KiSS-1 Modulation by Epigenetic Agents Improves the Cisplatin Sensitivity of Lung Cancer Cells.

Epigenetic alterations my play a role in the aggressive behavior of Non-Small Cell Lung Cancer (NSCLC). Treatment with the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA, vorinostat) has been reported to interfere with the proliferative and invasive potential of NSCLC cells. In addition, the DNA methyltransferase inhibitor azacytidine (AZA, vidaza) can modulate the levels of the metastasis suppressor KiSS-1. Thus, since cisplatin is still clinically available for NSCLC therapy, the aim of this study was to evaluate drug combinations between cisplatin and SAHA as well as AZA using cisplatin-sensitive H460 and -resistant H460/Pt NSCLC cells in relation to KiSS-1 modulation. An analysis of drug interaction according to the Combination-Index values indicated a more marked synergistic effect when the exposure to SAHA or AZA preceded cisplatin treatment with respect to a simultaneous schedule. A modulation of proteins involved in apoptosis (p53, Bax) was found in both sensitive and resistant cells, and compared to the treatment with epigenetic agents alone, the combination of cisplatin and SAHA or AZA increased apoptosis induction. The epigenetic treatments, both as single agents and in combination, increased the release of KiSS-1. Finally, the exposure of cisplatin-sensitive and -resistant cells to the kisspeptin KP10 enhanced cisplatin induced cell death. The efficacy of the combination of SAHA and cisplatin was tested in vivo after subcutaneous inoculum of parental and resistant cells in immunodeficient mice. A significant tumor volume inhibition was found when mice bearing advanced tumors were treated with the combination of SAHA and cisplatin according to the best schedule identified in cellular studies. These results, together with the available literature, support that epigenetic drugs are amenable for the combination treatment of NSCLC, including patients bearing cisplatin-resistant tumors.

PKC-alpha modulation by miR-483-3p in platinum-resistant ovarian carcinoma cells.

The occurrence of drug resistance limits the efficacy of platinum compounds in the cure of ovarian carcinoma. Since microRNAs (miRNAs) may contribute to this phenomenon by regulating different aspects of tumor cell response, the aim of this study was to exploit the analysis of expression of miRNAs in platinum sensitive/resistant cells in an attempt to identify potential regulators of drug response. MiR-483-3p, which may participate in apoptosis and cell proliferation regulation, was found up-regulated in 4 platinum resistant variants, particularly in the IGROV-1/Pt1 subline, versus parental cells. Transfection of a synthetic precursor of miR-483-3p in IGROV-1 parental cells elicited a marked up-regulation of the miRNA levels. Growth-inhibition and colony-forming assays indicated that miR-483-3p over-expression reduced cell growth and conferred mild levels of cisplatin resistance in IGROV-1 cells, by interference with their proliferative potential. Predicted targets of miR-483-3p included PRKCA (encoding PKC-alpha), previously reported to be associated to platinum-resistance in ovarian carcinoma. We found that miR-483-3p directly targeted PRKCA in IGROV-1 cells. In keeping with this finding, cisplatin sensitivity of IGROV-1 cells decreased upon molecular/pharmacological inhibition of PKC-alpha. Overall, our results suggest that overexpression of miR-483-3p by ovarian carcinoma platinum-resistant cells may interfere with their proliferation, thus protecting them from DNA damage induced by platinum compounds and ultimately representing a drug-resistance mechanism. The impairment of cell growth may account for low levels of drug resistance that could be relevant in the clinical setting.

Antitumor activity of a novel homodimeric SMAC mimetic in ovarian carcinoma.

