Rapid Response to Sunitinib in a Patient with Lung Adenocarcinoma Harboring KIF5B-RET Fusion Gene

Targeting Rearranged during Transfection in Cancer: A Perspective on Small-Molecule Inhibitors and Their Clinical Development

Rearranged during transfection (RET) is a receptor tyrosine kinase essential for the normal development and maturation of a diverse range of tissues. Aberrant RET signaling in cancers, due to RET mutations, gene fusions, and overexpression, results in the activation of downstream pathways promoting survival, growth, and metastasis. Pharmacological manipulation of RET is effective in treating RET-driven cancers, and efforts toward developing RET-specific therapies have increased over the last 5 years. In 2020, RET-selective inhibitors pralsetinib and selpercatinib achieved clinical approval, which marked the first approvals for kinase inhibitors specifically developed to target the RET oncoprotein. This Perspective discusses current development and clinical applications for RET precision medicine by providing an overview of the incremental improvement of kinase inhibitors for use in RET-driven malignancies.

Uncommon targets in non-small cell lung cancer: Everyone wants a slice of cake

Target therapies completely changed the clinical approach in EGFR mutated and ALK rearranged non-small cell lung cancer, ensuring these patients exceptional outcomes with a better toxicity profile compared to conventional chemotherapy. In recent years, beyond EGFR and ALK alterations, new data are emerging about less common alterations, new drugs have been already approved and others agents have been recently investigated or are currently under investigation. In this review we will discuss some uncommon alterations in non-small cell lung cancer such as ROS1, BRAF, RET, HER2, NTRK, MET and other targets that are in an early evaluation phase. We will summarize the characteristics of patients harboring these alterations, the already approved or under investigation therapies and the related resistance mechanisms.

Chasing the Target: New Phenomena of Resistance to Novel Selective RET Inhibitors in Lung Cancer. Updated Evidence and Future Perspectives

Simple Summary

REarranged during Transfection (RET) is an emerging target for several types of cancer, including non-small cell lung cancer (NSCLC). The recent U.S. FDA approval of pralsetinib and selpercatinib raises issues regarding the emergence of secondary mutations and amplifications involved in parallel signaling pathways and receptors, liable for resistance mechanisms. The aim of this review is to explore recent knowledge on RET resistance in NSCLC in pre-clinic and in clinical settings and accordingly, the state-of-the-art in new drugs or combination of drugs development.

Abstract

The potent, RET-selective tyrosine kinase inhibitors (TKIs) pralsetinib and selpercatinib, are effective against the RET V804L/M gatekeeper mutants, however, adaptive mutations that cause resistance at the solvent front RET G810 residue have been found, pointing to the need for the development of the next-generation of RET-specific TKIs. Also, as seen in EGFR- and ALK-driven NSCLC, the rising of the co-occurring amplifications of KRAS and MET could represent other escaping mechanisms from direct inhibition. In this review, we summarize actual knowledge on RET fusions, focusing on those involved in NSCLC, the results of main clinical trials of approved RET-inhibition drugs, with particular attention on recent published results of selective TKIs, and finally, pre-clinical evidence regarding resistance mechanisms and suggestion on hypothetical and feasible drugs combinations and strategies viable in the near future.

Emerging targets in advanced non-small-cell lung cancer

New therapeutic options in non-small-cell lung cancer have been available through a great in-depth and genomic research, improving preclinical disease patterns and identifying the specific toxicity of target therapy. The multidisciplinary approach, increasingly practiced among clinicians, researchers, pharmaceutical companies and ethics committees has allowed the emergence of a new generation of translational clinical trials and the adoption of new technologies (e.g., point-of-care sequencing), then speeding up the development and trade of these new drugs. Consequently, there is a long list of therapeutic candidates that need to be efficiently evaluated early in the context of Phase I clinical trials. In this review, we discuss some of the key developments and novelties in the main histological groups.

Clinical development of RET inhibitors in RET-rearranged non-small cell lung cancer: Update

Precision oncology is now the evidence-based standard of care for the management of many advanced non-small cell lung cancers (NSCLC). Notably, new molecular profiling technologies have permitted dynamic growth in the identification of actionable driver oncogenes including RET rearrangements. RET oncogenes cannot be adequately detected by immunohistochemistry, although fluorescence in situ hybridization, reverse transcriptase polymerase chain reaction and next-generation sequencing are complementary diagnostic tools. In the clinical setting, the benefit of the most developed RET inhibitors, i.e., cabozantinb, vandetanib and lenvatinb, in terms of response and median progressionfree survival has been demonstrated. The absence of striking clinical results of RET inhibitors underscores the clear need for development of more selective and potent RET inhibitors. This paper reviews the clinical data available on RET inhibitors in RET-associated NSCLC.

