Pharmacokinetics and pharmacodynamics of 17-demethoxy 17-[[(2-dimethylamino)ethyl]amino]geldanamycin (17DMAG, NSC 707545) in C.B-17 SCID mice bearing MDA-MB-231 human breast cancer xenografts.

PURPOSE

17-demethoxy 17-[[(2-dimethylamino)ethyl]amino]geldanamycin (17DMAG, NSC 707545) is a water-soluble analogue of 17-(allylamino)-17-demethoxygeldanamycin (17AAG), a compound currently in clinical trials. These preclinical studies: (1) characterized 17DMAG concentrations in plasma, normal tissues, and tumor after i.v. delivery to mice; and (2) correlated tumor and normal tissue 17DMAG concentrations with alterations in heat shock protein 90 (HSP90) and selected HSP90-chaperoned proteins.

METHODS

At specified times after i.v. administration of 75 mg/kg 17DMAG, SCID mice bearing s.c. MDA-MB-231 human breast xenografts were killed and plasma and tissues were retained. 17DMAG concentrations were determined by HPLC. Raf-1, heat shock protein 70 (HSP70), and HSP90 in tissues were determined by Western blotting.

RESULTS

Peak plasma 17DMAG concentration was 15.4+/-1.4 microg/ml. The area under the plasma 17DMAG concentration versus time curve was 1072 microg/ml min, corresponding to a total body clearance of 70 ml/kg/min. Peak 17DMAG concentrations in liver (118.8+/-5.7 microg/g), kidney (122.9+/-10.6 microg/g), heart (81.3+/-8.1 microg/g), and lung (110.6+/-25.4 microg/g) occurred at 5-10 min, while peak concentrations in spleen (70.6+/-9.6 microg/g) and tumor (9.0+/-1.0 microg/g) occurred at 30-45 min. At 48 h, 17DMAG was detectable in tumor but not in any normal tissue. Raf-1 in tumors of 17DMAG-treated mice killed at 4, 7, 24 and 48 h was about 20% lower than in tumors from vehicle-treated mice. HSP90 and HSP70 in tumors of 17DMAG-treated animals were significantly lower than in tumors of control animals at 4, 7, and 24 h. Hepatic Raf-1 was decreased by more than 60% at all times after 17DMAG treatment; however, hepatic HSP90 was not affected. HSP70 was undetectable in livers of vehicle-treated mice or mice killed at 2 or 4 h after 17DMAG treatment, but was detected in livers at 7, 24 and 48 h. 17DMAG did not affect renal Raf-1. In contrast, renal HSP70 and HSP90 were decreased by more than 50% at 2 and 4 h after 17DMAG treatment. Renal HSP70 increased approximately twofold above that in kidneys from vehicle-treated control mice at 7 and 24 h, while HSP90 relative protein concentration was no different from that in controls.

CONCLUSIONS

Plasma pharmacokinetics of 17DMAG in tumor-bearing mice were similar to those previously reported in nontumor-bearing mice. 17DMAG was distributed widely to tissues but was retained for longer in tumors than normal tissues. Raf-1, HSP90, and HSP70 were altered to different degrees in tumors, livers, and kidneys of 17DMAG-treated animals. These data illustrate the complex nature of the biological responses to 17DMAG.