Ripretinib and MEK Inhibitors Synergize to Induce Apoptosis in Preclinical Models of GIST and Systemic Mastocytosis

Current status of drugs targeting PDGF/PDGFR

As an important proangiogenic factor, platelet-derived growth factor (PDGF) and its receptor PDGFR are highly expressed in a variety of tumors, fibrosis, cardiovascular and neurodegenerative diseases. Targeting the PDGF/PDGFR pathway is therefore a promising therapeutic strategy. At present, a variety of PDGF/PDGFR targeted drugs with potential therapeutic effects have been developed, mainly including PDGF agonists, inhibitors targeting PDGFR and proteolysis targeting chimera (PROTACs). This review clarifies the structure, biological function and disease correlation of PDGF and PDGFR, and it discusses the current status of PDGFR-targeted drugs, so as to provide a reference for subsequent research.

KIT/PDGFRA inhibitors for the treatment of gastrointestinal stromal tumors: getting to the gist of the problem

INTRODUCTION

Approximately 90% of gastrointestinal stromal tumors (GISTs) are driven by activating mutations in receptor tyrosine-kinases KIT or PDGFRA. Despite the outstanding results of first-line imatinib in advanced GIST, resistance ultimately occurs mainly through secondary mutations in KIT/PDGFRA. Other tyrosine-kinase inhibitors (TKIs) with a broader spectrum of activity against these mutations are approved after imatinib failure. However, response rates and progression-free survival are drastically lower compared to imatinib. Notably, imatinib also triggers early tolerance adaptation mechanisms, which precede the occurrence of secondary mutations.

AREAS COVERED

In this review, we outline the current landscape of KIT inhibitors, discuss the novel agents, and present additional biological pathways that may be therapeutically exploitable.

EXPERT OPINION

The development of broad-spectrum and highly selective TKIs able to induce a sustained KIT/PDGFRA inhibition is the pillar of preclinical and clinical investigation in GIST. However, it is now recognized that the situation is more intricate, with various factors interacting with KIT and PDGFRA, playing a crucial role in the response and resistance to treatments. Future strategies in the management of advanced GIST should integrate driver inhibition with the blockade of other molecules to enhance cell death and establish enduring responses in patients.

Ripretinib in combination with tyrosine kinase inhibitor as a late-line treatment option for refractory gastrointestinal stromal tumors: two case reports and literature review

Background: This case report presents two clinical cases of metastatic refractory gastrointestinal stromal tumor (GIST) with treatment history of 6-14 years. The follow-up treatment of both cases comprised ripretinib dose escalation and its combination with other tyrosine kinase inhibitors (TKIs). To the best of our knowledge, this is the first report that explored ripretinib combination therapy in the late-line treatment of GISTs. Case description: Case-1 represents a 57-year-old female patient who underwent surgical resection for retroperitoneal GIST in 2008. After tumor recurrence in 2009, imatinib was started with complete response for 8 years. Imatinib was followed by sunitinib and regorafenib treatment. In March 2021, due to progressive disease (PD), the patient started ripretinib (150 mg QD) and achieved partial response (PR). Six months later, the patient showed PD. Subsequently, ripretinib dose was increased (150 mg BID) followed by ripretinib (100 mg QD) and imatinib (200 mg QD) combination. CT performed in February 2022 revealed stable lesions with internal visible necrosis. Combination therapy achieved stable disease (SD) for 7 months. On further follow-up in July 2022, the patient showed PD and died in September 2022. Case-2: represents a 73-year-old female patient diagnosed with unresectable duodenal GIST with liver, lung, and lymph node metastases in 2016. After treatment with imatinib, followed by sunitinib, regorafenib, and imatinib rechallenge, ripretinib (150 mg QD) was administered in May 2021, and SD was achieved. Ripretinib dose was increased (200 mg QD) due to PD in December 2021. The tumor showed heterogeneous manifestations, with overall size increase and regression in right posterior lobe. In February 2022, ripretinib (150 mg) plus sunitinib (25 mg) QD was commenced. On follow-up in April 2022, the patient showed slightly improved symptoms with stable hematologic parameters. Combination therapy achieved SD for 5 months and the patient showed PD in July 2022 and discontinued the treatment later. The patient was in poor general condition and was receiving nutritional therapy until last follow-up in October 2022. Conclusion: This case report provides evidence that combination therapy of ripretinib with other TKIs could be an effective late-line treatment option for refractory GIST patients.

LIX1 Controls MAPK Signaling Reactivation and Contributes to GIST-T1 Cell Resistance to Imatinib

Gastrointestinal stromal tumor (GIST), the most common sarcoma, is mainly caused by an oncogenic mutation in the KIT receptor tyrosine kinase. Targeting KIT using tyrosine kinase inhibitors, such as imatinib and sunitinib, provides substantial benefit; however, in most patients, the disease will eventually progress due to KIT secondary mutations leading to treatment failure. Understanding how GIST cells initially adapt to KIT inhibition should guide the selection of appropriate therapies to overcome the emergence of resistance. Several mechanisms have been broadly implicated in the resistance to imatinib anti-tumoral effects, including the reactivation of MAPK signaling upon KIT/PDGFRA targeted inhibition. This study provides evidence that LImb eXpression 1 (LIX1), a protein we identified as a regulator of the Hippo transducers YAP1 and TAZ, is upregulated upon imatinib or sunitinib treatment. LIX1 silencing in GIST-T1 cells impaired imatinib-induced MAPK signaling reactivation and enhanced imatinib anti-tumor effect. Our findings identified LIX1 as a key regulator of the early adaptative response of GIST cells to targeted therapies.

