Biomedical subjects

L Milas

Publications and source records attributed to L Milas.

At least 109 records · Page 6Linked to original sources

PubMed1991

Changes in TCD50 as a measure of clonogen doubling time in irradiated and unirradiated tumors.

Dose-cure experiments have been carried out on a moderately well differentiated murine mammary carcinoma, designated MCA-4, at different stages of growth after tumor-cell inoculation or after 8 mm established tumors had been exposed to 60 Gy. TCD50 assays were performed at 1, 3, 7, 14, or 21 days after tumor cell inoculation, or when tumors reached a size of 6 or 8 mm. Likewise, TCD50 assays were performed at 0.25, 1, 3, 5, 8, 12, 16, or 21 days after 8 mm tumors had been exposed to a 60 Gy priming dose, or when the recurrent tumors reached 6 or 8 mm. All irradiations were performed under hypoxic conditions. The TCD50 (95% confidence limits) was 64.0 (61.7-68.3) Gy for the 6-mm and 71.9 (70.1-73.9) Gy for the 8 mm tumors, and these values were unaffected by preirradiation. Direct analysis was used for the simultaneous estimation of D0, clonogen number, and clonogen doubling time from the pooled data. There was no significant difference between D0 estimates for the preirradiated and control tumors, and the pooled estimate was 10.6 (9.6-11.8) Gy for tumors assayed at specified time points where the size was unknown. This is clearly higher than in tumors of known size [estimate for 6- and 8-mm tumors: D0 = 5.4 (4.5-6.6) Gy] owing to size and other heterogeneity. The clonogen doubling times (Tclon) were 3.4 (3.0-4.0) days in the preirradiated tumors and 5.8 (4.9-7.1) days in the unirradiated tumors. It is not unreasonable to assume that the systematic error due to heterogeneity was approximately the same for D0 and Tclon (since variable clonogen number is likely the predominant source of heterogeneity), and thus the ratio of D0 for tumors of unknown sizes (10.6 Gy) and D0 for tumors of known sizes (5.4 Gy) can be used to "correct" the Tclon estimates, with the result that Tclon (preirradiated) = 1.7 days and Tclon (unirradiated) = 3.0 days. We conclude that the clonogen doubling time was shorter in tumors exposed to a single high-dose irradiation than in unirradiated controls, which implies the existence of faster cell repopulation in irradiated tumors.

Animals↗

PubMed1991

An intradermal assay for quantification and kinetics studies of tumor angiogenesis in mice.

A method is reported for the study of early phases of neovascularization in syngeneic murine tumors and human tumor xenografts in nude mice. Using this method, the effect of irradiation of tumor cells or tumor bed on tumor angiogenesis was studied. Tumor cells were injected intradermally in the abdominal skin flap, which was reopened at 2-day intervals to quantify newly formed blood vessels at the site of tumor cell injection. Both tumor cell injection and blood vessel counting were performed under a dissecting microscope. Using three syngeneic murine tumors and two clones of a human colonic adenocarcinoma, it was observed that new blood vessels started appearing within a few days after tumor cell injection and that this event preceded measurable tumor growth. The number of blood vessels increased exponentially for several days but then their further growth slowed. The extent of angiogenesis depended on the tumor type and the number of tumor cells injected. The exposure of the skin flap to ionizing radiation prior to tumor cell injection reduced neovascularization. We further observed that heavily irradiated tumor cells retained their ability to induce angiogenic response and that lymphoid cells (peritoneal exudate and spleen cells) could also elicit an angiogenic response, although it is weaker than the response elicited by tumor cells. Thus this method is suitable for quantification and kinetics of early phases of tumor angiogenesis in individual mice bearing transplants of syngeneic tumors or human tumor xenografts, and it can be useful for investigating various regulators of tumor angiogenesis.

Animals↗

PubMed1991

Apoptosis in irradiated murine tumors.

