Selective RET Inhibitors Research Articles

Abstract 5833: Genomic mechanisms of RET inhibitor resistance in RET-fusion positive NSCLC

Abstract RET fusions are a driver oncogene detected in 1-2% of non-small cell lung cancer (NSCLC) cases. Currently, two selective RET inhibitors (RETi), selpercatinib and pralsetinib have received FDA approval for RET fusion-positive NSCLC. However, RET fusions are highly heterogeneous and the impact of specific fusion partners and breakpoints on RETi sensitivity is not well understood. Moreover, most patients eventually develop resistance to RETi, and secondary RET mutations are thought to be a key mechanism of acquired resistance. Thus, we aimed to identify RET-dependent mechanism of RETi resistance in effort to improve treatment options and clinical outcomes. We engineered a panel of Ba/F3 cells expressing various RET fusion partners and breakpoints observed in clinical cases of NSCLC and evaluated their drug sensitivity profile against a panel of RETi including selpercatinib, pralsetinib, TPX-0046, lovatinib, zeteletinib and ponatinib. We determined that individual RET fusions impart distinct sensitivities to RETi. For example, cells expressing KIF-RET (K22, R12) were sensitive to selpercatinib and pralsetinib but less sensitive to ponatinib, whereas cells expressing KIF-RET (K15, R12) were highly sensitive to selpercatinib, pralsetinib, and ponatinib. Moreover, using RET-fusion positive NSCLCs, we observed that the RETi sensitivity profile of human cell lines was similar to that observed using Ba/F3 models. To identify potential resistance mutations, we utilized the LentiMutate approach. In KIF5B-RET (K15, R12) expressing cells, we identified G810S as being associated with resistance to both selpercatinib and pralsetinib, a finding consistent with previous reports and clinical observations. In addition, we identified Y806H/N, V804M/E, and M918T as being associtated with selpercatinib-resistance and L730I/V, E732K, and Y806H/N as being associated with pralsetinib-resistance. We next constructed Ba/F3 cells expressing KIF5B-RET in combination with each secondary mutation and evaluated RETi sensitivity. G810S and Y806N conferred resistance to selpercatinib and pralsetinib, as well as to RET-targeting multi-kinase inhibitors. V804M/E mutations conferred resistance to selpercatinib but not pralsetinib, whereas L730I/V and E732K mutations conferred resistance to pralsetinib but not selpercatinib, demonstrating RETi-specific resistance mutations. Cells expressing G810S secondary mutations were resistant to selpercatinib and pralsetinib, but sensitive to zeteletinib. Collectively, we show that individual RET fusion variants have distinct drug sensitivity profiles and that secondary resistance mutations are non-overlapping between RETi. The comprehensive characterization of RET-dependent mechanisms of resistance to RETi may provide therapeutic guidance for treating RET-fusion driven NSCLC and provide structural insights that can guide the development of new therapeutic regimens. Citation Format: Ximeng Liu, Monique Nilsson, Tomohiro Takehara, Junqin He, Xiaofang Huo, Ashwani Kumar, John Heymach, Ralf Kittler. Genomic mechanisms of RET inhibitor resistance in RET-fusion positive NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5833.

Adaptive Darwinian off-target resistance mechanisms to selective RET inhibition in RET driven cancer

Patients treated with RET protein tyrosine kinase inhibitors (TKIs) selpercatinib or pralsetinib develop RET TKI resistance by secondary RET mutations or alterative oncogenes, of which alterative oncogenes pose a greater challenge for disease management because of multiple potential mechanisms and the unclear tolerability of drug combinations. A patient with metastatic medullary thyroid carcinoma (MTC) harboring a RET activation loop D898_E901del mutation was treated with selpercatinib. Molecular alterations were monitored with tissue biopsies and cfDNA during the treatment. The selpercatinib-responsive MTC progressed with an acquired ETV6::NTRK3 fusion, which was controlled by selpercatinib plus the NTRK inhibitor larotrectinib. Subsequently, tumor progressed with an acquired EML4::ALK fusion. Combination of selpercatinib with the dual NTRK/ALK inhibitor entrectinib reduced the tumor burden, which was followed by appearance of NTRK3 solvent-front G623R mutation. Preclinical experiments validated selpercatinib plus larotrectinib or entrectinib inhibited RET/NTRK3 dependent cells, whereas selpercatinib plus entrectinib was necessary to inhibit cells with RET/NTRK3/ALK triple alterations or a mixture of cell population carrying these genetic alterations. Thus, RET-altered MTC adapted to selpercatinib and larotrectinib with acquisition of ETV6::NTRK3 and EML4::ALK oncogenes can be managed by combination of selpercatinib and entrectinib providing proof-of-concept of urgency of incorporating molecular profiling in real-time and personalized N-of-1 care transcending one-size-fits-all approach.

