Patent Application
20140044648
The present invention relates to imaging agents, and more particularly to probes for use as contrast agents that may become activated in an environment with a pH less than a normal physiological pH.
Magnetic resonance imaging (MRI) has become a powerful technique in the clinical diagnosis of disease and in animal imaging.1-4 MRI is capable of obtaining tomographic images of living subjects with high spatial resolution. It is based on the interaction of water protons with surrounding molecules within tissues in the presence of an external magnetic field.5-8 MR contrast agents9-11 typically enhance contrast for more accurate diagnosis. Most recently, MR agents have been modified to allow for targeting imaging by conjugating targeting ligand (e.g. antibody, peptide) is conjugated to MR contrast agent.12,13 Among these probes, superparamagnetic nanoparticles14-16 and paramagnetic metal chelates8 are the most commonly used.17-21 Superparamagnetic nanoparticles are typically composed of an iron oxide nanoparticle (IONP) surrounded by a polymeric coating to facilitate increased stability in aqueous media.22 They work by shortening the traverse relaxation time (T2) of surrounding water protons, resulting in a decrease of the signal (negative contrast, dark signal) using the T2-weighted sequences for the MR scanner.23-28 On the other hand, paramagnetic gadolinium chelates create an increase in signal intensity on T1-weighted images (positive contrast, bright signal) by shortening the longitudinal relaxation time (T1) of surrounding water protons.10,17,29-38
The development of an activatable MR imaging agent that reports on a biological process associated with diseases would greatly advance medical imaging of disease at a molecular level.39-41 Activatable T1 or T2 agents, those that results in modulation of either the T1 or T2 relaxation time upon target binding, enzymatic activity or biological process associated with disease would be attractive MR imaging agents, resulting in high sensitivity and high signal to noise ratios with low background.20,42-48 Activatable Gd-based T1 agents have been previously described8,49,50 and include those designed to be biologically activated by an enzyme such as β-Galactosidase51,52 and β-Glucoronidase42,44 as well as those activated by a release of a drug.53,54 Activatable T2 IONP based agents are less common as it is often difficult to “quench” the strong superparamagnetic nature of these nanoparticles.26-29,55 Magnetic relaxation switches, have been developed based on IONP that cluster in the presence of a target or enzymatic activity leading to detectable changes in the T2 relaxation times.56-59 However, the use of these T2 activatable agents has been difficult to implement in cells or animal studies and it has been limited to their use as nanosensors in molecular diagnostic applications.57,60
An activatable T1 agent, one that can induce a faster T1 relaxation, would result in an increase in the T1-weighted MR signal intensity upon target recognition for better diagnosis. Such an activatable agent could be beneficial in cancer diagnosis if it were designed to become activated upon tumor targeting, resulting in a brighter signal.
In accordance with an aspect, there is now described the design, synthesis and characterization of a novel probe that becomes activated in an environment having a less than normal physiological pH, resulting in an increase in the T1-weighted signal (brighter contrast). In one aspect, the designed probe is composed of a superparamagnetic core, such as an iron oxide nanoparticle, that encapsulates a paramagnetic agent, such as a gadolinium and diethylenetriaminepentacetate (Gd-DTPA) chelate, within hydrophobic pockets of the nanoparticle's polymeric matrix, e.g., a polyacrylic acid (PAA) coating (IO-PAA-Gd-DTPA). While not wishing to be bound by theory, it is believed that the strong magnetic field of the superparamagnetic iron oxide core will affect the relaxation process of the much weaker paramagnetic Gd-DTPA, resulting in quenching of its T1 signal (
In addition, the present inventors have found that the superparamagnetic iron oxide nanocrystal acted as a magnetic quencher for the Gd-DTPA T1 only when the Gd-DTPA is encapsulated within the nanoparticle's polymeric coating in close proximity to the superparamagnetic core. Also, it was confirmed that the T2 activation of the probes was not quenched upon encapsulation of Gd-DTPA complex. Furthermore, when the IO-PAA-Gd-DTPA nanocomposite was conjugated with a targeting agent, such as folic acid, its selective internalization and lysosomal localization within folate receptor positive cells allow for selective activation due to the lysosome's acidic pH. Still further, when the folate receptor targeting nanocomposite was used to co-encapsulate a cytotoxic drug (e.g., Taxol), dual delivery of the drug and T1 imaging activation was achieved. Taken together, the newly developed activatable probes (IO-PAA-Gd-DTPA) combine features of several important modalities, such as: (i) activatable T1-weighted MRI contrast, (ii) T2-weighted MRI contrast, (iii) receptor-targeted internalization, (iv) biodegradable and biocompatible and/or (v) tumor delivery of anticancer drug(s). These features render the described probes as particularly suitable MR-activatable agents for cancer.
According to an aspect of the present invention, there is provided an activatable probe comprising a superparamagnetic core and a polymeric matrix coating the metal oxide core. A paramagnetic agent is encapsulated within the polymeric matrix. The polymeric matrix is configured to release the paramagnetic agent when subjected to a medium having a pH less than a normal physiological pH.
In another aspect, there is provided an activatable probe that includes the following characteristics: (i) an activatable T1-weighted MRI contrast; (ii) a T2-weighted MRI contrast; (iii) receptor-targeted internalization; (iv) biodegradable and biocompatible; and/or (v) tumor delivery of anticancer drug.
In another aspect, there is provided is an activatable probe comprising the following components: (a) a metal particle; (b) Gd-DTPA; and (c) a polymeric matrix; wherein the Gd-DTPA is associated with the polymeric matrix. In another embodiment, there is provided an iron oxide particle associated with Gd-DTPA via a polymeric, e.g., PAA, matrix.
