Pralsetinib: chemical and therapeutic development with FDA authorization for the management of RET fusion-positive non-small-cell lung cancers

Design, synthesis and evaluation of (E)-1-(4-(2-(1H-pyrazol-5-yl)vinyl)phenyl) derivatives as next generation selective RET inhibitors overcoming RET solvent front mutations (G810C/R)

RET is a well-recognized drug target for cancer treatment. Despite the promising efficacy of selective second-generation RET inhibitors Selpercatinib and Pralsetinib, the clinical benefits have been compromised due to the quickly developed resistance to these drugs. RET G810 mutations at the solvent front site have been identified as the major on-target mutations contributing to resistance against Selpercatinib and Pralsetinib. Therefore, there is an urgent need for the development of next-generation RET inhibitors to overcome acquired solvent-front resistance mutations. In this study, a series of (E)-1-(4-(2-(1H-pyrazol-5-yl)vinyl)phenyl) derivatives have been identified as selective next-generation RET inhibitors. The representative compound, CQ1373 exhibits potent cellular potency with IC50 values of 13.0, 25.7 and 28.4 nM against BaF3 cells expressing CCDC6-RET, CCDC6-RET-G810C and CCDC6-RET-G810R, respectively. A comprehensive selectivity profile across 89 kinases reveals that CQ1373 demonstrates good selectivity toward wild-type RET and solvent front mutants G810C/R with IC50 values of 4.2, 7.1 and 32.4 nM, respectively. Furthermore, western blot analysis reveals that CQ1373 effectively inhibits RET phosphorylation and downstream signaling through SHC. It also induces apoptosis and cell cycle arrest in a dose-dependent manner in BaF3 cells harboring CCDC6-RET, CCDC6-RET-G810C and CCDC6-RET-G810R fusions. More significantly, CQ1373 exhibits promising in vivo anti-tumor efficacy in a CCDC6-RET-G810R mice xenograft model, highlighting its potentials for RET-driven cancers treatment.

Discovery of an Efficacious RET PROTAC Degrader with Enhanced Antiproliferative Activity against Resistant Cancer Cells Harboring RET Solvent-Front Mutations

Rearranged during transfection (RET) kinase is a validated therapeutic target for various cancers characterized by RET alterations. Although two selective RET inhibitors, selpercatinib and pralsetinib, have been approved by the FDA, acquired resistance through solvent-front mutations has been identified rapidly. Developing proteolysis targeting chimera (PROTAC) targeting RET mutations offers a promising strategy to combat drug resistance. Herein, we describe the design, synthesis, and evaluation of a series of RET PROTAC degraders. The representative compound QZ2135 (20) effectively degraded RET kinase and its resistant mutants, such as V804M and G810C/R. It also exhibited superior antiproliferative activity against Ba/F3 cells stably expressing oncogenic fusions of RET with solvent-front mutants, including G810C/R/S, compared to its parental inhibitor. Notably, QZ2135 demonstrated in vivo antitumor efficacy in a Ba/F3-KIF5B-RET-G810C xenograft mouse model. Together, this study provides a potential alternative strategy for overcoming acquired resistance to RET inhibitors mediated by solvent-front mutations.

Clinical evidence and adverse event management update of patients with RET- rearranged advanced non-small-cell lung cancer (NSCLC) treated with pralsetinib

Current non-small cell lung cancer (NSCLC) management relies on genome-driven precision oncology thus shifting treatment paradigm towards biomarker-guided tumor-agnostic approaches. Recently, rearranged during transfection (RET) has been endorsed as tissue-agnostic target with sensitivity to RET inhibition. There are currently two selective RET tyrosine kinase inhibitors, pralsetinib and selpercatinib. The recent introduction of pralsetinib in the treatment algorithm of RET-rearranged tumor along with the mounting clinical evidence of pralsetinib durable activity from both randomized and observational studies holds the potential to disclose new avenues in the management of RET fusion positive NSCLC patients. Our narrative review aims to discuss the available clinical evidence on pralsetinib efficacy, particularly on brain metastases, and tolerability profile. In addition, our work explores the relevance of detecting RET fusions upfront in the disease history of patients with NSCLC.

Expanded Access Program Pralsetinib in Advanced Non-Small Cell Lung Cancer with Rearranged during Transfection (RET) Gene Rearrangement

PURPOSE

Rearranged during transfection (RET) gene rearrangement is a well-known driver event in non-small cell lung cancer (NSCLC). Pralsetinib is a selective inhibitor of RET kinase and has shown efficacy in oncogenic RET-altered tumors. This study evaluated the efficacy and safety of expanded access program (EAP) use of pralsetinib in pretreated, advanced NSCLC patients with RET rearrangement.

MATERIALS AND METHODS

Patients who received pralsetinib as part of the EAP at Samsung Medical Center were evaluated through a retrospective chart review. The primary endpoint was overall response rate (ORR) per the Response Evaluation Criteria in Solid Tumors (RECIST) ver. 1.1 guidelines. Secondary endpoints were duration of response, progression-free survival (PFS), overall survival (OS), and safety profiles.