Systemic therapies for advanced thyroid cancer - an update

Based on phase III clinical studies, four multi-kinase inhibitors (MKI) are approved for the treatment of progressive radioiodine-refractory differentiated thyroid carcinoma (rrDTC) and medullary thyroid carcinoma (MTC) in Germany. Only recently, based on the randomized trial COSMIC-311, Cabozantinib has been approved as a second-line treatment option in advanced rrDTC. As first in-label selective RET-Inhibitor, Selpercatinib showed promising efficacy in advanced MTC (first line) with RET mutations and rrDTC (second line) with RET fusions along with fewer side effects. Changes and new approaches for the treatment of ATC have been summarised in the current ATA guidelines.

Management of Advanced Medullary Thyroid Carcinoma: Current Systemic Therapy Options.

The current rapid development of more selective and effective drugs for the treatment of thyroid cancer has open a new era in the treatment of patients with this condition, in the past limited to the possibility of only radioactive iodine for well differentiated tumor and surgery for medullary thyroid carcinoma (MTC). The treatment of advanced medullary thyroid carcinoma has evolved in the last few years and options for patients with advanced disease are now available. Multikinase inhibitors (MKIs) with nonselective RET inhibition like Vandetanib and Cabozantinib were approved for the treatment of MTC, although the efficacy is limited due to the lack of specificity resulting in a higher rate of drug-related adverse events, leading to subsequent dose reductions, or discontinuation, and the development of a resistance mechanism like seen on the RET Val804 gatekeeper mutations. MTC is associated with mutations in the RET protooncogene, and new highly selective RET inhibitors have been developed including Selpercatinib and Pralsetinib, drugs that have demonstrate excellent results in clinical trials, and efficacy even in the presence of gatekeeper mutations. However, despite their efficacy and great tolerability, mechanisms of resistance have been described, such as the RET solvent front mutations. Due to this, the need of constant evolution and drug research is necessary to overcome the emergence of resistance mechanisms.

Chinese expert consensus on the diagnosis and treatment of advanced RET fusion-positive non-small cell lung cancer (2023 edition)

Lung cancer is the most common cancer and the leading cause of cancer death in China. Non-small cell lung cancer (NSCLC) is the most common histological type of lung cancer. Mutations of driver genes have major impacts on incidence and progression of lung cancer. Advances in molecular biology research and clinical research have promoted the discovery of rare tumor driver genes, as well as the development and application of new targeted drugs. Nearly 1% to 2% of NSCLCs harbor RET fusions, and this patient population may not respond well to traditional treatments like chemotherapy or radiation therapy. After the new highly selective RET inhibitors pralsetinib (BLU-667) and selpercatinib (LOXO-292) entered clinical application, the diagnosis and treatment of RET fusion positive NSCLC has made breakthrough progress. At present, there is a lack of guiding consensus on the standardized diagnosis and treatment of RET fusion-positive NSCLC in China. The Society of Cancer Precision of Chinese Anti-Cancer Association and Lung Cancer Expert Group of Chinese Medical Journal, invited 38 experts form respiratory medicine, medical oncology, oncology radiotherapy and pathology to form a consensus development group. Based on the existing research evidence, combined with China's clinical practice experience, a standardized process for the diagnosis and treatment of advanced RET fusion-positive NSCLC is proposed, including suitable populations and methods for RET gene fusion, treatment drug selection, treatment of resistance to highly selective RET inhibitors, and management of adverse reactions to treatment, with a view to providing guidance for clinicians.

Abstract B043: Preliminary results from a phase I/II study evaluating the safety, tolerability, and efficacy of EP0031, a next generation selective RET inhibitor, in patients with advanced RET-altered malignancies

