Brief report: Response to pralsetinib observed in meningeal-metastatic EGFR-mutant NSCLC with acquired RET fusion

Preclinical evaluation of targeted therapies for central nervous system metastases

The central nervous system (CNS) represents a site of sanctuary for many metastatic tumors when systemic therapies that control the primary tumor cannot effectively penetrate intracranial lesions. Non-small cell lung cancers (NSCLCs) are the most likely of all neoplasms to metastasize to the brain, with up to 60% of patients developing CNS metastases during the disease process. Targeted therapies such as tyrosine kinase inhibitors (TKIs) have helped reduce lung cancer mortality but vary considerably in their capacity to control CNS metastases. The ability of these therapies to effectively target lesions in the CNS depends on several of their pharmacokinetic properties, including blood-brain barrier permeability, affinity for efflux transporters, and binding affinity for both plasma and brain tissue. Despite the existence of numerous preclinical models with which to characterize these properties, many targeted therapies have not been rigorously tested for CNS penetration during the discovery process, whereas some made it through preclinical testing despite poor brain penetration kinetics. Several TKIs have now been engineered with the characteristics of CNS-penetrant drugs, with clinical trials proving these efforts fruitful. This Review outlines the extent and variability of preclinical evidence for the efficacy of NSCLC-targeted therapies, which have been approved by the US Food and Drug Administration (FDA) or are in development, for treating CNS metastases, and how these data correlate with clinical outcomes.

Combined Dacomitinib and Selpercatinib Treatment for a Patient with EGFR-Mutant Non-Small Cell Lung Cancer and Acquired CCDC6-RET Fusion

RET rearrangements are recognized drivers in lung cancer, representing a small subset (1-2%) of non-small cell lung cancer (NSCLC). Additionally, RET fusions also serve as a rare acquired resistance mechanism in EGFR-mutant NSCLC. Only a few NSCLC cases have been reported with co-occurrence of EGFR mutations and RET fusions as an acquired resistance mechanism induced by EGFR-tyrosine kinase inhibitors (TKIs). A 68-year-old man diagnosed with lung adenocarcinoma harboring EGFR L858R mutation initially responded well to dacomitinib, a second-generation EGFR-tyrosine kinase inhibitor (TKI). Afterward, he developed acquired resistance accompanied by a RET rearrangement. Next-generation sequencing (NGS) analysis revealed that the tumor possessed both the new CCDC6-RET fusion and the EGFR L858R mutation. Subsequently, he was treated with a combination of cisplatin, pemetrexed, and bevacizumab resulting in a partial response. Nevertheless, his condition deteriorated as the disease progressed, manifesting as hydrocephalus, accompanied by altered consciousness and lower limb weakness. The subsequent combined treatment with dacomitinib and selpercatinib resulted in a significant improvement in neurological symptoms. Here, we first identified acquired CCDC6-RET fusion with a coexisting EGFR L858R mutation following dacomitinib treatment. Our findings highlight the importance of NGS for identifying RET fusions and suggest the potential combination of dacomitinib and selpercatinib to overcome this resistance. For NSCLC patients with RET rearrangements and no access to RET inhibitors, pemetrexed-based chemotherapy provides a feasible alternative.

RET rearrangement as a mechanism of resistance to ALK-TKI in non-small cell lung cancer patient with EML4-ALK fusion: A case report

Patients with non-small cell lung cancer (NSCLC) and anaplastic lymphoma kinase (ALK) mutations have previously derived substantial benefits from ALK tyrosine kinase inhibitors (ALK-TKIs). However, resistance may develop in some patients. We present a case of co-mutation with anaplastic lymphoma kinase (ALK) and rearranged during transfection (RET)-rearranged NSCLC, representing a novel resistance mechanism to ALK-TKIs, in which the patient exhibited a favorable response to combination therapy with ensartinib and pralsetinib. Notably, the patient survived 12 months without experiencing adverse events, a rare occurrence in ALK-rearranged lung adenocarcinoma cases. This case provides further evidence for the existence of RET rearrangements in ALK-positive lung cancer and their potential treatment response to a combination of ALK inhibitors and pralsetinib. This case underscores that a dual-target therapy involving ALK inhibitors, specifically ensartinib and pralsetinib, could be a viable approach in cases of RET-rearranged lung cancer with concurrent targetable ALK mutations. We propose the consideration of this dual-target approach, specifically employing ensartinib and pralsetinib, in managing RET-rearranged lung cancer coexisting with targetable ALK mutations. Given the potential efficacy of these treatments, it is imperative to proactively conduct molecular profiling tests in NSCLC patients upon the emergence of resistance.

