Biomedical subjects

L Milas

Publications and source records attributed to L Milas.

At least 91 records · Page 5Linked to original sources

PubMed1994

Enhancement of tumor radioresponse of a murine mammary carcinoma by paclitaxel.

Paclitaxel is a chemotherapeutic agent with potent microtubule stabilizing activity that arrests cells in G2-M. Because G2 and M are the most radiosensitive phases of the cell cycle, paclitaxel has potential as a cell cycle-specific radiosensitizer. In this study, we investigated the ability of paclitaxel to increase tumor radioresponse in vivo using a murine mammary carcinoma and the dependency of this response on accumulation of tumor cells in mitosis. Mice bearing 8-mm tumors were treated with paclitaxel (60 mg/kg i.v.), 9, 15, or 21 Gy of single-dose radiation, or with a regimen of both agents in which radiation was given 1, 9, or 24 h after paclitaxel. The effect of the treatments was determined by tumor growth delay. Microscopically, the percentage of mitotically arrested cells was only 4% 1 h after treatment with paclitaxel, increased to a maximum value of 30% at 9 h, and decreased to 12% 24 h after paclitaxel. Paclitaxel enhanced tumor radioresponse by factors of 1.21 to 2.49. The degree of enhancement increased with increases in both the dose of radiation and the time between paclitaxel administration and radiation delivery. Radiation efficiently destroyed mitotically arrested cells by apoptosis. The greatest enhancement of radiation response was not at the time of the highest mitotic arrest but at 1 day after paclitaxel treatment, showing that paclitaxel potentiates tumor radioresponse by mechanisms in addition to blocking the cell cycle in mitosis, possibly by tumor reoxygenation. Thus, these results show that paclitaxel is a potent in vivo radiopotentiating agent and has the potential to be usefully combined with radiotherapy.

Animals↗

PubMed1994

Is tumor cell radiation resistance correlated with metastatic ability?

Patients who experience local failure following radiation treatment of epithelial malignancies exhibit a substantially higher rate of distant metastasis than those patients who achieve permanent local control. This fact has raised concern that the local failure to control the primary/regional tumor may serve as a marker of a particularly malignant neoplasm, i.e., high metastatic activity and radiation resistance. If this were true, there would be no gains in survival by increasing the efficacy of treating the primary/regional disease because the new local controls would develop distant metastasis. To investigate this concept, the relationship between distant metastasis probability and tumor cell radiation resistance has been studied by examining laboratory and clinical data (in vitro and in vivo assays) from six collaborating centers. TCD50s (radiation dose which inactivates half of the irradiated tumors) and incidence of distant metastasis in mice with local control have been evaluated for 24 murine tumor systems. SF2s (surviving fraction after 2 Gy) were determined in vitro for cell lines from 8 human, 13 mouse, and 15 rat tumors/tumor sublines and the metastatic activity assessed after injection of the cells into syngeneic murine hosts and xenogenic hosts for the human tumors. SF2s of cells from carcinomas of the head/neck, cervix, and endometrium which were controlled locally by radiation +/- surgery from four centers were compared for those which did and those which did not metastasize. The total number of patients studied was 222. The cumulative distributions of SF2s of locally controlled tumors which did and did not metastasize were not different in each of the data sets. Similarly, there was no demonstrable relationship between TCD50s and metastatic frequency in local control mice. Furthermore, the SF2s of murine and human tumor cell lines did not track with metastatic activity. Radiation sensitivity of clinical and laboratory tumors did not correlate with metastatic activity in studies of data from six centers.

Animals↗

PubMed1994

Protection by WR-2721 against radiation plus cis-diamminedichloroplatinum II caused injury to colonic epithelium in mice.

