Study of renal cell carcinoma metastasized to the skeleton wins Lanier Award
By Joen Kinnan
Kristy Weber, MD; Michele Doucet, MS; and Scott Kominsky, PhD received the 2006 Kappa Delta Elizabeth Winston Lanier Award for their paper “Growth Factor Receptor Signaling Blockade in Renal Cell Carcinoma Bone Metastasis.”
Scott Kominsky, PhD, Michele Doucet, MS, and Kristy Weber, MD.
Patients with renal cell carcinoma (RCC) whose disease metastasizes to the bone enter a terminal phase with the possibility of severe, persistent pain; fractures; and spinal compression. Although other researchers have advanced the understanding of breast and prostate bone metastasis, this is the first significant work on RCC metastasized to bone.
Because this particular cancer in bone remains relatively resistant to both radiation and chemotherapy, Weber and her team anticipate that new treatments may derive from their five-year study of the biology of RCC bone metastasis. Their work included development of bone-derived cell lines and an experimental animal model as well as important advancements in the understanding of molecular signaling in RCC bone metastasis.
Developing an orthotopic model
“When we began this work in 2000,” reported Dr. Weber, “the only available models of RCC involved cell lines developed from primary kidney tumors used for renal subcapsule or subcutaneous injections in rodent models. An orthotopic model was necessary to study how RCC cells interact in the bone microenvironment with its unique population of osteoclasts, osteoblasts, endothelial cells, growth factors, and pro-angiogenic molecules.”
The team’s initial cell line—RBM1—used gross tissue from a metastatic RCC humeral lesion at risk for fracture. The RBM1 cells have high constitutive levels of the epidermal growth factor receptor (EGF-R) and c-Met. They express important cytokines involved in bone resorption and osteoclast activation.
Subsequently, select tissues from 35 Institutional Review Board-approved human bone metastasis tissues collected from patients requiring surgery yielded eight more bone-derived cell lines that grow continuously in cell culture. The research team also developed two cell lines from primary RCC.
“All of our cell lines overexpress the EGF-R and produce transforming growth factor-alpha (TGF-a) in an autocrine loop,” reported Dr. Weber. “Importantly, the EGF-R is also present in dividing endothelial cells.”
In the initial experimental nude mouse model, a six-week-old nude mouse received an injection of RBM1 cells directly into the tibia. Lytic lesions developed similar to those found in a clinical setting. Further manipulation of the RBM1 cell line yielded a more aggressive RBM1-IT4 subline that reduced the time to development of large lytic lesions.
Investigators injected equal numbers of RBM1 and RBM1-IT4 cells into the tibia and evaluated them at 11 weeks. “There was a marked difference in the extent of bone destruction between the cell lines,” reported Dr. Weber. “There was a more aggressive bone lesion and development of a soft tissue mass in the mice injected with RBM1-IT4 cells.”
Because this model provides a reliable reproduction of the clinical situation, and it allows for evaluation of the efficacy of targeted therapeutic interventions, the RBM1-IT4 cells were used for most in vivo experiments.
“RCC bone metastasis signals a potentially devastating change in the quality of life for patients with this disease,” wrote Dr. Weber. “Clinically their care is challenging for the orthopaedic surgeon because of the highly lytic, vascular nature of the tumors. To affect any improvement in survival from this inherently chemo- and radioresistant disease, a better understanding of the molecular mechanisms is required.”
Understanding molecular mechanisms
Using the novel bone-derived RCC cell lines and the experimental mouse model developed in their laboratory, these researchers were the first to document the importance of the TGF-a/EGF-R signaling pathway in RCC bone metastasis.
“These EGF-R signaling mechanisms have been associated with development and progression of RCC metastasis, but the importance of this pathway was not previously demonstrated in bone metastasis,” said Dr. Weber.
Over a two-year period, the team used multiple agents to inhibit the TGF-a/EGF-R pathway in their RCC cell lines. They were able to successfully demonstrate, both in vitro and in vivo, that blocking this pathway is effective in decreasing tumor growth and bone destruction.
Another important contribution was the further definition of molecular events that occur between RCC cells and local host cells in the bone microenvironment. In humans, bone is the most abundant repository for TGF-b, which is released during osteoclast-mediated bone destruction. Therefore, it seemed likely that TGF-b plays a role in the targeting or growth of metastatic tumors within the bone.
In another nude mouse study, “RCC cells with a defective TGF-β recptor produced smaller tumors and less bone destruction than the control cells,” said Dr. Weber. “These data suggest that TGF-b plays a substantial role in the growth of RCC bone metastasis.”
The authors also suggested the need for further studies to identify molecular targets with less potential morbidity, including cytokines, MMPs, and growth factors stimulated by TGF-b that are also involved in bone destruction.
Dr. Weber is an associate professor in the Departments of Orthopaedic Surgery and Oncology at Johns Hopkins University; Dr. Kominsky is assistant director of the Orthopaedic Basic Science Laboratory at Johns Hopkins.