Control of capillary formation by membrane-anchored extracellular inhibitor of phospholipase A(2)

Secretory phospholipase A2 responsive liposomes exhibit a potent anti-neoplastic effect in vitro, but induce unforeseen severe toxicity in vivo

The clinical use of liposomal drug delivery vehicles is often hindered by insufficient drug release. Here we present the rational design of liposomes optimized for secretory phospholipase A₂ (sPLA₂) triggered drug release, and test their utility in vitro and in vivo. We hypothesized that by adjusting the level of cholesterol in anionic, unsaturated liposomes we could tune the enzyme specificity based on membrane fluidity, thus obtaining liposomes with an improved therapeutic outcome and reduced side effects. Cholesterol is generally important as a component in the membranes of liposome drug delivery systems due to its stabilizing effects in vivo. The incorporation of cholesterol in sPLA₂ sensitive liposomes has not previously been possible due to reduced sPLA₂ activity. However, in the present work we solved this challenge by optimizing membrane fluidity. In vitro release studies revealed enzyme specific drug release. Treatment of two different cancer cell lines with liposomal oxaliplatin revealed efficient growth inhibition compared to that of clinically used stealth liposomes. The in vivo therapeutic effect was evaluated in nude NMRI mice using the sPLA₂ secreting mammary carcinoma cell line MT-3. Three days after first treatment all mice having received the novel sPLA₂ sensitive liposome formulation were euthanized due to severe systemic toxicity. Thus the present study demonstrates that great caution should be implemented when utilizing sPLA₂ sensitive liposomes and that the real utility can only be disclosed in vivo. The present studies have clinical implications, as sPLA₂ sensitive formulations are currently undergoing clinical trials (LiPlaCis®).

A bactericidal homodimeric phospholipases A2 from Bungarus fasciatus venom

Group IIA secretory phospholipases A(2) (sPLA(2)-II) is generally known to display potent gram-positive bactericidal activity, while group IA sPLA(2) (sPLA(2)-I) reportedly is not. In this work, a novel sPLA(2)-I named BFPA was identified from Bungarus fasciatus venom, and its antimicrobial activity was studied as well. The amino acid sequence of the venomous protein precursor was 145-amino acid in length, and contained a predicted 27-amino acid signal peptide and a 118-amino acid mature protein. Unlike the well-known sPLA(2)-Is, which have 14 half-cysteines forming 7 intramolecular disulfide bridges, BFPA possesses 15 half-cysteines. The additional cysteine might contribute to the formation of an intermolecular disulfide bridge of the homodimeric protein. In the biological activities assays, BFPA displayed the activities of anticoagulation and bactericidal against Escherichia coli and Staphylococcus aureus. This study is the first report about gram-positive bactericidal activity of sPLA(2)-I.

Secretory phospholipase A2 as a tumor-specific trigger for targeted delivery of a novel class of liposomal prodrug anticancer etherlipids

The use of many common clinically relevant chemotherapeutics is often limited due to insufficient delivery to the tumor and dose-limiting systemic toxicities. Therefore, therapeutics that specifically target tumor cells and are nontoxic to normal cells are required. Here, we report the development of a novel class of liposomes composed of lipid prodrugs, which use the increased secretory phospholipase A2 type IIA (sPLA2) activity of the tumor microenvironment as a trigger for the release of anticancer etherlipids (AEL). Treatment of sPLA2-secreting tumor cells in vitro with liposomes consisting of proAELs resulted in growth inhibition comparable with addition of the AELs alone. Using a specific sPLA2 inhibitor, we showed the low cytotoxicity of the nonhydrolyzed proAEL liposomes and have proven the sPLA2 dependency of the activation of proAELs to cytotoxic AELs. In addition, we showed that our proAEL liposomes circumvent the inherent hemolytic toxicities associated with the use of etherlipids, thereby allowing i.v. administration of such therapeutics as nontoxic prodrug liposomes. Furthermore, using a sPLA2-secreting human colon cancer xenograft model, we showed that the proAEL liposomes are capable of inducing a tumor growth delay in vivo. Taken together, these data support the validity of this novel tumor-selective liposomal prodrug delivery strategy. This new approach also provides a promising system for tumor-selective delivery and release of conventional chemotherapeutics encapsulated in the sPLA2-degradable prodrug liposomes.

Phospholipase A2 expression in tumours: a target for therapeutic intervention?

Phospholipase A(2) (PLA(2)) enzymes are involved in lipid metabolism and, as such, are central to several cellular processes. The different PLA(2)s identified to date can be classified into three groups: secreted PLA(2) (sPLA(2)), calcium-independent PLA(2) (iPLA(2)) and calcium-dependent cytosolic PLA(2) (cPLA(2)). In addition to their role in cellular signalling, PLA(2)s have been implicated in diverse pathological conditions, including inflammation, tissue repair and cancer. Elevated levels of sPLA(2) and cPLA(2) have been reported in several tumour types. Here, we summarize the current views on the PLA(2)s, and look at their expression, role in human malignancy and potential as targets for anticancer drug development.