In another aspect, there is provided an activatable probe comprising the following components: (a) a metal particle; (b) Gd-DTPA; (c) an anti-tumor agent and/or anti-cancer agent; and (d) a polymeric matrix, wherein the Gd-DTPA is associated with the polymeric matrix. The probe is activatable when subjected to a less than normal physiological pH. When subjected to such environment, the GD-DTPA and/or the anti-tumor and/or anti-cancer agent is released.
In yet another aspect, there is provided an anti-tumor agent and/or anti-cancer agent conjugated with the GD-DTPA component. In a particular embodiment, there is provided a Doxorubicin-S-S-Gd-DTPA activatable nanoprobe. It will be appreciated by those skilled in the art that the Doxorubicin component can be substituted with another anti-tumor agent or anti-cancer agent.
In yet another aspect, there is provided a method of enhancing imaging sensitivity of cancer tissue in a subject. The method includes administering to the subject an effective amount of an activatable probe as disclosed herein, and subjecting the subject to an imaging technique. Typically, the imaging technique pertains to MRI.
In yet another aspect, there is provided a method of imaging release of a biologically active agent in a subject. The method involves administering to the subject a therapeutically effective amount of an activatable probe disclosed herein that includes: (a) a metal particle; (b) Gd-DTPA; (c) an anti-tumor agent and/or anti-cancer agent; and (d) a polymeric matrix, wherein the Gd-DTPA is associated with the polymeric matrix. The method also involves subjecting the subject to an imaging technique. The imaging technique typically involves MRI.
As used herein, the term “about” refers to values that are ±10% of the stated value.
As used herein, the terms “administering,” “administration,” or the like includes any route of introducing or delivering to a subject a composition (e.g., pharmaceutical composition or wound dressing) to perform its intended function. The administering or administration can be carried out by any suitable route, including topically, orally, intranasally, parenterally (intravenously, intramuscularly, intraperitoneally, or subcutaneously), rectally, or topically. Administering or administration includes self-administration and the administration by another.
As used herein, the term “anti-cancer agent” refers to any biologically effective agent that has an anti-cancer effect on a cell in a subjecting, including but not limited a cytotoxic effect, an apoptotic effect, an anti-mitotic effect, an anti-angiogenesis effect, or an anti-metastatic effect.
As used herein, the term “biologically effective agent” refers to any material used to treat or prevent any disease, disorder or abnormal condition in a subject.
As used herein, the term “cancer” refers to all types of cancers or neoplasm or malignant tumors found in a subject.
As used herein, the terms “effective amount,” “amount effective,” “therapeutically effective amount,” or the like, refer to an amount effective at dosages and for periods of time necessary to achieve the desired result.
As used herein, the term “paramagnetic material” is meant to include any material which possesses a magnet moment that can be aligned by an external magnetic field. In the probes described herein, the T1 relaxation rate of the paramagnetic agent as described herein is quenched by the superparamagnetic core to at least some extent.
As used herein, the term “subject” refers to any human or nonhuman mammal.
As used herein, the term “superparamagnetic” refers to a class of substances that have a similar magnetism as ferromagnetic materials in an external magnetic field, but do not have a remnant magnetization after removal of the external magnetic field. Typically, superparamagnetic agents work by shortening the traverse relaxation time (T2) of surrounding water protons, resulting in a signal decrease using the T2-weighted sequences for the magnetic resonance scanner. In the nanoprobes described herein, the superparamagnetic materials have an ability to at least quench (reduce) the T1 relaxation rate of the paramagnetic agent as described herein to at least some extent.
The superparamagnetic core may comprise any suitable material having an ability to at least quench (reduce) the T1-weighted signal of the paramagnetic agent as described herein to at least some degree. In one aspect, the superparamagnetic material comprises a metal. The metal may comprise a compound comprising at least one of the group consisting of Au, Ag, Pd, Pt, Cu, Ni, Co, Fe, Mn, Ru, Rh, Os, and Ir, for example. In one embodiment, the superparamagnetic core comprises a superparamagnetic iron platinum particle (SIPP). In another embodiment, the superparamagnetic core comprises a metal oxide, including but not limited to a member from the group consisting of zinc oxide, titanium dioxide, iron oxide, silver oxide, copper oxide, aluminum oxide, and silicon dioxide particles. In a particular embodiment, the superparamagnetic core comprises iron oxide. The core of the probe may be in any suitable form, such as a magnetic bead, nanoparticle, microparticle, and the like.
In certain embodiments, the superparamagnetic core comprises a nanoparticle having a longest dimension of less than about 1000 nm, and in certain embodiments less than 100 nm. In addition, in certain embodiments, the probes described herein comprise nanoprobes, even when the remaining components described herein are included with the nanoparticle (e.g., polymeric matrix, paramagnetic agent, targeting agent, and/or biologically active agent). In other embodiments, the superparamagnetic core is a micron-sized particle and the corresponding probes are micron-sized.
The polymeric matrix may be any polymeric material that degrades and/or swells at a pH less than normal physiological conditions (typically about 7.4). In this way, in the probes described herein, the polymeric matrix can release the agents contained therein, such as a paragmagnetic agent, targeting agent and/or biologically active agent at pH's less than a normal physiological pH. In certain embodiments, the polymeric matrix comprises a polymeric material that degrades and/or swells at a pH within the range of about 4.0 to about 7.4. In a particular embodiment, the polymeric matrix comprises a polymeric material that degrades and/or swells at a pH within the range of about 5.0 to about 6.0. It is appreciated that at normal pH's, the polymeric matrix effectively encapsulates the cargo so as to substantially maintain the cargo therein. By “encapsulate,” it is meant that at least a portion of the cargo (paramagnetic agent, targeting agent, and/or biologically active agent) is encapsulated within the polymeric matrix, e.g., not on a surface of the matrix. Exemplary polymeric materials include but are not limited to polyacrylic acid, dextran, and chitosan. In a particular embodiment, the polymeric matrix comprises polyacrylic acid (PAA).
