Delivery of contrasting agents for magnetic resonance imaging
09629933 ยท 2017-04-25
Assignee
Inventors
Cpc classification
A61K49/1896
HUMAN NECESSITIES
Y10S977/93
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
Y10S977/773
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
International classification
Abstract
Erythrocytes exposed to dialysis with an hypotonic buffer stably take up superparamagnetic iron oxide nanoparticles and may be used MRI contrast agents. Such erythrocytes may also be used as drug delivery vehicles.
Claims
1. A method for magnetic resonance imaging, said method comprising: administering a preparation comprising a plurality of erythrocytes to a subject in need thereof, and thereafter subjecting said subject to magnetic resonance imaging, wherein the plurality of erythrocytes comprises viable erythrocytes that contain superparamagnetic nanoparticulate iron oxide (SPIO), wherein the SPIO is substantially encapsulated within the cytosol of the erythrocytes such that the erythrocytes are not recognized by macrophages unless they are at the end of their physiological life, wherein the amount of SPIO present in the preparation is sufficient that the preparation is useful as a magnetic resonance imaging contrast agent, wherein the erythrocytes that contain superparamagnetic nanoparticulate iron oxide are viable in vivo having a half-life similar to the half-life of native erythrocytes, and wherein the SPIO is coated with carboxydextran.
2. A method according to claim 1, wherein the amount of SPIO in the erythrocytes is between about 1 mM and 40 mM.
3. A method according to claim 1, wherein the average total particle size of the SPIO is no greater than 80-90 nm.
4. A method according to claim 1, wherein the erythrocytes comprise one or more drugs.
5. A method according to claim 4, wherein the drug is selected from the group consisting of: anti-inflammatory drugs, immunosuppressive drugs, antiviral drugs, antiretroviral drugs, anticancer drugs, oligonucleotides, monoclonal antibodies, peptides, peptide nucleic acids, photosensitizing drugs, infra red fluorescent agents, and mixtures of any two or more thereof.
6. A method according to claim 1, wherein the SPIO has the general formula Fe.sub.2.sup.3+O.sub.3M.sup.2+O where M.sup.2+ is a divalent metal cation.
7. A method according to claim 6, wherein the SPIO is magnetite (M.sup.2+ is ferrous iron).
8. A method according to claim 6, wherein M.sup.2+ is selected from the group consisting of: ferrous iron, manganese, nickel, cobalt, and magnesium.
9. A method for the treatment of a condition wherein the erythrocytes are localisable by external magnetic force in the vicinity of an area to be treated, said method comprising: administering a preparation comprising a plurality of erythrocytes to a subject in need thereof, and thereafter exposing said subject to an external magnetic force in the vicinity of the area to be treated, wherein the plurality of erythrocytes comprises viable erythrocytes that contain superparamagnetic nanoparticulate iron oxide (SPIO), wherein the SPIO is substantially encapsulated within the cytosol of the erythrocytes such the erythrocytes are not recognized by macrophages unless they are at the end of their physiological life, wherein the amount of SPIO present in the preparation is sufficient that the preparation is useful as a magnetic resonance imaging contrast agent, wherein the erythrocytes that contain superparamagnetic nanoparticulate iron oxide are viable in vivo having a half-life similar to the half-life of native erythrocytes, and wherein the SPIO is coated with carboxydextran.
10. A method of resonance imaging, comprising: administering viable erythrocytes that contain superparamagnetic nanoparticulate iron oxide (SPIO) to a subject in need thereof, and thereafter subjecting said subject to magnetic resonance imaging, wherein the SPIO is substantially encapsulated within the cytosol of the erythrocytes such that the erythrocytes are not recognized by macrophages unless they are at the end of their physiological life, wherein the erythrocytes that contain superparamagnetic nanoparticulate iron oxide are viable in vivo having a half-life similar to the half-life of native erythrocytes, and wherein the SPIO is coated with carboxydextran.
11. A method according to claim 10, wherein erythrocytes are: removed from a patient, separated from other blood cells, loaded with SPIO to produce viable erythrocytes containing SPIO, wherein the SPIO is substantially encapsulated within the cytosol of the erythrocytes such that the erythrocytes are not recognized by macrophages unless they are at the end of their physiological life, the loaded erythrocytes are thereafter reintroduced into the patient, and wherein the erythrocytes that contain superparamagnetic nanoparticulate iron oxide are viable in vivo having a half-life similar to the half-life of native erythrocytes.
12. A method according to claim 10, wherein the amount of SPIO in the erythrocytes is between about 1 mM and 40 mM.
13. A method according to claim 10, wherein the average total particle size of the SPIO is no greater than 80-90 nm.
14. A method according to claim 10, wherein the erythrocytes comprise one or more drugs.
15. A method according to claim 14, wherein the drug is selected from the group consisting of: anti-inflammatory drugs, immunosuppressive drugs, antiviral drugs, antiretroviral drugs, anticancer drugs, oligonucleotides, monoclonal antibodies, peptides, peptide nucleic acids, photosensitizing drugs, infrared fluorescent agents, and mixtures of any two or more thereof.
