Scheduling of radiation with angiogenesis inhibitors anginex and Avastin improves therapeutic outcome via vessel normalization.

PURPOSE: To test whether a direct antiangiogenic peptide (anginex) and a vascular endothelial growth factor antibody (bevacizumab, Avastin) can transiently normalize vasculature within tumors to improve oxygen delivery, alleviate hypoxia, and increase the effect of radiation therapy. EXPERIMENTAL DESIGN: Tumor oxygenation levels, microvessel density and pericyte coverage were monitored in three different solid tumor models (xenograft human ovarian carcinoma MA148, murine melanoma B16F10, and murine breast carcinoma SCK) in mice. Multiple treatment schedules were tested in these models to assess the influence on the effect of radiation therapy. RESULTS: In all three tumor models, we found that tumor oxygenation levels, monitored daily in real time, were increased during the first 4 days of treatment with both anginex and bevacizumab. From treatment day 5 onward, tumor oxygenation in treated mice decreased significantly to below that in control mice. This "tumor oxygenation window" occurred in all three tumor models varying in origin and growth rate. Moreover, during the treatment period, tumor microvessel density decreased and pericyte coverage of vessels increased, supporting the idea of vessel normalization. We also found that the transient modulation of tumor physiology caused by either antiangiogenic therapy improved the effect of radiation treatment. Tumor growth delay was enhanced when single dose or fractionated radiotherapy was initiated within the tumor oxygenation window as compared with other treatment schedules. CONCLUSIONS: The results are of immediate translational importance because the clinical benefits of bevacizumab therapy might be increased by more precise treatment scheduling to ensure radiation is given during periods of peak radiosensitivity. The oxygen elevation in tumors by non-growth factor-mediated peptide anginex suggests that vessel normalization might be a general phenomenon of agents directed at disrupting the tumor vasculature by a variety of mechanisms.     

Simultaneous inhibition of the receptor kinase activity of vascular endothelial, fibroblast, and platelet-derived growth factors suppresses tumor growth and enhances tumor radiation response

We have investigated the effect of simultaneous inhibition of multiple angiogenic growth factor signaling pathways on tumor growth, tumor blood perfusion, and radiation-induced tumor-growth delay using SU6668, an inhibitor of the receptor-tyrosine kinase activity of vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), and platelet-derived growth factor (PDGF). The SCK mammary carcinoma, FSaII fibrosarcoma, and CFPAC human pancreatic carcinoma were grown s.c. in the hind leg of A/J mice, C3H mice, and Balb/cAnNCrl-nuBr nude mice, respectively. Daily i.p. injection of 100 mg/kg of SU6668 markedly suppressed the growth of these three tumor types. SU6668 also markedly prolonged the survival time of host mice bearing SCK tumors, which appeared to be caused by a reduction of metastatic tumor growth in the lung. There was little or no change in normal tissue blood perfusion, whereas in SCK tumors the perfusion decreased by 50% at 1 h after a single i.p. injection of SU6668, slightly recovered at 4 h, and completely recovered by 8 h. Interestingly, the tumor blood flow was significantly increased above the baseline level 24 h after SU6668 injection. After extended daily i.p. injections of SU6668, the tumor blood flow in all of the three tumor types studied was markedly decreased compared with control. The observed effects of this drug on tumor blood perfusion may partially explain the effectiveness of the compound in suppressing tumor growth and extending survival of tumor-bearing mice. We also observed that daily SU6668 administration and a single dose of 15 Gy of X-irradiation was significantly more effective than either treatment alone in suppressing tumor growth. Our results suggest that SU6668 increased the radiosensitivity of tumor blood vessels. We conclude that SU6668 is a potent therapeutic agent potentially useful to suppress tumor growth and enhance the response of tumors to radiotherapy.     

