In vivo radioprotective effect of Moringa oleifera leaves.

Radioprotective property of Moringa oleifera leaves was investigated in healthy adult Swiss albino mice. Animals were injected (ip) with 150 mg/kg body weight of 50% methanolic extract (ME) of M. oleifera leaves, as a single dose, or in 5 daily fractions of 30 mg/kg each, and exposed to whole body gamma irradiation (RT, 4 Gy) 1 hr later. Five animals from each group were sacrificed at 1, 2 and 7 days after treatment. Bone marrow protection was studied by scoring aberrations in metaphase chromosomes and micronucleus induction in polychromatic erythrocytes and normochromatic erythrocytes. Pretreatment with a single dose of 150 mg/kg ME significantly reduced the percent aberrant cells to 2/3rd that of RT alone group on day 1 and brought the values to normal range by day 7 post-irradiation. A similar effect was also seen for the micronucleated cells. Fractionated administration of ME (30 mg/kg x 5) gave a higher protection than that given by the same dose administered as a single treatment. ME also inhibited the Fenton reaction-generated free radical activity in vitro in a concentration dependent manner. These results demonstrate that pretreatment with the methanolic leaf extract of M. oleifera confers significant radiation protection to the bone marrow chromosomes in mice and this may lead to the higher 30 day survival after lethal whole body irradiation.

Modulation of glutathione and antioxidant enzymes by Ocimum sanctum and its role in protection against radiation injury.

Aqueous extract (OE) of the leaves of Ocimum sanctum, the Indian holy basil, has been found to protect mouse against radiation lethality and chromosome damage and to possess significant antioxidant activity in vitro. Therefore a study was conducted to see if OE protects against radiation induced lipid peroxidation in liver and to determine the role, if any, of the inherent antioxidant system in radioprotection by OE. Adult Swiss mice were injected intraperitoneally (i.p.) with 10 mg/kg of OE for 5 consecutive days and exposed to 4.5 Gy of gamma radiation 30 min after the last injection. Glutathione (GSH) and the antioxidant enzymes glutathione transferase (GST), reductase (GSRx), peroxidase (GSPx) and superoxide dismutase (SOD), as well as lipid peroxide (LPx) activity were estimated in the liver at 15 min, 30 min, 1, 2, 4 and 8 hr post-treatment. LPx was also studied after treatment with a single dose of 50 mg/kg of OE with/without irradiation. OE itself increased the GSH and enzymes significantly above normal levels whereas radiation significantly reduced all the values. The maximum decline was at 30-60 min for GSH and related enzymes and at 2 hr for SOD. Pretreatment with the extract checked the radiation induced depletion of GSH and all the enzymes and maintained their levels within or above the control range. Radiation significantly increased the lipid peroxidation rate, reaching a maximum value at 2 hr after exposure (approximately 3.5 times that of control). OE pretreatment significantly (P < 0.0001) reduced the lipid peroxidation and accelerated recovery to normal levels. The results indicate that Ocimum extract protects against radiation induced lipid peroxidation and that GSH and the antioxidant enzymes appear to have an important role in the protection.

Effect of plumbagin on the radiation induced cytogenetic and cell cycle changes in mouse Ehrlich ascites carcinoma in vivo.

The effect of plumbagin, a naphthoquinone from the roots of the Indian medicinal plant Plumbago rosea, and Cobalt-60 gamma radiation was studied on Ehrlich ascites carcinoma in vivo, taking cytogenetic damage and cell cycle changes as experimental endpoints. Plumbagin (5 mg/kg body wt, P1) administered intraperitoneally produced a significant increase in the percentage of S-phase as well as G2-M cells with a corresponding decrease in the G1 phase at different post-treatment times. Radiation (7.5 Gy, RT) alone produced the classical G2 block at 1 hr, which persisted with a continuous increase throughout the post-treatment observation period. The combination treatment produced a similar effect as that of RT on G2-M cells, but its effect on the G1 phase was more pronounced than the latter. While P1 treatment produced a small increase in the percentage of labeled S-phase cells, combination treatment significantly reduced the labeled S-phase cells with a corresponding increase in the unlabeled fraction. Drug or radiation alone significantly increased micronuclei induction at various post-treatment times and the combination of the two further enhanced this effect additively. The mechanism of interaction of P1 with radiation in bringing about this effect is not clear.

