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A H Bootsma, C H J van Eijck, L J Hofland and S W J Lamberts

INTRODUCTION

Breast cancer affects approximately 1 in every 12 women in western countries, where it is the leading cause of cancer death in women. Because of the heterogeneity of disease that has been observed at clinical, biological and genetic levels, investigation of the mechanism of breast cancer development is difficult. Delineating this heterogeneity will give opportunities to gain further insight into the cellular mechanisms that lead to breast cancer. It will also be clinically helpful, aiding the development of diagnostic screening programmes for women at risk, and facilitating the estimation of prognosis and the design of rational therapies adjusted to specific subgroups.

In this review we summarize the current understanding of the functional role of somatostatin (SST) receptors (SSTRs) in human breast cancer cells. The distribution of SSTR subtypes, their relationship with the neuroendocrine differentiation of the cancers and genetic and patient characteristics, the role of in vivo SSTR visualization,

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W W de Herder, L J Hofland, A J van der Lely and S W J Lamberts

Five somatostatin receptor (sst) subtype genes, sst(1), sst(2), sst(3), sst(4) and sst(5), have been cloned and characterised. The five sst subtypes all bind natural somatostatin-14 and somatostatin-28 with high affinity. Endocrine pancreatic and endocrine digestive tract tumours also express multiple sst subtypes, but sst(2) predominance is generally found. However, there is considerable variation in sst subtype expression between the different tumour types and among tumours of the same type. The predominant expression of sst(2) receptors on pancreatic endocrine or carcinoid tumours is essential for the control of hormonal hypersecretion by the octapeptide somatostatin analogues such as octreotide and lanreotide. Somatostatin and its octapeptide analogues are also able to inhibit proliferation of normal and tumour cells. The high density of sst(2) or sst(5) on pancreatic endocrine or carcinoid tumours further allows the use of radiolabelled somatostatin analogues for in vivo visualisation. The predominant expression of sst(2) receptors in these tumours and the efficiency of sst(2) receptors to undergo agonist-induced internalisation is also essential for the application of radiolabelled octapeptide somatostatin analogues. Currently, [(111)In-DTPA(0)]octreotide, [(90)Y-DOTA(0),Tyr(3)]octreotide, [(177)Lu-DOTA(0)Tyr(3)]octreotate, [(111)In-DOTA(0)]lanreotide and [(90)Y-DOTA(0)]lanreotide can be used for this purpose.

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R van der Pas, W W de Herder, L J Hofland and R A Feelders

Cushing's syndrome (CS) is a severe endocrine disorder characterized by chronic cortisol excess due to an ACTH-secreting pituitary adenoma, ectopic ACTH production, or a cortisol-producing adrenal neoplasia. Regardless of the underlying cause, untreated CS is associated with considerable morbidity and mortality. Surgery is the primary therapy for all causes of CS, but surgical failure and ineligibility of the patient to undergo surgery necessitate alternative treatment modalities. The role of medical therapy in CS has been limited because of lack of efficacy or intolerability. In recent years, however, new targets for medical therapy have been identified, both at the level of the pituitary gland (e.g. somatostatin, dopamine, and epidermal growth factor receptors) and the adrenal gland (ectopically expressed receptors in ACTH-independent macronodular adrenal hyperplasia). In this review, results of preclinical and clinical studies with drugs that exert their action through these molecular targets, as well as already established medical treatment options, will be discussed.

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S G Creemers, L J Hofland, E Korpershoek, G J H Franssen, F J van Kemenade, W W de Herder and R A Feelders

