Nefarious NTRK oncogenic fusions in pediatric sarcomas: Too many to Trk

Critical domains for NACC2-NTRK2 fusion protein activation

Neurotrophic receptor tyrosine kinases (NTRKs) belong to the receptor tyrosine kinase (RTK) family. NTRKs are responsible for the activation of multiple downstream signaling pathways that regulate cell growth, proliferation, differentiation, and apoptosis. NTRK-associated mutations often result in oncogenesis and lead to aberrant activation of downstream signaling pathways including MAPK, JAK/STAT, and PLCγ1. This study characterizes the NACC2-NTRK2 oncogenic fusion protein that leads to pilocytic astrocytoma and pediatric glioblastoma. This fusion joins the BTB domain (Broad-complex, Tramtrack, and Bric-a-brac) domain of NACC2 (Nucleus Accumbens-associated protein 2) with the transmembrane helix and tyrosine kinase domain of NTRK2. We focus on identifying critical domains for the biological activity of the fusion protein. Mutations were introduced in the charged pocket of the BTB domain or in the monomer core, based on a structural comparison of the NACC2 BTB domain with that of PLZF, another BTB-containing protein. Mutations were also introduced into the NTRK2-derived portion to allow comparison of two different breakpoints that have been clinically reported. We show that activation of the NTRK2 kinase domain relies on multimerization of the BTB domain in NACC2-NTRK2. Mutations which disrupt BTB-mediated multimerization significantly reduce kinase activity and downstream signaling. The ability of these mutations to abrogate biological activity suggests that BTB domain inhibition could be a potential treatment for NACC2-NTRK2-induced cancers. Removal of the transmembrane helix leads to enhanced stability of the fusion protein and increased activity of the NACC2-NTRK2 fusion, suggesting a mechanism for the oncogenicity of a distinct NACC2-NTRK2 isoform observed in pediatric glioblastoma.

Beyond Clinical Trials: Understanding Neurotrophic Tropomyosin Receptor Kinase Inhibitor Challenges and Efficacy in Real-World Pediatric Oncology

PURPOSE

Our study aimed to explore real-world treatment scenarios for children and adolescents with neurotrophic tropomyosin receptor kinase (NTRK)-fused tumors, emphasizing access, responses, side effects, and outcomes.

PATIENTS AND METHODS

Pooled clinical data from 17 pediatric cases (11 soft-tissue sarcomas, five brain tumors, and one neuroblastoma) treated with larotrectinib and radiologic images for 14 patients were centrally reviewed. Testing for gene fusions was prompted by poor response to treatment, tumor progression, or aggressiveness.

RESULTS

Six different NTRK fusion subtypes were detected, and various payment sources for testing and medication were reported. Radiologic review revealed objective tumor responses (OR) in 11 of 14 patients: Complete responses: two; partial responses: nine; and stable disease: three cases. Grades 1 or 2 Common Terminology Criteria for Adverse Events adverse effects were reported in five patients. Regarding the entire cohort's clinical information, 15 of 17 patients remain alive (median observation time: 25 months): four with no evidence of disease and 11 alive with disease (10 without progression). One patient developed resistance to the NTRK inhibitor and died from disease progression while another patient died due to an unrelated cause.

CONCLUSION

This real-world study confirms favorable agnostic tumor OR rates to larotrectinib in children with NTRK-fused tumors. Better coordination to facilitate access to medication remains a challenge, particularly in middle-income countries like Brazil.

Current and emerging sequencing-based tools for precision cancer medicine

Current precision cancer medicine is dependent on the analyses of a plethora of clinically relevant genomic aberrations. During the last decade, next-generation sequencing (NGS) has gradually replaced most other methods for precision cancer diagnostics, spanning from targeted tumor-informed assays and gene panel sequencing to global whole-genome and whole-transcriptome sequencing analyses. The shift has been impelled by a clinical need to assess an increasing number of genomic alterations with diagnostic, prognostic and predictive impact, including more complex biomarkers (e.g. microsatellite instability, MSI, and homologous recombination deficiency, HRD), driven by the parallel development of novel targeted therapies and enabled by the rapid reduction in sequencing costs. This review focuses on these sequencing-based methods, puts their emergence in a historic perspective, highlights their clinical utility in diagnostics and decision-making in pediatric and adult cancer, as well as raises challenges for their clinical implementation. Finally, the importance of applying sensitive tools for longitudinal monitoring of treatment response and detection of measurable residual disease, as well as future avenues in the rapidly evolving field of sequencing-based methods are discussed.

