Agar Colony Formation Research Articles

Hyperexpression of Interleukin-7 Is Not Necessary or Sufficient for Transformation of a Pre-B Lymphoid Cell Line

Interleukin-7 (IL-7) is a potent stimulator of pre-B-lymphocyte proliferation. Pre-B cells transformed by a variety of oncogenes including those of the ABL protein tyrosine kinase family were screened for endogenous IL-7 mRNA expression by polymerase chain reaction and a sensitive bioassay for secreted IL-7. Some v-abl but none of the BCR/ABL, v-src, v-fms, v-myc, v-ras, or v-raf transformants analyzed contained elevated IL-7 transcripts. None of the cell lines secreted detectable bioactivity. We overexpressed IL-7 via a retroviral vector in an IL-7-dependent pre-B cell line to assess the potential for autocrine growth stimulation and malignant transformation. We achieved dramatic deregulation of IL-7 translational suppression by removing portions of the 5' flanking region. Levels of IL-7 expression much greater than those needed to establish factor-independent growth did not induce colony formation in agar by IL-7-expressing pre-B cell lines, and the majority of these lines were nontumorigenic in syngeneic mice. The same pre-B cell line transformed by v-abl displayed a highly malignant phenotype while containing dramatically lower IL-7 transcript levels. We conclude that endogenous IL-7 expression is not a necessary event in transformation of pre-B cells, nor is it sufficient to explain the malignant phenotype in v-abl-transformed cells. Up regulation of endogenous IL-7 expression in some transformed pre-B cells may be one of several synergistic events which can lead to malignant conversion.

Strong and persistent activation of inositol lipid breakdown induces early mitogenic events but not Go to S phase progression in hamster fibroblasts. Comparison of thrombin and carbachol action in cells expressing M1 muscarinic acetylcholine receptors.

In order to evaluate the role of phosphoinositide turnover in growth factor action, we expressed human M1 muscarinic acetylcholine (Hm1) receptors in Chinese hamster lung fibroblasts (CCL39 cell line). In the transfected cells (39M1-81 clone), but not in wild type fibroblasts, the muscarinic agonist carbachol induced a release of inositol phosphates as strong as alpha-thrombin, a very potent growth factor and activator of phosphoinositide-specific phospholipase C (PLC) in this cell system. In contrast to thrombin, carbachol-stimulated PLC activity was not inhibited by pertussis toxin treatment of cells. At concentrations that elicited a comparable initial rate of inositol phosphate release (10 nM for thrombin and 0.1 mM for carbachol), both agents gave rise to an identical calcium signal and equally stimulated Na+/H+ exchange and the transcription of the early genes c-jun, c-fos, and c-myc. Surprisingly, however, carbachol is not a mitogen for 39M1-81 cells, and even if tested in association with insulin or fibroblast growth factor, its effects on cell proliferation remained weak when compared with thrombin. Also, the muscarinic agonist did not stimulate soft agar colony forming capacity and did not prevent growth arrest in Go upon serum deprivation of cycling 39M1-81 cells. The failure of carbachol to induce cell proliferation could not be attributed to rapid and complete desensitization of Hm1 receptors nor to the activation of inhibitory pathways like adenylyl cyclase stimulation. We conclude that strong and persistent activation of phosphoinositide turnover elicits early biochemical events generally associated with mitogenesis, but is not sufficient to stimulate or maintain continuous cell proliferation. On the basis of our results, we postulate that thrombin mitogenesis depends critically on signaling events different from phosphoinositide turnover, possibly the stimulation of a receptor tyrosine kinase or a Gi protein-activated tyrosine kinase.

In vitro and in vivo anticancer activity of mitozolomide and sparsomycin in human tumor xenografts, murine tumors and human bone marrow

