Selective protection against cis-diamminedichloroplatinum(II)-induced toxicity in kidney, gut, and bone marrow by diethyldithiocarbamate

Diethyldithiocarbamate (DDTC) has been shown to inhibit nephrotoxicity induced by cis-platinum (DDP) without inhibition of tumor response in the rat. We report here that DDTC at doses of 25-300 mg/kg inhibits DDP-induced nephrotoxicity and bone marrow toxicity in C57BL/6 X DBA/2F1 (hereafter called B6D2F1) mice, F344 rats, and beagle dogs and is also antiemetic in the dog. DDTC doses which afford excellent protection do not decrease median survival time following DDP treatment in L1210 and P388 leukemias, B16 melanoma, and Lewis lung and colon 26 carcinomas in B6D2F1 mice when DDTC is given 2 h after DDP. Preliminary experiments indicate that DDTC does not alter median survival time after treatment of P388 leukemia with the platinum analogues diammine(1,1-cyclobutanedicarboxylato)platinum(II) and cis-diisopropylamine-cis-dichloro-trans-dihydroxyplatinum(IV ). Maximum blood urea nitrogen levels after DDP treatment are reduced significantly by DDTC in all species; blood urea nitrogen elevation, total kidney platinum, weight loss, and leukopenia correlate with DDP-DDTC interval in the rat and indicate optimum protection at 2 h, the shortest interval examined. Bone marrow toxicity was assessed by peripheral white blood cell counts in all species and by marrow cellularity in the mouse. White blood cell nadirs were higher and bone marrow recovered more rapidly after DDTC compared with DDP given alone. DDP reduced marrow cellularity 50-60% in the mouse; administration of DDTC 2 h after DDP afforded no protection to the lymphocytes in the marrow but maintained the granulocyte + precursor population near control levels. DDTC plasma pharmacokinetic values have been determined after s.c., i.p., and i.v. administration in the mouse, rat, and dog. Peak plasma levels of 0.3-1.2 mM are observed after a 250-mg/kg dose, with a plasma half-life of 10-20 min. Our data indicate that DDTC may provide protection against most clinically significant toxicities arising from cis-platinum at doses which do not inhibit tumor response.     

Diethyldithiocarbamate inhibition of murine bone marrow toxicity caused by cis-diamminedichloroplatinum(II) or diammine-(1,1-cyclobutanedicarboxylato)platinum(II)

We report here the effects of diethyldithiocarbamate (DDTC) rescue on myelotoxicity caused by carboplatin (CBDCA) and cisplatin (DDP) in C57BL/6 x DBA/2 F1 mice. All drugs were administered by injection into the tail vein. Myelotoxicity was assessed by WBC, bone marrow cellularity, and assays for pluripotent bone marrow stem cells (spleen colony forming unit) and granulocyte/macrophage progenitor cells (granulocyte/macrophage colony forming unit in culture). The most significant protection occurred in stem cells, where a single dose of DDTC (300 mg/kg) produced a platinum-drug dose modification factor of 3.3; i.e., the addition of DDTC reduced stem cell toxicity to the level produced by approximately one-third the dose of platinum drug alone. On a molar basis, DDP was 2.4 times as toxic to stem cells as CBDCA. The response of the stem cells to CBDCA and DDP was linear both with and without rescue, and the dose modification factor remained constant for doses of CBDCA up to 120 mg/kg and doses of DDP up to 15 mg/kg. Moreover, stem cell rescue appeared to be independent of DDTC dose (100-750 mg/kg) and time of administration (1.5 h before to 5 h after platinum drug). DDTC protection was less impressive for more mature hematological cells (granulocyte/macrophage colony forming units in culture). In studies of bone marrow cellularity, addition of DDTC (300 mg/kg) to DDP treatment (10 mg/kg) produced a 50% increase in the granulocyte-predominant cell population but had no effect on the lymphocyte population. Peripheral WBC showed no significant difference between rescued and unrescued groups and did not reflect the toxicity observed directly in the bone marrow.     