16. A method according to claim 10, wherein the SPIO has the general formula Fe.sub.2.sup.3+O.sub.3M.sup.2+O where M.sup.2+ is a divalent metal cation.
17. A method according to claim 16, wherein the SPIO is magnetite (M.sup.2+ is ferrous iron).
18. A method according to claim 16, wherein M.sup.2+ is selected from the group consisting of: ferrous iron, manganese, nickel, cobalt, and magnesium.
19. A method of increasing the resonance imaging resolution of superparamagnetic iron oxide, comprising: substantially encapsulating said superparamagnetic iron oxide within the cytosol of the erythrocytes as to produce viable erythrocytes that are not recognizable by macrophages unless they are at the end of their physiological life, and resonance imaging said erythrocytes in vivo, wherein the erythrocytes that contain superparamagnetic nanoparticulate iron oxide are viable in vivo having a half-life similar to the half-life of native erythrocytes, and wherein the SPIO is coated with carboxydextran.
20. A method for magnetic resonance imaging, said method comprising: administering a preparation comprising a plurality of erythrocytes to a subject in need thereof, and thereafter subjecting said subject to magnetic resonance imaging, wherein the plurality of erythrocytes comprises viable erythrocytes that contain monodispersed superparamagnetic nanoparticulate iron oxide (SPIO), wherein the SPIO is substantially encapsulated within the cytosol of the erythrocytes by dialysing a preparation of said erythrocytes against a hypotonic buffer having an osmolarity of between 60 and 120 mOsm, wherein the amount of SPIO present in the preparation is sufficient that the preparation is useful as a magnetic resonance imaging contrast agent, and wherein the SPIO is coated with carboxydextran.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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BRIEF DESCRIPTION OF THE INVENTION
(9) By the term viable is meant an erythrocyte that is still recognised as viable by the host into which it is injected. Non-viable, or dead, erythrocytes, such as the crenated erythrocytes prepared in the art, are immediately recognised as non-viable and are eliminated from the host system. The advantage of the erythrocytes of the present invention is that they are able to survive for a number of days without being eliminated, and often have a lifespan comparable to that of untreated erythrocytes. In this regard, the RBCs (red blood cells) may also be referred to as stable erythrocytes. In particular, it is preferred that the RBCs can substantially avoid immune clearance and that around at least 50%, and more preferably at least 60% to least 70% or 80% of the loaded RBC's have statistically significant comparable lifespans in vivo to unmodified RBC's.
(10) The terms red blood cells and erythrocytes are used interchangeably herein.
(11) The cytosolic superparamagnetic iron oxide is also referred to herein as encapsulated or substantially internalised superparamagnetic iron oxide, or encapsulated or substantially internalised SPIO, and is distinct from vesicular or micellar SPIO. The size of the particles is discussed herein below, but is not restricted to SPIO, and the range of sizes includes USPIO. It is preferred that the total size of each particle, including any coating, such as dextran, is no greater than 80-90 nm, and is preferably between 20 and 60 nm, more preferably between 3 and 50 nm, more preferably between 10 and 100 nm, more preferably between 10 and 30 nm, more preferably between 20 and 50 nm, more preferably between 50 and 80 nm, and most preferably between 40 and 60 nm.
(12) It will be understood that the present nanoparticles can also be referred to as SPION (SPIO Nanoparticles).
(13) As further discussed in the Results section of the Examples, previous attempts in the prior art have resulted in erythrocytes that show contrast material on the cell surface.
(14) This membrane modification could leads to immune clearance due to opsonisation of the erythrocytes. The present invention, however, avoids this by substantially internalising the contrast agent nanoparticles within the cytoplasm of the cell. WO 2006/048321 A1 relates to the incorporation in mammalian cells (including blood cells and thus erythrocytes) of active substances and diagnostically active substances in the form of nanoparticles. However, a recent paper from the same applicants and others (Nano Letters 6, 2505-2509, 2006) demonstrate that the method proposed generates erythrocytes that contain nanoparticles bound to the membrane. Therefore, the cells are surface modified and the presence of adsorbed contrast agent nanoparticles on the cell surface leads to immune clearance. Thus, this method does not result in viable or stable erythrocytes.
(15) WO 91/16080 A1 (Guerbet) is an old publication and relates to a contrast agent encapsulated into erythrocytes by a lysis resealing technique. The focus of the application is towards the use of chelates of Gadolinium or Iodum as the contrast agent. There is brief reference to contrast agents including superparamagnetic colloids, but no further discussion thereof or experimental work on this, as evidenced by the fact that issues such as dispersion are ignored. Furthermore, no mention of nanoparticles is made and, indeed, no reference to the possible size of these superparamagnetic colloids is reported.
(16) Since this publication, it has become apparent that superparamagnetic colloids can actually result in erythrocyte interactions and damage. Thus, this publication does not teach viable erythrocytes, nor does it describe the use of nanoparticles. Furthermore, their method of encapsulation is a lysis resealing technique. Based on their work with Gadolinium and Iodide, the authors merely speculate that a similar behaviour could have been followed by other contrasting agents including iron oxide. However, recent evidence (including the paper in Nano Letters supra) teaches against this and it is now clear that conditions based on those appropriate for Gadolinium chelates and Iodine-containing molecules are not suitable for SPIO nanoparticles.