Determination of Pralsetinib in Human Plasma and Cerebrospinal Fluid for Therapeutic Drug Monitoring by Ultra-performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS)

BACKGROUND

Ultra-performance Liquid Chromatography-tandem Mass Spectrometry (UPLC-MS/MS) is widely used for concentration detection of many Tyrosine Kinase Inhibitors (TKIs), including afatinib, crizotinib, and osimertinib. In order to analyze whether pralsetinib takes effect in Rearranged during Transfection (RET)-positive patients with central nervous system metastasis, we aimed to develop a method for the detection of pralsetinib concentrations in human plasma and Cerebrospinal Fluid (CSF) by UPLC-MS/MS.

METHODS

The method was developed using the external standard method, and method validation included precision, accuracy, stability, extraction recovery, and matrix effect. Working solutions were all obtained based on stock solutions of pralsetinib of 1mg/mL. The plasma/CSF samples were precipitated by acetonitrile for protein precipitation and then separated on an ACQUITY UPLC HSS T3 column (2.1×100 mm, 1.8 μm) with a gradient elution using 0.1% formic acid (solution A) and acetonitrile (solution B) as mobile phases at a flow rate of 0.4 mL/min. The tandem mass spectrometry was performed by a triple quadrupole linear ion trap mass spectrometry system (QTRAPTM 6500+) with an electrospray ion (ESI) source and Analyst 1.7.2 data acquisition system. Data were collected in Multiple Reaction Monitoring (MRM) and positive ionization mode.

RESULTS

A good linear relationship of pralsetinib in both plasma and CSF was successfully established, and the calibration ranges were found to be 1.0-64.0 μg/mL and 50.0ng/mL-12.8 μg/mL for pralsetinib in the plasma and CSF, respectively. Validation was performed, including calibration assessment, selectivity, precision, accuracy, matrix effect, extraction recovery, and stability, and all results have been found to be acceptable. The method has been successfully applied to pralsetinib concentration detection in a clinical sample, and the concentrations have been found to be 475 ng/mL and 61.55 μg/mL in the CSF and plasma, respectively.

CONCLUSION

We have developed a quick and effective method for concentration detection in both plasma and CSF, and it can be applied for drug monitoring in clinical practice. The method can also provide a reference for further optimization.

Progress and challenges in RET-targeted cancer therapy

The rearranged during transfection (RET) is a receptor protein tyrosine kinase. Oncogenic RET fusions or mutations are found most often in non-small cell lung cancer (NSCLC) and in thyroid cancer, but also increasingly in various types of cancers at low rates. In the last few years, two potent and selective RET protein tyrosine kinase inhibitors (TKIs), pralsetinib (BLU-667) and selpercatinib (LOXO-292, LY3527723) were developed and received regulatory approval. Although pralsetinib and selpercatinib gave high overall response rates (ORRs), < 10% of patients achieved a complete response (CR). The RET TKI-tolerated residual tumors inevitably develop resistance by secondary target mutations, acquired alternative oncogenes, or MET amplification. RET G810 mutations located at the kinase solvent front site were identified as the major on-target mechanism of acquired resistance to both selpercatinib and pralsetinib. Several next-generation of RET TKIs capable of inhibiting the selpercatinib/pralsetinib-resistant RET mutants have progressed to clinical trials. However, it is likely that new TKI-adapted RET mutations will emerge to cause resistance to these next-generation of RET TKIs. Solving the problem requires a better understanding of the multiple mechanisms that support the RET TKI-tolerated persisters to identify a converging point of vulnerability to devise an effective co-treatment to eliminate the residual tumors.

Cerebrospinal Fluid Concentration of the RET Inhibitor Pralsetinib: A Case Report

Introduction

Pralsetinib is used to treat metastatic RET fusion-positive non-small cell lung cancer. Preclinical studies of pralsetinib have shown blood-brain barrier (BBB) penetration and intracranial activity. The intracranial efficacy of pralsetinib in patients with brain metastasis is considered to be greater compared to older multikinase tyrosine kinase inhibitors. However, CSF concentrations of pralsetinib in patients are not well described in the literature.

Case Presentation

We report a case of a patient with RET fusion-positive NSCLC treated with pralsetinib. Despite extracranial clinical and radiological remission, the patient developed progressive brain metastasis during treatment with pralsetinib. We measured the pralsetinib concentration in plasma and in CSF to determine the CSF-to-unbound plasma ratio. The measured pralsetinib concentrations in plasma and CSF were 1,951 ng/mL (∼57 unbound) and 14 ng/mL, respectively, reflecting a CSF-to-unbound plasma concentration ratio of 0.25. Our findings were compared with data from the literature.

Conclusion

We showed that pralsetinib penetrates the CSF well and is expected to be an effective treatment for brain metastasis of RET fusion-positive NSCLC. Lack of intracranial efficacy is more likely to be caused by intrinsic or acquired tumor resistance instead of suboptimal exposure of pralsetinib in the brain.