Development of an in vitro colony formation assay for the evaluation of in vivo chemotherapy of a rat brain tumor

Neutron Capture Enhances Dose and Reduces Cancer Cell Viability in and out of Beam During Helium and Carbon Ion Therapy

PURPOSE

Neutron capture enhanced particle therapy (NCEPT) is a proposed augmentation of charged particle therapy that exploits thermal neutrons generated internally, within the treatment volume via nuclear fragmentation, to deliver a biochemically targeted radiation dose to cancer cells. This work is the first experimental demonstration of NCEPT, performed using both carbon and helium ion beams with 2 different targeted neutron capture agents (NCAs).

METHODS AND MATERIALS

Human glioblastoma cells (T98G) were irradiated by carbon and helium ion beams in the presence of NCAs [10B]-BPA and [157Gd]-DOTA-TPP. Cells were positioned within a polymethyl methacrylate phantom either laterally adjacent to or within a 100 × 100 × 60 mm spread out Bragg peak (SOBP). The effect of NCAs and location relative to the SOBP on the cells was measured by cell growth and survival assays in 6 independent experiments. Neutron fluence within the phantom was characterized by quantifying the neutron activation of gold foil.

RESULTS

Cells placed inside the treatment volume reached 10% survival by 2 Gy of carbon or 2 to 3 Gy of helium in the presence of NCAs compared with 5 Gy of carbon and 7 Gy of helium with no NCA. Cells placed adjacent to the treatment volume showed a dose-dependent decrease in cell growth when treated with NCAs, reaching 10% survival by 6 Gy of carbon or helium (to the treatment volume), compared with no detectable effect on cells without NCA. The mean thermal neutron fluence at the center of the SOBP was approximately 2.2 × 109 n/cm2/Gy (relative biological effectiveness) for the carbon beam and 5.8 × 109 n/cm2/Gy (relative biological effectiveness) for the helium beam and gradually decreased in all directions.

CONCLUSIONS

The addition of NCAs to cancer cells during carbon and helium beam irradiation has a measurable effect on cell survival and growth in vitro. Through the capture of internally generated neutrons, NCEPT introduces the concept of a biochemically targeted radiation dose to charged particle therapy. NCEPT enables the established pharmaceuticals and concepts of neutron capture therapy to be applied to a wider range of deeply situated and diffuse tumors, by targeting this dose to microinfiltrates and cells outside of defined treatment regions. These results also demonstrate the potential for NCEPT to provide an increased dose to tumor tissue within the treatment volume, with a reduction in radiation doses to off-target tissue.

The clonogenic assay: robustness of plating efficiency-based analysis is strongly compromised by cellular cooperation

BACKGROUND

The clonogenic assay is a versatile and frequently used tool to quantify reproductive cell survival in vitro. Current state-of-the-art analysis relies on plating efficiency-based calculations which assume a linear correlation between the number of cells seeded and the number of colonies counted. The present study was designed to test the validity of this assumption and to evaluate the robustness of clonogenic survival results obtained.

METHODS

A panel of 50 established cancer cell lines was used for comprehensive evaluation of the clonogenic assay procedure and data analysis. We assessed the performance of plating efficiency-based calculations and examined the influence of critical experimental parameters, such as cell density seeded, assay volume, incubation time, as well as the cell line-intrinsic factor of cellular cooperation by auto-/paracrine stimulation. Our findings were integrated into a novel mathematical approach for the analysis of clonogenic survival data.

RESULTS

For various cell lines, clonogenic growth behavior failed to be adequately described by a constant plating efficiency, since the density of cells seeded severely influenced the extent and the dynamics of clonogenic growth. This strongly impaired the robustness of survival calculations obtained by the current state-of-the-art method using plating efficiency-based normalization. A novel mathematical approach utilizing power regression and interpolation of matched colony numbers at different irradiation doses applied to the same dataset substantially reduced the impact of cell density on survival results. Cellular cooperation was observed to be responsible for the non-linear clonogenic growth behavior of a relevant number of cell lines and the impairment of survival calculations. With 28/50 cell lines of different tumor entities showing moderate to high degrees of cellular cooperation, this phenomenon was found to be unexpectedly common.

