Normal Tissue Protection Research Articles

Thermal Sensitivity and Thermotolerance in Normal Porcine Tissues

We have previously presented a histopathological grading scheme for thermal damage in normal porcine adipose and skeletal muscle tissues. Here we have used this scheme to assess the heat sensitivity of these tissues, and evaluate the protective benefit of thermotolerance as induced by a prior thermal exposure. Tissues were exposed to temperatures ranging from 40-50 degrees for 30 min. Half of all sites also received a thermal exposure of 41.0-43.0 degrees 4 hr earlier. Biopsies for histological evaluation were obtained at 18 to 24 hr (acute) and at 28 to 31 days following treatment. Only mild acute injury was seen in the early samples, following either single or double heat exposures, at all temperature levels. Minimal chronic damage was also seen in the late samples following single exposures of 45 degrees or less. Higher single exposures caused important chronic lesions, the severity of which was dose dependent. Regions that had received the earlier conditioning thermal exposure showed a significant protection against the subsequent thermal exposure. In such regions, mean (chronic) pathology scores were reduced by 76 to 86% over the temperature range 45-48 degrees. The degree of acute damage failed to predict the degree of chronic damage. Overall, induction of thermotolerance provided an advantage of 2 degrees or more in normal tissue protection.

Phase I clinical trials of WR-2721 with alkylating agent chemotherapy

WR-2721 is an organic thiophosphate which in the animal model provides selective protection of normal tissues against the toxicity of radiation and alkylating agent chemotherapy. Phase I trials of WR-2721 in man have been initiated to establish the dose modification factors for this agent when used in combination with escalating doses of alkylating agents beyond the level currently tolerated, and to determine whether protection of normal tissues and tumors occurs. Three Phase I trials are in progress. Initially, we used a fixed 450 mg/M 2 dose of WR-2721 prior to escalating doses of either cyclophosphamide (CYC) or cis-platinum (PL) as single agents. More recently, the current maximum tolerated dose of WR-2721(740 mg/M 2) was administered prior to PL and to nitrogen mustard (HN 2). Ten patients received 19 courses of CYC after 450 mg/M 2 of WR-2721. At the 1800 mg/M 2 LV. dose level of CYC, moderate leukopenia was noted with a median WBC nadir of 1800/mm 3 on day 10. Twenty-two courses of PL were administered to 13, patients after 450–740 mg/M 2 of WR-2721. Hydration was used, but no mannitol diuresis was employed. Transient nephrotoxicity was noted in five courses at PL doses between 80–120 mg/M 2. Mild to moderate leukopenia has been noted with HN 2 at 10–16 mg/M 2 following WR-2721 (450–750 mg/M 2). Objective anti-tumor responses have been observed. These preliminary results suggest that WR-2721 may provide normal tissue protection when administered prior to cyclophosphamide or nitrogen mustard, although the level of protection is not yet of clinical benefit. However, using a 450–740 mg/M 2 dose of WR-2721 did not provide protection against platinum-induced nephrotoxicity. WR-2721 does not appear to protect against the anti-tumor activity of alkylating agents (objective tumor responses were noted), nor does there appear to be increased acute toxicity when it is combined with alkylating agent chemotherapy.

Influence of WR 2721 on the efficacy of radiotherapy and chemotherapy of murine tumors

The effect of WR 2721 on the response of tumors to radiation, antineoplastic alkylating drugs, and DNA binding agents was evaluated and compared to the degree of normal tissue protection provided by WR 2721 against these agents. WR 2721 administered to mice bearing P388 leukemia or Lewis lung carcinoma was found to reduce the radiosensitivity of the leukemia and lung tumor by dose modifying factors of 1.4 and 1.3, respectively. WR 2721 protected bone marrow, intestine, and skin from radiation by factors of 1.9, 1.5, and 1.8. WR 2721 protected mice from the lethality of cyclophosphamide by a factor of only 1.2 wheras protection from melphalan toxicity was more dramatic with a dose modifying factor of 1.6. In chemotherapy studies of established M5076 ovarian tumor, the combination of WR 2721 plus cyclophosphamide was equivalent in activity to cyclophosphamide alone. WR 2721 did not modify the antitumor activity of melphalan in early Lewis lung carcinoma but did decrease the antileukemic effects of this agent by a factor of 2.6 indicating tumor protection greater than host protection in the leukemia. The antitumor activity of the DNA binding agents etoposide (VP16–213) and mitoxantrone against systemic P388 leukemia was not diminished by WR 2721, while a substantial increase in host toxicity was noted for the combinations. The protective effects of WR 2721 against radiation and drug damage were, therefore, not entirely selective for normal tissues. In some cases the degree of tumor protection can be similar to, or greater than, normal tissue protection.

