Dose dependent inhibition of B-16 melanoma growth in vivo by a synthetic analogue of PGE2

Daily intratumor administration of 16, 16-dimethyl-PGE₂-methyl ester in two different dosages inhibited tumor growth in C57B1/6J mice bearing subcutaneous B-16 melanomas. The larger dose (20γg/day/mouse) produced a 68% decrease in tumor volume, a 69% decrease in tumor weight and a 60% decrease in the number of cells in mitotic phase. The smaller dose (10μg/day/mouse) was one fifth less effective than the 20μg dose but produced similar changes. Histological examination of tumors revealed no significant differences either in the inflammatory cell population or the amount of necrosis in the control and di-M-PGE₂-treated tumors.     

The change in hypoxic and chronically hypoxic cell fraction in murine tumors treated with hyperthermia

The effect of hyperthermia on the size of hypoxic and chronically hypoxic cell fractions in murine tumors was studied. The chronically hypoxic cell fraction was defined as a fraction of tumor cells which were not oxygenated under hyperbaric oxygen. Animals were C3Hf/Sed mice derived from our defined flora mouse colony. Tumors were FSa-II and MCa which were early generation isotransplants of a spontaneous fibrosarcoma and a mammary carcinoma, respectively. TCD50 (50% tumor control dose) or the radiation dose which yields a local tumor control in half the treated animals and TG (tumor growth) time or the time required for half the treated tumors to reach 1000 mm3 from the first treatment day were experimental end points. Hyperthermia was given by immersing animal feet into a water bath maintained at 43.5 +/- 0.1 degrees C. Animal tumors were irradiated with a 137Cs unit under hypoxic conditions, in air or under O2 30 psi. The hypoxic cell fraction increased immediately after hyperthermia in both MCa and FSa-II tumors. The chronically hypoxic cell fraction was, on the other hand, decreased following hyperthermia. The decrease was more substantial in the MCa than in FSa-II.     

The interactions between indomethacin and cytotoxic drugs in mice bearing B-16 melanomas

We have compared the effects of indomethacin alone (100 microgram/mouse/day) with those of indomethacin plus adriamycin, 5-FU, nitrogen mustard, thioTEPA, and vincristine on B-16 tumor cell proliferation in vivo. As we have previously described, after four days of treatment with indomethacin, subcutaneous tumors were slightly smaller and lighter in weight, but contained more melanoma cells. Addition of indomethacin to cytotoxic regimens resulted in either no change or a decrease in the effectiveness of the chemotherapy. In previous studies we demonstrated that treatment of tumor-bearing mice with a long-acting synthetic analogue of PGE2 (di-M-PGE2) stimulated the synthesis of endogenous prostaglandins. In order to evaluate if these endogenously synthesized prostaglandins were responsible for the inhibition of B-16 growth in vivo, mice were treated with di-M-PGE2 or di-M-PGE2 plus indomethacin. Addition of indomethacin did not alter the tumor inhibitory effects of di-M-PGE2.     

Treatment and survival study in the C57BL/6J-APC(Min)/+(Min) mouse with R-flurbiprofen

Our previous studies with the mouse model of familial adenomatous polyposis (FAP), C57BL/6J-APC(Min)/+ or Min mouse, demonstrated the optimal dose for adenoma reduction with R-flurbiprofen was 10 mg/kg/day as an undivided dose. Divided doses exhibited no increased efficaciousness. This study examines 10 mg/kg R-flurbiprofen daily (qd) on survival as well as a second daily (q.o.d.) schedule and compares it with sulindac sulfone. The q.o.d. schedule at 10 mg/kg was equally efficacious as qd treatment at the same dose. For the q.o.d. group, tumor number decreased similarly (p<0.01); while body weight gain (p<0.01), hematocrit and average tumor area (both, p<0.05) were improved compared with qd treatment. Treatment with R-flurbiprofen (10 mg/kg/day) increased survival significantly (p=0.0004, log-rank) compared to vehicle treated animals. Major biological endpoints (hematocrit, weight gain, tumor number, average and total area [99% reduction]) were significantly improved in treated animals (p<0.01). Sulindac sulfone treatment (50 mg/kg/day) of the Min mouse produced no significant biological benefit. The dose schedule study suggests that for tumor reduction it is necessary to attain a threshold drug-level but not necessarily sustain it over 24 hrs (pharmacodynamic t1/2 > pharmacokinetic t1/2). During the period of administration R-flurbiprofen dramatically prolongs survival for the mouse model of the human disease, FAP.     

