These results suggest that the effective numbers of -particles emitted at the target per delivered 225Ac using MUVELs could be significant, thus providing a promising therapeutic modality for disseminated micrometastatic disease. -particle emitting daughters. Retention of 225Ac daughters at BQ-123 the target increases efficacy; escape and distribution throughout the body increases toxicity. During circulation, molecular carriers conjugated to 225Ac cannot retain any of the daughters. We previously proposed liposomal encapsulation of 225Ac to retain the daughters, whose retention was shown to be liposome-size dependent. However, daughter retention was lower than expected: 22% of theoretical maximum decreasing to 14%, partially due to binding of 225Ac to the phospholipid membrane. In this study, MUltiVEsicular Liposomes (MUVELs) composed of different phospholipids were developed to increase BQ-123 daughter retention. MUVELs are large liposomes with entrapped smaller lipid-vesicles containing 225Ac. PEGylated MUVELs stably retained over time 98% of encapsulated 225Ac. Retention of 213Bi, the last daughter, was 31% of the theoretical maximum retention of 213Bi for the liposome sizes studied. MUVELs were conjugated to an anti-HER2/neu antibody (immunolabeled MUVELs), and were evaluated with SKOV3-NMP2 ovarian cancer cells, exhibiting significant cellular internalization (83%). This work demonstrates that immunolabeled MUVELs Mouse monoclonal to CD69 could be able to deliver higher fractions of generated -particles per targeted 225Ac compared to the relative fractions of -particles delivered by 225Ac-labeled molecular carriers. for targeted delivery of 225Ac to ovarian carcinoma cells (SKOV3-NMP2). Open in a separate window Figure 1 Cryo-TEM image of multivesicular liposomes (horizontal edge is approximately 400 nm), and schematic representation of MUltiVEsicular Liposomes (MUVELs) and their components. Experimental Procedures (Materials and Methods) Reagents The lipids 1,2-Dimyristoyl-biodistributions of 225Ac-loaded immunolabeled-liposomes (MUVELs and LLs) that were administered intraperitoneally in BALB/c nude mice bearing intraperitoneally disseminated SKOV3-NMP2 tumors resembling micrometastatic disease (37), suggest that MUVELs retain 225Ac to a larger extent than LLs, and therefore deliver higher activities of 213Bi to the tumor sites. In addition, both types of immunoliposome compositions exhibit significant hepatic and splenic uptake that is characteristic of this size of drug carriers and could determine the maximum tolerated dose. The short range of alpha-particles emitted at the sites of normal organs could, however, result in relatively low toxicities at these organs due to the short range of alpha-particles. Finally, immunolabeled MUVELs may be particularly useful in delivering lethal radiation doses to cancer cells with low expression levels of molecular targets (38). Actinium-225 labeled antibodies have generally low specific activity (1.406 MBq/mg in this study) that corresponds to one conjugated 225Ac atom per 2,300 antibodies. For MUVELs, two passive entrapment steps are required (each with a maximum of 10% encapsulation efficiency). Thus, for 370 MBq (10mCi) 225Ac initial activity, and 1% actinium overall entrapment efficacy, we can encapsulate one actinium nuclide per MUVEL and two actinium nuclides in every 8 MUVELs (for 41012 liposomes with a mean diameter of 750nm). Our current work is focused on increasing the encapsulated 225Ac BQ-123 activity within small vesicles using active (ionophore-driven) loading (39). Additional structural optimization of MUVELs is also required to further increase 213Bi retention at the liposome sites. Intraperitoneal micrometastatic disease constitutes a treatment challenge, and is common among patients with advanced gynecological and gastrointestinal cancers. In this work, the ovarian carcinoma cells SKOV3-NMP2 were selected to prove, em in vitro /em , the feasibility of targeted delivery of the -particle nanogenerator 225Ac and its radioactive daughters using immunolabeled MUVELs that can potentially be used against disseminated intraperitoneal micrometastases following locoregional administration. Our findings show that immunolabeled MUVELs retain a third of the theoretical maximum of the radioactive daughters, BQ-123 and the cell bound structures become considerably more internalized by ovarian cancer cells than the radiolabeled antibody. These results suggest that the effective numbers of -particles emitted at the target per delivered 225Ac using MUVELs could be significant, thus providing a promising therapeutic modality for disseminated micrometastatic disease. Additional optimization of MUVELs is necessary to increase the encapsulated radioactivity of 225Ac in order to enable the evaluation of these liposomes potential for therapeutic use. Additional increase in daughter retention could be achieved by further increasing the size of the delivery carrier (to 1 1 micron diameter), but given the limitations of stable intact liposomes of such large diameters, probably different materials could be evaluated BQ-123 to form the outer large shell encapsulating Small Vesicles (SVs) with entrapped 225Ac. Supplementary Material 1File001Supporting Information Available: Binding of rhodamine-lipid-containing immuno-liposomes to HER2/neu expressing SKOV3-NMP2 cells by flow cytometry. Two types of immunoliposomes were evaluated: liposomes that were labeled with the anti-HER2/neu antibody Trastuzumab (green line), and liposomes labeled with an isotype-control antibody, Rituximab (blue line). Red line: SKOV3-NMP2 cells alone. Click here to view.(59K, pdf) Acknowledgments Work supported by the USAMRMC Concept Award DAMD170010657, USAMRMC IDEA Award DAMD170310755, NIH R01 CA55349, the Experimental Therapeutics Center, and the Goodwin Commonwealth Foundation for Cancer Research. D.A.S. is a Doris Duke Distinguished Science Professor. S.S. is the recipient of Dr. Frederick E.G. Valergakis Graduate Research Grant of the Hellenic University Club.