Tetrachloro-1,4-benzoquinone (TCBQ), an active metabolite of pentachlorophenol (PCP), is genotoxic and potentially carcinogenic. As an electrophilic and oxidative molecule, TCBQ can conjugate with deoxyguanosine in DNA molecules and/or impose oxidative stress in cells. In the current study, we investigated the effects of TCBQ on intracellular ROS production, apoptosis, and cytotoxicity against three different subtypes of human breast cancer cells. Luminal A subtype MCF7 (ER+, PR+, HER2−) cells maintained the highest intracellular ROS level and were subjected to TCBQ-induced ROS reduction, apoptosis, and cytotoxicity. HER2 subtype Sk-Br-3 (ER−, PR−, HER2+) cells possessed the lowest intracellular ROS level. TCBQ promoted ROS production, inhibited apoptosis, and elevated cytotoxicity (due to necrosis) against Sk-Br-3 cells. Triple-negative/basal-like subtype MDA-MB-231 cells were less sensitive towards TCBQ treatment. Therefore, the effect of prolonged exposure to PCP and its active metabolites on cancer growth is highly cancer-cell-type specific.
Hedyotis diffusa is a Chinese herbal medicine widely used in combination with other herbal medicines such as Scutellaria barbata to treat various types of cancer. Late-stage and recurrent cancer patients usually use H. diffusa during chemotherapy in expecting to achieve additive or synergistic therapeutic effects. Several classes of active ingredients, including anthraquinones, iridoid glucosides and stigmasterols, have been isolated and characterized from H. diffusa. In the current study, we isolated alkaloid/flavonoid from H. diffusa and showed that the crude alkaloid/flavonoid extract rather than its three major components possessed antitumor activity against human breast cancer cell line MCF7. Co-administration of H. diffusa water extract diminished the cytotoxicities of chemotherapy drugs doxorubicin, cyclophosphamide and docetaxel towards the MCF7 cells, implicating that H. diffusa should not be used during breast cancer chemotherapy.
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