(17) In contrast, the present inventors have surprisingly found that SPIO can provide at least one of the following separate but complimentary advantages. Firstly, the erythrocytes of the present invention are not cleared by the immune system when loaded with the paramagnetic material, which is a significant advantage over erythrocytes which have even a small amount of paramagnetic material bound to their cell surface. This provides the present erythrocytes with an improved life span in vivo therefore significantly aiding MRI diagnosis in a clinical setting where delays can occur and also allows the erythrocytes to enter deep into body tissues. Indeed, the increased stability and viability of the erythrocytes allows the same patient to be imaged on number of occasions over time, thereby allowing a time-lapsed data set to be obtained, which could be used to study drug efficacy over several days or even weeks.
(18) A further and quite unexpected advantage is that we have discovered that superparamagnetic nanoparticles encapsulated, or loaded, into RBCs generate (under identical conditions) a T2* relaxation time significantly lower than the signal measured by adding the same amount of nanoparticles to an identical RBC (Red Blood Cell) suspension or to intact blood. By lowering the T2* relaxation time, the resolution of the MRI image is improved. This will aid physicians detect even smaller tumours, for instance.
(19) It is particularly preferred that the superparamagnetic nanoparticles have the general formula Fe.sub.2.sup.3+O.sub.3M.sup.2+O where M.sup.2+ is a divalent metal cation such as ferrous iron, manganese, nickel, cobalt or magnesium.
(20) Preferably, the SPIO is magnetite. This occurs when the metal ion (M.sup.2+) is ferrous iron (Fe.sup.2+), giving superparamagnetic nanoparticles of the formula FeFe.sub.2O.sub.4. Thus, it is preferred that M.sup.2+ is ferrous iron (Fe.sup.2+).
(21) However, it is also preferred that the SPIO comprises alternatives to ferrous iron, although it will be understood that this is for M.sup.2+ and that the SPIO is still an oxide of iron. In other words, only the M.sup.2+ is substituted, not the Fe.sub.2.sup.3+ element of the SPIO general formula Fe.sub.2.sup.3+O.sub.3M.sup.2+O. Thus, other non-magnetite based SPIOs are also preferred.
(22) Thus, it is particularly preferred that M.sup.2+ is at least one of the following divalent cations, selected from the group consisting of manganese, nickel, cobalt, and magnesium. This provides MnFe.sub.2O.sub.4, NiFe.sub.2O.sub.4, CoFe.sub.2O.sub.4 and MgFe.sub.2O.sub.4, as taught in Nature Medicine, Vol. 13, number 1, page 95-99, January 2007(Jae-Hyun Lee et al.) and in Eur. Radiol. Vol. 11, page 2319-2331, 2001 (Yi-Xiang J. Wang et al.). Manganese, giving MnFe.sub.2O.sub.4, is particularly preferred as it provides a strong Magnetic Resonance contrast effect, due to its high relaxivity value.
(23) The present invention further provides a process for the preparation of one or more erythrocytes as defined herein, the said process comprising dialysis of a preparation of the said erythrocytes against a hypotonic buffer sufficient to permeabilise the erythrocytes, and wherein said preparation comprises monodispersed SPIO, and subsequently resealing the erythrocytes.
(24) The loading of magnetic nanoparticles into erythrocytes using the procedure of the invention occurs through pores in the RBC membrane arising from dialysis of the RBC suspension in an hypotonic buffer. This is different from that described in previous reports were the authors have reported the entrapment of ferrofluids in erythrocytes by a technique that produced crenated ghost cells (Jain, 1994) with limited stability.
(25) The term monodispersed indicates that the particles of SPIO are treated such as not to agglomerate, and it is preferred to obtain the SPIO pre-prepared in such a fashion, rather that to treat the SPIO within the preparation of erythrocytes. It is particularly preferred that the SPIO nanoparticles are sufficiently small that they can readily pass into the erythrocytes when they become porous on exposure to the hypotonic buffer. Such nanoparticles are preferably coated in dextran, although any other means for obtaining monodispersion are also envisaged by the present invention. Monodispersed magnetic nanomaterial PMP-50, sold by G. Kisker GbR, is preferred. A particularly preferred ferrofluid is that sold by Schering as SHU 555A (Resovist).
(26) The hypotonic buffer may be present in any concentration suitable to achieve poration of the erythrocytes. If the osmolarity of the hypotonic buffer is too high, then poration may not happen, whilst if the osmolarity is too low, then excessive damage can occur to the erythrocytes, and insufficient viable cells recovered. Thus, by way of a guide, an osmolarity of between 60 and 120 mOsm is preferred, with a range of 70 to 110 mOsm being more preferred.
(27) It has been found that recovery rates of in excess of 70% of erythrocytes exposed to a hypotonic buffer can be achieved whilst obtaining sufficiently high internal concentrations of SPIO where the osmolality of the erythrocytes does not fall below 90 mOsm after treatment.
(28) The volume of the buffer as a ratio to the preparation of erythrocytes is preferably between about 15 and infinity, with a range of between about 20 and 100 being more preferred and a range of 40-80 being particularly preferred.