The colony formation in agar of human tumor xenografts, of murine tumors and of human bone marrow was used as a test system to determine the in vitro activity of the two novel cytostatic agents, mitozolamide and sparsomycin. Mitozolomide was additionally studied in vivo in nine human tumor xenografts. The comparison of in vitro/in vivo activity allows an assessment of the relevant in vitro dose based on in vivo pharmacological behavior of a compound. Both compounds showed clear dose/response effects in vitro. A dose of 3 micrograms/ml mitozolomide, given by continuous exposure, was active (colony number of test less than 30% of the control group) in 12/42 (29%) human tumor xenografts as well as in the four murine tumors, P388, L1210, B16 melanoma and colon carcinoma 38, whereas the two human bone marrows showed no significant suppression of the ability to form colonies in culture. The comparison of in vitro with in vivo activity suggests that the in vitro dose of 3 micrograms/ml corresponds best to the activity observed in animal experiments. The highest activity was observed in small-cell cancer of the lung (4/5), followed by melanomas (2/7) and non-small-cell cancer of the lung (2/9). Furthermore, activity was found in a cancer of the large bowel, stomach, breast and in one sarcoma. In the treatment of nine human tumor xenografts growing subcutaneously in nude mice, mitozolomide effected a complete or partial remission in 6 out of 9 tumors. In comparison to standard drugs mitozolomide is one of the most effective compounds in these tumors. These data indicate that mitozolomide possesses potent broad-spectrum activity in human tumor xenografts. Sparsomycin (0.1 micrograms/ml, continuous exposure) was active in 11/46 (24%) human tumor xenografts and in 4/5 of the murine tumors, whereas the colony-forming capacity of four human bone-marrows showed no inhibition, suggesting that this dose level may be the relevant in vitro dose. However, the high in vitro activity in murine tumors is incompatible with the in vivo activity. In mice the only responsive tumor was leukemia P388, whereas the L1210, B16 melanoma and colon carcinoma 38 were resistant. At the dose level of 0.03 microgram/ml only 3/30 (10%) of the human tumor xenografts were sensitive. In an earlier clinical phase I study the dose-limiting adverse effect was eye toxicity and not bone-marrow suppression.(ABSTRACT TRUNCATED AT 400 WORDS)

A host-dependent temperature-sensitive mutant of rous sarcoma virus: Evidence for host factors affecting transformation

We have characterized a host range mutant of Rous sarcoma virus in order to identify host cell factors involved in transformation. This mutant, tsLA33-1, which was isolated from a stock of the temperature-sensitive mutant tsLA33, is not temperature-sensitive for transformation of chicken embryo fibroblasts, as judged by its ability to induce morphological changes and agar colony formation at both 36 and 41.5°. In Rat-3 cells, however, this mutant induced a temperature-dependent transformation: infected Rat-3 cells were transformed at 34° but not at 39.5°. Retransformants were isolated from tsLA33-1-infected Rat-3 cells by growth in agar suspension at 39.5°. Virus rescued from these retransformants induced a temperature-dependent transformation when reintroduced into rat cells. The level of expression of pp60 v- src at 39.5° was unchanged in the retransformants. When the retransformants were treated with herbimycin, an antibiotic which induces turnover of certain protein-tyrosine kinases, they reverted to a normal phenotype, indicating that the transformed phenotype of the retransformants was dependent on continued expression of pp v- src . The re-transformants are therefore pseudorevertants in which a cellular alteration has occurred that allows transformation at 39.5° by the mutant pp60 v- src . Thus the temperature-dependence of transformation by tsLA33-1 is affected by the cellular environment, and is suppressed or complemented both in chicken cells and in the rat cell pseudorevertants. No clear correlation between levels of phosphorylation at tyrosine and transformation was observed. In Rat-3 cells the pp60 v- src encoded by tsLA33-1 may be defective in its interaction with low abundance substrates that are critical for transformation; alternatively the nonpermissive cells may require a higher threshold dose of pp60 v- src for transformation.

Partially transformed, anchorage-independent human diploid fibroblasts result from overexpression of the c-sis oncogene: mitogenic activity of an apparent monomeric platelet-derived growth factor 2 species.

A human c-sis cDNA in an expression vector was introduced into human diploid fibroblasts by transfection or electroporation. Fibroblast clones showing an aberrant, densely packed colony morphology were isolated and found to overexpress a 3.6-kilobase sis mRNA species and associated immunoprecipitable platelet-derived growth factor (PDGF) 2 proteins. Parallel analyses in cell clones of sis mRNA expression and colony formation in agar indicated that, above a threshold, a linear, positive correlation existed between sis overexpression and acquired anchorage independence. The sis-overexpressing cells formed transient, regressing tumor nodules when injected into nude mice, consistent with the finite life span which they retained. Protein products generated from the transfected c-sis construct in two overexpressing clones were immunoprecipitated with anti-human PDGF antibodies. One clone contained an apparent PDGF dimer of 21 kilodaltons; the second clone contained only an apparent PDGF monomer of 12 kilodaltons, which was shown to account for all of the mitogenic activity present in the cells, essentially all of which was concentrated in the membrane fraction. The results demonstrate a clear link between sis overexpression and acquisition of a partially transformed, anchorage-independent phenotype, and when combined with previous observations of sis overexpression in human tumors, clearly implicate sis overexpression as a genetic mechanism which contributes to human cell transformation.

