Streptozotocin inhibits O-GlcNAcase via the production of a transition state analog

Streptozotocin (STZ) is a 2-deoxy-d-glucopyranose derivative of a class of drugs known as alkylnitrosoureas, and is an established diabetogenic agent whose cytotoxic affects on pancreatic beta-cells has been partially explained by the presence of its N-methyl-N-nitrosourea side chain, which has the ability to release nitric oxide as well as donate methyl groups to nucleotides in DNA. It has also been observed that STZ administration results in a rise in the level of O-GlcNAcylated proteins within beta-cells. Not coincidentally, STZ has also been shown to directly inhibit the O-GlcNAcase activity of the enzyme NCOAT in vitro, which is the only enzyme that possesses the ability to remove O-GlcNAc modifications on proteins in the nucleus and cytosol. Since O-GlcNAc modification plays a role on a number of proteins in a vast amount of cellular processes, this shift in whole-cell protein O-GlcNAcylation state affords another source of cell death. We set about to find the exact mechanism by which STZ inhibits O-GlcNAcase activity. Inhibition is achievable because the GlcNAc analog STZ targets the active site of the enzyme whereby it is catalyzed. During this process, the enzyme converts STZ to a compound that closely resembles the natural ligand transition state, but is distinctly more stable energetically. As a result, this analog is catalyzed to completion at a much slower rate, thereby out-competing GlcNAc substrate for the active site, and inhibiting the enzyme.

Pre-clinical evaluation of a novel chloroethylating agent, Clomesone

The in vitro activity of the novel chloroethylating agent, Clomesone, was investigated in a panel of established murine and human tumour cell lines. In vivo anti-tumour activity was examined against three transplantable adenocarcinomas of the mouse colon and in vivo bone marrow toxicity was assessed using a spleen colony forming unit assay. The pharmacokinetic behaviour of the drug in vivo and drug stability in vitro was analysed by gas chromatography with electron capture detection. Clomesone exhibited no activity in vitro against the majority of cell lines derived from solid human colorectal carcinomas. Anti-tumour activity against the murine tumours in vivo was not impressive and was accompanied by myelosuppression. Pharmacokinetic data suggested that the lack of in vivo activity was due to the failure to achieve effective anti-neoplastic drug concentrations at the tumour site. It was concluded that this study found no evidence to suggest that Clomesone was toxicologically more selective than the chloroethylnitrosoureas.

Phase II trial of chlorozotocin and fluorouracil in islet cell carcinoma: a Southwest Oncology Group study

PURPOSE

A phase II trial that used fluorouracil (5-FU) and chlorozotocin (CTZ) was performed in patients with metastatic islet cell carcinoma to determine the response rate and toxicity.

PATIENTS AND METHODS

Patients received four cycles of induction chemotherapy. Good-risk patients received 5-FU 800 mg/m2/d days 1 to 4 as a continuous intravenous (IV) infusion (CIV) and CTZ 175 mg/m2 IV on day 1. Poor-risk patients (previous radiation to > or = 25% bone marrow-bearing areas; serum bilirubin > or = 5 mg/dL; creatinine > 1.0 mg/dL) received 5-FU 600 mg/m2/d and CTZ 75 mg/m2 in a similar manner. In responding or stable patients, reduced doses of 5-FU and CTZ were continued as maintenance therapy (maximum, 18 months).

RESULTS

Forty-seven of 51 patients were eligible, and 44 received chemotherapy. Fourteen of 44 patients had partial responses, with 13 of 36 (36%; 95% confidence interval [CI], 21.0% to 54.0%) good-risk patients and one of eight (12%; 95% CI, 0.3 to 52.6%) poor-risk patients responding. Median survival of all patients was 25 months, and the median response duration was 11 months. Side effects were moderate to severe and included myelosuppression and gastrointestinal toxicity. Thirteen patients developed renal toxicity, which was severe or life-threatening in five. This seemed to be related to the administration of cumulative doses of CTZ > or = 1,500 mg.

CONCLUSION

These results demonstrate that the combination of 5-FU and CTZ has activity in islet cell carcinoma, but the occurrence of renal toxicity secondary to CTZ may limit the use of this agent.

Formation and disappearance of DNA interstrand cross-links in human colon tumor cell lines with different levels of resistance to chlorozotocin

Three human colon tumor (HCT) cell lines, designated C, Moser and 116, exhibiting a gradation of resistance to chlorozotocin, a glucose-linked chloroethylnitrosourea (1-, 2.9-, and 5.8-fold respectively) were examined to assess the determinants of drug sensitivity. Although the O6-alkylguanine-DNA transferase content was relatively higher in the most resistant 116 cells than in the sensitive cell line C, its level in Moser cells did not correlate with the intermediate chlorozotocin sensitivity. Glutathione content in these tumor cell lines did not show a parallelism with drug resistance. The ethidium bromide fluorescence assay was used to quantitate the kinetics of DNA interstrand cross-link formation and its removal after drug exposure. The peak levels of DNA interstrand cross-links induced in HCT cells correlated with their resistance to chlorozotocin with cross-link indices of 0.03, 0.10 and 0.20, respectively, for 116, Moser and C cell lines. All three cell lines demonstrated DNA cross-link repair to different extents. While the smaller number of cross-links formed in resistant 116 and Moser cells were eliminated in a rapid phase of repair, the lesions formed at a much greater frequency in C cells remained largely unrepaired. These results draw attention to the role of increased DNA cross-link repair as a mechanism of nitrosourea resistance in the HCT cells studied.

Streptozocin-doxorubicin, streptozocin-fluorouracil or chlorozotocin in the treatment of advanced islet-cell carcinoma

BACKGROUND

The combination of streptozocin and fluorouracil has become the standard therapy for advanced islet-cell carcinoma. However, doxorubicin has also been shown to be active against this type of tumor, as has chlorozotocin, a drug that is structurally similar to streptozocin but less frequently causes vomiting.

METHODS

In this multicenter trial, we randomly assigned 105 patients with advanced islet-cell carcinoma to receive one of three treatment regimens: streptozocin plus fluorouracil, streptozocin plus doxorubicin, or chlorozotocin alone. The 31 patients in whom the disease did not respond to treatment were crossed over to chlorozotocin alone or to one of the combination regimens.

RESULTS

Streptozocin plus doxorubicin was superior to streptozocin plus fluorouracil in terms of the rate of tumor regression, measured objectively (69 percent vs. 45 percent, P = 0.05), and the length of time to tumor progression (median, 20 vs. 6.9 months; P = 0.001). Streptozocin plus doxorubicin also had a significant advantage in terms of survival (median, 2.2 vs. 1.4 years; P = 0.004) that was accentuated when we considered long-term survival (greater than 2 years). Chlorozotocin alone produced a 30 percent regression rate, with the length of time to tumor progression and the survival time equivalent to those observed with streptozocin plus fluorouracil. Crossover therapy after the failure of either chlorozotocin alone or one of the combination regimens produced an overall response rate of only 17 percent, and the responses were transient. Toxic reactions to all regimens included vomiting, which was least severe with chlorozotocin; hematologic depression; and, with long-term therapy, renal insufficiency.