Protection of Normal Tissue against Late Radiation Injury by WR-2721

The ability of WR-2721 to protect against late radiation damage has been studied in skin, muscle, and vascular tissues of rats. Animals treated with and without WR-2721 received irradiation to the left hind limb; representative groups were killed at intervals ranging from 72 h to 6 months. Comparison of all drug-treated and non-drug-treated animals showed significant protection (P = less than or equal to 0.05). The time pattern of injury in non-drug-treated rats was biphasic, with significant damage occurring at 72 h and 1 week, returning to normal between 1 and 3 months, but showing significant late damage at 6 months (P = less than or equal to 0.001). Again, this injury pattern did not appear in WR-2721-treated rats. Thus the ability of WR-2721 to protect against acute and chronic radiation injury in vessels, skin, and muscle indicates that an increased therapeutic gain can be expected when this drug is used in clinical radiation therapy.

Chemoradioprotection of the Rat Parotid Gland by Combined Use of WR-2721 and Ro-07-0582

The radioprotection of the rat parotid gland by WR-2721 alone (DMF, 2.4) was compared to the protection afforded when WR-2721 was given in combination with the hypoxic cell radiosensitizer Ro-07-0582 (DMF, 2.6). It was concluded that the radiosensitizer of malignant tumor cells Ro-07-0582 was compatible with and did not reduce the protection of normal tissue afforded by WR-2721.

Enhancement of anti-cancer activity of cytotoxic chemotherapy with protection of normal tissues by inhibition of P.G. synthesis

Enhancement of anti-cancer activity of cytotoxic chemotherapy with protection of normal tissues by inhibition of P.G. synthesis

The Selective Protection of Normal Tissues by Irradiation of Tumor-Bearing Mice in Hypoxic Hypoxia

YARMONENKO, S. P., WAINSON, A. A., BEREZNOVA, L. I., KRIMKER, V. M., OVAKIMOV, V. G., PETROSIAN, E. P., AND SHMAKOVA, N. L. The Selective Protection of Normal Tissues by Irradiation of Tumor-Bearing Mice in Hypoxic Hypoxia. Radiat. Res. 67, 447458 (1976). The possibility of selective protection of normal tissues was demonstrated when mice with solid tumors were irradiated in an atmosphere of 95% N2 and 5% 02. Irradiation of animals in this gas mixture increased their survival with a dose-modifying factor (DMF) = 2.5, decreased the number of cells with chromosomal aberration in bone marrow (DMF, 2) and the degree of hair follicle damage (DMF, 1.6). The protective effect of hypoxia drastically diminished 40 min after its application. Local irradiation of allogeneic tumors under hypoxic conditions, on the other hand, resulted in an increased rate of their regression in comparison with irradiation in air. The mechanism of the observed phenomenon is under investigation.

Protection of normal tissues by WR2721 during fractionated irradiation

The radioprotective effect of S-2-(3-aminopropylamino)ethyl phosphorothioate (WR2721) was studied in two normal mouse tissues-skin and small intestine—that were given single and fractionated doses of 137Cs radiation. A total of two-thirds of the toxic LD 50 of WR2721 could be given before single-dose irradiation. However, toxicity increased when the same drug dose was given in two or more fractions before split-dose irradiation: less than one-half of the single drug dose could he administered safely. In the skin, WR2721 was slightly less protective with fractionated irradiation (DMF = 1.3–1.5) than with single-dose irradiation (DMF = 1.5–1.7). The DMF decreased with increased radiation dose in both cases. In the small intestine, WR2721 protection was essentially the same with single-dose irradiation (DMF = 1.6) and fractionated doses (DMF = 1.7). This degree of radioprotection in skin and intestine, in spite of a greatly reduced drug concentration, supports the possibility of clinical use.