Abstract BACKGROUND Emergence of resistance to 1st generation (gen) selective RET inhibitors (SRIs, selpercatinib/pralsetinib) is an area of high unmet need. EP0031 (A400/KL590586) has promise as a next gen SRI. Clinical data was recently reported from an ongoing Phase I/II study in China that included 109 patients (pts) with RET-altered tumours (NCT05265091, Zhou et al. JCO 2023, 41:16, suppl. 3007). ORR was 80.8 and 69.7%, across 40-120 mg QD doses, in treatment-naïve or pre-treated metastatic NSCLC, respectively. Responses durable with longest 14.5 mo ongoing, median DoR not reached. Responses, including in the CNS, observed in 5/7 pts that previously received 1st gen SRI. EP0031 had an encouraging safety and tolerability profile. 90mg QD was selected as RP2D. Here we report initial data from the dose ranging and optimisation module of a parallel Phase I/II study in the US and Europe. EXPERIMENTAL PROCEDURES This study (NCT05443126) is recruiting pts with RET-altered NSCLC, thyroid cancer or other solid tumours. Study includes male or female pts ≥ 18 years of age, PS 0 or 1 with/without asymptomatic, stable brain metastases. The first module is a dose escalation to investigate safety, tolerability, PK/PD and define the MTD and/or RP2D. This is based on rolling 6 design and is expected to recruit up to 40 pts. RESULTS As of 10th July 2023, a total of 15 pts, 5 medullary thyroid cancer (MTC), 2 CRC and 8 NSCLC, have been included across dose cohorts of 20mg (N=3), 60mg (N=6) and 90mg (N=6). PK profile is comparable with Chinese pts and consistent with QD dosing. 60mg QD predicted to achieve IC50 for inhibition of RET fusions/mutations. No DLTs and no serious adverse events reported. No dose reductions, interruptions or discontinuations have been required. AEs have been mainly Grade 1 or 2. No neutropenia, hypertension, neurotoxicity or QTc prolongation observed. Three pts (all MTC) that received 20 mg QD had their dose escalated to 60mg (after 5-7 cycles at 20mg). 2 of those pts, both SRI naïve, have ongoing stable disease for >23 weeks. 1 pt (prior SRI) with a new target lesion continues to derive clinical benefit and remains on treatment. Of 4 evaluable pts at 60 mg, 2 pts with NSCLC (prior SRI) have achieved a PR, treatment is ongoing and 2 pts with MTC (prior SRI) had PD, one of whom continues to derive clinical benefit and remains on treatment. The remaining pts at 60 or 90mg (potential RP2D) are not yet evaluable for efficacy. Genomic analyses for RET/non-RET resistance mechanisms are ongoing. Expansion of the 60mg and 90mg cohorts is planned for dose optimization. Expanded efficacy, safety and PK/PD data from dose ranging and optimization cohorts will be presented. CONCLUSIONS These preliminary data are encouraging, consistent with that reported from a larger cohort of Chinese patients, with early evidence that EP0031 is active in pts that received prior 1st gen SRI. Once RP2D confirmed, the study will expand cohorts of both SRI-naïve and pre-treated pts with RET-altered NSCLC, thyroid and other solid tumours. Citation Format: Elena Garralda, Alonso Guzman, Pilar Garrido, Andrew G Gianoukakis, Matthew Taylor, Sarina Piha-Paul, Matthew G Krebs, Antoine Italiano, Liz Clark, Geoff Fisher, Tobi Arkenau, Vivek Subbiah. Preliminary results from a phase I/II study evaluating the safety, tolerability, and efficacy of EP0031, a next generation selective RET inhibitor, in patients with advanced RET-altered malignancies [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B043.

Can New Structure of RET Inhibitors Capable of Suppressing Resistant in Non-Small-Cell Lung Cancer?

In 2012, RET rearrangements are observed in 1-2% of Non-Small-Cell Lung Cancer (NSCLC) patients and result in the constitutive activation of downstream pathways normally implied in cell proliferation, growth, differentiation and survival. Several compounds have been reported, including some traditional kinases inhibitors and the discovery of some new structure of natural products. Cabozantinib and vandetanib are multikinase inhibitors have been explored in the clinic for NSCLC patients. As a result of the nonselective nature of these multikinase inhibitors, patients had off-target adverse effects. Then, the discovery and clinical validation of highly potent selective RET inhibitors such as pralsetinib and selpercatinib demonstrating improved effificacy and a more favorable toxicity profile. However, acquired resistance mediated by secondary mutations in the solvent-front region of the kinase (e.g. G810C/S/R) becomes a major challenge for selective RET inhibitor therapies. In this review, we will highlight typical RET inhibitors developed during these years and provide a reference for more potential RET inhibitors exploration in the future.

2211MO Uncovering the mechanisms of persistent disease in RET-altered thyroid cancers: Insights from patient-derived xenograft models treated with selective RET inhibitors

2211MO Uncovering the mechanisms of persistent disease in RET-altered thyroid cancers: Insights from patient-derived xenograft models treated with selective RET inhibitors

TMEM127 suppresses tumor development by promoting RET ubiquitination, positioning, and degradation

The TMEM127 gene encodes a transmembrane protein of poorly known function that is mutated in pheochromocytomas, neural crest-derived tumors of adrenomedullary cells. Here, we report that, at single-nucleus resolution, TMEM127-mutant tumors share precursor cells and transcription regulatory elements with pheochromocytomas carrying mutations of the tyrosine kinase receptor RET. Additionally, TMEM127-mutant pheochromocytomas, human cells, and mouse knockout models of TMEM127 accumulate RET and increase its signaling. TMEM127 contributes to RET cellular positioning, trafficking, and lysosome-mediated degradation. Mechanistically, TMEM127 binds to RET and recruits the NEDD4 E3 ubiquitin ligase for RET ubiquitination and degradation via TMEM127 C-terminal PxxY motifs. Lastly, increased cell proliferation and tumor burden after TMEM127 loss can be reversed by selective RET inhibitors invitro and invivo. Our results define TMEM127 as a component of the ubiquitin system and identify aberrant RET stabilization as a likely mechanism through which TMEM127 loss-of-function mutations cause pheochromocytoma.

RET-Altered Cancers-A Tumor-Agnostic Review of Biology, Diagnosis and Targeted Therapy Activity.

RET alterations, such as fusions or mutations, drive the growth of multiple tumor types. These alterations are found in canonical (lung and thyroid) and non-canonical (e.g., gastrointestinal, breast, gynecological, genitourinary, histiocytic) cancers. RET alterations are best identified via comprehensive next-generation sequencing, preferably with DNA and RNA interrogation for fusions. Targeted therapies for RET-dependent cancers have evolved from older multikinase inhibitors to selective inhibitors of RET such as selpercatinib and pralsetinib. Prospective basket trials and retrospective reports have demonstrated the activity of these drugs in a wide variety of RET-altered cancers, notably those with RET fusions. This paved the way for the first tumor-agnostic selective RET inhibitor US FDA approval in 2022. Acquired resistance to RET kinase inhibitors can take the form of acquired resistance mutations (e.g., RET G810X) or bypass alterations.

