Gloria Ravegnini

Association between imatinib transporters and metabolizing enzymes genotype and response in newly diagnosed chronic myeloid leukemia patients receiving imatinib therapy.

Imatinib has so far been the first-choice treatment in chronic myeloid leukemia with excellent results. However, only a proportion of patients achieve major molecular response – hence the need to find biological predictors of outcome to select the optimal therapeutic strategy now that more potent inhibitors are available. We investigated a panel of 20 polymorphisms in seven genes, potentially associated with the pharmacogenetics of imatinib, in a subset of 189 patients with newly diagnosed chronic myeloid leukemia enrolled in the TOPS trial. The analysis included polymorphisms in the transporters hOCT1, MDR1, ABCG2, OCTN1, and OATP1A2, and in the metabolizing genes CYP3A4 and CYP3A5. In the overall population, the OCTN1 C allele (rs1050152), a simple combination of polymorphisms in the hOCT1 gene and another combination in the genes involved in imatinib uptake were significantly associated with major molecular response. The combination of polymorphisms in imatinib uptake was also significantly associated with complete molecular response. Analyses restricted to Caucasians highlighted the significant association of MDR1 CC (rs60023214) genotype with complete molecular response. We demonstrate the usefulness of a pharmacogenetic approach for stratifying patients with chronic myeloid leukemia according to their likelihood of achieving a major or complete molecular response to imatinib. This represents an attractive opportunity for therapy optimization, worth testing in clinical trials.

MED12 mutations in leiomyosarcoma and extrauterine leiomyoma

Leiomyoma and leiomyosarcoma share morphological features and smooth muscle differentiation, and both arise most frequently within the uterine corpus of middle-aged women. However, they are considered biologically unrelated tumors due to their disparate clinical, cytogenetic, and molecular features. MED12, the mediator complex subunit 12 gene, has been recently implicated as an oncogene in as many as 70% of sporadic uterine leiomyoma. In the present study, we show MED12 hotspot exon 2 mutations in extrauterine leiomyoma (3 of 19 cases) and in leiomyosarcoma (3 of 13 uterine cases). We also show that MED12 mutations are found in both primary and metastatic leiomyosarcoma. Immunoblotting studies demonstrated MED12 protein expression in 100% of leiomyomas (13) and leiomyosarcomas (20), irrespective of MED12 exon 2 mutation status or histological grade. These findings indicate that MED12 has oncogenic roles in a broad range of smooth muscle neoplasia, including tumors arising in extrauterine locations.

KRAS and KIT Gatekeeper Mutations Confer Polyclonal Primary Imatinib Resistance in GI Stromal Tumors: Relevance of Concomitant Phosphatidylinositol 3-Kinase/AKT Dysregulation

Introduction KIT juxtamembrane oncogenic mutations (encoded by KIT exon 11) are found in 67% of GI stromal tumors (GISTs) and are inhibited potently by imatinib. Virtually all patients with these mutations therefore achieve clinical benefit when treated with imatinib. Imatinib resistance in KIT exon 11–mutant GISTs typically occurs after 18 to 24 months of response or disease stabilization, most often resulting from expansion of multiple tumor clones harboring secondary KIT kinase domain mutations. However, approximately 10% of patients with GISTs have primary imatinib resistance, defined by clinical progression within 3 to 6 months after initiating therapy. Such GISTs typically lack KIT and platelet-derived growth factor receptor alpha (PDGFRA) mutations, or contain particular mutations, such as PDGFRA D842V, that are intrinsically imatinib resistant. To our knowledge, this is the first report of polyclonal heterogeneity—including KRAS mutation— as a mechanism of primary imatinib resistance in a patient with GIST.

Clinical relevance of pharmacogenetics in gastrointestinal stromal tumor treatment in the era of personalized therapy

Gastrointestinal stromal tumor (GIST) is a well-recognized and now relatively well-understood mesenchymal tumor. Before the imatinib era, the treatment of metastatic GIST was frustrating owing to its refractoriness to conventional chemotherapy and radiotherapy. After a metastatic GIST patient was granted compassionate use of imatinib in 2000, the treatment of this disease has emerged as a model for the development of other molecularly targeted therapies. In this article the authors review how tumor genotypes, in particular KIT and PDGFRA mutational analysis, have been integrated in the optimal clinical management of GIST patients. The authors also discuss the potential practical relevance of pharmacogenetics, which, integrated with therapeutic drug monitoring, should receive greater consideration, with the aim of personalized therapy.

Environmental exposure to benzene, micronucleus formation and polymorphisms in DNA-repair genes: A pilot study

This report is part of a biomarker study conducted in an Italian population with exposure to environmental benzene ranging from 1.43 to 31.41 μg/m³ (values from personal sampling). DNA damage induced by benzene is the crucial mechanism of its genotoxicity, which leads to chronic benzene poisoning, haematotoxicity and leukaemia. Therefore, genetic variation in DNA-repair genes may modulate susceptibility to benzene-induced DNA damage. In light of this, the effects of polymorphisms in DNA-repair genes (APEX1, hOGG1, NBS1, XPD, XRCC1, and XRCC3) on micronucleus (MN) formation as a biomarker of early biological effects were evaluated. A significantly higher median MN frequency was recorded in traffic wardens than in controls. However, none of the analysed polymorphisms was significantly associated with the median MN frequency. A gene-gender interaction was observed for the APEX1 genotype. The APEX1 variant genotype was associated with significantly lower median MN frequency in men, not in women. Statistical analysis did not reveal any association between the score of the protective alleles - hypothetically pushing the pathway towards optimal DNA-damage repair - and MN. Even though there are some limitations in the study, our results indicate that the general population may be exposed to benzene concentrations higher than the threshold level for air-quality standards in the European Union of 10 μg/m³. Furthermore, urban traffic wardens are exposed to significantly higher levels of benzene than individuals spending most of the time indoors. This higher exposure may contribute to DNA damage, suggesting that benzene might be implicated both as an environmental and occupational risk factor in leukaemia and other haematological diseases. In conclusion, this study suggest the need for (i) regular monitoring of traffic wardens for possible exposure to benzene, as a precautionary step to reduce the associated health risks, and (ii) more comprehensive studies in order to better elucidate the involvement of APEX1 genotypes in benzene genotoxicity.

