c-<i>myc</i> Antisense Oligonucleotides Sensitize Human Colorectal Cancer Cells to Chemotherapeutic Drugs

Abstract

Background/Aims: Overexpression of the c-myc oncogene frequently occurs in both colon tumors and colon carcinoma cell lines. We examined the sensitization of human colorectal cancer cells to chemotherapeutic drugs using c-myc antisense (AS) phosphorothioate oligonucleotides ([S]ODNs). Methods: Cancer cells were treated with c-myc [S]ODNs, taxol, 5-fluorouracil (5-FU), doxorubicin and vinblastine individually and in combination. The antiproliferative effects, type of interaction between c-myc [S]ODNs and cytotoxic drugs, cell cycle, apoptosis and expression of cell-cycle- and apoptosis-regulatory genes were evaluated. Results: After treatment withc-myc AS[S]ODNs, the growth of cancer cells was markedly inhibited in a dose- and time-dependent manner and the levels of c-myc mRNA and protein were greatly decreased (p < 0.0001). The combinations of c-myc AS[S]ODNs and cytotoxic drugs produced greater growth inhibition of human colorectal cancer cells compared to single treatment with either c-myc AS[S]ODNs (p < 0.006) or cytotoxic drugs (p < 0.0001). These combinations exhibited time- and dose-dependent additive and/or synergistic antiproliferative effects. Cancer cells treated with cytotoxic drugs were growth arrested in the S phase. In contrast, cells treated with either c-myc AS[S]ODNs or by the combination of c-myc AS[S]ODNs and cytotoxic drugs were growth arrested in the G₂/M and S phases. The combination treatments also exhibited a marked apoptotic effect compared to single treatments. c-myc AS[S]ODN treatment reduced the mRNA levels of Bcl2, BclxL, cdk2, cyclin E1, cdk1 and cyclin B1, while increasing the mRNA levels of p21, p27, bax and caspase-3. Conclusion: This two-hit approach may be important in the quest to overcome drug resistance in cancer patients whose tumors carry an overexpressed c-myc gene.

Disablingc-Mycin Childhood Medulloblastoma and Atypical Teratoid/Rhabdoid Tumor Cells by the Potent G-Quadruplex Interactive Agent S2T1-6OTD

“…Based on previously published work, it is well established that the suppression of c-Myc expression is closely linked to the specific arrest in the G 0 -G 1 cell cycle phase (69)(70)(71)(72) and downregulation of c-Myc inhibits both cyclins and CDK2 expression in rhabdomyosarcoma (73), in T lymphocytes (74), and in colorectal cancer cells (75). Our results show that under the conditions where inhibition of both proliferation and c-Myc activity was observed, S2T1-6OTD treatment resulted in a decrease in the protein expression of the cell cycle activator CDK2 and in a clear G 0 -G 1 cell cycle arrest in all brain tumor cell lines tested and decreased the percentage of the cells that were able to enter the S phase.…”

Valproic acid, an anti-epileptic drug and a histone deacetylase inhibitor, in combination with proteasome inhibitors exerts antiproliferative, pro-apoptotic and chemosensitizing effects in human colorectal cancer cells: Underlying molecular mechanisms

“…Cell proliferation assay was performed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, as previously described (11). The cells were treated with various concentrations of VPA (0.5-8 mM) for 24 h and then exposed to MG132 (0.15 and 0.25 µM), PI-1 (7.8 and 15.6 nM) or PR-39 (106 and 112 pM) for an additional 48 h. For single-agent treatment, the cells were exposed to VPA for 72 h. Upon the completion of the treatments, the media were discarded and 100 µl/well of MTT (5 mg/ml in culture medium filter-sterilized) was added, and the plates were incubated for 4 h at 37˚C.…”

“…A colony formation assay was carried out as previously described (11) to confirm the effects of VPA, PIs (MG132, PI-1 or PR-39) and their combinations on the colorectal cancer cells. Briefly, the SW1116 and SW837 cells (2.5x10 5 cells/ml) were seeded into 24-well plates and incubated for 18 h. The cells were then treated with VPA (2.5 mM) or the PIs MG132 (1.5 µM), PI-1 (36 nM), or PR-39 (2 nM), as well as combinations of VPA with each of the PIs.…”

5-Fluorouracil-loaded poly(&epsilon;-caprolactone) nanoparticles combined with phage E gene therapy as a new strategy against colon cancer

“…29 This is of interest given the relationship between colon cancer drug resistance and invasive/metastatic ability. 30 The nanomedicine inhibited cell proliferation in a dose-dependent manner with a much lower IC 50 (concentrations of the drug needed to reduce population growth by 50% in vitro) value (0.1 µM) than that reported previously for SW480 cells (IC 50 5-FU: 4 µM), 31 showing that the antitumor effect of 5-FU-loaded PCL NPs in SW480 was 40-fold higher than that for the free drug ( Figure 3B). …”