Challenges in the care of patients with RET-altered thyroid cancer: a multicountry mixed-methods study

BackgroundThe discovery of driver oncogenes for thyroid carcinomas and the identification of genomically targeted therapies to inhibit those oncogenes have altered the treatment algorithm in thyroid cancer (TC), while germline testing for RET mutations has become indicated for patients with a family history of RET gene mutations or hereditary medullary TC (MTC). In the context of an increasing number of selective RET inhibitors approved for use, this paper aims to describe challenges and barriers affecting providers’ ability to deliver optimal care for patients with RET-altered TC across the patient healthcare journey.MethodsA mixed-method educational and behavioral needs assessment was conducted in Germany (GER), Japan (JPN), the United Kingdom (UK), and the United States (US) prior to RET-selective inhibitor approval. Participants included medical oncologists (MO), endocrinologists (EN) and clinical pathologists (CP) caring for patients affected with TC. Data collection tools were implemented in three languages (English, German, Japanese). Qualitative data were coded and thematically analyzed in NVivo. Quantitative data were analyzed via frequency and crosstabulations in SPSS. The findings presented here were part of a broader study that also investigated lung cancer challenges and included pulmonologists.ResultsA total of 44 interviews and 378 surveys were completed. Suboptimal knowledge and skills were self-identified among providers, affecting (1) assessment of genetic risk factors (56%, 159/285 of MOs and ENs), (2) selection of appropriate genetic biomarkers (59%, 53/90 of CPs), (3) treatment plan initiation (65%, 173/275 of MOs and ENs), (4) management of side effects associated with multitargeted tyrosine kinase inhibitors (78%, 116/149 of MOs and ENs), and (5) transfer of patients into palliative care services (58%, 160/274 of MOs and ENs). Interviews underscored the presence of systemic barriers affecting the use of RET molecular tests and selective inhibitors, in addition to suboptimal knowledge and skills necessary to manage the safety and efficacy of targeted therapies.ConclusionThis study describes concrete educational needs for providers involved in the care of patients with RET-altered thyroid carcinomas. Findings can be used to inform the design of evidence-based education and performance improvement interventions in the field and support integration into practice of newly approved RET-selective inhibitors.

Efficacy and safety of pralsetinib in patients with advanced RET fusion-positive non-small cell lung cancer.

Pralsetinib is a potent, selective RET inhibitor targeting oncogenic RET alterations. As part of the global, phase 1/2 ARROW trial (NCT03037385), the efficacy and safety of pralsetinib in Chinese patients with advanced RET fusion-positive non-small cell lung cancer (NSCLC) were evaluated. Adult patients with advanced, RET fusion-positive NSCLC with or without prior platinum-based chemotherapy were enrolled into two cohorts receiving 400-mg once-daily oral pralsetinib. Primary end points were objective response rates assessed by blinded independent central review and safety. Of 68 patients enrolled, 37 had received prior platinum-based chemotherapy (48.6% with ≥3 prior systemic regimens) and 31 were treatment-naïve. As of March 4, 2022 (data cutoff), of the patients with measurable lesions at baseline, a confirmed objective response was observed in 22 (66.7%; 95% confidence interval [CI], 48.2-82.0) of 33 pretreated patients, including 1 (3.0%) complete response and 21 (63.6%) partial responses; and in 25 (83.3%; 95% CI, 65.3-94.4) of 30 treatment-naïve patients, including two (6.7%) complete responses and 23 (76.7%) partial responses. Median progression-free survival was 11.7months (95% CI, 8.7-not estimable) in pretreated patients and 12.7months (95% CI, 8.9-not estimable) in treatment-naïve patients. The most common grade 3/4 treatment-related adverse events in 68 patients were anemia (35.3%) and decreased neutrophil count (33.8%). Eight (11.8%) patients discontinued pralsetinib because of treatment-related adverse events. Pralsetinib showed robust and durable clinical activity with a well-tolerated safety profile in Chinese patients with RET fusion-positive NSCLC. NCT03037385.

A phase I study of KL590586, a next-generation selective RET inhibitor, in patients with RET-altered solid tumors.

