Tumor-bearing Tissue Research Articles

Cutting Edge: Expression of TNFR2 Defines a Maximally Suppressive Subset of Mouse CD4+CD25+FoxP3+ T Regulatory Cells: Applicability to Tumor-Infiltrating T Regulatory Cells

TNFR2 is predominantly expressed by a subset of human and mouse CD4(+)CD25(+)FoxP3(+) T regulatory cells (Tregs). In this study, we characterized the phenotype and function of TNFR2(+) Tregs in peripheral lymphoid tissues of normal and tumor-bearing C57BL/6 mice. We found that TNFR2 was expressed on 30-40% of the Tregs of the peripheral activated/memory subset that were most highly suppressive. In contrast, TNFR2(-) Tregs exhibited the phenotype of naive cells and only had minimal suppressive activity. Although not typically considered to be Tregs, CD4(+)CD25(-)TNFR2(+) cells nevertheless possessed moderate suppressive activity. Strikingly, the suppressive activity of TNFR2(+) Tregs was considerably more potent than that of reportedly highly suppressive CD103(+) Tregs. In the Lewis lung carcinoma model, more highly suppressive TNFR2(+) Tregs accumulated intratumorally than in the periphery. Thus, TNFR2 identifies a unique subset of mouse Tregs with an activated/memory phenotype and maximal suppressive activity that may account for tumor-infiltrating lymphocyte-mediated immune evasion by tumors.

Innovations in image-guided radiotherapy

The limited ability to control for the location of a tumour compromises the accuracy with which radiation can be delivered to tumour-bearing tissue. The resultant requirement for larger treatment volumes to accommodate target uncertainty restricts the radiation dose because more surrounding normal tissue is exposed. With image-guided radiotherapy (IGRT) these volumes can be optimized and tumoricidal doses can be delivered, achieving maximal tumour control with minimal complications. Moreover, with the ability of high-precision dose delivery and real-time knowledge of the target volume location, IGRT has initiated the exploration of new indications for radiotherapy, some of which were previously considered infeasible.

Methods for image segmentation should be standardized and calibrated

Methods for image segmentation should be standardized and calibrated

Multi-modality imaging identifies key times for annexin V imaging as an early predictor of therapeutic outcome.

Radiolabeled annexin V may provide an early indication of the success or failure of anticancer therapy on a patient-by-patient basis as an in vivo marker of tumor cell killing. An important question that remains is when, after initiation of treatment, should annexin V imaging be performed. To address this issue, we obtained simultaneous in vivo measurements of tumor burden and uptake of radiolabeled annexin V in the syngeneic orthotopic murine BCL1 lymphoma model using in vivo bioluminescence imaging (BLI) and small animal single-photon emission computed tomography (SPECT). BCL1 cells labeled for fluorescence and bioluminescence assays (BCL1-gfp/luc) were injected into mice at a dose that leads to progressive disease within two to three weeks. Tumor response was followed by BLI and SPECT before and after treatment with a single dose of 10 mg/kg doxorubicin. Biodistribution analyses revealed a biphasic increase of annexin V uptake within the tumor-bearing tissues of mice. An early peak occurring before actual tumor cells loss was observed between 1 and 5 hr after treatment, and a second longer sustained rise from 9 to 24 hr after therapy, which heralds the onset of tumor cell loss as confirmed by BLI. Multimodality imaging revealed the temporal patterns of tumor cell loss and annexin V uptake revealing a better understanding of the timing of radiolabeled annexin V uptake for its development as a marker of therapeutic efficacy.

