Rearranged During Transfection Inhibitors Research Articles

Recent Advances in the Development of RET Inhibitors

Background: Rearranged during transfection (RET) is a receptor tyrosine kinase and a bona fide oncogene that drives various cancers. Oncogenic RET induces abnormal activation of RET kinase, causing tumorigenesis. RET can be abnormally activated through RET point mutations and RET fusions. Although RET kinase has been discovered in tumors more than 30 years ago, patients with RET-altered tumors gain limited benefits from multikinase inhibitors (MKIs). In 2020, pralsetinib and selpercatinib were approved by FDA for the treatment of RET-altered tumors. Objective: Recently reported RET inhibitors were reviewed to provide an overview of the development of novel RET inhibitors. Methods: Literatures, patents, and conference proceedings published in the past five years were collected. Only RET inhibitors with novel scaffolds or in vivo efficacy were discussed in this review. The enzymebased and cell-based activities, PK profiles, antitumor activities in vivo, and clinical efficacy of the selected RET inhibitors were described. Results: Great efforts have been spent on the development of RET inhibitors, leading to increased RETtargeted therapies. Due to high potency and specificity, pralsetinib and selpercatinib resulted in a >8- month improvement in overall survival, compared to MKIs. However, solvent-front mutants emerged and contributed to the acquired resistance to pralsetinib and selpercatinib. To overcome solvent front mutants, TPX-0046, TAS0953, and LOX-260 are investigated in early clinical studies. Conclusion: Zeteletinib, SYHA1815, TPX-0046, TAS0953, and LOX-260 are potential therapies for RET-altered cancers. In addition, macrocyclic inhibitors, allosteric inhibitors, and PROTACs are three promising strategies to address the potential drug resistance of RET.

Targeting RET alterations in non-small cell lung cancer

Rearranged during transfection (RET) alterations, which lead to aberrant activation of the RET proto-oncogene, have been identified in various cancers. In non-small cell lung cancer (NSCLC), RET mutations often manifest as RET fusion genes and are observed in 1–2 % of patients with NSCLC. In recent years, selective RET inhibitors such as selpercatinib and pralsetinib, approved by the Food and Drug Administration (FDA) in 2020, have been part of the revolutionary changes in the treatment landscape for non-small cell lung cancer. While first-generation RET inhibitors have become part of the standard of care for RET-fusion positive NSCLC, a new challenge has emerged: acquired resistance to RET inhibitors. RET resistance is a complex phenomenon that can manifest as either on-target or off-target resistance. Numerous studies have been conducted to identify the mechanisms behind this resistance. This review provides an overview of the biology of RET in NSCLC, methods of RET testing, and a comprehensive analysis of the clinical outcomes associated with multikinase and selective RET inhibitors for NSCLC. Additionally, we will explore future perspectives for RET fusion-positive NSCLC, including ongoing trials and the challenges involved in overcoming resistance to RET inhibitors.

Unraveling the Promise of RET Inhibitors in Precision Cancer Therapy by Targeting RET Mutations.

Over the past decades, the role of rearranged during transfection (RET) alterations in tumorigenesis has been firmly established. RET kinase inhibition is an essential therapeutic target in patients with RET-altered cancers. In clinical practice, initial efficacy can be achieved in patients through the utilization of multikinase inhibitors (MKIs) with RET inhibitory activity. However, the effectiveness of these MKIs is impeded by the adverse events associated with off-target effects. Recently, many RET-selective inhibitors, characterized by heightened specificity and potency, have been developed, representing a substantial breakthrough in the field of RET precision oncology. This Perspective focuses on the contemporary understanding of RET mutations, recent advancements in next-generation RET inhibitors, and the challenges associated with resistance to RET inhibitors. It provides valuable insights for the development of next-generation MKIs and selective RET inhibitors.

Primary Resistance to RET Inhibition in a RET Fusion-Positive Pancreatic Neuroendocrine Carcinoma.

