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Published on: August 12, 2015
Combination silencer RNA (siRNA) targeting Bcl-2 antagonizes siRNA against thymidylate synthase in human tumor cell
Aleksandra A Pandyra1, Randal Berg, Mark Vincent
1London Regional Cancer Centre, 790 Commissioners Rd. East, London, ON, Canada N6A 4L6.
Abstract:
Nonspecific toxicity and resistance to traditional cytotoxic drugs are impediments to effective cancer therapy. Development of drugs targeting cellular molecules that mediate malignant characteristics may improve therapy. Antisense drugs that reduce mRNA and protein on which tumor cells depend for viability and treatment resistance are examples of such candidates. In particular, combining antisense drugs to simultaneously reduce multiple mRNAs/proteins is predicted to enhance antitumor effects. We hypothesized that combined treatment with silencer RNAs (siRNAs) targeting molecules mediating both proliferation (thymidylate synthase; TS) and survival (Bcl-2) would decrease proliferation and sensitize human tumor cells to nonantisense drugs in a greater-than-additive manner. We report that simultaneous treatment of human cervical carcinoma (HeLa) and breast tumor (MCF-7) cell lines with siRNAs targeting both TS and Bcl-2 had unexpected, nonreciprocal antagonistic effects. Two siRNAs targeting different Bcl-2 mRNA sequences reduced the capacity of TS siRNA to reduce TS mRNA and protein, with no evidence of converse effects by TS siRNA on Bcl-2 mRNA or protein. Moreover, treatment of HeLa cells with siRNA targeting Bcl-2 resulted in increased TS mRNA and protein. Pretreatment of HeLa and MCF-7 cells with TS siRNA sensitized cells to TS-targeting drugs, but addition of antagonistic Bcl-2 siRNA to the pretreatment regimen abrogated sensitization. Combined targeting of separate physiological pathways by antisense reagents may be a useful approach in treatment of cancer, but antagonistic interactions could abrogate advantages or reduce effectiveness of other antisense and nonantisense reagents.
Insights
Combining silencer RNAs (siRNAs) against thymidylate synthase (TS) and Bcl-2 showed unexpected antagonistic effects, reducing cancer cell sensitization to drugs. This highlights potential challenges in combined antisense therapy for cancer treatment.
Area of Science:
- Molecular Biology
- Cancer Therapeutics
- RNA Interference
Background:
- Nonspecific toxicity and drug resistance limit current cancer therapies.
- Targeting molecules crucial for tumor cell viability and resistance, such as via antisense drugs, offers a promising therapeutic avenue.
- Simultaneous reduction of multiple messenger RNAs (mRNAs) and proteins using antisense agents is predicted to enhance antitumor efficacy.
Purpose of the Study:
- To investigate the combined effects of silencer RNAs (siRNAs) targeting thymidylate synthase (TS) and Bcl-2 in human cancer cell lines.
- To determine if simultaneous siRNA targeting of proliferation (TS) and survival (Bcl-2) pathways enhances antitumor effects and drug sensitization.
- To evaluate potential synergistic or antagonistic interactions between siRNAs targeting distinct cellular pathways.
Main Methods:
- Human cervical carcinoma (HeLa) and breast tumor (MCF-7) cell lines were treated with siRNAs targeting TS and Bcl-2.
- mRNA and protein levels of TS and Bcl-2 were quantified to assess the efficacy of siRNA-mediated gene silencing.
- Cellular proliferation and sensitization to TS-targeting drugs were evaluated following combined siRNA treatments.
Main Results:
- Simultaneous treatment with siRNAs targeting TS and Bcl-2 resulted in unexpected, nonreciprocal antagonistic effects.
- Bcl-2 siRNAs diminished the capacity of TS siRNA to reduce TS mRNA and protein; TS siRNA did not affect Bcl-2 levels.
- Treatment with Bcl-2 siRNA alone increased TS mRNA and protein levels, and combining Bcl-2 siRNA with TS siRNA abrogated drug sensitization.
Conclusions:
- Combined targeting of separate physiological pathways using antisense reagents may present significant antagonistic interactions.
- These interactions can potentially abrogate therapeutic advantages or reduce the effectiveness of both antisense and nonantisense drugs.
- Careful consideration of potential drug-drug interactions is crucial for developing effective combination therapies in cancer treatment.
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