Anti-tumour activity and toxicity of the new prodrug 9-aminocamptothecin glucuronide (9ACG) in mice

Abstract

Cancer chemotherapy is limited by the modest therapeutic index of most antineoplastic drugs. Some glucuronide prodrugs may display selective anti-tumour activity against tumours that accumulate beta-glucuronidase. We examined the toxicity and anti-tumour activity of 9-aminocamptothecin glucuronide, a new glucuronide prodrug of 9-aminocamptothecin, to evaluate its potential clinical utility. 9-aminocamptothecin glucuronide was 25-60 times less toxic than 9-aminocamptothecin to five human cancer cell lines. Beta-glucuronidase activated 9-aminocamptothecin glucuronide to produce similar cell killing as 9-aminocamptothecin or topotecan. The in vivo toxicity of 9-aminocamptothecin glucuronide in BALB/c mice was dose-, route-, sex- and age-dependent. 9-aminocamptothecin glucuronide was significantly less toxic to female than to male mice but the difference decreased with age. 9-aminocamptothecin glucuronide and 9-aminocamptothecin produced similar inhibition (approximately 80%) of LS174T human colorectal carcinoma tumours. 9-aminocamptothecin glucuronide cured a high percentage of CL1-5 human lung cancer xenografts with efficacy that was similar to or greater than 9-aminocamptothecin, irinotecan and topotecan. The potent anti-tumour activity of 9-aminocamptothecin glucuronide suggests that this prodrug should be further evaluated for cancer treatment.

Figure 1

Toxicity of 9ACG. A single i.v. injection of 50 mg kg^-1 9ACG was given to male and female 7–8 weeks old BALB/c mice. Control male and female mice were untreated. Mean weights of three mice relative to initial body weights are shown. Significant differences between prodrug and control groups at weight nadirs are indicated: *P⩽0.05. Bars, s.e.

Figure 2

Influence of age and sex on 9ACG toxicity. Male (A–C) and female (D–F) mice aged 5 weeks (A, D), 10 weeks (B, E) or 20 weeks (C, F) were i.v. injected with 50 mg kg⁻¹ 9ACG or s.c. injected with 5 mg kg⁻¹ 9AC. Body mass was followed and compared to non-treated animals of the same age and sex. Mean weights of three mice relative to initial body weights are shown. Significant differences between drug and control groups at weight nadirs are indicated: *P⩽0.05; **P⩽0.005. Bars, s.e.

Figure 3

Anti-tumour activity of 9ACG against LS174T xenografts. (A, B) BALB/c nu/nu mice bearing LS174T tumours were i.v. injected with PBS, i.v. injected with 50 mg kg⁻¹ 9ACG or s.c. injected with 3 mg kg⁻¹ 9AC in Lipiodol on day 10. Mean tumour sizes (A) and weights (B) of six mice relative to mean values at the initiation of therapy (day 10) are shown. The mean size of drug-treated (9AC and 9ACG) tumours was significantly (P⩽0.05) smaller than control tumours after day 13. (C) BALB/c nu/nu mice bearing LS174T tumours were untreated, i.v. injected with 50 mg kg⁻¹ 9ACG or s.c. injected with 5 mg kg⁻¹ 9AC in Lipiodol on day 10, or i.v. injected with 10 mg kg⁻¹ 9ACG or irinotecan on days 10, 12 and 14. Results represent mean tumour size of 7–8 mice relative to mean tumour size on day 10. The mean size of drug-treated (9AC, 9ACG and irinotecan) tumours was significantly (P⩽0.05) smaller than control tumours after day 12. Bars, s.e.

Figure 4

Anti-tumour activity of 9ACG against CL1-5 human lung adenocarcinoma xenografts. (A) BALB/c nu/nu mice implanted with CL1-5 tumour cells on day 0 were i.v. injected with PBS (solid lines) or 50 mg kg⁻¹ 9ACG (dashed lines) on days 10 and 20. Results show the tumour sizes of individual mice. Mean body weights of control or 9ACG-treated mice are shown relative to mean weights on day 5. Bars, s.e. (B) Nude mice implanted with CL1-5 cells on day 0 were i.v. injected with PBS (PBS) or 50 mg kg⁻¹ 9ACG (9ACG) on day 10, s.c. injected with 3 mg kg⁻¹ 9AC in Lipiodol on day 10 (9AC), or i.v. injected with 10 mg kg⁻¹ irinotecan on days 10, 12 and 14 (CPT-11). The ratio of long-term survivors (>120 days tumour-free) in each group is indicated. (C) Nude mice implanted with CL1-5 cells on day 0 received i.v. injections of PBS (PBS) or 8 mg kg⁻¹ 9ACG (9ACG) on days 11, 13, 15, 24, 26 and 28 or 1.8 mg kg⁻¹ topotecan on days 11, 12, 13, 14 and 15 (topotecan). Mean body weights of the PBS, 9ACG or topotecan treated mice are shown relative to mean weights on day 8. Significant differences between the mean weight of mice treated with topotecan or PBS are indicated: *P⩽0.05; **P⩽0.0005. Error bars are not shown for clarity.