Abstract 5231: Zoledronic acid encapsulated into liposomes and nanoparticles: Enhanced antitumor activity in 3D-prostate carcinoma spheroids
Authors: Ohlmann Carsten , Schmidt Johannes , Kamradt Joern , Stoeckle Michael , Salzano Giuseppina , Junker Kerstin , Caraglia Michele , Rosa Giuseppe De , Unteregger Gerhard 
Published: August 2012

Abstract
Introduction: Zoledronic acid is currently used for the treatment of bone metastases in hormone-resistant prostate cancer patients. The rapid plasma half-life and the high affinity for Osteoclasts, the primary targets of bisphosphonates, limit the use for extra-skeletal tissues. Moreover, it remains still unclear, whether cancer-associated fibroblasts (CAF) influence the toxicity of ZOL. The use of nanomedicine is one promising strategy to improve the availability of drugs within the tumor tissue. To investigate the benefit of such approach, we used two different nanovectors encapsulating ZOL on 3D-spheroids from prostate carcinoma cells and CAF in combination with standard toxicity assays. Material and Methods: Stealth liposomes (PGNP_ZOL) and a new generation of nanovector, named self-assembly nanoparticles (NP_ZOL), were prepared using standard protocols already described. The prostate carcinoma cell lines PC-3, DU-145 and LNCaP were cultivated in 96-well MTP's and as Spheroids on agarose coated 96-well MTP's. Heterologous spheroids were prepared by mixing tumor cells with different ratios of normal (NAF) or tumor-associated (CAF) fibroblasts. Cell cultures/spheroids were incubated with ZOL, NP_ZOL/PGNP_ZOL for up to 120 h. Changes in growth behavior and toxicity (apoptosis/necrosis) were quantified from spheroid-cultures by modifications of standard assays (CDD+, LDH+). The adaptability of these techniques for 3D- cultures was assessed using thapsygargin/tunicamycin as apoptosis-inducing agents. Results: Standard-viability assays revealed a significant enhancement of antitumor activity of NP_ZOL/PGNP_ZOL as compared to the free drug in cell cultures of DU-145 and LNCaP, whereas these effects were less pronounced in PC-3 cells. The antitumor efficacy of NP_ZOL/PGNP_ZOL was caused by a strong inhibition of tumor cell proliferation as revealed by the BrDU-assay; on the other hand, both CDD+ and LDH+ failed to detect both apoptosis and necrosis after drug treatment for up to 120 h. The average IC50 values in the tumor cells ranges from 10-20µM/L, but the fibroblasts exhibit complete growth inhibition at concentrations between 2-5µm/L ZOL. Conclusion: These results confirm the hypothesis that the use of nanomedicine enables the extension in therapeutic applications of drugs such as bisphosphonates. In this context, ZOL seems to exert benefits even onto the primary tumor cells. Homo-/heterologeous 3D-spheroids offer advanced models mimicking the microenvironment within a tumor tissue grows thus bridging the gap between cell culture and live tissue. Moreover, the rapid generation of single-tumor spheroids allows for a high-throughput cell function and toxicity analysis.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5231. doi:1538-7445.AM2012-5231