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H Robson

Publications and source records attributed to H Robson.

18 recordsLinked to original sources
PubMed2002

Platinum agents in the treatment of osteosarcoma: efficacy of cisplatin vs. carboplatin in human osteosarcoma cell lines.

BACKGROUND: Cisplatin (cDDP), when used either alone or, more often, in combination with other agents, especially adriamycin, achieves a high response rate in osteosarcoma. Its use, however, is limited by severe nephro- and neuro-toxicity. Second generation platinum compounds, most notably carboplatin (CBDCA), have been developed in order to attempt to reduce these dose-limiting toxicities, and thus improve the therapeutic ratio. Studies evaluating the role of combination CT containing CBDCA vs. cDDP have demonstrated differing results depending on the tumor type tested and its role in the treatment of osteosarcoma has yet to be clarified. PROCEDURE: In this study, we compared the in vitro anti-tumor activity of cDDP and CBDCA in a panel of three human osteosarcoma cell lines (HOS, MG63, and U2OS). RESULTS: cDDP and CBDCA (0-20 micromol) showed marked variation in cytotoxicity among the three cell lines. EC(50) values for CBDCA in HOS and MG63 cells were approximately two-fold higher than for cDDP and the ratio of AUC(CBDCA) to AUC(cDDP) varied from 1.8 in the HOS cell line to 2.3 in the MG63 cell line. Exposure of MG63 and HOS cells to either cDDP or CBDCA (1.67 and 13.5 micromol) caused a G2/M cell cycle arrest by 24 hr. Also evident was a sub G1 peak indicative of cell death by apoptosis. U2OS cells were relatively resistant to the cytotoxic effects of both drugs, although a cell cycle arrest in response to DNA damage was observed. This suggests that unlike MG63 and HOS cells, U2OS cells have either a more efficient repair pathway for platinum-induced DNA damage or are able to evade apoptosis. Examination of apoptotic events and cellular recovery demonstrated that both an 8-16-fold higher concentration and longer treatment period for CBDCA compared with cDDP was required to produce equivalent cell death and a loss of the ability of single cell clones to form colonies in both the HOS and MG63, but not the U2OS cell line. CONCLUSIONS: Our findings suggest that CBDCA at a two- to four-fold higher concentration than cDDP has potential therapeutic activity in platinum sensitive osteosarcomas, particularly when cDDP cytotoxicity compromises therapeutic efficacy.

Antineoplastic Agents↗
PubMed2002

Thyroid status affects number and localization of thyroid hormone receptor expressing mast cells in bone marrow.

Thyroid hormone (T(3)) plays a key role in endochondral ossification. The process relies on the coordinated synthesis and degradation of cartilage matrix and is disrupted in juvenile hypothyroidism, leading to abnormal skeletal development. Mast cells synthesize and store matrix-degrading enzymes. We examined whether thyroid status influences skeletal mast cell distribution in growing rats to determine whether they might modulate the actions of T(3) in bone. Tibiae were collected for histological, histochemical, immunohistochemical, and immunofluorescence analysis. Mast cells were increased throughout the bone marrow in hypothyroid rats compared with euthyroid, thyrotoxic, and hypothyroid-thyroxine replaced animals. Large numbers were present in metaphyseal marrow adjacent to the growth plate in hypothyroid animals and cells were distributed evenly throughout the marrow. Very few mast cells were present in metaphyseal marrow in other groups, but their numbers increased with increasing distance from the growth plate. T(3) receptor alpha1 (TRalpha1) was expressed in the nucleus and cytoplasm of skeletal mast cells, whereas TRalpha2 and TRbeta1 were restricted to the cytoplasm. Localization of TRs was not affected by altered thyroid status. Thus, disrupted endochondral ossification in hypothyroidism may be mediated in part by skeletal mast cells, which express TR proteins and may function as T(3) target cells.

Animals↗
PubMed2002

Dexamethasone inhibits and thyroid hormone promotes differentiation of mouse chondrogenic ATDC5 cells.