Multi-modality Imaging Identifies Key Times for Annexin V Imaging as an Early Predictor of Therapeutic Outcome

Radiolabeled annexin V may provide an early indication of the success or failure of anticancer therapy on a patient-by-patient basis as an in vivo marker of tumor cell killing. An important question that remains is when, after initiation of treatment, should annexin V imaging be performed. To address this issue, we obtained simultaneous in vivo measurements of tumor burden and uptake of radiolabeled annexin V in the syngeneic orthotopic murine BCL1 lymphoma model using in vivo bioluminescence imaging (BLI) and small animal single-photon emission computed tomography (SPECT). BCL1 cells labeled for fluorescence and bioluminescence assays (BCL1-gfp/luc) were injected into mice at a dose that leads to progressive disease within two to three weeks. Tumor response was followed by BLI and SPECT before and after treatment with a single dose of 10 mg/kg doxorubicin. Biodistribution analyses revealed a biphasic increase of annexin V uptake within the tumor-bearing tissues of mice. An early peak occurring before actual tumor cells loss was observed between 1 and 5 hr after treatment, and a second longer sustained rise from 9 to 24 hr after therapy, which heralds the onset of tumor cell loss as confirmed by BLI. Multimodality imaging revealed the temporal patterns of tumor cell loss and annexin V uptake revealing a better understanding of the timing of radiolabeled annexin V uptake for its development as a marker of therapeutic efficacy.

Fluorescence diagnosis: a novel method to guide radical inguinal lymph node dissection in penile cancer.

In penile cancer there is still a diagnostic dilemma between over treatment of lymph node-negative patients and the missing of occult metastases by watchful waiting. In the current study the value of fluorescence diagnosis during radical inguinal lymph node dissection was evaluated. Five patients with penile cancer were elected to undergo groin dissection. All patients received 5-aminolevulinic acid (5-ALA) orally before the operation for fluorescence diagnosis. Intraoperatively, fluorescence detection of the lymph nodes was performed by visual detection and spectroscopy. Two of the five patients had positive inguinal lymph nodes. Fluorescence in tumor-bearing tissue was detectable in the exposed lymph nodes. Protoporphyrin IX (PPIX) is accumulated in tumor-positive lymph nodes, making fluorescence diagnosis in penile cancer possible. More studies with higher patient numbers are necessary to evaluate optimal dosage and excitation conditions to detect tumor-bearing nodes in vivo.

Involvement of vascular endothelial growth factor receptor-3 in maintenance of integrity of endothelial cell lining during tumor angiogenesis

AbstractVascular endothelial growth factor (VEGF) plays a major role in tumor angiogenesis. VEGF-C, however, is thought to stimulate the growth of lymphatic vessels because an expression of its specific receptor, VEGF receptor-3 (VEGFR-3), was demonstrated to be restricted to lymphatic vessels. Here we demonstrate that the inactivation of VEGFR-3 by a novel blocking monoclonal antibody (mAb) suppresses tumor growth by inhibiting the neo-angiogenesis of tumor-bearing tissues. Although VEGFR-3 is not expressed in adult blood vessels, it is induced in vascular endothelial cells of the tumor-bearing tissues. Hence, VEGFR-3 is another receptor tyrosine kinase involved in tumor-induced angiogenesis. Micro-hemorrhage in the tumor-bearing tissue was the most conspicuous histologic finding specific to AFL4 mAb-treated mice. Scanning microscopy demonstrated disruptions of the endothelial lining of the postcapillary venule, probably the cause of micro-hemorrhage and the subsequent collapse of the proximal vessels. These findings suggest the involvement of VEGFR-3 in maintaining the integrity of the endothelial lining during angiogenesis. Moreover, our results suggest that the VEGF-C/VEGFR-3 pathway may serve another candidate target for cancer therapy.

