Osteomimetic properties of prostate cancer cells: a hypothesis supporting the predilection of prostate cancer metastasis and growth in the bone environment

BACKGROUND

Unlike most other malignancies, prostate cancer metastasizes preferentially to the skeleton and elicits osteoblastic reactions.

METHODS

We present a hypothesis, based upon results obtained from our laboratory and others, on the nature of progression of prostate cancer cells and their predilection to growth and metastasis in the bone microenvironment. We propose the hypothesis that osseous metastatic prostate cancer cells must be osteomimetic in order to metastasize, grow, and survive in the skeleton. The reciprocal interaction between prostate cancer and bone stromal growth factors, including basic fibroblast growth factor (bFGF), hepatocyte growth factor/scatter factor (HGF/SF), and especially the insulin growth factor (IGF) axis initiates bone tropism, and is enhanced by prostate secreted endothelin-1 (ET-1) and urokinase-type plasminogen activator (uPA). Growth factors and peptides that have differentiating activity, such as transforming growth factor beta (TGF-beta), parathyroid hormone-related protein (PTH-rp), and the bone morphogenetic proteins (BMPs), can shift local homeostasis to produce the characteristic blastic phenotype, via interaction with prostate-secreted human kalikrein 2 (hK2), and prostate-specific antigen (PSA). This proposal asserts that altering the expression of certain critical transcription factors, such as Cbfa and MSX in prostate cancer cells, which presumably are under the inductive influences of prostate or bone stromal cells, can confer profiles of gene expression, such as osteopontin (OPN), osteocalcin (OC), and bone sialoprotein (BSP), that mimic that of osteoblasts.

RESULTS AND CONCLUSIONS

Elucidation of common proteins, presumably driven by the same promoters, expressed by both prostate cancer and bone stromal cells, could result in the development of novel preventive and therapeutic strategies for the treatment of prostate cancer skeletal metastasis. Agents developed using these strategies could have the potential advantage of interfering with growth and enhancing apoptosis in both prostate cancer and bone stromal compartments. The selective application of gene therapy strategy, driven by tissue-specific and tumor-restricted promoters for the safe delivery and expression of therapeutic genes in experimental models of prostate cancer metastasis, is discussed.

Vibration sonoelastography and the detectability of lesions

Vibration sonoelastography has been developed for the detection of hard lesions in relatively soft tissue. The basic concept is to propagate low-amplitude and low-frequency shear waves (with displacements below 0.1 mm and frequencies typically below 1000 Hz) through deep organs, and displaying the vibration response in real-time using advanced color Doppler imaging techniques. A hard inhomogeneity, such as a tumor, will produce a localized disturbance in the vibration pattern, forming the basis for detection even when the tumor is isoechoic on B-scan images. This paper focuses on the important quantitative issues concerning the detectability or inherent contrast of lesions. The specific factors of lesion size, relative stiffness and vibration frequency are studied using theoretical models, finite element methods and experimental measurements on tissue-mimicking materials. The results indicate that detectability increases with vibration (shear wave) frequency; however, loss mechanisms ultimately limit the penetration of higher vibration frequencies (in the kHz range).

Regions of prostate-specific antigen (PSA) promoter confer androgen-independent expression of PSA in prostate cancer cells

Prostate-specific antigen (PSA) is expressed primarily by both normal prostate epithelium and the vast majority of prostate cancers. Increases in serum PSA during endocrine therapy are generally considered as evidence for prostate cancer recurrence or progression to androgen independence. The mechanisms by which PSA up-regulation occurs in androgen-refractory prostate cancer cells are unknown. In this study, by using LNCaP and its lineage-derived androgen-independent PSA-producing subline, C4-2, we identified two cis-elements within the 5.8-kilobase pair PSA promoter that are essential for the androgen-independent activity of PSA promoter in prostate cancer cells. First, a previously reported 440-bp androgen-responsive element enhancer core (AREc) was found to be important for the high basal PSA promoter activity in C4-2 cells. Both mutation analysis and supershift experiments demonstrated that androgen receptor (AR) binds to the AREs within the AREc and activate the basal PSA promoter activity in C4-2 cells under androgen-deprived conditions. Second, a 150-bp pN/H region was demonstrated to be a strong AR-independent positive-regulatory element of the PSA promoter in both LNCaP and C4-2 cells. Through DNase I footprinting and linker scan mutagenesis, a 17-bp RI site was identified as the key cis-element within the pN/H region. Data from electrophoretic mobility shift analysis and UV cross-linking experiments further indicated that a 45-kDa (p45) cell-specific transcription factor associates with RI in prostate cancer cells and may be responsible for driving the PSA promoter activity independent of androgen and AR. Furthermore, by juxtaposing AREc and pN/H, we produced a chimeric PSA promoter (supra-PSA) that exhibits 2-3-fold higher activity than the wild type PSA promoter in both LNCaP and C4-2 cells.

