Mechanisms of resistance to cisplatin

Apoptin-derived peptide reverses cisplatin resistance in gastric cancer through the PI3K-AKT signaling pathway

The prognosis of gastric cancer (GC) remains poor due to clinical drug resistance, and novel drugs are urgently needed. Apoptin-derived peptide (AdP) is an antitumor polypeptide constructed in our laboratory that has been used to combat cisplatin (CDDP) resistance in GC cells. MTT and colony-formation assays and Hoechst 33342 staining were used to measure the cytotoxicity of CDDP and AdP in GC cells. Cell apoptosis was measured using an Annexin-V-FITC/PI dual staining assay. Western blot analysis was conducted to detect the expression of proteins in the PI3K/AKT signaling pathway and resistance-related markers. AdP exerted a specific cytotoxic effect on GC cells and CDDP-resistant GC cells in a concentration- and time-dependent manner. AdP also suppressed cell invasion and migration. Additionally, AdP inhibited the expression of p85, AKT, p-p85, p-AKT, multidrug resistance 1 (MDR1), and aryl hydrocarbon nuclear translocator (ARNT) in the PI3K/AKT/ARNT signaling pathway, which promoted apoptosis and necrosis in GC cells. AdP promoted apoptosis in CDDP-resistant GC cells by suppressing the PI3K/AKT/ARNT signaling pathway and might be considered a candidate agent for the clinical treatment of cisplatin-resistant GC.

Reactivity of kiteplatin with S-donor biomolecules and nucleotides

Kiteplatin, (cis-1,4-DACH)dichloridoplatinum(ii), contains an isomeric form of the carrier ligand present in the successful antitumor drug oxaliplatin and has been recently found to be very active against oxaliplatin-resistant colon cancers, confirming that, by changing the nature of the amine ligand, it is possible to obtain platinum drugs that are not cross-resistant to those already in clinical use. Apart from interaction with DNA, another factor that can affect the activity of platinum drugs is their metabolic fate in the cellular environment. Therefore, kiteplatin has been reacted with S-donor biomolecules, such as glutathione, cysteine, and methionine. The investigation has further confirmed the different reactivity of methionine as compared to cysteine-containing peptides and has unraveled the possibility of cis-1,4-DACH to become mono-coordinated with one free end (a situation never seen for isomeric 1,2-DACH ligands) and to labilize cis ligands as a consequence of its large steric hindrance. The reaction of kiteplatin-GSH adducts with 5'-GMP has also shown how the reaction products can be different depending upon the aerobic or anaerobic reaction conditions used.

Gli1 contributes to cellular resistance to cisplatin through altered cellular accumulation of the drug

Cellular resistance to platinum anticancer compounds is governed by no less than two molecular processes; DNA repair and cellular accumulation of drug. Gli1 is an upstream regulator of nucleotide excision repair, effecting this process through c-jun. We, therefore, investigated whether Gli1 plays a role in cellular accumulation of cisplatin. Using a Gli1-specific shRNA, we explored the role of Gli1 in the cellular accumulation and efflux of cisplatin, in cisplatin-resistant A2780-CP70 human ovarian cancer cells. When Gli1 is inhibited, cellular uptake of cisplatin was approximately 33% of the level of uptake under control conditions. When Gli1 is inhibited, cellular efflux of cisplatin was completely abrogated, over a 12-h period of observation. We assayed nuclear lysates from these cells, for the ability to bind the DNA sequence that is the Gli-binding site (GBS) in the 5'UTR for each of five known cisplatin transmembrane transporters. Four of these transporters are active in cisplatin uptake; and, one is active in cisplatin efflux. In each case, nuclear lysate from A2780-CP70 cells binds the GBS of the respective cisplatin transport gene. We conclude that Gli1 plays a strong role in total cellular accumulation of cisplatin in these cells; and, that the combined effects on cellular accumulation of drug and on DNA repair may indicate a role for Gli1 in protecting cellular DNA from lethal types of DNA damage.

