Differential effects of procarbazine and methylnitrosourea on the accumulation of O6-methylguanine and the depletion and recovery of O6-alkylguanine-DNA alkyltransferase in rat tissues

The Recombinant Oncolytic Virus VV-GMCSF-Lact and Chemotherapy Drugs against Human Glioma

Virotherapy is one of the perspective technologies in the treatment of malignant neoplasms. Previously, we have developed oncolytic vaccinia virus VV-GMCSF-Lact and its high cytotoxic activity and antitumor efficacy against glioma was shown. In this work, using immortalized and patient-derived cells with different sensitivity to VV-GMCSF-Lact, we evaluated the cytotoxic effect of chemotherapy agents. Additionally, we studied the combination of VV-GMCSF-Lact with temozolomide which is the most preferred drug for glioma treatment. Experimental results indicate that first adding temozolomide and then the virus to the cells is inherently more efficient than dosing it in the reverse order. Testing these regimens in the U87 MG xenograft glioblastoma model confirmed this effect, as assessed by tumor growth inhibition index and histological analysis. Moreover, VV-GMCSF-Lact as monotherapy is more effective against U87 MG glioblastoma xenografts comparing temozolomide.

Serendipity in Cancer Drug Discovery: Rational or Coincidence?

Novel drug development leading to final approval by the US FDA can cost as much as two billion dollars. Why the cost of novel drug discovery is so expensive is unclear, but high failure rates at the preclinical and clinical stages are major reasons. Although therapies targeting a given cell signaling pathway or a protein have become prominent in drug discovery, such treatments have done little in preventing or treating any disease alone because most chronic diseases have been found to be multigenic. A review of the discovery of numerous drugs currently being used for various diseases including cancer, diabetes, cardiovascular, pulmonary, and autoimmune diseases indicates that serendipity has played a major role in the discovery. In this review we provide evidence that rational drug discovery and targeted therapies have minimal roles in drug discovery, and that serendipity and coincidence have played and continue to play major roles. The primary focus in this review is on cancer-related drug discovery.

Cilengitide with metronomic temozolomide, procarbazine, and standard radiotherapy in patients with glioblastoma and unmethylated MGMT gene promoter in ExCentric, an open-label phase II trial

Newly diagnosed glioblastoma multiforme with unmethylated MGMT promoter has a poor prognosis, with a median survival of 12 months. This phase II study investigated the efficacy and safety of combining the selective integrin inhibitor cilengitide with a combination of metronomic temozolomide and procarbazine for these patients. Eligible patients (newly diagnosed, histologically confirmed supratentorial glioblastoma with unmethylated MGMT promoter) were entered into this multicentre study. Cilengitide (2000 mg IV twice weekly) was commenced 1 week prior to radiotherapy combined with daily temozolomide (60 mg/m(2)) and procarbazine (50 or 100 mg) and, after 4 weeks' break, followed by six adjuvant cycles of temozolomide (50-60 mg/m(2)) and procarbazine (50 or 100 mg) on days 1-20, every 28 days. Cilengitide was continued for up to 12 months or until disease progression or unacceptable toxicity. The primary endpoint for efficacy was a 12-month overall survival rate of 65 %. Twenty-nine patients completed study treatment. Sixteen patients survived for 12 months or more, an overall survival rate of 55 %. The median overall survival was 14.5 months (95 % CI 11.1-19.6) and the median progression-free survival was 7.4 months (95 % CI 6.1-8). Cilengitide combined with metronomic temozolomide and procarbazine in MGMT-promoter unmethylated glioblastoma did not improve survival compared with historical data and does not warrant further investigation.

