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L Milas

Publications and source records attributed to L Milas.

At least 73 records · Page 4Linked to original sources
PubMed1996

Therapeutic potential of paclitaxel-radiation treatment of a murine ovarian carcinoma.

BACKGROUND: Paclitaxel has been shown to radiosensitize tumor cells in culture by arresting them in the most radiosensitive G2 and M cell cycle phases. In vivo preclinical studies are now necessary to obtain full insight into the radiopotentiating potential of this drug and its ability to increase the therapeutic gain of radiotherapy. We tested its ability to enhance the tumor radioresponse of an ovarian carcinoma and to influence the normal tissue radioresponse of recipient mice. METHODS: Mice bearing 8-mm isotransplants of a syngeneic ovarian carcinoma, designated OCA-I, in their legs were treated with 40 mg/kg paclitaxel i.v., 14-60 Gy single-dose local tumor irradiation, or both; radiation was given under ambient conditions 1-96 h after paclitaxel. Tumor growth delay, tumor cure rate (TCD50 assay), and delay in tumor recurrences were measured. Normal tissue radioresponse was determined using jejunal crypt cell survival at 3.5 days after exposure of mice to 9-14 Gy single dose of total body irradiation; the mice were untreated or treated with 40 mg/kg i.v. paclitaxel 4-96 h before irradiation. RESULTS: Paclitaxel alone was effective against OCA-I, but its combination with irradiation produced supra-additive tumor growth delay. It also reduced TCD50 values and delayed tumor recurrences. The enhancement of tumor radioresponse ranged from 1.33 to 1.96; the value increased as the time between paclitaxel administration and tumor irradiation increased up to 48 h, but then decreased again at 96 h. In contrast, paclitaxel protected jejunum against radiation damage by factors of 1.03 to 1.07 when given 24-96 h before irradiation. It showed some potentiation of damage (by a factor of 1.07), but only when given 4 h before irradiation. CONCLUSIONS: Paclitaxel potentiated tumor radioresponse if given within 4 days before irradiation, whereas it caused radioprotection of normal tissue (jejunum) at that time. Therefore, paclitaxel significantly increased therapeutic gain and so has potential for use in combination with radiotherapy for pelvic malignancies.

Animals↗
PubMed1996

Synthesis and evaluation of water-soluble polyethylene glycol-paclitaxel conjugate as a paclitaxel prodrug.

Water-soluble paclitaxel may cause less side effects and be less costly to administer in comparison to a taxol formulation using a cremophor EL/alcohol vehicle. In this study, polyethylene glycol (PEG; MW 5000) was conjugated to the 2' position of paclitaxel through a spacer succinyl group. PEG-paclitaxel as a non-ionic paclitaxel prodrug was highly water soluble (> 20 mg equiv. paclitaxel/ml). The release of paclitaxel from phosphate-buffered solution was pH dependent. The half-life of PEG-paclitaxel was 7.6, 54 and 311 min at pH 9.0, 7.4 and 6.0, respectively. PEG-paclitaxel inhibited the growth of B16 melanoma cells to an extent similar to that of paclitaxel. In MCA-4 mammary tumor-bearing mice, a single dose of PEG-paclitaxel (40 mg equiv. paclitaxel/kg body weight) significantly delayed tumor growth. The average number of days for the tumor to reach 12 from 8 mm in diameter increased from 6.5 days for control animals to 8.5 days for PEG-paclitaxel-treated animals and 9.4 days for paclitaxel-treated animals. These studies demonstrated that PEG may be used as an effective solubilizing carrier for paclitaxel.

Animals↗
PubMed1996

Evaluation of [131I]iodoerythronitroimidazole as a predictor for the radiosensitizing effect.

