Evaluation of the interaction of mononuclear phagocytes with ovarian carcinoma cells in a colony assay

A neurotoxic and gliotrophic fragment of the prion protein increases plasma membrane microviscosity

Prion-related encephalopathies are characterized by astrogliosis and nerve cell degeneration and loss. These lesions might be the consequence of an interaction between the abnormal isoform of the cellular prion protein that accumulates in nervous tissue and the plasma membranes. Previously we found that a synthetic peptide, homologous to residues 106-126 of the human prion protein, is fibrillogenic and toxic to neurons and trophic to astrocytes in vitro. This study dealt with the ability of the peptide to interact with membranes. Accordingly, we compared PrP 106-126 with different synthetic PrP peptides (PrP 89-106, PrP 127-147, a peptide with a scrambled sequences of 106-126, and PrP 106-126 amidated at the C-terminus) as to the ability to increase the microviscosity of artificial and natural membranes. The first three had no effect on nerve and glial cells in vitro, whereas the amidated peptide caused neuronal death. Using a fluorescent probe that becomes incorporated into the hydrocarbon core of the lipid bilayer and records the lipid fluidity, we found PrP 106-126 able to increase significantly the membrane microviscosity of liposomes and of all cell lines investigated. This phenomenon was associated with the distribution of the peptide over the cell surface, but not with changes in the membrane lipid or protein content, or with membrane lipid phase transitions. Accordingly, we deduced that increased membrane microviscosity was unrelated to changes in the membrane native components and was the result of increased lipid density following PrP 106-126 embedding into the lipid bilayer. No control peptides had comparable effects on the membrane microviscosity, except PrP 106-126 amidated at the C-terminus. Since the latter was as neurotoxic, but not as fibrillogenic, as PrP 106-126, we argued that the ability of PrP 106-126 to increase membrane microviscosity was unrelated to the propensity of the peptide to raise fibrils. Rather, it could be connected with the primary structure of PrP 106-126, characterized by two opposing regions, one hydrophilic and the other hydrophobic, that enabled the peptide to interact with the lipid bilayer. Based on these findings, we speculated that the glial and nerve cell involvement occurring in prion-related encephalopathies might be caused by the interaction with the plasma membrane of a PrP 106-126-like fragment or of the sequence spanning residues 106-126 of the abnormal isoform of the prion protein.

Inhibition of head and neck tumor cell colony growth by lymphokine activated killer cells

The antiproliferative effect of lymphokine activated killer (LAK) cells on head and neck tumor cells has not previously been elucidated. We studied the inhibitory effects of recombinant interleukin-2 activated lymphocytes on tumor colony formation in semisolid agar, using head and neck tumor cells prepared from established tumor cell lines (K562, HT29, HLaC78) and xenografted head and neck squamous cell carcinomas on nude mice (XKN, XLL, XFL, XKF). LAK cells demonstrated a significant inhibitory effect on colony formation. The effects of LAK cells on cultured tumor cell lines were evaluated in a dose dependent manner using effector: target ratios. In addition, the colony formation of tumor cells derived from xenografted nude mouse was inhibited by LAK cells. These results suggest that LAK cells generate an antiproliferative effect on head and neck tumor cells.

Separation of clonogenic and differentiated cell phenotypes of ovarian cancer cells (HOC-7) by discontinuous density gradient centrifugation

We isolated clonogenic cells from differentiated HOC-7 ovarian cancer cells. Both cell subsets were characterised in respect to morphology, growth behaviour, DNA content and expression of tumour-associated antigens and nuclear oncogenes. Ten cell fractions (Fr) were separated by centrifugation in a discontinuous density gradient (Fr 1 less than 1.037 g/ml to Fr 10 greater than 1.069 g/ml, steps 0.004 g/ml). Large adenoid cells containing vacuoles filled with neutral polysaccharides were concentrated in Fr 1-4. These cells were non-clonogenic in soft agar. The growth on solid substrate was highest in Fr 6 and 7, intermediate in Fr 2-5 and Fr 8-10 and lowest in Fr 1. The mean cloning efficiencies of the fractions in soft agar were highest in Fr 6 (8.1%) and lowest in Fr 2 and 3 (0.1%). Diploid and near tetraploid cell subsets were found with similar frequency in all fractions. Immunocytochemistry revealed 4-7% Ki-67 positive cells in Fr 1-6 and 12-20% in Fr 7-10. In Fr 3-10 greater than or equal to 79% of the cells expressed CA 125. Positivity for c-myc, c-myb and c-fos (greater than or equal to 74%) was not correlated with clonogenicity. In conclusion, differentiated cells (Fr 1-4) were separated from cells with higher growth rates (Fr 5-10). Clonogenic cells were enriched in Fr 6. These data indicate that discontinuous density gradient fractionation represents a useful method for separation of cells with different degrees of differentiation, growth potential and clonogenicity.

