Mucronulatol from Caribbean propolis exerts cytotoxic effects on human tumor cell lines.
OBJECTIVE
Mucronulatol is one of the most cytotoxic substances present in Caribbean propolis. This work aimed at initially characterizing the biological effects of mucronulatol in cancer cell lines comprehending both wildtype and resistant sublines.


METHODS
An RP-HPLC technique was employed to separate and purify mucronulatol. IC(50) values were determined using the sulforhodamine B (SRB) proliferation assay. FACS-based cell cycle studies were carried out combining propidium iodide staining and 5-bromo-2'-deoxyuridine incorporation. Cell cycle regulator proteins were detected by Western blotting. The transcription of genes of interest was analyzed using RT-PCR.


RESULTS
In MDR1-/MDR3+ cells, mucronulatol exhibited cytotoxicity in the range of 2.7 - 10.2 microg/ml, while no cytotoxic effects were observed in MDR1+ systems at up to 100 microg/ml. Cytometric studies revealed that mucronulatol promoted a global reduction in all cell cycle phases, with a remarkable increase of the apoptotic sub-G1 population. Immunoblotting showed that mucronulatol induced an up-regulation of p21(Cip1) and p27(Kip1) while down-regulating cyclin E and CDK4 in a drug concentration-dependent manner. No effect on topoisomerase I was observed, while we detected an altered expression of topoisomerases II-I+/-/I(2). RT-PCR studies showed that 2-fold the IC(50) in HCT8 colon carcinoma cells was sufficient for altering the expression pattern of genes in this cell line, including topoisomerase I, thymidilate synthase, EGF receptor and c-myc, amongst others.


CONCLUSIONS
Here, we demonstrate for the first time that mucronulatol exerts cytotoxicity in cancer cell lines by targeting the control of cell cycle progression, indicating that the mechanism of action of this compound involves interference with the cell cycle machinery.
Abteilung Klinische Pharmakologie, Ruhr-Universität Bochum, Germany. david.diaz-carballo@rub.de
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Diaz-Carballo
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Freistã Hler
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Malak
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Bardenheuer
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Reusch
D000970:Antineoplastic Agents / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology*; D015153:Blotting, Western; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D019008:Drug Resistance, Neoplasm; D006801:Humans; D029883:Indigofera; D007529:Isoflavones / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014900:West Indies
D000970:Antineoplastic Agents; D007529:Isoflavones; C530737:mucronulatol