Treatment of ovarian carcinoma often fails to be curative because of drug resistance, and many efforts are directed to overcome tumor cell resistance by increasing apoptosis induction. The potential of second mitochondria-derived activator of caspases (SMAC) mimetics (SMACm) has appeared in preclinical studies, but novel proapoptotic agents of this class with improved pharmacological profile are needed. To identify novel treatment options for ovarian carcinoma by interfering with antiapoptotic factors, in the present study a novel homodimeric SMACm (SM83) was employed in preclinical models both in vitro and in vivo. An investigation of the structural features of dimeric SM83 as compared to a closely related reference compound indicated slight differences, likely because of the interaction between one of the terminal phenyl groups and triazole rings of SM83 with the BIR2 domain. Although SM83 per se did not inhibit cell proliferation, it displayed a synergistic effect in combination with TNF-related apoptosis inducing ligand (TRAIL) in cell sensitivity assays. Because the tumor microenvironment is a reservoir of cytokines that may act in conjunction with SMACm to affect tumor growth, the activity of the novel compound was tested in vivo in ovarian carcinoma cells subcutaneously xenografted into immunodeficient mice. A significant tumor volume inhibition was observed together with activation of caspase 3 and apoptotic cell death. A biochemical analysis of tumor necrosis factor (TNF) and TRAIL content in specimens from xenografted mice indicated that SM83 downmodulated the levels of human TNF in plasma samples and tended to upmodulate human TRAIL levels in tumors. Thus, TRAIL appears to contribute to the antitumor activity of novel SMACm SM83 in subcutaneously grown ovarian carcinoma. Overall, our results indicate that SM83 is an attractive candidate for further development.

Caffeic acid phenethyl ester targets ubiquitin-specific protease 8 and synergizes with cisplatin in endometrioid ovarian carcinoma cells.

Deubiquitinases (DUBs) mediate the removal of ubiquitin from diverse proteins that participate in the regulation of cell survival, DNA damage repair, apoptosis and drug resistance. Previous studies have shown an association between activation of cell survival pathways and platinum-drug resistance in ovarian carcinoma cell lines. Among the strategies available to inhibit DUBs, curcumin derivatives appear promising, thus we hypothesized their use to enhance the efficacy of cisplatin in ovarian carcinoma preclinical models. The caffeic acid phenethyl ester (CAPE), inhibited ubiquitin-specific protease 8 (USP8), but not proteasomal DUBs in cell-free assays. When CAPE was combined with cisplatin in nine cell lines representative of various histotypes a synergistic effect was observed in TOV112D cells and in the cisplatin-resistant IGROV-1/Pt1 variant, both of endometrioid type and carrying mutant TP53. In the latter cells, persistent G1 accumulation upon combined treatment associated with p27kip1 protein levels was observed. The synergy was not dependent on apoptosis induction, and appeared to occur in cells with higher USP8 levels. In vivo antitumor activity studies supported the advantage of the combination of CAPE and cisplatin in the subcutaneous model of cisplatin-resistant IGROV-1/Pt1 ovarian carcinoma as well as CAPE activity on intraperitoneal disease. This study reveals the therapeutic potential of CAPE in cisplatin-resistant ovarian tumors as well as in tumors expressing USP8.

The deubiquitinase USP8 regulates ovarian cancer cell response to cisplatin by suppressing apoptosis.

The identification of therapeutic approaches to improve response to platinum-based therapies is an urgent need for ovarian carcinoma. Deubiquitinases are a large family of ubiquitin proteases implicated in a variety of cellular functions and may contribute to tumor aggressive features through regulation of processes such as proliferation and cell death. Among the subfamily of ubiquitin-specific peptidases, USP8 appears to be involved in modulation of cancer cell survival by still poorly understood mechanisms. Thus, we used ovarian carcinoma cells of different histotypes, including cisplatin-resistant variants with increased survival features to evaluate the efficacy of molecular targeting of USP8 as a strategy to overcome drug resistance/modulate cisplatin response. We performed biochemical analysis of USP8 activity in pairs of cisplatin-sensitive and -resistant cells and found increased USP8 activity in resistant cells. Silencing of USP8 resulted in decreased activation of receptor tyrosine kinases and increased sensitivity to cisplatin in IGROV-1/Pt1 resistant cells as shown by colony forming assay. Increased cisplatin sensitivity was associated with enhanced cisplatin-induced caspase 3/7 activation and apoptosis, a phenotype also observed in cisplatin sensitive cells. Increased apoptosis was linked to FLIPL decrease and cisplatin induction of caspase 3 in IGROV-1/Pt1 cells, cisplatin-induced claspin and survivin down-regulation in IGROV-1 cells, thereby showing a decrease of anti-apoptotic proteins. Immunohistochemical staining on 65 clinical specimens from advanced stage ovarian carcinoma indicated that 40% of tumors were USP8 positive suggesting that USP8 is an independent prognostic factor for adverse outcome when considering progression free survival as a clinical end-point. Taken together, our results support that USP8 may be of diagnostic value and may provide a therapeutic target to improve the efficacy of platinum-based therapy in ovarian carcinoma.

