Decitabine (DAC) in combination with doxorubicin (DOX) and cyclophosphamide (CTX) in relapsed neuroblastoma (NBL): A Children's Oncology Group Study

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Background: Loss of caspase-8 expression causes resistance to apoptosis-inducing agents and potentiates metastasis in NBL. In vitro treatment of NBL cell lines with DAC results in increased caspase-8 expression and enhanced apoptosis following exposure to DOX. As a component of a pediatric phase 1 study, we evaluated low-dose DAC with DOX and CTX in a cohort of children with relapsed NBL. Promoter specific DNA methylation in peripheral blood mononuclear cells (PBMC) was studied. Methods: Patients received a 1-hour infusion of DAC, 5 mg/m2, daily on days 0–6, followed on day 7 by 45 mg/m2 of DOX (with dexrazoxane) and 1 g/m2 of CTX. All patients received G-CSF. Cycles were repeated every 28 days. Methylation-specific and quantitative PCR were used to measure promoter-specific DNA methylation in PBMC prior to and after DAC (day 7 and day 28). Results: Twelve patients with recurrent NBL (median age 9 years, 10 males) were enrolled. DAC/DOX/CTX was well tolerated with grade 4 myelosuppression being the predominant toxicity. Grade 4 neutropenia, median 11 days duration, occurred in 10 pts and grade 4 thrombocytopenia, median 10 days, in 7 patients. Eight patients had progressive disease after = 2 courses of therapy. The remaining 4 patients had stable disease with 5 to 8 courses. Methylation and subsequent demethylation (40–90% decreased methylation) of the MAGE-1 promoter was detected before and after DAC respectively, in PBMC from 6 of 9 patients analyzed to date. Re-expression of MAGE-1 mRNA was also demonstrated in post treatment samples. Caspase-8 demethylation was not detected in PBMC; nor was hypermethylation of caspase-8 detected in pre-treatment PBMC, possibly due to low tumor burden in blood. Conclusions: DAC in combination with cytotoxic chemotherapy was relatively well tolerated in heavily pre-treated children with relapsed NBL. Low-dose DAC induces demethylation and re-expression of MAGE-1 in PBMC, and may be a potential surrogate marker of demethylation within tumor cells. The use of low dose DAC in combination with other agents warrants further study in NBL.

No significant financial relationships to disclose.

Allelic imbalance on chromosome 2q and alterations of the caspase 8 gene in neuroblastoma

We previously reported a high incidence of loss of heterozygosity (LOH) on chromosome 2q33 in neuroblastoma (NB), observed in various types of human cancers including lung cancer, head and neck cancer and follicular thyroid carcinoma. To better elucidate the role of chromosome 2q aberrations in NB, we examined common allelic imbalance (AI) regions on chromosome 2q in 82 NB patients using 10 polymorphic microsatellite markers. AI on 2q was detected in 26 (32%) of 82 NB cases. There was a distinct common AI region between the D2S115 and D2S307 markers on 2q33. The distance between these markers was about 2.0 cM. Recently, the caspase 8 and caspase 10 genes, both of which encode cystein protease, were mapped to chromosome 2q33. Since the common AI region on 2q33 includes the caspase 8 and caspase 10 genes, the alterations of these genes were examined further. Absent or reduced expression of caspase 8 and caspase 10 were found in 19 (70%) of 27 and two (7%) of 27 NB cell lines by reverse transcription-polymerase chain reaction, respectively. A missense mutation was detected at codon 96, GCT (Alanine) to GTT (Valine), of the caspase 8 gene in one of the NB cell lines lacking caspase 8 expression. Thirteen (68%) of 19 cell lines lacking caspase 8 expression displayed methylation of the CpG island of the caspase 8 gene, whereas only one (13%) of eight cell lines with caspase 8 expression showed caspase 8 methylation (P=0.031). Furthermore, there was a significant association between AI at 2q33 and loss of caspase 8 expression (P=0.026). These results indicated that there was a tumor suppressor gene in the common AI region on chromosome 2q33 involved in the pathogenesis of a subset of NB. It is possible that the caspase 8 gene is one of the candidate tumor suppressor genes for NB and inactivation of this gene plays an important role in the tumorigenesis of NB through mainly its methylation.

Absent or reduced expression of the caspase 8 gene occurs frequently in neuroblastoma, but not commonly in Ewing sarcoma or rhabdomyosarcoma

PROCEDURE

To clarify whether the caspase 8 gene is involved in the pathogenesis of neuroblastoma (NB), we examined alterations of the caspase 8 gene in 15 NB, seven Ewing sarcoma (ES), and eight rhabdomyosarcoma (RMS) cell lines, using reverse transcription-polymerase chain reaction (RT-PCR) and RT-PCR single-strand conformation polymorphism (SSCP) analyses.