Personalized Medicine in Gastrointestinal Stromal Tumor (GIST): Clinical Implications of the Somatic and Germline DNA Analysis

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract. They are characterized by gain of function mutations in KIT or PDGFRA tyrosine kinase receptors, with their consequent constitutive activation. The gold standard therapy is imatinib that offers a good and stable response for approximately 18–36 months. However, resistance is very common and it is vital to identify new biomarkers. Up until now, there have been two main approaches with focus to characterize novel targets. On the one hand, the focus is on the tumor genome, as the final clinical outcome depends mainly from the cancer specific mutations/alterations patterns. However, the germline DNA is important as well, and it is inconceivable to think the patients response to the drug is not related to it. Therefore the aim of this review is to outline the state of the art of the personalized medicine in GIST taking into account both the tumor DNA (somatic) and the patient DNA (germline).

Pharmacogenetics of tyrosine kinase inhibitors in gastrointestinal stromal tumor and chronic myeloid leukemia

ABSTRACT Introduction: Gastrointestinal stromal tumors (GIST) and chronic myeloid leukemia (CML) are two tumor types deeply different from each other. Despite the differences, these disorders share treatment with tyrosine kinase inhibitor imatinib. Despite the success of imatinib, the response rates vary among different individuals and pharmacogenetics may play an important role in the final clinical outcome. Areas covered: In this review, the authors provide an overview of the pharmacogenetic literature analyzing the role of polymorphisms in both GIST and CML treatment efficacy and toxicity. Expert opinion: So far, several polymorphisms influencing the pharmacokinetic determinants of imatinib have been identified. However, the data are not yet conclusive enough to translate pharmacogenetic tests in clinical practice. In this context, the major obstacles to pharmacogenetic test validation are represented by the small sample size of most studies, ethnicity and population admixture as confounding source, and uncertainty related to genetic variants analyzed. In conclusion, a combination of different theoretical approaches, experimental model systems and statistical methods is clearly needed, in order to appreciate pharmacogenetics applied to clinical practice in the near future.

miRNA profiling in gastrointestinal stromal tumors: implication as diagnostic and prognostic markers

MicroRNAs are a class of short noncoding RNAs, that play a relevant role in multiple biological processes, such as differentiation, proliferation and apoptosis. Gastrointestinal stromal tumors (GIST) are considered as a paradigm of molecular biology in solid tumors worldwide, and after the discovery of specific alterations in the KIT and PDGFRA genes, they have emerged from anonymity to become a model for targeted therapy. Epigenetics have an emerging and relevant role in different steps of GIST biology such as tumorigenesis, disease progression, prognosis and drug resistance. The aim of the present review was to summarize the current evidence about the role of microRNAs in GIST, including their potential application as well as their limits.

Folate-related polymorphisms in gastrointestinal stromal tumours: susceptibility and correlation with tumour characteristics and clinical outcome

The folate metabolism pathway has a crucial role in tumorigenesis as it supports numerous critical intracellular reactions, including DNA synthesis, repair, and methylation. Despite its importance, little is known about the influence of the folate pathway on gastrointestinal stromal tumour (GIST), a rare tumour with an incidence ranging between 6 and 19.6 cases per million worldwide. The importance of folate metabolism led us to investigate the influence of polymorphisms in the genes coding folate-metabolising enzymes on GIST susceptibility, tumour characteristics and clinical outcome. We investigated a panel of 13 polymorphisms in 8 genes in 60 cases and 153 controls. The TS 6-bp deletion allele (formerly rs34489327, delTInsTTAAAG) was associated with reduced risk of GIST (OR=0.20, 95% CI 0.05–0.67, P=0.0032). Selected polymorphisms in patients stratified by age, gender, and other main molecular and clinical characteristics showed that few genotypes may show a likely correlation. We also observed a significant association between the RFC AA/AG genotype and time to progression (HR=0.107, 95% CI 0.014–0.82; P=0.032). Furthermore, we observed a tendency towards an association between the SHMT1 variant allele (TT, rs1979277) and early death (HR=4.53, 95% CI 0.77–26.58, P=0.087). Aware of the strengths and limitations of the study, these results suggest that polymorphisms may modify the risk of GIST and clinical outcome, pointing to the necessity for further investigations with information on folate plasma levels and a larger study population.

Gastrointestinal stromal tumors (GIST): Facing cell death between autophagy and apoptosis

ABSTRACT Autophagy and apoptosis are 2 fundamental biological mechanisms that may cooperate or be antagonistic, although both are involved in deciding the fate of cells in physiological or pathological conditions. These 2 mechanisms coexist simultaneously in cells and share common upstream signals and stimuli. Autophagy and apoptosis play pivotal roles in cancer development. Autophagy plays a key function in maintaining tumor cell survival by providing energy during unfavorable metabolic conditions through its recycling mechanism, and supporting the high energy requirement for metabolism and growth. This review focuses on gastrointestinal stromal tumors and cell death through autophagy and apoptosis, taking into account the involvement of both of these processes in tumor development and growth and as mechanisms of drug resistance. We also focus on the crosstalk between autophagy and apoptosis as an emerging field with major implications for the development of novel therapeutic options.