The aim of this study was to evaluate whether radiolabeled iodoerythronitroimidazole (IETNIM) could predict the radiosensitization effect on tumors. Tumor-bearing mice were irradiated at a dose of 25, 31 and 37 Gy after the injection of IETNIM. They were also exposed to 37 Gy radiation at 35, 70, 140 and 240 min after the i.p. injection of IETNIM. After the irradiation, tumor growth assays were conducted and the effect of IETNIM as a radiosensitizer was estimated as enhancement factor (EF). Tumor uptake was measured at 35, 70, 140 and 240 min after i.p. injection of [131I]IETNIM, which were the same intervals used in the radiosensitization study. EF of IETNIM in mice treated with 25, 30 and 37 Gy irradiation was 0.72, 0.98 and 1.28, respectively. EF of IETNIM in mice irradiated at 35, 70, 140 and 240 min after the injection was 1.50, 1.69, 1.46 and 1.08, which corresponded to the tumor uptake and blood clearance of [131I]IETNIM. [131I]IETNIM may be a suitable radiopharmaceutical to predict the radiosensitization effect of misonidazole analogs on tumors.

Animals↗
PubMed1996

Antimutagenic effects of amifostine: clinical implications.

The radioprotector S-2-(3-aminopropylamino) ethylphosphorothioic acid (amifostine; WR-2721) was evaluated for its ability to protect against cyclophosphamide-induced mutagenesis at the hypoxanthine-guanine phosphoribosyl transferase (HPRT) locus in mouse splenocytes under conditions that do not interfere with cyclophosphamide's therapeutic effectiveness against fibrosarcoma lung tumors. Mutations at the HPRT locus increase in frequency as a function of the dose of cyclophosphamide used. With a spontaneous mutation frequency in C3H mice of 1.5 x 10(-6), mutation frequencies increased from 6.2 x 10(-6) to 2.0 x 10(-5) as the cyclophosphamide dose increased from 50 to 200 mg/kg. C3H male mice had 3.5 x 10(5) viable fibrosarcoma cells injected into their tail veins. This resulted in an average of 68 tumor colonies per mouse. Four days following injection, animals received cyclophosphamide 100 mg/kg, which provided significant tumor cell killing and a reduction in tumor colony number to an average of less than one per animal. Amifostine at a concentration of 100 mg/kg did not affect cyclophosphamide's therapeutic efficacy. However, amifostine 100 mg/kg was effective in reducing cyclophosphamide-induced HPRT mutation frequency in mice from 160 to 35 per 10(5) viable cells regardless of whether it was administered 30 minutes before or 2 hours after the cyclophosphamide.

Amifostine↗
PubMed1996

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

Fludarabine, an effective repair inhibitor of radiation-induced chromosome breaks, and indomethacin, an inhibitor of prostaglandin synthesis, were shown previously to improve the therapeutic ratio of radiotherapy for murine tumors. The purpose of this study was to determine whether the combination of these two radiosensitizers with different mechanisms of action could further increase the therapeutic ratio of radiotherapy in an FSA mouse sarcoma after single and fractionated irradiation. The effect of the combined treatment on tumors was assessed by the local tumor control assay (TCD50) in mice bearing an FSA sarcoma in the leg. The effect of the combination on normal tissues was assessed by skin desquamation, hair loss and leg contracture in the legs of non-tumor-bearing mice. For the TCD50 assay, after single irradiation, the radiation dose modification factor (DMF) reached 1.2 for both indomethacin (35 micrograms/ml in the drinking water for 10 days) and fludarabine (800 mg/kg intraperitoneally 3 h prior to irradiation). For both drugs combined, the DMF increased to 1.7. No significant increase in normal tissue toxicity was observed with any of the combinations. After fractionated irradiation (16 fractions over 4 days), the DMFs for local tumor control reached 1.3 for indomethacin and 1.8 for fludarabine darabine (400 mg/kg every day for 4 days). The combination of both drugs produced a DMF of 2.0. None of the combinations altered the effects of radiation on skin desquamation, hair loss or leg contracture significantly. The present study suggests that the therapeutic ratio of radiotherapy for a murine sarcoma can be improved by the combination of indomethacin and fludarabine, two agents differing in their mechanisms of radiopotentiation.

Animals↗
PubMed1995

Sequence-dependent antitumor activity of paclitaxel (taxol) and cisplatin in vivo.