The paramagnetic agent may comprise any material that whose T1 signal may be quenched by the superparamagnetic core in a probe as described herein to at least some degree. The paramagnetic agent may include a member selected of the transition metals and lanthanides of groups 1b, 2b, 3a, 3b, 4a, 4b, 5b, 6b, 7b, and 8. In certain embodiments, the paramagnetic agent comprises a member from the group consisting of gadolinium (Gd), dysprosium (Dy), chromium (Cr), and manganese (Mn). In a particular embodiment, the paramagnetic agent comprises Gd.
In one aspect, the paramagnetic agent also comprises a chelating moiety, capable of forming chelate-complexes with the paramagnetic agent. Exemplary chelating moieties include but are not limited to diethylenetriamine pentaacetic acid (DTPA), ethylene diamine tetraacetic acid (EDTA), triethylene tetraamine hexaacetic acid (TTHA), tetraethylene pentaamine heptaacetic acid, and polyazamacrocyctic compounds, such as 1,4,7,10-tetra-azacyclododecane-1,4,7,10-tetraacetic acid (DOTA)]. In certain embodiments, as described herein, the paramagnetic agent comprises a GD-DTPA complex.
The polymeric matrix is effective to release its cargo when subjected to a medium having a pH less than a normal physiological pH and to encapsulate the cargo within its polymeric matrix at normal physiological pH. In this way, the polymeric matrix can be tuned to release an effective amount of its cargo as desired for the particular application. The present inventors have found that the probes described herein are particularly useful for imaging cancer cells that have a pH environment less than a normal physiological pH. This is particularly advantageous as it is becoming of increasing interest that tumor cell survival relies on adaptation to acidic conditions in the tumor microenvironment. In fact, it has been found that the physiological relevant pH range in certain tumor cells, including but not limited to breast, lung, cervical, and pancreatic cancer cells, is about pH 5 to pH 6. As such, the probes described herein are particularly suitable for imaging such tumor cells or monitoring delivery of biological agents thereto. The cancer cells suitable for targeting and/or imaging are without limitation so long as they produce a microenvironment that has a pH less than a normal physiological pH.
To render the probes selective for imaging particular cells or tissue, in one aspect, the probes may further include a targeting agent having an affinity for a predetermined molecular target, such as a cell receptor. In certain embodiments, the targeting agent is also encapsulated within the polymeric matrix along with the paramagnetic agent. In one embodiment, for example, the targeting agent comprises a folate targeting compound that targets cancer cells that overexpress folate receptors. The folate targeting compound may comprise folate, folic acid, or derivatives thereof. Examples of folate derivatives include, but are not limited to, dihydrofolate, tetrahydrofolate, 5,-methyl-tetrahydrofolate and 5,10-methylene tetrahydrofolate. Humans and other mammals express a number of proteins which bind to folate and transport it into cells. For example, in humans, alpha- and beta-folate receptors have been identified, each of which can occur in several isoforms (e.g. as a result of differential glycosylation). These proteins are referred to as “folate receptors.” Thus, a folate receptor is considered to be any protein expressed on the surface of a cell, such as a cancer cell, which binds the folate targeting compound in preference to other moieties or compounds.
Additionally, in other embodiments, the targeting agent may be one or more of an aptamer, a peptide, an oligonucleotide, an antigen, an antibody, or combinations thereof having an affinity for a predetermined molecular target. In one embodiment, the targeting agent comprises an aptamer having an affinity for a cancer cell. The aptamer may include any polynucleotide- or peptide-based molecule, for example. A polynucleotidal aptamer is a DNA or RNA molecule, usually comprising several strands of nucleic acids that adopt highly specific three-dimensional conformation designed to have appropriate binding affinities and specificities towards specific target molecules, such as peptides, proteins, drugs, vitamins, among other organic and inorganic molecules. Such polynucleotidal aptamers can be selected from a vast population of random sequences through the use of systematic evolution of ligands by exponential enrichment. A peptide aptamer is typically a loop of about 10 to about 20 amino acids attached to a protein scaffold that bind to specific ligands. Peptide aptamers may be identified and isolated from combinatorial libraries, using methods such as the yeast two-hybrid system.
In addition to the targeting agent or in lieu thereof, the probes described herein may include a biologically active agent encapsulated within the polymeric matrix. Since some cancer cells are particularly useful targets due to their reduced pH microenvironments, the biologically active agent may be an anti-cancer agent in certain embodiments. The composition of the anti-cancer agent is without limitation as the anti-cancer agent is typically only encapsulated within the polymeric matrix, and not bonded thereto. Exemplary anti-cancer agents are disclosed in U.S. Published Application No. 20130045949, the entirety of which is incorporated by reference herein. In a particular embodiment, the anti-cancer agent is selected from the group consisting of taxol and doxorubicin.
