KHT Cells Research Articles

Dissemination via the lymphatic or angiogenic route impacts the pathology, microenvironment and hypoxia-related drug response of lung metastases.

Complications associated with the development of lung metastases have a detrimental effect on the overall survival rate of many cancer patients. Preclinical models that mimic the clinical aspects of lung metastases are an important tool in developing new therapy options for these patients. The commonly used intravenous models only recapitulate dissemination of cancer cells to the lungs via the haematological route. Here we compared spontaneous and intravenous lung metastases of the highly metastatic KHT mouse fibrosarcoma cells after injecting KHT cells into the subcutaneous layer of the skin or directly into the tail vein. In contrast to the intravenous model, metastases spontaneously arising from the subcutaneous tumours disseminated most consistent with the lymph nodes/lymphatics route and were more hypoxic than the metastases observed following tail-vein administration and haematological spread. To ascertain whether this impacted on drug response, we tested the effectiveness of the hypoxia-sensitive cytotoxin AQ4N (Banoxantrone) in both models. AQ4N was more effective as an anti-metastatic drug in mice with subcutaneous KHT tumours, significantly reducing the metastatic score. Complementing the KHT studies, pathology studies in additional models of spontaneous lung metastases showed haematological (HCT116 intrasplenic implant) or mixed haematological/lymphatic (B16 intradermal implant) spread. These data suggest that preclinical models can demonstrate differing, clinically relevant dissemination patterns, and that careful selection of preclinical models is required when evaluating new strategies for targeting metastatic disease.

Impact of the small molecule Met inhibitor BMS-777607 on the metastatic process in a rodent tumor model with constitutive c-Met activation

c-Met tyrosine kinase hyperactivation is strongly associated with tumor metastasis. In a prior study we showed that BMS-777607, a novel selective small molecule Met kinase inhibitor, potently suppressed ligand-mediated functions in prostate cancer cells. Herein we evaluated the impact of this agent on the potential of the highly metastatic murine KHT sarcoma that carries constitutive activated c-Met. MET gene knockdown was found to reduce spontaneous cell scatter and motility, suggesting a c-Met-dependent disseminating ability in KHT cells. Furthermore, BMS-777607 treatment potently inhibited KHT cell scatter, motility and invasion at doses in the nanomolar range. In contrast, cell proliferation and clonogenicity were modestly affected by BMS-777607. At the molecular level, BMS-777607 potently blocked phosphorylation of c-Met and downstream pathways over the same dose range that impacted metastasis-associated cell functions. In vivo, daily treatment with BMS-777607 (25 mg/kg/day) over the course of the study significantly decreased the number of KHT lung tumor nodules (28.3 ± 14.9%, P < 0.001) without apparent systemic toxicity. While treatment for short intervals (day 1 or 4) clearly reduced the foci number, delaying the initiation of BMS-777607 treatment until 8 days after tumor cell injection failed to show any reduction, implying that impairment of the initiation phases of the secondary growth via c-Met targeting is required to constrain the formation of macroscopic metastases. Together, the present findings demonstrate that the disruption of c-Met signaling by BMS-777607 significantly impairs the metastatic phenotype, suggesting that this agent may have therapeutic utility in targeting cancer metastasis.

The biological characterization of 99mTc-BnAO-NI as a SPECT probe for imaging hypoxia in a sarcoma-bearing mouse model

