Pharmacokinetics, Dose-Proportionality, and Tolerability of Intravenous Tanespimycin (17-AAG) in Single and Multiple Doses in Dogs: A Potential Novel Treatment for Canine Visceral Leishmaniasis

Abstract

In the New World, dogs are considered the main reservoir of visceral leishmaniasis (VL). Due to inefficacies in existing treatments and the lack of an efficient vaccine, dog culling is one of the main strategies used to control disease, making the development of new therapeutic interventions mandatory. We previously showed that Tanespimycin (17-AAG), a Hsp90 inhibitor, demonstrated potential for use in leishmaniasis treatment. The present study aimed to test the safety of 17-AAG in dogs by evaluating plasma pharmacokinetics, dose-proportionality, and the tolerability of 17-AAG in response to a dose-escalation protocol and multiple administrations at a single dose in healthy dogs. Two protocols were used: Study A: four dogs received variable intravenous (IV) doses (50, 100, 150, 200, or 250 mg/m²) of 17-AAG or a placebo (n = 4/dose level), using a cross-over design with a 7-day "wash-out" period; Study B: nine dogs received three IV doses of 150 mg/m² of 17-AAG administered at 48 h intervals. 17-AAG concentrations were determined by a validated high-performance liquid chromatographic (HPLC) method: linearity (R² = 0.9964), intra-day precision with a coefficient of variation (CV) ≤ 8%, inter-day precision (CV ≤ 20%), and detection and quantification limits of 12.5 and 25 ng/mL, respectively. In Study A, 17-AAG was generally well tolerated. However, increased levels of liver enzymes-alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyl transferase (GGT)-and bloody diarrhea were observed in all four dogs receiving the highest dosage of 250 mg/m². After single doses of 17-AAG (50-250 mg/m²), maximum plasma concentrations (Cmax) ranged between 1405 ± 686 and 9439 ± 991 ng/mL, and the area under the curve (AUC) plotting plasma concentration against time ranged between 1483 ± 694 and 11,902 ± 1962 AUC 0-8 h μg/mL × h, respectively. Cmax and AUC parameters were dose-proportionate between the 50 and 200 mg/m² doses. Regarding Study B, 17-AAG was found to be well tolerated at multiple doses of 150 mg/m². Increased levels of liver enzymes-ALT (28.57 ± 4.29 to 173.33 ± 49.56 U/L), AST (27.85 ± 3.80 to 248.20 ± 85.80 U/L), and GGT (1.60 ± 0.06 to 12.70 ± 0.50 U/L)-and bloody diarrhea were observed in only 3/9 of these dogs. After the administration of multiple doses, Cmax and AUC 0-48 h were 5254 ± 2784 μg/mL and 6850 ± 469 μg/mL × h in plasma and 736 ± 294 μg/mL and 7382 ± 1357 μg/mL × h in tissue transudate, respectively. In conclusion, our results demonstrate the potential of 17-AAG in the treatment of CVL, using a regimen of three doses at 150 mg/m², since it presents the maintenance of high concentrations in subcutaneous interstitial fluid, low toxicity, and reversible hepatotoxicity.

Keywords: Tanespimycin (17-AAG); canine visceral leishmaniasis; dogs; dose-escalation protocol; pharmacokinetics; toxicity.

Figure 1

Relationship between doses of 17-AAG and plasma AUC or Cmax following intravenous administration in dogs. (A,C) Doses from 50 to 250 mg/m²; (B,D) Doses from 50 to 200 mg/m².

Figure 2

Plasma concentration levels of various doses of 17-AAG were assessed for up to 12 h following intravenous administration through a 30 min continuous infusion in dogs.

Figure 3

Concentrations of 17-AAG in plasma and subcutaneous interstitial fluid in intravenously treated dogs. This figure shows the levels of 17-AAG in plasma and subcutaneous interstitial fluid of dogs, measured up to 104 h after administering multiple intravenous doses of 150 mg/m². The dashed lines represent the 17-AAG concentration previously proven effective against Leishmania promastigotes in in vitro studies.

Figure 4

Histological images depicting alterations in various organs of dogs treated with 17-AAG. Animals were treated with three intravenous administrations of 150 mg/m2 of 17-AAG at 48 h intervals. (A) Shows vacuolar degeneration of the renal tubular epithelium. (B) Illustrates mobilization of Kupffer cells in the liver. (C) Displays plasmocytic hyperplasia and disorganization of type II/III in the spleen. All images are at 40× magnification.

Figure 5

Histological images depicting alterations in the large intestine of dogs treated with 17-AAG, as described in Figure 2. Panels (A,B) show the presence of colitis in the treated dogs. Image (A) is at 4× magnification, and image (B) is at 40× magnification.