The expression of P-glycoprotein is causally related to a less aggressive phenotype in human osteosarcoma cells

Systematic review of comparative transcriptomic studies of cellular resistance to genotoxic stress

The development of resistance by tumor cells to various types of therapy is a significant problem that decreases the effectiveness of oncology treatments. For more than two decades, comparative transcriptomic studies of tumor cells with different sensitivities to ionizing radiation and chemotherapeutic agents have been conducted in order to identify the causes and mechanisms underlying this phenomenon. However, the results of such studies have little in common and often contradict each other. We have assumed that a systematic analysis of a large number of such studies will provide new knowledge about the mechanisms of development of therapeutic resistance in tumor cells. Our comparison of 123 differentially expressed gene (DEG) lists published in 98 papers suggests a very low degree of consistency between the study results. Grouping the data by type of genotoxic agent and tumor type did not increase the similarity. The most frequently overexpressed genes were found to be those encoding the transport protein ABCB1 and the antiviral defense protein IFITM1. We put forward a hypothesis that the role played by the overexpression of the latter in the development of resistance may be associated not only with the stimulation of proliferation, but also with the limitation of exosomal communication and, as a result, with a decrease in the bystander effect. Among down regulated DEGs, BNIP3 was observed most frequently. The expression of BNIP3, together with BNIP3L, is often suppressed in cells resistant to non-platinum genotoxic chemotherapeutic agents, whereas it is increased in cells resistant to ionizing radiation. These observations are likely to be mediated by the binary effects of these gene products on survival, and regulation of apoptosis and autophagy. The combined data also show that even such obvious mechanisms as inhibition of apoptosis and increase of proliferation are not universal but show multidirectional changes.

The strategy and clinical relevance of in vitro models of MAP resistance in osteosarcoma: a systematic review

Over the last 40 years osteosarcoma (OS) survival has stagnated with patients commonly resistant to neoadjuvant MAP chemotherapy involving high dose methotrexate, adriamycin (doxorubicin) and platinum (cisplatin). Due to the rarity of OS, the generation of relevant cell models as tools for drug discovery is paramount to tackling this issue. Four literature databases were systematically searched using pre-determined search terms to identify MAP resistant OS cell lines and patients. Drug exposure strategies used to develop cell models of resistance and the impact of these on the differential expression of resistance associated genes, proteins and non-coding RNAs are reported. A comparison to clinical studies in relation to chemotherapy response, relapse and metastasis was then made. The search retrieved 1891 papers of which 52 were relevant. Commonly, cell lines were derived from Caucasian patients with epithelial or fibroblastic subtypes. The strategy for model development varied with most opting for continuous over pulsed chemotherapy exposure. A diverse resistance level was observed between models (2.2-338 fold) with 63% of models exceeding clinically reported resistance levels which may affect the expression of chemoresistance factors. In vitro p-glycoprotein overexpression is a key resistance mechanism; however, from the available literature to date this does not translate to innate resistance in patients. The selection of models with a lower fold resistance may better reflect the clinical situation. A comparison of standardised strategies in models and variants should be performed to determine their impact on resistance markers. Clinical studies are required to determine the impact of resistance markers identified in vitro in poor responders to MAP treatment, specifically with respect to innate and acquired resistance. A shift from seeking disputed and undruggable mechanisms to clinically relevant resistance mechanisms may identify key resistance markers that can be targeted for patient benefit after a 40-year wait.