Klotho sensitizes human lung cancer cell line to cisplatin via PI3k/Akt pathway

Klotho was first identified in 1997 and has been considered as an anti-aging gene. Emerging evidence demonstrates that klotho has a close relationship with cancers, including lung cancer, breast cancer, etc, by inhibiting the proliferation and promoting apoptosis of cancer cells. Cisplatin has been the most widely used drug in the first-line chemotherapy. However, the increase in cisplatin-resistant cancer cells has become a major obstacle in clinical management of cancers. In our study, we for the first time demonstrated that klotho could attenuate the resistance of lung cancer to cisplatin based chemotherapy and the apoptosis of the resistant cells with klotho overexpression was markedly increased. However, klotho knockdown cells showed enhanced resistance to chemotherapy. Further analysis showed that inhibition of PI3K/Akt pathway with specific inhibitor (LY294002) attenuated the promotive effects on cancer growth following interfering with klotho shRNA. Moreover, we demonstrated that klotho modulated the resistance to cisplatin in a xenograft nude mice model. These observations suggested that klotho could improve the resistance of lung cancer cells to chemotherapy and may serve as a potential target for the gene therapy of lung cancers resistant to cisplatin based chemotherapy.

TP53 Mutations and Pathologic Complete Response to Neoadjuvant Cisplatin and Fluorouracil Chemotherapy in Resected Oral Cavity Squamous Cell Carcinoma

Purpose

To find out if TP53 functional status predicts response to neoadjuvant chemotherapy and thus may be helpful during treatment decision making of oral cavity squamous cell carcinoma (SCC) patients.

Patients and Methods

We analyzed the predictive value of TP53 mutations and their functional status on the basis of the transactivation activity of p53 mutant proteins in 53 pretreatment biopsies of oral cavity SCC patients receiving primary cisplatin and fluorouracil chemotherapy followed by surgery.

Results

The surgical specimens showed that 15 patients (28%) achieved a pathologic complete remission (pCR) at both T and N sites, and 38 patients had residual tumor cells. Among the 53 pretreatment biopsies, 24 (45%) displayed TP53 mutations: 22 single-nucleotide substitutions and two deletions. According to functional status that could be determined only for the 22 substitutions, 21 mutations were nonfunctional and one was partially functional. TP53 mutation was found in four (27%) of 15 patients who achieved a pCR and in 20 (53%) of 38 nonresponder patients; the difference was not statistically significant (P = .12). In contrast, two (14%) of 14 cases with pCR carried a nonfunctional TP53 mutation, a frequency significantly less than that found in the nonresponders (19 [51%] of 37; P = .02). TP53 mutation predicted pCR in four (17%) of 24 patients and a nonfunctional mutation in only two (9%) of 22 patients.

Conclusion

The results indicate that the loss of function (transactivation activities) of p53 mutant proteins may predict a significant low pCR rate and suboptimal response to cisplatin-based neoadjuvant chemotherapy in patients with oral cavity SCC.

Trans labilization of am(m)ine ligands from platinum(II) complexes by cancer cell extracts

Cisplatin, cis-[Pt(NH(3))(2)Cl(2)], is an effective anticancer agent in wide clinical use whose efficacy is affected by cellular interactions with sulfur-containing nucleophiles. These interactions can potentially enhance the efficacy of the drug by mediating its delivery to nuclear DNA or inactivate the drug by binding to it irreversibly or by labilizing the NH(3) ligands. Despite the potential importance of trans-labilization reactions in the mechanism of action of the drug, few detailed studies on trans labilization of the ammines have been conducted. We used 2D NMR to show that some trans labilization occurs in proliferating cells and that aqueous extracts of cancer cells labilized 20% of the amine ligands of cis-[PtCl(2)((13)CH(3)NH(2))(2)] after a 12-h incubation. Both low molecular mass nucleophiles (less than 3 kDa) and high molecular mass nucleophiles (more than 3 kDa) labilize the amines with similar efficiency. Studies with model compounds show that thiols and thioethers bind to platinum(II) at similar rates, but thioethers are significantly more efficient at labilizing the am(m)ine at lower pH. N-Acetylcysteine is a more efficient trans-labilizer than glutathione, suggesting that the displacement of the amine proceeds through an associative mechanism. The lag time, the time that elapses from the formation of the Pt-S bond till the release of the amine trans to the sulfur, depends on the pH (for thiols), increasing at lower pH. Quantification of the platinum adducts obtained from incubation of cisplatin with cell extracts indicates that two thirds of the platinum is bound to cellular components with molecular mass greater than 3 kDa.

