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Biomedical subjects

A Pihl

Publications and source records attributed to A Pihl.

At least 73 records · Page 4Linked to original sources
PubMed1981

Cultivation of human melanomas in soft agar. Factors influencing plating efficiency and chemosensitivity.

As part of a programme to study the predictive clinical value of a soft agar assay for measuring chemosensitivity of human melanomas in vitro, we have observed the effect of three disaggregation methods on the yield of tumor cells, plating efficiency in soft agar and chemosensitivity. The yields and plating efficiencies obtained, as well as sensitivity to DTIC, CCNU, vinblastine and abrin, were about the same whether collagenase/pronase/DNase-treatment, trypsin/EDTA-treatment or mechanical treatment was used. When melanoma xenografts of different sizes were studied, an inverse relationship between tumor size and plating efficiency was found, whereas chemosensitivity was unaffected by tumor size. The highest plating efficiencies of melanoma cells, both from patient biopsies and from xenografts, were obtained when red blood cells were present and a low oxygen concentration (5%) was used. The results demonstrate that, in the case of melanomas, the fraction of tumor cells that are clonogenic in vitro depends on the size of the tumors, and even more so on the culture conditions used. An important finding was that chemosensitivity in vitro appears to be unaffected by the disaggregation method and by tumor size.

Abrin↗
PubMed1981

Chimeric toxins.

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Animals↗
PubMed1981

Comparison of two soft-agar methods for assaying chemosensitivity of human tumours in vitro: malignant melanomas.

Two soft-agar methods for assaying chemosensitivity of human cancers in vitro were compared with respect to colony morphology, plating efficiency (PE) and chemosensitivity of human melanomas. In 9 xenografts and 9 patients' biopsy specimens Method A (essentially that of Courtenay & Mills, 1978) gave considerably higher PE that Method B (essentially that of Hamburger & Salmon, 1977) and, in contrast to Method B, the number of colonies was proportional to the number of cells plated. Evidence was obtained that the observed differences in PE could be attributed to the low O2 concentration and the presence of rat red blood cells in Method A. Colony morphology was similar in the 2 assays. When cells from 4 xenografted melanomas were treated in vitro with DTIC, CCNU, vinblastine and abrin, and the inhibition of colony formation was assayed concurrently in the 2 soft-agar methods, the tumour cells appeared to be more sensitive to 3 of the drugs in Method B than in A. The results demonstrate that chemosensitivity data obtained with the 2 assays cannot be directly compared.

Abrin↗
PubMed1981

Do cell lines in vitro reflect the properties of the tumours of origin? A study of lines derived from human melanoma xenografts.

The characteristics of 7 human melanoma cell lines were compared with those of the xenografts from which they were established. The ultrastructure, melanin content, isozyme pattern and chromosome numbers of the cell lines were closely similar to those of the corresponding xenografts. The different cell lines gave rise to colonies in soft agar of size and morphology similar to the parent xenografts, and the plating efficiencies were clearly correlated. However, no correlation was found between the growth rates in vivo and either the doubling times and saturation densities in monolayer cultures or the plating efficiencies in soft agar. Moreover, one of the cell lines lost its tumorigenic ability upon establishment in culture. Thus, although the properties of the cell lines by and large reflected those of the parent xenografts, important inconsistencies were seen. The data emphasize that extrapolations from continuous cell lines in vitro to tumour cells in vivo are not necessarily valid. A high content of cellular fibronectin was correlated with a compact colony morphology in soft agar and rapid attachment and spreading on plastic. The growth rates and cellular morphology of the cell lines were strongly influenced by TPA, DMSO, retinoic acid and theophylline, but not by alpha-melanocyte-stimulating hormone. A murine cell line established from one of the xenografts grew in soft agar and produced sarcoma in mice. The malignant murine cells had arisen by transformation of murine stromal cells during the first subcultures in vitro, possibly caused by a factor produced by the human melanoma cells.

Animals↗
PubMed1981

Radioimmunoassays of abrin and ricin in blood.

Radioimmunoassays for abrin and ricin are described. There is little cross-reactivity between the two toxins. The procedures described are capable of determining blood concentrations down to 50-100 pg/ml, permitting identification of abrin and ricin poisoning and monitoring of the blood concentrations in cancer patients treated with these agents.

Abrin↗
PubMed1980

In vitro sensitivity of human melanoma xenografts to cytotoxic drugs. Correlation with in vivo chemosensitivity.

Single-cell suspensions prepared from five human melanomas, grown serially as xenografts in athymic nude mice, were exposed in vitro to increasing concentrations of DTIC (Dacarbazine), CCNU (Lomustine), procarbazine, vinblastine, and the cancerostatic lectins abrin and ricin. The in vitro chemosensitivity of the cells, as measured by the drug concentrations required to inhibit colony formation in soft agar by 50%, was correlated with the growth delay of the xenografts in vivo, previously observed after treatment of the animals with maximum tolerable doses of the same drugs. It was found that for each drug the in vitro sensitivity of the different xenografts was strongly correlated with their response in vivo. The results provide evidence that the soft agar test, as carried out here, adequately reflects the relative sensitivity of the xenografts in vivo. The data indicate that human xenografts may be used to develop quantitative in vitro chemosensitivity tests.