Anti-tumor activity of the novel angiogenesis inhibitor anginex

Anginex is a novel cytokine-like peptide with potent anti-angiogenic activity, which operates specifically against angiogenically-activated endothelial cells via prevention of cell adhesion/migration on the extracellular matrix and subsequent induction of apoptosis. Here, we demonstrate that anginex inhibits tumor growth in vivo in mouse xenograft models. In the MA148 ovarian carcinoma model, tumor growth was inhibited dose-dependently by up to 80% when systemically administered via osmotic mini-pumps starting at the time of tumor cell inoculation. The optimal dose was found to be 10 mg/kg per day. When tested against established tumors, mini-pump-administered anginex demonstrated essentially the same effectivity at this optimal dose, whereas once or twice-daily injections were only half as effective. When anginex was conjugated to human serum albumin, effectivity was significantly improved, most likely due to increased bioavailability of the conjugate. Immunohistochemical analysis of microvessel density indicated that the anti-tumor activity of anginex is mediated by angiogenesis inhibition. This was confirmed in an in vitro angiogenesis assay based on tube formation in a collagen gel. Animals demonstrated no signs of toxicity as judged by unaltered behavior, normal weight gain, blood markers and macro- and microscopic morphology of internal organs upon autopsy. Overall, these in vivo studies indicate that anginex is an effective anti-tumor agent.     

Tumor cell radiosensitivity is a major determinant of tumor response to radiation

Substantial evidence suggests that the radiosensitivity of the tumor cells is the primary determinant of tumor response to radiation. More recent studies suggest that tumor stroma radiosensitivity is the principle determinant of response. To assess the relationship between intrinsic tumor cell radiosensitivity and tumor response, we altered the intrinsic radiosensitivity of a cloned tumor cell line and analyzed the effect of this alteration on tumor response. A cloned tumor cell line derived from DNA double-strand break repair--deficient severe combined immunodeficient mice was transfected with the double-strand break repair gene DNA-PKcs. The intrinsic radiosensitivity of the transfected tumor line was decreased by a factor of approximately 1.5. The isogenic lines were used to initiate tumors in NCr-nu/nu mice. When transplanted in the same strain of mice and exposed to the same dose of radiation, the isogenic tumors may be expected to exhibit a similar response to radiation if radiation damage to host stroma is the principle determinant of response. This was not observed. Over the dose range of 20 Gy in four 5-Gy fractions to a single dose of 30 Gy, the 1.5-fold increase in intrinsic tumor cell radioresistance conferred by the introduction of DNA-PKcs caused a 1.5-fold decrease in tumor growth delay. The results show that the intrinsic radiosensitivity of tumor cells is a major determinant of tumor response to radiation.     

Antiangiogenesis therapy using a novel angiogenesis inhibitor, anginex, following radiation causes tumor growth delay

Background The present study investigated whether treatment with anginex, a novel antiangiogenic peptide, could block re-vascularization after radiation treatment. Methods A squamous cell (SCCVII) xenograft tumor mouse model was employed to assess the effects of anginex given post-radiation on tumor growth, microvessel density (MVD), and oxygen levels. The oxygen status was determined by the partial pressure of O₂. Results Tumors in untreated mice increased threefold in 7.0 days, anginex-treated tumors (10 mg/kg intraperitoneal, twice) required 7.3 ± 0.9 days, and tumors exposed to 8-Gy radiation increased threefold over 11 days. Combination treatment of anginex and radiation caused the tumors to grow threefold in 16.1 ± 1.6 days, a delay which was significant and deemed supra-additive. Oxygen levels in tumors treated by stand-alone or combination therapies were significantly reduced; for example from 19.5 ± 4.9 mmHg in controls to 9.7 ± 1.9 mmHg in combination-treated, size-matched tumors. In addition, immunohistochemistry showed a decrease in MVD in the tumors treated with anginex, radiation, or the combination. These results suggest that a combination of anginex and radiation can greatly affect the amount of functional vasculature in tumors and prolong radiation-induced tumor regression. Conclusion Antiangiogenesis therapy with anginex, in addition to radiotherapy, will be useful by blocking angiogenesis-dependent regrowth of vessels.     

