Improved tumor imaging and therapy via i.v. IgG-mediated time-sequential modulation of neonatal Fc receptor.

The long plasma half-life of IgG, while allowing for enhanced tumor uptake of tumor-targeted IgG conjugates, also results in increased background activity and normal-tissue toxicity. Therefore, successful therapeutic uses of conjugated antibodies have been limited to the highly sensitive and readily accessible hematopoietic tumors. We report a therapeutic strategy to beneficially alter the pharmacokinetics of IgG antibodies via pharmacological inhibition of the neonatal Fc receptor (FcRn) using high-dose IgG therapy. IgG-treated mice displayed enhanced blood and whole-body clearance of radioactivity, resulting in better tumor-to-blood image contrast and protection of normal tissue from radiation. Tumor uptake and the resultant therapeutic response was unaltered. Furthermore, we demonstrated the use of this approach for imaging of tumors in humans and discuss its potential applications in cancer imaging and therapy. The ability to reduce the serum persistence of conjugated IgG antibodies after their infusion can enhance their therapeutic index, resulting in improved therapeutic and diagnostic efficacy.

Tumor targeting with antibody-functionalized, radiolabeled carbon nanotubes.

UNLABELLED: Single-walled carbon nanotubes (CNT) are mechanically robust graphene cylinders with a high aspect ratio that are comprised of sp(2)-bonded carbon atoms and possessing highly regular structures with defined periodicity. CNT exhibit unique mechanochemical properties that can be exploited for the development of novel drug delivery platforms. We hypothesized that novel prototype nanostructures consisting of biologics, radionuclides, fluorochromes, and CNT could be synthesized and designed to target tumor cells. METHODS: Tumor-targeting CNT constructs were synthesized from sidewall-functionalized, water-soluble CNT platforms by covalently attaching multiple copies of tumor-specific monoclonal antibodies, radiometal-ion chelates, and fluorescent probes. The constructs were characterized spectroscopically, chromatographically, and electrophoretically. The specific reactivity of these constructs was evaluated in vitro by flow cytometry and cell-based immunoreactivity assays and in vivo using biodistribution in a murine xenograft model of lymphoma. RESULTS: A soluble, reactive CNT platform was used as the starting point to build multifunctional constructs with appended antibody, metal-ion chelate, and fluorescent chromophore moieties to effect specific targeting, to carry and deliver a radiometal-ion, and to report location, respectively. These nanoconstructs were found to be specifically reactive with the human cancer cells they were designed to target in vivo in a model of disseminated human lymphoma and in vitro by flow cytometry and cell-based immunoreactivity assays versus appropriate controls. CONCLUSION: The key achievement in these studies was the selective targeting of tumor in vitro and in vivo by the use of specific antibodies appended to a soluble, nanoscale CNT construct. The ability to specifically target tumor with prototype-radiolabeled or fluorescent-labeled, antibody-appended CNT constructs was encouraging and suggested further investigation of CNT as a novel delivery platform.

Mitigation of radiation nephropathy after internal alpha-particle irradiation of kidneys.

PURPOSE: Internal irradiation of kidneys as a consequence of radioimmunotherapy, radiation accidents, or nuclear terrorism can result in radiation nephropathy. We attempted to modify pharmacologically, the functional and morphologic changes in mouse kidneys after injection with the actinium ((225)Ac) nanogenerator, an in vivo generator of alpha- and beta-particle emitting elements. METHODS AND MATERIALS: The animals were injected with 0.35 muCi of the (225)Ac nanogenerator, which delivers a dose of 27.6 Gy to the kidneys. Then, they were randomized to receive captopril (angiotensin-converting enzyme inhibitor), L-158,809 (angiotensin II receptor-1 blocker), spironolactone (aldosterone receptor antagonist), or a placebo. RESULTS: Forty weeks after the (225)Ac injection, the placebo-control mice showed a significant increase in blood urea nitrogen (BUN) (87.6 +/- 6.9 mg/dL), dilated Bowman spaces, and tubulolysis with basement membrane thickening. Captopril treatment accentuated the functional (BUN 119.0 +/- 4.0 mg/dL; p <0.01 vs. placebo controls) and histopathologic damage. In contrast, L-158,809 offered moderate protection (BUN 66.6 +/- 3.9 mg/dL; p = 0.02 vs. placebo controls). Spironolactone treatment, however, significantly prevented the development of histopathologic and functional changes (BUN 31.2 +/- 2.5 mg/dL; p <0.001 vs. placebo controls). CONCLUSIONS: Low-dose spironolactone and, to a lesser extent, angiotensin receptor-1 blockade can offer renal protection in a mouse model of internal alpha-particle irradiation.