Embolization of Dog Prostates With Yttrium-90 Microspheres

Experiments exploring means for the protection of adjacent normal tissue while delivering a destructive dose of radiation to malignant tissue were conducted. By injection of radioactive ceramic spheres or particles, too large to pass through capillaries or arteriovenous shunts, relatively high doses of radiation can be distributed homogeneously to a circumscribed area. Attempts were made to determine the uniformity of distribution and the radiation effect of varying doses of spheres injected into the arterial supply of the dog prostate. Nonradioactive and radioactive ceramic microspheres of 60 mu dia were used since this size exceeds the diameter of capillaries and arteriovenous shunts. Yttrium-90 microspheres of varying radioactivity were used. Doses injected into right and left hypogastric arteries varied from 0.69 to 28.4 mc/side (92-1260 mc/ g prostate). Homogeneous distribution of radioactivity within the prostate was demonstrated by autoradiography. Distribution to some other organs (rectum, penis, and bladder) occurred because arterial supply to these structures was not isolated and occluded. The amount of radioactivity found in the lungs suggested more venous drainage in some cases than seemed apparent, and because of the infarctions of pelvic organs may have leaked radioactive spheres into the venous circuit. In 6 of the 8 dogs whichmore » died prematurely (2 to 7 days after surgery) obvious infarction of the prostate and in some other pelvic structures had occurred. That the radioactivity contributed to the infarction is suggested by the results in the dogs which received large doses of radioactivity (18.9 and 28.4 mc per side) in minimal amounts of spheres (100to 150 mg per side). The intensely concentrated radioactivity within the arteriolar lumens may have caused vasculitis and subsequent thrombosis. Although homogeneous destruction of the prostate gland occurred, the effect of a given dose ranged unpredictably through three groups: no apparent effect at all, destruction of the prostate, and early death with infarction of the prostate and other pelvic organs. It was concluded that with the present technique the range between the dose of radioactivity which caused no obvious response and the dose which is related to acute death is too narrow to allow reasonably predictable results, but that further refinement of technique might increase control over tissue destruction.« less

Radical preoperative roentgen therapy in primarily inoperable advanced cancers of the head and neck.

The misconception of the prohibitive risk of major surgery in heavily irradiated tissues is still prevalent in the minds of many surgeons and even of some radiologists. The most significant progress in radiation therapy during the last decade or two consists perhaps in our ability to introduce high cancerocidal doses with preservation of the vasculoconnective tissues by the judicious use of two modalities: longer protraction and radiation of shorter wave lengths. Baclesse (1) has recently reviewed some 2,000 epitheliomas treated between 1919 and 1950 with medium-volt roentgen therapy protracted between two and twelve weeks. By using this modality alone, without the advantage of higher voltages, he could increase the differential between tumor vulnerability and that of normal structures sufficiently to bring some otherwise incurable advanced carcinomas within the realm of curative radiation therapy. He also emphasized that, because of the better protection of normal tissues, the scope of preoperative irrad...

The effect of combined irradiation and chemotherapy on cancer growth with special reference to studies with folic acid analogues.

During the past four years we have been investigating the effects of chemicals on the radiation sensitivity of various biological systems. Particular emphasis has been given to the study of combined chemical and radiation therapy in the treatment of cancer. Chemical compounds which have been used include various porphyrins, folic acid analogues, sulfhydryl compounds, cortisone, sodium cyanide, and di-chlorovinyl-cysteine (1–4). Of these, the folic acid analogues have received special attention (5, 6) and are the subject of this report. By combining chemical and radiation therapy it may be possible to increase “therapeutic ratio,” which has been defined as the ratio of the radiosensitivity of tumor tissue relative to surrounding normal tissue (7). If the therapeutic ratio can be increased by chemical means, it would be possible to deliver a cancericidal dose of radiation with less damage to normal tissue. This may be accomplished either by sensitizing tumors to the effects of x-rays or by preferential protection of normal tissues. One reason for expecting synergistic action of certain chemicals and radiation in the treatment of malignant tumors is evidence that alternate metabolic pathways exist in cells, so that blocking one path by administration of a particular chemical or by radiation therapy may not produce the desired response. However, if both a major pathway and its alternates were blocked, a specific result might be achieved, such as the inhibition of nucleic acid synthesis in tumors. Folic acid is apparently the immediate precursor of folinic acid, which is considered to be the active form of the vitamin in most animals. Although the metabolic role of this vitamin is not completely understood, there is evidence that its functional forms are intimately associated with processes involving methylation, such as are required for synthesis of purines and pyrimidines. Animals deficient in folic acid and folinic acid exhibit a decreased capacity to utilize carbon dioxide, formate, and glycine for nucleic acid synthesis. Since the development of the first folic acid antagonist by the Lederle group in 1947 (8), for use by Farber and his associates in the clinical investigation of acute leukemia in childhood (9), the literature on this subject has become voluminous. Higgins and Woods (10) reported that aminopterin restricted the growth of transplanted mammary tumors in C3H mice during the period of administration. The effects of either aminopterin or 6-mercaptopurine combined with radiation in the treatment of cancer have been described by Thomas (11), who reported dramatic improvement in a patient receiving this combined therapy. Limited trials on tumors in mice, however, were discouraging because of the high mortality among treated animals. Several investigators (12, 13) have demonstrated that aminopterin inhibits the growth of sarcoma 180 in mice. Taylor and Carmichael (14) have shown that this analogue causes preferential inhibition of mouse mammary tumor in embryonated eggs.