Adrenocortical carcinoma (ACC) is a rare disease with a poor prognosis. Discrimination between ACCs and adrenocortical adenomas (ACAs) remains challenging, with the current gold standard being the Weiss score, consisting of several histopathological characteristics. However, new markers like Ki67, a marker for proliferation, and the staining of reticulins are promising not only as it comes to identifying malignancy but also as prognostic markers in patients with ACC. Currently, surgery is still the only curative treatment for ACC. Mitotane, an adrenolytic drug, is used in the adjuvant setting and in case of metastatic or advanced disease. Patients with progressive disease are frequently treated with mitotane, alone or in combination with etoposide, doxorubicine and cisplatin. Radiotherapy is indicated in selected cases. The low response rates and high toxicity of the systemic therapies emphasize the need for markers that enable the identification of responders and non-responders. Consequently, research is focusing on predictive factors varying from the expression of DNA repair genes to clinical patient characteristics. Subgroups of ACC with different prognosis have been identified based on transcriptome characteristics. As a conclusion from large molecular studies, ACCs appear to harbor many abnormalities compared to ACAs. Altered pathways driving ACC pathogenesis include the IGF, TP53 and the Wnt signaling pathway, allowing these as new potential targets for medical therapy. However, despite efforts in preclinical and clinical studies investigating efficacy of targeting these pathways, most novel therapies appear to be effective in only a subset of patients with ACC. New treatment concepts are therefore urgently needed.

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S G Creemers, P M van Koetsveld, W W De Herder, F Dogan, G J H Franssen, R A Feelders and L J Hofland

Chemotherapy for adrenocortical carcinoma (ACC) has limited efficacy and is accompanied by severe toxicity. This lack of effectiveness has been associated with high tumoral levels of the multidrug resistance (MDR) pump P-glycoprotein (P-gp), encoded by the MDR1 gene. In this study, effects of P-gp inhibition on the sensitivity of ACC cells to cytotoxic drugs were evaluated. MDR1 mRNA and P-gp expression were determined in human adrenal tissues and cell lines. H295R, HAC15 and SW13 cells were treated with mitotane, doxorubicin, etoposide, cisplatin and streptozotocin, with or without the P-gp inhibitors verapamil and tariquidar. Cell growth and surviving fraction of colonies were assessed. MDR1 mRNA and P-gp protein expression were lower in ACCs than in adrenocortical adenomas (P < 0.0001; P < 0.01, respectively). MDR1 and P-gp expression were positively correlated in ACC (P < 0.0001, ρ = 0.723). Mitotane, doxorubicin, cisplatin and etoposide dose dependently inhibited cell growth in H295R, HAC15 and SW13. Tariquidar, and in H295R also verapamil, increased the response of HAC15 and H295R to doxorubicin (6.3- and 7.5-fold EC50 decrease in H295R, respectively; all P < 0.0001). Sensitivity to etoposide was increased in H295R and HAC15 by verapamil and tariquidar (all P < 0.0001). Findings were confirmed when assessing colony formation. We show that cytotoxic drugs, except streptozotocin, used for ACC treatment, inhibit ACC cell growth and colony formation at clinically achievable concentrations. P-gp inhibition increases sensitivity to doxorubicin and etoposide, suggesting that MDR1 is involved in sensitivity to these drugs and could be a potential target for cytotoxic treatment improvement in ACC.

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Y M H Jonkers, S M H Claessen, A Perren, S Schmid, P Komminoth, A A Verhofstad, L J Hofland, R R de Krijger, P J Slootweg, F C S Ramaekers and E-J M Speel

Endocrine pancreatic tumors (EPTs) comprise a highly heterogeneous group of tumors with different clinical behavior and genetic makeup. Insulinomas represent the predominant syndromic subtype of EPTs. The metastatic potential of insulinomas can frequently not be predicted using histopathological criteria, and also molecular markers indicating malignant progression are unreliable because of the small number of cases per subtype studied so far. For the identification of reliable indicators of metastatic disease, we investigated 62 sporadic insulinomas (44 benign and 18 tumors with metastases) by means of comparative genomic hybridization (CGH). In addition, the role of MEN1 (multiple endocrine neoplasia type 1) gene mutations was determined to assess specific chromosomal alterations associated with dysfunction of this endocrine tumor-related tumor suppressor gene. Only one case with a somatic MEN1 mutation was identified (1527del7bp), indicating that the MEN1 gene plays a minor pathogenic role in sporadic insulinomas. CGH analysis revealed that the total number of aberrations per tumor differs strongly between the benign and the malignant group (4.2 vs 14.1; P<0.0001). Furthermore, chromosome 9q gain was found to be the most frequent aberration in both benign and malignant insulinomas, whereas chromosome 6q losses and 12q, 14q and 17pq gains are strongly associated with metastatic disease. Our study shows that chromosomal instability, as defined by ≥5 gains together with ≥5 losses, or total number of gains and losses ≥8, rather than parameters such as tumor size and proliferation index, is the most powerful indicator for the development of metastatic disease in patients with sporadic insulinoma.

