Abstract 4336: Direct genotyping of CYP2A6 whole gene deletion: A new biomarker for prognosis of lung adenocarcinoma in Japanese smoking male

Purpose: Cytochrome P450 (CYP2A6) is known as an enzyme responsible for the metabolism of activation of tobacco-specific nitrosamines to their ultimate carcinogenic forms and metabolism of nicotine. We here report that the genetic polymorphisms of human CYP2A6*4 is associated with primary lung cancer and their overall survival.

Experimental Design: We prepared genomic DNA samples from 387 Japanese patients with primary lung cancer and the genetic polymorphisms of human CYP2A6*4 (whole gene deletion) by the rapid genetic testing method we developed in this study. We analyzed the association between the CYP2A6*4 gene, NRF2 gene and overall survival.

Results: Patients harboring wild-type CYP2A6*1 and whole gene deletion CYP2A6*4/*4 numbered 380 (98.2%) and 7 (1.8%), respectively. Its frequency was four-fold higher in male patients than in female (P = 0.038).Multivariate logistic regression models revealed that the genetic polymorphisms of human CYP2A6*4 were significantly related to gender and smoking behavior. Interestingly, lung cancer patients carrying CYP2A6*4/*4 (whole gene deletion), the NRF2 SNP heterozygous (c.-617C/A) and wild-type homozygous (c.-617C/C) exhibited remarkable survival over 1,500 days after surgical operation.

Conclusion: CYP2A6*4/*4 whole gene is considered to be a prognostic biomarker for assessing both the gender-related risk of lung adenocarcinoma in the smoking sub-population and their overall survival.

Citation Format: Yasuko Okano, Yasushi Ichikawa, Yohei Miyagi, Takashi Chishima, Yutaka Natsumeda. Direct genotyping of CYP2A6 whole gene deletion: A new biomarker for prognosis of lung adenocarcinoma in Japanese smoking male. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4336. doi:10.1158/1538-7445.AM2015-4336

Recent trends in colonic diverticulosis in Yokohama City: a possibility of changing to a more Western profile

OBJECTIVE

Right-sided type colonic diverticulosis has been predominant in Japan, in contrast to European counties where the left-sided type is predominant. Considering the recent change in the dietary habits of Japanese people to a more Western diet in urban areas of Japan, the features of colonic diverticulosis may also change to reflect a more Western type. Therefore, we attempted to clarify the current situation.

METHODS

A total of 435 consecutive outpatients who agreed to a barium enema and complete examination were enrolled in this study.

RESULTS

113 patients (26.0%) revealed colon diverticulosis; 50.4% of the patients had more than ten diverticula. The percentage of man with ten or more diverticula (67.4%) was significantly higher than that of women patients (40.0%, p<0.01). Among the 88 patients who had four or more diverticula, 39 patients (44.3%) were right-side dominant, 27 (30.7%) left-side dominant and 22 (25.0%) were both-sides. Thirteen (68.4%) of the 19 patients who had more than 30 diverticula were left-side dominant.

CONCLUSION

The clinical features of colon diverticulosis in the patients living in Yokohama may be changing to reflect a more Western type, in particular decreased right-side dominance, increases in the left-side and both-sides dominant patients, and the emergence of patients with crowded diverticula in the left-side colon was observed.

Abstract 1857: Prognostic biomarker for SNP (-617C-A) in ARE-like loci of the NRF2 gene in lung adenocarcinoma

Purpose: We here report that SNP (c.-617C&gt;A; rs6721961) in the ARE-like region of NRF2 gene is associated with Japanese non-smoking female patients with adenocarcinoma and their overall survival.

Experimental Design: We prepared genomic DNA samples from 387 Japanese patients with primary lung cancer and detected a SNP (-617C&gt;A) in NRF2 gene by the rapid genetic testing method we developed in this study. We analyzed the association between the SNP in the NRF2 gene and overall survival.

Results:Patients harboring wild-type -617C/C, -617C/A, and -617A/A alleles numbered 216 (55.8%), 147 (38.0%), and 24 (6.2%), respectively. Multivariate logistic regression models revealed that SNP homozygote (-617A/A) was significantly related to gender. Its frequency was four-fold higher in female patients than in males (10.8% female vs 2.7% male) and was associated with female non-smokers with adenocarcinoma. Interestingly, lung cancer patients carrying the SNP homozygous alleles (-617A/A) and the 309T (WT) allele in the MDM2 gene exhibited remarkable survival over 1,700 days after surgical operation (log-rank p=0.021). Conclusion: SNP homozygous (-617 A/A) alleles in the NRF2 gene are associated with female non-smokers with adenocarcinoma and regarded as a prognostic biomarker for assessing overall survival of patients with lung adenocarcinoma.

Citation Format: Yasuko Okano, Yasushi Ichikawa, Yohei Miyagi, Keiichi Kondo, Yutaka Natsumeda. Prognostic biomarker for SNP (-617C-A) in ARE-like loci of the NRF2 gene in lung adenocarcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1857. doi:10.1158/1538-7445.AM2014-1857

Conditional knockout of the leptin receptor in the colonic epithelium revealed the local effects of leptin receptor signaling in the progression of colonic tumors in mice

Leptin, secreted by the adipose tissue and known to be related to obesity, is considered to be involved in the onset and progression of colorectal cancer. However, the exact role of leptin in colorectal carcinogenesis is still unclear, as several controversial reports have been published on the various systemic effects of leptin. The aim of this study was to clarify the local and precise roles of leptin receptor (LEPR)-mediated signaling in colonic carcinogenesis using intestinal epithelium-specific LEPRb conditional knockout (cKO) mice. We produced and used colonic epithelium-specific LEPRb cKO mice to investigate the carcinogen-induced formation of aberrant crypt foci (ACF) and tumors in the colon, using their littermates as control. There were no differences in the body weight or systemic condition between the control and cKO mice. The tumor sizes and number of large-sized tumors were significantly lower in the cKO mice as compared with those in the control mice. On the other hand, there was no significant difference in the proliferative activity of the normal colonic epithelial cells or ACF formation between the control and cKO mice. In the control mice, marked increase of the LEPRb expression level was observed in the colonic tumors as compared with that in the normal epithelium; furthermore, signal transducer and activator of transcription (STAT3) was activated in the tumor cells. These findings suggest that STAT3 is one of the important molecules downstream of LEPRb, and LEPRb/STAT3 signaling controls tumor cell proliferation. We demonstrated the importance of local/regional LEPR-mediated signaling in colorectal carcinogenesis.

SNP (-617C>A) in ARE-like loci of the NRF2 gene: a new biomarker for prognosis of lung adenocarcinoma in Japanese non-smoking women

Purpose

The transcription factor NRF2 plays a pivotal role in protecting normal cells from external toxic challenges and oxidative stress, whereas it can also endow cancer cells resistance to anticancer drugs. At present little information is available about the genetic polymorphisms of the NRF2 gene and their clinical relevance. We aimed to investigate the single nucleotide polymorphisms in the NRF2 gene as a prognostic biomarker in lung cancer.

Experimental Design

We prepared genomic DNA samples from 387 Japanese patients with primary lung cancer and detected SNP (c.–617C>A; rs6721961) in the ARE-like loci of the human NRF2 gene by the rapid genetic testing method we developed in this study. We then analyzed the association between the SNP in the NRF2 gene and patients’ overall survival.