The established antitumor efficacy of paclitaxel and cisplatin as single agents and their distinctly different mechanisms of action have prompted laboratory and clinical research into their use in combination. Our in vivo study was performed to investigate the importance of sequence of administration and inter-agent interval. C3Hf/Kam mice bearing OCa-I tumors received paclitaxel and cisplatin. The antitumor efficacy of the combination, measured as re-growth delay and expressed as the enhancement factor (EF), was determined for inter-agent intervals of 1, 9, 24, 48 and 72 hr. Morphometric analysis was used to determine the contribution of induced apoptosis. Our findings showed an additive effect when cisplatin preceded paclitaxel by 1 and 24 hr, producing EF of 1.1 and 1.0, respectively, and a greater than additive effect for 9 and 48 hr, producing EF of 1.3 and 1.8, respectively. This sequence, however, was associated with significant morbidity and mortality. When paclitaxel preceded cisplatin the effect was greater than additive with the EF for 1, 9 and 24 hr, being 1.2, 1.5 and 1.5, respectively, and increasing to a maximum of 1.9 at 48 hr. Thus, for this combination, the therapeutic ratio was improved when paclitaxel preceded cisplatin and was greatest when a 48 hr interval was allowed between drugs. We were unable to attribute the efficacy of the drug combination to increased induction of apoptosis and suggest other possible mechanisms.

Animals↗
PubMed1995

Role of reoxygenation in induction of enhancement of tumor radioresponse by paclitaxel.

We reported previously (L. Milas et al., Cancer Res., 54: 3506-3510, 1994) that paclitaxel greatly enhances the response of a murine mammary carcinoma to subsequent irradiation and hypothesized that the enhanced radioresponse was mediated by tumor cell reoxygenation caused by treatment with paclitaxel. Because paclitaxel induced massive tumor cell destruction by apoptosis, it was reasoned that as apoptotic cells were removed from the tumor more hypoxic cells would have access to oxygen, be reoxygenated, and, thus, become more sensitive to radiation. The present study tested this hypothesis by assessing the effect of 60 or 40 mg/kg paclitaxel on radioresponse of an 8-mm MCA-4 tumor irradiated under air-breathing or hypoxic conditions 9, 24, 48, or 72 h after paclitaxel administration. If the hypothesis was correct, paclitaxel would enhance tumor radioresponse more under air breathing than under hypoxic conditions, and the enhancement would increase as the time between paclitaxel administration and tumor irradiation increased within a few days after paclitaxel treatment but only when radiation was given under air-breathing conditions. The effect of the treatments was determined by tumor growth delay and the radiation dose required to control 50% of the tumors (TCD50). Paclitaxel greatly enhanced tumor radioresponse under air-breathing (and not hypoxic) conditions, increasing tumor growth delay, and reducing TCD50. These effects increased as the time interval between paclitaxel administration and tumor irradiation increased within the observation period of 72 h after paclitaxel treatment. The enhancement factors for tumor growth delay ranged from 1.19 at 9 h to 1.86 at 48 h and for TCD50, from 1.16 at 9 h to 1.47 at 72 h after paclitaxel. Direct measurements of tumor pO2 showed a median value in untreated tumors of 6.2 mmHg, which increased to 10.5 mmHg at 24 h and to 31.2 mmHg at 48 h after paclitaxel administration. Overall, these results show that paclitaxel is a potent enhancer of tumor radioresponse and that its effect is mediated by reoxygenation of hypoxic tumor cells.

Animals↗
PubMed1995

Effect of paclitaxel (taxol) alone and in combination with radiation on the gastrointestinal mucosa.

