Pallavi Rajaputra

Far-red light activatable, multifunctional prodrug for fluorescence optical imaging and combinational treatment

We recently developed “photo-unclick chemistry”, a novel chemical tool involving the cleavage of aminoacrylate by singlet oxygen, and demonstrated its application to visible light-activatable prodrugs. In this study, we prepared an advanced multifunctional prodrug, Pc-(L-CA4)2, composed of the fluorescent photosensitizer phthalocyanine (Pc), an SO-labile aminoacrylate linker (L), and a cytotoxic drug combretastatin A-4 (CA4). Pc-(L-CA4)2 had reduced dark toxicity compared with CA4. However, once illuminated, it showed improved toxicity similar to CA4 and displayed bystander effects in vitro. We monitored the time-dependent distribution of Pc-(L-CA4)2 using optical imaging with live mice. We also effectively ablated tumors by the illumination with far-red light to the mice, presumably through the combined effects of photodynamic therapy (PDT) and released chemotherapy drug, without any sign of acute systemic toxicity.

Synthesis and in vitro biological evaluation of lipophilic cation conjugated photosensitizers for targeting mitochondria

Mitochondria-specific photosensitizers were designed by taking advantage of the preferential localization of delocalized lipophilic cations (DLCs) in mitochondria. Three DLC-porphyrin conjugates: CMP-Rh (a core modified porphyrin-rhodamine B cation), CMP-tPP (a core modified porphyrin-mono-triphenyl phosphonium cation), CMP-(tPP)(2) (a core modified porphyrin-di-tPP cation) were prepared. The conjugates were synthesized by conjugating a monohydroxy core modified porphyrin (CMP-OH) to rhodamine B (Rh B), or either one or two tPPs, respectively, via a saturated hydrocarbon linker. Their ability for delivering photosensitizers to mitochondria was evaluated using dual staining fluorescence microscopy. In addition, to evaluate the efficiency of the conjugates as photosensitizers, their photophysical properties and in vitro biological activities were studied in comparison to those of CMP-OH. Fluorescence imaging study suggested that CMP-Rh specifically localized in mitochondria. On the other hand, CMP-tPP and CMP-(tPP)(2) showed less significant mitochondrial localization. All conjugates were capable of generating singlet oxygen at rates comparable to CMP-OH. Interestingly, all cationic conjugates showed dramatic increase in cellular uptake and phototoxicity compared to CMP-OH. This improved photodynamic activity might be primarily due to an enhanced cellular uptake. Our study suggests that Rh B cationic group is better at least for CMP than tPP as a mitochondrial targeting vector.

Far-Red Light-Activatable Prodrug of Paclitaxel for the Combined Effects of Photodynamic Therapy and Site-Specific Paclitaxel Chemotherapy

Paclitaxel (PTX) is one of the most useful chemotherapeutic agents approved for several cancers, including ovarian, breast, pancreatic, and nonsmall cell lung cancer. However, it causes systemic side effects when administered parenterally. Photodynamic therapy (PDT) is a new strategy for treating local cancers using light and photosensitizer. Unfortunately, PDT is often followed by recurrence due to incomplete ablation of tumors. To overcome these problems, we prepared the far-red light-activatable prodrug of PTX by conjugating photosensitizer via singlet oxygen-cleavable aminoacrylate linker. Tubulin polymerization enhancement and cytotoxicity of prodrugs were dramatically reduced. However, once illuminated with far-red light, the prodrug effectively killed SKOV-3 ovarian cancer cells through the combined effects of PDT and locally released PTX. Ours is the first PTX prodrug that can be activated by singlet oxygen using tissue penetrable and clinically useful far-red light, which kills the cancer cells through the combined effects of PDT and site-specific PTX chemotherapy.

Asymmetric ZnPc-rhodamine B conjugates for mitochondrial targeted photodynamic therapy.

Design, synthesis, characterization, and photodynamic activity of mitochondria specific asymmetric ZnPc-Rh B conjugates are described. Conjugation of asymmetric ZnPc-OH chromophores 3a and 3b with rhodamine B via the corresponding DIC-activated ester gave the desired near IR-absorbing asymmetric ZnPc-Rh B conjugates 1a and 1b. Conjugates 1a and 1b were shown to produce singlet oxygen upon illumination in DMSO, MeOH and THF. Fluorescence aggregation studies of the dyes 1a, 1b, 3a and 3b in DMSO and phosphate buffered saline (PBS) solution showed that conjugates 1a and 1b were less aggregated compared to the corresponding non-conjugates 3a and 3b suggesting that incorporation of Rh B lowered aggregation of the conjugates in the PBS solution. The four dyes studied have logD7.4 values between 2.31 and 2.48, with the sulfur-containing conjugate 1b being the most hydrophobic. All the dyes showed negligible dark toxicity when colon 26 cells were treated with 5 μM of the dyes while 10-15% cell death was observed for dye concentrations of 15 μM. Illumination (700±40 nm, 45 J/cm(2), 15 min) of the cells ([dye]=15 μM) gave 70% cell death for ZnPc-Rh B conjugates 1a and 1b while no killing for non-conjugates 3a and 3b suggesting that the incorporation of the Rh B in the photosensitizer lowered the aggregation and subsequently improved cellular uptake and phototoxicity.

Photodynamic therapy via FRET following bioorthogonal click reaction in cancer cells

Longer wavelength light (650-800nm) is desired to treat large tumors in photodynamic therapy (PDT). However, shorter wavelength light is needed in PDT for thin tumors, not to cause undesirable local side effects. We proposed a strategy for stepwise optical imaging and PDT using a bioorthogonal click chemistry and fluorescence resonance energy transfer (FRET). We prepared azidyl rhodamine (Rh-N3, clickable FD) and cyclooctynyl phthalocyanine [Pc-(DIBAC), clickable PS], with which, here, we demonstrate that the non-catalytic click chemistry is rapid and efficient in cancer cells and FRET from a fluorescence dye (FD) to a photosensitizer (PS) is sufficient to generate enough singlet oxygen killing cancer cells by using shorter wavelength light.