Selective type II TRK inhibitors overcome xDFG mutation mediated acquired resistance to the second-generation inhibitors selitrectinib and repotrectinib

Neurotrophic receptor kinase (NTRK) fusions are actionable oncogenic drivers of multiple pediatric and adult solid tumors, and tropomyosin receptor kinase (TRK) has been considered as an attractive therapeutic target for "pan-cancer" harboring these fusions. Currently, two generations TRK inhibitors have been developed. The representative second-generation inhibitors selitrectinib and repotrectinib were designed to overcome clinic acquired resistance of the first-generation inhibitors larotrectinib or entrectinib resulted from solvent-front and gatekeeper on-target mutations. However, xDFG (TRKAG667C/A/S, homologous TRKCG696C/A/S) and some double mutations still confer resistance to selitrectinib and repotrectinib, and overcoming these resistances represents a major unmet clinical need. In this review, we summarize the acquired resistance mechanism of the first- and second-generation TRK inhibitors, and firstly put forward the emerging selective type II TRK inhibitors to overcome xDFG mutations mediated resistance. Additionally, we concluded our perspectives on new challenges and future directions in this field.

Food Effect on the Pharmacokinetics of VC004, a Tropomyosin Receptor Kinase Inhibitor: A Randomized Crossover Trial in Healthy Chinese Subjects

BACKGROUND AND OBJECTIVE

VC004 is a novel next-generation tropomyosin receptor kinase (TRK) inhibitor that is approved for the treatment of advanced or metastatic NTRK fusion-positive solid tumors and abrogated the drug resistance of the first-generation TRK inhibitors. The objective of the present study was to evaluate the effect of food on the pharmacokinetics and safety of VC004.

METHODS

The study was a randomized, open-label, two-period crossover, single-dose, phase I clinical trial. A total of 16 healthy subjects participated the trial. Subjects fasted for 10 h before drug administration in both fasting and fed states. Subjects received VC004 50 mg orally in the fasting state and after a high caloric food in the fed state. Blood samples at the designated time points were collected to determine the plasma concentration of VC004. Safety evaluation in both the fasted and fed periods were assessed via vital sign monitoring and clinical laboratory tests.

RESULTS

The maximum plasma concentration (Cmax) of VC004 in fed group decreased by 32.8%, corresponding with the slower absorption rate (time to Cmax (Tmax) delayed by almost 3 h) compared with the fasting group. Ratios of geometric means (GMRs) and 90% confidence intervals (90% CIs) of Cmax, the area under the curve of plasma concentration-time from zero to the last measurable concentration (AUC0-t), and AUC from zero to infinity (AUC0-∞) for VC004 between the two states were 67.18 (58.16-77.60), 103.59 (95.04-112.92) and 103.55 (95.63-112.11), respectively. No serious adverse events (AEs) occurred; only three grade 1 or grade 2 adverse events occurred in the fasted group, who recovered by the end of the study.

CONCLUSIONS

The intake of high calorie food decreased the absorption rate and increased the Tmax of VC004, while the AUC values were similar in both groups. No serious adverse event was reported. In conclusion, food does not alter the pharmacokinetics and safety profile of VC004 in a clinically meaningful manner.

TRIAL REGISTRATION

ClinicalTrials.gov ID: NCT055528120.

The Safety Profiles of Two First-Generation NTRK Inhibitors: Analysis of Individual Case Safety Reports from the FDA Adverse Event Reporting System (FAERS) Database

The first-generation tropomyosin receptor kinase (TRK) inhibitors, larotrectinib and entrectinib, represent exciting new developments in cancer treatment that offer relevant, rapid, and long-lasting clinical benefits. Larotrectinib and entrectinib are recommended as first-line treatments for locally advanced or metastatic non-small cell lung cancer (NSCLC) patients with positive TRK gene fusions. In this study, using the U.S. Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS) database between 2019 and 2022, a retrospective analysis was conducted to evaluate the safety profiles of these drugs. During our study period, 807 individual case safety reports (ICSRs) related to larotrectinib or entrectinib were retrieved from the FAERS database, of which 48.7% referred to females and 24.7% referred to adult patients (18-64 years) with a median age of 61.0 years. A total of 1728 adverse drug reactions (ADRs) were identified. The most frequently reported ADRs were dizziness and pain, which belong to the System Organ Classes (SOCs) "nervous system disorders" and "general disorders and administration site conditions". Regarding all ADRs, the median time to onset was 37.0 days for larotrectinib and 12.0 days for entrectinib. No evident safety concerns emerged in the long-term safety profiles (>365 days). Only 18 ICSRs were related to pediatric populations (≤16 years), of which 94.0% of the ICSRs were related to larotrectinib. The median age was 10.5 years, while most patients were female (44.4%). Our results show favorable risk-benefit profiles for larotrectinib and entrectinib. Considering the increased use of neurotrophic tyrosine receptor kinase (NTRK) inhibitors, continuous safety monitoring of larotrectinib and entrectinib is required for the detection of possible new adverse drug reactions.