Increased serum levels of KiSS1-derived peptides in non-small cell lung cancer patient liquid biopsies and biological relevance.

Background: The secreted products of the metastasis suppressor gene KiSS1 may represent useful biomarkers in non-small cell lung cancer (NSCLC) but their levels in patients have remained poorly investigated. We previously found that forced expression of KiSS1 decreased the invasive capability of NSCLC drug-resistant cells and a pro-apoptotic role for KiSS1 has been proposed in head and neck cancer. Thus, we designed a translational investigation including a pilot study to analyze KiSS1 levels in liquid biopsies, and in vitro experiments to explore the biological relevance of KiSS1 modulation. Methods: KiSS1-derived peptide levels in liquid biopsies from 60 NSCLC patients were assayed by ELISA. Preclinical experiments were carried out using quantitative real time polymerase chain reaction (qRT-PCR), ELISA, annexin V-binding and caspase activation assays. Results: We compared KiSS1 release in 3 different matrices (serum, plasma and urine) and the highest levels were detectable in serum (range, 0-4.5 ng/mL). We observed increased levels of seric KiSS1 in NSCLC patients as compared to healthy donors. KiSS1 serum concentrations, after surgical procedure and/or adjuvant therapy. We observed differences among disease stages in urine samples. In preclinical models, KiSS1 mRNA levels were increased by short term exposure to azacytidine, enhanced KiSS1 release was induced by the combination of azacytidine and cisplatin and KiSS1-derived peptides enhanced cisplatin-induced apoptosis. KiSS1 increase was observed upon exposure neurons-enriched cultures to tumor cell conditioned medium. Conclusions: Our results showing a peculiar modulation of KiSS1 levels in liquid biopsies of NSCLC patients and a regulation of cisplatin-induced apoptosis by KiSS1-derived peptides support an involvement of KiSS1 in cell response to treatment and highlight its promising features as a potential biomarker in NSCLC.

Proteomic analysis of cellular response to novel proapoptotic agents related to atypical retinoids in human IGROV-1 ovarian carcinoma cells.

Novel agents characterized by the scaffold of the atypical retinoid ST1926, but containing different chemical functions (carboxylic or hydroxamic acid), exhibit potent proapoptotic activity. In the present paper, we show that the treatment of the IGROV-1 ovarian cancer cell line with compounds sharing structural features with ST1926 (ST1898, ST3595, ST3056) determines a strong inhibition of proliferation mainly due to apoptotic cell death. In an effort to understand the mechanism of action of these compounds, we performed a proteomics analysis of IGROV-1 total lysates and nuclear extracts. Using this approach, we found that deregulation of calcium homeostasis, oxidative stress, cytoskeleton reorganization, and deregulation of proteasome function may represent important pathways involved in response of IGROV-1 cells to the studied compounds. The most prominent effect was down-regulation of factors involved in protein degradation, an event more marked in cells treated with ST3595. In addition, we identified proteins specifically modulated by each treatment, including prohibitin and cochaperone P23 (ST1898), pre-mRNA splicing factor SF2p32 and clathrin light chain (ST3595), as well as Far upstream element (FUSE) binding protein 1 and DNA-binding protein B (ST3056). By identifying proteins modulated by novel proapoptotic agents, this study provides insights into critical aspects of their mechanism of action.

Deregulated FASN Expression in BRAF Inhibitor-Resistant Melanoma Cells Unveils New Targets for Drug Combinations.

Metabolic changes promoting cell survival are involved in metastatic melanoma progression and in the development of drug resistance. In BRAF-inhibitor resistant melanoma cells, we explored the role of FASN, an enzyme involved in lipogenesis overexpressed in metastatic melanoma. Resistant melanoma cells displaying enhanced migratory and pro-invasive abilities increased sensitivity to the BRAF inhibitor PLX4032 upon the molecular targeting of FASN and upon treatment with the FASN inhibitor orlistat. This behavior was associated with a marked apoptosis and caspase 3/7 activation observed for the drug combination. The expression of FASN was found to be inversely associated with drug resistance in BRAF-mutant cell lines, both in a set of six resistant/sensitive matched lines and in the Cancer Cell Line Encyclopedia. A favorable drug interaction in resistant cells was also observed with U18666 A inhibiting DHCR24, which increased upon FASN targeting. The simultaneous combination of the two inhibitors showed a synergistic interaction with PLX4032 in resistant cells. In conclusion, FASN plays a role in BRAF-mutated melanoma progression, thereby creating novel therapeutic opportunities for the treatment of melanoma.