Results

Patients harboring wild-type (WT) homozygous (c.–617C/C), SNP heterozygous (c.–617C/A), and SNP homozygous (c.–617A/A) alleles numbered 216 (55.8%), 147 (38.0%), and 24 (6.2%), respectively. Multivariate logistic regression models revealed that SNP homozygote (c.–617A/A) was significantly related to gender. Its frequency was four-fold higher in female patients than in males (10.8% female vs 2.7% male) and was associated with female non-smokers with adenocarcinoma. Interestingly, lung cancer patients carrying NRF2 SNP homozygous alleles (c.–617A/A) and the 309T (WT) allele in the MDM2 gene exhibited remarkable survival over 1,700 days after surgical operation (log-rank p = 0.021).

Conclusion

SNP homozygous (c.–617A/A) alleles in the NRF2 gene are associated with female non-smokers with adenocarcinoma and regarded as a prognostic biomarker for assessing overall survival of patients with lung adenocarcinoma.

Increased oxidative stress and coenzyme Q10 deficiency in juvenile fibromyalgia: amelioration of hypercholesterolemia and fatigue by ubiquinol-10 supplementation

Fibromyalgia (FM) is characterized by generalized pain and chronic fatigue of unknown etiology. To evaluate the role of oxidative stress in this disorder, we measured plasma levels of ubiquinone-10, ubiquinol-10, free cholesterol (FC), cholesterol esters (CE), and free fatty acids (FFA) in patients with juvenile FM (n=10) and in healthy control subjects (n=67). Levels of FC and CE were significantly increased in juvenile FM as compared with controls, suggesting the presence of hypercholesterolemia in this disease. However, plasma level of ubiquinol-10 was significantly decreased and the ratio of ubiquinone-10 to total coenzyme Q10 (%CoQ10) was significantly increased in juvenile FM relative to healthy controls, suggesting that FM is associated with coenzyme Q10 deficiency and increased oxidative stress. Moreover, plasma level of FFA was significantly higher and the content of polyunsaturated fatty acids (PUFA) in total FFA was significantly lower in FM than in controls, suggesting increased tissue oxidative damage in juvenile FM. Interestingly, the content of monoenoic acids, such as oleic and palmitoleic acids, was significantly increased in FM relative to controls, probably to compensate for the loss of PUFA. Next, we examined the effect of ubiquinol-10 supplementation (100 mg/day for 12 weeks) in FM patients. This resulted in an increase in coenzyme Q10 levels and a decrease in %CoQ10. No changes were observed in FFA levels or their composition. However, plasma levels of FC and CE significantly decreased and the ratio of FC to CE also significantly decreased, suggesting that ubiquinol-10 supplementation improved cholesterol metabolism. Ubiquinol-10 supplementation also improved chronic fatigue scores as measured by the Chalder Fatigue Scale.

Abstract 2361: SNP (-617G&gt;A) in ARE-like loci of the NRF2 gene: a new biomarker for prognosis of lung adenocarcinoma

Purpose: Accumulating evidence suggests nuclear factor (erythroid-derived 2)-like 2 (NRF2) plays an important role as cellular defense, tumor suppression, and oncogenesis. However, little information is available as to the genetic polymorohisms of the NRF2 gene and their clinical relevance. We aimed to validate the NRF2 gene as a prognostic biomarker in lung cancer.

Experimental Design: We prepared genomic DNA from 392 Japanese patients with primary lung cancer and detected a SNP (c.-617C&gt;A) in the ARE-like loci of the human NRF2 gene by the rapid genetic testing method we developed in this study. We analyzed an association between the NRF2 gene and overall survival.

Results: We detected homozygous (A/A) and heterozygous (C/A) alleles with the SNP (c.-617C&gt;A) in 24 (6.2%) and 147 (38.0%) patients, respectively. The frequency of the homozygote (A/A) was four-fold higher in females than in males (11.0% versus 2.7%). Multivariate logistic regression models including standard lung cancer factors revealed that the homozygous alleles (c.-617A/A) were significantly related to gender. Interestingly, lung cancer patients carrying the homozygous alleles (c.-617A/A) exhibited remarkable survival over 1,700 days after surgical operation (log-rank p=0.021).

Conclusion: The homozygous allele (c.-617A/A) in the NRF2 gene is considered to be a prognostic biomarker for assessing both the gender-related risk of lung adenocarcinoma in the non-smoking sub-population and their overall survival.

Citation Format: Yasuko Okano, Yasushi Ichikawa, Yohei Miyagi, Yutaka Natsumeda, Toshihisa Ishikawa. SNP (-617G&gt;A) in ARE-like loci of the NRF2 gene: a new biomarker for prognosis of lung adenocarcinoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2361. doi:10.1158/1538-7445.AM2013-2361

Eicosapentaenoic acid (EPA) efficacy for colorectal aberrant crypt foci (ACF): a double-blind randomized controlled trial

BACKGROUND

Colorectal cancer (CRC) is one of the most commonly occurring neoplasms and a leading cause of cancer death worldwide, and new preventive strategies are needed to lower the burden of this disease. Eicosapentaenoic acid (EPA), the omega-3 polyunsaturated fatty acid that is widely used in the treatment of hyperlipidemia and prevention of cardiovascular disease, has recently been suggested to have a suppressive effect on tumorigenesis and cancer cell growth. In CRC chemoprevention trials, in general, the incidence of polyps or of the cancer itself is set as the study endpoint. Although the incidence rate of CRC would be the most reliable endpoint, use of this endpoint would be unsuitable for chemoprevention trials, because of the relatively low occurrence rate of CRC in the general population and the long-term observation period that it would necessitate. Moreover, there is an ethical problem in conducting long-term trials to determine whether a test drug might be effective or harmful. Aberrant crypt foci (ACF), defined as lesions containing crypts that are larger in diameter and stain more darkly with methylene blue than normal crypts, are considered as a reliable surrogate biomarker of CRC. Thus, we devised a prospective randomized controlled trial as a preliminary study prior to a CRC chemoprevention trial to evaluate the chemopreventive effect of EPA against colorectal ACF formation and the safety of this drug, in patients scheduled for polypectomy.

METHODS

This study is a multicenter, double-blind, placebo-controlled, randomized controlled trial to be conducted in patients with both colorectal ACF and colorectal polyps scheduled for polypectomy. Eligible patients shall be recruited for the study and the number of ACF in the rectum counted at the baseline colonoscopy. Then, the participants shall be allocated randomly to either one of two groups, the EPA group and the placebo group. Patients in the EPA group shall receive oral 900-mg EPA capsules thrice daily (total daily dose, 2.7 g per day), and those in the placebo group shall receive oral placebo capsules thrice daily. After one month's treatment with EPA/placebo, colonoscopic examination and polypectomy will be performed to evaluate the formation of ACF, and the cell-proliferative activity and cell-apoptotic activity in normal colorectal mucosa and colorectal polyps.

DISCUSSION

This is the first study proposed to explore the effect of EPA against colorectal ACF formation in humans.This trial has been registered in the University hospital Medical Information Network (UMIN) Clinical Trials Registry as UMIN000008172.

Capsule-endoscopic findings of ulcerative colitis patients

BACKGROUND/AIMS

Ulcerative colitis (UC) is a chronic inflammatory bowel disease characterized by diffuse mucosal inflammation, traditionally regarded as being limited to the colorectum. Although several gastroduodenal lesions have also been reported recently in cases of UC, in general, small-bowel lesions in UC are believed to be extremely rare. The aim of this study was to examine the small bowel by capsule endoscopy in patients with UC.