Effect of diethyldithiocarbamate on toxicity of doxorubicin, cyclophosphamide and cis-diamminedichloroplatinum (II) on mice haemopoietic progenitor cells

DBA/2NCr1BR F1 mice received a single i.v. injection of doxorubicin (4.32, 7.20 or 12.00 mg kg-1), cyclophosphamide (70, 120 or 200 mg kg-1) or cis-diamminechloroplatinum (5.4, 9.0 or 15.0 mg kg-1), alone or 2 h before an i.p. injection of 1,000 mg kg-1 of diethyldithiocarbamate (DDTC). Twenty-four hours after, survival of bone marrow colony forming units-spleen and granulocyte-macrophage colony forming cells, was determined. On the whole, administration of DDTC reduced the toxic effect of the three anticancer drugs on haemopoietic progenitors. The effect was in general more evident at the lower than at the higher doses of the antitumour drugs.     

Mechanism of diethyldithiocarbamate modulation of murine bone marrow toxicity

Sodium diethyldithiocarbamate (DDTC) has been shown to modulate the myelosuppression that commonly occurs following treatment with anticancer drugs in mice. In order to investigate the mechanism of action of this myeloprotector, murine long-term bone marrow cultures were treated with DDTC alone or were preceded by the anticancer drug cis-diammine(cyclobutanedicarboxylato)platinum(II) (CBDCA), and the granulocyte/macrophage colony-stimulating activity of the supernatants was measured. The supernatants harvested from DDTC-treated cultures enhanced proliferation of granulocyte/macrophage progenitor cells almost 4-fold compared to cultures treated with no drug or with CBDCA alone. Pretreatment of cultures with CBDCA neither enhanced nor inhibited DDTC-induced colony-stimulating activity. Similar results were obtained by using marrow stromal cell cultures free of hematopoietic cells. Thus, DDTC may hasten bone marrow recovery by augmenting stromal cell production of a factor(s) with hematopoietic colony-stimulating activity.     

Modification of cisplatin toxicity with diethyldithiocarbamate

Diethyldithiocarbamate (DDTC), a heavy metal-chelating agent, has been shown to decrease cisplatin (CP) toxicity in preclinical studies. This phase I dose-escalation study was undertaken to investigate DDTC as a chemoprotector in patients with advanced cancer. Thirty-five courses of CP in doses ranging from 120 to 160 mg/m2 were given intravenous (IV) bolus to 19 patients. DDTC at 4 g/m2 was infused over 1 hour, starting 45 minutes after CP. There was minimal nephrotoxicity with a mean creatine clearance of 99 mL/min +/- 4 pretreatment and 86 mL/min +/- 4 on day 21. Two courses were associated with a WBC count less than 2,000/mm3 and one course with a platelet count of 15,000/mm3. Two patients had grade 2 neurotoxicity. Hearing loss occurred in 11 patients: five greater than or equal to 20 dB, five greater than or equal to 40 dB, and one greater than or equal to 60 dB. All patients who received cranial irradiation had ototoxicity compared with 43% of those without radiation (P less than .05). All patients experienced toxicity during the DDTC infusion, including hypertension, flushing, diaphoresis, agitation, and local burning. We conclude that DDTC can protect against CP nephrotoxicity at doses up to 160 mg/m2. Ototoxicity became the dose-limiting factor.     

cis-diamminedichloroplatinum(II) nephrotoxicity: tubular function after rescue with sodium diethyldithiocarbamate in rats