PURPOSE: Paclitaxel is a potentially useful drug for augmenting the cytotoxic action of radiotherapy because it has independent cytotoxic activity against certain cancers and blocks cells in the radiosensitive mitotic phase of the cell cycle. However, all rapidly proliferating tissues, both normal and neoplastic, may be affected by this therapeutic strategy. The aim of this study was to define the in vivo response of rapidly dividing cells of the small bowel mucosa to paclitaxel given alone and in combination with radiation. METHODS AND MATERIALS: Mice were given single IV doses of 10 or 40 mg/kg paclitaxel or four doses of 10 mg/kg paclitaxel at 6, 12, or 24 h intervals. The kinetics of mitotic arrest and apoptosis in jejunal crypts of mice at 1-24 h after treatment were defined histologically. An in vivo stem cell microcolony assay was used to assess the radiosensitizing potential of paclitaxel when radiation was delivered at the peak of mitosis and at 24 h after drug treatment. RESULTS: Paclitaxel blocked jejunal crypt cells in mitosis and induced apoptosis in a dose-dependent manner. Fractionating the paclitaxel dose over 1-4 days did not result in any greater accumulation of mitotically blocked cells than did a single dose. Mitosis peaked 2-4 h after paclitaxel and returned to near normal by 24 h. Apoptosis lagged several hours behind mitosis and peaked about 6 h later than mitosis. Despite these kinetic perturbations, there was little or no enhancement of radiation effect when single doses were delivered 2-4 h after paclitaxel administration. The maximum sensitizer enhancement ratio of 1.07 observed after a single paclitaxel dose of 40 mg/kg is consistent with independent crypt cell killing. Conversely, when radiation was given 24 h after paclitaxel, a significant protective effect of the drug (SER 0.89-0.92), most probably due to a regenerative overshoot induced by paclitaxel, was observed. CONCLUSION: Stem cells of the jejunal mucosa determining radiation response were not radiosensitized by paclitaxel with the drug concentrations and dose delivery schedules used, although additive cytotoxicity was observed with the highest drug dose. A radioprotective effect was observed when radiation was given 24 h after paclitaxel administration.

Animals↗
PubMed1995

ASTRO Research Fellowship: apoptosis as a predictor of tumor response to radiation in stage IB cervical carcinoma. American Society for Therapeutic Radiology and Oncology.

PURPOSE: Levels of apoptosis predict for tumor responsiveness to radiation in various animal systems. To investigate the potential role of apoptosis as a predictor of response in human tumors, a retrospective review was undertaken of patients with adenocarcinoma of the cervix whose primary lesion at presentation measured at least 4 cm and who underwent definitive radiation therapy. A previous report had indicated that roughly half this group of patients should have a long-term relapse free survival. METHODS AND MATERIALS: Pretreatment biopsy specimens of 44 patients with Stage IB adenocarcinoma of the cervix, whose primary lesion at presentation measured at least 4 cm in greatest dimension, were scored for apoptosis by two independent investigators without knowledge of the treatment outcome, and the results were averaged. Actuarial methods were used to assess overall survival, disease-free survival, determinate survival, and local control as a function of the baseline level of apoptosis. Patients ranged in age from 21 to 87 years and were treated with definitive radiotherapy between 1964 and 1989. Follow-up for the surviving patients ranged from 1 to 278 months, with a mean of 101 months. RESULTS: Patients whose tumors had a baseline level of apoptosis above the median value (2%) had a better overall survival than those with lower levels of apoptosis (p = 0.056). A similar trend for disease-free survival (p = 0.32) and determinate survival (p = 0.27) did not reach statistical significance, perhaps because of the small number of patients. Because only 6 of the 44 patients (13%) had a local tumor failure, it was not possible to establish a correlation between the pretreatment level of apoptosis and the local tumor control by radiation. CONCLUSION: The baseline level of apoptosis predicted for survival in patients with Stage IB cervical adenocarcinoma. Further investigation of the measurement of apoptosis as a potential predictive assay is warranted in other human tumor systems.

Adenocarcinoma↗
PubMed1995

Kinetics of cisplatin-induced apoptosis in murine mammary and ovarian adenocarcinomas.

There is mounting evidence to indicate that the mode of cell death known as apoptosis plays an important role in cancer therapy. Most supporting observations have come from experiments conducted in vitro, and it is important to extend such studies to in vivo systems. We have therefore evaluated the magnitude and kinetics of apoptosis induction in tumors from mice treated with cisplatin (CP). Two transplantable murine tumors were studied: a mammary adenocarcinoma, MCa-4, and an ovarian adenocarcinoma, OCa-1. Tumor-bearing mice were injected with various doses of CP, and specimens were obtained over several days. Apoptosis was scored by morphometric analysis of histological sections of the tumors using the features characteristic of cells undergoing this mode of cell death. The results showed a significant apoptotic response in both tumors within a few hours after injection of the drug. The kinetics were very broad, with apoptotic cells present over essentially the entire time course studied. Dose-response relationships for CP-induced apoptosis were compared to the tumor response measured in terms of tumor growth delay.

Adenocarcinoma↗
PubMed1995

Kinetics of mitotic arrest and apoptosis in murine mammary and ovarian tumors treated with taxol.