METHODS

The study was conducted in 23 well-documented UC patients and 23 control volunteers. The frequency of small-bowel lesions, the number of small-bowel lesions per patient and the capsule endoscopy score were comparatively evaluated between the two groups.

RESULTS

Of the 23 UC patients, 13 (57%) showed small-bowel lesions, and 8 (35%) had erosions. There were significant differences in the frequency of the small-bowel lesions (p < 0.001) and erosions (p = 0.009) between the two groups. The capsule endoscopy score was correlated with the UC disease activity index (r = 0.718, p < 0.001).

CONCLUSIONS

This is the first capsule-endoscopic study conducted to examine the small-bowel involvement in UC patients as compared with the healthy volunteers. It was concluded that UC, a chronic inflammatory bowel disease, can also involve the small bowel.

Heterogeneity of the efficacy of the 23-valent pneumococcal polysaccharide vaccine caused by various underlying conditions of chronic pulmonary disease in older patients: prospective cohort study

OBJECTIVE

To determine the ideal conditions for use of the 23-valent pneumococcal polysaccharide vaccine (PPV23) in older outpatients with chronic pulmonary diseases.

DESIGN

Prospective cohort study.

PARTICIPANTS

1378 outpatients with chronic pulmonary diseases ≥ 60 years of age.

INTERVENTION

Participants were educated about PPV23, and those who responded affirmatively were vaccinated between August and November 2002. The participants who chose no intervention served as controls. The prevaccine period was defined as August 2001 to August 2002. Participants were followed for 2 years from December 2002 or until death.

MAIN OUTCOME MEASURES

Events of interest included the first episode of bacterial (including pneumococcal) pulmonary infection (primary endpoint) and death of any cause (secondary endpoint).

RESULTS

Frequent episodes of pulmonary infection during the prevaccine period significantly decreased event-free survival during the 2-year observation period (p<0.001). Chronic respiratory failure was associated with a decreased event-free survival only when the pulmonary infection episode did not occur in the prevaccine period (p<0.001). No significant differences in event-free survival were observed between the vaccinated and unvaccinated group during analysis of the entire cohort. In the Cox proportional hazards regression model, event-free survival decreased significantly when pulmonary infection occurred in the prevaccine period. In the subgroup analysis, the first episode of bacterial pulmonary infection (but not death of any cause) was reduced significantly by PPV23 only in patients with chronic respiratory failure who had no episodes of pulmonary infection during the prevaccine period (p=0.019).

CONCLUSION

The efficacy of PPV23 against pulmonary infection and death of any cause might be unachievable if pulmonary infection occurs during the prevaccine period. PPV23 needs to be given to older patients with chronic pulmonary disease at an earlier time in which infectious complications in the lung have not yet occurred.

Pravastatin potentiates increases in serum adiponectin concentration in dyslipidemic patients receiving thiazolidinedione: the DOLPHIN study

AIM

A reduced risk of type 2 diabetes has been reported following treatment with pravastatin. Adiponectin is an adipocyte-derived protein that has an antidiabetic property. The objective of this study was to evaluate the effect of pravastatin on serum adiponectin concentration and other influencing factors.

METHODS

This study was a multicenter observational study: Dyslipidemia Open-labeled observational study by Lipid-lowering therapy with Pravastatin of the effect on High-molecular weight adiponectin in Nippon Yokohama (DOLPHIN). The protocol was registered in the UMIN Clinical Trial Registry as UMIN000000791. All patients received pravastatin 10 mg/day for 6 months and the change in concentration of total and high molecular weight adiponectin was assessed before and after follow-up. The difference in the change in total adiponectin concentration by patient characteristics was analyzed by an unpaired t-test. Influences of continuous variable factors on the change in total adiponectin concentration were estimated by simple linear regression analyses. Finally, in order to estimate the influences of factors that potentially affect the change in total adiponectin concentration induced by pravastatin, multiple linear regression analysis was conducted.

RESULTS

After 6 months, total adiponectin concentration was increased significantly by 23.2% from 11.7±6.4 to 13.7±8.6 µg/mL (p=0.002). The use of thiazolidinedione as a concomitant medication was the only significant influencing factor (β=0.580, p<0.001).

CONCLUSION

Pravastatin increased the serum adiponectin concentration in Japanese dyslipidemic patients without previous coronary artery disease. Interestingly, this effect was seen synergistically in combination with thiazolidinedione.

A phase I study of the safety and pharmacokinetics of edotecarin (J-107088), a novel topoisomerase I inhibitor, in patients with advanced solid tumors

PURPOSE

To assess the maximum tolerated dose, safety, and pharmacokinetic (PK) profile of escalating doses of the novel topoisomerase I (topo I) inhibitor edotecarin (J-107088) given as a 2-h intravenous (IV) infusion once every 21 days in patients with advanced solid tumors who had not responded to standard therapy.

PATIENTS AND METHODS

Twenty-nine patients (18M:11F) received a 2-h IV infusion of edotecarin in doses of 6, 8, 11, 13, or 15 mg/m(2) every 21 days (with an additional 1-2 weeks permitted for recovery) and were evaluated for safety, PK, and tumor response.

RESULTS

The most common non-hematologic toxicities were grade 1-2 nausea, fatigue, anorexia, vomiting, and fever. The most common hematologic toxicities were grade 1-2 thrombocytopenia and grade 3-4 neutropenia, leukopenia, and anemia. No grade 3-4 diarrhea was reported. Dose-limiting toxicities were observed in four patients at the 15 mg/m(2) dose and one patient at the 13 mg/m(2) dose. These toxicities included grade 3 nausea, vomiting, headache, and fatigue, as well as grade 4 neutropenia and febrile neutropenia. The maximum tolerated dose was declared at 15 mg/m(2). One patient with bladder cancer had a confirmed partial response at a dose of 13 mg/m(2). There was a trend to dose-proportional increases in edotecarin peak plasma concentrations and area under the curve values. Renal excretion of edotecarin was minimal (3-8% of the dose).

CONCLUSION

The recommended Phase II dose of edotecarin is 13 mg/m(2) once every 21 days. The toxicities in this study were those typical of cytotoxic chemotherapy and less severe than those associated with other topo I inhibitors. The observed safety profile and preliminary evidence of clinical benefit warrant further investigation of this drug as monotherapy or part of combination therapy in patients with solid tumors.

Preferential inhibition of human phosphodiesterase 4 by ibudilast

Ibudilast ophthalmic solution exhibited an improved clinical efficacy over cromoglycate in the treatment of allergic conjunctivitis. To further characterize its principal mode of action, the phosphodiesterase (PDE) inhibitory profile of ibudilast has been examined using human recombinant enzymes. Ibudilast, but not the other commonly used anti-allergic ophthalmic solutions including cromoglycate, ketotifen, tranilast and levocabastine, potently inhibits purified human PDE4A, 4B, 4C and 4D with IC50 values at 54, 65, 239 and 166 nM, respectively. Ibudilast effectively blocks lipopolysaccharide (LPS)-induced tumor necrosis factor (TNFalpha, IC50 = 6.2 microM) and N-formyl-Met-Leu-Phe (fMLP)-induced leukotriene (LT) B4 biosynthesis (IC50 = 2.5 microM) in human whole blood, which are 3 and 6-fold more potent than cilomilast, respectively. The attenuated inflammatory and allergic responses from the potent and preferential PDE4 inhibition of ibudilast may have contributed significantly to its beneficial pharmacological responses and distinguishes ibudilast from the other ophthalmic solutions in the treatment of ocular allergy.