CONCLUSIONS

The combination of streptozocin and doxorubicin is superior to the current standard regimen of streptozocin plus fluorouracil in the treatment of advanced islet-cell carcinoma. Chlorozotocin alone is similar in efficacy to streptozocin plus fluorouracil, but it produces fewer gastrointestinal side effects than the regimens containing streptozocin. It therefore merits study as a constituent of combination drug regimens.

2-Nitroimidazole potentiation of nitrosourea induced cytotoxicity in subcutaneous implants of rat 9L brain tumor cells

To determine if the 2-nitroimidazole (2-NI) and the nitrosourea (NU) in a brain tumor chemopotentiation trial should be selected on the basis of known structure-activity relationships (electron affinity, lipophilicity, alkylating activity, carbamoylating activity), s.c. implants of rat 9L brain tumor cells were treated with combinations of misonidazole (MISO) or etanidazole (SR-2508) administered under oxic and hypoxic conditions, and BCNU, CCNU or chlorozotocin (CLZ) administered under oxic conditions. Cell kill was assessed by an in vivo to in vitro colony formation assay. To mimic the 'preincubation effect', the 2-NI was injected i.p., and 30 min later the tumor was clamped. After 2 hr, the clamp was released, and the NU administered immediately. MISO (2.5 mmole/kg) and SR-2508 (3.75 mmole/kg) reached the same peak tumor concentration in 30 min. Both 2-NIs were metabolized at the same rate in the clamped tumors; however, metabolism of the 2-NIs by hypoxic cells over the 2 hr clamping period did not produce any measurable s.c. 9L cell kill. The relative effectiveness of the NUs for killing oxic s.c. 9L tumor cells was: BCNU greater than CCNU greater than CLZ. Clamping the tumor prior to NU administration did not change the NU cytotoxicity. No potentiation of the NU cytotoxicity by the 2-NIs was observed in oxic tumors. Although metabolism of MISO by hypoxic cells did not result in potentiation of CLZ cytotoxicity at any dose, it resulted in potentiation of BCNU cytotoxicity at all doses and CCNU cytotoxicity at high doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of O6-benzylguanine analogues on sensitivity of human tumor cells to the cytotoxic effects of alkylating agents

The effect of O6-benzylguanine, O6-(p-chlorobenzyl)guanine, and O6-(p-methylbenzyl)guanine on the sensitivity of various human tumor cell lines to alkylating agents is evaluated. The sensitivity of human colon tumor cells, HT29, to the chloroethylating agents, 1,3-bis(2-chloroethyl)-1-nitrosourea, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, 2-chloroethyl(methylsulfonyl) methanesulfonate (clomesone), and chlorozotocin was increased by pretreatment for 2 h with 25 microM of each analogue. O6-Benzylguanine was slightly more effective as a sensitizer in HT29 cells than the p-chlorobenzyl and p-methylbenzyl analogues. However, all analogues sensitized SF767 glioma cells to the cytotoxic effects of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, 1,3-bis(2-chloroethyl)-1-nitrosourea, and clomesone to the same degree. Both cell lines were sensitized to the methylating agents streptozotocin and 5-(3-methyl-1-triazeno)imidazole-4-carboxamide, the active intermediate of 5-(3,3-dimethyl-1-triazenyl)imidazole-4-carboxamide, by pretreatment with 10 microM O6-benzylguanine for 2 h. The number of Raji cells surviving 50 microM clomesone decreased 3-fold upon pretreatment for 2 h with 1 microM O6-benzylguanine. The degree of enhancement was dependent on the amount of alkyltransferase protein present in cell lines. For example, HT29 cells (alkyltransferase activity, 381 fmol/mg protein) exhibited a greater degree of enhancement when treated with O6-benzylguanine than SF767 (77 fmol/mg protein) and M19-MEL melanoma (36 fmol/mg protein) cells. There was no enhancement observed in mer- cell lines, U251 (less than 2 fmol/mg protein), and BE (3 fmol/mg protein), or with alkylating agents which did not produce a cytotoxic lesion at the O6 position of guanine in DNA such as cisplatin or 4-hydroperoxycyclophosphamide. Our studies suggest that O6-benzylguanine analogues may have utility in mer+ tumors as an adjuvant to a variety of alkylating agents which produce a toxic lesion at the O6 position of guanine.

Immunomodulatory effects of nitrosoureas on the phenotype and functions of T cells in the thymus and periphery

We have recently demonstrated that nitrosoureas such as 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU) and chlorozotocin (CLZ) can cure almost 100% of mice bearing LSA tumor, syngeneic to C57BL/6 mice. In contrast, similar or higher doses of streptozotocin (STZ) completely failed to cure LSA-bearing mice. Further studies revealed that the efficacy of nitrosoureas may depend on their immunomodulating properties. In the current study, therefore, we investigated the effect of these nitrosoureas on the immune system of normal mice. Treatment of C57BL/6 mice with 5 intraperitoneal injections of 20 mg/kg body weight of BCNU or CLZ caused an increase in the percentage of CD4(-)CD8- T cells and a decrease in the percentage of CD4(+)CD8+ T cells in the thymus. In addition, such treatment also caused an increase in the percentage of CD4+ T cells without significantly affecting the CD8+ T cells in the thymus. However, when total cellularity of the thymus was studied, BCNU and CLZ were found to decrease the total number of CD4(+)CD8+ T cells without significantly affecting the other subsets. In contrast, similar or higher (100 mg/kg body weight) doses of STZ had no significant effect on the total number and percentages of T cell subsets in the thymus. Also BCNU and CLZ but not STZ treatment caused a 50% decrease in the total number of CD4+ and CD8+ T cells in the spleen. When T cells in the spleens of nitrosourea-treated mice were functionally analysed, it was observed that BCNU and CLZ caused a dramatic decrease in the T cell responsiveness to ConA, anti-CD3 and phorbol myristate acetate plus calcium ionophore stimulation. In contrast, STZ treatment failed to significantly inhibit the T cell responsiveness to these activation signals. Using the accessory cell-dependent and -independent assays, BCNU and CLZ were found to suppress the functions of both T cells and macrophages. Also, addition of growth factors such as IL-1, IL-2, IL-4 and IL-6 failed to reconstitute the defective responsiveness of BCNU- and CLZ-treated T cells and macrophages. Together our data suggest that nitrosoureas have varying immunomodulating properties and this may in turn determine their efficacy in the treatment of cancer.

DNA interstrand crosslinking and strand break repair in human glioma cell lines of varying [1,3-bis(2-chloroethyl)-1-nitrosourea] resistance

The production of DNA interstrand crosslinks (ISC) by BCNU and other bifunctional alkylators and the effects of these drugs on the repair of radiation-induced DNA-single strand breaks (SSB) were studied in two human glioblastoma used to assess both DNA-ISCs and DNA-SSBs. BCNU-treated UWR2 and UWR3 cells showed a significant BCNU dose-dependent increase in radiation-induced DNA-SSBs at 6 hrs post-drug treatment, and at 100 microM BCNU DNA-ISC was completely masked in UWR2 cells. There was no enhancement of radiation-induced DNA-SSBs in both cell lines after treatment with cis-DDP, CHZ, or MNU. In the capillary clonogenic cell assay, UWR2 cells were 3.2 times more resistant than UWR3 cells; 0(6)-methylguanine-DNA methyltransferase activity was also 1.8 times higher in UWR2 than in UWR3. Our data suggest caution in the use of the standard alkaline elution technique (with 6 hrs between drug exposure and irradiation) to measure BCNU-induced DNA-ISC induction in highly BCNU-resistant cell lines. We provide evidence that the synergism between BCNU and radiation in the generation of DNA-SSBs is the result of low DNA-SSB repair capacity of the cells, and is further potentiated by the carbamoylating action of BCNU.

