A Combinatorial Strategy for TargetingBRAFV600E-Mutant Cancers with BRAFV600E Inhibitor (PLX4720) and Tyrosine Kinase Inhibitor (Ponatinib)

Abstract

◥Purpose: Most aggressive thyroid cancers are commonly associated with a BRAF V600E mutation. Preclinical and clinical data in BRAF V600E cancers suggest that combined BRAF and MEK inhibitor treatment results in a response, but resistance is common. One mechanism of acquired resistance is through persistent activation of tyrosine kinase (TK) signaling by alternate pathways. We hypothesized that combination therapy with BRAF and multitargeting TK inhibitors (MTKI) might be more effective in BRAF V600E thyroid cancer than in single-agent or BRAF and MEK inhibitors.Experimental Design: The combined drug activity was analyzed to predict any synergistic effect using highthroughput screening (HTS) of active drugs. We performed follow-up in vitro and in vivo studies to validate and determine the mechanism of action of synergistic drugs. Results:The MTKI ponatinib and the BRAF inhibitor PLX4720 showed synergistic activity by HTS. This combination significantly inhibited proliferation, colony formation, invasion, and migration in BRAF V600E thyroid cancer cell lines and downregulated pERK/MEK and c-JUN signaling pathways, and increased apoptosis. PLX4720resistant BRAF V600E cells became sensitized to the combination treatment, with decreased proliferation at lower PLX4720 concentrations. In an orthotopic thyroid cancer mouse model, combination therapy significantly reduced tumor growth (P < 0.05), decreased the number of metastases (P < 0.05), and increased survival (P < 0.05) compared with monotherapy and vehicle control.Conclusions: Combination treatment with ponatinib and PLX4720 exhibited significant synergistic anticancer activity in preclinical models of BRAF V600E thyroid cancer, in addition to overcoming PLX4720 resistance. Our results suggest this combination should be tested in clinical trials.

Combinatorial Therapies in Thyroid Cancer: An Overview of Preclinical and Clinical Progresses

“…Hematoxylin and eosin staining demonstrated a reduction of pulmonary metastasis in the vemurafenib treated group and combination treated group. Finally, assays on 8505C resistant to vemurafenib showed that the combination with ponatinib overcomes the acquired resistance [51].…”

“…Vemurafenib is a mutant BRAF inhibitor and it is one of these molecules that are failing in clinical assays as monotherapy [52]. In vitro studies have been conducted to elucidate resistance mechanisms but reasons explaining the higher resistance observed of thyroid BRAFV600E mutant thyroid cancer in comparison to melanoma to BRAF inhibitor remains unclear [51]. Compensatory/alternative mechanisms have been highlighted to promote such resistance, bypassing pharmacologic inhibition of BRAFV600E via the activation of intracellular signaling pathways, leading to the reactivation and phosphorylation of ERK1/2, NRAS mutation, mutant BRAF amplification, or alternative splicing [51].…”

“…The failed attempts of vemurafenib used as monotherapy have been studied in the field of thyroid cancer and has already been well-documented in melanoma and colorectal cancer. One critical aspect to improve cancer therapy is not only to inhibit the primary oncogenic pathway reducing by this way the proliferation but simultaneously prevent functional redundancies and pathways crosstalk that facilitates survival of cancer cell populations, rendering tumors resistant to treatment [51].…”

“…Monotherapies are often associated with resistance, recurrence, and sometimes worsening of the disease [49,50]. Approximately 1/5 of patients harboring activating mutations in BRAF develop intrinsic resistance and do not respond to the BRAF inhibitor [51]. Vemurafenib is a mutant BRAF inhibitor and it is one of these molecules that are failing in clinical assays as monotherapy [52].…”

First reported case of BRAF V600E mutation in T‐cell prolymphocytic leukaemia

“…Unfortunately, 10 days after venetoclax initiation, the patient was admitted with neutropaenic fever and tumour lysis syndrome (TLS), requiring a hold on his therapy. Vemurafenib, an FDA‐approved BRAF V600E inhibitor, 9 was initiated based on the molecular results, at a dose of 960 mg PO Q12. Receiving a total of 20 days of therapy, the patient had improvement in renal function and WBC count.…”