The effects of glucocorticoid (GC) excess, thyrotoxicosis, and hypothyroidism on linear growth indicate that growth plate chondrocytes are exquisitely sensitive to GC and thyroid hormone (T(3)). Murine ATDC5 cells undergo chondrogenesis in vitro and were used to evaluate the effects of dexamethasone (Dex) and T(3) on cell proliferation and differentiation. Immature and differentiated ATDC5 cells expressed glucocorticoid and T(3)-receptor mRNAs. Cells proliferated and organized into cartilage-like nodules after 7 days. Chondrocyte maturation progressed over 9-40 days, with increasing alkaline phosphatase (ALP) activity, secretion of an Alcian blue-positive matrix, and mineralization of cartilage-like nodules. Dex reduced cell number over the 40 day period, causing inhibition of ALP activity and matrix production with failure of mineralization. Following withdrawal of Dex, chondrocytes proliferated and re-entered the differentiation and mineralization program, indicating that GC inhibition of chondrogenesis is reversible. In contrast, T(3) reduced cell proliferation, but induced ALP activity and increased matrix secretion earlier than in control cultures. Thus, GCs and T(3) regulate growth plate chondrocyte differentiation by distinct mechanisms. GCs arrest cell proliferation, differentiation, and cartilage mineralization and maintain chondrocyte precursors in a state of quiescence with the capacity to re-enter chondrogenesis. T(3) inhibits cell proliferation but accelerates differentiation to stimulate chondrogenesis.

Animals↗
PubMed2002

Effects of chemotherapy on bone metabolism and skeletal growth.

In recent years there has been a significant increase in both acute and chronic toxicity associated with the more successful but now highly intensive chemotherapy (CT) regimens used to treat childhood cancers. The incidence of childhood cancers coincides with periods of rapid skeletal development. Consequently, short stature and osteoporosis are important long-term effects in adult survivors. Clinical data indicate that the effects of CT, including glucocorticoids, on final height are due to direct effects of these drugs on the skeleton. The multiple modes of action of CT drugs suggest a complex and diverse influence on chondrocytes, extracellular matrix and bone cells. However, only limited data demonstrate these direct effects on the proliferative capacity of growth plate chondrocytes and on key steps of endochondral ossification, the multistep process that determines rate and extent of long bone growth. Endochondral ossification requires coordinated maturation, proliferation and differentiation of growth plate chondrocytes leading to hypertrophic cells which eventually undergo apoptosis to leave a cartilaginous scaffold that is mineralized prior to the laying down of new bone. Disruption of the physiological cellular activity of growth plate chondrocytes and/or bone cells result in skeletal growth disturbances. Thus, CT drugs which disrupt normal cell division may manifest their effects on the growth plate as either a reduction in cell number and/or the loss of functional integrity of extracellular matrix. Histological and cell kinetic studies, using in vivo and in vitro models of long bone growth, are essential to increase our understanding of the cellular mechanisms involved and to finally determine how the individual growth potential might be maintained during treatment for childhood cancers.

Antineoplastic Agents↗
PubMed2001

Glucocorticoids, thyroid hormone and growth hormone interactions: implications for the growth plate.

Linear growth occurs during childhood and results from endochondral ossification in the growth plate. Prepubertal growth is primarily regulated by growth hormone (GH) and insulin-like growth factor (IGF)-I, with important contributions from glucocorticoids (GC) and thyroid hormone (T(3)). The somatomedin hypothesis proposed that GH stimulates hepatic IGF-I production, which then regulates growth via IGF-I receptor expressing chondrocytes in an endocrine fashion. Recent studies indicate that locally acting IGF-I is a key determinant of endochondral ossification and that GH, GC and T(3) regulate expression of IGF-I and its receptor in the growth plate directly. Analysis of hormone imbalance during childhood and studies of genetically modified mice provide support for an important GH and IGF-I autocrine/paracrine pathway and for direct effects of GC and T(3) during endochondral ossification. Thus, the epiphyseal growth plate is a key site for convergent hormone action that mediates the control of linear growth.

Animals↗
PubMed2000

An investigation into the release of cefuroxime axetil from taste-masked stearic acid microspheres. III. The use of DSC and HSDSC as means of characterising the interaction of the microspheres with buffered media.