Early radiation responses of transplantable murine ovarian (OCaI) and hepatocellular (HCaI) carcinomas were examined at 6, 24, 48, 96, and 144 h after single photon doses of 25, 35, or 45 Gy. Previous studies using tumor growth delay and tumor radiocurability assays had shown OCaI tumors to be relatively radiosensitive and HCaI tumors to be radioresistant. At 6 h, approximately 20% of nuclei in OCaI tumors showed aberrations characteristic of cell death by apoptosis. This contrasted to an incidence of 3% in HCaI tumors. Mitotic activity was eliminated in OCaI tumors but was only transiently suppressed in HCaI tumors. At 24-96 h, OCaI tumors continued to display apoptosis and progressive necrosis, whereas HCaI tumors responded by exhibiting marked pleomorphism. Factors other than mitotic activity may influence tumor radiosensitivity, and one of these may be susceptibility to induction of apoptosis (programmed cell death), because this was a prominent early radiation response by the radiosensitive OCaI tumors.

Animals↗

PubMed1990

Dependence of indomethacin-induced potentiation of murine tumor radioresponse on tumor host immunocompetence.

In a previous study (Furuta, Y., Hunter, N., Barkley, H. T., Jr., Hall, E., and Milas, L., Cancer Res., 48:3008-3013, 1988), we demonstrated that inhibition of prostaglandins in murine tumors by indomethacin results in the augmentation of tumor response to single doses of ionizing radiation. The results of the present study show that indomethacin augmented tumor response to fractionated irradiation as well, the enhancement factor being more than 2. The effect of indomethacin on tumor growth and on tumor radioresponse was assayed in normal mice, mice deficient in T-cells (nude mice), and mice whose general immunocompetence was suppressed by whole-body irradiation. The antitumor activity of indomethacin was not significantly influenced by the immunocompetence of the tumor host. Since indomethacin inhibited tumor neoangiogenesis, we postulated that this inhibition is a major mechanism responsible for the antitumor activity of indomethacin. In contrast, potentiation of tumor radioresponse by indomethacin was greatly dependent on immunocompetence of tumor host: it was significantly reduced, or even abolished, when tumor grew in nude and whole-body irradiation mice. Thus, while immunocompetence of the tumor host has no significant effect on antitumor action by indomethacin, it plays a decisive role in the potentiation of tumor radioresponse by indomethacin.

Animals↗

PubMed1990

Tumor necrosis factor as an adjunct to fractionated radiotherapy in the treatment of murine tumors.

Recombinant murine tumor necrosis factor (TNF) was investigated for its ability to increase the response of a murine mammary carcinoma to fractionated local tumor irradiation. When tumors in the leg of syngeneic mice grew to 8 mm in diameter (268 mm3), they were exposed to 3, 4 or 5 Gy gamma-rays daily for 10 days. Tumor necrosis factor was given 3 hr after each irradiation at a dose of 2 micrograms per mouse. Tumor growth delay was used as the endpoint. The effect of treatment with both agents combined was greater than the additive effect of the individual treatments. Tumor necrosis factor increased local tumor radiotherapy response by a factor of about 1.2, and by itself was effective in retarding the growth of both immunogenic and nonimmunogenic tumors. These experiments suggest that tumor necrosis factor in combination with radiotherapy may be beneficial for the treatment of cancer patients.

Animals↗

PubMed1990

Comparative effect of the thiols dithiothreitol, cysteamine and WR-151326 on survival and on the induction of DNA damage in cultured Chinese hamster ovary cells exposed to gamma-radiation.