The kinetics of taxol-induced mitotic arrest and apoptosis in murine mammary carcinoma MCA-4 and ovarian carcinoma OCA-I tumors were determined to establish a possible causative relationship between mitotic arrest and apoptosis and to see whether these cellular effects of taxol would correlate with the extent of its antitumor efficacy. Mice bearing 8-mm tumors in a hind leg were given taxol i.v. at a dose of 10-80 mg/kg. Both tumors responded to taxol by significant growth delay or transient regression; in general, the response was greater as the dose of taxol was increased. For kinetics studies the mice were treated with 60 mg/kg taxol given once when tumors were 8 mm in size or twice, with the second dose being given 3 days after the first. At various times ranging from 1 to 96 h after treatment with taxol, tumors were histologically analyzed to quantify mitotic and apoptotic activity. After a single dose of taxol, mitotic arrest was visible at 1 h, and the mitotic index increased with time to reach peak values of 36% in MCA-4 tumors and 22% in OCA-I tumors at 9 h. The index then declined to a baseline of 1%-3% at 3 days for MCA-4 tumors and 1 day for OCA-I tumors. Apoptosis followed mitotic arrest, beginning at the time of peak mitotic arrest, increasing to the highest level of about 20% at 18-24 h after treatment and gradually declining to the normal level of 3%-6% after 3-4 days. Nuclear material progressively condensed in mitotically arrested cells, culminating in the frank appearance of multiple apoptotic bodies. The change in cell morphology plus the dynamics of apoptosis development imply that a large percentage of tumor cells arrested in mitosis by taxol die by apoptosis. Kinetic analysis undertaken after the second dose of taxol showed a considerably lower percentage of cells arrested in mitosis as compared with that seen after a single dose, and the induction of apoptosis by the second dose was minimal. However, the antitumor efficacy of the second dose of taxol was similar to or better than that of the first dose, implying that in addition to mitotic arrest and apoptosis, there exist other mechanisms by which taxol exerts its antitumor action.

Animals↗
PubMed1995

Apoptosis in murine tumors treated with chemotherapy agents.

There is increasing attention directed to the hypothesis that apoptosis plays a role in the response to cancer treatment including chemotherapy. However, the evidence to support this hypothesis has come almost entirely from experiments conducted in cultured cell systems. To extend this hypothesis to the therapeutic setting it is necessary to address this critical question in tumors treated in vivo. We have therefore evaluated the extent of apoptosis induced in murine tumors treated in vivo with cancer chemotherapy agents. Seven different murine tumors, comprising a mammary adenocarcinoma (MCa-4), an ovarian adenocarcinoma (OCa-1), a lymphoma (LY-TH), three sarcomas (FSA, NFSA and SA-NH) and a squamous cell carcinoma (SSC-7), were examined 8 and 24 h after treatment with cisplatin or cyclophosphamide (CY). Apoptosis was scored by morphometric analysis of histological sections of the tumors. The results showed that MCa-4, OCa-1 and LY-TH had a significant apoptotic response to both cisplatin and CY, and the other tumors had essentially no apoptotic response. In addition, two of these tumors, MCa-4 and OCa-1, underwent apoptosis in response to adriamycin, 5-fluorouracil, Ara-C, etoposide, camptothecin and fludarabine. These observations demonstrate that apoptosis may be a feature of tumor response to chemotherapy in vivo, and illustrate the heterogeneity of apoptotic response amongst different tumor types and to different cytotoxic agents.

Adenocarcinoma↗
PubMed1995

Tumor reoxygenation as a mechanism of taxol-induced enhancement of tumor radioresponse.