The influence of radiation dose on the magnitude and kinetics of reoxygenation in a C3H mammary carcinoma

The variation in hypoxic fraction as a function of time after various priming doses of radiation has been investigated in a C3H mouse mammary carcinoma in situ. The hypoxic fraction was calculated from data for local tumor control. Untreated tumors were found to contain 4.8% radiobiologically hypoxic cells. Within minutes after a priming dose of 20 Gy given in air, the hypoxic fraction increased to a value not significantly different from 100%. After 4 h, reoxygenation was complete (hypoxic fraction 1.3%), and the hypoxic fraction stabilized at a level significantly below the untreated value. Following a priming dose of 40 Gy the reoxygenation pattern was different: The hypoxic fraction stayed above the pretreatment value for 4 h, and pronounced reoxygenation occurred after 12 h (hypoxic fraction 0.4%). At longer time intervals the hypoxic fraction again increased to--and slightly above--the oxygenation level of untreated tumors. The present findings show that reoxygenation in solid tumors is a function of radiation dose, and the data suggest that mechanisms other than a decrease in tumor cell O2 consumption are involved in tumor reoxygenation.     

Progressive iron overload enhances chemically mediated tumor promotion in murine skin

Iron overload has been shown to enhance chemically mediated cutaneous tumor promotion in animals. However, the majority of these animal studies have used high concentrations of iron before initiating tumor development. The current study was designed to evaluate the effect of small doses of iron on the promotion stage of chemically mediated cutaneous carcinogenesis. We found an increased tumor response in mice initiated with dimethylbenz(a)anthracene (DMBA) when iron at the dose levels of 0.5, 1.0, and 1.5mg/mouse was injected (intramuscularly) once a week into mice at the promotion stage of skin carcinogenesis, employing 12-O-tetradecanoyl phorbol-13-acetate (TPA)/benzoyl peroxide (BPO) as tumor promoter. The appearance of first papilloma and the number of tumors/mouse were recorded weekly. When compared to the control (non-iron-treated) group, the iron-treated groups showed an augmented incidence of tumors and number of tumors/mouse. In iron-treated mice, tumors appeared earlier than in the control group. TPA/BPO treatment resulted in a significant decrease in the activities of antioxidant enzymes and depletion in the level of epidermal reduced glutathione (GSH). TPA treatment in non-iron-treated mice resulted in approximately 20-40% decrease in GSH level and in the activities of antioxidant enzymes, whereas 1.5-mg iron treatment along with TPA treatment resulted in about approximately 30-70% decrease in GSH level and in the activities of antioxidant enzymes. Similarly, treatment of iron along with BPO treatment resulted in a dose-dependent higher depletion of GSH and the antioxidant enzymes as compared to non-iron-treated animals treated with BPO. Further, TPA/BPO-mediated induction in ornithine decarboxylase activity and [3H]thymidine incorporation in cutaneous DNA was approx two- to threefold higher in mice treated with iron as compared to non-iron-treated mice. Cutaneous lipid peroxidation and iron levels were also higher in mice treated with iron as compared to non-iron-treated mice. These data suggest that progressive iron overload can enhance the tumor promotion ability of TPA/BPO in DMBA-initiated murine skin.     

Effects of Fluosol DA 20% and carbogen on the radioresponse of SCK tumors and skin of A/J mice

The effect of Fluosol DA 20%, an emulsion of perfluorochemicals, in combination with carbogen (95% O2 and 5% CO2) breathing on the response of mouse tumors to radiation was studied. When A/J mice bearing SCK tumors in the right hind limb were injected iv with Fluosol DA 20% at 12 ml/kg and exposed to carbogen for 1 h before and during the irradiation of tumors, the response of tumors to a single dose of X irradiation was significantly enhanced. The dose modification factors for growth delay and cure of SCK tumors were 2.10 +/- 0.01 (SE) and 1.86 +/- 0.18 (SE), respectively. Such a treatment slightly increased the radiation-induced skin damage by a factor of 1.17 +/- 0.02 (SE), resulting in a therapeutic gain of 1.79 +/- 0.01 (SE) for the growth delay and 1.59 +/- 0.09 (SE) for the curability. Carbogen breathing alone also increased the response of tumor and skin to radiation, but it was far less effective than the combination of Fluosol DA 20% and carbogen breathing. It was concluded that iv injection of Fluosol DA 20% in conjunction with carbogen breathing significantly increased the O2 transport to hypoxic areas in the SCK tumors and thus significantly enhanced the tumoricidal effect of radiation on SCK tumors.     

