Oral absorption and in vivo biodistribution of α-conotoxin MII and a lipidic analogue

Conotoxins are highly constrained peptide toxins that exhibit pharmaceutically relevant biological activities. We herein report the extent of absorption and profile of distribution of a native α-conotoxin, MII and a lipophilic analogue of MII (N-LaaMII) after intravenous (iv) and oral administration to male Sprague–Dawley rats. N-LaaMII is formed by coupling 2-amino-d,l-dodecanoic acid (Laa) to the N-terminus of MII and has previously been shown to exhibit significantly improved permeability across Caco-2 cell monolayers compared to the native MII while maintaining the potency in inhibition of nAChRs of the parent peptide. Both peptides crossed the GI tract after oral administration (∼6% after 30 m). While Laa conjugation did not significantly improve absorption, it did greatly increase the accumulation of the compound in the liver after iv administration. Neither peptide crossed the blood–brain barrier to any significant extent. This is the first study of the in vivo biodistribution of an α-conotoxin after oral administration.