Genetic Silencing of AKT Induces Melanoma Cell Death via mTOR Suppression.

Aberrant activation of the PI3K-AKT pathway is common in many cancers, including melanoma, and AKT1, 2 and 3 (AKT1-3) are bona fide oncoprotein kinases with well-validated downstream effectors. However, efforts to pharmacologically inhibit AKT have proven to be largely ineffective. In this study, we observed paradoxical effects following either pharmacologic or genetic inhibition of AKT1-3 in melanoma cells. Although pharmacological inhibition was without effect, genetic silencing of all three AKT paralogs significantly induced melanoma cell death through effects on mTOR. This phenotype was rescued by exogenous AKT1 expression in a kinase-dependent manner. Pharmacological inhibition of PI3K and mTOR with a novel dual inhibitor effectively suppressed melanoma cell proliferation in vitro and inhibited tumor growth in vivo. Furthermore, this single-agent-targeted therapy was well-tolerated in vivo and was effective against MAPK inhibitor-resistant patient-derived melanoma xenografts. These results suggest that inhibition of PI3K and mTOR with this novel dual inhibitor may represent a promising therapeutic strategy in this disease in both the first-line and MAPK inhibitor-resistant setting.

Structure/function characterization of micro-conotoxin KIIIA, an analgesic, nearly irreversible blocker of mammalian neuronal sodium channels.

Peptide neurotoxins from cone snails continue to supply compounds with therapeutic potential. Although several analgesic conotoxins have already reached human clinical trials, a continuing need exists for the discovery and development of novel non-opioid analgesics, such as subtype-selective sodium channel blockers. Micro-conotoxin KIIIA is representative of micro-conopeptides previously characterized as inhibitors of tetrodotoxin (TTX)-resistant sodium channels in amphibian dorsal root ganglion neurons. Here, we show that KIIIA has potent analgesic activity in the mouse pain model. Surprisingly, KIIIA was found to block most (>80%) of the TTX-sensitive, but only approximately 20% of the TTX-resistant, sodium current in mouse dorsal root ganglion neurons. KIIIA was tested on cloned mammalian channels expressed in Xenopus oocytes. Both Na(V)1.2 and Na(V)1.6 were strongly blocked; within experimental wash times of 40-60 min, block was reversed very little for Na(V)1.2 and only partially for Na(V)1.6. Other isoforms were blocked reversibly: Na(V)1.3 (IC50 8 microM), Na(V)1.5 (IC50 284 microM), and Na(V)1.4 (IC50 80 nM). "Alanine-walk" and related analogs were synthesized and tested against both Na(V)1.2 and Na(V)1.4; replacement of Trp-8 resulted in reversible block of Na(V)1.2, whereas replacement of Lys-7, Trp-8, or Asp-11 yielded a more profound effect on the block of Na(V)1.4 than of Na(V)1.2. Taken together, these data suggest that KIIIA is an effective tool to study structure and function of Na(V)1.2 and that further engineering of micro-conopeptides belonging to the KIIIA group may provide subtype-selective pharmacological compounds for mammalian neuronal sodium channels and potential therapeutics for the treatment of pain.