Tumor growth beyond the region where vascular oxygen can reach creates a hypoxic domain. In this study, BnAO, a ligand that had been labeled with (99m)Tc-pertechnetate for hypoxia imaging, was conjugated with 2-nitroimidazole to give 3,3,10,10-tetramethyl-1-(2-nitro-1H-imidazo-1-y1)-4,9-diazadodecane-2,11- dionedioxime (BnAO-NI) as a potential ligand for hypoxia detection. Pentoxifylline is a peripheral vasodilator and has been used as a radiosensitizer in tumor radiotherapy. (99m)Tc-BnAO-NI/SPECT was applied to noninvasively assess the pharmacological effect of pentoxifylline in reducing tumor hypoxia in vivo. BnAO-NI was synthesized and formulated with methylene diphosphonate (MDP), stannous chloride and carbonate buffer to afford kits. After mixing with (99m)Tc-pertechnetate, (99m)Tc-BnAO-NI injection can be readily prepared. The partition coefficient, radiochemical purity and in vitro stability were determined. Cellular uptake of radiotracers in KHT cells under hypoxia was conducted in a CO(2) incubator at 37°C under hypoxia or normoxia. A biodistribution study after intravenous injection of (99m)Tc-BnAO-NI in KHT sarcoma-implanted C3H mice was performed. The effect of pentoxifylline (100 mg/kg) on reducing tumor hypoxia was also studied. The radiochemical purity (RCP) of the (99m)Tc-BnAO-NI preparation was greater than 96% and stable at ambient temperature for 24h (RCP>90%). The accumulation of (99m)Tc-BnAO-NI and (99m)Tc-BnAO in KHT cells under hypoxia were 3.57 and 4.13-fold higher than those under normoxic environment, indicating unambiguous oxygen-dependent uptakes of these two probes. The distribution of (99m)Tc-BnAO-NI in KHT sarcoma-bearing mice revealed rapid clearance from the blood circulation. The tumor uptake peaked at 2h post-injection (0.32 ± 0.05%ID/g) with tumor-to-blood and tumor-to-muscle ratios of 10.32 and 3.96, respectively. The effect of pentoxifylline on the tumor blood perfusion was obvious. The tumor-to-muscle ratios at 2h post-injection of (99m)Tc-BnAO-NI with and without pentoxifylline pretreatment were 1.67 ± 0.38 and 2.59 ± 0.25, respectively (p = 0.025, n = 3). This study demonstrates that (99m)Tc-BnAO-NI is a hypoxia-sensitive radio probe for monitoring hypoxic regions in a malignant neoplasm. However, (99m)Tc-BnAO-NI, though with higher lipophilicity than (99m)Tc-BnAO, did not achieve better specific accumulation in hypoxic tissues. (99m)Tc-BnAO-NI/SPECT could be applied in clinics to noninvasively evaluate the feasibility of using pentoxifylline as a radiosensitizer by reducing tumor hypoxia in vivo.

Abstract B107: Targeting metastatic tumor cell functions by Src signaling interference using the small molecule Src inhibitor, saracatinib (AZD0530)

Abstract Introduction: The metastatic spread of cancer cells remains the principal cause of treatment failure. Src is a non-receptor tyrosine kinase that is frequently over-expressed in malignances, and increased Src activity may be associated with poor patient prognosis. Src tyrosine kinase plays an important role in tumor cell survival, proliferation, migration and invasion. Since these cellular functions are key components of the metastatic cascade, Src may be a novel target for cancer therapy. The present studies were undertaken to investigate whether molecular intervention in Src associated signaling could reduce the metastatic spread of tumor cells. Specifically, the efficacy of saracatinib a potent, selective and orally available Src inhibitor, was evaluated in the highly metastatic rodent KHT sarcoma cell line. Methods: The effect of saracatinib treatment on tumor cell functions, including viability, migration, invasion, and attachment, were examined by clonogenicity, migration/invasion and attachment assays, respectively. To assess saracatinib therapeutic effects on metastatic growth, tumor cells were either pretreated with saracatinib prior to intravenous injection or injected intravenously and then the mice were treated with saracatinib. In the latter case three protocols commencing immediately after tumor cell inoculation were investigated: a single 10 mg/kg dose of saracatinib; four 10 mg/kg doses of saracatinib given at 24 hr intervals; daily 10 mg/kg doses of saracatinib administered over a period of 3 weeks; in all protocols saracatinib was administered p.o. Twenty-one days after cell injection the number of lung metastases were determined. Results: In vitro saracatinib doses ranging from 0.5–5.0 µM significantly reduced Src phosphorylation and functionally inhibited KHT cell proliferation, migration, invasion and adhesion. Pretreating KHT cells with saracatinib (1 or 5 µM, 24 hr) also reduced (2–4-fold) the ability of these cells to form lung metastases when injected into C3H mice via the tail vein. In vivo, daily doses of saracatinib (10 mg/kg) reduced the number of metastases formed at the end of a 3 week period by a factor of ∼2. A similar reduction in lung colonies was achieved with four 10 mg/kg doses of saracatinib given daily commencing immediately after tumor cell injection, or even a single 10 mg/kg treatment administered immediately after tumor cell inoculation. Conclusions: The present studies explored the possibility of utilizing a molecular targeting strategy directed against key aspects of the metastatic cascade. The present findings demonstrate that saracatinib treatment significantly inhibits the ability of the cancer cells to escape the blood stream and invade at a secondary site supporting the notion that Src signal inhibition may hold considerable promise in impairing metastases formation. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B107.