We present a 54-year-old White male with a diagnosis of stage IV pancreatic neuroendocrine carcinoma. Next-generation sequencing of the tumor/blood identified a complex tumor genome, which included a rearranged during transfection (RET) gene fusion. The patient initially received cytotoxic chemotherapy with a significant radiographic response. After 4 cycles of chemotherapy, the patient was transitioned to a clinical trial using selpercatinib, a RET inhibitor, as maintenance therapy. Unfortunately, our patient developed progression of disease at the first treatment monitoring scan. Our patient suffered primary resistance to RET-targeted therapy. Proposed mechanisms of resistance include intrinsic resistance of the nuclear receptor co-activator 4-RET fusion to RET inhibition, the RET fusion representing a passenger alteration to another tumorigenic driver pathway and/or decreased efficacy of RET inhibition after platinum-based chemotherapy. Our patient's clinical course highlights the fact that "actionable" genomic alterations do not always equate to patient benefit.

Generating Potential RET-Specific Inhibitors Using a Novel LSTM Encoder-Decoder Model.

The receptor tyrosine kinase RET (rearranged during transfection) plays a vital role in various cell signaling pathways and is a critical factor in the development of the nervous system. Abnormal activation of the RET kinase can lead to several cancers, including thyroid cancer and non-small-cell lung cancer. However, most RET kinase inhibitors are multi-kinase inhibitors. Therefore, the development of an effective RET-specific inhibitor continues to present a significant challenge. To address this issue, we built a molecular generation model based on fragment-based drug design (FBDD) and a long short-term memory (LSTM) encoder-decoder structure to generate receptor-specific molecules with novel scaffolds. Remarkably, our model was trained with a molecular assembly accuracy of 98.4%. Leveraging the pre-trained model, we rapidly generated a RET-specific-candidate active-molecule library by transfer learning. Virtual screening based on our molecular generation model was performed, combined with molecular dynamics simulation and binding energy calculation, to discover specific RET inhibitors, and five novel molecules were selected. Further analyses indicated that two of these molecules have good binding affinities and synthesizability, exhibiting high selectivity. Overall, this investigation demonstrates the capacity of our model to generate novel receptor-specific molecules and provides a rapid method to discover potential drugs.

Real-world clinical profile, RET mutation testing, treatments, and PROs for MTC in Europe.

This study aimed to describe real-world patient and physician characteristics, rearranged during transfection (RET) mutation testing and results, treatment patterns, and patient-reported outcomes (PROs) in advanced or metastatic medullary thyroid cancer (aMTC) across five populous European countries. Cross-sectional physician and patient surveys were used to collect quantitative and qualitative data in France, Germany, Italy, Spain, and the UK from July to December 2020, prior to the introduction of selective RET inhibitors in Europe. Physicians completed patient record forms and a survey about their specialty and practice site. Patients were asked to provide PRO data using four validated instruments, including the EuroQol 5 Dimension (EQ-5D) questionnaire. The physician-reported sample included 275 patients with aMTC, including 79 patients with RET mutation-positive disease; median age was 60 and 56 years, respectively. Overall, 75% were tested for RET mutation (35% germline only, 21% somatic only, 44% both). Common physician-cited barriers to RET mutation testing included high cost, difficulty accessing latest tests, and time delay for results. First-line systemic therapy (most commonly vandetanib or cabozantinib) was prescribed for 69% of patients overall and 82% of the RET mutation-positive subgroup. Second-line therapy was prescribed for 12% of patients who received first-line therapy; most patients remained on first-line therapy at data capture. PROs revealed substantial disease/treatment burden. Patients with aMTC report substantial disease/treatment burden. Outcomes could be improved by identifying patients eligible for treatment with selective RET inhibitors through more optimal RET mutation testing.

Selpercatinib: A narrative drug review

Rearranged during transfection (RET) alteration promotes oncogenesis in a few cancers. RET mutation positivity is seen in approximately 70% of medullary thyroid cancers, around 30% of differentiated papillary thyroid cancers, and 1-2% of non-small-cell lung cancers (NSCLC). To write this narrative drug review, we searched various websites like the United States Food and Drug Administration, PubMed, Google Scholar, UpToDate, and recently published papers in various international conferences using the search terms “RET,” “RET alteration,” “Retevmo,” “RET inhibitors,” and “selpercatinib.” We shortlisted 31 articles published between January 1980 and January 2024. We discuss the history, mechanism of action, resistance, pharmacodynamics, pharmacokinetics, dosing, toxicity, pivotal trials, and indications of selpercatinib. Selective RET inhibitors like selpercatinib are indicated in the treatment of RET-altered NSCLC and thyroid cancer.

