Karen Davidson

Effects of androgens on telomerase activity in normal and malignant prostate cells in vitro.

Recent studies have shown that sex hormones regulate telomerase activity in endometrium and breast tissues. The present study was designed to clarify the effects of androgen on telomerase activity in normal and malignant prostate cells.

Activity of the multitargeted antifolate LY231514 in the human tumor cloning assay

Purpose: This study was performed to evaluate the activity of the multitargeted antifolate (MTA or LY231514) against a broad range of human tumors taken directly from patients. Materials and methods: Human tumor colony-forming units were treated with MTA at concentrations of 0.1, 1.0, and 10 μg/ml in 1-h exposure studies. The responses of a limited number of specimens were also evaluated concurrently in 1-h exposures to cisplatin, fluorouracil, irinotecan, and/or paclitaxel. Results: Of 358 specimens plated in the 1-h exposure studies, 148 (41%) were evaluable. Overall, responses were observed in 3% of specimens (4/144) at 0.1 μg/ml, 11% (17/148) at 1.0 μg/ml, and 23% (33/141) at 10 μg/ml. In this range of concentrations achievable clinically, there was a significant concentration-response relationship. At 10 μg/ml in the 1-h exposure studies, the response rate in colorectal cancer specimens was 32% (9/28), and the response rate in non-small-cell lung cancer was 25% (6/24). Responses were also observed in several chemoresistant tumors, including renal cell carcinoma, hepatocellular carcinoma, mesothelioma, and pancreatic carcinoma. The activity of MTA was not completely cross-resistant with that of cisplatin, fluorouracil, irinotecan, and paclitaxel. Conclusions: MTA demonstrated in vitro activity against a spectrum of tumors, including several tumors generally considered chemoresistant.

Efficient induction of apoptosis by ONYX-015 adenovirus in human colon cancer cell lines regardless of p53 status.

The ONYX-015 virus is a mutated adenovirus that in theory selectively replicates and induces cytolysis in tumor cells lacking functional p53. The present study investigated whether ONYX-015 viral infection alone or in combination with conventional chemotherapeutic agents could significantly increase apoptosis in human colon cancer cell lines, regardless of p53 status, compared to untreated cells. A pair of colon cancer cell lines that differ only in their p53 status (RKO with wild-type p53 and RKOp53 with deficient p53) was tested. Two chemotherapeutic agents, 5-fluorouracil (5-FU) and CPT-11, were tested in combination with ONYX-015. Final concentrations of these agents corresponded to peak plasma levels achievable in patients. ONYX-015 concentration was 10 p.f.u./cell. In RKO and RKOp53 cell lines, ONYX-015 viral infection alone or in combination with 5-FU or CPT-11 induced a significant increase in apoptosis compared to chemotherapeutic agents alone, regardless of p53 status. Moreover, the combination of ONYX-015 and chemotherapeutics induced more apoptosis than chemotherapeutics alone in the two colon cancer cell lines independently of their p53 status. We conclude that ONYX-015 virus infection alone or in combination with 5-FU or CPT-11 induced apoptosis in human colon cancer cell lines, independently of p53 status.

Phase I and Pharmacologic Study of PN401 and Fluorouracil in Patients With Advanced Solid Malignancies

PURPOSE To assess the feasibility of administering PN401, an oral uridine prodrug, as a rescue agent for the toxic effects of fluorouracil (5-FU), and to determine the maximum-tolerated dose of 5-FU when given with PN401, with an 8-hour treatment interval between these agents. PATIENTS AND METHODS Patients with advanced solid malignancies were treated with escalating doses of 5-FU, given as a rapid intravenous infusion weekly for 3 consecutive weeks every 4 weeks. PN401 was administered orally 8 hours after 5-FU administration, to achieve sustained plasma uridine concentrations of at least 50 micromol/L. Initially, patients received 6 g of PN401 orally every 8 hours for eight doses (schedule 1). When dose-limiting toxicity (DLT) was consistently noted, patients then received 6 g of PN401 every 2 hours for three doses and every 6 hours thereafter for 15 doses (schedule 2). RESULTS Twenty-three patients received 50 courses of 5-FU and PN401. Among patients on schedule 1, DLT (grade 4 neutropenia complicated by fever and diarrhea) occurred in those receiving 5-FU 1,250 mg/m(2)/wk. Among patients on schedule 2, 5-FU 1,250 mg/m(2)/wk was well tolerated, but grade 4, protracted (> 5 days) neutropenia was consistently noted in those treated with higher doses of the drugs. Nonhematologic effects were uncommon and rarely severe. The pharmacokinetics of 5-FU, assessed in 12 patients on schedule 2, were nonlinear, with the mean area under the time-versus-concentration curve (AUC) increasing from 298 +/- 44 to 962 +/- 23 micromol/L and mean clearance decreasing from 34 +/- 4 to 15.6 +/- 0.38 L/h/m(2) as the dose of 5-FU was increased from 1,250 to 1,950 mg/m(2)/wk. 5-FU AUCs achieved with 5-FU 1,250 mg/m(2)/wk for 6 weeks along with the intensified PN401 dose schedule were approximately five-fold higher than those achieved with 5-FU alone. Plasma uridine concentrations increased with each of the three PN401 doses given every 2 hours, and uridine steady-state concentrations were greater than 50 micromol/L. CONCLUSION Treatment with oral PN401 beginning 8 hours after 5-FU administration is well tolerated and results in sustained plasma uridine concentrations above therapeutic-relevant levels. The recommended 5-FU dosage for phase II evaluations is 1,250 mg/m(2)/wk for 3 weeks every 4 weeks with the intensified PN401 dose schedule (schedule 2). At this dose, systemic exposure to 5-FU as measured by AUC was five-fold higher than that observed after administration of a conventional 5-FU bolus.

