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PURPOSE: The aminoflavone analogue (AF) exhibits antitumor activity in vitro, particularly against neoplastic cells of renal origin. We identified cellular correlates of responsiveness to AF in continuous human tumor renal cell carcinoma lines and in tumor cell isolates, termed renal carcinoma cell strains, from patients with clear cell and papillary renal neoplasms. MATERIALS AND METHODS: In vitro antiproliferative activity of AF was evaluated using the sulforhodamine B protein dye assay. In vivo antitumor activity of the drug was determined in mice bearing xenografts. Covalent binding of AF/metabolite(s) was assessed following exposure of cells to AF for 16 hours. CYP1A1 and CYP1B1 mRNA and apoptosis were quantitated by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. RESULTS: AF produced total growth inhibition in vitro in 3 of 6 human tumor renal cell lines at concentrations of 90 to 400 nM. In vivo treatment of mice bearing xenografts of the Caki-1 renal cell carcinoma, sensitive to AF in vitro, resulted in significant antitumor activity, including tumor-free survivors. Studies in 13 renal cell strains isolated from patients with clear cell (9) or papillary (4) renal cell carcinoma indicated that 3 of 4 papillary strains were sensitive to AF compared with 2 of 9 clear cell strains. AF sensitive renal cell lines and strains exhibited induction of CYP1A1 and CYP1B1 gene expression, increased covalent binding of AF metabolite(s) and apoptosis. CONCLUSIONS: AF has noteworthy antitumor activity against certain human tumor renal cell lines in vitro and in vivo, which correlates with drug metabolism to covalently binding metabolites after CYP1A1 and CYP1B1 gene expression. We hypothesize that it leads to apoptosis induction. AF sensitive renal cell strains are predominantly of the papillary histological type. These results are limited by the small numbers of cell lines and cell strains but they are suggestive of the need for further testing in larger collections of cell strains.

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The fluorinated benzothiazole analogue 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F 203, NSC 703786) is a novel agent with potent and selective antitumour properties and, in the form of its L-lysylamide prodrug Phortress (NSC 710305), is a current candidate for early phase clinical studies. Previous findings have indicated that cytochrome P450 1A1 (CYP1A1) may play a role in the antitumour activity of molecules in the benzothiazole series including the nonfluorinated parent compound 2-(4-amino-3-methylphenyl)benzothiazole (DF 203, NSC 674495) (Kashiyama et al, 1999; Chua et al, 2000; Loaiza-Pérez et al, 2002). In this study, we assessed and verified that a fully functional aryl hydrocarbon receptor (AhR) signalling pathway is a necessary requisite for the induction of efficient cytotoxicity by 5F 203 in MCF-7 wild-type sensitive cells. Drug exposure caused MCF-7 sensitive cells to arrest in G(1) and S phase, and induced DNA adduct formation, in contrast to AhR-deficient AH(R100) variant MCF-7 cells. In sensitive MCF-7 cells, induction of CYP1A1 and CYP1B1 transcription (measured by luciferase reporter assay and real-time reverse transcriptase-polymerase chain reaction (RT-PCR)), and 7-ethoxyresorufin-O-deethylase (EROD) activity was demonstrated, following treatment with 5F 203. In contrast, in resistant AH(R100) cells, drug treatment did not affect CYP1A1 and CYP1B1 transcription and EROD activity. Furthermore, AH(R100) cells failed to produce either protein/DNA complexes on the xenobiotic responsive element (XRE) sequence of CYP1A1 promoter (measured by electrophoretic mobility shift assay) or DNA adducts. The data confirm that activation of the AhR signalling pathway is an important feature of the antitumour activity of 5F 203.

