Vitamin C sensitizes BRAFV600E thyroid cancer to PLX4032 via inhibiting the feedback activation of MAPK/ERK signal by PLX4032

Abstract

Background BRAFV600E mutation is the most common mutation in thyroid cancer. It strongly activates MAPK/ERK pathway and indicates an invasive subtype of thyroid cancer. PLX4032 is a selective oral inhibitor of the BRAFV600 kinase although with limited effect in treating this panel of thyroid cancer, due to the feedback activation of MAPK/ERK as well as PI3K/AKT pathways. It was investigated that Vitamin C plays a positive role in inhibiting these pathways in thyroid cancer. However, whether Vitamin C could enhance the antitumor effect of PLX4032 remains largely unclear. Methods The antitumor efficacy of combination therapy with PLX4032 and Vitamin C on BRAFMT thyroid cancer cell was assessed by the MTT assay, EdU assay and colony formation, Chou-Talalay way was employed to analyze the synergistic effect. Flow cytometry were employed to assess cells’ apoptosis and cell cycle arrest in response to combination therapy. Xenograft models were used to test its in vivo antitumor activity. Western blot and IHC were applied to investigate the mechanism underlying synergistic effect. Results PLX4032 or Vitamin C monotherapy was mildly effective in treating BRAFMT thyroid cancer cell and xenografts model. The combination therapy significantly inhibited cancer cell proliferation and tumor growth in nude mice, and induced cell apoptosis and cell cycle arrest compared to either monotherapy. PLX4032 monotherapy induced feedback activation of MAPK/ERK as well as PI3K/AKT pathway; while combination therapy significantly relieved this feedback. Conclusion Vitamin C promotes the antitumor effect of PLX4032 in BRAFMT thyroid cancer cell and xenografts model via relieving the feedback activation of MAPK/ERK as well as PI3K/AKT pathway. PLX4032/Vitamin C combination may be a potential therapeutic approach to treat BRAFMT thyroid cancer.

High-dose intravenous vitamin C, a promising multi-targeting agent in the treatment of cancer

“…Similarly, a remarkable kinase modulator effect was observed in several studies, mostly by reducing phosphorylation levels of ERK, BRAF and AKT [ 64 , 99 , 109 , 122 , 123 ] (Figs. 2 and 4 ).…”

“…Similarly, resistance to BRAFV600 inhibitor vemurafenib was also abrogated by VitC in melanoma in vivo [ 123 ]. Recent findings reinforce the promising synergistic effects of VitC with kinase inhibitors such as BRAFV600 inhibitor PLX4032 in thyroid cancer in vivo [ 64 ] and with BTK inhibitor ibrutinib and PI3K inhibitor idelalisib in chronic lymphocytic leukemia (CLL) patient-derived cells [ 104 ].…”

“…The most widely described mechanism by which VitC is cytotoxic to cancer cells in a selective manner is its pro-oxidant facet, which targets redox imbalance. More recent studies have reported additional mechanisms such as epigenome regulation, oxygen-sensing, immunomodulatory functions, epithelial-to-mesenchymal transition and kinase activity regulation [ 1 , 2 , 5 , 60 , 64 , 99 , 109 , 217 , 218 ] (Figs. 4 and 6 ).…”

“…In terms of safety and tolerability, several studies have shown that high-dose VitC does not increase toxicity levels in vivo yet protects from other treatment sideeffects when used as an adjuvant agent [15,[62][63][64].…”

Novel Inhibitor-Based Therapies for Thyroid Cancer—An Update

“…For example, a recent in vitro study performed on BRAF V600E-positive TC cell lines indicated antiproliferative and re-differentiative effects of dabrafenib and vemurafenib [ 131 ]. Moreover, vemurafenib-treated BRAF V600E-positive PTC cells exhibited an increased apoptosis level [ 132 ], whereas ascorbic acid (vitamin C) was found to sensitize BRAF V600E-positive thyroid cancer cells to this agent [ 133 ]. Recent reports suggest, that co-therapy based on dabrafenib and trametinib may lead to durable disease control and prolonged benefit in patients with a BRAF -mutated PTC [ 134 ].…”