Myotonic dystrophy type 1 (DM1) is an autosomal dominant multisystemic disorder with no approved therapeutics targeting the disease mechanism. DM1 is caused by the expression of expanded CUG repeat RNA (CUGexp), which sequester the muscleblind-like (MBNL) family of RNA binding proteins leading to dysregulated alternative splicing and a host of downstream impacts. While previous studies showed that diamidines rescued DM1 dysregulated alternative splicing events, their potential was limited by toxicity and off-target effects. A new class of modified polycyclic compounds (MPCs), based on diamidines, were created and screened in DM1 patient-derived cell lines. This approach identified MPC03 and MPC04 as being capable of rescuing DM1 dysregulated splicing events at low nanomolar concentrations with no obvious toxicity and limited off-target effects. In a DM1 mouse model, treatment with MPC03 and MPC04 reduced CUGexp RNA levels and partially rescued DM1 mis-splicing. Binding data and modeling showed that lead MPCs bind to CUGexp RNA, and in cells lacking CUG repeats, MPC activity was absent, suggesting that these compounds displace sequestered MBNL proteins from CUGexp RNA. Taken together, MPCs show therapeutic promise across multiple DM1 models.