ognizant Communication Corporation

ONCOLOGY RESEARCH
AN INTERNATIONAL JOURNAL
INCORPORATING ANTI-CANCER DRUG DESIGN

ABSTRACTS
VOLUME 15, NUMBER 6

Oncology Research, Volume 15, pp. 291-294
0965-0407/05 $20.00 + .00
E-ISSN 1555-3906
Copyright © 2005 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.

Do Negative Feedback Oscillations Drive Variations in the Length of the Tumor Cell Division Cycle?

Bruce C. Baguley and Elaine Marshall

1Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand

The cell cycle length of individual cells within a tumor cell population is known to vary, mainly as a consequence of differences in the length of G1 phase. A number of observations suggest that the distribution of G1 phase transit times is well described by models where the transition from G1 to S phase is governed by a probability mechanism. However, entry into S phase as a consequence of progressive accumulation of cyclin E with time, to the point where cyclin-dependent kinase-2 (cdk2) is activated, does not provide a basis for a probability mechanism. We suggest that oscillation of the activity of the E2F-1 transcription factor during G1 phase could provide a mechanism that explains the kinetic behavior of G1 phase cells. A negative feedback loop controlling oscillation is possible because activation of cdk2, following activation by cyclin E, phosphorylates the E2F-1 transcription factor, marking it for ubiquitination by the Skp2-cullin-F-box complex and subsequent proteolytic removal. The activity of several cellular transcription factors, including p53 and NF-kB, has been shown to oscillate by negative feedback loops leading to ubiquitination and subsequent proteolytic degradation. The oscillatory mechanisms for p53 and NF-kB suggest that transitions from the cell cycle to apoptosis are also governed by probability functions.

Key words: Cell cycle length; Negative feedback oscillation; Probability mechanism

Address correspondence to Bruce C. Baguley, Auckland Cancer Society Research Centre, University of Auckland School of Medicine, Private Bag 92019, Auckland, New Zealand. Tel: (64-9) 3737 999; Fax: (64-9) 3737 502; E-mail: b.baguley@auckland.ac.nz




Oncology Research, Volume 15, pp. 295-300
0965-0407/05 $20.00 + .00
E-ISSN 1555-3906
Copyright © 2005 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.

Transient Absorption Spectra and Kinetics of Folic Acid (Vitamin B11) and Some Kinetic Data of Folinic Acid and Methotrexate

Nikola Getoff

Ludwig Boltzmann Institute for Radiation Chemistry and Radiation Biology, The University of Vienna, Vienna, Austria

Folic acid (FA; vitamin B11) exhibits antitumor properties. Its transients, resulting from reaction with OH radicals, are of special interest and were studied by pulse radiolysis. The complex composition of FA offers the formation of numerous transients having different electronic structure stability (lifetime). Investigating their kinetic profiles of decay at various wavelengths, it was established that transients with very unstable electron structure (very short-lived radicals) tend to convert into more stable electronic structures (longer lived) by intramolecular electron transfer process. The biological importance of a FA radical depends on its concentration and on its specific reaction rate constant (k value) for a given process. The rate constant for the OH attack is k(OH + FA) = 1.1 x 1010 L mol-1 s-1. Superimposed absorption spectra of FA radicals as well as formation and decay rate constants of total processes are presented. The primary spectrum is characterized by l = 425 nm, e = 1.64 x 104 L mol-1 s-1. The chemical structure of FA is similar to that of folinic acid (FNA) and of methotrexate (MTX), but their biological properties are different. Therefore, their rate constants for the reactions with e-aq and OH were also determined for comparison: k(FNA + e-aq) = 3.1 x 1010 L mol-1 s-1, k(FNA + OH)  = 0.8 x 1010 L mol-1 s-1, k(MTX + e-aq) = 1 x 1010 L mol-1 s-1; k(MTX + OH)  = 2.3 x 1010 L mol-1 s-1, and k(FA + e-aq) = 1.9 x 1010 L mol-1 s-1.