Phase I and pharmacokinetic study of edotecarin, a novel topoisomerase I inhibitor, administered once every 3 weeks in patients with solid tumors

PURPOSE

Edotecarin (J-107088) is a potent indolocarbazole topoisomerase I inhibitor which is structurally distinct from the camptothecins. This study aimed to determine the maximum tolerated dose (MTD), the recommended dose for future Phase II studies and the safety, pharmacokinetic profile, and preliminary antitumor activity of edotecarin in a population of patients with advanced solid tumors.

EXPERIMENTAL DESIGN

Edotecarin was administered as a single dose by IV infusion over 2 h every 21 days (with 1 week permitted for recovery from toxicities, if needed) in patients with advanced solid tumors. Doses ranged from 8 to 15 mg/m(2). Pharmacokinetic assessments were performed during and after the first administration.

RESULTS

Twenty-four patients received 61 cycles of therapy. Dose-limiting toxicities (infection, febrile neutropenia, constipation, ileus, and prolonged grade 4 granulocytopenia) were observed in 3 of 5 evaluable patients at the 15 mg/m(2) dose, defining the MTD. The most commonly reported non-hematologic toxicities were anorexia, nausea, malaise, and constipation. Diarrhea was neither frequent nor severe. Neutropenia was the most common hematologic toxicity (grade 3-4 in 21/23 patients during cycle 1). Plasma concentrations of edotecarin rose rapidly following the start of the 2-hour infusion, reaching C (max) values of 103+/-17 ng/ml at the 13 mg/m(2) dose, and decreased steeply after the end of the infusion. Plasma concentrations declined to approximately 1-2 ng/ml at 26 h post start of infusion, the last PK sampling time point. The mean apparent plasma half-life of the drug was 20 h, which should be considered a preliminary estimate until results from studies with a longer duration of plasma sampling are available. A mean of 1.4-3.6% of the dose was recovered as unchanged drug in the urine over 48 h. Unconfirmed tumor regression > or =50% was observed in 2 patients, 1 with metastatic gastric carcinoma and 1 with esophageal cancer.

CONCLUSIONS

The MTD of edotecarin administered IV over 2 h every 21 days was 15 mg/m(2). The recommended dose for Phase II studies with a 3-week schedule (with 1 week permitted for recovery from toxicities, if needed) is 13 mg/m(2). The observed safety profile and preliminary evidence of antitumor activity warrant further investigation of this drug in solid tumors.

Finasteride in the treatment of Japanese men with male pattern hair loss

Finasteride is a type 2 5 alpha-reductase inhibitor that inhibits conversion of testosterone to dihydrotestosterone, a key mediator of male pattern hair loss (androgenetic alopecia). The objective of this study was to identify the optimal dosage of finasteride and to evaluate its efficacy and safety in the treatment of Japanese men with male pattern hair loss. In this double- blind randomized study, 414 Japanese men with male pattern hair loss received finasteride 1 mg (n = 139), finasteride 0.2 mg (n = 137), or placebo (n = 38) once daily for 48 weeks. Efficacy was evaluated by global photographic assessment, patient self-assessment, and investigator assessment. All efficacy endpoints showed significant improvement with finasteride therapy by 12 weeks (p < 0.05 versus placebo). At 48 weeks, 58%, 54%, and 6% of men in the finasteride 1 mg, finasteride 0.2 mg, and placebo groups, respectively, had improved based on assessments of global photographs. All efficacy endpoints were numerically superior for the 1 mg dose over the 0.2 mg dose at 48 weeks. Finasteride treatment was generally well tolerated. Finasteride 1 mg\day slows hair loss and improves hair growth in Japanese men with male pattern hair loss.

[Rizatriptan (Maxalt), a new entity of triptan for migraine: pharmacology and therapeutic relevance]

Rizatriptan is a highly potent, selective serotonin 5-HT(1B/1D)-receptor agonist. Current theories on the mechanism of migraine suggest the central role of vasodilation of intracranial, extracerebral blood vessels and activation of perivascular trigeminal sensory nerves. There abundantly exist 5-HT(1B) receptors in meningeal blood vessels and 5-HT(1D) receptors in the trigeminal ganglia. The therapeutic activity of rizatriptan in migraine can most likely be attributed to agonist effects at 5-HT(1B/1D) receptors on these target sites. Two types of the 10 mg formulation, a tablet (Maxalt) tablet) and an orally disintegrating tablet (Maxalt)RPD tablet), are available. The latter may have a clinical relevance for patients who administer it without liquid. Pharmacokinetic study demonstrated the approximate T(max) of 1.0 or 1.1 h in tablets and 1.3 h in RPD tablets, resulting in early onset for headache relief and also pain free. Bioavailability was estimated to be about 45%. The efficacy and good tolerability and underlying profiles of pharmacokinetics of rizatriptan are almost similar between Japanese and other races, and a reduction in headache response up to 2 h can be attained in a large majority of patients. Several reports have described the favorable clinical profile of rizatriptan in comparison to other triptans. Rizatriptan is thus effective and provides migraine sufferers with an appropriate quality of life.

Mycophenolic acid, an inhibitor of IMP dehydrogenase that is also an immunosuppressive agent, suppresses the cytokine-induced nitric oxide production in mouse and rat vascular endothelial cells

Mycophenolic acid (MPA), an inhibitor of IMP dehydrogenase and de novo GTP biosynthesis, also has immunosuppressive activity. The effect of MPA on nitric oxide (NO) production by rodent brain vascular endothelial cells in culture was investigated. MPA inhibited NO production by mouse and rat brain endothelial cells that had been stimulated with a combination of interferon-gamma and tumor necrosis factor-alpha. The 50% inhibitory concentration (EC50) was in the range of 0.5-1.0 microM. However, MPA had no effect on basal NO production in mouse brain vascular endothelial cells. Brequinar, an inhibitor of de novo pyrimidine synthesis, had no effect on NO production in cytokine stimulated endothelial cells. Guanosine, which can act as a salvage pathway precursor for GTP biosynthesis, reversed the inhibitory effect of MPA in a dose-dependent fashion. We suggest that inducible NO synthase activity is dependent on GTP level and can be blocked by curtailing IMP dehydrogenase activity.

Tissue-differential expression of two distinct genes for human IMP dehydrogenase (E.C.1.1.1.205)

Human IMP dehydrogenase (E.C. 1.1.1.205) is recently regarded as a potent targeting enzyme for immunosuppressive drugs. Tissue differential expressions of human type I and type II IMP dehydrogenase were investigated in sixteen human adult organs (heart, brain, placenta, lung, liver, skeletal muscle, kidney, pancreas, spleen, thymus, prostate, testis, ovary, small intestine, colon, peripheral blood leukocytes) and five human fetal organs (heart, brain, lung, liver, kidney) using Northern blot analysis. In all tissues examined in this study, the sizes of mRNAs of each isoform were identical, respectively. The 2.3 kb type II mRNA was shown predominantly, and the 3.5 kb type I mRNA level was lower than type II in most human tissues examined. In contrast, type I IMPDH gene expressed higher than type II in peripheral blood leukocytes, uniquely. We also demonstrated that both type I and type II IMPDH genes are widely distributed among various species by Southern blot analysis. Interestingly, type I IMPDH gene may have multiple gene families in primates.