Sodium diethyldithiocarbamate (DDTC) administered following cis-diamminedichloroplatinum(II) (DDP) has been reported to attenuate structural renal damage and elevation of blood urea nitrogen in rats. Since DDP damages primarily proximal tubular epithelium in this species, we compared proximal tubular function, glomerular function, and histology in male Sprague-Dawley rats treated with DDP followed by either DDTC or 0.9% NaCl solution (NS) rescue. Male Sprague-Dawley rats received a single i.p. injection of DDP (7.5 mg/kg)-mannitol (75 mg/kg)-NaCl (67.5 mg/kg). Forty-five min later, rats were given i.p. injections of either DDTC (750 mg/kg) dissolved in 0.5 ml of NS (DDP + DDTC group; ten rats) or 0.5 ml NS (DDP + NS group; nine rats); additional rats received either DDTC only (DDTC group; six rats) or no treatment (untreated control group; six rats). All groups were sacrificed 5 days later by ether anesthesia and exsanguination. Compared to the untreated control group, the DDTC group had slightly lower mean blood urea nitrogen at sacrifice [12.5 +/- 0.5 (S.E.) versus 15.4 +/- 0.8 mg/dl; p less than 0.025 by unpaired Student's t test]; there was no difference in serum creatinine. The DDP + DDTC group had no diarrhea and no presacrifice deaths in contrast to diarrhea and three presacrifice deaths in the DDP + NS group. Blood urea nitrogen was also lower in the DDP + DDTC group at sacrifice (187 +/- 30 versus 383 +/- 39 mg/dl; p less than 0.005). However, weight loss and serum creatinine were not different. Structural acute tubular necrosis was marked in both DDP groups but was less severe in the DDP + DDTC group than in the DDP + NS group. Proximal tubular function was indexed by the uptake of the organic base N-[14C]methyl nicotinamide (NMN) and the organic acid p-aminohippurate in renal cortical slices incubated 90 min in Cross and Taggart medium. NMN uptake (expressed as slice to medium ratio) was slightly lower in the DDTC group than in untreated controls (4.1 +/- 0.2 versus 5.0 +/- 0.2; p less than 0.025). Marked depression of p-aminohippurate and NMN uptake occurred in both DDP + DDTC and DDP + NS groups. There was no difference in NMN uptake, but depression of p-aminohippurate uptake was slightly less severe in the DDP + DDTC group (5.3 +/- 0.7 versus 3.1 +/- 0.3; p less than 0.005). We conclude that DDTC rescue attenuates structural DDP injury in this animal model. DDP-mediated proximal tubular dysfunction was only marginally attenuated by DDTC; glomerular filtration rate, as indexed by serum creatinine, was not protected. DDTC attenuation of DDP toxicity may be mediated in part via reducing volume depletion due to DDP-associated diarrhea.     

Diethyldithiocarbamate modulation of murine bone marrow toxicity induced by cis-diammine(cyclobutanedicarboxylato)platinum (II)

Diethyldithiocarbamate (DDTC) has been shown to ameliorate the myelosuppression induced by the platinum cancer chemotherapeutic drugs in mice. Optimal drug scheduling for DDTC and cis-diammine(cyclobutanedicarboxylato)platinum(II) (CBDCA) has been determined in C57BL/6 x DBA/2 F1 mice, using the pluripotent stem cell assay to assess hematological toxicity. DDTC, at doses of 0.3 to 300 mg/kg given 3 h after 60 mg/kg CBDCA, tripled the number of proliferating spleen colony-forming units compared to treatment with CBDCA alone. No significant difference in efficacy was noted among these doses. DDTC, at the lowest myeloprotective dose (0.3 mg/kg), was most active when administered from 1 to 3 h after CBDCA. The combination of DDTC with CBDCA in vivo did not alter the clonogenic survival of L1210 cells compared to CBDCA alone. CBDCA depressed both bone marrow and tumor cell DNA synthesis. DDTC given 3 h after CBDCA hastened the recovery of DNA synthesis only in marrow cells; the addition of DDTC to CBDCA did not alter DNA synthesis in tumor cells. DDTC alone did not significantly affect DNA synthesis in either normal or tumor cells. These results suggest that the mechanism of DDTC myeloprotection involves stimulation of bone marrow cell proliferation and that the selectivity of DDTC is based upon the absence of stimulation in tumor cells.     

Inhibition of cis-diamminedichloroplatinum (II) — induced renal toxicity in the rat

Summary The hydroxyl-containing dithiocarbamates, sodium (di(hydroxyethl)-dithiocarbamate (NaY) and sodium N-methyl, N-dithiocarboxy-D-glucamine (NaG), appear to possess definite advantages over sodium diethyldithiocarbamate (DDTC) in reducing the cis-dichlorodiammineplatinum (Cis-Pt)-induced renal damage in rats given Cis-Pt as an IV bolus of 7.5 mg/kg 1 h before the IP administration of the dithiocarbamate. Renal damage, as estimated by blood urea nitrogen (BUN) values and serum creatinine levels, was less at all times up until sacrifice in animals given naY or NaG than in those given DDTC.An even more effective method for suppression of Cis-Pt renal toxicity is to use a combination of procedures. The most efficacious combination involves a 24-h pretreatment with DDTC or NaG plus acetazolamide and normal saline hydration 30 min before administration of Cis-Pt, followed by post-treatment with NaG. With this combination therapy renal function can be almost completely spared. Although DDTC or NaG pretreatment is highly effective when used in conjunction with NaG post-treatment, DDTC or NaG pretreatment alone has no renal sparing effect on renal function or renal platinum accumulation.In experiments in which antidotes were given 1 h after Cis-Pt and the animals were followed up for 75 days, a chronic interstitial nephritis at 75 days, suggesting a persistent cell-mediated immune response to Cis-Pt-induced renal damage, may be the basis for chronically abnormal renal function resulting from Cis-Pt. Treatment with all three dithiocarbamates, NaY, NaG, and DDTC, reduced the intensity of this cellular reaction and also reduced platinum levels in the kidneys.Although NaY and NaG are effective heavy metal chelators and renal function is spared and kidney platinum levels are substantially reduced by the dithiocarbamates, no parallel loss of antineoplastic activity by Cis-Pt on the rat Walker carcinoma was observed. Since the dithiocarbamates have no known human toxicity that would disqualify their clinical use, phase 1 clinical trials are indicated.This work was supported in part by the Natural Sciences Committee of the College of Arts and Sciences, Vanderbilt University     