Randomized trial of chemoradiotherapy and adjuvant chemotherapy with nimustine (ACNU) versus nimustine plus procarbazine for newly diagnosed anaplastic astrocytoma and glioblastoma (JCOG0305)

PURPOSE

Glioblastoma (GBM) is one of the worst cancers in terms of prognosis. Standard therapy consists of resection with concomitant chemoradiotherapy. Resistance to nimustine hydrochloride (ACNU), an alkylating agent, has been linked to methylguanine DNA methyltransferase (MGMT). Daily administration of procarbazine (PCZ) has been reported to decrease MGMT activity. This study investigated the efficacy of ACNU + PCZ compared to ACNU alone for GBM and anaplastic astrocytoma (AA).

METHODS

Patients (20-69 years) who had newly diagnosed AA and GBM were randomly assigned to receive radiotherapy with ACNU alone or with ACNU + PCZ. The primary endpoint was overall survival (OS). This was designed as a phase II/III trial with a total sample size of 310 patients and was registered as UMIN-CTR C000000108.

RESULTS

After 111 patients from 19 centers in Japan were enrolled, this study was terminated early because temozolomide was newly approved in Japan. The median OS and median progression-free survival (PFS) with ACNU alone (n = 55) or ACNU + PCZ (n = 56) in the intention-to-treat population were 27.4 and 22.4 months (p = 0.75), and 8.6 and 6.9 months, respectively. The median OS and median PFS of the GBM subgroup treated with ACNU alone (n = 40) or ACNU + PCZ (n = 41) were 19.0 and 19.5 months, and 6.2 and 6.3 months, respectively. Grade 3/4 hematologic adverse events occurred in more than 40 % of patients in both arms, and 27 % of patients discontinued treatment because of adverse events.

CONCLUSIONS

The addition of PCZ to ACNU was not beneficial, in comparison with ACNU alone, for patients with newly diagnosed AA and GBM.

Reduced methylation-induced mutagenesis in rat splenocytes in vivo by sub-chronic low dose exposure to N-metyl-N-nitrosourea

Estimates of genotoxic effects of mutagens at low and protracted doses are often based on linear extrapolation of data obtained at relatively high doses. To test the validity of such an approach, a comparison was made between the mutagenicity of N-methyl-N-nitrosourea (MNU) in T-lymphocytes of the rat following two treatment protocols, i.e. sub-chronic exposure to a low dose (15-45 repeated exposures to 1mg/kg of MNU) or acute exposure to a single high dose (15, 30 or 45 mg/kg of MNU). Mutation induction appeared dramatically lower following sub-chronic treatment compared to treatment with a single high exposure. Furthermore, DNA sequence analysis of the coding region of the hprt gene in MNU-induced mutants showed that acute high dose treatment causes mainly GC-->AT base pair changes, whereas sub-chronic treatment results in a significant contribution of AT base pair changes to mutation induction. We hypothesize that O(6)-methylguanine-DNA methyltransferase is saturated after acute treatments, while after sub-chronic treatment most O(6)-methylguanine is efficiently repaired. These data suggest (i) that risk estimations at low and protracted doses of MNU on the basis of linear extrapolation of effects measured at high dose are too high and (ii) that the protective effects of DNA repair processes are relatively strong at low sub-chronic exposure.

Nasal cytotoxic and carcinogenic activities of systemically distributed organic chemicals

Toxicity and carcinogenicity in the mucosa of the nasal passages in rodents has been produced by a variety of organic chemicals which are systemically distributed. In this review, 14 such chemicals or classes were identified that produced rodent nasal cytotoxicity, but not carcinogenicity, and 11 were identified that produced nasal carcinogenicity. Most chemicals that affect the nasal mucosa were either concentrated in that tissue or readily activated there, or both. All chemicals with effects in the nasal mucosa that were DNA-reactive, were also carcinogenic, if adequately tested. None of the rodent nasal cytotoxins has been identified as a human systemic nasal toxin. This may reflect the lesser biotransformation activity of human nasal mucosa compared to rodent and the much lower levels of human exposures. None of the rodent carcinogens lacking DNA reactivity has been identified as a nasal carcinogen or other cancer hazard to humans. Some DNA-reactive rodent carcinogens that affect the nasal mucosa, as well as other tissues, have been associated with cancer at various sites in humans, but not the nasal cavity. Thus, findings in only the rodent nasal mucosa do not necessarily predict either a toxic or carcinogenic hazard to that tissue in humans.