Characterization of human type I and type II IMP dehydrogenases

Human IMP dehydrogenase, a target for anticancer and immunosuppressive chemotherapy, exists as two isoforms, types I and II. Nonfusion sequences of each isoform were overexpressed in an IMP dehydrogenase-deficient strain of Escherichia coli and purified to homogeneity. Both recombinant isoforms were tetramers, which was in agreement with the subunit structure of the native mammalian enzyme. The results of initial velocity and product inhibition studies were consistent with an Ordered Bi Bi kinetic mechanism for both isoforms. Substrate affinities were similar for types I and II with Km values of 18 and 9.3 microM, respectively, for IMP, and 46 and 32 microM, respectively, for NAD.kcat values were 1.5 and 1.3 s-1 at 37 degrees C for types I and II, respectively. Xanthosine 5'-monophosphate and NADH inhibited the two isoforms with identical inhibition patterns and inhibition constants. Mycophenolic acid, however, inhibited the type II enzyme with a 4.8-fold lower K than the type I. Selective inhibitors of the inducible type II isoform may mitigate toxicity caused by inhibition of the constitutively expressed type I isoform.

Inhibition by tiazofurin of inosine 5′-phosphate dehydrogenase (IMP DH) activity in extracts of ovarian carcinomas

Cancer cells have an increased ability to synthesize GTP (guanosine triphosphate) because of increased activity of IMP DH (inosine 5'-phosphate dehydrogenase, EC 1.1.1.205). Because IMP DH activity is rate limiting for de novo biosynthesis of GTP, this enzyme was suggested as a sensitive target for chemotherapy. Tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide) is converted in the cells into the active metabolite, TAD, (thiazole-4-carboxamide adenine dinucleotide) which potently inhibits IMP DH activity. By adding TAD to tissue extracts one can determine the extent of inhibition of IMP DH. We applied the IMP DH assay method to extracts of normal ovaries (N = 11) and epithelial ovarian carcinomas (N = 10). The IMP DH activity (mean +/- SE) in ovarian carcinoma was 21.1 +/- 5.8 which was markedly higher than that observed in normal ovaries (2.9 +/- 0.7 nmol/hr/mg protein) (P < 0.05%). The inhibition by TAD of IMP DH activity in ovarian carcinomas (N = 4) was 81%. The results indicate that IMP DH activity is elevated sevenfold in ovarian carcinomas as compared to normal ovary and can be inhibited by exposure to tiazofurin (TAD). Similar high IMP DH activity and inhibition of the activity by TAD was observed in patients with chronic granulocytic leukemia in blast crisis among whom 70 to 80% remissions were reported. Since there is increased IMP DH activity in human ovarian carcinomas and in OVCAR-5 cells and tiazofurin and TAD inhibit IMP DH activity of these cells and the proliferation of human ovarian carcinoma xenografts in the mouse, tiazofurin may merit serious consideration for a Phase II trial for patients with recurrent/refractory epithelial ovarian carcinoma.

Direct assay method for guanosine 5'-monophosphate reductase activity

A sensitive and simple micromethod for the accurate measurement of GMP reductase (EC 1.6.6.8) activity in crude extracts is described. The reaction product of [8-14C]IMP was separated from the substrate [8-14C]GMP by descending chromatography on Whatman DE81 ion-exchange paper. This separation method provides an analysis of the possible interfering reactions, such as the metabolic conversion of the substrate GMP to GDP, GTP, and/or guanosine, and guanine and the loss of the product IMP to inosine, hypoxanthine, and other metabolites. Low blank values (70-90 cpm) were obtained consistently with this assay because the IMP spot moves faster than the GMP spot. The major advantages of this method are direct measurement of GMP reductase activity in crude extracts, high sensitivity (with a limit of detection of < 10 pmol of IMP production), high reproducibility (< +/- 5%), and capability to measure activity in small samples (9 micrograms protein).

Reciprocal alterations of GMP reductase and IMP dehydrogenase activities during differentiation in HL-60 leukemia cells

The study was undertaken to elucidate the regulatory roles of GMP reductase (GMPR) and IMP dehydrogenase (IMPDH) on purine interconversion during differentiation. Treatment of HL-60 cells with retinoic acid (1 microM) induced granulocytic differentiation which was accompanied with a 2.4-fold increase in GMPR and 55% decrease in IMPDH activities. Maturation induced by 12-O-tetradecanoylphorbol 13-acetate or dimethylsulfoxide was also associated with similar reciprocal alterations. Incubation with guanosine (200 microM), which expands the guanine nucleotide pool, elevated GMPR (1.9-fold) and decreased IMPDH (73%) activities. The synchronous and opposing alterations in GMPR and IMPDH activities should amplify the metabolic response due to differentiation or guanylate pool expansion.

Proliferation-linked regulation of type II IMP dehydrogenase gene in human normal lymphocytes and HL-60 leukemic cells

Human IMP dehydrogenase (IMPDH; EC 1.1.1.205) was recently found to consist of two molecular species (types I and II) with high expression of type II isozyme in leukemic cells. Here we report that the low level of type II mRNA in normal lymphocytes was up-regulated by phytohemagglutinin stimulation (3.2-fold) and Epstein-Barr viral transformation (5.7-fold). The type II mRNA expression in quiescent HL-60 cells was also elevated 2.8-fold by serum stimulation. Conversely the enhanced level of type II IMPDH mRNA in HL-60 cells was down-regulated to less than 5% along with differentiation induced by retinoic acid (1 microM), phorbol-12-myristate-13-acetate (33 nM), or dimethyl sulfoxide (1.25%) independent of end-stage phenotype. By contrast, type I IMPDH mRNA was expressed constitutively in the various states of proliferation and differentiation. The type II IMPDH stringently linked with cell proliferation should be a crucial target for antileukemic and immunosuppressive chemotherapy.

Regulation of GTP biosynthesis

In the regulation of GTP biosynthesis, complex interactions are observed. A major factor is the behavior of the activity of IMPDH, the rate-limiting enzyme of de novo GTP biosynthesis, and the activity of GPRT, the salvage enzyme of guanylate production. The activities of GMP synthase, GMP kinase and nucleoside-diphosphate kinase are also relevant. In neoplastic transformation, the activities and amounts of all these biosynthetic enzymes are elevated as shown by kinetic assays and by immunotitration for IMPDH. In cancer cells, the up-regulation of guanylate biosynthesis is amplified by the concurrent decrease in activities of the catabolic enzymes, nucleotidase, nucleoside phosphorylase, and the rate-limiting purine catabolic enzyme, xanthine oxidase. The up-regulation of the capacity for GTP biosynthesis is also manifested in the stepped-up capacity of the overall pathways of de novo and salvage guanylate production. The linking with neoplasia is also seen in the elevation of the activities of IMPDH and GMP synthase and de novo and salvage pathways as the proliferative program is expressed as cancer cells enter log phase in tissue culture. The activity of GMP reductase showed no linkage with neoplastic or normal cell proliferation; however, in induced differentiation in HL-60 cells the activity increased concurrently with the decline in the activity of IMPDH. This reciprocal regulation of the two enzymes is observed in differentiation induced by retinoic acid, DMSO or TPA in HL-60 cells. In support of enzyme-pattern-targeted chemotherapy, evidence was provided for synergistic chemotherapy with tiazofurin (inhibitor of IMPDH) and hypoxanthine (competitive inhibitor of GPRT and guanine salvage activity) in patients and in tissue culture cell lines. These investigations should contribute to the clarification of the controlling factors of GMP biosynthesis, the role of the various enzymes, the behavior of GMP reductase in mammalian cells and the application of the approaches of enzyme-pattern-targeted chemotherapy in patients.

