Complement C3 mediated targeting of liposomes to granulocytic myeloid derived suppressor cells

Abstract

In cancer patients, granulocytic myeloid derived suppressor cells (G-MDSCs) expand in number, infiltrating tumor and lymphatic tissues where they suppress an anti-tumor immune response. We report here the development of a liposomal drug delivery system that selectively targets GMDSCs. The liposomes form a disulfide bond with activated complement C3 after intravenous injection and are taken up by G-MDSCs, which express the receptor for activated C3. In vitro experiments utilizing serum from a C3 knockout mouse demonstrate that G-MDSCs take up these liposomes in a C3-dependent manner. After systemic administration to tumor bearing mice, liposomes were incorporated by 22% of G-MDSCs in the blood and were also present in a percentage of G-MDSCs in the tumor (11%), spleen (22%), liver (35%) and lungs (26%). This liposomal system offers a versatile means of targeted drug delivery to G-MDSCs and could be an important tool for restoring anti-tumor immunity in cancer patients.

Complement C3-dependent uptake of targeted liposomes into human macrophages, B cells, dendritic cells, neutrophils, and MDSCs

“…6,7 Western blot analysis reveals that incubation of OPSS-liposomes in serum for 1 hour allows conjugation of C3b to the liposomes and that this binding is relatively specific with little other protein attached. C3b targets the complement CR1 receptor, but can be further metabolized to iC3b and C3dg, which …”

“…6,7 Various strategies have been employed in the nanoparticle field to target macrophages and dendritic cells including cationic, mannose, Fc-targeted, CD11c-targeted, and DC-SIGN-targeted liposome carriers. 8,9 These have had various degrees of success, but often have the drawback of requiring complex targeting molecules or antibodies that present challenges to large-scale production and storage.…”

“…9 To overcome these shortcomings and challenges, we have designed a system that utilizes the patient's own endogenous complement C3. 7 The liposomes would bind to C3 after injection, resulting in targeting to cell types that have the receptor for C3. The system utilizes small molecules that would allow for scaling up and storage, binds to endogenous C3 which would cut down on toxicities, and targets a wide variety of immune cells that regulate the antitumor immune response.…”

“…In a previous study, we have shown that liposomes containing OPSS bind to complement C3 in mouse serum, resulting in uptake by immune cells that have the receptor for complement. 7 We went on to show that upon systemic administration into tumor-bearing mice, liposomes were taken up by MDSCs which infiltrated the spleen and tumor. 7 The goal of the current study was to establish if the liposomes also bound to human complement C3, and if so to fully characterize the cell types in human blood that engulf C3 bound liposomes using flow cytometry analysis.…”

“…33,34 While overactivation of the complement system is a concern, preliminary studies in mice with systemic administration of C3-liposomes did not appear to cause any signs of distress. 7 The tumor microenvironment causes an overall suppression of the immune system, so there is a possibility that activation of immune cells upon binding of the complement receptor could be beneficial. 18,35 More experimentation will be done to characterize the response of immune cells to C3-liposomes.…”