Selenium-induced protection against cis-diamminedichloroplatinum(II) nephrotoxicity in mice and rats

The influence of selenium on cis-diamminedichloroplatinum(II) (c-DDP) nephrotoxicity in mice and rats was assessed, using single doses of both compounds. Sodium selenite, 2 mg of selenium per kg, given 1 h before c-DDP, greatly reduced blood urea nitrogen and creatinine levels and morphological kidney damage in both BALB/c mice and Wistar rats, while administration 1 h after c-DDP did not. Liver toxicity of selenium was evaluated by measuring serum glutamic pyruvate transaminase and serum glutamic oxalate transaminase and by routine histology. No liver damage was observed in animals treated with sodium selenite, 2 mg of selenium per kg, and physiological saline or c-DDP. Pretreatment with sodium selenite did not reduce the antitumor activity of c-DDP against MPC 11 plasmacytoma or Prima breast tumor in BALB/c mice. The present results indicate that sodium selenite may provide protection against c-DDP nephrotoxicity, when it is given before c-DDP. Moreover, selenium has an antineoplastic activity against several tumors. The combination of these qualities may open new perspectives in cancer chemotherapy.     

Prevention of lethal and renal toxicity of cis-diamminedichloroplatinum(II) by induction of metallothionein synthesis without compromising its antitumor activity in mice

The participation of renal metallothionein (MT) in the toxicity and antitumor activity of cis-diamminedichloroplatinum(II) (cis-DDP) in male mice was examined. Preinduction of MT in the kidney by the s.c. administration of bismuth compounds decreased the lethality and renal and gastrointestinal toxicity caused by a single s.c. injection of cis-DDP. In the present study a correlation between the protective effect of pretreatment with bismuth nitrate against cis-DDP toxicity and the preinduced MT levels in the kidney was observed. Bismuth nitrate pretreatment showed no effect on the antitumor activity of cis-DDP against several transplantable tumors, probably because it induces MT in the kidney but not in tumor tissues. The fact that p.o. preadministration of bismuth subnitrate, an antidiarrheal drug, also depressed the lethal toxicity of cis-DDP is promising for its prompt application in medical attention. Thus, bismuth pretreatment allows higher doses of cis-DDP with no apparent toxicity, resulting in more efficient utilization of this anticancer drug.     

Effect of diethyldithiocarbamate on cis-diamminedichloroplatinum(II)-induced cytotoxicity, DNA cross-linking, and gamma-glutamyl transpeptidase inhibition