Selective up-regulation of type II inosine 5'-monophosphate dehydrogenase messenger RNA expression in human leukemias

The discovery of isozymes (types I and II) of IMP dehydrogenase (IMPDH; EC 1.1.1.205), the rate-limiting enzyme of de novo GTP biosynthesis, has attracted attention as a possible novel approach to cancer diagnosis and selective tumor cell chemotherapy. To elucidate differences in expression and regulation of the two IMPDH isozymes, we examined the steady-state levels of these mRNAs in various types of leukemic cells from patients. Northern blot analysis revealed that type II IMPDH was more active transcriptionally (1.5- to 5.1-fold) in all the leukemic cells examined than in normal lymphocytes, whereas type I expression was similar. The increased expression of type II mRNA in leukemic cells was closely linked with the increase in total IMPDH activity (r = 0.92). When leukemic cells from a patient with chronic granulocytic leukemia in blast crisis were separated into blast-rich and mature leukocyte-rich fractions, the expression of type II mRNA correlated positively with the population of immature leukemic cells, whereas type I expression was unchanged. Treatment of leukemic blasts with 12-O-tetradecanoyl-phorbol-13-acetate for 5 days resulted in a 90% decrease in the expression of type II mRNA with macrophage-like differentiation, while the expression of type I mRNA was relatively stable. These observations suggest that expression of type II IMPDH is stringently linked with immature characteristics of leukemic cells; thus, it should be a selective target for antileukemic chemotherapy.

Tiazofurin down-regulates expression of c-Ki-ras oncogene in a leukemic patient

The increased activity in cancer cells of inosine 5'-monophosphate dehydrogenase (IMP DH, EC 1.1.1.205), the rate-limiting enzyme of de novo GTP biosynthesis, was suggested as a sensitive target for chemotherapy. Tiazofurin (NSC 286193), through its conversion to the active metabolite, thiazole-4-carboxamide adenine dinucleotide (TAD), is a strong inhibitor of IMP DH. In our clinical trial, tiazofurin caused return to the chronic phase in patients with chronic granulocytic leukemia in blast crisis (Tricot, G.; Jayaram, H.N.; Weber, G.; Hoffman, R. Tiazofurin: Biological effects and clinical uses. Int. J. Cell Cloning 8:161-170; 1990). In K562 human leukemic cells, tiazofurin down-regulated the expression of c-Ki-ras and c-myc oncogenes, which was followed by induced differentiation. We now report down-regulation by tiazofurin of the c-Ki-ras oncogene in a patient with chronic granulocytic leukemia in blast crisis. A single tiazofurin infusion (2,200 mg/m2) on days one and two decreased IMP dehydrogenase activity (the apparent t1/2 was 30 min), GTP concentration (the apparent t1/2 was 6 hr), and expression of ras (the apparent t1/2 was 8 hr) and c-myc (the apparent t1/2 was 38.5 hr) oncogenes in the leukemic cells. No further tiazofurin was given, because on days three and four the chemotherapeutic impact became evident in a tumor-lysis syndrome and the blast cells were cleared from the periphery by day five. The decrease in IMP DH activity, GTP concentration, and expression of c-Ki-ras oncogene were early markers of the successful chemotherapeutic impact of tiazofurin in a patient with chronic granulocytic leukemia in blast crisis.

Expression of human IMP dehydrogenase types I and II in Escherichia coli and distribution in human normal lymphocytes and leukemic cell lines

Two distinct cDNAs encoding proteins with 84% sequence identity have been isolated for human IMP dehydrogenase (EC 1.1.1.205) (Natsumeda, Y., Ohno, S., Kawasaki, H., Konno, Y., Weber, G., and Suzuki, K. (1990) J. Biol. Chem. 265, 5292-5295), an important target in antileukemic chemotherapy. We constructed expression plasmids containing these cDNAs in full length with pUC plasmids and produced lacZ'-IMP dehydrogenase fusion proteins in Escherichia coli. Both synthesized proteins exhibited IMP dehydrogenase activity and were partially separated from endogenous E. coli IMP dehydrogenase. By injecting the fusion proteins into mice we generated a polyclonal antibody specific to type I IMP dehydrogenase and an antibody which reacted with both types. Immunoblot analysis revealed that the total amounts of types I and II enzymes increased in human leukemic cell lines K562 and HL-60 in agreement with the increase in IMP dehydrogenase activity to 7.8- and 9.4-fold, respectively, above that of normal lymphocytes. The extent of expression of type I IMP dehydrogenase was similar in these cells, however, indicating that the increase in IMP dehydrogenase amount in leukemic cells was due to specific up-regulation of type II enzyme. Northern blot analysis also showed specific and predominant expression of type II in the leukemic cells. Thus, de novo GTP biosynthesis may be controlled differently in normal and neoplastic cells by different IMP dehydrogenase molecular species.

Regulation of de novo and salvage pathways in chemotherapy

An overview was presented of our approach of inhibition of de novo and salvage pathways in pyrimidine and purine metabolism. 1. Combination of acivicin, an inhibitor of de novo biosynthesis, and dipyridamole, a transport inhibitor, provided synergistic cytotoxicity in hepatoma and colon carcinoma cells. 2. AZT, a competitive inhibitor of the salvage enzyme, thymidine kinase, and 5-FU or MTX provided synergistic cytotoxicity in hepatoma 3924A. In human colon carcinoma HT-29 cells AZT and methotrexate yielded synergistic cytotoxicity and thymidine and hypoxanthine together provided protection from the action of these drugs. 3. These observations are significant because in rat hepatoma 3924A and in human cell lines HT-29, HL-60 and K562 thymidine kinase activity was 16- to 67-fold higher than that of dTMP synthase. Therefore, inhibition of dTMP synthase activity alone may provide poor responses because the salvage pathways can circumvent this block. 4. In leukemic patients treated with tiazofurin, an inhibitor of IMP dehydrogenase, the rate-limiting enzyme of GTP biosynthesis, and with allopurinol, which inhibits GPRT activity through raising plasma hypoxanthine levels, synergistic therapeutic results were obtained. The responses in sensitive patients entailed a decrease in IMP dehydrogenase activity and GTP concentration in leukemic cells and down-regulation of the ras and myc oncogenes. The down-regulation of the ras oncogene by tiazofurin through the decrease of GTP concentration has now been shown in K562, HL-60 and hepatoma cells and in patients with chronic granulocytic leukemia in blast crisis. Tiazofurin may be useful in studies on selective depression of the expression of the ras oncogene. 5. In 27 consecutive patients 50% responded positively to tiazofurin treatment. From this group, 10 out of 12 patients (83%) with chronic granulocytic leukemia in blast crisis responded to tiazofurin treatment.