Involvement of vascular endothelial growth factor receptor-3 in maintenance of integrity of endothelial cell lining during tumor angiogenesis

Vascular endothelial growth factor (VEGF) plays a major role in tumor angiogenesis. VEGF-C, however, is thought to stimulate the growth of lymphatic vessels because an expression of its specific receptor, VEGF receptor-3 (VEGFR-3), was demonstrated to be restricted to lymphatic vessels. Here we demonstrate that the inactivation of VEGFR-3 by a novel blocking monoclonal antibody (mAb) suppresses tumor growth by inhibiting the neo-angiogenesis of tumor-bearing tissues. Although VEGFR-3 is not expressed in adult blood vessels, it is induced in vascular endothelial cells of the tumor-bearing tissues. Hence, VEGFR-3 is another receptor tyrosine kinase involved in tumor-induced angiogenesis. Micro-hemorrhage in the tumor-bearing tissue was the most conspicuous histologic finding specific to AFL4 mAb-treated mice. Scanning microscopy demonstrated disruptions of the endothelial lining of the postcapillary venule, probably the cause of micro-hemorrhage and the subsequent collapse of the proximal vessels. These findings suggest the involvement of VEGFR-3 in maintaining the integrity of the endothelial lining during angiogenesis. Moreover, our results suggest that the VEGF-C/VEGFR-3 pathway may serve another candidate target for cancer therapy.

Physics study of microbeam radiation therapy with PSI-version of Monte Carlo code GEANT as a new computational tool.

Microbeam radiation therapy (MRT) is a currently experimental method of radiotherapy which is mediated by an array of parallel microbeams of synchrotron-wiggler-generated x-rays. Suitably selected, nominally supralethal doses of x-rays delivered to parallel microslices of tumor-bearing tissues in rats can be either palliative or curative while causing little or no serious damage to contiguous normal tissues. Although the pathogenesis of MRT-mediated tumor regression is not understood, as in all radiotherapy such understanding will be based ultimately on our understanding of the relationships among the following three factors: (1) microdosimetry, (2) damage to normal tissues, and (3) therapeutic efficacy. Although physical microdosimetry is feasible, published information on MRT microdosimetry to date is computational. This report describes Monte Carlo-based computational MRT microdosimetry using photon and/or electron scattering and photoionization cross-section data in the 1 eV through 100 GeV range distributed publicly by the U.S. Lawrence Livermore National Laboratory (LLNL) in the 1990s. These are compared with Monte Carlo-based microdosimetric computations using a code and physical data available in the 1980s. With the aim of using the PSI-version of GEANT Monte Carlo code for future macro- and micro/nano-dosimetric studies of Microbeam Radiation Therapy (MRT) a comparison of this code is made with the INHOM(EGS4) (version 1990), Dilmanian-CPE and Persliden-CPE Monte Carlo photon-electron codes (both version 1990) with which the absorbed dose distributions were calculated in 1990 and 1991 considering, (a) a single cylindrical microbeam, (b) multiple cylindrical microbeams in an orthogonal square bundle, and (c) multiple planar microbeams. It is shown that the PSI-version of GEANT can potentially deliver more accurate results (a) using presently the most advanced atomic data, and especially (b) employing "Single-collision" electron transport instead of only the "Condensed-history" electron transport as in code INHOM(EGS4). In contrast Dilmanian-CPE and Persliden-CPE codes deposit the electron energy locally instead of transporting it to the correct position.

Circulating vascular endothelial growth factor in patients with colorectal cancer.

The expression of vascular endothelial growth factor (VEGF), a glycoprotein that selectively promotes proliferation of endothelial cells, has been associated with cancer development. The aim of the present study was to determine whether serum levels of VEGF correlate with disease progression in patients with colorectal cancer. VEGF levels were measured by a highly sensitive enzyme-linked immunosorbent assay in sera from 67 patients with colorectal cancer, 14 patients with colorectal adenomas, and 72 healthy volunteers, and in tissue homogenates from 10 patients with colorectal cancer. Serum VEGF levels were significantly higher in patients with colorectal cancer than in patients with colorectal adenomas or in normal controls (p < 0.01). In patients with colorectal cancer, serum VEGF levels were significantly associated with Dukes stage (p < 0.01) and with carcinoembryonic antigen levels (r = 0.725, p < 0.001). Patients with hepatic and/or lymph node metastasis had higher serum VEGF levels than those without. Surgical resection of the colorectal tumor led to a decrease in serum VEGF levels whether or not metastasis was present (p < 0.05). The tumor-bearing tissue contained significantly more VEGF than normal-appearing mucosa (p < 0.05). VEGF is involved in the development of colorectal cancer. Measurement of VEGF in the serum may be a useful noninvasive clinical marker for evaluating the disease status.