CONCLUSIONS

Our study reveals that plating efficiency-based analysis of clonogenic survival data is profoundly compromised by cellular cooperation resulting in strongly underestimated assay-intrinsic errors in a relevant proportion of established cancer cell lines. This severely questions the use of plating efficiency-based calculations in studies aiming to achieve more than semiquantitative results. The novel approach presented here accounts for the phenomenon of cellular cooperation and allows the extraction of clonogenic survival results with clearly improved robustness.

The tumor suppressor FBXO31 preserves genomic integrity by regulating DNA replication and segregation through precise control of cyclin A levels

F-box protein 31 (FBXO31) is a reported putative tumor suppressor, and its inactivation due to loss of heterozygosity is associated with cancers of different origins. An emerging body of literature has documented FBXO31's role in preserving genome integrity following DNA damage and in the cell cycle. However, knowledge regarding the role of FBXO31 during normal cell-cycle progression is restricted to its functions during the G₂/M phase. Interestingly, FBXO31 levels remain high even during the early G₁ phase, a crucial stage for preparing the cells for DNA replication. Therefore, we sought to investigate the functions of FBXO31 during the G₁ phase of the cell cycle. Here, using flow cytometric, biochemical, and immunofluorescence techniques, we show that FBXO31 is essential for maintaining optimum expression of the cell-cycle protein cyclin A for efficient cell-cycle progression. Stable FBXO31 knockdown led to atypical accumulation of cyclin A during the G₁ phase, driving premature DNA replication and compromised loading of the minichromosome maintenance complex, resulting in replication from fewer origins and DNA double-strand breaks. Because of these inherent defects in replication, FBXO31-knockdown cells were hypersensitive to replication stress-inducing agents and displayed pronounced genomic instability. Upon entering mitosis, the cells defective in DNA replication exhibited a delay in the prometaphase-to-metaphase transition and anaphase defects such as lagging and bridging chromosomes. In conclusion, our findings establish that FBXO31 plays a pivotal role in preserving genomic integrity by maintaining low cyclin A levels during the G₁ phase for faithful genome duplication and segregation.

A comparison of in vitro cytotoxicity assays in medical device regulatory studies

Medical device biocompatibility testing is used to evaluate the risk of adverse effects on tissues from exposure to leachates/extracts. A battery of tests is typically recommended in accordance with regulatory standards to determine if the device is biocompatible. In vitro cytotoxicity, a key element of the standards, is a required endpoint for all types of medical devices. Each validated cytotoxicity method has different methodology and acceptance criteria that could influence the selection of a specific test. In addition, some guidances are more specific than others as to the recommended test methods. For example, the International Organization for Standardization (ISO¹) cites preference for quantitative methods (e.g., tetrazolium (MTT/XTT), neutral red (NR), or colony formation assays (CFA)) over qualitative methods (e.g., elution, agar overlay/diffusion, or direct), while a recent ISO standard for contact lens/lens care solutions specifically requires a qualitative direct test. Qualitative methods are described in United States Pharmacopeia (USP) while quantitative CFAs are listed in Japan guidance. The aim of this review is to compare the methodologies such as test article preparation, test conditions, and criteria for six cytotoxicity methods recommended in regulatory standards in order to inform decisions on which method(s) to select during the medical device safety evaluation.

Protein tyrosine phosphatase mu regulates glioblastoma cell growth and survival in vivo

Glioblastoma multiforme (GBM) is the most lethal primary brain tumor. Extensive proliferation and dispersal of GBM tumor cells within the brain limits patient survival to approximately 1 year. Hence, there is a great need for the development of better means to treat GBM. Receptor protein tyrosine phosphatase (PTP)µ is proteolytically cleaved in GBM to yield fragments that promote dispersal of GBM cells. While normal brain tissue retains expression of full-length PTPµ, low-grade human astrocytoma samples have varying amounts of full-length PTPµ and cleaved PTPµ. In the highest-grade astrocytomas (i.e., GBM), PTPµ is completely proteolyzed into fragments. We demonstrate that short hairpin RNA mediated knockdown of full-length PTPµ and PTPµ fragments reduces glioma cell growth and survival in vitro. The reduction in growth and survival following PTPµ knockdown is enhanced when cells are grown in the absence of serum, suggesting that PTPµ may regulate autocrine signaling. Furthermore, we show for the first time that reduction of PTPµ protein expression decreases the growth and survival of glioma cells in vivo using mouse xenograft flank and i.c. tumor models. Inhibitors of PTPµ could be used to reduce the growth and survival of GBM cells in the brain, representing a promising therapeutic target for GBM.