Expression of key enzymes of purine and pyrimidine metabolism in a hepatocyte-derived cell line at different phases of the growth cycle

The effect of growth phase on enzymatic activities of the de novo and salvage pathways for purine and pyrimidine nucleotide synthesis was studied in a hepatocyte-derived cell line from the rat. The cells were in lag phase after plating for 36 h; log phase started at 48 h and persisted up to 120 h of culture. Then the cells stopped growing and entered into plateau phase (144 h). In non-proliferating cells (144 h of culture) the basal activities of the enzymes of purine de novo biosynthesis were 1.7- to 6.8-fold higher than in normal rat liver, those of pyrimidine de novo synthesis showed 0.6- to 30-fold increase in activity. The purine salvage enzymes were unchanged, and the pyrimidine salvage enzymes were 3.1- to 7.4-fold higher compared to normal liver. During the growth cycle all enzymes except the purine salvage enzymes, which did not change, showed a peak in activity at 72 h of culture (log phase). The increase in activity in log phase compared to plateau phase was 1.3- to 2.4-fold for purine de novo synthetic enzymes, 1.1- to 2.4-fold for pyrimidine de novo enzymes, and 1.4- to 4.7-fold for pyrimidine salvage enzymes. The specific activities of the enzymes in exponentially growing cells were comparable either to that in 24-h regenerating liver, or to that in hepatomas of low or medium growth rate. It was concluded that the enzymatic pattern and metabolic state of the cells shared some features with regenerating liver, others with tumors, although they were not tumorigenic after transplantation into athymic nude mice.

Two distinct cDNAs for human IMP dehydrogenase

IMP dehydrogenase (EC 1.1.1.205), the rate-limiting enzyme of de novo GTP biosynthesis, is a promising target in antileukemic chemotherapy. We have isolated two distinct cDNA clones (types I and II) encoding IMP dehydrogenase from a human spleen cDNA library. Both clones encode closely related proteins of 514 residues showing 84% sequence identity. Northern hybridization analyses of poly(A)+ RNA from human normal leukocytes and human ovarian tumors demonstrated a striking contrast in mRNA expression in that type I mRNA is the main species in normal leukocytes and type II predominates over type I in the tumor. This is the first report suggesting the existence of two distinct types of human IMP dehydrogenase molecular species which may have different sensitivities to the drugs targeted against IMP dehydrogenase.

Azidothymidine inhibition of thymidine kinase and synergistic cytotoxicity with methotrexate and 5-fluorouracil in rat hepatoma and human colon cancer cells

Azidothymidine (AZT, 3'-azido-3'-deoxythymidine, zidovudine) competitively inhibited the activity of thymidine kinase (EC 2.7.1.21) in extracts of rat hepatoma and sarcoma cells; Dixon plots yielded a Ki = 1-2 microM. Azidothymidine (100 microM) exerted synergistic cytotoxicity with methotrexate (0.05 microM) in hepatoma cells in culture in clonogenic assay. Thymidine (50 microM) counteracted the effect of azidothymidine and prevented synergistic action. Azidothymidine (10 microM) was synergistically cytotoxic with 5-fluorouracil (0.3 and 0.5 microM) in HT-29 human colon carcinoma cells. Thymidine (10 microM) abolished synergism. These studies suggest a new role for azidothymidine which, as an inhibitor of thymidine salvage, should enhance synergistically the clinical anticancer impact of blockers of de novo biosynthesis of thymidylates (methotrexate, 5-fluorouracil).

Synergistic action of tiazofurin and retinoic acid on differentiation and colony formation of HL-60 leukemia cells

Tiazofurin and retinoic acid synergistically induced differentiation and inhibited colony formation in HL-60 human promyelocytic leukemia cells in cell culture. The synergism was the result of different mechanisms of action, since the effect of tiazofurin, unlike that of retinoic acid, was prevented by addition of guanosine. Since it has been shown that tiazofurin down-regulated the expression of c-Ki-ras oncogene, and retinoic acid that of the myc oncogene, the joint impact of these drugs is of clinical interest particularly in end-stage leukemia where the therapeutic usefulness of tiazofurin has recently been demonstrated.

Tiazofurin action in leukemia: evidence for down-regulation of oncogenes and synergism with retinoic acid

New light was thrown on the action of tiazofurin in the treatment of end-stage leukemic patients and in leukemic cells in tissue culture. 1. In a population of 21 consecutive patients 50% responded to tiazofurin treatment, confirming the usefulness of this therapy in end-stage leukemia. 2. In leukemic patients treated with tiazofurin and allopurinol reciprocal action was manifested in the increase in hypoxanthine and the decrease in uric acid concentrations in the plasma. On discontinuation of allopurinol, hypoxanthine levels steeply declined but uric acid concentration increased slowly, taking days to reach pretreatment level. 3. With a new and sensitive method the concentration of the active metabolite of tiazofurin, TAD, was measured in the mononuclear cells of tiazofurin-treated patients. Approximately 5 to 13% of the plasma tiazofurin level was observed as TAD in the mononuclear cells. This TAD concentration was sufficient to account for the inhibition of IMP DH in these cells. 4. Tiazofurin or retinoic acid caused differentiation of HL-60 leukemic cells and inhibition of cell proliferation. 5. By treating leukemic cells incubated with tiazofurin or retinoic acid also with guanosine it was elucidated that the mechanism of the two drugs differed since only the tiazofurin effects were counteracted by guanosine. 6. Tiazofurin and retinoic acid together in HL-60 cells provided synergistic impact on differentiation and cytotoxicity. 7. Tiazofurin resulted in down-regulation of the expression of ras and myc oncogenes in three systems: K562 human erythroleukemic cells, rat hepatoma 3924A cells and human HL-60 leukemia cells. 8. Because both tiazofurin and retinoic acid are licensed drugs, their potential use in combination chemotherapy may have clinical relevance in the treatment of end-stage leukemia where our earlier studies have demonstrated the usefulness of tiazofurin.

Histone acetyltransferase activity in rat hepatomas

In view of various reports describing differences in histone acetylation between normal rat liver and hepatomas, the behaviour of histone acetyltransferase (EC 2.3.1.48) activity was elucidated in normal rat liver and in a spectrum of well-characterized rat hepatomas of slow, intermediate and rapid growth rates. In all tumours the acetyltransferase specific activity, expressed as nmol h-1 mg total protein-1, was higher than in the corresponding normal livers and the rise correlated positively with the proliferation rates of the tumors. No difference is observed if acetyltransferase activity is expressed per milligram of histone. This is explained by elevated ratios of histones and of DNA to total protein in the hepatomas compared to the ratios in normal liver. Electrophoretic analysis of [3H]acetate-labeled histones revealed similar patterns in hepatoma and normal liver. The extent of histone H4 acetylation, as indicated by the frequency distribution of non-, mono-, di-, tri-, and tetraacetylated H4-species, was found to be identical in hepatomas and normal liver. The histone protein and acetate labeling patterns were near normal in the slowly growing hepatomas.