Endothelial and epithelial expression of sialyl Lewis(x) and sialyl Lewis(a) in lesions of breast carcinoma.

Tumor cells can invade and generate metastasis via either lymphatics or blood vessels. When tumor cells are circulating in the blood, they must adhere to the vessel wall, which is lined by endothelium, before they can extravasate and form new metastases. Several families of adhesion molecules have been identified to play a role in the extravasation cascade. Selectins and their sialyl Lewis(x) and/or sialyl Lewis(a) (sLe(x) and sLe(a), respectively) containing ligands play an initiating role in this cascade; we have now analyzed their role in the generation of metastatic breast carcinoma lesions. We examined expression of endothelial E- and P-selectin, expression of epithelial and endothelial sLe(x) and sLe(a) normal tissues compared with primary and metastatic breast in carcinoma lesions within individual patients. While normal breast epithelial cells do not express sLe(x) or sLe(a), epithelial expression of these oligosaccharide epitopes was enhanced in primary breast carcinoma lesions. Furthermore, epithelial expression levels of sLe(x) and/or sLe(a) were even higher in most patients (9 of 12) who had metastatic compared with primary lesions. We show that endothelia in primary lesions express more sLe(x) than in normal tissue and that metastatic lesions express even higher amounts of sLe(x) compared with primary lesions. The expression of P- and E-selectin was also greatly enhanced in tumor-bearing tissue compared with normal tissue. Our data support the hypothesis that while they are circulating in the blood, sLe(x)- and/or sLe(a)-expressing carcinoma cells have a higher probability for extravasation at sites where the endothelium expresses E- and P-selectin and for generation of new metastases.

Cathepsin B in the growth of colorectal cancer: increased activity of cathepsin B in human colorectal cancer.

Cathepsin B, a thiol protease, is involved in cancer metastasis. To clarify the role of cathepsin B in tumor progression in human colorectal cancer, the relationship between its activity, immunohistochemical staining, and clinical tumor progression was investigated. Cathepsin B activity in adenocarcinomas was significantly elevated compared with that in the tumor-bearing tissue. Furthermore, the tumor/tumor-bearing tissue (T/Tb) ratio of the activity was significantly higher than that of colorectal adenoma. Immunohistochemical studies demonstrated intense staining in the cancerous tissue. With respect to the clinical stage of tumors, the activity tended to be higher in tumors that had invaded the serosa or subserosa than in those that invaded the proper muscle. The results suggest that cathepsin B participates in the progression of human colorectal cancer, and its increased expression is a sensitive marker of the differentiation between colorectal adenoma and adenocarcinoma.

Cathepsin B in the growth of colorectal cancer: suppressive effect of leupeptin on the growth of DMH-induced rat colon neoplasm.

Cathepsin B, a thiol protease, has been reported to be involved in cancer progression and metastasis. The suppressive effects of two kinds of protease inhibitors, leupeptin and dietary camostate (FOY-305), on tumorigenesis and progression in 1, 2-dimethylhydrazine (DMH)-induced rat colon neoplasm were examined in relation to tissue cathepsin B activity. Male Donryu rats were treated with leupeptin or FOY-305 during or after the administration of DMH. There were no significant differences in average tumor numbers among all DMH-treated groups. However, the percentage of small tumors was significantly higher in the group in which leupeptin was supplied during DMH administration. This trend was not recognized in the FOY-305-treated groups. The ratio of cathepsin B activity in the tumors to that in the tumor-bearing tissue (T/Tb) was significantly increased with increasing tumor size (P = 0.009). The cathepsin B activity levels in the tumor-bearing mucosa in the groups which received leupeptin or FOY-305 following DMH treatment were both significantly lower than that in the group which received neither protease inhibitor (P = 0.046 and P = 0.0067, respectively). The results obtained indicate that leupeptin may have suppressed tumor growth by lowering the tissue cathepsin B activity.