Effects of beta-endorphin on body temperature in mice at different ambient temperatures

The effect of intracerebroventricular injection of beta-endorphin (beta-END) on body temperature of mice was studied at ambient temperatures (Ta) of 10 degrees, 20 degrees and 31 degrees C. Doses between 0.1 and 10.0 microgram/mouse were studied. The lower (less than 1 microgram) doses of beta-END produced a hyperthermia at all Ta's studied. The higher doses of beta-END produced hyper- or hypothermia depending on the Ta. The subcutaneous injection of naloxone (1 mg/kg) antagonized the high dose hypothermic effects, but not the hyperthermic effect of beta-END. These data suggest that there may be different receptors and/or sites of action for high and low doses of beta-END.     

Radiosensitization of murine tumors by Fluosol-DA 20%

The effect of perfluorochemicals in combination with carbogen breathing on the response of SCK tumors of mice to fractionated irradiation was investigated. The SCK tumors of A/J mice were irradiated twice a day at 3 Gy per fraction (6 Gy per day), with a total dose of 18 Gy over 3 days. When the host animals were treated with an intravenous (iv) injection of 12 ml/kg of Fluosol-DA 20% before the first daily tumor irradiation and carbogen breathing during every X irradiation with Fluosol-DA 20% injection without carbogen breathing. The hypoxic cell fraction, as determined by an in vivo-in vitro cloning assay, decreased significantly, and the intratumor pO2, as determined with microelectrodes, was markedly increased by Fluosol-DA 20% injection and carbogen breathing. It was concluded that oxygenation of hypoxic cells in SCK tumors during the course of fractionated irradiation was improved by the iv injection of Fluosol-DA 20% and carbogen breathing.     

Host cell cytotoxicity, cellular repopulation dynamics, and phase-specific cell survival in X-irradiated rat rhabdomyosarcoma tumors

Postirradiation tumor volume response, cellular repopulation dynamics, cell-cycle perturbations, and phase-specific cell survival were characterized in rat rhabdomyosarcoma R-1 tumors (the R2C5 subline) following an in situ 10-Gy dose of 225-kVp X rays. This X-ray dose produced a 7.5-day delay in tumor growth to twice the volume measured at the time of irradiation, and reduced the initial surviving fraction of R2C5 cells to 0.17 as measured by the excision assay procedure. The surviving fraction of R2C5 cells returned to unity by the 16th day after tumor irradiation. On the basis of flow cytometry measurements of DNA content in tumor cells stained with a noncytotoxic concentration of Hoechst 33342 (5 microM, 2 h, 37 degrees C), a transient G2 block was observed 1 day after irradiation. Flow cytometry measurements also demonstrated that the tetraploid R2C5 cells constituted only 30% of the total tumor cell population, with the remainder being diploid host cells comprised of macrophages, monocytes, lymphocytes, and granulocytes. Large numbers of host cells infiltrated the irradiated tumors, leading to an increase in the percentage of diploid cells by Day 2 and reaching a level of more than 80% of the total tumor cell population by 4 to 8 days after irradiation. The influx of host cells into irradiated tumors was correlated temporally with a significant 12-fold decrease in the surviving fraction of R2C5 cells that occurred between Days 2 and 4 postirradiation. When the diploid host cell population was removed by cell sorting procedures, the surviving fraction of R2C5 cells at Day 4 was substantially greater than that in the presence of the host cells. Experiments involving the mixing of 4/1 and 12/1 ratios of diploid host cells and tetraploid tumor cells isolated from irradiated and unirradiated tumors demonstrated that the cytotoxic effect of the host cells was specific for the irradiated tumor cells. The significant toxic effect of host cells on irradiated tumor cells was observed only at 2 to 4 days after irradiation, and not at earlier or later times. The data obtained in these experiments indicate that the immunogenicity of R2C5 cells is increased significantly by irradiation, and a resultant cell-mediated host immune response produced a delayed decrease in tumor cell survival that is most pronounced 4 days after irradiation. The cell survival characteristics of R2C5 cells in different cell-cycle phases were found to be similar through the 16-day postirradiation interval that was studied.(ABSTRACT TRUNCATED AT 250 WORDS)     