Evaluating the impact of co-administered drug and disease on ripretinib exposure: A physiologically-based pharmacokinetic modeling approach

Ripretinib, as an oral kinase inhibitor, has been approved to treat advanced gastrointestinal stromal tumors (GIST) and is often used in combination with other drugs to slow disease progression, thus potential drug-drug Interactions (DDIs) and drug-disease interactions (DDZIs) have received much attention. To guide clinical rational drug use, this study assessed the effect of co-administered drugs and diseases on ripretinib exposure. Simcyp® Simulator was used to develop the physiologically-based pharmacokinetic (PBPK) model of ripretinib, which was validated and refined with clinical data. We then examined the impact of several CYP3A4 inhibitors and inducers as well as different diseases on ripretinib exposure using the validated model. In the DDI simulation, moderate CYP3A4 inhibitors and inducers changed the exposure of ripretinib by 1.25-2 fold. In hepatic impairment (HI), the simulation showed that ripretinib's AUC increased by 32%, 100%, and 152% for Child-Pugh A, B, and C classification while C_max increased by 2%, 10%, and 15%, respectively. In renal impairment (RI), the model-simulated AUC in moderate and severe RIs increased by 27% and 20%. In conclusion, PBPK models demonstrated quantitative prediction of ripretinib's pharmacokinetic changes under varying conditions that might be useful for its rational use.

Ripretinib for the treatment of adult patients with advanced gastrointestinal stromal tumors

INTRODUCTION

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gastrointestinal tract. Imatinib mesylate revolutionized the management of advanced/metastatic GIST, and remains the standard first-line therapy in this setting. Upon development of secondary resistance, sunitinib and regorafenib are used as subsequent treatments, although clinical benefit is often non-durable. Ripretinib is a type II kinase inhibitor targeting KIT and PDGFRA mutations and resistance through switching active I and inactive II forms.

AREAS COVERED

This drug profile article provides an overview of the current state of the art treatment algorithm for advanced/metastatic GIST, focusing on the role of ripretinib in the fourth-line setting as defined by currently available clinical trials evidence. The mechanism of action, the safety profile, efficacy, and clinical application of ripretinib are presented. In addition, the Phase I study (NCT02571036) through which the optimal dose was established and the Phase III trials that assessed the efficacy and safety of ripretinib as fourth- (INVICTUS) and second-line treatment (INTRIGUE) are presented.

EXPERT OPINION

Ripretinib is a safe and an effective therapy for the fourth-line setting in advanced/metastatic GIST. Future studies should evaluate combination schedules and the identification of markers predictive of benefit from ripretinib.

Small Gastric Stromal Tumors: An Underestimated Risk

BACKGROUND AND OBJECTIVES

Small gastrointestinal stromal tumors (GISTs) are defined as tumors less than 2 cm in diameter, which are often found incidentally during gastroscopy. There is controversy regarding the management of small GISTs, and a certain percentage of small GISTs become malignant during follow-up. Previous studies which used Sanger targeted sequencing have shown that the mutation rate of small GISTs is significantly lower than that of large tumors. The aim of this study was to investigate the overall mutational profile of small GISTs, including those of wild-type tumors, using whole-exome sequencing (WES) and Sanger sequencing.

METHODS

Thirty-six paired small GIST specimens, which were resected by endoscopy, were analyzed by WES. Somatic mutations identified by WES were confirmed by Sanger sequencing. Sanger sequencing was performed in an additional 38 small gastric stromal tumor samples for examining hotspot mutations in KIT, PDGFRA, and BRAF.

RESULTS

Somatic C-KIT/PDGFRA mutations accounted for 81% of the mutations, including three novel mutation sites in C-KIT at exon 11, across the entire small gastric stromal tumor cohort (n = 74). In addition, 15% of small GISTs harbored previously undescribed BRAF-V600E hotspot mutations. No significant correlation was observed among the genotype, pathological features, and clinical classification.

CONCLUSIONS

Our data revealed a high overall mutation rate (~96%) in small GISTs, indicating that genetic alterations are common events in early GIST generation. We also identified a high frequency of oncogenic BRAF-V600E mutations (15%) in small GISTs, which has not been previously reported.