The designed angiostatic peptide anginex synergistically improves chemotherapy and antiangiogenesis therapy with angiostatin

Recently, we demonstrated that the designed peptide anginex displays potent antiangiogenic activity. The aim of the present study was to investigate anginex treatment as a single-agent therapy and to test its ability to improve conventional chemotherapy and antiangiogenesis therapy. In a human ovarian carcinoma mouse model, anginex inhibited tumor growth by 70%. When anginex was combined with a suboptimal dose of carboplatin, tumors regressed to an impalpable state. Anginex plus angiostatin worked synergistically to inhibit tumor growth. Assessment of microvessel density suggested that the antitumor activity of anginex is mediated by angiogenesis inhibition. In any of the experiments, no sign of anginex-induced toxicity was observed.     

TS-1 enhances the effect of radiotherapy by suppressing radiation-induced hypoxia-inducible factor-1 activation and inducing endothelial cell apoptosis

The therapeutic effect of concurrent chemoradiotherapy with TS-1 has been confirmed in various solid tumors; however, the detailed mechanism of action has not yet been fully elucidated. In the present study, we identified hypoxia-inducible factor-1 (HIF-1) as one of the targets of TS-1 in chemoradiotherapy. In growth delay assays using a tumor xenograft of non-small-cell lung carcinoma, H441, TS-1 treatment enhanced the therapeutic effect of single gamma-ray radiotherapy (14 Gy) and significantly delayed tumor growth by 1.58-fold compared to radiotherapy alone (P < 0.01). An optical in vivo imaging experiment using a HIF-1-dependent 5HRE-luc reporter gene revealed that TS-1 treatment suppressed radiation-induced activation of HIF-1 in the tumor xenografts. The suppression led to apoptosis of endothelial cells resulting in both a significant decrease in microvessel density (P < 0.05; vs radiation therapy alone) and a significant increase in apoptosis of tumor cells (P < 0.01; vs radiation therapy alone) in tumor xenografts. All of these results indicate that TS-1 enhances radiation-induced apoptosis of endothelial cells by suppressing HIF-1 activity, resulting in an increase in radiosensitivity of the tumor cells. Our findings strengthen the importance of both HIF-1 and its downstream gene, such as vascular endothelial cell growth factor, as therapeutic targets to enhance the effect of radiotherapy.     

Alpha-sulfoquinovosylmonoacylglycerol is a novel potent radiosensitizer targeting tumor angiogenesis

Angiogenesis is a promising target for the treatment of cancer, and varying types of antiangiogenic agents have been developed. However, limitations and problems associated with antiangiogenic therapy have recently arisen. Although radiotherapy can be combined with antiangiogenic compounds to overcome these difficulties, almost all previously described angiogenesis inhibitors could still cause side effects at effective doses, and only additive effects are seen in current combination therapy. In this study, we identified a member of the sulfoquinovosylacylglycerols, alpha-sulfoquinovosylmonoacylglycerol (alpha-SQMG), originally derived from sea urchins, as a potent radiosensitizer. The agent synergistically inhibits angiogenesis at low doses when combined with ionizing radiation. Combined treatment with alpha-SQMG and radiation seems to promote the adoption of a senescence-like phenotype by vascular endothelial cells. Finally, the agent remarkably enhances the radioresponse of human tumors transplanted into nude mice, accompanied by a significant reduction in the vascularity of the tumors. Collectively, alpha-SQMG may be a novel potent radiosensitizer targeting angiogenesis.     

VEGF-associated tyrosine kinase inhibition increases the tumor response to single and fractionated dose radiotherapy

PURPOSE: In this study, the efficacy of combining ZD6474 (Zactima), a vascular endothelial growth factor (VEGF) receptor 2-associated tyrosine kinase inhibitor currently undergoing Phase II clinical trial evaluation, with single and fractionated dose radiation exposures was examined in a human colorectal carcinoma model (HT29). METHODS AND MATERIALS: HT29 xenograft-bearing mice were treated with either single-dose (10 Gy) or multifraction (2 Gy/day for 2 weeks) radiotherapy alone or in conjunction with a 2-week course of ZD6474 (25 mg/kg). In the single-dose investigation, ZD6474 treatment followed radiotherapy, whereas in the fractionated dose studies the antiangiogenic therapy was given before, after, or concurrent with the radiation. Tumor response was determined by tumor growth delay. RESULTS: ZD6474 increased the response of HT29 xenografts to both single and fractionated dose radiotherapy. In the fractionation studies sequencing of therapies had little impact on treatment outcomes; the time for the median tumors in each of the treatment groups to grow to five times the starting size was 53, 53.5, and 49 days, respectively. CONCLUSIONS: These studies indicate that ZD6474, when used in conjunction with radiation therapy, has a clear therapeutic advantage, providing a rationale for considering the combination of this agent with radiotherapy in the clinic.     