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The rat monoclonal antibody LMR-12 was shown earlier to react with a plasma membrane protein, upregulated in multidrug-resistant cell lines. In this study, we observed distinct LMR-12 staining in 36 out of 55 non-drug-selected tumour cell lines, including melanomas, renal cell-, colon- and lung carcinomas, whereas in other tumour types, such as leukaemia and ovarian cancer, LMR-12 staining was generally low or absent. The cDNA encoding the LMR-12 antigen was isolated from a library of the multidrug-resistant human fibrosarcoma cell line HT1080/DR4 by expression cloning in MOP8 cells. Sequence analysis showed that the LMR-12 antigen is identical to the major histocompatibility complex class I molecule beta 2-microglobulin (beta2-m). The LMR-12/ beta2-m staining results were confirmed by mRNA microarray data from an independent National Cancer Institute study, as well as by newly obtained reverse transcriptase polymerase chain reaction data. Further analysis of the microarray data showed that beta2-m levels closely reflected levels of major histocompatibility complex class I heavy chains and the transporter associated with antigen processing. Since the ABC transporter associated with antigen processing was previously shown to contribute to multidrug-resistance, it may very well be that the observed LMR-12/ beta2-m levels are secondary to (elevated) levels of the transporter associated with antigen processing. A perspective arising from the present study is that drug resistant tumour cells may, by having elevated levels of major histocompatibility complex related molecules, be particular good candidates for alternative therapeutic therapies, such as cytotoxic T cell mediated immune-therapies.

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UCN-01 is undergoing Phase I evaluation and is a candidate for combination strategies in the clinic. UCN-01 has been shown to have a variety of effects on cellular targets and the cell cycle. It has also been reported to sensitize cells to several clinical drugs in vitro, possibly in a manner related to p53 status. Thus, combinations of UCN-01 with a series of clinical agents in variety of cell lines have been investigated in vitro. Certain cell lines demonstrated synergistic interactions with combinations of UCN-01 (20-150 nM) and thiotepa, mitomycin C, cisplatin, melphalan, topotecan, gemcitabine, fludarabine or 5-fluorouracil. In contrast, UCN-01 combinations with the antimitotic agents, paclitaxel and vincristine, or topoisomerase II inhibitors, adriamycin and etoposide, did not result in synergy, only in additive toxicity. Cells with non-functional p53 were significantly more susceptible to the supra-additive effects of certain DNA-damaging agents and UCN-01 combinations, than cells expressing functional p53 activity. In contrast, there was no significant relationship between p53 status and susceptibility to synergy between antimetabolites and UCN-01. The mechanism behind the observed synergy appeared unrelated to effects on protein kinase C or abrogation of the cell cycle in G2. Moreover, increased apoptosis did not fully explain the supradditive response. These data indicate that UCN-01 sensitizes a variety of cell lines to certain DNA-damaging agents (frequently covalent DNA-binding drugs) and antimetabolites in vitro, but the mechanism underlying this interaction remains undefined.

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The Met receptor tyrosine kinase and its ligand, hepatocyte growth factor/scatter factor (HGF/SF), have been implicated in human tumor development and metastasis. HGF/SF induces the expression of urokinase plasminogen activator (uPA) and the uPA receptor (uPAR), important mediators of cell invasion and metastasis. We have developed a cell-based assay to screen for inhibitors of this signaling system using the induction of endogenous uPA and uPAR and the subsequent conversion of plasminogen to plasmin as the biological end point. Assay validation was established using a neutralizing antiserum to HGF/SF and a uPA inhibitor (B428), as well as inhibitors of the MKK-MAPK1/2 pathway, shown previously to be important in the induction of uPA and uPAR. Using this assay, we found several classes of molecules that exhibited inhibition of HGF/SF-dependent plasmin activation. However, we discovered that certain members of the geldanamycin family of anisamycin antibiotics are potent inhibitors of HGF/SF-mediated plasmin activation, displaying inhibitory properties at femtomolar concentrations and nine orders of magnitude below their growth inhibitory concentrations. At nanomolar concentrations, the geldanamycins down-regulate Met protein expression, inhibit HGF/SF-mediated cell motility and invasion, and also revert the phenotype of both autocrine HGF/SF-Met transformed cells as well as those transformed by Met proteins with activating mutations. Thus, the geldanamycins may have important therapeutic potential for the treatment of cancers in which Met activity contributes to the invasive/metastatic phenotype.