Hypoxia enhances metastatic efficiency by up-regulating Mdm2 in KHT cells and increasing resistance to apoptosis.

Tumor hypoxia has been reported to be a negative prognostic factor in a number of tumor sites. Both clinical and experimental studies have suggested a positive correlation between tumor hypoxia and increased metastatic efficiency; however, the mechanisms are not understood. In this study, the mechanisms of hypoxia-enhanced metastasis have been investigated in murine KHT fibrosarcoma and SCC VII cells. We have observed that hypoxia-pretreated KHT-C cells have a higher survival rate than control KHT-C cells after being arrested in mouse lungs. cDNA microarray analysis revealed many hypoxia-regulated genes, most of which have been reported to be involved in cell survival and growth. Among these genes, we have confirmed the up-regulation of Mdm2 by hypoxia and have demonstrated that this up-regulation is p53 independent. The up-regulation of Mdm2 by hypoxia is associated with decreased p53 protein and inhibition of the transactivation of p53 downstream proapoptotic genes. Overexpression of Mdm2 or suppression of p53 by transient transfection increased metastatic efficiency in KHT-C cells. These data suggest that hypoxia can increase tumor cell metastatic efficiency by rendering the tumor cells less sensitive to stress-induced cell death, e.g., through modifying the levels of Mdm2 and p53.

Mechanisms of enhancement of the antitumour activity of melphalan by the tumour-blood-flow inhibitor 5,6-dimethylxanthenone-4-acetic acid.

Several studies show that the antitumour activity of melphalan (MEL) and other alkylating agents can be enhanced by the selective inhibition of tumour blood flow, although the mechanism(s) underlying these interactions are unclear. 5,6-Dimethylxanthenone-4-acetic acid (DMXAA), a new anticancer agent currently in phase I clinical trial, inhibits blood flow in murine tumours. DMXAA increased the activity of MEL against the MDAH-MCa-4 mouse mammary tumour maximally when MEL was given about 2 h after DMXAA, without compromising the maximal dose of the alkylating agent that could be given. The plasma pharmacokinetics of MEL were unchanged by DMXAA pretreatment, but the area under the concentration-time curve (AUC) for the tumour increased by 33% as a result of decreasing clearance (consistent with falling tumour blood flow). However, inhibition of tumour blood flow also leads to microenvironmental changes (e.g. acidosis and hypoxia) that might influence sensitivity to MEL. The sensitivity of KHT cells (freshly isolated from tumours) to MEL in vitro was increased by lowering of either pH or oxygen concentration (pO2), with an overall dose-modifying factor of 15 being recorded for aerobic cells at pH 7.4 versus hypoxic cells at pH 6.5. The cellular uptake of MEL by KHT cells was increased by 74% under hypoxia. Thus, DMXAA appears to augment the antitumour activity of MEL through two different mechanisms, increased exposure (via decreased tumour clearance of MEL) and increased sensitivity resulting from changes to the tumour microenvironment, both of which result from inhibition of tumour blood flow.