3007 Background: KL590586 (A400/EP0031) is a potent next-generation selective RET inhibitor (SRI) with activity against acquired resistance mutations to first-generation SRIs, and brain metastases (mets). Here we present preliminary data of the phase Ⅰ part from a phase I/II study (KL400-I/II-01, NCT05265091) in patients (pts) with RET-altered advanced tumors to define safety, pharmacokinetics (PK) and efficacy. Methods: The phase Ⅰ of KL400-I/Ⅱ-01 consisted of dose-escalation (Bayesian Optimal Interval design) and dose-expansion. Primary endpoints were to determine the maximum tolerated dose (MTD) and/or Recommended Phase II Dose. Secondary endpoints included safety, PK, objective response rate (ORR), disease control rate (DCR), and duration of response (DoR) as per RECIST 1.1. Results: As of Dec. 30, 2022, 87 pts with RET-altered tumors were treated at 6 doses levels (10 to 120 mg QD). No DLTs were observed, and MTD was not reached. Incidence of treatment-related adverse events (TRAEs, any grade) was 93.1% (81/87), most (74.7%) were grade 1-2, reversible and included (>25%): AST increase (50.6%), ALT increase (48.3%), creatinine increase (33.3%), bilirubin increase (32.2%), constipation (32.2%) and headache (31%). 24.1% of pts had grade ≥3 TRAEs, the most common (occurring in >2% of pts) were ALP increase (2.3%), GGT increase (2.3%), ileus (2.3%). TRAEs led to dose reduction or treatment discontinuation in 4.6% and 6.9% of pts, respectively. Hypertension, QT interval prolongation, platelets decrease and lymphocytes decrease (leading to 1st gen SRI dose delays and modifications frequently) were rare (<5%) and low-grade. The exposure increased dose-dependently and the mean half-life was found to be 34.1-99.8 h. Clinical responses were observed from 40mg onwards. 69 pts treated at the 40-120mg dose levels (57 NSCLC, 10 MTC, 1 pancreatic cancer, 1 ovarian cancer) were evaluable for efficacy analysis, ORR was 64% (NSCLC, MTC and pancreatic cancer). Most pts (58/69) remained on treatment, with the longest >11 months. The ORR in pts with systemic pretreated NSCLC (median prior treatment: 2, range 1-9, 28% pretreated with anti-PD1/PD-L1 therapy) was 63%(20/32, 1 CR), DCR 91% with median DoR not reached. 9 pts received prior 1st gen SRI, 7 with tumor shrinkage of -10% to -69%, with 3 PR and 4 SD. 11 pts with brain mets (without radiotherapy):4/5 with measurable brain disease had 100%, 100%, 80%, and 47% shrinkage. Overall CNS DCR was 100%.The ORR in treatment naïve NSCLC was 76% (19/25, 1 CR), DCR 92% and median DoR not reached. 3/4 pts with brain mets (without radiotherapy) had complete or partial disappearance of baseline brain lesions. Conclusions: KL590586 was well-tolerated, and associated with robust clinical activity in RET-altered tumors regardless of tumor type, including NSCLC pts with resistance to1st gen SRIs and with CNS mets. Pivotal studies are planned. Clinical trial information: NCT05265091 .

A first-in-human phase I, dose-escalation and dose-expansion study of SY-5007, a highly potent and selective RET inhibitor, in Chinese patients with advanced RET positive solid tumors.

9111 Background: RET gene fusions have been identified as oncogenic drivers in 1-2% of non-small-cell lung cancer (NSCLC) and 10-20% of papillary thyroid carcinomas. Activating RET mutations occur in 50-60% of medullary thyroid cancer (MTC). Recently, selective RET TKIs, selpercatinib and pralsetinib, were approved for RET positive solid tumors by FDA. SY-5007 is a highly potent RET inhibitor that selectively targets RET fusions and mutations. This study is to investigate the safety, PK characteristics and preliminary efficacy of SY-5007 in Chinese patients with advanced RET-altered solid tumors. Methods: In this first-in-human phase I study, eligible patients previously treated and with positive RET were enrolled. In the dose escalation phase, following 3+3 design, the patients were administered orally with SY-5007 20 mg once daily, or 20, 40, 80, 120, 160, 200 mg twice daily in a 28-day cycle. The expansion doses (160 and 200 mg twice daily) were executed in a dose expansion phase to determine a recommended phase II dose (RP2D). Then three cohorts ( RET fusion-positive NSCLC or thyroid cancers and RET mutant MTC) at RP2D were expanded in eligible patients. Primary endpoints included safety, tolerability, MTD, DLTs. Secondary endpoints included PK and preliminary antitumor activity of SY-5007 per RECIST v1.1. Results: As of Feb.06, 2023, a total of 60 patients including 55 RET fusion NSCLC and 5 RET mutant solid tumors were enrolled into dose escalation cohorts (n = 17) and dose expansion cohorts (n = 43).Totally, 55 (91.7%) patients experienced treatment-related adverse events (TRAEs) including increased aspartate aminotransferase (50.0%), increased alanine aminotransferase (41.7%), diarrhea (41.7%), etc. Grade ≥3 TRAEs were observed in 22 (36.7%) patients including hypertension (15%), diarrhea (5%), increased alanine aminotransferase (3.3%), etc. PK study showed SY-5007 was absorbed rapidly, exposure of SY-5007 increased in a dose-dependent manner at doses between 20 and 160 mg twice daily, and it was saturated at 160 mg twice daily. In 50 evaluable patients, the overall ORR and DCR was 62.0% (95% CI, 47.2-75.4) and 94.0 % (95% CI, 83.5-98.8), respectively. 29 patients (24 NSCLC, 4 MTC) received SY-5007 at 160 mg twice daily, 27 of 28 (96.4%) evaluable patients showed tumor regression, ORR and DCR was 72.4% (95% CI, 52.8-87.3) and 89.7% (95% CI, 72.7-97.8), respectively. For NSCLC patients, the ORR and DCR was 75.0% (95% CI, 53.3-90.2) and 91.7% (95% CI, 73.0-99.0), respectively. Conclusions: SY-5007 was well tolerated in patients. Preliminary antitumor activity was also observed in patients with advanced RET-fusion positive NSCLS and RET mutant MTC. The pivotal Phase II clinical study of SY-5007 in NSCLC patients is ongoing. Research Sponsor: Shouyao Holdings (Beijing) Co., Ltd. Clinical trial information: NCT05278364 .

