[(18)F]FHBG PET/CT Imaging of CD34-TK75 Transduced Donor T Cells in Relapsed Allogeneic Stem Cell Transplant Patients: Safety and Feasibility.

Described herein is a first-in-man attempt to both genetically modify T cells with an imagable suicide gene and track these transduced donor T cells in allogeneic stem cell transplantation recipients using noninvasive positron emission tomography/computerized tomography (PET/CT) imaging. A suicide gene encoding a human CD34-Herpes Simplex Virus-1-thymidine kinase (CD34-TK75) fusion enabled enrichment of retrovirally transduced T cells (TdT), control of graft-versus-host disease and imaging of TdT migration and expansion in vivo in mice and man. Analysis confirmed that CD34-TK75-enriched TdT contained no replication competent γ-retrovirus, were sensitive to ganciclovir, and displayed characteristic retroviral insertion sites (by targeted sequencing). Affinity-purified CD34-TK75(+)-selected donor T cells (1.0-13 × 10(5))/kg were infused into eight patients who relapsed after allogeneic stem cell transplantation. Six patients also were administered 9-[4-((18)F)fluoro-3-hydroxymethyl-butyl]guanine ([(18)F]FHBG) to specifically track the genetically modified donor T cells by PET/CT at several time points after infusion. All patients were assessed for graft-versus-host disease, response to ganciclovir, circulating TdT cells (using both quantitative polymerase chain reaction and [(18)F]FHBG PET/CT imaging), TdT cell clonal expansion, and immune response to the TdT. This phase 1 trial demonstrated that genetically modified T cells and [(18)F]FHBG can be safely infused in patients with relapsed hematologic malignancies after allogeneic stem cell transplantation.

IFNγR signaling mediates alloreactive T-cell trafficking and GVHD.

The clinical goal of allogeneic hematopoietic stem cell transplantation (allo-HSCT) is to minimize GVHD while maintaining GvL. Here, we show that interferon γ receptor-deficient (IFNγR(-/-)) allogeneic Tconv, which possess normal alloreactivity and cytotoxicity, induce significantly less GVHD than wild-type (WT) Tconv. This effect is mediated by altered trafficking of IFNγR(-/-) Tconv to GVHD target organs, especially the gastrointestinal (GI) tract. We show that the chemokine receptor CXCR3 is induced via IFNγR-mediated signaling and partially contributes to the trafficking of WT Tconv to GVHD target organs. Indeed, CXCR3(-/-) Tconv recapitulate the reduced GVHD potential of IFNγR(-/-) Tconv in a minor-mismatched GVHD model. Most importantly, IFNγR(-/-) (and CXCR3(-/-)) Tconv mediate a robust and beneficial GvL effect. In addition, we show that IFNγR(-/-) regulatory T cells (Tregs) are fully suppressive in vitro although defective in suppressor function in vivo and that WT Tregs suppress GVHD in vivo only when allogeneic Tconv produce interferon γ (IFNγ), suggesting that the IFNγR signaling pathway is the major mechanism for both Tregs and Tconv to migrate to GVHD target organs. Finally, pharmacologic inhibition of IFNγR signaling with inhibitors of JAK1/JAK2, which are mediators of IFNγR signaling, results in the decreased expression of CXCR3 and reduced GVHD and improved survival after allo-HSCT and this effect is mediated by altered trafficking of Tconv to GVHD target organs.

Breast Cancer Mutations HER2V777L and PIK3CAH1047R Activate the p21-CDK4/6-Cyclin D1 Axis to Drive Tumorigenesis and Drug Resistance.