Multilevel and motion model-based ultrasonic speckle tracking algorithms

A multilevel motion model-based approach to ultrasonic speckle tracking has been developed that addresses the inherent trade-offs associated with traditional single-level block matching (SLBM) methods. The multilevel block matching (MLBM) algorithm uses variable matching block and search window sizes in a coarse-to-fine scheme, preserving the relative immunity to noise associated with the use of a large matching block while preserving the motion field detail associated with the use of a small matching block. To decrease further the sensitivity of the multilevel approach to noise, speckle decorrelation and false matches, a smooth motion model-based block matching (SMBM) algorithm has been implemented that takes into account the spatial inertia of soft tissue elements. The new algorithms were compared to SLBM through a series of experiments involving manual translation of soft tissue phantoms, motion field computer simulations of rotation, compression and shear deformation, and an experiment involving contraction of human forearm muscles. Measures of tracking accuracy included mean squared tracking error, peak signal-to-noise ratio (PSNR) and blinded observations of optical flow. Measures of tracking efficiency included the number of sum squared difference calculations and the computation time. In the phantom translation experiments, the SMBM algorithm successfully matched the accuracy of SLBM using both large and small matching blocks while significantly reducing the number of computations and computation time when a large matching block was used. For the computer simulations, SMBM yielded better tracking accuracies and spatial resolution when compared with SLBM using a large matching block. For the muscle experiment, SMBM outperformed SLBM both in terms of PSNR and observations of optical flow. We believe that the smooth motion model-based MLBM approach represents a meaningful development in ultrasonic soft tissue motion measurement.

Feature-adaptive motion tracking of ultrasound image sequences using a deformable mesh

By exploiting the correlation of ultrasound speckle patterns that result from scattering by underlying tissue elements, two-dimensional tissue motion theoretically can be recovered by tracking the apparent movement of the associated speckle patterns. Speckle tracking, however, is an ill-posed inverse problem because of temporal decorrelation of the speckle patterns and the inherent low signal-to-noise ratio of medical ultrasonic images. This paper investigates the use of an adaptive deformable mesh for nonrigid tissue motion recovery from ultrasound images. The nodes connecting the mesh elements are allocated adaptively to stable speckle patterns that are less susceptible to temporal decorrelation. We use the approach of finite element analysis in manipulating the irregular mesh elements. A novel deformable block matching algorithm, making use of a Lagrange element for higher-order description of local motion, is proposed to estimate a nonrigid motion vector at each node. In order to ensure that the motion estimates are admissible to a physically plausible solution, the nodal displacements are regularized by minimizing the strain energy associated with the mesh deformations. Experiments based on ultrasound images of a tissue-mimicking phantom and a muscle undergoing contraction, and on computer simulations, have shown that the proposed algorithm can successfully track nonrigid displacement fields.

Copine-I represses NF-kappaB transcription by endoproteolysis of p65

Nuclear factor-kappaB (NF-kappaB) is a dynamic transcription factor that regulates important biological processes involved in cancer initiation and progression. Identifying regulators that control the half-life of NF-kappaB is important to understanding molecular processes that control the duration of transcriptional responses. In this study we identify copine-I, a calcium phospholipid-binding protein, as a novel repressor that physically interacts with p65 to inhibit NF-kappaB transcription. Knockdown of copine-I by siRNA increases tumor necrosis factor alpha-stimulated NF-kappaB transcription, while copine-I expression blocks endogenous transcription. Copine-I abolishes NF-kappaB transcription by inducing endoprotease processing of the N-terminus of p65, a process antagonized by IkappaB alpha. Copine-I stimulates endoproteolysis of p65 within a conserved region that is required for base-specific contact with DNA. p65 proteins lacking the N-terminus fail to bind to DNA and act as dominant-negative molecules that inhibit NF-kappaB transcription. Our work provides evidence that copine-I regulates the half-life of NF-kappaB transcriptional responses through a novel mechanism that involves endoproteolysis of the p65 protein.