Metformin as an adjuvant drug against pediatric sarcomas: hypoxia limits therapeutic effects of the drug

Metformin, a well-known insulin-sensitizer commonly used for type 2 diabetes therapy, has recently emerged as potentially very attractive drug also in oncology. It is cheap, it is relatively safe and many reports have indicated effects in cancer prevention and therapy. These desirable features are particularly interesting for pediatric sarcomas, a group of rare tumors that have been shown to be dependent on IGF and insulin system for pathogenesis and progression. Metformin exerts anti-mitogenic activity in several cancer histotypes through several molecular mechanisms. In this paper, we analyzed its effects against osteosarcoma, Ewing sarcoma and rhabdomyosarcoma, the three most common pediatric sarcomas. Despite in vitro metformin gave remarkable antiproliferative and chemosensitizing effects both in sensitive and chemoresistant cells, its efficacy was not confirmed against Ewing sarcoma xenografts neither as single agent nor in combination with vincristine. This discrepancy between in vitro and in vivo effects may be due to hypoxia, a common feature of solid tumors. We provide evidences that in hypoxia conditions metformin was not able to activate AMPK and inhibit mTOR signaling, which likely prevents the inhibitory effects of metformin on tumor growth. Thus, although metformin may be considered a useful complement of conventional chemotherapy in normoxia, its therapeutic value in highly hypoxic tumors may be more limited. The impact of hypoxia should be considered when novel therapies are planned for pediatric sarcomas.

Epigenetic regulation of MDR1 gene through post-translational histone modifications in prostate cancer

BACKGROUND

Multidrug resistance 1 (MDR1) gene encodes for an ATP binding cassette transporter--P-glycoprotein (P-gp)-- involved in chemoresistance to taxanes. MDR1 promoter methylation is frequent in prostate carcinoma (PCa), suggesting an epigenetic regulation but no functional correlation has been established. We aimed to elucidate the epigenetic mechanisms involved in MDR1 deregulation in PCa.

RESULTS

MDR1 promoter methylation and P-gp expression were assessed in 121 PCa, 39 high-grade prostatic intraepithelial neoplasia (HGPIN), 28 benign prostatic hyperplasia (BPH) and 10 morphologically normal prostate tissue (NPT) samples, using quantitative methylation specific PCR and immunohistochemistry, respectively. PCa cell lines were exposed to a DNA methyltransferases inhibitor 5-aza-2'deoxycytidine (DAC) and histone deacetylases inhibitor trichostatin A (TSA). Methylation and histone posttranscriptional modifications status were characterized and correlated with mRNA and protein expression. MDR1 promoter methylation levels and frequency significantly increased from NPTs, to HGPIN and to PCa. Conversely, decreased or absent P-gp immunoexpression was observed in HGPIN and PCa, inversely correlating with methylation levels. Exposure to DAC alone did not alter significantly methylation levels, although increased expression was apparent. However, P-gp mRNA and protein re-expression were higher in cell lines exposed to TSA alone or combined with DAC. Accordingly, histone active marks H3Ac, H3K4me2, H3K4me3, H3K9Ac, and H4Ac were increased at the MDR1 promoter after exposure to TSA alone or combined with DAC.

CONCLUSION

Our data suggests that, in prostate carcinogenesis, MDR1 downregulation is mainly due to histone post-translational modifications. This occurs concomitantly with aberrant promoter methylation, substantiating the association with P-gp decreased expression.

Biological indicators of prognosis in Ewing's sarcoma: an emerging role for lectin galactoside-binding soluble 3 binding protein (LGALS3BP)

Starting from an experimental model that accounts for the 2 most important adverse processes to successful therapy of Ewing's sarcoma (EWS), chemoresistance and the presence of metastasis at the time of diagnosis, we defined a molecular signature of potential prognostic value. Functional annotation of differentially regulated genes revealed 3 major networks related to cell cycle, cell-to-cell interactions and cellular development. The prognostic impact of 8 genes, representative of these 3 networks, was validated in 56 EWS patients. High mRNA expression levels of HINT1, IFITM2, LGALS3BP, STOML2 and c-MYC were associated with reduced risk to death and lower risk to develop metastasis. At multivariate analysis, LGALS3BP, a matricellular protein with a role in tumor progression and metastasis, was the most important predictor of event-free survival and overall survival. The association between LGALS3BP and prognosis was confirmed at protein level, when expression of the molecule was determined in tumor tissues but not in serum, indicating a role for the protein at local tumor microenvironment. Engineered enhancement of LGALS3BP expression in EWS cells resulted in inhibition of anchorage independent cell growth and reduction of cell migration and metastasis. Silencing of LGALS3BP expression reverted cell behavior with respect to in vitro parameters, thus providing further functional validation of genetic data obtained in clinical samples. Thus, we propose LGALS3BP as a novel reliable indicator of prognosis, and we offer genetic signatures to the scientific communities for cross-validation and meta-analysis, which are indispensable tools for a rare tumor such as EWS.