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P-glycoprotein-mediated multidrug resistance can be reversed by the action of a group of compounds known as chemosensitizers. The interactions with P-glycoprotein of two novel hydrophobic peptide chemosensitizers (reversins 121 and 205) have been studied in model systems in vitro, and in a variety of MDR1-expressing intact tumor cells. The reversins bound to purified P-glycoprotein with high affinity (77-154 nM), as assessed by a quenching assay using fluorescently labeled purified protein. The peptides modulated P-glycoprotein ATPase activity in Sf9 insect cell membranes expressing human MDR1, plasma membrane vesicles from multidrug-resistant cells, and reconstituted proteoliposomes. Both peptides induced a large stimulation of ATPase activity; however, higher concentrations, especially of reversin 205, led to inhibition. This pattern was different from that of simple linear peptides, and resembled that of chemosensitizers such as verapamil. In both membrane vesicles and reconstituted proteoliposomes, 1-2 microM reversins were more effective than cyclosporin A at blocking colchicine transport. Reversin 121 and reversin 205 restored the uptake of [3H]daunorubicin and rhodamine 123 in MDR1-expressing cells to the level observed in the drug-sensitive parent cell lines, and also effectively inhibited the extrusion of calcein acetoxymethyl ester from intact cells. In cytotoxicity assays, reversin 121 and reversin 205 eliminated the resistance of MDR1-expressing tumor cells against MDR1-substrate anticancer drugs, and they had no toxic effects in MDR1-negative control cells. We suggest that peptides of the reversin type interact with the MDR1 protein with high affinity and specificity, and thus they may be good candidates for the development of MDR1-modulating agents to sensitize drug resistance in cancer.

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PURPOSE: Increasing use of paclitaxel in clinical oncology has stimulated interest in its mechanisms of resistance and ways to overcome these. Studies were performed with paclitaxel to determine the role of P-glycoprotein in drug sensitivity, and the effect of schedule on relative resistance. We have previously reported that prolonged exposure to P-glycoprotein substrates decreases relative resistance in multidrug resistant cells. METHODS: Using both unselected and drug-selected cell lines, cross-resistance and cytotoxicity reversal studies using cyclosporin A were performed. In multidrug-resistant cells, cross-resistance was evaluated after 3-, 24-, and 96-h exposures to paclitaxel. RESULTS: Cross-resistance to paclitaxel in P-glycoprotein-expressing sublines was shown to be comparable to that of other drugs transported by P-glycoprotein. Sensitivity to paclitaxel could be modulated by cyclosporin A in unselected cell lines expressing P-glycoprotein and not in P-glycoprotein-negative cell lines. Resistance to paclitaxel was reduced tenfold by increasing the duration of exposure in P-glycoprotein-expressing cells. This effect was not observed in a paclitaxel-resistant cell line which does not express P-glycoprotein. CONCLUSIONS: These studies extend observations on the schedule dependence of paclitaxel cytotoxicity and the role of P-glycoprotein in mediating paclitaxel sensitivity. The schedule dependence of relative resistance suggests that infusional paclitaxel may help in overcoming P-glycoprotein-mediated resistance.

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Reversal of drug resistance offers the hope of increasing the efficacy of conventional chemotherapy. We tested dexverapamil as a P-glycoprotein antagonist in combination with EPOCH chemotherapy in refractory non-Hodgkin's lymphoma. In a cross-over design, dexverapamil was added to EPOCH after disease stabilization or progression occurred. Objective responses were observed in 10 of 41 assessable patients. Biopsies for mdr-1 were obtained before EPOCH treatment and at the time of cross-over to dexverapamil. Levels of mdr-1 were low before EPOCH, but increased fourfold or more in 42% of patients in whom serial samples were obtained. Pharmacokinetic analysis revealed median peak concentrations of dexverapamil and its metabolite, nor-dexverapamil, of 1.66 µmol/l and 1.58 µmol/l, respectively. Since both are comparable antagonists, a median peak total reversing concentration of 3.24 µmol/l was achieved. Pharmacokinetic analysis of doxorubicin and etoposide levels confirmed a delay in the clearance of doxorubicin ranging from 5% to 24%; no change in the pharmacokinetics of etoposide was observed. This study provides sufficient rationale for testing dexverapamil in a randomized clinical trial.

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Reversal of drug resistance offers the hope of increasing the efficacy of conventional chemotherapy. We tested dexverapamil as a P-glycoprotein antagonist in combination with EPOCH chemotherapy in refractory non-Hodgkin's lymphoma. In a cross-over design, dexverapamil was added to EPOCH after disease stabilization or progression occurred. Objective responses were observed in 10 of 41 assessable patients. Biopsies for mdr-1 were obtained before EPOCH treatment and at the time of cross-over to dexverapamil. Levels of mdr-1 were low before EPOCH, but increased four-fold or more in 42% of patients in whom serial samples were obtained. Pharmacokinetic analysis revealed median peak concentrations of dexverapamil and its metabolite, nor-dexverapamil, of 1.66 mumol/l and 1.58 mumol/l, respectively. Since both are comparable antagonists, a median peak total reversing concentration of 3.24 mumol/l was achieved. Pharmacokinetic analysis of doxorubicin and etoposide levels confirmed a delay in the clearance of doxorubicin ranging from 5% to 24%; no change in the pharmacokinetics of etoposide was observed. This study provides sufficient rationale for testing dexverapamil in a randomized clinical trial.

