of neutral hydroxyl metabolites rather than charged aquated metabolites, and these neutral metabolites would be expected to react less readily with intracellular molecules and to efflux more readily across cell membranes. Since we have previously documented a threefold increase in glucose utilization and lactate production in the DDP-resistant variants of the human HTB56 lung cancer cell lines, and this increased lactate production would have been expected to reduce the intracellular pH instead of raising it, it is possible that our alkaline-resistant cells have a higher Na+/H+ exchanger activity which would protect them from intracellular acidification.

The effects of terbium on the cellular accumulation of cisplatin in MDA-MB-231 human breast tumor cells.

Cisplatin (DDP) is an effective antitumor agent limited in its efficacy by the development of tumor cell resistance. The defective accumulation of DDP has been shown to be a prominent feature in many DDP-resistant cell lines. In an effort to circumvent this problem, we examined the cellular accumulation of DDP in the presence of terbium (Tb3+). We also examined the effects of verapamil on the cellular accumulation of DDP in order to delineate the specific interaction of Tb3+ and DDP. All experiments were performed on DDP-sensitive or DDP-resistant MDA-MB-231 human breast tumor cells. The cellular accumulation of DDP and verapamil were determined by electrothermal atomic absorption spectrophotometry. Time-resolved luminescence spectroscopy was used to obtain equilibrium binding constants for the Tb3+/MDA cell complexes. We found that 100 microM Tb3+ increased DDP accumulation in the parent MDA cell line, 5.7-fold resistant MDA/A13 and 10-fold resistant MDA/CH cells by 56.2 +/- 7.4, 71.9 +/- 9.4 and 50.8 +/- 9.4%, respectively (P < 0.0001 for all MDA cell types). In contrast, 20 microM verapamil had no significant effect on DDP accumulation in the MDA cell lines. In addition, a positive correlation between the membrane binding of Tb3+ and the cellular accumulation of DDP was found to exist in the parent cell line and sublines (r = 0.9). In agreement with earlier studies, the plasma membrane of MDA cell lines contain a specific Tb(3+)-binding protein. Our findings suggest that the Tb(3+)-binding protein may be intimately associated with the accumulation of DDP in breast tumor cells.

In vitro modulation of cisplatin accumulation in human ovarian carcinoma cells by pharmacologic alteration of microtubules.

We have previously shown that forskolin and 3-isobutyl-1-methylxanthine (IBMX) increased accumulation of cisplatin (DDP) in DDP-sensitive 2008 human ovarian carcinoma cells in proportion to their ability to increase cAMP. Since the major function of cAMP is to activate protein kinase A, it was conjectured that the stimulation of DDP accumulation was mediated by a protein kinase A substrate. We now show that exposure of 2008 cells to forskolin resulted in phosphorylation of a prominent 52-kD membrane protein. Microsequencing of the band demonstrated it to be human beta-tubulin. Similarly, pretreatment of 2008 cells with the microtubule stabilizing drug taxol increased platinum accumulation in a dose-dependent manner. In 11-fold DDP-resistant 2008/C13*5.25 cells, decreased DDP accumulation was associated with enhanced spontaneous formation of microtubule bundles and decreased expression of beta-tubulin and the tubulin-associated p53 antioncogene relative to 2008 cells. 2008/C13*5.25 cells had altered sensitivity to tubulin-binding drugs, being hypersensitive to taxol and cross-resistant to colchicine. We conclude that pharmacologic alterations of tubulin enhance accumulation of DDP, and that the DDP-resistant phenotype in 2008/C13*5.25 cells is associated with tubulin abnormalities.

Cellular accumulation of the anticancer agent cisplatin: a review.

Acquired resistance to cisplatin (DDP) is a major clinical problem in the treatment of ovarian, testicular, and head and neck carcinomas; decreased accumulation of DDP is the most consistently observed alteration in resistant cells. It has been postulated that DDP enters the cell by passive diffusion based on the observations that DDP accumulation is proportional to the drug concentration, accumulation is not saturable, and that structural analogs of DDP do not inhibit accumulation. However, recent studies show that DDP accumulation can be specifically stimulated or inhibited by pharmacological agents and the activation of signal transduction pathways. This paper reviews the existing data on the mechanism of DDP accumulation and develops the postulate that some component of transport occurs through a gated ion channel.

Modulation of cisplatin sensitivity and growth rate of an ovarian carcinoma cell line by bombesin and tumor necrosis factor-alpha.

A twofold change in the cisplatin (DDP) sensitivity of 2008 human ovarian carcinoma cells is sufficient to reduce tumor response in vivo. The DDP sensitivity of these cells can be enhanced by activation of the epidermal growth factor and protein kinase C signal transduction pathways. We report here that two endogenous growth factors, bombesin and tumor necrosis factor alpha (TNF alpha), enhanced DDP sensitivity by factors of 1.7 +/- 0.1 (SD)-fold and 1.8 +/- 0.1 (SD)-fold, respectively. Both agents also produced sensitization in an 11-fold DDP-resistant 2008 subline. Neither bombesin nor TNF alpha changed the accumulation of DDP, glutathione content, or glutathione-S-transferase activity in 2008 cells. However, a 2-h exposure to both bombesin and TNF alpha was sufficient to increase 2008 cloning efficiency by up to 2.6 +/- 0.1 (SD)-fold and 2.2 +/- 0.1 (SD)-fold, and it increased average colony size by 1.35 +/- 0.1 (SD)-fold and 1.55 +/- 0.1 (SD)-fold, respectively. Bombesin increased intracellular free calcium, and this was blocked by the bombesin receptor-specific antagonist SC196, demonstrating that 2008 cells have functional bombesin receptors. These results indicate that bombesin and TNF alpha can enhance sensitivity to DDP in both DDP sensitive and resistant variants of a human ovarian carcinoma and that both agents serve as growth factors for this tumor.