Partially transformed, anchorage-independent human diploid fibroblasts result from overexpression of the c-sis oncogene: mitogenic activity of an apparent monomeric platelet-derived growth factor 2 species.

A human c-sis cDNA in an expression vector was introduced into human diploid fibroblasts by transfection or electroporation. Fibroblast clones showing an aberrant, densely packed colony morphology were isolated and found to overexpress a 3.6-kilobase sis mRNA species and associated immunoprecipitable platelet-derived growth factor (PDGF) 2 proteins. Parallel analyses in cell clones of sis mRNA expression and colony formation in agar indicated that, above a threshold, a linear, positive correlation existed between sis overexpression and acquired anchorage independence. The sis-overexpressing cells formed transient, regressing tumor nodules when injected into nude mice, consistent with the finite life span which they retained. Protein products generated from the transfected c-sis construct in two overexpressing clones were immunoprecipitated with anti-human PDGF antibodies. One clone contained an apparent PDGF dimer of 21 kilodaltons; the second clone contained only an apparent PDGF monomer of 12 kilodaltons, which was shown to account for all of the mitogenic activity present in the cells, essentially all of which was concentrated in the membrane fraction. The results demonstrate a clear link between sis overexpression and acquisition of a partially transformed, anchorage-independent phenotype, and when combined with previous observations of sis overexpression in human tumors, clearly implicate sis overexpression as a genetic mechanism which contributes to human cell transformation.

The effect of tumor necrosis factor on normal human hematopoietic progenitors.

Tumor necrosis factor-alpha (TNF-alpha), a product of activated macrophages that is cytotoxic to tumor cells, could be used to purge tumor cells from bone marrow before autologous bone marrow transplantation for hematologic malignancies and/or solid tumors. To determine whether exposure to TNF-alpha would have an inhibitory effect on hematopoietic progenitors, we incubated normal human bone marrow with a wide range of concentrations of recombinant human TNF. In order to mimic the conditions that would be used in bone marrow purging, bone marrow cell suspensions were incubated with TNF in doses ranging from 500 to 100,000 U/ml for 24 hours, and were assayed for colony formation in agar. We noted a dose-dependent inhibition of total colony-forming units (CFU) at days 7 and 14, with 50% inhibition occurring at 60,000 U/ml of TNF. TNF exerted a differential effect on CFU so that colony formation by erythroid (CFU-E), multipotential (CFU-GEMM), and macrophage (CFU-M) progenitors was suppressed to a greater extent than that by granulocyte progenitors (CFU-G). However, even after preincubation with TNF at high doses such as 100,000 U/ml, the inhibitory effects of TNF could be abolished by washing cells before culturing. This study demonstrates that hematopoietic precursors survive treatment with TNF at doses that have been shown to be cytotoxic to tumor cells. Although TNF has a significant inhibitory effect on the growth of erythroid, multipotential, and macrophage progenitors in vitro, this effect depends on continuous exposure to TNF for more than 24 hours. Thus, TNF may be useful as a bone marrow purging agent against tumor cells, with relative sparing of normal marrow elements.

A conserved domain regulates interactions of the v-fps protein-tyrosine kinase with the host cell.

All cytoplasmic protein-tyrosine kinases (PTKs) share a noncatalytic domain, termed SH2, which comprises approximately 100 residues located immediately N-terminal to the kinase domain. A linker in the AX9m mutant of Fujinami avian sarcoma virus (FSV) introduces a dipeptide insertion into the SH2 domain of the P130gag-fps PTK, which abolishes its ability to transform Rat-2 cells. However, at 36 degrees C AX9m FSV elicits focus formation and agar colony formation in infected chicken embryo fibroblasts (CEF) with single hit kinetics. At 41.5 degrees C AX9m FSV is nontransforming for CEF, and the mutant is therefore both host and temperature dependent for transforming activity. Both in vitro and in vivo, the specific kinase activity of AX9m FSV P130gag-fps, measured by autophosphorylation and phosphorylation of exogenous substrates, correlated with transforming activity. The consequences of the AX9m mutation for enzymatic function and transforming activity therefore depend on the cellular environment in which the altered v-fps protein is expressed. We conclude that the SH2 domain directs the interaction of the P130gag-fps catalytic domain with cellular proteins such as substrates for phosphorylation or regulators of kinase activity important for its transforming ability.