Immunomodulation by various nitrosoureas and its effect on the survival of the murine host bearing a syngeneic tumor

Chemotherapeutic efficacies of the nitrosoureas 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), chlorozotocin (CLZ), and streptozotocin (STZ) were investigated against the LSA tumor which is syngeneic to C57BL/6 mice. It was observed that a single injection of 20 mg/kg body weight of BCNU or CLZ, even at an advanced stage of tumor growth, completely cured greater than 90% of the tumor-bearing mice. Furthermore, BCNU-cured or CLZ-cured mice could specifically reject secondary rechallenge with the LSA tumor. In contrast, a single dose treatment with STZ at 20-200 mg/kg body weight failed to cure the tumor-bearing mice (0% survival). The failure of STZ to cure tumor-bearing mice was next addressed considering three possible mechanisms: (a) STZ was less tumoricidal; (b) STZ suppressed the immunity of the host; and (c) STZ failed to eliminate tumor-specific suppressor T-cells. The failure of STZ to cure tumor-bearing mice was not totally related to its tumoricidal properties since STZ at higher doses did possess significant tumoricidal activity in vitro and in vivo, comparable to that of BCNU or CLZ. When spleen cells from normal mice treated with BCNU, CLZ, or STZ were assayed for their responsiveness to the T-cell mitogens concanavalin A or phytohemagglutinin, it was observed that STZ was in fact less immunosuppressive than BCNU or CLZ. The fact that STZ did not suppress the immunity of the host was also suggested by the findings that BCNU-cured mice treated with STZ or CLZ could still reject secondary rechallenge with the specific tumor LSA. Following treatment of tumor-bearing mice with BCNU or CLZ, tumor-specific delayed type hypersensitivity responses were demonstrable in these mice but not in STZ-treated mice. The inability of STZ-treated tumor-bearing mice to elicit a delayed type hypersensitivity response was not due to selective depletion of delayed type hypersensitivity-inducing CD4+ T-cells but was probably due to failure of STZ to eliminate tumor-specific suppressor cells. Together these findings suggested that the failure of STZ to cure LSA tumor-bearing mice was not due to lack of tumoricidal activity or related to suppression of tumor-specific effector T-cell function but may be due to the failure of STZ to eliminate tumor-specific T suppressor cells. The present study suggests that the outcome of chemotherapy with nitrosoureas depends, in addition to the tumoricidal activity of the drug, on the immunomodulating action on the immune mechanisms of the host.

Ethylidene glucose-substituted new analogue of streptozotocin cannot induce diabetes: study on the basis of structure and activity relationship

4,6-O-Ethylidene glucose (ethylidene glucose), a specific inhibitor at the outer surface of a glucose transporter in the cell membranes, substituted analogue of streptozotocin was newly synthesized. This compound did not induce diabetes in rats and also did not show cytotoxic effect on pancreatic beta cells of neonatal rats in a monolayer culture system. The reasons why such a molecule was designed and why it showed no biological effects are discussed on the basis of a structure-activity relationship. Our results afford positive evidence for the presence of a glucose transport system or a glucose transporter on pancreatic beta cells and its involvement in the action of streptozotocin on beta cells.

Therapy of advanced gastric carcinoma. The Georgetown-Lombardi Cancer Center experience

Gastric carcinoma, despite a decreasing incidence in the United States over the past 40 years, is the seventh most common cause of cancer death in this country and remains a significant worldwide problem. The 5-fluorouracil, Adriamycin (doxorubicin), and mitomycin (FAM) chemotherapy regimen, which was initially reported by Georgetown in 1979, has become a standard for advanced gastric carcinoma with response rates in the 40% range. The FAM regimen as well as subsequent trials conducted at Georgetown and our current approach to management of this tumor are discussed. Despite a decade of intensive clinical research, we have not identified a modification or innovation that is superior to the original FAM.

Response of cultured human cell lines from rhabdomyosarcoma xenografts to treatment with chloroethylnitrosoureas

DNA interstrand cross-links are thought to be the cytotoxic lesion resulting from treatment of cells with the chlorethylnitrosoureas (CENUs). We showed in an earlier study that the resistance of xenografts of pediatric rhabdomyosarcoma to therapy with CENUs correlates with levels of O6-alkylguanine-DNA alkyltransferase. We now demonstrate a relationship between levels of the alkyltransferase and CENU-induced cytotoxicity and DNA-interstrand cross-link formation in two cell lines recently established from such rhabdomyosarcoma xenografts. Rh18 cells were derived from the HxRh18 xenograft line, which contains the alkyl-transferase and is relatively resistant to CENUs, and Rh28 cells were derived from the HxRh28 xenograft line, which lacks detectable alkyltransferase activity and is sensitive to treatment with the CENUs. In vitro, Rh28 cells were 5- to 6-fold more sensitive to growth inhibition by 1,3-bis(2-chloroethyl)nitrosourea than Rh18 cells. Extracts of Rh18 cells contained 3.8 units of the alkyltransferase per mg of protein, whereas such activity was undetectable in Rh28 cells, a unit of the alkyltransferase being defined as 1 pmol of [3H] methyl transferred from [3H]methyl-labeled DNA to protein. DNA interstrand cross-links, measured by alkaline elution 6 h after a 1-h pulse treatment with CENU, could not be detected in Rh18 cells but were found in the Rh28 line. The phenotypes of the parental xenograft lines defined by their alkyltransferase levels and by responses to CENU therapy of the mice have clearly been retained in the cultured cell lines, and as predicted, cross-link formation was inhibited in the alkyltransferase-containing Rh18 cells. These two new cell lines thus provide a useful model for studying the role of DNA repair in rhabdomyosarcoma resistance to these alkylating agents.

Enhancement by streptozotocin of O2- radical generation by the xanthine oxidase system of pancreatic beta-cells

Spin-trapping techniques and electron spin resonance (ESR) spectroscopy were used to study the relationship between the effect of streptozotocin (STZ) on pancreatic beta-cells and free radical formation by these cells. Results showed that STZ enhanced generation of the DMPO-OH radical adduct, which is a degradation product of the superoxide anion (O2-) in the presence of cellular components, in a hypoxanthine-xanthine oxidase (XOD) system with a homogenate of beta-cells. This enhancing effect was also observed in a system without cellular components; STZ increased the signal height due to the O2- radical in a concentration-dependent manner and caused a maximum of 150% enhancement at a concentration of 1.5 mM. Thus, STZ seemed to enhance the generation of the O2- radical in the XOD system, probably by some mechanism of its interaction with XOD. Pancreatic beta-cells exhibited a high XOD activity and a very low superoxide dismutase activity. Therefore, the present result supports the possibility that the cytotoxic effect of STZ is closely related to free radical generation in pancreatic beta-cells.