(29) The nature of the buffer is not particularly important, provided that it is not harmful to the erythrocytes for the patient in such a way as to either drastically reduce the number of erythrocytes surviving the treatment or to be toxic to the patient in an undesired manner. Suitable buffers include carbonate and phosphate buffers.
(30) In order to obtain a satisfactory degree of viability for the erythrocytes, it is preferred to use a hypotonic buffer comprising ingredients to ensure the continued well-being of the erythrocytes whilst porated. In this respect, the presence of a balanced pH, preferably at about 7.4, is preferred, together with glucose and ATP. Other ingredients may also be incorporated, such as glutathione, in order to enhance the viability and recovery of viable erythrocytes.
(31) The duration of exposure of the erythrocytes to the hypotonic buffer may be as long as desired, but is preferably between 20 minutes and 5 hours, more preferably between 30 minutes and 4 hours, and more preferably 1 hour to 3 hours. It is particularly preferable to minimise the amount of exposure as far as possible, whilst ensuring the uptake of the maximum amount of SPIO, as porated erythrocytes are vulnerable.
(32) Resealing of the treated erythrocytes is performed by known techniques after removing the dialysis buffer. It is preferred that, after the resealing, the erythrocytes are washed to remove any extracellular SPIO. A suitable washing agent is Hepes buffer. The erythrocytes may then be stored in Hepes buffer or any other suitable solution, such as artificial plasma, prior to use.
(33) The present invention further provides the use of a preparation of erythrocytes as defined herein in a magnetic residence imaging technique.
(34) The present invention further provides the use of a preparation of erythrocytes as defined herein in the treatment of a condition wherein erythrocytes of the invention are localisable in the vicinity of an area to be treated by external magnetic force.
(35) It will be appreciated that erythrocytes may be from any animal, but are preferably from a mammal, and particularly preferably from a human. Likewise, the subject to be treated or imaged may be animal, preferably mammal, and particularly preferably human. Although it is preferable to use erythrocytes from the patient, it is also acceptable to use erythrocytes prepared from a compatible donor and, particularly preferably, a universal donor.
(36) The present invention further provides a method of removing red blood cells from a patient and optionally separating them from other blood cells and optionally the serum, loading the red blood cells with SPIO and reintroducing the red blood cells into the patient. Preferably, the red blood cells can be stored at any stage, and most preferably, once they have been loaded with SPIO, so as to allow a pre-prepared store of loaded erythrocytes useful in emergency situations, for instance. In such cases, it is preferred that the erythrocytes are universal donor, blood type O.
(37) Methods of resonance imaging are also provided, comprising administering the present RBCs loaded with SPIO. The method also preferably comprises removing red blood cells from a patient and optionally separating them from other blood cells and optionally the serum, loading the red blood cells with SPIO and reintroducing the red blood cells into the patient. Preferably, the red blood cells can be stored at any stage, and most preferably, once they have been loaded with SPIO, as above.
(38) Also provided is a method to lower the T2* relaxation time of superparamagnetic iron oxide by encapsulation thereof in erythrocytes, said encapsulated erythrocytes being viable.
(39) In a further aspect, there is provided a method of increasing the resolution of resonance imaging of superparamagnetic iron oxide, by encapsulation of superparamagnetic iron oxide in viable erythrocytes.
(40) In a still further aspect, there is provided a pharmacologically active preparation comprising superparamagnetic material encapsulated in viable erythrocytes, suitable for administration to patient for resonance imaging.
(41) Thus, we have now found a strategy for loading SPIO nanoparticles in human erythrocytes in a manner that avoids RES clearance, and which offers a novel approach for intravascular drug delivery and blood pool imaging. We have found, unexpectedly, that superparamagnetic nanoparticles can be encapsulated within human erythrocytes in amounts high enough to be useful as contrasting agents and that these constructs are stable. In contrast to superparamagnetic nanoparticles, these particle-loaded erythrocytes are not recognised by macrophages unless they are at the end of their physiological life or unless specifically modified.
(42) These superparamagnetic iron oxide loaded erythrocytes are artificial constructs useful as contrasting agents, especially for imaging of the circulatory system and in the detection of occluded vessels or altered angiogenesis in defined body areas or damaged vessels resulting in bleeding.
(43) The present invention provides human erythrocytes loaded with superparamagnetic nanoparticles useful as MRI contrasting agents, especially in the imaging of the circulatory system. Said erythrocytes can also contain one or more drugs co-encapsulated with said superparamagnetic nanoparticles and can be driven by an external magnetic field to release the encapsulated drug within selected organs or preferentially in selected body districts.
(44) The present invention will now be described with reference to the following, non-limiting Examples. All references cited herein are incorporated by reference unless otherwise apparent and to the extent that they complement the teaching of the present application.
EXAMPLES
Materials and Methods
(45) Materials
(46) Erythrocytes loading procedure was performed with a commercially available ferrofluid SHU 555A (Resovist, 0.5 mmol Fe/ml) obtained from Schering pharmaceutical company, consisting of superparamagnetic iron oxide nanoparticles carboxydextran coated, 60 nm in diameter.