The chronic administration of drugs that inhibit the regulation of intracellular pH: in vitro and anti-tumour effects

Mean values of extracellular pH (pHe) in tumours tend to be about 0.5 pH units lower than in normal tissues, whereas values of intracellular pH (pHi) in tumours and normal tissues are similar. Previous studies have shown that drugs that acidify cells at lower pHe such as nigericin, used alone or with agents that inhibit the regulation of pHi, have toxicity to cultured cells at pHe < 6.5 in short-term exposure; these agents also lead to modest anti-tumour effects in mice when given acutely. To evaluate the long-term effects of these drugs at levels of pHe that might occur commonly in tumours, we exposed cells for up to 72h at pHe 6.8 or 7.2 in vitro. Nigericin (0.033 microM) caused time-dependent cell killing of murine KHT and EMT-6 cells at pHe 6.8 (but not at pHe 7.2) with a surviving fraction approximately 5 x 10(-3) after 72 h exposure. Cell killing was increased in the presence of 4,4-diisothiocyanstilbene 2,2-disulphonic acid (DIDS), an inhibitor of Na+-dependent HCO3-/CI- exchange, and to a lesser extent in the presence of 5-(N-ethyl-N-isopropyl) amiloride (EIPA), an inhibitor of Na+/H+ exchange. Cell killing was exquisitely sensitive to the level of pHe. Osmotic pumps were used to obtain a 72 h continuous infusion of nigericin in mice; this led to dose-dependent killing of cells in KHT tumours with surviving fraction of approximately 0.1 at maximum tolerated doses. Hydralazine, which may cause tumour hypoxia and lower pHi as well as pHe, caused cytotoxity when given alone by chronic infusion, and enhanced the cytotoxicity due to nigericin. The addition of DIDS and/or EIPA (using two pumps) further enhanced anti-tumour toxicity, with a surviving fraction of approximately 0.002 at tolerated doses of the four drugs used to treat KHT tumours. The experiments demonstrate the activity of drugs that inhibit the regulation of pHi against murine tumours when delivered by chronic infusion.

Potentiation of alkylating chemotherapy by dual function nitrofurans in multi-cell spheroids and solid tumors

The cytotoxicity and chemosensitizing potential of four dual function nitrofurans was determined in human HT-29 multi-cell spheroids and rodent KHT sarcoma solid tumors. Spheroids were treated with a range of doses of the bioreductive drugs for a period of up to 48 h and the extent of cell kill was assessed at various times after treatment. Cytotoxicity was determined using a clonogenic cell-survival assay. The results demonstrated that two of the nitrofurans were even more toxic to spheroid cells than was the potent bioreductive nitroimidazole aziridine RSU 1069. The dose of the nitrofuran which, after a 24-h exposure, led to a survival value between 0.5 and 1.0, then was chosen for subsequent studies aimed at assessing the ability of these agents to potentiate the efficacy of the nitrosourea CCNU. Exposure to this chemotherapeutic agent was for a period of 1 h. The results indicated that all four dual function nitrofurans enhanced the cell killing of the conventional chemotherapeutic agent by factors ranging from 1.1 to 1.7. Subsequent studies evaluated the therapeutic benefit of combining these bioreductive agents and CCNU in KHT sarcoma-bearing C3H/HeJ mice. The nitrofurans were administered i.p. 0.5 h prior to the chemotherapy and tumor response was assessed by measuring the survival of clonogenic KHT cells 22–24 h after treatment. Normal tissue toxicity was determined using a bone marrow stem cell (CFU-GM) assay. Combining these bioreductive agents with CCNU increased the tumor cell kill by factors of 1.2 to 1.7. Bone marrow toxicity increased with CCNU dose, but the addition of the nitrofurans failed to enhance this endpoint of normal tissue toxicity.

