The Mitogen-Activated Protein Kinase Pathway Facilitates Resistance to the Src Inhibitor Dasatinib in Thyroid Cancer

Abstract

Advanced stages of papillary and anaplastic thyroid cancer represent a highly aggressive subset, in which there are currently few effective therapies. We and others have recently demonstrated that c-Src is a key mediator of growth, invasion, and metastasis, and therefore represents a promising therapeutic target in thyroid cancer. However clinically, Src inhibitor efficacy has been limited, and therefore further insights are needed to define resistance mechanisms and determine rational combination therapies. We have generated four thyroid cancer cell lines with a greater than 30-fold increase in acquired resistance to the Src inhibitor, dasatinib. Upon acquisition of dasatinib-resistance, the two RAS-mutant cell lines acquired the c-Src gatekeeper mutation (T341M), whereas the two BRAF-mutant cell lines did not. Accordingly, Src signaling was refractory to dasatinib treatment in the RAS-mutant dasatinib-resistant cell lines. Interestingly, activation of the Mitogen Activated Protein (MAP) Kinase pathway was increased in all four of the dasatinib-resistant cell lines, likely due to B-Raf and c-Raf dimerization. Furthermore, MAP2K1/MAP2K2 (MEK1/2) inhibition restored sensitivity in all four of the dasatinib-resistant cell lines, and overcome acquired resistance to dasatinib in the RAS-mutant Cal62 cell line, in vivo. Together, these studies demonstrate that acquisition of the c-Src gatekeeper mutation and MAP Kinase pathway signaling play important roles in promoting resistance to the Src inhibitor, dasatinib. We further demonstrate that up-front combined inhibition with dasatinib and MEK1/2 or ERK1/2 inhibitors drives synergistic inhibition of growth and induction of apoptosis, indicating that combined inhibition may overcome mechanisms of survival in response to single agent inhibition.

Targeting SRC Kinase Signaling in Pancreatic Cancer Stem Cells

“…In conclusion, agents that target SFKs or FAK are clinically available and/or are under development; however, as mentioned above, inhibitors of SRC kinases (e.g., DAS) have been shown to be ineffective in PDAC patients, even when combined with gemcitabine as shown in the Mettu et al study [ 79 ]. It should be noted that the gatekeeper threonine (T) at SRC amino acid 341 is related to DAS resistance, as a T341I– SRC variant made different cell types insensitive to SRC tyrosine kinase inhibition by DAS [ 90 , 91 , 92 ]. It would be interesting to assess the status of T341 in the PDAC patients treated in the Mettu et al study and in the PDX-derived cultures used in the study, particularly Panc185.…”

Oscillatory dynamics of p38 activity with transcriptional and translational time delays

“…At present, three major subgroups of MAPKs have been identified in higher eukaryotes, including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 MAPK (p38) families. Each MAPK pathway contains a three-tiered kinase cascade involving a MAPKK kinase (MAPKKK, MAP3K, MEKK or MKKK), a MAPK kinase (MAPKK, MAP2K, MEK or MKK) and the MAPK, that regulates various cellular activities such as proliferation, differentiation, apoptosis, survival, inflammation, and innate immunity 4 – 6 .…”

Establishment and Characterization of Four Novel Thyroid Cancer Cell Lines and PDX Models Expressing the RET/PTC1 Rearrangement, BRAFV600E, or RASQ61R as Drivers

“…CUTC48 cells (10 7 ) were injected into the flanks of 5 athymic nu/nu mice [Hsd:Athymic Nude-Foxn1 nu (069) from Envigo], 5 SCID/Beige mice (C.B-17/IcrHsd-Prkdc scid Lyst bg-J from Envigo), or 3 NOD/RAGKO/IL-2RgammaKO mice [NOD.Cg-Rag1tm1Mo-mIl2rgtm1Wjl/SzJ (#007799) from Jackson Laboratory] using high-concentration Matrigel (Corning #354248) 1:1 with RPMI 1640 (#11875119; Gibco Life Technologies), as described previ-ously (36). Growth was monitored over 97 days (nude and SCID mice) or 6 months (NOD/RAGKO/IL-2RgammaKO).…”