Neuropeptide receptor status in human tumor cell lines.

Tumor types expressing a neuroendocrine phenotype secrete neuropeptides with paracrine or autocrine growth factor activity. The efficacy of these paracrine or autocrine loops depends on the expression of specific receptors on tumor cells. Once specific receptors are identified, specific neuropeptide antagonists disrupting paracrine and autocrine loops could be potential treatments in neuropeptide-secreting tumors. In the present study, 11 human tumor cell lines representing astrocytoma, lymphoma, and pancreatic, prostate, lung and colon carcinomas were examined for expression of five different neuropeptide receptors (cholecystokinin, neurotensin, vasopressin, tachykinine substance P and cannabinoid) using RT-PCR and radioligand binding. The presence of various neuropeptide receptors in different human cancer cell lines supports development of new antitumor treatments based on disruption of neuropeptide autocrine growth pathways.

A human breast cancer model for the study of telomerase inhibitors based on a new biotinylated-primer extension assay

SummaryTelomerase is an RNA-dependent polymerase that synthesizes telomeric DNA (TTAGGG)n repeats. The overall goal of our work was to establish human cancer models that can be used to design clinical trials with telomerase inhibitors. The objectives of this study were (1) to set up a human breast cancer system that allows evaluation of the effects of telomerase inhibitors in cultured cells using a non-amplified telomerase assay and (2) to test this system using two drugs (cisplatin and TMPyP4) that affect the telomerase expression in breast cancer cells in culture. We first compared the telomerase activity in a variety of human breast cancer cell lines to that of other tumour types using a new biotinylated-primer extension assay. Our method, based on a non-amplified primer extension assay shows the direct incorporation of 32P-labelled nucleotides induced by telomerase on human telomeric primers. The 32P-dGTP labelled telomerase-extended 5′-biotinylated (TTAGGG)3 primer can subsequently be separated using streptavidin-coated magnetic beads. As compared to other non-amplified method, we showed that this procedure improved the characterization and the quantification of the banding pattern resulting from telomerase extension by reducing the radioactive background. Using this method, we observed that telomerase activity varies markedly in a panel of 39 human cancer cell lines. For example, MCF7 breast cancer cells in culture showed intermediate telomerase activity corresponding to 33.8 ± 3.4% of that of the HeLa cells (reference cell line). Similarly, the telomere length varied with each cell line (average: 6.24 ± 6.16). No correlation between the level of telomerase and telomere length was observed, suggesting that a high processivity is not required to maintain telomeres and that, in some cell lines, another mechanism of telomere elongation can maintain telomere length. From this study, we selected MCF7 and MX1 models that showed reproducible telomerase activity and a relatively limited telomere length for the testing of potential telomere–telomerase interacting agents. Using cisplatin and a new porphyrin-derived compound TMPyP4, we showed that our model was able to detect a down-regulation of the telomerase activity in MCF7 cells in culture and in a human MX1 tumour xenografts. Based on these results, a breast cancer model for evaluating telomerase and telomere interactive agents is proposed.

