Curtis Hose

Interaction of the P-glycoprotein multidrug transporter (MDR1) with high affinity peptide chemosensitizers in isolated membranes, reconstituted systems, and intact cells.

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.

Cediranib for Metastatic Alveolar Soft Part Sarcoma

PURPOSE Alveolar soft part sarcoma (ASPS) is a rare, highly vascular tumor, for which no effective standard systemic treatment exists for patients with unresectable disease. Cediranib is a potent, oral small-molecule inhibitor of all three vascular endothelial growth factor receptors (VEGFRs). PATIENTS AND METHODS We conducted a phase II trial of once-daily cediranib (30 mg) given in 28-day cycles for patients with metastatic, unresectable ASPS to determine the objective response rate (ORR). We also compared gene expression profiles in pre- and post-treatment tumor biopsies and evaluated the effect of cediranib on tumor proliferation and angiogenesis using positron emission tomography and dynamic contrast-enhanced magnetic resonance imaging. RESULTS Of 46 patients enrolled, 43 were evaluable for response at the time of analysis. The ORR was 35%, with 15 of 43 patients achieving a partial response. Twenty-six patients (60%) had stable disease as the best response, with a disease control rate (partial response + stable disease) at 24 weeks of 84%. Microarray analysis with validation by quantitative real-time polymerase chain reaction on paired tumor biopsies from eight patients demonstrated downregulation of genes related to vasculogenesis. CONCLUSION In this largest prospective trial to date of systemic therapy for metastatic ASPS, we observed that cediranib has substantial single-agent activity, producing an ORR of 35% and a disease control rate of 84% at 24 weeks. On the basis of these results, an open-label, multicenter, randomized phase II registration trial is currently being conducted for patients with metastatic ASPS comparing cediranib with another VEGFR inhibitor, sunitinib.

DNA damage and cell cycle arrest induced by 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F 203, NSC 703786) is attenuated in aryl hydrocarbon receptor deficient MCF-7 cells

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 G1 and S phase, and induced DNA adduct formation, in contrast to AhR-deficient AHR100 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 AHR100 cells, drug treatment did not affect CYP1A1 and CYP1B1 transcription and EROD activity. Furthermore, AHR100 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.

UCN-01 Enhances the In Vitro Toxicity of Clinical Agents in Human Tumor Cell Lines

UCN-01 is undergoing Phase I evaluation and is a candidate forcombination strategies in the clinic. UCN-01 has been shown to havea variety of effects on cellular targets and the cell cycle. It hasalso been reported to sensitize cells to several clinical drugsin vitro, possibly in a manner related to p53 status. Thus,combinations of UCN-01 with a series of clinical agents in varietyof cell lines have been investigated in vitro. Certain celllines demonstrated synergistic interactions with combinations ofUCN-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 andvincristine, or topoisomerase II inhibitors, adriamycin andetoposide, did not result in synergy, only in additive toxicity.Cells with non-functional p53 were significantly more susceptibleto the supra-additive effects of certain DNA-damaging agents andUCN-01 combinations, than cells expressing functional p53 activity.In contrast, there was no significant relationship between p53status and susceptibility to synergy between antimetabolites andUCN-01. The mechanism behind the observed synergy appearedunrelated to effects on protein kinase C or abrogation of the cellcycle in G2. Moreover, increased apoptosis did not fully explainthe supradditive response. These data indicate that UCN-01sensitizes a variety of cell lines to certain DNA-damaging agents(frequently covalent DNA-binding drugs) and antimetabolites invitro, but the mechanism underlying this interaction remainsundefined.

Identification of CBX3 and ABCA5 as Putative Biomarkers for Tumor Stem Cells in Osteosarcoma

Recently, there has been renewed interest in the role of tumor stem cells (TSCs) in tumorigenesis, chemoresistance, and relapse of malignant tumors including osteosarcoma. The potential exists to improve osteosarcoma treatment through characterization of TSCs and identification of therapeutic targets. Using transcriptome, proteome, immunophenotyping for cell-surface markers, and bioinformatic analyses, heterogeneous expression of previously reported TSC or osteosarcoma markers, such as CD133, nestin, POU5F1 (OCT3/4), NANOG, SOX2, and aldehyde dehydrogenase, among others, was observed in vitro. However, consistently significantly lower CD326, CD24, CD44, and higher ABCG2 expression in TSC-enriched as compared with un-enriched osteosarcoma cultures was observed. In addition, consistently higher CBX3 expression in TSC-enriched osteosarcoma cultures was identified. ABCA5 was identified as a putative biomarker of TSCs and/or osteosarcoma. Lastly, in a high-throughput screen we identified epigenetic (5-azacytidine), anti-microtubule (vincristine), and anti-telomerase (3,11-difluoro-6,8,13-trimethyl- 8H-quino [4,3,2-kl] acridinium methosulfate; RHPS4)-targeted therapeutic agents as candidates for TSC ablation in osteosarcoma.