Paclitaxel is a novel chemotherapeutic agent that arrests cells in the radiosensitive G2 and M phases of the cell cycle and as such may act as a specific cell cycle radiosensitizer. We recently reported that paclitexel induces mitotic arrest in the MCA-4 murine mammary carcinoma and enhances radio-response of this tumor. However, the greatest enhancement was observed not when radiation was given at the time of peak mitotic arrest, which was 9 h after paclitaxel administration, but when it was given 24 h after paclitaxel. This implied the involvement of other mechanisms in radiosensitization; we hypothesized that tumor reoxygenation was a likely mechanism based on the observed massive loss of mitotically arrested cells at 24 h. The present study shows that paclitaxel greatly enhanced MCA-4 tumor radioresponse when radiation was given under air-breathing conditions (DMF = 1.74), but not when it was performed under hypoxic conditions. This observation supports the hypothesis of tumor reoxygenation as a mechanism of enhancement of tumor radioresponse. That reoxygenation occurred in tumors treated with paclitaxel 24 h earlier was confirmed by direct measurements of pO2 values, using the Eppendorf pO2 histograph. Median pO2 values increased from 6.2 mmHg in untreated tumors to 10.0 mmHg in tumors treated with paclitaxel. These observations emphasize the importance of timing of paclitaxel administration in relation to radiation treatment.

Animals↗
PubMed1995

The prostaglandin E1 analog, misoprostol, a normal tissue protector, does not protect four murine tumors in vivo from radiation injury.

The clinical development of radioprotectors, such as misoprostol, to protect normal tissue during cancer treatment must proceed with the assurance that tumors are not protected similarly or significantly. To provide data on this critical question, radiation-induced growth delay with or without the presence of misoprostol was measured in four murine tumors grown in the flanks of mice: the Lewis lung carcinoma, M-5076 ovarian sarcoma, FSA and NFSA. The effect of misoprostol on the tumor control dose (TCD50) of radiation was measured in FSA-bearing mice with or without prior treatment with the nonsteroidal anti-inflammatory agent, indomethacin. Misoprostol did not influence the in vivo growth of any of the four tumors, nor did it protect any of the tumors from radiation-induced growth delay. Likewise, there was no increase in the radiation TCD50 to treat the FSA in vivo in control or indomethacin-treated tumor-bearing mice. To measure any possible influence of tumor burden on the protective effect of misoprostol on normal tissue in mice, the protective effect of misoprostol on the survival of intestinal clonogenic cells was measured in M-5076-bearing mice and found to be the same as in non-tumor-bearing mice. These data suggest that misoprostol protects normal tissue in mice without protecting at least four experimental murine tumors. The data support the contention that misoprostol can achieve therapeutic gain by protecting normal tissues without protecting tumors.

Animals↗
PubMed1994

The role of fludarabine-induced apoptosis and cell cycle synchronization in enhanced murine tumor radiation response in vivo.

We have previously reported that fludarabine, an adenine nucleoside analogue, significantly enhances radiation-induced tumor regrowth delay and local cure in several mouse tumors. Although fludarabine potentiated tumor regrowth delay at various times from -36 h to +6 h in a SA-NH mouse sarcoma model, the greatest enhancement was observed when fludarabine was administered 24 h before irradiation. The purpose of this study was to understand the basis for in vivo enhancement of radiation efficacy by fludarabine. To examine the effect of fludarabine on DNA synthesis and cell cycle progression, tumor-bearing mice were given fludarabine by an i.p. route and then bromodeoxyuridine at various times up to 36 h, followed 0.5 h later by tumor harvest. Two-parameter flow cytometry analysis of the tumor cells using an anti-bromodeoxyuridine antibody demonstrated that an 800-mg/kg fludarabine dose stops DNA synthesis within 3 h with recovery starting at 12 h. By 24 h after fludarabine treatment, a synchronized wave of cycling tumor cells appeared in G2-M phase. The degree of DNA synthesis shutdown and the timing of the reinitiation of DNA synthesis and cell cycle progression were all fludarabine dose dependent. Interestingly, DNA synthesis reinitiated only at the G1-S boundary; cells in the S phase at the time of fludarabine administration appeared to disappear from the tumor population. To confirm these observations more directly, we pretreated tumor-bearing mice i.p. with chlorodeoxyuridine to mark the cells in the S phase, gave them fludarabine 0.5 h later, and then gave them iododeoxyuridine 0.5 h before tumor harvest. Flow cytometry analysis using antibodies specific for chlorodeoxyuridine- and iododeoxyuridined-labeled cells confirmed that cells in the S phase at the time of fludarabine administration never reinitiated DNA synthesis and disappeared from the tumor population. Immunohistological analysis of tumor sections obtained after fludarabine administration demonstrated that prelabeled S-phase cells took on an apoptotic appearance and gradually disappeared from the tumors. An in situ DNA end labeling assay demonstrated DNA fragmentation in these morphologically apoptotic cells. These results suggest that the mechanism of fludarabine enhancement of radiation response involves induced S-phase cell loss through an apoptotic pathway and subsequent synchronization of the remaining cells to a more radiosensitive cell cycle phase at the time of irradiation.

