The cellular pharmacology of oxaliplatin resistance

Investigations of cellular copper metabolism in ovarian cancer cells using a ratiometric fluorescent copper dye

Imbalances in metal homeostasis have been implicated in the progression and drug response of cancer cells. Understanding these changes will enable identification of new treatment regimes and precision medicine approaches to cancer treatment. In particular, there has been considerable interest in the interplay between copper homeostasis and response to platinum-based chemotherapeutic agents. Here, we have studied differences in the Cu uptake and distributions in the ovarian cancer cell line, A2780, and its cisplatin resistant form, A2780.CisR, by measuring total Cu content and the bioavailable Cu pool. Atomic absorption spectroscopy (AAS) revealed a lower total Cu uptake in A2780.CisR compared to A2780 cells. Conversely, live-cell confocal microscopy studies with the ratiometric Cu(I)-sensitive fluorescent dye, InCCu1, revealed higher relative cellular content of labile Cu in A2780.CisR cells compared with A2780 cells. These results demonstrate that Cu trafficking, homeostasis and speciation are different in the Pt-sensitive and resistant cells and may be associated with the predominance of different phenotypes for A2780 (epithelial) and A2780.CisR (mesenchymal) cells.

The Current Treatment Paradigm for Pancreatic Ductal Adenocarcinoma and Barriers to Therapeutic Efficacy

Pancreatic ductal adenocarcinoma (PDAC) has a dismal prognosis, with a median survival time of 10-12 months. Clinically, these poor outcomes are attributed to several factors, including late stage at the time of diagnosis impeding resectability, as well as multi-drug resistance. Despite the high prevalence of drug-resistant phenotypes, nearly all patients are offered chemotherapy leading to modest improvements in postoperative survival. However, chemotherapy is all too often associated with toxicity, and many patients elect for palliative care. In cases of inoperable disease, cytotoxic therapies are less efficacious but still carry the same risk of serious adverse effects, and clinical outcomes remain particularly poor. Here we discuss the current state of pancreatic cancer therapy, both surgical and medical, and emerging factors limiting the efficacy of both. Combined, this review highlights an unmet clinical need to improve our understanding of the mechanisms underlying the poor therapeutic responses seen in patients with PDAC, in hopes of increasing drug efficacy, extending patient survival, and improving quality of life.

Roles of Nrf2 in Gastric Cancer: Targeting for Therapeutic Strategies

Nuclear Factor Erythroid 2-Related Factor 2 (Nrf2) is a specific transcription factor with potent effects on the regulation of antioxidant gene expression that modulates cell hemostasis under various conditions in tissues. However, the effects of Nrf2 on gastric cancer (GC) are not fully elucidated and understood. Evidence suggests that uncontrolled Nrf2 expression and activation has been observed more frequently in malignant tumors, including GC cells, which is then associated with increased antioxidant capacity, chemoresistance, and poor clinical prognosis. Moreover, Nrf2 inhibitors and the associated modulation of tumor cell redox balance have shown that Nrf2 also has beneficial effects on the therapy of various cancers, including GC. Based on previous findings on the important role of Nrf2 in GC therapy, it is of great interest to scientists in basic and clinical tumor research that Nrf2 can be active as both an oncogene and a tumor suppressor depending on different background situations.

Benzyl isothiocyanate inhibits HNSCC cell migration and invasion, and sensitizes HNSCC cells to cisplatin

Metastasis and chemoresistance represent two detrimental events that greatly hinder the outcome for those suffering with head and neck squamous cell carcinoma (HNSCC). Herein, we investigated benzyl isothiocyanate's (BITC) ability to inhibit HNSCC migration and invasion and enhance chemotherapy. Our data suggests that treatment with BITC 1) induced significant reductions in the viability of multiple HNSCC cell lines tested (HN12, HN8, and HN30) after 24 and 48 h, 2) decreased migration and invasion of the HN12 cells in a dose dependent manner, and 3) inhibited expression and altered localization of the epithelial-mesenchymal transition (EMT) marker, vimentin. We also observed that a pretreatment of BITC followed by cisplatin treatment 1) induced a greater decrease in HN12, HN30, and HN8 cell viability and total cell count than either treatment alone and 2) significantly increased apoptosis when compared to either treatment alone. Taken together these data suggest that BITC has the capacity to inhibit processes involved in metastasis and enhance the effectiveness of chemotherapy. Consequently, the results indicate that further investigation, including in vivo studies, are warranted.

Omega-3 eicosapentaenoic acid decreases CD133 colon cancer stem-like cell marker expression while increasing sensitivity to chemotherapy

Colorectal cancer is the third leading cause of cancer-related death in the western world. In vitro and in vivo experiments showed that omega-3 polyunsaturated fatty acids (n-3 PUFAs) can attenuate the proliferation of cancer cells, including colon cancer, and increase the efficacy of various anticancer drugs. However, these studies address the effects of n-3 PUFAs on the bulk of the tumor cells and not on the undifferentiated colon cancer stem-like cells (CSLCs) that are responsible for tumor formation and maintenance. CSLCs have also been linked to the acquisition of chemotherapy resistance and to tumor relapse. Colon CSLCs have been immunophenotyped using several antibodies against cellular markers including CD133, CD44, EpCAM, and ALDH. Anti-CD133 has been used to isolate a population of colon cancer cells that retains stem cells properties (CSLCs) from both established cell lines and primary cell cultures. We demonstrated that the n-3 PUFA, eicosapentaenoic acid (EPA), was actively incorporated into the membrane lipids of COLO 320 DM cells. 25 uM EPA decreased the cell number of the overall population of cancer cells, but not of the CD133 (+) CSLCs. Also, we observed that EPA induced down-regulation of CD133 expression and up-regulation of colonic epithelium differentiation markers, Cytokeratin 20 (CK20) and Mucin 2 (MUC2). Finally, we demonstrated that EPA increased the sensitivity of COLO 320 DM cells (total population) to both standard-of-care chemotherapies (5-Fluorouracil and oxaliplatin), whereas EPA increased the sensitivity of the CD133 (+) CSLCs to only 5-Fluorouracil.

Contribution of tumoral and host solute carriers to clinical drug response

Members of the solute carrier family of transporters are responsible for the cellular uptake of a broad range of endogenous compounds and xenobiotics in multiple tissues. Several of these solute carriers are known to be expressed in cancer cells or cancer cell lines, and decreased cellular uptake of drugs potentially contributes to the development of resistance. As result, the expression levels of these proteins in humans have important consequences for an individual's susceptibility to certain drug-induced side effects, interactions, and treatment efficacy. In this review article, we provide an update of this rapidly emerging field, with specific emphasis on the direct contribution of solute carriers to anticancer drug uptake in tumors, the role of these carriers in regulation of anticancer drug disposition, and recent advances in attempts to evaluate these proteins as therapeutic targets.

