One- and Two-Photon Activated Release of Oxaliplatin from a Pt(IV)-Functionalized Poly(phenylene ethynylene)

Abstract

We report a water-soluble poly(phenylene ethynylene) (PPE-Pt(IV)) that is functionalized with oxidized oxaliplatin Pt(IV) units and its use for photoactivated chemotherapy. The photoactivation strategy is based on photoinduced electron transfer from the PPE backbone to oxaliplatin Pt(IV) as an electron acceptor; this process triggers the release of oxaliplatin, which is a clinically used anticancer drug. Mechanistic studies carried out using steady-state and time-resolved fluorescence spectroscopy coupled with picosecond-nanosecond transient absorption support the hypothesis that electron transfer triggers the drug release. Photoactivation is effective, producing oxaliplatin with a good chemical yield in less than 1 h of photolysis (400 nm, 5 mW cm^-2). Photorelease of oxaliplatin from PPE-Pt(IV) can also be effected with two-photon excitation by using 100 fs pulsed light at 725 nm. Cytotoxicity studies using SK-OV-3 human ovarian cancer cells demonstrate that without photoactivation PPE-Pt(IV) is not cytotoxic at concentrations up to 10 μM in polymer repeating unit (PRU) concentration. However, following a short period of 460 nm irradiation, oxaliplatin is released from PPE-Pt(IV), resulting in cytotoxicity at concentrations as low as 2.5 μM PRU.

Keywords: oxaliplatin; photoactivated chemotherapy; photoinduced electron transfer; two-photon absorption; water-soluble poly(phenylene ethynylene).

Figure 1.

UV–visible absorption and emission spectra of $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$ (25 μM) without (a, c) and with (b, d) NaAs (0.5 mM) in water for different irradiation times. The excitation wavelength was 405 nm. The irradiation was carried out using a 400 nm LED light with a power density of 5 mW/cm². (e, f) Hydrodynamic diameter of $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$ aggregates with different irradiation times (25 μM, no NaAs present).

Figure 2.

(a) Chemical yield of oxaliplatin upon photolysis of $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$ (50 μM) or dark treatment of $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$ (50 μM) with NaAs (1 mM). The fluence of the 400 nm LED was 5 mW/cm². (b) HPLC (270 nm) chromatograms of oxaliplatin (25 μM), $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$ (50 μM) irradiated with a 400 nm LED light for 30 min with or without NaAs (1 mM), $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$ (50 μM) irradiated with a 725 nm fs pulsed laser for 60 min with NaAs (1 mM), $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$ (50 μM) with NaAs (1 mM) in the dark for 24 h, NaAs alone (20 μM), and oxaliplatin(OH)₂(ox)(15 μM).

Figure 3.

Picosecond transient absorption (psTA) spectra of (a) $\mathbf{P}\mathbf{P}\mathbf{E}$ and (b) $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$ in water at the indicated delay times following a 405 nm laser excitation pulse (100 fs pulse width, 100 nJ/pulse). (c) Kinetic decay traces of $\mathbf{P}\mathbf{P}\mathbf{E}$ and $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$ detected at 661 nm.

Figure 4.

Light-dependent effects of $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$ on viability and DNA damage in SK-OV-3 human ovarian cancer cells. (a, b) Percent viability of SK-OV-3 cells after incubation with $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$, $\mathbf{P}\mathbf{P}\mathbf{E}$, or oxaliplatin at the indicated concentrations (PRU) for 24 h prior to 20 min of light activation at 460 nm with a power density of 7.0 mW/cm². The cell viability in comparison to controls was measured by the sulforhodamine B (SRB) assay after cells were incubated for an additional 48 h after light activation either without (a) or with (b) removal of residual compound in the media (n = 2–5 independent experiments). (c) Percent viability of SK-OV-3 cells after incubation with $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$, $\mathbf{P}\mathbf{P}\mathbf{E}$, or oxaliplatin at the indicated concentrations (PRU) for 1 h prior to 20 min of light activation at 460 nm with a power density of 7.0 mW/cm². Cell viability in comparison to controls was measured by the SRB assay after cells were incubated for an additional 48 h after light activation without removal of residual compound in the medium (n = 3 independent experiments). Statistical significance in (a–c) was determined by two-way ANOVA with Dunnett’s post hoc test for multiple comparisons with significance compared to $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$ light at each concentration indicated. (d) Nuclear intensity of γH2A.X (P-Ser139) per cell measured by immunofluorescence after incubation with $\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)$ or oxaliplatin at the indicated concentration in comparison to control for 1 h prior to light activation and incubation for an additional 18 h postactivation. Statistical significance was determined by one-way ANOVA with Tukey’s post hoc test for multiple comparisons (n = 3 wells per condition with closed circles representing individual wells). ****p < 0.0001, ***p = 0.0003, **p < 0.01, and *p < 0.05.

Scheme 1.. (a) Chemical Structure of PPE-PtIV and (b) Photoactivation of PPE-PtIV to Generate Oxaliplatin for Chemotherapy Based on Photoinduced Electron Transfer

Scheme 2.. Synthesis of PPE-PtIV

Scheme 3.. Hypothesized Mechanism of Photorelease of Oxaliplatin from PPE-PtIV^a

^a$\mathbf{P}\mathbf{P}\mathbf{E}\mathbf{-}\mathbf{P}\mathbf{t}\left(\mathbf{I}\mathbf{V}\right)\prime$ is the regenerated polymer that is obtained via the reduction of a $\mathbf{P}\mathbf{P}\mathbf{E}$ cation radical by NaAs. It should be noted that on average there is one oxaliplatin(OH)₂(ox) for every two repeating units. Here, as a simplified illustration, we draw one oxaliplatin(OH)₂(ox) on each repeating unit.