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Identifying new chemotherapeutic agents and characterizing mechanisms of resistance may improve cancer treatment. The Anticancer Drug Screen of the National Cancer Institute uses 60 cell lines to identify new agents. Expression of mdr-1/P-glycoprotein was measured by quantitative PCR. Expression was detected in 39 cell lines; the highest levels were in renal and colon carcinomas. Expression was also detected in all melanomas and central nervous system tumors, but in only one ovarian carcinoma and one leukemia cell line. Using a modified version of the COMPARE program, a high correlation was found between expression of mdr-1 and cellular resistance to a large number of compounds. Evidence that these compounds are P-glycoprotein substrates includes: (a) enhancement of cytotoxicity by verapamil; (b) demonstration of cross-resistance in a multidrug-resistant cell line, (c) ability to antagonize P-glycoprotein, increasing vinblastine accumulation by decreasing efflux; and (d) inhibition of photoaffinity labeling by azidopine. Identification of many heretofore unrecognized compounds as substrates indicates that P-glycoprotein has a broader substrate specificity than previously recognized. This study confirms the validity of this novel approach and provides the basis for similar studies examining a diverse group of gene products, including other resistance mechanisms, putative drug targets, and genes involved in the cell cycle and apoptosis.

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Fifty-eight cell lines in the National Cancer Institute drug screen were analyzed for their ability to efflux the fluorescent dye rhodamine 123 as a functional assay for P-glycoprotein (Pgp). Using flow cytometry, the rhodamine fluorescence was measured for each cell line under four incubation conditions, i.e., after accumulation in the presence or absence of the Pgp antagonist cyclosporin A and after efflux in rhodamine-free medium in the presence or absence of cyclosporin A. The results in some cell lines were compatible with Pgp-mediated efflux. There was a significant correlation between mdr-1 expression and rhodamine efflux in the 58 cell lines (r = 0.788, p = 0.0001). Using the rhodamine efflux data as a seed for COMPARE analysis with the cytotoxicity data on > 30,000 compounds in the National Cancer Institute drug screen database, hundreds of compounds with high correlation coefficients were identified. Selected compounds were tested for reversal of cross-resistance in a multidrug-resistant cell line. A high degree of reversibility, up to 10,000-fold, for some of the compounds was noted in the presence of the Pgp antagonist PSC 833. This finding suggested that compounds with predominately Pgp-mediated resistance were being identified. Using these compounds as seeds for COMPARE analysis against a more restricted database of 187 standard agents, a series of standard compounds were repeatedly identified as having high correlation coefficients with the newly identified Pgp substrates. These standard agents, including phyllanthoside, bisantrene, and homoharringtonine, constitute an mdr-1 profile. New agents identified as being highly correlated with these compounds may benefit from clinical trials with Pgp antagonists.

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We describe here the development and implementation of a pilot-scale, in vitro, anticancer drug screen utilizing a panel of 60 human tumor cell lines organized into subpanels representing leukemia, melanoma, and cancers of the lung, colon, kidney, ovary, and central nervous system. The ultimate goal of this disease-oriented screen is to facilitate the discovery of new compounds with potential cell line-specific and/or subpanel-specific antitumor activity. In the current screening protocol, each cell line is inoculated onto microtiter plates, then preincubated for 24-28 hours. Subsequently, test agents are added in five 10-fold dilutions and the culture is incubated for an additional 48 hours. For each test agent, a dose-response profile is generated. End-point determinations of the cell viability or cell growth are performed by in situ fixation of cells, followed by staining with a protein-binding dye, sulforhodamine B (SRB). The SRB binds to the basic amino acids of cellular macromolecules; the solubilized stain is measured spectrophotometrically to determine relative cell growth or viability in treated and untreated cells. Following the pilot screening studies, a screening rate of 400 compounds per week has been consistently achieved.

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