Diethyldithiocarbamate (DDTC) has been shown to protect against the toxicity of cis-diamminedichloroplatinum(II) (DDP) without inhibition of antitumor effect. We report here that DDTC is unreactive toward DDP complexes in which both chlorides have been replaced by guanine residues but removes platinum from a variety of other ligands, and that this difference in reactivity may provide the basis for the selective protection observed with DDTC. Platinum-DNA complexes were unreactive toward DDTC (10 mM, greater than 4 h) when the platinum:base ratio r less than 0.02. DDTC did not react with the 1:2 complex of DDP:guanosine but reacted rapidly with the 1:1 complex and with the 1:2 complexes of DDP:adenosine. Reaction of DDP with DDTC was second order with a rate constant k = 4.4 M-1 min-1 at 37 degrees C, corresponding to a t 1/2 = 150 min at [DDTC] = 1 mM. Treatment of L1210 cells with DDTC (0.5-1 mM) after exposure to DDP indicated that DDTC had no effect on cell kill if DDTC treatment was delayed for 1 h after DDP. The effect of DDTC on DDP-induced DNA interstrand cross-links was also examined in L1210 cells. Interstrand cross-links were decreased by approximately 50% when cells were treated with DDTC immediately after DDP; no change in DNA interstrand cross-links was observed when DDTC treatment occurred 3 h after DDP. A modified alkaline elution procedure was used to evaluate the effects of high concentrations of DDTC, thiourea, and cyanide on platinum:DNA cross-links from L1210 DNA. Exposure to DDTC (0.5 M, 4 h) did not alter interstrand cross-links, but both thiourea and cyanide caused extensive reversal of cross-links at concentrations as low as 10 and 1 mM, respectively. Both commercial and rat kidney brush border preparations of gamma-glutamyl transpeptidase were inhibited by exposure to 2 mM DDP; exposure of the inhibited enzyme to DDTC (1 or 10 mM) resulted in significant restoration of enzyme activity. These data indicate that DDTC has unique chemical specificity in its reactions with platinum complexes and that this specificity is ideal for application as a chemoprotective drug against cis-platinum toxicity.     

Inactivation of cis-diamminedichloroplatinum (II) in blood and protection of its toxicity by sodium thiosulfate in rabbits

Summary The mode of inactivation of cis-diamminedichloroplatinum(II) (DDP) in the bloodstream and protection from its toxicity by sodium thiosulfate (STS) were investigated in rabbits.Plasma ultrafiltrate in rabbits given 5 mg/kg DDP IV and various excess molar ratios of STS IV were assayed for the active platinum levels with a new microbiological assay system using an E. coli strain. The active platinum species in the plasma were inactivated completely by coadministration of a 400-fold excess of STS IV. The rabbits were almost completely protected against both BUN increase and body weight loss normally caused by DDP when 400-fold doses of STS were given. Diuretic effects were also observed.Our data provide evidence for the basis of optimum use of STS to protect against DDP toxicity. [6, 9]. This TRC with DDP and STS is now in clinical trial [7, 8], but the precise mode of protective action of STS against DDP toxicity has not been determined.We now present evidence that this protective effect is due to inactivation of biologically active DDP in the bloodstream.Supported by a Grant-in Aid for Cancer Research from the Ministry of Education, Science and Culture, and from the Ministry of Health and Welfare, Japan     

Inactivation of cis-diamminedichloroplatinum (II) in blood by sodium thiosulfate

The mode of inactivation of cis-diamminedichloroplatinum (II) (DDP) in the bloodstream by sodium thiosulfate (STS) was investigated experimentally and clinically by a bioassay system using the phytohemagglutinin stimulation assay of human peripheral blood mononuclear cells. Active DDP in the plasma of dogs after 3 mg/kg of DDP injection, assessed by the bioassay system, was almost completely inactivated, when the level of STS in the plasma was more than 500 times higher at molar STS/DDP ratios than that of DDP. In 6 patients with hepatic malignancies who were treated with hepatic artery infusion of 3 mg/kg DDP and systemic STS, active DDP in the plasma was not detectable in the concurrent presence of STS at molar ratios of more than 500. Severe DDP toxicity in these patients was completely protected. The results indicate that an inactivation of DDP in the bloodstream after DDP injection and, further, an effective protection against DDP toxicity can be achieved by the concurrent presence of STS at molar ratios of more than 500 in the plasma of these patients.     

Selective reduction of cis-diamminedichloroplatinum(II) nephrotoxicity by ebselen