Intracellular adenosine triphosphate as a measure of human tumor cell viability and drug modulated growth.

Adenosine triphosphate is the primary energy unit for cells, and levels of this compound offer a potential marker for cell viability and growth. The availability of a bioluminescence assay allows for a rapid, sensitive, and reproducible measurement of ATP. A method is described for the quantification of intracellular ATP levels in human cancer cells. ATP levels were linearly related to the number of viable cells and increased with time in human cancer cell line cultures correlating with growth kinetics. The effect of 5-fluorouracil, doxorubicin, methotrexate, cytosine arabinoside, nitrogen mustard, melphalan, vinblastine, and cisplatin on the growth of human cancer cell lines was studied utilizing ATP levels. ATP levels and colony formation in agar of drug-exposed cells were compared. Overall there was a significant correlation between drug effects on colony formation and ATP levels. The ATP assay is rapid, simple, reproducible, and a relatively inexpensive method of quantifying drug effects on malignant cells. This makes it a potentially useful method for screening new anticancer drugs in human cancer cell lines.

The Effects of GM-CSF and G-CSF in Promoting Growth of Clonogenic Cells in Acute Myeloblastic Leukemia

A small subset of leukemic cells from most patients with acute myeloblastic leukemia (AML) have properties of stem cells and can be assayed by colony formation in agar or methylcellulose. Colony formation generally requires the addition of exogenous growth factors, but the exact factors required are incompletely defined. The AML colony-promoting activities of two recombinant human colony-stimulating factors (GM-CSF and G-CSF) were investigated by using blasts from 48 patients with AML. In nine cases, no colonies formed with either CSF. In seven cases colonies formed only in response to G-CSF and in 11 cases only in response to GM-CSF. In 21 cases colonies formed in response to either GM-CSF or G-CSF, and in 12 of these cases there was an additive effect between the two CSFs in determining maximum colony size. For cases responding to both GM- and G-CSF, the total number of colonies formed in response to the combination of both CSFs was almost always less than additive compared with the number of colonies formed in response to the individual CSFs. Further, the AML-CFU responding to either GM-CSF or G-CSF could not be distinguished by surface markers or by the cytochemical staining pattern of the colonies. These results suggest that there is considerable overlap between the GM-CSF- and G-CSF-responsive AML-CFU subpopulations in most cases. For five of seven cases, the combination of GM-CSF and G-CSF could replace a leukocyte feeder layer in providing maximum growth stimulation. These results indicate that GM-CSF and G-CSF are active growth factors for AML cells and are frequently additive in promoting maximum colony size.

The effects of GM-CSF and G-CSF in promoting growth of clonogenic cells in acute myeloblastic leukemia

A small subset of leukemic cells from most patients with acute myeloblastic leukemia (AML) have properties of stem cells and can be assayed by colony formation in agar or methylcellulose. Colony formation generally requires the addition of exogenous growth factors, but the exact factors required are incompletely defined. The AML colony- promoting activities of two recombinant human colony-stimulating factors (GM-CSF and G-CSF) were investigated by using blasts from 48 patients with AML. In nine cases, no colonies formed with either CSF. In seven cases colonies formed only in response to G-CSF and in 11 cases only in response to GM-CSF. In 21 cases colonies formed in response to either GM-CSF or G-CSF, and in 12 of these cases there was an additive effect between the two CSFs in determining maximum colony size. For cases responding to both GM- and G-CSF, the total number of colonies formed in response to the combination of both CSFs was almost always less than additive compared with the number of colonies formed in response to the individual CSFs. Further, the AML-CFU responding to either GM-CSF or G-CSF could not be distinguished by surface markers or by the cytochemical staining pattern of the colonies. These results suggest that there is considerable overlap between the GM-CSF- and G- CSF-responsive AML-CFU subpopulations in most cases. For five of seven cases, the combination of GM-CSF and G-CSF could replace a leukocyte feeder layer in providing maximum growth stimulation. These results indicate that GM-CSF and G-CSF are active growth factors for AML cells and are frequently additive in promoting maximum colony size.