Stearic acid coated cefuroxime axetil (SACA) microspheres have been studied using differential scanning calorimetry (DSC) and high sensitivity DSC (HSDSC) in order to examine the interaction between the spheres and a range of buffer systems, with a view to further enhance the understanding of the mechanism of drug release developed in earlier studies [Robson et al., 1999, 2000]. DSC studies indicated that after immersion in Sorensens modified phosphate buffer (SMPB) pH 5.9 followed by washing and drying, no change in the thermal properties of the spheres was detected up to 60 min of immersion, with a single endotherm noted at circa 56 degrees C, that corresponded to the melting of the stearic acid used in this study; similar results were obtained for systems immersed in distilled water. After immersion in SMPB pH 7.0 and 8.0, however, a second peak was noted at approximately 67 degrees C that increased in magnitude relative to the lower temperature endotherm with increasing exposure time to the medium. Spheres that had not been previously washed prior to drying showed complete conversion to the higher temperature endotherm for these two buffers. Systems which had been exposed to a range of pH 7.0 buffers (citrate-phosphate buffer (CPB), phosphate buffer mixed (PBM), boric acid buffer (BAB)) were then examined. Only the CPB systems showed evidence for conversion to the higher melting form. PBM systems to which further sodium had been added were then examined. A maximum conversion was found at 0.05 M sodium, which was in agreement with the maximum in release rate found in a previous study [Robson et al., 2000]. HSDSC was then used to examine systems that were immersed in the buffer. For SMPB, pH 5.9 and distilled water, only the endotherm corresponding to the stearic acid melting was seen. However, for SMPB pH 7.0 and 8.0, three peaks were seen, two corresponding to those seen for the DSC studies and a further lower temperature peak at circa 44 degrees C. Studies on PBM systems to which additional sodium had been added showed small levels of conversion to the higher temperature form at higher sodium contents. The data was discussed in terms of the correlation with earlier dissolution studies on the same systems [Robson et al., 1999; 2000].

Buffers↗
PubMed2000

An investigation into the release of cefuroxime axetil from taste-masked stearic acid microspheres. II. The effects of buffer composition on drug release.

The influence of buffer composition on the release of cefuroxime axetil from stearic acid microspheres has been investigated, with particular emphasis on establishing the relationship between buffer composition and release at a single pH value. Studies of drug dissolution and release from spheres in pH 7.0 citrate phosphate buffer (CPB), boric acid buffer (BAB), phosphate buffer mixed (PBM) and Sorensens modified phosphate buffer (SMPB) indicated marked differences in release profile from the spheres, with an approximate rank order of SMPB > CPB approximately BAB > PBM. The role of added sodium was then investigated by examining the release profiles in SMPB and PBM to which sodium ions had been added. Increases in the sodium content from approximately 0.11 to 0.2 M were found to decrease the release rate for the SMPB, while increases from 0.007 to 1.0 M sodium in PBM resulted in a maximum release being seen for the systems containing 0.05 M sodium. Studies on surface disintegration, using scanning electron microscopy (SEM) and sodium uptake using flame emission spectroscopy, indicated an interrelationship between medium composition, disintegration and release. The data are discussed in terms of the possible mechanisms associated with drug release from these spheres.

Buffers↗
PubMed2000

Thyroid hormone acts directly on growth plate chondrocytes to promote hypertrophic differentiation and inhibit clonal expansion and cell proliferation.

T3 is an important regulator of endochondral bone formation in epiphyseal growth plates. Growth arrest in juvenile hypothyroidism results from disorganization of growth plate chondrocytes and their failure to undergo hypertrophic differentiation, but it is unclear how T3 acts directly on chondrocytes or whether its actions involve other pathways. To address this issue, we investigated whether thyroid hormone receptors (TR) were localized to discrete regions of the unfused epiphysis by immunohistochemistry performed in tibial growth plates from 21-day-old rats and examined the effects of T3 on growth plate chondrocytes in agarose suspension cultures in vitro. TRalpha1, -alpha2, and -beta1 were expressed in reserve and proliferating zone chondrocytes, but not in hypertrophic cells, suggesting that progenitor cells and immature chondrocytes are the major T3 target cells in the growth plate. Chondrocytes in suspension culture expressed TRalpha1, -alpha2, and -beta1 messenger RNAs and matured by an ordered process of clonal expansion, colony formation, and terminal hypertrophic differentiation. Clonal expansion and proliferation of chondrocytes were inhibited by T3, which also induced alkaline phosphatase activity, expression of collagen X messenger RNA, and secretion of an alcian blue-positive matrix as early as 7 days after hormone stimulation. Thus, T3 inhibited chondrocyte clonal expansion and cell proliferation while simultaneously promoting hypertrophic chondrocyte differentiation. These data indicate that thyroid hormones concurrently and reciprocally regulate chondrocyte cell growth and differentiation in the endochondral growth plate.

Animals↗
PubMed2000

Thyroid hormones regulate hypertrophic chondrocyte differentiation and expression of parathyroid hormone-related peptide and its receptor during endochondral bone formation.