REThinking the role of the RET oncogene in breast cancer.

The REarranged during Transfection (RET) receptor tyrosine kinase plays a crucial role in the development of various anatomical structures during embryogenesis and it is involved in many physiological cellular processes. This protein is also associated with the initiation of various cancer types, such as thyroid cancer, non-small cell lung cancer, and multiple endocrine neoplasms. In breast cancer, and especially in the estrogen receptor-positive (ER+) subtype, the activity of RET is of notable importance. Indeed, RET seems to be involved in tumor progression, resistance to therapies, and cellular proliferation. Nevertheless, the ways RET alterations could impact the prognosis of breast cancer and its response to treatment remain only partially elucidated. Several inhibitors of RET kinase have been developed thus far, with various degrees of selectivity toward RET inhibition. These molecules showed notable efficacy in the treatment of RET-driven tumors, including some breast cancer cases. Despite these encouraging results, further investigation is needed to fully understand the potential role RET inhibition in breast cancer. This review aims to recapitulate the existing evidence about the role of RET oncogene in breast cancer, from its pathogenic and potentially prognostic role, to the clinical applications of RET inhibitors.

Selective RET Inhibitors (SRIs) in Cancer: A Journey from Multi-Kinase Inhibitors to the Next Generation of SRIs.

RET is a receptor tyrosine kinase that plays an important role in the development of neurons and kidneys. The gene encoding the rearranged-during-transfection (RET) receptor tyrosine kinase was first discovered in the 1980s. Activating RET mutations and rearrangements have since been identified as actionable drivers of oncogenesis in numerous cancer types and are most prevalent in thyroid and non-small-cell lung cancer. Following the modest success of repurposed RET-active multikinase inhibitors, the first selective RET inhibitors (SRIs), selpercatinib and pralsetinib, received regulatory approval in 2020. Now, thousands of patients with RET-altered cancers have benefited from first-generation SRIs, with impressive deep and durable responses. However, following prolonged treatment with these SRIs, a number of acquired on-target resistance mutations have been identified together with other non-RET-dependent resistance mechanisms. Today, the focus is on how we can further evolve and improve the treatment of RET-altered tumors with next-generation SRIs, and a number of candidate drugs are in development. The ideal next-generation SRIs will be active against on-target acquired resistance alterations, including those that emerge in the CNS, and will have improved safety and tolerability relative to first-generation SRIs. In this review, we will provide an update on these candidates and their potential to meet the unmet clinical need for patients who progress on first-generation SRIs.

Modeling RET-Rearranged Non-Small Cell Lung Cancer (NSCLC): Generation of Lung Progenitor Cells (LPCs) from Patient-Derived Induced Pluripotent Stem Cells (iPSCs).

REarranged during Transfection (RET) oncogenic rearrangements can occur in 1-2% of lung adenocarcinomas. While RET-driven NSCLC models have been developed using various approaches, no model based on patient-derived induced pluripotent stem cells (iPSCs) has yet been described. Patient-derived iPSCs hold great promise for disease modeling and drug screening. However, generating iPSCs with specific oncogenic drivers, like RET rearrangements, presents challenges due to reprogramming efficiency and genotypic variability within tumors. To address this issue, we aimed to generate lung progenitor cells (LPCs) from patient-derived iPSCs carrying the mutation RETC634Y, commonly associated with medullary thyroid carcinoma. Additionally, we established a RETC634Y knock-in iPSC model to validate the effect of this oncogenic mutation during LPC differentiation. We successfully generated LPCs from RETC634Y iPSCs using a 16-day protocol and detected an overexpression of cancer-associated markers as compared to control iPSCs. Transcriptomic analysis revealed a distinct signature of NSCLC tumor repression, suggesting a lung multilineage lung dedifferentiation, along with an upregulated signature associated with RETC634Y mutation, potentially linked to poor NSCLC prognosis. These findings were validated using the RETC634Y knock-in iPSC model, highlighting key cancerous targets such as PROM2 and C1QTNF6, known to be associated with poor prognostic outcomes. Furthermore, the LPCs derived from RETC634Y iPSCs exhibited a positive response to the RET inhibitor pralsetinib, evidenced by the downregulation of the cancer markers. This study provides a novel patient-derived off-the-shelf iPSC model of RET-driven NSCLC, paving the way for exploring the molecular mechanisms involved in RET-driven NSCLC to study disease progression and to uncover potential therapeutic targets.

