Pharmacokinetics and pharmacodynamics of liposomal chemophototherapy with short drug-light intervals

Abstract

Chemophototherapy (CPT) merges photodynamic therapy with chemotherapy and can substantially enhance drug delivery. Using a singular liposomal formulation for CPT, we describe a semi-mechanistic pharmacokinetic-pharmacodynamic (PK/PD) model to investigate observed antitumor effects. Long-circulating, sterically-stabilized liposomes loaded with doxorubicin (Dox) stably incorporate small amounts of a porphyrin-phospholipid (PoP) photosensitizer in the bilayer. These were administered intravenously to mice bearing low-passage, patient-derived pancreatic cancer xenografts (PDX). Dox PK was described with a two-compartment model and tumor drug disposition kinetics were modeled with first-order influx and efflux rates. Tumor irradiation with 665 nm laser light (200 J/cm²) 1 h after liposome administration increased tumor vascular permeabilization and drug accumulation, which was accounted for in the PK/PD model with increased tumor influx and efflux rates by approximately 12- and 4- fold, respectively. This modeling approach provided an overall 7-fold increase in Dox area under the curve in the tumor, matching experimental data (7.4-fold). A signal transduction model based on nonlinear direct cell killing accounted for observed tumor growth patterns. This PK/PD model adequately describes the CPT anti-PDX tumor response based on enhanced drug delivery at the short drug-light interval used.

Keywords: Chemophototherapy; Drug delivery; Pharmacodynamics; Pharmacokinetics; Photodynamic therapy; PoP liposomes.

Figure 1. Enhanced drug uptake by LC-Dox-PoP liposomes following tumor laser treatment.

SCID mice bearing dual PDX tumors were administered 7 mg/kg LC-Dox-PoP liposomes intravenously 1 hr before laser treatment. (A) Tumor accumulation of Dox was measured 30 min or 24 hr after laser treatment (250 mW/cm² for 20 min, 300 J/cm² Distribution of Dox (B) or PoP (C) in other key organs 30 min or 24 hr following administration and laser treatment. Data represent mean±S.D. for n=5 animals per group.

Figure 2. Pharmacokinetic-Pharmacodynamic (PK/PD) model of LC-Dox-PoP liposomes.

Cp and Ct are the concentrations of Dox in serum (central compartment Vp) and tissue (second compartment V_t), respectively. Cl is clearance from the central compartment, and Q is distribution to second compartment. X_tu is the mass of Dox in the tumor. k1 and k₂ represent the influx and efflux rate of Dox in the tumor without laser treatment, repsectively. v₁ and v₂ represent the vascular permeabilization factor on the tumor influx and efflux rate, respectively. Laser treatment increases both k₁ and k₂ but to different degrees. See additional symbol definitions in the methods, Table 1, and Table 2.

Figure 3. Observed and modeled Dox serum and tumor kinetics.

SCID mice bearing dual PDX tumors were administered LC-Dox-PoP (4 mg/kg) intravenously and 1 hr later, only one of the tumors was laser-irradiated (200 mW/cm² for 16.7 min, 200 J/cm²). (A) Observed (symbols) and PK/PD model-predicted profiles (solid or dashed lines) of Dox serum concentration and Dox tumor kinetics with or without tumor laser treatment (in the same animal). (B) Observed PoP concentration kinetics in tumors with or without laser treatment (in the same animal). (C) Ratio of Dox and PoP uptake in tumors with or without laser treatment (in the same animal) at various time post laser treatment. Experimental data represents mean ± S.D. for n=6 mice per group.

Figure 4. Observed and modeled tumor growth.

Symbols represent observed data and solid lines are the PK/PD model-fitted profiles. (A) Tumor growth in untreated control mice. (B) Tumor growth in mice administered PDT (empty PoP liposomes and treated with laser). Laser treatment was applied 1 hr after dosing (0.59 mg/kg PoP). PDT was ineffective under these conditions and the tumor growth rate estimated by the PK/PD model was the same for A and B. (C) Tumor growth in mice given 4 mg/kg LC-Dox-PoP liposomes intravenously but without laser treatment. (D) Tumor growth in mice given 4 mg/kg LC-Dox-PoP liposomes intravenously with laser treatment (200 mW/cm² for 16.7 min, 200 J/cm²) applied 1 hr post dosing. Data show mean ± S.D. for N=5 per group.

Figure 5. Fluorescence microscopy of LC-Dox-PoP liposomes deposition in tumor slices.

Two group mice were administered LC-Dox-PoP liposomes (10 mg/kg Dox). One group of mice were laser-irradiated 1 hr after liposome administration, using the conditions described (Methods), and sacrificed 8 hrs later. Selected area of tumors treated with or without laser. Purple signal indicates Dox, and yellow indicates PoP. Scale bars are 400 μm.

Figure 6. LC-Dox-PoP liposome efficacy and tumor blood flow during laser treatment with longer DLI.

(A) Observed tumor growth in mice treated with various DLIs. LC-Dox-PoP liposomes were administered intravenously (4 mg/kg) and laser treatment (200 mW/cm² for 16.7 min, 200 J/cm²) was applied 1 hr, 6 hr, or 24 hr later. Data show mean ± s.d. for n=5 per group. No statistical difference between each laser treated group was found at any time (One-way ANOVA followed by Tukey’s test). (B) Relative moral blood flow during laser treatments shown in B. Laser was initiated at time 0 and ends at 1000s. Data show mean ± s.d. for N=3 per group.