Target specificity and off-target effects as determinants of cancer drug efficacy

Targeted therapeutics are aimed to hit one or a few key cellular targets. Agents that target single signaling molecules (such as EGFR and IGF-R1) often show limited clinical activities, at least in the major groups of solid tumors. Nevertheless, some signaling inhibitors are effective in the treatment of previously difficult-to-treat diseases such as renal carcinoma. Similarly, these drugs inhibit multiple kinases and/or may display off-target activities. Inhibition of cellular targets such as the proteasome, heat-shock protein 90, and histone deacetylase induces complex cellular effects, and agents that inhibit these targets show promising clinical activities. Clinically effective targeted agents are therefore reminiscent of conventional agents such as cisplatin and doxorubicin, which are known to have several cellular targets. It is becoming increasingly clear that a comprehensive understanding of the spectrum of effects exerted by an anticancer agent is fundamental for understanding its efficacy and toxicity profile.

Cytoplasmic initiation of cisplatin cytotoxicity

The mechanism of action of cisplatin as a chemotherapeutic agent has been attributed to DNA binding, while its mechanism of action as a nephrotoxin is unresolved. Only approximately 1% of intracellular cisplatin interacts with DNA, primarily forming intrastrand cross-linked adducts, and many studies have implicated both nuclear and cytoplasmic causes of cisplatin-induced death in cultured cells. We have demonstrated that cisplatin cytotoxicity depends on cdk2 activity, which is at least partly through the cdk2-E2F1 pathway. The mechanism of the dependency on cdk2, and whether cdk2 activation of E2F1 represents the only cell death pathway involved, is still unclear. Our previous work showed that deletion of the nuclear localization signal from p21 WAF1/CIP1, a cdk2 inhibitor, did not alter its protective action against cisplatin cytotoxicity. Active cdk2-cyclin complexes are localized in both the nucleus and cytoplasm, and it was reported that cdk2 translocated to the cytoplasm after an apoptotic stimulus. Herein, we show that cisplatin caused cell death in enucleated mouse kidney proximal tubule cells (TKPTS), which was prevented by cdk2 inhibition. Also, we localized cytoplasmic cdk2 to both the endoplasmic reticulum (ER) and Golgi compartments, and ER stress was blocked by specific cdk2 inhibition. We conclude that cisplatin can induce nuclear independent apoptosis, cisplatin cytotoxicity can be initiated by cytoplasmic events, and cytoplasmic cdk2 plays an important role in apoptosis signaling.

Recent insights into platinum drug resistance in cancer

Cisplatin and its analogs have become important components of chemotherapeutic regimens for the treatment of solid tumors, however, their overall effectiveness is limited by the emergence of drug-resistant tumor cells. Resistance to the platinum drugs is multifactorial consisting of mechanisms that prevent the formation of lethal platinum-DNA adducts and mechanisms that operate downstream of the drug/target interaction to promote cell survival. Continued progress in the study of the drug resistance phenotype as well as the development of new platinum analogs may eventually lead to improved therapies and increased survival rates.

