combination of paclitaxel with ht reduced mcf - 7 and mda - mb - 231 cell viability in vitro, and tumor volume in breast cancer - bearing sprague – dawley rats ( in vivo injected ht dose = 0. 5 mg / kg / day ). in ht - 29 and widr colorectal cancer cell lines, combination of 10 μm ht and monoclonal anti - epidermal growth factor receptor ( egfr ) antibod y cetuximab reduced cell growth, both in the presence and in the absence of epidermal growth factor ( egf ) stimulation, inducing g1 / s and g2 / m phase cell cycle arrest. in human osteosarcoma mg - 63 cell line, 20 μg / ml ( ≈37 μm ) ole had an additive effect on anthracycline adriamycin - induced reduction in cell viability, with a mechanism that did not alter the g2 / m phase blockade elicited by adriamycin. similarly, in 143b osteosarcoma cells, ole showed a synergistic, antiproliferative, and anti - migratory effect in combination with estradiol metabolite 2 - methoxyestradiol at all ole concentrations tested ( 1 – 250 μm for proliferation, and 100 μm for wound healing assay ). on the contrary, ht did not modify doxorubicin - mediated growth inhibition of human osteosarcoma cells u - 2 os. in neuroblastoma cells t98g, 277. 5 μm and 555 μm ole showed a synergistic effect with alkylating agent temozolomide on cell viability, increasing the expression of mirnas involved in tumor growth suppression, mainly let - 7d. ole and ht may also magnify the efficacy of other types of cancer treatment. in nasopharyngeal cancer cell line hne1 and hone1, 200 μm ole enhanced cell radiosensitivity in vitro and in vivo after injection in balb / c nude mice, with a mechanism involving ole - dependent removal of hif - 1α hypoxic repression exerted at mir - 519d promoter region, upregulation of mir - 519d, and mir - 519d targeting of dna damage - regulated protein 1 ( pdrg1 ). despite these encouraging results, since both ole and ht may act as transcriptional regulators and are extensively metabolized by the liver ( see sections above ), a careful analysis of the effects of both phenols on phase i and phase ii enzyme kinetics and expression should be performed before considering the use of ole and ht during chemotherap eutic treatments. preliminary data obtained in human liver microsomes point towards ole - mediated inhibition of cy3a and cyp1a2 activity. on the contrary, a study performed in 129 / sv wt and ppara - null mice demonstrated that ole ( ingested with food, thus absorbed through the intestinal wall ) stimulated the transcription of cytochrome p450 genes cyp1a1, cyp1a2, cyp1b1, cyp3a14, cyp3a25, cyp2c29, cyp2c44, cyp2d22, and cyp2e1 in the liver, with a mechanism mediated by peroxisome proliferator - activated receptor α ( pparα ). studies defining the effects of ole and ht on the expression of and interaction with phase i and phase ii enzymes are still missing, but they should be considered absolutely necessary in order to determine if ole and ht are able to modify the metabolism of other drugs. besides their possible synergic / additive actions, ole and ht might also be seen as useful support agents during cancer treatment. a lot of experimental data in vivo and in vitro have definitively demonstrated the ros scavenger ability of ole and ht, which can also act on antioxidant cellular mechanisms restoring ros homeostasis, including promotion of the increase in reduced glutathione levels ( gsh ), depletion of lipid peroxidation product malondialdehyde ( mda ), intensification of the expression and / or activity of detoxicating enzymes sod, cat, glutathione - s - transferase ( gst ), and glutathione peroxidase ( gsh - px ), and nuclear factor e2 - related factor 2 ( nrf2 ) upregulation / transactivation, which in turn regulates the expression of fundamental enzymes protecting cells from oxidative damage, like ho - 1. radical and non - radical ros ( including hydrogen peroxide h2o2, superoxide anion radical o2, and hydroxyl radical oh ) may have a pro - tumorigenic effect; they are involved in cancer insurgence determining dna damage, genomic instability, and interference with signalling and metabolic pathways, enhance cell proliferation through the activation of pro - survival pathways in cancer cells while promoting the reorganization of cellular antioxidant capacities and adaptation to hypoxic conditions, are involved in the development of anti - cancer therapy resistance ( through the expansion of cell antioxidant capacities ), push the activation of metastasis cellular programs via emt, and boost immunosupp ression and angiogenesis in the cancer microenvironment. however, if ros concentration overcomes cancer cell defenses against oxidative stress and damage, or cancer cell - produced ros balance is perturbated, ros may account for fatal cell damage and trigger apoptosis. this may explain the fact that the mechanism of action of some common cancer treatments ( e. g., radiation, inorganic compounds, tyrosine kinase inhibitors, monoclonal antibod ies, protease inhibitors, pyrimidine analogues, alkylating agents, and anthracyclines ) relies on oxidative stress and ros - dependent apoptosis. ole and ht cytotoxic actions themselves in part depend on ros generation; moreover, 200 μm ole reduced hif - 1α mrna and protein levels in hne - 1 and hone - 1 nasopharyngeal cancer cell lines, and pro - apoptotic ole concentration corresponding to 100 μm was able to increase ros production in mda - mb - 231 cell line, with the maximum peak obtained after 4 h incubation. ros - mediated damage at least in part accounts for chemotherap y - dependent toxicity detected at the tissue level on non - cancer cells. however, ole and ht have shown an important ability to mitigate the toxicity elicited by chemotherap eutic agents mainly through their largely demonstrated antioxidant and ros scavenger activity. in fact, in vivo, 50 mg / kg, 100 mg / kg, and 200 mg / kg ole showed a dose - dependent antioxidant activity, accounting for amelioration of cisplatin - induced pancreatic, liver, lung, and stomach damage in spraque – dawley rats. in the same in vivo model of cisplatin - induced oxidative stress, 50 mg / kg, 100 mg / kg, and 200 mg / kg ole improved anemia, thrombocytopenia, and leukopenia. in cyclophosphamide - and epirubicin - induced toxicity in sprague – dawley rats, four cycles of 150 mg / kg / week ole reduced lipid peroxidation and increased the activity of antioxidant enzymes in heart, kidney, and liver. moreover, in a model of cyclophosphamide - induced immunosupp ression in broilers, a solution containing 200 mg / l ht reduced duodenal mda levels while increasing the activity of antioxidant enzymes. in vitro, 50 μm and 70 μm ht reduced doxorubicin - mediated toxicity in embryonic rat cardiomyoblasts h9c2 ( 2 - 1 ) after 48 h incubation. also, 24 and 48 h incubation with 50 μm ht reduced doxorubicin - dependent intracellular ros accumulation, increasing sod2 levels and protecting cells from doxorubicin - induced apoptosis. ole - and ht - dependent redox homeostasis restoration might represent a potential issue with respect to ole and ht use at nu trit ionally relevant concentrations as both anticancer drugs and detoxicating agents ( especially during chemotherap y ). low concentrations of both ole and ht ( 10 μm ) protected hl - 60 and pbmcs from h2o2 - induced dna damage, and lymphocytes from pma - stimulated monocyte - mediated oxidative dna damage. this piece of information sounds particularly alarming, since arsenic trioxide ( as2o3 ) is one of the agents utilized to treat acute promyelocytic leukemia, especially in combinatory first-line therapy, and its mechanism of action relies on ros increase. incubation with 30 μm ht for 48 h was not sufficient to reduce viability of hep3b cells, but significantly improved cellular antioxidant capacities. similarly, 5 – 200 μm ht was ineffective as a cytotoxic reagent, but reduced the level of oxidative stress in mcf - 7 cells after 16 h incubation.