2-Phenyl-1,2-benzisoselenazol-3(2H)-one (ebselen) is classified as a relatively nontoxic selenium compound, probably because of its bound selenium moiety. In thiol-rich tissues, such as the kidneys, ebselen is converted into selenol intermediates. Selenols are nucleophilic agents which might be able to react with platinum compounds. The influence of ebselen on cis-diamminedichloroplatinum(II) (cisplatin)-induced nephrotoxicity in mice was assessed, using single doses of both compounds. Ebselen prevented cisplatin-induced elevations of blood urea nitrogen and serum creatinine levels and morphological kidney damage in BALB/c mice. This protective effect of ebselen was dose dependent: at a cisplatin dose of 14.5 mg/kg, maximal protection was achieved when a single dose of 10 mg of ebselen/kg was administered 1 h before cisplatin. Administration of ebselen, 10 mg/kg, 1 h after cisplatin also protected against severe nephrotoxicity. Treatment with ebselen did not reduce the antitumor activity of cisplatin against MPC 11 plasmacytoma or Prima breast tumor in BALB/c mice. However, this reduction of cisplatin-induced nephrotoxicity would be of little clinical value if it was achieved at toxic doses of ebselen. Ebselen, 10 mg/kg, did not induce blood urea nitrogen, serum creatinine, serum glutamic pyruvate transaminase, or serum glutamic oxalate elevations in the mice. These results are in agreement with the reported low toxicity of ebselen, which is now in Phase I clinical trials as an antiinflammatory drug. The present results indicate that ebselen may provide protection against cisplatin-induced nephrotoxicity, when it is given before or after cisplatin. This might open new perspectives in cancer chemotherapy.     

Correlation between cell killing by cis-diamminedichloroplatinum(II) in six mammalian cell lines and binding of a cis-diamminedichloroplatinum(II)-DNA antiserum

The relationship between cell killing and the binding of the anticancer drug cis-diamminedichloroplatinum(II) (cis-DDP) to DNA was studied in six mammalian cell lines. Two of the human cell lines (COV413B) were of the same origin, comprising one sensitive to cis-DDP and the other with induced resistance to the drug. The four other lines, two rodent (RIF-1, Chinese hamster ovary) and two human (A2780, A1847), were unrelated. The cell lines differed in their sensitivity to cis-DDP, as tested in a clonogenic assay. cis-DDP-DNA binding was determined by quantitative immunocytochemistry using an antiserum against cis-DDP-modified DNA. The resistance factors relative to RIF-1, calculated from full survival curves for cis-DDP, were 3.8 +/- 0.4 for Chinese hamster ovary cells and 8.8 +/- 0.7 for both A2780 and A1847 lines. Using quantitative immunocytochemistry, the levels of the adduct-specific nuclear staining density compared with RIF-1 cells were 4.8 +/- 0.2 for Chinese hamster ovary cells, 9.1 +/- 0.2 for A2780, and 10.0 +/- 0.1 for A1847 cells, i.e., in good agreement with the resistance factors. In studies with the COV413B cells and their cis-DDP-resistant counterpart COV413B-PtR, immunologically detected adduct levels again correlated closely with resistance factors (correlation coefficient = 0.97). The kinetics of cis-DDP-DNA adduct formation and loss was investigated in RIF-1, A2780, and A1847 cells by the immunocytochemistry technique. Adduct levels after a 1-h incubation with approximately equitoxic doses of cis-DDP increased by 18 to 32% (average, 27%) between 0 and 6.5 h after treatment and then declined. Adduct half-lives in this latter phase did not correlate with the sensitivities of the cells for cis-DDP. These results indicate that the initial level of cis-DDP-DNA binding measured by quantitative immunocytochemistry may be a reasonable predictor of sensitivity to this chemotherapeutic drug.     

Enhancement of the antiproliferative activity of cis-diamminedichloroplatinum(II) by quercetin

We have shown previously that the flavonoid quercetin (3,3',4',5,7-pentahydroxyflavone) enhances the antiproliferative activity of cis-diamminedichloroplatinum(II) (cis-DDP) in vitro. In order to investigate whether this observation could be exploited in cancer treatment, we tested this drug combination in human tumor xenografts. The established human large-cell cancer of the lung (LXFL 529) was implanted s.c. into nude mice. Tumors were allowed to grow to a mean diameter of approximately 5 mm and the animals were subsequently treated intraperitoneally with quercetin, cis-DDP or a combination of both. Treatment was given 3 times at 3-day intervals. Twenty milligrams quercetin per kg body weight caused no inhibition in tumor growth compared to untreated controls; 3 mg cis-DDP per kg body weight with the same time schedule reduced tumor growth, compared to quercetin-treated and control animals. Concomitant treatment with 20 mg quercetin and 3 mg cis-DDP per kg body weight reduced tumor growth to a significantly greater degree than cis-DDP alone. Toxicity of this treatment was relatively low as determined by measurements of the body weight of the mice. A combination of 4 mg or 5 mg cis-DDP with 20 mg quercetin per kg body weight also reduced tumor growth compared to single cis-DDP treatment. The toxicity of treatment with these increased doses was high, as shown by the high lethality and the loss of body weight of surviving animals.     

