The Role of Alpha 6 Integrin in Prostate Cancer Migration and Bone Pain in a Novel Xenograft Model

Of the estimated 565,650 people in the U.S. who will die of cancer in 2008, almost all will have metastasis. Breast, prostate, kidney, thyroid and lung cancers metastasize to the bone. Tumor cells reside within the bone using integrin type cell adhesion receptors and elicit incapacitating bone pain and fractures. In particular, metastatic human prostate tumors express and cleave the integrin A6, a receptor for extracellular matrix components of the bone, i.e., laminin 332 and laminin 511. More than 50% of all prostate cancer patients develop severe bone pain during their remaining lifetime. One major goal is to prevent or delay cancer induced bone pain. We used a novel xenograft mouse model to directly determine if bone pain could be prevented by blocking the known cleavage of the A6 integrin adhesion receptor. Human tumor cells expressing either the wildtype or mutated A6 integrin were placed within the living bone matrix and 21 days later, integrin expression was confirmed by RT-PCR, radiographs were collected and behavioral measurements of spontaneous and evoked pain performed. All animals independent of integrin status had indistinguishable tumor burden and developed bone loss 21 days after surgery. A comparison of animals containing the wild type or mutated integrin revealed that tumor cells expressing the mutated integrin resulted in a dramatic decrease in bone loss, unicortical or bicortical fractures and a decrease in the ability of tumor cells to reach the epiphyseal plate of the bone. Further, tumor cells within the bone expressing the integrin mutation prevented cancer induced spontaneous flinching, tactile allodynia, and movement evoked pain. Preventing A6 integrin cleavage on the prostate tumor cell surface decreased the migration of tumor cells within the bone and the onset and degree of bone pain and fractures. These results suggest that strategies for blocking the cleavage of the adhesion receptors on the tumor cell surface can significantly prevent cancer induced bone pain and slow disease progression within the bone. Since integrin cleavage is mediated by Urokinase-type Plasminogen Activator (uPA), further work is warranted to test the efficacy of uPA inhibitors for prevention or delay of cancer induced bone pain

Epigenetic silencing of DSC3 is a common event in human breast cancer

INTRODUCTION: Desmocollin 3 (DSC3) is a member of the cadherin superfamily of calcium-dependent cell adhesion molecules and a principle component of desmosomes. Desmosomal proteins such as DSC3 are integral to the maintenance of tissue architecture and the loss of these components leads to a lack of adhesion and a gain of cellular mobility. DSC3 expression is down-regulated in breast cancer cell lines and primary breast tumors; however, the loss of DSC3 is not due to gene deletion or gross rearrangement of the gene. In this study, we examined the prevalence of epigenetic silencing of DSC3 gene expression in primary breast tumor specimens. METHODS: We used bisulfite genomic sequencing to analyze the methylation state of the DSC3 promoter region from 32 primary breast tumor specimens. We also used a quantitative real-time RT-PCR approach, and analyzed all breast tumor specimens for DSC3 expression. Finally, in addition to bisulfite sequencing and RT-PCR, we used an in vivo nuclease accessibility assay to determine the chromatin architecture of the CpG island region from DSC3-negative breast cancer cells lines. RESULTS: DSC3 expression was downregulated in 23 of 32 (72%) breast cancer specimens comprising: 22 invasive ductal carcinomas, 7 invasive lobular breast carcinomas, 2 invasive ductal carcinomas that metastasized to the lymph node, and a mucoid ductal carcinoma. Of the 23 specimens showing a loss of DSC3 expression, 13 (56%) were associated with cytosine hypermethylation of the promoter region. Furthermore, DSC3 expression is limited to cells of epithelial origin and its expression of mRNA and protein is lost in a high proportion of breast tumor cell lines (79%). Lastly, DNA hypermethylation of the DSC3 promoter is highly correlated with a closed chromatin structure. CONCLUSION: These results indicate that the loss of DSC3 expression is a common event in primary breast tumor specimens, and that DSC3 gene silencing in breast tumors is frequently linked to aberrant cytosine methylation and concomitant changes in chromatin structure

Development of cancer-induced spontaneous pain, tactile allodynia, and movement-evoked pain in animals 21 days after surgery.

