Primary and secondary kinase genotypes correlate with the biological and clinical activity of sunitinib in imatinib-resistant gastrointestinal stromal tumor

Advances in the treatment of gastrointestinal stromal tumor

GIST (gastrointestinal stromal tumor) is a rare soft tissue malignancy arising in the gut. It has become well known recently because of the effectiveness of anti-KIT tyrosine kinase inhibitors. From a disease that 10 years ago was only treatable with surgery, now multiple phase 2 and phase 3 trials have identified active first-line systemic therapy, appropriate dosing, an active second-line agent, and established the role of adjuvant therapy after surgery for patients with intermediate- and high-risk tumors. These are accomplishments that took decades to achieve for other more common diseases such as breast cancer or lung cancer. GIST has been the ideal disease system for studying targeted therapy in solid tumors. The progress in treating GIST has come directly from the advances that have been made in the laboratory, understanding the basic biology of tyrosine kinases, the oncogenic activity of c-KIT, and how that enzymatic activity can be inhibited. By studying model diseases such as GIST, we should be able to develop paradigms to treat more common cancers as well.

[Gastrointestinal stromal tumors: recommendations for diagnosis, treatment and aftercare in Austria]

Diagnosis and treatment of gastrointestinal stromal tumors (GIST) requires an interdisciplinary treatment approach. This strategy should be reflected by the content of this article. Austrian representatives of 'GIST relevant' specialties authored this publication on a consensual base. This manuscript should be regarded as a guideline for 'GIST involved' colleagues in Austria.

Advanced gastrointestinal stromal tumor in Europe: a review of updated treatment recommendations

The European Society for Medical Oncology (ESMO) recommendations on the management of gastrointestinal stromal tumor (GIST) have recently been updated. Imatinib 400 mg/day remains the standard first-line treatment for patients with metastatic GIST. Mutational analysis has received a strong recommendation for diagnostic purposes. Furthermore, patients with KIT exon 9-activating mutations are now recommended to receive imatinib 800 mg/day as first-line treatment. Following progression during treatment with imatinib 400 mg/day, increasing the imatinib dose to 800 mg/day is advised. In the case of further progression or intolerance to imatinib, sunitinib 50 mg/day (schedule 4/2) is recommended. This article reviews the evidence underlying the updates to the ESMO recommendations on the management of GIST and discusses the implications of the changes.

Pharmacological management of gastrointestinal stromal tumours: an update on the role of sunitinib

The efficacy and tolerability of the receptor tyrosine kinase inhibitor, sunitinib malate, have been demonstrated in phase I-III clinical trials of patients with imatinib-resistant or imatinib-intolerant gastrointestinal stromal tumours (GIST) as well as in a worldwide expanded-access study and in a continuous daily dosing (CDD) trial. Tumour genotype may have a significant influence on the activity of sunitinib in patients with imatinib-resistant GIST. Sunitinib activity was observed across different GIST genotypes and particularly in patients with wild-type and KIT exon 9 mutations (all relatively resistant to standard-dose imatinib) and in patients with secondary KIT exons 13 and 14 mutations. Adverse events with sunitinib were generally mild to moderate and easily managed by dose reduction, dose interruption or standard supportive measures. Treatment discontinuation can be avoided in most patients by close monitoring before and during treatment with appropriate adverse event management as necessary. The correlation between treatment exposure and clinical response is prompting the search for new approaches to treatment optimisation to ensure that patients derive maximum benefit from sunitinib therapy, including dose adjustments based on blood testing to ensure optimal drug exposure, and the use of the alternative CDD regimen to avoid treatment interruption.

Sunitinib treatment in pediatric patients with advanced GIST following failure of imatinib

BACKGROUND

Sunitinib inhibits KIT and other members of the split-kinase-domain family of receptor tyrosine kinases. Sunitinib prolongs survival in adult patients with imatinib-resistant gastrointestinal stromal tumor (GIST). We report the experience with sunitinib in pediatric patients with advanced GIST following failure of imatinib.

PROCEDURE

Sunitinib therapy was provided through a treatment-use protocol. Patients were 10-17 years old at enrollment. All patients had GIST resistant to imatinib therapy. Sunitinib was administered daily for 4 weeks in 6-week treatment cycles. KIT and platelet-derived growth factor receptor alpha (PDGFRA) genotyping of tumor tissue were performed.

