Naltrindole hydrochloride is a cell permeable, highly selective non-peptide δ opioid antagonist (Ki = 0.02 nM).

In U266 cells, naltrexone treatment can significantly reduce the active phosphorylated form of kinases, and extracellular signaling regulates kinase and Akt levels, which may be related to its anti-proliferative activity[1].

In mice, naltrindole (20 mg/kg, s.c) antagonizes the δ-selective agonist effect of enkephalin (DSLET), but does not prevent the anti-nociceptive effects of morphine or U50488H. Naltrexone is the only highly selective delta antagonist that is active when administered peripherally[2].

References:

[1]. Mundra J J, et al. Naltrindole inhibits human multiple myeloma cell proliferation in vitro and in a murine xenograft model in vivo. J Pharmacol Exp Ther, 2012, 342(2): 273-87.

[2]. Portoghese P S, et al. Naltrindole, a highly selective and potent non-peptide delta opioid receptor antagonist. Eur J Pharmacol, 1988, 146(1): 185-6.