The interaction of a new anti-tumour drug, KAR-2 with calmodulin.
1. KAR-2 (3"-(beta-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). 2. 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 microM) in the presence of Ca2+ was comparable to that of vinblastine. 3. KAR-2 was able to interact with apo-calmodulin as well; in the absence of Ca2+ the binding was of cooperative nature. 4. The effect of drugs on Ca2+ homeostasis in human neutrophil cells was investigated by means of a specific fluorescent probe. Trifluoperazine extensively inhibited the elevation of intracellular Ca2+ level, vinblastine did not appreciably affect it, KAR-2 stimulated the Ca2+ influx and after a transient enhancement the Ca2+ concentration reached a new steady-state level. 5. 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.
Orosz
F
F
Institute of Enzymology, Hungarian Academy of Sciences, Budapest, Hungary.
Vértessy
B G
BG
Salerno
C
C
Crifo
C
C
Capuozzo
E
E
Ovádi
J
J
D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000378:metabolism / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002417:Cattle; D002942:Circular Dichroism; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007074:Immunoglobulin G; D007527:Isoenzymes / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism; D010732:Phosphofructokinase-1 / Q000037:antagonists & inhibitors; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D014268:Trifluoperazine / Q000494:pharmacology; D014747:Vinblastine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology
D000972:Antineoplastic Agents, Phytogenic; D002147:Calmodulin; D007074:Immunoglobulin G; D007527:Isoenzymes; D014268:Trifluoperazine; D014747:Vinblastine; C107832:deacetoxyvinzolidine; D010732:Phosphofructokinase-1; D002118:Calcium