The present disclosure provides nucleic acid compositions that incorporate one or more halouracil molecules. More specifically, the present disclosure reveals that the replacement of uracil nucleotides within a microRNA nucleotide sequence with a 5-halouracil increases the ability of the micro-RNA to inhibit cancer progression and tumorigenesis. As such, the present disclosure provides various nucleic acid (e.g., microRNA) compositions having 5-halouracil molecules incorporated in their nucleic acid sequences and methods for using the same. The present disclosure further provides pharmaceutical compositions comprising the modified nucleic acid compositions, and methods for treating cancers using the same.