Feasibility and response to 1-(4-amino-2-methyl-5-pyrimidynyl) methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride chemotherapy with pre-treated procarbazine for elderly patients with newly diagnosed glioblastoma

PURPOSE

To evaluate the feasibility of 1-(4-amino- 2-methyl-5-pyrimidynyl) methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride (ACNU) of pre-treated procarbazine for elderly patients with newly diagnosed glioblastomas.

PATIENTS AND METHODS

From January 2004 to March 2005, 7 patients with glioblastoma were enrolled. After maximal surgical resection, patients were treated with two to four cycles of procarbazine (100 mg/m(2) for day 1 to 5), ACNU (80 mg/m(2)/day(1) for day 5), cepharantine (70 mg for day 5 and 12) and vincristine (1.4 mg/m(2) for day 5 and 12).

RESULTS

Significant toxicities of this regimen, including infectious toxicities, are described. Among the 7 patients enrolled, there were 6 patients were died, and one was still alive with disease at 13 months. The 6-month progression-free survival and 1-year overall survival are 29% (95% CI, 16% to 73%) and 29% (95% CI, 16% to 73%), respectively.

CONCLUSION

The chemotherapy regimen is active but too toxic for elderly patients with newly diagnosed glioblastoma.

Randomized Controlled Trial on Malignant Brain Tumors-Activities of the Japan Clinical Oncology Group-Brain Tumor Study Group-

The Japan Clinical Oncology Group (JCOG)-Brain Tumor Study Group was organized with the support of the Health and Labour Sciences Research Grants of the Ministry of Health, Labour and Welfare. The group is now preparing a multi-institutional randomized controlled phase II/III study of chemoradiotherapy using ACNU versus procarbazine and ACNU for astrocytoma grades 3 and 4. The overall survival and response rates will be compared between the patients treated with ACNU and those treated with ACNU plus procarbazine. This study, under the surveillance of the JCOG, aims to set a standard protocol for treating patients with malignant glioma. Moreover, the study will establish a proper methodology for performing randomized studies in the field of neuro-oncology.

Phase I study of temozolamide (TMZ) combined with procarbazine (PCB) in patients with gliomas

Temozolomide (TMZ) is an oral alkylating agent with a good safety profile and proven efficacy in the treatment of malignant glioma. Procarbazine (PCB) has been used for treating gliomas for many years and here both agents were combined in the treatment. This phase I study was designed to evaluate the efficacy and safety of TMZ alone (course 1) and TMZ in combination with PCB in subsequent courses in chemotherapy-naïve patients with malignant glioma. Patients with anaplastic astrocytoma (AA), glioblastoma multiforme (GBM) and low-grade glioma were treated with TMZ 200 mg m(-2) on days 1-5 on a 28-day cycle for course 1. Beginning with course 2, cohorts of patients received TMZ at full dose with escalating doses of PCB (50/75/100/125 mg m(-2) days 1-5 given 1 h prior to TMZ). A total of 28 patients were enrolled with three patients each at dose level 1 and 2, 16 patients at dose level 3 and six patients at dose level 4 received 182+ cycles of treatment and were included in this analysis. In all, 16 patients had GBM, seven patients had AA, five had grade 1 or 2 glioma and the median age was 47 years. The patients had received prior surgery and radiotherapy. Responses were seen at all dose levels. Overall, there were 10 (36%) responses lasting from 2 to 17+ months. Treatment was generally well tolerated with few grade 3 or 4 toxicities, except at dose level 4, where four patients had grade 3/4 had thrombocytopaenia at this dose and several patients had moderate-to-severe lethargy. TMZ 200 mg m(-2) and PCB 100 mg m(-2) were well tolerated on a daily 5 x and four weekly cycle in patients with malignant glioma and clearly had antitumour activity.

