Pamela J. Snyder

Phase II Clinical Trial of Sorafenib in Metastatic Medullary Thyroid Cancer

PURPOSE Mutations in the RET proto-oncogene and vascular endothelial growth factor receptor (VEGFR) activity are critical in the pathogenesis of medullary thyroid cancer (MTC). Sorafenib, a multikinase inhibitor targeting Ret and VEGFR, showed antitumor activity in preclinical studies of MTC. PATIENTS AND METHODS In this phase II trial of sorafenib in patients with advanced MTC, the primary end point was objective response. Secondary end points included toxicity assessment and response correlation with tumor markers, functional imaging, and RET mutations. Using a two-stage design, 16 or 25 patients were to be enrolled onto arms A (hereditary) and B (sporadic). Patients received sorafenib 400 mg orally twice daily. RESULTS Of 16 patients treated in arm B, one achieved partial response (PR; 6.3%; 95% CI, 0.2% to 30.2%), 14 had stable disease (SD; 87.5%; 95% CI, 61.7% to 99.5%), and one was nonevaluable. In a post hoc analysis of 10 arm B patients with progressive disease (PD) before study, one patient had PR of 21+ months, four patients had SD >or= 15 months, four patients had SD <or= 6 months, and one patient had clinical PD. Median progression-free survival was 17.9 months. Arm A was prematurely terminated because of slow accrual. Common adverse events (AEs) included diarrhea, hand-foot-skin reaction, rash, and hypertension. Although serious AEs were rare, one death was seen. Tumor markers decreased in the majority of patients, and RET mutations were detected in 10 of 12 sporadic MTCs analyzed. CONCLUSION Sorafenib is reasonably well tolerated, with suggestion of clinical benefit for patients with sporadic MTC. Caution should be taken because of the rare but fatal toxicity potentially associated with sorafenib.

Sphingosine kinase-1 expression correlates with poor survival of patients with glioblastoma multiforme: roles of sphingosine kinase isoforms in growth of glioblastoma cell lines.

Sphingosine-1-phosphate is a bioactive lipid that is mitogenic for human glioma cell lines by signaling through its G protein-coupled receptors. We investigated the role of sphingosine-1-phosphate receptors and the enzymes that form sphingosine-1-phosphate, sphingosine kinase (SphK)-1, and -2 in human astrocytomas. Astrocytomas of various histologic grades expressed three types of sphingosine-1-phosphate receptors, S1P1, S1P2, and S1P3; however, no significant correlation with histologic grade or patient survival was detected. Expression of SphK1, but not SphK2, in human astrocytoma grade 4 (glioblastoma multiforme) tissue correlated with short patient survival. Patients whose tumors had low SphK1 expression survived a median 357 days, whereas those with high levels of SphK1 survived a median 102 days. Decreasing SphK1 expression using RNA interference or pharmacologic inhibition of SphK significantly decreased the rate of proliferation of U-1242 MG and U-87 MG glioblastoma cell lines. Surprisingly, RNA interference to knockdown SphK2 expression inhibited glioblastoma cell proliferation more potently than did SphK1 knockdown. SphK knockdown also prevented cells from exiting G1 phase of the cell cycle and marginally increased apoptosis. Thus, SphK isoforms may be major contributors to growth of glioblastoma cells in vitro and to aggressive behavior of glioblastoma multiforme.

Molecular analysis of spinal muscular atrophy and modification of the phenotype by SMN2

Purpose: This study describes SMN1 deletion frequency, carrier studies, and the effect of the modifying SMN2 gene on the spinal muscular atrophy (SMA) phenotype. A novel allele-specific intragenic mutation panel increases the sensitivity of SMN1 testing.Methods: From 1995 to 2001, 610 patients were tested for SMN1 deletions and 399 relatives of probands have been tested for carrier status. SMN2 copy number was compared between 52 type I and 90 type III patients, and between type I and type III patients with chimeric SMN genes. A fluorescent allele-specific polymerase chain reaction (PCR) -based strategy detected intragenic mutations in potential compound heterozygotes and was used on 366 patients.Results: Less than half of the patients tested were homozygously deleted for SMN1. A PCR-based panel detected the seven most common intragenic mutations. SMN2 copy number was significantly different between mild and severely affected patients.Conclusions: SMN1 molecular testing is essential for the diagnosis of SMA and allows for accurate carrier testing. Screening for intragenic mutations in SMN1 increases the sensitivity of diagnostic testing. Finally, SMN2 copy number is conclusively shown to ameliorate the phenotype and provide valuable prognostic information.

