OPRK1 and myeloid sarcoma: With a molecular weight of ∼3000Da they bridge the gap between small molecules (<500 Da) and largebiologics (>5000 Da).24 Their topologicallystable structure in combination with amenability to combinatorialsequence variations further warrants the potential of cyclotides inthe design and development of peptide-based therapeutics.57 In this study, we identified cyclotides as modulatorsof the KOR, an emerging target for developing therapeutics for painand MS.