CD109 release from the cell surface in human keratinocytes regulates TGF-β receptor expression, TGF-β signalling and STAT3 activation: relevance to psoriasis

Transforming growth factor (TGF)-β is an important cytokine that negatively regulates keratinocyte proliferation. Deregulation of TGF-β signalling has been reported in psoriasis, where despite increased expression of TGF-β, psoriatic keratinocytes continue to hyperproliferate. Recently, we have identified CD109, a glycosyl phosphatidylinositol (GPI)-anchored protein, as a novel co-receptor and negative regulator of TGF-β signalling. In the current work, we demonstrate that release of CD109 from the cell surface or the addition of CD109 protein results in downregulation of TGF-β signalling and TGF-β receptor expression in human keratinocytes. Moreover, these effects are associated with an increase in phospho-STAT3 levels, enhanced total STAT3 and Bcl-2 expression and an increase in cell growth and survival, suggesting that released/soluble CD109 is able to induce molecular changes that are known to occur in psoriasis. Analysis of CD109 expression in psoriasis patients reveals that CD109 protein expression is markedly decreased in psoriatic epidermis as compared to adjacent uninvolved skin. In contrast, CD109 mRNA expression is unchanged in psoriatic plaques in comparison with normal skin. This raises a possibility that CD109 protein release is enhanced in psoriatic keratinocytes. Furthermore, psoriatic epidermis displays decreased expression of TGF-β receptors, consistent with the results obtained in vitro in keratinocytes with CD109 release or addition of CD109 recombinant protein. Together our findings suggest that aberrant CD109 release from the cell surface in human keratinocytes may induce molecular changes that are usually observed in psoriasis and may explain TGF-β receptor downregulation and decrease in TGF-β signalling in psoriasis.

Correlation between initial chromatid damage and survival of various cell lines exposed to heavy charged particles

The biophysical characteristics of heavy ions make them a rational source of radiation for use in radiotherapy of malignant tumours. Prior to radiotherapy treatment, a therapeutic regimen must be precisely defined, and during this stage information on individual patient radiosensitivity would be of very great medical value. There are various methods to predict radiosensitivity, but some shortfalls are difficult to avoid. The present study investigated the induction of chromatid breaks in five different cell lines, including one normal liver cell line (L02), exposed to carbon ions accelerated by the heavy ion research facility in Lanzhou (HIRFL), using chemically induced premature chromosome condensation (PCC). Previous studies have reported the number of chromatid breaks to be linearly related to the radiation dose, but the relationship between cell survival and chromatid breaks is not clear. The major result of the present study is that cellular radiosensitivity, as measured by D0, is linearly correlated with the frequency of chromatid breaks per Gy in these five cell lines. We propose that PCC may be applied to predict radiosensitivity of tumour cells exposed to heavy ions.

Diffusion imaging for evaluation of tumor therapies in preclinical animal models

The increasing development of novel targeted therapies for treating solid tumors has necessitated the development of technology to determine their efficacy in preclinical animal models. One such technology that can non-invasively quantify early changes in tumor cellularity as a result of an efficacious therapy is diffusion MRI. In this overview we present some theories as to the origin of diffusion changes as a result of tumor therapy, a robust methodology for acquisition of apparent diffusion coefficient maps and some applications of determining therapeutic efficacy in a variety therapeutic regimens and animal models.