Chemosensitivity profile of cancer cell lines and identification of genes determining chemosensitivity by an integrated bioinformatical approach using cDNA arrays

We have established a panel of 45 human cancer cell lines (JFCR-45) to explore genes that determine the chemosensitivity of these cell lines to anticancer drugs. JFCR-45 comprises cancer cell lines derived from tumors of three different organs: breast, liver, and stomach. The inclusion of cell lines derived from gastric and hepatic cancers is a major point of novelty of this study. We determined the concentration of 53 anticancer drugs that could induce 50% growth inhibition (GI50) in each cell line. Cluster analysis using the GI50s indicated that JFCR-45 could allow classification of the drugs based on their modes of action, which coincides with previous findings in NCI-60 and JFCR-39. We next investigated gene expression in JFCR-45 and developed an integrated database of chemosensitivity and gene expression in this panel of cell lines. We applied a correlation analysis between gene expression profiles and chemosensitivity profiles, which revealed many candidate genes related to the sensitivity of cancer cells to anticancer drugs. To identify genes that directly determine chemosensitivity, we further tested the ability of these candidate genes to alter sensitivity to anticancer drugs after individually overexpressing each gene in human fibrosarcoma HT1080. We observed that transfection of HT1080 cells with the HSPA1A and JUN genes actually enhanced the sensitivity to mitomycin C, suggesting the direct participation of these genes in mitomycin C sensitivity. These results suggest that an integrated bioinformatical approach using chemosensitivity and gene expression profiling is useful for the identification of genes determining chemosensitivity of cancer cells.

Kinetic study on the reaction of cisplatin with metallothionein

The binding of cisplatin to metallothionein (MT) was investigated at 37 degrees C in 10 mM Tris-NO3 (pH approximately 7.4) and 4.62 mM NaCl. The conditions were chosen to mimic passage of clinical concentrations of cisplatin through the cytosol. The reactions were monitored by high-performance liquid chromatography (HPLC), atomic absorption spectroscopy, and ultraviolet (UV) absorption spectroscopy. The UV data showed that several reactions occur, the first of which does not affect the absorbance (no Pt-sulfur bond formation). They also suggested that if [cisplatin] is large compared with [MT], the rate of subsequent reaction is between first and second order in [cisplatin] and between zeroth and first order in [MT]. HPLC eluates with 24 < retention time (tR) < 27 min contained undialyzable Pt, which increased with reaction time and corresponded to Pt-thionein product. Eluates with 3 < tR < 7 min corresponded to unbound cisplatin and allowed determination of second-order rate constants (k), using the second-order rate equation. The k value for cisplatin reacting with apo-MT was approximately 0.14 M-1 s-1, Cd/Zn-MT approximately 0.75 M-1 s-1, Cd7-MT approximately 0.53 M-1 s-1, and Zn7-MT approximately 0.65 M-1 s-1. Thus, cisplatin displaced Cd and Zn equally well. Leukocyte MT concentration was approximately 1.0 mM, so that the kinetics of cisplatin binding to cellular MT is pseudo-first order (pseudo-first-order rate constant, approximately 0.63 x 10-3 s-1; half-life, approximately 18 min). With [cisplatin] = 10 microM, the rate of cisplatin reaction with MT is approximately 6.3 micromol s-1 cm-3. We conclude that cellular MT can trap significant amounts of cisplatin and may efficiently contribute to cisplatin resistance.

Kinetic study of the reaction of cisplatin with thiols

The reactions of cisplatin [cis-diamminedichloroplatinum(II), CDDP] with glutathione (GSH) and drug thiols were investigated at 37 degrees C in 100 mM Tris-NO(3), pH approximately 7.4, using a clinically relevant concentration of CDDP (33 micro M), a large excess of GSH (16.5 mM), and [NaCl] of 4.62 mM. The conditions were designed to mimic passage of CDDP through the cytosol. The reactions were studied by UV-absorption spectroscopy, high-pressure liquid chromatography (HPLC), and atomic absorption spectroscopy. The initial rates, detected by UV absorbance, confirmed that the reactions are first order in [CDDP]. The HPLC peak corresponding to CDDP was analyzed for platinum content by atomic absorption spectroscopy, which decreased exponentially with time, confirming that the reactions are first order in [CDDP] and allowing determination of the pseudo first order rate constants (k(1)). For reaction of the dichloro form of CDDP with GSH, the k(1) value was approximately 2.2 x 10(-4) s(-1) (t(1/2) of approximately 53 min), giving the second order rate constant value (k(2)) of approximately 1.3 x 10(-2) M(-)1 s(-1). Reaction of a mixture of the aquated forms of CDDP with GSH gave a lower k(1) value ( approximately 0.9 x 10(-4) s(-1)). Reaction of CDDP with sodium 2-mercaptoethanesulfonate (mesna) gave a k(1) value of approximately 1.8 x 10(-4) s(-1) (t(1/2) of approximately 65 min and k(2) of approximately 1.1 x 10(-2) M(-1) s(-1)). Reaction of CDDP with S-2-(3-aminopropylamino)ethanethiol (WR-1065) gave a k(1) value of approximately 12.0 x 10(-4) s(-1) (t(1/2) of approximately 10 min and k(2) of approximately 7.3 x 10(-2) M(-)1 s(-1)). The relatively slow reaction rate of CDDP with GSH is consistent with the efficient DNA platination by CDDP in the presence of millimolar concentration of GSH in the cytosol.