Comparative kinase and cancer cell panel profiling of kinase inhibitors approved for clinical use from 2018 to 2020

During the last two decades, kinase inhibitors have become the major drug class for targeted cancer therapy. Although the number of approved kinase inhibitors increases rapidly, comprehensive in vitro profiling and comparison of inhibitor activities is often lacking in the public domain. Here we report the extensive profiling and comparison of 21 kinase inhibitors approved by the FDA for oncology indications since June 2018 and 13 previously approved comparators on panels of 255 biochemical kinase assays and 134 cancer cell line viability assays. Comparison of the cellular inhibition profiles of the EGFR inhibitors gefitinib, dacomitinib, and osimertinib identified the uncommon EGFR p.G719S mutation as a common response marker for EGFR inhibitors. Additionally, the FGFR inhibitors erdafitinib, infigratinib, and pemigatinib potently inhibited the viability of cell lines which harbored oncogenic alterations in FGFR1-3, irrespective of the specific clinical indications of the FGFR inhibitors. These results underscore the utility of in vitro kinase inhibitor profiling in cells for identifying new potential stratification markers for patient selection. Furthermore, comparison of the in vitro inhibition profiles of the RET inhibitors pralsetinib and selpercatinib revealed they had very similar biochemical and cellular selectivity. As an exception, an NTRK3 fusion-positive cell line was potently inhibited by pralsetinib but not by selpercatinib, which could be explained by the targeting of TRK kinases in biochemical assays by pralsetinib but not selpercatinib. This illustrates that unexpected differences in cellular activities between inhibitors that act through the same primary target can be explained by subtle differences in biochemical targeting. Lastly, FLT3-mutant cell lines were responsive to both FLT3 inhibitors gilteritinib and midostaurin, and the PI3K inhibitor duvelisib. Biochemical profiling revealed that the FLT3 and PI3K inhibitors targeted distinct kinases, indicating that unique dependencies can be identified by combined biochemical and cellular profiling of kinase inhibitors. This study provides the first large scale kinase assay or cell panel profiling study for newly approved kinase inhibitors, and shows that comprehensive in vitro profiling of kinase inhibitors can provide rationales for therapy selection and indication expansion of approved kinase inhibitors.

Ripretinib in advanced gastrointestinal stromal tumors: an overview of current evidence and drug approval

Over the past 20 years, the management of gastrointestinal stromal tumors has acted as an important model in the advancement of molecularly targeted therapies for solid tumors. The success of imatinib has established it as a lasting therapy in the management of early-stage and advanced disease in the first-line setting. Imatinib resistance inevitably develops, resulting in the need for further lines of therapy. Ripretinib is an orally administered switch-control tyrosine kinase inhibitor, specifically developed to target both primary and secondary KIT and PDGFRα resistance mutations. Herein, the authors discuss the molecular rationale, the preclinical evidence and the clinical use of ripretinib in the treatment of gastrointestinal stromal tumors in the advanced stages of disease.

The GIST of Advances in Treatment of Advanced Gastrointestinal Stromal Tumor

Gastrointestinal stromal tumor (GIST) is the most common malignant neoplasm of mesenchymal origin and a compelling clinical and biologic model for the rational development of molecularly targeted agents. This is because the majority of GISTs are driven by gain-of-function mutations in KIT or PDGFRA receptor tyrosine kinases. Specific GIST mutations circumscribe well-defined molecular subgroups that must be determined during the diagnostic work-up to guide clinical management, including therapeutic decisions. Surgery is the cornerstone treatment in localized disease and can also be clinically relevant in the metastatic setting. The correct combination and sequence of targeted agents and surgical procedures improves outcomes for patients with GIST and should be discussed individually within multidisciplinary expert teams. All currently approved agents for the treatment of GIST are based on orally available tyrosine kinase inhibitors targeting KIT and PDGFRA oncogenic activation. Although first-line imatinib achieves remarkable prolonged disease control, the benefit of subsequent lines of treatment is more modest. Novel therapeutic strategies focus on overcoming the heterogeneity of KIT or PDGFRA secondary mutations and providing more potent inhibition of specific challenging mutations. This article reviews the current understanding and treatment of GIST, with an emphasis on recent advances.

New treatment strategies for advanced-stage gastrointestinal stromal tumours

When gastrointestinal stromal tumour (GIST), the most common form of sarcoma, was first recognized as a distinct pathological entity in the 1990s, patients with advanced-stage disease had a very poor prognosis owing to a lack of effective medical therapies. The discovery of KIT mutations as the first and most prevalent drivers of GIST and the subsequent development of the first KIT tyrosine kinase inhibitor (TKI), imatinib, revolutionized the treatment of patients with this disease. We can now identify the driver mutation in 99% of patients with GIST via molecular diagnostic testing, and therapies have been developed to treat many, but not all, molecular subtypes of the disease. At present, seven drugs are approved by the FDA for the treatment of advanced-stage GIST (imatinib, sunitinib, regorafenib, ripretinib, avapritinib, larotrectinib and entrectinib), all of which are TKIs. Although these agents can be very effective for treating certain GIST subtypes, challenges remain and new therapeutic approaches are needed. In this Review, we discuss the molecular subtypes of GIST and the evolution of current treatments, as well as their therapeutic limitations. We also highlight emerging therapeutic approaches that might overcome clinical challenges through novel strategies predicated on the biological features of the distinct GIST molecular subtypes.