Synthesis and topoisomerase poisoning activity of A-ring and E-ring substituted luotonin A derivatives

https://doi.org/10.1016/j.bmc.2007.03.067Get rights and content

Abstract

A series of A-ring and E-ring analogues of the natural product luotonin A, a known topoisomerase I poison, was evaluated for growth inhibition in human carcinoma and leukemia cell lines. Rational design of structures was based on analogues of the related alkaloid camptothecin, which has been demonstrated to exert cytotoxic effects by the same mechanism of action. When compared to luotonin A, several compounds exhibited an improved topoisomerase I-dependent growth inhibition of a human leukemia cell line.

Introduction

Luotonin A (1a, Fig. 1) is a pyrroloquinazolinoquinoline alkaloid isolated from Peganum nigellastrum, a Chinese herbal medicinal plant.1 It was first reported as a cytotoxic agent due to its activity against the murine leukemia P-388 cell line (IC50 1.8 μg/mL or 6.3 μM), although at that time the inhibitory mechanism of action was not determined.1, 2 In late 2003 it was demonstrated by Hecht and co-workers that luotonin A was able to stabilize the covalent ‘cleavable complex’ between the DNA phosphodiester backbone and the nuclear enzyme topoisomerase I.3 In a side-by-side comparison, this mode of action was demonstrated to be identical to the means by which the structurally analogous alkaloid camptothecin (CPT) interacts with DNA and topoisomerase I to induce cellular apoptosis.

Topoisomerase I (topo I) represents a family of omnipresent biological protein isoforms that catalyze the relaxation of supercoiled DNA during a number of critical cellular processes (e.g., during replication, transcription, and repair).4 Since intracellular levels of topoisomerase I are elevated in a number of human solid tumors relative to the respective normal tissues, an intense interest continues toward the development of drugs which can affect the DNA replication process by selectively interfering with topo I function.

Early enzymology studies uncovered the mechanism by which the natural product alkaloid camptothecin exerts a cytotoxic effect through interference with the topoisomerase I-catalyzed DNA unraveling process.5 However, it was the better understanding of molecular binding interactions described by the resolved X-ray crystal structures of camptothecin/topo I/DNA non-covalent complexes6 that has led to a renewed recent interest in DNA topoisomerase I inhibitors as oncologics.7, 8

The aforementioned report by Hecht and co-workers3 described the ability of luotonin A to stabilize a DNA/topo I binary complex by the same mechanism of action as camptothecin. In this same study, the potencies for the growth inhibition of an Saccharomyces cerevisiae strain by these two natural products were measured at 5–12 μM for luotonin A and ∼0.80 μM for camptothecin.9 While the difference in these two IC50 values represents close to an order of magnitude difference in activity, we were intrigued by the challenge of creating a more drug-like analogue of luotonin A through a rational design approach. Our goal was to optimize the binding activity of the luotonin A scaffold through substitution to take advantage of the reported key hydrogen-bonding interactions identified by the resolved CPT/DNA/topoisomerase I ternary complex X-ray crystal structures6 and through molecular modeling experiments7 (some shown in Fig. 2). Another aim was to increase water solubility of luotonin A analogues by capitalizing on substitution patterns reported for the potent (and water-soluble) camptothecin analogues now in commercial use. The recent research reports by other research groups working concurrently in this same arena10, 11 have prompted us to report here our efforts toward the preparation of A-ring and E-ring analogues of luotonin A and the results from their evaluation for in vitro cytotoxicity in three tumor cell lines.

Section snippets

Chemistry

To date there have been more than a dozen publications describing the total (or formal) synthesis of luotonin A, all more or less convergent routes that make devising analogue syntheses amenable at various stages.1(c), 12 We chose to utilize the route devised by Harayama and co-workers,12(m), 12(q) in which we coupled appropriately substituted 2-chloro-3-(bromomethyl)quinolines 2 with substituted 4(3H)-quinazolinones 3, followed by a palladium-mediated cyclization of the 3-amidomethylquinoline

In vitro antiproliferative activities

Luotonin A (1a) and the seven E-ring analogues 1bh were subjected to testing in three cell lines: cervical carcinoma (HeLa), breast carcinoma (MCF7), and adriamycin-resistant breast carcinoma (ADR-Res). These results are shown in Table 1. In all cases growth inhibition was measured at five concentration points versus a control, and the growth inhibition was expressed in GI50 values (defined as the concentrations corresponding to 50% growth inhibition). Luotonin A and its analogues were also

General methods

All non-aqueous reactions were performed under an atmosphere of dry nitrogen unless otherwise specified. Commercial grade reagents and anhydrous solvents were used as received from vendors and no attempts were made to purify or dry these components further. Removal of solvents under reduced pressure was accomplished with a Buchi rotary evaporator using a Teflon-linked KNF vacuum pump. Data for proton NMR spectra were obtained on a Bruker AC nuclear magnetic resonance spectrometer at 300 or 500 

Acknowledgments

The authors thank Professor Mark P. Wentland of Rensselaer Polytechnic Institute and Dr. William G. Earley of Albany Molecular Research, Inc. for useful discussions and to acknowledge Albany Molecular Research, Inc. for funding of this work at Albany Medical College.