Novel targeted therapeutics for MEN2

The rearranged during transfection (RET) proto-oncogene was recognized as the multiple endocrine neoplasia type 2 (MEN2) causing gene in 1993. Since then, much effort has been put into a clear understanding of its oncogenic signaling, its biochemical function and ways to block its aberrant activation in MEN2 and related cancers. Several small molecules have been designed, developed or redirected as RET inhibitors for the treatment of MEN2 and sporadic MTC. However, current drugs are mostly active against several other kinases, as they were not originally developed for RET. This limits efficacy and poses safety issues. Therefore, there is still much to do to improve targeted MEN2 treatments. New, more potent and selective molecules, or combinatorial strategies may lead to more effective therapies in the near future. Here, we review the rationale for RET targeting in MEN2, the use of currently available drugs and novel preclinical and clinical RET inhibitor candidates.

Beyond ALK and ROS1: RET, NTRK, EGFR and BRAF gene rearrangements in non-small cell lung cancer

The discovery of gene rearrangements involving the receptor tyrosine kinase genes ALK and ROS1 has revolutionized management of the subset of non-small cell lung cancers characterized by these alterations. The oncogenic fusion proteins expressed in these tumors drive cancer cell growth and survival, and targeted inhibition of this signaling can lead to dramatic and durable responses in patients. While the best characterized gene fusions in non-small cell lung cancer (NSCLC) involve ALK and ROS1, fusions involving other kinases including RET, NTRK, EGFR and BRAF are now established as additional targetable drivers. Here we review data supporting the roles of these fusions as oncogenic drivers, and the potential for targeting these fusions for improved clinical outcomes. These discoveries should encourage multiplexed molecular profiling of lung cancers using next-generation platforms which identify these gene fusions in order to expand treatment options for patients.

New Targets in Non-Small Cell Lung Cancer

With the implementation of genomic technologies into clinical practice, we have examples of the predictive benefit of targeted therapy for oncogene-addicted cancer and identified molecular dependencies in non-small cell lung cancer. The clinical success of tyrosine kinase inhibitors against epidermal growth factor receptor and anaplastic lymphoma kinase activation has shifted treatment emphasize the separation of subsets of lung cancer and genotype-directed therapy. Advances have validated oncogenic driver genes and led to the development of targeted agents. This review highlights treatment options, including clinical trials for ROS1 rearrangement, RET fusions, NTRK1 fusions, MET exon skipping, BRAF mutations, and KRAS mutations.

Treatment of lung adenocarcinoma by molecular-targeted therapy and immunotherapy

Lung adenocarcinoma (LADC) is a cancer treatable using targeted therapies against driver gene aberrations. EGFR mutations and ALK fusions are frequent gene aberrations in LADC, and personalized therapies against those aberrations have become a standard therapy. These targeted therapies have shown significant positive efficacy and tolerable toxicity compared to conventional chemotherapy, so it is necessary to identify additional druggable genetic aberrations. Other than EGFR mutations and ALK fusions, mutations in KRAS, HER2, and BRAF, and driver fusions involving RET and ROS1, have also been identified in LADC. Interestingly, the frequency of driver gene aberrations differs according to ethnicity, sex, and smoking, which leads to differences in treatment efficacy. To date, several molecular-targeted drugs against driver genes have been developed, and several clinical trials have been conducted to evaluate the efficacy. However, targeted therapies against driver-gene-negative cases have not yet been well developed. Efforts to identify a new druggable target for such cases are currently underway. Furthermore, immune checkpoint blockade therapy might be effective for driver-negative cases, especially those with accumulated mutations.

Mechanisms of Resistance to Target Therapies in Non-small Cell Lung Cancer

Targeted therapies are revolutionizing the treatment of advanced non-small cell lung cancer (NSCLC). The discovery of key oncogenic events mainly in lung adenocarcinoma, like EGFR mutations or ALK rearrangements, has changed the treatment landscape while improving the prognosis of lung cancer patients. Inevitably, virtually all patients initially treated with targeted therapies develop resistance because of the emergence of an insensitive cellular population, selected by pharmacologic pressure. Diverse mechanisms of resistance, in particular to EGFR, ALK and ROS1 tyrosine-kinase inhibitors (TKIs), have now been discovered and may be classified in three different groups: (1) alterations in the target (such as EGFR T790M and ALK or ROS1 mutations); (2) activation of alternative pathways (i.e. MET amplification, KRAS mutations); (3) phenotype transformation (to small cell lung cancer, epithelial-mesenchymal transition). These basic mechanisms are informing the development of novel therapeutic strategies to overcome resistance in the clinic. Novel-generation molecules include osimertinib, for EGFR-T790M-positive patients, and new ALK-TKIs. Nevertheless, the possible concomitant presence of multiple resistance mechanisms, as well as their heterogeneity among cells and disease localizations, makes research in this field particularly arduous. In this chapter, available evidence and perspectives concerning precise mechanisms of escape to pharmacological inhibition in oncogene-addicted NSCLC are reported for single targets, including but not limited to EGFR and ALK.