Biochemically directed therapy of leukemia with tiazofurin, a selective blocker of inosine 5'-phosphate dehydrogenase activity

Tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide, NSC 286193), a selective inhibitor of the activity of IMP dehydrogenase (EC 1.1.1.205), the rate-limiting enzyme of de novo GTP biosynthesis, provided in end stage leukemic patients a rapid decrease of IMP dehydrogenase activity and GTP concentration in the blast cells and a subsequent decline in blast cell count. Sixteen consecutive patients with end stage acute nonlymphocytic leukemia or myeloid blast crisis of chronic granulocytic leukemia were treated with tiazofurin. Allopurinol was also given to inhibit xanthine oxidase activity to decrease uric acid excretion and to elevate the serum concentration of hypoxanthine, which should competitively inhibit the activity of hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8), the salvage enzyme of guanylate synthesis. Assays of IMP dehydrogenase activity and GTP concentration in leukemic cells provided a method to monitor the impact of tiazofurin and allopurinol and to adjust the drug doses. In this group of patients with poor prognosis, five attained a complete hematological remission and one showed a hematological improvement. A marked antileukemic effect was seen in two other patients. All five evaluable patients with myeloid blast crisis of chronic granulocytic leukemia reentered the chronic phase of their disease. Five patients with acute nonlymphocytic leukemia were refractory to tiazofurin and three were unevaluable for hematological effect because of early severe complications. Responses with intermittent 5- to 15-day courses of tiazofurin lasted 3-10 months. Tiazofurin had a clear antiproliferative effect, but the pattern of hematological response indicated that it appeared to induce differentiation of leukemic cells. In spite of toxicity with severe or life-threatening complications in 11 of 16 patients, tiazofurin was better tolerated in most patients than other antileukemic treatment modalities and provided a rational, biochemically targeted, and biochemically monitored chemotherapy which should be of interest in the treatment of leukemias and as a paradigm in enzyme pattern-targeted chemotherapy.

IMP dehydrogenase: inhibition by the anti-leukemic drug, tiazofurin

Tiazofurin through its active metabolite thiazole-4-carboxamide adenine dinucleotide (TAD) inhibits IMP dehydrogenase, the rate-limiting enzyme of GTP biosynthesis. IMP dehydrogenase activity in human leukemic cell extracts (33.4 +/- 0.1 nmol/h/mg protein) was increased 11-fold compared to normal leukocytes (3.1 +/- 0.5). Km values for IMP and NAD+ of leukemic IMP dehydrogenase were 22.7 and 44.0 microM, respectively. XMP inhibited competitively with IMP and noncompetitively with NAD+. NADH exerted mixed type inhibition with respect to both IMP and NAD+. The inhibitory pattern of TAD was quite similar to that of NADH; however, the affinity of TAD to leukemic IMP dehydrogenase (Ki = 0.1 microM) was three orders of magnitude higher than the natural product NADH (Ki = 150 microM). These results contribute to an understanding of the mechanism of action of tiazofurin in the treatment of leukemia.

Clinical and molecular impact of inhibition of IMP dehydrogenase activity by tiazofurin

The impact of tiazofurin on inhibition of IMP dehydrogenase was discussed at the clinical and molecular levels. 1. Evidence was provided for the role of IMP dehydrogenase and guanylates in the expression of the neoplastic program in cancer cells with particular relevance to human leukemic cells. 2. The argument for expecting an impact of tiazofurin in human myelocytic cells was provided. 3. Similarity of the kinetics of human leukemic cell IMP dehydrogenase to the rat hepatoma enzyme was documented. 4. New evidence was provided for the role of salvage in chemotherapy and the function of hypoxanthine in inhibiting guanine salvage. 5. The action of tiazofurin and retinoic acid was reported in HL-60 leukemic cells. 6. The effect of tiazofurin and retinoic acid on proliferation and cytotoxicity was outlined for hepatoma 3924A cells. 7. The effect of guanine on induced differentiation by tiazofurin and retinoic acid was examined. 8. Biochemical basis was provided for the lack of development of resistance in patients treated with tiazofurin. 9. Presumptive evidence was provided that tiazofurin treatment induced differentiation of leukemic cells in the patients. 10. The molecular biology of tiazofurin-induced differentiation in K-562 cells was reviewed with the possible relevance to clinical treatment that tiazofurin might also act through down-regulation of ras oncogene.

Significance of purine salvage in circumventing the action of antimetabolites in rat hepatoma cells

The flux activities of de novo and salvage purine synthesis were compared in rat hepatoma 3924A cells in various growth phases. The initial rate assays of [14C]adenine, [14C]hypoxanthine, and [14C]guanine incorporation yielded Michaelis-Menten kinetics with Kms of 5, 7, and 7 microM, respectively. After replating plateau phase cells in lag and log phases the activity of purine de novo pathway increased 4.5- to 8-fold with a preferential rise in guanylate synthesis, whereas purine salvage activities increased only 1.6- to 2.1-fold. However, for the syntheses of IMP, AMP, and GMP, the activities of purine salvage pathways were 2- to 7-fold, 5- to 28-fold, and 2- to 32-fold higher than those of the de novo purine pathway. Treatment of cells with acivicin, an inhibitor of the activity of amidophosphoribosyltransferase, phosphoribosylformylglycinamidine synthase, and GMP synthase, inhibited the flux activities of de novo purine, adenylate, and guanylate syntheses to 37, 73, and 3% of the controls and decreased the concentration of GTP to 42%; the concentration of ATP did not change and that of 5-phosphoribosyl 1-pyrophosphate increased 3.1-fold. Under these conditions the activities of salvage synthesis from hypoxanthine and guanine were enhanced 2.5-fold. Treatment of hepatoma cells with IMP dehydrogenase inhibitors, tiazofurin, ribavirin, and 4-carbamoylimidazolium 5-olate, to block de novo guanylate synthesis accelerated the flux activity of guanine salvage pathway. The higher capacity of purine salvage pathway than that of the de novo one and the further rise of the activity in response to the drugs targeted against the de novo pathway highlight the important role salvage synthesis might play in circumventing the impact of antimetabolites of de novo purine synthesis in cancer chemotherapy.

Induction of erythroid differentiation and modulation of gene expression by tiazofurin in K-562 leukemia cells

Tiazofurin (2-beta-D-ribofuranosyl-4-thiazole-carboxamide; NSC 286193), an antitumor carbon-linked nucleoside that inhibits IMP dehydrogenase (IMP:NAD+ oxidoreductase; EC 1.1.1.205) and depletes guanylate levels, can activate the erythroid differentiation program of K-562 human leukemia cells. Tiazofurin-mediated cell differentiation is a multistep process. The inducer initiates early (less than 6 hr) metabolic changes that precede commitment to differentiation; among these early changes are decreases in IMP dehydrogenase activity and in GTP concentration, as well as alterations in the expression of certain protooncogenes (c-Ki-ras). K-562 cells do express commitment-i.e., cells exhibit differentiation without tiazofurin. Guanosine was effective in preventing the action of tiazofurin, thus providing evidence that the guanine nucleotides are critically involved in tiazofurin-initiated differentiation. Activation of transcription of the erythroid-specific gene that encodes A gamma-globin is a late (48 hr) but striking effect of tiazofurin. Down-regulation of the c-ras gene appears to be part of the complex process associated with tiazofurin-induced erythroid differentiation and relates to the perturbations of GTP metabolism.

Synergistic cytotoxic effect of tiazofurin and ribavirin in hepatoma cells

Tiazofurin, an anti-cancer drug, which induces remissions in human leukemia, and ribavirin, an anti-viral agent, bind at separate sites (NADH and IMP-XMP sites, respectively) on the target enzyme, IMP dehydrogenase. Now we show that the binding to IMP dehydrogenase of these drugs at two separate sites is translated into synergistic inhibition of de novo guanylate biosynthesis and synergistic toxicity in rat hepatoma 3924A cells. These results may be utilized in the chemotherapy of neoplastic diseases and in the treatment of hepatitis virus infection and hepatocellular carcinoma.