Intrapatient comparative efficacy of selective RET inhibitors using growth modulation index in patients with RET aberrant cancers.

3086 Background: Selective RET inhibitors (RETi) have changed the paradigm for treatment of RET altered cancers. Current evidence on their efficacy comes from single-arm basket trials. In this study, we performed intrapatient efficacy comparison between approved selective RETi (selpercatinib and pralsetinib) and prior and/or subsequent therapies. We used growth modulation index (GMI) as a tool to compare efficacy, where a value of >1.33 is presumed a cutoff to establish superior efficacy. Methods: We included patients with RET-positive tumors who were treated at our institution as part of RETi clinical trials. We excluded patients with no other systemic therapy received before or after the RETi of interest. We also excluded patients who received both drugs to avoid overlapping efficacy bias, and patients who were treated for ≤ 30 days or had non-evaluable disease. Since some patients have been treated beyond progression or discontinued RETi due to intolerance, we used ratios for both time to treatment takeoff (TTT) and time to progression (TTP) to compare efficacy of RETi (at the RETi treatment line (n)) to prior therapy (n-1) and to subsequent therapy (n+1). GMI was defined as the ratio between TTT/TTT (n±1) or TTP to TTP (n±1). Results: We included 66 patients who received RETi and met our inclusion criteria [39 received selpercatinib and 27 received pralsetinib]. Most patients had GMI>1.33 using either TTT or TTP (61% (n=40) and 58% (n=38), respectively). The median GMI based on pre-RETi therapy was 2.1 and 1.6 (using TTT and TTP, respectively); while the median GMI based on post-RETi therapy was 4.9 and 4.4 (using TTT and TTP, respectively). Patients with GMI>1.33 were more likely to have PR as best response compared to patients with GMI<1.33 (85% vs 53%, p=0.005 using TTT; and 87% vs 54%, p=0.003 using TTP). GMI using TTT (n/n-1) was higher in patients with RET fusions compared to patients with RET mutations (3.7 vs 1.4, p=0.048). GMI using TTT and GMI using TTP(n/n+1) were lower in patients with WBCs <8 at baseline (2.6 vs 13.8, p=0.014; 2.6 vs 11.1, p=0.014; for TTT and TTP) and GI cancer diagnosis (0.4 vs 9.3, p=0.042; 0.4 vs 10.4, p=0.042; for TTT and TTP). Conclusions: Intrapatient efficacy comparisons are feasible using GMI calculations and provide a proof of concept on the favorability of selective RETi compared to other systemic therapies. [Table: see text]

Amplification of wild-type RET and clinical response to selpercatinib for non–small-cell lung cancer (NSCLC).

9123 Background: RET rearrangements and RET kinase domain mutations represent targetable genomic alterations in various cancer types. However, the frequency and characteristics of RET amplification in cancer and its potential role as a targetable oncogenic driver are not well-characterized. Methods: In a pan-cancer cohort of patients at the Dana-Farber Cancer Institute (DFCI) whose tumors underwent next-generation sequencing (NGS), we evaluated the frequency of wild-type (wt) RET amplification (defined as ≥6 copies) in the absence of RET rearrangements or activating mutations. We validated our findings using merged data from the TCGA, GENIE, and China Pan-Cancer datasets. Results: The frequency of wt RET amplification across all cancers was 0.08% (28/34,463) in the DFCI cohort and 0.16% (145/91,466) in the validation cohort. In NSCLC, the frequency of RET amplification was 0.10% (5/4773) in the DFCI cohort and 0.13% (15/11,622) in the validation cohort. Other cancer types with RET amplification included hepatobiliary cancer, prostate cancer, and breast cancer, among others. For 22 RET-amplified cases with available copy number data , the median RET gene copy number was 7 (range 6-36). Among 20 RET-amplified NSCLCs, 10 had no other known driver mutations, and 10 had concurrent driver mutations (including MET exon 14 skipping, MET amplification, KRAS G12C/S/D, EGFR L858R, EGFR exon 20 insertion, and EGFR exon 19 deletion). In cases with available smoking status, 5 out of 6 patients with RET-amplified NSCLC had a history of tobacco use. A 69-year-old man with unresectable stage III NSCLC had disease recurrence after chemoradiation and durvalumab. Both the initial and recurrent biopsy samples showed focal high-level RET amplification (22 and 28 copies, respectively); genomic and RNA sequencing showed no other driver mutations or RET rearrangements. He experienced partial response to the selective RET inhibitor selpercatinib with decrease of both intracranial and systemic tumor burden. Conclusions: Amplification of wt RET represents a novel, targetable, rare molecular subset of NSCLC and other cancers.