A comparative study of radioprotection by Ocimum flavonoids and synthetic aminothiol protectors in the mouse.

The radioprotective effects of two flavonoids, orientin (Ot) and vicenin (Vc), obtained from the leaves of Ocimum sanctum, and the synthetic compounds WR-2721 and MPG (2-mercaptopropionyl glycine) have been compared by examining chromosome aberration in cells of bone marrow in irradiated mice. Healthy adult Swiss mice were injected intraperitoneally (i.p.) with 50 micrograms kg-1 body weight of Ot or Vc; 20 mg kg-1 of MPG; 150 mg kg-1 of WR-2721 or double distilled water (DDW). They were exposed to whole body irradiation of 2.0 Gy gamma radiation 30 min later. After 24 h, chromosomal aberrations were studied in the bone marrow of the femur by routine metaphase preparation after colchicine treatment. Radiation (2 Gy) increased the number of aberrant cells from less than 1% in controls to almost 20%. Pre-treatment with all the protective compounds resulted in a significant reduction in the percentage of aberrant metaphases as well as in the different types of aberration scored. Vc produced the maximum reduction in percent aberrant cells while MPG was the least effective; Ot and WR-2721 showed an almost similar effect. However, WR-2721 was the most effective against reduction of complex an almost similar effect. However, WR-2721 was the most effective against reduction of complex aberrations, followed by Vc. Neither flavonoids had any systemic toxicity, even at 200 mg kg-1 body weight. Considering the low dose needed for protection and the high margin between the effective and toxic doses, the ocimum flavonoids may be promising for human radiation protection.

Enhancement of bone marrow radioprotection and reduction of WR-2721 toxicity by Ocimum sanctum.

The radioprotective effect of the leaf extract of Ocimum sanctum (OE) in combination with WR-2721 (WR) was investigated on mouse bone marrow. Adult Swiss mice were injected intraperitoneally (i.p.) with OE (10 mg/kg on 5 consecutive days), or 100-400 mg/kg WR (single dose) or combination of the two or double-distilled water (DDW) and whole-body exposed to 4.5 Gy gamma-irradiation (RT). Metaphase plates were prepared from femur bone marrow on days 1, 2, 7 and 14 post-treatment and chromosomal aberrations were scored. The maximum number of aberrant cells was observed at 24 h after irradiation in all the groups. However, pretreatment with OE or WR individually resulted in a significant decrease in aberrant cells as well as different types of aberrations. The combination of the two further enhanced this effect; resulting in a 2-fold increase in the protection factor (PF = 6.68) compared to 400 mg/kg WR alone. The percent aberrant cells decreased linear-quadratically with WR dose when given individually, while in the OE + WR pretreatment animals the values showed a linear dose response. Combination of OE with WR doses above 200 mg/kg completely eliminated rings, polyploidy and pulverization of chromosomes. Percent aberrant cells decreased with time in all groups, though the values remained higher than normal even on day 14 in the RT alone as well as those treated with single agent + RT. WR doses above 200 mg/kg before RT resulted in significantly higher frequency of aberrant cells compared to RT and OE + RT groups on day 14, suggesting delayed WR toxicity; but combination of OE with WR brought down these values to normal level, indicating that OE combination, in addition to enhancing WR protection, may also act as a detoxifier. The protective effect of OE and WR is also reflected in the enhancement of bone marrow CFU survival. Both OE and WR possessed significant free radical scavenging activity in vitro. The combination of the two further enhanced this effect, suggesting that the enhanced free radical scavenging activity by combining the two protectors results in the higher bone marrow cell protection. The significant elevation in chromosome protection obtained by combining OE with WR, with reduction in the latter's toxicity at higher doses, suggests that the combination may have promise for radioprotection in humans.

