Long-term vemurafenib treatment drives inhibitor resistance through a spontaneous KRAS G12D mutation in a BRAF V600E papillary thyroid carcinoma model

Abstract

The BRAF V600E mutation is commonly observed in papillary thyroid cancer (PTC) and predominantly activates the MAPK pathway. Presence of BRAF V600E predicts increasing risk of recurrence and higher mortality rate, and treatment options for such patients are limited. Vemurafenib, a BRAF V600E inhibitor, is initially effective, but cells inevitably develop alternative mechanisms of pathway activation. Mechanisms of primary resistance have been described in short-term cultures of PTC cells; however, mechanisms of acquired resistance have not. In the present study, we investigated possible adaptive mechanisms of BRAF V600E inhibitor resistance in KTC1 thyroid cancer cells following long-term vemurafenib exposure. We found that a subpopulation of KTC1 cells acquired resistance to vemurafenib following 5 months of treatment with the inhibitor. Resistance coincided with the spontaneous acquisition of a KRAS G12D activating mutation. Increases in activated AKT, ERK1/2, and EGFR were observed in these cells. In addition, the resistant cells were less sensitive to combinations of vemurafenib and MEK1 inhibitor or AKT inhibitor. These results support the KRAS G12D mutation as a genetic mechanism of spontaneously acquired secondary BRAF inhibitor resistance in BRAF V600E thyroid cancer cells.

Unique mutation patterns in anaplastic thyroid cancer identified by comprehensive genomic profiling

“…Two patient samples did have both BRAF non‐ V600E and RAS mutations; BRAF D594G with HRAS and BRAF amplification with NRAS Q61K. Although rare, co‐occurrence of RAS and BRAF has been previously described in thyroid cancer . RAS mutations may represent the development of resistance to anti‐ BRAF therapy, but that cannot be determined to be the case in this dataset.…”

“…Although rare, co-occurrence of RAS and BRAF has been previously described in thyroid cancer. 17 RAS mutations may represent the development of resistance to anti-BRAF therapy, but that cannot be determined to be the case in this dataset. As larger scale genomic studies are performed, it may be possible to rapidly differentiate ATC from DTC with a high degree of confidence by using specific GA signature unique to each malignancy.…”

Strategies for Overcoming Resistance in Tumours Harboring BRAF Mutations

“…The Kristen rat sarcoma viral oncogene homologue ( KRAS ) mutation G12D has been identified in many tumour types, including colorectal cancers. The acquisition of this activating mutation following BRAF inhibitor exposure has been linked to the development of resistance in the BRAFV600E mutant parathyroid cancer cell line [85]. Similarly, resistance in a colorectal cell line has been linked to the appearance KRAS G12D and G13D mutations [86], suggesting activating mutations in this RAS pathway may contribute to intrinsic and acquired resistance.…”

Evolution of resistance to thyroid cancer therapy

“…BRAF V600E inhibitors, MEK inhibitors) and HER signaling inhibitors such as lapatinib, which prevents phospho-ERK1/2 rebound and sensitizes BRAF V600E -positive anaplastic thyroid cancer cells to BRAF V600E inhibitors [6]. In the third paper, Danysh et al showed that development of secondary resistance following long-term vemurafenib treatment in a PTC model was coincident with a spontaneous KRAS G12D mutation [7]. Activation of AKT, ERK1/2, and EGFR were observed in this model.…”

“…Activation of AKT, ERK1/2, and EGFR were observed in this model. In addition, the resistant cells were less sensitive to combinations of vemurafenib and MEK1 inhibitor or AKT inhibitor [7]. As KRAS is well known to be undruggable, it will be crucial to identify KRAS-dependent downstream targets that induce PTC cell survival in order to identify druggable targets for KRAS mutated thyroid tumors.…”