CXCR4 Promotes Neuroblastoma Growth and Therapeutic Resistance through miR-15a/16-1-Mediated ERK and BCL2/Cyclin D1 Pathways

CXCR4 expression in neuroblastoma tumors correlates with disease severity. In this study, we describe mechanisms by which CXCR4 signaling controls neuroblastoma tumor growth and response to therapy. We found that overexpression of CXCR4 or stimulation with CXCL12 supports neuroblastoma tumorigenesis. Moreover, CXCR4 inhibition with the high-affinity CXCR4 antagonist BL-8040 prevented tumor growth and reduced survival of tumor cells. These effects were mediated by the upregulation of miR-15a/16-1, which resulted in downregulation of their target genes BCL-2 and cyclin D1, as well as inhibition of ERK. Overexpression of miR-15a/16-1 in cells increased cell death, whereas antagomirs to miR-15a/16-1 abolished the proapoptotic effects of BL-8040. CXCR4 overexpression also increased miR-15a/16-1, shifting their oncogenic dependency from the BCL-2 to the ERK signaling pathway. Overall, our results demonstrate the therapeutic potential of CXCR4 inhibition in neuroblastoma treatment and provide a rationale to test combination therapies employing CXCR4 and BCL-2 inhibitors to increase the efficacy of these agents.Significance: These results provide a mechanistic rationale for combination therapy of CXCR4 and BCL-2 inhibitors to treat a common and commonly aggressive pediatric cancer.Cancer Res; 78(6); 1471-83. ©2017 AACR.

Albumin/vaccine nanocomplexes that assemble in vivo for combination cancer immunotherapy

Subunit vaccines have been investigated in over 1000 clinical trials of cancer immunotherapy, but have shown limited efficacy. Nanovaccines may improve efficacy but have rarely been clinically translated. By conjugating molecular vaccines with Evans blue (EB) into albumin-binding vaccines (AlbiVax), here we develop clinically promising albumin/AlbiVax nanocomplexes that self-assemble in vivo from AlbiVax and endogenous albumin for efficient vaccine delivery and potent cancer immunotherapy. PET pharmacoimaging, super-resolution microscopies, and flow cytometry reveal almost 100-fold more efficient co-delivery of CpG and antigens (Ags) to lymph nodes (LNs) by albumin/AlbiVax than benchmark incomplete Freund's adjuvant (IFA). Albumin/AlbiVax elicits ~10 times more frequent peripheral antigen-specific CD8⁺ cytotoxic T lymphocytes with immune memory than IFA-emulsifying vaccines. Albumin/AlbiVax specifically inhibits progression of established primary or metastatic EG7.OVA, B16F10, and MC38 tumors; combination with anti-PD-1 and/or Abraxane further potentiates immunotherapy and eradicates most MC38 tumors. Albumin/AlbiVax nanocomplexes are thus a robust platform for combination cancer immunotherapy.

Screening of cancer tissue arrays identifies CXCR4 on adrenocortical carcinoma: correlates with expression and quantification on metastases using 64Cu-plerixafor PET

Expression of the chemokine receptor CXCR4 by many cancers correlates with aggressive clinical behavior. As part of the initial studies in a project whose goal was to quantify CXCR4 expression on cancers non-invasively, we examined CXCR4 expression in cancer samples by immunohistochemistry using a validated anti-CXCR4 antibody. Among solid tumors, we found expression of CXCR4 on significant percentages of major types of kidney, lung, and pancreatic adenocarcinomas, and, notably, on metastases of clear cell renal cell carcinoma and squamous cell carcinoma of the lung. We found particularly high expression of CXCR4 on adrenocortical cancer (ACC) metastases. Microarrays of ACC metastases revealed correlations between expression of CXCR4 and other chemokine system genes, particularly CXCR7/ACKR3, which encodes an atypical chemokine receptor that shares a ligand, CXCL12, with CXCR4. A first-in-human study using ⁶⁴Cu-plerixafor for PET in an ACC patient prior to resection of metastases showed heterogeneity among metastatic nodules and good correlations among PET SUVs, CXCR4 staining, and CXCR4 mRNA. Additionally, we were able to show that CXCR4 expression correlated with the rates of growth of the pulmonary lesions in this patient. Further studies are needed to understand better the role of CXCR4 in ACC and whether targeting it may be beneficial. In this regard, non-invasive methods for assessing CXCR4 expression, such as PET using ⁶⁴Cu-plerixafor, should be important investigative tools.

Novel "Add-On" Molecule Based on Evans Blue Confers Superior Pharmacokinetics and Transforms Drugs to Theranostic Agents

One of the major design considerations for a drug is its pharmacokinetics in the blood. A drug with a short half-life in the blood is less available at a target organ. Such a limitation dictates treatment with either high doses or more frequent doses, both of which may increase the likelihood of undesirable side effects. To address the need for additional methods to improve the blood half-life of drugs and molecular imaging agents, we developed an "add-on" molecule that contains 3 groups: a truncated Evans blue dye molecule that binds to albumin with a low micromolar affinity and provides a prolonged half-life in the blood; a metal chelate that allows radiolabeling for imaging and radiotherapy; and maleimide for easy conjugation to drug molecules. Methods: The truncated Evans blue molecule was conjugated with the chelator NOTA or DOTA, and the resulting conjugate was denoted as NMEB or DMEB, respectively. As a proof of concept, we coupled NMEB and DMEB to c(RGDfK), which is a small cyclic arginine-glycine-aspartic acid (RGD) peptide, for targeting integrin α_vβ₃ NMEB and DMEB were radiolabeled with ⁶⁴Cu and ⁹⁰Y, respectively, and tested in xenograft models. Results: The resulting radiolabeled conjugates showed a prolonged circulation half-life and enhanced tumor accumulation in integrin α_vβ₃-expressing tumors. Tumor uptake was markedly improved over that with NOTA- or DOTA-conjugated c(RGDfK). Tumor radiotherapy experiments in mice with ⁹⁰Y-DMEB-RGD showed promising results; existing tumors were eliminated. Conclusion: Conjugation of our novel add-on molecule, NMEB or DMEB, to potential tracers or therapeutic agents improved blood half-life and tumor uptake and could transform such agents into theranostic entities.