Enhanced Singlet Oxygen Generation from a Porphyrin–Rhodamine B Dyad by Two‐Photon Excitation through Resonance Energy Transfer

Mitochondrial‐targeting photosensitizers have been associated with effective photodynamic responses. However, most photosensitizers absorb light between 400 and 700 nm, where light penetration through tissues is limited. Two‐photon excitation is a rational approach to improve light penetration through tissues. In this report, the two‐photon photophysical properties of a porphyrin–rhodamine B conjugate (TPP‐Rh), previously demonstrated to target the mitochondria, were evaluated. The properties studied included: two‐photon absorption (TPA) cross sections (σ2); resonance energy transfer (RET) kinetics and dynamics; and singlet oxygen generation. The conjugation of Rh B to TPP‐OH approximately doubled the σ2 of TPP‐Rh at 800 nm (40 ± 4 GM) compared with the parent porphyrin, TPP‐OH (16 ± 4 GM). Furthermore, the rate of DPBF oxidation by singlet oxygen generated from TPP‐Rh was twice as fast compared with that from TPP‐OH (73 % versus 33% in 10 min) following two‐photon excitation at 800 nm. In addition, a significantly stronger luminescence signal was detected from TPP‐Rh, than from TPP‐OH at 1270 nm, following two‐photon excitation. This study indicates that conjugating photosensitizers to Rh B could provide greater TPA at the near‐infrared range in addition to preferential mitochondrial accumulation for improved photodynamic responses.

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

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.

In vitro and in vivo photodynamic activity of core-modified porphyrin IY69 using 690 nm diode laser

Core‐modified porphyrins have been explored as the second‐generation photosensitizers due to their excellent photophysical properties. IY69 [(5‐phenyl‐10,15‐bis(4‐carboxylatomethoxyphenyl)‐20‐(2‐thienyl)‐21,23‐dithiaporphyrin] was developed from the structure optimization guided by in vitro phototoxicity, showing potent activity (IC50 = 80 nm, broadband at 5 J cm−2, R3230AC cells). The present study demonstrates in vivo photodynamic therapy (PDT) efficacy of IY69 using a murine tumor model (colon 26 cells on BALB/c mice) and 690 nm diode laser. In vitro phototoxicity of IY69 with the diode laser was compared with that with broadband light against colon 26 cells. Attenuation of the laser light by tissue samples was determined to estimate actual power density at targets. Biodistribution in various organs 24, 48, 72 h after i.p. administration was determined. Even though IY69 phototoxicity with the diode laser was less effective than that with the broadband light, the diode laser was quite effective in vitro (IC50 = 0.1 μm, 10 J cm−2, colon 26 cells). Concentration and light dose‐dependent phototoxicity was observed. A significant light attenuation of 95% and 99% was observed by skin and 3 mm muscle with skin. IY69 PDT showed significant damage on tumor and delay in tumor growth in a dose‐dependent manner.

Abstract 1361: Progress in light activatable prodrug for the combinational treatment of PDT and site-specific chemotherapy: paclitaxel prodrugs

We developed the photoactivatable prodrug of Paclitaxel (PTX) for the combinational treatment of chemo and photodynamic therapy (PDT). PTX causes dose-limiting side effects as other anticancer drugs when administered systemically. On the other hand, PDT suffers from incomplete ablation and subsequent reoccurrence in part due to the short half-life and poor diffusion rate of singlet oxygen. We prepared a conjugate of PTX with phthalocyanine via a singlet oxygen cleavable linker, as a unique prodrug of PTX, to overcome the problems of PDT and systemic chemotherapy. The PTX prodrug was evaluated for tubulin polymerization, the release rate of PTX from prodrug upon illumination at 690 nm, stability in complete media, and the combination effect in killing ovarian cancer cells in vitro (SKOV-3). The PTX prodrug did not enhance the tubulin polymerization unlike PTX. While it was stable in the media under dark, it rapidly released PTX upon illumination with far-red light: > 90% release in 30 min. The prodrug showed much lower dark toxicity compared to PTX. When illuminated with 690 nm at 5.6 mW/cm2, the prodrug showed very potent phototoxicity: IC50 = 3.9 nM, through the combinational effect of PDT and PTX. In conclusion, we found that the PTX prodrug have desired properties as light-activatable prodrug expressing the combinational effect of PDT and local PTX chemotherapy. Animal study is underway to evaluate the antitumor effect of the PTX prodrug. Citation Format: Pritam Thapa, Mengjie Li, Moses Bio, Pallavi Rajaputra, Yajing Sun, Sukyung Woo, Youngjae You. Progress in light activatable prodrug for the combinational treatment of PDT and site-specific chemotherapy: paclitaxel prodrugs. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1361.

Abstract 1671: Local release of combretastatin A-4 from NIR-light activatable prodrugs overcomes areal and temporal limitations of photodynamic therapy

A unique prodrug strategy for treating localized cancers, in which NIR light-illuminated prodrug effectively ablates tumors through the combined effects of photodynamic therapy (i.e., singlet oxygen [SO]) and locally released anticancer drugs has been proposed. Due to short distance of action ( Citation Format: Pallavi Rajaputra, Moses Bio, Gregory Nkepang, Pritam Thapa, Sukyung Woo, Youngjae You. Local release of combretastatin A-4 from NIR-light activatable prodrugs overcomes areal and temporal limitations of photodynamic therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1671.