Hypothyroidism in children causes developmental abnormalities in bone and growth arrest, while thyrotoxicosis accelerates growth rate and advances bone age. To determine the effects of thyroid hormones on endochondral bone formation, we examined epiphyseal growth plates in control, hypothyroid, thyrotoxic, and hypothyroid-thyroxine (hypo-T4)-treated rats. Hypothyroid growth plates were grossly disorganized, contained an abnormal matrix rich in heparan sulfate, and hypertrophic chondrocyte differentiation failed to progress. These effects correlated with the absence of collagen X expression and increased parathyroid hormone-related protein (PTHrP) messenger RNA (mRNA) expression. In thyrotoxic growth plates, histology essentially was normal but PTHrP receptor (PTHrP-R) mRNA was undetectable. PTHrP is a potent inhibitor of hypertrophic chondrocyte differentiation that acts in a negative feedback loop with the secreted factor Indian hedgehog (Ihh) to regulate endochondral bone formation. Thyroid hormone receptor alpha1(TRalpha1), TRalpha2, and TRbeta1 proteins were localized to reserve zone progenitor cells and proliferating chondrocytes in euthyroid rat cartilage; regions in which PTHrP and PTHrP-R expression were affected by thyroid status. Thus, dysregulated Ihh/PTHrP feedback loop activity may be a key mechanism that underlies growth disorders in childhood thyroid disease.

Animals↗
PubMed1998

Glucocorticoid pretreatment reduces the cytotoxic effects of a variety of DNA-damaging agents on rat tibial growth-plate chondrocytes in vitro.

It is apparent that cytotoxic chemotherapy used to treat childhood malignancies has a major impact on subsequent growth. Our initial studies have demonstrated a direct adverse effect of individual glucocorticoids and cytotoxic agents on the proliferative capacity of rat tibial growth-plate chondrocytes in vitro. In the present study we investigated the interaction between these classes of agents using in vitro cultures of chondrocytes and examined the potential of these cells to recover from the adverse effects of the drugs as applied either alone or in combination. The glucocorticoids prednisolone and dexamethasone significantly reduced the growth rate of chondrocytes when present in cultures for 3 days. The growth rate increased following the removal of prednisolone and dexamethasone from cultures and reached 83.9+/-0.8% and 62.4+/-4.0%, respectively, of the control values after 11 days of culture. In contrast, cell numbers were significantly reduced when the DNA-damaging agents cisplatin, carboplatin, etoposide or actinomycin-D were present in cultures for 3 days. Very little recovery of cell growth was observed after removal of the drugs from cultures, with cell loss occurring in the cisplatin- and actinomycin-D-treated cultures. However, pretreatment of chondrocytes with either of the glucocorticoids completely ameliorated the cytotoxic effects of etoposide and carboplatin and significantly reduced those of cisplatin and actinomycin-D. Recovery of the cells treated with a combination of glucocorticoid and DNA-damaging agent was demonstrated by a significant increase in their ability to form colonies in suspension culture. Colony numbers were increased by a factor of between 5 and 80 as compared with the cells receiving medium alone followed by DNA-damaging agent. The glucocorticoids offer a protective effect in terms of the reduced cytotoxicity of DNA-damaging agents and improve the subsequent clonogenicity and recovery of growth-plate chondrocytes. This has important implications for treatment schedules involving both cytotoxic agents and glucocorticoids in childhood malignancies.

Animals↗
PubMed1998

Chemotherapeutic agents used in the treatment of childhood malignancies have direct effects on growth plate chondrocyte proliferation.

Short stature is one of the most well recorded long term sequelae for adult survivors of childhood malignancies. It has become increasingly apparent that cytotoxic chemotherapy, as well as craniospinal irradiation, has a major impact on growth, but there are virtually no studies which explore the mechanisms by which these cytotoxic drugs affect growth. We have used an in vitro system to investigate the direct effects of a range of chemotherapeutic agents on the proliferative responses of rat tibial growth plate chondrocytes, both in suspension and monolayer culture. The glucocorticoids and purine anti-metabolites reduced chondrocyte proliferation both in monolayer and suspension cultures and this resulted from an increase in cell doubling times with a concomittant reduction in the numbers of S phase cells. DNA damaging agents (e.g. actinomycin-D) were also able to reduce chondrocyte proliferation, both in monolayer and suspension culture. This, however, was the result of a cell cycle arrest and subsequent cell death. In our studies, methotrexate had no significant effect on the proliferative responses of the chondrocytes either in monolayer or suspension culture. These results indicate direct effects of a range of chemotherapeutic agents on the proliferative responses of growth plate chondrocytes. Both cytostatic and cytotoxic effects were observed although the impact of either the potential loss of cells from the proliferative pool during chondrocyte differentiation, or the reduction in the rate of chondrocyte turnover on long bone growth remains to be elucidated.

Animals↗
PubMed1997

Differential influence of TGFbeta1 and TGFbeta3 isoforms on cell cycle kinetics and postirradiation recovery of normal and malignant colorectal epithelial cells.

