Loss-of-Function Mutations in PTPN11 Cause Metachondromatosis, but Not Ollier Disease or Maffucci Syndrome

Metachondromatosis (MC) is a rare, autosomal dominant, incompletely penetrant combined exostosis and enchondromatosis tumor syndrome. MC is clinically distinct from other multiple exostosis or multiple enchondromatosis syndromes and is unlinked to EXT1 and EXT2, the genes responsible for autosomal dominant multiple osteochondromas (MO). To identify a gene for MC, we performed linkage analysis with high-density SNP arrays in a single family, used a targeted array to capture exons and promoter sequences from the linked interval in 16 participants from 11 MC families, and sequenced the captured DNA using high-throughput parallel sequencing technologies. DNA capture and parallel sequencing identified heterozygous putative loss-of-function mutations in PTPN11 in 4 of the 11 families. Sanger sequence analysis of PTPN11 coding regions in a total of 17 MC families identified mutations in 10 of them (5 frameshift, 2 nonsense, and 3 splice-site mutations). Copy number analysis of sequencing reads from a second targeted capture that included the entire PTPN11 gene identified an additional family with a 15 kb deletion spanning exon 7 of PTPN11. Microdissected MC lesions from two patients with PTPN11 mutations demonstrated loss-of-heterozygosity for the wild-type allele. We next sequenced PTPN11 in DNA samples from 54 patients with the multiple enchondromatosis disorders Ollier disease or Maffucci syndrome, but found no coding sequence PTPN11 mutations. We conclude that heterozygous loss-of-function mutations in PTPN11 are a frequent cause of MC, that lesions in patients with MC appear to arise following a “second hit,” that MC may be locus heterogeneous since 1 familial and 5 sporadically occurring cases lacked obvious disease-causing PTPN11 mutations, and that PTPN11 mutations are not a common cause of Ollier disease or Maffucci syndrome

Occam’s razor need not apply: Advanced HIV infection presenting with five simultaneous opportunistic infections and central nervous system lymphoma

Patients with Human Immunodeficiency Virus (HIV) infection and Acquired Immunodeficiency Syndrome (AIDS) are at risk for multiple infectious and oncologic complications. In such cases, Occam’s razor need not apply: multiple infections and malignancies are often present concurrently upon presentation to care. A patient off anti-retroviral therapy (ART) for several years developed advanced HIV infection (CD4 count 19 cells/uL) and presented with five simultaneous opportunistic infections including Pneumocystis jiroveci pneumonia (PJP), cytomegalovirus (CMV) retinitis, Mycobacterium avium complex (MAC) bloodstream infection, chronic hepatitis B virus (HBV), and Epstein-Barr virus (EBV) viremia. Simultaneously, he was found to have primary central nervous system (CNS) B-cell lymphoma.Treatment decisions for such patients are often complex, as ideal therapy for one disease may directly counter or interact with therapy for another. For instance, methotrexate for primary CNS lymphoma and trimethoprim/sulfamethoxazole for PJP is a strictly contraindicated medication combination. It is important to understand not just the management of any single opportunistic disease in patients with advanced HIV, but how to balance management for patients with a variety of concurrent processes. In an era when HIV care is becoming increasingly simplified, patients presenting with advanced infection highlight the lack of data on how best to manage patients with multiple concurrent disease processes. Significant further research is needed to clarify ideal comparative therapy. Keywords: Human Immunodeficiency Virus, Acquired Immunodeficiency Disorder, Opportunistic infectio

Phenothiazines induce PP2A-mediated apoptosis in T cell acute lymphoblastic leukemia

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive cancer that is frequently associated with activating mutations in NOTCH1 and dysregulation of MYC. Here, we performed 2 complementary screens to identify FDA-approved drugs and drug-like small molecules with activity against T-ALL. We developed a zebrafish system to screen small molecules for toxic activity toward MYC-overexpressing thymocytes and used a human T-ALL cell line to screen for small molecules that synergize with Notch inhibitors. We identified the antipsychotic drug perphenazine in both screens due to its ability to induce apoptosis in fish, mouse, and human T-ALL cells. Using ligand-affinity chromatography coupled with mass spectrometry, we identified protein phosphatase 2A (PP2A) as a perphenazine target. T-ALL cell lines treated with perphenazine exhibited rapid dephosphorylation of multiple PP2A substrates and subsequent apoptosis. Moreover, shRNA knockdown of specific PP2A subunits attenuated perphenazine activity, indicating that PP2A mediates the drug's antileukemic activity. Finally, human T-ALLs treated with perphenazine exhibited suppressed cell growth and dephosphorylation of PP2A targets in vitro and in vivo. Our findings provide a mechanistic explanation for the recurring identification of phenothiazines as a class of drugs with anticancer effects. Furthermore, these data suggest that pharmacologic PP2A activation in T-ALL and other cancers driven by hyperphosphorylated PP2A substrates has therapeutic potential