SU11248 maintenance therapy prevents tumor regrowth after fractionated irradiation of murine tumor models

Receptor tyrosine kinase activation contributes to cell viability during cytotoxic therapy. The novel broad spectrum receptor tyrosine kinase inhibitor, SU11248, inhibits vascular endothelial growth factor receptor 2, platelet-derived growth factor receptor, c-kit, and fetal liver tyrosine kinase 3. In this study, we maintained SU11248 plasma levels beyond the completion of radiotherapy to determine whether tumor regrowth can be delayed. The antiangiogenic effects of SU11248 were demonstrated using human umbilical vein endothelial cells in vitro. Apoptosis increased and clonogenic survival decreased when SU11248 was used in combination with radiation from 0 to 6 Gy on endothelial cells. In vivo tumor growth delay was increased in C57B6J mice with Lewis lung carcinoma or glioblastoma multiform (GL261) hind limb tumors. Mice were treated with daily i.p. injections (40 mg/kg) of SU11248 during 7 days of radiation treatment (21 Gy). Combined treatment with SU11248 and radiation significantly reduced tumor volume as compared with either treatment alone. Concomitant reduction in vasculature was confirmed using the dorsal vascular window model. The vascular length established using images taken from a consistent quadrant in the window show the combination therapy was more effective in destroying tumor vasculature than either treatment alone. SU11248 maintenance administration beyond the completion of radiotherapy results in prolongation of tumor control. In summary, SU11248 enhances radiation-induced endothelial cytotoxicity, resulting in tumor vascular destruction and tumor control when combined with fractionated radiotherapy in murine tumor models. Moreover, inhibition of angiogenesis well beyond radiation therapy may be a promising treatment paradigm for refractory human neoplasms.     

Radiosensitization of Lewis lung tumor by perfluorochemical emulsion comparison between single and fractionated irradiation

Previously perfluorochemical emulsion (FDAS) was shown to enhance tumor growth delay, when applied together with breathing carbogen (95% O2+5% CO2) before and during irradiation. In the present paper, radiosensitizing effects of FDAS in tumor bearing mice were examined on a single (10 Gy) and fractionated irradiation (4 Gy, 4 times) and on the dose of administration. The results were as follows; 1) All groups of single irradiation with injection of FDAS 10-40 ml/kg could enhance the radiosensitivity of LLC bearing mice. 2) Tumor growth of even fractionated irradiation groups was significantly delayed by administration of FDAS more than 5 ml/kg. 3) In case of fractionated irradiation, the minimum effective dose of FDAS was estimated to be 5 ml/kg per irradiation, which coincided with that of single irradiation. It was concluded that FDAS in fractionated irradiation could increase the radiosensitivity in tumor bearing mice with more than 5 ml/kg injection. Therefore, FDAS may be useful as a radiosensitizer for clinical application in fractionated radiation therapy. Furthermore, since irradiation doses of single (10 Gy) and even fractionated irradiation (4 Gy X 4 times) were approximately iso effective dose, it may be considered that administration of more than 5 ml/kg (minimum effective dose) FDAS at each irradiation gave similar radiosensitizing effects to both single and fractionated irradiation.     