Induction of sister-chromatid exchanges in L1210 leukemia cells by new antitumor 2-haloethyl(methylsulfonyl) methanesulfonate compounds

The antitumor 2-halo(chloro, bromo, and fluoro)-ethyl(methylsulfonyl) methanesulfonates, ethyl(methylsulfonyl) methanesulfonate, and chlorozotocin, a 2-chloroethylnitrosourea, were evaluated for their potential to induce SCEs in L1210 cells. The results indicate that all the compounds induced approximately 2-fold or greater increases in SCEs in a dose-related manner. 2-Chloroethyl(methylsulfonyl) methanesulfonate, a DNA-interacting agent and a drug selected for clinical trials, exhibited the highest SCE increase in these cells.

Application of in vivo and in vitro pharmacokinetics for physiologically relevant drug exposure in a human tumor clonogenic cell assay

The biological half-lives and decay rate constants under the conditions of a human brain tumor clonogenic cell assay were determined for six clinically used anticancer agents. The agents studied were: 1,3-bis(2-chloroethyl)-1-nitrosourea; 3-(2-chloroethyl-3-nitrosoureido-2-deoxy-D-glucopyranose; cis-diaminedichloroplatinum(II); 2,5-diaziridinyl-3,6-bis-(carboethoxyamino)-1,4-benzoquinone; 4-demethylepipodophylotoxin-D-thylidene glucoside; and 9-hydroxy-2-N-methylellipticine. In vitro decay of all six drugs was found to be according to first order kinetics. The half-lives of two drugs, namely, 1,3-bis(2-chloroethyl-1-nitrosourea and 3-(2-chloroethyl-3-nitrosoureido-2-deoxy-D-glucopyranose under the human tumor clonogenic cell assay (HTCA) conditions were found to be similar to their terminal in vivo half-lives in humans. For the other drugs, however, there was a very large difference between their in vitro and in vivo pharmacokinetics. In the case of 2,5-diaziridinyl-3,6-bis(carboethoxyamine)-1,4-benzoquinone, we observed about an 80-fold difference between its in vitro half-life of 40.76 h and its in vivo terminal half-life of 0.52 h. We describe the principles upon which these data can be used to design clinically more relevant in vitro drug exposure protocols in HTCAs. Since, generally, tumor cells are exposed to drugs in the HTCA either continuously or for a specified duration, e.g., 1 or 2 h, we computed the initial in vitro drug concentrations to which tumor cells should be exposed such that the resulting in vitro (c X t) after a 2-h or a continuous exposure will be within clinically achievable levels. The application of these in vivo and in vitro pharmacokinetic principles will provide for more physiological testing of patient tumor cell sensitivity to anticancer drugs in the HTCA, and is likely to result in lower rates of false positive responses in clinical trials using clonogenic cell assays.

Immunogenic capacity of tum--variants isolated from a rat rhabdomyosarcoma

An increasing number of reports highlight the fact that tumour cells are able to give rise in vitro to immunogenic variants, which are defined in vivo as being non tumorigenic, tum-. We have observed the emergence of immunogenic variants, derived from a primary nickel-induced rat rhabdomyosarcoma established in culture (RMS 9-4/0), resistant to treatment with the chloronitrosourea, chlorozotocin (CZT) (R-lines). They were separated from the whole population of cells by a cloning procedure. Furthermore, we demonstrate that the cloning procedure by itself allows the isolation of tum- variant designated as C-lines. In both cases, the tum- phenotype was observed after s.c. injection of cells into syngeneic rats with a broad range of R9 or C8 cells (10(4) to 10(7). This characteristic was inherited in a stable manner. Athymic mice developed tumours of rat rhabdomyosarcoma origin when grafted with 10(5) cells. Immunization of rats with one R variant (R9) tum- protected the rats grafted with the parental RMS 9-4/0 cells against metastatic invasion of the lungs, but not against local tumour growth, and rats grafted with a CZT-resistant tum+ cell variant S4T (in vivo-derived) against its hepatic and pulmonary metastases, while the local tumour progressed as usual. Immunization of rats with one C variant (C8) tum- cells did not protect them against either metastases or local growth of the implanted tumours. Both R and C lines cells became progressively resistant to NK- and macrophage-induced cytotoxicity. Splenic lymphocyte transfer from immune rats into nude mice, i.e., the Winn test, showed a complete degree of protection against C8 or R9 tumour growth. We conclude that two different antigenicities were revealed, one common to R9 and C8 cells in relation with their selection procedure by repeated cloning. Another antigenicity appeared in the R9 line, selected by CZT-resistance. The anti R9 cell immunization against CZT-resistant tum+ S4T could argue in favour of CZT action in the acquisition of R9 cell antigenicity. More likely, an amplification of antigens rather than induction of a new antigen could explain the protection of anti R9 immunized rats against parental tumour metastases.

The effect of a novel taurine nitrosourea, 1-(2-chloroethyl)-3-[2-(dimethylaminosulfonyl)ethyl]-1-nitrosour ea (TCNU) on cytotoxicity, DNA crosslinking and glutathione reductase in lung carcinoma cell lines

A novel nitrosourea, 1-(2-chloroethyl)-3-[2-(dimethylaminosulfonyl)ethyl]-1-nitrosourea (TCNU) has been investigated with respect to cytotoxic mechanisms in rat and human cell lines which either possess (Mer+) or lack (Mer-) 0(6)-alkylguanine transferase activity. TCNU produced significantly greater cytotoxicity in the Mer- cells (Walker 256 rat breast carcinoma resistant to nitrogen mustards; human lung carcinoma A427) than in the Mer+ cells (Walker 256 wild-type; human lung carcinoma A594). This correlated with results generated by alkaline elution studies which showed that TCNU caused DNA interstrand crosslinks in A427 but not in A549 cells. Inhibition of glutathione reductase activity by TCNU demonstrated that in carbamoylating activity the drug was intermediate between chlorozotocin and 1,(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) in both A427 and A549 cells. These data suggest that the presence of taurine in the drug structure does little to alter the cytotoxicity or the alkylating or carbamoylating properties of TCNU, and that any clinical advantages with TCNU will be the consequence of other factors.

[Effects of derivatives of Ara-C, 5-fluorouracil and nitrosourea against intracerebral implanted L1210 leukemia]

The effects of Ara-C derivatives, 5-FU derivatives and water-soluble nitrosoureas on L1210 leukemia implanted intracerebrally have been evaluated. Daily treatment with BH-AC showed a similar effect to that of Ara-C and intermittent treatment with BH-AC showed a marked effect. Daily treatment with FT-207, UFT and HCFU, 5-FU derivatives, resulted in more than 50% ILS but the effects of these compounds were inferior to those of ACNU and BH-AC. MCNU, a water-soluble nitrosourea, was effective, but less so than ACNU.