Osteocalcin is incompletely spliced in non-osseous tissues

Osteocalcin (OC) is known to be a bone tissue-specific protein, expression of which is believed to be controlled by the OC promoter. In this communication, we provided evidence to demonstrate that tissue-specific expression of OC was also regulated at the RNA splicing level. We identified incompletely spliced variants of human OC mRNA, which retain one or more introns during RNA splicing, existing dominantly in non-osseous organs. Northern blot analysis identified two OC RNA transcripts expressed in normal human tissues, but the expression level of the transcripts varied between the tissues. Most non-osseous tissues expressed transcripts with higher molecular weight, prominent in ovary, kidney, pancreas, spleen, thymus, prostate, and testis, than the expected size of OC mRNA as seen in bone marrow. RT-PCR analysis identified up to six OC transcripts in most tissues tested except bone marrow. Sequence analysis showed that four of five RNA variants contained intron 1 in common and the dominant one contained all three introns. MG63, an osteoblastic osteosarcoma cell, expressed only the completely-spliced form of OC, whereas incompletely spliced RNA was dominant in most prostate tumor cells. Combined study of in situ hybridization and immunohistochemistry revealed that OC RNA was highly expressed in prostate tumor epithelial cells while only very low levels of protein were detected, which confirms that there are OC RNA variants in non-osseous tissues. In conclusion, we demonstrated that OC mRNA is also expressed in several non-osseous tissues. However, only bone preferentially underwent the complete splicing event of all three introns. The function of other splicing variants of OC mRNA needs to be further investigated.

A luciferase transgenic mouse model: visualization of prostate development and its androgen responsiveness in live animals

Numerous mouse models of prostate carcinogenesis have been developed, but hitherto there has been no model in which the prostate gland could be imaged in live animals. The transgenic model generated here targeted mouse prostate gland using a firefly luciferase enzyme under the control of a small but highly active and specific supra prostate-specific antigen (sPSA) promoter. We evaluated postnatal prostate development, involution and androgen-induced restoration of prostate growth in adult transgenic mice using bioluminescence imaging. Results of our study showed that: (i) the prostate gland of male offspring did not yield a significant bioluminescence signal until after sexual maturity. Luciferase was detected in the luminal epithelial cells of the ventral and dorsolateral lobes of the prostate gland and caput epididymis, with little or no activity in 18 other organs evaluated. (ii) While a constant high level of bioluminescence was detected in the mouse prostate from 5 to 35 weeks of age, a slight drop in bioluminescence was detected at 36 to 54 weeks. (iii) Upon castration, the luciferase activity signal associated with mouse prostate detected by a cooled charge-coupled device camera was dramatically reduced. This signal could be rapidly restored to pre-castration levels after androgen administration. Androgen-induced luciferase activity subsided to nearly basal levels 5 days following the last injection. These data demonstrate that a bioluminescent mouse model with luciferase activity restricted to the prostate gland under the control of a (sPSA) promoter can be used on a real-time basis in live animals to investigate the development and responsiveness of the prostate gland to exogenously administered androgen. This model can be extended to detect the responsiveness of the prostate gland to therapy and used as a founder strain to visualize tumors in hosts with different genetic backgrounds.

Cross-cultural validation of the London Handicap Scale in Hong Kong Chinese

STUDY OBJECTIVE

To investigate the cross-cultural validity of London Handicap Scale in Hong Kong Chinese.

DESIGN

Ratings of the utility of 10 hypothetical health scenarios were given by groups of HK Chinese subjects. Measured scores were compared with calculated scores from published scale weights of London Handicap Scale, which were based on utility ratings made by UK subjects.

SETTING

A rehabilitation hospital in Hong Kong.

SUBJECTS

A total of 164 HK Chinese, comprising doctors, medical students, nonmedical hospital staff, geriatric day hospital stroke and nonstroke patients, community day-care centre elderly, old age hostel elderly, young disabled inpatients and young community-dwelling disabled citizens.

MAIN RESULTS

There was a close correlation between the mean scores of HK subjects and the calculated scores derived from the published UK scale weights, apart from one scenario (Pearson's correlation coefficient r = 0.87 p = 0.001). The correlations were high for all subgroups, between which there was good consensus. Measured utilities were significantly different between subgroups for only one scenario. For this scenario of moderate to severe handicap in mobility, physical dependence, occupation and social integration, but with excellent orientation and economic self sufficiency: (1) older age groups gave better scores than younger age groups (p < 0.0005); (2) subjects with poor subjective health status gave better scores than those with good subjective health status (p = 0.002); (3) subjects related to the medical or hospital field, i.e. doctors, medical students and nonmedical hospital staff, gave worse scores than other subject groups (p < 0.0005).

CONCLUSION

The concept of handicap applies across cultures. Perception of severity of selected real life handicap scenarios by HK Chinese were well estimated using scale weights from UK populations developed for the London Handicap Scale. Significant differences in perception of certain handicap scenarios by different population subgroups deserve further study.