We compared the ability of three thiols--dithiothreitol (DTT), cysteamine and WR-151326--to protect aerated Chinese hamster ovary cells from the lethal and DNA-damaging effects of gamma-radiation. These results were compared with earlier measurements for WR-1065 and WR-255591. The time-course and the concentration dependence of protection against cell killing was determined after 10 Gy of gamma-rays. The aminothiols cysteamine and WR-151326 protected at much lower extracellular concentrations than the simple thiol DTT; however, there was no clear difference between the behaviour of cysteamine, WR-151326, WR-1065 and WR-255591 in this respect. Protection by DTT and cysteamine was complete within 1 min, whereas for WR-151326, WR-1065 and WR-255591 about 30 min was required before protection began to reach a plateau. Based on these data, complete radiation survival curves were generated for each thiol and protection factors calculated. Effects on the induction of DNA single-strand breaks (ssb) and double-strand breaks (dsb) by gamma-rays were measured using alkaline (pH 12.1) and neutral (pH 7.0 and 9.6) elution, respectively. All three thiols protected against ssb induction, although to a significantly lower extent than against cell killing measured under identical conditions. Each thiol also protected against dsb induction. After high radiation doses the protection factors for dsb induction were also less than the protection factors for cell survival; however, when dsb were assayed using the low-dose replicate plating neutral elution method, the relative effect of each thiol on cell survival and on dsb induction appeared to be equivalent. The hierarchy of protection against both ssb and dsb induction (based on the extracellular thiol concentration required to produce a given degree of protection) was similar to that for cell survival, i.e., WR-151326 congruent to cysteamine less than DTT.

Animals↗

PubMed1990

Radioprotection of hematopoietic tissues in mice by indomethacin.

We recently reported that indomethacin, an inhibitor of prostaglandin (PG) synthesis, increased the radioresponse of PG-producing murine tumors, but it protected the hematopoietic system from radiation damage [Furuta et al., Cancer Res. 48, 3008-3013 (1988)]. Here we have investigated possible mechanisms responsible for the radioprotective effect of indomethacin. In the exogenous spleen colony assay, bone marrow cells from indomethacin-treated mice showed a similar radioresponse to those from mice not treated with indomethacin, thus excluding true radioprotection as a mechanism. Also, neither the total number of bone marrow cells nor the number of stem cells in bone marrow were affected by the treatment with indomethacin. However, indomethacin induced significant splenomegaly, which was associated with an increased number of both nucleated cells and hematopoietic stem cells in the spleen. The latter was determined by the exogenous spleen colony assay. Thus indomethacin protected hematopoietic tissue indirectly through stimulation of hematopoietic cells in the spleen. When indomethacin was combined with WR-2721, which is a true radioprotector, we obtained a greater radioprotective effect than with either used alone according to the endogenous spleen colony assay.

Amifostine↗

PubMed1990

Tumor bed effect in murine tumors: relationship to tumor take and tumor macrophage content.

This study investigated whether the clonogenic ability of tumor cells to establish subcutaneous tumors and the tumor-associated macrophage (TAM) content correlate with the development and extent of the tumor bed effect (TBE). Ten tumors, five sarcomas and five carcinomas, syngeneic to C3Hf/Kam mice were used. Tumors were grown subcutaneously in the right thighs of mice that had or had not been irradiated with 20 Gy of gamma rays 1 day before tumor cell transplantation. Of the 10 tumors, 7 exhibited a significant TBE. The severity of the TBE, which varied greatly among these tumors, was significantly positively correlated (correlation coefficient = 0.81) with TD50 values (i.e., the number of tumor cells needed to produce tumors in 50% of injected sites). In addition, a trend toward a negative correlation between degree of TBE and TAM content was apparent. The implication of these results is that tumors with high clonogenic ability (low TD50 values) and high macrophage content are less likely to demonstrate the TBE. The data suggest that tumor angiogenic potential, provided by both tumor cells and TAM, is an important parameter in the development of the TBE.

Animals↗

PubMed1989

Adoptive immunotherapy as an adjunctive treatment to thoracic irradiation for pulmonary tumor deposits in mice.