Ortho-Stabilized (18) F-Azido Click Agents and their Application in PET Imaging with Single-Stranded DNA Aptamers

Azido (18) F-arenes are important and versatile building blocks for the radiolabeling of biomolecules via Huisgen cycloaddition ("click chemistry") for positron emission tomography (PET). However, routine access to such clickable agents is challenged by inefficient and/or poorly defined multistep radiochemical approaches. A high-yielding direct radiofluorination for azido (18) F-arenes was achieved through the development of an ortho-oxygen-stabilized iodonium derivative (OID). This OID strategy addresses an unmet need for a reliable azido (18) F-arene clickable agent for bioconjugation reactions. A ssDNA aptamer was radiolabeled with this agent and visualized in a xenograft mouse model of human colon cancer by PET, which demonstrates that this OID approach is a convenient and highly efficient way of labeling and tracking biomolecules.

Pre-treatment of allogeneic bone marrow recipients with the CXCR4 antagonist AMD3100 transiently enhances hematopoietic chimerism without promoting donor-specific skin allograft tolerance

Hematopoietic chimerism established by allogeneic bone marrow transplantation is known to promote donor-specific organ allograft tolerance; however, clinical application is limited by the need for toxic host conditioning and "megadoses" of donor bone marrow cells. A potential solution to this problem has been suggested by the observation that recipient bone marrow mobilization by the CXCR4 antagonist AMD3100 promotes chimerism in congenic bone marrow transplantation experiments in mice. Here we report that a single subcutaneous dose of 10 mg/kg AMD3100 in recipient C57BL/6 mice was able to enhance hematopoietic chimerism when complete MHC-mismatched BALB/c donor bone marrow cells were transplanted 1h after drug dosing. However, levels of chimerism measured 30 days post-transplantation were not sustained when mice were reexamined on day 90 post-transplantation. Moreover, transient chimerism induced by this protocol did not support robust donor-specific skin allograft tolerance. Using the same transient immunosuppression protocol, we confirmed that "megadoses" of donor bone marrow cells could induce durable chimerism associated with donor-specific skin allograft tolerance without AMD3100 pre-treatment. We conclude that in this protocol AMD3100 pretreatment may empty bone marrow niches that become reoccupied by allogeneic donor hematopoietic progenitor cells but not by true long-lived donor hematopoietic stem cells, resulting in short-lived chimerism and failure to support durable donor-specific allograft tolerance.

18F-Labeled Single-Stranded DNA Aptamer for PET Imaging of Protein Tyrosine Kinase-7 Expression

Protein tyrosine kinase-7 (PTK7), a member of receptor tyrosine kinase superfamily initially identified as colon carcinoma kinase-4, is highly expressed in various human malignancies. Its expression was found to correlate with aggressive biologic behaviors such as increased cell proliferation, invasiveness, and migration. Despite the importance and unmet need of imaging PTK7 in vivo, there is currently no clinically relevant method to visualize tumoral PTK7 expression noninvasively such as PET or SPECT. This study aimed to develop a specific, selective, and high-affinity PET radioligand based on single-stranded DNA aptamer to address this challenge.

METHODS

Sgc8, a 41-oligonucleotide that targets to PTK7, was labeled with (18)F using a 2-step radiochemical synthesis, which featured a direct 1-step radiofluorination on the distinctive spirocyclic hypervalent iodine(III) precursor to give (18)F-fluorobenzyl azide followed by copper-mediated click conjugation with Sgc8-alkyne. (18)F-Sgc8 was evaluated in vitro and in vivo in 2 cell lines, HCT116 and U87MG, which express high and low amounts of PTK7, respectively.

RESULTS

Sgc8 was labeled efficiently with (18)F in an isolated radiochemical yield of 62% ± 2%, non-decay-corrected based on (18)F-fluorobenzyl azide. (18)F-Tr-Sgc8 was found to possess high-affinity binding to both cell lines, with binding affinity values of 2.7 ± 0.6 nM for HCT116 and 16.9 ± 2.1 nM for U87MG. In vivo PET imaging clearly visualized PTK7 expression in HCT116 xenografted mice, with tumor uptake of 0.76 ± 0.09 percentage injected dose per gram (%ID/g) at 30 min after injection for the subcutaneous tumor model and greater than 1.5 %ID/g for the liver metastasis model. U87MG xenograft tumors had much lower tracer accumulation (0.13 ± 0.06 %ID/g at 30 min after injection), which was consistent with the lower expression of PTK7 in this tumor model. The labeled aptamer was rapidly cleared from the blood through the kidneys and bladder to give high tumor-to-blood and tumor-to-muscle ratios of 7.29 ± 1.51 and 10.25 ± 2.08, respectively.

CONCLUSION

The (18)F-radiolabeling methodology shown here is a robust procedure for labeling aptamers and similar chemical moieties and can be applied to many different targets. Quantification of PTK7 using (18)F-Tr-Sgc8 may be suitable for clinical translation and might help in the future to select and monitor appropriate therapies.

