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The interaction of a new anti‐tumour drug, KAR‐2 with calmodulin
Author(s) -
Orosz F,
Vértessy B G,
Salerno C,
Crifo C,
Capuozzo E,
Ovádi J
Publication year - 1997
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0701190
Subject(s) - calmodulin , trifluoperazine , vinblastine , dissociation constant , chemistry , in vivo , biological activity , mechanism of action , biochemistry , in vitro , calcium , biophysics , enzyme , pharmacology , biology , chemotherapy , receptor , microbiology and biotechnology , organic chemistry , genetics
KAR‐2 (3′′‐(β‐chloroethyl)‐2′′,4′′‐dioxo‐3,5′′‐spiro‐oxazolidino‐4‐deacetoxy‐vinblastine) is a semisynthetic bis‐indol derivative, with high anti‐microtubular and anti‐tumour activities but with low toxicity. KAR‐2, in contrast to other biologically active bis‐indols (e.g. vinblastine), did not show anti‐calmodulin activity in vitro (enzyme kinetic, fluorescence anisotropy and immunological tests). Direct binding studies (fluorescence resonance energy transfer, circular dichroism) provided evidence for the binding of KAR‐2 to calmodulin. The binding affinity of KAR‐2 to calmodulin (dissociation constant was about 5 μ M ) in the presence of Ca 2+ was comparable to that of vinblastine. KAR‐2 was able to interact with apo‐calmodulin as well; in the absence of Ca 2+ the binding was of cooperative nature. The effect of drugs on Ca 2+ homeostasis in human neutrophil cells was investigated by means of a specific fluorescent probe. Trifluoperazine extensively inhibited the elevation of intracellular Ca 2+ level, vinblastine did not appreciably affect it, KAR‐2 stimulated the Ca 2+ influx and after a transient enhancement the Ca 2+ concentration reached a new steady‐state level. Comparison of the data obtained with KAR‐2 and bis‐indols used in chemotherapy suggests that the lack of anti‐calmodulin potency resides on the spiro‐oxazolidino portion of KAR‐2. This character of KAR‐2 manifested itself in various systems and might result in its low in vivo toxicity, established in an anti‐tumour test.