(47) This particulate suspension is generally used to enhance the signal from magnetic resonance imaging (MRI) examinations. Silica coated magnetite nanoparticles suspension, SiMagn (27 mg/ml) with a size of around 40-140 nm was also used.
(48) Encapsulation of Magnetic Nanoparticles in Human Erythrocytes
(49) Human blood was collected from healthy volunteers into heparinised tubes.
(50) Red blood cells (RBCS) were isolated by centrifugation at 1400 g at 4 C. for 10 min from freshly drawn blood. The serum and buffy coat were removed and the packed cells were washed three times with Hepes buffer (10 mM Hepes, 140 mM NaCl, 5 mM glucose, pH 7.4) and then resuspended in the same buffer at a 70% haematocrit. These cells were dialysed in presence of magnetic nanoparticles for 75 min using a tube with a 12-14 kDa cut-off in 50 vol of 10 mM NaHCO.sub.3, 10 mM NaH.sub.2PO.sub.4, 20 mM glucose, 4 mM MgCl.sub.2 pH 7.4, containing 2 mM ATP and 3 mM reduced glutathione. The osmolarity of dialysis buffer was 64 mOsm.
(51) All these procedures were performed at 4 C. under sterile conditions. Resealing of RBC was obtained by adding 0.1 vol of 5 mM adenine, 100 mM inosine, 2 mM ATP, 100 mM glucose, 100 mM sodium pyruvate, 4 mM MgCl.sub.2, 194 mM NaCl, 1.606 M KCl, 35 mM NaH.sub.2PO.sub.4, pH 7.4 (PIGPA) per vol of dialysed RBC and by incubating at 37 C. for 45 min.
(52) The resealed cells were recovered by centrifugation at 400 g and washed four times with Hepes buffer to remove unentrapped magnetic particles.
(53) Following the same procedure unloaded erythrocytes (UL-RBC) were prepared, with the exception that they were dialysed in absence of magnetic material.
(54) Then the magnetic susceptibility of the loaded erythrocytes (L-RBC) and other different parameters were evaluated.
(55) Magnetite Concentration
(56) Erythrocytes were loaded using different amounts of SHU 555A (0.5 mmol Fe/ml or 28 mg/ml).
(57) 1 ml of RBC has dialysed both in presence of 5.6 mg Fe (200 l) (L1-RBC) and 22.4 mg Fe (800 l) (L2-RBC). The loading efficiency was evaluated by different parameters.
(58) In Vitro Characterisation of SHU 555A-Loaded Erythrocytes;
(59) Percentage Cell Recovery
(60) Percentage cell recovery was determined by counting the number of total intact erythrocytes before and after magnetite loading using a hemocytometer.
(61) Assessment of Cell Integrity
(62) To determine whether the loaded cells retained the properties of native red cells, several features of cell integrity were examined. Mean corpuscular volume, mean haemoglobin concentration, and mean corpuscular haemoglobin concentration were measured with an automated cytometer (Model MICROS O.T, HoribaABX Diagnostics, Italy).
(63) Magnetic Responsiveness
(64) 110.sup.9 loaded erythrocytes were placed in a micro tube and their magnetic responsiveness was evaluated by an incubation near to a magnet of 3000 Gauss. The magnetic erythrocytes localised at the site of magnet application were separated from RBC non attracted by washing in Hepes buffer, collected and counted by an automated cytometer and the percentage of attracted cells were calculated respect to initial number cells.
(65) NMR Relaxation Measurements of Loaded Erythrocyte Suspensions and Determination of the Entrapped Magnetite Concentration.
(66) The magnetite concentration in loaded erythrocytes was determined by NMR relaxation measurements using a dose-response curve generated by adding known amounts of SHU 555A contrast agent to human and murine blood samples. The concentration range studied was 0 to 15 mM Fe with at least 9 concentration levels. The longitudinal (T.sub.1) and transverse (T.sub.2) relaxation times of these samples at 44% of haematocrit were measured at magnetic field strength of 4.7 Tesla at 37 C. using an AC-200 NMR-Bruker spectrometer. T.sub.1 was measured using a 180--90 inversion recovery sequence with a fixed relaxation delay of at least 5T.sub.1. The times of inversion () were chosen on the basis of an estimated T.sub.1 value. T.sub.2 was measured using the Carr-Purcell-Meiboom-Gill method (CPMG). The echo-times were chosen on the basis of an estimated T.sub.2 value.
(67) The values of (1/T.sub.1.sup.c1/T.sub.1.sup.0) (where T.sub.1.sup.c is the relaxation time at the concentration [c] of contrast agent and T.sub.1.sup.0 the relaxation time of the RBC sample without SHU 555A) were plotted versus the concentration of SHU 555A and were fitted by least squares method to a straight line, the slope of which is the longitudinal relaxivity (r1).
(68) Two different r1 values were obtained in two concentration ranges: r1=2.49 sec.sup.1 mM.sup.1 in the range 0.1 mM<[c]<1 mM and r1=1.95 sec.sup.1mM.sup.1 in the range 1 mM<[c]<15 mM.