References and notes (22)

  • X.-H. Xiao et al.

    Chin. J. Pharmacol. Toxicol.

    (1988)
    J.S. Yadav et al.

    Tetrahedron Lett.

    (2002)
  • X. Wang et al.

    Biochemistry

    (1998)
    D.-K. Kim et al.

    Mini-Rev. Med. Chem

    (2002)
    J.C. Wang

    Nat. Rev. Mol. Cell Biol.

    (2002)
  • B.R. Baker et al.

    J. Org. Chem.

    (1952)
  • Z.-Z. Ma et al.

    Heterocycles

    (1997)
    Z.-Z. Ma et al.

    Bioorg. Med. Chem. Lett

    (2004)
    Z.-Z. Ma et al.

    Heterocycles

    (2005)
  • A. Cagir et al.

    J. Am. Chem. Soc.

    (2003)
  • C.D. Lima et al.

    Nature

    (1994)
    K.W. Kohn et al.

    Ann. N.Y. Acad. Sci.

    (2000)
    R.M. Wadkins et al.

    Curr. Med. Chem., Anti-Cancer Agents

    (2004)
  • B.L. Staker et al.

    Proc. Natl. Acad. Sci. U.S.A.

    (2002)
    B.L. Staker et al.

    J. Med. Chem

    (2005)
    X. Xiao et al.

    J. Med. Chem.

    (2006)
    M.R. Redinbo et al.

    Science

    (1998)
    L. Stewart et al.

    Science

    (1998)
  • Y. Fan et al.

    J. Med. Chem.

    (1998)
    Y. Fan et al.

    J. Med. Chem.

    (2001)
    X. Xiao et al.

    J. Am. Chem. Soc.

    (2005)
    D. Chauvier et al.

    J. Mol. Struct.

    (2003)
    D. Sriram et al.

    Nat. Prod. Res.

    (2005)
  • F. Zunino et al.

    Curr. Pharm. Des.

    (2002)
    G. Toffoli et al.

    Curr. Med. Chem., Anti-Cancer Agents

    (2003)
    W. Du

    Tetrahedron

    (2003)
    C.J. Thomas et al.

    Bioorg. Med. Chem

    (2004)
    V. Srivastava et al.

    Bioorg. Med. Chem

    (2005)
    Q.-Y. Li et al.

    Curr. Med. Chem.

    (2006)
  • A. Cagir et al.

    Bioorg. Med. Chem.

    (2004)
    A. Cagir et al.

    Bioorg. Med. Chem. Lett.

    (2004)
    S. Dallavalle et al.

    Bioorg. Med. Chem. Lett.

    (2004)
    S. Antony et al.

    Synlett

    (2005)
    N.J. Rahier et al.

    Bioorg. Med. Chem.

    (2005)
    E.S. Lee et al.

    Heterocycles

    (2006)
  • Cited by (47)

    • A-ring and E-ring modifications of the cytotoxic alkaloid Luotonin A: Synthesis, computational and biological studies

      2020, Bioorganic and Medicinal Chemistry
      Citation Excerpt :

      Like the latter, Luotonin A has been reported to act as a topoisomerase I (Top1) poison by stabilizing the Top1/DNA cleavable complex.2 While this mode of action has been generally accepted for CPT and its clinically used derivatives (such as Topotecan3) as well as for Luotonin A, there are also indications that topoisomerase I might not be the only biological target that is involved in the antiproliferative activity of Luotonin A derivatives.4,5 In our previous publication,6 we described the synthesis of four isomeric A-ring amino derivatives of Luotonin A, bearing a primary amino group at positions 1, 2, 3, or 4.

    • DNA interaction, antimicrobial, antioxidant and anticancer studies on Cu(II) complexes of Luotonin A

      2017, Journal of Photochemistry and Photobiology B: Biology
      Citation Excerpt :

      Luotonin A is structurally identical to another anticancer drug camptothecin which has strong topoisomerase I characteristics [6,7]. There is a considerable interest in the study of biological properties of Luotonin A, because of its lower toxicity a higher chemical stability compared with campatothecin [8–10]. The biological activities such as anticancer, topoisomerase I inhibition) of natural products (Curcumin, Salinomycin, etc.) were enhanced by complex formation with metals.

    View all citing articles on Scopus
    View full text