RESULTS

One patient achieved a partial response, five patients had stable disease and one patient had progressive disease on sunitinib. The duration of disease stabilization was between 7 and 21+ months, with a mean of 15 months. Time to tumor progression was longer on sunitinib than on prior imatinib treatment for five of six patients. Two patients experienced grade 3 adverse events. All other adverse events were grade 1-2. None of the five patients tested had mutations in KIT or PDGFRA.

CONCLUSION

Sunitinib treatment was associated with substantial initial antitumor activity and acceptable tolerability in this group of pediatric patients with imatinib-resistant GIST.

Current clinical strategy for imatinib-resistant gastrointestinal stromal tumors

Before the advent of imatinib, no effective agent was available for the treatment of unresectable or metastatic gastrointestinal stromal tumors (GISTs). However, the treatment strategy changed and the prognosis of patients with advanced or recurrent GIST improved remarkably after the development of imatinib. Despite the high rate of clinical benefit of imatinib in GIST patients, more than half of GIST patients eventually develop primary or secondary resistance to imatinib, resulting in the progression of the disease. It has also been reported that about 5% of patients are intolerant to imatinib. An effective treatment strategy for imatinib-resistant GIST is needed. The National Comprehensive Cancer Network guidelines recommend a multidisciplinary approach, but the therapeutic modalities are still limited, and none are able to achieve complete remission. In this review, we summarize the current understandings of the mechanism of imatinib resistance and the clinical strategies used against imatinib-resistant GIST, including surgical intervention, escalation of imatinib dose, and use of sunitinib or other agents. Understanding these issues may help in the development of a new treatment paradigm for GIST patients.

Multitarget drugs: the present and the future of cancer therapy

Target therapies for the treatment of human cancers have revolutionized the concept of oncological medicine. This type of therapeutic approach is directed to the inhibition of molecular targets that play a pivotal role in tumor progression -- such as tyrosine kinase receptors (TKIs) controlling cell proliferation and survival -- mainly by means of compounds able to block their activity. In the beginning, the aim of target therapies was specifically to hit a single molecule expressed in neoplastic cells. Now the prevailing idea is that inhibiting both cancer cells and cells of the stroma supporting the tumor would gain better results in fighting the disease. Therefore, the single-target therapy is fading in favor of a multitarget approach and the new generation of TKIs is selected on the basis of their ability simultaneously to target different molecules. This review summarizes the molecular basis of multitarget therapies and the most relevant results obtained in different cancer types.

FLT3 inhibition and mechanisms of drug resistance in mutant FLT3-positive AML

An appealing therapeutic target in AML is constitutively activated, mutant FLT3, which is expressed in a subpopulation of AML patients and is generally a poor prognostic indicator in patients under the age of 65. There are currently several FLT3 inhibitors that are undergoing clinical investigation. However, the discovery of drug-resistant leukemic blast cells in FLT3 inhibitor-treated AML patients has prompted the search for novel, structurally diverse FLT3 inhibitors that could be alternatively used to circumvent drug resistance. Here, we provide an overview of FLT3 inhibitors under preclinical and clinical investigation, and we discuss mechanisms whereby AML cells develop resistance to FLT3 inhibitors, and the ways in which combination therapy could potentially be utilized to override drug resistance. We discuss how the cross-talk between major downstream signaling pathways, such as PI3K/PTEN/Akt/mTOR, RAS/Raf/MEK/ERK, and Jak/STAT, can be exploited for therapeutic purposes by targeting key signaling molecules with selective inhibitors, such as mTOR inhibitors, HSP90 inhibitors, or farnesyltransferase inhibitors, and identifying those agents with the ability to positively combine with inhibitors of FLT3, such as PKC412 and sunitinib. With the widespread onset of drug resistance associated with tyrosine kinase inhibitors, due to mechanisms involving development of point mutations or gene amplification of target proteins, the use of a multi-targeted therapeutic approach is of potential clinical benefit.

Kinase mutations and efficacy of imatinib in Korean patients with advanced gastrointestinal stromal tumors

PURPOSE

This study analyzed the relationship between treatment outcome and kinase mutational status in Korean patients with advanced gastrointestinal stromal tumors (GISTs).

EXPERIMENTAL DESIGN

Clinical data were collected from 113 consecutive patients with metastatic or unresectable GISTs treated with imatinib from June 2001 through June 2005 at five institutions in Korea. KIT exons 9, 11, 13, and 17 and PDGFRA exons 12 and 18 were examined.

