The effect of benzamide riboside on the VX2 model of liver cancer in rabbits

Anti-Tumor Potential of IMP Dehydrogenase Inhibitors: A Century-Long Story

The purine nucleotides ATP and GTP are essential precursors to DNA and RNA synthesis and fundamental for energy metabolism. Although de novo purine nucleotide biosynthesis is increased in highly proliferating cells, such as malignant tumors, it is not clear if this is merely a secondary manifestation of increased cell proliferation. Suggestive of a direct causative effect includes evidence that, in some cancer types, the rate-limiting enzyme in de novo GTP biosynthesis, inosine monophosphate dehydrogenase (IMPDH), is upregulated and that the IMPDH inhibitor, mycophenolic acid (MPA), possesses anti-tumor activity. However, historically, enthusiasm for employing IMPDH inhibitors in cancer treatment has been mitigated by their adverse effects at high treatment doses and variable response. Recent advances in our understanding of the mechanistic role of IMPDH in tumorigenesis and cancer progression, as well as the development of IMPDH inhibitors with selective actions on GTP synthesis, have prompted a reappraisal of targeting this enzyme for anti-cancer treatment. In this review, we summarize the history of IMPDH inhibitors, the development of new inhibitors as anti-cancer drugs, and future directions and strategies to overcome existing challenges.

Variability of apoptosis and response in N1-S1 rodent hepatomas to benzamide riboside and correlation to early changes in water apparent diffusion coefficient and sodium MR imaging

PURPOSE

This pilot trial assesses variability of apoptosis and response 1 day after hepatic intraarterial (IA) benzamide riboside (BR) in rodent hepatomas and its correlation to water apparent diffusion coefficient (ADC) and single-quantum (SQ) and triple-quantum-filtered (TQF) sodium-23 ((23)Na) magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Sprague-Dawley rats (n = 8) were inoculated with 10(6) N1-S1 cells. IA BR (20 mg/kg) was infused after 14 days. Animals were killed 1 day (n = 4) or 21 days (n = 4) after therapy. Imaging was performed 1 day before and after treatment. Volume was assessed over 2 weeks. Percentage apoptosis was counted from terminal deoxynucleotidyl transferase dUTP nick-end labeling-stained slides at 400×magnification. Kruskal-Wallis tests were used to compare apoptosis, and Wilcoxon signed-rank tests were used to compare MR signal intensity (SI).

RESULTS

Apoptosis was marginally greater in tumor than in nontumor (6.7% vs 1.3%; P = .08), varying from 2% to 10%. Before treatment, MR SI was greater in tumor than in nontumor (ADC, 1.18 vs 0.76 [P = .0078]; SQ, 1.20 vs 1.04 [P = .03]; TQF, 0.55 vs 0.34 [P = .03]). After treatment, tumors increased in volume (0.62 vs 0.33; P = .016) variably over 2 weeks. MR SI remained greater in tumor than in nontumor (ADC, 1.20 vs 0.77 [P = .0078]; SQ, 1.76 vs 1.15 [P = .016]; TQF, 0.84 vs 0.49 [P = .03]). SQ and TQF SI increased by 47% (P = .016) and 53% (P = .016) in tumors, whereas ADC did not change.

CONCLUSIONS

Apoptosis was marginal and varied from 2% to 10%. Water ADC, SQ, and TQF MR imaging distinguished tumor from nontumor. Changes in water ADC and sodium MR imaging correlated to apoptosis and volume in select cases, but additional animals are needed to validate this trend against tumor growth.

Tumor response and apoptosis of N1-S1 rodent hepatomas in response to intra-arterial and intravenous benzamide riboside

PURPOSE

Benzamide riboside (BR) induces tumor apoptosis in multiple cell lines and animals. This pilot study compares apoptosis and tumor response in rat hepatomas treated with hepatic arterial BR (IA) or intravenous (IV) BR.

METHODS

A total of 10(6) N1-S1 cells were placed in the left hepatic lobes of 15 Sprague-Dawley rats. After 2 weeks, BR (20 mg/kg) was infused IA (n=5) or IV (n=5). One animal in each group was excluded for technical factors, which prevented a full dose administration (1 IA and 1 IV). Five rats received saline (3 IA and 2 IV). Animals were killed after 3 weeks. Tumor volumes after IA and IV treatments were analyzed by Wilcoxon rank sum test. The percentage of tumor and normal liver apoptosis was counted by using 10 fields of TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling)-stained slides at 40× magnification. The percentage of apoptosis was compared between IV and IA administrations and with saline sham-treated rats by the Wilcoxon rank sum test.

RESULTS

Tumors were smaller after IA treatment, but this did not reach statistical significance (0.14 IA vs. 0.57 IV; P=0.138). There was much variability in percentage of apoptosis and no significant difference between IA and IV BR (44.49 vs. 1.52%; P=0.18); IA BR and saline (44.49 vs. 33.83%; P=0.66); or IV BR and saline (1.52 vs. 193%; P=0.18).

CONCLUSIONS

Although differences in tumor volumes did not reach statistical significance, there was a trend toward smaller tumors after IA BR than IV BR in this small pilot study. Comparisons of these treatment methods will require a larger sample size and repeat experimentation.