Pralsetinib in Patients with Advanced/Metastatic Rearranged During Transfection (RET)-Altered Thyroid Cancer: Updated Efficacy and Safety Data from the ARROW Study.

Background: Rearranged during transfection (RET) alterations are targetable oncogenic drivers in thyroid cancer. Primary data from the open-label, phase 1/2 ARROW study demonstrated clinical activity and manageable safety with pralsetinib, a selective RET inhibitor, in patients with advanced/metastatic RET-altered thyroid cancer. We present an updated analysis with more patients and longer follow-up. Methods: Adult patients with advanced/metastatic RET-mutant medullary thyroid cancer (MTC) or RET fusion-positive thyroid cancer who initiated oral pralsetinib at 400 mg once daily were included. Primary endpoints were overall response rate (ORR) by blinded independent central review (per RECIST v1.1) and safety. Secondary endpoints included duration of response (DoR), progression-free survival (PFS), and overall survival. Responses were assessed in three cohorts of patients with baseline measurable disease: patients with RET-mutant MTC who had received prior cabozantinib and/or vandetanib (C/V), treatment-naïve patients with RET-mutant MTC, and patients with previously treated RET fusion-positive thyroid cancer. Patient-reported outcomes (PROs) were an exploratory endpoint. Results: As of October 18, 2021, the measurable disease population comprised of 61 patients with RET-mutant MTC and prior C/V, 62 treatment-naïve patients with RET-mutant MTC, and 22 patients with RET fusion-positive thyroid cancer who had received prior systemic therapy, including radioactive iodine. The ORR was 55.7% [confidence interval; 95% CI: 42.4-68.5] in patients with RET-mutant MTC and prior C/V, 77.4% [95% CI: 65.0-87.1] in treatment-naïve patients with RET-mutant MTC, and 90.9% [95% CI: 70.8-98.9] in patients with previously treated RET fusion-positive thyroid cancer. Median DoR and median PFS were both 25.8 months in patients with RET-mutant MTC and prior C/V, not reached in treatment-naïve patients with RET-mutant MTC, and 23.6 and 25.4 months, respectively, in patients with previously treated RET fusion-positive thyroid cancer. In the RET-altered thyroid cancer safety population (N = 175), 97.1% of patients reported a treatment-related adverse event (TRAE); these led to discontinuation in 5.7% and dose reduction in 52.6% of patients. There was one death (0.6%) due to a TRAE. PROs improved or remained stable after pralsetinib treatment. Conclusions: In this updated analysis of the ARROW study, pralsetinib continued to show deep and durable clinical activity and a manageable safety profile in patients with advanced/metastatic RET-altered thyroid cancer. Clinical Trial Registration: NCT03037385.

Expert consensus on the diagnosis and treatment of RET gene fusion non-small cell lung cancer in China.

The rearranged during transfection (RET) gene is one of the receptor tyrosine kinases and cell-surface molecules responsible for transmitting signals that regulate cell growth and differentiation. In non-small cell lung cancer (NSCLC), RET fusion is a rare driver gene alteration associated with a poor prognosis. Fortunately, two selective RET inhibitors (sRETi), namely pralsetinib and selpercatinib, have been approved for treating RET fusion NSCLC due to their remarkable efficacy and safety profiles. These inhibitors have shown the ability to overcome resistance to multikinase inhibitors (MKIs). Furthermore, ongoing clinical trials are investigating several second-generation sRETis that are specifically designed to target solvent front mutations, which pose a challenge for first-generation sRETis. The effective screening of patients is the first crucial step in the clinical application of RET-targeted therapy. Currently, four methods are widely used for detecting gene rearrangements: next-generation sequencing (NGS), reverse transcription-polymerase chain reaction (RT-PCR), fluorescence in situ hybridization (FISH), and immunohistochemistry (IHC). Each of these methods has its advantages and limitations. To streamline the clinical workflow and improve diagnostic and treatment strategies for RET fusion NSCLC, our expert group has reached a consensus. Our objective is to maximize the clinical benefit for patients and promote standardized approaches to RET fusion screening and therapy.

