Selective Antitumor Activity of Datelliptium toward Medullary Thyroid Carcinoma by Downregulating RET Transcriptional Activity

Medullary thyroid carcinoma (MTC) is a rare aggressive form of thyroid cancer with high rates of metastasis. Sporadic and hereditary MTC are strongly driven by somatic and germline mutations, respectively, in the transmembrane REarranged during Transfection (RET) proto-oncogene, which encodes a receptor tyrosine kinase. Our previous study identified datelliptium as a novel RET transcription inhibitor, which stabilizes the RET G-quadruplex structures and suppresses RET oncogene transcription. The present study aimed to elucidate the effect of datelliptium on the suppression of epithelial-to-mesenchymal transition (EMT) and metastasis-related behaviors of MTC cells, including cell migration and formation of cancer stem cells (CSCs). Our results demonstrated that datelliptium downregulated the expression of the mesenchymal markers, including N-cadherin, vimentin, slug, snail, and claudin-1. Compared to untreated cells, datelliptium significantly decreased the migration of TT cells in a dose-dependent manner in a wound healing assay. Additionally, datelliptium significantly reduced the size of preformed spheroids from TT cells over the time course. Finally, datelliptium inhibited approximately 75% of MTC xenograft growth with minimal systemic toxicity. In conclusion, datelliptium exerts its antitumor activity against MTC cells by reducing the EMT program, migratory ability, and self-renewal capacity of TT cells, thus preventing invasive and metastatic behavior of MTC.

Cytochrome C Oxidase Subunit 4 (COX4): A Potential Therapeutic Target for the Treatment of Medullary Thyroid Cancer

The nuclear-encoded subunit 4 of cytochrome c oxidase (COX4) plays a role in regulation of oxidative phosphorylation and contributes to cancer progression. We sought to determine the role of COX4 in differentiated (DTC) and medullary (MTC) thyroid cancers. We examined the expression of COX4 in human thyroid tumors by immunostaining and used shRNA-mediated knockdown of COX4 to evaluate its functional contributions in thyroid cancer cell lines. In human thyroid tissue, the expression of COX4 was higher in cancers than in either normal thyroid (p = 0.0001) or adenomas (p = 0.001). The level of COX4 expression correlated with tumor size (p = 0.04) and lymph-node metastases (p = 0.024) in patients with MTCs. COX4 silencing had no effects on cell signaling activation and mitochondrial respiration in DTC cell lines (FTC133 and BCPAP). In MTC-derived TT cells, COX4 silencing inhibited p70S6K/pS6 and p-ERK signaling, and was associated with decreased oxygen consumption and ATP production. Treatment with potassium cyanide had minimal effects on FTC133 and BCPAP, but inhibited mitochondrial respiration and induced apoptosis in MTC-derived TT cells. Our data demonstrated that metastatic MTCs are characterized by increased expression of COX4, and MTC-derived TT cells are vulnerable to COX4 silencing. These data suggest that COX4 can be considered as a novel molecular target for the treatment of MTC.

YAP confers resistance to vandetanib in medullary thyroid cancer

Medullary thyroid cancer (MTC) is the third most common thyroid cancer. RET (Rearranged in Transformation) gene mutations are considered as one of the major drivers of MTC. Vandetanib suppresses RET activity, and has shown promise in clinical trials. Unfortunately, acquired resistance to vandetanib has been observed in MTC, although the mechanism was largely unknown. We investigated the critical role of YAP (Yes-Associated Protein) on vandetanib resistance in MTC. For this, TT cells (medullary thyroid cancer cells) were treated with vandetanib for 3 months to generate a vandetanib-resistant cell line (TT-R). We investigated the role of YAP on vandetanib-resistance in TT-R cells by performing cell proliferation and colony formation assays, and examined the antitumor effects of YAP inhibitor and vandetanib in a mouse model of xenografted MTC. The TT-R cells displayed 6-fold higher IC50 to vandetanib than the TT cells. Overexpression of YAP resulted in resistance to vandetanib, whereas knockdown of YAP re-sensitized the TT-R cells to vandetanib. The YAP inhibitor synergized with vandetanib on tumor inhibition. Our results suggest that YAP plays an important role in acquired resistance to vandetanib in MTC, providing basis for combating MTC with YAP inhibitor and vandetanib.