Abstract LB330: FHND5071: a selective RET inhibitor with unique pharmacokinetic profile

Abstract Background: Gene rearrangements (fusions) and mutations in RET have the potential to be oncogenic drivers and have been observed in a variety of tumors types. Selective RET inhibitors selpercatinib and pralsetinib have been approved for patients with RET-altered cancers. FHND5071 is a novel kinase inhibitor which specifically targets RET activated forms and has unique pharmacokinetic profile. Methods: The pharmacological profile of FHND5071 have been confirmed in in vitro and in vivo evaluations, including enzyme and cell-based assays, PK/PD study, and RET-dependent tumor models. Results: In enzymatic assays, FHND5071 potently inhibited RET wild type, RET fusions and mutations with the IC50 of 4.47~19.26 nM and demonstrated 89-fold selectivity over KDR (VEGFR-2). FHND5071-M2, the active metabolite identified in pre-clinical pharmacokinetics, had the same potency as FHND5071. In cellular settings, FHND5071 inhibited the proliferation of Ba/F3 engineered cells (RET WT, RET V804M, RET M918T) and inhibited RET phosphorylation in HEK-293 engineered cells (WT, V804M, RET M918T, KIF5B-RET, CCDC6-RET) with the similar potency compared with selpercatinib. In PK/PD study (Ba/F3 KIF5B-RET allograft model), compared with selpercatinib, FHND5071 had longer Tmax and MRT in plasma and tumor tissue. FHND5071 preferred to be distributed into tissues. The exposure of FHND5071 in tumor tissue (AUC0-t) was ~28 times that of selpercatinib and the concentration of FHND5071 in brain tissue was ~33 times that of selpercatinib at 4 h after dosing. Meanwhile, after FHND5071 administration, RET phosphorylation and the downstream signaling protein (pAKT, pErk1/2) were significantly inhibited in tumor tissue and the inhibition was maintained for 24 h at least. But the duration of inhibition with selpercatinib was shorter than that of FHND5071. In tumor models, FHND5071 exhibited significant anti-tumor efficacy in Ba/F3 KIF5B-RET model at oral dose levels ≥3 mg/kg once daily (QD) without inducing significant toxicity. FHND5071 QD exhibited similar anti-tumor activity as selpercatinib administrated twice a day (BID) at 30 mg/kg. 30 mg/kg FHND5071 (QD) demonstrated significant anti-tumor efficacy with 100% TGI in patient-derived xenograft models (colorectal cancer with CCDC6-RET and ovarian cancer with NCOA4-RET). In CCDC6-RET intracranial xenograft model, 30 mg/kg FHND5071 (QD) significant prolonged life time of model mice. The median survival time was 56 days and the increase in life-span was 51% (p<0.005 compared with the vehicle group). Conclusions: FHND5071 demonstrated excellent selectivity and anti-tumor efficacy. The unique pharmacokinetic profile of FHND5071 supported the frequency of once-a-day dosing and better efficacy in target organ and brain tumor in clinical. FHND5071 has received IND approval from NMPA and FDA. It is currently in the dose-escalation segment of a first-in-human phase 1 trial for patients with RET-driven solid tumors. Citation Format: Yongqiang Zhu, Jia Wang, Minghong Shang. FHND5071: a selective RET inhibitor with unique pharmacokinetic profile [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB330.

Abstract CT252: A modular, open-label, phase I/II study to evaluate the safety, tolerability, pharmacokinetics and efficacy of EP0031, a next generation selective RET inhibitor, in patients with advanced RET-altered malignancies

Abstract Background: Addressing resistance to 1st generation selective RET inhibitors (SRI) is an area of high unmet need, with a number of RET dependent and independent pathways identified1,2. The ideal profile of a next generation SRI has been proposed: broad activity against RET fusions/mutations, inhibition of both V804M/L gatekeeper and G810C/S/R solvent front mutations and penetration of the CNS to address brain metastases1,2. This trial is evaluating whether EP0031, an orally available next generation SRI, can address resistance to 1st generation SRIs and improve on their clinical profile. Methods: This Phase 1/2 study (NCT05443126) is recruiting up to 265 patients with NSCLC, thyroid cancer or other solid tumors with RET aberrations. The 1st part of the study is a dose escalation to investigate safety, tolerability, PK and PD and to define the maximum tolerated dose (MTD) and/or Recommended Phase II Dose (RP2D). Dose escalation is based on a rolling 6 design and is expected to recruit up to 40 patients. Once an RP2D is established, expansion cohorts of approximately 25 evaluable patients each will further explore the safety and tolerability of EP0031, and provide preliminary efficacy data in selected patient populations with RET-altered tumors:•Four cohorts of patients with NSCLC and medullary thyroid cancer who have progressed on 1st generation SRI therapy and in patients with no prior SRI•Two cohorts of patients with other solid tumors, including differentiated thyroid cancer, who have progressed following 1st generation SRI therapy, and in patients with no prior SRI Key inclusion criteria are as follows:•Male or female ≥ 18 years of age, with a diagnosis of an advanced solid tumor with documented RET altered malignancy •ECOG Performance Status of 0 or 1 at screening with no deterioration over the previous 2 weeks. For expansion cohorts patients must have a solid tumor measurable by RECIST v1.1, with/without asymptomatic, stable brain metastases Recruitment was initiated in the US in November 2022 and is expanding to centers across Europe and rest of world. A parallel Phase I/II trial is ongoing in China (A400, NCT05265091, Kelun Biotech). 1Annals of Oncology 32(2) S66 (2021)2Journal Thoracic Oncol 15(4) 542 (2020) Citation Format: Andrew G. Gianoukakis, Susanne Arnold, Saad Khan, Matthew Taylor, Hendrik-Tobias Arkenau, Liz Clark, Geoffrey Fisher, Vivek Subbiah. A modular, open-label, phase I/II study to evaluate the safety, tolerability, pharmacokinetics and efficacy of EP0031, a next generation selective RET inhibitor, in patients with advanced RET-altered malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT252.