BcI-xL antisense treatment sensitizes Bcl-xL-overexpressing squamous cell carcinoma cells to carboplatin

Carboplatin (CBDCA) has been widely used for the treatment of oral squamous cell carcinoma (SCC). The Bcl-2 family member Bcl-xL has been demonstrated to provide resistance to chemotherapeutic agents including CBDCA. Morpholino Bcl-xL antisense oligonucleotides (oligos) were employed to down-regulate Bcl-xL in CBDCA-resistant (MIT8, MIT16) as well as CBDCA-sensitive (MIT7) SCC cell lines. The oligos were delivered to adherent cells using a scrape-load procedure. The Bcl-xL antisense reduced Bcl-xL levels without altering the level of control actin, suggesting the specificity of this agent. The addition of Bcl-xL antisense oligos substantially prevented the cell growth of both CBDCA-sensitive and-resistant cells. The CBDCA-induced partial prevention of cell growth was further augmented by the addition of the Bcl-xL, but not the control, antisense oligos. The morpholino type Bcl-xL antisense oligos may be useful for the treatment of SCC, especially multidrug-resistant tumors with enhanced Bcl-xL levels.

Particular aspects of platinum compounds used at present in cancer treatment

The history of platinum in cancer treatment began 150 years ago with the first synthesis of cisplatin; but it was not used in the clinic before 30 years ago. Then 3000 derivatives were synthesised and tested, with poor successes: three other derivatives only are available today. Clearly they are not more active, but they are less toxic than cisplatin, although two, carboplatin and nedaplatin, yield a cross-resistance, while one, oxaliplatin, does not. Their mechanisms of action are similar: these four pro-drugs form adducts with DNA, impairing DNA synthesis and repair then. Their pharmacokinetics are complicated since we always measure two overlapping pharmacokinetics: those of the parent compound and of the bound platinum. Cisplatin is now recommended for few cancers, it is replaced by less-toxic carboplatin, and therefore more easily used in combination. Oxaliplatin give interesting results in a number of cancers. The official recommendation in Japan for nedaplatin is head and neck, testicular, lung, oesophageal, ovarian, and cervical cancer.

Kinetics of cisplatin binding to cellular DNA and modulations by thiol-blocking agents and thiol drugs

DNA platination by cisplatin (CDDP) was investigated in peripheral blood mononuclear cells and ovarian cancer cells using atomic absorption spectroscopy. Plots showing the amount of platinum (Pt) bound to DNA versus the molar concentration of cisplatin in the incubation medium ([CDDP]) were nonlinear. For [CDDP] < about 5 microM, the amount of Pt bound to DNA increased slowly with added drug. However, for larger [CDDP], the slope of the plot increased significantly. To study the role of thiols in affecting cisplatin binding to DNA, cells were treated with N-ethylmaleimide, which modifies thiol groups, rendering them incapable of binding cisplatin. Analysis using high-pressure liquid chromatography showed that approximately 99% of cellular glutathione was modified by N-ethylmaleimide. A plot of the amount of Pt bound to DNA versus [CDDP] for thiol-blocked cells is linear, with a slope similar to that of unblocked cells at high [CDDP]. Neither S-2-(3 aminopropylamino)ethanethiol (WR-1065) nor mesna, when added at clinically achievable concentrations (i.e., < approximately 300 microM), affected DNA platination. However, DNA platination was totally abolished by millimolar concentrations of the drug thiols (approximately 1.25 mM WR-1065 or approximately 5 mM mesna). Thus, the data show that endogenous thiols intercept cellular cisplatin, but this mechanism is less important at high [CDDP]. Moreover, therapeutic concentrations of drug thiols do not significantly affect DNA platination. A simple model that reproduces the experimental results of the amount of cisplatin binding to DNA as a function of [CDDP], time, and thiol content is proposed. The model takes into account passage of cisplatin and thiols through the cell membrane, binding of cisplatin to cellular thiols, and platination of DNA.