The study was performed to determine whether local thoracic irradiation (LTI) causes accumulation of adoptively transferred peritoneal exudate (PE) cells in the lung and whether such treatment improves the response of tumor deposits in the lung to LTI. Tumors in the lung were generated by sarcoma SA-NH cells injected i.v. into syngeneic (C3Hf/Kam mice. Exposure of mice to a single dose of gamma-rays ranging from 2 to 10 Gy caused a dose-dependent decrease in the number of alveolar exudate cells. Also, LTI caused a dose-dependent reduction in the number of lung tumor nodules in mice that were treated with tumor cells 4 days before irradiation. Adoptive i.v. transfer of syngeneic PE cells several hours or 2 days after LTI not only restored the radiation-depleted alveolar exudate cells to their normal levels but also led to an accumulation of transferred cells in the irradiated lung to a several-fold excess of the normal value. Maleic anhydride-divinyl ether-2-activated PE cells accumulated in the irradiated lung much more than normal PE cells and exerted antitumor activity in normal mice and in mice exposed to LTI. Their antitumor action, however, was much more pronounced in the latter, resulting in the augmentation of radioresponse of tumor nodules by a factor of 1.23. The better antitumor action of activated PE cells in mice given LTI can be ascribed to accumulation of these cells in the irradiated lung. Thus, these results show that the irradiation of the lung predisposes this tissue to accumulation of lymphoid cells, which can be beneficial in the therapy of malignant tumors by combinations of radiotherapy and adoptive immunotherapy.

Animals↗

PubMed1989

Combination of N-methylformamide with cis-diamminedichloroplatinum (II) in murine mammary carcinoma: importance of timing.

The maturational agent N-methylformamide (NMF) is an antitumor agent that also enhances the response of tumor cells in vitro to chemotherapeutic agents. Here, we tested whether NMF can improve therapy of the murine MCA-K mammary carcinoma with cis-diamminedichloroplatinum(II) (cis-DDP). Although the in vitro cell cultures of MCA-K tumor cells exhibited increased sensitivity to cis-DDP cytotoxicity when they were first treated with NMF, administration of NMF to mice bearing MCA-K tumors did not enhance cis-DDP-induced tumor growth delay. However, when NMF treatment was begun after cis-DDP administration, the growth delays were significantly greater than those induced by the individual treatment, with an increase in temporary tumor regression and a small proportion of cures. These results indicate that therapeutic benefit can be achieved in this experimental tumor system when NMF is administered after cis-DDP. In addition, they demonstrate the significance of the timing of administration in combined protocols involving NMF.

Animals↗

PubMed1989

Tumor bed effect-induced reduction of tumor radiocurability through the increase in hypoxic cell fraction.

Two murine tumors, designated FSA and SA-NH, that exhibit strong tumor bed effect (TBE), were found to be less radiocurable if they grew in the preirradiated s.c. tissue. Tumors were transplanted into the right thighs irradiated with 30 Gy one day earlier, and were irradiated when they grew to 6 mm. The TBE-caused reduction in tumor radiocurability was manifested by the increase in TCD50 values. Tumor irradiation under hypoxic conditions increased TCD50 values less, and the hypoxic cell radiosensitizer misonidazole reduced TCD50 values more, when tumors grew in preirradiated than when they grew in unirradiated legs. This implies that TBE-induced increase in TCD50 was due to increase in hypoxic fraction of tumor cells. For 6 mm SA-NH tumor the estimated increase in hypoxic cell fraction was from the control value of 3% to 12%. Thus, TBE causes the reduction in tumor radiocurability through the increase in hypoxic fraction of tumor cells.

Aerobiosis↗

PubMed1989

Protection of cultured Chinese hamster ovary cells by the aminothiol WR-255591 from the lethal and DNA-damaging effects of fast neutrons.

We examined the radioprotective effect of the aminothiol WR-255591 on cultured aerated Chinese hamster ovary cells irradiated with cyclotron-generated fast neutrons. The effects of a 30 min pretreatment with 6 mM WR-255591 on the induction of DNA single-strand breaks (SSBs) and double-strand breaks (DSBs) were measured using alkaline (pH 12.1) and neutral (pH 7.0) filter elution, respectively. Molecular protection factors (PFs) calculated from these data were compared with the PF measured using the biological endpoint of cell survival. WR-255591 afforded significant protection against cell killing by neutrons (PF = 1.36) although protection was less efficient than against cell killing by gamma-rays (PF = 2.30). Whereas for gamma-rays, the PFs were in the order survival greater than or equal to DSB induction much greater than SSB induction, the magnitude of the modification of the induction of both SSBs (PF = 1.38) and DSBs (PF = 1.38) after neutron irradiation was the same as that of cell killing.