In certain embodiments, the targeting agent and/or the biologically active agent are bonded (covalently or ionically, and typically covalently) to the paramagnetic complex. For example, as shown in the examples, there is provided an 10 (iron oxide)-doxorubicin-S-S-Gd-DTPA probe wherein the doxorubicin molecule is bonded to the Gd-DTPA complex via a disulfide bond. The disulfide bond is expected to be broken down upon release of the doxorubicin-Gd DTPA complex from the polymeric matrix under normal physiological conditions or conditions having a pH lower than the normal physiological conditions. This approach guarantees that upon the release of the drug (Doxorubicin), activation of the MR signal will occur indicating assessment of drug release by MRI. In an embodiment, the cleavable “Doxo-S-S-Gd-DTPA” conjugate was synthesized using a facile nucleophilic substitution reaction before encapsulating with IO-PAA as described earlier in the case of IO-PAA-Gd-DTPA. In a typical reaction, the aqueous solution of doxorubicin hydrochloride salt (1.75 mmol) was added to PBS buffer solution (pH=8.4) to obtain doxorubicin with free amine group. The resulting solution was centrifuged and the solid pallet was soluble in DMSO. Then, p-NH2-Bn-Gd-DTPA complex (1.75 mmol, in PBS, pH 7.4) and dithiobis(succinimidyl propionate) (DSP) solution (1.75 mmol, in DMSO) were added drop-wise. A catalytic amount of triethylamine (0.5 μL in DMSO) was added to the reaction mixture. The reaction mixture was incubated at room temperature for 30 minutes, before overnight incubation at 4° C. (
The probes herein can be utilized for enhancing imaging sensitivity of tissue in a subject comprising by administering to the subject an effective amount of an activatable probe for a time sufficient to release the paramagnetic agent from the polymeric matrix, and subjecting the subject to an imaging technique, typically an MRI technique. For example, in an embodiment, the activatable probe may be administered intravenously into the subject either prior to or during an MRI examination, such as by hypodermic injection or by catheter. In one embodiment, the administration site is at or adjacent to the site where the examination is to be made. In another embodiment, the probe is transferred to the site of examination, such as via the bloodstream.
One skilled in the art would readily appreciate that the administration, duration, and dosing (e.g., concentration) of the components of the probes/compositions described herein may be determined or adjusted based on the age, body weight, general condition, sex, diet, and/or the intended use thereof. Effective amounts of the probes can be provided in a single administration or multiple administrations. When administering the probes described herein, the imaging amount may range from 3 to 50 milliliters in a suitable concentration, for example, depending upon the purpose of the administration. Once administered, the imaging may be performed by suitable methods and devices as known in the art. Exemplary MR imaging methods and devices are disclosed in D. M. Kean and M. A. Smith, Magnetic Resonance Imaging: Principles and Applications (William and Wilkins, Baltimore 1986); U.S. Pat. Nos. 6,151,377, 6,144,202, 6,128,522, 6,127,825, 6,121,775, 6,119,032, 6,115,446, 6,111,410 and U.S. Published Patent Application No. 20110200534, the entirety of each of which is hereby incorporated herein by reference.
In addition, in another aspect, there are provided methods of imaging a release of a biologically active agent in a subject comprising administering to the subject an effective amount of an activatable probe as described herein, and subjecting the subject to an imaging technique, typically an MRI technique.
The following examples are provided as an aid in examining particular aspects of the invention, and represent only certain embodiments and explanations of embodiments. The examples are in no way meant to be limiting of the invention scope. The materials and methods provided below are those which were used in performing the examples that follow.
A IO-PAA-Gd-DTPA probe was synthesized by direct addition of Gd-DTPA during the course of the IO-PAA synthesis using a modified version of a published protocol.22 In brief, an aqueous solution of PAA (0.45 mmol) and Gd-DTPA (0.04 mmol) was added and mixed thoroughly before addition of a mixture of iron salts (2.26 mmol of FeCl3.6H2O and 1.61 mmol of FeCl2.4H2O in dilute HCl solution) in aqueous ammonium hydroxide solutions (0.05 M). The resulting dark-brown colored suspension of composite IO-PAA-Gd-DTPA nanoprobe was stirred for 1 h at room temperature and then centrifuged at 4000 rpm for 30 minutes to get rid of free polyacrylic acid, not encapsulated Gd-DTPA complex and other unreacted reagents. Finally, the composite nanoprobe suspension was purified using a magnetic column (Miltenyi Biotech) and washed with phosphate buffer saline (pH=7.4) solution. This “in situ” encapsulation approach proved to be effective for the encapsulation of Gd-DTPA as no change in the size and relaxivity of the nanoprobes were found over the long period of time (Table 1). The encapsulation of Gd-DTPA within the nanoprobe was confirmed by measuring the amount of Gd using ICP-MS (0.289 mg Gd/mL). Magnetic relaxation measurements at 0.47 T of the composite nanoprobes resulted in a Gd-concentration based relaxivity of R1=50.2±1.8 mM−1Sec−1 and R2=87.3±2.4 mM-1 Sec-1; and R1=43.3±2.1 mM−1Sec−1 and R2=230±3 mM−1Sec−1 based on Fe concentration. Dynamic light scattering studies indicated the presence of a stable and monodisperse suspension of nanoparticles with a hydrodynamic diameter of D 79±2 nm. The diameters of these magnetic nanoprobes were further confirmed by scanning transmittance electron microscopic (STEM) experiments, which show an average diameter of 80 nm (
1.2 pH-Dependent Activation of the Gd-DTPA Composite Magnetic Nanoprobes.