In metastatic breast cancer, HER2-activating mutations frequently co-occur with mutations in PIK3CA, TP53, or CDH1. Of these co-occurring mutations, HER2 and PIK3CA are the most commonly comutated gene pair, with approximately 40% of HER2-mutated breast cancers also having activating mutations in PIK3CA. To study the effects of co-occurring HER2 and PIK3CA mutations, we generated genetically engineered mice with the HER2V777L; PIK3CAH1047R transgenes (HP mice) and studied the resulting breast cancers both in vivo as well as ex vivo using cancer organoids. HP breast cancers showed accelerated tumor formation in vivo and increased invasion and migration in in vitro assays. HP breast cancer cells were resistant to the pan-HER tyrosine kinase inhibitor, neratinib, but were effectively treated with neratinib plus the HER2-targeted antibody-drug conjugate trastuzumab deruxtecan. Proteomic and RNA-seq analysis of HP breast cancers identified increased gene expression of cyclin D1 and p21WAF1/Cip1 and changes in cell-cycle markers. Combining neratinib with CDK4/6 inhibitors was another effective strategy for treating HP breast cancers, with neratinib plus palbociclib showing a statistically significant reduction in development of mouse HP tumors as compared to either drug alone. The efficacy of both the neratinib plus trastuzumab deruxtecan and neratinib plus palbociclib combinations was validated using a human breast cancer patient-derived xenograft with very similar HER2 and PIK3CA mutations to the HP mice. Further, these two drug combinations effectively treated spontaneous lung metastasis in syngeneic mice transplanted with HP breast cancer organoids. This study provides valuable preclinical data to support the ongoing phase 1 clinical trials of these drug combinations in breast cancer. SIGNIFICANCE: In HER2-mutated breast cancer, PIK3CA mutation activates p21-CDK4/6-cyclin D1 signaling to drive resistance to HER2-targeted therapies, which can be overcome using CDK4/6 inhibitors.

In vivo administration of hypomethylating agents mitigate graft-versus-host disease without sacrificing graft-versus-leukemia.

Regulatory T cells (Tregs) suppress graft-versus-host disease (GVHD) while preserving a beneficial graft-versus-leukemia (GVL) effect. Thus, their use in allogeneic stem cell transplantation (SCT) provides a promising strategy to treat GVHD. However, 3 obstacles prevent their routine use in human clinical trials: (1) low circulating number of Tregs in peripheral blood, (2) loss of suppressor function after in vitro expansion, and (3) lack of Treg-specific surface markers necessary for efficient purification. FOXP3 is exclusively expressed in Tregs and forced expression in CD4(+)CD25(-) T cells can convert these non-Tregs into Tregs with functional suppressor function. Here, we show that the FDA-approved hypomethylating agents, decitabine (Dec) and azacitidine (AzaC), induce FOXP3 expression in CD4(+)CD25(-) T cells both in vitro and in vivo. Their suppressor function is dependent on direct contact, partially dependent on perforin 1 (Prf1), but independent of granzyme B (GzmB), and surprisingly, Foxp3. Independence of Foxp3 suggests that genes responsible for the suppressor function are also regulated by DNA methylation. We have identified 48 candidate genes for future studies. Finally, AzaC treatment of mice that received a transplant of major histocompatibility complex mismatched allogeneic bone marrow and T cells mitigates GVHD while preserving GVL by peripheral conversion of alloreactive effector T cells into FOXP3(+) Tregs and epigenetic modulation of genes downstream of Foxp3 required for the suppressor function of Tregs.

CS1 CAR-T targeting the distal domain of CS1 (SLAMF7) shows efficacy in high tumor burden myeloma model despite fratricide of CD8+CS1 expressing CAR-T cells.

Despite improvement in treatment options for myeloma patients, including targeted immunotherapies, multiple myeloma remains a mostly incurable malignancy. High CS1 (SLAMF7) expression on myeloma cells and limited expression on normal cells makes it a promising target for CAR-T therapy. The CS1 protein has two extracellular domains - the distal Variable (V) domain and the proximal Constant 2 (C2) domain. We generated and tested CS1-CAR-T targeting the V domain of CS1 (Luc90-CS1-CAR-T) and demonstrated anti-myeloma killing in vitro and in vivo using two mouse models. Since fratricide of CD8 + cells occurred during production, we generated fratricide resistant CS1 deficient Luc90- CS1- CAR-T (ΔCS1-Luc90- CS1- CAR-T). This led to protection of CD8 + cells in the CAR-T cultures, but had no impact on efficacy. Our data demonstrate targeting the distal V domain of CS1 could be an effective CAR-T treatment for myeloma patients and deletion of CS1 in clinical production did not provide an added benefit using in vivo immunodeficient NSG preclinical models.

Chemosensitization of acute myeloid leukemia (AML) following mobilization by the CXCR4 antagonist AMD3100.

