Conclusions: RKIP does not inﬂuence the tumorigenic properties of human prostate cancer cells. It appears to be a novel and clinically
relevant suppressor of metastasis that may function by decreasing vascular invasion.
The Raf kinase inhibitor protein (RKIP) has been identiﬁed as a novel metastasis suppressor gene in prostate cancer. It is the thirteenth
metastasis suppressor gene with known functional data described in the literature. RKIP expression was detectable by immunohistochem-
istry in all noncancerous prostate tissues and decreased to an undetectable level in all prostate cancer metastases. To evaluate the role of
RKIP in cancer metastasis, the authors created a sense RKIP vector to increase RKIP expression in the invasive C4-2B prostate cancer cells
and an antisense RKIP vector to decrease RKIP expression in LNCaP prostate cancer cells. Expression of sense RKIP vector in C4-2B cells
was associated with an average 48.5% decrease in in vitro invasive ability among sense RKIP-transfected clones. In contrast, expression
of antisense RKIP vector in LNCaP cells resulted in an average 102.3% increase in in vitro invasive ability among antisense-transfected
clones. Although RKIP did not inﬂuence primary tumor growth, its expression decreased the number of lung metastases in the animal model.
Furthermore, lung metastases in these animals lacked RKIP expression, whereas RKIP was detectable in normal prostate tissue and primary
prostate tumors. Vascular invasion was also reduced independent of VEGF production. Antisense expression was associated with increased
MEK and ERK phosphorylation, suggesting the possibility that RKIP regulates tumor invasion through MEK activity. This article reinforces
the importance of the Ras/Raf/MEK/ERK signaling pathway in the control cancer metastasis and identiﬁes a new molecular therapeutic
Kwanchanit Tantivejkul, Ph.D., Kenneth J. Pienta, M.D.
Commentary on the next two abstracts follows the second abstract.
Differences in the cytokine proﬁles associated with prostate cancer cell induced osteoblastic and osteolytic lesions in bone. Lee Y,
Schwarz E, Davies M, Jo M, Gates J, Wu J, Zhang X, Lieberman JR, Department of Orthopaedic Surgery, UCLA School of Medicine, Los
J Orthop Res 2003;21:62–72
Prostate adenocarcinoma is associated with the formation of osteoblastic metastases in bone. It is hypothesized that osteoclastogenesis
is a critical component in the development of skeletal metastases. These ﬁndings, however, were generally noted in predominantly osteolytic
lesions. The pathophysiology of osteoblastic lesions remains unknown but the type of bone lesion formed may be inﬂuenced by the
cytokines produced by prostate tumors. To test this theory, we implanted PC-3 and LAPC-9 cells into the tibias of SCID mice. These mice
were sacriﬁced at 1, 2, 4, 6, and 8 weeks after implantation and histologic analysis was performed on these tibias. PCR analysis was also
performed on bulk tumors. The results showed that the PC-3 implanted tibias developed pure osteolytic lesions while the LAPC-9 implanted
tibias developed pure osteoblastic lesions on radiographs. Analysis of tibias after injection with PC-3 cells revealed progressive osteolytic
lesions with abundant osteoclast activity at 2 weeks and destruction of the proximal tibia at 6 weeks after cell implantation. In contrast, the
LAPC-9 cells formed osteoblastic lesions six weeks after cell injection. There were rare osteoclasts prior to the establishment of the
osteoblastic lesions but greater osteoclast activity was noted with remodeling of the osteoblastic lesion 8 weeks after implantation of the
tumor cells. PCR analysis revealed that PC-3 cells produced RANKL, IL-1, and TNF-
, which are associated with osteoclastogenesis. In
contrast, LAPC-9 cells produced osteoprotegerin, which blocks osteoclast production and no detectable levels of RANKL or IL-1 and only
minimal amounts of TNF-
were noted. These cells secreted BMP-2, -4, -6, and IL-6, which are associated with bone formation. These
results suggest that the role of the osteoclast in the development of a metastatic lesion is variable depending on the phenotype of the prostate
cancer cells, and that tumor-induced osteolysis may not be required for osteoblastic metastases.
Osteogenic activity of the fourteen types of human bone morphogenetic proteins (BMPs). Cheng H, Jiang W, Phillips FM, Haydon RC,
Peng Y, Zhou L, Luu HH, An N, Breyer B, Vanichakarn P, Szatkowski JP, Park JY, He TC, Department of Surgery, The University of
Chicago Medical Center, Chicago, IL.
J Bone Joint Surg Am 2003;85A:1544–52
Background: Bone morphogenic proteins (BMPs) are known to promote osteogenesis, and clinical trials are currently underway to
evaluate the ability of certain BMPs to promote fracture-healing and spinal fusion. The optimal BMPs to be used in different clinical
applications have not been elucidated, and a comprehensive evaluation of the relative osteogenic activity of different BMPs is lacking.
Methods: To identify the BMPs that may possess the most osteoinductive activity, we analyzed the osteogenic activity of BMPs in
mesenchymal progenitor and osteoblastic cells. Recombinant adenoviruses expressing fourteen human BMPs (BMP-2 to BMP-15) were
constructed to infect pluripotent mesenchymal progenitor C3H10T1/2 cells, preosteoblastic C2C12 cells, and osteoblastic TE-85 cells.
Osteogenic activity was determined by measuring the induction of alkaline phosphatase, osteocalcin, and matrix mineralization upon BMP
79K. Tantivejkul, K.J. Pienta / Urologic Oncology: Seminars and Original Investigations 22 (2004) 71–84