NONO and RALY proteins are required for YB-1 oxaliplatin induced resistance in colon adenocarcinoma cell lines

Background

YB-1 is a multifunctional protein that affects transcription, splicing, and translation. Overexpression of YB-1 in breast cancers causes cisplatin resistance. Recent data have shown that YB-1 is also overexpress in colorectal cancer. In this study, we tested the hypothesis that YB-1 also confers oxaliplatin resistance in colorectal adenocarcinomas.

Results

We show for the first time that transfection of YB-1 cDNA confers oxaliplatin resistance in two colorectal cancer cell lines (SW480 and HT29 cell lines). Furthermore, we identified by mass spectrometry analyses important YB-1 interactors required for such oxaliplatin resistance in these colorectal cancer cell lines. A tagged YB-1 construct was used to identify proteins interacting directly to YB-1 in such cells. We then focused on proteins that are potentially involved in colorectal cancer progression based on the Oncomine microarray database. Genes encoding for these YB-1 interactors were also examined in the public NCBI comparative genomic hybridization database to determine whether these genes are localized to regions of chromosomes rearranged in colorectal cancer tissues. From these analyses, we obtained a list of proteins interacting with YB-1 and potentially involved in oxaliplatin resistance. Oxaliplatin dose response curves of SW480 and HT29 colorectal cancer cell lines transfected with several siRNAs corresponding to each of these YB-1 interactors were obtained to identify proteins significantly affecting oxaliplatin sensitivity upon gene silencing. Only the depletion of either NONO or RALY sensitized both colorectal cancer cell lines to oxaliplatin. Furthermore, depletion of NONO or RALY sensitized otherwise oxaliplatin resistant overexpressing YB-1 SW480 or HT29 cells.

Conclusion

These results suggest knocking down NONO or RALY significant counteracts oxaliplatin resistance in colorectal cancers overexpressing the YB-1 protein.

Improving drug potency and efficacy by nanocarrier-mediated subcellular targeting

Nanocarrier-mediated drug targeting is an emerging strategy for cancer therapy and is being used, for example, with chemotherapeutic agents for ovarian cancer. Nanocarriers are selectively accumulated in tumors as a result of their enhanced permeability and retention of macromolecules, thereby enhancing the antitumor activity of the nanocarrier-associated drugs. We investigated the real-time subcellular fate of polymeric micelles incorporating (1,2-diaminocyclohexane) platinum(II) (DACHPt/m), the parent complex of oxaliplatin, in tumor tissues by fluorescence-based assessment of their kinetic stability. These observations revealed that DACHPt/m was extravasated from blood vessels to the tumor tissue and dissociated inside each cell. Furthermore, DACHPt/m selectively dissociated within late endosomes, enhancing drug delivery to the nearby nucleus relative to free oxaliplatin, likely by circumvention of the cytoplasmic detoxification systems such as metallothionein and methionine synthase. Thus, these drug-loaded micelles exhibited higher antitumor activity than did oxaliplatin alone, even against oxaliplatin-resistant tumors. These findings suggest that nanocarriers targeting subcellular compartments may have considerable benefits in clinical applications.

Enhancing lipophilicity as a strategy to overcome resistance against platinum complexes?

Decreased influx represents one of the major resistance mechanisms of platinum complexes. In order to address the question if this mechanism of resistance can be overcome by enhancing the lipophilicity of platinum complexes, we investigated the influence of lipophilicity on cellular accumulation and cytotoxicity in a panel of oxaliplatin analogues with different carrier ligands. Cellular accumulation, DNA platination and cytotoxicity were measured in a cisplatin-sensitive and -resistant ovarian carcinoma (A2780/A2780cis) and in an oxaliplatin-sensitive and -resistant ileocecal colorectal adenocarcinoma (HCT-8/HCT-8ox) cell line pair. Platinum concentrations were determined by flameless atomic absorption spectrometry or adsorptive stripping voltammetry. Passive diffusion represented the main influx mechanism of oxaliplatin analogues during the first minutes of incubation as indicated by a correlation between lipophilicity and early influx rate. Afterwards, the predominant influx mechanism was lipophilicity-independent. More lipophilic complexes showed a reduced cytotoxic activity, although the early influx rate was increased. The resistance profiles of the two cell line pairs were found to be different: HCT-8ox cells were less resistant against more lipophilic complexes, whereas A2780cis cells exhibited a comparable degree of resistance against all investigated compounds. However, the reduction in resistance factor of HCT-8ox cells cannot be explained by increased influx suggesting that other resistance mechanisms are circumvented upon exposure to more lipophilic compounds. Though resistance against more lipophilic platinum complexes analogues is lower we conclude that enhancing lipophilicity is not a successful strategy to overcome platinum resistance as higher lipophilicity is also associated with lower cytotoxic activity.

Drug transporters of platinum-based anticancer agents and their clinical significance

Platinum-based drugs are among the most active anticancer agents and are successfully used in a wide variety of human malignancies. However, acquired and/or intrinsic resistance still represent a major limitation. Lately, in particular mechanisms leading to impaired uptake and/or decreased cellular accumulation of platinum compounds have attracted attention. In this review, we focus on the role of active platinum uptake and efflux systems as determinants of platinum sensitivity and -resistance and their contribution to platinum pharmacokinetics (PK) and pharmacodynamics (PD). First, the three mostly used platinum-based anticancer agents as well as the most promising novel platinum compounds in development are put into clinical perspective. Next, we describe the presently known potential platinum transporters--with special emphasis on organic cation transporters (OCTs)--and discuss their role on clinical outcome (i.e. efficacy and adverse events) of platinum-based chemotherapy. In addition, transporter-mediated tumour resistance, the impact of potential platinum transporter-mediated drug-drug interactions, and the role of drug transporters in the renal elimination of platinum compounds are discussed.

Lunasin induces apoptosis and modifies the expression of genes associated with extracellular matrix and cell adhesion in human metastatic colon cancer cells

SCOPE

Lunasin is an arginine-glycine-aspartic acid (RGD) cancer preventive peptide. The objective was to evaluate the potential of lunasin to induce apoptosis in human colon cancer cells and their oxaliplatin-resistant (OxR) variants, and its effect on the expression of human extracellular matrix and adhesion genes.