Role of antioxidant systems in human androgen-independent prostate cancer cells

BACKGROUND

Most prostate cancer cells respond to initial hormonal therapy; however, some of them eventually acquire resistance to the hormonal therapy. Hormone-independent prostate cancer usually exhibits resistance to chemotherapy and radiotherapy. Antioxidant systems are known to be involved in the resistance of cancer cells to chemotherapy and radiotherapy. Therefore, it is of significance to examine antioxidant systems of hormone-independent prostate cancer for enhancing the efficacy of cancer therapy.

METHODS

Three cell lines of human hormone-independent prostate cancer (PC-3, PC-3 MA2, and HPC36M) were examined for activities of superoxide dismutase, catalase, and glutathione peroxidase, and for levels of protein and nonprotein thiols such as metallothionein, glutathione, and thioredoxin. Sensitivity of these cells to anticancer drugs and inducers of reactive oxygen species such as paraquat, tert-butylhydroperoxide, and hydrogen peroxide was determined by microtiter assay.

RESULTS

PC-3 and PC-3 MA2, which were derived from bone metastases, were resistant to paraquat, hydrogen peroxide, and cisplatin compared with HPC36M, which was obtained from the primary prostate cancer. However, HPC36M was resistant to vinblastine compared with PC-3 and PC-3 MA2. Both PC-3 and PC-3 MA2 had higher activities of catalase and glutathione peroxidase and higher levels of glutathione and metallothionein than HPC36M.

CONCLUSIONS

These data suggest that enhanced ability in scavenging free radicals by antioxidant enzymes and thiol compounds may, at least in part, contribute to the resistance of bone metastatic prostate cancer during chemotherapy.

P-glycoprotein-expressing tumor cells are resistant to anticancer drugs in human gastrointestinal cancer

The resistance to doxorubicin (DOX) by some tumor cells is mainly due to the effect of P-glycoprotein encoded by the multidrug resistance-1 (mdr1) gene. We tried to prove the correlations between P-glycoprotein expression and the sensitivity for anticancer drugs including DOX and other cytotoxic drugs that are currently used for gastrointestinal cancer patients. We quantified the P-glycoprotein expression by flow cytometry techniques, and the sensitivity for anticancer drugs using a tetrazolium salt, 3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), assay in highly purified fresh human tumor cells obtained from 25 cancer patients. The inhibition rates were the lowest in DOX and mitomycin C (MMC), compared with other drugs. The most significant correlation between DOX and MMC was seen in the inhibition rates. A significant correlation was also seen between the inhibition rates for DOX and P-glycoprotein expression, whereas only a slight correlation between the sensitivity for MMC and P-glycoprotein expression was observed. We should therefore pay close attention to the effect of P-glycoprotein when treating cancer patients, especially if both the inhibition rates of DOX and MMC are low based on the findings of an MTT assay.

