The purpose of this review was to determine whether imatinib mesylate (STI571, Gleevec) has a role in the treatment of osteosarcoma. The expression of plateletderived growth factor (PDGF) receptor and its ligand was examined in a panel of surgical specimens obtained from 54 osteosarcoma patients, and then the expression was compared with prognosis. The effects of imatinib mesylate on growth and molecular events in 10 patient-derived osteosarcoma cell cultures were investigated. Immunohistochemical studies demonstrated frequent expression of PDGF-AA (80.4%) and PDGF-a receptor (79.6%) and their correlation with inferior event-free survival (P < .05). PDGF-B-B and PDGF-b-receptor expressions were also frequent (75.4% and 86%, respectively); however, statistically significant inferior event-free survival was not demonstrated (P 5 .15). In vitro studies demonstrated that imatinib mesylate had a variable cytotoxic effect on various osteosarcoma primary cultures, with an IC 50 of 5.6 lM to 9.5 lM, and blocked the PDGF-induced intracellular signal transduction as well as inhibition of downstream Akt phosphorylation. Mitogen-activated protein kinase (MAPK) was constitutively activated despite PDGF stimulation and imatinib mesylate treatment in 7 of 10 osteosarcoma cultures, perhaps explaining uncontrolled proliferation and relative unresponsiveness to imatinib. Imatinib mesylate could not be viewed as having a role as a single agent at current conventional doses for the treatment of osteosarcoma. These findings predicted activity in osteosarcoma clinical trials and suggested that in vitro model systems predict clinical behavior and that PDGF and its receptor expression could potentially be used for determining prognosis of osteosarcoma.

Protein phosphatase inhibitors are often considered as tumor promoters. Protein phosphatase 1 regulatory subunit 1A (PPP1R1A) is a potent protein phosphatase 1 (PP1) inhibitor; however, its role in tumor development is largely undefined. Here we characterize, for the first time, the functions of PPP1R1A in Ewing sarcoma (ES) pathogenesis. We found that PPP1R1A is one of the top ranked target genes of EWS/FLI, the master regulator of ES, and is upregulated by EWS/FLI via a GGAA microsatellite enhancer element. Depletion of PPP1R1A resulted in a significant decrease in oncogenic transformation and cell migration in vitro as well as xenograft tumor growth and metastasis in an orthotopic mouse model. RNA-sequencing and functional annotation analyses revealed that PPP1R1A regulates genes associated with various cellular functions including cell junction, adhesion and neurogenesis. Interestingly, we found a significant overlap of PPP1R1A-regulated gene set with that of ZEB2 and EWS, which regulates metastasis and neuronal differentiation in ES, respectively. Further studies for characterization of the molecular mechanisms revealed that activation of PPP1R1A by PKA phosphorylation at Thr35, and subsequent PP1 binding and inhibition, was required for PPP1R1A-mediated tumorigenesis and metastasis, likely by increasing the phosphorylation levels of various PP1 substrates. Furthermore, we found that a PKA inhibitor impaired ES cell proliferation, tumor growth and metastasis, which was rescued by the constitutively active PPP1R1A. Together, these results offered new insights into the role and mechanism of PPP1R1A in tumor development and identified an important kinase and phosphatase pathway, PKA/PPP1R1A/PP1, in ES pathogenesis. Our findings strongly suggest a potential therapeutic value of inhibition of the PKA/PPP1R1A/PP1 pathway in the treatment of primary and metastatic ES.

Background Febrile neutropenia is a common reason for the hospitalization of pediatric oncology patients. The initiation of antibiotics and the overall decline in rates of bacteremia, would predict a low yield of detection of bacteremia in repeated blood cultures. Despite little evidence supporting the utility of serial cultures, repeat culturing with fever persists. Procedure To determine the rate of follow-up blood culture growth when the initial blood culture showed no bacterial growth and patient risk factors for this occurrence, we reviewed the records of oncology patients admitted to the Children's Hospital at Montefiore Pediatric Hematology/Oncology service for febrile neutropenia from 2004-2009. Results We identified 457 febrile neutropenia episodes in 137 patients. The initial blood culture was positive in 84 episodes (18.4%). In 220 episodes comprising 105 patients, the initial blood culture was negative and a subsequent culture was obtained. In 24 episodes (10.9%), bacterial growth was detected in the repeat culture. Risk factors included a previous history of bacteremia and hospitalization for more than 48 hours prior to onset of fever. Conclusions In patients with febrile neutropenia, bacteremia is detected nearly twice as frequently in initial blood cultures than in repeat blood cultures obtained when the initial blood culture is negative. Despite an initial negative blood culture, bacteremia can be detected in more than 10% of episodes when a repeat blood culture is obtained. The risk more than doubles for patients with a previous history of bacteremia or hospitalized for more than 48 hours prior to the onset of fever.