Different Effects of Epigenetic Modifiers on the Cytotoxicity Induced by 5-Fluorouracil, Irinotecan or Oxaliplatin in Colon Cancer Cells

Abstract

We investigated the effects of epigenetic modifiers such as DNA methyltransferase (DNMT) or histone deacetylase (HDAC) inhibitors on the cytotoxicity induced by 3 anticancer drugs (5-fluorouracil (5-FU), irinotecan (CPT-11) or its active form SN38, and oxaliplatin (L-OHP)) in human colorectal cancer (CRC) cells. Cytotoxicity in 4 CRC cell lines (HT29, SW480, SW48 and HCT116) was examined by colorimetric assay after drug treatment for 72 h. The effects of drug combinations were analyzed by an isobologram method. SW480 cells showed the lowest sensitivity to cytotoxicity induced by the anticancer drugs among the 4 CRC cell lines. In SW480 cells, DNMT inhibitors, such as decitabine (DAC), azacytidine and zebularine (Zeb), showed synergic effects on the cytotoxicity induced by anticancer drugs except for SN-38 plus Zeb, while HDAC inhibitors, trichostatin A, suberoylanilide hydroxamic acid and valproic acid, showed antagonistic effects. DAC showed the most potent synergic effects among the epigenetic modifiers studied. Thus, we examined whether the synergic effect of DAC is observed in other different CRC cell lines, HT29, SW48 and HCT116 cells. In all 4 CRC cell lines, the cytotoxicity of L-OHP was enhanced in a synergic manner by cotreatment with DAC. However, synergic effects of DAC with 5-FU or CPT-11 (SN-38) were not observed in 4 CRC cell lines.Key words DNA methyltransferase inhibitor; synergism; colorectal cancer; isobologram; histone deacetylase inhibitor Colorectal cancer (CRC) is the second leading cause of cancer-related deaths in the world.1) CRC treatment strategies are highly dependent on tumor stage. Metastatic CRC (stage IV) is treated with combined chemotherapy, including 5-fluorouracil (5-FU) plus either irinotecan (CPT-11) or oxaliplatin (L-OHP). Recently, it has been reported that combined chemotherapy plus biological agents (anti-angiogenic or antiepidermal growth factor receptor molecules) increased stage IV patients' median survival period.2) Despite many therapeutic options, an efficient drug combination remains to be found for CRC patients. In addition, tailored therapy for each CRC patient is still a challenge.It is well-established that epigenetic alterations such as DNA methylation and histone modifications play a crucial role in the initiation and progression of cancer, including CRC. Unlike genetic alterations, epigenetic alterations are reversible and can be targeted by epigenetic modifiers.3) Epigenetic modifiers such as DNA methyltransferase (DNMT) inhibitors and histone deacetylase (HDAC) inhibitors have been administered for several years and have been evaluated as a treatment approach for a variety of cancers in the United States. DNMT inhibitors, such as decitabine (5-aza-2′-deoxycytidine; DAC) and 5-azacytidine (AC), are being used for the treatment of myelodysplastic syndromes (MDS), but the efficacy is variable. 4,5) In addition, DAC is used usually for patients with acute myeloid leukemia who are not candidates for standard remission, including chemotherapy. 6) On the other h...

Differential sensitization of two human colon cancer cell lines to the antitumor effects of irinotecan combined with 5-aza-2'-deoxycytidine

“…5-Aza-2'-deoxycytidine (DAC) is a DNA methyltransferase (DNMT) inhibitor, a DNA demethylating agent, and a cell cycle-arresting agent (7)(8)(9). Preliminary studies have been conducted on the combined use of DNMT inhibitors with existing antitumor agents (10)(11)(12). Accordingly, a preliminary experiment was conducted on a combination of a specific antitumor agents, including CPT-11, SN-38 or 5-FU with one of several epigenetic modifiers including DAC in two different human CRC cell lines; HCT116 and HT29 (13).…”

Epigenetic polypharmacology: A new frontier for epi‐drug discovery

“…44 Regarding epi-drugs, it has been recently highlighted their capability (mostly HDACi and DNMTi) 45,46 to increase chromatin accessibility to conventional DNA-damaging chemotherapeutic agents, markedly enhancing their effects and establishing a rationale for their combination. Several pieces of evidence showed that the CpG island methylation is responsible for the induction of drug resistance, and this effect can be reversed through the treatment with hypomethylating agents [47][48][49][50] including zebularine 50 and decitabine 2. 50,51 The combination of HDACi with cytostatic agents (such as doxorubicin and paclitaxel) has been widely evaluated in both preclinical and clinical contexts.…”

“…Several pieces of evidence showed that the CpG island methylation is responsible for the induction of drug resistance, and this effect can be reversed through the treatment with hypomethylating agents [47][48][49][50] including zebularine 50 and decitabine 2. 50,51 The combination of HDACi with cytostatic agents (such as doxorubicin and paclitaxel) has been widely evaluated in both preclinical and clinical contexts. Here, a reliable increase in the therapeutic outcome was achieved, due to the downregulation of proangiogenic and tumorigenic factors (ie, hypoxia-inducible factor 1 [HIF-1α] and vascular endothelial growth factor [VEGF]), 52,53 the repression of DNA repair systems 54 as well as the enhancement of apoptosis induction.…”

“…For these compounds, the ability to bind also BET bromodomain has been reported (IC 50 [299][300][301] Starting from SAR studies focused on 70 (Figure 8 (Figure 9) and the benzamide 73 304 (MC2392; Figure 9), strictly related to ATRA, to be tested in leukemia. While 72 did not show any significant activity in leukemia cells, 73, despite its weak retinoid activity and general no HDAC inhibition in vitro and in vivo, was able to induce changes in H3 acetylation at a small subset of PML-RARα-binding sites, to alter expression of stress-responsive and apoptotic genes, and to induce massive cell death specifically in PML-RARα expressing APL cells, while solid and other leukemic tumors were not affected.…”

Synergistic Anti-glioma Effects <i>in Vitro</i> and <i>in Vivo</i> of Enediyne Antibiotic Neocarzinostatin and Paclitaxel <i>via</i> Enhanced Growth Delay and Apoptosis-Induction

“…All the experiments were carried out in triplicate. By the method of Chou and Talalay, [35][36][37] the combination indexes (CIs) isobologram were calculated and plot with Calcusyn software, and a CI value >1, CI value=1, and CI value <1 mean antagonism, additivity, or synergism, respectively.…”