Comparison of hypersensitivity reactions to PEG-asparaginase in children after intravenous and intramuscular administration.

INTRODUCTION: Polyethylene-glycolated (PEG)-asparaginase (PEG-ASP) is a crucial component of pediatric acute lymphoblastic leukemia therapy. Although hypersensitivity reactions to PEG-ASP occur less frequently than with other formulations, they are not uncommon and have an adverse impact on patient outcomes. Intravenous (IV) administration of PEG-ASP reduces patient pain and anxiety and is being used with increasing frequency in children. MATERIALS AND METHODS: A retrospective review was performed to compare the incidence of hypersensitivity reactions to PEG-ASP in children when administered either by intramuscular (IM) or IV routes between January 2006 and May 2008. RESULTS: Of 68 patients studied, 7 experienced a hypersensitivity reaction (10.3%). Two of 16 patients (12.5%) who received only IV PEG-ASP and 3 of 27 patients (11.1%) exposed to only IM PEG-ASP experienced a hypersensitivity reaction. Severe reactions (grade 3 or 4) occurred only once after 119 total doses (0.8%) of IV PEG-ASP and once after 215 total doses (0.5%) of IM PEG-ASP (P=1.0). Thrombosis or pancreatitis were rare and were not increased after IV PEG-ASP administration. DISCUSSION: IV PEG-ASP is well tolerated and does not result in a significant increase in the incidence of hypersensitivity reactions in children.

The use of zoledronic acid in pediatric cancer patients.

BACKGROUND: The third generation bisphosphonate zoledronic acid has demonstrated efficacy in reducing skeletal-related events in adult patients with multiple cancer types that have skeletal disease. The use of zoledronic acid in pediatric oncology patients with bone metastases for the purpose of reducing pain, improving bone strength and altering the progression of metastatic disease has not been thoroughly evaluated. PROCEDURE: From October 2005 to December 2008, 19 patients at the Aflac Cancer Center received one or more doses of zoledronic acid as part of their therapy. A retrospective review of these patients was performed and information was collected including indication for treatment, toxicities, and outcomes. RESULTS: Most patients (n = 15) received zoledronic acid following relapse of their malignancy with metastatic disease present in one or more bony sites. Hypocalcemia and hypophosphatemia were frequent, but did not result in clinical symptoms. More significant toxicities associated with zoledronic acid, including clinically apparent renal insufficiency and osteonecrosis of the jaw, were not seen. Overall, zoledronic acid was well tolerated in this population. CONCLUSIONS: The benefits of zoledronic acid seen in randomized trials of adults with bone metastases have sparked interest in its use for children with metastatic cancer. The administration of zoledronic acid in pediatric oncology appears safe, and may result in improved bone strength and pain control. Further evaluation is warranted to prospectively evaluate its efficacy and long-term safety in pediatric patients with cancer and skeletal metastases.

Mutations that mimic phosphorylation of the HIV-1 matrix protein do not perturb the myristyl switch.

Recent studies indicate that the matrix domain (MA) of the HIV-1 Gag polyprotein directs Gag to the plasma membrane for virus assembly via a phosphatidylinositol-4,5-bisphosphate (PIP(2))-dependent myristyl switch mechanism. MA also has been reported to direct nuclear trafficking via nuclear import and export functions, and some studies suggest that nuclear targeting may be regulated by MA phosphorylation (although this proposal remains controversial). We have prepared and studied a series of HIV-1 MA mutants containing Ser-to-Asp substitutions designed to mimic phosphorylation, including substitutions in regions of the protein involved in protein-protein interactions and known to influence the myristyl switch (S6D, S9D, S67D, S72D, S6D/S9D, and S67D/S72D). We were particularly interested in substitutions at residue 6, since conservative mutations adjacent to this site strongly perturb the myristyl switch equilibrium, and this site had not been genetically tested due to its involvement in post-translational myristylation. Our studies reveal that none of these mutations, including S6D, influences the PIP(2)- or concentration-dependent myristyl switch equilibrium. In addition, all of the mutants bind liposomes with affinities that are only slightly reduced in comparison with the native protein. In contrast, the myristylated mutants bind liposomes with substantially greater affinity than that of the native, unmyristylated protein. These findings support the hypothesis that phosphorylation is unlikely to significantly influence membrane-mediated intracellular trafficking.

Electrostatic interactions drive membrane association of the human immunodeficiency virus type 1 Gag MA domain.

The assembly of most retroviruses occurs at the plasma membrane. Membrane association is directed by MA, the N-terminal domain of the Gag structural protein. For human immunodeficiency virus type 1 (HIV-1), this association is mediated in part by a myristate fatty acid modification. Conflicting evidence has been presented on the relative importance of myristoylation, of ionic interactions between protein and membrane, and of Gag multimerization in membrane association in vivo. We addressed these questions biochemically by determining the affinity of purified myristoylated HIV-1 MA for liposomes of defined composition, both for monomeric and for dimeric forms of the protein. Myristoylation increases the barely detectable intrinsic affinity of the apo-protein for liposomes by only 10-fold, and the resulting affinity is still weak, similar to that of the naturally nonmyristoylated MA of Rous sarcoma virus. Membrane binding of HIV-1 MA is absolutely dependent on the presence of negatively charged lipid and is abrogated at high ionic strength. Forced dimerization of MA increases its membrane affinity by several orders of magnitude. When green fluorescent protein fusions of monomeric or dimeric MA are expressed in cells, the dimeric but not the monomeric protein becomes strongly membrane associated. Computational modeling supports these results and suggests a molecular mechanism for the modest effect of myristoylation on binding, wherein the membrane provides a hydrophobic environment for the myristate that is energetically similar to that provided by the protein. Overall, the results imply that the driving force for membrane association stems largely from ionic interactions between multimerized Gag and negatively charged phospholipids.

Biochemical characterization of rous sarcoma virus MA protein interaction with membranes.

The MA domain of retroviral Gag proteins mediates association with the host cell membrane during assembly. The biochemical nature of this interaction is not well understood. We have used an in vitro flotation assay to directly measure Rous sarcoma virus (RSV) MA-membrane interaction in the absence of host cell factors. The association of purified MA and MA-containing proteins with liposomes of defined composition was electrostatic in nature and depended upon the presence of a biologically relevant concentration of negatively charged lipids. A mutant MA protein known to be unable to promote Gag membrane association and budding in vivo failed to bind to liposomes. These results were supported by computational modeling. The intrinsic affinity of RSV MA for negatively charged membranes appears insufficient to promote efficient plasma membrane binding during assembly. However, an artificially dimerized form of MA bound to liposomes by at least an order of magnitude more tightly than monomeric MA. This result suggests that the clustering of MA domains, via Gag-Gag interactions during virus assembly, drives membrane association in vivo.