CpG Hypermethylation ofMDR1Gene Contributes to the Pathogenesis and Progression of Human Prostate Cancer

Multidrug resistance 1 (MDR1) gene encodes for P-glycoprotein (P-gp), a Mr 170,000 transmembrane calcium-dependent efflux pump that is inactivated in prostate cancer. We hypothesize that inactivation of the MDR1 gene through CpG methylation contributes to the pathogenesis and progression of prostate cancer. To test this hypothesis, CpG methylation status of the MDR1 promoter and its correlation with clinicopathological findings were evaluated in 177 prostate cancer samples and 69 benign prostate hypertrophy (BPH) samples. Cellular proliferation index and apoptotic index were determined by proliferating cell nuclear antigen (PCNA) and single-strand DNA immunostaining, respectively. After 5-aza-2'-deoxycytidine treatment, increased expression of MDR1 mRNA transcript was found in prostate cancer cell lines (DU145, DuPro, and ND1). MDR1 methylation frequency was significantly higher in prostate cancer samples compared with BPH samples (54.8 versus 11.6%, respectively, P < 0.001). Logistic regression analysis revealed that PC patients are 11.5 times more likely to have MDR1 methylation than BPH patients (95% confidence interval 4.87-27.0) and that MDR1 methylation is independent of the age. Significant correlation of MDR1 methylation was observed with high pT category (P < 0.001), high Gleason sum (P = 0.008), high preoperative prostate-specific antigen (P = 0.01), and advancing pathological features. In addition, PCNA-labeling index were significantly higher in methylation-specific PCR (MSP)-positive than in MSP-negative prostate cancer samples (P = 0.048). In contrast, no significant difference in apoptotic index was found between MSP-positive and -negative prostate cancer samples. These findings suggest that CpG hypermethylation of MDR1 promoter is a frequent event in prostate cancer and is related to disease progression via increased cell proliferation in prostate cancer cells.

Human osteosarcoma xenografts and their sensitivity to chemotherapy

Despite the increased survival rates of osteosarcoma patients attributed to adjuvant chemotherapy, at least one third of the patients still die due to their disease. Further improvements in the management of osteosarcoma may rely on a more individualised treatment strategy, as well as on the introduction of new drugs. To aid in the preclinical evaluation of new candidate substances against osteosarcoma, we have established 11 human osteosarcoma xenograft lines and characterised them with regard to response to five different reference drugs. Doxorubicin, cisplatin methotrexate, ifosfamide and lomustine were effective in 3/11, 3/11, 1/10, 5/11 and 4/11 of the xenografts, respectively. Five xenografts were resistant to all compounds tested. We also assessed the mRNA expression levels of the xenografts for the O(6)-Methylguanine DNA Methyltransferase (MGMT), DNA topoisomerase II- (Topo II)-alpha, Gluthathione-S-transferase (GST)-pi, Multidrug-resistance related protein (MRP) 1 and Multidrug-resistance (MDR) 1 genes. There was an inverse correlation between the transcript levels of GST-pi and doxorubicin growth inhibition (r=-0.66; p<0.05), and between the transcript levels of MGMT and the effect of lomustine (r=-0.72; p<0.01), whereas the expression of MRP1 and cisplatin growth inhibition was positively correlated (r=0.82; p<0.005). This panel of xenografts should constitute a good tool for pharmacological and molecular studies in osteosarcoma.