Novel bis-platinum complexes endowed with an improved pharmacological profile.

Multinuclear platinum complexes are characterized by a peculiar DNA binding mode and higher cytotoxic potency than the mononuclear complexes, and efficacy against a wide range of preclinical tumor models. To reduce the high irreversible plasma protein binding and improve the chemical and metabolic drug stability, novel bis-platinum complexes were designed starting from the parent compound CT-3610. The novel second-generation bis-platinum complexes utilize alkylcarboxylate as leaving groups to improve their pharmacokinetic and pharmacodynamic profiles, thus overcoming the limitations of the previously developed multinuclear compounds. The selected compounds [CT-47518 and CT-47463, respectively (bis-capronate) platinum and (bis-butyrate) platinum], have similar in vitro degradation kinetics in human and murine plasma and, above all, an increased stability when compared to CT-3610, particularly in human plasma. In addition, both compounds exhibited a marked cytotoxic potency as compared with cisplatin and oxaliplatin. Interestingly, they were capable of overcoming resistance mediated by DNA mismatch repair defects in different cellular models. The complexes showed marked antitumor efficacy in Pt-refractory tumor xenografts, with remarkable activity in terms of tumor growth inhibition and tumor growth delay. The improved stability profile in human plasma compared to early bis- and triplatinum complexes together with the marked activity in cellular systems as well as in in vivo models, make CT-47518 and CT-47463 attractive candidates for further development.

Synergistic Interaction of Histone Deacetylase 6- and MEK-Inhibitors in Castration-Resistant Prostate Cancer Cells.

In spite of new knowledge on prostate cancer molecular landscape, this has been only partially translated to the therapeutic setting. The activation of Ras/Mitogen-activated protein kinase (MAPK) signaling plays an important role in progression of prostate cancer in which deregulation of histone deacetylases (HDAC) is frequent. Based on the notion that HDAC inhibitors may reactivate the expression of genes favoring cell response to drugs, the aim of this study was to investigate the interaction between the HDAC6-specific inhibitor ricolinostat (ACY1215) and the MEK-inhibitor selumetinib (AZD6244) to identify effective combinations in prostate cancer models. Using cell lines exhibiting differential activation of survival pathways (PC3, DU145, 22Rv1) and following different treatment schedules, a synergistic interaction was observed in all cell models, the drug combination being particularly effective in 22Rv1 cells. Marginal levels of apoptosis were observed in PC3 cells after combined treatment, whereas higher levels were achieved in DU145 and 22Rv1 cells. RNAi-mediated knockdown of HDAC6 in selumetinib-treated 22Rv1 cells resulted in increased apoptosis. Combined treatment suppressed the constitutively deregulated survival pathways in all cell lines. A decrease of androgen receptor (AR)-dependent gene (KLK2, DUSP1) mRNA levels was observed in 22Rv1 treated cells, associated with increased AR cytoplasmatic expression, suggesting AR signaling down-regulation, not involving Hsp90 acetylation. When a taxane was used in combination with AZD6244 and ACY1215 by a simultaneous schedule, a synergistic cytotoxic effect together with increased apoptosis was evidenced in all cell models. These results support a rational use of targeted agents to improve prostate cancer cell apoptotic response.

Modulation of survival pathways in ovarian carcinoma cell lines resistant to platinum compounds.

Because cytotoxic stress elicits various signaling pathways that may be implicated in cell survival or cell death, their alterations may have relevance in the development of platinum-resistant phenotype. Thus, in the present study, we investigated cell response to the epidermal growth factor receptor (EGFR) inhibitor gefitinib of ovarian carcinoma cell lines, including cells selected for resistance to cisplatin (IGROV-1/Pt1) and oxaliplatin (IGROV-1/OHP). Resistant sublines exhibited a marked decrease in sensitivity to gefitinib and resistance to apoptosis. Gefitinib was capable of inhibiting the phosphorylation of EGFR in all the studied cell lines. The Akt and extracellular signal-regulated kinase 1/2 (ERK1/2) kinases, which act downstream of EGFR, were constitutively active in the three cell lines, but phospho-ERK1/2 levels were increased in the two resistant sublines. This feature was associated with reduced sensitivity to the MEK1/2 inhibitor U0126. Pretreatment of resistant cells with U0126 resulted in restoration of sensitivity to gefitinib. Gefitinib was more effective in inhibiting ERK1/2 and Akt phosphorylation in IGROV-1 cells than in IGROV-1/OHP and IGROV-1/Pt1 cells. Phospho-p38 was up-regulated in the resistant sublines, indicating the concomitant activation of distinct mitogen-activated protein kinases. The up-regulation of phospho-p38 was associated with a peculiar localization of EGFR, which, in resistant sublines, was mainly internalized. In conclusion, our results indicate that the development of resistance to platinum drugs is associated with multiple alterations including deregulation of survival pathways activated by EGFR resulting in a reduced cellular response to gefitinib.