Newborn and carrier screening for spinal muscular atrophy

Spinal muscular atrophy (SMA) is a common autosomal recessive neuromuscular disorder caused by mutations in the survival motor neuron (SMN1) gene, affecting approximately 1 in 10,000 live births. The homozygous absence of SMN1 exon 7 has been observed in the majority of patients and is being utilized as a reliable and sensitive SMA diagnostic test. Treatment and prevention of SMA are complementary responses to the challenges presented by SMA. Even though a specific therapy for SMA is not currently available, a newborn screening test may allow the child to be enrolled in a clinical trial before irreversible neuronal loss occurs and enable patients to obtain more proactive treatments. Until an effective treatment is found to cure or arrest the progression of the disease, prevention of new cases through accurate diagnosis and carrier and prenatal diagnosis is of the utmost importance. The goal of population‐based SMA carrier screening is to identify couples at risk for having a child with SMA, thus allowing carriers to make informed reproductive choices. During this study we performed two pilot projects addressing the clinical applicability of testing in the newborn period and carrier screening in the general population. We have demonstrated that an effective technology does exist for newborn screening of SMA. We also provide an estimate of the carrier frequency among individuals who accepted carrier screening, and report on patients knowledge and attitudes toward SMA testing.

Kennedy's disease A clinicopathologic correlation with mutations in the androgen receptor gene

We confirmed a mutation of the androgen receptor gene as the cause for Kennedys disease, also called “X-linked recessive spinal and bulbar muscular atrophy” or “bulbospinal neuronopathy.” The mutation is characterized by an increased size of a polymorphic tandem CAG repeat within the first exon of the gene. The study population consisted of 17 patients from seven families (five distinct kinships and two isolated cases). Two patients were as yet asymptomatic and had normal examinations. Four carrier females showed the mutant as well as the normal allele; none showed clinical features of Kennedys disease. There was no large expansion of the mutation observed in three generations of one family. Phenotypic expression between and within families was variable and not related to the size of the mutation. This contrasts with the gene mutations found in myotonic dystrophy and fragile X syndrome, where increased severity of disease correlates with the number of tandem triplet repeats. The findings reported here appear to explain the failure to find genetic anticipation in Kennedys disease. The DNA test for Kennedys disease can now be used for definitive diagnosis and carrier detection. In addition, mutation analysis allows early detection, which has implications for potential treatment.

Comparison of Cytogenetic and Molecular Genetic Detection of t(8;21) and inv(16) in a Prospective Series of Adults With De Novo Acute Myeloid Leukemia: A Cancer and Leukemia Group B Study

PURPOSE To prospectively compare cytogenetics and reverse transcriptase-polymerase chain reaction (RT-PCR) for detection of t(8;21)(q22;q22) and inv(16)(p13q22)/t(16;16)(p13;q22), aberrations characteristic of core-binding factor (CBF) acute myeloid leukemia (AML), in 284 adults newly diagnosed with primary AML. PATIENTS AND METHODS Cytogenetic analyses were performed at local laboratories, with results reviewed centrally. RT-PCR for AML1/ETO and CBFbeta/MYH11 was performed centrally. RESULTS CBF AML was ultimately identified in 48 patients: 21 had t(8;21) or its variant and AML1/ETO, and 27 had inv(16)/t(16;16), CBFbeta/MYH11, or both. Initial cytogenetic and RT-PCR analyses correctly classified 95.7% and 96.1% of patients, respectively (P =.83). Initial cytogenetic results were considered to be false-negative in three AML1/ETO-positive patients with unique variants of t(8;21), and in three CBFbeta/MYH11-positive patients with, respectively, an isolated +22; del(16)(q22),+22; and a normal karyotype. The latter three patients were later confirmed to have inv(16)/t(16;16) cytogenetically. Only one of 124 patients reported initially as cytogenetically normal was ultimately RT-PCR-positive. There was no false-positive cytogenetic result. Initial RT-PCR was falsely negative in two patients with inv(16) and falsely positive for AML1/ETO in two and for CBFbeta/MYH11 in another two patients. Two patients with del(16)(q22) were found to be CBFbeta/MYH11-negative. M4Eo marrow morphology was a good predictor of the presence of inv(16)/t(16;16). CONCLUSION Patients with t(8;21) or inv(16) can be successfully identified in prospective multi-institutional clinical trials. Both cytogenetics and RT-PCR detect most such patients, although each method has limitations. RT-PCR is required when the cytogenetic study fails; it is also required to determine whether patients with suspected variants of t(8;21), del(16)(q22), or +22 represent CBF AML. RT-PCR should not replace cytogenetics and should not be used as the only diagnostic test for detection of CBF AML because of the possibility of obtaining false-positive or false-negative results.