Evaluation of P-glycoprotein, HER-2/ErbB-2, p53, and Bcl-2 in primary tumor and metachronous lung metastases in patients with high-grade osteosarcoma

BACKGROUND

Investigation of the relation between primary tumor and metastatic disease is necessary for the identification of predictive factors for postrecurrence survival (PRS) in patients with recurrent osteosarcoma.

METHODS

Cellular levels of P-glycoprotein, ErbB-2, p53, and Bcl-2 expression were evaluated in primary tumor biopsy and metachronous pulmonary metastasis specimens from 19 patients with high-grade osteosarcoma. Results were analyzed for differences between primary tumor and pulmonary metastases and for correlations between expression patterns and survival.

RESULTS

Positive staining in lung metastases was noted in 68%, 53%, 32%, and 84% of patients for P-glycoprotein, ErbB-2, p53, and Bcl-2, respectively. These percentages were higher than those observed in primary tumor specimens for all genetic markers evaluated, with a significant difference in the percentage of patients with positive staining for P-glycoprotein (68% vs. 32%; P = 0.05) and a near-significant difference in the percentage of patients with positive staining for Bcl-2 (84% vs. 53%; P = 0.08). Patients with ErbB-2 expression in the primary tumor were more likely to have multiple metastases and shorter recurrence-free intervals compared with patients in whom ErbB-2 expression was not observed, whereas differences in P-glycoprotein, p53, and Bcl-2 expression were not related to differences in metastatic pattern. PRS was influenced by p53 expression levels in pulmonary metastases, with patients who had negative staining for p53 having a significantly better PRS rate relative to patients with positive staining for p53 (3-year PRS rate: p53-negative, 64%; p53-positive, 17%; P = 0.008).

CONCLUSIONS

In the current study of patients with high-grade osteosarcoma, most patients exhibited increased cellular expression of P-glycoprotein, ErbB-2, and Bcl-2 in recurrent pulmonary metastases compared with primary tumor. Further studies aimed at investigating the relation between altered p53 expression in lung metastases and postrecurrence survival are recommended.

The association of P-glycoprotein with response to chemotherapy and clinical outcome in patients with osteosarcoma. A meta-analysis

BACKGROUND

There is controversy regarding whether P-glycoprotein (Pgp) may be a prognostic factor for the response to chemotherapy and clinical disease progression in patients with osteosarcoma.

METHODS

The authors conducted a meta-analysis of 14 studies (n = 631 patients) that evaluated the correlation between Pgp and histologic response to chemotherapy and clinical disease progression (death, metastasis, or recurrence). Data were synthesized in receiver operating characteristic curves and with fixed-effects and random-effects likelihood ratios and risk ratios.

RESULTS

Pgp had no discriminating ability for identifying poor responders versus good responders to chemotherapy: The positive likelihood ratio was 1.15 (95% confidence interval [95% CI], 0.93-1.43), and the negative likelihood ratio was 0.88 (95% CI, 0.65-1.18; random-effects calculations). There was some between-study heterogeneity, but no study showed strong discriminating ability. Conversely, Pgp positivity increased the risk of disease progression 1.92-fold (95% CI, 1.18-3.13; random-effects calculations) with some between-study heterogeneity that disappeared when only studies that employed immunohistochemistry were considered (risk ratio, 2.23; 95% CI, 1.37-3.64). The results were robust in various sensitivity analyses, although smaller studies tended to show stronger associations with the risk of disease progression compared with larger studies (P = 0.03).

CONCLUSIONS

The available evidence showed conclusively that Pgp was not associated with the histologic response of patients with osteosarcoma to combination chemotherapy regimens. Conversely, Pgp positivity, as determined by immunohistochemistry, was a strong correlate of more rapid disease progression, although there was heterogeneity across the performed studies that, to some extent, may have reflected bias, differential measurements of Pgp, or confounding with other risk factors.

