ABSTRACT
Purpose: Radium-223 dichloride (radium-223, Xofigo), a targeted alpha therapy, is currently used for the treatment of patients with castration-resistant prostate cancer (CRPC) with bone metastases. This study examines the mode-of-action and antitumor efficacy of radium-223 in two prostate cancer xenograft models.Experimental Design: Mice bearing intratibial LNCaP or LuCaP 58 tumors were randomized into groups (n = 12-17) based on lesion grade and/or serum PSA level and administered radium-223 (300 kBq/kg) or vehicle, twice at 4-week intervals. X-rays and serum samples were obtained biweekly. Soft tissue tumors were observed macroscopically at sacrifice. Tibiae were analyzed by gamma counter, micro-CT, autoradiography and histology.Results: Radium-223 inhibited tumor-induced osteoblastic bone growth and protected normal bone architecture, leading to reduced bone volume in LNCaP and abiraterone-resistant LuCaP 58 models. Furthermore, radium-223 resulted in lower PSA values and reduced total tissue and tumor areas, indicating that treatment constrains prostate cancer growth in bone. In addition, radium-223 suppressed abnormal bone metabolic activity as evidenced by decreased number of osteoblasts and osteoclasts and reduced level of the bone formation marker PINP. Mode-of-action studies revealed that radium-223 was deposited in the intratumoral bone matrix. DNA double-strand breaks were induced in cancer cells within 24 hours after radium-223 treatment, and PSA levels were significantly lower 72 hours after treatment, providing further evidence of the antitumor effects.Conclusions: Taken together, radium-223 therapy exhibits a dual targeting mode-of-action that induces tumor cell death and suppresses tumor-induced pathologic bone formation in tumor microenvironment of osseous CRPC growth in mice. Clin Cancer Res; 23(15); 4335-46. ©2017 AACR.
Subject(s)
Antineoplastic Agents/administration & dosage , Bone Neoplasms/radiotherapy , Prostatic Neoplasms, Castration-Resistant/radiotherapy , Radium/administration & dosage , Animals , Bone Neoplasms/pathology , Bone Neoplasms/secondary , Bone and Bones/pathology , Bone and Bones/radiation effects , Cell Line, Tumor , Cell Proliferation/radiation effects , Disease Models, Animal , Humans , Male , Mice , Osteoclasts/radiation effects , Prostatic Neoplasms, Castration-Resistant/pathology , Radioisotopes/administration & dosage , Tumor Microenvironment/radiation effectsABSTRACT
MicroRNAs are small non-coding RNAs that control gene expression at the post-transcriptional level by binding to 3'-untranslated regions (3'-UTR) of their target mRNAs. They present a promising tool to delineate the molecular mechanisms regulating differentiation of human mesenchymal stromal cells (hMSCs) and to improve the controlled differentiation of hMSCs in therapeutic applications. Here we show that three microRNAs, miR-96, miR-124, and miR-199a, were differentially expressed during osteogenic, adipogenic, and chondrogenic induction of human bone marrow-derived MSCs. miR-96 expression was increased during osteogenesis and adipogenesis, but not during chondrogenesis. miR-124 was exclusively expressed in adipocytes, whereas miR-199a was upregulated in osteoblasts and chondrocytes. Furthermore, functional studies with synthetic miRNA precursors and inhibitors demonstrated that miR-96, miR-124, and miR-199a regulated the expression of genes important for hMSC differentiation, such as aggrecan, transcription factor SOX9, and fatty acid binding protein 4 (FABP4). Modulation of miR-96, miR-124, and miR-199a expression may thus be useful in specific targeting of hMSC differentiation, for e.g., MSC-based therapies. J
