Abstract 1493: Development of 5-FU-modified tumor suppressor microRNAs as a platform for novel microRNA-based cancer therapeutics
Authors: Yuen John G. , Fesler Andrew , Hwang Ga-Ram , Dahl Thomas , Chen Lan-Bo , Chen Henry , Ju Jingfang 
Published: June 2022

MicroRNA (miRNAs) are small non-coding RNAs that regulate gene expression and are frequently dysregulated, affecting many key oncogenic pathways. Drug resistance is one of the key barriers in the treatment of cancer, contributing to the poor prognoses in patients. To overcome this hurdle, we sought to exploit the inherent multi-targeted nature of miRNAs for the development of cancer therapeutics. Despite its potential, it remains a challenge to deliver nucleic acid-based therapies, including miRNAs, to cancer cells. We recently developed a novel approach to modify miRNAs by replacing its uracil bases with 5-fluorouracil (5-FU) in the guide strand of tumor suppressor miRNAs. This modification combines the therapeutic effects of a traditional chemotherapeutic with the effect of a tumor suppressor miRNA to create a potent, multi-targeted therapeutic molecule. We have previously demonstrated that 5-FU-modified miR-15a (where the prefix 5-FU- refers to the modified miRNA mimetic, i.e., 5-FU-miR-15a) and 5-FU-miR-129 have several key features such as the retention of target gene specificity, vehicle-free delivery, enhanced potency, and stability in colon and pancreatic cancer. To demonstrate the general applicability of this approach for other tumor suppressor miRNAs we selected 12 well-studied tumor suppressor miRNAs and modified them with 5-FU. The efficacy of these 12 different miRNA mimetics were screened in several cancer types including gastric, lung, breast, pancreatic, and blood cancer. Our results show that 5-FU-modified miRNAs are more effective at inhibiting cancer cell proliferation than its unmodified counterparts. In gastric cancer, there is an 8.4-fold increase in efficacy after modifying let-7a (let-7a IC50 = 59.5 nM vs. 5-FU-let-7a IC50 = 7.1 nM) and a 4.3-fold increase for miR-145 (miR-145 IC50 = 20.9 nM vs. 5-FU-miR-145 IC50 = 4.9 nM). Similarly in lung cancer, there is a 6.3-fold increase in efficacy after modifying let-7a (let-7a IC50 = 143.5 nM vs. 5-FU-let-7a IC50 = 22.8 nM) and a 13.8-fold increase (miR-145 IC50 = 51.7 nM vs. 5-FU-miR-145 IC50 = 11.0 nM). We also show that these miRNA mimetics can be delivered into cancer cells without the aid of a delivery vehicle. Additionally, this modification preserves miRNA target gene suppression activity and has 5-FU activity from its breakdown products. Lastly, in a CT26 syngeneic mouse colon cancer model, we demonstrate that 5-FU-miR-15a inhibits tumor growth by 58.2% without vehicle and is enhanced to 97.2% with a low concentration of vehicle. Notably, there was no observable toxicity in the animal studies. This work demonstrates the potential of fluoropyrimidine-modification that can be applicable to a broad spectrum of tumor suppressor miRNAs in different cancer types and represents an advancement in the development of therapeutic miRNAs for cancer treatment.

Citation Format: John G. Yuen, Andrew Fesler, Ga-Ram Hwang, Thomas Dahl, Lan-Bo Chen, Henry Chen, Jingfang Ju. Development of 5-FU-modified tumor suppressor microRNAs as a platform for novel microRNA-based cancer therapeutics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1493.