AXL Downstream Targeting Unravels Synergistic Drug Combinations in Ovarian Carcinoma Cells.

BACKGROUND: Platinum-based therapy represents the main pharmacological treatment for ovarian carcinoma. Since molecular targeting of receptor tyrosine kinases (RTK) affects factors that may modulate drug response, the aim of this study was to examine whether downstream targets of AXL RTK could be exploited to improve cell response to cisplatin. MATERIALS AND METHODS: Inhibitors of p38 (SB203580) and of signal transducer and activator of transcription 3 (stattic) were employed in combination with cisplatin in ovarian carcinoma cell lines. Apoptosis assay and western blot analysis were performed to evaluate cell response after treatment. RESULTS: SB203580 produced a synergistic effect in combination with cisplatin in cisplatin-resistant IGROV-1/Pt1 cells. In addition, a favorable drug interaction was observed in A2780 cells when pre-incubated with cisplatin prior to stattic. The analysis of cell response after combined treatment showed down-regulation of the pro-apoptotic protein BCL2-associated agonist of cell death (BAD). CONCLUSION: Our results support the notion that downstream targets of AXL in ovarian carcinoma cells can be exploited to increase cisplatin activity in ovarian carcinoma models.

The human homolog of fission yeast Rad17 is implicated in tumor growth.

The Schizosaccharomyces pombe rad17 is a checkpoint protein critical for maintenance of genomic stability. Since the loss of checkpoint control is a common feature of tumor cells, we investigated the biological function of the human homolog hRAD17. Expression of hRAD17 in a fission yeast rad17 deleted strain reduced growth of yeast colonies and caused slower progression through cell cycle. Immunoprecipitated hRad17 exhibited exonuclease activity. hRAD17 delayed growth of NIH3T3 fibroblasts transformed by the H-ras oncogene in nude mice. Our results support that hRAD17, similarly to other human genes involved in checkpoint mechanisms, plays a role in control of tumor growth.

Molecular alterations of cells resistant to platinum drugs: role of PKCalpha.

Development of resistance to platinum compounds may involve not only overexpression of defence mechanisms but also alterations in cellular response to the drug-induced genotoxic stress. To investigate the cellular bases of response to platinum compounds, we examined the profile of gene expression of ovarian carcinoma cells exhibiting sensitivity (A2780) or resistance (A2780/BBR3464) to platinum compounds. Using display PCR, we found that acquisition of resistance to the multinuclear platinum complex BBR3464 was associated with modulation of several transcripts, including up-regulation of the major substrate of protein kinase C (PKC), the myristoylated alanine-rich C kinase substrate (MARCKS). This feature was associated with PKCalpha down-regulation. To explore the role of PKCalpha in cellular sensitivity to platinum compounds, resistant cells were transfected with a PKCalpha-containing vector. PKCalpha-overexpressing resistant cells exhibited a decrease in sensitivity to cisplatin, whereas no significant change in sensitivity to BBR3464 was observed. A number of approaches designed to modulate the function or expression of PKCalpha support that the isoenzyme may play a role in determining resistance only to cisplatin but not to BBR3464, which is known to activate a different pathway of cell response. In conclusion, in spite of PKCalpha down-regulation in our model, its regulatory function was not apparently implicated in the development of resistance to platinum compounds and the present results do not support a general role of PKCalpha as a determinant of the resistance status.

Sensitization to gimatecan-induced apoptosis by tumor necrosis factor-related apoptosis inducing ligand in prostate carcinoma cells.