Characterization of translational frame exception patients in Duchenne/Becker muscular dystrophy

The clinical progression of Duchenne muscular dystrophy (DMD) patients with deletions can be predicted in 93% of cases by whether the deletion maintains or disrupts the translational reading frame (frameshift hypothesis). We have identified and studied a number of patients who have deletions that do not conform to the translational frame hypothesis. The most common exception to the frameshift hypothesis is the deletion of exons 3 to 7 which disrupts the translational reading frame. We identified a Becker muscular dystrophy (BMD) patient, an intermediate, and a DMD patient with this deletion. In all three cases, dystrophin was detected and localized to the membrane. One DMD patient with an inframe deletion of exons 4-18 produced no dystrophin. One patient with a mild intermediate phenotype and a deletion of exon 45, which shifts the reading frame, produced no dystrophin. Two patients with large inframe deletions had discordant phenotypes (exons 3-41, DMD; exons 13-48, BMD), but both produced dystrophin that localized to the sarcolemma. The DMD patient, 113, indicates that dystrophin with an intact carboxy terminus can be produced in Duchenne patients at levels equivalent to some Beckers. The dystrophin analysis from these patients, together with patients reported in the literature, indicate that more than one domain can localize dystrophin to the sarcolemma. Lastly, the data shows that although most patients show correlation of clinical severity to molecular data, there are rare patients which do not conform.

Sphingosine-1-phosphate stimulates human glioma cell proliferation through Gi-coupled receptors: role of ERK MAP kinase and phosphatidylinositol 3-kinase β

The regulation of glioma cell proliferation by sphingosine-1-phosphate (S1P) was studied using the human glioblastoma cell line U-373 MG. U-373 MG cells responded mitogenically to nanomolar concentrations of S1P, and express mRNA encoding the S1P receptors S1P1/endothelial differentiation gene (EDG)-1, S1P3/EDG-3 and S1P2/EDG-5. S1P-induced proliferation required extracellular signal-regulated kinase activation and was partially sensitive to pertussis toxin and wortmannin, indicating involvement of a Gi-coupled receptor and phosphatidylinositol 3-kinase. Moreover, S1P1, S1P3 and S1P2 receptors are expressed in the majority of human glioblastomas as determined by reverse transcriptase-polymerase chain reaction analysis. Thus, S1P signaling through EDG receptors may contribute to glioblastoma growth in vivo.

Congenital lethal motor neuron disease with a novel defect in ribosome biogenesis

Objective: We describe a novel congenital motor neuron disease with early demise due to respiratory insufficiency with clinical overlap with spinal muscular atrophy with respiratory distress (SMARD) type 1 but lacking a mutation in the IGHMBP2 gene. Methods: Exome sequencing was used to identify a de novo mutation in the LAS1L gene in the proband. Pathogenicity of the mutation was validated using a zebrafish model by morpholino-mediated knockdown of las1l. Results: We identified a de novo mutation in the X-linked LAS1L gene in the proband (p.S477N). The mutation is in a highly conserved region of the LAS1L gene predicted to be deleterious by bioinformatic analysis. Morpholino-based knockdown of las1l, the orthologous gene in zebrafish, results in early lethality and disruption of muscle and peripheral nerve architecture. Coinjection of wild-type but not mutant human RNA results in partial rescue of the phenotype. Conclusion: We report a patient with a SMARD phenotype due to a mutation in LAS1L, a gene important in coordinating processing of the 45S pre-rRNA and maturation of the large 60S ribosomal subunit. Similarly, the IGHMB2 gene associated with SMARD type 1 has been suggested to have an important role in ribosomal biogenesis from its role in processing the 45S pre-rRNA. We propose that disruption of ribosomal maturation may be a common pathogenic mechanism linking SMARD phenotypes caused by both IGHMBP2 and LAS1L.

Dystrophin expression in a Duchenne muscular dystrophy Patient with a frame shift deletion

Article abstract-The exon 45 deletion is a common dystrophin gene deletion. Although this is an out-of-frame deletion, which should not allow for protein synthesis, it has been observed in mildly affected patients. We describe a patient with an exon 45 deletion who produced protein, but still had a severe Duchenne muscular dystrophy phenotype. RT-PCR analysis and cDNA sequencing from the muscle biopsy sample revealed that the exon 45 deletion induced exon skipping of exon 44, which resulted in an in-frame deletion and the production of dystrophin. A conformational change in dystrophin induced by the deletion is proposed as being responsible for the severe phenotype in the patient. We feel that the variable clinical phenotype observed in patients with the exon 45 deletion is not due to exon splicing but may be the result of other environmental or genetic factors, or both. NEUROLOGY 1997;48: 486-488