The next-generation RET inhibitor TPX-0046 is active in drug-resistant and naïve RET-driven cancer models.

3616 Background: RET fusions/mutations drive oncogenesis in lung and thyroid cancers, and several other malignancies. Selective RET inhibitors (selpercatinib/pralsetinib) are active in patients with these cancers; unfortunately, resistance often occurs. On-target resistance includes the acquisition of solvent front mutations (SFMs i.e. RET G810 substitutions). TPX-0046 is a structurally differentiated RET inhibitor that is potent against a range of RET fusions and mutations including SFMs. Methods: The rationally-designed, compact, macrocyclic RET/SRC inhibitor TPX-0046 was characterized in RET-driven in vitro and in vivo tumor models. Results: In enzymatic assays, TPX-0046 showed low nanomolar potency against wild-type RET and 18 RET mutations/fusions. It was potent against SRC and spared VEGFR2/KDR. TPX-0046 inhibited RET phosphorylation (IC50 < 10 nM) in tumor cell lines (LC2/ad, CCDC6-RET; TT, RET C634W) and Ba/F3 engineered RET models (WT, G810R). In cell proliferation assays, TPX-0046 inhibited KIF5B-RET Ba/F3, LC2/ad, and TT cells with IC50 values ~1 nM. Ba/F3 RET engineered cells with SFMs (e.g. G810C/R/S) were potently inhibited by TPX-0046 (mean proliferation IC50 1–17 nM). TPX-0046 demonstrated marked in vivo anti-tumor efficacy in RET-driven cell-derived and patient-derived xenograft tumor models. In a Ba/F3 KIF5B-RET xenograft model, a single dose of 5 mg/kg TPX-0046 inhibited > 80% of RET phosphorylation (corresponding mean free plasma concentration: 51 nM). At 5 mg/kg BID, tumor regression was observed in RET-dependent xenograft models, including those that harbor RET SFMs: TT, CTG-0838 PDX (NSCLC, KIF5B-RET), CR1520 PDX (CRC, NCOA4-RET), Ba/F3 KIF5B-RET, and Ba/F3 KIF5B-RET G810R. Conclusions: TPX-0046 is a unique next-generation RET inhibitor that possesses potent in vitro and in vivo activity against a diverse range of RET alterations, including SFM-mediated resistance. A phase 1/2 trial for RET inhibitor-resistant and naïve RET-driven cancers is on-going (NCT04161391).

MON-513 Suppressing the Growth of Human Medullary Thyroid Cancer Cells Using FDA-Approved Drug

Medullary thyroid carcinoma (MTC) is a solid tumor of the parafollicular cells in the thyroid gland. MTC has worse prognosis, when compared with other differentiated thyroid cancers, and MTC patients with distant metastases have a low survival rate unless thyroidectomy is performed at an early stage. Furthermore, conventional treatments have only marginal benefits. Therefore, there is a need to develop novel therapeutics for MTC. Several drugs that are developed and tested in preclinical trials fail in clinical trials. Therefore, repurposing the already US Food and Drug Administration (FDA)-approved drugs towards the treatment of cancers may have potential benefits, like saving the lives of cancer patients and lowering the investment cost of drug development. Here, we explored a novel precision treatment for thyroid cancers by repurposing the FDA-approved small molecule anti-parasitic drug Nitazoxanide (NTZ). In our study, we examined the anticancer effects of NTZ on human MTC cells using the TT cell line. We treated the TT cells with different concentrations of NTZ and assessed the cell proliferation by water-soluble tetrazolium salt (WST-1) assay and oxygen consumption rate (OCR) by Seahorse extracellular flux analysis (Seahorse XFe24 Analyzer). Additionally, we determined the effects of NTZ on the protein expression of key signaling molecules that regulate MTC cell growth by western blot analysis. Our results indicated that NTZ significantly suppressed the growth of TT cells at 24 h treatment. Very importantly, NTZ reduced the basal OCR demonstrating the inhibition of mitochondrial respiration. Moreover, protein expression studies revealed that NTZ markedly reduced the key Hippo signaling pathway effector molecule TAZ and the oncogene c-myc. Interestingly, NTZ decreased the expression of epidermal growth factor receptor (EGFR) that plays an important role for RET activation in MTC. Importantly, NTZ increased the expression of p53 upregulated modulator of apoptosis (Puma). Taken together, our findings demonstrate for the first time that NTZ inhibits the growth of MTC cells and decreases the cancer cell metabolism. The mechanisms by which NTZ targets the MTC cells involve the suppression of key oncogenic proteins and upregulation of tumor suppressor molecule. Thus, our study highlights that repurposing this FDA-approved currently used drug may have a greater advantage of being tested in preclinical models of MTC, and therefore, for the rapid consideration of NTZ as a potential therapeutic drug to treat MTC patients in the near future.