Factors Influencing the Thermosensitivity of Two Rodent Tumors

When SCCVII or KHT tumors (150 mm3) growing in the dorsum of the hind feet of mice were heated in a water bath at 44 degrees C for 60 min, the local control rate was 75 or 5%, respectively. To investigate factors responsible for the differential thermosensitivity between SCCVII and KHT tumors, the intratumor temperature distributions during heating and the thermosensitivities of the tumor cells were studied. Significant temperature heterogeneity was observed in heated tumors. The thermal dose distribution during heating for the sensitive SCCVII tumors was found to be more homogeneous than that for the resistant KHT tumors. For cells grown and heated in culture, SCCVII and KHT cells had similar thermosensitivities. However, when heated in vivo, both SCCVII and KHT cells were more sensitive than their counterparts grown in culture and SCCVII cells were more sensitive than KHT cells. If cells dispersed from the tumors were cultured in medium for 6 h and then heated, both types of cells became as resistant as cells grown in culture. One possible reason for tumor cells to be more sensitive to heating in vivo than in vitro, the temperature of unheated tumors, was examined. It was found that the temperature in the same region in unheated tumors varied temporally by several degrees with an average temperature of 31-32 degrees C. We found no evidence that the temperature during tumor growth could greatly influence the thermosensitivity of the tumor cells. Our findings indicate that a more homogeneous distribution of temperature in the tumor during heating and higher in vivo thermosensitivity of the tumor cells are characteristics of the more heat-sensitive tumor.

Glucose starvation and acidosis: effect on experimental metastatic potential, DNA content and MTX resistance of murine tumour cells

Exposure to oxygen deprivation in vitro has been reported to cause drug resistance in CHO cells (Rice et al., 1986; PNAS 83, 5978) and enhancement of experimental metastatic (colonisation) ability of murine tumour cells (Young et al., 1988; PNAS 85, 9533). Both these studies also demonstrated the induction of a subpopulation of cells with excess DNA content. Since the micromilieu in tumours results in exposure of the tumour cells to conditions of acid pH and nutrient deprivation, as well as hypoxia, we have examined the effect of exposure to acidosis (pH 6.5) and glucose starvation on drug resistance, cellular DNA content and the experimental metastatic ability of KHT sarcoma and B16F1 melanoma cells. Cells were exposed to these conditions for 24 and 48 h and tested for resistance to methotrexate (MTX) or experimental metastatic ability either immediately following these exposures or after 24 or 48 h of recovery in normal growth medium. Both cell lines demonstrated an enhancement of colonisation potential, which was most marked when cells were injected after 48 h of exposure followed by a 24 or 48 h recovery period. Flow cytometric analysis demonstrated an increase in the fraction of KHT cells with excess DNA following both glucose starvation and acidosis we observed only a small increase in MTX resistance following acidic exposure of cells and no change following glucose starvation. Since both acidosis and glucose starvation are known to induce glucose regulated proteins (grp), a subset of the stress protein family, we studied the effect of treatment with another known inducer, 2-deoxyglucose. We found that this agent affected the metastatic efficiency of KHT cells in a manner similar to that observed following exposure to glucose starvation and acidosis. However, further studies are required to establish what role, if any, grp play in this effect. In conclusion this study shows that transient exposure of murine tumour cells to an acidic or glucose deprived environment can cause progression in terms of metastatic potential.

Glutathione diminishes the anti-tumour activity of 4-hydroperoxycyclophosphamide by stabilising its spontaneous breakdown to alkylating metabolites