METHODS AND RESULTS

Various human colon cancer cell lines which underwent metastasis were evaluated in vitro using cell flow cytometry and fluorescence microscopy. Lunasin cytotoxicity to different colon cancer cells correlated with the expression of α(5) b(1) integrin, being most potent to KM12L4 cells (IC(50) = 13 μM). Lunasin arrested cell cycle at G2/M phase with concomitant increase in the expression of cyclin-dependent kinase inhibitors p21 and p27. Lunasin (5-25 μM) activated the apoptotic mitochondrial pathway as evidenced by changes in the expressions of Bcl-2, Bax, nuclear clusterin, cytochrome c and caspase-3 in KM12L4 and KM12L4-OxR. Lunasin increased the activity of initiator caspase-9 leading to the activation of caspase-3 and also modified the expression of human extracellular matrix and adhesion genes, downregulating integrin α(5), SELE, MMP10, integrin β(2) and COL6A1 by 5.01-, 6.53-, 7.71-, 8.19- and 10.10-fold, respectively, while upregulating COL12A1 by 11.61-fold.

CONCLUSION

Lunasin can be used in cases where resistance to chemotherapy developed.

Enhanced expression of nuclear factor I/B in oxaliplatin-resistant human cancer cell lines

Oxaliplatin is a third-generation platinum drug that has favorable activity in cisplatin-resistant cells. However, the molecular mechanisms underlying oxaliplatin resistance are not well understood. To investigate the molecular mechanisms involved, resistant cell lines were independently derived from colon cancer (DLD1) and bladder cancer (T24) cells. Oxaliplatin-resistant DLD1 OX1 and DLD1 OX2 cell lines were approximately 16.3-fold and 17.8-fold more resistant to oxaliplatin than the parent cell lines, respectively, and had 1.7- and 2.2-fold higher cross-resistance to cisplatin, respectively. Oxaliplatin-resistant T24 OX2 and T24 OX3 cell lines were approximately 5.0-fold more resistant to oxaliplatin than the parent cell line and had 1.9-fold higher cross-resistance to cisplatin. One hundred and fifty-eight genes commonly upregulated in both DLD1 OX1 and DLD1 OX2 were identified by microarray analysis. These genes were mainly involved in the function of transcriptional regulators (14.6%), metabolic molecules (14.6%), and transporters (9.5%). Of these, nuclear factor I/B (NFIB) was upregulated in all oxaliplatin-resistant cells. Downregulation of NFIB rendered cells sensitive to oxaliplatin, but not to cisplatin. Forced expression of NFIB induced resistance to oxaliplatin, but not to cisplatin. Taken together, these results suggest that NFIB is a novel and specific biomarker for oxaliplatin resistance in human cancers.

The role of the N-terminus of mammalian copper transporter 1 in the cellular accumulation of cisplatin

The mammalian copper transporter 1 (CTR1) is responsible for the uptake of copper (Cu) from the extracellular space, and has been shown to play a major role in the initial accumulation of platinum-based drugs. In this study we re-expressed wild type and structural variants of hCTR1 in mouse embryo fibroblasts in which both alleles of mCTR1 had been knocked out (CTR1(-/-)) to examine the role of the N-terminal extracellular domain of hCTR1 in the accumulation of cisplatin (cDDP). Deletion of either the first 45 amino acids or just the (40)MXXM(45) motif in the N-terminal domain did not alter subcellular distribution or the amount of protein in the plasma membrane but it eliminated the ability of hCTR1 to mediate the uptake of Cu. In contrast it only partially reduced cDDP transport capacity. Neither of these structural changes prevented cDDP from triggering the rapid degradation of hCTR1. However, they did alter the potency of the cDDP that achieved cell entry, possibly reflecting the fact that hCTR1 may mediate the transport of cDDP both through the pore it forms in the plasma membrane and via endocytosis. We conclude that cDDP interacts with hCTR1 both at (40)MXXM(45) and at sites outside the N-terminal domain that produce the conformational changes that trigger degradation.

Differential transport of platinum compounds by the human organic cation transporter hOCT2 (hSLC22A2)

BACKGROUND

Solute carriers (SLCs), in particular organic cation transporters (OCTs), have been implicated in the cellular uptake of platinum-containing anticancer compounds. The activity of these carriers may determine the pharmacokinetics and the severity of side effects, including neuro- and nephrotoxicity of platinum-based chemotherapy. As decreased drug accumulation is a key mechanism of platinum resistance, SLCs may also contribute to the development of resistance. Here, we define the role of hSLC22A2 (OCT2) in the cellular uptake of platinum compounds.

EXPERIMENTAL APPROACH

Human embryonic kidney (HEK) 293 cells stably expressing the hSLC22A2 gene (HEK293/hSLC22A2) were used in platinum accumulation studies. Following a 2 h exposure to various platinum compounds (100 microM), intracellular platinum levels were determined by flameless atomic absorption spectrometry.

KEY RESULTS

HEK293/hSLC22A2 cells, compared with HEK293/Neo control cells, displayed significant increases in oxaliplatin (28.6-fold), Pt[DACH]Cl(2) (20.6-fold), ormaplatin (8.1-fold), tetraplatin (4.5-fold), transplatin (3.7-fold) and cisplatin (1.3-fold), but not carboplatin. SLC22A2-mediated transport could be inhibited by 1-methyl-4-phenylpyridinium. Furthermore, hSLC22A2-mediated oxaliplatin and cisplatin accumulation was time- and concentration-dependent, but non-saturable. Expression of hSLC22A2 in HEK293 cells resulted in enhanced sensitivity to oxaliplatin (12-fold) and cisplatin (1.8-fold). Although, hSLC22A2 mRNA expression was frequently found in ovarian cancer cell lines, its expression in clinical ovarian cancer specimens (n= 80) was low and did not correlate with the treatment outcome of platinum-based regimens.

CONCLUSIONS AND IMPLICATIONS

The hSLC22A2 drug transporter is a critical determinant in the uptake and cytotoxicity of various platinum compounds, particularly oxaliplatin.

Genetic prognostic and predictive markers in colorectal cancer

Despite many studies of the likely survival outcome of individual patients with colorectal cancer, our knowledge of this subject remains poor. Until recently, we had virtually no understanding of individual responses to therapy, but the discovery of the KRAS mutation as a marker of probable failure of epidermal growth factor receptor (EGFR)-targeted therapy is a first step in the tailoring of treatment to the individual. With the application of molecular analyses, as well as the ability to perform high-throughput screens, there has been an explosive increase in the number of markers thought to be associated with prognosis and treatment outcome in this disease. In this Review, we attempt to summarize the sometimes confusing findings, and critically assess those markers already in the public domain.