Diagnostic and prognostic value of colony formation of hematopoietic progenitor cells in myeloid malignancies

Hematopoietic progenitor cells are capable of forming colonies of mature blood cells in semisolid media in response to specific growth factors. Colony assays have been extensively used for many years to study normal and malignant hematopoiesis in vitro. In fact, these assays have provided an excellent research tool for investigating growth and differentiation of progenitor cells in response to positive and negative regulators of hematopoiesis. However, apart from their role in basic research, colony assays are also widely used in routine clinical practice in the diagnosis of various hematologic disorders, such as aplastic anemia, myelodysplastic syndromes and myeloproliferative disorders. This review summarizes our current knowledge on the diagnostic value and prognostic significance of the growth of progenitor cells in peripheral blood and bone marrow in patients with myeloid malignancies.

Fractionated radiosurgery for 9L gliosarcoma in the rat brain

PURPOSE

Fractionated radiosurgery is being carried out in the clinic to improve the therapeutic ratio of single-dose radiosurgery using various fractionation schemes. Because there is a paucity of experimental radiobiological data in the literature on the tumor response and late-responding normal tissue of critical intracranial structures to radiosurgery, the present animal study was designed to compare the response following a single high dose of radiation with that obtained from calculated fractionated doses of radiosurgery.

METHODS AND MATERIALS

Male Fischer rats with 9L gliosarcoma growing in their brains were stereotactically irradiated and assayed for the tumor control rate and brain tissue damage. The radiation dose needed for 50% tumor control (TCD50) was used as the endpoint of the efficacy of radiosurgery. Normal brain damage was measured histologically following a period of time over 270 days. Histological evaluation included hematoxylin-eosin (H & E), Luxol fast blue and periodic acid Schiff (LFB/PAS) for the presence of myelin and glial fibrillary acidic protein (GFAP) for the assessment of astrocytic re-activity. The optical density of optic nerves and chiasms staining with LFB/PAS was quantitatively measured using a computer image analysis to assess the magnitude of demyelination.

RESULTS

Radiosurgery (RS) was found to be more effective in curing small tumors than large tumors. The dose required to control 50% of the tumored animals for 120 days was 24, 31, and 40 Gy for 2-, 6-, and 12-day-old tumors, respectively. Using 12-day-old brain tumors, two fractions of 23.5 Gy and three fractions of 18.5 Gy were found to be equivalent to the single dose of 35 Gy for tumor control. For normal brain damages, the visual pathways including optic nerves and chiasm were found to be highly radiosensitive structures. A single dose of 35 Gy produced 100% severe optic neuropathy. The fractionated RS regimens spared substantial optic nerve damage.

CONCLUSION

The present data provide a strong radiobiological rationale for the use of fractionated RS in the treatment of tumors located near critical normal structures, including visual pathways. The sparing effect of fractionated RS is greater for late-responding tissues, relative to the rapidly proliferating tumor tissues. This report also characterizes the dose/time tolerance relationship of optic neuropathy after single and fractionated RS.

Effect of pharmacologic doses of zinc on the therapeutic index of brain tumor chemotherapy with carmustine

To evaluate the potential differential effect of pretreatment with pharmacologic doses of the trace element zinc on the chemosensitivity of glioma cells and bone marrow cells for carmustine (BCNU), we performed in vitro and in vivo studies of zinc toxicity as well as of the combined treatment with zinc and the anticancer drug. We studied the in vitro effects on established human and rat glioma cell lines using a microcolorimetric growth assay and on murine bone marrow using a clonogenic assay for committed progenitor cells of the granulocyte-monocyte lineage. Zinc exposures of up to 100 microM for 120 h did not influence the growth of six of seven human glioma cell lines. Only U87MG demonstrated statistically significant toxicity during high zinc exposure (100 microM over 120 h). Dose-response growth curves generated for BCNU did not show protection against the anticancer agents by a 48-h pretreatment with different zinc concentrations. The clonogenic capacity of bone marrow cells was slightly reduced by in vitro culture for 24 and 48 h. Although this effect appeared to be more prominent in the presence of zinc supplementation, overall a statistically significant inhibition was seen only after exposure to a concentration of 100 microM zinc over 48 h. As compared with chemotherapy alone, in vitro pretreatment with 50 microM zinc over 48 h followed by chemotherapy resulted in an increased number of colony-forming unit-granulocyte monocyte (CFU-GM): CFU-GM increased by a factor of 2 for BCNU (60 microM x 2 h). This statistically significant in vitro chemoprotection would translate into a dose-protection factor of 1.5, i.e., for the same level of myelosuppression, zinc pretreatment would allow administration of a 50% increased dose of BCNU. The in vivo studies were performed in an s.c. xenograft model of the human glioma cell line U87MG in athymic mice. The maximal tolerable pretreatment with zinc was determined to be a 10-day course of daily i.p. injections of 10 mg/kg ZnCl2. The subsequent i.p. administration of the dose lethal to 10% of the mice (LD10) and of a 1.5 x LD10 dose of BCNU resulted in less bone marrow toxicity in pretreated animals than in non-zinc-pretreated mice as determined in a CFU-GM assay. Glioma colony-forming efficiency (CFE) assays, on the other hand, did not show any zinc-related difference in the BCNU sensitivity of U87MG.(ABSTRACT TRUNCATED AT 400 WORDS)