Drug-Induced Expression of Nonsteroidal Anti-Inflammatory Drug-Activated Gene/Macrophage Inhibitory Cytokine-1/Prostate-Derived Factor, a Putative Tumor Suppressor, Inhibits Tumor Growth

A common in vitro response for many chemopreventive and antitumor agents, including some cyclooxygenase inhibitors, is the increased expression of nonsteroidal anti-inflammatory drug-activated gene (NAG)-1/macrophage inhibitory cytokine (MIC)-1/prostate-derived factor (PDF). The experimental anticancer drug 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F203) was a potent inducer of NAG-1 expression, and in MCF-7 cells, it inhibited cell growth and induced apoptosis. NAG-1 small interfering RNA blocked NAG-1 expression and 5F203-induced apoptosis in MCF-7 cells, indicating that NAG-1 may mediate the apoptosis and anticancer activity. One mechanism by which 5F203 increases NAG-1 expression is by increasing the stability of NAG-1 mRNA, dependent of de novo protein synthesis. Extracellular signal-regulated kinase (ERK) 1/2 phosphorylation was increased by 5F203, and inhibition of ERK1/2 phosphorylation abolished the induction of NAG-1 protein expression and increased the stability of NAG-1 mRNA. Thus, 5F203 regulates NAG-1 expression by a unique mechanism compared with other drugs. A mouse orthotopic mammary tumor model was used to determine whether 5F203 increased NAG-1 expression in vivo and suppressed tumor growth. Treatment of the mice with Phortress, the prodrug of 5F203, increased the in vivo expression of NAG-1 as measured by real-time reverse transcription-polymerase chain reaction from RNA obtained by needle biopsy, and the expression correlated with a reduction of tumor volume. These results confirm that NAG-1 suppresses tumor growth, and its in vivo expression can be controlled by treating mice with anticancer drugs, such as Phortress. Drugs that target NAG-1 could lead to a unique strategy for the development of chemotherapeutic and chemopreventive agents.

FLUORINATED 2-(4-AMINO-3-METHYLPHENYL)BENZOTHIAZOLES INDUCE CYP1A1 EXPRESSION, BECOME METABOLIZED, AND BIND TO MACROMOLECULES IN SENSITIVE HUMAN CANCER CELLS

Fluorinated 2-(4-amino-3-methylphenyl)benzothiazoles possess potent antiproliferative activity against certain cancer cells, similar to the unfluorinated 2-(4-amino-3-methylphenyl)benzothiazole (DF 203, NSC 674495). In “sensitive” cancer cells, DF 203 is metabolized by, can induce expression of, and binds covalently to CYP1A1. Metabolism appears to be essential for its antiproliferative activity through DNA adduct formation. However, a biphasic dose-response relationship compromises its straightforward development as a chemotherapeutic agent. We investigated whether fluorinated benzothiazoles inhibit cancer cell growth without the biphasic dose-response, and whether the fluorinated benzothiazoles are also metabolized into reactive species, with binding to macromolecules in sensitive cancer cells. One fluorinated benzothiazole, 2-(4-amino-methylphenyl)-5-fluorobenzothiazole (5F 203, NSC 703786) did exhibit potent, antiproliferative activity without a biphasic dose-response. The fluorinated benzothiazoles were also metabolized only in cells, which subsequently showed evidence of cell death. We used microsomes from genetically engineered human B-lymphoblastoid cells expressing cytochromes P450 (CYP1A1, CYP1A2, or CYP1B1) to clarify the basis for fluorinated benzothiazole metabolism. 5F 203 induced CYP1A1 and CYP1B1 mRNA expression in sensitive breast and renal cancer cells, whereas 5F 203 induced CYP1A1 mRNA but not CYP1B1 mRNA expression in sensitive ovarian cancer cells. 5F 203 did not induce CYP1A1 or CYP1B1 mRNA expression in any “resistant” cancer cells. The fluorinated benzothiazoles induced CYP1A1 protein expression exclusively in sensitive cells. [14C]5F 203 bound substantially to subcellular fractions in sensitive cells but only minimally in resistant cells. These data are concordant with the antiproliferative activity of fluorinated benzothiazoles deriving from their ability to become metabolized and bind to macromolecules within sensitive cells.

Clinical Reversal of Multidrug Resistance

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‐Hodgkins 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 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.

Resistance to paclitaxel mediated by P-glycoprotein can be modulated by changes in the schedule of administration

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.

The antitumor drug candidate 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole induces NF-kappaB activity in drug-sensitive MCF-7 cells.

2-(4-Amino-3-methylphenyl)-5-fluoro-benzothiazole (5F 203) potently inhibits MCF-7 breast cancer cell growth in part by activating the aryl hydrocarbon receptor (AhR) signaling pathway. Ligands for the AhR (i.e. dioxin) have also been shown to modulate the NF-κB signaling cascade, affecting physiological processes such as cellular immunity, inflammation, proliferation and survival. The objective of this study was to investigate the effect of 5F 203 treatment on the NF-κB signaling pathway in breast cancer cells. Exposure of MCF-7 cells to 5F 203 increased protein–DNA complex formation on the NF-κB-responsive element as determined by electrophoretic mobility shift assay, but this effect was eliminated in MDA-MB-435 cells, which are resistant to the antiproliferative effects of 5F 203. An increase in NF-κB-dependent transcriptional activity was confirmed by a significant increase in NF-κB-dependent reporter activity in sensitive MCF-7 cells, which was absent in resistant MDA-MB-435 cells and AhR-deficient subclones of MCF-7 cells. Inhibition of NF-κB activation enhanced the increase in xenobiotic response element-dependent reporter activity in MCF-7 cells when treated with 5F 203. The drug candidate 5F 203 also induced mRNA levels of IL-6, an NF-κB-responsive gene, in MCF-7 cells, but not in MDA-MB-435 cells, as determined by quantitative RT-PCR. These findings suggest that 5F 203 activation of the NF-κB signaling cascade may contribute to 5F 203-mediated anticancer activity in human breast cancer MCF-7 cells.