Imatinib in combination with phosphoinositol kinase inhibitor buparlisib in patients with gastrointestinal stromal tumour who failed prior therapy with imatinib and sunitinib: a Phase 1b, multicentre study

Molecular Targeting of the Phosphoinositide-3-Protein Kinase (PI3K) Pathway across Various Cancers

The dysregulation of the phosphatidylinositol-3-kinase (PI3K) pathway can lead to uncontrolled cellular growth and tumorigenesis. Targeting PI3K and its downstream substrates has been shown to be effective in preclinical studies and phase III trials with the approval of several PI3K pathway inhibitors by the Food and Drug Administration (FDA) over the past decade. However, the limited clinical efficacy of these inhibitors, intolerable toxicities, and acquired resistances limit the clinical application of PI3K inhibitors. This review discusses the PI3K signaling pathway, alterations in the PI3K pathway causing carcinogenesis, current and novel PI3K pathway inhibitors, adverse effects, resistance mechanisms, challenging issues, and future directions of PI3K pathway inhibitors.

Advances in Drug Therapy for Gastrointestinal Stromal Tumour

INTRODUCTION

Gastrointestinal stromal tumour (GIST) is a common gastrointestinal sarcoma located in the stromal cells of the digestive tract, and molecular studies have revealed the pathogenesis of mutations in KIT and PDGFRA genes. Since imatinib opened the era of targeted therapy for GIST, tyrosine kinase inhibitors (TKIs) that can treat GIST have been developed successively. However, the lack of new drugs with satisfactory therapeutic standards has made addressing resistance a significant challenge for TKIs in the face of the resistance to first-line and second-line drugs. Therefore, we need to find as many drugs and new treatments that block mutated genes as possible.

METHODS

We conducted a comprehensive collection of literature using databases, integrated and analysed the selected literature based on keywords and the comprehensive nature of the articles, and finally wrote articles based on the content of the studies.

RESULTS

In this article, we first briefly explained the relationship between GIST and KIT/ PDGFRα and then introduced the related drug treatment. The research progress of TKIs was analyzed according to the resistance of the drugs.

CONCLUSION

This article describes the research progress of some TKIs and briefly introduces the currently approved TKIs and some drugs under investigation that may have better therapeutic effects, hoping to provide clues to the research of new drugs.

The role of KRAS splice variants in cancer biology

The three mammalian RAS genes (HRAS, NRAS and KRAS) encode four proteins that play central roles in cancer biology. Among them, KRAS is mutated more frequently in human cancer than any other oncogene. The pre-mRNA of KRAS is alternatively spliced to give rise to two products, KRAS4A and KRAS4B, which differ in the membrane targeting sequences at their respective C-termini. Notably, both KRAS4A and KRAS4B are oncogenic when KRAS is constitutively activated by mutation in exon 2 or 3. Whereas KRAS4B is the most studied oncoprotein, KRAS4A is understudied and until recently considered relatively unimportant. Emerging work has confirmed expression of KRAS4A in cancer and found non-overlapping functions of the splice variants. The most clearly demonstrated of these is direct regulation of hexokinase 1 by KRAS4A, suggesting that the metabolic vulnerabilities of KRAS-mutant tumors may be determined in part by the relative expression of the splice variants. The aim of this review is to address the most relevant characteristics and differential functions of the KRAS splice variants as they relate to cancer onset and progression.

An overview of agents and treatments for PDGFRA-mutated gastrointestinal stromal tumors

Platelet-derived growth factor receptor A (PDGFRA) mutations occur in approximately 10-15% of gastrointestinal stromal tumors (GISTs). These tumors with PDGFRA mutations have a different pathogenesis, clinical characteristics, and treatment response compared to tumors with receptor tyrosine kinase protein (KIT) mutations (60-70%). Many clinical studies have investigated the use of tyrosine kinase inhibitors mainly in patients with KIT mutations; however, there is a lack of attention to the PDGFRA-mutated molecular subtype. The main effective inhibitors of PDGFRA are ripretinib, avapritinib, and crenolanib, and their mechanisms and efficacy in GIST (as confirmed in clinical trials) are described in this review. Some multi-targeted tyrosine kinase inhibitors with inhibitory effects on this molecular subtype are also introduced and summarized in this paper. This review focuses on PDGFRA-mutated GISTs, introduces their clinical characteristics, downstream molecular signaling pathways, and existing resistance mechanisms. We focus on the most recent literature that describes the development of PDGFRA inhibitors and their use in clinical trials, as well as the potential benefits from different combination therapy strategies.