Interaction of the anti-cancer drug cisplatin with phosphatidylserine in intact and semi-intact cells

The anti-cancer drug cisplatin (cis-diamminedichloroplatinum(II)) forms a stable coordination complex with phosphatidylserine (PS) in model membrane systems (Speelmans et al., Biochemistry 36 (1997) 10545-10550). Because a similar interaction in vivo would be expected to have important physiological implications we studied cisplatin-PS interaction in human erythrocytes and tumor cell lines. Although cisplatin was efficiently taken up by intact erythrocytes, a cisplatin-PS complex was only detected in cells which had lysed as a result of prolonged storage or hypotonic shock. Despite the use of highly sensitive detection methods, and despite efficient cellular uptake of cisplatin, a complex could also not be detected in four human tumor cell lines, unless cells were permeabilized. In experiments in which cisplatin was incubated with PS-containing liposomes in the presence of an alternative cellular substrate, such as reduced glutathione, the relative affinity of cisplatin for PS was found to be low. Moreover, loading erythrocyte ghosts with physiological concentrations of glutathione strongly reduced cisplatin-PS complexation. Thus, in intact (tumor) cells a complex is not detected, most likely, because of the presence of higher affinity substrates. Though a transient complexation of cisplatin to PS cannot be excluded, our data suggest that cisplatin-PS does not play a direct role in the cellular (cyto)toxicity of cisplatin.

Replication protein A (RPA) binding to duplex cisplatin-damaged DNA is mediated through the generation of single-stranded DNA

Replication protein A (RPA) is a heterotrimeric protein composed of 70-, 34-, and 14-kDa subunits that has been shown to be required for DNA replication, repair, and homologous recombination. We have previously shown preferential binding of recombinant human RPA (rhRPA) to duplex cisplatin-damaged DNA compared with the control undamaged DNA (Patrick, S. M., and Turchi, J. J. (1998) Biochemistry 37, 8808-8815). Here we assess the binding of rhRPA to DNA containing site-specific cisplatin-DNA adducts. rhRPA is shown to bind 1.5-2-fold better to a duplex 30-base pair substrate containing a single 1,3d(GpXpG) compared with a 1,2d(GpG) cisplatin-DNA intrastrand adduct, consistent with the difference in thermal stability of DNA containing each adduct. Consistent with these data, a 21-base pair DNA substrate containing a centrally located single interstrand cisplatin cross-link resulted in less binding than to the undamaged control DNA. A series of experiments measuring rhRPA binding and concurrent DNA denaturation revealed that rhRPA binds duplex cisplatin-damaged DNA via the generation of single-stranded DNA. Single-strand DNA binding experiments show that rhRPA binds 3-4-fold better to an undamaged 24-base DNA compared with the same substrate containing a single 1,2d(GpG) cisplatin-DNA adduct. These data are consistent with a low affinity interaction of rhRPA with duplex-damaged DNA followed by the generation of single-stranded DNA and then high affinity binding to the undamaged DNA strand.

High-mobility group 1 protein inhibits helicase catalyzed displacement of cisplatin-damaged DNA

We have determined the effect of HMG-1 bound to cisplatin-damaged DNA on the activities of calf helicase E. DNase I protection analysis demonstrated HMG-1 bound a cisplatin-damaged 24 base oligonucleotide annealed to M13mp18. Exonuclease digestion experiments revealed that greater than 90% of the DNA substrates contained a single site specific cisplatin adduct and, maximally, 65% of the substrates were bound by HMG-1. Helicase E catalyzed displacement of the cisplatin-damaged DNA oligonucleotide was inhibited by HMG-1 in a concentration-dependent manner. Time course experiments revealed a decreased rate of displacement in reactions containing HMG-1. The maximum inhibition observed was 55% and taking into account that only 65% of the substrates had HMG-1 bound, approximately 85% inhibition was observed on platinated DNA substrates containing HMG-1. Inhibition of helicase activity was proportional to the amount of substrate bound by HMG-1 based on the displacement and exonuclease assays at varying HMG-1 concentrations. The ability of helicase E to displace an undamaged DNA oligonucleotide from a cisplatin-damaged DNA template was also inhibited by HMG-1. Interestingly, HMG-1 had no effect on the rate of DNA-dependent ATP hydrolysis catalyzed by helicase E on the same DNA substrate. The inhibition of helicase activity by HMG-1 binding cisplatin-damaged DNA further supports a role for HMG-1 inhibiting DNA repair which may contribute to cellular sensitivity to cisplatin.