Modification of bone marrow radiosensensitivity by medicinal plant extracts.

Withaferin A (WA), a steroidal lactone, and Plumbagin (Pl), a naphthoquinone, from the roots of Withania somnifera and Plumbago rosea, respectively, have been shown to possess growth inhibitory and radiosensitizing effects on experimental mouse tumours. An aqueous extract of the leaves of Ocimum sanctum (OE) was found to protect mice against radiation lethality. Therefore, the radiomodifying effects of the above plant products on the bone marrow of the adult Swiss mouse was studied. Single doses of WA (30 mg kg-1) or Pl (5 mg kg-1) were injected intraperitoneally (ip) and OE (10 mg kg-1) was injected ip once daily for five consecutive days. Administration of extracts was followed by 2 Gy whole body gamma irradiation. Bone marrow stem cell survival was studied by an exogenous spleen colony unit (CFU-S) assay. The effects of WA and Pl were compared with that of cyclophosphamide (CP) and radioprotection by OE was compared with that of WR-2721 (WR). Radiation reduced the CFU-S to less than 50% of normal. WA, CP and Pl significantly enhanced this effect and reduced the CFU-S to almost the same extent (to < 20% of normal), although individually WA and Pl were less cytotoxic than CP. These results indicate that radiosensitization by WA and Pl is not tumour specific. OE significantly increased CFU-S compared with radiotherapy (RT) alone. OE+RT gave a higher stem cell survival (p < 0.05) than that produced by WR+RT. While WR alone had a toxic effect, OE treatment showed no such effect, suggesting that the latter may have an advantage over WR in clinical application.

Protection against radiation-induced chromosome damage in mouse bone marrow by Ocimum sanctum.

The radioprotective effect of the leaf extract of Ocimum sanctum (Ocimum extract, OE) was investigated by taking chromosome aberrations as the end point. Adult Swiss mice were whole-body exposed to 1-6 Gy of gamma radiation with/without pretreatment with 10 mg/kg b.wt. of OE intraperitoneally for 5 consecutive days. Radiation was given 30 min after the last injection. Metaphase plates were prepared from femur marrow on days 1, 2, 7 and 14 post-treatment and the frequency of aberrant cells and individual aberrations were scored. OE alone did not have any significant effect on the chromosomes. Maximum percent of aberrant cells was observed at 24 h in all the exposed groups. The percent aberrant cells showed a linear quadratic increase with radiation dose, in both radiation alone (RT) and OE + RT-treated groups. Exchange (dicentrics and rings) and multiple (pulverized and severely damaged cells) aberrations also showed a similar response. However, the slopes of OE + RT was significantly shallower than RT groups (p < 0.05). A dose-modifying factor of 2.63 was obtained taking percent aberrant cells for 2 Gy as the base. Progressive decline in the percent aberrant cells as well as the number of aberrations with time after irradiation was observed in both RT and OE + RT groups. OE treatment resulted in a faster recovery compared to RT alone group. At doses below 3 Gy, OE pretreatment almost completely eliminated the exchange aberrations from the cell population by day 2. Studies on a chemical system demonstrated that OE significantly reduced the generation of hydroxyl radical; a lower dose of OE (1 mg/ml) was more effective than 5 mg/ml and this effect was more pronounced than that produced by DMSO. These results show that OE affords in vivo protection against radiation-induced cytogenetic damage. Free radical scavenging is a likely mechanism of OE protection.

Withania somnifera Dunal (Ashwagandha): potential plant source of a promising drug for cancer chemotherapy and radiosensitization.