PET imaging of tenascin-C with a radiolabeled single-stranded DNA aptamer

Tenascin-C is an extracellular matrix glycoprotein that is expressed by injured tissues and by various cancers. Recent publications showed that tenascin-C expression by cancer lesions predicts tumor growth, metastasis, and angiogenesis, suggesting tenascin-C as a potential therapeutic target. Currently there is no noninvasive method to determine tumoral tenascin-C expression in vivo. To address the need for an agent to image and quantify tenascin-C, we report the development of a radioactive PET tracer based on a tenascin-C-specific single-stranded DNA aptamer (tenascin-C aptamer).

METHODS

Tenascin-C aptamer was radiolabeled with (18)F and (64)Cu. PET imaging studies for the evaluation of tumor uptake and pharmacokinetics of tenascin-C aptamer were performed in comparison to a nonspecific scrambled aptamer (Sc aptamer).

RESULTS

The labeled tenascin-C aptamer provided clear visualization of tenascin-C-positive but not tenascin-C-negative tumors. The uptake of tenascin-C aptamer was significantly higher than that of Sc aptamer in tenascin-C-positive tumors. The labeled tenascin-C aptamer had fast clearance from the blood and other nonspecific organs through the kidneys, resulting in high tumor contrast.

CONCLUSION

Our data suggest that suitably labeled tenascin-C aptamer can be used as a PET tracer to image tumor expression of tenascin-C with a high tumor-to-background ratio and might provide insightful and personalized medical data that will help determine appropriate treatment and monitoring.

Conventional NK cells can produce IL-22 and promote host defense in Klebsiella pneumoniae pneumonia

It was reported that host defense against pulmonary Klebsiella pneumoniae infection requires IL-22, which was proposed to be of T cell origin. Supporting a role for IL-22, we found that Il22(-/-) mice had decreased survival compared with wild-type mice after intratracheal infection with K. pneumoniae. Surprisingly, however, Rag2(-/-) mice did not differ from wild-type mice in survival or levels of IL-22 in the lungs postinfection with K. pneumoniae. In contrast, K. pneumoniae-infected Rag2(-/-)Il2rg(-/-) mice failed to produce IL-22. These data suggested a possible role for NK cells or other innate lymphoid cells in host defense and production of IL-22. Unlike NK cell-like innate lymphoid cells that produce IL-22 and display a surface phenotype of NK1.1(-)NKp46(+)CCR6(+), lung NK cells showed the conventional phenotype, NK1.1(+)NKp46(+)CCR6(-). Mice depleted of NK cells using anti-asialo GM1 showed decreased survival and higher lung bacterial counts, as well as increased dissemination of K. pneumoniae to blood and liver, compared with control-treated mice. NK cell depletion also led to decreased production of IL-22 in the lung. Within 1 d postinfection, although there was no increase in the number of lung NK cells, a subset of lung NK cells became competent to produce IL-22, and such cells were found in both wild-type and Rag2(-/-) mice. Our data suggest that, during pulmonary infection of mice with K. pneumoniae, conventional NK cells are required for optimal host defense, which includes the production of IL-22.

Inflammation-induced hepatocellular carcinoma is dependent on CCR5 in mice

Human hepatocellular carcinoma (HCC) is an inflammation-induced cancer, which is the third-leading cause of cancer mortality worldwide. We investigated the role of the chemokine receptors, CCR5 and CCR1, in regulating inflammation and tumorigenesis in an inflammation-induced HCC model in mice. Multidrug resistance 2 gene (Mdr2)-knockout (Mdr2-KO) mice spontaneously develop chronic cholestatic hepatitis and fibrosis that is eventually followed by HCC. We generated two new strains from the Mdr2-KO mouse, the Mdr2:CCR5 and the Mdr2:CCR1 double knockouts (DKOs), and set out to compare inflammation and tumorigenesis among these strains. We found that in Mdr2-KO mice lacking the chemokine receptor, CCR5 (Mdr2:CCR5 DKO mice), but not CCR1 (Mdr2:CCR1 DKO), macrophage recruitment and trafficking to the liver was significantly reduced. Furthermore, in the absence of CCR5, reduced inflammation was also associated with reduced periductal accumulation of CD24(+) oval cells and abrogation of fibrosis. DKO mice for Mdr2 and CCR5 exhibited a significant decrease in tumor incidence and size.

CONCLUSIONS

Our results indicate that CCR5 has a critical role in both the development and progression of liver cancer. Therefore, we propose that a CCR5 antagonist can serve for HCC cancer prevention and treatment.

Sequential administration of the high affinity CXCR4 antagonist BKT140 promotes megakaryopoiesis and platelet production

Platelets are the terminal differentiation product of megakaryocytes (MKs). Cytokines, such as thrombopoietin (TPO), are known to influence different steps in MK development; however, the complex differentiation and platelet localization processes are not fully understood. MKs express the receptor CXCR4 and have been shown to migrate in response to CXCL12 and to increase their platelet production. In this study, we studied the role of CXCR4 in platelet production with the high affinity CXCR4 antagonist, BKT140. Single and sequential administration of BKT140 significantly increased the number of MKs and haematopoietic progenitors (HPCs) within the bone marrow (BM). Increased megakaryopoiesis was associated with increased platelet production. Single and sequential administration of BKT140 also increased the number of HPCs in the blood. In a model of 5-fluorouracil-induced thrombocytopenia, BKT140 significantly reduced the severity and duration of thrombocytopenia and cytopenia when administered before and after chemotherapy. Our results demonstrated that the CXCR4 antagonist, BKT140, mediated unique beneficial effects by stimulating megakaryopoiesis and platelet production. These results provide evidence for the possible therapeutic use of BKT140 for modulating platelet numbers in thrombocytopenic conditions.

