Activation of the JAK/STAT Pathway Leads to BRAF Inhibitor Resistance in BRAFV600E Positive Thyroid Carcinoma

A subset of thyroid cancers, recurrent differentiated thyroid cancers and anaplastic thyroid cancer (ATC), are difficult to treat by thyroidectomy and systemic therapy. A common mutation in thyroid cancer, BRAFV600E, has targetable treatment options; however, the results have been disappointing in thyroid cancers compared with BRAFV600E melanoma, as thyroid cancers quickly become resistant to BRAFV600E inhibitor (BRAFi). Here, we studied the molecular pathway that is induced in BRAFV600E thyroid cancer cells and patient-derived tumor samples in response to BRAFi, vemurafenib, using RNA-sequencing and molecular analysis. Both inducible response to BRAFi and acquired BRAFi resistance in BRAFV600E thyroid cancer cells showed significant activation of the JAK/STAT pathway. Functional analyses revealed that the combination of BRAFi and inhibitors of JAK/STAT pathway controlled BRAFV600E thyroid cancer cell growth. The Cancer Genome Atlas data analysis demonstrated that potent activation of the JAK/STAT signaling was associated with shorter recurrence rate in patients with differentiated thyroid cancer. Analysis of tumor RNA expression in patients with poorly differentiated thyroid cancer and ATC also support that enhanced activity of JAK/STAT signaling pathway is correlated with worse prognosis. Our study demonstrates that JAK/STAT pathway is activated as BRAFV600E thyroid cancer cells develop resistance to BRAFi and that this pathway is a potential target for anticancer activity and to overcome drug resistance that commonly develops to treatment with BRAFi in thyroid cancer.

IMPLICATIONS

Dual inhibition of BRAF and JAK/STAT signaling pathway is a potential therapeutic treatment for anticancer activity and to overcome drug resistance to BRAFi in thyroid cancer.

PD1 Blockade Enhances ICAM1-Directed CAR T Therapeutic Efficacy in Advanced Thyroid Cancer

PURPOSE

Advanced thyroid cancers, including poorly differentiated and anaplastic thyroid cancer (ATC), are lethal malignancies with limited treatment options. The majority of patients with ATC have responded poorly to programmed death 1 (PD1) blockade in early clinical trials. There is a need to explore new treatment options.

EXPERIMENTAL DESIGN

We examined the expression of PD-L1 (a ligand of PD1) and intercellular adhesion molecule 1 (ICAM1) in thyroid tumors and ATC cell lines, and investigated the PD1 expression level in peripheral T cells of patients with thyroid cancer. Next, we studied the tumor-targeting efficacy and T-cell dynamics of monotherapy and combination treatments of ICAM1-targeting chimeric antigen receptor (CAR) T cells and anti-PD1 antibody in a xenograft model of ATC.

RESULTS

Advanced thyroid cancers were associated with increased expression of both ICAM1 and PD-L1 in tumors, and elevated PD1 expression in CD8⁺ T cells of circulating blood. The expression of ICAM1 and PD-L1 in ATC lines was regulated by the IFNγ-JAK2 signaling pathway. ICAM1-targeted CAR T cells, produced from either healthy donor or patient T cells, in combination with PD1 blockade demonstrated an improved ability to eradicate ICAM1-expressing target tumor cells compared with CAR T treatment alone. PD1 blockade facilitated clearance of PD-L1 high tumor colonies and curtailed excessive CAR T expansion, resulting in rapid tumor clearance and prolonged survival in a mouse model.

CONCLUSIONS

Targeting two IFNγ-inducible, tumor-associated antigens-ICAM1 and PD-L1-in a complementary manner might be an effective treatment strategy to control advanced thyroid cancers in vivo.

Abstract 1895: The role of the IFNγ pathway in the development of vemurafenib resistance in BRAFV600E mutant thyroid carcinoma

BRAFV600E is the most common driver mutation in anaplastic thyroid cancer, and BRAF inhibitors are increasingly being used in the treatment of this disease. However, the therapeutic benefit of BRAFV600E inhibitors, such as vemurafenib, has been limited in thyroid cancer due to rapid development of drug resistance in clinical practice. Here, we characterize a targetable mechanism of vemurafenib resistance by studying vemurafenib-resistant clones derived from BRAFV600E mutant anaplastic thyroid cancer cell lines (8505C and FRO), and propose a drug combination to overcome resistance. Vemurafenib resistance in these established clones was verified by persistent activation of ERK1/2 after vemurafenib treatment by western blot analysis. RNA-sequencing and subsequent ingenuity pathway analysis (IPA) was used to identify differences in pathway activation after vemurafenib treatment in parental and vemurafenib-resistant cell lines. Treatment of parental cells with vemurafenib resulted in differential gene expression correlating with upstream activation of the IFNγ-STAT1-IRF1 pathway (All FDR < 0.05). Furthermore, parental cells treated with vemurafenib demonstrated higher HLA-II and HLA-A2 expression than untreated cells when analyzed by flow cytometry, implying the activation of IFNγ signaling pathway. In the IPA of a vemurafenib-resistant clone (8505C Res1), IFNγ, STAT1 and IRF1 expression was upregulated compared to their respective untreated parental cell line (All FDR < 0.05). Increased IRF1 expression in 8505C Res1 compared to parental cells was also demonstrated by qPCR, supporting innate IFNγ activation in the resistant clone. Inhibition of the IFNγ pathway with increasing concentrations of neutralizing anti-IFNγ antibody sensitized resistant thyroid cancer cells to vemurafenib. Pharmacologically blocking the IFNγ downstream pathway in resistant clones with AZD1480 (JAK2 inhibitor) or fludarabine (STAT1 inhibitor), resulted in decreased cell viability in combination treatment groups compared to vemurafenib treatment only (cell viability: 92% vemurafenib vs 19% fludarabine combination, p < 0.05) (cell viability: 73% vemurafenib vs 37% AZD1480 combination, p < 0.05). These results demonstrate that activation of the IFNγ pathway is a potential mechanism for the development of resistance of anaplastic thyroid cancer to BRAFV600E inhibitors. Our study suggests that blockade of the IFNγ pathway may potentiate the therapeutic benefit of vemurafenib treatment in this disease.

Citation Format: Jessica Limberg, Katherine D. Gray, Mandeep Singh, Timothy M. Ullmann, Brian Wyrwas, Weibin Wang, Zachary Lowenstein, Steve El Eshaky, Heng Liang, Wei Li, Tuo Zhang, Jenny Xiang, Dessislava Stefanova, Rasa Zarnegar, Thomas J. Fahey, Irene M. Min. The role of the IFNγ pathway in the development of vemurafenib resistance in BRAFV600E mutant thyroid carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1895.