(69) The transversal relaxivity (r2) was calculated in a similar way in the interval 0.1 mM<[c]<0.3 mM by plotting the values of)(1/T.sub.2.sup.C1/T.sub.2.sup.0 versus [c] resulting in r2=153.6 sec.sup.1 mM.sup.1. All analysis was performed in EXCEL (Microsoft Corporation).
(70) For the correlation to be considered linear the following criteria were defined: correlation coefficient (R squared) greater than 0.990 and the distribution of points around the regression curve must be randomly distributed.
(71) Consequently, it was possible to estimate the concentration of SHU 555A encapsulated in the erythrocytes by using the inverse formula [c]=(1/T.sub.11/T.sub.1.sup.0)/r1 and [c](1/T.sub.21/T.sub.2.sup.0)/r2 in correspondence of the measured T.sub.1 and T.sub.2 values of loaded erythrocyte suspensions at haematocrit of 44%.
(72) We also determined the T.sub.2* value, obtained from the NMR FIDs measured at 37 C., in suspension samples of control RBCs, L1-RBC and in a sample of control RBC mixed to the same quantity of SHU 555A agent L1-RBC incorporated.
(73) Morphology
(74) Normal, unloaded and loaded erythrocytes were examined by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). For TEM analysis cells were quickly washed in 0.1 M Srensen phosphate buffer pH 7.3, sedimented at 600 g and immediately fixed in 2.5% glutaraldehyde in the same buffer for 1 h. The cells were then postfixed in 1% OsO4 in phosphate buffer, dehydrated with ethanol and embedded in araldite. Thin sections were collected on nickel grids, stained with uranyl acetate and lead citrate, and analysed with a Philips CM10 electron microscope. For SEM analysis, RBCs were washed and fixed in suspension with 2.5% glutaraldehyde in Srensen buffer and drops of the suspension were deposited on poly-Lysine-coated cover slips. The adhesion was carried out overnight in a moist and sealed chamber at 4 C. The slides were then washed and postfixed 1% OsO4 in phosphate buffer for 1 h.
(75) A gentle progressive alcohol dehydration was performed and specimens were critical point-dried.
(76) After mounting on conventional SEM stubs by means of silver glue, slides were gold-coated by a sputtering device. Observations were carried out with a Philips 515 scanning electron microscope.
(77) In Vitro Stability
(78) Loaded cells were resuspended at a haematocrit of 6% in phosphate-buffered saline, PBS (154 mM NaCl, 5 mM K.sub.2HPO.sub.4/NaH.sub.2PO.sub.4, pH 7.4) containing 5 mM glucose, plated in petri dishes and incubated at 37 C. At various time intervals the samples were removed and packed by centrifugation at 600 g for 10 min.
(79) Haemoglobin released in the sample supernatants was measured at 540 nm spectrophotometrically, and percentage haemolysis was determined by comparing the absorbance of supernatant with the absorbance obtained after complete haemolysis of same number of cells in distilled water.
(80) Moreover, the pellets of these samples diluted in Hepes buffer at a haematocrit of 44% were characterised by relaxivity NMR measurements.
(81) Recognition of Magnetic Nanoparticles-Loaded RBCs by Human Macrophages
(82) Human monocyte-derived macrophages from blood samples of healthy donors were obtained by separation in Lymphoprep solution (specific density 1.077; Axis-Shield PoC AS, Norway).
(83) Monocytes were separated from lymphocytes by adherence to plastic dishes overnight at 37 C. After removal of nonadhering cells by repeated washes, cells were cultured in RPMI 1640 medium supplemented with 10% (v/v) heat-inactivated fetal calf serum (FCS), 1% antibiotics (penicillin/streptomycin), and 2 mM L-glutamine at 37 C. in a humidified 5% CO.sub.2 atmosphere. The culture medium was changed every 2 days and after 7 days of culture the great majority of the adherent cells were differentiated macrophages. Magnetic nanoparticles loaded-RBCs were prepared by a dialysis of RBC in presence of 6 mg of SHU 555A or SiMagn nanoparticle suspensions.
(84) 110.sup.6 macrophages were incubated for 16 h in the presence of SHU 555A-loaded RBC or SiMagn-loaded RBC or unloaded RBC at a ratio of 100 RBC per macrophage. After this time, RBC were carefully removed by repeated washes and macrophages were fixed in methanol and observed after May-Grunwald Giemsa stain by an Olympus IX51 light microscope.
(85) In Vivo Studies
(86) Animal Preparation
(87) Female Balb/C mice (Nossan, Milan, Italy) were housed at 221 C. with a 12-h light/dark cycle, 605% humidity, and 12 air changes/h.
(88) In the pharmacokinetic experiments each mouse received intraperitoneally 250 l of a suspension of loaded-RBC at 10% of haematocrit, derived from an erythrocyte suspension containing 1.5 mol of paramagnetic iron/ml RBC.
(89) After the end of injection, the withdrawals of blood samples from ocular arteries have been done at 2, 3, 6, 10, 13 days and aliquots of whole blood were analysed by NMR measurements.