Positron emission tomography imaging of tumors expressing the human chemokine receptor CXCR4 in mice with the use of 64Cu-AMD3100

PURPOSE

Expression of CXCR4 in cancers has been correlated with poor prognosis and increased metastasis. Quantifying CXCR4 expression non-invasively might aid in prognostication and monitoring therapy. We evaluated a radiolabeled antagonist of CXCR4, ⁶⁴Cu-AMD3100, as a positron-emitting imaging agent.

PROCEDURES

CXCR4-transfected or non-transfected cell lines were injected into mice to form xenografts. Accumulation of ⁶⁴Cu-AMD3100 in tumors was analyzed by small-animal PET and biodistribution assays.

RESULTS

⁶⁴Cu-AMD3100 accumulated in CXCR4-expressing, but not CXCR4-negative, tumors. For CXCR4-expressing tumors, tumor-to-blood and tumor-to-muscle ratios were 23-41 and 50-59, respectively, depending on tumor type. Excess of unlabeled Cu-AMD3100 or AMD3100 significantly reduced ⁶⁴Cu-AMD3100 accumulation in CXCR4-expressing tumors. Human-absorbed dose calculations predicted a dose limit of 444 MBq.

CONCLUSIONS

CXCR4 can be imaged in tumors using ⁶⁴Cu-AMD3100. Dosimetry studies suggest that imaging in humans is feasible. We conclude that ⁶⁴Cu-AMD3100 should be investigated as a potential agent for imaging and quantifying CXCR4 in tumors.

MicroPET imaging of integrin αvβ3 expressing tumors using 89Zr-RGD peptides

PURPOSE

The dimeric transmembrane integrin, α(v)β(3), is a well-investigated target by different imaging modalities through suitably labeled arginine-glycine-aspartic acid (RGD) containing peptides. In this study, we labeled four cyclic RGD peptides with or without PEG functional groups: c(RGDfK) (denoted as FK), PEG(3)-c(RGDfK) (denoted as FK-PEG(3)), E[c(RGDfK)](2) (denoted as [FK](2)), and PEG(4)-E[PEG(4)-c(RGDfK)](2) (denoted as [FK](2)-3PEG(4)), with (89)Zr (t(1/2) = 78.4 h), using the chelator desferrioxamine-p-SCN (Df) for imaging tumor integrin α(v)β(3).

METHODS

The Df conjugated RGD peptides were subjected to integrin α(v)β(3) binding assay in vitro using MDA-MB-435 breast cancer cells. The (89)Zr-labeled RGD peptides were then subjected to small animal positron emission tomography (PET) and direct tissue sampling biodistribution studies in an orthotopic MDA-MB-435 breast cancer xenograft model.

RESULTS

All four tracers, (89)Zr-Df-FK, (89)Zr-Df-FK-PEG(3), (89)Zr-Df-[FK](2), and (89)Zr-Df-[FK](2)-3PEG(4), were labeled in high radiochemical yield (89 ± 4%) and high specific activity (4.07-6 MBq/μg). Competitive binding assay with (125)I-echistatin showed that conjugation of the RGD peptides to the Df chelator did not have significant impact on their integrin α(v)β(3) binding affinity and the dimeric peptides were shown to be more potent than the monomers. In agreement with binding results, tumor uptake of (89)Zr-Df-[FK](2) and (89)Zr-Df-[FK](2)-3PEG(4) was significantly higher (4.32 ± 1.73%ID/g and 4.72 ± 0.66%ID/g, respectively, at 2 h post-injection) than the monomers (89)Zr-Df-FK and (89)Zr-Df-FK-PEG(3) (1.97 ± 0.38%ID/g and 1.57 ± 0.49%ID/g, respectively, at 2 h post-injection). Out of the four labeled peptides, (89)Zr-Df-[FK](2)-3PEG(4) gave the highest tumor-to-background ratio (18.21 ± 2.52 at 2 h post-injection and 19.69 ± 3.99 at 4 h post-injection), with the lowest uptake in metabolic organs. Analysis of late time points biodistribution data revealed that the uptake in the tumor was decreased, along with increase in the bone, which implies decomplexation of (89)Zr-Df.

CONCLUSION

Efficient radiolabeling of peptides with an appropriate chelator such as Df-RGD with (89)Zr was observed. The (89)Zr radiolabeled peptides provided high-quality and high-resolution microPET images in xenograft models. (89)Zr-Df-[FK](2)-3PEG(4) demonstrated the highest tumor-to-background ratio of the compounds tested. Preparation of (89)Zr peptides to take advantage of the longer half-life is unwarranted due to the relatively rapid clearance from the tumor region of peptide tracers prepared for this study and the increased uptake in the bone of transchelated (89)Zr with time (2.0 ± 0.36%ID/g, 24 h post-injection).