The CXCR4-SDF-1 axis plays a central role in the trafficking and retention of normal and malignant stem cells in the bone marrow (BM) microenvironment. Here, we used a mouse model of acute promyelocytic leukemia (APL) and a small molecule competitive antagonist of CXCR4, AMD3100, to examine the interaction of mouse APL cells with the BM microenvironment. APL cells from a murine cathepsin G-PML-RARalpha knockin mouse were genetically modified with firefly luciferase (APL(luc)) to allow tracking by bioluminescence imaging. Coculture of APL(luc) cells with M2-10B4 stromal cells protected the leukemia cells from chemotherapy-induced apoptosis in vitro. Upon injection into syngeneic recipients, APL(luc) cells rapidly migrated to the BM followed by egress to the spleen then to the peripheral blood with death due to leukostasis by day 15. Administration of AMD3100 to leukemic mice induced a 1.6-fold increase in total leukocytes and a 9-fold increase of circulating APL blast counts, which peak at 3 hours and return to baseline by 12 hours. Treatment of leukemic mice with chemotherapy plus AMD3100 resulted in decreased tumor burden and improved overall survival compared with mice treated with chemotherapy alone. These studies provide a proof-of-principle for directing therapy to the critical tethers that promote AML-niche interactions.

Dissection of platelet and myeloid cell defects by conditional targeting of the beta3-integrin subunit.

The purpose of this work was to determine platelet and myeloid cell-specific requirements for beta3-containing integrins in hemostasis, bone resorption, and tumor growth. LoxP-flanked mice were generated to study the conditional deletion of beta3-integrin in platelets [knockout in platelets (KOP)] and myeloid cells [knockout in myeloid (KOM)]. Using the beta3KOP and beta3KOM strains of mice, we studied the role of beta3-integrin in hemostasis, bone resorption, and subcutaneous tumor growth. Tissue-specific deletion of platelet beta3-integrins in beta3KOP mice did not affect bone mass but resulted in a severe bleeding phenotype. No growth difference of tumor xenografts or in neoangiogenesis were found in beta3KOP mice, in contrast to the defects observed in germline beta3(-/-) mice. Conditional deletion of myeloid beta3-integrins in beta3KOM mice resulted in osteopetrosis but had no effect on hemostasis or mortality. Tumor growth in beta3KOM mice was increased and accompanied by decreased macrophage infiltration, without increase in blood vessel number. Platelet beta3-integrin deficiency was sufficient to disrupt hemostasis but had no effect on bone mass or tumor growth. Myeloid-specific beta3-integrin deletion was sufficient to perturb bone mass and enhance tumor growth due to reduced macrophage infiltration in the tumors. These results suggest that beta3-integrins have cell-specific roles in complex biological processes.-Morgan, E. A., Schneider, J. G., Baroni, T. E., Uluçkan, O., Heller, E., Hurchla, M. A., Deng, H., Floyd, D., Berdy, A., Prior, J. L., Piwnica-Worms, D., Teitelbaum, S. L., Ross, F. P., Weilbaecher, K. N. Dissection of platelet and myeloid cell defects by conditional targeting of the beta3-integrin subunit.

Generation of a highly inducible Gal4-->Fluc universal reporter mouse for in vivo bioluminescence imaging.

Full understanding of the functional complexity of the protein interactome requires mapping of biomolecular complexes within the cellular environment over biologically relevant time scales. New approaches to imaging interacting protein partners in vivo will allow the study of functional proteomics of human biology and disease within the context of living animals. Herein, we describe a universal transgenic reporter mouse strain that expresses firefly luciferase (Fluc) under the regulatory control of a concatenated Gal4 promoter (Tg(G4F(+/-))). Using an adenovirus to deliver a fused binding-domain-activator chimera (Gal4BD-VP16), induction of bioluminescence in Tg(G4F(+/-)) tissues of up to 4 orders of magnitude was observed in fibroblasts, liver, respiratory epithelia, muscle, and brain. The Tg(G4F(+/-)) reporter strain allowed noninvasive detection of viral infectivity, duration of the infection as well as viral clearance in various tissues in vivo. To demonstrate protein-protein interactions in live mice, the well characterized interaction between tumor suppressor p53 (fused to Gal4BD) and large T antigen (TAg) (fused to VP16) was visualized in vivo by using a two-hybrid strategy. Hepatocytes of Tg(G4F(+/-)) mice transfected with p53/TAg demonstrated 48-fold greater induction of Fluc expression in vivo than noninteracting pairs. Furthermore, to demonstrate the feasibility of monitoring experimental therapy with siRNA in vivo, targeted knockdown of p53 resulted in markedly reduced light output, whereas use of a control siRNA had no effect on protein interaction-dependent induction of Fluc. Thus, this highly inducible Gal4-->Fluc conditional reporter strain should facilitate imaging studies of protein interactions, signaling cascades, viral dissemination, and therapy within the physiological context of the whole animal.