Key words: Folic acid (vitamin B11); Pulse radiolysis of folic acid; Intramolecular electron transfer; Kinetics of FA, FNA, and MTX

Address correspondence to Nikola Getoff, Ludwig Boltzmann Institute for Radiation Chemistry and Radiation Biology, c/o The University of Vienna, UZA II, AlthanstraBe 14, A-1090 Vienna, Austria. Tel: +43-1-4277/52710; Fax: +43-1-4277/52795; E-mail: nikola.getoff@univie.ac.at




Oncology Research, Volume 15, pp. 301-311
0965-0407/05 $20.00 + .00
E-ISSN 1555-3906
Copyright © 2005 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.

Effect of Glibenclamide on N-Nitroso-N-Methylurea-Induced Mammary Tumors in Diabetic and Nondiabetic Rats

Claudia Cocca,1 Gabriela Martín,1 Mariel Núñez,1 Alicia Gutiérrez,1 Graciela Cricco,1 Nora Mohamad,1 Vanina Medina,1 Máximo Croci,2 Ernesto Crescenti,2 Elena Rivera,1 and Rosa Bergoc1,3

1Radioisotopes Laboratory, School of Pharmacy and Biochemistry, University of Buenos Aires, Buenos Aires, Argentina
2Institute of Immunooncology, Buenos Aires, Argentina
3School of Medicine, Barcelo University, Buenos Aires, Argentina

The objective of this study was to evaluate the antitumor effect of glibenclamide (Gli) alone or in combination with tamoxifen (Tam) on experimental mammary tumors induced by N-nitroso-N-methylurea (NMU) in nondiabetic and diabetic rats. For experimental diabetes induction, Sprague-Dawley rats were injected with streptozotocin (STZ) on the second day of life. For experimental mammary tumor induction, nondiabetic and diabetic rats were injected IP with NMU at 50, 80, and 110 days of life. Nondiabetic and diabetic rats bearing mammary tumors were treated with 0.06 mg/day of Gli orally, Tam 1 mg/kg/day SC, or with the combined treatment (Gli + Tam). After 20 days of treatment, different responses were observed. In nondiabetic rats, 64% of tumors were responsive to Gli treatment (they regressed or remained stable), whereas 57% of tumors under treatment with Tam exhibited a response. Results of the combined Gli + Tam treatment indicated that all tumors were responsive: 58% regressed and 42% remained stable. Diabetic rats receiving Gli treatment did not show response to this treatment, while 65% of the tumors of Tam-treated diabetic rats showed regression. Histopathologic observation indicated an important intratumor secretion in all tumors of Gli-, Tam-, or Gli + Tam-treated rats. No secondary toxic effect was observed after treatment at any assayed doses. In conclusion, the present data demonstrate the in vivo antitumor action of Gli treatment on the experimental mammary tumors employed, indicating that Gli exerted a direct effect on tumor cells in nondiabetic rats. The combined Gli + Tam treatment potentiated the antitumor effect of each drug alone. Future research will examine the molecular aspects of these findings.

Key words: Glibenclamide; Mammary tumors; N-Nitroso-N-methylurea; Rats; Streptozotocin; Diabetes

Address correspondence to Prof. Rosa M. Bergoc, Ph.D., Laboratorio de Radioisótopos, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956-1113 Buenos Aires, Argentina. Tel: +54 11 4964 8277/+54 11 4743 2857; Fax: +54 11 4743 2857; E-mail: rmbergoc@ffyb.uba.ar or rmbergoc@arnet.com.ar




Oncology Research, Volume 15, pp. 313-325
0965-0407/05 $20.00 + .00
E-ISSN 1555-3906
Copyright © 2005 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.

The Antineoplastic Efficacy of the Prodrug CloretazineTM Is Produced by the Synergistic Interaction of Carbamoylating and Alkylating Products of its Activation

Raymond P. Baumann, Helen A. Seow, Krishnamurthy Shyam, Philip G. Penketh, and Alan C. Sartorelli

Department of Pharmacology and Developmental Therapeutics Program, Cancer Center, Yale University School of Medicine, New Haven, CT 06520, USA

