Targeting BRAFV600E in thyroid carcinoma: therapeutic implications

Abstract

B-Raf is an important mediator of cell proliferation and survival signals transduced via the Ras-Raf-MEK-ERK cascade. BRAF mutations have been detected in several tumors, including papillary thyroid carcinoma, but the precise role of B-Raf as a therapeutic target for thyroid carcinoma is still under investigation. We analyzed a panel of 93 specimens and 14 thyroid carcinoma cell lines for the presence of BRAF mutations and activation of the mitogen-activated protein/ERK kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway. We also compared the effect of a B-Raf small inhibitory RNA construct and the B-Raf kinase inhibitor AAL881 on both B-Raf wild-type and mutant thyroid carcinoma cell lines. We found a high prevalence of the T1799A (V600E) mutation in papillary and anaplastic carcinoma specimens and cell lines. There was no difference in patient age, B-Raf expression, Ki67 immunostaining, or clinical stage at presentation between wild-type and BRAF V600E specimens. Immunodetection of phosphorylated and total forms of MEK and ERK revealed no difference in their phosphorylation between wild-type and BRAF V600E patient specimens or cell lines. Furthermore, a small inhibitory RNA construct targeting the expression of both wild-type B-Raf and B-Raf V600E induced a comparable reduction of viability in both wild-type and BRAF V600E mutant cancer cells. Interestingly, AAL881 inhibited MEK and ERK phosphorylation and induced apoptosis preferentially in BRAF V600E -harboring cells than wild-type ones, possibly because of better inhibitory activity against B-Raf V600E . We conclude that B-Raf is important for the pathophysiology of thyroid carcinomas irrespective of mutational status. Small molecule inhibitors that selectively target B-Raf V600E may provide clinical benefit for patients with thyroid cancer.

Dual targeting of Raf and VEGF receptor 2 reduces growth and metastasis of pancreatic cancer through direct effects on tumor cells, endothelial cells, and pericytes

“…However, targeting the B-Raf kinase isoform appears to be most effective when activating mutations are present in cancer cells, such as the reported V600E Raftype mutation in thyroid cancer and melanoma (27,37). In our study, we investigated the effects of a small-molecule inhibitor to Raf and VEGFR2 on pancreatic cancer cells, although the Raf signaling cascade in this cancer entity is predominantly activated via KRAS (10), an oncogene known to be mutated in >90% of pancreatic adenocarcinomas (38,39).…”

“…The Raf/VEGFR2 inhibitor NVP-AAL881 was kindly provided by Novartis and dissolved for in vitro experiments in DMSO (25). For in vivo use, NVP-AAL881 was prepared as described elsewhere (25,27). The selective VEGFR2 inhibitor Tyrphostin (AG1478) was purchased from Calbiochem (EMD).…”

“…Mice were randomized into groups (n = 5-6 per group) receiving either vehicle (controls) or NVP-AAL881 (100 mg/kg/d) by oral gavages. The dose of NVP-AAL881 was chosen based on previous reports and in the intention not to use this compound at the maximal tolerated dose (25,27). In this first model, mice were sacrificed on day 21 after tumor cell inoculation and excised tumors were measured and weighed.…”

“…Importantly, a significant antitumor activity by NVP-AAL881 treatment was observed when tumor cells did harbor mutations in B-Raf (V600E; ref. 27). Nevertheless, the value of using dual Raf/VEGFR2 targeting agents for therapy of pancreatic cancer has not been determined to date.…”

New therapeutic advances in the management of progressive thyroid cancer

“…This inhibition paralleled a decrease in RET phosphorylation. Another study targeting the BRAF expression using a small inhibitory RNA construct in thyroid cancer cell lines induced a comparable reduction of viability in both wild-type BRAF and BRAF V600E mutant cancer cells (Mitsiades et al 2007). Furthermore, AAL881, BRAF kinase inhibitors, inhibited MEK and ERK phosphorylation, and induced apoptosis preferentially in BRAF V600E -harboring cells over wild-type cells.…”