Calcium carbonate nanoparticles stimulate tumor metabolic reprogramming and modulate tumor metastasis.

AIM: CaCO3 nanoparticles (nano-CaCO3) can neutralize the acidic pHe of solid tumors, but the lack of intrinsic imaging signal precludes noninvasive monitoring of pH-perturbation in tumor microenvironment. We aim to develop a theranostic version of nano-CaCO3 to noninvasively monitor pH modulation and subsequent tumor response. MATERIALS & METHODS: We synthesized ferromagnetic core coated with CaCO3 (magnetite CaCO3). Magnetic resonance imaging (MRI) was used to determine the biodistribution and pH modulation using murine fibrosarcoma and breast cancer models. RESULTS: Magnetite CaCO3-MRI imaging showed that nano-CaCO3 rapidly raised tumor pHe, followed by excessive tumor-associated acid production after its clearance. Continuous nano-CaCO3 infusion could inhibit metastasis. CONCLUSION: Nano-CaCO3 exposure induces tumor metabolic reprogramming that could account for the failure of previous intermittent pH-modulation strategies to achieve sustainable therapeutic effect.

APT102, a novel adpase, cooperates with aspirin to disrupt bone metastasis in mice.

Platelets contribute to the development of metastasis, the most common cause of mortality in cancer patients, but the precise role that anti-platelet drugs play in cancer treatment is not defined. Metastatic tumor cells can produce platelet alphaIIb beta3 activators, such as ADP and thromboxane A(2) (TXA(2)). Inhibitors of platelet beta3 integrins decrease bone metastases in mice but are associated with significant bleeding. We examined the role of a novel soluble apyrase/ADPase, APT102, and an inhibitor of TXA(2) synthesis, acetylsalicylic acid (aspirin or ASA), in mouse models of experimental bone metastases. We found that treatment with ASA and APT102 in combination (ASA + APT102), but not either drug alone, significantly decreased breast cancer and melanoma bone metastases in mice with fewer bleeding complications than observed with alphaIIb beta3 inhibition. ASA + APT102 diminished tumor cell induced platelet aggregation but did not directly alter tumor cell viability. Notably, APT102 + ASA treatment did not affect initial tumor cell distribution and similar results were observed in beta3-/- mice. These results show that treatment with ASA + APT102 decreases bone metastases without significant bleeding complications. Anti-platelet drugs such as ASA + APT102 could be valuable experimental tools for studying the role of platelet activation in metastasis as well as a therapeutic option for the prevention of bone metastases.

P-glycoprotein deficiency at the blood-brain barrier increases amyloid-beta deposition in an Alzheimer disease mouse model.

Accumulation of amyloid-beta (Abeta) within extracellular spaces of the brain is a hallmark of Alzheimer disease (AD). In sporadic, late-onset AD, there is little evidence for increased Abeta production, suggesting that decreased elimination from the brain may contribute to elevated levels of Abeta and plaque formation. Efflux transport of Abeta across the blood-brain barrier (BBB) contributes to Abeta removal from the brain. P-glycoprotein (Pgp) is highly expressed on the luminal surface of brain capillary endothelial cells and contributes to the BBB. In Pgp-null mice, we show that [I]Abeta40 and [I]Abeta42 microinjected into the CNS clear at half the rate that they do in WT mice. When amyloid precursor protein-transgenic (APP-transgenic) mice were administered a Pgp inhibitor, Abeta levels within the brain interstitial fluid significantly increased within hours of treatment. Furthermore, APP-transgenic, Pgp-null mice had increased levels of brain Abeta and enhanced Abeta deposition compared with APP-transgenic, Pgp WT mice. These data establish a direct link between Pgp and Abeta metabolism in vivo and suggest that Pgp activity at the BBB could affect risk for developing AD as well as provide a novel diagnostic and therapeutic target.

Factors affecting human T cell engraftment, trafficking, and associated xenogeneic graft-vs-host disease in NOD/SCID beta2mnull mice.

