SSO111 sodium, a 20mer fully modified antisense oligonucleotide, targets the oncogene? HER2. SSO111 sodium induces exon 15 skipping during splicing, leading to the generation of a novel mRNA transcript that excludes exon 15. SSO111 sodium downregulated HER2 mRNA , which resulted in the inhibition of proliferation and induction of apoptosis in HER2-overexpressing tumor cells.