Animals↗

PubMed1989

The proportion of stem cells in murine tumors.

Considerable evidence suggests that tumors contain only a minority of cells which are capable of regrowing the tumor (ie. tumor stem cells). Since all tumor stem cells must be killed if treatment is to be successful, the number of stem cells in a tumor can be expected to be an important determinant of curability. We have attempted to examine the proportion of stem cells in a variety of murine tumors by making measurements of three different parameters which might be expected to be related to stem cell content: (a) the radiation dose required to control the tumor (TCD50); (b) the number of cells required to transplant the tumor (TD50) and (c) the in vitro plating efficiency. An inverse correlation has been demonstrated between measured TCD50 and TD50 values for two independent groups of murine tumors of varying histopathological type. An inverse correlation was also obtained between the TD50 value and in vitro plating efficiency for a group of spontaneous murine mammary tumors. These correlations most likely reflect underlying differences in the stem cell content of the tumors, and indicate that there is a wide range (2-3 orders of magnitude) of stem cell proportions in different murine tumors, even those which have been transplanted a number of times.

Animals↗

PubMed1989

Protection by WR-3689 against gamma-ray-induced intestinal damage: comparative effect on clonogenic cell survival, mouse survival, and DNA damage.

The aminophosphorothioate WR-3689 was characterized for its ability to protect mouse jejunal cells in vivo from single doses of X or gamma radiation. First, the effect of the drug on the survival of jejunal stem cells was examined using a clonogenic end point, the crypt microcolony assay. When WR-3689 was administered 30 min prior to whole-body irradiation, the number of surviving crypt cells was markedly increased at all doses of the drug, although protection began to level out at doses larger than 600 mg/kg. Protection was maximal when the drug was given 30 min before whole-body irradiation and declined rapidly with both shorter and longer intervals. Protection factors (PFs) were obtained by measuring survival curves for clonogenic crypt cells as a function of radiation dose; WR-3689 given 30 min before whole-body irradiation protected jejunum in the microcolony assay with a PF of 1.26 +/- 0.02, 1.50 +/- 0.10, and 1.65 +/- 0.10 at doses of 200, 400, and 800 mg/kg, respectively. Next, the effect of WR-3689 on the survival of jejunal stem cells was determined by assaying the survival of mice given X-ray doses to the whole abdomen in the range leading to death from the gastrointestinal syndrome. The PFs based on the LD50 values for 11-day survival were 1.31 +/- 0.05 (200 mg/kg) and 1.48 +/- 0.05 (400 mg/kg). Crypt-cell survival and animal survival were thus modified to a similar extent by this agent. Finally, the effect of WR-3689 on the induction of DNA single-strand breaks (SSBs) in jejunal cells was measured using an adaptation of the alkaline elution methodology. In mice treated with WR-3689 (400 or 800 mg/kg) 30 min prior to whole-body irradiation with 10 Gy there was no significant reduction in the number of DNA SSBs induced either in samples of the jejunum or in the cycling crypt cells, providing further evidence that there is no simple relationship between the modification of DNA SSBs and the survival of jejunal stem cells.

Amifostine↗

PubMed1989

Radioprotection of cultured mammalian cells by the aminothiols WR-1065 and WR-255591: correlation between protection against DNA double-strand breaks and cell killing after gamma radiation.

We compared the effects of the radioprotective aminothiols WR-1065 and WR-255591 on the induction of DNA double-strand breaks (DSBs) and on the survival of aerated Chinese hamster ovary cells exposed to 60Co gamma radiation. DSBs were measured using the pH 9.6 neutral elution method. In agreement with earlier studies, protection factors for both drugs measured using the end point of clonogenic cell survival were significantly greater than the protection factors for DSB induction when DSBs were measured after gamma-ray doses ranging from 20 to 90 Gy. However, when DSBs and cell survival measurements were made on the same cell populations after low radiation doses (between 3 and 30 Gy) using the replicate plating method, there appeared to be a close correlation between the modification of DSB induction and the modification of cell survival produced by both drugs. The major influence accounting for the differences between these and previously obtained results appears to be the range of radiation doses used, suggesting that protection against DSB induction is radiation-dose dependent.