Anin VitroFlow Model to Study Streaming during Pelvic Intra-arterial Drug Infusions

Regional delivery of suitable drugs by intra-arterial infusion may offer a therapeutic advantage. High concentrations in the tumor are sought with reduced systemic toxicity. Adequate mixing of drug solutions with perfusing blood is essential to provide uniform distribution of drug to tumor-bearing tissue distal to the infusion site. Using a glass model of the iliofemoral and pelvic arteries, we have demonstrated that a streaming phenomenon occurs. Laminar "streamers" of slowly infused drug solution originate at the catheter tip and proceed nonuniformly into distal arterial branches. The intensity of streaming and the pattern of distribution are highly sensitive to catheter tip placement and quite unpredictable. The consequence of regional therapy under streaming conditions is severe maldistribution of drug in the infused tissues with potentially high levels delivered to normal tissues and simultaneous subtherapeutic levels delivered to tumor. Our in vitro model can be used to test appropriate infusion techniques that enhance mixing such as pulsed infusions and novel catheter designs.

A surgeon's valedictory.

PERSPECTIVES IN BIOLOGY AND MEDICINE Volume 37 ¦ Number 2 ¦ Winter 1994 A SURGEON'S VALEDICTORY SHERWIN B. NULAND* A year has passed since I walked out of an operating room for the last time. After a career of three decades in a large universitycommunity hospital, preceded by six years of training in general surgery , the time had come to pass the burden and the pleasure into younger hands. General surgeons love to operate; general surgeons (at least general surgeons of my generation) love to sit at a bedside, or some other quiet place, and puzzle out a complex problem in diagnosis and therapy; general surgeons love clinical conferences and rounds, where they can match wits with their most agile colleagues; general surgeons are among the most vigorous and outspoken participants in the hurly-burly of hospital politics, and they love the corridors of power. I was by no means an exception to any of those characterizations. I have been, in fact, the whole package writ large. And yet, I don't for a moment miss the surgical life that has brought me so much fulfillment since I first discovered it almost forty years ago. As so often happens over the course of a long career, the field that was such an endless source of gratification when it first beckoned has become something else. The something else nonetheless had until recently seemed so much the natural progression of the original that its very evolution continued to provide immense satisfaction. No matter the new discoveries and innovations in technique, the values and viewpoints ofthe specialty did not change in any basic way during most ofmy professional lifetime. The Weltanschauung with which general surgeons envisioned pathophysiology and treatment remained steady and certain. A little personal history is in order here. In 1953, I was a third-year medical student determined to pursue a career in internal medicine, when I was one day taken in hand by an imaginative surgical resident who introduced me to an unanticipated aesthetic in his specialty. The *Address: P. O. Box 6356, Hamden, Connecticut 06517.© 1994 by The University of Chicago. All rights reserved. 003 1-5982/94/3702-086 1$0 1 .00 Perspectives in Biology and Medicine, 37, 2 ¦ Winter 1994 159 secrets of disease and the body's wondrous skill at restoring itself, I was made to realize, are discoverable less by words than by the visual and tactile elements that exist within human curiosity. From this perspective, a surgeon's uniquely cultivated skills could be seen as a way to reveal and express the beauty to be found through his mind's engagement with sickness and healing. Tissue teaches more than text, pathophysiology more than the printed page. Touching and seeing open the most direct paths to the surgeon's mind. I soon came to view surgeons as expeditors of nature's response to disease. An inflamed organ is removed, an obstruction is bypassed, excessive hormone levels are reduced, a cancerous region is swept clean of tumor-bearing tissue; surgeons are agents of the process by which an offending force may be sufficiently held at bay to aid physiology in its natural tendency to restore health. Surgery is the distilled essence of W. H. Auden's perceptive précis of all medicine: "Healing," said the poet, "is not a science, but the intuitive art of wooing Nature." For the wooing to take place, it is necessary not only to make an accurate diagnosis, but actually to visualize in one's mind a pathological process in all its multicolored, palpable, tangible reality. To predict the image of the territory I would enter—this became the ultimate diagnostic aim, just as the correction of disharmony is the ultimate goal of the operation. To me, surgery was a form of artistry, and the surgeon the personification of the art of medicine. There was in this clinical epiphany the kind of exhilaration that Percy Shelley must have been feeling when at twenty-four, the same age at which I began my surgical internship, he wrote his "Hymn to Intellectual Beauty." The poem now took on a new meaning for me, and I even heard an authentic note in two...