Expression profiling of osteosarcoma cells transfected with MDR1 and NEO genes: regulation of cell adhesion, apoptosis, and tumor suppression-related genes

The expression patterns of the osteosarcoma cell line U-2 OS, and three derived subclones containing stably transfected MDR1, NEO and MDR1/NEO genes were compared using cDNA microarrays comprising 8976 known genes and expressed sequenced tags. Data provided new insights into three critical issues. First, MDR1 overexpression was associated with altered expression of genes related to several cellular pathways, including (a). drug influx/efflux (eg, dynamin 3), (b). metabolic enzymes (eg, monoamine oxidase A), (c). cell adhesion (eg, EPCAM), (d). apoptotic signaling (eg, I-TRAF), (e). senescence (eg, telomerase RNA binding protein staufen), (f). tumor suppression-related genes (eg, KISS-1 and ephrin B3), and (g). immune system receptors (eg, LENG2). MDR1, EPCAM, and ephrin B3 expression was confirmed by immunohistochemistry. Second, MDR1 transfected cells selected with either doxorubicin or neomycin showed distinct expression profiles that could be related to differential selection. Moreover, hierarchical clustering indicated that cells transfected with MDR1 alone, or cotransfected with NEO, displayed more closely related expression profiles than cells transfected only with NEO. Third, transfection with NEO and selection with neomycin produced a considerable number of expression changes within the cell. This study further elucidates the genetic events associated with MDR1 expression and identifies novel targets associated with multidrug resistance.

Value of P-glycoprotein and clinicopathologic factors as the basis for new treatment strategies in high-grade osteosarcoma of the extremities

PURPOSE

To evaluate the prognostic value of P-glycoprotein and clinicopathologic parameters in a large series of high-grade osteosarcoma (OS) patients treated at the Rizzoli Institute.

PATIENTS AND METHODS

With the use of immunohistochemistry, P-glycoprotein was assessed in 149 patients with primary, nonmetastatic, high-grade OS who were homogeneously treated with chemotherapy protocols based on doxorubicin, high-dose methotrexate, and cisplatin and the addition of ifosfamide in the postoperative phase.

RESULTS

P-glycoprotein positivity was found in 47 of 149 cases (32%) and was significantly associated with a higher incidence of relapse and a worse outcome, as was age younger than 12 years and tumor volume greater then 150 mL at diagnosis. Multivariate analysis further confirmed the prognostic value of these parameters, which all were independent adverse prognostic factors. Event-free survival and proportional hazards regression analyses confirmed that overexpression of P-glycoprotein at clinical onset is the most important adverse prognostic factor for high-grade OS patients treated with these chemotherapy protocols.

CONCLUSION

Increased P-glycoprotein levels, together with tumor volume and age, should be taken into consideration to identify, at time of diagnosis, subgroups of OS patients with a higher risk of recurrence. This subgroup identification will constitute the basis for drawing individualized treatment protocols on the basis of risk evaluation, with the aim of using more aggressive chemotherapy, or combination chemotherapy with other adjuvants, only in those patients for which more aggressive regimens are strictly necessary and warranted.

Establishment of human osteosarcoma cell lines with high metastatic potential to lungs and their utilities for therapeutic studies on metastatic osteosarcoma

Relevant animal models for metastasis of osteosarcoma is needed to understand the biology and to develop the treatment modality of metastasis of human osteosarcoma. Therefore, we screened six human osteosarcoma cell lines for metastatic ability in nude mice. The HuO9 cell line was identified as being metastatic to the lung after intravenous injection. We established two sublines, HuO9-M112 and HuO9-M132, with high metastatic potential to the lung from the parental HuO9 cells by in vivo selection. There were no differences between these two sublines and the parental cells in the growth rate in vitro and the tumorigenicity after subcutaneous injection in nude mice, however, mice injected with the metastatic sublines became moribund earlier than mice injected with the parental HuO9 cells did. Thus, adriamycin (ADR) and recombinant interleukin-12 (IL-12) were administered to mice injected with the HuO9-M112 subline to suppress experimental lung metastases. Production of lung colonies was significantly suppressed and the prognoses of mice were significantly improved by both ADR and IL-12 treatments. These results indicate that both ADR and IL-12 are effective agents against pulmonary metastatic osteosarcoma, and that these sublines are useful for studies on the biological behavior and treatment of pulmonary metastatic osteosarcoma.