Patterns of Treatment Failure After Selective Rearranged During Transfection (RET) Inhibitors in Patients With Metastatic Medullary Thyroid Carcinoma.

Medullary thyroid cancer (MTC) harbors frequent mutations in RET oncogene. Selective RET inhibitors (RETi) have emerged as effective treatments. However, resistance almost invariably occurs. MTC patients who were initiated on RETi between 2018 and 2022 were included. Baseline characteristics, RET mutational status, RETi response, available tumor tissue and molecular profiles sampled pre- and post-RETi were analyzed. Among 46 MTC patients on RETi during the study period, 26 patients had discontinued at data cut-off because of progression (n = 16), death (n = 4), and toxicity (n = 6). The most frequent RET mutations at baseline were p.M918T (n = 29), and p.C634X (n = 6). Pre- and post-RETi molecular profiles were available in 14 patients. There was no primary resistance on pre-RETi samples. Post-RETi profiles revealed a bypass mechanism of resistance in 75% of the cases including RAS genes mutations (50%), FGFR2 and ALK fusions and and MYC p.P44L. RET solvent from and hinge region mutations was the only resistance mechanisms in 25% of the cases. Tumor samples from initial thyroidectomy, pre- and post-RETi, from six patients, showed an increase of the mean Ki 67-index of 7%, 17% and 40% respectively (P = 0.037) and a more aggressive poorly differentiated histology in three patients. Bypass resistance may be the most frequent mechanism of progression under RETi. A more aggressive histology may arise following RETi and warrants further investigation.

Selpercatinib monotherapy in a Chinese patient with RET fusion/EGFR co-mutated nonsmall cell lung cancer from the Phase II LIBRETTO-321 study: a case report.

Rearranged during transfection (RET) fusions and epidermal growth factor receptor (EGFR) mutations are potent oncogenic drivers in patients with nonsmall cell lung cancer (NSCLC), but rarely co-exist. Concurrent RET/EGFR mutations have been reported in patients with NSCLC who develop resistance to EGFR tyrosine kinase inhibitors but are even less frequent in treatment-naïve patients. Consequently, there is no standard treatment for RET/EGFR-mutated NSCLC. We report a case of RET/EGFR mutant NSCLC successfully treated with the oral, potent, highly selective RET inhibitor selpercatinib (160 mg daily for 28-day cycles) in an ongoing phase II study in Chinese patients with NSCLC (LIBRETTO-321). The patient, a female nonsmoker, was diagnosed with de-novo left lung adenocarcinoma with neuroendocrine differentiation, and a RET fusion was detected by next-generation sequencing testing. The patient had two tumors in the pleura, a third in the subcarinal lymph node, and a nontarget tumor in the pleura. Pleural biopsy analysis confirmed a RET fusion KIF5B (K15;R12) and an EGFR exon 19 deletion. The patient achieved a partial response (PR) with selpercatinib (absence of target tumors in pleura and reduction in the size of lymph node tumor). The PR persisted for 14.7 months, with disease progression in the nontarget lesion in the pleura and a new lesion in the liver (the PR had persisted), resulting in the discontinuation of selpercatinib. The only notable adverse event was grade 3 elevated transaminase, that was effectively managed by dose reduction. These data may support the use of selpercatinib in patients with RET/EGFR co-mutated NSCLC.

Current perspectives on the management of patients with advanced RET-driven thyroid cancer in Europe.

