Inhibition of Prostate Cancer Osteoblastic Progression with VEGF121/rGel, a Single Agent Targeting Osteoblasts, Osteoclasts, and Tumor Neovasculature

Authors

Khalid A. Mohamedali, Zhi Gang Li, Michael W. Starbuck, Xinhai Wan, Jun Yang, Sehoon Kim, Wendy Zhang, Michael G. Rosenblum, and Nora M. Navone

Abstract

A hallmark of prostate cancer (PCa) progression is the development of osteoblastic bone metastases, which respond poorly to available therapies. We previously reported that VEGF121/rGel targets osteoclast precursors and tumor neovasculature. Here we tested the hypothesis that targeting nontumor cells expressing these receptors can inhibit tumor progression in a clinically relevant model of osteoblastic PCa. Experimental Design: Cells from MDA PCa 118b, a PCa xenograft obtained from a bone metastasis in a patient with castrate-resistant PCa, were injected into the femurs of mice. Osteoblastic progression was monitored following systemic administration of VEGF121/rGel. VEGF121/rGel was cytotoxic in vitro to osteoblast precursor cells. This cytotoxicity was specific as VEGF121/rGel internalization into osteoblasts was VEGF121 receptor driven. Furthermore, VEGF121/rGel significantly inhibited PCa-induced bone formation in a mouse calvaria culture assay. In vivo, VEGF121/rGel significantly inhibited the osteoblastic progression of PCa cells in the femurs of nude mice. Microcomputed tomographic analysis revealed that VEGF121/rGel restored the bone volume fraction of tumor-bearing femurs to values similar to those of the contralateral (non–tumor-bearing) femurs. VEGF121/rGel significantly reduced the number of tumor-associated osteoclasts but did not change the numbers of peritumoral osteoblasts. Importantly, VEGF121/rGel-treated mice had significantly less tumor burden than control mice. Our results thus indicate that VEGF121/rGel inhibits osteoblastic tumor progression by targeting angiogenesis, osteoclastogenesis, and bone formation. Targeting VEGF receptor (VEGFR)-1- or VEGFR-2–expressing cells is effective in controlling the osteoblastic progression of PCa in bone. These findings provide the basis for an effective multitargeted approach for metastatic PCa.

Link to Article

http://dx.doi.org/10.1158/1078-0432.CCR-10-2943

Distinct p53 Transcriptional Programs Dictate Acute DNA-Damage Responses and Tumor Suppression

Authors

Colleen A. Brady, Dadi Jiang, Stephano S. Mello, Thomas M. Johnson, Lesley A. Jarvis, Margaret M. Kozak, Daniela Kenzelmann Broz, Shashwati Basak, Eunice J. Park, Margaret E. McLaughlin, Anthony N. Karnezis, Laura D. Attardi

Abstract

The molecular basis for p53-mediated tumor suppression remains unclear. Here, to elucidate mechanisms of p53 tumor suppression, we use knockin mice expressing an allelic series of p53 transcriptional activation mutants. Microarray analysis reveals that one mutant, p5325,26, is severely compromised for transactivation of most p53 target genes, and, moreover, p5325,26 cannot induce G1-arrest or apoptosis in response to acute DNA damage. Surprisingly, p5325,26 retains robust activity in senescence and tumor suppression, indicating that efficient transactivation of the majority of known p53 targets is dispensable for these pathways. In contrast, the transactivation-dead p5325,26,53,54 mutant cannot induce senescence or inhibit tumorigenesis, like p53 nullizygosity. Thus, p53 transactivation is essential for tumor suppression but, intriguingly, in association with a small set of novel p53 target genes. Together, our studies distinguish the p53 transcriptional programs involved in acute DNA-damage responses and tumor suppression—a critical goal for designing therapeutics that block p53-dependent side effects of chemotherapy without compromising p53 tumor suppression.