Effects of antimetastatic, antiinvasive and cytotoxic agents on the growth and spread of transplantable leukemias in mice

The effects of cytotoxic (cyclophosphamide, CCNU, GANU), antiinvasive (vincristine, vinblastine) and antimetastatic (ICRF-159, DM-COOK) agents have been compared in mice-bearing P388 and L1210 leukemias, and TLX5 lymphoma. The drugs tested increase the survival time of the treated mice in a manner consistent with a cytotoxic action in the case of cyclophosphamide, CCNU, GANU, vincristine and vinblastine. Leukemic infiltration of the brain after i.p. tumor implantation has been determined by bioassay of this organ, and is reduced by treatment with all of the drugs tested, with the exception of ICRF-159. DM-COOK appears to increase the life-span of the treated animals by the inhibition of leukemic spread rather than by a cytotoxic action. The marked cytotoxicity of vincristine and vinblastine is sufficient to account for failure to detect any antimetastatic effects of these agents. The lack of antidisseminative effect observed for ICRF-159 under the experimental conditions employed might be connected with the observation that the antimetastatic action of this drug on solid tumors is due to its effects on tumor blood vessels.

DNA damage in cultured L1210 cells by 2-haloethyl esters of (methylsulfonyl)methanesulfonic acid

The effects of the 2-chloroethyl, 2-bromoethyl, and 2-fluoroethyl esters of (methylsulfonyl)methanesulfonic acid upon the DNA of cultured L1210 cells have been measured and compared with each other and with the effects of chlorozotocin. Results obtained by the alkaline elution method indicated that, at equimolar and equitoxic concentrations, the esters caused more strand scission than chlorozotocin, but at compound concentrations that caused a 50% reduction in colony formation by cells following an exposure period of 2 h, they caused no detectable cross-linking, whereas chlorozotocin did cause cross-linking. Two in vitro experimental methods that are based upon the complexing of ethidium to calf thymus DNA also yielded data showing that, at equimolar concentrations, chlorozotocin caused cross-linking of calf thymus DNA, but the 2-chloroethyl ester did not. These results indicate that these esters might not kill cells by producing DNA-DNA cross-links. The three esters caused qualitatively similar effects, but the fluoro esters caused less strand scission than the chloro and bromo esters, which caused about the same extent of strand scission.

Enhancement of pulmonary metastases induced by decreased lung natural killer cell activity

Administration of repeated high doses of 7.5 mg chlorozotocin [(CZT) CAS: 54749-90-5]/kg to syngeneic WAG rats bearing the rhabdomyosarcoma 9-4/0 enhanced the incidence of spontaneous metastasis compared to its incidence in untreated rats. This enhancement was observed concomitantly with an increase in the survival of 9-4/0 rhabdomyosarcoma and P 77 fibrohistiocytoma tumor cells, labeled with [125I]5-iodo-2'-deoxyuridine or 51Cr and injected iv. Within the first 24 hours after P 77 cell injection, the lungs retained 10% of the cells while the lungs of controls or of rats given one CZT injection only retained 0.06%. The natural killer (NK) cell cytotoxicity of cells flushed out from lung capillaries [lung intracapillary cells (LIC)] was studied concomitantly in a 4-hour 51Cr release assa against YAC-1 and P 77 target cells. A large reduction was again observed in NK cytotoxicity but only after repeated injections of 7.5 mg CZT/kg. Lung defenses were gradually restored after treatment stopped. Administration of polyinosinic-polycytidylic acid with CZT restored the NK cell cytotoxicity of LIC and inhibited lung metastases amplification. The close relationship between metastasis and NK activity indicates the need for caution as regards the effects of chemotherapy on NK activity.

Antitumor activity and bone marrow toxicity of aminoglucose mustard anticancer agents in mice

In previous structure-activity studies, we have demonstrated that attachment of a glucose molecule to the chloroethylnitrosourea cytotoxic group produces a compound with reduced murine bone marrow toxicity and retention of full antitumor activity. To further define this protective role conferred by the glucose moiety in bone marrow cells, we have replaced the nitrosourea cytotoxic group with another class of alkylating agent, a bifunctional nitrogen mustard. In a detailed structure-activity analysis, we have now characterized four analogues, with the mustard cytotoxic group positioned at carbon 2 [1,3,4,6-tetra-O-acetyl-2-(di-2-chloroethyl)amino-2-deoxy-D-glucopyranos e (TGM)], carbon 6, or carbon 1 (D- and L-isomers) of the aminoglucose molecule. On a molar basis, TGM was most toxic to normal BALB/c X DBA/2 F1 mice, with a 10% lethal dose (LD10) of 3.8 mumol/kg. The D- and L-isomers of 2,3,4,6-tetra-O-acetyl-N,N-bis(2-chloroethyl)glucopyranosylamine (C-1) were the least toxic, with an LD10 of 73 mumol/kg for both. Optimal antitumor activity against the murine P388 leukemia (single i.p. administration of the LD10) did not differ significantly among the four analogues, with increased life span ranging from 83-86%. P388 antitumor activity for nitrogen mustard (HN2) was significantly less, 60% increased life span (P = 0.01), while p-di(2-chloroethyl)amino-L-phenylalanine produced an increased life span of greater than 101%. An LD10 of 6-bis-(2-chloroethyl) amino-6-deoxy-D-glucose (C-6) or TGM produced significantly less depression of WBC counts than did an equitoxic dose of the C-1 isomers, HN2, or p-di(2-chloroethyl)amino-L-phenylalanine. The mean nadir WBC count for C-6 equaled 86% of control, and for TGM, 80% of control. Consistent with this sparing effect on the peripheral WBC, C-6 and TGM produced significantly less in vivo murine bone marrow DNA synthesis depression, 77 and 64% of control, respectively, as compared to the depression nadir produced by HN2 (27% of control), the D-isomer of C-1 (17%), the L-isomer of C-1 (18%), and p-di(2-chloroethyl)amino-L-phenylalanine (2%). These structure-activity studies demonstrate that conjugation of the mustard cytotoxic group to carbon 6 or carbon 2 of glucose produces an analogue that retains P388 antitumor activity significantly greater than that of HN2, with a concomitant reduction in murine bone marrow toxicity.