The magnetic relaxation activation of the IO-PAA-Gd-DTPA nanoprobes in buffered solution within a pH range of 4.0 to 7.4 was evaluated. In these experiments, the T1 and T2 of increasing concentrations of IO-PAA-Gd-DTPA nanoprobes was measured at physiological (pH=7.4) and acidic (pH=4.0-6.0) buffered solutions. T1 and T2 readings were taken upon addition of the magnetic nanoprobes, immediately (0 h) and after a 24 h of incubation of the magnetic nanoprobes in the corresponding buffered solutions at 37° C. First, it was observed that the T1 relaxation rate (1/T1) of the IO-PAA-Gd-DTPA nanoprobe (0 h,
To confirm that the superparamagnetic nature of the iron oxide core is responsible for quenching the magnetic relaxation of the Gd-DTPA, a PAA coated cerium oxide nanoparticle encapsulating Gd-DTPA (NC-PAA-Gd-DTPA) was synthesized. In this design, a non-magnetic metal oxide core composed of cerium oxide (nanoceria) replaced the magnetic iron oxide core. The NC-PAA-Gd-DTPA nanoprobes were synthesized following a procedure similar to the one used to synthesize the IO-PAA-Gd-DTPA nanoprobe. Briefly, to a PAA solution in water, Gd-DTPA was added and mixed thoroughly before addition to a solution of cerium nitrate in ammonium hydroxide solutions (Scheme 3 shown in
It was stated that the close proximity of Gd (a weak paramagnetic ion) within the polymeric matrix of iron oxide nanoparticles (a strong superparamagnetic nanocrystal) affects the T1 relaxation of Gd. If this hypothesis is correct, conjugation of a Gd-DTPA directly on the nanoparticle's surface should not result in quenching of the T1 values. To further test this hypothesis, a IO-PAA-Gd-DTPA magnetic nanoprobe was synthesized where the Gd-DTPA was conjugated directly on the IO-PAA surface carboxylic acid groups (
Results showed no change in Δ1/T1 (
Meanwhile, the R1 and R2 relaxation values based on Gd concentrations of the IO-PAA-Gd-DTPA nanoprobes indicate a significant pH-dependent increase in the R1 of the nanoprobes when the Gd is encapsulated within the polymeric coating of the iron oxide nanoparticles (Table 2). Results show that by decreasing the pH of the solution to a mildly acidic condition (pH 6.0), a significant percent increase of 44% in the Gd based R1 is observed. This value contrast with a small increase of 5% observed when the Gd is conjugated on the nanoparticle surface, further indicating that indeed encapsulation within the nanoparticle's polymeric matrix is essential for the observed T1 activation. The observed increase in R1 is larger at higher pH, observing a 68% increasing at pH 5.0, the typical pH within lysosomes. Even though pH-dependent percent changes in R2 are also observed in the Gd encapsulated nanocomposite, they are not as large as the values obtained with R1. Taken together, these results confirm the T1 activation of the IO-PAA-Gd-DTPA nanoprobes upon increases in pH, particularly within the physiological relevant range (pH 5-6) observed in tumors.
Next, it was investigated if the observed pH-dependent increases in R1 of the IO-PAA-Gd-DTPA nanoprobe result in increases in T1-weighted signal in MR images, leading to an increase in the brightness of the image. For these experiments, the T1- and T2-weighted MR images (MRI, B=4.7 T) of nanoprobe solutions at pH 5.0 were acquired immediately (FIG. 10A1) and after a 24 h incubation (FIG. 10A2) in the pH 5.0 buffer. An increase in the T1-weighted MR signals was observed as the concentration of the activatable IO-PAA-Gd-DTPA nanoprobes increased (from 0.3 mM to 11.5 mM), resulting in an increase in the signal of the corresponding MR images (FIG. 10A2). The observed signal increase after a 24 h incubation in the pH 5.0 buffer corresponded to an increase in the (1/T1) relaxation rate (▴,
To evaluate the potential biomedical applications of the activatable IO-PAA-Gd-DTPA nanoprobes, their magnetic activations were assessed using cultured cells. It was hypothesized that upon receptor mediated endocytosis, the nanoparticles will localize in acidic lysosomes, therefore becoming activated as the encapsulated Gd-DTPA complex gets released at lower pH. For these experiments, the magnetic nanoprobes were functionalized with folic acid, following published protocols,22,63 in order to assess their targeted imaging capabilities towards folate receptor (FR)-expressing cancer cells. It was hypothesized that upon internalization into FR expressing cancer cells, T1 activation of the composite IO-PAA-Gd-DTPA-Fol nanoprobe would be triggered by the lysosomal acidic environment (pH=5.0), resulting in vitro activation of the MRI signals. In these experiments, we used a FR positive human cervical carcinoma cell line (HeLa cells, 10,000 cells/well) and as negative control we used H9c2 cardiomyocyte (10,000 cells/well) that do not express FR. Cells were incubated with the nanoprobes (100 μL, 28 mM) at different time-points, trypsinized, centrifuged and resuspended in PBS (pH=7.4) before measuring T1 and T2 of the nanoparticle cell suspension.
As hypothesized, compared to the control IO-PAA-Fol nanoprobes, significant activation in inverse spin-lattice magnetic relaxations (1/TI) was observed in HeLa cells incubated with the activatable IO-PAA-Gd-DTPA-Fol nanoprobes (,
1.7 pH-Dependent Dual Release of the Gd-DTPA Complex and Taxol.
IO-PAA-Gd-DTPA nanoprobes were used to encapsulate Taxol as previously described using a solvent diffusion method.22,63 Briefly, to a suspension of IO-PAA-Gd-DTPA nanoprobes (2.5 mL, 28 mmol) in PBS, the dimethyl sulfoxide (DMSO) solution of Taxol (10 μL, 0.5 μg/μL) was added drop-wise at room temperature. The resulting purified IO-PAA-Gd-DTPA-Taxol nanoparticles were characterized by measuring their size using DLS (D=84±2 nm), taxol encapsulation efficiency (EE)=52±2.4% using HPLC (λabs=227 nm) and calculating the Gd concentration (0.215 mg/mL) by performing ICP-MS experiments. To evaluate the dual release of Taxol and Gd, the IO-PAA-Gd-DTPA-Taxol nanoprobe were incubated in a pH 5.0 buffered PBS solutions and the rate of release of the drug and Gd was accessed using a dynamic dialysis technique. Briefly, the IO-PAA-Gd-DTPA-Taxol nanoprobes (50 μL, 28 mM) were taken in a small dialysis cup (MWCO 6-8 KDa) and incubated in PBS buffer (pH=5.0) solution at 37° C. The rate of release of taxol and Gd was monitored by collecting aliquots from the outside reservoir buffer and measuring the amount of released taxol via HPLC experiment (λabs=227 nm) and Gd by measuring the increase in T1 relaxation rate with time.