CloretazineTM {1,2-bis(methylsulfonyl)-1-[(2-chloroethyl)-2-(methylamino)carbonyl]hydrazine; VNP40101M; 101M} is a sulfonylhydrazine prodrug that possesses broad spectrum antitumor efficacy against transplanted murine and human tumor models and has shown activity in clinical trials against relapsed or refractory acute myeloid leukemia. Base catalyzed activation of this prodrug generates two different reactive intermediates: chloroethylating species that covalently interact with DNA at the O6-position of guanine residues that progress to a G-C interstrand cross-link, and a carbamoylating agent, methyl isocyanate. Previous findings from this laboratory have provided initial evidence that methyl isocyanate can contribute to the efficacy of CloretazineTM by enhancing the cytotoxicity of the generated chloroethylating species. This action may be due in part to inhibition of the DNA repair protein O6-alkylguanine-DNA alkyltransferase (AGT); however, activity in cells devoid of AGT indicates that other actions are involved in the synergistic cytotoxicity. Herein we demonstrate that O6-benzylguanine can also produce synergistic cell kill with the alkylating component of CloretazineTM but differs from methyl isocyanate in that the enhancement occurs in AGT-containing cells, but not in cells devoid of AGT. Methyl isocyanate generated by the decomposition of 1,2-bis(methylsulfonyl)-1-[methylaminocarbonyl]hydrazine also acts to enhance the activity of a variety of DNA cross-linking agents, while only producing additive cytotoxicity with methylating agents. Flow cytometric studies using annexin as a marker for apoptosis indicate that in Chinese hamster ovary cells and in human leukemia cells CloretazineTM-induced apoptosis is primarily caused by the generated methyl isocyanate. Comet assays designed to detect DNA cross-links in intact cells indicate that the chloroethylating species generated by the activation of CloretazineTM produce DNA cross-links, with the co-generated methyl isocyanate increasing the degree of cross-linking produced by the reactive chloroethylating species. These findings provide further evidence that the methyl isocyanate produced by the activation of CloretazineTM can be a major contributor to the cytotoxicity produced by this antineoplastic agent.

Key words: CloretazineTM; Sulfonylhydrazine prodrugs; AGT; Chloroethylation; Carbamoylation

Address correspondence to Alan C. Sartorelli, Department of Pharmacology, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06520, USA. Tel: (203) 785-4533; Fax: (203) 737-2045; E-mail: alan.sartorelli@yale.edu




Oncology Research, Volume 15, pp. 327-332
0965-0407/05 $20.00 + .00
E-ISSN 1555-3906
Copyright © 2005 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.

Inhibition of Protein Kinase CKII Activity by Euchrestaflavanone B Purified From Cudrania tricuspidata

Soon-Hee Kim,1 Soo-Hyun Yoon,1 Byong Won Lee,2 Ki Hun Park,2 Young Ho Kim,3 and Young-Seuk Bae1

1Department of Biochemistry, College of Natural Sciences, Kyungpook National University, Daegu 702-701, Korea
2Division of Applied Life Science, Department of Agricultural Chemistry, Gyeongsang National University, Jinju 660-701, Korea
3Department of Microbiology, College of Natural Sciences, Kyungpook National University, Daegu 702-701, Korea

The CKII (EC 2.7.1.37) inhibitory compound was purified from the root barks of Cudrania tricuspidata and identified as (2S)-2-[2,4-dihydroxy-5-(3-methyl-but-2-enyl)-phenyl]-5,7-dihyroxy-6-(3-methyl-but-2-enyl)-chroman-4-one (euchrestaflavanone B). Euchrestaflavanone B was shown to inhibit the phosphotransferase activity of CKII with IC50 of about 78 mM. Steady-state studies revealed that euchrestaflavanone B acted as a competitive inhibitor with respect to the substrate ATP. A value of 16.4 mM was obtained for the apparent Ki. Concentration of 0.8 mM euchrestaflavanone B caused 50% growth inhibition of human cancer cells U937 and HeLa. Euchrestaflavanone B-induced cell death was characterized with the cleavage of poly(ADP-ribose) polymerase and procaspase-3, indicating that the inhibitor triggered apoptosis. Because protein kinase CKII is involved in cell proliferation and oncogenesis, these results suggest that euchrestaflavanone B may function by inhibiting oncogenic disease, at least in part, through the inhibition of CKII activity.

Key words: Euchrestaflavanone B; Protein kinase CKII; Enzyme inhibitor; Apoptosis; Anticancer drug

Address correspondence to Prof. Young-Seuk Bae, Department of Biochemistry, College of Natural Sciences, Kyungpook National University, Daegu 702-701, Korea. Tel: 53-950-6355; Fax: 53-943-2762; E-mail: ysbae@mail.knu.ac.kr