Dimethyl sulfoxide (DMSO) causes a reversible inhibition of telomerase activity in a Burkitt lymphoma cell line

INTRODUCTION Telomerase is an enzyme that is required for maintenance of telomeres. This enzyme has been shown to be present in germline tissues and majority of tumors and tumor cell lines. The regulation of telomerase is an area of active investigation in different models because, potentially, inhibition of this enzyme could be important in cancer therapy. To study the regulation of this enzyme in lymphoma cell lines, we used DMSO to produce a reversible G0/G1 arrest in Raji cell line, as shown earlier [Sawai M, Takase K, Teraoka H, Tsukada K. Reversible G1 arrest in the cell cycle of human lymphoid cell lines by dimethyl sulphoxide. Exp Cell Res 1990;187:4-10]. METHODS In this study, we use a highly quantifiable conventional (non-amplified) assay to study the effect of DMSO on telomerase. In addition, we studied cellular proliferation and cell cycle profiles of the cells treated and, subsequently, released from DMSO induced blockage. RESULTS In this model, DMSO reversibly inhibited telomerase activity that could be restored after release from the blockage. The inhibition of telomerase seems to parallel cellular proliferation and it appears that telomerase is regulated upon entry into the cell cycle. This view is consistent with other previously published views on relationship of telomerase with exit from cell cycle. CONCLUSION Our observations demonstrate a novel effect of DMSO on cellular mechanisms in Raji cell line. It may provide an attractive model to further study regulation of telomerase in this cell line.

Exploring the mechanisms of action of FB642 at the cellular level.

Abstract FB642(methyl-2-benzimidazolecarbamate, carbendazim) is a systemic fungicide belonging to the benzimidazole family with antitumor activity against a broad spectrum of tumors both in vitro and in vivo such as pancreas, prostate, colon, and breast. Although the preclinical antitumor activity of FB642 has been well explored, its mechanism of action has not been as well delineated. Previous studies indicate that FB642 may interfere with mitosis and thus may disrupt or inhibit microtubule function resulting in apoptosis. This study seeks to determine if FB642 is a sufficiently novel agent worthy of further development by examining the effect of FB642 on apoptosis, the cell cycle, p53-positive and -negative tumors, and drug-resistant and MDR cell lines. The results of this present study indicate that FB642 increases the degree of apoptosis in all examined tumor cell lines, may induce G2/M uncoupling, may selectively kill p53 abnormal cells, and exhibits antitumor activity in drug- and multidrug-resistant cell lines. The induction of apoptosis by FB642, particularly in p53-deficient cells, its impressive in vivo activity against a broad spectrum of murine and human tumors, as well as an acceptable toxicity profile in animals, make FB642 an excellent candidate for further evaluation in clinical trials in cancer patients.

Pharmacokinetics of hydroxyurea in nude mice

Extrachromosomal DNA is the predominant form of gene amplification In human tumors. Hydroxyurea (HU) concentrations of 100-150 IAM have been promising In vitro for extrachromosomal DNA elimination. The study objective was to determine the HU dose-concentration relationship in nude mice with HU doses from 0 to 200 mg/kg. For HU t1/2 determination, mice were Injected with HU 100 mg/kg. A plasma concentration of 159 p.M was achieved and a t1/2 of 11.3 mln determined. Based on these findings, In vivo elimination studies will require frequent administration of HU to maintain plasma concentrations from 100 to 150 µM.

Mitoguazone induces apoptosis via a p53-independent mechanism.

Mitoguazone (methylglyoxal bisguanylhydrazone, methyl-GAG or MGBG) is a synthetic polycarbonyl derivative with activity in patients with Hodgkins and non-Hodgkins lymphoma, head and neck cancer, prostate cancer, and esophageal cancer. Mitoguazone has also recently been documented to have activity in patients with AIDS-related lymphoma. Among anticancer drugs, mitoguazone has a unique mechanism of action via interference with the polyamine biosynthetic pathway. Polyamines stabilize DNA structure by non-covalent cross-bridging between phosphate groups on opposite strands. In addition, mitoguazone causes uncoupling of oxidative phosphorylation. In this study, the ability of mitoguazone to induce apoptosis by inhibiting the polyamine pathway was assessed in three Burkitts lymphoma cell lines (Raji, Ramos and Daudi) and one prostate carcinoma cell line (MPC 3). Additional evaluations were performed in two human breast cancer cell lines (MCF7 with wild-type p53 and VM4K with mutated p53) to determine whether the p53 tumor suppressor gene was required for efficient apoptosis induction. The present study demonstrated that mitoguazone induces apoptosis in all the different human cancer cell lines tested in a concentration- and time-dependent way, and triggers a p53-independent programmed cell death in the human breast cancer MCF7 cell line.