Animals↗
PubMed1994

Reemergence of apoptotic cells between fractionated doses in irradiated murine tumors.

PURPOSE: The purpose of this investigation was to follow up our previous studies on the development of apoptosis in irradiated murine tumors by testing whether an apoptotic subpopulation of cells reemerges between fractionated exposures. METHODS AND MATERIALS: Mice bearing a murine ovarian carcinoma, OCa-I, were treated in vivo with two fractionation protocols: two doses of 12.5 Gy separated by various times out to 5 days and multiple daily fractions of 2.5 Gy. Animals were killed 4 h after the last dose in each protocol, and the percent apoptosis was scored from stained histological sections made from the irradiated tumors according to the specific features characteristic of this mode of cell death. RESULTS: The 12.5 + 12.5 Gy protocol yielded a net total percent apoptosis of about 45% when the two doses were separated by 5 days (total dose = 25 Gy), whereas the 2.5 Gy per day protocol yielded about 50% net apoptotic cells when given for 5 days (total dose = 12.5 Gy). These values are to be compared to the value of 36% apoptotic cells that is yielded by large single doses (> 25 Gy). Thus, these results indicate that an apoptotic subpopulation of cells reemerged between the fractions in both protocols, but the kinetics appeared to be delayed in the 12.5 + 12.5 Gy vs. the multiple 2.5 Gy protocol. CONCLUSION: This reemergence of cells with the propensity for radiation-induced apoptosis between fractionated exposures is consistent with a role for this mode of cell death in the response of tumors to radiotherapy and may represent the priming of a new subpopulation of tumor cells for apoptosis as part of normal tumor homeostasis to counterbalance cell division.

Animals↗
PubMed1994

Fludarabine improves the therapeutic ratio of radiotherapy in mouse tumors after single-dose irradiation.

PURPOSE: Fludarabine, an adenine nucleoside analogue, and an effective inhibitor of chromosome repair, was previously shown to synergistically enhance radiation-induced regrowth delay in three murine tumors. The purpose of this study was to assess whether fludarabine can increase the therapeutic ratio of radiotherapy in murine tumors, that is, to increase local tumor control without significantly modifying the radiation-induced normal tissue response. METHODS AND MATERIALS: Mice bearing 8-mm tumors in the right thigh (SA-NH sarcoma and MCA-K mammary carcinoma) were given 800 mg/kg fludarabine IP 3 h or 24 h before single doses of photon irradiation. Local tumor control was assessed by the TCD50 assay 100 days after treatment. Acute normal tissue toxicity was assessed in the skin (degree of epilation 30 days after irradiation) and in the jejunum (crypt regeneration assay), and late normal tissue toxicity was assessed by a leg contracture assay 120 days after treatment. RESULTS: In both tumors and with both drug schedules, fludarabine enhanced radiation-induced local tumor control (dose modification factors (DMF) of 1.24 (95% confidence limits 1.19-1.31) and 1.26 (95% confidence limits 1.20-1.32) for SA-NH, and 1.38 (95% confidence limits 1.25-1.50) and 1.35 (95% confidence limits 1.22-1.16) for MCA-K tumors). When given 3 h before radiation, fludarabine offered a slight protection from skin toxicity (DMF = 0.83, 95% confidence limits 0.77-0.86) but enhanced jejunum toxicity (DMF = 1.53). When fludarabine was given 24 h before irradiation, the reverse trend was observed (DMF = 1.11 (95% confidence limits 1.07-1.16) and 0.89, respectively). No enhancement of leg contracture was observed for either fludarabine schedule. CONCLUSION: The data presented here demonstrate that fludarabine can potentiate local tumor control induced by single-dose irradiation. While jejunum sensitization limited the relative effectiveness when fludarabine was administered 3 h before irradiation, a therapeutic ratio greater than one was always achieved when fludarabine was given 24 h before irradiation.

Animals↗