Overactivation of Akt Contributes to MEK Inhibitor Primary and Acquired Resistance in Colorectal Cancer Cells

Abstract

RAS and BRAF-mutated colorectal cancers are associated with resistance to chemotherapy and poor prognosis, highlighting the need for new therapeutic strategies. Although these cancers sometimes respond to mitogen activated protein kinase kinase (MEK) inhibitor treatment, they often acquire resistance via mechanisms, which are poorly understood. Here, we investigated the mechanism of MEK inhibitor resistance in primary- and acquired-resistant cells. Cell viability was examined using the trypan blue dye exclusion assay. Protein expression was analyzed by western blotting. Somatic mutations in colorectal cancer cells were investigated using the polymerase chain reaction array. PD0325901 and trametinib induced cell death in LoVo and Colo-205 cells but not in DLD-1 and HT-29 cells, which have a PIK3CA mutation constitutively activating Akt and NF-κB. Treatment with PD0325901 and trametinib suppressed ERK1/2 activation in all four cell lines but only induced Akt and NF-κB activation in DLD-1 and HT-29 cells. Inhibition of Akt but not NF-κB, overcame MEK inhibitor resistance in DLD-1 and HT-29 cells. Acquired-resistant LoVo/PR, Colo-205/PR and LoVo/TR cells have constitutively active Akt due to a M1043V mutation in the kinase activation loop of PIK3CA and Akt inhibitor resensitized these cells to MEK inhibitor. These results demonstrate that the overactivation of Akt plays a critical role in MEK inhibitor primary and acquired resistance and implicate combined Akt/MEK inhibition as a potentially useful treatment for RAS/BRAF-mutated colorectal cancer.

Activation of Serum/Glucocorticoid Regulated Kinase 1/Nuclear Factor-κB Pathway Are Correlated with Low Sensitivity to Bortezomib and Ixazomib in Resistant Multiple Myeloma Cells

“…The effect of bortezomib, ixazomib, GSK650394, PD166866, C-C chemokine receptor type 2 (CCR2) antagonist, and dimethyl fumarate (DMF) on cell viability was assessed by the trypan blue stain exclusion assay as previously described [ 21 , 22 , 23 , 24 ].…”

MEK inhibitor resistance mechanisms and recent developments in combination trials

“…Additionally, mutations farther down the pathway such as activating mutations in PIK3CA or the loss of PTEN, a tumor suppressor gene, can also over activate this pathway when MEK inhibition is active [69]. For example, a study of MEKi resistance in CRC cell lines indicated that mutated PIK3CA contributed to MEKi intrinsic resistance by activating AKT to regulate expression of BCL-2 and BCL-XL, two anti-apoptotic factors, as well as expression of BAX and BIM, two pro-apoptotic factors [70]. Additionally, a recent study directly implicated PTEN loss as a major mechanism of intrinsic resistance to MEK inhibition in AML and went on to show that deletion of PTEN in AML cell lines was enough to confer MEKi resistance [71].…”

“…Initial studies involving inhibiting the PI3K pathway through either AKT inhibitors, PI3K inhibitors, or dual PI3K/mTOR inhibitors in conjunction with MEKi and/or BRAFi have shown promising preclinical data [23]. Studies conducted on multiple BRAFi/MEKi-resistant melanoma cell lines showed that combining inhibition of the PI3K/AKT pathway with MAPK inhibitors could reverse acquired resistance and lead to tumor cell death [70,81,82]. Other studies, including one involving a KRAS-mutant lung cancer mouse model, showed that inhibition of MAPK and PI3K signaling pathways had a synergistic effect on tumor cells [83].…”

Dasatinib reverses drug resistance by downregulating MDR1 and Survivin in Burkitt lymphoma cells

“…HS-Sultan cells with acquired resistance to adriamycin, vincristine, dexamethasone, or melphalan were produced as previously described [12,37,38].…”