Relationship between plasma exposure of 9-nitrocamptothecin and its 9-aminocamptothecin metabolite and antitumor response in mice bearing human colon carcinoma xenografts.
9-Nitrocamptothecin has completed phase III studies in patients with newly diagnosed and refractory pancreatic cancer; however, the optimal 9-nitrocamptothecin treatment regimen is unclear. We used an intermittent schedule of 9-nitrocamptothecin to evaluate the relationship between plasma exposure of 9-nitrocamptothecin and its 9-aminocamptothecin metabolite and antitumor response in mice bearing human colon carcinoma xenografts. 9-Nitrocamptothecin was given orally at 0.44, 0.67, or 1.0 mg/kg/d qd x 5d x 2 weeks repeated q 4 weeks for two cycles to female C.B-17 SCID mice bearing HT29 or ELC2 human colon xenografts. Pharmacokinetic studies were done after oral administration of 0.67 mg/kg x 1. Serial samples were obtained and 9-nitrocamptothecin and 9-aminocamptothecin lactone concentrations in plasma were determined by high-performance liquid chromatography analysis with fluorescence detection. The areas under plasma concentration versus time curve (AUC) from 0 to infinity for 9-nitrocamptothecin and 9-aminocamptothecin were calculated. The antitumor activity of 9-nitrocamptothecin was dose-dependent in both colon xenografts. At all doses, 9-nitrocamptothecin treatment resulted in significant antitumor activity in both xenografts compared with vehicle-treated and control groups and achieved levels of tumor regression that met criteria (minimum %T/C < or = 40%) for antitumor activity. In mice bearing HT29 xenografts, the 9-nitrocamptothecin and 9-aminocamptothecin lactone AUCs after administration of 9-nitrocamptothecin at 0.67 mg/kg were 41.3 and 5.7 ng/mL h, respectively. The responses seen in these xenograft models occurred at systemic exposures that are tolerable in adult patients. These results suggest that the intermittent schedule of 9-nitrocamptothecin may be an active regimen in patients with colorectal carcinoma.
Zamboni
William C
WC
Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, Pennsylvania 15213-1863, USA. zamboniwc@msx.upmc.edu
Jung
Laura L
LL
Egorin
Merrill J
MJ
Hamburger
Deborah R
DR
Joseph
Erin
E
Jin
Ruzhi
R
Strychor
Sandra
S
Ramanathan
Ramesh K
RK
Eiseman
Julie L
JL
D000818:Animals; D000970:Antineoplastic Agents / Q000097:blood / Q000493:pharmacokinetics* / Q000627:therapeutic use; D019540:Area Under Curve; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics / Q000627:therapeutic use; D045744:Cell Line, Tumor; D002851:Chromatography, High Pressure Liquid; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D005260:Female; D019073:HT29 Cells; D006801:Humans; D051379:Mice; D016513:Mice, SCID; D016896:Treatment Outcome; D023041:Xenograft Model Antitumor Assays / Q000379:methods*
D000970:Antineoplastic Agents; C080125:9-aminocamptothecin; C079905:rubitecan; D002166:Camptothecin