Evidence was obtained showing that GSH protects against the cytotoxicity of 4-hydroperoxycyclophosphamide (4-OOH-CP) by minimizing the spontaneous fission of 4-hydroxycyclophosphamide (4-OH-CP), its breakdown product, to the ultimate toxic species, phosphoramide mustard (PM). This conclusion was borne out in two series of experiments. The first demonstrated that 4-OH-CP was progressively more stable in aqueous solutions containing increasing concentrations of GSH. The second series of experiments were carried out with tumour cell lines with high (SKOV-3) and low (KHT) GSH contents. The cytotoxicity of 4-OOH-CP, a stable precursor that rapidly gives rise to 4-OH-CP spontaneously under physiological conditions, was enhanced in GSH-depleted SKOV-3 cells, but was unchanged in GSH-depleted KHT cells. It is concluded that the high GSH content of SKOV-3 cells provides a significant protection against 4-OH-CP by limiting the breakdown/activation of 4-OH-CP. Deschloro-4-hydroperoxycyclophosphamide (deschloro-4-OOH-CP), an analogue of 4-OOH-CP that generates acrolein (AC) but not PM in the spontaneous fission reaction, is essentially non-toxic when compared with 4-OOH-CP but is equally potent in depleting GSH. It is postulated that AC may promote the cytotoxicity of the parent 4-OH-CP by depleting cellular GSH. Consequently, the stabilising influence of GSH on 4-OH-CP is removed, leading to increased formation of PM, the ultimate cytotoxic agent.

Sulfated glycoconjugate determinants recognized by monoclonal antibody, SG-1, correlate with the experimental metastatic ability of KHT fibrosarcoma cells

We have examined the binding and functional activity of monoclonal antibody (MAb) SG-1 that was raised by immunization against embryonal carcinoma cells and screened using KHT fibrosarcoma cells. Quantitative absorption, binding and in situ immunochemical staining assays indicate that the MAb SG-1-defined epitopes are expressed preferentially by the highly metastatic KHT35-L1 cells relative to the weakly metastatic, parental KHTp cells. Furthermore, there was a significant correlation (p less than 0.05) between the expression of MAb SG-1-defined antigen on the cells, following trypsin treatment, and their metastatic ability. Binding of MAb SG-1 to antigen was inhibited by specific sulfated polysaccharides including cerebroside sulfate (brain sulfatide), fucoidan, and dextran sulfate (500 kD) but not by heparan, chondroitin, keratan or dextran (5 kD) sulfates. Initial characterization of antigen from KHT cells indicates that the epitope of MAb SG-1 is defined by sulfated glycoconjugates containing galactose and sulfate but not N-acetylglucosamine. In the total lipid extracts of KHT35-L1 cells the antigen was detected in the delipidated protein fraction as well as in the chloroform/methanol fraction. These results suggest that the sulfated glycoconjugate determinants identified by MAb SG-1 may be relevant to the metastatic process of KHT fibrosarcoma cells.

The influence of the surgical wound on local tumor recurrence.

Failure of a primary surgical treatment for cancer is often caused by recurrence of the tumor at the surgical site. The KHT mouse tumor system recapitulates this experience and provides a useful model to test strategies for reducing the incidence of local recurrence after surgical excision. There was an 82% local recurrence of the KHT tumor after surgery. A cell dilution assay indicated that it would require only 39 tumor cells injected into the wound site to result in the same (82%) incidence of tumors. This figure is in contrast to 340 cells required when the cells were injected into an unwounded flank. With the B16 melanoma in C57B1 mice and the Meth A sarcoma in BALB/c mice, the number of cells necessary to induce a tumor (TD/50) was also significantly reduced when the cells were injected into a surgical wound rather than into nonwounded tissue. The difference in cell number was interpreted as the result of the presence of growth factors derived from the traumatized tissue and the inflammatory cells at the wound site. Neither a 5 nor a 15 Gy dose of x-radiation delivered to the wound site immediately after surgical excision of the KHT tumor resulted in a significant reduction in the incidence of local recurrences. When the same doses of x-radiation were given immediately after injecting 36 KHT cells into a wound, no tumors developed. This difference was believed to have resulted from the hypoxic condition in the wound site and the presence of residual clonogenic tumor cells in a nonproliferating (radioresistant) state.

