We present a cohort of 41 patients with osimertinib resistance biopsies, including two with an acquired CCDC6-RET fusion. While RET fusions have been identified in resistant EGFR-mutant NSCLC, their role in acquired resistance to EGFR inhibitors is not well described. To assess the biological implications of RET fusions in an EGFR-mutant cancer, we expressed CCDC6-RET in PC9 (EGFR del19) and MGH134 (EGFR L858R/T790M) cells and found that CCDC6-RET was sufficient to confer resistance to EGFR-TKIs. The selective RET inhibitors BLU-667 or cabozantinib resensitized CCDC6-RET-expressing cells to EGFR inhibition. Finally, we treated two patients with EGFR-mutant NSCLC and RET-mediated resistance with osimertinib and BLU-667. The combination was well-tolerated and led to rapid radiographic response in both patients. This study provides proof-of-concept that RET fusions can mediate acquired resistance to EGFR TKIs and that combined EGFR and RET inhibition with osimertinib/BLU-667 may be a well-tolerated and effective treatment strategy for such patients.

Crizotinib is the standard of care for advanced non-small cell lung cancer (NSCLC) patients harboring the anaplastic lymphoma kinase (ALK) fusion gene, but resistance invariably develops. Unlike crizotinib, alectinib is a selective ALK tyrosine kinase inhibitor (TKI) with more potent antitumor effects and a favorable toxicity profile, even in crizotinib-resistant cases. However, acquired resistance to alectinib, as for other TKIs, remains a limitation of its efficacy. Therefore, we investigated the mechanisms by which human NSCLC cells acquire resistance to alectinib. We established two alectinib-resistant cell lines that did not harbor the secondary ALK mutations frequently occurring in crizotinib-resistant cells. One cell line lost the EML4-ALK fusion gene, but exhibited increased activation of insulin-like growth factor-1 receptor (IGF1R) and human epidermal growth factor receptor 3 (HER3), and overexpressed the HER3 ligand neuregulin 1. Accordingly, pharmacologic inhibition of IGF1R and HER3 signaling overcame resistance to alectinib in this cell line. The second alectinibresistant cell line displayed stimulated HGF autocrine signaling that promoted MET activation and remained sensitive to crizotinib treatment. Taken together, our findings reveal two novel mechanisms underlying alectinib resistance that are caused by the activation of alternative tyrosine kinase receptors rather than by secondary ALK mutations. These studies may guide the development of comprehensive treatment strategies that take into consideration the various approaches ALK-positive lung tumors use to withstand therapeutic insult.

The discovery of an echinoderm microtubule-associated protein-like 4 (EML4)-anaplastic lymphoma kinase (ALK) fusion gene led to improved clinical outcomes in patients with lung cancer after the development of the first ALK-targeting agent, crizotinib. Some second-generation ALK tyrosine kinase inhibitors (TKIs), which might be more potent than crizotinib or effective on crizotinib-resistant patients, have been developed. Although these ALK-TKIs show an excellent response initially, most patients eventually acquire resistance. Therefore, careful consideration of the resistance mechanisms might lead to superior therapeutic strategies. Here, we summarize the history of ALK-TKIs and their underlying resistance mechanisms in both the preclinical and clinical settings. In addition, we discuss potential future treatment strategies in ALK-TKI-naïve and -resistant patients with lung cancer harboring the EML4-ALK fusion gene.

Background: Programmed cell death protein-1 (PD-1) and programmed death ligand-1 (PD-L1) play a major role in suppressing the immune system by forming the PD-1/PD-L1 complex, which transmits an inhibitory signal to reduce T-cell activity. PD-L1 is often expressed in various malignant tumors. On the other hand, PD-1 is generally observed in activated lymphocytes and myeloid-derived dendritic cells. Of the malignant cells, only Jurkat cells (under special conditions) and angioimmunoblastic T-cell lymphoma tissue cells express PD-1 on their surface. Purpose: To clarify whether PD-1/PD-L1 complex participates in the immunotolerance on small-cell lung cancer (SCLC) cells. Materials and methods: We examined the expression levels of PD-1 and PD-L1 on the cell surface of SCLC cell lines using flowcytometry and reverse transcription polymerase chain reaction. Subsequently, the soluble PD-L1 (sPD-L1) concentration was measured using enzyme-linked immunosorbent assay, and the cell growth inhibitory effect of IFN-γ was determined by direct cell counting using a hemocytometer and Trypan blue staining. Results: Among the four SCLC cell lines examined, only SBC-3 cells expressed both PD-1 and PD-L1. The sPD-L1 concentrations in culture medium gradually increased according to cell growth. Although IFN-γ alone inhibited the growth of SBC-3 cells, PD-L1 expression on the cell surface was not induced by IFN-γ. Conclusions: We demonstrated that both PD-1 and PD-L1 molecules are co-expressed on the surface of SCLC cells. Although the biological implications of this remain unclear, we speculate that PD-1 and its ligand on the SCLC cells may participate in the growth inhibition of tumor cells as is reported in cytotoxic T cells. Citation Format: Hiromichi Yamane, Hideko Isozaki, Nobuaki Ochi, Kenichiro Kudo, Yoshihiro Honda, Tomoko Yamagishi, Toshio Kubo, Katsuyuki Kiura, Nagio Takigawa. Both programmed cell death protein 1 and programmed death-ligand 1 molecules can be expressed on the cell surface of small-cell lung cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1323. doi:10.1158/1538-7445.AM2015-1323