Intragenic deletions and a deep intronic mutation affecting pre-mRNA splicing in the dihydropyrimidine dehydrogenase gene as novel mechanisms causing 5-fluorouracil toxicity

Dihydropyrimidine dehydrogenase (DPD) is the initial enzyme acting in the catabolism of the widely used antineoplastic agent 5-fluorouracil (5FU). DPD deficiency is known to cause a potentially lethal toxicity following administration of 5FU. Here, we report novel genetic mechanisms underlying DPD deficiency in patients presenting with grade III/IV 5FU-associated toxicity. In one patient a genomic DPYD deletion of exons 21–23 was observed. In five patients a deep intronic mutation c.1129–5923C>G was identified creating a cryptic splice donor site. As a consequence, a 44 bp fragment corresponding to nucleotides c.1129–5967 to c.1129–5924 of intron 10 was inserted in the mature DPD mRNA. The deleterious c.1129–5923C>G mutation proved to be in cis with three intronic polymorphisms (c.483 + 18G>A, c.959–51T>G, c.680 + 139G>A) and the synonymous mutation c.1236G>A of a previously identified haplotype. Retrospective analysis of 203 cancer patients showed that the c.1129–5923C>G mutation was significantly enriched in patients with severe 5FU-associated toxicity (9.1%) compared to patients without toxicity (2.2%). In addition, a high prevalence was observed for the c.1129–5923C>G mutation in the normal Dutch (2.6%) and German (3.3%) population. Our study demonstrates that a genomic deletion affecting DPYD and a deep intronic mutation affecting pre-mRNA splicing can cause severe 5FU-associated toxicity. We conclude that screening for DPD deficiency should include a search for genomic rearrangements and aberrant splicing

High prevalence of the IVS14 + 1G>A mutation in the dihydropyrimidine dehydrogenase gene of patients with severe 5-fluorouracil-associated toxicity

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-fluorouracil (5FU) and a DPD deficiency is increasingly being recognized as an important pharmacogenetic factor in the aetiology of severe 5FU-associated toxicity. In this study, we evaluated the DPD activity and the prevalence of the common splice site mutation IVS14 + 1G>A in tumour patients suffering from severe grade 3-4 toxicity after the administration of 5FU. DPD activity was measured with a radiochemical assay and screening for the presence of the IVS14 + 1G>A mutation was performed by restriction fragment length polymorphism. A decreased DPD activity could be detected in peripheral blood mononuclear cells in 60% of the cases. Furthermore, a high prevalence of the IVS14 + 1G>A mutation was noted as 28% of all patients were heterozygous or homozygous for this mutation. In patients with a low DPD activity, 42% were heterozygous and one patient (3%) was homozygous for the IVS14 + 1G>A mutation. In contrast, the IVS14 + 1G>A mutation could be detected in only one out of 24 (4%) patients with a normal DPD activity. Our study demonstrates that a DPD deficiency is the major determinant of 5FU-associated toxicity. The apparently high prevalence of the IVS14 + 1G>A mutation warrants genetic screening for this mutation in cancer patients before the administration of 5F

Increased risk of grade IV neutropenia after administration of 5-fluorouracil due to a dihydropyrimidine dehydrogenase deficiency: high prevalence of the IVS14+1g>a mutation

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-fluorouracil (5-FU), and it is suggested that patients with a partial deficiency of this enzyme are at risk of developing severe 5-FU-associated toxicity. We evaluated the importance of DPD deficiency, gender and the presence of the IVS14+1G>A mutation in the etiology of 5-FU toxicity. In 61% of cases, decreased DPD activity could be detected in peripheral blood mononuclear cells. Furthermore, the number of females (65%) in the total group of patients appeared to be higher than the number of males (35%) (p = 0.03). Patients with partial DPD deficiency appeared to have a 3.4-fold higher risk of developing grade IV neutropenia than patients with normal DPD activity. Analysis of the DPYD gene of patients suffering from grade IV neutropenia for the presence of the IVS14+1G>A mutation showed that 50% of the patients investigated were heterozygous or homozygous for the IVS14+1G>A mutation. Adopting a threshold level for DPD activity of 70% of that observed in the normal population, 14% of the population is prone to the development of severe 5-FU-associated toxicity. Below this threshold level, 90% of individuals heterozygous for a mutation in the DPYD gene can be identified. Considering the common use of 5-FU in the treatment of cancer, the severe 5-FU-related toxicities in patients with low DPD activity and the apparently high prevalence of the IVS14+1G>A mutation, screening of patients at risk before administration of 5-FU is warrante

Cyclopentenyl cytosine-induced activation of deoxycytidine kinase increases gemcitabine anabolism and cytotoxicity in neuroblastoma

The effect of the CTP synthetase inhibitor cyclopentenyl cytosine (CPEC) on the metabolism and cytotoxicity of 2',2'-difluorodeoxycytidine (dFdC, gemcitabine) and the expression and activity of deoxycytidine kinase (dCK) was studied in human neuroblastoma cell lines. The cytotoxicity of dFdC and CPEC was studied in a panel of MYCN-amplified and MYCN-single-copy neuroblastoma cell lines using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazollum bromide-assays. dFdC-metabolism was studied in SK-N-BE(2)c cells using [H-3]-radiolabeled dFdC. dCK activity and expression were measured using enzyme assays, immunoblot and quantitative PCR, respectively. Both MYCN-amplified and MYCN-single-copy neuroblastoma cell lines were highly sensitive to dFdC, with concentration of the drug resulting in 50% effect when compared to untreated controls (ED50) values in the nanomolar range after a 3-h exposure to dFdC. There was no correlation of the observed ED50 with the dCK activity. Treatment with dFdC induced cell death in MYCN-amplified cells whereas MYCN-single-copy-cell lines underwent neuronal differentiation. Pre-incubation with CPEC significantly increased dFdC-cytotoxicity from 1.3 to 5.3-fold in 13 out of 15 cell lines. [H-3]dFdC-anabolism increased 6-44 fold in SK-N-BE(2)c cells after incubation with CPEC and was paralleled by a significant increase in expression and activity of dCK. In conclusion, the combination of dFdC and CPEC is highly toxic to neuroblastoma in vitr