PURPOSE: The study was designed to investigate the ability of S-2-(3-aminopropylamino) ethylphosphorothioic acid (WR-2721) to protect mouse colon mucosa against damage produced by the combined radiation plus cis-diamminedichloroplatinum II (cis-DDP) treatment. METHODS AND MATERIALS: The mucosal damage was quantified by using microcolony assay, which measures the survival of epithelial cells in colon crypts. Radiation doses ranged from 8-24 Gy gamma rays. Cis-diamminedichloroplatinum at a dose of 13 mg/kg and WR-2721 at a dose of 400 mg/kg body weight were given IP before or after irradiation. RESULTS: Addition of cis-DDP to radiation within 24 h before and 48 h after irradiation reduced the number of crypt cells more than did radiation alone. The highest reduction was seen when the drug was given 2 or 6 h before irradiation: the damage was increased by a factor of 1.5. Protective effects of WR-2721 were tested in the radiation plus cis-DDP combination in which cis-DDP was given 2 h before or 2 h after radiation. In the former sequencing, WR-2721 was given 30 min before radiation (90 min after cis-DDP); damage was reduced more than the amount of damage contributed by cis-DDP (PF = 1.6). When cis-DDP was given 2 h after irradiation, WR-2721 was administered 30 min either before irradiation or 30 min before cis-DDP. Here, the protective effect was achieved only when WR-2721 was given before radiation: the PF was 1.3 in that case and only 1.1 when WR-2721 was given before cis-DDP. Thus, WR-2721 must be given before irradiation, but even then the degree of protection achieved depends on whether cis-DDP is applied before or after irradiation, with the protection being greater in the former situation. CONCLUSION: Our observations showed that WR-2721 is a potent protector against the injury of mouse colon mucosa produced by the combined radiation plus cis-DDP treatment. They have important implications in the clinic, indicating that proper timing of WR-2721 administration is crucial for preventing side effects of the cis-DDP and radiotherapy combination, where damage to mucosal epithelial cells is dose limiting.

Amifostine↗

PubMed1994

Proliferation kinetics of recruited cells in a mouse mammary carcinoma.

Solid tumors contain populations of proliferating (P) and quiescent (Q) cells. Shifting between these populations occurs continuously and cells are recruited from quiescence to proliferate (Q-->P) as a result of exogenously applied or endogenous cell depleting stimuli. Direct measurements of the proliferation kinetics of these Q-->P cells in solid tumors are difficult to make because of the much larger percentage of P-cells. In order to specifically analyze the kinetics of the Q-->P cells, double thymidine analogue labeling was used. This was accomplished by first labeling in vivo all of the P-cells in MCaK tumors using continuous exposure to chlorodeoxyuridine (CldUrd) administered by a minipump over 21 h. About 75% of the aneuploid cells are P-cells based on CldUrd labeling. At different times after the pumps were removed, the tumors were pulse-labeled with iododeoxyuridine (IdUrd) and harvested 6 h later. A 3-color flow cytometry assay was used to simultaneously and independently analyze CldUrd and IdUrd incorporation, as well as DNA content. The Q-->P cells were identified as having only been labeled with IdUrd. The length of their S-phase was calculated from the movement of the Q-->P cells during the 6 h after IdUrd labeling. The results showed the length of S-phase for the recruited cells to be slightly, but significantly, longer than the length of S-phase for the total cells (11 h versus 9 h, respectively). Thus, the recruited cells appear to have slightly slower kinetics than the proliferating cells in the absence of a perturbing stimulus such as radiotherapy or chemotherapy.

Animals↗

PubMed1994

Potentiation of radiation-induced regrowth delay in murine tumors by fludarabine.

Fludarabine (9-beta-D-arabinofuranosyl-2-fluoroadenine-5'-monophosphate), an adenine nucleoside analogue, has previously been shown to inhibit the repair of radiation-induced chromosome damage. Thus fludarabine may have therapeutic utility in combination with photon irradiation. The purpose of this study was to determine whether fludarabine could enhance radiation-induced murine tumor regrowth delay and to determine the most effective dose and schedule of the combination. A significant (P < 0.05) absolute regrowth delay enhancement was observed in three murine tumor models (SA-NH, a sarcoma; and MCA-K and MCA-4, mammary carcinomas) when fludarabine (800 mg/kg) was given 1 h prior to 25 Gy gamma-irradiation. While fludarabine enhanced radiation-induced tumor regrowth delay when given between -36 h and +6 h of radiation (SA-NH tumor), the greatest enhancement was observed when fludarabine was given at -24 h prior to irradiation (radiation dose modification factor of 1.82 at -24 h compared to 1.57 at -3 h prior to radiation). The degree of fludarabine enhancement (at -3 or -24 h) was dose dependent at doses above 200 mg/kg. When fludarabine and radiation were administered on a fractionated schedule (fludarabine given 3 h prior to radiation each day for 4 days), the dose modification factor increased to 2.14 (1.63 if the effect of fludarabine alone is subtracted). These results suggest that fludarabine enhances radiation-induced tumor regrowth delay in a more than additive fashion after both single and fractionated treatments, and the degree of enhancement is dependent on the sequence and timing of administration, the fludarabine dose, and the tumor type. Thus, fludarabine may have clinical potential as a radiation enhancer in the treatment of solid tumors.

