Letter Cite This: Nano Lett. 2018, 18, 1331−1336
pubs.acs.org/NanoLett
Multicolor Liposome Mixtures for Selective and Selectable Cargo Release Upendra Chitgupi, Shuai Shao, Kevin A. Carter, Wei-Chiao Huang, and Jonathan F. Lovell* Department of Biomedical Engineering, University at Buffalo, State University of New York, Buffalo, New York 14260, United States S Supporting Information *
ABSTRACT: Many approaches exist for stimuli-triggered cargo release from nanocarriers, but few can provide for ondemand release of multiple payloads, selectively. Here, we report the synthesis of purpurin-phospholipid (Pur-P), a lipid chromophore that has near-infrared absorbance red-shifted by 30 nm compared to a structurally similar pyropheophorbidephospholipid (Pyr-P). Liposomes containing small amounts of either Pur-P or Pyr-P exhibited similar physical properties and fluorescence self-quenching. Loaded with distinct cargos, PurP and Pyr-P liposomes were mixed into a single colloidal suspension and selectively released cargo depending on irradiation wavelength. Spatiotemporal control of distinct cargo release was achieved by controlling multicolor laser placement. Using basic orange and doxorubicin anthraquinones, multidimensional cytotoxicity gradients were established to gauge efficacy against cancer cells using light-released drug. Wavelength selectivity of cargo release was maintained following intramuscular administration to mice. KEYWORDS: Liposomes, nanocarriers, stimuli-responsive, controlled release, photoactivatable, porphyrin
T
found that unsaturated lipids increase the rate of PoP-mediated, light-triggered cargo release.36 The aqueous absorption of liposomes containing 2 mol % PoP is shown in Figure 1B. Pyr-P liposomes have an absorption peak at 665 nm, whereas Pur-P liposomes have a red-shifted peak near 700 nm, likely owing to delocalization of π-electrons in the additional carbonyl group in the Pur-P exocyclic ring. This difference in absorption enables selective Pyr-P liposome excitation with a 665 nm laser and selective Pur-P liposomes excitation with a 690 nm laser. Pyr-P liposomes were 120 nm in diameter while Pur-P liposomes were slightly larger with a diameter of 160 nm (Figure 1C). The polydispersity index of Pyr-P liposomes was slightly higher than Pur-P liposomes with a value of 0.16, compared to 0.06 (Figure 1D). To characterize photophysical properties, liposomes were formed with increasing amounts of Pyr-P or Pur-P Figure 1E). The emission spectra of the PoPs is shown in Figure S2. At higher PoP concentrations, both Pyr-P and Pur-P liposomes exhibited fluorescence self-quenching (Figure S3). Both types of liposomes containing 2 mol % PoP had the highest fluorescence, and were used for further study. Previously, 2% Pyr-P was found to be optimal for triggered release.37 Fluorescence self-quenching correlates with singlet oxygen self-quenching38 and the release mechanism is related to photooxidation.36 When PoPs were loaded at self-quenching
riggered release of cargo from carriers is an area of research interest.1−5 Liposomes are a prototypical nanoscale carrier.6,7 Intrinsic mechanisms of triggering cargo release include enzyme activation8 and pH.9 Thermal-triggered cargo release from liposomes has been developed for decades and advanced to clinical studies.10−12 Light activation has also been explored for releasing cargos.13−24 We have shown that liposomes incorporating small amounts of porphyrin-phospholipid (PoP) release cargo in response to near-infrared light.25−27 Most PoP-related studies have made use of pyropheophorbidea phosphatidylcholine, although other PoPs have been explored, including metal-chelated versions of this28−30 and related metallochlorins,31,32 bacteriochlorophylls33,34 and texaphyrin35 conjugates. These have modulated light absorption, enabling wavelength-selective PoP excitation. In this work, multicolor PoP liposome mixtures are developed and used for selective and selectable light-activated cargo release. Results and Discussion. Multicolor Liposomes. Purpurinphospholipid (Pur-P) was synthesized with the same route as pyropheophorbide-phospholipid (Pyr-P), but using purpurin18 as a starting material (Figure S1). Figure 1A shows the structure of both PoPs; Pyr-P and Pur-P. Unless indicated otherwise, liposomes were formed with cholesterol (CHOL), distearoylphosphatidylcholine (DSPC), dioleoylphosphatidylcholine (DOPC), distearoylphosphatidylethanolamine-polyethylene glycol (2 kDa) (PEG-lipid), and PoP with a molar ratio [CHOL/DSPC/DOPC/PEG-lipid/PoP] of [50:33:10:5:2]. DOPC was included since prior studies have © 2018 American Chemical Society