Results showed a time dependent increase in the amount of Taxol (▴,
Finally, the differential in vitro cytotoxicity of the functionalized magnetic nanoprobes (35 μL, 28 mM in PBS pH=7.4) was examined using FR expressing human cervical cancer cells (HeLa, 2500 cells/well) and FR negative cardiomyocyte cell lines (H9c2, 2500 cells/well). Results confirmed a time-dependent decrease in the number of viable HeLa cells, when incubated with folate-decorated IO-PAA-Gd-DTPA-Taxol nanoprobes 5 (
In one aspect, a novel activatable Gd-DTPA-encapsulating iron oxide NMR/MRI probe is reported where the longitudinal (spin-lattice) magnetic relaxation (T1) of the encapsulated Gd-DTPA was quenched (low 1/T1) by the iron oxide nanoparticles (IONP-PAA). The above results clearly indicated that the magnetic relaxation of Gd-DTPA complex (T1 agent) is quenched as a result of such encapsulation, whereas the transverse (spin-spin) magnetic relaxation (T2) of iron oxide had a minimal increase. The T1 relaxation of the Gd-DTPA complex becomes activated (dequenched, higher 1/T1) and the corresponding enhanced contrast in T1-weighted MRI experiments is observed upon acid-mediated degradation and release of the T1 agent. In addition, it was confirmed that the T2 activation of the probes was not quenched upon encapsulation of Gd-DTPA complex.
The results also demonstrated that the folate receptor-mediated internalization and the subsequent lysosomal acidic pH-induced intracellular release of Gd-DTPA complex resulted in an enhanced 1/T1 signal. In addition, when the taxol-encapsulating activatable magnetic nanoprobes are incubated, the drug's homing was monitored through an enhanced MRI signal, as further confirmed in the cytotoxicity assays. The presence of folate on the activatable magnetic nanoprobe guarantees a selective activation and release of drug only in folate-receptor positive cells, minimizing toxicity to healthy cells. In contrast, no T1 activation is observed in Gd-DTPA surface conjugating IONPs or Gd-DTPA encapsulating non-magnetic NC-PAA, confirming that quenching was due to the close residence of the Gd-DTPA to the superparamagnetic iron oxide (IO) core and not due to the presence of any non-magnetic metallic core (cerium oxide) or polymeric (PAA) coatings. Finally, the excellent physiological and plasma stability of the designed activatable and theranostic NMR/MRI probes may play an important role for the detection and treatment of cancer in clinical settings.
Iron salts: ferrous(II) chloride tetrahydrate (FeCl2.4H2O) and ferric(III) chloride hexahydrate (FeCl3.6H2O), gadolinium(III) chloride hexahydrate (GdCl3.6H2O), cerium(III) nitrate hexahydrate (CeNO3.6H2O), diethylenetriaminepentaacetic acid (DTPA), ammonium hydroxide, hydrochloric acid, sodium hydroxide, chloropropryl amine, sodium azide, copper(I) iodide, ethylenediamine (EDA), folic acid, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), N-hy droxysuccinimide (NHS), 2-(N-morpholino) ethanesulfonic acid (MES), polyacrylic acid (PAA) and other chemicals were purchased from Sigma-Aldrich. 2-(4-isothiocyanatobenzyl)-diethylenetriaminepentaacetic acid [p-SCN-Bn-DTPA] was purchased from Macrocyclics. EDC [1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride] was obtained from Pierce Biotechnology. The human cervical carcinoma (HeLa) and cardiomyocyte (H9c2) cell lines were obtained from ATCC. Magnetic columns (LS Column) were purchased from Miltenyi Biotech for the purification of magnetic nanoprobes using QuadroMACS separators. Dialysis membranes were obtained from Spectrum Laboratories. Nitrogen purged DI water was used in all synthesis.
Chelation of the rare-earth element Gadolinium (Gd) with diethylenetriaminepentaacetic acid (DTPA) or with functional DTPA, p-SCN-Bn-DTPA [2-(4-isothiocyanatobenzyl)-diethylenetriaminepentaacetic acid] results in a strongly paramagnetic, stable complex that is well tolerated in animals. These complexes were synthesized following the literature reported method.64,65 Briefly, a solution of GdCl3.6H2O (4.49 g, 0.0121 mol) in H2O (10 mL) was added drop-wise to a solution of DTPA (5.0 g, 0.0127 mol) or p-SCN-Bn-DTPA (0.0127 mol) in H2O (30 mL) containing 2N NaOH (5.0 mL) solution. The pH of the final reaction mixture was maintained at pH 6.8 by constant addition of 2N NaOH solution. The reaction was continued at 80° C. for 12 h before concentrated to 20 mL. The observed white crystals were dissolved in minimum amount of water before precipitating in ethanol. The precipitate was filtered and dried under vacuum to obtain the Gd(III) complex as a white solid (Yield: 86%).