Toxicity of :RSU-1069 for KHT cells treated in vivo or in vitro: Evidence for a diffusible toxic product

RSU-1069 is a highly effective hypoxic cell cytotoxin in KHT sarcomas treated in vivo. However, relative to the hypoxic cells, the oxic cells in the tumor appear more sensitive to the drug than would have been predicted on the basis of results with CHO (AA8-4) cells treated in vitro with the drug under oxic and hypoxic conditions. To examine possible reasons for this difference, suspensions of KHT cells were prepared from tumors growing in vivo, and treated with RSU-1069 in vitro under oxic or hypoxic conditions. The sensitivity of the KHT cells was similar to that of AA8-4 cells, regardless of whether the cells were obtained from untreated tumors or from tumors given 15 Gy in vivo just prior to the preparation of the cell suspension. We observed, however, that the sensitivity of both AA8-4 cells and KHT cells to drug treatment under hypoxic conditions increased with the density of the cells in the treated suspension. This result suggests the possibility that a diffusible toxic product may be released from cells. Such a product could contribute to the toxicity of the drug for oxic cells in tumors in situ.

Characterization of radiation resistant hypoxic cell subpopulations in KHT sarcomas. (II). Cell sorting.

Hypoxic cells in KHT sarcomas were characterized using fluorescence activated cell sorting based on the diffusion properties of the fluorochrome Hoechst 33342. Tumour-bearing female C3H/HeJ mice were injected i.v. with 10 micrograms g-1 Hoechst 33342 and the cells derived from the tumours sorted on the basis of their staining intensities. For each sorted fraction the DNA histogram was evaluated using FCM analysis. The results indicated that the bright and dim cells were not equally distributed about the cell cycle. For example, a greater proportion of S phase cells were in the bright subpopulations whereas the dim subpopulations contained an increased proportion of cells in G1. When the tumours were irradiated with a single dose of radiation prior to cell sorting, the dim cells survived preferentially. Dose response curves for the 20% most dim and 20% most bright cells, sorted on the basis of fluorescence intensity, then were determined. The survival curves of the dim and bright cells were found to have slopes similar to those of KHT cells irradiated in situ in dead animals or in vitro under fully oxic conditions, respectively. In addition, when KHT sarcoma-bearing mice were given a 2.5 mmol kg-1 dose of misonidazole (MISO) prior to irradiation and cell sorting, the dim subpopulation was sensitized whereas the bright subpopulation was not. These findings suggest that (i) compared to well-oxygenated areas, hypoxic regions of KHT tumours contain a smaller percentage of cells actively proliferating and (ii) Hoechst 33342 sorting may allow the detailed in situ evaluation of agents acting directly against hypoxic cells in solid tumours.

Potentiation of CCNU activity by misonidazole in metastases.

The KHT sarcoma is a model system in which metastases can be studied in multiple organs without prior clonal selection. The present series of experiments were designed to evaluate and compare the extent of potentiation of chemotherapeutic agent activity by radiosensitizers when KHT sarcoma cells were grown in different anatomical sites. In these studies the effect of combining misonidazole (MISO) and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) on KHT lung nodules and ovarian metastases was determined. Ovarian metastases were a consequence of the direct spread of tumor cells growing as lung nodules. Once established, KHT cells in the lungs and ovaries grew with a similar doubling time (1-2 days). Response of tumors at either site to chemotherapy in the presence or absence of a sensitizer was assessed using an in vivo to in vitro excision assay. MISO (1.0 mmol/kg) was administered simultaneously with a range of CCNU doses and survival of clonogenic tumor cells was measured 24 h after treatment. The results demonstrate that the addition of MISO to CCNU treatment potentiated the action of this chemotherapeutic agent at both tumor sites although greater cell kill enhancement occurred in the ovarian metastases. In the lung nodules, when combined with CCNU, a 1.0 mmol/kg dose of MISO was found to yield a dose modifying factor (DMF) of approximately 1.3. The same combination resulted in a DMF of approximately 1.8 in the ovarian metastases. This difference in DMF was not a result of an intrinsic difference in sensitivity to CCNU since cells grown at either site gave rise to the same dose response curve. Rather the difference in dose modification by MISO appears to be a consequence of the larger fraction of radiobiologically hypoxic cells in the ovarian tumors (approximately 50 per cent) than in the lung nodules (approximately 5 per cent) at the time of treatment. These findings suggest the use of drug-sensitizer combinations to treat disseminated disease and provide further evidence for the requirement of hypoxia in chemopotentiation by radiosensitizers.