Chronic Ketamine Exposure Causes White Matter Microstructural Abnormalities in Adolescent Cynomolgus Monkeys

Acute and repeated exposures to ketamine mimic aspects of positive, negative, and cognitive symptoms of schizophrenia in humans. Recent studies by our group and others have shown that chronicity of ketamine use may be a key element for establishing a more valid model of cognitive symptoms of schizophrenia. However, current understanding on the long-term consequences of ketamine exposure on brain circuits has remained incomplete, particularly with regard to microstructural changes of white matter tracts that underpin the neuropathology of schizophrenia. Thus, the present study aimed to expand on previous investigations by examining causal effects of repeated ketamine exposure on white matter integrity in a non-human primate model. Ketamine or saline (control) was administered intravenously for 3 months to male adolescent cynomolgus monkeys (n = 5/group). Diffusion tensor imaging (DTI) experiments were performed and tract-based spatial statistics (TBSS) was used for data analysis. Fractional anisotropy (FA) was quantified across the whole brain. Profoundly reduced FA on the right side of sagittal striatum, posterior thalamic radiation (PTR), retrolenticular limb of the internal capsule (RLIC) and superior longitudinal fasciculus (SLF), and on the left side of PTR, middle temporal gyrus and inferior frontal gyrus were observed in the ketamine group compared to controls. Diminished white matter integrity found in either fronto-thalamo-temporal or striato-thalamic connections with tracts including the SLF, PTR, and RLIC lends support to similar findings from DTI studies on schizophrenia in humans. This study suggests that chronic ketamine exposure is a useful pharmacological paradigm that might provide translational insights into the pathophysiology and treatment of schizophrenia.

Current landscape and potential future applications of artificial intelligence in medical physics and radiotherapy

Artificial intelligence (AI) has seen tremendous growth over the past decade and stands to disrupts the medical industry. In medicine, this has been applied in medical imaging and other digitised medical disciplines, but in more traditional fields like medical physics, the adoption of AI is still at an early stage. Though AI is anticipated to be better than human in certain tasks, with the rapid growth of AI, there is increasing concerns for its usage. The focus of this paper is on the current landscape and potential future applications of artificial intelligence in medical physics and radiotherapy. Topics on AI for image acquisition, image segmentation, treatment delivery, quality assurance and outcome prediction will be explored as well as the interaction between human and AI. This will give insights into how we should approach and use the technology for enhancing the quality of clinical practice.

Nutritional status of older Tibetans in rural Sichuan China

OBJECTIVE

To examine the nutritional status of older Tibetans in rural China.

DESIGN

Cross sectional study.

SETTING

Remote mountainous region of Sichuan province of Western China.

SUBJECTS AND METHOD

Forty four male and forty six female Tibetans, over 60 years old were recruited. Body weight, standing height, triceps and bicep skinfold thicknesses (TSF, BSF), mid arm circumference (MAC) and waist circumference (WC) were measured. Dietary intakes were assessed by a twenty-four hour dietary recall. Based on skinfold thicknesses and MAC, total body fat and corrected arm muscle area (CAMA) were calculated by published equations. Their nutritional status and dietary intakes were compared with those of normal older people in Hong Kong and a rural area near Tianjin in the east coast of China.

RESULTS

Compared with Hong Kong older women, the Tibetan older women had similar BMI and total body fat, but their CAMA was significantly greater (p<0.01). The Tibetan older men had lower BMI, total body fat (p<0.05), and higher CAMA than the Hong Kong older men (p<0.05). The average calorie intake in the Tibetans was lower than that of older people in Hong Kong and rural Tianjin. Intakes of protein, vitamins and minerals were the lowest in Tibetans and the highest in older people in Hong Kong.

CONCLUSIONS

Older Tibetans had more lean mass than Hong Kong older Chinese despite having lower caloric and protein intakes. Older Tibetan women were fatter than their male counterparts, and they were as fat as the older people in Hong Kong, despite having low caloric intakes.

A Comparison of the Long-term Health Related Quality of Life and Handicap of Stroke Patients in Mainland China and Hong Kong

Purpose

To compare health related quality of life (HRQOL) and handicap of stroke survivors in Hong Kong (HK) and Chengdu (CD) in Mainland China.

Method

Fifty-four pairs of first ever stroke patients in CD and in HK matched by age, sex and Modified Barthel Index (MBI) were interviewed using a structured questionnaire at 16–36 months after stroke. HRQOL and handicap outcomes were evaluated by the Chinese version of the Short-Form Health Survey (SF-36) and London Handicap Scale (LHS) respectively.

Results

Compared to stroke patients in CD, HK subjects reported significantly greater handicap, especially in the occupation domain. HK subjects also had significantly lower HRQOL Z scores in domains of role limitations due to emotional or physical problems, and bodily pain. CD subjects had more social support, but had more difficulties in meeting medical costs, and were less likely to have regular medical follow-up and dysphagia symptom. After adjusting for social and health related factors, the site differences in handicap and the role limitation (physical) domain of SF36 became insignificant.

Conclusions

CD stroke survivors had better scores in HRQOL and fewer handicaps than their counterparts in HK, because of social and health related factors.