Study of antitumor and radiosensitizing properties of W. somnifera (Ashwagandha), a well known medicinal plant, have yielded encouraging results. The alcoholic extract of the dried roots of the plant as well as the active component withaferin A isolated from the extract showed significant antitumor and radiosensitizing effects in experimental tumors in vivo, without any noticeable systemic toxicity. Withaferin A gave a sensitizer enhancement ratio of 1.5 for in vitro cell killing of V79 Chinese hamster cells at a non toxic concentration of approximately 2 microM. The mechanism of action of this compound is not known. The studies so far indicate that W. somnifera could prove to be a good natural source of a potent and relatively safe radiosensitizer/chemotherapeutic agent. Further studies are needed to explore the clinical potential of this plant for cancer therapy.

Multimodality treatment using AK-2123, hydralazine, radiation & hyperthermia on a transplantable mouse tumour.

The in vivo response of a transplantable mouse tumour, Sarcoma 180 to AK-2123 (AK), local irradiation (RT) and local hyperthermia, as influenced by a vasoactive drug, hydralazine (HDZ), was assessed on the basis of tumour cure (complete response CR), volume doubling time (VDT), regrowth delay (RD) and animal survival up to 120 days. A single ip injection of 200 mg/kg b.wt. AK produced more than 15 per cent CR. Combination of any two agents resulted in a better response than the single agent treatments. AK in combination with 43 degrees C, 30 min (HT) was more effective than HT combination with 10 Gy. The presence of 5 mg/kg HDZ, injected immediately after 5 Gy, in combination with AK increased the therapeutic effect over that produced by AK+10Gy. Combination of all the three agents (AK+10Gy+HT) produced 100 per cent CR and prolonged disease free animal survival. A similar response could be obtained by the presence of HDZ with a lower radiation dose of 5 Gy in combination with AK and HT (AK+5Gy+HDZ+HT). This multimodality treatment offers the possibility of further reduction in the doses of individual agents, and in the possible side effects on normal tissues without compromising the tumour cure effect.

Response of mouse sarcoma-180 to cis-platin in combination with radiation & hyperthermia.

The in vivo response of a transplantable mouse tumour, sarcoma-180, to cis-platin (cDDP, 1.0, 2.5 or 5.0 mg/kg b.wt), local hyperthermia (HT, 42 degrees C, 30' or 60' and 43 degrees C, 30') and irradiation (RT, 10 Gy) was assessed on the basis of tumour cure (complete response, CR), volume doubling time (VDT) and regrowth delay (RD) as well as animal survival up to 120 days. Each agent was given as a single modality or in different combination regimens. A single injection of cDDP produced a dose dependent increase in all the parameters. Of all the single treatments, HT at 43 degrees C, 30' gave the maximum tumour cure. Combination of any of the two treatments resulted in a better response than all the single treatments. The chemosensitizing effect of heat was more pronounced than its radiosensitizing effect. Combination of all the three modalities, cDDP (2.5 mg/kg) + RT + HT (43 degrees C, 30') resulted in 100 per cent CR, without any local recurrence. This treatment also resulted in a significant increase in 120 day tumour free survival compared to all single modality treatments and bimodality treatments, except cDDP + 43 degrees C, 30'. This study indicates a potential advantage of the trimodality approach over single and bimodality treatments in the local control of solid tumours.

Withaferin A: a new radiosensitizer from the Indian medicinal plant Withania somnifera.

Withaferin A, a steroidal lactone isolated from the roots of the Indian medicinal plant Withania somnifera, reduced survival of V79 cells in a dose-dependent manner. LD50 for survival was 16 microM. One-hour treatment with a non-toxic dose of 2.1 microM before irradiation significantly enhanced cell killing, giving a sensitizer enhancement ratio (SER) of 1.5 for 37% survival and 1.4 for 10% survival. SER increased with drug dose, but at higher doses the increased lethality appears to be due to two effects-- drug toxicity and radiosensitization. The drug induced a G2/M block, with a maximum accumulation of cells in G2-M phase at 4 h after treatment with 10.5 microM withaferin A in 1 h. The applicability of this drug as a radiosensitizer in cancer therapy needs to be explored.

