Effects of AKT inhibitor therapy in response and resistance to BRAF inhibition in melanoma

Abstract

BackgroundThe clinical use of BRAF inhibitors for treatment of metastatic melanoma is limited by the development of drug resistance. In this study we investigated whether co-targeting the MAPK and the PI3K-AKT pathway can prevent emergence of resistance or provide additional growth inhibitory effects in vitro.MethodsAnti-tumor effects of the combination of the BRAF inhibitor (BRAFi) dabrafenib and GSK2141795B (AKTi) in a panel of 23 BRAF mutated melanoma cell lines were evaluated on growth inhibition by an ATP-based luminescent assay, on cell cycle and apoptosis by flow cytometry and on cell signaling by western blot. Moreover, we investigated the possibilities of delaying or reversing resistance or achieving further growth inhibition by combining AKTi with dabrafenib and/or the MEK inhibitor (MEKi) trametinib by using long term cultures.ResultsMore than 40% of the cell lines, including PTEN-/- and AKT mutants showed sensitivity to AKTi (IC50 < 1.5 μM). The combination of dabrafenib and AKTi synergistically potentiated growth inhibition in the majority of cell lines with IC50 > 5 nM dabrafenib. Combinatorial treatment induced apoptosis only in cell lines sensitive to AKTi. In long term cultures of a PTEN-/- cell line, combinatorial treatment with the MAPK inhibitors, dabrafenib and trametinib, and AKTi markedly delayed the emergence of drug resistance. Moreover, combining AKTi with the MAPK inhibitors from the beginning provided superior growth inhibitory effects compared to addition of AKTi upon development of resistance to MAPK inhibitors in this particular cell line.ConclusionsAKTi combined with BRAFi-based therapy may benefit patients with tumors harboring BRAF mutations and particularly PTEN deletions or AKT mutations.

Treatment of Vemurafenib-Resistant SKMEL-28 Melanoma Cells with Paclitaxel

“…Our result indicated that 100 nM of paclitaxel induced apoptosis of SKMEL-28 R about 3.3 folds, from 4.3% in the SKMEL-28 R control cells to 14.2% in paclitaxel-treated SKMEL-28 R cells (Figure 4g-h). Moreover, in previous studies, they showed that the combination of AKT inhibitors and BRAF inhibitors caused the decrease in melanoma development in cell lines and patients (Rebecca et al, 2012;Lassen et al, 2014). That means our result matches well with these previous studies to suggest that the simultaneous inhibitions of both AKT and BRAF could be beneficial for melanoma patients.…”

Increased MAPK reactivation in early resistance to dabrafenib/trametinib combination therapy of BRAF-mutant metastatic melanoma

“…Instead, many tumours carried pre-existing genetic variants, including RAC1, PTEN and AKT3 mutations that activate the PI3K-PTEN-AKT cascade. Consequently, although the sole activation of PI3K activity may not be sufficient to confer CombiDT resistance, we predict that PI3K activity modulates tumour responses to MAPK inhibitors and contributes to early resistance, and that combination MAPK and PI3K/AKT inhibition may be best administered upfront to delay the emergence of resistance 35 . Preclinical data have confirmed that PI3K activation (via NRAS mutations and receptor tyrosine kinase activation) diminished melanoma cell responses to combination BRAF and MEK inhibitors 14 .…”

“…Furthermore, these data suggest that, in unselected patients with CombiDT failure, drug combinations involving PI3K/AKT inhibition (for example, NCT 01902173; ref. 35) may prove less successful than additional therapies inhibiting MAPK at multiple nodes, such as those targeting MEK, ERK and possibly CDK4 (NCT01777776, NCT01543698).…”

New Drug Combination Strategies in Melanoma: Current Status and Future DirectionsNew Drug Combination Strategies in Melanoma: Current Status and Future Directions

“…Therefore, acquired and innate oncogenic alteration in the PI3K/AKT signaling can explain the inefficiency of single pathway inhibition and the rationale for the concurrent targeting of both MAPK and PI3K/AKT pathways ( Figure 1) to counteract resistance and obtain beneficial long-term clinical effects. Several studies have demonstrated antitumor activity and pointed out synergistic effect of cotargeting MAPK and PI3K/AKT pathways in BRAF and NRAS mutant melanomas (22,24,31,(38)(39)(40).…”