Received: November 28, 2017 Revised: January 21, 2018 Published: January 31, 2018 1331
DOI: 10.1021/acs.nanolett.7b05025 Nano Lett. 2018, 18, 1331−1336
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Figure 1. Multicolor PoP liposomes. (A) Structure of PoPs used in this study. (B) Absorbance of liposomes containing 2 mol % PoP in PBS. Laser irradiation wavelengths used in this study are shown with arrows. (C) Hydrodynamic size of Pyr-P and Pur-P liposomes. (D) Polydispersity index of Pyr-P and Pur-P liposomes. (E) Brightness of liposomes containing varying amounts of PoPs.
Figure 2. Selective, selectable light triggered cargo release of Doxorubicin (Dox) or Basic Orange (BO) from PoP liposomes. Indicated liposomes mixtures were subjected to laser irradiation to release liposomal cargo with a (A) 665 nm laser or (B) 690 nm laser. (C,D) Light-triggered release of indicated cargos from liposomes with indicated irradiation.
concentrations (10 mol %), fluorescence self-quenching was maintained in serum, unlike the free porphyrins, indicating stability and lack of exchange with serum factors (Figure S4). Selective Cargo Release. To assess selective release from multicolor liposomes, Pyr-P and Pur-P liposomes were loaded with doxorubicin (Dox) and basic orange (BO) respectively, via ammonium sulfate gradient. These two types of liposomes were then combined and irradiated with a 665 nm laser at 125 mW cm−2, to selectively excite Pyr-P liposomes. As shown in Figure 2A, in these conditions, only Dox was released from Pyr-P liposomes, with irradiation with minimal release of BO from Pur-P liposomes. In contrast, when a 690 nm laser was used to selectively excite Pur-P liposomes, only BO release was induced (Figure 2B). It was observed that the Dox release rates were slower than the BO release, a phenomenon which has been reported previously,39 suggesting the difference in release rates have to do with the cargo leakage rates, rather than differences in PoPmediated light-induced membrane permeabilization. Figure 2C and Table S1 summarize those results, demonstrating that by selecting the appropriate wavelength, cargo can be selectively released. In a control experiment, the liposomes were used to load the opposite cargos of the preceding experiments. As shown in Figure 2D, selectivity was still maintained when cargo loading was reversed. In general, less selectivity was observed with 665 nm excitation, likely owing to the partial excitation of the Pur-P liposomes at that same wavelength. Light-triggered release responses that are nonlinear with fluence have been observed with actively loaded cargo in PoP liposomes.36 Selective, Spatial Control of Release. To demonstrate selective, selectable release with spatial control, sulforhodamine B (SRB), a hydrophilic fluorophore was passively loaded into Pyr-P liposomes. SRB was chosen since it is a bright fluorophore and does not have spectral overlap with other cargos used. BO was also used due to its brightness. Pyr-P and Pur-P liposomes were mixed, and then added to every single