Tumors established with cell lines selected for oxaliplatin resistance respond to oxaliplatin if combined with cetuximab

PURPOSE

To establish whether cetuximab, a chimeric IgG1 antibody targeting epidermal growth factor receptor, has the potential to restore responsiveness to oxaliplatin in preclinical cancer models, as has been shown with irinotecan in irinotecan refractory metastatic colorectal cancer patients.

EXPERIMENTAL DESIGN

The effects of cetuximab and oxaliplatin, alone or in combination, were tested in vitro and in vivo using human colorectal cancer cell lines selected for oxaliplatin resistance, as well as parental control cell lines. Evaluations were made of subcutaneous xenograft tumor growth in nu/nu athymic mice, as well as activation of mitogen-activated protein kinase (extracellular signal-regulated kinase 1/2) and AKT, expression of DNA repair genes, density of apurinic/apyrimidinic DNA damage, and accumulation of platinum-DNA adducts in vitro.

RESULTS

Oxaliplatin + cetuximab efficacy in murine subcutaneous xenograft models was greater than that of monotherapies and independent of the responsiveness to oxaliplatin monotherapy. In vitro, cetuximab reduced expression of excision repair cross-complementation group 1 and XPF, which are key components of the nucleotide excision repair pathway involved in the excision of platinum-DNA adducts. In addition, cetuximab reduced expression of XRCC1, a component of the base excision repair pathway responsible for the repair of apurinic/apyrimidinic sites. Effects of cetuximab on DNA repair protein levels were downstream to effects on mitogen-activated protein kinase and AKT pathway activation. In line with effects on DNA repair protein expression, cetuximab increased the accumulation of platinum and apurinic/apyrimidinic sites on DNA during oxaliplatin treatment.

CONCLUSIONS

Cetuximab has the potential to salvage the benefits of oxaliplatin in oxaliplatin-resistant colorectal cancer patients by reducing DNA repair capacity.

Cell cycle checkpoint models for cellular pharmacology of paclitaxel and platinum drugs

A pharmacokinetic-pharmacodynamic mathematical model is developed for cellular pharmacology of chemotherapeutic drugs for which the decisive step towards cell death occurs at a point in the cell cycle, presumably corresponding to a cell cycle checkpoint. For each cell, the model assumes a threshold level of some intracellular species at that checkpoint, beyond which the cell dies. The threshold level is assumed to have a log-normal distribution in the cell population. The kinetics of formation of the lethal intracellular species depends on the drug, and on the cellular pharmacokinetics and binding kinetics of the cell. Specific models are developed for paclitaxel and for platinum drugs (cisplatin, oxaliplatin and carboplatin). In the case of paclitaxel, two separate mechanisms of cell death necessitate a model that accounts for two checkpoints, with different intracellular species. The model was tested on a number of in vitro cytotoxicity data sets for these drugs, and found overall to give significantly better fits than previously proposed cellular pharmacodynamic models. It provides an explanation for the asymptotic convergence of dose-response curves as exposure time becomes long.

Exposure-response relationships for oxaliplatin-treated colon cancer cells

Data are lacking for an optimal infusion length for oxaliplatin administered intraperitoneally. Our objectives were to establish the roles of hyperthermia and an effective length of oxaliplatin treatment in maximizing antitumor activity. SW620 cells were treated for 0.5 vs. 2 h and at 37 vs. 42 degrees C. Cytotoxicity, cell cycle analysis, subG1 and survival were assessed with the MTT assay, flow cytometry and the clonogenic assay. The IC50 for cells treated at 37 degrees C was 2.90+/-0.83 microg/ml and at 42 degrees C, 1.99+/-0.66 microg/ml (P=0.14). The Emax for 37 degrees C was 93.9+/-2.57% and for 42 degrees C, 97.8+/-1.59% (P=0.05). The subG1 fraction did not differ between cells treated at 37 and 42 degrees C (P=0.12). The IC50 for the cells treated for 0.5 h was 10.6+/-0.60 microg/ml and for 2 h, 2.80+/-1.70 microg/ml (P=0.02). The Emax for 0.5 h was 87.9+/-5.13% and for 2 h, 96.6+/-3.35% (P=0.09). SubG1 for 0.5 h was 8.24+/-1.33% and for 2 h, 15.8+/-2.45% (P=0.02). Clonogenic assays demonstrated diminished survival when treated with low concentrations (10 microg/ml) of oxaliplatin combined with heat treatment (P=0.017) for 2 h, but not 0.5 h. Similar clonogenic assay experiments were performed with the oxaliplatin-resistant WiDr cell line, and differences in survival following oxaliplatin and heat treatment were again observed for 2 h, but not for 0.5 h (P=0.002). Drug treatment for 2 h of both SW620 and WiDr cell lines is superior to treatment for 0.5 h. Cell kill effects are reliant on treatment length; hence, the choice of time exposure must be made with a view to maintaining a balance between the cell kill effects and the clinical feasibility of treating the patient.

Pharmacogenomics in colorectal cancer: The first step for individualized-therapy

Interindividual differences in the toxicity and response to anticancer therapies are currently observed in practically all available treatment regimens. A goal of cancer therapy is to predict patient response and toxicity to drugs in order to facilitate the individualization of patient treatment. Identification of subgroups of patients that differ in their prognosis and response to treatment could help to identify the best available drug therapy according the genetic profile. Several mechanisms have been suggested to contribute to chemo-therapeutic drug resistance: amplification or overexpression of membrane transporters, changes in cellular proteins involved in detoxification or in DNA repair, apoptosis and activation of oncogenes or tumor suppressor genes. Colorectal cancer (CRC) is regarded as intrinsically resistant to chemotherapy. Several molecular markers predictive of CRC therapy have been included during the last decade but their results in different studies complicate their application in practical clinical. The simultaneous testing of multiple markers predictive of response could help to identify more accurately the true role of these polymorphisms in CRC therapy. This review analyzes the role of genetic variants in genes involved in the action mechanisms of the drugs used at present in colorectal cancer.

Annexin XI is associated with cisplatin resistance and related to tumor recurrence in ovarian cancer patients

PURPOSE

Ovarian cancer patients treated with cisplatin-based chemotherapy often develop acquired cisplatin resistance and, consequently, cancer recurrence. The precise nature of chemoresistance remains unclear. In this study, a protein identified to be associated with cisplatin resistance in ovarian cancer cells was investigated in ovarian cancer tissues to address its clinical significance.

EXPERIMENTAL DESIGN

Antibody microarrays were used to identify proteins consistently differentially expressed across three pairs of cisplatin-sensitive and cisplatin-resistant ovarian cancer cell lines. Immunoblotting was used to confirm observed alteration of protein expression. The protein expression was further evaluated by immunohistochemical staining using tissue microarrays containing various human normal and malignant tissues and 164 surgical specimens derived from primary and recurrent ovarian cancer patients who underwent primary debulking surgery followed by standard chemotherapeutic regimen.