Experimental basis for increasing the therapeutic index of cis-diamminedicarboxylatocyclobutaneplatinum(II) in brain tumor therapy by a high-zinc diet

Metallothionein (MT), a ubiquitous intracellular protein, confers resistance to the toxic effects of platinum compounds. Since a high-zinc diet has been shown to induce MT synthesis in extracerebral tissues but not in brain, we investigated whether it could provide an experimental basis for decreasing the hematotoxicity of carboplatin without impairing its activity against brain tumors. After 2 weeks on either a high-zinc diet or a control diet (zinc content, 180 vs 10 ppm), mice and rats received various doses of carboplatin or Hanks' balanced salt solution by i.p. injection. The hematotoxicity of carboplatin was evaluated with an assay of colony-forming units of granulocytes and mononuclear cells in mice. The high-zinc diet enabled a 50% increase in the carboplatin dose without increasing hematotoxicity. The antitumor activity was evaluated with an assay of the colony-forming efficiency of gliosarcoma cells from 9L brain tumors in rats. The high-zinc diet did not alter the efficacy of carboplatin against this brain tumor. Northern blot analysis confirmed that the high-zinc diet induced MT mRNA in the kidney but not in the brain of mice and rats; it also showed MT mRNA induction in bone marrow cells of mice but not in rat 9L brain tumors. These results suggest that increasing the dietary intake of zinc might increase the therapeutic index of carboplatin in the treatment of brain tumors.

The in-vitro chemosensitivity of three cell lines derived from the VM/DK spontaneous murine astrocytoma

Three cell lines, VM/Dk P497 P540 and P560 derived from the VM spontaneous murine astrocytoma have previously been fully characterised and found to differ in their degree of astrocytic differentiation. The in vitro chemosensitivity of the three lines has been investigated using the 35S-methionine uptake assay. Differential chemosensitivity was found to exist between the cell lines. The pattern of chemosensitivity in relation to astrocytic differentiation was complex but the least differentiated cell line, P497, tended to be the least chemosensitive.

Comparison of tumour age response to radiation for cells derived from tissue culture or solid tumours

Direct comparison of the cell age response of 9L and KHT tumour cells derived either from tissue culture or solid tumours was achieved. Cells from dissociated KHT and 9L tumours (the latter implanted either subcutaneously or intracerebrally) and cells from tissue culture were separated into homogeneous sized populations by centrifugal elutriation. In both tumour models these homogeneous sized populations correspond to populations enriched at different stages of the cell cycle. The survival of these elutriated cell populations was measured after a single dose of Cs-137 gamma rays. For cells isolated from 9L solid tumours, there was little variation in radiosensitivity throughout the cell cycle; however, a very small but significant increase in resistance was found in late G1 cells. This lack of a large variation in radiosensitivity through the cell cycle for 9L cells from solid tumours also was seen in 9L cells growing in monolayer tissue culture. When similar experiments were performed using the KHT sarcoma tumour model, the results showed that KHT cells in vitro exhibited a fairly conventional increase in radioresistance in both mid G1 and late S. However, the cell age response of KHT cells from solid tumours was different; particularly in the late S and G2 + M phases. These data demonstrate that direct extrapolation of in vitro cell age responses to the in situ situation may not always be valid.