<p>(A) Spontaneous pain as measured by flinching of the ipsilateral hindlimb was determined in sham injected animals (control) or those injected with tumor cells expressing the wild type integrin (PC3N-A6-WT) or those injected with tumor cells expressing the mutated integrin (PC3N-A6-RR). Elevation in flinching behavior is indicative of an increased pain response. (B) Tactile allodynia as measured by paw-withdrawal from von Frey filaments in sham injected animals (Control) or those injected with tumor cells expressing the wild type integrin (PC3N-A6-WT) or those injected with tumor cells expressing the mutated integrin (PC3N-A6-RR). A decrease in the withdrawal threshold is indicative of an increased pain response. (C) Movement evoked pain was observed in sham injected animals (control) or those injected with tumor cells expressing the wild type integrin (PC3N-A6-WT) or those injected with tumor cells expressing the mutated integrin (PC3N-A6-RR).</p

Biochemical and migration phenotype of PC3N-A6-WT and PC3N-A6- RR cells expressing the wildtype(cleavable) and RR(uncleavable) integrin A6, respectively.

<p>(A) The expression of the full length 6 integrin ( 6) and uPA dependent production of the 6p variant ( 6p) was determined by western blot analysis. Integrin status within total cell lysates from doxycycline (Dox) or urokinase (uPA) untreated (−) and treated (+) PC3N-A6-WT and PC3N-A6-RR cell lines was determined. (B) Surface expression of wild type and mutated integrin 6 in doxycycline induced PC3N-A6-WT and PC3N-A6-RR cells was determined by flow cytometry. PC3N-A6-WT and PC3NA6- RR cells were incubated with primary Rat anti-integrin A6 antibody J1B5 followed by Alexa 488 anti-rat antibody and visualized using the BD FACScan. The grey peak indicates fluorescence signal from secondary antibody only. (C) Schematic to illustrate the cleavage of the full length form of the 6 integrin to yield the 6p variant. The definition of the PC3N-A6-WT and PC3N-A6-RR cells with regard to integrin status is shown. (D) Integrin mediated migration of PC3N-A6-WT cells (top panels) and PC3NA6- RR cells (bottom panels) on matrigel. The cells were placed on matrigel in the presence of a coverslip to create a cell free zone on the matrigel surface. After cell adhesion was complete, the coverslips were removed from the matrigel surface to allow migration into the cell free zone indicated by white or black curved line. Cells migration occurred under optimal growth conditions at 37 for approximately 18 hours. Cells were either allowed to migrate in the absence (left panels) or presence (right panels) of integrin blocking antibody AIIB2. Images were collected using a Zeiss Axiovert microscope equipped with a 2.5X objective.</p

Histological examination of bone destruction, tumor cell distribution and verification of mutated integrin expression after injection of prostate tumor cells.

<p>(A) Hematoxylin-eosin staining of the normal bone (control) or bone injected with PC3N-A6-WT cells (WT, middle panel and inset) and PC3N-A6-RR cells (RR, bottom panel and inset). The growth plate of the bone (epiphyseal plate) is oriented at the top left of each panel for comparison purposes. (B) RT-PCR analysis to detect expression of the mutated 6 integrin in the bone marrow. Twenty one days following injection, bone marrow was harvested, RNA was extracted and analyzed. RNA from PC3N-A6-WT cells and PC3N-A6-RR cells growing in tissue culture was compared to the bone marrow isolated from mice injected with PC3N-A6-WT cells (Bone marrow-WT cells) or PC3NA6- RR cells (bone marrow-RR cells). GAPDH amplification was carried out as control and the kB markers are as shown.</p