Caveolin-1 inhibits anchorage-independent growth, anoikis and invasiveness in MCF-7 human breast cancer cells

Caveolin-1 is an essential structural constituent of caveolae that has been implicated in mitogenic signaling and oncogenesis. Caveolin-1 is down-regulated in oncogene-transformed and tumor-derived cells. Antisense suppression of caveolin-1 or expression of a dominant negative form are sufficient for inducing cellular transformation. Expression of recombinant caveolin-1 inhibits anchorage-independent growth in cancer cells. The present study was designed to determine whether this is caused by inhibition of cancer cell survival or cell proliferation, and to test if another important property of cancer cells, i.e. matrix invasion, is modulated by expression of caveolin. Utilizing MCF-7 human breast adenocarcinoma cells stably transfected with caveolin-1 (MCF-7/Cav1), we demonstrate that caveolin-1 expression decreases MCF-7 cell proliferation rate and markedly reduces their capacity to form colonies in soft agar. The loss of anchorage-independent growth is not associated with stimulation of anoikis; in fact, MCF-7/Cav1 cells exhibit increased survival after detachment as compared with MCF-7 cells, indicating that in these cells caveolin-1 inhibits anoikis. Analysis of matrix metalloprotease release and matrix invasion revealed that expression of caveolin-1 inhibits also these important metastasis-related phenomena. Plating MCF-7 cells on a laminin matrix resulted in activation of ERK1/2, which was dramatically inhibited in MCF-7/Cav1 cells. We conclude that high expression level of caveolin-1 in human breast cancer cells exerts a negative modulatory effect on anchorage-independent growth by inhibiting cell proliferation even though matrix-independent cell survival is enhanced. Caveolin-1 expression inhibits also matrix invasion and blocks laminin-dependent activation of ERK1/2. The inhibitory effect of caveolin-1 on these transformation-dependent processes supports the hypothesis that caveolin-1 acts as a tumor suppressor protein which may impose major phenotypic changes when expressed in human cancer cells.

Identification of RB1CC1, a novel human gene that can induce RB1 in various human cells

Multidrug resistance to anti-cancer agents (MDR) is a major barrier to successful cancer treatment. Current knowledge about genes that contribute to MDR is limited, however, and its mechanisms remain unclear. To identify genes involved in MDR, we performed differential display analysis and isolated a novel human gene, RB1CC1 (RBI-inducible Coiled-Coil 1). The 6.6-kb RB1CC1 cDNA encodes a putative 1594-amino-acid protein that contains a nuclear localization signal, a leucine zipper motif and a coiled-coil structure. Western blot analysis and immunocytochemical staining with anti-RB1CC1 antibody showed that endogenously expressed RB1CC1 protein localized to the nucleus. In MDR variants of human osteosarcoma cells, RB1CC1 expression increased in response to doxorubicin-induced cytotoxic stress and remained elevated for the duration of drug treatment. RB1CC1 expression levels correlated closely with those of RB1 (retinoblastoma 1) in cancer cell lines as well as in various normal human tissues. Moreover, introduction of wild-type RB1CC1 significantly induced RB1 expression in human leukemic cells. These data suggest that RB1CC1 may be a key regulator of RB1 gene expression.

Intracellular pH regulation in U-2 OS human osteosarcoma cells transfected with P-glycoprotein