Animals↗

PubMed1994

Induction of apoptosis in murine tumors by cyclophosphamide.

Whereas there have been several recent reports of the induction of apoptosis by chemotherapy agents in cell culture systems, much less is known about the role of this mode of cell death in tumors treated in vivo. We therefore quantitated the proportion of apoptotic cells induced as a function of time and dose in two murine tumors treated with cyclophosphamide in vivo. The two tumors were a mammary adenocarcinoma, MCa-4, and an ovarian adenocarcinoma, OCa-1. The percent apoptosis was scored from stained histological sections of the tumors using a system based on the characteristic features of the apoptotic nuclei. The kinetics of apoptosis development were determined over a 5-day period following treatment of the mice with 200 mg/kg. The percent apoptosis peaked between 10-18 h in both tumors and then slowly declined to background levels by 5 days after treatment. The dose responses showed that even much lower doses, 25 mg/kg, could induce significant apoptosis and that the proportion of apoptotic cells plateaued at doses higher than 100 mg/kg. These results are compared and contrasted with our previous reports on apoptosis induction in these same tumors with ionizing radiation.

Animals↗

PubMed1994

Radiation-induced apoptosis in a murine lymphoma in vivo.

A number of radiobiologic parameters of radiation-induced apoptosis were investigated in a syngeneic murine B-cell lymphoma, designated LY-TH. These included radiation dose effect, kinetics of apoptosis development, the effect of hypoxia and split-dose recovery. Tumors, 8 mm in size, were locally irradiated with graded doses ranging from 1 to 10-Gy gamma rays. Radiation-induced apoptosis was observed as early as 1 h after irradiation, peaked between 4 and 6 h and could no longer be detected 24 h later. The magnitude of the apoptotic response generally increased with radiation dose, but lower doses seemed to be relatively more effective than higher doses. Tumor hypoxia, produced by tumor clamping, inhibited induction of apoptosis by a factor of about 2.5. When two doses of radiation were separated by times of 1-10 days, the proportion of apoptotic cells induced by the second dose was greatly reduced compared to the initial dose. This reduction was the greatest when the second dose was given 2 days after the first dose. The proportion of apoptotic cells induced by the second dose slowly recovered after 2 days but it did not return to the initial levels after as long as 10 days.

Animals↗

PubMed1994

Dynamics of tumor cell clonogen repopulation in a murine sarcoma treated with cyclophosphamide.

Experiments were performed to establish the extent and kinetics of tumor cell repopulation in a murine sarcoma, designated SA-NH, treated with cyclophosphamide (CY). Mice bearing 8-mm leg tumors were treated with 200 mg/kg CY which caused a transient tumor regression. Changes in the absolute clonogen content of tumors was determined by the change in TCD50 values (50% tumor control) obtained under hypoxic conditions of local tumor irradiation at different times after CY treatment until tumors regrew to the pretreatment size. For comparison, hypoxic TCD50 values were determined during the growth of tumors not treated with CY. CY greatly depleted tumors of clonogenic cells as manifested by the reduction in the control TCD50 value of 64.5 Gy to 32.8 Gy 1 day after CY treatment. The reduced TCD50 value remained unchanged for 2 weeks after treatment with CY, at which time the TCD50 began to rapidly increase, continuing until the end of the observation period of 21 days when tumors reached the pretreatment size. In contrast, there was a constant but slower increase in TCD50 values during the growth of tumors not treated with CY. The daily increase in TCD50 was more than twice as high in CY-treated than in CY-untreated tumors: 4.5 Gy/day versus 2.1 Gy/day. This implies that the rate of clonogen production in CY-treated tumors was twice as high as that of unperturbed tumors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Heterogeneity in the development of apoptosis in irradiated murine tumours of different histologies.