The incidence of thyroid cancer is increasing worldwide with the disease burden in Europe second only to that in Asia. In the last several decades, molecular pathways central to the pathogenesis of thyroid cancer have revealed a spectrum of targetable kinases/kinase receptors and oncogenic drivers characteristic of each histologic subtype, such as differentiated thyroid cancer, including papillary, follicular, and medullary thyroid cancer. Oncogenic alterations identified include B-Raf proto-oncogene (BRAF) fusions and mutations, neurotrophic tyrosine receptor kinase (NTRK) gene fusions, and rearranged during transfection (RET) receptor tyrosine kinase fusion and mutations. Multikinase inhibitors (MKIs) targeting RET in addition to multiple other kinases, such as sorafenib, lenvatinib and cabozantinib, have shown favourable activity in advanced radioiodine-refractory differentiated thyroid cancer or RET-altered medullary thyroid cancer; however, the clinical utility of MKI RET inhibition is limited by off-target toxicity resulting in high rates of dose reduction and drug discontinuation. Newer and selective RET inhibitors, selpercatinib and pralsetinib, have demonstrated potent efficacy and favourable toxicity profiles in clinical trials in the treatment of RET-driven advanced thyroid cancer and are now a therapeutic option in some clinical settings. Importantly, the optimal benefits of available specific targeted treatments for advanced RET-driven thyroid cancer require genetic testing. Prior to the initiation of systemic therapy, and in treatment-naïve patients, RET inhibitors may be offered as first-line therapy if a RET alteration is found, supported by a multidisciplinary team approach.

Discovery of 3,5-diaryl-1H-pyrazol-based ureas as potent RET inhibitors.

Rearranged during transfection (RET) is a promising target for antitumor drug development. Multikinase inhibitors (MKI) have been developed for RET-driven cancers but displayed limited efficacy in disease control. Two selective RET inhibitors were approved by FDA in 2020 and proved potent clinical efficacy. However, the discovery of novel RET inhibitors with high target selectivity and improved safety is still highly desirable. Herein, we reported a class of 3,5-diaryl-1H-pyrazol-based ureas as new RET inhibitors. The representative compounds 17a/b displayed high selectivity to other kinases, and potently inhibited isogenic BaF3-CCDC6-RET cells harboring wild-type, or gatekeeper mutation (V804M). They also displayed moderate potency against BaF3-CCDC6-RET-G810C with solvent-front mutation. Compound 17b showed better pharmacokinetics properties and demonstrated promising oral in vivo antitumor efficacy in a BaF3-CCDC6-RET-V804M xenograft model. It may be utilized as a new lead compound for further development.

Highly sensitive droplet digital PCR for detection of RET fusion in papillary thyroid cancer

BackgroundThyroid cancer is the most frequent malignancy of the endocrine system, of which papillary thyroid cancer (PTC) is the predominant form with a rapid increasing incidence worldwide. Rearranged during transfection (RET) fusions are common genetic drivers of PTC and the potent RET inhibitor selpercatinib has been recently approved for treating advanced or metastatic RET fusion-positive thyroid cancer. In this study we aimed to develop a droplet digital PCR (ddPCR) system to accurately detect RET fusion in PTC samples.MethodsThe frequency and distribution of RET fusions in PTC were analyzed using genomic data of 402 PTC patients in The Cancer Genome Atlas (TCGA) database. To establish the ddPCR system for detecting CCDC6::RET fusion, a plasmid containing CCDC6::RET infusion fragment was constructed as standard template, the annealing temperature and concentrations of primers and probe were optimized. The analytical performance of ddPCR and quantitative reverse transcription PCR (qRT-PCR) were assessed in standard templates and tissue samples from 112 PTC patients. Sanger sequencing was performed in all the RET fusion-positive samples identified by ddPCR.ResultsRET fusions were observed in 25 (6.2%) of the 402 TCGA samples, and 15 (60%) of the RET fusion-positive patients had the CCDC6::RET fusion. Compared with qRT-PCR, the ddPCR method showed a lower limit of detection (128.0 and 430.7 copies/reaction for ddPCR and qRT-PCR, respectively). When applying the two methods to 112 tissue samples of PTC, eleven (9.8%) CCDC6::RET fusion-positive samples were detected by qRT-PCR, while ddPCR identified 4 additional positive samples (15/112, 13.4%). All the CCDC6::RET fusion-positive cases identified by ddPCR were confirmed by Sanger sequencing except for one case with 0.14 copies/uL of the fusion.ConclusionThe accurate and sensitive ddPCR method reported here is powerful to detection CCDC6::RET fusion in PTC samples, application of this method would benefit more RET fusion-positive patients in the clinic.

