Anti–Prostate-Specific Membrane Antigen Liposomes Loaded with²²⁵Ac for Potential Targeted Antivascular α-Particle Therapy of Cancer

Abstract

This study evaluates targeted liposomes loaded with the a-particle generator 225 Ac to selectively kill prostate-specific membrane antigen (PSMA)-expressing cells with the aim to assess their potential for targeted antivascular radiotherapy. Methods: In this study, PEGylated liposomes were loaded with 225 Ac and labeled with the mouse antihuman PSMA J591 antibody or with the A10 PSMA aptamer. The targeting selectivity, extent of internalization, and killing efficacy of liposomes were evaluated on monolayers of prostate cancer cells intrinsically expressing PSMA (human LNCaP and rat Mat-Lu cells) and on monolayers of HUVEC induced to express PSMA (induced HUVEC). Results: The loading efficiency of 225 Ac into preformed liposomes ranged from 58.0% 6 4.6% to 85.6% 6 11.7% of introduced radioactivity. The conjugation reactions resulted in approximately 17 6 2 J591 antibodies and 9 6 2 A10 aptamers per liposome. The average size of liposomes, 107 6 2 nm in diameter, was not affected by conjugation or loading. LNCaP cells exhibit 2:1:0.5 relative PSMA expression, compared with MatLu and induced HUVEC, respectively, based on flow cytometry detecting association of the J591 antibody. J591-labeled liposomes display higher levels of total specific binding to all cell lines than A10 aptamer-labeled liposomes. Specific cell association of targeted liposomes increases with incubation time. Cytotoxicity studies demonstrate that radiolabeled J591-labeled liposomes are most cytotoxic, with median lethal dose values, after 24 h of incubation, equal to 1.96 (5.3 · 10 25 ), 2.92 · 10 2 (7.9 · 10 23 ), and 2.33 · 10 1 Bq/mL (6.3 · 10 24 mCi/mL) for LNCaP, Mat-Lu, and induced HUVEC, respectively, which are comparable to the values for the radiolabeled J591 antibody. For A10 aptamer-labeled liposomes, the corresponding values are 3.70 · 10 1 (1.0 · 10 23 ), 1.85 · 10 3 (5.0 · 10 22 ), and 4.07 · 10 3 Bq/mL (1.1 · 10 21 mCi/mL), respectively. Conclusion: Our studies demonstrate that anti-PSMA-targeted liposomes loaded with 225 Ac selectively bind, become internalized, and kill PSMA-expressing cells including endothelial cells induced to express PSMA. These findings-combined with the unique ability of liposomes to be easily tuned, in terms of size and surface modification, for optimizing biodistributions-suggest the potential of PSMA-targeting liposomes encapsulating a-particle emitters for selective antivascular a radiotherapy.

Radionuclide therapy using 131I-labeled anti-epidermal growth factor receptor-targeted nanoparticles suppresses cancer cell growth caused by EGFR overexpression

“…The use of active targeting radionuclide nanoparticles in internal radiotherapy has been successfully employed to image and treat tumor models preclinically. These radionuclide nanoparticles include human atherosclerotic plaque-specific peptide-1-targeted 111 In-labeled liposomes (Yang et al 2012), monoclonal antinuclear autoantibody 2C5 (mAb 2C5) targeting 111 In-immunoliposome for lung carcinoma (Elbayoumi et al 2007), α v β 3 -integrintargeted 111 In perfluorocarbon nanoparticles for targeted tumor imaging (Hu et al 2007), rituximab targeting 111 In carbon nanotubes for targeted tumor imaging (McDevitt et al 2007), RGD-or VEGF-targeted 64 Cu quantum dots or iron oxide for PET/NIRF and PET/MRI imaging Lee et al 2008), EGFR-targeted 99m Tc-chelated quantum dots for breast cancer imaging and therapy (Jung et al 2011), RGD-targeted 125 I-labeled gold nanoparticles for tumor imaging (Kim et al 2011), HER2-targeted nanoparticles loaded with an 125 I-labeled DNA intercalator (Fondell et al 2011), anti-prostate-specific membrane antigen nanoparticles loaded with 225 Ac for potential targeted anti-vascular α-particle therapy (Bandekar et al 2014), 76 Br-labeled RGD-directed-dendritic nanoprobes for PET imaging (Almutairi et al 2009), and integrin antagonist or anti-Flk-1 antibody-coated 90 Y-labeled nanoparticles (Li et al 2004).…”

Improving vascular maturation using noncoding RNAs increases antitumor effect of chemotherapy

“…has been conjugated to doxorubicin micelles, which led to an increased uptake by PSMA-positive CWR22R-nu1 prostate cancer cells and resulted in higher cytotoxicity than that achieved using nontargeting micelles (25). More recently, a similar strategy was used in constructing 225 Ac-loaded liposomes to target and selectively kill PSMA-expressing cells such as LNCaP, Mat-Lu, and HUVEC using radiation (26). However, aptamers utilized in these studies were selected on the basis of binding to isolated surface markers or recombinant proteins, which might poorly reflect the native protein conformations owing to denaturing conditions during purification (27,28).…”

Targeted and Nontargeted α-Particle Therapies

“…In cytotoxicity studies against human umbilical vein en-dothelial cells that were induced to express human PSMA, Bandekar et al (104) demonstrated that targeted liposomes exhibited comparable median lethal dose values to the values measured for the radiolabeled J591 antibody.…”