Fifteen different murine tumours were evaluated with respect to the degree of apoptosis development that occurs in the tumour tissue in the first few hours following irradiation in vivo. Animals were killed at 3 or 6 h following irradiation with 0, 2.5, 10 or 25 Gy. Apoptosis was scored as percent aberrant nuclei by microscopic examination of histological sections made from the tumour specimens. Results showed that three of four mammary adenocarcinomas, one ovarian adenocarcinoma, and one lymphoma displayed at least 10% apoptotic cells after 25 Gy, whereas five sarcomas, three squamous cell carcinomas, and a hepatocarcinoma did not. The time courses and dose responses were similar in those tumours that responded. These data were compared with the known response of these same tumours when analysed using conventional assays. The tumours that did respond by significant apoptosis had longer specific growth delays and lower TCD50 (dose to cure 50% of animals) doses, thus suggesting that an acute apoptotic response following irradiation may be a feature of certain tumours that respond well to irradiation. Additionally, this analysis revealed heterogeneity in the apoptotic response both within an individual tumour specimen and among different tumour types. These observations of intra and intertumour heterogeneity are consistent with the idea that the propensity for apoptosis in tumours is genetically regulated.

Adenocarcinoma↗

PubMed1993

Stimulation of hematopoietic cell recovery by tetrachlorodecaoxide in sublethally irradiated mice.

This study investigated whether tetrachlorodecaoxide (TCDO), a potent wound-healing agent, promotes recovery of hematopoietic tissue of mice depleted by sublethal X irradiation. Mice were exposed to 3 Gy total-body irradiation and were given 1 ml/kg TCDO intravenously daily from day 1 to 5 or day 4 to 8 after irradiation. The effect was assessed by the change in the total number of nucleated cells in bone marrow and spleen, endogenous spleen colony formation, and 30-day mouse lethality. In the spleen there were profound effects on spleen weight, total organ cellularity, and endogenous colony formation. The TCDO produced radiation dose-modifying factors between 1.4 and 1.5 for endogenous spleen colony formation in mice primed with 3 Gy and reirradiated 4 days after treatment. This stimulated cellular recovery resulted in an increased protection of mice from lethality caused by subsequent total-body irradiation by factors of 1.12-1.18. The results show that TCDO is a potent stimulator of cellular recovery in the spleen of sublethally irradiated mice.

Animals↗

PubMed1993

Biochemical modulation of radiation-induced apoptosis in murine lymphoma cells.

Considerable effort in our laboratory has been directed toward characterizing the role of apoptosis as a mode of cell death in model tumors irradiated in vivo. These studies have shown that apoptosis is an important response in some tumors, correlating with tumor growth delay and tumor cure. However, the response is heterogeneous among both the various tumors examined and the cells in a given tumor, suggesting that the propensity for cells to undergo apoptosis upon irradiation is regulated by unknown factors in tumors. To develop a model system for investigating these regulatory pathways in vitro at the molecular and biochemical levels, we have established cells from a tumor that displays a dramatic apoptotic response in vivo, the TH lymphoma, in cell culture. In this article, we review some of the results of our studies using this model system. To date, we have shown that the dose-response relationship and kinetics of the development of apoptosis for these cells in culture are similar to what we observed for the tumor response in vivo. Moreover, the roles of calcium and signal transduction pathways as important regulatory factors in radiation-induced apoptosis have been defined in this system. Ultimately such investigations may yield the insight necessary for designing protocols to modulate apoptosis biochemically in irradiated normal and tumor tissues to therapeutic advantage.

Animals↗

PubMed1993

Development of apoptosis in irradiated murine tumors as a function of time and dose.