A comparative analysis of drug-induced DNA effects in a nitrogen mustard resistant cell line expressing sensitivity to nitrosoureas

In the Walker 256 rat mammary carcinoma cell line, WR, resistance to nitrogen mustards (NM) is accompanied by collateral sensitivity to chloroethylnitrosoureas (CENUs). DNA-interstrand cross-links, DNA-protein cross-links, and sister chromatid exchange (SCE) induction were assayed in WR and the parent cell line (WS) after treatment with nitrogen mustard (HN2), phosphoramide mustard (PM), chlorozotocin (CLZ) and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU). Treatment of cells with HN2 caused extensive levels of cross-links, approximately 50% of which were DNA-interstrand, equal in both WR and WS, whereas PM caused no detectable cross-links in either cell line. CLZ induced low levels of DNA-interstrand cross-links, similar in WR and WS, but no DNA-interstrand cross-links could be detected in either cell line after treatment with CCNU. Both CLZ and CCNU induced low levels of DNA-protein cross-links in both cell lines, though higher in WR than WS. There was no difference in the rate of removal of HN2-induced DNA-interstrand or DNA-protein cross-links or total CLZ-induced cross-links by the two cell lines, suggesting that differential repair was not relevant to the expression of resistance. Both HN2 and PM caused more SCEs in WS than in WR, whereas CLZ and CCNU induced more SCEs in WR. Thus, NM-induced SCEs were related to cell killing but not cross-linking, whilst CENU-induced SCEs were related to cell killing and DNA-protein but not DNA-interstrand cross-links. Furthermore, the collateral sensitivity of WR cells to CENUs was not due to the differential induction of DNA-interstrand cross-links or repair of total cross-links, or repair of total cross-links, although higher levels of DNA-protein cross-links occurred in WR, and these may be either a cause or a consequence of increased susceptibility of these cells to CENUs. Presumably NMs and CENUs have several distinct and separate macromolecular targets which result in differential cell killing. It is concluded that a range of lesions occurred after treatment of WR and WS cells with either NMs or CENUs and that, in these cell lines, there is no simple correlation between drug-induced cross-linking, SCE induction and cytotoxicity.

Comparative nephrotoxicity of 1-(2-chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea (MeCCNU) and chlorozotocin: functional-structural correlations in the Fischer 344 rat

1-(2-Chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea (MeCCNU) and chlorozotocin (CZ; 2-[3-(2-chloroethyl)-3-nitrosoureido]-D-glucopyranose) are structurally related anticancer agents which differ by virtue of the increased water solubility, and comparatively low carbamylating activity, of CZ relative to MeCCNU. In the present study, a single sc injection of either of these chloroethylnitrosoureas was nephrotoxic to male Fischer 344 rats. However, at equimolar doses, CZ was shown to be a much more potent nephrotoxicant. A lethal 40-mg/kg dose of CZ (127 microM) initially resulted in acute tubular necrosis of the proximal tubules of the cortex, followed later by a necrosis of papillary collecting ducts. In contrast, lethal doses of MeCCNU (100-180 mg/kg; 400-730 microM) produced only minimal proximal tubule injury. A 250-mg/kg (1 mM) dose of MeCCNU resulted in massive papillary necrosis within 7 days, with only limited necrosis to the proximal tubules. Sublethal doses of either drug, resulted in a similar, chronic, progressive nephropathy which was delayed in onset and was characterized by polyuria, enzymuria, a decrease in urine concentrating ability, and in renal slice organic ion accumulation. Alterations in less sensitive indicators of renal toxicity (i.e., proteinuria, glucosuria, and elevated blood urea nitrogen) were observed no earlier than 3 to 7 days after administration of only the highest tested doses of CZ (40 mg/kg) or MeCCNU (250 mg/kg). At sublethal doses, administration of either drug resulted in karyomegaly to the collecting ducts in the renal medulla within 2 to 4 weeks. These studies demonstrate that carbamylation-mediated reactions may not be necessary for nephrotoxicity to develop following administration of this class of antitumor agent.

Comparative interactions of streptozotocin and chlorozotocin with DNA of an insulin-secreting cell line (RINr)

Both streptozotocin and chlorozotocin, the 2-chloroethyl analogue of streptozotocin, are diabetogenic chemicals in rodents. Although these chemicals are similar structurally, they appear to act on pancreatic B cells via different mechanisms. In studies here, damage and repair of DNA after exposure of an insulin-secreting cell line to streptozotocin and chlorozotocin were assessed by nucleoid sedimentation and alkaline elution. Equitoxic concentrations of streptozotocin and chlorozotocin caused significant single-strand breakage of DNA (p less than 0.005). These lesions were repaired in a time-dependent manner, with most repair completed by 24-h post-exposure to chemicals. Additionally, chlorozotocin caused DNA-DNA and DNA-protein crosslinks in insulinoma cells. When proteinase K was included in the crosslinking assay, a substantial proportion of the chlorozotocin-associated crosslinks proved to be DNA interstrand in nature. Analysis of the amount of interstrand crosslinking in insulinoma cells after exposure to chlorozotocin for 1 h showed that formation of interstrand crosslinks was slow. Increasing amounts appeared over a 24-h period. These results suggest that the formation of irreversible DNA interstrand crosslinks may be a critical factor in cytotoxicity and diabetogenicity caused by chlorozotocin.

Sequential morphologic analysis of the nephrotoxicity produced in rats by single doses of chlorozotocin

Chlorozotocin is a chloroethylnitrosourea antitumor agent that is in clinical trial for a variety of human tumors. Renal failure has been a reported side effect of treatment with several of the chloroethylnitrosoureas, including chlorozotocin. To better understand the pathogenesis of this target organ toxicity, we have studied the nephrotoxicity of a single high, intermediate, or low dose of chlorozotocin in male F344 rats. We report here the sequence of histopathologic changes seen over a 1-10-day (high dose) or 1-28-day (intermediate or low dose) period. The single high dose (40 mg/kg, s.c.) produced an acute cortical necrosis involving the proximal tubules, followed by later necrotic changes in the collecting ducts in the inner medulla. Karyomegaly was noted at 10 days in occasional cells of the papillary collecting ducts and urinary epithelium lining the papilla. A single intermediate dose (25 mg/kg, s.c.) caused a similar but less severe injury of later onset. Proximal tubule injury was less severe and more limited. Necrosis of papillary collecting ducts was not seen; however, karyomegaly was pronounced in cells of the collecting ducts in the inner stripe of the outer medulla and inner medulla, and in the urinary epithelium covering the papilla. No discernible histopathology was present following the low dose (12.5 mg/kg, s.c.) of chlorozotocin. The histopathology was correlated with biochemical parameters. Our findings have possible implications for monitoring the severity of nephrotoxic side effects in patients, as well as provide preliminary evidence that this antineoplastic agent may itself cause preneoplastic changes, a finding with important long term implications.

New diabetogenic streptozocin analogue, 3-O-methyl-2-([(methylnitrosoamino) carbonyl]amino)-D-glucopyranose. Evidence for a glucose recognition site on pancreatic B-cells

The nonmetabolizable glucose analogue 3-O-methyl-glucose is known to protect pancreatic B-cells against streptozocin (STZ) when injected with or just before STZ. If 3-O-methyl-glucose and the sugar moiety of STZ compete for a glucose recognition site on B-cells, it seemed likely that 3-O-methyl-2-deoxy-2-( [(methylnitrosoamino)carbonyl]amino)-D-glucopyranose, an analogue of STZ with a 3-O-methyl-glucosyl residue, would cause experimental diabetes. This possibility was tested by synthesis of this analogue (alpha-anomer) and comparison of its diabetogenic activity in Wistar rats with that of STZ. Results showed that the compound was diabetogenic and as potent as STZ. This new analogue is the first of the various STZ derivatives reported to show diabetogenic activity. Its activity supports the idea that 3-O-methyl-glucose and STZ bind competitively with a glucose recognition site on pancreatic B-cells.