Next questions for the medical treatment of gastrointestinal stromal tumor

PURPOSE OF REVIEW

Since its approval in 2002, imatinib remains the standard first-line treatment for patients with advanced gastrointestinal stromal tumors (GISTs). Overall, all the drugs approved for patients who have developed secondary resistance to imatinib are less effective than imatinib in first-line. Even if, overall survival of patients with advanced GIST has improved over time the last 20 years, imatinib-resistant GIST remains therefore a difficult-to-treat cancer. The aim of this review is to elaborate on the potential strategies to improve outcome for patients with imatinib-refractory disease.

RECENT FINDINGS

New-generation potent KIT and PDGFRA inhibitors such as ripretinib and avapritinib developed for the treatment of GIST have shown very promising clinical activity in patients with highly refractory disease. However, both failed to improve outcome in comparison with standard of care in earlier lines settings. Clinical trials investigating the efficacy of multikinase inhibitor with highly specific KIT inhibitors are currently ongoing. Targeting the microenvironment of GIST may also represent a promising approach and is investigated in several clinical studies.

SUMMARY

Imatinib-refractory GIST still represent a therapeutic challenge. It is likely that only combination therapies with new generation of tyrosine kinase inhibitors (TKIs) and/or immune-oncology agents might potentially result in an enhanced therapeutic efficacy compared with current standard of care.

Decrypting a path based approach for identifying the interplay between PI3K and GSK3 signaling cascade from the perspective of cancer

Cancer is one of those leading diseases worldwide, which takes millions of lives every year. Researchers are continuously looking for specific approaches to eradicate the deadly disease, ensuring minimal adverse effects along with more therapeutic significance. Targeting of different aberrantly regulated signaling pathways, involved in cancer, is surely one of the revolutionary chemotherapeutic approach. In this instance, GSK3 and PI3K signaling cascades are considered as important role player for both the oncogenic activation and inactivation which further leads to cancer proliferation and metastasis. In this review, we have discussed the potential role of GSK3 and PI3K signaling in cancer, and we further established the crosstalk between PI3K and GSK3 signaling, through showcasing their cross activation, cross inhibition and convergence pathways in association with cancer. We also exhibited the effect of GSK3 on the efficacy of PI3K inhibitors to overcome the drug resistance and preventing the cell proliferation, metastasis in a combinatorial way with GSK3 inhibitors for a better treatment strategy in clinical settings.

Identification of Novel Imatinib-Resistant Genes in Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors (GISTs) are common ICC precursor sarcomas, which are considered to be a potential malignant mesenchymal tumor driven by specific KIT or PDGFRA signals in the gastrointestinal tract. The standard treatment for GIST without metastasis is surgical resection. GIST with metastasis is usually treated with tyrosine kinase inhibitors (TKIs) only but cannot be cured. The TKI imatinib is the main drug of GIST drug therapy. In adjuvant therapy, the duration of imatinib adjuvant therapy is 3 years. It has been proved that imatinib can improve the overall survival time (OS). However, many GIST patients develop drug resistance due to the long-term use of imatinib. We were forced to look for new strategies to treat GIST. The purpose of the current academic work is to study the drug-resistant genes of imatinib and their potential mechanisms. A total of 897 differentially expressed genes (DEGs) were found between imatinib-sensitive cell line GIST882 and imatinib-resistant cell line GIST430 by RNA sequencing (RNA-seq). After analyzing the DEGs, 10 top genes were selected (NDN, FABP4, COL4A1, COLEC11, MEG3, EPHA3, EDN3, LMO3, RGS4, and CRISP2). These genes were analyzed by RT-PCR, and it was confirmed that the expression trend of FABP4, COL4A1, and RGS4 in different imatinib-resistant cell lines was in accord with the GEO database. It is suggested that these genes may play a potential role in the clinical diagnosis and treatment of imatinib resistance in GIST.

A multicenter, dose-finding, phase 1b study of imatinib in combination with alpelisib as third-line treatment in patients with advanced gastrointestinal stromal tumor

BACKGROUND

Acquired resistance to approved tyrosine kinase inhibitors limits their clinical use in patients with gastrointestinal stromal tumor (GIST). This study investigated the safety, tolerability and efficacy of alpelisib, a phosphatidylinositol 3-kinase inhibitor, used in combination with imatinib in patients with advanced GIST who had failed prior therapy with both imatinib and sunitinib.

METHODS

This phase 1b, multicenter, open-label study consisted of 2 phases: dose escalation and dose expansion. Dose escalation involved 200 mg once daily (QD) alpelisib, initially, followed by 250 and 350 mg. These were combined with 400 mg QD imatinib until maximum tolerated dose (MTD) and/or a recommended phase 2 dose (RP2D) of alpelisib in combination with imatinib was determined. This MTD/RP2D dose was tested to evaluate the clinical activity of this combination in dose expansion.