Coincidence of counter-antigonadal and counter-antithyroid action of melatonin administration via the drinking water in male golden hamsters

Administration of melatonin via the drinking water prevented the gonadal involution and the thyroid hormone depletion normally observed in blinded hamsters. Ten weeks after blinding male hamsters had plasma thyroxin levels that were 57% of controls and testis weights that were 8% of controls. Administration of melatonin (80 microgram melatonin/ml drinking water) to blinded hamsters restored thyroxin levels to 86% of controls and testis weights to 93% of controls. Dose response data showed that as little as 1.25 microgram (approximately 10 microgram/hamster/day) produced a significant effect on testis weight, whereas the lowest dose required to produce a significant increase in thyroxin levels was 10 microgram/ml. The coincidence of counter-antigonadal and counter-antithyroid actions of melatonin suggests a single site of action.     

Either chick embryo dermis or retinoid-treated mouse dermis can initiate glandular morphogenesis from mammalian epidermal tissue

Excess retinoids can cause developing mouse vibrissa follicles to be transformed into mucous glands in organ culture. The objective was to test the hypothesis that retinoids act in this system by altering morphogenetic properties of the dermis. After inititation by retinoic acid (RA) in organ culture, glands were shown to develop further in embryonic skin grafted to the chick chorioallantoic membrane (CAM). Recombinants of 12.5 day mouse epidermis with untreated or RA-treated mouse or chick dermis were then grafted to CAM for 7 days. For homospecific recombinants, 13.5 day mouse dermis originated from 11.5 day skin cultured for 2 days, with or without 5.2 microgram/ml RA. For heterospecific recombinants, 12 day dermis came from chick embryos, previously injected with 250 microgram RA. Glands were absent from the homospecific recombinants including untreated mouse dermis, but appeared in 26% of those with RA-treated dermis. Among heterospecific recombinants, 75% of those with RA-treated chick dermis and 29% of those with untreated dermis had glands. Untreated 10-12 day chick skin contained two forms of endogenous vitamin A, retinol (4.5 microgram/g protein) and dehydroretinol (3.7 microgram/g protein), while 13-14 day mouse skin contained only retinol (1.8 microgram/g protein), as shown by high performance liquid chromatography. RA injection increased retinol and dehydroretinol in chick skin, while RA was undetectable. Thus RA can act through mouse dermis to form epithelial glands and through chick dermis to increase the incidence of glands. The glands in recombinants with untreated chick dermis may result from the higher levels of endogenous retinoids in chick skin, compared with mouse skin.     

Hypotensive action of prolactin in rats with spontaneous hypertension

Rats (SHR) weighing 240 +/- 10 g with spontaneous hypertension were given intraperitoneally porcine prolactin in doses from 0.2 to 2000 micrograms/kg of body weight. The systolic pressure was measured before hormone administration and 2 hours after it. It was found that prolactin in doses of 200 to 2000 micrograms/kg caused a decrease of the systolic pressure by 22%. The dose of 20 micrograms/kg decreased this pressure by 9% and the dose of 0.2 microgram/kg by 7.9%.     