Cytotoxic effects of glutathione synthesis inhibition by L-buthionine-(SR)-sulfoximine on human and murine tumor cells.

The glutathione (GSH) synthesis inhibitor, buthionine sulfoximine (BSO) was tested for cytotoxicity and thiol depletion in murine and human tumor cells in vitro, and for its antitumor activity and toxicity in vivo. The cell lines used in these studies included murine L-1210 leukemia, human RPMI 8226 myeloma, MCF-7 breast cancer and WiDr colon carcinoma. Soft agar colony forming assays showed that BSO was most effective at reducing tumor colony formation when exposed continuously to cells in vitro. Drug concentrations which inhibited colony formation to 50% of control levels ranged from 2.0-6.2 mM (for 1 hour exposures), 2-100 mM for 24 hour exposures and 0.4-1.40 microM (for continuous BSO exposures). Human myeloma cells proved most sensitive to BSO. In vitro cytotoxicity correlated with depletion of intracellular nonprotein sulfhydryls to less than or equal to 10% of control values in both L-1210 and 8226 cells. This was routinely achieved with prolonged exposures to mM BSO concentrations for greater than 24 hours. Normal mice tolerated high BSO doses (up to 5.0 g/kg) without evidence of acute toxicity. BSO was not active against L-1210 leukemia-bearing DBA/2 mice. When tested in vivo against MOPC-315 plasmacytoma-bearing BALB/c mice, BSO was not active at doses up to 4.0 g/kg. In contrast, the bifunctional alkylating agent melphalan (L-PAM) was active against MOPC-315 and this activity was enhanced by a 24 hour pretreatment of mice with 50 mg/kg of L-BSO.(ABSTRACT TRUNCATED AT 250 WORDS)

7-Hydroxymethotrexate cytotoxicity and selectivity in a human Burkitt's lymphoma cell line versus human granulocytic progenitor cells: Rescue by folinic acid and nucleosides

The cytotoxicity of 7-hydroxymethotrexate (7-OH-MTX), the primary plasma metabolite of methotrexate (MTX) in humans, was assessed by inhibition of colony formation in agar, using human bone marrow granulocyte-macrophage stem cells (CFU) from healthy volunteers and RAJI cells, a human Burkitt's lymphoma cell line. After a 2 hr exposure of cells to 7-OH-MTX, the concentrations necessary to produce a 50% inhibition of colony formation were 180 μ M and 10 μ M for bone marrow cells and for RAJI cells respectively. A continuous incubation with 20 μ M folinic acid (CF) protected the RAJI cells from 7-OH-MTX cytotoxicity at concentrations below 5 μ M but was not able to completely reverse 7-OH-MTX effects at higher doses. Continuous incubation of 7-OH-MTX-preloaded cells (2 hr, id 90) with the end products of folate-dependent reactions, adenosine (100 μ M) and thymidine (10 μ M), completely rescued RAJI cells from the 7-OH-MTX cytotoxic effects. Moreover, while thymidine alone had no effect on the 7-OH-MTX response curve, both adenosine alone or CF-adenosine combination produced 75% and 90% protection respectively. CF and adenosine concentrations necessary to achieve 90% protection were 20 and 100 μ M respectively. This study demonstrates that ( i) 7-OH-MTX can exhibit a cytotoxic selectivity for this human Burkitt's lymphoma cell line as compared to human bone marrow stem cells and ( ii) the cytotoxicity of 7-OH-MTX cannot be reversed by CF alone. These data suggest that 7-OH-MTX and/or its polyglutamylated derivatives may play an important role on different enzyme(s) involved in the interconversion of tetrahydrofolate cofactors necessary for the de novo purine biosynthesis.

Malignant transformation of Bloom syndrome B-lymphoblastoid cell lines by carcinogens.