Link to Article

http://dx.doi.org/10.1016/j.bone.2011.04.020

Vitamin D deficiency promotes growth of MCF-7 human breast cancer in a rodent model of osteosclerotic bone metastasis

Authors

Li Laine Ooi, Yu Zheng, Hong Zhou, Trupti Trivedi, Arthur D. Conigraveb, Markus J. Seibel, Colin R. Dunstan

Abstract

Breast cancer metastases to bone are common in advanced stage disease. We have recently demonstrated that vitamin D deficiency enhances breast cancer growth in an osteolytic mouse model of breast cancer metastasis. In this study, we examined the effects of vitamin D deficiency on tumor growth in an osteosclerotic model of intra-skeletal breast cancer in mice. The effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on proliferation and apoptosis of MCF-7 breast cancer cells, and changes in the expression of genes within the vitamin D metabolic pathway (VDR, 1α- and 24-hydroxylase) were examined in vitro. MCF-7 breast cancer cells were injected intra-tibially into vitamin D deficient and vitamin D sufficient mice co-treated with and without osteoprotegerin (OPG). The development of tumor-related lesions was monitored via serial X-ray analysis. Tumor burden and indices of proliferation and apoptosis were determined by histology along with markers of bone turnover and serum intact PTH levels. In vitro, MCF-7 cells expressed critical genes for vitamin D signalling and metabolism. Treatment with 1,25(OH)2D3 inhibited cell growth and proliferation, and increased apoptosis. In vivo, osteosclerotic lesions developed faster and were larger at endpoint in the tibiae of vitamin D deficient mice compared to vitamin D sufficient mice (1.49±0.08mm2 versus 1.68±0.15mm2, P<0.05). Tumor area was increased by 55.8% in vitamin D deficient mice (0.81±0.13mm2 versus 0.52±0.11mm2 in vitamin D sufficient mice). OPG treatment inhibited bone turnover and caused an increase in PTH levels, while tumor burden was reduced by 90.4% in vitamin D sufficient mice and by 92.6% in vitamin D deficient mice. Tumor mitotic activity was increased in the tibiae of vitamin D deficient mice and apoptosis was decreased, consistent with faster growth. Vitamin D deficiency enhances both the growth of tumors and the tumor-induced osteosclerotic changes in the tibiae of mice following intratibial implantation of MCF-7 cells. Enhancement of tumor growth appears dependent on increased bone resorption rather than increased bone formation induced by these tumors.

Link to Article

http://dx.doi.org/10.1016/j.bone.2010.07.012

Inhibition of RANKL increases the anti-tumor effect of the EGFR inhibitor panitumumab in a murine model of bone metastasis

Authors

Jude Canon, Rebecca Bryant, Martine Roudier, Tao Osgood, Jon Jones, Robert Miller, Angela Coxon, Robert Radinsky, William C. Dougall

Abstract

Bone metastases cause severe skeletal complications and are associated with osteoclast-mediated bone destruction. RANKL is essential for osteoclast formation, function, and survival, and is the primary effector of tumor-induced osteoclastogenesis and osteolysis. RANKL inhibition by its soluble decoy receptor osteoprotegerin (OPG) prevents tumor-induced osteolysis and decreases skeletal tumor burden. Because

osteoclast-mediated bone resorption releases growth factors from the bone matrix, the host bone micro-environment induces a vicious cycle of bone destruction and tumor proliferation and survival. A prediction of

this vicious cycle hypothesis is that targeting the host bone microenvironment by osteoclast inhibition would reduce tumor growth and survival and may enhance the anti-tumor effects of targeted therapies. The

epidermal growth factor receptor (EGFR) pathway regulates critical processes such as cell growth and survival, and anti-EGFR therapies can cause tumor cell arrest and apoptosis. We evaluated whether reduction

of osteolysis by RANKL inhibition could enhance the anti-tumor effects of an anti-EGFR antibody (panitumumab) in a novel murine model of human A431 epidermoid carcinoma bone metastasis. Skeletal tumor progression was assessed longitudinally by bioluminescence imaging. RANKL inhibition by OPG-Fc treatment resulted in a reduction in tumor progression in bony sites. OPG-Fc treatment also caused a dose-

dependent reduction in tumor-induced osteolysis, supporting the essential role of RANKL in this process. In combination, RANKL inhibition increased the anti-tumor efficacy of an anti-EGFR antibody, and completely blocked tumor-induced bone breakdown, demonstrating that addition of the indirect anti-tumor effect of RANKL inhibition increases the anti-tumor efficacy of panitumumab, a targeted anti-EGFR antibody.