Abstract 4264: The genomic landscape of RET fusions in non-small cell lung cancer and the impact of co-occurring genomic alterations on the efficacy of selective RET inhibitors

Abstract Purpose: RET fusions drive oncogenesis in 1-2% of non-small cell lung cancer (NSCLC) and are sensitive to the selective RET inhibitors selpercatinib and pralsetinib. They have also emerged as mechanisms of acquired resistance to other targeted therapies. The genomic landscape of RET fusions and the impact of co-occurring genomic alterations on the efficacy of selective RET inhibitors is yet to be fully described. Methods: A total of 678 RET fusion-positive samples were analyzed from three cohorts: Guardant360® circulating tumor DNA (ctDNA) (n=467), tissue and/or plasma from the American Association for Cancer Research Project Genomics Evidence Neoplasia Information Exchange (AACR Project GENIE) non-squamous NSCLC cohort (n=161), and the MD Anderson Cancer Center (MDACC) cohort of patients treated with selpercatinib or pralsetinib (n=50). Molecular characteristics were compared across all three cohorts and to the entire non-RET non-squamous NSCLC AACR Project GENIE cohort (n=17770). Fisher’s exact test was used to evaluate the difference in response rate between patient groups, and Cox proportional hazard models were used to calculate hazard ratios for time-to-event endpoints for patients in the MDACC clinical cohort (n=51, 50 patients with RET fusion, 1 patient with RET point mutation). Results: The most common fusion partner in all cohorts was KIF5B (ctDNA: 73%; GENIE: 69%; MDACC: 71%), followed by CCDC6 (19%; 17%; 18%) and NCOA4 (5%; 1%; 7%). Across all cohorts, co-mutations in TP53 were most common (60%; 34%; 40%) and EGFR, CDKN2A/B, MET, and ATM consistently co-occurred across all cohorts. EGFR co-occurred more frequently with non-KIF5B fusion partners (chi-square p < 0.006). MYC and CCND1 amplifications were enriched in all three cohorts compared to the non-RET cohort. In the MDACC clinical cohort (n=51), the majority were female, never-smokers, with adenocarcinoma histology. The median follow-up time was 28.3 months (95% CI: 15.2 ~ 35 months). Overall response rate (ORR) was 74.4% (95% CI: 58.8 ~ 86.5%), where patients with TP53 mutation had numerically lower ORR compared to patients without TP53 mutation (58.5% vs. 87.5%; p = 0.0632). Median progression-free survival (PFS) time was 16.5 months (95% CI: 13.5 ~ 27.4 months) and KIF5B fusions trended towards worse PFS outcome compared to non-KIF5B fusions (HR: 2.24; 95% CI: 0.88 ~ 5.67; p = 0.0896). TP53 alterations were associated with a significantly worse overall survival (OS) (HR: 2.93; 95% CI: 1.08 ~ 7.95; p = 0.0346). Conclusion: In the largest RET fusion-positive NSCLC cohort to date, RET fusions frequently co-occurred with other genomic alterations, most commonly in TP53. TP53 alterations are associated with a significant reduction in overall survival in patients treated with the selective RET inhibitors. Additional analysis is underway. Citation Format: Tuqa Al Khalaf, Simon Heeke, Lei Feng, Leylah M. Drusbosky, Jeff Lewis, Waree Rinsurongkawong, Vadeerat Rinsurongkawong, Jack Lee, Jianjun Zhang, Don Gibbons, Ara Vaporciyan, Vincent Lam, Vivek Subbiah, John Heymach, Yasir Elamin. The genomic landscape of RET fusions in non-small cell lung cancer and the impact of co-occurring genomic alterations on the efficacy of selective RET inhibitors. [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 4264.

Selpercatinib: First approved selective RET inhibitor

Selpercatinib is a small molecule that binds at the RET kinase active site. It inhibits activity of constitutively dimerized RET fusion proteins and activated point mutants, thereby blocking downstream signals for proliferation and survival. It is the first selective RET inhibitor to be FDA approved for tumor agnostic targeting of oncogenic RET fusion proteins. To view this Bench to Bedside, open or download the PDF.