Radioprotective effect of leaf extract of Indian medicinal plant Ocimum sanctum.

Water or aqueous ethanol extract of O. sanctum was given ip, either as a single dose or multiple doses, before a whole-body exposure to 11 Gy(LD100/30) of 60Co gamma radiation in albino mice. The water extract was more effective and less toxic than the aqueous ethanol extract. An optimum ip dose of 50 mg/kg (< 1/100 LD50) of the water extract, at 10 mg/kg/day for 5 consecutive days, gave the maximum survival. Increasing the dose per treatment or the number of treatments did not increase protection. Intraperitoneal administration gave the best protection (70% survival). Other routes (im, iv and po) were less effective and produced 37-47% survival. The optimum dose (ip) gave a dose modifying factor of 1.28. Since the extract may contain a number of chemical compounds, it is not possible to attribute the observed protection to any particular compound at present.

Modification of radiation-induced chromosome damage and micronucleus induction in mouse bone marrow by misonidazole and hyperthermia.

The effect of misonidazole (MISO), local hyperthermia (HT) and their combination on radiation-induced chromosome damage and micronucleus (MN) induction was studied in mouse bone marrow cells. It was found that MISO treatment did not enhance the clastogenic effect of radiation, which indicates a lack of radiosensitization of bone marrow chromosomes. But post-irradiation HT increased the frequency of aberrant cells and MN. A combination of MISO and HT produced a significant increase in the frequency of radiation-induced aberrant cells and MN at all the radiation doses as compared to radiation alone. The percentage of aberrant cells as well as the percentage of MN showed a linear quadratic increase with radiation dose in all the treatment groups. At higher radiation doses, cells with > 1 MN increased quadratically with a pronounced increase in cells bearing > 2 MN and severely damaged cells (SDCs) at radiation doses above 3.0 Gy in the HT and MISO+HT treated groups. Our results indicate that though MISO itself may not have a radiosensitizing effect on mouse chromosomes, a combination of MISO with HT can enhance the radiation damage in normal bone marrow.

In vivo tumor inhibitory and radiosensitizing effects of an Indian medicinal plant, Plumbago rosea on experimental mouse tumors.

Tumor growth inhibitory and radiosensitizing effects of the alcoholic root extract of P. rosea was studied on experimental mouse tumors, S-180 solid tumor and Ehrlich ascites carcinoma in vivo. Intraperitoneal injection of 50 mg/kg of Plumbago extract (PE) for 10 days starting from 24 hr after intradermal inoculation of S-180 cells in BALB/c mice produced about 16% complete response (CR). The CR% increased with increase in drug dose, to 50% at 100 mg/kg for 10 days. As 100 mg/kg produced toxic side effects, lower doses were used with other treatment modalities, radiation (RT) and hyperthermia (HT). Treatment of 50 mm3 tumor with PE (75 mg/kg) for 10 days with local RT (10 Gy) and/or HT (43 degrees C, 30 min) subadditively increased the CR% and tumor free survival. The combination also significantly reduced the growth rates of uncured tumors. The PE significantly reduced the tumor glutathione content and this effect was markedly enhanced by the combination of the three modalities. PE alone was not very effective in preventing the growth of Ehrlich ascites carcinoma in Swiss mice, though it increased mean survival time and ILS% of the mice. But with radiation it produced a synergistic effect in increasing the tumor inhibition and 120 day animal survival from 10% to 50%. The results demonstrate that though PE may have only a weak antitumor effect, it may be a good candidate for use with radiation to enhance the tumor killing effect.

Determination of potential doubling times in human melanoma cell cultures subjected to irradiation and/or hyperthermia by flow cytometry.