Hypoxic cells and in situ chemopotentiation of the nitrosoureas by misonidazole

Intracerebral (i.c.) and subcutaneous (s.c.) 9L tumours were treated simultaneously with various doses of the nitrosoureas, BCNU or CCNU, and 2.5 mmol kg-1 of misonidazole (MISO). After 24 h, tumours were removed, dissociated into single cell suspensions and the cells plated for colony formation. In both i.c. and s.c. tumours, no cell kill was observed after exposure to MISO alone, and no additional cell kill was observed when MISO was combined with either nitrosourea. If s.c. 9L tumours were clamped 30 min after i.p. injection of 2.5 mmol kg-1 MISO, then 2 h later the clamps were removed and the nitrosourea injected, an increase in cell kill was observed. This increase in cell kill was statistically significant (P less than 0.01) for each dose of BCNU administered, but not statistically significant (P greater than 0.05) for the moderate dose of CCNU administered. Clamping did not alter the colony forming efficiency of cells from untreated 9L s.c. tumours or from those treated with each drug alone. These data demonstrate that hypoxic cells are required for misonidazole to potentiate the cell-killing effects of the nitrosoureas and that s.c. 9L tumours contain no such cells.

Improved treatment of a brain-tumor model. Part 2: Sequential therapy with BCNU and 5-fluorouracil

A combination chemotherapy regimen for brain tumors was developed, based on investigations of the survival of animals harboring the intracerebral 9L rat brain-tumor model and on analyses of their clonogenic tumor cells. Fischer 344 rats harboring 9L brain tumors were treated with 2-day courses of 5-fluorouracil (5-FU), in order to expose all cycling tumor cells to the drug during DNA synthesis and achieve maximum anti-tumor activity for this cell-cycle-specific anti-metabolite. Although a 74% cell kill was obtained for a total dose of 45 mg/kg or greater, animal life span was not increased over that of untreated tumor-bearing controls. However, when 5-FU (48 to 96 mg/kg total dose over 2 days) was administered after a single LD10 dose of BCNU (13.3 mg/kg), additive cell kill was suggested. In three large series, long-term animal survivors and occasional tumor cures were observed with this drug combination, a result never observed following BCNU alone. Schedule dependency was not apparent. A previously published protocol for treating recurrent malignant gliomas with sequential courses of BCNU and 5-FU was partially planned based upon these initial observations. Anti-tumor activity with the combination of drugs was superior to therapy with BCNU alone. Both animal and human studies confirm that, contrary to presently accepted oncological tenets, a chemotherapeutic agent that kills significant numbers of tumor cells but is clinically ineffective when given alone might, nevertheless, be useful in combination therapy regimens.

Improved treatment of a brain-tumor model. Part 1: Advantages of single- over multiple-dose BCNU schedules

Clonogenic cell and animal survival studies were used to determine the most effective BCNU therapy schedule in the 9L rat brain-tumor model. Survival of tumor cells following a single LD10 dose of BCNU (13.3 mg/kg intraperitoneally) was compared to cell survival after one to four daily 0.5 X LD10 doses. The posttreatment kinetics of surviving clonogenic cells were investigated at various times after BCNU was given in single doses of 0.25 to 1 X LD10 and in two daily doses of 0.5 X LD10. The cell kill was greater, time to reinitiation of cell growth was later, posttreatment rate of clonogenic cell proliferation was slower, and the interval to total repopulation of the clonogenic cell pool was longer with a single LD10 dose as compared to the multiple-dose schedules. Animal survival studies confirmed that a single LD10 dose of BCNU was at least as effective as a cumulative level of up to 1 1/2 times that amount when treatment was administered in smaller doses, regardless of the fractionation schedule. Clinical experience with patients harboring malignant brain tumors has shown that a single BCNU dose of 185 to 200 mg/sq m is tolerated well. Results of these animal experiments suggest that this therapy should have anti-tumor activity at least equivalent to the more commonly employed schedule of 80 mg/sq m/day given for 3 days. Although direct comparison of treatment efficacy using the two schedules is not possible, no adverse clinical effects have been observed with the recently adopted single-dose schedule. Furthermore, the duration of patient hospitalization for chemotherapy has decreased.

