(W0930-05-30) Comparison of Paclitaxel Distribution across CNS and PNS Barriers after Administration of Cremophor EL/Ethanol Solubilized, Albumin-Bound and Micellar Paclitaxel

Purpose: Chemotherapy-induced peripheral neuropathy (CIPN) is a common adverse event observed in patients receiving paclitaxel formulated in polyethylated castor oil with ethanol (CreEL-PTX), in albumin-bound nanoparticles (nab-PTX) or in XR17 micelles (micellar-PTX). CIPN has been associated with pathological changes at various anatomical sites, herein named CIPN-sites (1). A meta-analysis revealed that nab-PTX has significantly higher odds ratio for the development of severe CIPN compared to CreEL-PTX (OR = 4.01, 95%CI: 2.51–6.41) (2). Further, a phase III study has showed similar CIPN frequency between CreEL-PTX and micellar-PTX (3), while another study showed slightly higher incidence rate of CIPN in micellar-PTX treatment arm comparing to nab-PTX (4). We hypothesize that predisposition to CIPN development for nab-PTX and micellar-PTX is governed by the higher CIPN-sites exposure compared to CreEL-PTX. Hence, this study aimed to examine the formulation impact on paclitaxel’s distribution to CIPN-sites in the central nervous (CNS; brain, spinal cord) and peripheral nervous (PNS; sciatic nerve, dorsal root ganglia (DRG)) systems as well as skeletal muscle, by evaluating the extent of transport across blood-tissue barriers using the unbound drug partition coefficient, K_p,uu,tissue.

Methods: In vivo studies were performed as a 4-hour constant-rate infusion of 4 mg/kg CreEL-PTX (N=8), 4 mg/kg nab-PTX (n=7) or 1 mg/kg micellar-PTX (n=6) in male and female rats to maintain paclitaxel plasma steady-state concentration. Plasma and terminal samples of CNS, PNS tissues and skeletal muscle were collected. K_p,tissue was estimated as a total paclitaxel concentration in the examined tissues divided by terminal total plasma concentration. Equilibrium dialysis was used to determine the fraction of unbound paclitaxel in plasma, f_u,plasma. Drug tissue uptake assay was performed to estimate the unbound volume of distribution of paclitaxel in tissues, V_u,tissue. All samples were analyzed using UPLC-MS/MS. Obtained parameters were used to determine unbound tissue-to-plasma concentration ratio, K_p,uu,tissue using the Combinatory Mapping Approach, i.e., by correction of obtained K_p,tissue values for plasma protein binding and tissue uptake (5). K_p,uu,tissue characterizes an extent of drug transport across the blood-tissue barriers, e.g., higher than unity value shows predominant active uptake. Statistical significance between the groups was determined by using two-way ANOVA analysis for K_p,tissue data with treatment and tissue factors. One-way ANOVA was separately performed by the tissue for K_p,uu,tissue data analysis. All analysis were followed by Tukey’s multiple comparison test. Data are presented as mean ± SD.

Results: Total paclitaxel plasma concentration at steady-state was 369 ± 124 ng/mL, 83 ± 17 ng/mL and 43 ± 22 ng/mL in the CreEL-PTX, nab-PTX and micellar-PTX groups, respectively (Fig. 1A). The K_p,tissue values were significantly lower in CreEL-PTX group in comparison to the other formulations (Fig. 1B). Highest mean K_p,tissue values were observed in skeletal muscles with K_p,SM of 5.36, 14.76 and 17.54 in CreEL-PTX, nab-PTX and micellar-PTX groups, respectively. The largest differences in K_p,tissue values between treatment groups were associated with primary CIPN development sites sciatic nerve (SN) and DRG with K_p,SN of 2.24 vs 5.47 vs 7.12 , and K_p,DRG of 2.10 vs 8.61 vs 7.83, in CreEL-PTX, nab-PTX and micellar-PTX groups, respectively (Fig. 1B). The pattern of unbound paclitaxel distribution into the tissues was similar in all treatment groups with the following K_p,uu ranking: skeletal muscle > SN > DRG > brain ≥ spinal cord. More than 2-fold difference in K_p,uu,tissue values between formulations was observed in blood-DRG barrier (Fig. 2). Further, higher than unity K_p,uu,tissue values were mostly observed in SN, K_p,uu,SN of 0.89 vs 1.41 vs 1.71, and skeletal muscle, K_p,uu,SM of 1.68 vs 2.98 vs 3.30 in CreEL-PTX, nab-PTX and micellar-PTX groups, respectively (Fig. 2).