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T Vandamme, M Beyens, G Boons, A Schepers, K Kamp, K Biermann, P Pauwels, W W De Herder, L J Hofland, M Peeters, G Van Camp and K Op de Beeck

Mutations in DAXX/ATRX, MEN1 and genes involved in the phosphoinositide-3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway have been implicated in pancreatic neuroendocrine neoplasms (pNENs). However, mainly mutations present in the majority of tumor cells have been identified, while proliferation-driving mutations could be present only in small fractions of the tumor. This study aims to identify high- and low-abundance mutations in pNENs using ultra-deep targeted resequencing. Formalin-fixed paraffin-embedded matched tumor-normal tissue of 38 well-differentiated pNENs was sequenced using a HaloPlex targeted resequencing panel. Novel amplicon-based algorithms were used to identify both single nucleotide variants (SNVs) and insertion-deletions (indels) present in >10% of reads (high abundance) and in <10% of reads (low abundance). Found variants were validated by Sanger sequencing. Sequencing resulted in 416,711,794 reads with an average target base coverage of 2663 ± 1476. Across all samples, 32 high-abundance somatic, 3 germline and 30 low-abundance mutations were withheld after filtering and validation. Overall, 92% of high-abundance and 84% of low-abundance mutations were predicted to be protein damaging. Frequently, mutated genes were MEN1, DAXX, ATRX, TSC2, PI3K/Akt/mTOR and MAPK-ERK pathway-related genes. Additionally, recurrent alterations on the same genomic position, so-called hotspot mutations, were found in DAXX, PTCH2 and CYFIP2. This first ultra-deep sequencing study highlighted genetic intra-tumor heterogeneity in pNEN, by the presence of low-abundance mutations. The importance of the ATRX/DAXX pathway was confirmed by the first-ever pNEN-specific protein-damaging hotspot mutation in DAXX. In this study, both novel genes, including the pro-apoptotic CYFIP2 gene and hedgehog signaling PTCH2, and novel pathways, such as the MAPK-ERK pathway, were implicated in pNEN.

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S G Creemers, P M van Koetsveld, F J van Kemenade, T G Papathomas, G J H Franssen, F Dogan, E M W Eekhoff, P van der Valk, W W de Herder, J A M J L Janssen, R A Feelders and L J Hofland

Adrenocortical carcinoma (ACC) is a rare malignancy with a poor prognosis. Discrimination of ACCs from adrenocortical adenomas (ACAs) is challenging on both imaging and histopathological grounds. High IGF2 expression is associated with malignancy, but shows large variability. In this study, we investigate whether specific methylation patterns of IGF2 regulatory regions could serve as a valuable biomarker in distinguishing ACCs from ACAs. Pyrosequencing was used to analyse methylation percentages in DMR0, DMR2, imprinting control region (ICR) (consisting of CTCF3 and CTCF6) and the H19 promoter. Expression of IGF2 and H19 mRNA was assessed by real-time quantitative PCR. Analyses were performed in 24 ACCs, 14 ACAs and 11 normal adrenals. Using receiver operating characteristic (ROC) analysis, we evaluated which regions showed the best predictive value for diagnosis of ACC and determined the diagnostic accuracy of these regions. In ACCs, the DMR0, CTCF3, CTCF6 and the H19 promoter were positively correlated with IGF2 mRNA expression (P<0.05). Methylation in the most discriminating regions distinguished ACCs from ACAs with a sensitivity of 96%, specificity of 100% and an area under the curve (AUC) of 0.997±0.005. Our findings were validated in an independent cohort of 9 ACCs and 13 ACAs, resulting in a sensitivity of 89% and a specificity of 92%. Thus, methylation patterns of IGF2 regulatory regions can discriminate ACCs from ACAs with high diagnostic accuracy. This proposed test may become the first objective diagnostic tool to assess malignancy in adrenal tumours and facilitate the choice of therapeutic strategies in this group of patients.