OBJECTIVE: Graft-vs-host disease (GVHD) is the major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Models of immunodeficient mice that consistently and efficiently reconstitute with xenoreactive human T cells would be a valuable tool for the in vivo study of GVHD, as well as other human immune responses. MATERIALS AND METHODS: We developed a consistent and sensitive model of human GVHD by retro-orbitally injecting purified human T cells into sublethally irradiated nonobese diabetic/severe combined immunodeficient (NOD/SCID)-beta2m(null) recipients. In addition, we characterized for the first time the trafficking patterns and expansion profiles of xenoreactive human T cells in NOD/SCID-beta2m(null) recipients using in vivo bioluminescence imaging. RESULTS: All NOD/SCID-beta2m(null) mice conditioned with 300 cGy total body irradiation and injected with 1 x 10(7) human T cells exhibited human T-cell engraftment, activation, and expansion, with infiltration of multiple target tissues and a subsequent >20% loss of pretransplantation body weight. Importantly, histological examination of the GVHD target tissues revealed changes consistent with human GVHD. Furthermore, we also showed by in vivo bioluminescence imaging that development of lethal GVHD in the NOD/SCID-beta2m(null) recipients was dependent upon the initial retention and early expansion of human T cells in the retro-orbital sinus cavity. CONCLUSION: Our NOD/SCID-beta2m(null) mouse model provides a system to study the pathophysiology of acute GVHD induced by human T cells and aids in development of more effective therapies for human GVHD.

An "off-the-shelf" fratricide-resistant CAR-T for the treatment of T cell hematologic malignancies.

T cell malignancies represent a group of hematologic cancers with high rates of relapse and mortality in patients for whom no effective targeted therapies exist. The shared expression of target antigens between chimeric antigen receptor (CAR) T cells and malignant T cells has limited the development of CAR-T because of unintended CAR-T fratricide and an inability to harvest sufficient autologous T cells. Here, we describe a fratricide-resistant "off-the-shelf" CAR-T (or UCART7) that targets CD7+ T cell malignancies and, through CRISPR/Cas9 gene editing, lacks both CD7 and T cell receptor alpha chain (TRAC) expression. UCART7 demonstrates efficacy against human T cell acute lymphoblastic leukemia (T-ALL) cell lines and primary T-ALL in vitro and in vivo without the induction of xenogeneic GvHD. Fratricide-resistant, allo-tolerant "off-the-shelf" CAR-T represents a strategy for treatment of relapsed and refractory T-ALL and non-Hodgkin's T cell lymphoma without a requirement for autologous T cells.

Metalloprobes: synthesis, characterization, and potency of a novel gallium(III) complex in human epidermal carcinoma cells.

Multidrug resistance (MDR) mediated by overexpression of the MDR1 gene product, P-glycoprotein (Pgp), represents one of the best characterized barriers to chemotherapeutic treatment in cancer and may be a pivotal factor in progression of Alzheimer's disease (AD). Thus, agents capable of probing Pgp-mediated transport could be beneficial in biomedical imaging. Herein, we synthesized and structurally characterized a gallium(III) complex (5) of the naphthol-Schiff base ligand. The crystal structure revealed octahedral geometry for the metallodrug. Cytotoxicity profiles of 5 were evaluated in KB-3-1 (Pgp-) and KB-8-5 (Pgp+) human epidermal carcinoma cell lines. Compared with an LC(50) (the half-maximal cytotoxic concentration) value of 1.93 microM in drug-sensitive (Pgp-) cells, the gallium(III) complex 5 demonstrated an LC(50) value>100 microM in drug-resistant (Pgp+) cells, thus indicating that 5 was recognized by the Pgp as its substrate, thereby extruded from the cells and sequestered away from their cytotoxic targets. Radiolabeled analogues of 5 could be beneficial in noninvasive imaging of Pgp-mediated transport in vivo.

A new model of multi-visceral and bone metastatic prostate cancer with perivascular niche targeting by a novel endothelial specific adenoviral vector.