Radiation-Related Wounds Of The Chest Wall

Irradiation-associated chest wall lesions pose a significant health hazard to the patient. The principles of management include (1) biopsy of any open wounds to rule out the recurrence or persistence of tumor, (2) aggressive debridement of all offending tissues, and (3) reconstruction with well-vascularized flap tissue. Numerous questions arise regarding the practical management of these patients. The controversies that have arisen during our management of more than 100 of these patients have been discussed. It is appropriate to perform reconstruction following nonhealing of a superficial ulcer or immediately following the excision of a full-thickness chest wall defect. Hyperbaric oxygen can serve as a useful adjunct. It is rarely necessary to use a prosthetic material for the purpose of chest wall stabilization during the reconstruction of full-thickness defects. Paradoxic chest wall movement in the postoperative period does not significantly affect pulmonary function tests and is generally a transient problem. Subtotal excisions are frequently necessary. As long as all of the necrotic or tumor-bearing tissue has been fully removed, these wounds can be expected to heal in most instances by placing vascularized tissue into the defect. Operative sites in previously irradiated chest wall tissue can be expected to heal if proper and careful surgical technique is employed. Nevertheless, there is a risk of wound breakdown following any surgery in irradiated tissue. Finally, we believe it is appropriate to proceed with aesthetic recontouring of chest wall deformities associated with irradiation exposure.

Analysis and pharmacokinetics of N-l-leucyldoxorubucin and metabolites in tissues of tumor-bearing BALB/c mice.

Leucyldoxorubicin (Leu-Dox) was developed as a prodrug of doxorubicin (Dox) with the aim of lowering the cardiotoxicity and improving the therapeutic index produced by Dox. To support the preclinical findings on its antitumor activity and cardiotoxicity, concentrations of Leu-Dox and its metabolites were determined in plasma, heart, and tumor after the administration of Leu-Dox to tumor-bearing mice. A liquid-liquid extraction procedure employing a chloroform/2-propanol/dimethylsulfoxide (DMSO) mixture was developed. By means of high-performance liquid chromatography (HPLC) with fluorescence detection, Leu-Dox and six of its metabolites could be assayed in the tissues with high sensitivity. Detection limits ranged from 0.01 nmol/g tissue for the aglycons to 0.06 nmol/g for Dox. Recoveries were in the range of 82%-110%, and calibration curves were linear over the concentration range tested (0.1-10 nmol/g tissue, r > or = 0.998). Concentration versus time curves were constructed for plasma, heart, and tumor over the first 72 h, and areas under the curves (AUCs) for the first 48 h were determined by the trapezoidal rule. Dox was rapidly formed from Leu-Dox, reaching peak levels in plasma within 5 min and in tissues within 1 h after i.v. administration of Leu-Dox (12 mg/kg). The elimination of Leu-Dox was also fast as illustrated by final half-lives of 1.1, 0.8, and 0.9 h in the plasma, heart, and tumor, respectively. For Dox, the final half-lives were 16.7 h in plasma, 15.3 h in heart tissues, and 27.4 h in tumor tissues. AUC values determined for Leu-Dox and Dox were 221 and 51 nmol ml-1 min, 443 and 4,262 nmol g-1 min, and 153 and 1,466 nmol g-1 min in the plasma, heart, and tumor, respectively. Comparison of these values with those obtained after an equimolar dose of Dox indicated 26%, 30%, and 16% of Leu-Dox appeared as Dox in the plasma, heart, and tumor, respectively. Thus, not only is the plasma compartment not representative for calculations of the conversion of Leu-Dox into Dox in tissue, but differences in its appearance also exist between the tissue compartments. The AUC values found for Dox in the heart may explain the reduced cardiotoxicity elicited by Leu-Dox as compared with Dox; however, the values obtained for Dox in the insensitive murine colon tumor cannot explain the enhanced antitumor activity exerted by Leu-Dox in the sensitive human tumor xenografts in nude mice.