well in 384-well plate (Figure 3A). Next, only selected parts of the plate were irradiated, first with a 665 nm laser to trigger release from Pyr-P liposomes (Figure 3B). SRB release from Pyr-P liposomes was readily observed only in the laser-exposed portions of the plate. In those same wells, minimal release of BO from Pur-P liposomes occurred. Next, a 690 nm laser was used to release BO from Pur-P liposomes in an adjacent portion of the plate. The laser irradiation area was selected in such a way that there was an overlap in the center of the well plate. Figure 3C shows the overlaid image, demonstrating that the areas in which both 690 and 665 laser was irradiated released both SRB and BO (shown in yellow). To ensure specificity of cargo release was related to the multicolor activation of the liposomes rather than the cargo properties, the liposomes were loaded with the opposite cargos and irradiation was repeated (Figure 3D). Release occurred selectively based on the wavelength of irradiation and the liposome type with good spatial control. Multidimensional Gradients of Released Cargos. We next sought to use light to establish gradients of released cargo. Time-based release studies were carried out with SRB and BO loaded Pyr-P and Pur-P liposomes, respectively. Samples were subjected to 665 and 690 nm laser irradiation both individually and sequentially as shown in Figure 4A. With increasing 665 nm irradiation, SRB could be increasingly released from the Pyr-P liposomes while with increasing 690 nm irradiation triggered increasing release of BO from Pur-P liposomes. When the liposomes were increasingly irradiated with both 665 and 690 nm, both SRB and BO were released in increasing amounts. Thus, these results show that selectable gradients of cargo can be released selectively with light. Figure S5 shows 1332
DOI: 10.1021/acs.nanolett.7b05025 Nano Lett. 2018, 18, 1331−1336
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Figure 4. Multidimensional gradients of released cargos. (A) Selective and increasing release of SRB and/or BO based on irradiation time. (B) Cell viability of U87 cells incubated with empty Pyr-P or Pur-P liposomes irradiated as indicated. (C) Cell viability of U87 cells treated with BO-loaded Pyr-P and Dox-loaded Pur-P liposomes treated with indicated laser. One asterisks denotes statistical significance with P < 0.05 and two indicates significance with P < 0.01 with Posthoc Tukey’s test, n = 3 triplicates per condition.
immobilize the liposomes) into the leg of mice, which were then imaged (Figure 5A). Initially, minimal fluorescence of SRB or calcein was observed. Specific in vivo cargo release was
Figure 3. Selective and selectable spatial control of release. (A) Fluorophore-loaded Pyr-P and Pur-P liposome were mixed and distributed to each well of a 384 well microplate. (B) Sequential irradiation of the microplate with the indicated pattern of two different laser irradiation wavelengths. (C) Fluorescence image of a 384 well microplate with mixed liposomes in every well, selectively irradiated as indicated. (D) Similar experiment as in C, but cargo was loaded in the opposite types of PoP liposomes. Released SRB is shown in red, BO in green, and the overlapping signal in yellow.
that light gradients can be used to create continuous released cargo gradients. Next, multidimensional cargo release gradients were used to examine the chemotherapeutic drug toxicity. The cytotoxic anthraquinones Dox and BO were loaded into Pyr-P and Pur-P liposomes, respectively. Without laser irradiation, minimal drug release was observed during a 3 h period (Figure S6). Following incubation in serum, light-irradiation induced cargo release, indicating both liposomes and cargo were intact and that the PoP was still embedded in the bilayer (Figure S7). Liposomes were incubated with human glioblastoma cells, irradiated immediately. When empty PoP liposomes were used, laser irradiation did not decrease cell viability (Figure 4B). However, the drug-loaded liposomes inhibited cell growth in an increasing fashion when exposed to light (Figure 4C). This is due to increasing amounts of drug being released from the liposomes and being made more available for cell uptake. In this manner, gradients could be useful for assessing synergies between multiple drugs using free drug concentrations established by light-triggered release. Selective, Multicolor Release in Vivo. To test whether cargo release of Pyr-P and Pur-P liposomes could occur selectively in vivo, Pyr-P and Pur-P liposomes (with DSPC as the main lipid) were loaded with SRB and calcein at self-quenching concentrations. Liposomes were injected intramuscularly (to