While modern therapies for metastatic prostate cancer (PCa) have improved survival they are associated with an increasingly prevalent entity, aggressive variant PCa (AVPCa), lacking androgen receptor (AR) expression, enriched for cancer stem cells (CSCs), and evidencing epithelial-mesenchymal plasticity with a varying extent of neuroendocrine transdifferentiation. Parallel work revealed that endothelial cells (ECs) create a perivascular CSC niche mediated by juxtacrine and membrane tethered signaling. There is increasing interest in pharmacological metastatic niche targeting, however, targeted access has been impossible. Here, we discovered that the Gleason 7 derived, androgen receptor negative, IGR-CaP1 cell line possessed some but not all of the molecular features of AVPCa. Intracardiac injection into NOD/SCID/IL2Rg -/- (NSG) mice produced a completely penetrant bone, liver, adrenal, and brain metastatic phenotype; noninvasively and histologically detectable at 2 weeks, and necessitating sacrifice 4-5 weeks post injection. Bone metastases were osteoblastic, and osteolytic. IGR-CaP1 cells expressed the neuroendocrine marker synaptophysin, near equivalent levels of vimentin and e-cadherin, all of the EMT transcription factors, and activation of NOTCH and WNT pathways. In parallel, we created a new triple-targeted adenoviral vector containing a fiber knob RGD peptide, a hexon mutation, and an EC specific ROBO4 promoter (Ad.RGD.H5/3.ROBO4). This vector was expressed in metastatic microvessels tightly juxtaposed to IGR-CaP1 cells in bone and visceral niches. Thus, the combination of IGR-CaP1 cells and NSG mice produces a completely penetrant metastatic PCa model emulating end-stage human disease. In addition, the metastatic niche access provided by our novel Ad vector could be therapeutically leveraged for future disease control or cure.

Independent circadian oscillations of Period1 in specific brain areas in vivo and in vitro.

Behavioral and physiological circadian rhythms in mammals are controlled by a master pacemaker in the hypothalamic suprachiasmatic nuclei (SCN). Recently, circadian oscillations of hormone secretion, clock gene expression, and electrical activity have been demonstrated in explants of other brain regions. This suggests that some extra-SCN brain regions contain a functional, SCN-independent circadian clock, but in vivo evidence for intrinsic pacemaking is still lacking. We developed a novel method to image bioluminescence in vivo from the main olfactory bulbs (OB) of intact and SCN-lesioned (SCNX) Period1::luciferase rats for 2 d in constant darkness. The OBs expressed circadian rhythms in situ with a reliable twofold increase from day to night, similar to the phase and amplitude of ex vivo rhythms. In vivo cycling persisted for at least 1 month in the absence of the SCN. To assess indirectly in vivo rhythmicity of other brain areas, we measured the phase-dependence of their in vitro rhythms on the time of surgery. Surgery reliably reset the phase of the pineal gland and vascular organ of the lamina terminalis (VOLT) harvested from SCNX rats but had little effect on the phase of the OB. We deduce that the SCN and OB contain self-sustained circadian oscillators, whereas the pineal gland and VOLT are weak oscillators that require input from the SCN to show coordinated circadian rhythms. We conclude that the mammalian brain comprises a diverse set of SCN-dependent and SCN-independent circadian oscillators.

In vivo RNA interference-mediated ablation of MDR1 P-glycoprotein.

Multidrug resistance (MDR) remains a major obstacle to successful chemotherapeutic treatment of cancer and can be caused by overexpression of P-glycoprotein, the MDR1 gene product. To further validate a knockdown approach for circumventing MDR, we developed a P-glycoprotein inhibition strategy using short hairpin RNA interference (shRNAi) and now show efficacy and target specificity in vivo. Two of eight tested shRNAi constructs targeted against human MDR1 mRNA inhibited expression of P-glycoprotein by >90%, whereas control shRNAi had no effect. Ablation of P-glycoprotein in cells stably transduced with retroviral-mediated shRNAi was documented by Western blot and functionally confirmed by increased sensitivity of MDR1-transfected cells toward the cytotoxic drugs vincristine, paclitaxel, and doxorubicin as well as by transport of (99m)Tc-Sestamibi. shRNAi-mediated down-regulation of P-glycoprotein transport activity both in cultured cells and in tumor implants in living animals could be followed by direct noninvasive bioluminescence imaging using the Renilla luciferase fluorophore, coelenterazine, a known P-glycoprotein transport substrate. Furthermore, after somatic gene transfer by hydrodynamic infusion of a MDR1-Firefly luciferase (MDR1-FLuc) fusion construct into mouse liver, the effect of shRNAi delivered in vivo on P-glycoprotein-FLuc protein levels was documented with bioluminescence imaging using d-luciferin. ShRNAi against MDR1 reduced bioluminescence output of the P-glycoprotein-FLuc reporter 4-fold in vivo compared with mice treated with control or scrambled shRNAi. Targeted down-regulation of a somatically transferred P-glycoprotein-eGFP fusion reporter also was observed using fluorescence microscopy. Our results show that shRNAi effectively inhibited MDR1 expression and function in cultured cells, tumor implants and mammalian liver, documenting the feasibility of a knockdown approach to reversing MDR in vivo.