Antiangiogenic scheduling of chemotherapy improves efficacy against experimental drug-resistant cancer

To reveal the antiangiogenic capability of cancer chemotherapy, we developed an alternative antiangiogenic schedule for administration of cyclophosphamide. We show here that this antiangiogenic schedule avoided drug resistance and eradicated Lewis lung carcinoma and L1210 leukemia, an outcome not possible with the conventional schedule. When Lewis lung carcinoma and EMT-6 breast cancer were made drug resistant before therapy, the antiangiogenic schedule suppressed tumor growth 3-fold more effectively than the conventional schedule. When another angiogenesis inhibitor, TNP-470, was added to the antiangiogenic schedule of cyclophosphamide, drug-resistant Lewis lung carcinomas were eradicated. Each dose of the antiangiogenic schedule of cyclophosphamide induced the apoptosis of endothelial cells within tumors, and endothelial cell apoptosis preceded the apoptosis of drug-resistant tumor cells. This antiangiogenic effect was more pronounced in p53-null mice in which the apoptosis of p53-null endothelial cells induced by cyclophosphamide was so vigorous that drug-resistant tumors comprising 4.5% of body weight were eradicated. Thus, by using a dosing schedule of cyclophosphamide that provided more sustained apoptosis of endothelial cells within the vascular bed of a tumor, we show that a chemotherapeutic agent can more effectively control tumor growth in mice, regardless of whether the tumor cells are drug resistant.     

Effect of normobaric oxygen on tumor radiosensitivity: fractionated studies

The sensitizing ability of 100% normobaric oxygen was investigated in a mouse mammary carcinoma (CaNT) using a variety of fractionated regimens. Both regrowth delay and local control were used as assays of tumor response. With both assays, there was a similar and significant increase in radiosensitivity for all fractionated schedules. Enhancement ratios ranged from 1.24 to 1.45, the highest increase being observed with a 30 fraction schedule given in an overall time of 6 weeks. Thus, in CaNT tumors normobaric oxygen is a far more efficient radiosensitizer in fractionated treatments than the oxygen-mimetic compound misonidazole; an oxygen effect being observed at doses per fraction as low as 1.8 Gy. These results suggest strongly that normobaric gases could play an important role in the clinical management of tumors where hypoxia may limit the outcome of radiotherapy.     

Vascular endothelial growth factor receptor-2-blocking antibody potentiates radiation-induced long-term control of human tumor xenografts

Antiangiogenic therapy can enhance radiation-induced tumor growth inhibition. However, the effects of combined antiangiogenic and radiation therapy on long-term tumor control and normal tissue response have not been reported. We treated mice bearing two different human tumor xenografts with anti-vascular endothelial growth factor receptor-2 antibody (DC101) and five dose fractions of local radiation and followed them for at least 6 months. DC101 significantly decreased the dose of radiation necessary to control 50% of tumors locally. The decrease was 1.7- and 1.3-fold for the moderately radiosensitive small cell lung carcinoma 54A and the highly radioresistant glioblastoma multiforme U87, respectively. In contrast to tumors, no increase in skin radiation reaction by the antibody was detected. Surprisingly, 44% of mice bearing 54A tumor developed clear ascites after DC101 treatment at its highest dose; this was fatal to 20% of mice. This adverse effect was seen only in mice that received whole-body irradiation 1 day before tumor implantation. The encouraging results on two human tumor xenografts suggest that vascular endothelial growth factor receptor-2 blockade merits further investigation to assess its potential as an enhancer of radiation therapy in the clinic.     

In vivo radiosensitizing activity of a new fluorinated hypoxic cell radiosensitizer, KU-2285, in combination with radiation dose fractionation

Since most clinical radiotherapy is given as multiple small irradiation fractions, the present study was undertaken to test the in vivo radiosensitizing activity of a new hypoxic cell radiosensitizer, KU-2285, in combination with radiation dose fractionation. Radiosensitizing activity was measured by a growth delay assay using a transplanted mammary tumor in C3H/He mice, and by an in vivo-in vitro assay using the SCC VII tumor. KU-2285 was injected intraperitoneally 30 min before irradiation in all experiments. The in vivo-in vitro assay using SCC VII tumors showed that 12.5 micrograms/g of KU-2285 sensitized the tumors to irradiation (5 Gy/fr x 5 fr/48 hr or 6 Gy/fr x 3 fr/48 hr). KU-2285 also sensitized the transplanted mammary tumors to fractionated irradiation. We concluded that KU-2285 was able to sensitize two different murine tumors when given in combination with radiation dose fractionation.     