RESULTS

Between April 2020 and September 2021, 23 of 27 patients were enrolled in the EAP study. Two patients who were not analyzed due to brain metastasis and two patients whose expected survival was within 1 month were excluded from the analysis. After a median follow-up period of 15.6 months (95% confidence interval [CI], 10.0 to 21.2), ORR was 56.5%, the median PFS was 12.1 months (95% CI, 3.3 to 20.9), and the 12-month OS rate was 69.6%. The most frequent treatment-related adverse events (TRAEs) were edema (43.5%) and pneumonitis (39.1%). A total of 8.7% of patients experienced extra-pulmonary tuberculosis. TRAEs with a common grade of three or worse were neutropenia (43.5%) and anemia (34.8%). Dose reduction was required in nine patients (39.1%).

CONCLUSION

Pralsetinib presents a clinical benefit when used in patients with RET-rearranged NSCLC, consistent with a pivotal study.

Small Molecule Inhibitors as Therapeutic Agents Targeting Oncogenic Fusion Proteins: Current Status and Clinical

Oncogenic fusion proteins, arising from chromosomal rearrangements, have emerged as prominent drivers of tumorigenesis and crucial therapeutic targets in cancer research. In recent years, the potential of small molecular inhibitors in selectively targeting fusion proteins has exhibited significant prospects, offering a novel approach to combat malignancies harboring these aberrant molecular entities. This review provides a comprehensive overview of the current state of small molecular inhibitors as therapeutic agents for oncogenic fusion proteins. We discuss the rationale for targeting fusion proteins, elucidate the mechanism of action of inhibitors, assess the challenges associated with their utilization, and provide a summary of the clinical progress achieved thus far. The objective is to provide the medicinal community with current and pertinent information and to expedite the drug discovery programs in this area.

RET fusions as primary oncogenic drivers and secondary acquired resistance to EGFR tyrosine kinase inhibitors in patients with non-small-cell lung cancer

BACKGROUND

RET fusions are rare oncogenic drivers in non-small cell lung cancer (NSCLC). While activating RET rearrangements are found in NSCLC patients harboring epidermal growth factor receptor (EGFR) genetic alterations at resistance to EGFR inhibitors, the extent to which co-occurring genomic alterations exist and how they might affect prognosis or therapy response is poorly understood.

METHODS

Targeted next-generation sequencing (NGS) was used to assess 380 baseline patients with primary RET fusions and 71 EGFR-mutated NSCLC patients who acquired RET fusions after developing resistance to EGFR-tyrosine kinase inhibitors (EGFR-TKIs).

RESULTS

Primary RET fusions were more likely associated with females and younger age, with KIF5B being the predominant fusion partner. In baseline patients, both SMAD4 (5.3% vs. 0.0%, P = 0.044) and MYC copy-number gain variants (6.9% vs. 0.0%, P = 0.009) were more frequently co-mutated with KIF5B-RET than CCDC6-RET. By contrast, CDKN2A (11.3% vs. 2.4%, P = 0.003) mutations were significantly enriched in CCDC6-RET-rearranged baseline patients. A significant increase in the proportion of CCDC6-RET was observed in acquired RET-rearranged patients (47.3% vs. 22.5%, P < 0.001). The median progression-free survival (PFS) of patients harboring RB1 and TP53 double-mutations (5.5 vs. 10.0 months, P = 0.020) or ERBB2 amplification (5.6 vs. 10.0 months, P = 0.041) was significantly shorter than the wild-type counterparts. Moreover, we identified that RET fusions were more likely associated with acquired resistance (AR) to third-generation EGFR-TKIs than previous generations of EGFR-TKIs.

CONCLUSIONS

In conclusion, we depicted the mutational profiles of NSCLC patients who harbor RET fusions at baseline or after resistance to EGFR-TKIs. Furthermore, our results suggest that RET fusions mediate secondary resistance to third-generation EGFR-TKIs and might be associated with poor prognosis in patients with NSCLC.

Selective RET inhibitors shift the treatment pattern of RET fusion-positive NSCLC and improve survival outcomes

PURPOSE

Rearranged during transfection (RET) fusions are important genetic drivers in non-small cell lung cancer (NSCLC). Selective RET inhibitors are setting a new paradigm in RET-driven NSCLC. However, the real-world treatment patterns, outcomes and toxicity remain largely unknown.

METHODS

Data from RET fusion-positive NSCLC patients treated in our centre were retrospectively analysed. Of them, patients diagnosed before and after August 2018 were included in analysis of treatment patterns; and patients received selective RET inhibitors were eligible for analysis of adverse events (AEs).

RESULTS

Patients diagnosed before August 2018 (n = 30) predominantly received chemotherapy and immunotherapy (83%) as initial therapy, while patients diagnosed after August 2018 (n = 39) mainly received selective RET inhibitors (38.5% at first-line; 50.0% at second-line). In the total 69 patients, overall survival (OS) was prolonged in patients treated with selective RET inhibitors versus untreated patients (median 34.3 versus 17.5 months; p = 0.002) during a median follow-up of 28.7 months. But there was no difference between patients treated with immunotherapy versus untreated patients. In the 38 patients received selective RET inhibition, median progression-free survival (PFS) was 11.9 months. AEs ≥ grade 3 occurred in 42.1% patients and were not associated with PFS (p = 0.63) or OS (p = 0.60). Haematological toxicity ≥ grade 3 occurred in 31.6% patients and was the leading cause of drug discontinuation.

CONCLUSION

Selective RET inhibitors are increasingly being adopted into clinical practice and are associated with improved OS. However, treatment-related ≥ grade 3 AEs, especially haematologic AEs, occur frequently in real-world setting.