For the synthesis of Gd-DTPA-encapsulating composite nanoprobe (IO-PAA-Gd-DTPA), a novel water-based, ‘in situ’ encapsulation approach was used for the successful encapsulation of Gd-DTPA complex. In this approach, three different solutions were prepared; an iron salt solution [0.61 g of FeCl3. 6H2O and 0.32 g of FeCl2. 4H2O in dilute HCl solution (100 μL of 12 N HCl in 2.0 mL H2O)]; an alkaline solution [1.8 mL of 30% NH4OH solution in 15 mL of N2 purged DI water]; and a paramagnetic stabilizing solution [800 mg of PAA and 20 mg of Gd-DTPA complex in 5 mL of DI water]. To synthesize the composite IO-PAA-Gd-DTPA nanoprobe, the iron salt solution was added to the alkaline solution under vigorous stirring. The resulting dark suspension of iron oxide nanoparticles was stirred for 10 seconds before addition of the paramagnetic stabilizing solution and stirred for 1 h. The resulting suspension of composite IO-PAA-Gd-DTPA nanoprobe was then centrifuged at 4000 rpm for 30 minutes to get rid of free polyacrylic acid, Gd-DTPA complex and other unreacted reagents. Finally, the composite IO-PAA-Gd-DTPA nanoprobe suspension was purified using magnetic columns and washed with phosphate buffer saline (pH=7.4) solution. The iron concentration and magnetic relaxation of the PAA-IONPs was determined as previously reported.22 The successful coating of the IONPs with PAA was confirmed by the presence of a negative zeta-potential (ζ=−41 mV) and the characteristic acid carbonyl band on the FT-IR spectroscopic analysis of the nanoparticles (
Taxol was encapsulated in the PAA polymer coating of magnetic nanoprobe, following the previously reported solvent diffusion method.22,66 Briefly, to a suspension of IO-PAA-Gd-DTPA nanoprobes (2.5 mL, 28 mmol) in PBS, a dimethyl sulfoxide (DMSO) solution of Taxol (10 μL, 0.5 μg/μL) was added drop-wise at room temperature with continuous stirring at 1000 rpm. The taxol-encapsulating nanoprobes (IO-PAA-Gd-DTPA-Taxol) were purified using magnetic column (Miltenyi Biotech) and then dialyzed (using 6-8K MWCO dialysis bag) three times against deionized water and finally against phosphate buffered saline solution. The resulting IO-PAA-Gd-DTPA-Taxol nanoparticles were characterized by measuring their size using DLS (D=84±2 nm), the taxol encapsulation efficiency (EE)=52±2.4% using HPLC (λabs=227 nm).
To synthesize folate-decorated functional IO-PAA nanoprobes, the surface carboxylic acid groups of the nanoprobes were alkynated using propargylamine as a reagent and the water-based carbodiimide chemistry was followed as previously reported.22 The resulting alkynated IO-PAA nanoprobes were purified using magnetic columns. The highly specific “click” chemistry was used to conjugate an azide-functionalized folic acid with the purified alkynated IO-PAA, as described in the previously reported methods.22,67 Briefly, the alkynated IO-PAA (4.0×10−3 mmol) in bicarbonate buffer (pH=8.5) were taken to an eppendorf tube containing catalytic amount of CuI (5.0×10−10 mmol) in 250 μL of bicarbonate buffer (pH=8.5) and vortexed. To the resulting solution, the azide-functionalized folic acid22,63 (8.0×10−2 mmol) in DMSO was added and the reaction was incubated at room temperature for 12 h. The synthesized folate-decorated IO-PAA was purified using the magnetic column and finally washed using PBS solution (pH=7.4). The folate-decorated IO-PAA was stored in refrigerator for further characterization.
For the synthesis of Gd-DTPA-encapsulating composite nanoceria, we have modified our previously reported stepwise method61,68 and followed the ‘in situ’ encapsulation approach. In this approach, 1M cerium(III) nitrate (2.17 g in 5.0 mL of water) solution was added to 30.0 mL of ammonium hydroxide solution (30% w/v) under continuous stirring at room temperature. Then, after 45 seconds of stirring, an aqueous mixture containing the PAA polymer and Gd-DTPA complex (800 mg of PAA and 20 mg of Gd-DTPA in 5 mL of water) was added and allowed to stir for 3 h at room temperature. The preparation was then centrifuged at 4000 rpm for two 30 minute cycles to settle down any debris and large agglomerates. The supernatant solution was then purified from free PAA, Gd-DTPA complex or other chemicals and concentrated using SpectrumLab's KrosFlo filtration system.
The polyacrylic acid coated iron oxide nanoparticles (IO-PAA) were synthesized using our previously reported alkaline precipitation method.22 Briefly, a Fe+3/Fe+2 solution in water was rapidly mixed with an ammonium hydroxide solution for 30 seconds, prior to addition of the PAA polymer solution in water. The synthesized IO-PAA were purified using magnetic columns to remove any unreacted reagents and phosphate buffered saline (PBS, pH 7.4) was used as running solvent. To incorporate amine groups to the nanoparticles, ethylenediamine was used as an aminating agent and the water-based carbodiimide chemistry (using EDC and NHS reagents) was followed, as previously reported.22,62 The successful amination of the IO-PAA nanoparticles were confirmed by measuring their overall positive surface charge (zeta potential ζ=+15 mV) using Malvern's Zetasizer. To synthesize the Gd-DTPA surface conjugating IO-PAA nanoprobe, the aminated IO-PAA was reacted with the isothiocyanate group of the p-SCN-Bn-DTPA chelated with GdCl3.6H2O salt. In a typical reaction, the isothiocyanate functional Gd-DTPA chelate (pSCN-Bn-Gd-DTPA, 25 mmol) was added to the aminated IO-PAA nanoprobe (1 mmol) in the presence of basic phosphate buffered saline (PBS, pH 8.4) and incubated overnight at room temperature. The resulting Gd-DTPA surface conjugating IO-PAA nanoprobe was purified using small magnetic columns (Miltenyi Biotech) and washed with phosphate buffered saline (PBS, pH=7.4), prior to characterizations and magnetic relaxation measurements.