Dihydropyrimidine Dehydrogenase Deficiency in Two Malaysian Siblings with Abnormal MRI Findings

Dihydropyrimidine dehydrogenase (DPD) deficiency is an autosomal recessive disorder of the pyrimidine metabolism. Deficiency of this enzyme leads to an accumulation of thymine and uracil and a deficiency of metabolites distal to the catabolic enzyme. The disorder presents with a wide clinical spectrum, ranging from asymptomatic to severe neurological manifestations, including intellectual disability, seizures, microcephaly, autistic behavior, and eye abnormalities. Here, we report on an 11-year-old Malaysian girl and her 6-year-old brother with DPD deficiency who presented with intellectual disability, microcephaly, and hypotonia. Brain MRI scans showed generalized cerebral and cerebellar atrophy and callosal body dysgenesis in the boy. Urine analysis showed strongly elevated levels of uracil in the girl and boy (571 and 578 mmol/mol creatinine, respectively) and thymine (425 and 427 mmol/mol creatinine, respectively). Sequence analysis of the DPYD gene showed that both siblings were homozygous for the mutation c.1651G>A (pAla551Thr

Gene expression profiling in response to the histone deacetylase inhibitor BL1521 in neuroblastoma

Neuroblastoma is a childhood tumor with a poor survival in advanced stage disease despite intensive chemotherapeutic regimes. The new historic deacetylase (HDAC) inhibitor BL1521 has shown promising results in neuroblastoma. Inhibition of HDAC resulted in a decrease in proliferation and metabolic activity, induction of apoptosis and differentiation of neuroblastoma cells. In order to elucidate the mechanism mediating the effects of BL1521 on neuroblastoma cells, we investigated the gene expression profile of an MYCN single copy (SKNAS) and an MYCN amplified (IMR32) neuroblastoma cell line after treatment with BL1521 using the Affymetrix oligonucleotide array U133A. An altered expression of 255 genes was observed in both neuroblastoma cell lines. The majority of these genes were involved in gene expression, cellular metabolism, and cell signaling. We observed changes in the expression of vital genes belonging to the cell cycle (cyclin D1 and CDK4) and apoptosis (BNIP3, BID, and BCL2) pathway in response to BL1521. The expression of 37 genes was altered by both BL1521 and Trichostatin A, which could indicate a common gene set regulated by different HDAC inhibitors. BL1521 treatment changed the expression of a number of MYCN-associated genes. Several genes in the Writ and the Delta/Notch pathways were changed in response to BL1521 treatment, suggesting that BL1521 is able to induce the differentiation of neuroblastoma cells into a more mature phenotype. (c) 2005 Elsevier Inc. All rights reserve

Identification of three novel mutations in the dihydropyrimidine dehydrogenase gene associated with altered pre-mRNA splicing or protein function

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of the pyrimidine bases uracil and thymine, as well as of the widely used chemotherapeutic drug 5-fluorouracil (5FU). Analysis of the DPD gene (DPYD) in two patients presenting with complete DPD deficiency and the parents of an affected child showed the presence of three novel mutations, including one splice site mutation IVS11 +1G --> T and the missense mutations 731A --> C (E244V) and 1651G --> A (A551T). The G --> T mutation in the invariant GT splice donor site flanking exon 11 (IVS11+1G --> T) created a cryptic splice site within exon 11. As a consequence, a 141-bp fragment encoding the aminoacid residues 400-446 of the primary sequence of the DPD protein was missing in the mature DPD mRNA. Analysis of the crystal structure of pig DPD suggested that the E244V mutation might interfere with the electron flow between NADPH and the pyrimidine binding site of DPD. The A551T point mutation might prevent binding of the prosthetic group FMN and affect folding of the DPD protein. The identification of these novel mutations in DPYD will allow the identification of patients with an increased risk of developing severe 5FU-associated toxicit

Dihydropyrimidinase deficiency and severe 5-fluorouracil toxicity

Dihydropyrimidinase (DHP) is the second enzyme in the catabolism of 5-fluorouracil (5FU), and it has been suggested that patients with a deficiency of this enzyme are at risk from developing severe 5FU-associated toxicity. In this study, we demonstrated for the first time that in one patient the severe toxicity, after a treatment with 5FU, was attributable to a partial deficiency of DHP. Analysis of the DHP gene showed that the patient was heterozygous for the missense mutation 833G>A (G278D) in exon 5. Heterologous expression of the mutant enzyme in Escherichia coli showed that the G278D mutation leads to a mutant DHP enzyme without residual activity. An analysis for the presence of this mutation in 96 unrelated Dutch Caucasians indicates that the allele frequency in the normal population is <0.5%. Our results show that a partial DHP deficiency is a novel pharmacogenetic disorder associated with severe 5FU toxicit