Conclusion: Based on our preclinical study results, the nab-PTX and micellar-PTX formulations showed similar tendency to higher total and unbound tissue-to-plasma concentration ratios in comparison to CreEL-PTX in all investigated tissues. Further, there was no significant difference in estimated K_p,tissue and K_p,uu,tissue between nab-PTX and micellar-PTX formulations. In line with our hypothesis, after a 4-hour constant rate infusion we observed higher extent of distribution of total and unbound paclitaxel to CIPN-sites in nab-PTX and micellar-PTX groups compared to CreEL-PTX. This may contribute to higher CIPN-sites exposure of nab-PTX and micellar-PTX, at a given similar to CreEL-PTX unbound plasma exposure. The latter may predispose for higher incidence rates of CIPN in patients receiving nab-PTX and micellar-PTX formulations and, hence, dedicated clinical pharmacokinetic-pharmacodynamic investigations are required.

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3. Shi M, Gu A, Tu H, Huang C, Wang H, Yu Z, et al. Comparing nanoparticle polymeric micellar paclitaxel and solvent-based paclitaxel as first-line treatment of advanced non-small-cell lung cancer: an open-label, randomized, multicenter, phase III trial. Annals of oncology: official journal of the European Society for Medical Oncology. 2021;32(1):85-96.
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Acknowledgements: The study was funded by the Swedish Research Council (Vetenskapsrådet, VR 2022- 01098), Innovative Medicines Initiative two Joint Undertaking project NeuroDeRisk (grant 821528) and Vilnius University. The study was approved by the Animal Ethics Committee of Uppsala, Sweden (ethical approval Dnr. 5.8.18-12230/2019). We gratefully acknowledge the technical assistance of Jessica Dunhall (tPKPD, Uppsala University).

Figure 1. Total plasma and tissue distribution pharmacokinetics of paclitaxel after administration of a 4-hour intravenous constant infusion of 4 mg/kg CreEL-PTX (N=8, black), 4 mg/kg nab-PTX (N=7, magenta) and 1 mg/kg micellar-PTX (N=6, turquoise) formulations. Semilogarithmic graph representing total paclitaxel plasma concentration (ng/mL) (A) and semilogarithmic scatter dot plot of total paclitaxel tissue-to-plasma concentration ratios in brain (Br), spinal cord (SC), skeletal muscle (SM), sciatic nerve (SN) and dorsal root ganglia (DRG) (B). Values represented as a mean ± SD. In case of Kp,tissue comparison between treatment arms was performed using two-way ANOVA test followed by Tukey’s multiple comparison test. Significance levels are depicted as follows: ≥ 0.05 (non-significant), < 0.05 (*), < 0.01 (**), < 0.001 (***), < 0.0001 (****).

Figure 2. Unbound paclitaxel tissue distribution after administration of CreEL-PTX (N=8, black), nab-PTX (N=7, magenta) and micellar-PTX (N=6, turquoise) formulations. Semilogarithmic scatter dot plot of mean ± SD values of unbound paclitaxel tissue-to-plasma concentration ratios in brain (Br), spinal cord (SC), skeletal muscle (SM), sciatic nerve (SN) and dorsal root ganglia (DRG). Dotted line indicates Kp,uu,tissue of unity. Comparison between treatment arms was performed using one-way ANOVA test followed by Tukey’s multiple comparison test within each tissue separately. Significance levels as follows: ≥ 0.05 (non-significant), < 0.05 (*), < 0.01 (**), < 0.001 (***), < 0.0001 (****).