Effects of three new nitrosourea analogs (CNCC, RFCNU and chlorozotocin) on in vivo destruction of L 1210 leukemia cells and on the immune response

Three new nitrosourea analogs (CNCC, RFCNU, and chlorozotocin) had comparable activities in vivo against L1210 leukemia cells. In addition to the antileukemia effect, these drugs also decreased both the humoral immune response to sheep red blood cells and the delayed hypersensitivity reaction to oxazolone. The immunodepression induced by these agents lasted at least 25 days, and could not be reversed by the transplantation of normal syngenic bone marrow cells into treated animals.

Cure rates and tumor resistance in cured mice after nitrosourea treatment of EMT6 ascites tumors

Single-dose BCNU or chlorozotocin (CLZ) treatment of EMT6 mammary carcinoma tumors of the BALB/c mouse has only a transient effect on tumor growth, after which tumors follow control growth patterns. To test the hypothesis that drug access to tumor cells might be a factor in cell killing, we adapted the EMT6/KY tumor to ascites form. Injection of 10(5) EMT6/KY cells i.p. kills BALB/c mice with a mean survival time of 13.0 +/- 1.0 days. We have surveyed several nitrosoureas for their effects on the EMT6/KY ascites tumor after intraperitoneal injection of the drugs. Cure rates and percent increase in life span were used as endpoints. Also, we tested for induced host tumor resistance (TR) in cured mice, by challenging survivors with live EMT6 cells. Highest cure rates were obtained for treatment on days 2, 3, or 4 after inocula of 10(5) cells: CLZ (10 mg/kg), 83.3%; cis-acid (20 mg/kg), 75%, and CCNU (30 mg/kg), 70%. Other nitrosoureas, i.e. BCNU, PCNU, GANU, STZN, FCNU, ACNU, MeCCNU, NSC-88104 produced lower cure rates. Cured mice surviving challenges of 10(6) EMT6 cells were considered TR. TR mice did not correlate with cure rates for the 3 nitrosoureas giving high cure rates. As percent of survivors, TR mice were (for day 3 treatment): FCNU, 100%, BCNU, 100.0% and CLZ, 50.0%. Thus, cure rates and TR seem to depend on the structure of the nitrosourea, but through different mechanisms.

In vitro analysis of BCNU-sensitivity in human malignant gliomas. I. A model study with alkylating, cross-linking and carbamoylating agents in anaplastic astrocytomas of pediatric age

Like all chloroethyl-nitrosoureas of major clinical use, 1,3 bis-(2-chloroethyl)-1-nitrosourea (BCNU) - which is one of the most effective chemotherapeutic agents for CNS malignancies - biologically degrades into active alkylating and carbamoylating moieties. Using a human brain tumor stem cell assay, we analyzed a series of anaplastic astrocytomas of pediatric age, characterized by different degrees of BCNU-resistance. Early (2-4) passage cultures from these tumors were treated in vitro with model drugs for alkylation (BCNU, CHLZ (2-[3-(2-chloroethyl)-3-nitrosoureido]-2-deoxy-D-glucopyranose), ENU (N-ethyl-N-nitrosourea), cross-linking (BCNU, CHLZ) and carbamoylation BHCNU (1,3 bis (trans-4-hydrocyclohexyl)-1-nitrosourea): dose-schedules were compatible with clinically achievable levels. Results of chemosensitivity tests confirmed that - as previously reported in malignant gliomas of the adult - cellular resistance to BCNU was closely related to the cross-linking activity of alkylating species. However, in pediatric gliomas the levels of cell kill after treatment with the purely carbamoylating agent BHCNU, even at the highest doses tested, were lower than expected.

DNA repeat length in chromatin from murine bone marrow and L1210 leukaemia cells

Previous studies have suggested that 1-(4-amino-2-methylpyrimidine-5-yl)-methyl-3-(2-chloroethyl) -3-nitrosoureahydrochloride (ACNU) and 1,(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) bind specifically to the nucleosomal DNA of murine bone marrow and L1210 leukaemia cells whereas the glucose nitrosoureas, 2-(3-(2-chloroethyl)-3-nitrosoureido)-2-deoxy-D-glucopyranose, (chlorozotocin, CLZ) and 1-(2-chloroethyl)-3-(-D-glucopyranosyl)-1-nitrosourea (GANU), bind preferentially to the linker DNA of bone marrow but not tumour cell chromatin. In order to provide an explanation for this differential, the DNA repeat and linker lengths in murine bone marrow and L1210 leukaemia cells were measured using electrophoresis of micrococcal nuclease-digested DNA. The linker length of bone marrow chromatin was approximately 22% longer than that in L1210 leukaemia cells from mouse ascites. The linker length of L1210 cells maintained in suspension culture was 27% less than in those from ascites fluid. The tissue-specific toxicity of sugar nitrosoureas and the differential binding of these drugs to chromatin does not appear to correlate quantitatively with differences in DNA linker length.

Chlorozocin. A diabetogenic analogue of streptozocin with dissimilar mechanisms of action on pancreatic beta cells

Chlorozotocin (chlorozocin, CLZ), the 2-chloroethyl analogue of streptozocin (STZ), was evaluated in three species of rodents. The drug is currently being used in phase II chemotherapeutic trials in man, and appears to be effective in the treatment of certain tumors. In our studies, hyperglycemia was induced in hamsters as early as 2 days after a single intraperitoneal (i.p.) injection of 30-60 mg/kg and was most striking at 4 days. Greater concentrations of CLZ (greater than or equal to 50 mg/kg) were required to produce hyperglycemia in CD-1 mice. Degranulation and necrosis of beta cells developed in hamsters and mice, whereas alpha and acinar cells of the pancreas revealed no morphologic changes. Hyperglycemia was not induced in rats at any concentration tested; however, animals showed abnormal carbohydrate tolerance after administration of 100 mg/kg CLZ (LD50 dosage). The nature of damage by CLZ to beta cells was investigated both in vivo and in vitro. Pretreatment of hamsters with nicotinamide (500 mg/kg, i.p.) failed to alter the extent of CLZ-induced beta cell injury and associated hyperglycemia, but decreased the amount of beta cell necrosis and hyperglycemia in animals receiving STZ. The nonmetabolizable sugar, 3-O-methylglucose (3-O-MG), and 3-aminobenzamide, an inhibitor of the nuclear enzyme, polyADPribose synthetase, prevented STZ-associated damage to beta cells in islet cell cultures, but only 3-O-MG reduced CLZ-induced toxicity. Thus, in comparison to STZ, CLZ appears to be a diabetogenic agent with different species specificity and alternative mechanisms of cytotoxicity. The glucose moiety of both drugs appears critical in the induction of beta cell damage.

Enhanced cloning efficiency of murine rhabdomyosarcoma cells after chlorozotocin treatment: relationship with enhanced lung metastasis

The effect of chlorozotocin [(CZT) CAS: 54749-90-5; 2-(3-(2-chloroethyl)-3-nitrosoureido)-D-gluco-pyranose] was studied on a series of tumor cells, cultured or extracted fresh primary or transplanted tumors, by means of clonogenic assay. The ability of most rat rhabdomyosarcoma cells to form colonies in soft agar was enhanced when exposed to the water-soluble nitrosourea chloride CZT. The tumor cells tested were derived from a) several primary tumors induced in WAG rats by colloidal nickel, then cultured and exposed to CZT early during in vitro passage; b) the 9-4 tumor, also Ni-induced but maintained in long-term culture; and c) the Ni-induced 9-4/0 tumor, maintained by transplantation in syngeneic rats. No inhibition of colony formation was observed in any of the cell lines even at high concentrations of CZT. Adriamycin, chosen as a control treatment, strongly inhibited the cloning efficiency (CE) of the tumor cells. In vivo, the weekly injection of 10 mg CZT/kg body weight into syngeneic rats bearing transplanted tumors led to an enhancement of lung metastasis formation. The CZT enhancement of CE of tumor cells and its relationship to increased in vivo tumor metastasis is discussed.