Enhancing the effect of anticancer drugs against the colorectal cancer cell line with electroporation

Electroporation was applied in vitro and in vivo in the treatment of human colorectal cancer cell lines to study whether it can enhance the effect of bleomycin (BLM), 5-fluorouracil (5-FU) and cis-platinum (CDDP). We used LS174T and Colo320 cells derived from human colon cancer as target cells in this study. When the LS174T cells were used as target cells, the IC50 of BLM decreased to 10(-3) times, while that of 5-FU decreased to only about one fifth with the application of electric current. In the case of the Colo320 cells, the IC50 of BLM and 5-FU were about one hundredth and a half, respectively. The effect of CDDP was not enhanced with electric current. In vivo experiments were also performed using LS174T cells transplanted subcutaneously (s.c.) into nude mice. By treatment with intravenously (i.v.) administered BLM and simultaneous application of the electric current, tumors were markedly decreased in size after three weeks.

TCA-100 tumour chemosensitivity assay: differences in sensitivity between cultured tumour cell lines and clinical studies

The BATLE LE TCA-100 tumour chemosensitivity assay has been used to evaluate chemotherapeutic drug sensitivity of cultured tumour cell lines. Studies were performed using test drug concentrations calibrated to discriminate sensitivity and resistance of clinical specimens. Strong sensitivity which appeared to be inconsistent with clinical experience was detected for some drugs and cell lines. Findings of strong sensitivity were consistent with basic differences between sensitivity testing cultured cell lines and clinical specimens. Results with cell lines frequently may not apply directly to clinical applications. Characterization of differences between cell lines and clinical specimens may assist in application of cell line findings to clinical trials.

Effect of pharmacologic doses of zinc on the therapeutic index of brain tumor chemotherapy with carmustine

To evaluate the potential differential effect of pretreatment with pharmacologic doses of the trace element zinc on the chemosensitivity of glioma cells and bone marrow cells for carmustine (BCNU), we performed in vitro and in vivo studies of zinc toxicity as well as of the combined treatment with zinc and the anticancer drug. We studied the in vitro effects on established human and rat glioma cell lines using a microcolorimetric growth assay and on murine bone marrow using a clonogenic assay for committed progenitor cells of the granulocyte-monocyte lineage. Zinc exposures of up to 100 microM for 120 h did not influence the growth of six of seven human glioma cell lines. Only U87MG demonstrated statistically significant toxicity during high zinc exposure (100 microM over 120 h). Dose-response growth curves generated for BCNU did not show protection against the anticancer agents by a 48-h pretreatment with different zinc concentrations. The clonogenic capacity of bone marrow cells was slightly reduced by in vitro culture for 24 and 48 h. Although this effect appeared to be more prominent in the presence of zinc supplementation, overall a statistically significant inhibition was seen only after exposure to a concentration of 100 microM zinc over 48 h. As compared with chemotherapy alone, in vitro pretreatment with 50 microM zinc over 48 h followed by chemotherapy resulted in an increased number of colony-forming unit-granulocyte monocyte (CFU-GM): CFU-GM increased by a factor of 2 for BCNU (60 microM x 2 h). This statistically significant in vitro chemoprotection would translate into a dose-protection factor of 1.5, i.e., for the same level of myelosuppression, zinc pretreatment would allow administration of a 50% increased dose of BCNU. The in vivo studies were performed in an s.c. xenograft model of the human glioma cell line U87MG in athymic mice. The maximal tolerable pretreatment with zinc was determined to be a 10-day course of daily i.p. injections of 10 mg/kg ZnCl2. The subsequent i.p. administration of the dose lethal to 10% of the mice (LD10) and of a 1.5 x LD10 dose of BCNU resulted in less bone marrow toxicity in pretreated animals than in non-zinc-pretreated mice as determined in a CFU-GM assay. Glioma colony-forming efficiency (CFE) assays, on the other hand, did not show any zinc-related difference in the BCNU sensitivity of U87MG.(ABSTRACT TRUNCATED AT 400 WORDS)