In a previous paper (Radiat. Res. 127, 308-316, 1991), we reported that a moderately radiosensitive, transplantable murine ovarian carcinoma (OCaI) displayed apoptosis after irradiation whereas a radioresistant hepatocellular carcinoma (HCaI) did not. These initial observations have been followed up in this detailed analysis of the development of apoptosis in these two tumors as a function of time and dose. Histological sections of OCaI and HCaI carcinomas were scored at various times between 0.5 and 24 h after single doses of 2.5 or 25 Gy gamma radiation for the incidence of apoptosis. The percentage of nuclei undergoing apoptosis in untreated tumors was 5% in OCaI and 0.6% in HCaI. The peak in the number of apoptotic bodies occurred in the OCaI tumors 3-5 h after either dose. After 2.5 Gy, the peak incidence was about 20% and after 25 Gy it was about 30%. Irrespective of dose, HCaI tumors had an incidence of apoptosis of less than 3%. Based on the results of this time course, 4 h after irradiation was chosen for the determination of the dose response, over doses ranging from 2.5 to 25 Gy. The dose response for the OCaI tumors reached a plateau at 25-30% apoptotic nuclei after doses of about 7.5 Gy and above. Autoradiographic analysis of histological sections from mice injected with [3H]thymidine showed that some apoptotic bodies in the OCaI tumors arose from cycling cells. These results confirm that the apoptotic mode of cell death may represent an important response in some irradiated tumors.

Animals↗

PubMed1993

Improvement in radiotherapy for a murine sarcoma by indomethacin plus WR-2721.

The study was designed to determine whether the improvement in the therapeutic ratio of radiotherapy by indomethacin, a potentiator of tumor radioresponse through immunostimulation, can be improved further by combining it with WR-2721, a potent radioprotector of normal tissue. Mice bearing the syngeneic sarcoma FSA (8 mm) in the leg were treated with single graded doses of gamma rays to the tumor or with gamma rays plus indomethacin, WR-2721, or both. The effect of these compounds was assessed on local tumor control, radiation-caused hair loss, and radiation-induced leg contracture. Indomethacin increased local tumor control by a factor of 1.7, a value that was not influenced significantly by the addition of WR-2721. Indomethacin did not affect radiation-induced hair loss or radiation-induced leg contracture, whereas WR-2721 protected against them by factors of 1.4 and 1.5, respectively. These protection factors were not influenced by the addition of indomethacin. Thus the combination of indomethacin and WR-2721 can increase the therapeutic ratio of radiotherapy more than either drug given alone.

Amifostine↗

PubMed1992

Combination of interleukin-2 and irradiation in therapy of murine tumors.

Experiments were designed to investigate the therapeutic efficacy of interleukin-2 (IL-2) combined with radiotherapy. The effect of IL-2 and local thoracic irradiation (LTI) was determined on 4-day-old lung micrometastases, generated by i.v. injection of tumor cells into mice. IL-2 alone reduced the number of lung nodules more effectively when given from 1 to 4 than 4 to 7 days after tumor cell injection. The combination of IL-2 and LTI reduced the number of lung nodules more than did the individual treatments alone. When IL-2 therapy was combined with local irradiation of 8-mm leg tumors, there was no change in the TCD50 (radiation dose yielding 50% local tumor control). However, the combination of IL-2 treatment on days 1-4 with irradiation of tumor-bearing legs on day 1 after inoculation of tumor cells reduced the TCD50 by a factor of 1.3. These results show that IL-2 improves tumor radiotherapy, but that the improvement depends on anatomic localization and tumor size at the time of treatment.

Animals↗

PubMed1992

Effects of size and growth time of a murine sarcoma on its metastatic spread.