RESULTS

Annexin XI was down-regulated in all three cisplatin-resistant cell lines as compared with their parent cells. Annexin XI expression was observed in the majority of human normal organs and decreased in some of the most common human malignancies. The expression level of Annexin XI in first recurrent ovarian cancers was much lower than that in primary ovarian cancers (P = 0.0004). Increased Annexin XI immunoreactivity in ovarian cancers seemed to prolong the disease-free interval of patients (P = 0.03). Annexin XI immunoreactivity inversely correlated with in vitro cisplatin resistance in ovarian cancers (P = 0.01).

CONCLUSION

Decreased expression of Annexin XI is characteristic for cisplatin-resistant cancer cells and may contribute to tumor recurrence. Annexin XI may be a potential marker for chemoresistance and earlier recurrence of ovarian cancer patients.

The influence of temperature on antiproliferative effects, cellular uptake and DNA platination of the clinically employed Pt(II)-drugs

Cellular uptake of a drug is one of the most important factors influencing its pharmacodynamics and pharmacokinetics. Our laboratory has previously studied platinum uptake following cisplatin, carboplatin and oxaliplatin treatment at sub-lethal doses of selected tumour cell lines. Here we report on the influence of temperature on dose-dependent antiproliferative effects, cellular uptake and DNA platination of these platinum-based drugs tested on MCF-7 human mammary carcinoma cell line. Inductively coupled plasma-mass spectrometry (ICP-MS) technique has been chosen to perform Pt determinations on cells treated with drug concentrations similar with those usually found in vivo in human plasma. The high sensitivity and analytical rapidity of this technique made possible to carry out a very large amount of Pt determinations (about 300) necessary for this study. Hyperthermia (43 degrees C) proved a synergistic effect with cisplatin on cell growth inhibition, while only an additive effect was demonstrated for carboplatin and oxaliplatin. This behaviour might be explained by the higher DNA platination ratio between data at 43 and 37 degrees C of cisplatin with respect to those of carboplatin and oxaliplatin.

Modeling oxaliplatin drug delivery to circadian rhythms in drug metabolism and host tolerance

To make possible the design of optimal (circadian and other period) time-scheduled regimens for cytotoxic drug delivery by intravenous infusion, a pharmacokinetic-pharmacodynamic (PK-PD, with circadian periodic drug dynamics) model of chemotherapy on a population of tumor cells and its tolerance by a population of fast renewing healthy cells is presented. The application chosen for identification of the model parameters is the treatment by oxaliplatin of Glasgow osteosarcoma, a murine tumor, and the healthy cell population is the jejunal mucosa, which is the main target of oxaliplatin toxicity in mice. The model shows the advantage of a periodic time-scheduled regimen, compared to the conventional continuous constant infusion of the same daily dose, when the biological time of peak infusion is correctly chosen. Furthermore, it is well adapted to using mathematical optimization methods of drug infusion flow, choosing tumor population minimization as the objective function and healthy tissue preservation as a constraint. Such a constraint is in clinical settings tunable by physicians by taking into account the patient's state of health.

Accumulation, platinum–DNA adduct formation and cytotoxicity of cisplatin, oxaliplatin and satraplatin in sensitive and resistant human osteosarcoma cell lines, characterized by p53 wild-type status

P53 gene status is implicated in the cytotoxic drug sensitivity and published research has been mostly addressed to cisplatin (CDDP) activity. Previous study in our laboratory considered p53 mutant cell lines A431 (parental) and A431/Pt (CDDP-resistant counterpart, resistance factor R.F.=2.6). For a comparison which contributes to a deeper appreciation of the process that mediates the Pt drug cellular effects, we extended our investigation to the p53 wild-type cell lines U2-OS (human osteosarcoma) and its CDDP-resistant counterpart U2-OS/Pt (R.F.=5). We compared the activity of CDDP, oxaliplatin (L-OHP) and satraplatin (JM216) whose hydrophobicity rank is JM216>L-OHP>CDDP. In U2-OS cells the three drugs accumulated similarly, while in U2-OS/Pt the most hydrophobic drugs were privileged. No significant differences in efflux were observed between sensitive and resistant cell lines. The growing of CDDP resistance seems to be overcome by increasing the hydrophobicity of the Pt agent. An almost linear trend seems to relate R.F. and drug hydrophobicity in U2-OS/Pt and A431/Pt cells. DNA platination in U2-OS as in A431 cells is at the lowest levels for L-OHP. In U2-OS cell line the IC(50) of CDDP (17.6 microM) and JM216 (88.02 microM) do not correlate with their similar levels of Pt-DNA adducts (mean value approximately 0.14 pmol Pt/microg DNA). The presence of a wild-type p53 exalts either CDDP cytotoxicity (two-fold more active in U2-OS than in A431 cells) and CDDP resistance in comparison to a p53 mutant type. The p53 status seems to not improve JM216 or L-OHP cytotoxicity in both cell lines.

Inhibition of G1/S transition potentiates oxaliplatin-induced cell death in colon cancer cell lines

In a series of colorectal cancer cell lines, both necrosis and apoptosis were induced upon exposure to oxaliplatin, and enhanced by co-administration of the Hsp90 inhibitor 17-AAG. We analyzed the effects of these interventions on the cell cycle, and found that oxaliplatin treatment caused G1 and G2 arrest in HCT116 cells, and S-phase accumulation in two p53-deficient cell lines (HT29 and DLD1). Addition of 17-AAG enhanced cell cycle effects of oxaliplatin in HCT116, and induced G1 arrest and decrease in S-phase population in the other cell lines. Analysis of cell cycle proteins revealed that the major difference between the cell lines was that in HCT116, 17-AAG resulted in profound inhibition of expression and phosphorylation of late G1 proteins cyclin E and cdk2, with no effect on p21/WAF1 induction. Consistent with these, an HCT116 p53(-/-) line, lacking p21, showed resistance to oxaliplatin, failure to enter apoptosis, and an accumulation of cells in S-phase. Introduction of p21 in these cells caused reversal of that phenotype, including restoration of the G1 block and re-sensitization to oxaliplatin. Inhibition of G1/S progression using cdk2 inhibitor also enhanced oxaliplatin cytotoxicity. We conclude that in colon cancer cells with impaired p53 function, interventions directed to cycle arrest in G1 may potentiate oxaliplatin activity.