Improvement of CXCR4 tracer specificity for PET imaging

Tumors expressing the chemokine receptor CXCR4 have been reported to be more aggressive and to produce more metastatic seeding in specific organs, such as the bone marrow. However, evaluation of tumors for CXCR4 expression requires testing of ex vivo biopsy samples, and is not routinely done in cancer management. In prior work to address this issue, we and others have developed tracers for positron emission tomography (PET) that targeted CXCR4, but in addition to binding to CXCR4 these tracers also bound to red blood cells (and to other unrelated targets) in vivo. Here we report two new tracers based on the CXCR4 peptide antagonist 4F-benzoyl-TN14003 (T140) that bind to CXCR4, but not to undesired targets. These tracers, NOTA-NFB and DOTA-NFB, show slight reductions in both 1) binding affinities for CXCR4 and 2) inhibition of CXCL12 induced migration, compared to T140, in vitro. Both NOTA-NFB and DOTA-NFB specifically accumulate in CXCR4-positive, but not CXCR4-negative, tumor xenografts in mice and allow clear visualization of CXCR4 expression by PET. Evaluation of NOTA-NFB and DOTA-NFB for their potential to mobilize immune cells and progenitor cells from the bone marrow to the peripheral blood revealed slightly reduced, but still comparable, results to the parent molecule T140. The tracers reported here may allow the evaluation of CXCR4 expression in primary tumors and metastatic nodules, and enable better informed, more personalized treatment for patients with cancer.

PET imaging of CXCR4 using copper-64 labeled peptide antagonist

Expression of CXCR4 in cancer has been found to correlate with poor prognosis and resistance to chemotherapy. In this study we developed a derivative of the CXCR4 peptide antagonist, T140-2D, that can be labeled easily with the PET isotope copper-64, and thereby enable in vivo visualization of CXCR4 in tumors. T140 was conjugated to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid mono (N-hydroxysuccinimide ester) (DOTA-NHS) to give T140-2D, which contains a DOTA molecule on each of the two lysine residues. ⁶⁴Cu-T140-2D was evaluated in vitro by migration and binding experiments, and in vivo by microPET imaging and biodistribution, in mice bearing CXCR4-positive and CXCR4-negative tumor xenografts. T140-2D was labeled with copper-64 to give ⁶⁴Cu-T140-2D in a high radiochemical yield of 86 ± 3% (not decay-corrected) and a specific activity of 0.28 - 0.30 mCi/µg (10.36 - 11.1 MBq/µg). ⁶⁴Cu-T140-2D had antagonistic and binding characteristics to CXCR4 that were similar to those of T140. In vivo, ⁶⁴Cu-T140-2D tended to bind to red blood cells and had to be used in a low specific activity form. In this new form ⁶⁴Cu-T140-2D enabled specific imaging of CXCR4-positive, but not CXCR4-negative tumors. Undesirably, however, ⁶⁴Cu-T140-2D also displayed high accumulation in the liver and kidneys. In conclusion, ⁶⁴Cu-T140-2D was easily labeled and, in its low activity form, enabled imaging of CXCR4 in tumors. It had high uptake, however, in metabolic organs. Further research with imaging tracers targeting CXCR4 is required.

Prokineticin receptor 1 antagonist PC-10 as a biomarker for imaging inflammatory pain

Prokineticin receptor 1 (PKR1) and its ligand Bv8 were shown to be expressed in inflammation-induced pain and by tumor-supporting fibroblasts. Blocking this receptor might prove useful for reducing pain and for cancer therapy. However, there is no method to quantify the levels of these receptors in vivo.

METHODS

A nonpeptidic PKR1 antagonist, N-{2-[5-(4-fluoro-benzyl)-1-(4-methoxy-benzyl)-4,6-dioxo-1,4,5,6-tetrahydro-[1,3,5]triazin-2-ylamino]-ethyl}-guanidine, which contains a free guanidine group, was labeled with (18)F by reacting the guanidine function with N-succinimidyl-4-(18)F-fluorobenzoate to give the guanidinyl amide N-(4-(18)F-fluoro-benzoyl)-N'-{2-[5-(4-fluoro-benzyl)-1-(4-methoxy-benzyl)-4,6-dioxo-1,4,5,6-tetrahydro-[1,3,5]triazin-2-ylamino]-ethyl}-guanidine ((18)F-PC-10). Inflammation was induced in C57BL/6 mice by subcutaneous injection of complete Freund adjuvant in the paw. The mice were imaged with (18)F-PC-10, (18)F-FDG, and (64)Cu-pyruvaldehyde bis(4-methyl-3-thiosemicarbazone) ((64)Cu-PTSM) at 24 h after complete Freund adjuvant injection using a small-animal PET device.

RESULTS

(18)F-PC-10 was synthesized with a radiochemical yield of 16% ± 3% (decay-corrected). (18)F-PC-10 accumulated specifically in the inflamed paw 4- to 5-fold more than in the control paw. Compared with (18)F-PC-10, (18)F-FDG and (64)Cu-PTSM displayed higher accumulation in the inflamed paw but also had higher accumulation in the control paw, demonstrating a reduced signal-to-background ratio. (18)F-PC-10 also accumulated in PKR1-expressing organs, such as the salivary gland and gastrointestinal tract.

CONCLUSION

(18)F-PC-10 can be used to image PKR1, a biomarker of the inflammation process. However, the high uptake of (18)F-PC-10 in the gastrointestinal tract, due to specific uptake and the metabolic processing of this highly lipophilic molecule, would restrict its utility.

Ccr5 deficiency regulates the proliferation and trafficking of natural killer cells under physiological conditions

Chemokines were shown to govern the trafficking of immune cells and may also play important roles in the survival and activation of these cells. We report here that under physiological conditions, the bone marrow (BM), spleen, blood and liver of Ccr5, but not of Ccr1-deficient mice, contain reduced numbers of NK cells. NK cells in the BM of Ccr5-deficient mice proliferate to a lesser extent compared to WT mice. Furthermore, spleen NK cells derived from Ccr5-deficient mice that were transplanted into irradiated recipients failed to proliferate in the host. Ccr5, but not Ccr1-deficient NK cells, failed to migrate in vitro in response to RANTES and MIP-1β but not MIP-1β or SDF-1 and had reduced activation, lower expression levels of NK cell markers and a slightly reduced capacity to adhere to target cells and stimulate their killing. Using the polyI:C mouse model for NK trafficking, we found that in the absence of Ccr5, but not Ccr1, NK cells failed to accumulate in the liver. In contrast, using the influenza viral infection as a model to evaluate NK cell proliferation, we found that Ccr5-deficient NK cells in the BM had a higher proliferation rate than WT NK cells. These results suggest a role for Ccr5 in NK cell proliferation and circulation under physiological conditions and a complex role for Ccr5 in determining the fate of NK cells under pathological conditions.

Rapid and simple one-step F-18 labeling of peptides

Labeling biomolecules with ¹⁸F is usually done through coupling with prosthetic groups, which requires several time-consuming radiosynthesis steps and therefore in low labeling yield. In this study, we designed a simple one-step ¹⁸F-labeling strategy to replace the conventional complex and the long process of multiple-step radiolabeling procedure. Both monomeric and dimeric cyclic RGD peptides were modified to contain 4-NO₂-3-CF₃ arene as precursors for direct ¹⁸F labeling. Binding of the two functionalized peptides to integrin α(v)β₃ was tested in vitro using the MDA-MB-435 human breast cell line. The most promising functionalized peptide, the dimeric cyclic RGD, was further evaluated in vivo in an orthotopic MDA-MB-435 tumor xenograft model. The use of relatively low amount of precursor (~0.5 μmol) gave reasonable yield, ranging from 7 to 23% (decay corrected, calculated from the start of synthesis) after HPLC purification. Overall reaction time was 40 min, and the specific activity of the labeled peptide was high. Modification of RGD peptides did not significantly change the biological binding affinities of the modified peptides. Small animal PET and biodistribution studies revealed integrin specific tumor uptake and favorable biokinetics. We have developed a novel one-step ¹⁸F radiolabeling strategy for peptides that contain a specific arene group, which shortens reaction time and labor significantly, requires low amount of precursor, and results in specific activity of 79 ± 13 GBq/μmol. Successful introduction of 4-fluoro-3-trifluoromethylbenzamide into RGD peptides may be a general strategy applicable to other biologically active peptides and proteins.

CXCR4 antagonist 4F-benzoyl-TN14003 inhibits leukemia and multiple myeloma tumor growth

OBJECTIVE

The chemokine receptor CXCR4 and its ligand CXCL12 are involved in the progression and dissemination of a diverse number of solid and hematological malignancies. Binding CXCL12 to CXCR4 activates a variety of intracellular signal transduction pathways that regulate cell chemotaxis, adhesion, survival, proliferation, and apoptosis.

MATERIALS AND METHODS

Here, we demonstrate that the CXCR4 antagonist, 4F-benzoyl-TN14003 (BKT140), but not AMD3100, exhibits a CXCR4-dependent preferential cytotoxicity toward malignant cells of hematopoietic origin. BKT140 significantly and preferentially stimulated multiple myeloma apoptotic cell death. BKT140 treatment induced morphological changes, phosphatidylserine externalization, decreased mitochondrial membrane potential, caspase-3 activation, sub-G1 arrest, and DNA double-stranded breaks.

RESULTS

In vivo, subcutaneous injections of BKT140 significantly reduced, in a dose-dependent manner, the growth of human acute myeloid leukemia and multiple myeloma xenografts. Tumors from animals treated with BKT140 were smaller in size and weights, had larger necrotic areas and high apoptotic scores.

CONCLUSIONS

Taken together, these results suggest a potential therapeutic use for BKT140 in multiple myeloma and leukemia patients.

PET of tumor CXCR4 expression with 4-18F-T140

Expression of the chemokine receptor CXCR4 by cancers has been shown to correlate with tumor aggressiveness and poor prognosis and may also contribute to metastatic seeding of organs that express its ligand SDF-1. However, fully optimized PET agents for determining CXCR4 expression by tumor cells in vivo are not yet available. This study aims to develop a stable, (18)F-labeled peptide that enables in vivo quantification of CXCR4 in cancer.

METHODS

4-F-benzoyl-TN14003 (4-F-T140), a short peptide antagonist of CXCR4 with 1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl protecting groups on the ε-amino groups of the lysine residues, was labeled with (18)F-fluoride via N-succinimidyl-4-(18)F-fluorobenzoate conjugation, followed by deprotection to give 4-(18)F-T140 that was exclusively labeled on the α-amine at the N terminus. Cell binding, migration, biodistribution, and small-animal PET studies of 4-(18)F-T140 were performed.

RESULTS

4-F-T140 was radiolabeled by coupling with N-succinimidyl-4-(18)F-fluorobenzoate, with an overall decay-corrected radiochemical yield of 15% ± 5% calculated from the start of synthesis. The mean measured specific activity (±SD) was 7 ± 2 GBq/μmol (0.19 ± 0.05 Ci/μmol), and radiochemical purity was greater than 99%. 4-(18)F-T140 was found to bind specifically to red blood cells in vitro and in vivo. The binding of 4-(18)F-T140 to red blood cells was blocked with a small amount of cold 4-F-T140, which led to higher uptake of 4-(18)F-T140 by Chinese hamster ovarian (CHO)-CXCR4 tumors. Biodistribution experiments at 3 h after injection with the addition of 10 μg of cold 4-F-T140 showed a 3.03 ± 0.31 percentage injected dose per gram uptake in CHO-CXCR4 tumors, with a tumor-to-blood ratio of 27.1 ± 8.7 and a tumor-to-muscle ratio of 21.6 ± 7.1. PET studies demonstrated clear visualization of CXCR4-transfected, but not CXCR4-negative, CHO tumors.

CONCLUSION

4-(18)F-T140 can be used as a PET tracer to image tumor expression of CXCR4, with a high tumor-to-background ratio. The knowledge of whether tumors express or do not express CXCR4 might be beneficial in determining appropriate treatment and monitoring.

Focal liver necrosis appears early after partial hepatectomy and is dependent on T cells and antigen delivery from the gut

INTRODUCTION

Progressive liver failure may develop following removal of a large part of the liver or transplantation of a small for size liver graft. The pathophysiology of this clinical syndrome is only partially understood.

METHODS

We assessed liver damage and hepatocyte 5-bromo-2'-deoxyuridine (BrdU) incorporation following partial hepatectomy (PH) in C57BL/6, BALB/C and immune-deficient mice. Hepatic lymphocyte subpopulations were characterized. Lipopolysaccharide (LPS) treatment and bowel decontamination determined the role of gut antigens.

RESULTS

Discrete, round necrotic lesions were observed as early as 2 h following 70%, but not 30% PH. In immune competent mice the extent of hepatocyte necrosis inversely correlated with BrdU incorporation. T, natural killer and natural killer T cells were recruited to the liver early after PH; however, only T-cell depletion abrogated hepatic necrosis. Hepatic injury was significantly reduced in non-obese diabetic/severe combined immunodeficient mice undergoing PH, while BrdU incorporation was not affected. Liver injury was augmented by LPS injection and reduced by gut decontamination.

CONCLUSIONS

A distinct pattern of early focal hepatic necrosis is observed following extensive PH in mice. T cells infiltrating the liver immediately after PH and gut-derived antigens are indispensable for the observed liver necrosis and may thus provide therapeutic targets to ameliorate liver damage following PH.

Interaction between CXCR4 and CCL20 pathways regulates tumor growth

The chemokine receptor CXCR4 and its ligand CXCL12 is overexpressed in the majority of tumors and is critically involved in the development and metastasis of these tumors. CXCR4 is expressed in malignant tumor cells whereas its ligand SDF-1 (CXCL12) is expressed mainly by cancer associated fibroblasts (CAF). Similarly to CXCR4, the chemokine CCL20 is overexpressed in variety of tumors; however its role and regulation in tumors is not fully clear. Here, we show that the chemokine receptor CXCR4 stimulates the production of the chemokine CCL20 and that CCL20 stimulates the proliferation and adhesion to collagen of various tumor cells. Furthermore, overexpression of CCL20 in tumor cells promotes growth and adhesion in vitro and increased tumor growth and invasiveness in vivo. Moreover, neutralizing antibodies to CCL20 inhibit the in vivo growth of tumors that either overexpress CXCR4 or CCL20 or naturally express CCL20. These results reveal a role for CCL20 in CXCR4-dependent and -independent tumor growth and suggest a therapeutic potential for CCL20 and CCR6 antagonists in the treatment of CXCR4- and CCL20-dependent malignancies.

64Cu-AMD3100--a novel imaging agent for targeting chemokine receptor CXCR4

CXCR4 is a chemokine receptor which has been shown to be exploited by various tumors for increased survival, invasion, and homing to target organs. We developed a one step radiosynthesis for labeling the CXCR4-specific antagonist AMD3100 with Cu-64 to produce (64)Cu-AMD3100 with a specific activity of 11.28Ci/ micromol (417GBq/ micromol) at the end of radiosynthesis. Incorporation of Cu(II) ion into AMD3100 did not change its ability to inhibit cellular migration in response to the (only) CXCR4 ligand, SDF-1/CXCL12. (64)Cu-AMD3100 binding affinity to CXCR4 was found to be 62.7 microM. Biodistribution of (64)Cu-AMD3100 showed accumulation in CXCR4-expressing organs and tissues, a renal clearance pathway, and an anomalous specific accumulation in the liver. We conclude that (64)Cu-AMD3100 exhibits promise as a potential PET imaging agent for visualization of CXCR4-positive tumors and metastases and might be used to guide and monitor anti-CXCR4 tumor therapy.

Chemokines in hepatitis C virus infection: Pathogenesis, prognosis and therapeutics

Hepatitis C virus infection and its associated liver inflammatory disease is a major global health problem affecting over 170 million people worldwide. Following viral infection, multiple pro-inflammatory mediators contribute to recruitment of immune cells to the liver and to the generation of an anti-viral immune response. However, when this vigorous immune response fails to eliminate the virus, chronic infection is established. This in turn, results in an ongoing process of inflammation, regeneration and fibrosis that in many cases leads to the development of cirrhosis and of hepatocellular carcinoma. Multiple recent publications mark chemokines and their receptors as key players in leukocyte recirculation through the inflamed liver. Furthermore, chemokines may also be involved in liver regeneration, fibrosis, and in malignant transformation, which is induced by the persistence of inflammation. Accumulating data indicates that distinct chemokines and chemokine receptors may be associated with different stages of the chronic hepatitis C virus infection-associated liver disease. Multiple small molecules and peptide antagonizing chemokines and their receptors are in advanced phase 3 and phase 2 clinical trials. In the near future, such drugs are expected to enter clinical use raising the question whether they may be applicable for the treatment of chronic viral infection-associated liver disease. In this review, recent advances in understanding the role of chemokines and their receptors in the pathogenesis of chronic viral infection-associated liver disease are presented. Furthermore, the clinical implications of these novel findings, which mark chemokines as prognostic markers and therapeutic targets for immune-modulation during chronic liver viral infection, are documented.

Enhanced unique pattern of hematopoietic cell mobilization induced by the CXCR4 antagonist 4F-benzoyl-TN14003

An increase in the number of stem cells in blood following mobilization is required to enhance engraftment after high-dose chemotherapy and improve transplantation outcome. Therefore, an approach that improves stem cell mobilization is essential. The interaction between CXCL12 and its receptor, CXCR4, is involved in the retention of stem cells in the bone marrow. Therefore, blocking CXCR4 may result in mobilization of hematopoietic progenitor and stem cells. We have found that the CXCR4 antagonist known as 4F-benzoyl-TN14003 (T-140) can induce mobilization of hematopoietic stem cells and progenitors within a few hours post-treatment in a dose-dependent manner. Furthermore, although T-140 can also increase the number of white blood cells (WBC) in blood, including monocytes, B cells, and T cells, it had no effect on mobilizing natural killer cells. T-140 was found to efficiently synergize with granulocyte colony-stimulating factor (G-CSF) in its ability to mobilize WBC and progenitors, as well as to induce a 660-fold increase in the number of erythroblasts in peripheral blood. Comparison between the CXCR4 antagonists T-140 and AMD3100 showed that T-140 with or without G-CSF was significantly more potent in its ability to mobilize hematopoietic stem cells and progenitors into blood. These results demonstrate that different CXCR4 antagonists may have different therapeutic potentials.

CD4+CXCR4highCD69+ T Cells Accumulate in Lung Adenocarcinoma

The chemokine receptor CXCR4 is involved in the growth and metastasis of tumor cells. However, the expression of its ligand, the chemokine CXCL12, in tumors and its role in regulating the accumulation of immune cells within the tumors is not clear. Using ELISA and immunohistochemistry we found that CXCL12 is expressed in the majority of nonsmall cell lung cancer tissue sections obtained from stage IA to IIB nonsmall cell lung cancer patients undergoing operation. Histopathologic examination of these sections indicated that high CXCL12 expression correlated with increased tumor inflammation. In addition, disease recurrence rates in a subgroup of adenocarcinoma patients showed a tendency to correlate with high CXCL12 expression in the tumor. Isolation of adenocarcinoma-infiltrating immune cells demonstrated an increase in the percentage of CD4+CD69+CXCR4+ T cells as compared with normal lung tissue. About 30% of these cells expressed the regulatory T cell markers CD25high and FoxP3. The percentage of CD8 T cells within the tumor did not change, however; the percentage of NK and NK T cells was significantly reduced. In correlation with CXCR4 expression, CD4 T cells showed increased migration in response to CXCL12 compared with CD8 T cells and NK cells. Overall, these observations suggest that CXCL12 expression may influence tumor progression by shaping the immune cell population infiltrating lung adenocarcinoma tumors.

IFN-gamma acts on T cells to induce NK cell mobilization and accumulation in target organs

The mechanism(s) that regulates NK cell mobilization and the significance of this process to NK cell activity are unknown. After Con A-induced hepatitis, NK cells are mobilized from the spleen and bone marrow into the periphery in an IFN-gamma-dependent fashion. Intraperitoneal administration of IFN-gamma stimulates the mobilization of NK cells into the circulation, but not their cell death or proliferation. Increased number of circulating NK cells was coupled with their accumulation in the peritoneum, liver, and tumor-bearing lung tissue. Furthermore, increased number of NK cells in the lung reduced metastasis of Lewis lung carcinoma cells (3LL cell line) resulting in significantly extended NK-dependent survival. Mobilization of NK cells was specific and required the presence of T cells. Moreover, mobilization and migration of spleen NK cells in response to IFN-gamma treatment is dependent on the chemokine receptor CXCR3. Mechanistic insights regarding the role of IFN-gamma in the regulation of NK cell mobilization and their accumulation at sites of tumor metastasis may lead to the development of novel immunotherapy for cancer.

Involvement of the CXCL12/CXCR4 pathway in the recovery of skin following burns

Burn wound healing is a complex process consisting of an inflammatory phase, the formation of granulation tissue, and remodeling. The role of the CXCL12/CXCR4 pathway in the recovery of skin following burns is unknown. We found that CXCL12 is similarly expressed in human, swine, and rat skin by pericyte and endothelial cells, fibrous sheet, fibroblasts, and axons. Following burns, the levels of CXCL12 were markedly increased in human burn blister fluids. One day after injury, there was a gradual increase in the expression of CXCL12 in the hair follicles and in blood vessel endothelium surrounding the burn. Three to 11 days following burns, an increased number of fibroblasts expressing CXCL12 were observed in the recovering dermis of rat, swine, and human skin. In contrast to CXCL12, CXCR4 expression was detected in proliferating epithelial cells as well as in eosinophils and mononuclear cells infiltrating the skin. In vitro, CXCL12 was expressed by primary human skin fibroblasts, but not by keratinocytes, and was stimulated by wounding a confluent cell layer of these fibroblasts. Blocking the CXCR4/CXCL12 axis resulted in the significant reduction in eosinophil accumulation in the dermis and improved epithelialization. Thus, blocking CXCR4/CXCL12 interaction may significantly improve skin recovery after burns.