ABSTRACT
Vascular endothelial growth factor (VEGF) inhibitors, such as bevacizumab, have improved outcomes in metastatic colorectal cancer (CRC). Recent studies have suggested that VEGF can delay the onset of cellular senescence in human endothelial cells. As VEGF receptors are known to be upregulated in CRC, we hypothesized that VEGF inhibition may directly influence cellular senescence in this disease. In our study, we observed that treatment with bevacizumab caused a significant increase (p < 0.05) in cellular senescence in vitro in several CRC cells, such as MIP101, RKO, SW620 and SW480 cells, compared to untreated or human IgG-treated control cells. Similar results were also obtained from cells treated with a VEGFR2 kinase inhibitor Ki8751. In vivo, cellular senescence was detected in MIP101 tumor xenografts from 75% of mice treated with bevacizumab, while cellular senescence was undetectable in xenografts from mice treated with saline or human IgG (p < 0.05). Interestingly, we also observed that the proportion of senescent cells in colon cancer tissues obtained from patients treated with bevacizumab was 4.4-fold higher (p < 0.01) than those of untreated patients. To understand how VEGF inhibitors may regulate cellular senescence, we noted that among the two important regulators of senescent growth arrest of tumor cells, bevacizumab-associated increase in cellular senescence coincided with an upregulation of p16 but appeared to be independent of p53. siRNA silencing of p16 gene in MIP101 cells suppressed bevacizumab-induced cellular senescence, while silencing of p53 had no effect. These findings demonstrate a novel antitumor activity of VEGF inhibitors in CRC, involving p16.
Subject(s)
Angiogenesis Inhibitors/pharmacology , Antibodies, Monoclonal, Humanized/pharmacology , Cellular Senescence/drug effects , Colorectal Neoplasms/metabolism , Vascular Endothelial Growth Factor A/antagonists & inhibitors , Angiogenesis Inhibitors/administration & dosage , Animals , Antibodies, Monoclonal, Humanized/administration & dosage , Bevacizumab , Cell Line, Tumor , Cell Survival/drug effects , Colorectal Neoplasms/drug therapy , Colorectal Neoplasms/genetics , Cyclin-Dependent Kinase Inhibitor p16/genetics , Humans , Mice , Mice, Nude , Xenograft Model Antitumor AssaysABSTRACT
The study set out to determine the potential for commercially available preparations of black cohosh (Actaea racemosa), chaste tree berry (Vitex agnus-castus), crampbark (Viburnum opulus) and false unicorn (Chamaelirium luteum) to inhibit the major human drug metabolizing enzymes CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 as well as CYP1A1 which activates some carcinogens. In vitro microplate-based assays using cDNA-expressed CYP450 isoforms and fluorogenic substrates were used. Components of the commercial herbal preparations interfered with the assays and limited the concentration ranges that could be tested. Nevertheless, the fluorogenic assays were robust, reproducible and easy to perform and thus are still useful for initial screening for potential herb-drug interactions. None of the preparations affected CYPs 1A1 or 2C9 at the concentrations tested but all preparations inhibited some of the enzymes with potencies around 1 µg/mL. The three most potent interactions were: chaste tree berry and CYP2C19 (IC50) 0.22 µg/mL); chaste tree berry and CYP3A4 (IC50) 0.3 µg/mL); black cohosh and CYP2C19 (IC50) 0.37 µg/mL,). Thus, the study successfully identified the potential for the commercial herbal preparations to inhibit human drug metabolizing enzymes. Whether this potential translates into clinically significant herb-drug interactions can only be confirmed by appropriate in vivo studies.
Subject(s)
Cytochrome P-450 Enzyme System/metabolism , Plant Extracts/adverse effects , Plants, Medicinal/adverse effects , Biotransformation , Cimicifuga/adverse effects , Cimicifuga/chemistry , Cytochrome P-450 Enzyme Inhibitors , Fluorescent Dyes/metabolism , Herb-Drug Interactions , Humans , Plants, Medicinal/chemistry , Viburnum/adverse effects , Viburnum/chemistry , Vitex/chemistryABSTRACT
The goal of our study was to determine whether maternal exposure to red raspberry leaf (RRL) and its constituents can permanently alter biotransformation of fluorogenic substrates by cytochrome P450 (CYP) in the livers of male and female offspring. Nulliparous female rats received vehicle, raspberry leaf, kaempferol, quercetin, or ellagic acid orally once breeding had been confirmed until parturition. Hepatic microsomes were prepared from animals at birth (postnatal day 1 [PND1]), weaning (PND21), PND65, and PND120 to determine the biotransformation of 8 fluorogenic substrates. The pattern of biotransformation of all but 2 of the substrates was gender specific. Maternal consumption of RRL increased biotransformation of 3 substrates by female offspring at PND120 resulting in a more masculine profile. Kaempferol and quercetin had a similar effect to RRL. These results suggest that maternal consumption of either RRL or some of its constituents leads to long-term alterations of CYP activity in female offspring.