Animals↗

PubMed1988

Anti-tumor effects of tumor necrosis factor alone or combined with radiotherapy.

Recombinant human tumor necrosis factor (rHuTNF) was investigated for its ability to increase the response of murine tumors to ionizing radiation. Both multiple i.v. administrations of rHuTNF and local tumor irradiation caused a significant delay in tumor growth. The effect of treatment with both agents combined was greater than the additive effect of the individual treatments. Furthermore, rHuTNF significantly increased tumor radiocurability, as assessed by the TCD50 assay. rHuTNF was not cytotoxic to tumor cells, nor did it affect their radiosensitivity. The in vivo anti-tumor effect of rHuTNF and its augmentation of tumor radioresponse were mediated through indirect mechanisms, either immunological or non-immunological. rHuTNF was also effective in reducing the damaging effect of ionizing radiation on bone-marrow progenitor cells, which could increase the therapeutic advantage of the rHuTNF-radiotherapy combination. These experiments suggest that rHuTNF is potentially beneficial in combination with radiotherapy.

Animals↗

PubMed1988

Prostaglandin production by murine tumors as a predictor for therapeutic response to indomethacin.

We investigated whether there is a relationship between the production of eicosanoids by murine solid tumors and their response to the prostaglandin H (PGH) synthase inhibitor indomethacin. Three sarcomas, designated FSA, NFSA, and SA-NH, and two carcinomas, designated MCA-K and HCA-I, syngeneic to C3Hf/Kam mice were used. In general, FSA and NFSA produced more PGH synthase products than lipoxygenase products, whereas HCA-I produced both types of metabolites in large quantities. All three tumors responded well to indomethacin treatment by slowing their growth. In contrast, MCA-K and SA-NH tumors produced insignificant quantities of PGH synthase products, but substantial amounts of lipoxygenase products. Their growth was not affected by treatment with indomethacin. Indomethacin did not influence tumor cell survival either in vitro or in vivo, but it reduced the proportion of S-phase cells in the tumors. The antitumor effect of indomethacin was not reduced by immunosuppression of the tumor host and was independent of tumor immunogenicity, implying that indomethacin acted through nonimmunological mechanisms. Thus, the effectiveness of indomethacin was directly related to the ability of tumors to produce PGs. Consequently, the eicosanoid profile of tumors could serve as a valuable way to select patients likely to respond to indomethacin and other PGH synthase inhibiting agents.

6-Ketoprostaglandin F1 alpha↗

PubMed1988

Increase in radioresponse of murine tumors by treatment with indomethacin.

Indomethacin, an inhibitor of prostaglandin (PG) synthesis, was investigated for its ability to increase radioresponse of two fibrosarcomas, FSA and NFSA, in C3Hf/Kam mice. In addition, the effect of indomethacin on radioresponse of hematopoietic tissue, jejunum, hair follicles, and tissues involved in the development of radiation-induced leg contractures was determined. Indomethacin greatly increased radioresponse of 8-mm tumors, as assessed by both tumor growth delay and TCD50 assays. Enhancement factors for tumor growth delay and tumor radiocurability (TCD50) were 1.55 and 1.39, respectively, for FSA, and 1.4 and 1.26, respectively, for NFSA tumors. Of four normal tissues assessed, two (hair follicles and tissues responsible for development of leg contractures) showed no change in radioresponse after treatment with indomethacin, one (hematopoietic tissue) exhibited radioprotection, and one (jejunum) exhibited slight radiosensitization (enhancement factor, 1.12). Therefore, indomethacin significantly augmented tumor radiocurability but had minimal effect on radioresponse of some normal tissues.

Animals↗