Therapeutic efficacy of human recombinant interleukin-2 (TGP-3) alone or in combination with cyclophosphamide and immunocompetent cells in allogeneic,semi-syngeneic,and syngeneic murine tumors

Summary The potential for a recombinant human interleukin-2 (rIL-2, TGP-3) alone, in combination with cyclophosphamide, and in combination with cyclophosphamide and normal immunocompetent cells to manifest biological activity in vivo was tested using allogeneic, semi-syngeneic, and syngeneic tumor-host systems in mice. The biological activity of rIL-2 was evaluated by the inhibition of the growth of tumors and the inhibition of metastases in short-term assays and, in long-term assays, the prolongation of the survival time of mice bearing subcutaneously (s.c.) or intradermally transplanted tumors. rIL-2 was injected s. c. daily continuously for up to 40 days or intermittently two to four times into mice bearing established tumors. In the short-term assays, the dose and schedule dependence of activity of rIL-2 alone was significantly manifested against sarcoma 180 in ICR mice (allogeneic) by the regression of the tumor, and was confirmed against Meth-A fibrosarcoma in BALB/c mice (syngeneic) by retarding the growth of the tumor. When assessed using these tumors, it was found that the antitumor activity of rIL-2 was scheduledependent: the growth of tumors was more significantly suppressed when rIL-2 was injected every day for 10 days, starting on the 7th day after tumor transplantation, than when rIL-2 was injected five times every other day or twice every 5th day, even if the total amounts of rIL-2 injected were same. The continuous injection for 10 days was considered to be a standard regimen and the daily effective doses of rIL-2 were 5, 10, and 25 µg/mouse. Using the standard regimen and the effective doses, the activity of rIL-2 alone was also observed against two other syngeneic tumors: Colon carcinoma 26 in BALB/c mice, by retarding the growth of the tumor, and Lewis lung carcinoma in C57BL/6 mice by reducing the formation of lung metastases. When assessed using M5076 reticulum cell sarcoma, in a long-term assay, the activity of rIL-2 alone was not manifested in C57BL/6 mice (syngeneic) even when rIL-2 was injected for a long period (20 days) but it was observed in BDF1 (semi-syngeneic) mice. On the other hand, it was found that rIL-2 was effective in combination with cyclophosphamide in prolonging the survival time of C57BL/6 mice bearing the tumor. After cyclophosphamide (2.0 mg) had been administered orally to mice on the 6th day after tumor transplantation, the tumor regressed temporarily but regrew; however, when rIL-2 at a dose of 10 µg was also injected daily for a long period (40 days), the regrowth was retarded and the survival time of the mice was significantly prolonged. Moreover, when normal immunocompetent cells were transferred at the tumor sites, the regrowth of the tumors was retarded more significantly even at a daily dose of 1 µg or 3 µg rIL-2, and mice were observed to be cured by daily doses over 3 µg. The results obtained in the syngeneic tumor-host systems indicate that the continuous injection of rIL-2 is necessary and important for its activity to be manifest in vivo, and that, when combined with cytotoxic drugs and/or with immunocompetent cells, the potential efficacy of rIL-2 is valuable in cancer therapy.     

Changes in bromodeoxyuridine labeling index during radiation treatment of an experimental tumor

Cell proliferation kinetics in a spontaneous mouse fibrosarcoma (FSaII) growing in C3H mice has been studied by in vivo pulse labeling of cells synthesizing DNA with bromodeoxyuridine (BrdUrd). A monoclonal antibody to BrdUrd and flow cytometry were used to quantify these cells. Labeling indices (LI) were measured before and after radiation. Unirradiated 10-mm tumors had a mean LI of 17.5%. After a single dose of 20 Gy there was depression of LI after 1 day followed by a rapid increase to greater than control values after 5 days. Analysis performed after five fractions showed that LI was dependent on the dose per fraction and interval between fractions. After 5 and 7 Gy/fraction LI remained similar to control values during daily fractionation but was significantly depressed after twice daily fractionation. With doses greater than 10 Gy/fraction there was marked depression of LI using both fractionation schedules. These changes in LI correlated well with changes in tumor volume after radiation. Tumors were also biopsied after 5 fractions of a 20-fraction course to see if LI would predict for tumor control. LIs of greater than or equal to 10% were associated with lack of tumor control at 90 days while all controlled tumors had a significant depression of LI. Changes in LI after radiation were a reasonable indication of the amount of repopulation occurring and might be useful in selecting patients for altered fractionation schedules.     