RESULTS

Fifty-six patients were enrolled, 21 and 35 in the dose escalation and expansion phases, respectively. The MTD of alpelisib given with imatinib was determined as 350 mg QD. Combination treatment showed partial response in 1 (2.9%) and stable disease in 15 (42.9%) patients. Median progression-free survival was 2 months (95% CI 1.8-4.6). Overall, 92.9% patients had adverse events (AEs) while 46.4% had grade 3/4 AEs, hyperglycemia being the most common (23.2%).

CONCLUSIONS

The MTD of alpelisib was estimated as 350 mg QD when used in combination with imatinib 400 mg QD after oral administration in patients with advanced GIST. The safety and tolerability profile of this combination was acceptable; however, the combination did not demonstrate sufficient clinical activity to justify additional clinical testing.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01735968 (date of initial registration 28/11/2012).

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.

The Management of Unresectable, Advanced Gastrointestinal Stromal Tumours

Gastrointestinal stromal tumours (GISTs) are the most common gastrointestinal tract mesenchymal tumours. Tyrosine kinase inhibitors (TKIs) have transformed the management of advanced GIST. Imatinib was the first TKI to gain approval as management for patients with advanced GIST, establishing a new standard of care. Since then, as a result of several trials including the GRID and INVICTUS studies, we now have five lines of approved targeted therapy, including imatinib, sunitinib, regorafenib, ripretinib and avapritinib for the treatment of unresectable, advanced GISTs. In this review, the Australasian Gastrointestinal Trials Group (AGITG) provide an overview of the key trials that have changed clinical practice, discuss the molecular drivers of GISTs, the importance of molecular testing and directing therapy according to molecular targets, as well as future strategies in the management of advanced GISTs.

An updated review of the treatment landscape for advanced gastrointestinal stromal tumors

Before the introduction of tyrosine kinase inhibitors (TKIs), the overall survival of patients with advanced or metastatic gastrointestinal stromal tumors (GISTs) was 10 to 20 months because of the lack of approved therapies. In the last 20 years, a treatment algorithm for patients with advanced GISTs, which includes imatinib, sunitinib, and regorafenib as first‐, second‐, and third‐line therapies, respectively, has been established. Recently, 2 new TKIs have been approved: ripretinib for fourth‐line therapy and avapritinib as first‐line therapy in patients harboring platelet‐derived growth factor receptor α (PDGFRA) exon 18 D842V mutations. Additionally, there are several experimental therapies under investigation that could advance individualized patient care. All of these therapies have varying efficacies and safety profiles that warrant an updated treatment landscape review. This review article summarizes the efficacy and safety data currently available for conventional TKIs along with recently approved and experimental therapies.

With evolving treatment options and effective toxicity management, patients with advanced gastrointestinal stromal tumors are living longer than ever before. Recently approved targeted therapies and the investigation of experimental treatment options have the potential to alter the current treatment algorithm and encourage personalized patient care.

PI3K Inhibitors in Cancer: Clinical Implications and Adverse Effects

The phospatidylinositol-3 kinase (PI3K) pathway is a crucial intracellular signaling pathway which is mutated or amplified in a wide variety of cancers including breast, gastric, ovarian, colorectal, prostate, glioblastoma and endometrial cancers. PI3K signaling plays an important role in cancer cell survival, angiogenesis and metastasis, making it a promising therapeutic target. There are several ongoing and completed clinical trials involving PI3K inhibitors (pan, isoform-specific and dual PI3K/mTOR) with the goal to find efficient PI3K inhibitors that could overcome resistance to current therapies. This review focuses on the current landscape of various PI3K inhibitors either as monotherapy or in combination therapies and the treatment outcomes involved in various phases of clinical trials in different cancer types. There is a discussion of the drug-related toxicities, challenges associated with these PI3K inhibitors and the adverse events leading to treatment failure. In addition, novel PI3K drugs that have potential to be translated in the clinic are highlighted.

