Paclitaxel-loaded iron platinum stealth immunomicelles are potent MRI imaging agents that prevent prostate cancer growth in a PSMA-dependent manner

Robert M Taylor1 Department of Biochemistry and Molecular Biology;2 New Mexico Cancer Nanoscience and Microsystems Training CenterCorrespondence[email protected]

Laurel O Sillerud1 Department of Biochemistry and Molecular Biology;3 UNM Cancer Center, University of New Mexico, Albuquerque, NM, USA

Abstract

Background and methods

Problems with the clinical management of prostate cancer include the lack of both specific detection and efficient therapeutic intervention. We report the encapsulation of superparamagnetic iron platinum nanoparticles (SIPPs) and paclitaxel in a mixture of polyethyleneglycolated, fluorescent, and biotin-functionalized phospholipids to create multifunctional SIPP-PTX micelles (SPMs) that were conjugated to an antibody against prostate-specific membrane antigen (PSMA) for the specific targeting, magnetic resonance imaging (MRI), and treatment of human prostate cancer xenografts in mice.

Results

SPMs were 45.4 ± 24.9 nm in diameter and composed of 160.7 ± 22.9 μg/mL iron, 247.0 ± 33.4 μg/mL platinum, and 702.6 ± 206.0 μg/mL paclitaxel. Drug release measurements showed that, at 37°C, half of the paclitaxel was released in 30.2 hours in serum and two times faster in saline. Binding assays suggested that PSMA-targeted SPMs specifically bound to C4-2 human prostate cancer cells in vitro and released paclitaxel into the cells. In vitro, paclitaxel was 2.2 and 1.6 times more cytotoxic than SPMs to C4-2 cells at 24 and 48 hours of incubation, respectively. After 72 hours of incubation, paclitaxel and SPMs were equally cytotoxic. SPMs had MRI transverse relaxivities of 389 ± 15.5 Hz/mM iron, and SIPP micelles with and without drug caused MRI contrast enhancement in vivo.

Conclusion

Only PSMA-targeted SPMs and paclitaxel significantly prevented growth of C4-2 prostate cancer xenografts in nude mice. Furthermore, mice injected with PSMA-targeted SPMs showed significantly more paclitaxel and platinum in tumors, compared with nontargeted SPM-injected and paclitaxel-injected mice.

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Acknowledgements

This research was supported in part by funding from the National Institutes of Health (5RO1CA123194 to LOS) and the NCI New Mexico Cancer Nanotechnology Training Center (NIH R25CA153825 supporting RMT). Portions of this work were performed at the Center for Integrated Nano-technologies, a US Department of Energy, Office of Basic Energy Sciences, user facility. Sandia National Laboratories is a multiprogram laboratory operated by The Sandia Corporation, a Lockheed-Martin Company, for the US Department of Energy under Contract No DE-AC04-94AL85000. MRI was performed at the Brain Imaging Center, Albuquerque, NM. TEM images were generated at the UNM Electron Microscopy Facility. Some experiments used the facilities provided by the Keck-UNM Genomics Resource, a facility supported by grants from the WM Keck Foundation, the State of New Mexico, and the UNM Cancer Research and Treatment Center. We gratefully acknowledge the assistance of Medhi Ali of the Earth and Planetary Sciences Department at UNM, for the ICP-OES analyses, of Stephen Jett from the UNM Electron Microscopy Facility, and of Dale Huber from the Center for Integrated Nanotechnologies.

Disclosure

The authors report no conflicts of interest in this work.

Supplementary figures

Figure S1 Body weights of mice bearing C4-2 xenografts that were injected with treatments or controls.

Notes: Mice bearing C4-2 human prostate cancer cell xenografts were injected with the treatments or controls and weighed on the day of injection and on the day of euthanasia. None of the mice showed significant differences in loss of body weight over the 20 days.

Figure S2 Tissue weights of mice bearing C4-2 xenografts that were injected with treatments or controls.

Notes: Mice bearing C4-2 xenografts were injected with J591-SPMs (white bars), J591-SMs (gray bars), IgG-SPMs (blue bars), PTX alone (beige bars), or nothing (black bars) and 20 days later their tissues and tumors were collected and weighed. None of the mice showed significant differences in tissue weights post-mortem, although the mice injected with PTX alone, J591-SPMs, and IgG-SPMs showed decreased tumor mass compared to mice injected with SIPP-micelles without drug and mice that were not injected. *corresponds to significance of P < 0.05.

Figure S3 Hematoma around the tumors of mice injected with PTX alone. Representative images are shown for mice injected with PTX alone (A) and J591-SPMs (B) taken post-mortem. The mice injected with PTX alone clearly had extensive hematoma around the tumors and all along the right flanks, whereas the mice injected with J591-SPMs did not have this side effect, suggesting that in addition to targeting the drug, encapsulation of the drug also reduced side effects.