Modulation of in situ murine neuroblastoma tumor growth by the adrenergic nervous system: differential response of clonal cell lines to chemical sympathectomy

The in situ growth characteristics of C-1300, N1E-115 and NS20Y murine neuroblastoma (MNB) tumor cell lines were compared in normal and sympathectomized A/J mice. Adrenergic nerve ablation was produced in neonatal mice by administration of 6-hydroxydopamine (6-OHDA) at a dose of 100 micrograms/gm body weight on post-natal days 4, 6, 8 and 10; controls received equivalent volumes of the vehicle solution (0.9% NaCl/0.1% Ascorbic Acid). All mice were inoculated subcutaneously with 10(6) viable MNB cells four to six weeks after treatment with 6-OHDA or vehicle. The growth rates of tumors produced by the adrenergic MNB cell lines, C-1300 and N1E-115, were significantly lower in sympathectomized mice when compared to control animals. In contrast, tumors induced by the cholinergic MNB cell line, NS20Y, grew at similar rates in both sympathectomized and control mice. All tumors obtained from control and sympathectomized mice regardless of whether they derived from cell lines characterized as cholinergic (NS20Y) or adrenergic (C-1300, N1E-115), contained both norepinephrine and dopamine. Depletion of adrenergic neurotransmitter in A/J mice was induced by administration of reserpine (5-10 micrograms/kg/day) beginning 30 days prior to implantation of the C-1300 MNB cell line and continuing until sacrifice of the animal. The effect of this treatment on organ and tumor catecholamine concentrations was confirmed by high-pressure liquid chromatography. Splenic catecholamine levels in reserpine-treated animals were reduced to 20% of controls as compared to 9% in the neonatally-sympathectomized group. However, there was no discernible effect on C-1300 MNB tumor growth in the reserpine-treated animals. C-1300 MNB tumor concentrations of nor-epinephrine and dopamine were significantly lower in the reserpine-treated animals than in controls. The suppression of tumor growth by adrenergic nerve ablation is selective for specific MNB tumor cell lines. An anatomically intact sympathetic nervous system appears to exert a greater influence than competency of adrenergic neuro-humoral transmission on MNB tumor growth. These data support the hypothesis that modulation of MNB tumor growth by the adrenergic nervous system is not mediated via catecholamines but may be modulated by endogenous growth factor(s).     

Endogenous brain IL-1 mediates LPS-induced anorexia and hypothalamic cytokine expression

The present study was designed to determine the role of endogenous brain interleukin (IL)-1 in the anorexic response to lipopolysaccharide (LPS). Intraperitoneal administration of LPS (5-10 microgram/mouse) induced a dramatic, but transient, decrease in food intake, associated with an enhanced expression of proinflammatory cytokine mRNA (IL-1beta, IL-6, and tumor necrosis factor-alpha) in the hypothalamus. This dose of LPS also increased plasma levels of IL-1beta. Intracerebroventricular pretreatment with IL-1 receptor antagonist (4 microgram/mouse) attenuated LPS-induced depression of food intake and totally blocked the LPS-induced enhanced expression of proinflammatory cytokine mRNA measured in the hypothalamus 1 h after treatment. In contrast, LPS-induced increases in plasma levels of IL-1beta were not altered. These findings indicate that endogenous brain IL-1 plays a pivotal role in the development of the hypothalamic cytokine response to a systemic inflammatory stimulus.     

Observations on the effect of radiotherapy,followed by injection of pig lymph node cells,in reducing the number of pulmonary tumors induced by intravenous injection of tumor cells into isogenic mice

Summary Pulmonary tumors were produced in A. strain mice by intravenous injection of A. strain mammary carcinoma cells. The mesenteric lymph nodes of pigs were immunized by implantation of fragments from the same tumors into the pig mesentery.Tumor-immune pig lymph node cells when injected IV 7 days after tumor cells did not reduce the number of tumors, counted on day 14. However, when preceded by 200 rad thoracic irradiation on day 3 (which increased the number of pig cells settling in the lungs) tumor-immune cells given IV reduced the number of tumors compared with the effect of irradiation alone, or in combination with nonimmune pig cells.When tumor-immune pig cells were injected IP on day 7 (following thoracic irradiation on day 3), no antitumor effect was observed. Thus immediate pig cell/tumor cell contact is important in order to obtain an antitumor effect.Pig cells immunized against a human bladder carcinoma did not reduce pulmonary tumor formation by one of the mouse tumors.     

The antiangiogenic agents SU5416 and SU6668 increase the antitumor effects of fractionated irradiation.