Cell cycle arrest by oxaliplatin on cancer cells

Oxaliplatin (L-OHP) is the only platinum compound to show activity in colorectal cancer. We evaluated the cytotoxicity of L-OHP on four human cancer cell lines and its influence on the cell cycle, when treated during long exposure (72 h) and different post-incubation times (24 or 72 h). We used a panel of cell lines: HT29 (colon cancer), MCF7 (breast cancer), Hela (uterine cervix) and A549 (lung adenocarcinoma). Inhibition concentration (IC)(50) was assessed by MTT assay. Cell cycle modifications were determined using dual parameter bromodeoxyuridine and propidium iodide. L-OHP yielded a superior cytotoxicity on HT29 and MCF7 relative to Hela and A549 after treatment, the post-incubations demonstrate that growth inhibition was irreversible for HT29 and Hela cell lines contrary to MCF7 and A549. The main effects of L-OHP are G2/M cell cycle arrest and transient S phase delay. Taken together, L-OHP treatment results on HT29, MCF7 and Hela, are in favor of lengthening the infusion duration to patients during further clinical trials.

Clinical application of oxaliplatin in epithelial ovarian cancer

Platinum remains the most active drug class in ovarian cancer treatment; however, new single-agent and combination therapies are needed to improve the clinical outcome of ovarian cancer therapies. Oxaliplatin, a third-generation platinum derivative, has shown effective antitumor activity and a favorable toxicity profile in epithelial ovarian cancer. Preclinical evidence of the synergistic cytotoxic effect of oxaliplatin in combination with several other chemotherapeutic agents and clinical evidence of the absence of any dose-limiting hematologic toxicity associated with this agent have made oxaliplatin an attractive compound for combination agent therapy. This article reviews the current status of the clinical application of oxaliplatin alone and in a combination regimen in epithelial ovarian cancer treatment.

Different accumulation of cisplatin, oxaliplatin and JM216 in sensitive and cisplatin-resistant human cervical tumour cells

The significance of reduced drug accumulation in resistance to cisplatin was investigated by using cisplatin, oxaliplatin and JM216 (hydrophobicity rank: JM216>oxaliplatin>cisplatin) in human squamous cell carcinoma cell line A431 and its cisplatin-resistant counterpart A431/Pt. While cisplatin showed a resistance factor of 2.6, oxaliplatin and JM216 circumvented the resistance. Platinum accumulation after cisplatin exposure was lower (2.4-fold) in A431/Pt than in A431 cells, whereas a similar accumulation was found in the two cell lines when oxaliplatin or JM216 were used, thereby suggesting the capability of the latter drugs to bypass the accumulation defect. In the A431 cell line platinum accumulated to a similar extent after exposure to cisplatin, oxaliplatin or JM216, while in A431/Pt cells, Platinum accumulation depended on the hydrophobicity of the drug, and an increased hydrophobicity favours the uptake. No difference in efflux of cisplatin was found between the two cell lines. The values of platinum-DNA binding in A431 cells were similar for cisplatin and JM216 and higher than those of oxaliplatin. In A431/Pt cells: (i) Pt-DNA binding levels of JM216 remained as in sensitive ones; (ii) Pt-DNA levels of cisplatin and oxaliplatin were very similar and nearly two-fold lower than those of JM216. Such results, in this cell system characterized by a low level of cisplatin resistance, support a model whereby platinum uptake occurs by a mechanism of facilitated diffusion, perhaps involving a gated channel, which can be lost during the selection of the drug-resistant variant(s). The hydrophobicity of the drug can be the key to bypass resistance.

Novel mechanisms of platinum drug resistance identified in cells selected for resistance to JM118 the active metabolite of satraplatin

PURPOSE

The goal of this study was to identify molecular determinants of sensitivity and resistance to JM118, the active metabolite of satraplatin, an orally bioavailable cisplatin analog that has activity in prostate cancer.

EXPERIMENTAL DESIGN

Human ovarian carcinoma 2008/JM118 cells were derived from parental 2008 cells by repeated exposure to JM118; the revertant 2008/JM118/REV subline was isolated from the 2008/JM118 cells by growth in the absence of drug. Drug sensitivity was determined by clonogenic assay and Pt levels were measured by ICP-MS.

RESULTS

Eight sequential rounds of selection yielded the 2008/JM118 subline that was 4.9-fold resistant to JM118 and cross-resistant at varying levels to satraplatin, cisplatin, carboplatin, and oxaliplatin. Cross-resistance to the other Pt drugs was lost as resistance to JM118 waned. The same parental 2008 cells selected for resistance to cisplatin were partially cross-resistant to JM118. The 2008/JM118 cells accumulated significantly more Pt than the 2008 cells when exposed to low concentrations of either JM118 or cisplatin indicating a detoxification process that involves intracellular sequestration. In contrast, 2008 cells selected for cisplatin resistance accumulated less cisplatin and less JM118 reflecting a mechanism involving reduced accumulation. The 2008 and 2008/JM118 cells did not differ in their uptake or efflux of 64Cu, expression of Cu efflux transporters ATP7A or ATP7B or their glutathione content. The 2008/JM118 cells exhibited 3.0-7.7-fold hypersensitivity to docetaxel, paclitaxel and doxorubicin. Expression profiling identified 4 genes that were significantly up-regulated and 19 that were down-regulated in the 2008/JM118 cells at a false discovery rate of 1 gene.

CONCLUSIONS

While the cellular defense mechanisms that protect cells against JM118 also mediate resistance to the other Pt drugs, these mechanisms are quite different from those commonly found in cells selected for resistance to cisplatin. JM118-resistant cells accumulate more rather than less Pt and rely on an intracellular detoxification mechanism different from that involved in cisplatin resistance. This is consistent with clinical evidence suggesting that satraplatin has activity in diseases in which cisplatin does not. In this model, JM118 resistance is associated with substantial collateral hypersensitivity to docetaxel, paclitaxel, and doxorubicin.

Characterization of a clonal isolate of an oxaliplatin resistant ovarian carcinoma cell line A2780/C10

A single cell clonal sub-line A2780/C10B that is 18-fold resistant to oxaliplatin and approximately threefold cross-resistant to cisplatin and exhibiting a metastasis associated cellular phenotype was characterized for mechanisms of resistance. The cell line exhibited a 50% reduction in the accumulation of both oxaliplatin and cisplatin relative to the parent line, while extensive decline in Pt-DNA adduct levels occurred only following oxaliplatin treatment. The basal GSH levels were fivefold higher in A2780/C10B compared to A2780 and had a fivefold elevation in gamma-GT suggesting this may be the mechanism involved in GSH elevation. The basal levels of ERCC-1, XPA and MRP-2 mRNA levels in A2780/C10B were not higher than those in A2780. The highly reduced Pt-DNA adduct formation only for oxaliplatin, but not cisplatin may be a reflection of the fact that at equimolar concentrations oxaliplatin makes fewer Pt-DNA adducts than cisplatin. The data indicate that multiple lesions occur in a single cell to produce the resistant phenotype.