Single photon emission computed tomography and positron emission tomography imaging of multi-drug resistant P-glycoprotein--monitoring a transport activity important in cancer, blood-brain barrier function and Alzheimer's disease.

Overexpression of multi-drug resistant P-glycoprotein (Pgp) remains an important barrier to successful chemotherapy in cancer patients and impacts the pharmacokinetics of many important drugs. Pgp is also expressed on the luminal surface of brain capillary endothelial cells wherein Pgp functionally comprises a major component of the blood-brain barrier by limiting central nervous system penetration of various therapeutic agents. In addition, Pgp in brain capillary endothelial cells removes amyloid-beta from the brain. Several single photon emission computed tomography and positron emission tomography radiopharmaceutical have been shown to be transported by Pgp, thereby enabling the noninvasive interrogation of Pgp-mediated transport activity in vivo. Therefore, molecular imaging of Pgp activity may enable noninvasive dynamic monitoring of multi-drug resistance in cancer, guide therapeutic choices in cancer chemotherapy, and identify transporter deficiencies of the blood-brain barrier in Alzheimer's disease.

Molecular imaging of protein-protein interactions: controlled expression of p53 and large T-antigen fusion proteins in vivo.

Protein-protein interactions control essential steps in signal transduction pathways and other intracellular processes, and assembly of protein complexes modulates and responds to the regulatory events that exist in living animals. We have used microPET and fluorescence imaging to detect interactions between p53 tumor suppressor and large T antigen (TAg) of SV40 virus in a tetracycline-inducible two-hybrid system. To additionally validate this molecular imaging technique, we investigated whether expression of the reporter gene, comprised of a mutant thymidine kinase from herpes simplex virus 1 fused to green fluorescent protein could quantify relative differences in amounts of interacting hybrid proteins. In HeLa cells stably transfected with the reporter gene and interacting (p53-TAg) or noninteracting (p53 and polyoma virus coat protein) pairs of proteins, treatment with doxycycline produced time- and dose-dependent increases in expression of hybrid proteins. Proportional increases in amounts of reporter gene were produced only in cells expressing p53 and TAg. In mice bearing xenografts of these stably transfected HeLa cells, amounts of hybrid proteins were regulated with doxycycline. Both microPET imaging and biodistribution studies showed time- and dose-dependent increases in accumulation of the reporter substrate 9-(4-[(18)F]-fluoro-3-hydroxymethylbutyl)guanine only in p53-TAg tumors. Fluorescence microscopy of excised tumors also showed corresponding changes in expression of the fusion reporter gene in response to binding of p53 and TAg. These data demonstrate that the imaging two-hybrid system responds in a proportional fashion to increasing amounts of interacting proteins in vivo.

CXCR4 regulates growth of both primary and metastatic breast cancer.

The chemokine receptor CXCR4 and its cognate ligand CXCL12 recently have been proposed to regulate the directional trafficking and invasion of breast cancer cells to sites of metastases. However, effects of CXCR4 on the growth of primary breast cancer tumors and established metastases and survival have not been determined. We used stable RNAi to reduce expression of CXCR4 in murine 4T1 cells, a highly metastatic mammary cancer cell line that is a model for stage IV human breast cancer. Using noninvasive bioluminescence and magnetic resonance imaging, we showed that knockdown of CXCR4 significantly limited the growth of orthotopically transplanted breast cancer cells. Mice in which parental 4T1 cells were implanted had progressively enlarging tumors that spontaneously metastasized, and these animals all died from metastatic disease. Remarkably, RNAi of CXCR4 prevented primary tumor formation in some mice, and all mice transplanted with CXCR RNAi cells survived without developing macroscopic metastases. To analyze effects of CXCR4 on metastases to the lung, an organ commonly affected by metastatic breast cancer, we injected tumor cells intravenously and monitored cell growth with bioluminescence imaging. Inhibiting CXCR4 with RNAi, or the specific antagonist AMD3100, substantially delayed the growth of 4T1 cells in the lung, although neither RNAi nor AMD3100 prolonged overall survival in mice with experimental lung metastases. These data indicate that CXCR4 is required to initiate proliferation and/or promote survival of breast cancer cells in vivo and suggest that CXCR4 inhibitors will improve treatment of patients with primary and metastatic breast cancer.