The role of glucose in the growth of 9L multicell tumor spheroids

Monolayer-cultured 9L rat brain tumor cells grew optimally in culture media containing glucose concentrations greater than 0.07 mg/ml, but growth ceased at concentrations lower than this value. Assuming that this glucose concentration defines the proliferating fraction of cells in 9L multicell tumor spheroids, it is possible to simulate spheroid growth based on the intraspheroid glucose distribution derived by the author earlier. An excellent fit to experimental growth data was obtained by assigning the proliferating fraction a growth rate constant equal to 40% of that of monolayer-cultured cells. This definition is in accord with our observation that the colony-forming efficiency (CFE) of spheroid-derived cells is 40% of the CFE of cells maintained in monolayer. This suggests that the role of glucose in 9L cell growth is similar in spheroids and in monolayer culture.

Radiation and drug response of the rat glioma RG2

A clonogenic cell assay was developed for the chemically induced rat glioma RG2 that allows in vivo, in vitro, and in vivo to in vitro studies of cell survival after experimental therapy. RG2 monolayer cells were resistant to BCNU up to high concentrations. The radiation survival curves were characterized by a Do of 2.4 gray and n = 2.2 for monolayer cells, a Do of 3.5 gray and n = 1.3 for cells irradiated as brain tumors in air-breathing rats, and a Do of 5.9 gray and n = 1.2 for cells irradiated as brain tumors in nitrogen-asphyxiated rats. There was no evidence of a radiobiologically hypoxic fraction of cells in the brain tumors, but their radiosensitivity was definitely smaller than that of monolayer cells.

Ex vivo hemodialysis culture system for assessing the activity of cancer chemotherapeutic agents

An ex vivo culture system was developed for assessing the activity of cancer chemotherapeutic agents against tumor cells. The system utilizes artificial capillary culture units and the technique of hemodialysis to expose tumor cells to a chemotherapeutic drug and its metabolites following injection of the drug into an experimental animal. This ex vivo culture system was used to test the activity of 5-fluorouracil (5-FU) against four human colorectal adenocarcinoma cell lines (SW 403, SW 480, SW 620, and SW 707). Cell killing by 5-FU or its metabolites in blood dialysate following intravenous injection was measured by determining colony formation of cells attached to plastic and suspended in 0.3% agar after short-term exposures of 1 to 2 h. The technique was shown to discriminate between the sensitivities of these cell lines and the respective sensitivities to the drug were reproducible. Kinetics of drug clearance from the host animal's blood were shown to be similar to that in humans. The results suggest the system may be useful for testing diverse drugs, including those requiring metabolic activation, against a variety of types of tumor cells.

Cell survival as a determinant of tumor cure for rat 9L subcutaneous tumors following microwave-induced hyperthermia

The relationship of cell survival to tumor cure after local hyperthermia treatment was studied in subcutaneous 9L rat tumors. Tumors weighing 0.2-0.4 g were heated to 42.5, 43.0, 44.0 and 45.0 degrees C by local exposure to 2450 MHz microwaves. Cell survival data was obtained by an in vivo to in vitro colony forming technique and a cell survival curve was constructed for each temperature as a function of exposure duration (0-180 min). Cell survival followed a simple exponential function with an increasingly steeper slope as temperature increased. At 44 degrees C, it was observed that cells from large tumors (1.0-1.4 g) were inactivated at the same rate as those from small tumors. When tumor response was monitored in the small tumors for 90 days following treatment, a direct correlation between the percentage of tumor cures and time at 44 degrees C (0-60 min) was observed; therefore, at 44 degrees C, tumor cure was exponentially related to cell survival in this range. However, when approximately the same cell survival was obtained with 3 other temperature--time regimens, the resulting percentage of tumor cures was not the same. These results indicate that while cell survival is related to tumor cure, it is probably not the primary determinant of tumor response following local hyperthermia in these 9L subcutaneous tumors.