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PubMed1980

Response to chemotherapy of human, malignant melanoma xenografts in athymic, nude mice.

In attempts to elucidate the factors determining individual differences in response of tumors to chemotherapeutic agents, the sensitivity of six human malignant melanomas growing in athymic, nude mice was studied. Six agents, viz. DTIC, CCNU, vinblastine, procarbazine, as well as the toxic lectins abrin and ricin, were administered in maximum tolerable doses to the tumor-bearing mice. The response to treatment was expressed as tumor growth delay, i.e. the number of volume double times saved by the treatment. The xenografts had very nearly retined the morphology of the parent tumors and were histologically similar. They showed different and characteristic early growth rates and also wide variations in their response to the agents tested. Unexpectedly, in the case of DTIC, CCNU and procarbazine, the response of the xenografts proved to be inversely related to the early growth rates of the tumors. For vinblastine, abrin and ricin, no correlation between response and growth rate of the tumors was apparent. Procarbazine had the best overall effect among the agents here tested. DTIC, CCNU and vinblastine had somewhat less and about equal overall efficiency. The plant toxin abrin, which acts by inhibiting protein synthesis, was at least as effective as DTIC. When abrin was given together with DTIC, the effect on the two xenografts tested was superior to that of each agent given alone. The wide variations observed in the response of the histologically similar xenografts to the different agents demonstrate that testing of the chemosensitivity of human xenografts requires the use of a panel of tumors of each histological tpye. The clear relationship found between the early growth rate of the xenografts and their sensitivity to three of the drugs most commonly used in the treatment of malignant melanomas, may have clinical implications.

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PubMed1980

Turnover of the poly(A) moiety of mRNA in wheat-germ extract.

The synthesis and degradation of poly(A) were examined in wheat germ lysates under conditions used for protein synthesis. The lysate contained both poly(A)-polymerizing and poly(A)-hydrolytic activities. The synthetic activity was dependent on the presence of either poly(A) or polyadenylated mRNA as primer. Concurrent with the synthesis of poly(A), radioactivity was released from labeled poly(A) and from the poly(A) region of mRNA. Both poly(A) synthesis and hydrolysis were independent of Mn2+ and could proceed in the presence of Mg2+, the major divalent metal ion required for protein synthesis. The synthetic activity was favoured at high (1 mM) ATP concentration, whereas the hydrolytic activity was maximal in the absence of ATP or at low (0.1 mM) ATP concentration. These data indicate that the steady-state length of the poly(A) moeity of mRNAs in the cytoplasm may be regulated by the levels of ATP. Translation products of polyadenylated mRNAs isolated from myeloma cells before and after partial deadenylation were separated by dodecylsulfate/polyacrylamide gel electrophoresis. Shortening of the poly(A) moiety did not alter the relative amounts of the peptides synthesized, indicating that this process does not involve a preferential breakdown of certain species of mRNA.

Adenosine Triphosphate↗
PubMed1980

Variable rate of polypeptide chain elongation in vitro. Effect of spermidine.

Translation of rabbit globin mRNA and tobacco mosaic virus mRNA was studied in a wheat germ system. After a short pulse with labeled methionine, the reaction products were separated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate and visualized by fluorography. Discrete bands corresponding to incomplete products were detected both with globin and tobacco mosaic virus RNA as messenger at a time when no release of peptides from tRNA could be detected. In the absence of spermidine certain intermediate products accumulated during the chase period. With increasing incubation time, the radioactivity of most bands was chased into higher-molecular-weight products. This change in size distribution was more pronounced when magnesium was partially replaced by spermidine. Evidence is presented that some of the incomplete products had in part been released from tRNA. No such release of polypeptides could be detected in experiments using the artificial messenger poly(U), indicating that non-specific peptidyl-tRNA hydrolases were not present in the system. The transient accumulation of discrete bands during the chase period indicates that in the wheat germ system polypeptide chain elongation occurs at discontinuous rates. The fact that spermidine increases the rate of elongation and the yield of full-length translation products may be due to its ability to facilitate the movement of the ribosomes beyond regions where the elongation is retarded.

Animals↗
PubMed1980

Assessment of tumour growth and of response to chemotherapy of human melanomas in athymic, nude mice.

The growth of 6 different human melanomas xenografted into athymic mice was followed by measuring 2 vertical diameters twice weekly. The growth rate of the xenografts was expressed as the tumour doubling time, measured in the volume range 30-60 mm3. None of the xenografts increased their growth rate with increasing number of passages. The tumour lines, which were histologically very similar, showed individual, characteristic growth rates differing by a factor of 3. Evidence was obtained that resistance to cytostatic drugs in the patients is retained in the xenograft. Procedures for evaluating response to chemotherapy are discussed.

Animals↗
PubMed1980

Doxorubicin and ricin, a strongly synergistic combination in mouse leukemia.

The effect of combinations of doxorubicin (Adriamycin) and the cancerostatic plant lectin ricin on L1210 leukemic cells in mice was assessed by end-point dilution and spleen-colony assays. The combinations, which were well-tolerated by the mice, acted synergistically on leukemic cells in liver, spleen, and brain. In the bone marrow, a dramatically synergistic effect was obtained with combinations that had only slight effect on the survival of normal stem cells.

Animals↗