Abstract 3419: TY-1091, a highly selective and potent second-generation RET inhibitor, demonstrates superior antitumor activity in multiple RET-mutant models

Abstract Proto-oncoprotein RET (rearranged during transfection) is a receptor tyrosine kinase and belongs to the cadherin superfamily. RET fusion proteins and gatekeeper mutations represent strong cancer drivers involved in the development of a variety of cancers. Although selective RET inhibitors selpercatinib (LOXO-292) and pralsetinib (BLU667) were recently marketed for patients with RET-dependent NSCLC and thyroid cancers, RET solvent front mutations G810R/S/C/V and other secondary mutations such as Y806C/N and V728A have been identified as mechanisms counting for acquired resistance to the two drugs and limits the applications of the kinase inhibitors. To provide novel RET inhibitors effective to a broader spectrum of RET fusions and mutations, we identified TY-1091 as a novel next-generation RET inhibitor through the in-house RET program and systemic screening of RET compound candidates. TY-1091 was characterized for its anti-tumor activity through in vitro and in vivo testing of a variety of RET-dependent tumor models including a panel of 17 engineered RET mutant Ba/F3 cell lines and 2 cancer cell models. The results show that TY-1091 inhibits wild type and major RET mutants (IC50, nM): RET G810S (9.5 nM), RET V804M/L/E (2.8-12.6 nM), and double mutants RET V804M/G810S (23.5 nM) and M918T/G810S (47.0 nM) through a biochemical screening against a panel of 17 engineered RET mutant Ba/F3 cell lines. Importantly, the inhibitory activity of TY-1091 is much higher than that of first-generation RET inhibitor Cabozantinib, and comparable to other second-generation compounds LOXO-292 and BLU-667. Consistent with its mode of action, TY-1091 grants extraordinary inhibition effects to tumor cell proliferation compared to its peer compounds LOXO-292 and BLU-667 (including TT (thyroid cancer, RET C634W) and LC2/ad (NSCLC, CCDC6-RET)), and the inhibition of the RET pathway activation, i.e., inhibition of RET phosphorylation (IC50 < 1 nM), SHC phosphorylation (IC50 = 4.6 nM) and ERK phosphorylation (IC50 = 9.8 nM) in Ba/F3-KIF5B-RET cells further validated the above in vitro phenotype. The therapeutic potential of TY-1091 was then further validated through mouse pharmacology in that TY-1091 demonstrated remarkable anti-tumor efficacy in a variety of xenograft models including Ba/F3 KIF5B-RET (wt), Ba/F3 KIF5B-RET (V804L), TT (thyroid cancer, RET C634W), and LC2/ad (NSCLC, CCDC6-RET). Detailed data will be presented. In summary, TY-1091 is a highly potent, orally available, and safe small molecule inhibitor to pan-RET mutations in cancer, and may attenuate SFMs-mediated resistance to existing RET therapy. The IND clearance from the US FDA was received and Phase I clinical investigations of TY-1091 shall be launched in the US soon. *To Whom Correspondence should be addressed to: Jun Li, Chengshan Niu and Yusheng Wu Citation Format: Chengshan Niu, Maolin Zheng, Huan Wang, Kaige Ji, Meihua Li, Guohui Wang, Rongzhen Ni, Apeng Liang, Aishen Gong, Yazhen Zhang, Hui Su, Mingyu Jiang, Shaoqing Chen, Xiugui Chen, Jun Li, Yusheng Wu. TY-1091, a highly selective and potent second-generation RET inhibitor, demonstrates superior antitumor activity in multiple RET-mutant models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3419.

Assessment of In Silico and In Vitro Selpercatinib Metabolic Stability in Human Liver Microsomes Using a Validated LC-MS/MS Method.