The molecular mechanisms responsible for intracellular pH regulation in the U2-OS osteosarcoma cell line were investigated by loading with 2',7'-bis(2-carboxyethyl)-5(6) carboxyfluorescein ester and manipulation of Cl(-) and Na(+) gradients, both in HEPES- and HCO(3)(-)/CO(2)-buffered media. Both acidification and alkalinisation were poorly sensitive to 4,4'-diisothiocyanate dihydrostilbene-2,2'-disulfonic acid, inhibitor of the anion exchanger, but sensitive to amiloride, inhibitor of the Na(+)/H(+) exchanger. In addition to the amiloride-sensitive Na(+)/H(+) exchanger, another H(+) extruding mechanism was detected in U-2 OS cells, the Na(+)-dependent HCO(3)(-)/Cl(-) exchanger. No significant difference in resting pH(i) and in the rate of acidification or alkalinisation was observed in clones obtained from U-2 OS cells by transfection with the MDR1 gene and overexpressing P-glycoprotein. However, both V(max) and K' values for intracellular [H(+)] of the Na(+)/H(+) exchanger were significantly reduced in MDR1-transfected clones, in the absence and/or presence of drug selection, in comparison to vector-transfected or parental cell line. NHE1, NHE5 and at a lower extent NHE2 mRNA were detected in similar amount in all U2-OS clones. It is concluded that, although overexpression of P-glycoprotein did not impair pH(i) regulation in U-2 OS cells, the kinetic parameters of the Na(+)/H(+) exchanger were altered, suggesting a functional relationship between the two membrane proteins.

Amplification of the HER-2/neu oncogene is uncommon in pediatric osteosarcomas

BACKGROUND

Recent reports have described overexpression of p185(c-erbB2), the product of the HER-2/neu oncogene, in more than 40% of archival osteosarcomas that were examined by immunohistochemistry (IHC). However, IHC can be influenced by the method of fixation, extent of antigen retrieval, specificity and sensitivity of the antibody clone, and the use of an arbitrary semiquantitative scoring system. In contrast, fluorescence in situ hybridization (FISH) assays that assess HER-2/neu gene copy numbers in individual cells are more consistent, more reproducible, and less subjective than IHC.

METHODS

The authors examined pretreatment nondecalcified archival tissue from 21 high-grade pediatric osteosarcomas for amplification of the HER-2/neu oncogene using an Food and Drug Administration (FDA)-approved FISH assay (PathVysion, Vysis Inc., Downers Grove, IL). Additionally, IHC for p185(c-erbB2) was performed in all cases using the Dako polyclonal antibody clone A0485 (Dako Co., Carpinteria, CA).

RESULTS

None of the 21 osteosarcomas had evidence of HER-2/neu gene amplification by FISH, whereas p185(c-erbB2) IHC was negative in all cases.

CONCLUSIONS

HER-2/neu gene amplification appeared to be an uncommon event in pediatric osteosarcomas. The reason(s) for discordance between previous IHC data and the current FISH and IHC results was unknown, but might reflect intrinsic variations in antibody clones, or might suggest that, in some cases, the occurrence of protein overexpression is independent of gene amplification.

Elevated expression of hepatic proliferative markers during early hepatocarcinogenesis in hepatitis-B virus transgenic mice lacking mdr1a-encoded P-glycoprotein

Recent studies have shown that expression levels of the multidrug resistance gene MDR1, which encodes the drug transporter P-glycoprotein, correlate with prognostic outcomes of certain tumor types. These findings suggest that expression of MDR1 may affect tumor behaviors. To address this issue further, we investigated the expression of mdr1a, a human MDR1 homolog, on the development of hepatocellular carcinoma in a transgenic mouse model carrying the liver-targeted expression of human hepatitis-B virus (HBV) surface antigen. The pathogenetic program was compared in HBV mice carrying either mdr1a(+/+) or mdr1a(-/-). We found that the expressions of proliferative activity markers, Ki67 nuclear antigen, and proliferating cell nuclear antigen were elevated in mdr1a(-/-) mice younger than 10 wk in comparison with those in the same age group of wild-type animals. Replication in the hepatic population as determined by bromodeoxyuridine incorporation tended to support observation that mdr1a(-/-) mice exhibited elevated labeling indices in this age group. Moreover, histologic staining and flow-cytometric analysis showed that the mdr1a(-/-) animals exhibited a higher cell population with polyploidy than did the mdr1a(+/+) counterparts of the same age. However, no significant differences in the expression of the liver-injury markers serum alanine transaminase and aspartate transaminase were observed. Although our results showed that absence of mdr1a expression is correlated with modest enhanced proliferative characteristics in the livers at stage before the development of hepatocellular carcinoma, the overall life spans between these two strains of mice were not significantly different. The implication of these findings to the role of P-glycoprotein in tumor development and cancer chemotherapy is discussed.