Cell subpopulations dispersed from solid tumours and separated by centrifugal elutriation

The degree of non-neoplastic host-cell infiltration was assessed in 3 in vivo-in vitro tumour models commonly used in radiobiological studies: EMT6/Ro mammary carcinoma, 9L/Ro tumour and KHT sarcoma. While the 2 former tumour models have been shown to be moderately to highly immunogenic when grown s.c., the KHT sarcoma is apparently non-immunogenic. Using differential staining on single-cell suspensions from enzymatically dissociated solid tumours, all 3 tumour types were found to contain large proportions (30-60%) of non-neoplastic host cells. The actual host-cell component found in the cell suspensions differed both in type and percentage for the 3 tumours studied. These host and neoplastic cells in the cell suspensions prepared from the solid tumours could be readily separated by centrifugal elutriation. After separation the clonogenic potential of the neoplastic cells was assessed, and was found to be higher than the clonogenic capacity of the unseparated cell suspension by a factor directly related to the host/neoplastic cell ratio. Even after the removal of the host cells, the clonogenic capacities of the neoplastic EMT6 and 9L tumour cells were lower than that of the corresponding in vitro sublines (approximately 30 vs 75%). However, in the KHT sarcoma the removal of the host cell component raised the plating efficiency to approximately 60%, which was similar to the value for the in vitro cell subline of this tumour.

In vitro chemotherapeutic testing of urologic tumors

We studied 20 transitional cell tumors of the bladder and 25 adenocarcinomas of the kidney in vitro to determine their chemotherapeutic sensitivity. The different sensitivity patterns among the individual tumors were demonstrated. Identical drug sensitivity patterns could be identified in the primary and metastatic sites, and in tumor tissue removed from the primary and metastatic deposits in the same patient. Human renal adenocarcinoma maintained in the athymic mouse demonstrated identical chemotherapeutic sensitivity patterns in vitro and in vivo. Our data would support that these in vitro chemotherapy studies may assist in the selection of agents to use in human tumor-bearing hosts.

The 9L rat brain tumor: description and application of an animal model

Animal models allow determination of tumor response to anticancer agents under various experimental conditions. The chemically induced 9L rat brian tumor has been developed as both in vivo and in vitro models. Animal survival, clonogenic cell survival, and tumor growth delay provide means to measure the effectiveness of treatment modalities in this tumor model. Monolayer cultures, multicellular spheroid cultures, brain tumors, and flank tumors have been used to study the influence of different biological entities of the 9L model on the response to treatment with radiation and/or BCNU (1,3-bis (2-chloroethyl)-1-nitrosourea).

Brain-tumor therapy. Quantitative analysis using a model system

A recently developed colony-formation assay has been used to evaluate in vivo 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) therapy of a transplantable rat brain-tumor model. A comparison of the in vitro colony-forming capacity of treated and untreated tumor cells permits calculation of the fraction of clonogenic tumor cells surviving in vivo therapy; The plateau that we previously observed o the BCNU dose-response curve is not the result of repair of potentially lethal damage, since no change in the 0.1% of surviving clonogenic tumor cells occurs during the first 2 to 4 days after treatment. Although reanalysis of the dose-response curve indicates that sublethal damage exists, its repair is probably minimal. The most likely explanation for the observed limitation of the BCNU effect is the drug's failure to reach all clonogenic cells. A dose of BCNU that kills more than 99.9% of clonogenic tumor cells within 30 minutes of treatment results in only a 60% decrease in tumor weight by Day 14. This disparity is explained by retarded removal of dead cells, and, along with a previously determined 90% cell-kill threshold necessary to appreciate increased animal survival, demonstrates the inherent limitations of measurements of tumor size (including brain scans and clinical patient evaluations) in evaluating the efficacy of brain-tumor therapy. Following at LD10 dose of BCNU the surviving clonogenic tumor cells increase in number after latency period of 2 to 4 days; during regrowth the cell doubling time is 40 hours. Marked variability in tumor response and regrowth was noted. The determination of information regarding disturbed tumor cell kinetics and tumor heterogeneityis essential for the proper planning of combination chemotherapy and multimodality regimens.