DNA adducts and liver DNA replication in rats during chronic exposure to N-nitrosodimethylamine (NDMA) and their relationships to the dose-dependence of NDMA hepatocarcinogenesis

Exposure of rats to the hepatocarcinogen N-nitrosodimethylamine (NDMA) (0.2-2.64 ppm in the drinking water) for up to 180 days resulted in rapid accumulation of N7- and O6-methylguanine in liver and white blood cell DNA, maximum adduct levels being reached within 1-7 days, depending on the dose. The levels of both adducts remained constant up to treatment day 28, subsequently declining slowly to about 40% of maximal levels for the liver and 60% for white blood cells by day 180. In order to elucidate the role of DNA replication in NDMA hepatocarcinogenesis, changes in liver cell labeling index (LI) were also measured on treatment days 21, 120 and 180. Although the time- and dose-dependence of the observed effects were complex, a clear trend towards increased rates of hepatocyte LI, as indicated by BrdU incorporation, with increasing NDMA doses was evident, particularly above 1 ppm, a concentration above which NDMA hepatocarcinogenicity is known to increase sharply. In contrast, no increase in Kupffer cell DNA replication was found at any of the doses employed, in accordance with the low susceptibility of these cells to NDMA-induced carcinogenesis. No significant increase in the occurrence of necrotic or apoptotic cells was noted under the treatment conditions employed. These results suggest that, in addition to the accumulation of DNA damage, alterations in hepatocyte DNA replication during the chronic NDMA exposure may influence the dose-dependence of its carcinogenic efficacy.

Toxicity, mutation frequency and mutation spectrum induced by dacarbazine in CHO cells expressing different levels of O(6)-methylguanine-DNA methyltransferase

The toxicity and mutagenicity (including the mutation spectrum induced) of dacarbazine, a methylating cytostatic drug, was examined in CHO cells expressing different levels of the repair enzyme O(6)-methylguanine-DNA methyltransferase (MGMT). Expression of low or high levels of a transfected human MGMT gene under the control of the metallothionein promoter protected the cells against dacarbazine-induced toxicity and mutagenesis. In the absence of MGMT expression, the mutation spectrum in the HPRT locus was dominated by GC-->AT transitions (mostly found at 5'Pu-G sequences), while there were also a few AT-->GC transitions. Expression MGMT was associated with a substantial decrease of GC-->AT mutations, suggesting that these mutations arose primarily via O(6)-methylguanine. These data illustrate the important role of the latter lesion in the drug's mutagenic and cytotoxic activity.

Correlation of DNA adduct levels with tumor incidence: carcinogenic potency of DNA adducts

The quantitative relationship between DNA adducts and tumor incidence is evaluated in this review. All available data on DNA adduct levels determined after repeated administration of a carcinogen to rats or mice have been compiled. The list comprised 27 chemicals, of all major structural classes of carcinogens. For the correlation with tumor incidence, the DNA adduct levels measured at the given dose were normalized to the dose which resulted in a 50% tumor incidence under the conditions of a 2-year bioassay (TD50 dose). In rat liver, the calculated adduct concentration 'responsible' for a 50% hepatocellular tumor incidence spanned from 53 to 2083 adducts per 108 nucleotides, for aflatoxin B1, tamoxifen, IQ, MeIQx, 2,4-diaminotoluene, and dimethylnitrosamine (in this order). In mouse liver, the respective figures were 812 to 5543 adducts per 108 nucleotides, for ethylene oxide, dimethylnitrosamine, 4-aminobiphenyl, and 2-acetylaminofluorene. The observed span (40-fold in rats, 7-fold in mice) reflects differences between the various DNA adducts to lead to critical mutations. If additional carcinogens fit in with this astonishingly narrow range, the measurement of DNA adduct levels in target tissue has the potential to be not only an exposure marker but an individual cancer risk marker. For toremifen and styrene, low levels of DNA adducts were detected in rat liver at the end of a negative long-term bioassay. This shows that the limit of detection of DNA adducts can be well below the limit of detection of an increased tumor incidence. For a cancer risk assessment at low levels of DNA damage, treatment-related adducts must be discussed in relation to the background DNA damage and its inter- and intraindividual variability.