Angiogenesis is critical for tumor development, growth and metastasis. The vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF) and platelet-derived growth factor (PDGF) and their tyrosine kinase receptors are major regulators of angiogenesis. Radiation induces the production of VEGF, FGF and PDGF in many tumor cells. We hypothesized that inhibition of the function of these growth factors could inhibit tumor angiogenesis and thereby enhance the efficacy of radiation therapy. To test this hypothesis, we used the small molecule inhibitors SU5416 (an inhibitor for Vegf receptor) and SU6668 (an inhibitor for Vegf, Fgf and Pdgf receptors) alone and in combination with fractionated irradiation to treat C3H mice bearing SCC VII carcinomas. The SCC VII tumors express Vegf, Fgf2 (also known as bFGF), Pdgf and their associated receptors. Animals were given either SU5416 or SU6668 daily before or after irradiation (2 Gy per fraction per day for 5 days). The results from these experiments demonstrate that administration of either SU5416 or SU6668 without radiation delayed tumor growth. Administration of SU5416 at a dose of 25 mg/kg per day (the maximum tolerated effective dose) inhibited tumor growth by 17.9% on day 7 (P < 0.05 compared to untreated control mice) and produced an average tumor growth delay time of 0.5-2.0 days. When combined with fractionated irradiation, administration of SU5416 increased the inhibition of tumor growth to 50-53% on day 7 and the tumor growth delay time to 5.7-6.5 days (P < 0.001 compared with SU5416 alone; P < or = 0.05 compared with radiation alone). SU6668 alone inhibited tumor growth in a dose-dependent manner. Administration of SU6668 at a dose of 75 mg/kg per day (a suboptimal dose) inhibited tumor growth by 36% on day 7 and produced an average tumor growth delay time of 3.3 +/- 1.4 days. The combination of SU6668 with fractionated radiation increased inhibition of tumor growth to 66-70% and the tumor growth delay time from 3.3 days to 11.9 days (P < or = 0.001 compared with either radiation alone or SU6668 alone). Administration of these agents before or after irradiation produced similar results (P = 0.40 for SU5416; P = 0.98 for SU6668). SU5416 or SU6668 alone or in combination with radiation was very well tolerated with little or no toxicity. These results suggest that inhibition of Vegf, Fgf and Pdgf receptor function by SU5416 and SU6668 can enhance the efficacy of irradiation. The targeting of multiple tyrosine kinase receptors by SU6668 is more effective than inhibition of the Vegf receptor alone by SU5416 for the enhancement of tumor cell killing by fractionated irradiation.     

A longitudinal study of radiation-induced changes in tumor vasculature by contrast-enhanced magnetic resonance imaging

Dynamic contrast-enhanced MRI with two different-sized contrast agents, Gd-DTPA and Gadomer-17, was used to study the effects of radiation on the pharmacokinetics of the paramagnetic enhancement of water relaxation in the rat R3230 AC adenocarcinoma tumor model. The kinetics of enhancement was analyzed by a two-compartment pharmacokinetic model to derive parameters related to vascular volume (V(b)) and permeability (K(2)). Rats implanted with tumors were divided into two groups; one received 5 Gy and the other received 20 Gy (137)Cs gamma rays. Sequential dynamic contrast-enhanced MRI studies were performed, one before irradiation, one at day 1 after irradiation, and another at day 3 after irradiation, to investigate the effect of the radiation dose and the changes that occurred over time. The analysis was performed on a pixel-by-pixel basis to study the heterogeneity within the tumor. The pixel distribution profiles of V(b) and K(2) from each tumor were obtained to assess the regional radiation-induced effects on vascular volume and permeability. No significant change in vascular volume was detected with either Gd-DTPA or Gadomer-17 after irradiation of the tumor; however, a small dependence of K(2) on the radiation dose was observed. After low-dose (5 Gy) irradiation, the mean value of K(2) decreased by 46% at day 1 compared to the baseline, presumably due to cell swelling, and decreased further by 67% from the baseline on day 3. When the dose was increased to 20 Gy, the mean value of K(2) measured with Gadomer-17 did not show any significant changes at either day 1 or day 3 after irradiation. The value of K(2) measured with Gd-DTPA did not show any significant changes after either the low or the high radiation dose.