Rearranged during transfection (RET) rearrangement oncoprotein-mediated Ras/MAPK signaling cascade is constitutively activated in cancers. Here, we demonstrate a unique signal niche. The niche is a ternary complex based on the chimeric RET liquid-liquid phase separation. The complex comprises the rearranged kinase (RET fusion); the adaptor (GRB2), and the effector (SHC1). Together, they orchestrate the Ras/MAPK signal cascade, which is dependent on tyrosine kinase. CCDC6-RET fusion undergoes LLPS requiring its kinase domain and its fusion partner. The CCDC6-RET fusion LLPS promotes the autophosphorylation of RET fusion, with enhanced kinase activity, which is necessary for the formation of the signaling niche. Within the signal niche, the interactions among the constituent components are reinforced, and the signal transduction efficiency is amplified. The specific RET fusion-related signal niche elucidates the mechanism of the constitutive activation of the Ras/MAPK signaling pathway. Beyond just focusing on RET fusion itself, exploration of the ternary complex potentially unveils a promising avenue for devising therapeutic strategies aimed at treating RET fusion-driven diseases.

Lung cancer represents a significant global health concern and stands as the leading cause of cancer-related mortality worldwide. The identification of specific genomic alterations such as EGFR and KRAS in lung cancer has paved the way for the development of targeted therapies. While targeted therapies for lung cancer exhibiting EGFR, MET and ALK mutations have been well-established, the options for RET mutations remain limited. Importantly, RET mutations have been found to be mutually exclusive from other genomic mutations and to be related with high incidences of brain metastasis. Given these facts, it is imperative to explore the development of RET-targeting therapies and to elucidate the mechanisms underlying metastasis in RET-expressing lung cancer cells. In this study, we investigated PLM-101, a novel dual-target inhibitor of RET/YES1, which exhibits notable anti-cancer activities against CCDC6-RET-positive cancer cells and anti-metastatic effects against YES1-positive cancer cells. Our findings shed light on the significance of the YES1-Cortactin-actin remodeling pathway in the metastasis of lung cancer cells, establishing YES1 as a promising target for suppression of metastasis. This paper unveils a novel inhibitor that effectively targets both RET and YES1, thereby demonstrating its potential to impede the growth and metastasis of RET rearrangement lung cancer.

Triple-negative breast cancers (TNBC) represent a pathological subtype of breast cancer, which are characterized by strong invasiveness, high metastasis rate, low survival rate, and poor prognosis, especially in patients who have developed resistance to multiline treatments. Here, we present a female patient with advanced TNBC who progressed despite multiple lines of treatments; next-generation sequencing (NGS) was used to find drug mutation targets, which revealed a coiled-coil domain-containing protein 6 (CCDC6)-rearranged during transfection (RET) gene fusion mutation. The patient was then given pralsetinib, and after one treatment cycle, a CT scan revealed partial remission and adequate tolerance to therapy. Pralsetinib (BLU-667) is a RET-selective protein tyrosine kinase inhibitor that can inhibit the phosphorylation of RET and downstream molecules as well as the proliferation of cells expressing RET gene mutations. This is the first case in the literature of metastatic TNBC with CCDC6-RET fusion treated with pralsetinib, an RET-specific antagonist. This case demonstrates the potential efficacy of pralsetinib in cases of TNBC with RET fusion mutations and suggests that NGS may reveal new opportunities and bring new therapeutic interventions to patients with refractory TNBC.

The flurry of publications devoted to the functions of long non-coding RNAs (lncRNAs) published in the last decade leaves no doubt about the exceptional importance of lncRNAs in various areas including tumor biology. However, contribution of lncRNAs to the early stages of oncogenesis remains poorly understood. In this study we explored a new role for lncRNAs: stimulation of specific chromosomal rearrangements upon DNA damage. We demonstrated that lncRNA CASTL1 (ENSG00000269945) stimulates the formation of the CCDC6-RET inversion (RET/PTC1) in human thyroid cells subjected to radiation or chemical DNA damage. Facilitation of chromosomal rearrangement requires lncRNA to contain regions complementary to the introns of both CCDC6 and RET genes as deletion of these regions deprives CASTL1 of the ability to stimulate the gene fusion. We found that CASTL1 expression is elevated in tumors with CCDC6-RET fusion which is the most frequent rearrangement in papillary thyroid carcinoma. Our results open a new venue for the studies of early oncogenesis in various tumor types, especially those associated with physical or chemical DNA damage.

The receptor tyrosine kinase rearranged during transfection (RET) plays pivotal roles in several cancers, including thyroid carcinoma and non-small cell lung cancer (NSCLC). Currently, there are several FDA-approved RET inhibitors, but their indication is limited to thyroid cancer, and none can overcome their gatekeeper mutants (V804L and V804M). Here, we report the discovery of 9x representing a new chemotype of potent and selective RET inhibitors, using a rational design strategy of type II kinase inhibitors. 9x exhibited both superior antiproliferative activities against NSCLC-related carcinogenic fusions KIF5B-RET and CCDC6-RET and gatekeeper mutant-transformed Ba/F3 cells, with the lowest GI50 of 9 nM, and substantial inhibitory activities against wild-type RET and RET mutant proteins, with the best IC50 of 4 nM. More importantly, 9x also showed nanomole potency against RET-positive NSCLC cells LC-2/ad, but not against a panel of RET-negative cancer cells, such as A549, H3122, A375 or parental Ba/F3 cells, demonstrating its selective \'on-target\' effect. In mouse xenograft models, 9x repressed tumor growth driven by both wild type KIF5B-RET-Ba/F3 and gatekeeper mutant KIF5B-RET(V804M)-Ba/F3 cells in a dose-dependent manner. Together, these data establish that 9x provides a good starting point for the development of targeted therapeutics against RET-positive cancers, especially NSCLC.

We report the case of a patient with B-Cell Acute Lymphoblastic Leukemia (ALL) who was found to harbor a gene fusion involving the CCDC6 and RET genes. Although the RET mutations have been identified before in other malignancies, and it is thought to represent a driver mutation in these neoplasms, it has yet to be described in ALL. The identification of known fusion genes conferring activating tyrosine kinase activity in neoplasms can suggest potential therapeutic role of tyrosine kinase inhibitors (TKI), an approach that has been exploited in several other fusion genes.

The discovery of RET rearrangement in non-small cell lung cancer (NSCLC) has prompted development of molecularly targeted therapy for such tumors, with several clinical trials being under way to evaluate the therapeutic effects of multitargeted tyrosine kinase inhibitors. The sensitivity of RET fusion-positive NSCLC to cytotoxic chemotherapy has remained unclear, however. We here report a case of NSCLC positive for the CCDC6-RET fusion gene that benefited from treatment with pemetrexed over a period of 30 months, suggesting that thymidylate synthase-targeted drugs such as pemetrexed may show efficacy for NSCLC harboring RET fusions.