c-myc antisense oligonucleotides sensitize human colorectal cancer cells to chemotherapeutic drugs.
OBJECTIVE
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 with c-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 G(2)/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.


CONCLUSIONS
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.
Abaza
Mohamed-Salah I
MS
Molecular Biology, Department of Biological Sciences, College of Science, Kuwait University, Safat, State of Kuwait. abaza@kuc01.kuniv.edu.kw
Al-Saffar
Amal
A
Al-Sawan
Shorooq
S
Al-Attiyah
Rajaa
R
D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D003114:Colony-Forming Units Assay; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000473:pathology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D006801:Humans; D020319:Oligodeoxyribonucleotides, Antisense / Q000627:therapeutic use*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
D018797:Cell Cycle Proteins; C489427:MYC protein, human; D020319:Oligodeoxyribonucleotides, Antisense; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger