Renal iron accumulation occurs in lupus nephritis and iron chelation delays the onset of albuminuria

Proteins involved in iron homeostasis have been identified as biomarkers for lupus nephritis, a serious complication of systemic lupus erythematosus (SLE). We tested the hypothesis that renal iron accumulation occurs and contributes to renal injury in SLE. Renal non-heme iron levels were increased in the (New Zealand Black x New Zealand White) F1 (NZB/W) mouse model of lupus nephritis compared with healthy New Zealand White (NZW) mice in an age- and strain-dependent manner. Biodistribution studies revealed increased transferrin-bound iron accumulation in the kidneys of albuminuric NZB/W mice, but no difference in the accumulation of non-transferrin bound iron or ferritin. Transferrin excretion was significantly increased in albuminuric NZB/W mice, indicating enhanced tubular exposure and potential for enhanced tubular uptake following filtration. Expression of transferrin receptor and 24p3R were reduced in tubules from NZB/W compared to NZW mice, while ferroportin expression was unchanged and ferritin expression increased, consistent with increased iron accumulation and compensatory downregulation of uptake pathways. Treatment of NZB/W mice with the iron chelator deferiprone significantly delayed the onset of albuminuria and reduced blood urea nitrogen concentrations. Together, these findings suggest that pathological changes in renal iron homeostasis occurs in lupus nephritis, contributing to the development of kidney injury.

Investigation into the Biological Impact of Block Size on Cathepsin S-Degradable HPMA Copolymers

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymers have been studied as an efficient carrier for drug delivery and tumor imaging. However, as with many macromolecular platforms, the substantial accumulation of HPMA copolymer by the mononuclear phagocyte system (MPS)-associated tissues, such as the blood, liver, and spleen, has inhibited its clinical translation. Our laboratory is pursuing approaches to improve the diagnostic and radiotherapeutic effectiveness of HPMA copolymers by reducing the nontarget accumulation. Specifically, we have been investigating the use of a cathepsin S (Cat S)-cleavable peptidic linkers to degrade multiblock HPMA copolymers to increase MPS-associated tissue clearance. In this study, we further our investigation into this area by exploring the impact of copolymer block size on the biological performance of Cat S-degradable HPMA copolymers. Using a variety of in vitro and in vivo techniques, including dual labeling of the copolymer and peptide components, we investigated the constructs using HPAC pancreatic ductal adenocarcinoma models. The smaller copolymer block size (S-CMP) demonstrated significantly faster Cat S cleavage kinetics relative to the larger system (L-CMP). Confocal microscopy demonstrated that both constructs could be much more efficiently internalized by human monocyte-differentiated macrophage (hMDM) compared to HPAC cells. In the biodistribution studies, the multiblock copolymers with a smaller block size exhibited faster clearance and lower nontarget retention while still achieving good tumor targeting and retention. Based on the radioisotopic ratios, fragmentation and clearance of the copolymer constructs were higher in the liver compared to the spleen and tumor. Overall, these results indicate that block size plays an important role in the biological performance of Cat S-degradable polymeric constructs.

Cathepsin S-cleavable, multi-block HPMA copolymers for improved SPECT/CT imaging of pancreatic cancer

This work continues our efforts to improve the diagnostic and radiotherapeutic effectiveness of nanomedicine platforms by developing approaches to reduce the non-target accumulation of these agents. Herein, we developed multi-block HPMA copolymers with backbones that are susceptible to cleavage by cathepsin S, a protease that is abundantly expressed in tissues of the mononuclear phagocyte system (MPS). Specifically, a bis-thiol terminated HPMA telechelic copolymer containing 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Three maleimide modified linkers with different sequences, including cathepsin S degradable oligopeptide, scramble oligopeptide and oligo ethylene glycol, were subsequently synthesized and used for the extension of the HPMA copolymers by thiol-maleimide click chemistry. All multi-block HPMA copolymers could be labeled by (177)Lu with high labeling efficiency and exhibited high serum stability. In vitro cleavage studies demonstrated highly selective and efficient cathepsin S mediated cleavage of the cathepsin S-susceptible multi-block HPMA copolymer. A modified multi-block HPMA copolymer series capable of Förster Resonance Energy Transfer (FRET) was utilized to investigate the rate of cleavage of the multi-block HPMA copolymers in monocyte-derived macrophages. Confocal imaging and flow cytometry studies revealed substantially higher rates of cleavage for the multi-block HPMA copolymers containing the cathepsin S-susceptible linker. The efficacy of the cathepsin S-cleavable multi-block HPMA copolymer was further examined using an in vivo model of pancreatic ductal adenocarcinoma. Based on the biodistribution and SPECT/CT studies, the copolymer extended with the cathepsin S susceptible linker exhibited significantly faster clearance and lower non-target retention without compromising tumor targeting. Overall, these results indicate that exploitation of the cathepsin S activity in MPS tissues can be utilized to substantially lower non-target accumulation, suggesting this is a promising approach for the development of diagnostic and radiotherapeutic nanomedicine platforms.

Evaluation of DOTA-chelated neurotensin analogs with spacer-enhanced biological performance for neurotensin-receptor-1-positive tumor targeting

INTRODUCTION

Neurotensin receptor 1 (NTR1) is overexpressed in many cancer types. Neurotensin (NT), a 13 amino acid peptide, is the native ligand for NTR1 and exhibits high (nM) affinity to the receptor. Many laboratories have been investigating the development of diagnostic and therapeutic radiopharmaceuticals for NTR1-positive cancers based on the NT peptide. To improve the biological performance for targeting NTR1, we proposed NT analogs with a 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelation system and different lengths of spacers.

METHODS

We synthesized four NTR1-targeted conjugates with spacer lengths from 0 to 9 atoms (null (N0), β-Ala-OH (N1), 5-Ava-OH (N2), and 8-Aoc-OH (N3)) between the DOTA and the pharmacophore. In vitro competitive binding, internalization and efflux studies were performed on all four NT analogs. Based on these findings, metabolism studies were carried out on our best performing conjugate, (177)Lu-N1. Lastly, in vivo biodistribution and SPECT/CT imaging studies were performed using (177)Lu-N1 in an HT-29 xenograft mouse model.

RESULTS

As shown in the competitive binding assays, the NT analogs with different spacers (N1, N2 and N3) exhibited lower IC50 values than the NT analog without a spacer (N0). Furthermore, N1 revealed higher retention in HT-29 cells with more rapid internalization and slower efflux than the other NT analogs. In vivo biodistribution and SPECT/CT imaging studies of (177)Lu-N1 demonstrated excellent accumulation (3.1 ± 0.4%ID/g) in the NTR1-positive tumors at 4h post-administration.

CONCLUSIONS

The DOTA chelation system demonstrated some modest steric inhibition of the pharmacophore. However, the insertion of a 4-atom hydrocarbon spacer group restored optimal binding affinity of the analog. The in vivo assays indicated that (177)Lu-N1 could be used for imaging and radiotherapy of NTR1-positive tumors.

The influence of linker length on the properties of cathepsin S cleavable (177)Lu-labeled HPMA copolymers for pancreatic cancer imaging

N-(2-hydroxypropyl)-methacrylamide (HPMA) copolymers have shown promise for application in the detection and staging of cancer. However, non-target accumulation, particularly in the liver and spleen, hinders the detection of resident or nearby metastatic lesions thereby decreasing diagnostic effectiveness. Our laboratory has pursued the development of cathepsin S susceptible linkers (CSLs) to reduce the non-target accumulation of diagnostic/radiotherapeutic HPMA copolymers. In this study, we ascertain if the length of the linking group impacts the cleavage and clearance kinetics, relative to each other and a non-cleavable control, due to a reduction in steric inhibition. Three different CSLs with linking groups of various lengths (0, 6 and 13 atoms) were conjugated to HPMA copolymers. In vitro cleavage studies revealed that the longest linking group (13 atoms) led to more rapid cleavage when challenged with cathepsin S. The CSL incorporated HPMA copolymers demonstrated significantly higher levels of excretion and a significant decrease in long-term hepatic and splenic retention relative to the non-cleavable control. Contrary to in vitro observations, the length of the linking group did not substantially impact the non-target in vivo clearance. In the case of HPAC tumor retention, the CSL with the null (0 atom) linker demonstrated significantly higher levels of retention relative to the other CSLs. Given these results, we find that the length of the linking group of the CSLs did not substantially impact non-target clearance, but did influence tumor retention. Overall, these results demonstrate that the CSLs can substantially improve the non-target clearance of HPMA copolymers thereby enhancing clinical potential.

Changes in the frequencies of human hematopoietic stem and progenitor cells with age and site

This study enumerated CD45(hi)/CD34(+) and CD45(hi)/CD133(+) human hematopoietic stem cells (HSCs) and progenitor granulocyte-macrophage colony forming cells (GM-CFCs) in blood and trochanteric and femoral bone marrow in 233 individuals. Stem cell frequencies were determined with multiparameter flow cytometry and using an internal control to determine the intrinsic variance of the assays. Progenitor cell frequency was determined using a standard colony assay technique. The frequency of outliers from undetermined methodological causes was highest for blood, but less than 5% for all values. The frequency of CD45(hi)/CD133(+) cells correlated highly with the frequency of CD45(hi)/CD34(+) cells in trochanteric and femoral bone marrow. The frequency of these HSC populations in trochanteric and femoral bone marrow rose significantly with age. In contrast, there was no significant trend of either of these cell populations with age in the blood. Trochanteric marrow progenitor GM-CFCs showed no significant trends with age, but femoral marrow GM-CFCs trended downward with age, potentially because of the reported conversion of red marrow at this site to fat with age. Hematopoietic stem and progenitor cells exhibited changes in frequencies with age that differed between blood and bone marrow. We previously reported that side population (SP) multipotential HSC, which includes the precursors of CD45(hi)/CD133(+) and CD45(hi)/CD34(+), decline with age. Potentially the increases in stem cell frequencies in the intermediate compartment between SP and GM progenitor cells observed in this study represent a compensatory increase for the loss of more potent members of the HSC hierarchy.

Synthesis and in vitro and in vivo evaluation of hypoxia-enhanced 111In-bombesin conjugates for prostate cancer imaging

Receptor-targeted agents, such as gastrin-releasing peptide receptor (BB2r)-targeted peptides, have been investigated extensively in preclinical and clinical studies. In an attempt to increase the effectiveness of diagnostic or radiotherapeutic agents, we have begun to explore the incorporation of the hypoxia-selective prodrug 2-nitroimidazole into receptor-targeted peptides. Hypoxia is a well-known characteristic of many solid tumors, including breast, prostate, and pancreatic cancers. The aim of this approach is to use the hypoxia-trapping capability of 2-nitroimidazoles to increase the retention of the agent in hypoxic, BB2r-positive tumors. We have demonstrated that incorporation of one or more 2-nitroimidazoles into the BB2r-targeted peptide significantly increases the in vitro retention of the agent in hypoxic prostate cancer cells. The study described herein represents our first investigation of the in vivo properties of these hypoxia-enhanced BB2r-targeted agents in a PC-3 xenograft mouse model.

METHODS

Four (111)In-labeled BB2r-targeted conjugates--(111) IN-1, (111) IN-2, (111) IN-3, and (111) IN-4, composed of 2-nitroimidazole moieties of 0, 1, 2, and 3, respectively--were synthesized, labeled, and purified. The BB2r binding affinities, externalization, and protein-association properties of these radioconjugates were assessed using the BB2r-positive PC-3 human prostate cancer cell line under hypoxic and normoxic environments. The in vivo biodistribution and micro-SPECT/CT imaging of the (111) IN-1, (111) IN-2, and (111) IN-4 radioconjugates were investigated in PC-3 tumor-bearing severely combined immunodeficient mice.

RESULTS

All conjugates and (nat)In-conjugates demonstrated nanomolar binding affinities. (111) IN-1, (111) IN-2, (111) IN-3, and (111) IN-4 demonstrated 41.4%, 60.7%, 69.1%, and 69.4% retention, correspondingly, of internalized radioactivity under hypoxic conditions relative to 34.8%, 35.3%, 33.2%, and 29.7% retention, respectively, under normoxic conditions. Protein-association studies showed significantly higher levels of association under hypoxic conditions for 2-nitroimidazole-containing BB2r-targeted radioconjugates than for controls. On the basis of the initial 1-h uptake in the PC-3 tumors, (111) IN-1, (111) IN-2, and (111) IN-4 demonstrated tumor retentions of 1.5%, 6.7%, and 21.0%, respectively, by 72 h after injection. Micro-SPECT/CT imaging studies of (111) IN-1, (111) IN-2, and (111) IN-4 radioconjugates resulted in clear delineation of the tumors.

CONCLUSION

On the basis of the in vitro and in vivo studies, the BB2r-targeted agents that incorporated 2-nitroimidazole moieties demonstrated improved retention. These results indicate that further exploration into the potential of hypoxia-selective trapping agents for BB2r-targeted agents, as well as other targeted compounds, is warranted.

177Lu-labeled HPMA copolymers utilizing cathepsin B and S cleavable linkers: synthesis, characterization and preliminary in vivo investigation in a pancreatic cancer model

INTRODUCTION

A major barrier to the advancement of therapeutic nanomedicines has been the non-target toxicity caused by the accumulation of the drug delivery systems in organs associated with the reticuloendothelial system, particularly the liver and spleen. Herein, we report the development of peptide based metabolically active linkers (MALs) that are enzymatically cleaved by cysteine cathepsin B and S, two proteases highly expressed in the liver and spleen. The overall goal of this approach is to utilize the MALs to lower the non-target retention and toxicity of radiolabeled drug delivery systems, thus resulting in higher diagnostic and radiotherapeutic efficacy.

METHODS

In this study three MALs (MAL0, MAL1 and MAL2) were investigated. MAL1 and MAL2 are composed of known substrates of cathepsin B and S, respectively, while MAL0 is a non-cleavable control. Both MAL1 and MAL2 were shown to undergo enzymatic cleavage with the appropriate cathepsin protease. Subsequent to conjugation to the HPMA copolymer and radiolabeling with (177)Lu, the peptide-polymer conjugates were renamed (177)Lu-metabolically active copolymers ((177)Lu-MACs) with the corresponding designations: (177)Lu-MAC0, (177)Lu-MAC1 and (177)Lu-MAC2.

RESULTS

In vivo evaluation of the (177)Lu-MACs was performed in an HPAC human pancreatic cancer xenograft mouse model. (177)Lu-MAC1 and (177)Lu-MAC2 demonstrated 3.1 and 2.1 fold lower liver retention, respectively, compared to control ((177)Lu-MAC0) at 72h post-injection. With regard to spleen retention, (177)Lu-MAC1 and (177)Lu-MAC2 each exhibited a nearly fourfold lower retention, relative to control, at the 72h time point. However, the tumor accumulation of the (177)Lu-MAC0 was two to three times greater than (177)Lu-MAC1 and (177)Lu-MAC2 at the same time point. The MAL approach demonstrated the capability of substantially reducing the non-target retention of the (177)Lu-labeled HPMA copolymers.

CONCLUSIONS

While further studies are needed to optimize the pharmacokinetics of the (177)Lu-MACs design, the ability of the MAL to significantly decrease non-target retention establishes the potential this avenue of research may have for the improvement of diagnostic and radiotherapeutic drug delivery systems.

Development of hypoxia enhanced 111In-labeled Bombesin conjugates: design, synthesis, and in vitro evaluation in PC-3 human prostate cancer

The gastrin-releasing peptide receptor (BB2r) has shown great promise for tumor targeting due to the increase of the receptor expression in a variety of human cancers including prostate, breast, small-cell lung, and pancreatic cancer. From clinical investigations, prostate cancer has been shown to be among the most hypoxic of the cancers investigated. Many solid tumors contain regions of hypoxia due to poor organization and efficiency of the vasculature. However, hypoxia is typically not present in normal tissue. Nitroimidazoles, a thoroughly investigated class of hypoxia selective drugs, have been shown to be highly retained in hypoxic tissues. The purpose of this study is to determine if the incorporation of hypoxia trapping moieties into the structural paradigm of BB2r-targeted peptides will increase the retention time of the agents in prostate cancer tumors. The present work involves the design, syntheses, purification, and in vitro investigation of hypoxia enhanced (111)In-BB2r-targeted radioconjugates. A total of four BB2r-targeted conjugates (1-4) were synthesized and coupled with increasing numbers of 2-nitroimidazoles, a hypoxia trapping moiety. Conjugates were radiolabeled with (111)In and purified by HPLC prior to in vitro studies. Receptor saturation assays under both normoxic and hypoxic conditions showed that the BB2r receptor expression on the PC-3 human prostate cancer cell line was not significantly affected by oxygen levels. Competitive binding assays revealed that incorporation of 2-nitroimidazoles had a detrimental effect to BB2r binding when adequate spacer groups, between the hypoxia trapping agent and the pharmacophore, were not employed. All of the 2-nitroimidazole containing BB2r-targeted agents exhibited significantly higher longitudinal retention in PC-3 cells under hypoxic conditions compared to the analogous normoxic studies. Protein association analysis revealed a 3-fold increase in binding of a 2-nitroimidazole containing BB2r-targeted agent under hypoxic relative to normoxic conditions. The positive nature of these results indicate that further exploration into the potential of hypoxia selective trapping agents for BB2r-targeted agents, as well as other targeted compounds, is warranted.

Inflammation associated with obesity: relationship with blood and bone marrow endothelial cells

The purpose of this study was to assess the inflammatory nature of obesity and its effect on blood and bone marrow endothelial cell populations. Obese patients (BMI ≥30) had significantly higher concentrations of the inflammatory marker C-reactive protein (CRP) (P = 0.03) and lower concentrations of the anti-inflammatory cytokine interleukin-10 (IL-10) (P = 0.05). This cytokine profile is consistent with obesity being an inflammatory condition and is further supported by the significant correlation between total white blood cell count and BMI (r = 0.15; P = 0.035). High BMI was associated with significantly lower numbers of early endothelial cells (CD45(-)/CD34(+)) in the bone marrow (r = -0.20; P = 0.0068). There was also a significant inverse correlation between BMI and a more mature endothelial cell phenotype (CD45(-)/31(+)) in the blood (r = -0.17; P = 0.02). In addition, there was a significant correlation between BMI- and endothelial-related cells of hematopoietic origin (CD133(+)/VEGFR-2(+)) in the bone marrow (r = -0.26; P = 0.0007). Patients with higher plasma IL-10 and insulin-like growth factor (IGF) concentrations had higher numbers of endothelial phenotypes in the bone marrow suggesting a protective effect of these anti-inflammatory cytokines. In conclusion, this work confirms the inflammatory nature of obesity and is the first to report that obesity is associated with reduced endothelial cell numbers in the bone marrow of humans. These effects of obesity may be a potential mechanism for impaired tissue repair in obese patients.

Changes in human bone marrow fat content associated with changes in hematopoietic stem cell numbers and cytokine levels with aging

Hematological deficiencies increase with aging, including anemias, reduced responses to hematopoietic stress and myelodysplasias. This investigation tested the hypothesis that increased bone marrow (BM) fat content in humans with age was associated with decreased numbers of side population (SP) hematopoietic stem cells, and this decrease correlated with changes in cytokine levels. BM was obtained from the femoral head and trochanteric region of the femur removed at surgery for total hip replacement (N = 100 subjects). In addition, BM from cadavers (N = 36), with no evidence of hip disease, was evaluated for fat content. Whole trabecular marrow samples were ground in a sterile mortar and pestle, and cellularity and lipid content determined. Marrow cells were stained with Hoechst dye and SP profiles were acquired. Plasma levels of insulin-like growth factor (IGF)-1, stromal-derived factor (SDF)-1 and interleukin (IL)-6 were measured using ELISA. Fat content in the BM of human subjects and cadavers increased with age. The numbers of SP stem cells in BM as well as plasma IGF-1 and SDF-1 levels decreased in correlation with increased BM fat. IL-6 had no relationship to changes in marrow fat. These data suggest that increased BM fat may be associated with a decreased number of SP stem cells and IGF-1 and SDF-1 levels with aging. These data further raise a more general question as to the role of adipose cells in the regulation of tissue stem cells.

Human blood and marrow side population stem cell and Stro-1 positive bone marrow stromal cell numbers decline with age, with an increase in quality of surviving stem cells: correlation with cytokines

Hematological deficiencies increase with aging leading to anemias, reduced hematopoietic stress responses and myelodysplasias. This study tested the hypothesis that side population hematopoietic stem cells (SP-HSC) would decrease with aging, correlating with IGF-1 and IL-6 levels and increases in bone marrow fat. Marrow was obtained from the femoral head and trochanteric region of the femur at surgery for total hip replacement (N=100). Whole trabecular marrow samples were ground in a sterile mortar and pestle and cellularity and fat content determined. Marrow and blood mononuclear cells were stained with Hoechst dye and the SP-HSC profiles acquired. Marrow stromal cells (MSC) were enumerated flow cytometrically employing the Stro-1 antibody, and clonally in the colony forming unit fibroblast (CFU-F) assay. Plasma levels of IGF-1 (ng/ml) and IL-6 (pg/ml) were measured by ELISA. SP-HSC in blood and bone marrow decreased with age but the quality of the surviving stem cells increased. MSC decreased non-significantly. IGF-1 levels (mean=30.7, SEM=2) decreased and IL-6 levels (mean=4.4, SEM=1) increased with age as did marrow fat (mean=1.2mmfat/g, SEM=0.04). There were no significant correlations between cytokine levels or fat and SP-HSC numbers. Stem cells appear to be progressively lost with aging and only the highest quality stem cells survive.

Promises and pitfalls of stem cell therapy for promotion of bone healing

There is promise in combining stem cells with allogeneic bone matrix to promote bone healing. Murine bone marrow, peripheral blood, and compact bone cells were transplanted ectopically under the kidney capsule in mice, alone or in combination with allogeneic matrix products: powder and putty to determine their bone forming potential in comparison to transplanted femoral bone fragments and long-term cultured bone marrow cells. The end point was the amount of bone formed as determined by quantitative histology. Mononuclear cells from marrow, peripheral blood, or bone alone transplanted under the kidney capsule did not form bone. Mononuclear cell populations did not combine readily with matrix products and there was in vivo migration of the transplanted combinations. Kidney subcapsular transplanted cultured bone marrow cells formed bone in proportion to the culture period, but after 9 weeks, the extent was only 20% by area of that of similarly transplanted femoral bone fragments. An inductive stimulus for bone formation seemed necessary. Osteoprogenitor cells were not detected in significant numbers in blood unless high doses of cytokines were administered. A better definition of the optimal cell populations and manipulations required for promotion of bone healing is needed along with new (transplant) models that allow for cell tracking. Much work remains to overcome current pitfalls in the use of stem cells to promote allograft integration and bone healing.

LEVEL OF EVIDENCE

Therapeutic study, Level V (expert opinion). See the Guidelines for Authors for a complete description of levels of evidence.

Cardiolipin liposomes: a novel flow reagent for detection of anticardiolipin antibodies

The association of autoantibodies with specificity for phospholipids and an increased risk for thromboembolic phenomena has received considerable recent clinical attention. These autoantibodies have been reported in patients with defined autoimmune disorders as well as in patients with no other obvious autoimmune disease symptoms other than isolated or recurrent thromboembolic disease. A significant component of this autoimmune response appears to be related to cardiolipin-directed antibodies. Most studies reported to date have used either an enzyme immunoassay or a radioimmunoassay for detection and quantitation of antiphospholipid antibodies. We have developed a novel flow cytometric assay for detection of anticardiolipin antibodies. The assay, by analogy to polystyrene microsphere assay, utilizes cardiolipin liposomes as solid-phase microspheres for antigen presentation. In comparison to enzyme-linked immunosorbent assay, the flow assay shows similar sensitivity by serum titration, has immunoglobulin class specificity, and is semiquantitative as currently designed. The flow assay is relatively easy to perform and should allow detection of other antiphospholipid specificities with tailoring of the phospholipid makeup of the liposomes.