Basal and Treatment-Induced Activation of AKT Mediates Resistance to Cell Death by AZD6244 (ARRY-142886) in Braf-Mutant Human Cutaneous Melanoma Cells

Abstract

The majority of melanomas demonstrate constitutive activation of the RAS-RAF-MEK-MAPK pathway. AZD6244 is a selective MEK1/2 inhibitor which markedly reduces tumor P-MAPK levels, but it produced few clinical responses in melanoma patients. An improved understanding of the determinants of resistance to AZD6244 may lead to improved patient selection and effective combinatorial approaches. The effects of AZD6244 on cell growth and survival were tested in a total of 14 Braf-mutant and 3 wild-type human cutaneous melanoma cell lines. Quantitative assessment of phospho-protein levels in the Braf-mutant cell lines by reverse phase protein array (RPPA) analysis showed no significant association between P-MEK or P-MAPK levels and AZD6244 sensitivity, but activation-specific markers in the PI3K-AKT pathway correlated with resistance. We also identified resistant cell lines without basal activation of the PI3K-AKT pathway. RPPA characterization of the time-dependent changes in signaling pathways revealed that AZD6244 produced durable and potent inhibition of P-MAPK in sensitive and resistant Braf-mutant cell lines, but several resistant lines demonstrated AZD6244-induced activation of AKT. In contrast, sensitive cell lines demonstrated AZD6244 treatment-induced upregulation of PTEN protein and mRNA expression. Inhibition of AKT, TORC1/2, or IGF1R blocked AZD6244-induced activation of AKT and resulted in synergistic cell killing with AZD6244. These findings identify basal and treatment-induced regulation of the PI3K-AKT pathway as a critical regulator of AZD6244 sensitivity in Braf-mutant cutaneous melanoma cells, the novel regulation of PTEN expression by AZD6244 in sensitive cells, and suggest new combinatorial approaches for patients.

The novel anti-MEK small molecule AZD6244 induces BIM-dependent and AKT-independent apoptosis in diffuse large B-cell lymphoma

“…10,14,[18][19][20][21][22][23] AZD6244 is a benzimidazole and selective 2nd generation MEK inhibitor with reported activity at nanomolar concentrations against purified MEK1 enzyme in preclinical solid tumor studies. [18][19][20][21][22][23] Further, AZD6244 is a noncompetitive MEK inhibitor with preclinical antitumor activity in solid tumor models including hepatocellular, colon, myeloma, thyroid, pancreatic, melanoma, and breast cancers 19,20,41 and tested clinically in phase 1 24 and phase 2 trials of advanced, refractory colorectal, melanoma, and lung cancer. [25][26][27] AZD6244 has been examined in leukemia and myeloma models, [42][43][44] however to our knowledge, has never been tested in lymphoma.…”

“…15,17 ARRY-142886 (AZD6244, selumetinib; Astra Zeneca) is a selective nonATP-competitive 2nd generation oral MEK inhibitor studied primarily in solid tumor studies with reported nanomolar activity against purified MEK1 enzyme. [18][19][20][21][22][23] Furthermore, phase 1 and phase 2 solid tumor clinical trials have shown this agent to be well-tolerated and have encouraging clinical efficacy. [24][25][26][27] To our knowledge, minimal data are available on newer generation MEK inhibitors in lymphoma and moreover, this anti-MEK agent has never been examined in lymphoma.…”

The Akt signaling pathway

“…Akt has also been shown to mediate resistance to cell death induced by the potent, highly selective, uncompetitive inhibitor of MEK1/2 AZD6244 in melanoma cells harboring a mutant V600E B-Raf. 195 Melanoma cells expressing mutant V600E B-Raf and functional PTEN were found to be sensitive to AZD6244 treatment and showed no elevation in pAkt. 195 However, AZD6244 resistant cells, despite expressing normal PTEN showed elevated pAkt treatment indicating that Akt mediates the resistance to AZD6244.…”

“…195 Melanoma cells expressing mutant V600E B-Raf and functional PTEN were found to be sensitive to AZD6244 treatment and showed no elevation in pAkt. 195 However, AZD6244 resistant cells, despite expressing normal PTEN showed elevated pAkt treatment indicating that Akt mediates the resistance to AZD6244. 195 …”

“…195 However, AZD6244 resistant cells, despite expressing normal PTEN showed elevated pAkt treatment indicating that Akt mediates the resistance to AZD6244. 195 …”