Evaluation of diethyldithiocarbamate as a radioprotector of bone marrow

The radioprotective action of DDC on normal hematopoietic tissue in mice was evaluated. An increase in CFU-S and CFU-GM in DDC treated unirradiated control mice was consistently observed. When post-irradiation survival of CFU-S and CFU-GM from DDC treated animals was normalized to account for this observed increase, protection factors ranging from 0.9 to 1.6 were observed. These protection factors are significantly lower than those reported by others. Maximum radioprotection was observed when irradiations were performed 15 to 30 min after DDC treatment; maximum increase in GFU-GM occurred within one to two hr following treatment. The increase in CFU-GM is analogous to that observed in animals treated with endotoxin, a non-thiol radioprotector. When C3H/HeJ mice, which are genetically incapable of responding to endotoxin, were challenged with DDC, an average CFU-GM increase of 1.7 times was observed, suggesting that the stimulatory effects of DDC were not due to endotoxin contamination. DDC was administered daily for three days before irradiation and little or no increase in CFU-GM and no radioprotection was observed, suggesting that the marrow can become refractory to DDC. When WR-2721 was tested in similar studies, a dose-modifying radioprotection was observed, with no significant non-specific stimulation of hematopoietic cells.     

Cytogenetic toxicity of cisplatin in bone marrow cells of Swiss mice

The inorganic platinum compound cisplatin (CP) in Oncoplatin, an anticancer drug, as the test chemical and cyclophosphamide (CY) in Endoxan, another anticancer drug, as the positive control, were tested for their cytogenetic toxicity in bone marrow cells of Swiss mice. The end points selected were mitotic metaphase chromosomal aberration and mitotic index study at 24-hour post-treatment and micronucleus test at 30-hour post-treatment after a single intraperitoneal exposure. The doses of the chemicals tested were CP 2, 3 and 5 mg/kg and CY 40 mg/kg b.w. of mice. Each of the doses of CP induced a significant number of chromosomal aberrations, mostly chromatid breaks and fragments and a significant number of micronuclei. The mitotic index study indicated CP as nonmitotoxic. The female mice were found more sensitive to each of the doses of CP than the males by showing more chromosomal aberrations, a higher number of micronuclei and comparatively less percentages of dividing cells. CP was thus found to be highly clastogenic in bone marrow cells of Swiss mice.     

Tumor radiosensitization with concomitant bone marrow radioprotection: a study in mice using diethyldithiocarbamate (DDC) under oxygenated and hypoxic conditions

We have established, both in vitro and in vivo, that Diethyldithiocarbamate (DDC) protects mammalian cells from radiation. The in vivo protection, when non-toxic concentrations of DDC are present one-half hour before irradiation, is reflected by a dose modification factor (DMF) of 1.9 based on LD50/30 and 1.5 using survival of CFUs as an endpoint. Further experiments in vivo have extended our knowledge to the differential radioprotective effects of DDC on the bone marrow of animals breathing room air compared to a 5.5% oxygen in nitrogen mixture. The DMF (LD50/30) for DDC in air breathing animals, previously established as 1.9, can be contrasted with a DMF, obtained in the present study, of 1.2 for animals irradiated in the hypoxic state. Moreover the DMF (CFUs survival) previously established at 1.5 for air breathing animals, can be compared to a value of 1.3, obtained in the present study, for mice irradiated under hypoxic conditions. Modification of the dose response by DDC, for both bone marrow and tumor, was also examined in animals bearing a RIF sarcoma. Although protection of the bone marrow was confirmed (DMF = 2.1), the striking finding was that the tumor cells were sensitized, in both air breathing and nitrogen breathing animals, by the addition of DDC one-half hour before the radiation exposure. Moreover, the tumor radiosensitization, a factor greater than 2, in air breathing animals, appeared to be independent of dose (D0 = 200 rad, with or without DDC). The tumor radiosensitization was even more marked in the nitrogen breathing mice, in which a factor of 10 difference in survival was noted, together with a tendency towards greater sensitization at radiation doses in the clinical range. The results, demonstrating bone marrow radioprotection by DDC (aerobic greater than hypoxic) with concomitant tumor radiosensitization (hypoxic greater than aerobic) strongly suggest a large therapeutic gain factor (TGF) which could be further explored in a clinical setting.