Analysis of factors influencing clonogenic growth in vitro of cells from ovarian carcinoma patients

Clonogenic growth (defined as the formation of greater than or equal to 5 colonies per 5 x 10(5) viable nucleated cells per plate) of ovarian cancer specimens assessed in our clonogenic assay system was significantly associated with the proportion of tumor cells in the suspensions plated (N = 87; P = 0.0006), although there was no quantitative relationship with the corresponding plating efficiencies. An inverse correlation was observed between monocytes/macrophages/mesothelial cells (M) proportion and clonogenic growth (P = 0.013). These associations were most evident when only effusions were considered. Univariate analyses identified tumor cell content, M proportion and, to a lesser degree, granulocyte content as the only factors out of 12 examined to be correlated with colony formation. Multivariate analysis using a logistic regression model identified the proportion of tumor cells as the only significant factor predicting clonogenic growth in vitro (P = 0.0006). The overall accuracy of prediction for growth or non-growth was 63.2%.

The anti-tumor effect of in vitro tumor-stimulated autologous peripheral blood lymphocytes measured by the subrenal capsule assay

Lymphokine-activated killer cells (LAK) are able to kill natural killer (NK)-resistant fresh bioptic tumor cells. We have tried to increase the antitumor activity of peripheral blood lymphocytes by the simultaneous stimulation with interleukin-2 and autologous tumor extract (TE). The influence of LAK cells and LAK cells stimulated with TE was compared in the subrenal capsule assay in nude mice. Experiments were performed with eight head and neck tumors following their surgical extirpation. The tumors were first grown in the renal capsule space while lymphocytes were being stimulated in vitro. Following this, the lymphocytes were injected into the growing tumors. The autologous TE-stimulated LAK cells were more effective in treating tumors than were the LAK cells. Tumors regressed in some cases so treated, a finding which was never observed with LAK cells alone.

Human tumor cell lines with pleiotropic drug resistance are efficiently killed by interleukin-2 activated killer cells and by activated monocytes

Two human cell lines, the colon carcinoma Lovo and the transformed intestinal I-407, and their variants (Lovo/Dx and I-407/Dx), with pleiotropic resistance to cancer chemotherapeutic drugs, were examined for their susceptibility to human Interleukin-2-activated killer cells and to activated monocytes. These non-specific or broadly specific effector cells expressed cytotoxicity levels on pleiotropically resistant tumor cells comparable to those of the parental cell populations. This finding provides a rationale for immunological approaches designed to eradicate residual tumor cells surviving and resistant to cytotoxic chemotherapy.

The human tumor clonogenic assay as a model system in cell biology

The human tumor stem cell (clonogenic) assay (HTCA) is a soft agar system designed for growing fresh human tumor specimens in vitro. The assay has been extensively used in studies both of individual patients' response to chemotherapy and for screening new agents. The technical limitations of this assay have been extensively discussed. The use of this test as a model system to study fundamentals of tumor cell growth has not been stressed. The potentials and limitations of this assay for the study of the regulation of tumor growth are presented.

The radiosensitivity of cultured human and mouse keratinocytes

Clonogenic survival assays after gamma-radiation in vitro were performed on freshly isolated and subcultured keratinocytes from mouse skin, mouse tongue and human skin. Survival curves were constructed by fitting the data to a multi-target model of cell survival. When subcultured, keratinocytes from all sites produced survival curves which showed a reduced shoulder region and an increased D0 when compared with their freshly isolated counterparts. Freshly isolated human skin keratinocytes were more radiosensitive than mouse keratinocytes from either skin or tongue.