DNA adducts in humans after exposure to methylating agents

Human exposure to methylating agents appears to be widespread, as indicated by the frequent occurrence of methylated DNA adducts in human DNA. The high incidence of methylated DNA adducts even in humans thought not to have suffered extensive exposure to environmental methylating agents implies that chemicals of endogenous origin, probably N-nitroso compounds such as the strongly carcinogenic N-nitrosodimethylamine (NDMA), may be primarily responsible for their formation and raises the question of the carcinogenic risks associated with such exposure. In addition to accumulation of DNA damage, other factors (such as induced cell proliferation) appear to be important in determining the probability of induction of mutation or cancer by NDMA, implying that high to low dose risk extrapolations should not be based on the assumption of dose- or even adduct-linearity. Comparative studies of the accumulation and repair of methylated adducts in humans and animals treated with methylating cytostatic drugs do not reveal significant species differences. Based on this and the dosimetry of adduct accumulation in rats chronically exposed to very low doses of NDMA, it is suggested that the exposure needed to account for the levels of adducts found in human DNA may be of the order of hundreds of micrograms NDMA (or equivalent) per day, a level of exposure which may well represent a significant carcinogenic hazard for man.

Biological effect markers for exposure to carcinogenic compound and their relevance for risk assessment

In this review data are summarized on biomarkers that are used for biological effect monitoring of human populations exposed to genotoxic carcinogens. The biomarkers are DNA and protein adducts and cytogenetic effects. Most of these biomarkers are relevant for the process of carcinogenesis. Emphasis is on providing information on the properties of the biomarkers and on their relevance for predicting cancer risk. Overviews are presented of: (1) studies on effects of exposure in target tissues of human origin obtained by surgical biopsies or autopsies, (2) epidemiological studies on healthy (cancer-free) individuals, correlating the putative occupational, lifestyle or environmental exposure with increased levels of biomarkers in blood cells, and (3) studies with animal models on the relation between biomarkers and cancer. Finally, on the basis of epidemiological data the possibilities were explored to use biomarker data to estimate the risk of death due to cancer. For several biomarkers the increment of the cancer mortality risk was calculated on the basis of a lifetime doubling of the biomarker level.

Molecular dosimetry of chemical mutagens. Relationship between DNA adduct formation and genetic changes analyzed at the molecular level

This is a review of the work carried out by 16 collaborating institutes within a project which was part of the European Programme: Science and Technology for Environmental Protection (STEP). The purpose of the project was to investigate the relationship between the exposure to genotoxic chemicals and the induction of DNA damage and genetic effects as determined in in vitro and in vivo assays under laboratory conditions. Two types of investigation were performed: (i) determination of the relationship between the extent of exposure to a genotoxic chemical and the frequency of DNA adducts formed in the test organism and (ii) identification of those DNA adducts which are responsible for the biological effects of genotoxic chemicals. The research was carried out with a series of alkylating agents which all induce similar types of DNA damage but for which the proportions of the different types of adducts vary. The frequency of this type of DNA damage was also modulated by base excision repair processes. In addition, a number of genotoxic agents which cause DNA damage recognized by nucleotide excision repair were investigated. The consequences of DNA adduct formation, i.e., the induction of gene mutations, were analyzed at the DNA sequence level, generating mutational spectra. These investigations of the mutational specificities of carcinogens contributed to our understanding of the molecular mechanisms which are involved in cancer induction by genotoxins.