The proliferation of human melanoma cells in vitro after irradiation and/or hyperthermia was studied by means of two-parameter flow cytometry. Cultures were incubated with BrdU for 30 min and fixed either immediately or after a delay of several hours. Cells having synthesized DNA were identified with the help of an antibody against BrdU. DNA was stained quantitatively with propidium iodide. In this way the distribution of cells in the phases of cell cycle could be determined and the movement of labeled cells through the phases of the cycle could be analyzed. Experiments in which the cell cycle distribution was studied at 4-h intervals after treatment showed the following: (1) Irradiation (4 Gy X rays) causes the expected G2 block with a maximum after 12-16 h. The proportion of S-phase cells decreases continually during the first 48 h after treatment. (2) Hyperthermia (1 h, 43 degrees C) alone or in combination with irradiation causes a delay in S phase. The cells begin to move into G2 phase only after 12-16 h and accumulate there to some extent. From the progression of labeled cells through the cycle, the duration of S phase could be determined. Experiments and calculations of this kind were done 0, 24 and 48 h after treatment. The duration of S phase was increased only moderately (by 4 h) after irradiation, but a delay of about 30 h occurred after hyperthermia (alone or in combination with X rays). Smaller delays (up to 9 h) were observed 24 and 48 h after treatment. Two different methods were used to calculate potential doubling times. Both of them gave similar results, but a comparison with the actual population doubling times (determined by cell counting) showed that reasonable estimates could be achieved only for the untreated controls. With cultures subjected to irradiation and/or hyperthermia serious discrepancies were observed. This does not seem to be due to technical problems inasmuch as we are dealing with a whole set of data produced under well-defined in vitro conditions (in contrast to the clinical situation, where potential doubling times have to be estimated from single samples). Our results certainly do not encourage the extension of the method (which was originally intended for the prediction of unperturbed tumor growth) to a post-treatment setting.

Response of mouse sarcoma-180 to bleomycin in combination with radiation and hyperthermia.

The response of a transplantable mouse tumor, S-180, grown intradermally in inbred Balb/c mice, to bleomycin (BLM), irradiation (RT) and hyperthermia (HT) was studied by observing tumor growth changes up to 120 days after treatment. BLM, at 20 mg/kg body weight, and 10 Gy gamma radiation individually produced identical tumor cure, while hyperthermia at 42 degrees C, 60' or 43 degrees C, 30' resulted in a higher tumor response. Treatment with 43 degrees C, 30' after BLM was more effective than hyperthermia after radiation in effecting tumor cure as well as in inducing regrowth delay. In the drug +HT combination the low drug dose was almost equal in effect as the higher drug dose when followed by 43 degrees C, 30'. Combining the three modalities resulted in 100% tumor cure without any local recurrence during the observation period. The micronucleus study 24 h after treatment indicated enhanced cytogenetic damage by the combination treatments.

Antitumor and radiosensitizing effects of Withania somnifera (Ashwagandha) on a transplantable mouse tumor, Sarcoma-180.

Antitumor and radiosensitizing effects of alcoholic root extract of W. somnifera and their modification by heat were studied in vivo on Sarcoma-180 grown on the dorsum of adult BALB/c mouse. Ashwagandha (AT) was injected (ip) at a dose of 500 mg/kg body wt for 10 consecutive days into mouse bearing tumor of 50 +/- 5 mm3, with or without a local treatment of 10 Gy gamma radiation (RT) or hyperthermia at 43 degrees C for 30 min (HT) or both on 5th day of AT. The response was assessed on the basis of tumor regression, growth delay, animal survival and changes in the tumor GSH content. Ashwagandha, RT and HT individually produced 18, 38 and 45% complete response (CR) respectively, but RT gave the best long term survival. Ashwagandha increased the effect of radiation on tumor regression as well as growth delay, but AT + HT gave a better tumor cure. However, both these combinations gave almost identical long term survival, which was not much higher than that produced by RT alone. The combination of Ashwagandha for 10 days with one local exposure to RT followed by HT significantly increased the tumor cure, growth delay of partially responding tumors and animal survival. This combination also significantly and synergistically depleted the tumor GSH level, with no recovery even at 3 hr after treatment. It is concluded that Ashwagandha, in addition to having a tumor inhibitory effect, also acts as a radiosensitizer and heat enhances these effects. The severe depletion in the tumor GSH content by the combination treatment must have enhanced the tumor response, as the inherent protection by the thiol will be highly reduced.