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.

Toxicity of diethylaminoreserpine to tumor cells: Effects of drug alone and in combination with radiation

DL-152 is toxic to cells of two transplantable mouse tumors. Minimal numbers of surviving tumor cells are seen at 24 and 48 hours following administration of the drug to the tumor bearing mouse, the small fraction of cells surviving at this time (for doses as low as 5 mg/kg) indicates that both hypoxic and aerated cells are killed. For short (one hour) exposures in vivo, however, both acutely and chronically hypoxic cells are more sensitive to DL-152 than are their aerated counterparts. For KHT cells growing as lung nodules, DL-152 toxicity is not demonstrable until 11–14 days after initiation of the lung tumor, coinciding with the time at which an hypoxic fraction develops in this model. In vitro experiments using KHT cells in suspension showed certain concentrations of DL-152 to be selectively toxic to hypoxic cells. At higher concentrations both hypoxic and aerated cells were killed by the drug. The combined effect of DL-152 and irradiation has been investigated using, as an index of response, the time required for a transplantable tumor to regrow to a given volume after treatment. DL-152 was equally effective in prolonging the period of radiation-induced growth delay when it was given either shortly before or shortly after irradiation. Growth delay attributable to drug plus irradiation was greater than would be predicted if the effects of the two modalities were additive. It is concluded that DL-152 has a concentration-dependent specific toxicity for hypoxic cells and that the drug may require a hypoxic milieu to manifest toxicity.

The separation of a mixture of bone marrow stem cells from tumor cells: An essential step for autologous bone marrow transplantation

KHT tumor cells were mixed with mouse bone marrow to simulate a sample of bone marrow containing metastatic tumor cells. This mixture was separated into a bone marrow fraction and a tumor cell fraction by centrifugal elutriation. Elutriation did not change the transplantability of the bone marrow stem cells as measured by a spleen colony assay and an in vitro erythroid burst forming unit assay. The tumorogenicity of the KHT cells was similarly unaffected by elutriation. The data showed that bone marrow cells could be purified to less than 1 tumor cell in more than 10 6 bone marrow cells. Therefore, purification of bone marrow removed prior to lethal radiation-drug combined therapy for subsequent autologous transplantation appears to be feasible using modifications of this method if similar physical differences between human metastatic tumor cells and human bone marrow cells exist. This possibility is presently being explored.

A Comparison of the Effectiveness of NF-167 and Metronidazole as Hypoxic Cell Sensitizers of KHT Tumor Cells in Vitro

Two compounds, NF-167 (5-nitro-2-furaldehyde-5-[3-diethylaminopropyl] semioxamazone hydrochloride) and metronidazole (2-methyl-5-nitroimidazole-1-ethanol), were selected for in vitro testing of their abilities to sensitize hypoxic KHT tumor cells to ionizing radiation. Metronidazole had been shown previously to sensitize hypoxic KHT cells in mice while NF-167 had shown no in vivo sensitization. The acute and chronic toxicities of the drugs were determined and then sensitization was measured after a single dose of radiation as a function of drug concentration. Survival curves were determined at a cell concentration of $5\times 10^{5} \text{cells}/{\rm ml}$ using 27 μM NF-167 and 5.8 and 29 mM metronidazole. The enhancement ratio of NF-167 was found to be 1.5, and that of metronidazole was 1.4. The effect of cell density on the sensitizing abilities of these compounds was investigated and it was found that at densities near $10^{8} \text{cells}/{\rm ml}$ NF-167 lo...