Figure 5. Selectable light-triggered cargo release in vivo. (A) Cargoloaded PoP liposomes were mixed and injected intramuscularly into the leg of a mouse. (B) Mice legs were sequentially irradiated with 665 and 690 nm laser. SRB and calcein release was imaged. (C) Quantification of cargo release via fluorescence intensity in regions of interest. Values show standard error for n = 4 mice. 1333
DOI: 10.1021/acs.nanolett.7b05025 Nano Lett. 2018, 18, 1331−1336
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phosphocholine (16-lyso- PC), 4-dimethylaminopyridine (DMAP) and 1-ethyl- 3-(3- dimethylaminopropyl)carbodiimide (EDC) were dissolved in chloroform in the molar ratio 1:1:2:1. The mixture was reacted in dark with constant stirring for 24 h. The crude product was purified by column chromatography. The product fraction was collected and the organic solvent was removed by rotary evaporation. A 279 mg sample of final product powder was obtained after freeze-drying in 20% water in tert-butanol which amounted to a 76% reaction yield. Mass spectrometery data for Pur-P indicated a single m/z peak of 1044 g/mol which was close to theoretical value 0f 1042.24. HPLC data showed Pur-P to be over 90% pure. Liposome Preparation and Characterization. Liposomes were prepared with cholesterol (50 mol %), DOPC (10 mol %), DSPE-PEG (5 mol %), DSPC (33 mol %), and Pyr-P or Pur-P (2 mol %) by first preparing a 20 mg lipid film. In brief, all the lipids were dissolved in chloroform and dried. Remote loading was done as follows: 200 μL of ethanol was added to the lipid film and maintained at 60 °C for 30 min. 800 μL of 250 mM ammonium sulfate solution preheated to 60 °C was added to 200 μL of ethanol containing lipids at 60 °C. Resulting liposome solution of 1 mL was run over 10 mL G75 sephadex column with PBS to get rid of ethanol. For basic orange loading, phosphate buffer of pH 6.5 was used. The first 10 fractions (10 × 1 mL) were collected and liposome samples with highest concentrations were used as liposome stock solutions. For size measurement, 2 mol % PoP liposomes were prepared by ethanol injection method and were extruded 10 times with hand-held extruder using 100 nm membrane filter. Liposome quenching and brightness studies were carried out by preparing varying percentages of Pyr-P or Pur-P as indicated in Figure 1. Self-quenching of liposomes was determined by measuring the fluorescence of Pyr-P or Pur-P liposomes with and without Triton X-100 using a TECAN plate reader. Selfquenching serum stability studies involved incubating liposomes in 10% fetal bovine serum at 37 °C. These liposomes were formed with [CHOL/DSPC/DOPC/PEG:PoP] in the ratio of [50:25:10:5:10]. For pyro and purpurin-18 liposomes, Pur-P and Pur-P was replaced with pyropheophorbide-a and purpurin-18 respectively. Self-quenching was calculated as the ratio of fluorescence originating from liposomes to liposomes treated with Triton X-100. Brightness of liposomes was calculated by measuring the fluorescence of the liposomes while the absorbance at 410 nm was around 0.05. The ratio of fluorescence to absorbance was calculated as brightness of the sample. Cargo Loading and Drug Release. The ammonium sulfate gradient loading method was used for Dox and BO into Pyr-P and Pur-P liposomes.47 Briefly, liposomes made via an ethanol injection method were incubated with 1:10 drug/lipid ratio for 60 min, resulting in complete drug loading. Cargo loaded liposomes were dialyzed against PBS for 12 h (12,000−14,000 MWCO dialysis tubing, Fisher Cat. No. 21-152-16). Dialysate was replaced with fresh PBS every 4 h to remove excess free drug. Fluorescence quenching of the encapsulated drug was measured to ensure successful loading. For passive loading, liposomes were prepared by ethanol injection method by adding 200 μL ethanol to dry lipid-film and then injecting 800 μL 50 mM SRB/Calcein preheated to 60 °C. Liposomes were separated over a 10 mL Sephadex G75 column to separate free dye from loaded liposomes. A clear separation was observed