Since the intrinsic resistance of prostate carcinoma likely reflects a low susceptibility to drug-induced apoptosis, in this study we explored the possibility of sensitizing prostate carcinoma cells to apoptosis by combination of TRAIL with camptothecins. Indeed, these agents are known to activate different pathways of apoptosis. Topotecan- and gimatecan induced moderate up-regulation of TRAIL-R1 and -R2 which resulted in a different cell response to the combination in androgen-independent cells (DU-145 and PC-3). In DU-145 cells apoptosis was increased by lower TRAIL concentrations and was earlier than in PC-3 cells, as shown using Annexin V-binding assay. The relative resistance of PC-3 cells to drug-induced apoptosis was associated with constitutive Akt activation, higher levels of cFLIP-L and Bcl-2, and lower levels of Bax. The different expression/activation of apoptosis-related factors appears to influence the sensitization of prostate carcinoma cells by TRAIL. Potentiation of camptothecin-induced apoptosis by TRAIL appears dependent on cooperation between extrinsic and intrinsic pathways, as documented by loss of the sensitization to apoptosis following reduction of caspase 8 after small interfering RNA transfection. The efficacy of the approach may be critically dependent on the intrinsic susceptibility to apoptosis of different tumors. These observations support that the activation of multiple signals could enhance apoptotic response and suggest the therapeutic interest of the TRAIL/camptothecin combination.

Targeting peptidyl-prolyl isomerase pin1 to inhibit tumor cell aggressiveness.

PURPOSE: Because the peptidyl-prolyl isomerase PIN1 interacts with multiple protein kinases and phosphoproteins into a network orchestrating the cellular response to various stimuli, there is an increasing interest in exploiting its potential as therapeutic target. In the present study, the effect of targeting PIN1 was investigated in 2 human cancer cell lines characterized by increased aggressive potential, high expression of erbB receptor family members, and defective p53. METHODS: PIN1 silencing was carried out in skin squamous cell carcinoma A431 cells displaying elevated EGFR/HER1 levels and in ovarian adenocarcinoma SKOV-3 cells displaying high levels of erbB2 (HER2). Nonoverlapping siRNA duplexes targeting different regions of PIN1 mRNA were transfected in tumor cells, which were analyzed using Western blotting for the expression of selected proteins. In vivo tumorigenicity studies were carried out in athymic nude mice. RESULTS: A431 and SKOV-3 cell systems were found to be a source of cells with increased aggressive potential, i.e., cancer stem cell-like cells, as defined by the capability to grow as spheres. A marked decrease of PIN1 levels and of sphere-forming capability was observed in PIN1-silenced cells. The expression of phospho-p38 decreased following PIN1 silencing in A431 and SKOV-3 cells, as well as phospho-EGFR levels in A431 - silenced cells. PIN1 inhibition prolonged latency and reduced tumor take and growth of SKOV-3 cells in nude mice. CONCLUSIONS: Our results support that PIN1 may be a valuable target to hit in cancer cells characterized by increased aggressive potential, overexpression of erbB receptor family members, and defective p53.

Cellular basis of antiproliferative and antitumor activity of the novel camptothecin derivative, gimatecan, in bladder carcinoma models.

To investigate the cellular/molecular basis of the activity of a novel lipophilic camptothecin, gimatecan (ST1481), against slowly proliferating cells, we performed a comparative study of topotecan and gimatecan in human bladder cancer models (HT1376 and MCR). Gimatecan was significantly more effective than topotecan in inhibiting the growth of HT1376 tumor, thus reflecting antiproliferative potency. In both HT1376 and MCR cells, gimatecan caused a persistent S-phase arrest, indicating an efficient DNA damage checkpoint. This response was consistent with a cytostatic effect, because no evidence of apoptosis was detected. In contrast to gimatecan, topotecan at equitoxic concentrations caused an early and persistent downregulation of topoisomerase I. Modulation of protein level could not be solely ascribed to the proteasome-mediated degradation of the enzyme because the proteasome inhibitor PS341 sensitized MCR but not HT1376 cells to camptothecins, suggesting alternative mechanisms of drug-induced topoisomerase I downregulation. Indeed, the two camptothecins caused a differential inhibition of topoisomerase I transcription, which is more marked in topotecan-treated cells. The HT1376 model was more sensitive to this immediate decrease of mRNA level. Our data document a marked antitumor activity of gimatecan against a bladder carcinoma model. A limited downregulation of topoisomerase I by gimatecan provides additional insights into the cellular basis of drug potency.

Cellular pharmacology of cisplatin in relation to the expression of human copper transporter CTR1 in different pairs of cisplatin-sensitive and -resistant cells.