PURPOSE: A clonogenic assay was used to determine the effects of the growth factors TGFbeta1 and TGFbeta3 on the radiation responses of a normal rat epithelial cell line (IEC6) and a human colonic carcinoma epithelial cell line (Widr). METHODS AND MATERIALS: The radiation sensitivity and ability to recover from potentially lethal damage (PLD), of preconfluent monolayer cultures, was assessed in the presence of the growth factors for 24 h prior to, during, and after irradiation. RESULTS: The surviving fractions of both cell lines assessed immediately following irradiation were unaffected by TGFbeta1 or TGFbeta3. However, TGFbeta3 (but not TGFbeta1) significantly reduced the amount of PLD recovery in the Widr cells (but not in the IEC6 cells). This was associated with a reduction in the shoulder region of the survival curve, rather than a change in slope. A comparative analysis of the effects of TGFbetas 1 and 3 on cell cycle events in the two cell lines demonstrated significantly more Widr cells in the S phase, in the presence of TGFbeta3 only, compared to the controls. This remained constant both before and immediately following irradiation. In the IEC6 cell line TGFbeta3 produced an increase in the numbers of G1 phase cells, characteristic of a G1 arrest. CONCLUSION: It seems likely that TGFbeta3-induced radiosensitisation in Widr cells, 6 h after a single dose of irradiation, is related to its effects on cell cycle events such that the failure of these cells to arrest in G1, either before or after irradiation, results in significantly reduced recovery from DNA damage. This, however, may not be the only mechanism by which this growth factor produces this effect. Indeed, it will also be necessary to investigate these effects in in vivo models and to determine the response to fractionated irradiation before the potential therapeutic benefit of both the differential effects observed between the two TGFbeta isoforms and also between the malignant and normal cell lines can be fully assessed.

Animals↗
PubMed1996

Transforming growth factor beta 1 expression in human colorectal tumours: an independent prognostic marker in a subgroup of poor prognosis patients.

Members of the transforming growth factor beta (TGF-beta family, in particular TGF-beta 1, are some of the most potent inhibitory growth factors in a variety of cell types. Resistance to TGF-beta 1-induced growth inhibition is frequently observed in colorectal carcinomas and is associated with tumour progression. Perturbations of TGF-beta 1 expression and function, therefore, may contribute to the loss of some constraints on tumour cell growth. In this study we have examined the expression of TGF-beta 1 and its precursor latency-associated peptide (LAP)-TGF-beta in human colorectal tumours using immunohistochemical techniques. In 86% of the tumours the LAP-TGF-beta complex was present in both the stromal and epithelial cells, whereas the mature TGF-beta 1 peptide was expressed in the glandular epithelium of 58.3% of these tumours. Intense staining for TGF-beta 1 was positively associated with advanced Dukes' stage. Furthermore, there was a significant correlation between the presence of TGF-beta 1 in the tumours and a shorter post-operative survival. This was most significant in a subgroup of patients who had received only a palliative operation. These results suggest that TGF-beta 1 expression may be useful as an independent prognostic indicator for a subgroup of patients who have a particularly poor prognosis.

Adenocarcinoma↗
PubMed1987

Alterations in T-lymphocyte subpopulations in patients with head and neck cancer. Correlations with prognosis.

Impaired cell-mediated immunity has been consistently demonstrated in patients with advanced head and neck squamous cancer (HNSC); however, the results of prior studies of correlations of cellular immune parameters with treatment outcome have been inconsistent, and routine assessment of immune parameters has been of limited clinical use. To determine the prognostic importance of alterations in the proportions of various T-lymphocyte subpopulations in the peripheral blood of patients with HNSC, levels of T3, T4, T6, T8, T9, T10, T11, and Leu 7 cells were quantitated by flow cytometry in 80 previously untreated patients and prospectively correlated with tumor characteristics and clinical course (median length of follow-up, 27 months). The mean helper/suppressor cell ratio (T4/T8) increased progressively with increasing tumor stage and was significantly elevated among patients with cancer as a group and in patients with advanced (stage III or IV) disease compared with 40 normal subjects. Decreased disease-free survival was significantly associated with elevated T4/T8 ratios and low percent T8 and T11 cell levels. The prognostic significance of percent T8 (cytotoxic/suppressor) cell levels persisted even after adjusting for known prognostic factors of tumor stage, T class, N class, and tumor site. These correlations provide new insight into immune alterations in HNSC that may prove useful in identifying patients with early clinical disease who have a poor prognosis.

Adult↗