Towards Mechanical Clinical Markers in Sickle Cell Disease: Dynamics of Red Blood Cells in Low Shear Flow

Several regimes of motion are evident in red blood cells (RBCs) under shear flow and are known to be controlled by the shear flow rate and by the deformability of the cell. Above a certain shear flow rate, healthy RBCs present a fluidized regime analogous to that of a droplet: the membrane adopts a tank-treading motion, i.e. rotates around the centre of mass of the cell, and its orientation oscillates around a mean value (Fig. 1). This motion is not observed in rigid RBCs which keep the same regime of motion as with low shear flow rate. The transition from one motion to the other depends on several intrinsic parameters including membrane viscosity, elasticity and cytoplasmic viscosity. Sickle cell disease (SCD) is a hereditary hemolytic anemia due to the presence of mutant hemoglobin, Hb S, which tends to polymerize in RBCs, reducing its deformability and resulting ultimately in RBC sickling. We postulate that SCD may affect RBCs capacity to adopt the tank-treading motion. Thanks to microfluidic chips coupled with high speed video, we studied the fraction of RBCs displaying a tank-treading motion (% of TT) at moderate shear stresses (0.4-0.6 Pa), in homozygous SCD patients (n=30) and in normal subjects (n=12). At the time of sampling, SCD patients were in steady state (no vaso-occlusive crisis or other acute complications) and not transfused for at least 3 months. Around 3 microL of total blood were necessary for each measurement. RBCs were studied under atmospheric conditions and exhibited the normal discoid shape. We showed first that the % of TT is significantly different in SCD patients compared to controls, with no overlap between the values of each groups (respectively 70.4±12.9% versus 98.6±0.9%). Second, measurements performed on different cells fractions isolated by cell density or in the presence of different NaCl concentrations, showed that the % of TT cells is sensitive to cell density and hydration status, both in normal subjects and in SCD patients. Finally, we evaluate the % of TT in RBC samples drawn just before or during 10 episodes of vaso-occlusive crisis from 8 different patients. The definition of a vaso-occlusive crisis, for this specific study, was set as an episode with pain in at least 2 different locations requiring hospitalization at least for 24h. The results revealed that, for a given patient, the % of TT cells varies significantly for 12h before as well as during vaso-occlusive crises with kinetics comparable from one patient to another. In conclusion, we described here a new inexpensive biological test able to discriminate healthy RBCs from sickle RBCs, with preliminary results suggesting potential interest for monitoring the clinical status of SCD patients. Further analysis will be necessary to determine if this parameter is suitable for predicting the occurrence of vaso-occlusive crises early enough to allow preventive actions. Fig1: Schematic view of the regime of motion corresponding to tank-treading. Flow direction is from left to right and RBCs are observed from the direction of the shear gradient. The black dot on the RBCs displays the motion of a membrane element on the RBC surface. The axis of symmetry remains in the shear plane, the body of the RBC oscillates slightly as the membrane rotates around it Disclosures Thuret: Addmedica: Research Funding; bluebird bio: Research Funding; Novartis: Research Funding.