#2989 SELECTIVE RENAL DISPOSITION OF THE CALCINEURIN INHIBITORS VOCLSOPORIN, CYCLOSPORINE, AND TACROLIMUS
Authors: Zhou Simon , Rajanayake Krishani Kumari , He Miao , Wen Bo , Lkhagva Ankha , Yap Ernie , Sun Duxin , Cross Jennifer L , Engelke Kory , Huizinga Robert B 
Published: June 2023

Abstract

Background and Aims
The calcineurin inhibitors (CNI) cyclosporine (CSA) and tacrolimus (TAC) were revolutionary immunosuppressants when first introduced for solid organ transplantation in the 1980s. Voclosporin (VCS), a novel CNI, recently became the first oral therapy approved in the United States, Great Britain, and Europe for the treatment of active lupus nephritis based on positive results from Phase 2 and 3 clinical trials. Unlike CSA and TAC, VCS has demonstrated a consistent pharmacokinetic and pharmacodynamic profile, eliminating the need for therapeutic drug monitoring. Further, VCS is associated with a more favorable metabolic profile and has not been associated with electrolyte disturbances. Emerging evidence indicates small molecule therapeutics may display differential disposition within organ tissues. This suggests that CNIs may be differentially distributed and retained in the kidney, potentially explaining the difference in their efficacy and safety profiles. To evaluate renal disposition of CSA, TAC, and VCS, we assessed in mice and humans the disposition of each CNI in the kidney relative to its systemic drug exposure.

Method
Single 30 mg/kg doses of CSA, TAC and VCS were administered intravenously to mice. Following intravenous administration, kidneys were collected at 15 minutes, 30 minutes, 1 hour and 2 hours, flash frozen in liquid nitrogen, and stored at −20 °C until sectioning. Sections of 10 μm kidney tissue were mounted on indium tin oxide coated glass slides. Matrix of 10 mg/mL α-Cyano-4-hydroxycinnamic acid in 85% acetonitrile/13% ethanol + 2% water + 0.1% trifluoroacetic acid was sprayed on the tissue using an HTX tissue sprayer, dried for 10 minutes in the vacuum, and subjected to Matrix-assisted Laser Desorption and Ionization Mass Spectrometry Imaging (MALDI-MSI). The systemic and renal clearance in humans of CSA and TAC were obtained from the literature; pharmacokinetic data on VCS was obtained from data on file. Renal secretion of each drug was compared to its expected passive filtration based on glomerular filtration rate (GFR), fraction unbound in plasma (fu), and respective systemic drug exposure.

Results
MALDI-MSI demonstrated significantly higher concentrations of drug and more diffuse tissue disposition of CSA in mouse kidney compared to VCS (Figure 1). CSA was retained in all kidney tissues up to 2 hours post-administration. Higher concentrations and more diffuse disposition of TAC was also noted compared to VCS at 15 and 30 minutes; TAC was distinctively retained in the cortex and medulla. VCS had moderate distribution in the cortex and was rapidly excreted with low levels of drug present in the kidney after 1 hour. According to published data, CSA has a measured renal clearance of 1.48 mL/min in healthy human subjects, representing approximately 10% of expected passive filtration of 12.5 mL/min (Table 1). TAC has a renal clearance of 0.014 mL/min representing &lt;2% of expected passive filtration of 1.25 mL/min. VCS has a renal clearance of 7.82 mL/min representing approximately 200% of its expected passive filtration rate of 3.75 mL/min.

Conclusion
MALDI-MSI revealed differential retention and distribution of CSA, TAC and VCS in mice, consistent with their respective renal clearances in humans. Higher drug exposure and &gt;90% renal reabsorption was observed for both CSA and TAC in this study, whereas the renal handling of VCS suggested a significant component of tubular secretion. The higher rate of secretion and lower overall exposure of kidney tissue to VCS may be associated with an improved safety profile when compared to the more diffuse distribution and greater renal retention of CSA and TAC.