observed in response to Pyr-P or Pur-P liposome irradiation (Figure S8). A region injected with liposomes was then first irradiated with a 665 nm laser at 75 mW cm−2 for 5 min leading to the release of SRB from Pyr-P liposomes. Subsequently, the same leg was exposed to a 690 nm laser for 4 min, which led to the release of calcein from Pur-P liposomes (Figure 5B). The fluorescence intensities of cargo released after 665 nm laser exposure showed an 8-folds increase SRB intesntity in Pyr-P liposomes, whereas calcein increased just 1.9 fold (Figure 5C). On the other hand, with subsequent treatment with the 690 nm laser, there was a 5.4 fold increase observed in calcein in Pur-P liposomes, showing the selectable and selective release of cargo in vivo. SRB release with the 690 nm laser exposure increased an additional 1.6 folds, indicating that some amount of additional background release occurred. Conclusion. To the best of our knowledge, little work has been reported on carrying out on-demand, externally triggered release of multiple cargos, selectively. However, the potential benefit of temporal control of multiple drug release has been proposed for treating conditions such as periodontitis,40 melanogenesis,41 and cancer.42−44 Such approaches have relied on differential passive diffusion or degradation of polymers with limited temporal precision and no spatial selectivity of cargo release. In this work, we demonstrated that multicolor PoP liposomes can be loaded with various cargoes, mixed and then be irradiated with specific wavelengths of light to trigger selectable and selective cargo release. This approach lends itself toward high spatiotemporal control of release. We demonstrated that by varying light exposure, multidimensional drug release gradients can be established and this concept was demonstrated for two cytotoxic agents. Finally, pilot studies demonstrated the feasibility of this approach in vivo. This approach could potentially be applied to mixtures of other spectrally distinct colloidal nanocarriers mixtures such as polymeric nanoparticles,45 as long as nonthermal cargo release mechanisms are feasible. Because drug delivery methods requiring sustained release have used liposomes as carriers, treatment involving multiple drug combinations could make use of wavelength specific release of drugs from Pur-P and PyrP liposomes, especially in treating cancer. Experimental Section. Materials and Equipment. Lipids including 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (ammonium salt) (DSPE-PEG2000), and cholesterol were obtained from Corden Pharma. Doxorubicin hydrochloride was purchased from LC Laboratories (Cat. No. D-4000). Basic orange was obtained from TCI America (Cat. No. A0132). Sulforhodamine B and Calcein were procured from VWR. G-75 sephadex was obtained from GE Healthcare. Absorption spectra were measured using a PerkinElmer UV−vis spectrophotometer. For size and PDI measurement, Brookhaven 90Plus Zeta Sizer was used. Fluorescence measurements were made using TECAN plate reader. A PTI instrument was used to measure release kinetics. Mass spectroscopy and HPLC for Pur-P were performed with waters 2790 and waters micromass ZQ instrument. In vitro and in vivo imaging studies were imaged using IVIS fluorescence imaging system. Synthesis of PoP. Pyr-P was synthesized as described before.46 Pur-P was synthesized in similar method as Pyr-P. Purpurin 18 (200 mg), 1-hexadecanoyl- sn-glycero- 31334
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reader. Cell viability was calculated as (ATreated − ABlank)/ (AControl − ABlank) × 100. All cell based in vitro experiments were performed in triplicates. In Vivo Studies. Animal studies were performed in accordance with University at Buffalo Institutional Animal Care and Use Committee. ICR mice were used for in vivo studies. Mice were injected with 50 μL of 20 mg/mL liposome solution intramuscularly. Immediately after injection, the legs of mice were irradiated with 75 mW cm−2 665 and 690 nm laser irradiation for 5 min, then 4 min, respectively. All the images were obtained using IVIS fluorescence imaging. SRB was imaged with 535 nm excitation and emission was read using the dsRED filter. Calcein was imaged using 485 nm excitation and emission signal was read using the GFP filter.