RESULTS

The caspase 8 gene was not expressed in 11 (73%) of 15 NB cell lines, it was absent in only one of seven ES cell lines, but was present in all eight RMS cell lines examined. No mutations were detected in any cell lines examined.

CONCLUSIONS

Inactivation of the caspase 8 gene is considered to be involved in the pathogenesis of NB, but not ES or RMS.

Cloning and chromosomal location of a novel member of the myotonic dystrophy family of protein kinases

We have cloned a novel serine/threonine protein kinase (PK428) which is highly related (65%) within the kinase domain to the myotonic dystrophy protein kinase (DM-PK), as well as the cyclic AMP-dependent protein kinase (33%). Northern blots demonstrate that PK428 mRNA is distributed widely among tissues and is expressed at the highest levels in pancreas, heart, and skeletal muscle, with lower levels in liver and lung. Two PK428 mRNAs 10 and 3.8 kilobase pairs in size are seen in a number of cell lines, including hematopoietic and breast cancer cells. An antibody generated to a glutathione S-transferase-PK428 fusion protein detects a 65-kDa protein in these cell lines, and a similarly sized protein when the cloned cDNA is transiently expressed in Cos 7 cells. Immunoprecipitation of the transiently expressed PK428 protein and incubation with [gamma-32P]ATP demonstrate that it is capable of autophosphorylation. In addition, immunoprecipitates of the PK428 protein kinase also phosphorylated histone H1 and a peptide encoding a cyclic AMP-dependent protein kinase substrate. The gene corresponding to the 3.8-kb PK428 mRNA, and its corresponding 65-kDa protein, was isolated by polymerase chain reaction screening of a P1 phage human genomic library. Using this P1 phage clone as a probe, the PK428 gene was located on 1q41-42, a possible location for a human senescence gene, a gene associated with Rippling muscle disease, as well as a region associated with genetically acquired mental retardation.

Identification by molecular cloning of two forms of the alpha-subunit of the human liver stimulatory (GS) regulatory component of adenylyl cyclase

Two DNA molecules complementary to human liver mRNA coding for the alpha-subunit of the stimulatory regulatory component Gs of adenylyl cyclase were cloned. One of the two forms is a full-length cDNA of 1614 nucleotides plus a poly(A) tail of 59 nucleotides. The deduced sequence of 394 amino acids encoded by its open reading frame is essentially identical to that of the alpha-subunits of Gs identified by molecular cloning from bovine adrenals, bovine brain and rat brain. Two independent clones of the other type of cDNA were isolated. Both were incomplete, beginning within the open reading frame coding for the alpha s polypeptide. One codes for amino acids 5 through 394 and the other for amino acids 48 through 394 of the above described cDNA of 1614 nucleotides, and both have the identical 3'-untranslated sequence. They differ from the first cDNA, however, in that they lack a stretch of 42 nucleotides (numbers 214 through 255) and have nucleotides 213 (G) and 256 (G) replaced with C and A, respectively. This results in a predicted amino acid composition of another alpha-subunit of Gs that is shorter by 14 amino acids and contains two substitutions (Asp for Glu and Ser for Gly) at the interface between the deletion and the unchanged sequence. We call the smaller subunit alpha s1 and the larger alpha s2. This is the first demonstration of a structural heterogeneity in alpha s subunits that is due to a difference in amino acid sequence.

Regional location of alpha 1-antichymotrypsin and alpha 1-antitrypsin genes on human chromosome 14

The human protease inhibitor genes alpha 1 antitrypsin (alpha 1-PI) and alpha 1-antichymotrypsin (alpha 1-ACT) are acute-phase proteins which are induced in response to inflammation. These inhibitors function to limit the activity of serine proteases in vivo. alpha 1-PI acts as an inhibitor of neutrophil elastase to protect the elastin fibers of the lung. Genetic deficiencies of alpha 1-PI result in development of chronic pulmonary emphysema. The physiologic role of alpha 1-ACT has not been clearly defined, but it also appears to function in the maintenance of protease-protease inhibitor equilibrium in the lung. Nucleic acid and protein sequence homologies detected between alpha 1-PI and alpha 1-ACT suggested an evolutionary relationship. Gene mapping experiments were performed to determine if these protease inhibitor genes reside at the same chromosomal locus in man. In situ hybridization data demonstrate that both alpha 1-PI and alpha 1-ACT map to the same region, q31-q32.3, on chromosome 14.