Identification of genes whose expression is associated with cisplatin resistance in human ovarian carcinoma cells

The goal of this study was to identify genes consistently differentially expressed in multiple pairs of isogenic cisplatin (DDP)-sensitive and resistant human ovarian carcinoma cell lines using microarray-based expression profiling. Expression profiling was carried out on six pairs of ovarian carcinoma cells lines growing under identical conditions; each cell expression profile was independently replicated six times. No genes were differentially expressed in all six pairs of cells or even in even in any five of the six pairs. Eighteen genes and 1 EST were upregulated, and four genes and 1 EST were downregulated, in at least four cell pairs. Of these, only metallothionein 2A has previously been implicated in DDP resistance. Among the genes identified on the basis of six replicates, an average of 24.8% would have been missed if only five replicates had been performed, and 38.3% would have been missed with only four replicates. The genes did not identify a dominant biochemical pathway or ontology category as being linked to DDP resistance; however, hierarchical clustering provided evidence for two classes DDP-resistant phenotypes within which there are additional cell pair-specific alterations. Many of the genes identified in this study play important roles in cell surface interactions and trafficking pathways not previously linked to DDP resistance. The genes discovered by this extensively replicated analysis are candidates for prediction of DDP responsiveness in ovarian cancer patients.

Oxaliplatin induces drug resistance more rapidly than cisplatin in H69 small cell lung cancer cells

Cisplatin produces good responses in solid tumours including small cell lung cancer (SCLC) but this is limited by the development of resistance. Oxaliplatin is reported to show activity against some cisplatin-resistant cancers but there is little known about oxaliplatin in SCLC and there are no reports of oxaliplatin resistant SCLC cell lines. Studies of drug resistance mainly focus on the cellular resistance mechanisms rather than how the cells develop resistance. This study examines the development of cisplatin and oxaliplatin resistance in H69 human SCLC cells in response to repeated treatment with clinically relevant doses of cisplatin or oxaliplatin for either 4 days or 2 h. Treatments with 200 ng/ml cisplatin or 400 ng/ml oxaliplatin for 4 days produced sublines (H69CIS200 and H69OX400, respectively) that showed low level (approximately two-fold) resistance after eight treatments. Treatments with 1,000 ng/ml cisplatin or 2,000 ng/ml oxaliplatin for 2 h also produced sublines, however, these were not stably resistant suggesting shorter treatment pulses of drug may be more effective. Cells survived the first five treatments without any increase in resistance, by arresting their growth for a period and then regrowing. The period of growth arrest was reduced after the sixth treatment and the H69CIS200 and H69OX400 sublines showed a reduced growth arrest in response to cisplatin and oxaliplatin treatment suggesting that 'regrowth resistance' initially protected against drug treatment and this was further upregulated and became part of the resistance phenotype of these sublines. Oxaliplatin dose escalation produced more surviving sublines than cisplatin dose escalation but neither set of sublines were associated with increased resistance as determined by 5-day cytotoxicity assays, also suggesting the involvement of regrowth resistance. The resistant sublines showed no change in platinum accumulation or glutathione levels even though the H69OX400 subline was more sensitive to buthionine sulphoximine treatment. The H69CIS200 cells were cross-resistant to oxaliplatin demonstrating that oxaliplatin does not have activity against low level cisplatin resistance. Relative to the H69 cells, the H69CIS200 and H69OX400 sublines were more sensitive to paclitaxel and taxotere suggesting that the taxanes may be useful in the treatment of platinum-resistant SCLC. These novel cellular models of cisplatin and oxaliplatin resistant SCLC will be useful in developing strategies to treat platinum-resistant SCLC.

Identification of non-cross-resistant platinum compounds with novel cytotoxicity profiles using the NCI anticancer drug screen and clustered image map visualizations

The widespread clinical use of platinum compounds in cancer chemotherapy has prompted a search for new platinum agents. To search for platinum agents with novel profiles of activity, we used clustered image maps, the COMPARE algorithm, and other numerical methods to analyze platinum compounds submitted to the National Cancer Institute's anticancer drug screen and tested against the screen's 60 diverse human cancer cell lines (the NCI-60). A total of 107 platinum compounds for which the data were adequate could be clustered into 12 groups, 11 of which were characterized by distinctive activity profiles against the cell lines. Each group (except the mixed one) was then found to have a characteristic chemical structure as well. Four of the groups were subjected to further analysis. Mean graph representations of the averaged activity profiles of the different groups served to highlight their similarities and differences. To identify compounds that might retain activity in the setting of resistance to clinically used platinum compounds, we determined the activity levels of 38 of the compounds (representative of the different activity-structure groups) against cisplatin and oxaliplatin-resistant ovarian cancer cell lines. Many of the compounds retained activity against the resistant cells, providing evidence that they differ from cisplatin and oxaliplatin, not only in their selective activity against the various NCI-60 cell types, but are also in their susceptibility to mechanisms of resistance. Since platinum compounds have generally been classified as alkylating agents, we also compared their patterns of activity with those of representative alkylating agents, with NCI-60 growth rates, and with the profiles of 1582 molecular markers in the NCI-60 cells. Much more analysis remains to be done, but the absence of any definitive, biologically interpretable molecular predictor of activity is consistent with the idea that platinum compounds have multiple intracellular targets and that cells can have multiple mechanisms of resistance.

Increased expression of the copper efflux transporter ATP7A mediates resistance to cisplatin, carboplatin, and oxaliplatin in ovarian cancer cells

PURPOSE

The goal of this study was to determine the effect of small changes in ATP7A expression on the pharmacodynamics of cisplatin, carboplatin, and oxaliplatin in human ovarian carcinoma cells.

EXPERIMENTAL DESIGN

Drug sensitivity and cellular pharmacology parameters were determined in human 2008 ovarian carcinoma cells and a subline transfected with an ATP7A-expression vector ATP7A (2008/MNK). Drug sensitivity was determined by clonogenic assay, platinum (Pt) levels were measured by inductively coupled plasma mass spectroscopy, copper (Cu) accumulation was quantified with (64)Cu, and the subcellular distribution of ATP7A was assessed by confocal digital microscopy.