Results
(90) The results shown in
(91) Using electronic transmission microscopic analysis, the presence of nanoparticles was evaluated in at least 10 frames. For each field a central area of specimens was selected in which erythrocytes appeared homogeneously distributed. Microscopic analysis showed a similar morphologic aspect in all RBC loaded samples; each field presented a least 60% of erythrocytes containing magnetic nanoparticles, dispersed in cytoplasm (
(92) The loaded erythrocytes were slightly smaller on average than the untreated cells (MCV 78.5 and 60 versus 87 fl, respectively for L1-RBC and L2-RBC), with less haemoglobin per cell (MCH 20.1 and 16 versus 28 pg), but with a near normal mean cellular haemoglobin concentration (MCHC 31 and 28 versus 33 g/dl). It should be noted that the reduced MCV reported above is due to the dilution of RBC applied in these loading procedures (i.e. for L2 RBC: 1 ml RBC at 70% haematocrit with 800 l of SHU 555A) and not to the use of SHU 555A, as similar values were observed when unloaded erythrocytes were prepared using identical dilutions.
(93) The total preparation procedure typically resulted in a cell recovery of loaded erythrocytes ranging from 60% to 70%, similar to that for unloaded cells. This percentage of cell recovery is higher than the value obtained by other authors (Vyas, 1994; Johnson, 1998). The loaded erythrocytes were responsive to the external magnetic field, and maintain their magnetic susceptibility for several days.
(94) The results obtained are unexpected since the prior art teaches that all previous attempts to encapsulate nanomaterials within erythrocytes result in at least some nanoparticles bound on the external erythrocyte membrane. However, the presence of surface-bound nanoparticles leads to immediate immune clearance via the RES.
(95) For instance, WO 2006/048321 discloses diagnostically active substances including nanoparticles that can be introduced into biological cells but these nanoparticles are partially adsorbed onto the external surface of the erythrocyte membrane. This is clearly documented by the same inventors in Nano Letters 6, 2006 pag. 2505-2509. This occurs if the nanomaterials are made of silica-coated Superparamagnetic nanoparticles (
(96) In other words, the present inventors have discovered that only the use of SPIO in combination with a method of ensuring that the SPIO is present in the erythrocyte cytosol, rather than being adsorbed onto the cell surface, is sufficient to substantially avoid clearance of the erythrocyte and, therefore, lead to improved retention times.
(97) The presence of nanoparticles bound on the external erythrocyte membrane is a relevant phenomena when the aim is the MRI imaging of the vascular system since this condition would activate loaded RBCs recognition by tissue macrophages as those present in the reticuloendothelial system (RES) causing their rapid elimination from blood circulation. In fact, in vitro experiments performed to test loaded RBC uptake by human macrophages shows that SHU 555A-Loaded RBC are not phagocytosed while silica magnetite-loaded RBC containing nanoparticles bound onto the external erythrocyte membrane are actively recognized and phagocytosed by macrophages. (
(98)
(99) We estimated the final concentration of magnetic material in human erythrocytes by NMR analysis using the r1 and r2 values, obtained from calibration curve described in Materials and Methods (supra). SHU 555A incorporated into the human erythrocytes in an amount of 4.64 mM2, when 1 ml of RBCs was dialysed with 5.6 mg Fe, and 15.2 mM4 when the cells were dialysed with 22.4 mg Fe.
(100) The results show that the concentration of magnetic nanoparticles encapsulated increases both with increasing amounts of the contrast agent incubated with RBCs, and with a decrease in dialysis buffer milliosmolarity, but is not influenced by the dialysis time (Tablel and Table 2). NMR measurement of T.sub.2* value of RBCs (at 44% haematocrit) loaded with Superparamagnetic nanoparticles, are lower (0.38 ms) than value of whole blood and red blood cells cleaned from serum and not dialysed (ND), at the same haematocrit (21.9 and 30 ms respectively).
(101) TABLE-US-00001 TABLE 1 RESOVIST-loading experiments with different amount of agent and different dialysis times. T.sub.1 T.sub.2 Sample Sample description (msec) (msec) *[c] from r1 **[c] from r2 ND Not Dialysed RBC 2330 138 / / UL Dialysed and 2196 108 / / Unloaded RBC 50-Res-L-RBC Dose dependence: 355 <5 1.2 mM 100-Res-L-RBC 500 l of RBC70% 104 <5 4.7 mM 200-Res-L-RBC dialysed in presence 46 <5 10.9 mM 400-Res-L-RBC of different quantity 32 <5 15.8 mM of Resovist agent 100-Res-L-RBC Dialysis times 92 <5 5.3 mM 75 min dependence: 100-Res-L-RBC 500 l of RBC70% 87 <5 5.6 mM 135 min in presence of 100 l 100-Res-L-RBC Resovist agent 81 <5 6.1 mM 195 min All samples were measured at hematocrit of 44% and the paramagnetic iron content was calculated by the following formulas: *[c] = (1/T1c 1/T1o)/r1 **[c] = (1/T2c 1/T2o)/r2 T1o and T2o are the values of the control RBC (ND). The values indicated as <5 correspond to <5 msec and are not detectable due to instrumental sensibility.