Anti-Vascular endothelial growth factor treatment augments tumor radiation response under normoxic or hypoxic conditions

Recent studies in experimental animals have shown that combining antiangiogenic therapy with radiation can enhance tumor response. Whether this enhancement is mainly attributable to angiogenesis inhibition, endothelial cell radiosensitivity, tumor cell apoptosis, or a decrease in the number of hypoxic cells (improved oxygenation) is not known. We designed this study to discern the role of tumor oxygenation. We chose an anti-vascular endothelial growth factor (anti-VEGF) monoclonal antibody (mAb) which has a known target, human VEGF. We also measured interstitial fluid pressure (IFP) to test the hypothesis that the decreased vascular permeability induced by the anti-VEGF mAb can lower IFP. The effect of anti-VEGF mAb on vascular density, partial oxygen tension (pO2), and apoptosis was also measured. Athymic NCr/Sed nu/nu mice bearing 6-mm xenograft of the human glioblastoma multiforme (U87), or colon adenocarcinoma (LS174T) were treated with anti-VEGF mAb injected i.p. on alternate days for a total of six injections at a dosage of 100 microg/injection/mouse. For combined anti-VEGF and radiation, single radiation doses were given under normal blood flow (20 and 30 Gy) or clamped hypoxic conditions (30 and 40 Gy) 24 h after the sixth injection of mAb. The inhibition of the growth of U87 and LS174T tumors by the anti-VEGF mAb was associated with a significant reduction in tumor vascular density and a relatively small increase in the number of apoptotic cells. Compared with size-matched controls, IFP decreased by 74% in LS174T, and 73% in U87 in mice treated with anti-VEGF mAb. After antibody treatment PO2 increased significantly in U87, but did not change in LS174T tumors. Combined treatment induced in U87 tumors a tumor-growth delay (TGD) which was greater than additive; in LS174T except for the 40-Gy hypoxic group, the effect was only additive. In both U87 and LS174T the TGD induced by the antibody was independent of oxygen levels in the tumor at the time of radiation. The fact that the increase in TGD occurred under both normoxic and hypoxic conditions suggests that anti-VEGF mAb treatment can compensate for the resistance to radiation induced by hypoxia.     

C225 antiepidermal growth factor receptor antibody enhances the efficacy of docetaxel chemoradiotherapy

PURPOSE: C225 anti-EGFR (epidermal growth factor receptor) antibody has been shown to enhance tumor response to radiation and a number of chemotherapeutic agents. Because of increased use of concurrent chemoradiotherapy in cancer treatment, it is important to determine whether C225 enhances also the antitumor efficacy of radiation when combined with chemotherapy. This study assessed the effect of C225 on tumor response when combined with docetaxel plus single or fractionated radiation. METHODS AND MATERIALS: MDA468 human adenocarcinoma and A431 human epidermoid carcinoma cells growing as xenografts in the right hind leg of nude mice were used. Mice bearing 8-mm tumors were treated with C225 antibody at a dose of 1 mg given i.p. once, twice, or three times 3 days apart, 10 or 30 mg/kg docetaxel given i.v., and/or local tumor irradiation of 8 or 10 Gy single dose or fractionated irradiation consisting of 2 Gy daily for 5 days. When all three agents were combined, C225 was given 6 h before or 18 h after docetaxel, and radiation was given 24 h after docetaxel. The treatment end point was tumor growth delay. RESULTS: C225 enhanced the antitumor efficacy of docetaxel, local tumor irradiation, and docetaxel combined with radiation. The response of both MDA468 and A431 carcinomas was enhanced. The enhancement factors ranged from 1.19 to 8.52, the degree of the enhancement depending on experimental conditions such as administration of multiple vs. single dose C225 or single or fractionated irradiation. C225 given twice or 3 times was more effective than when administered as a single dose. The effect of C225 was more pronounced when combined with single than fractionated irradiation with or without docetaxel. The triple-agent therapy was more effective than a single agent or double combination therapies, expressed by both increased tumor growth delay and the rate of tumor cure. CONCLUSIONS: Our results show that C225 anti-EGFR antibody is a potent enhancer of tumor response to docetaxel or radiation as single agents, and to docetaxel when combined with radiation. Thus, these findings provide strong preclinical evidence in support of combination of anti-EGFR blockade with chemoradiotherapy.     