The size and dispersity of the synthesized composite IO-PAA was measured using dynamic light scattering (DLS) using PDDLS/CoolBatch 40T instrument with Precision Deconvolve 32 software. The overall surface charges (zeta potential) of this functional IO-PAA were measured using a Zetasizer Nano ZS from Malvern Instruments. These experiments were performed by placing 10 μL of the composite magnetic nanoprobes in 990 μL of distilled water.
Magnetic relaxation measurements were conducted with a compact magnetic relaxometer (0.47 T mq20, Bruker), by taking composite magnetic nanoprobes at the end of the experiment. Magnetic resonance imaging (MRI) of the magnetic phantoms was achieved using the MRI/MRS facility utilizing a 4.7-T 33-cm bore magnet imaging/spectroscopy system (MSKCC, New York).
HPLC experiments were carried out using PerkinElmer's Series 200 instrument to study drug release kinetics. In a typical experiment, upon addition of acidic PBS solution (pH=5.0) to the taxol-encapsulating IO-PAA-Gd-DTPA (50 μL, 28 mM), the rate of release of encapsulating taxol was monitored in a timely manner at 37° C. using HPLC (λabs=227 nm) chromatography.
The human cervical cancer (HeLa) and cardiomyocyte (H9c2) cells were obtained from ATCC, and maintained in accordance to the supplier's protocols. Briefly, the cervical cancer cells were grown in a 5%-FBS-containing DMEM medium supplemented with L-glutamine, streptomycin, amphotericin B and sodium bicarbonate. The H9c2 cells were propagated in a 10% FBS-containing MEM medium containing penicillin, streptomycin and bovine insulin (0.01 mg/mL). Cells were grown in a humidified incubator at 37° C. under 5% CO2 atmosphere.
The human cells (HeLa and H9c2, 10,000 cells/well) were incubated with the folate-decorated activatable IO-PAA-Gd-DTPA-Fol nanoprobe and the control IO-PAA-Fol nanoprobe (100 μL, 28 mM) at different incubation times. The cells were then trypsinized and centrifuged. The resulting cell pellet was suspended in phosphate buffer saline (PBS, pH=7.4) and magnetic relaxations of these solutions were measured using the bench-top magnetic relaxometer (B=0.47 T mq 20) from Bruker.
H9c2 and HeLa cells (2,500 cells/well) were seeded in 96-well plates, incubated with the corresponding composite IO-PAA nanoprobes (35 μL, 28 mM in PBS pH=7.4) at 37° C. After the specific time incubation, each well was washed three times with 1×PBS and treated with 30 μL MTT (2 μg/μL) for 2 h. The resulting formazan crystals were dissolved in acidic isopropanol (0.1 N HCl) and the absorbance was recorded at 570 and 750 nm (background), using a Synergy μQuant microtiter plate reader (Biotek). These experiments were performed in triplicates.
Detailed physical characterizations of the magnetic probes including dynamic light scattering (DLS), scanning transmittance electron microscopy (STEM), FT-IR, zeta potential, stability of the nanoprobes at different conditions, MRI-based magnetic relaxations, encapsulating drug release and cytotoxicity studies. This material is available free of charge via the Internet at http://pubs.acs.org.
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It was found that using a Doxorubicin-ss-Gd(DTPA), the effect on R2 is not as large as the effect on R1. Similar results were obtained by co-encapsulation Gd(DTPA) and Doxorubicin, although the changes are lower. This fact is significant as the release of the drug from the nanoparticle will result in activation of the probe with potential imaging monitoring of the drug release by MRI.
The cleavable “Doxo-S-S-Gd-DTPA” conjugate were synthesized using a facile nucleophilic substitution reaction before encapsulating with IO-PAA as described earlier in the case of IO-PAA-Gd-DTPA. In a typical reaction, the aqueous solution of doxorubicin hydrochloride salt (1.75 mmol) was added to PBS buffer solution (pH=8.4) to obtain doxorubicin with free amine group. The resulting solution was centrifuged and the solid pallet was soluble in DMSO. Then, p-NH2-Bn-Gd-DTPA complex (1.75 mmol, in PBS, pH 7.4) and dithiobis(succinimidyl propionate) (DSP) solution (1.75 mmol, in DMSO) were added drop-wise. A catalytic amount of triethylamine (0.5 μL in DMSO) was added to the reaction mixture. The reaction mixture was incubated at room temperature for 30 minutes, before overnight incubation at 4° C. (
It should be borne in mind that all patents, patent applications, patent publications, technical publications, scientific publications, and other references referenced herein and in the accompanying appendices are hereby incorporated by reference in this application to the extent not inconsistent with the teachings herein.
It is important to an understanding to note that all technical and scientific terms used herein, unless defined herein, are intended to have the same meaning as commonly understood by one of ordinary skill in the art. The techniques employed herein are also those that are known to one of ordinary skill in the art, unless stated otherwise. For purposes of more clearly facilitating an understanding the invention as disclosed and claimed herein, the following definitions are provided.
While a number of embodiments have been shown and described herein in the present context, such embodiments are provided by way of example only, and not of limitation. Numerous variations, changes and substitutions will occur to those of skilled in the art without materially departing from the invention herein. For example, the present invention need not be limited to best mode disclosed herein, since other applications can equally benefit from the teachings. Also, in the claims, means-plus-function and step-plus-function clauses are intended to cover the structures and acts, respectively, described herein as performing the recited function and not only structural equivalents or act equivalents, but also equivalent structures or equivalent acts, respectively. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims, in accordance with relevant law as to their interpretation.
This application claims priority to U.S. Provisional Application No. 61/668,622, filed on Jul. 6, 2012, and which is incorporated by reference herein in its entirety.
The invention was supported in part by the National Institute of Health via NIH grant GM084331. The U.S. government has rights in this invention.
| Number | Date | Country | |
|---|---|---|---|
| 61668622 | Jul 2012 | US |