between liposomes and free dye in the column indicating successful entrapment of dye in to the liposomes. Empty liposomes were prepared similar to cargo-loaded liposome by ethanol injection method, except ammonium sulfate was replaced with phosphate buffer saline. Cargo release kinetics were monitored using a fluorometer (PTI International) when the liposome sample was irradiated with 665/690 nm laser at the mentioned fluence rate (125 or 200 mW cm−2). A laser diode was used as the source of laser light. Ten microliters of Pyr-P- and Pur-P-based liposomes prepared at 20 mg/mL were diluted in PBS by 200 folds and were irradiated with laser for a period of 45 s. However, the release kinetics was monitored for 2 min. The samples were continuously stirred with the help of a stir-bar placed in the cuvette. Release of drug was measured based on the fluorescence of the drug. Percentage release was calculated with respect to the fluorescence of the lysed sample (liposome sample with Triton X-100). For Dox, 480 nm excitation and 590 nm emission settings were used. For BO and Calcein, 485 nm excitation and 525 nm emission was used. For SRB, 565 nm excitation and 585 nm emission was used. For microplate well experiments corresponding to timebased laser irradiated dye release, 20 μL of cargo-loaded liposomes of each cargo were diluted in 5 mL of PBS and 20 μL was added to each well of a 384-well plate. The left part of the plate was irradiated with 665 nm light and the right part with 690 nm light at 200 mW cm−2 for 5 and 10 s, respectively. Fluorescence measurements for well plate experiments were carried out using an IVIS fluorescence imaging system. Sulforhodamine B is displayed in red and basic orange in green. For in vitro serum stability, Dox or BO loaded Pur-P and Pyr-P liposomes were diluted 20 folds in 50% fetal bovine serum and incubated at 37 °C. For light-triggered release following serum incubation, liposomes were incubated with Pyr-P (Dox-loaded) or Pyr-P (BO-loaded) liposomes for 4 h at 37 °C. Pyr-P or Pur-P liposomes were added to 96-well plate and irradiated with 665 or 690 nm laser for 4 min at fluence rate of 125 mW cm−2 to ensure full release. Fluorescence measurements of the sample were carried out with the help of TECAN using 485/525 nm, 480/590 nm exicitation/emission wavelengths for BO and Dox, respectively. In Vitro Cytotoxicity. For cell-based in vitro experiments, human glioblastoma (U87) cells were maintained in a 25 cm3 flask in the incubator at 37 °C under 5% CO2 until the cells were 80% confluent and then trypsinized to seed in a well plate. Cells were seeded in a 96-well plate at 10,000 cells/well and were allowed to adhere for 24 h. Empty PoP liposomes (200 μg lipid/well) or doxorubicin/basic orange loaded PoP liposomes 20 μg drug/well) were added to each well and immediately treated with laser for the time indicated in Figure 4. Posttreatment, cells were placed in the incubator for 2 h. After 2 h, media containing liposomes was replaced with fresh media containing FBS after washing with PBS. Well plate was placed in the incubator for 24 h. Subsequently cell viability assay was performed. For cell viability assay, XTT stock solution was prepared in PBS by addition of 2,3-bis(2-methoxy-4-nitro-5sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) at 50 μg/ mL and N-methyl dibenzopyrazine methyl sulfate (PMS) at 60 μg/mL. Media from the well plate was removed and the cells were washed with PBS once. A 100 μL sample of the XTT reagent solution was added to each well and the well plate was placed in the incubator at 37 °C for 2 h. Well plate was read at 450 nm with 630 nm readings as reference using TECAN plate
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.nanolett.7b05025. Figures S1−S8: Synthetic scheme, PoP emission spectra, PoP liposome self-quenching, PoP liposome serum stability, in vitro release gradients, drug loading stability, light-triggered release following serum incubation, in vivo release selectivity, in vitro cargo release (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail: jflovell@buffalo.edu. ORCID
Jonathan F. Lovell: 0000-0002-9052-884X Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
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REFERENCES
This work was supported by the National Institutes of Health (R01EB017270 and DP5OD017898) the National Science Foundation (1555220) and the University at Buffalo Clinical and Translational Science Institute.
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DOI: 10.1021/acs.nanolett.7b05025 Nano Lett. 2018, 18, 1331−1336