Impact of radioimmunoguided surgery®

Radioimmunoguided surgery (RIGS) is a technique employed to locate tumor deposits with the aid of intravenously injected, tumor-specific, radiolabeled monoclonal antibodies and a small gamma detecting device. The gamma detecting probe (GDP) is a small, portable unit which has the capacity to be used intraoperatively to survey the entire peritoneal surface for increased radioactivity indicative of targeted tumor tissue during abdominal exploration for colorectal cancer. Trials in humans have demonstrated the ability of this system to locate clinically nonpalpable tumor deposits in patients undergoing carcinoembryonic antigen second-look laparotomies. This feature may be of value in improving the definition of tumor location and extent as well as allowing a more thorough resection of tumor-bearing tissue to be performed and hopefully improving overall patient survival.

The Effect of Tumor Burden on Ornithine Decarboxylase Activity in Mice

Polyamines are essential for cell growth of normal and neoplastic tissue, alpha-Difluoromethylornithine (DFMO) is a known irreversible inhibitor or ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis. The purpose of this study was to examine the effects of tumor burden on ODC in tissues of tumor-bearing compared with tumor-free mice. Twenty-eight male Balb/c mice were divided into four groups of 7 each. Groups 1 and 2 were inoculated subcutaneously with 10 x 10(6) MC-26 mouse colon adenocarcinoma cells. Groups 3 and 4 were kept as tumor-free controls. Ten days after inoculation, groups 2 and 4 were injected with DFMO (200 mg/kg) intraperitoneally (IP) while Groups 1 and 3 received saline. Two hours after the injection of DFMO the animals were sacrificed. The tumor, pancreas, kidney, and liver were excised and analyzed for ODC activity. DFMO caused a significant reduction (compared with controls that did not receive DFMO) in the ODC activity of tumors; however, ODC activity of the kidney, pancreas, and liver of tumor-bearing mice was not affected. Additionally, the basal ODC activity in the kidney, liver, and pancreas of tumor-bearing mice was significantly lower compared with tumor-free controls. DFMO lowered ODC activity in the kidney, pancreas, and liver of tumor-free mice. These results suggest that the presence of MC-26 tumor causes systemic effects that alter ODC activity and the response to a known inhibitor of ODC.

Inhibitory effect of selenium on hamster pancreatic cancer induction by n′‐nitrosobis(2‐oxopropyl)amine

The effect of selenium intake on the development of pancreatic cancer was investigated in female Syrian golden hamsters. Four-week-old hamsters were divided into 2 groups according to the selenium level in their drinking water and were fed a purified diet containing less than 0.05 ppm selenium. Starting 4 weeks later, groups received 10 s.c. injections at weekly intervals of N'-nitrosobis(2-oxopropyl)amine (BOP) dissolved in saline, while controls received saline alone. When the animals were killed 18 weeks after the last injection, palpable tumors were less frequent in the high-selenium group than in animals receiving low-selenium supplement, the numbers of histologically diagnosed cancerous lesions also being significantly reduced by high selenium intake. The selenium level and glutathione peroxidase activity in serum and pancreas were significantly greater in the high-selenium group. Moreover, selenium levels and glutathione peroxidase activity were both significantly higher in tumor-bearing tissue. The results suggest that glutathione peroxidase is involved as an intermediate factor in prevention of carcinogenesis by selenium.