Folate-PEG Conjugates of a Far-Red Light-Activatable Paclitaxel Prodrug to Improve Selectivity toward Folate Receptor-Positive Cancer Cells

Abstract

We recently demonstrated the far-red light-activatable prodrug of paclitaxel (PTX), Pc-(L-PTX)2. Upon illumination with a 690 nm laser, Pc-(L-PTX)2 showed combinational cell killing from rapid photodynamic therapy damage by singlet oxygen, followed by sustained chemotherapy effects from locally released PTX. However, its high lipophilicity (log D7.4 > 3.1) caused aggregation in aqueous solutions and has nonselectivity toward cancer cells. To solve these important problems, we prepared folic acid (FA)-conjugated and photoactivatable prodrugs of PTX with a polyethylene glycol (PEG) spacer of various chain lengths: FA-PEGn-Pc-L-PTX [n = 0 (0k, 5), ∼23 (1k, 7a), ∼45 (2k, 7b), ∼80 (3.5k, 7c), or ∼114 (5k, 7d)]. The PEGylated prodrugs 7a–d had a much improved hydrophilicity compared with the non-PEGylated prodrug, Pc-(L-PTX)2. As the PEG length increased, the hydrophilicity of the prodrug increased (log D7.4 values: 1.28, 0.09, −0.24, and −0.59 for 1k, 2k, 3.5k, and 5k PEG prodrugs, respectively). Fluorescence spectral data suggested that the PEGylated prodrugs had good solubility in the culture medium at lower concentrations (<1–2 μM), but showed fluorescence quenching due to limited solubility at higher concentrations (>2 μM). Dynamic light scattering indicated that all of the prodrugs formed nanosized particles in both phosphate-buffered saline and culture medium at a concentration of 5 μM. The PEG length affected both nonspecific and folate receptor (FR)-mediated uptake of the prodrugs. The enhanced cellular uptake was observed for the prodrugs with medium-sized PEGs (1k, 2k, or 3.5k) in FR-positive SKOV-3 cells, but not for the prodrugs with no PEG or with the longest PEG (5k), which suggests the optimal range of PEG length around 1k–3.5k for effective uptake of our prodrug system. Consistent with the cellular uptake pattern, medium-sized PEGylated prodrugs showed more potent phototoxic activity (IC50s, ∼130 nM) than prodrugs with no PEG or the longest PEG (IC50, ∼400 nM). In conclusion, we have developed far-red light-activatable prodrugs with improved water solubility and FR-targeting properties compared with the nontargeted prodrug.

Development of Prodrugs for PDT-Based Combination Therapy Using a Singlet-Oxygen-Sensitive Linker and Quantitative Systems Pharmacology

“…In the dark, low toxicity was observed for all folate-PEG-conjugated PTX prodrugs, as demonstrated by >90% survival of SKOV-3 cells after 72 h of incubation with prodrugs at a concentration of 500 nM. In the presence of light, medium-sized FA-PEG-conjugated prodrugs showed more potent photocytotoxicity (IC 50 s around 130 nM) than prodrugs with no PEG or longer PEG (114 PEG units, IC 50 ∼400 nM) [74].…”

“…To add, we found a high accumulation of our prodrug in the tumor area due to the target delivery. The tumor concentration (>2 µM) was kept above IC 50 from 12 to 48 h after prodrug administration [74]. Prodrug also accumulated in the liver, spleen, and kidney, which are the major organs for metabolism.…”

“…Paclitaxel is another drug that was investigated with our PDT activating system [11,72,74]. PTX was connected to the aminoacrylate linker by an ester bond with an alcoholic hydroxyl group of PTX (Table 1, entry 7).…”

“…We chose FA-PEG 45 -Pc-L-PTX to perform PK investigation because it showed the highest cancer cell accumulation in vitro [74]. The PK studies were performed in mice with an intravenous bolus administration of 2 µmol/kg prodrug [96].…”

Light‐Controlled Simultaneous “On Demand” Release of Cytotoxic Combinations for Bimodal Killing of Cancer Cells

“…[13][14][15][16][17] These constructs are conceived in such aw ay that the 1 O 2 produced serves not only forP DT,b ut also cleaves the linker with the chemotherapeutic agent, liberating it in its active form and resulting in superiorc ytotoxic effects. [13][14][15][16][17] These constructs are conceived in such aw ay that the 1 O 2 produced serves not only forP DT,b ut also cleaves the linker with the chemotherapeutic agent, liberating it in its active form and resulting in superiorc ytotoxic effects.…”