Effect of concentration and time of drug exposure on clonal growth of murine bladder cancer

The use of a tumor colony assay was evaluated for its ability to predict anticancer drug response in an N[4-(5-nitro-2-furyl)-2-thiazolyl] formamide mouse bladder tumor model. One-hour and continuous drug exposure were compared to determine what effect altering drug concentration and time of exposure would have on the predictability of the tumor colony assay in the murine model. Ten anticancer drugs were tested in the murine model, and tumor cells removed from control mice were used for in vitro drug testing. One-hour and continuous drug exposure (using the one-hour drug level) were performed simultaneously and the in vitro and in vivo data compared. Using one-hour drug incubation in the tumor colony assay resulted in a true positive predictive rate of 54 per cent and a true negative predictive rate of 70 per cent. Continuous drug incubation overestimated drug sensitivity resulting in a drop in the predictability of the tumor colony assay. We conclude that using one-hour drug exposure the tumor colony assay is predictive of chemotherapeutic drug response in this murine bladder tumor model.

Effect of cyclosporine and aminophylline on streptozotocin-induced diabetes in rats

Diabetes induced in rats by multiple low doses of streptozotocin is thought to mimic type 1 disease in man. We tested the effect of concomitant treatment with immunomodulator drugs in this diabetic experimental model. Administration of cyclosporine resulted in a rapid appearance of hyperglycemia, perhaps by a potentiation of the direct cytotoxic action of streptozotocin on beta cells. By contrast, aminophylline administration protected the animals from the diabetogenic action of streptozotocin. Concomitant treatment with aminophylline and cyclosporine failed to protect the rats from the hyperglycemia induced by streptozotocin.

Enhanced nitrosourea cytotoxicity in cell culture by sodium butyrate

In HeLa S3 cells, sodium butyrate was found to potentiate the cytotoxicity of chloroethylnitrosoureas and alkylating agents in vitro. Using a soft-agar colony-forming assay, 2.5 and 5.0 mM sodium butyrate pretreatment for 22 h increased the cell killing efficacy of both methyl- and chloroethylnitrosoureas by between 30 and 70%. The potentiation of cytotoxicity of bifunctional nitrogen mustards by butyrate was less than that of nitrosoureas, with a 15-30% increased cell kill at 5 mM butyrate. Sodium butyrate per se reduced plating efficiency and caused growth delay if residual levels (calculated at 100 microM for starting concentrations of 5 mM) were not removed by washing prior to plating.

Comparison of the experimental antitumor activities of three nitrosourea derivatives chlorozotocin, RFCNU and CNCC encapsulated in liposomes with those in the free state

L1210 leukemia was used to compare the antitumor activities of three nitrosoureas (chlorozotocin, RFCNU and CNCC) encapsulated in liposomes with those in the free state. The results obtained varied according to the chemical structure of the compound, its solubility in oil or water, the route of administration into the body, and the treatment dose. The application of liposomes in the chemotherapy of malignant disease deserves further investigations.

Phase I evaluation of chlorozotocin (NSC-178248): weekly schedule

A phase I trial of chlorozotocin was completed for a weekly times four dose schedule repeated every 8 weeks. Thrombocytopenia was the acute dose limiting toxicity. Nausea and vomiting were moderate to severe and dose related. Two cases of possible drug related irreversible nephrotoxicity were seen. Transient elevations of serum creatinine and mild proteinuria were noted. Also, transient elevations in SGOT were observed. One patient with a carcinoid tumor had a 60% reduction in his 5HIAA level after one course of therapy. The recommended dose for phase II clinical studies of chlorozotocin is 40 mg/m2 IV weekly for four weeks, repeated every 8 weeks.

Glomerular basement membrane splitting and microaneurysm formation associated with nitrosourea therapy

A patient who developed renal insufficiency following nitrosourea therapy is reported. Light, immunohistochemical, and electron microscopic studies of the renal biopsy disclosed an unusual glomerular basement membrane injury. Light microscopy showed extensive basement membrane splitting and capillary aneurysm formation. Electron microscopic examination revealed an extensive subendothelial accumulation of electron-lucent granular material. The glomerular basement membrane was separated from the mesangium and showed splitting of the lamina densa. Immunofluorescent and immunoperoxidase staining of the glomeruli was negative for immunoglobulin, complement, and fibrinogen. This form of nitrosourea-associated glomerular injury has not been described previously.

A phase II study of chlorozotocin in advanced large bowel carcinoma. A cooperative study between two institutions

Mayo clinic and georgetown university carried out a cooperative phase II study of chlorozotocin in measurable advanced large bowel carcinoma. Of 78 evaluable patients randomized, 39 received low-dose (120 mg/m2 if previously untreated, 100 mg/m2 if previously treated) and 39 high-dose (200 mg/m2 if previously untreated, 175 mg/m2 if previously treated) chlorozotocin intravenously at 6-week intervals. Both groups were comparable in regard to age, prior treatment, treating institution, site of metastases, and performance scores. Overall response rate was 8%, including 5% in low-dose patients and 10% in high-dose patients. Toxicity was mild to moderate, with gastrointestinal toxicity substantially, and hematologic toxicity somewhat less, than seen with other nitrosoureas. Time to progression and survival showed no significant difference between patients treated on the low- and high-dose schedules. As chlorozotocin produced less nausea and vomiting than other nitrosoureas, even in the high-dose regimen, it should be considered for evaluation in neoplasms where nitrosoureas have shown more activity than in colorectal carcinoma.

Nitroimidazoles as modifiers of nitrosourea pharmacokinetics

We have studied the effect of a number of nitroimidazole sensitizers of varying lipophilicity on the pharmacokinetics of CCNU in mice. It was found that the effectiveness of these compounds in producing pharmacokinetic effects correlated directly with their lipophilicity, viz. in the order: benznidazole (Benzo) greater than Ro07-1902 misonidazole greater than (MISO) greater than Ro05-9963. The effects of MISO on the pharmacokinetics of 4 nitrosoureas of differing lipophilicity were also investigated. The plasma clearances of CCNU, BCNU and MeCCNU (high lipophilicity) were slowed by MISO whereas that of chlorozotocin (Chlz) (low lipophilicity) was unaffected. Thus, it seems that for a pharmacokinetic interaction to occur between a nitroimidazole and a nitrosourea, both the modifier and the cytotoxic agent must have a requisite degree of lipophilicity. As the same requirement appears to hold for enhancement of tumor response, these data provide further evidence that pharmacokinetic modification plays a major role in chemosensitization.