RESULTS

The median patient age was 57 years (range, 31-82 years). The overall response rate was 67.2%. KIT mutations were found in exon 11 (n = 92, 81.4%) and exon 9 (n = 10, 8.8%). One patient had a PDGFRA exon 18 mutation. The overall mutation rate was 91.2%. Response rates were 68.4%, 50.0%, and 80.0% in patients with KIT exon 11 mutations, KIT exon 9 mutations, and no kinase mutations, respectively. With a median follow-up of 49.0 months, the median progression-free survival (PFS) time was 42.0 months and median overall survival (OS) time was not reached. PFS and OS times did not differ significantly according to KIT genotype.

CONCLUSION

This study was unable to find an association between KIT mutational status and clinical outcome of imatinib in Korean patients with advanced GISTs. There was a trend toward better outcomes for patients with wild-type KIT or exon 11 mutations compared with exon 9 mutations, although this was not statistically significant. Compared with previous studies in western populations, these results suggest that ethnic differences may influence the relationship between KIT genotype and clinical outcome to imatinib.

Analysis of a case with disappearance of the primary gastrointestinal stromal tumor and progressive liver metastases under long-term treatment with tyrosine kinase inhibitors

The response of gastrointestinal stromal tumors (GISTs) to tyrosine kinase receptor inhibitors (TKR-I) has been a breakthrough for small molecular therapy. We report here on the very different long-term outcome of a synchronous metastatic GIST with complete remission of the primary tumor and progressive liver metastases under TKR-I therapy. In 2003, a 52-year-old patient was diagnosed with gastric GIST and synchronous multiple liver metastases. Therapy with imatinib, 400 mg daily, was started immediately. Fifteen months later, the primary was no longer detectable by endoscopy. In 2006, progression of the liver metastases was observed. Mutation analysis of the initial biopsy specimen from the primary, as well as the biopsy from the three main liver metastases after 3 years of imatinib treatment, revealed the common KIT exon 11 deletion (W557_K558del) in all tumor samples. Two of the metastases had a separate secondary mutation in KIT exon 14 and 17, respectively, while the largest cystic metastatic lesion had no other mutation. Imatinib was then increased to a daily dose of 800 mg, and in April 2007 the treatment was changed to sunitinib. Fifty-two months after initial diagnosis, the patient died of liver failure. At no time point, relapse of the gastric primary tumor was observed. Whilst TKR-Is are commonly very effective in treating GISTs, the present case illustrates their varying effects regarding the clinical behavior and genetic variations within different tumors of the same patient after long-term treatment.

Advances in preclinical therapeutics development using small animal imaging and molecular analyses: the gastrointestinal stromal tumors model

The large use of target therapies in the treatment of gastrointestinal stromal tumors (GISTs) highlighted the urgency to integrate new molecular imaging technologies, to develop new criteria for tumor response evaluation and to reach a more comprehensive definition of the molecular target. These aspects, which come from clinical experiences, are not considered enough in preclinical research studies which aim to evaluate the efficacy of new drugs or new combination of drugs with molecular target. We developed a xenograft animal model GIST882 using nude mice. We evaluated both the molecular and functional characterization of the tumor mass. The mutational analysis of KIT receptor of the GIST882 cell lines and tumor mass showed a mutation on exon 13 that was still present after in vivo cell growth. The glucose metabolism and cell proliferation was evaluated with a small animal PET using both FDG and FLT. The experimental development of new therapies for GIST treatment requires sophisticated animal models in order to represent the tumor molecular heterogeneity already demonstrated in the clinical setting and in order to evaluate the efficacy of the treatment also considering the inhibition of tumor metabolism, and not only considering the change in size of tumors. This approach of cancer research on GISTs is crucial and essential for innovative perspectives that could cross over to other types of cancer.

KIT kinase mutants show unique mechanisms of drug resistance to imatinib and sunitinib in gastrointestinal stromal tumor patients

Most gastrointestinal stromal tumors (GISTs) exhibit aberrant activation of the receptor tyrosine kinase (RTK) KIT. The efficacy of the inhibitors imatinib mesylate and sunitinib malate in GIST patients has been linked to their inhibition of these mutant KIT proteins. However, patients on imatinib can acquire secondary KIT mutations that render the protein insensitive to the inhibitor. Sunitinib has shown efficacy against certain imatinib-resistant mutants, although a subset that resides in the activation loop, including D816H/V, remains resistant. Biochemical and structural studies were undertaken to determine the molecular basis of sunitinib resistance. Our results show that sunitinib targets the autoinhibited conformation of WT KIT and that the D816H mutant undergoes a shift in conformational equilibrium toward the active state. These findings provide a structural and enzymologic explanation for the resistance profile observed with the KIT inhibitors. Prospectively, they have implications for understanding oncogenic kinase mutants and for circumventing drug resistance.