Three types of Bloom syndrome B-lymphoblastoid cell lines, as well as one derived from a normal person, treated with 4-nitroquinoline-N-oxide and N-methyl-N'-nitro-N-nitrosoguanidine (0.3 micrograms/ml for 24 hr), were studied for tumorigenicity in nude mice, colony formation in soft agar, cytogenetic changes, and immunoglobulin markers. When normal and Bloom syndrome cells with normal sister chromatid exchange (SCE) levels and karyotypes (type I) were treated with carcinogens, no significant changes occurred in the immunoglobulin profile and karyotype, only rare colony formation was seen, and no tumors were produced. In contrast, when Bloom syndrome cells with high SCE levels (type II with normal karyotype and type III with an abnormal karyotype) were treated with carcinogens, tumors were produced in 22 of 53 nude mice injected; a high rate of colony formation in soft agar was seen; the cells exhibited virtual loss of immunoglobulin markers; and structural changes in chromosomes 1, 2, 3, 4, 5, 7, 11, 14, and 15 were found in the tumors in addition to the original chromosome abnormalities present in the injected cells. It appears that Bloom syndrome B-lymphoblastoid cell lines with high levels of SCE are highly susceptible to the action of carcinogens, as evidenced by tumor formation in nude mice and colony formation in agar. Apparently, the carcinogens were capable of transforming only those cells that had a critical level of SCE (approximately 140 per cell) and not those with only mildly increased levels (approximately 13 per cell).

Evolution and clinical application of a rapid chemosensitivity assay.

The clinical usefulness of the soft agar colony-formation assay of in vitro chemosensitivity developed by Hamburger and Salmon is limited by long turnaround time (2-3 weeks), low success rate for small specimens, and clumping artifacts that can lead to erroneous predictions of resistance (false-negative errors). An improved technique was developed for measuring in vitro growth by incorporation of tritiated thymidine that can be performed in 5 days. With this rapid assay, 819 tumors were processed, with an overall success rate of 59.3%. This result compared favorably to the overall success rate of 58.2% for 1591 colony-formation assays because more small specimens could be submitted for the rapid assay. Melanoma and ovarian cancer specimens grew particularly well (76% and 75% successful, respectfully). Sixty-five correlations of in vitro and in vivo responses are available to date. None of 30 tumors, predicted to be resistant in vitro responded to chemotherapy clinically. Patients whose tumors were predicted to be sensitive in vitro had a 43% clinical response rate. The assay appears to be particularly accurate for predicting clinical resistance to chemotherapy, possibly because clumping artifacts do not occur in this system and peak achievable plasma concentrations of chemotherapeutic agents can be used. Optimal in vitro drug concentrations and culture conditions are still being defined, and improved success rates are being seen with more recent specimens. The introduction of this technique underscores the fact that in vitro chemosensitivity tests must continuously evolve to maximize their clinical application.

Stimulation by feeder layers of human tumour-cell colony formation in agar

Stimulation by feeder layers of human tumour-cell colony formation in agar

Separation of human T-lymphocyte colony-forming cells on Percoll gradients.

Formation of T-lymphocyte colonies in semi-solid agar by mitogen-stimulated peripheral blood mononuclear cells is a sensitive indicator of a proliferative response. The exact identity of the T-lymphocyte colony forming cell (T-CFC) is not known, nor is it known if more than one T-CFC exists. It is possible that different subsets of mononuclear cells, each responding to diverse mitogens, give rise to different T-CFC. In this study, we separated mononuclear cells into seven subsets based on their density utilizing Percoll at concentrations of 40% to 55%. Following separation, the cells from each fraction were stimulated by phytohemagglutinin (PHA), pokeweed mitogen (PWM), concanavalin A (Con A), or staphylococcal protein A (SPA), and cultured in a semi-solid agar system. Each fraction was fully characterized by immunologic and cytochemical cell markers. Monocytes were found in the light density fraction, whereas T-lymphocytes and large granular lymphocytes were predominantly seen in the heavier density fractions. B lymphocytes were concentrated in the middle density fractions. Cells from fraction 1 (the lightest density fraction) formed significantly more T-cell colonies when stimulated by PHA than did fractions 4, 5, 6, or 7. This effect was not observed when other mitogens were used. We conclude that mononuclear cells can be separated into enriched cell subpopulations by Percoll fractionation and that PHA-stimulated T-CFC may also be enriched by Percoll fractionation. In addition, the data suggest that different subsets of T-CFC may exist.

Dissociation between transformed and differentiated phenotype in rat thyroid epithelial cells after transformation with a temperature-sensitive mutant of the Kirsten murine sarcoma virus.