The molecular mechanism of cisplatin uptake remains poorly defined and impaired drug accumulation may be implicated in the acquisition of resistance to cisplatin. Thus, we used cell lines of different tumor types (ovarian carcinoma A2780 and IGROV-1, osteosarcoma U2-OS, cervix squamous cell carcinoma A431) and stable cisplatin-resistant sublines, exhibiting variable levels of resistance (between 2.5 and 18.4), to investigate the mechanisms of cellular accumulation of cisplatin. Among the resistant lines we found that reduced cisplatin uptake was a common feature and ranged between 23 and 76%. In an attempt to examine the role of human copper transporter 1 (CTR1) in cisplatin accumulation by human cells, we selected the well characterized A431 cell line and the resistant variant A431/Pt. As compared with A431/Pt cells, A431/Pt transfectants overexpressing CTR1 (3.4-fold) exhibited increased uptake of copper, thereby supporting the expression of a functional transporter. However, no changes in cisplatin uptake and cellular sensitivity to drug were observed. Also overexpression of CTR1 in A431 cells did not produce modulation of cisplatin accumulation. An analysis of the expression of other factors that could affect drug accumulation indicated that A431/Pt cells displayed increased expression of ATPase, Cu(2+) transporting, alfa polypeptide. In conclusion, our results indicate that the overexpression of a functional CTR1 in a human cell line characterized by impaired cisplatin uptake fails (a) to restore cellular drug accumulation to the level of the parental cell line and (b) to modulate cisplatin sensitivity. Our data are consistent with the interpretation that the defects in cellular accumulation by resistant cells are not mediated by expression of CTR1, that plays a marginal role, if any, in cisplatin transport.

Fas/CD95-mediated apoptosis in human glioblastoma cells: a target for sensitisation to topoisomerase I inhibitors.

The expression of the death receptor Fas/CD95 is cell type-specific and can be modulated by different cytotoxic treatments. In spite of a frequent expression of Fas/CD95 in high-grade gliomas, these tumours are typically refractory to conventional therapy. Using a human glioblastoma cell line (GBM), we explored the possibility of modulating susceptibility to Fas/CD95-mediated apoptosis following cytotoxic treatment. GBM cells were sensitive to the antiproliferative effects of topoisomerase I inhibitors (topotecan and a novel lipophilic analog CPT83) and taxol, less sensitive to cisplatin and, in any case, rather resistant to drug-induced apoptosis. This pattern of cellular response was consistent with p53 mutation. GBM cells expressed low levels of Fas/CD95, which was associated with low susceptibility to antibody-stimulated Fas/CD95-mediated apoptosis. A significant up-regulation of Fas/CD95 expression was detected after exposure to topotecan and CPT83, whereas cisplatin induced a low increase and taxol did not modify Fas/CD95 expression. In addition, after treatment with topoisomerase I inhibitors, the up-regulation of Fas/CD95 resulted in an increased susceptibility of GBM cells to antibody-stimulated Fas/CD95-mediated apoptosis, while no synergistic effects were detected after treatment with cisplatin or taxol. Our data suggest that Fas/CD95 up-regulation can be a common response to DNA damage, whereas sensitisation to Fas/CD95-mediated apoptosis appears to be dependent on the type of DNA damage and on the pathway of cellular response. The observed effects might have important therapeutic implications for the design of novel therapeutic strategies in the treatment of malignant gliomas.

Differential outcome of MEK1/2 inhibitor-platinum combinations in platinum-sensitive and -resistant ovarian carcinoma cells.

Deregulated pro-survival signalling plays a role in ovarian carcinoma drug resistance. Here, we show that cisplatin or oxaliplatin in combination with the MEK1/2 inhibitor CI-1040 resulted in a synergistic effect associated with enhanced apoptotic response in platinum-sensitive cells. The drug combinations were additive in platinum-resistant cells exhibiting increased phospho-ERK1/2, down-regulation of apoptosis-related factors (BAX, PUMA, FOXO1) and of phosphatases inhibiting ERK1/2 (DUSP5, DUSP6). Consistently, FOXO1 knockdown in sensitive cells reduced the efficacy of the combination treatment. Pharmacological targeting of ERK1/2 pathway increases cell sensitivity to platinum compounds by interfering with multiple events, ultimately favouring apoptosis induction in selected molecular backgrounds.