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Direct Comparison of Chol-siRNA Polyplexes and Chol-DsiRNA Polyplexes Targeting STAT3 in a Syngeneic Murine Model of
Zhen Ye1, Mai Mohamed Abdelmoaty1,2, Stephen M Curran1
1Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, Omaha, NE 68198, USA.
Abstract:
RNA interference (RNAi) molecules have tremendous potential for cancer therapy but are limited by insufficient potency after intravenous (IV) administration. We previously found that polymer complexes (polyplexes) formed between 3'-cholesterol-modified siRNA (Chol-siRNA) or DsiRNA (Chol-DsiRNA) and the cationic diblock copolymer PLL[30]-PEG[5K] greatly increase RNAi potency against stably expressed LUC mRNA in primary syngeneic murine breast tumors after daily IV dosing. Chol-DsiRNA polyplexes, however, maintain LUC mRNA suppression for ~48 h longer after the final dose than Chol-siRNA polyplexes, which suggests that they are the better candidate formulation. Here, we directly compared the activities of Chol-siRNA polyplexes and Chol-DsiRNA polyplexes in primary murine 4T1 breast tumors against STAT3, a therapeutically relevant target gene that is overexpressed in many solid tumors, including breast cancer. We found that Chol-siSTAT3 polyplexes suppressed STAT3 mRNA in 4T1 tumors with similar potency (half-maximal ED50 0.3 mg/kg) and kinetics (over 96 h) as Chol-DsiSTAT3 polyplexes, but with slightly lower activity against total Stat3 protein (29% vs. 42% suppression) and tumor growth (11.5% vs. 8.6% rate-based T/C ratio) after repeated IV administration of equimolar, tumor-saturating doses every other day. Thus, both Chol-siRNA polyplexes and Chol-DsiRNA polyplexes may be suitable clinical candidates for the RNAi therapy of breast cancer and other solid tumors.
Insights
Both cholesterol-modified small interfering RNA (siRNA) and DsiRNA polyplexes show promise for cancer therapy. These formulations effectively target STAT3 in breast tumors, suggesting potential for treating solid tumors via RNA interference.
Area of Science:
- Biochemistry
- Molecular Biology
- Oncology
Background:
- RNA interference (RNAi) holds therapeutic potential for cancer but faces challenges with intravenous (IV) delivery and potency.
- Polymer complexes (polyplexes) of cholesterol-modified siRNA (Chol-siRNA) and DsiRNA (Chol-DsiRNA) with PLL[30]-PEG[5K] enhance RNAi potency in murine breast tumors.
- Chol-DsiRNA polyplexes demonstrate prolonged mRNA suppression compared to Chol-siRNA polyplexes.
Purpose of the Study:
- To directly compare the efficacy of Chol-siRNA polyplexes and Chol-DsiRNA polyplexes against the therapeutically relevant target gene STAT3 in primary murine 4T1 breast tumors.
- To evaluate the impact of these polyplexes on STAT3 mRNA and protein levels, as well as tumor growth.
- To assess the suitability of both formulations as clinical candidates for RNAi-based cancer therapy.
Main Methods:
- Formulation of polyplexes using 3'-cholesterol-modified siRNA (Chol-siRNA) or DsiRNA (Chol-DsiRNA) with the diblock copolymer PLL[30]-PEG[5K].
- Intravenous (IV) administration of equimolar, tumor-saturating doses of polyplexes every other day into murine 4T1 breast tumors.
- Quantification of STAT3 mRNA and protein suppression, and assessment of tumor growth inhibition using rate-based T/C ratios.
Main Results:
- Both Chol-siSTAT3 and Chol-DsiSTAT3 polyplexes demonstrated similar potency (ED50 of 0.3 mg/kg) and kinetics (over 96 hours) in suppressing STAT3 mRNA.
- Chol-DsiSTAT3 polyplexes showed slightly higher suppression of total Stat3 protein (42% vs. 29%) and tumor growth (8.6% vs. 11.5% rate-based T/C ratio) compared to Chol-siSTAT3 polyplexes.
- Repeated IV administration of equimolar doses every other day was employed for the comparison.
Conclusions:
- Both Chol-siRNA and Chol-DsiRNA polyplexes are effective in suppressing STAT3 mRNA and show potential for RNAi therapy in breast cancer.
- While Chol-DsiRNA polyplexes exhibited marginally superior effects on protein suppression and tumor growth, both formulations represent viable clinical candidates.
- These findings support the advancement of these polyplexes for RNAi-based treatment of breast cancer and other solid tumors.