RESULTS

The 1.5-fold higher expression of ATP7A in the 2008/MNK cells was sufficient to alter Cu cellular pharmacokinetics but not confer Cu resistance. In contrast, it was sufficient to render the 2008/MNK cells resistant to cisplatin, carboplatin, and oxaliplatin. Resistance was associated with increased rather than decreased whole-cell Pt drug accumulation and increased sequestration of Pt into the vesicular fraction. Cu triggered relocalization of ATP7A away from the perinuclear region, whereas at equitoxic concentrations the Pt drugs did not.

CONCLUSIONS

A small increase in ATP7A expression produced resistance to all three of the clinically available Pt drugs. Whereas increased expression of ATP7A reduced Cu accumulation, it did not reduce accumulation of the Pt drugs. Under conditions where Cu triggered ATP7A relocalization, the Pt drugs did not. Thus, although ATP7A is an important determinant of sensitivity to the Pt drugs, there are substantial differences between Cu and the Pt drugs with respect to how they interact with ATP7A and the mechanism by which ATP7A protects the cell.

cDNA microarray-based identification of genes and pathways associated with oxaliplatin resistance

In order to identify genes whose expression is associated with resistance to the chemotherapeutic agent oxaliplatin, transcripts differentially expressed between an oxaliplatin sensitive and a stably resistant subline were compared in six independent replicates using Stanford cDNA microarrays for five cell lines. "Significance analysis of microarrays" (SAM) was used to identify genes whose expression was statistically significantly different in the sensitive versus resistant members of each cell line pair. The biochemical pathways of the Kyoto Encyclopedia of Genes and Genomes (KEGG) database were searched to identify those pathways in which the number of SAM-identified genes exceeded the number expected. This identified four pathways in which upregulated genes were significantly associated with resistance in two of the cell line pairs, and two pathways in which the association was found in three cell line pairs. The search also identified 12 pathways in which downregulated genes were associated with resistance in two cell line pairs and one pathway in which the association reached statistical significance in three cell line pairs. Pathways identified included the ribosome pathway, the Huntington's disease pathway that includes caspase 8, and the ATP synthesis pathways. Determination of the chromosomal location of each SAM-identified gene revealed several locales within which genes lay in close proximity, including three genes (APACD, IF-2, and REV1L) located on chromosome 2 that lie immediately adjacent to each other and were significantly upregulated in three of five cell line pairs. Biochemical pathway and chromosomal mapping of genes identified by SAM as differentially expressed in related cell line pairs points to mechanisms and chromosomal sites not previously suspected of association with the oxaliplatin-resistant phenotype.

Oxaliplatin-induced mitochondrial apoptotic response of colon carcinoma cells does not require nuclear DNA

We previously established a model of acquired oxaliplatin resistance derived from the HCT116 oxaliplatin-sensitive cell line (HCT116S) and consisting in two resistant clones (HCT116R1, HCT116R2) and their total or partial revertants (HCT116Rev1 and HCT116Rev2, respectively). Using this cellular model, we explored the contribution of mitochondrial apoptosis and nuclear DNA to oxaliplatin-mediated apoptosis induction and oxaliplatin resistance. We showed that the activity of oxaliplatin is mediated by the induction of Bax/Bak-dependent mitochondrial apoptosis and that oxaliplatin resistance is mediated by a defect in Bax/Bak activation correlating with a reduced loss of the mitochondrial transmembrane potential (DeltaPsim). In addition, we observed that p53 only contributed marginally to oxaliplatin-induced cytotoxicity and was not involved in oxaliplatin resistance. Moreover and surprisingly, depletion of the nucleus in HCT116S cells did not abolish the oxaliplatin-induced DeltaPsim loss indicative of imminent apoptosis. Enucleation abolished the oxaliplatin resistance of HCT116R1 cells, while HCT116R2 cytoplasts conserved their resistant phenotype. Altogether, these data demonstrate that oxaliplatin exerts its cytotoxic effects by inducing mitochondrial apoptosis and that these effects can be initiated by interacting on other cellular structures than nuclear DNA. Resistance to oxaliplatin may imply both nuclear and cytoplasmic compartments.

Uptake of antitumor platinum(II)-complexes by cancer cells, assayed by inductively coupled plasma mass spectrometry (ICP-MS)

A systematic study on intracellular Pt uptake and Pt accumulation ratio in breast cancer MCF-7 cell line has been performed on a number of Pt(II)-complexes, namely cisplatin, carboplatin and oxaliplatin, clinically employed as antitumor drugs, trans- and cis-[Pt(Cl)2(pyridine)2] and cis-[Pt(Cl)2(pyridine)(5-SO3H-isoquinoline)] complexes, previously investigated also as potential telomerase inhibitors. In particular, long incubation times have been chosen in order to understand the fate of the complexes in the cells. For this purpose, sub-acute drug concentrations must be employed and, therefore, a very sensitive method of analysis like as inductively coupled plasma mass spectrometry (ICP-MS) superior to the widely employed atomic absorption spectroscopy (AAS) has been adopted. Any relationships among uptake/accumulation and several parameters such as drug structure, lipophilicity, drug concentration and incubation time have been sought and analyzed: the bulk of data point for a passive diffusion mechanism through the cell membrane.

Molecular Determinants of the Cytotoxicity of Platinum Compounds

Gene expression profiling of tumors allows the establishment of relationships between gene expression profiles and sensitivity to anticancer drugs. In an attempt to study the molecular determinants of the activity of platinum compounds, we explored the publicly available databases of the National Cancer Institute (NCI; http://dtp.nci.nih.gov), which allow access to the gene expression profiles of the 60 cell lines for which drug cytotoxicity patterns already existed. Using this database, we have conducted an in silico research to identify the genes the expression of which was positively or negatively correlated to the sensitivity to four platinum compounds (cisplatin, carboplatin, oxaliplatin and tetraplatin). Important similarities were noticed between cisplatin and carboplatin on one hand, and tetraplatin and oxaliplatin on the other hand. In the restricted panel of 1416 genes and molecular markers, we identified 204 markers, among which 120 corresponded to identified genes, that significantly correlated (P < 0.001) with the cytotoxicity of at least one platinum compound. For example, the functionality of the p53-activated pathway appeared positively correlated with the cytotoxicity of all platinum compounds. More specific are the positive correlations between RAS gene mutations and MYC expression and the cellular sensitivity to oxaliplatin. Among the parameters already known as related to the sensitivity to platinum compounds, we identified, in the complete set of 9400 genes, numerous significant relationships, such as the negative correlations between ERB-B2 and BCL-X(L) expressions and the cytotoxicity of the platinum compounds. Public databases mining, therefore, appears to be a valuable tool for the identification of determinants of anticancer drug activity in tumors.