Design of nonpeptidic topomimetics of antiangiogenic proteins with antitumor activities

The inhibition of angiogenesis is a promising avenue for cancer treatment. Although some angiostatic compounds are in the process of development and testing, these often prove ineffective in vivo or have unwanted side effects. We have designed, synthesized, and evaluated a small library of nonpeptidic, calixarene-based protein surface topomimetics that display chemical substituents to approximate the molecular dimensions and amphipathic features (hydrophobic and positively charged residues) of the antiangiogenic peptide anginex, which, like many antiangiogenic proteins, consists primarily of an antiparallel beta-sheet structure as the functional unit. Two of the topomimetics (0118 and 1097) were potent angiogenesis inhibitors in vitro, as determined by endothelial cell proliferation, migration, and chick embryo chorioallantoic membrane assays. Moreover, both compounds were highly effective at inhibiting tumor angiogenesis and growth in two mouse models (MA148 human ovarian carcinoma and B16 murine melanoma). Our results demonstrate the feasibility of designing nonpeptidic protein surface topomimetics as novel pharmaceutical agents for clinical intervention against cancer through angiostatic or other mechanisms.     

Comparison between in vitro radiosensitivity and in vivo radioresponse in murine tumor cell lines. II: In vivo radioresponse following fractionated treatment and in vitro/in vivo correlations

Survival in the low-dose region of in vitro radiation survival curves for human tumor cell lines may be correlated with the expected clinical radiocurability of tumors of similar histopathological type. The present investigation examined this hypothesis using a series of transplantable murine solid tumors. The in vivo radioresponse of the tumors following fractionated dose (10 fractions of 2 Gy given at 4 hr intervals) and single dose (20 Gy) radiation treatment was measured by growth delay and tumor cell survival assays. The measurements of tumor cell survival were initiated either immediately or 8 hr after the end of radiation treatment. There was no evidence for repair of potentially lethal damage in vivo in any of the tumors. The measurements of in vivo response were compared to parameters of in vitro radiation survival curves for the same tumor cell lines, which were measured concurrently. The tumor cell survival following 10 fractions of 2 Gy correlated best with the measured in vitro survival at 2 Gy, although good correlations were also observed with two parameters calculated from the in vitro data; the value of alpha from fitting the linear-quadratic (LQ) model and the mean inactivation dose (MID). Correlations were also observed between specific growth delay measured in vivo following 10 fractions of 2 Gy and these in vitro parameters. Despite the correlations observed, the measured survival values following 10 fractions of 2 Gy in vivo did not agree quantitatively with the theoretical values predicted from the in vitro survival data assuming equal effect for each fraction. This discrepancy indicates that other factors also contribute to the overall response of a tumor to fractionated irradiation. Nevertheless, these findings support the idea that intrinsic radiosensitivity plays a significant role in determining the overall response of a tumor to fractionated irradiation and provides strong support for the concept of testing the in vitro radiation sensitivity of biopsy specimens as a predictive assay of clinical radiocurability.     

Radiosensitizing effect of carbogen breathing during pulsed irradiation of the rat R1H tumor

The objective of the present study was to investigate the radiosensitizing effect of carbogen breathing during pulsed x-ray irradiation in an experimental tumor model. Rat R1H rhabdomyosarcoma tumors were irradiated with 36 Gy total dose in 1 Gy high dose rate pulses, either hourly repeated, or in an 'office hours' protocol with irradiation-free overnight intervals. With the hourly, pulsed irradiation scheme, tumor growth delay (TGD) was significantly increased from 24.4 ±0.7 days in air-breathing animals to 29.0 ±0.9 days in animals breathing carbogen during irradiation. With irradiation during office hours, the TGD was shortened, and carbogen was less effective. The data show that carbogen acts as a radiosensitizer when applied during pulsed irradiation. Translation of the experimental data to clinical practice indicates that hyperoxygenation of the tumor during pulsed dose rate (PDR) or high dose rate (HDR) brachytherapy might enhance the tumor response of patients.