Toxic effects of crude root extract of Plumbago rosea (Rakta chitraka) on mice and rats.

The ethanolic root extract of Plumbago rosea (Plumbaginaceae) was studied for acute toxicity in mice and subacute toxicity in rats. The 24 h LD50 values of the extract in mice were 239.88 mg and 1148.15 mg/kg b.wt. for intraperitoneal and oral routes, respectively. Oral administration of doses above 1250 mg/kg produced severe diarrhea. In subacute toxicity studies no mortality was observed when 50 mg/kg of the extract was injected i.p. daily for 30 days; however, there was no weight gain in the treated rats. Significant reduction in the weights of liver, kidney, thymus and testes was observed in the male rats, while the spleen weight showed a significant increase from control. The females showed a significant loss in thymus weight and a gain in the weight of the uterus, but the liver and spleen did not show any weight change from the control. There was a significant increase in total WBC and neutrophil counts as well as in the levels of serum alkaline phosphatase and alanine transaminase (ALT) in both sexes. Similarly, the liver alkaline phosphatase level was significantly higher than control, but a significant reduction was observed in the DNA, RNA and total proteins. Thus, a higher drug dose (total dose of 15 g/kg b.wt.) was tolerated in fractionated administration, but it had a growth inhibitory effect in both sexes. The males appear to be more susceptible than females when individual organs are considered.

In vivo growth inhibitory effect of Withania somnifera (Ashwagandha) on a transplantable mouse tumor, Sarcoma 180.

Withania somnifera is a medicinal plant used in the treatment of a variety of ailments in the Ayurvedic system. Alcoholic extract of the root of the plant was injected(ip) at daily doses of 200 to 1000 mg/kg body wt for 15 days starting from 24 hr after intradermal inoculation of 5 x 10(5) cells of S-180 in BALB/c mice. Solid tumor growth was monitored for 100 days. Doses of 400 mg/kg and above produced complete regression of tumor after an initial growth, the percentage of complete response (CR) increasing with increasing drug dose. A 55% CR was obtained at 1000 mg/kg drug administration, but this dose also produced some mortality among the animals. A significant increase in the volume doubling time and growth delay was seen when the drug dose was increased from 500 to 750 mg/kg body wt, but further increase in drug dose to 1000 mg/kg did not produce any significant increase in these responses. Cumulative doses of 7.5 to 10 g at daily doses of 500 or 750 mg/kg seems to produce a good response in this tumor.

Chromosome protection by WR-2721 and MPG-single and combination treatments.

The radioprotective action of thiol compounds 2-mercaptopropionylglycine (MPG) and S-2(aminopropylamino) ethyl phosphorothioic acid (WR-2721) was evaluated either alone or in combination on the bone marrow chromosomes of Swiss albino mice after 4.5 Gy of 60Co radiation. Single drug administration of WR-2721 at 300 mg/kg body weight resulted in a 50% reduction in the yield of aberrant cells at 24 hours post irradiation, while the other single drug doses were less effective. The combination of the two drugs increased the effect in the sense that 150 mg/kg WR-2721 with 20 mg/kg MPG gave equal protection as 300 mg/kg WR-2721 given alone. Moreover, on day 14, when WR-2721 produced an increase in the precent aberrant cells the above combination brought down the value to normal. It appears that MPG neutralizes to some extent the toxic effect of WR-2721, without impairing the protective efficiency.