Differentiated rat thyroid epithelial cells, infected in vitro with a temperature-sensitive mutant of the Kirsten murine sarcoma virus, expressed at the permissive temperature (33 degrees C) some phenotypic properties typical of transformed cells, including morphological features, colony formation in agar, and induction of tumors in newborn animals. Specific functional markers of these differentiated cells, i.e., synthesis/secretion of thyroglobulin, synthesis of thyroglobulin mRNA and iodide uptake, were blocked during growth at 33 degrees C. Normal morphology, failure to grow in agar, and the requirement of hormones for optimal growth were all restored after shifting to the temperature nonpermissive for transformation (39 degrees C), though the typical differentiated functions remained blocked. Infection with a leukemia helper virus clone (Moloney or Kirsten murine leukemia virus) did not lead to the loss of the differentiated phenotype of rat epithelial thyroid cells, thus demonstrating that the loss of the differentiated phenotype is caused by the sarcoma virus component. These results indicate that the expression of some of the phenotypic properties of transformed differentiated rat thyroid epithelial cells is under the direct control of the p21 thermosensitive activity, whereas the block in the expression of two typical differentiation markers of thyroid epithelial cells is irreversible and probably controlled by different mechanisms.

Heritable Variations in Growth Potential and Morphology Within a Clone of Balb/3T3 Cells and Their Relation to Tumor Formation<xref ref-type="fn" rid="FN2">2</xref><xref ref-type="fn" rid="FN3">3</xref>

A nontransformed clone and a spontaneously transformed clone were isolated from a twice-recloned line of Balb/3T3 cells. At different times two sublines were initiated from the nontransformed clone, and three were initiated from the transformed clone. The sublines were maintained in parallel passages under the same conditions. Each subline was distinctive in appearance and fell into the same rank order in a variety of growth parameters in vitro. Colony formation in agar and tumor formation in mice occurred only in the morphologically transformed sublines, but there was no quantitative correlation between the two properties or with the rate of glucose utilization. Two of the cell populations derived from noninbred NIH nude mouse tumors of the 3 transformed sublines differed in agar colony formation from the parental sublines. The results indicate that there is an immense capacity for variation in cultured animal cells involving many unrelated characteristics expressed in a way that is difficult, if not impossible, to explain by conventional genetic models.

Correlation of drug sensitivity on human colon adenocarcinoma cells grown in soft agar and in athymic mice.

A well-differentiated colorectal tumor T 219 which grows as a xenograft in athymic mice (human-tumor-nude-mouse system) and forms colonies in culture (soft agar colony-formation assay) has been used to test the correlation between the above two methods of exposure of human tumor cells to antineoplastic agents. In in vitro studies, two protocols were used: 1 h drug exposure and continuous drug exposure. In the 1 h drug exposure experiments six drugs, doxorubicin (DX), 4'-deoxydoxorubicin (deoDX), 4'epidoxorubicin(epiDX), 4'-O-methyldoxorubicin (O-DX), N-trifluoroacetyldoxorubicin-14-valerate (AD-32) and 5-fluorouracil (FUra) were studied, while in continuous drug exposure experiments four of the above drugs (DX, deoDX, epiDX, O-DX) were studied. The survival of the tumor clonogenic cells (HC219) was determined by counting the number of colonies formed during 13-14 days of incubation and dose-response curves were obtained. In in vivo studies, the mice were treated with all of the drugs used in in vitro 1 h drug exposure experiments (DX, deoDX, epiDX, O-DX, AD-32 and FUra). To quantitate the chemotherapeutic effectiveness of the drugs, T/C% (relative tumor volume of treated group as percentage of the control group) values were calculated each time the tumors were measured. The experimental data suggest that in vitro 1 h drug exposure results are in good agreement with the in vivo results, while the continuous drug exposure results do not agree with the in vivo data. The most active drug in in vivo studies, deoDX, was found to be the most active drug in the in vitro 1 h drug exposure experiments as well. However, in continuous drug exposure experiments, O-DX, not deoDX, was found to be the most active drug. Activities of the other drugs tested also differed from their respective activities in in vivo studies. Although the relative effectiveness of various drugs can be compared by determining molar concentrations of the drugs producing 50% inhibition of colonies (ID50) the expression, PEI = LD10/ID50 X 1000, which takes into consideration toxicity of the drugs, is probably a better indicator of the in vitro drug activity. The results suggest that soft agar colony-formation assay (with established cell lines from the same tumor) may be used for the prediction of in vivo activity of potential antineoplastic agents against human tumor xenografts in nude mice.