Clinical Activity of Alectinib in Advanced RET-Rearranged Non-Small Cell Lung Cancer

INTRODUCTION

Chromosomal rearrangements involving rearranged during transfection gene (RET) occur in 1% to 2% of NSCLCs and may confer sensitivity to rearranged during transfection (RET) inhibitors. Alectinib is an anaplastic lymphoma kinase tyrosine kinase inhibitor (TKI) that also has anti-RET activity in vitro. The clinical activity of alectinib in patients with RET-rearranged NSCLC has not yet been reported.

METHODS

We have described four patients with advanced RET-rearranged NSCLC who were treated with alectinib (600 mg twice daily [n = 3] or 900 mg twice daily [n = 1]) as part of single-patient compassionate use protocols or off-label use of the commercially available drug.

RESULTS

Four patients with metastatic RET-rearranged NSCLC were identified. Three of the four had received prior RET TKIs, including cabozantinib and experimental RET inhibitors. In total, we observed two (50%) objective radiographic responses after treatment with alectinib (one confirmed and one unconfirmed), with durations of therapy of 6 months and more than 5 months (treatment ongoing), respectively. Notably, one of these two patients had his dose of alectinib escalated to 900 mg twice daily and had clinical improvement in central nervous system metastases. In addition, one patient (25%) experienced a best response of stable disease lasting approximately 6 weeks (the drug discontinued for toxicity). A fourth patient who was RET TKI-naive had primary progression while receiving alectinib.

CONCLUSIONS

Alectinib demonstrated preliminary antitumor activity in patients with advanced RET-rearranged NSCLC, most of whom had received prior RET inhibitors. Larger prospective studies with longer follow-up are needed to assess the efficacy of alectinib in RET-rearranged NSCLC and other RET-driven malignancies. In parallel, development of more selective, potent RET TKIs is warranted.

Gene aberrations for precision medicine against lung adenocarcinoma

Lung adenocarcinoma (LADC), the most frequent histological type of lung cancer, is often triggered by an aberration in a driver oncogene in tumor cells. Examples of such aberrations are EGFR mutation and ALK fusion. Lung adenocarcinoma harboring such mutations can be treated with anticancer drugs that target the aberrant gene products. Additional oncogene aberrations, including RET,ROS1, and NRG1 fusions, skipping of exon 14 of MET, and mutations in BRAF,HER2,NF1, and MEK1, were recently added to the list of such “druggable” driver oncogene aberrations, and their responses to targeted therapies are currently being evaluated in clinical trials. However, approximately 30% and 50% of LADCs in patients in Japan and Europe/USA, respectively, lack the driver oncogene aberrations listed above. Therefore, novel therapeutic strategies, such as those that exploit the vulnerabilities of cancer cells with non‐oncogene aberrations, are urgently required. This review summarizes the current status of research on precision medicine against LADC and enumerates the research priorities for the near future.

Alterations in genes other than EGFR/ALK/ROS1 in non-small cell lung cancer: trials and treatment options

During the last decade, we have seen tremendous progress in the therapy of lung cancer. Discovery of actionable mutations in EGFR and translocations in ALK and ROS1 have identified subsets of patients with excellent tumor response to oral targeted agents with manageable side effects. In this review, we highlight treatment options including corresponding clinical trials for oncogenic alterations affecting the receptor tyrosine kinases MET, FGFR, NTRK, RET, HER2, HER3, and HER4 as well as components of the RAS-RAF-MEK signaling pathway.

Emerging targeted therapies in non-small cell lung cancer

Lung cancer is the leading cause of cancer-related deaths in United States, accounting for more than one-fourth of the deaths annually. Although comparatively rare and relatively less studied, genetic abnormalities other than epidermal growth factor receptor (EGFR) mutations, anaplastic lymphoma kinase (ALK) rearrangements, and Kirsten rat sarcoma (KRAS) mutations account for significant proportion of the driver mutations identified thus far. The targeted agents against B-rapidly accelerated fibrosarcoma (BRAF) V600E mutation, MNNG-HOS transforming gene (MET) pathway, ROS1 rearrangement, rearranged during transfection (RET) rearrangement, and HER2 pathways offer promising therapeutic options. Recruiting patients with these rarer mutations to well-designed, large multicenter trials to further validate the use of targeted agents remains a challenge. The clinical data and ongoing trials with these agents are reviewed in this article.