(102) What is also particularly unexpected is the discovery that this value (0.38 ms) is also very significantly lower than T.sub.2* of suspensions containing the same concentration of SHU 555A agent added to whole blood (0.5 ms) or not dialysed RBCs (0.64 ms) (Table 3). Thus, the present invention permits one to obtain a T2* value lower than that determined by the presence of nanoparticles in the blood. The result of this is an improved resolution in MRI imaging.
(103) We also evaluated the effect on T1 and T2 values of the dilution of loaded RBC samples in unprocessed blood. At the maximum dilution tested (1:250), corresponding to an injection of 20 ml of Loaded-RBC in a adult human body, the T1 values results 300 msec lower than T1 of whole blood (Table 4). Moreover T2* values of loaded RBCs (L1-RBCs) diluted 1:125 and 1:250 in unprocessed blood are lower than value of whole blood containing not encapsulated contrast agent at the same concentration of L1-RBC at the same dilutions (14.92 versus 16.65 ms and 17.32 versus 19.79 ms, respectively) (Table 3).
(104) TABLE-US-00002 TABLE 2 RESOVIST-loading experiments with dialysis buffer with different milliosmolalities. The values indicated as <5 are not significant due to instrumental sensibility. T.sub.1 Sample Sample Description (msec) T.sub.2 (msec) [c] from r1 [c] from r2 ND Not dialysed RBC 2289 149.4 / / Res-L-RBC Not dialysed RBC 1274 18.6 0.13 mM 0.31 mM (300mOsm) incubated with Resovist Res-L-RBC 500 l of RBC70% 75 <5 6.6 mM (64mOsm) dialysed in presence of Res-L-RBC 100 l Resovist 104 <5 4.7 mM (110mOsm) agent against dialysis Res-L-RBC buffer at different 656 12.4 0.44 mM 0.48 mM (165mOsm) milliosmolarity Res-L-RBC 800 13.2 0.33 mM 0.44 mM (212mOsm)
(105) TABLE-US-00003 TABLE 3 NMR measurement of T1, T2 and T2* values of loaded RBCs. T.sub.1 T.sub.2 T.sub.2* Sample Sample description (msec) (msec) (msec) Control Whole blood 21.96 ND Not dialysed RBC 2294 140.2 30 L1-RBCs 500 l of RBC70% dialysed in 142.5 2.27 0.38 presence of 100 l Resovist agent ND + res Resovist agent added to not 123.1 3.37 0.64 dialyzed RBC at the same concentration of L1- W.B. + Resovist agent added to whole 129.6 6.9 0.5 res blood at the same concentration of L1-RBCs L1-RBC Loaded RBC diluted with whole 1777 68.3 14.92 (1:125) blood L1-RBC 1894 86.58 17.32 (1:250) W.B + res W.B + res diluted with whole 1713 61.7 16.65 (1:125) blood W.B + res 1845 80.6 19.79 (1:250)
(106) TABLE-US-00004 TABLE 4 NMR measurement of SHU555A (Resovist) in Human Loaded Erythrocytes (5.6 mg Fe/ml RBC 70%) diluted with whole blood. The values indicated as <5 are not significant due to instrumental sensibility. [c] T.sub.1 T.sub.2 diluition Sample Sample description (msec) (msec) [c] from r1 [c] from r2 estimated Control Whole blood 2130 116.4 / / / Unloaded Dialyzed RBC 2114 105.6 / / / Ln.a. Res-loaded RBC 81 <5 6.1 mM not magnetically Ln.a 1:2 RBC-loaded diluted 134 <5 3.6 mM 3.05 mM Ln.a 1:50 with whole blood 1309 38.6 0.118 mM 0.113 0.122 mM Ln.a 1:100 1582 59.0 0.065 mM 0.054 0.061 mM Ln.a 1:200 1714 71.2 0.045 mM 0.036 0.030 mM Ln.a 1:250 1790 79.8 0.036 mM 0.026 0.024 mM
The in vitro stability of loaded erythrocytes incubated at 37 C. in physiological buffer for several times was characterised by NMR measurement (
(107) It is noteworthy that no significant amount of haemoglobin is released from loaded cells with respect to control cells (loaded 3.7% versus 2.7% of control cells not dialysed
(108) The same loading procedure was applied to murine erythrocytes obtaining an encapsulation of Resovist corresponding to a concentration of paramagnetic iron ranging from 1.5 mM to 3.75 mM (for 500 l of RBC treated with 100 l of Resovist), Table 5.
(109) TABLE-US-00005 TABLE 5 In vivo pharmacokinetic NMR results after intraperitoneal injection of 100-res-loaded erythrocytes in balb mice. Samples T.sub.1 (msec) T.sub.2 (msec) % Ht [c] ND 2300 134 44 / *100-Res-L-RBC 246 <5 44 1.5 mM ND 3411 401.7 10 / 100-Res-L-RBC 894 <5 10 0.3 mM (peritoneal injected) *500 l of RBC 70% are dialysed for 75 min in the presence of 100 l (2.8 mg Fe) Resovist agent
(110) The in vivo experiments on Balb/C mice were performed to investigated the presence of magnetic nanoparticle-loaded RBC in the vascular system and blood withdrawal samples were evaluated by NMR analysis during long intervals of time (days).
(111) The results reported in
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