Selpercatinib (SLP; brand name Retevmo®) is a selective and potent RE arranged during transfection (RET) inhibitor. On 21 September 2022, the FDA granted regular approval to SLP (Retevmo, Eli Lilly, and Company). It is considered the only and first RET inhibitor for adults with metastatic or locally advanced solid tumors with RET gene fusion. In the current experiment, a highly specific, sensitive, and fast liquid chromatography tandem mass spectrometry (LC-MS/MS) method for quantifying SLP in human liver microsomes (HLMs) was developed and applied to the metabolic stability evaluation of SLP. The LC-MS/MS method was validated following the bioanalytical methodology validation guidelines outlined by the FDA (linearity, selectivity, matrix effect, accuracy, precision, carryover, and extraction recovery). SLP was detected by a triple quadrupole detector (TQD) using a positive ESI source and multiple reaction monitoring (MRM) mode for mass spectrometric analysis and estimation of analytes ions. The IS-normalized matrix effect and extraction recovery were acceptable according to the FDA guidelines for the bioanalysis of SLP. The SLP calibration standards were linear from 1 to 3000 ng/mL HLMs matrix, with a regression equation (y = 1.7298x + 3.62941) and coefficient of variation (r2 = 0.9949). The intra-batch and inter-batch precision and accuracy of the developed LC-MS/MS method were -6.56-5.22% and 5.08-3.15%, respectively. SLP and filgotinib (FLG) (internal standard; IS) were chromatographically separated using a Luna 3 µm PFP (2) stationary phase (150 × 4.6 mm) with an isocratic mobile phase at 23 ± 1 °C. The limit of quantification (LOQ) was 0.78 ng/mL, revealing the LC-MS/MS method sensitivity. The intrinsic clearance and in vitro t1/2 (metabolic stability) of SLP in the HLMs matrix were 34 mL/min/kg and 23.82 min, respectively, which proposed an intermediate metabolic clearance rate of SLP, confirming the great value of this type of kinetic experiment for more accurate metabolic stability predictions. The literature review approved that the established LC-MS/MS method is the first developed and reported method for quantifying SLP metabolic stability.

Pralsetinib for RET Fusion-Positive Advanced Non-small-Cell Lung Cancer: An Evidence Review Group Perspective of a NICE Single Technology Appraisal.

The National Institute for Health and Care Excellence (NICE) invited the manufacturer (Roche) of pralsetinib (Gavreto®), as part of the single technology appraisal (STA) process, to submit evidence for the clinical effectiveness and cost effectiveness of pralsetinib for the treatment of adult patients with rearranged during transfection (RET) fusion-positive advanced non-small-cell lung cancer (NSCLC) not previously treated with a RET inhibitor. Kleijnen Systematic Reviews Ltd, in collaboration with University Medical Center Groningen, was commissioned to act as the independent Evidence Review Group (ERG). This paper summarizes the company submission (CS), presents the ERG's critical review of the clinical and cost-effectiveness evidence in the CS, highlights the key methodological considerations, and describes the development of the NICE guidance by the Appraisal Committee. The CS reported data from the ARROW trial. ARROW is a single-arm, multicenter, non-randomized, open-label, multi-cohort study in patients with RET fusion-positive NSCLC and other advanced solid tumors. The CS included both untreated and pre-treated RET fusion-positive NSCLC patients, among other disease types. The comparators in the untreated population were pembrolizumab + pemetrexed + chemotherapy and pembrolizumab monotherapy. The comparators for the pre-treated population were docetaxel monotherapy, docetaxel + nintedanib, and platinum-based chemotherapy ± pemetrexed. As no comparators were included in ARROW, an indirect treatment comparison was conducted to estimate relative effectiveness. The ERG's concerns included the immaturity of data, small sample size, and lack of comparative safety evidence. The ERG considers the clinical evidence presented to be insufficiently robust to inform the economic model. Even when all the ERG preferred assumptions were implemented in the model, uncertainty remained on a number of issues, such as the appropriateness of the hazard ratios and the methods and data used to derive them, long-term efficacy of pralsetinib, and direct evidence for health-related quality of life (HRQoL). NICE did not recommend pralsetinib within its marketing authorization for treating RET fusion-positive advanced non-small-cell lung cancer (NSCLC) in adults who have not had a RET inhibitor before. The uncertainty of the clinical evidence and the estimates of cost effectiveness were too high to be considered a cost-effective use of NHS resources. Therefore, pralsetinib was not recommended for routine use.