Link to Article

http://dx.doi.org/10.1016/j.bone.2010.03.001

Cancer treatment dosing regimens of zoledronic acid result in near-complete suppression of mandible intracortical bone remodeling in beagle dogs

Authors

Matthew R Allen, Daniel J Kubek, David B Burr

Abstract

Bisphosphonate doses used in cancer treatment are substantially higher than those used for osteoporosis. Little is known about the effects of these high doses on tissue-level remodeling suppression. The aim of this study was to assess the effects of cancer dosing regimens of zoledronic acid on tissue-level bone remodeling at different skeletal sites. Skeletally mature female beagle dogs were treated with monthly intravenous infusions of vehicle (VEH, saline) or zoledronic acid (ZOL, 0.067 mg/kg); an additional group of animals was treated daily with oral alendronate (ALN, 0.2 mg/kg/day). Doses of ZOL and ALN were, on a milligram per kilogram basis, consistent with those used for cancer and osteoporosis, respectively. Following either 3 or 6 months of treatment, animals were euthanized, and mandible, rib, and tibia were processed for dynamic bone histology. There was no evidence of oral lesions or bone matrix necrosis in the mandibles of any animals. After 3 months, the rate of intracortical bone remodeling in the mandible was significantly suppressed with ZOL (−95%) compared with VEH; by 6 months, ZOL had produced nearly complete suppression (−99%) compared with VEH. ZOL also significantly suppressed remodeling in the rib cortex at both 3 (−83%) and 6 (−85%) months compared with VEH; tibia cortex bone formation rate was nonsignificantly lower with ZOL treatment (−68% to −75%). Remodeling suppression in ZOL-treated animals was significantly greater than in ALN-treated animals at both the mandible and the rib; ALN and VEH were not different for any of the assessed parameters at any of the sites. Compared across skeletal sites, the absolute level of remodeling suppression with ZOL treatment was significantly greater at sites with higher remodeling, whereas the percent reduction was similar among the sites. These results document nearly complete intracortical remodeling suppression resulting from monthly intravenous zoledronic acid dosing, with changes being most dramatic at the mandible.

Link to Article

http://dx.doi.org/10.1359/jbmr.090713

Blockade of transforming growth factor-beta (TGFβ) signaling inhibits osteoblastic tumorigenesis by a novel human prostate cancer cell line

Authors

Sweta Mishra, Yuping Tang, Long Wang, Linda deGraffenried, I-Tien Yeh, Sherry Werner, Dean Troye, John A. Copland, Lu-Zhe Sun

Abstract

The skeleton is the most common site of prostate cancer metastasis, which often results in osteoblastic lesions. The role of transforming growth factor-beta (TGFβ) signaling in prostate cancer-induced osteoblastic metastasis is not clear. We investigated the role of TGFβ signaling in prostate cancer-induced bone metastasis using a novel human prostate cancer cell line, PacMetUT1. We injected PacMetUT1/Luc-GFP cells in male nude mice by intracardiac and intratibia injections and then investigated the effect of TGFβ signaling abrogation on osteoblastic tumor growth and incidence in vivo by using fluorescence and bioluminescence imaging analysis and quantifying bone and tumor volume by histomorphometry analysis. Osteoclasts were counted using TRAP assay. Osteoblastic bone metastasis in skull, rib, and femur was detected after 10–16 weeks of intracardiac injection of the PacMetUT1 cells. Stable knockdown of TGFβ1 with an shRNA resulted in decreased tumor incidence and bone formation when the cells were directly injected into the tibiae. Systemic administration of either a small inhibitor of TGFβ type I receptor kinase or a pan TGFβ binding protein (BGERII) also decreased bone tumor growth and osteoblastic bone formation in vivo after 7 weeks of treatment. Our results for the first time indicate that blockade of TGFβ signaling in the PacMetUT1 model significantly inhibits osteoblastic bone formation and tumor incidence. Thus, TGFβ signaling pathway may be a viable target for the prevention and treatment of prostate cancer-induced bone metastasis

Link to Article

http://dx.doi.org/10.1002/pros.21361