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Y M H Jonkers, S M H Claessen, A Perren, A M Schmitt, L J Hofland, W de Herder, R R de Krijger, A A J Verhofstad, A R Hermus, J A Kummer, B Skogseid, M Volante, A C Voogd, F C S Ramaekers and E J M Speel

The clinical behavior of endocrine pancreatic tumors (EPTs) is difficult to predict in the absence of metastases or invasion to adjacent organs. Several markers have been indicated as potential predictors of metastatic disease, such as tumor size ≥2 cm, Ki67 proliferative index ≥2%, cytokeratin (CK) 19 status, and recently in insulinomas, chromosomal instability (CIN). The goal of this study was to evaluate the value of these markers, and in particular of the CIN, to predict tumor recurrence or progression and tumor-specific death, using a series of 47 insulinomas and 24 non-insulinoma EPTs. From these EPT cases, a genomic profile has been generated and follow-up data have been obtained. The proliferative index has been determined in 68 tumors and a CK19 expression pattern in 50 tumors. Results are statistically analyzed using Kaplan–Meier plots and the log-rank statistic. General CIN, as well as specific chromosomal alterations such as 3p and 6q loss and 12q gain, turned out to be the most powerful indicators for poor tumor-free survival (P≤0.0004) and tumor-specific death (P≤0.0113) in insulinomas. The CIN, chromosome 7q gain, and a proliferative index ≥2% were reliable in predicting a poor tumor-free survival in non-insulinoma EPTs (P≤0.0181, whereas CK19 expression was the most optimal predictor of tumor-specific death in these tumors. In conclusion, DNA copy number status is the most sensitive and efficient marker of adverse clinical outcome in insulinomas and of potential interest in non-insulinoma EPTs. As a consequence, this marker should be considered as a prognosticator to improve clinical diagnosis, most practically as a simple multi-target test.

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Maria Cristina De Martino, Richard A Feelders, Wouter W de Herder, Peter M van Koetsveld, Fadime Dogan, Joseph A M J L Janssen, A Marlijn Waaijers, Claudia Pivonello, Steven W J Lamberts, Annamaria Colao, Ronald R de Krijger, Rosario Pivonello and Leo J Hofland

The mTOR pathway has recently been suggested as a new potential target for therapy in adrenocortical carcinomas (ACCs). The aim of the current study is to describe the expression of the mTOR pathway in normal adrenals (NAs) and pathological adrenals and to explore whether there are correlation between the expression of these proteins and the in vitro response to sirolimus. For this purpose, the MTOR, S6K1 (RPS6KB1), and 4EBP1 (EIF4EBP1) mRNA expression were evaluated in ten NAs, ten adrenal hyperplasias (AHs), 17 adrenocortical adenomas (ACAs), and 17 ACCs by qPCR, whereas total(t)/phospho(p)-MTOR, t/p-S6K, and t/p-4EBP1 protein expression were assessed in three NAs, three AHs, six ACAs, and 20 ACCs by immunohistochemistry. The effects of sirolimus on cell survival and/or cortisol secretion in 12 human primary cultures of adrenocortical tumors (ATs) were also evaluated. In NAs and AHs, layer-specific expression of evaluated proteins was observed. S6K1 mRNA levels were lower in ACCs compared with NAs, AHs, and ACAs (P<0.01). A subset of ATs presented a moderate to high staining of the evaluated proteins. Median t-S6K1 protein expression in ACCs was lower than that in ACAs (P<0.01). Moderate to high staining of p-S6K1 and/or p-4EBP1 was observed in most ATs. A subset of ACCs not having moderate to high staining had a higher Weiss score than others (P<0.029). In primary AT cultures, sirolimus significantly reduced cell survival or cortisol secretion only in sporadic cases. In conclusion, these data suggest the presence of an activated mTOR pathway in a subset of ATs and a possible response to sirolimus only in certain ACC cases.