Ripretinib in gastrointestinal stromal tumor: the long-awaited step forward

Gastrointestinal stromal tumor (GIST) represents a paradigm for clinically effective targeted inhibition of oncogenic driver mutations in cancer. Five drugs are currently positioned as the standard of care for the treatment of advanced or metastatic GIST patients. This is the result of continuous, deep understanding of KIT and PDGFRA GIST oncogenic drivers as well as the resistance mechanisms associated to tumor progression. However, the complexity of GIST molecular heterogeneity is an evolving field, and critical questions remain open. Specifically, the clinical benefit of approved and/or investigated targeted agents is strikingly modest at advanced stages of the disease when compared with the activity of first-line imatinib. Ripretinib is a novel switch-pocket inhibitor with broad activity against KIT and PDGFRA oncoproteins and has recently demonstrated antitumoral activity across phase I to phase III clinical trials. Therefore, ripretinib has emerged as a new standard of care for advanced, multi-resistant GIST patients. Based on this data, the Food and Drug Administration has granted in 2020 the approval of ripretinib for GIST patients after progression to imatinib, sunitinib and regorafenib. This, in turn, constitutes a major breakthrough in sarcoma drug development, as there have not been new treatment approvals in GIST for nearly a decade. Herein, we provide a critical review on the preclinical and clinical development of ripretinib in GIST. Furthermore, we seek to assess the biological and clinical impact of this new standard of care on the course of the disease, aiming to provide an insight on future treatments strategies for the next coming years.

The management of metastatic GIST: current standard and investigational therapeutics

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gastrointestinal tract. The majority of GISTs harbor gain of function mutations in either KIT or PDGFRα. Determination of the GIST molecular subtype upon diagnosis is important because this information informs therapeutic decisions in both the adjuvant and metastatic setting. The management of GIST was revolutionized by the introduction of imatinib, a KIT inhibitor, which has become the standard first line treatment for metastatic GIST. However, despite a clinical benefit rate of 80%, the majority of patients with GIST experience disease progression after 2-3 years of imatinib therapy. Second and third line options include sunitinib and regorafenib, respectively, and yield low response rates and limited clinical benefit. There have been recent FDA approvals for GIST including ripretinib in the fourth-line setting and avapritinib for PDGFRA exon 18-mutant GIST. This article aims to review the optimal treatment approach for the management of patients with advanced GIST. It examines the standard treatment options available but also explores the novel treatment approaches in the setting of imatinib refractory GIST.

Systemic therapy of advanced/metastatic gastrointestinal stromal tumors: an update on progress beyond imatinib, sunitinib, and regorafenib

Introduction: Discovery of oncogenic mutations in the KIT and PDGFRA tyrosine kinase receptor was a crucial step for the development of tyrosine kinase inhibitors (TKIs). Since then, GIST became a model for the development of molecular-targeted therapy, which led to dramatically improved median overall survival of advanced GIST. Still, further progress is needed after third-line or for TKI resistant mutations. Areas covered: In this review, after a brief introduction on imatinib, sunitinib, and regorafenib, an overview of TKIs that was evaluated beyond these drugs is provided, with a main focus on the novel approved TKIs. Expert opinion: Combination therapies have thus far not fulfilled their promise in GIST, nor did immunotherapy. Increased understanding of GIST and advances in the development of molecular-targeted drugs led to the introduction of ripretinib and avapritinib. Furthermore, NTRK inhibitors became available for ultrarare NTRK fusions. Solutions for NF1 and BRAF mutated and SDH-deficient GIST are still to be awaited. This all underlines the need for adequate molecular profiling of high-risk GISTs before treatment is started. Possibly by using circulating tumor DNA in the future, targeting resistance mutations with specific drugs along the course of the disease would be easier, avoiding multiple tumor biopsies.

Revolutions in treatment options in gastrointestinal stromal tumours (GISTs): the latest updates

OPINION STATEMENT

The treatment of advanced GIST is rapidly evolving with the development of novel molecular compounds such as avapritinib and ripretinib, but also promising results have been achieved with cabozantinib in a phase II trial. The availability of over five lines of treatment for patients with advanced GIST is likely to completely shift the current second-line and third-line treatment options, and will also potentially enable a personalised approach to treatment. Imatinib will most likely remain as the first-line treatment of choice for the vast majority of GIST patients. However, for GIST patients with tumours harbouring a D842V mutation in PDGFRA exon 18, avapritinib has shown efficacy and will become first-line therapy for this molecular subgroup. For second- and third-line treatment, results are awaited of a number of clinical trials. However, second-line and further treatment could potentially be tailored depending on secondary mutations found in imatinib-resistant GISTs. As secondary resistance to TKIs remains the biggest challenge in the treatment of GIST and despite negative results with alternating regimens in phase II, combination treatments should be further evaluated to tackle this issue. Moreover, the favourable safety profiles observed with avapritinib and ripretinib suggest that combination treatments are feasible, for instance, combining two TKIs or a TKI with drugs targeting downstream signalling pathways, such as PI3K inhibitors or MEK inhibitors. Finally, in line with further personalisation of treatment in GIST, a multidisciplinary approach is essential, and local treatment options, such as RFA, resection in case of unifocal progression, and radiotherapy, should be considered.