Osteosarcomas and other cancers of bone

The results of several studies suggest that alterations in various cell cycle regulatory genes are involved in the pathogenesis of osteosarcomas. Experiments in animal models provide preliminary data on the feasibility of gene therapy in osteosarcoma and chondrosarcoma. Prediction of response to chemotherapy remains a major focus of imaging research. Several clinicopathologic studies have explored the mechanisms underlying multidrug resistance in osteosarcoma patients receiving neoadjuvant chemotherapy. HER2/erbB2 expression, linked to poor prognosis, has been proposed as a therapeutic target in osteosarcoma. In clinical studies of osteosarcoma, further data confirm the activity of ifosfamide and carboplatin but provide little support for the use of immunotherapy. A retrospective analysis showed no value for dose intensification of doxorubicin/cisplatin, but the results of a prospective trial should be more informative. Recent evidence confirms that secondary osteosarcomas and malignant fibrous histiocytomas of bone should be treated with aggressive chemotherapy regimens, similar to those used for osteosarcomas.

Osteoblastic differentiation and P-glycoprotein multidrug resistance in a murine osteosarcoma model

A recent study of multidrug resistance (MDR) 1 gene transfected osteosarcoma cells found a cause-effect relationship between increased expression of P-glycoprotein (P-gp) and a low aggressive phenotype. However, several experimental and clinical studies have observed contradictory findings in that P-gp expression has been associated with tumour progression. In the present study, we characterized P-gp-positive and P-gp-negative single-cell clones of a murine osteosarcoma, to further investigate the relationship between P-gp expression and changes in cell phenotype. Although these clones were all selected by doxorubicin (DOX) exposure, they were heterogeneous with respect to MDR1 gene expression. The P-gp-positive clones revealed MDR phenotype, whereas the P-gp-negative clones showed no resistance to drugs. Morphological and functional analysis showed that both the P-gp-positive and P-gp-negative clones were more differentiated than the parent cells in terms of enhanced activity of cellular alkaline phosphatase, an increase in well-organized actin stress fibres and enhanced osteogenic activity. Moreover, these subclones all displayed a decrease in malignant potential such as oncogenic activity, tumour growth rate and metastatic ability, regardless of their P-gp status. These results indicate that the observed osteoblastic differentiation and less aggressive phenotype in DOX-selected osteosarcoma cells may not only be explained by the direct effect of P-gp, and accordingly, consideration of the effect of DOX, as well as P-gp, appears to be important.

Treatment of multidrug resistant (MDR1) murine leukemia with P-glycoprotein substrates accelerates the course of the disease

The prognosis of patients with tumors expressing P-glycoprotein (P-gp), the MDR1 gene product, is generally poor. It is assumed that this is due to decreased tumor responsiveness that results from decreased drug accumulation. We observed that treatment of animals bearing MDR1-transfected leukemic cells with P-gp substrates (i.e., drugs that are transported by P-gp) significantly worsened host survival compared to treatment with vehicle or non-P-gp substrates. This effect was seen with cancer chemotherapeutic agents (paclitaxel and vincristine) and with the MDR modulator, trans-flupenthixol. To determine the mechanism(s) underlying this observation, we studied alterations in pharmacokinetics, pharmacodynamics, and metastasis. We found that the drug-induced acceleration of disease was associated with increased metastases. P-gp(+) cells treated with P-gp substrates demonstrated several pro-metastatic features, including membrane ruffling and invasion through a hepatocyte monolayer. These results suggest that the treatment of MDR tumors with P-gp substrates may produce changes in malignant behavior that could adversely affect therapeutic outcomes.