The effects of the size of an implanted tumor and of its time of growth on metastasis were examined in the same tumor grown under two different conditions. Tumors were implanted either in the untreated legs of mice or in legs that had been irradiated one day earlier. The radiation slowed the growth of tumors. When the tumors grew to predetermined diameters, the legs were excised and 20 days later the mice were examined for the presence of lung metastases. Equal changes in the time to excision of the tumors grown under the two conditions led to nearly equal changes in the proportions of animals with metastases. Tumor volume effects were not apparent in this consideration of changes in metastasis rates with time. This work reanalyses the data of that study using the variability in growth rates within a tumor growth condition to investigate the effect of tumor size on metastatic intensity. This intensity increased at least linearly with tumor volume for both irradiated and control animals. The finding of equal effect at equal growth times of the implanted tumors under the two growth conditions was confirmed but is due to: (1) metastatic intensity changing five times as rapidly with tumor size in the irradiated group as compared to the control group and (2) non-exponential retarded growth of the tumors in the control treatment group.

Animals↗

PubMed1992

Radiation protection against early and late effects of ionizing irradiation by the prostaglandin inhibitor indomethacin.

Protective effects of indomethacin, a prototype prostaglandin-inhibiting agent, against early and late sequelae of radiation injury (after X-rays or gamma rays) in mice were investigated. The following tissues or organs were examined: hematopoietic tissue, esophagus, jejunum, colon, lung, hair follicles, and tissues involved in the development of radiation-induced leg contractures. In addition, the effect of indomethacin was tested against radiation-induced carcinogenesis. In all experiments, the radiation was delivered as a single dose. Indomethacin led to significant protection of hematopoietic tissue, by a factor of 1.3. There was also some protection against radiation-induced pneumonitis and against radiation-induced carcinogenesis (protection factor of 1.2). The other tissues tested showed no change in their radioresponse after being treated with indomethacin. Thus, indomethacin can act as a radioprotective agent against both early and late sequelae of radiation, but its effect is dependent on the tissue tested. This protection is smaller than that observed with WR-2721. However, indomethacin combined with WR-2721 produced a radioprotective effect greater than the radioprotection achieved by individual treatments.

Amifostine↗

PubMed1992

Modification of radiation-induced carcinogenesis in mice by misonidazole and WR-2721.

The effects of the radiosensitizer misonidazole (MISO) and the radioprotector WR-2721 on radiation-induced carcinogenesis in C3Hf/Kam mice were investigated. The right hind legs were exposed to graded single doses of gamma-rays. MISO and WR-2721 were given i.p. 30 min before irradiation at a dose of 1 mg/g and 0.4 mg/g, respectively. The RCD50, or radiation dose inducing tumors in 50% of the irradiated legs, was determined 650 days after treatment. The same animals were also checked for the effect of these drugs on hair loss and radiation-induced leg contractures. MISO enhanced radiation carcinogenesis by a factor of 1.43, whereas WR-2721 reduced it by a factor of 1.75. These effects on carcinogenesis correlated well with the modifying effects of the two agents on radiation-induced hair loss (early damage) and leg contractures (late damage).

Amifostine↗

PubMed1991

Improvement in therapeutic ratio of radiotherapy for a murine sarcoma by indomethacin plus misonidazole.

In this study we asked whether the improvement in the therapeutic ratio of radiotherapy by indomethacin (INDO), which potentiates tumor radioresponse through stimulation of the immune system, could be further improved by combining it with the hypoxic cell radiosensitizer misonidazole (MISO). Mice bearing the syngeneic sarcoma fibrosarcoma (8 mm) in the leg were treated with single graded doses of gamma-rays to the tumor or with irradiation combined with INDO, MISO, or both drugs. Local tumor control was the end point of tumor radioresponse. In addition, the effect of these drugs on radiation-caused hair loss and leg contractures was assessed. INDO increased tumor radioresponse by a factor of 1.31, but it did not affect either hair loss or leg contractures. MISO increased tumor radioresponse by a factor of 1.86, hair loss by a factor of 1.69, and leg contractures by a factor of 1.54, thus providing only a small therapeutic gain. The combined INDO plus MISO treatment increased tumor radioresponse by a factor of 2.72, which was more than the additive effect of the individual drugs. On the other hand, the combined treatment caused no additional hair loss compared to that caused by MISO only. Overall, our results show that INDO plus MISO treatment increased tumor radioresponse more than INDO or MISO alone and provided a significant therapeutic gain. Furthermore, they illustrate that combinations of two radiopotentiating agents with different mechanisms of action may improve the radiotherapeutic effect.

Animals↗