Natural killer cells license dendritic cell cross-presentation of B lymphoma cell--associated antigens.

PURPOSE: Presentation of exogenous antigen by MHC class I molecules, or cross-presentation, is a property of dendritic cells, which is considered crucial for the priming of cytotoxic T-cell response to tumor antigens. However, the precise mechanisms of this process are not fully understood. EXPERIMENTAL DESIGN AND RESULTS: We show here in a human in vitro system, using B lymphoma cells as a tumor model, that the cross-presentation of cell-associated antigens to T cells by dendritic cells requires "help" from natural killer cells. When autologous dendritic cells that had taken up apoptotic B lymphoma cells and induced to a fully mature state were used to stimulate nonadherent cells of peripheral blood mononuclear cells from healthy donors, they induced strong cytotoxicity against B lymphoma cells in a HLA-A0201-restricted manner. The cells failed to induce cytotoxicity, however, when purified T cells were used as effector cells. Depletion of CD56+ cells, but not CD14+ or CD19+ cells, abrogated the cytotoxicity of nonadherent cells, showing that the help was provided by natural killer cells. Further, when natural killer cells were present in the cultures, a strong and persistent production of interleukin-18, but not interleukin-12 and interleukin-15, was observed. Blocking interleukin-18 significantly reduced the cytotoxicity of nonadherent cells against B lymphoma cells. CONCLUSIONS: These results suggest that capture of tumor cells and a full maturation status of dendritic cells are not sufficient to cross-prime CD8 T cells. Effective cross-priming requires further activation of dendritic cells by natural killer cells and an abundant production of interleukin-18, which, along with other yet undefined mechanisms, contribute to the generation of CTL response against B-cell lymphoma.

Renal tubulointerstitial changes after internal irradiation with alpha-particle-emitting actinium daughters.

The effect of external gamma irradiation on the kidneys is well described. However, the mechanisms of radiation nephropathy as a consequence of targeted radionuclide therapies are poorly understood. The functional and morphologic changes were studied chronologically (from 10 to 40 wk) in mouse kidneys after injection with an actinium-225 (225Ac) nanogenerator, a molecular-sized, antibody-targeted, in vivo generator of alpha-particle-emitting elements. Renal irradiation from free, radioactive daughters of 225Ac led to time-dependent reduction in renal function manifesting as increase in blood urea nitrogen. The histopathologic changes corresponded with the decline in renal function. Glomerular, tubular, and endothelial cell nuclear pleomorphism and focal tubular cell injury, lysis, and karyorrhexis were observed as early as 10 wk. Progressive thinning of the cortex as a result of widespread tubulolysis, collapsed tubules, glomerular crowding, decrease in glomerular cellularity, interstitial inflammation, and an elevated juxtaglomerular cell count were noted at 20 to 30 wk after treatment. By 35 to 40 wk, regeneration of simplified tubules with tubular atrophy and loss with focal, mild interstitial fibrosis had occurred. A lower juxtaglomerular cell count with focal cytoplasmic vacuolization, suggesting increased degranulation, was also observed in this period. A focal increase in tubular and interstitial cell TGF-beta1 expression starting at 20 wk, peaking at 25 wk, and later declining in intensity with mild increase in the extracellular matrix deposition was noticed. These findings suggest that internally delivered alpha-particle irradiation-induced loss of tubular epithelial cells triggers a chain of adaptive changes that result in progressive renal parenchymal damage accompanied by a loss of renal function. These findings are dissimilar to those seen after gamma or beta irradiation of kidneys.

Efforts to control the errant products of a targeted in vivo generator.

Alpha-particle immunotherapy by targeted alpha-emitters or alpha-emitting isotope generators is a novel form of extraordinarily potent cancer therapy. A major impediment to the clinical use of targeted actinium-225 (225Ac) in vivo generators may be the radiotoxicity of the systemically released daughter radionuclides. The daughters, especially bismuth-213 (213Bi), tend to accumulate in the kidneys. We tested the efficacy of various pharmacologic agents and the effect of tumor burden in altering the pharmacokinetics of the 225Ac daughters to modify their renal uptake. Pharmacologic treatments in animals were started before i.v. administration of the HuM195-225Ac generator. 225Ac, francium-221 (221Fr), and 213Bi biodistributions were calculated in each animal at different time points after 225Ac generator injection. Oral metal chelation with 2,3-dimercapto-1-propanesulfonic acid (DMPS) or meso-2,3-dimercaptosuccinic acid (DMSA) caused a significant reduction (P < 0.0001) in the renal 213Bi uptake; however, DMPS was more effective than DMSA (P < 0.001). The results with DMPS were also confirmed in a monkey model. The renal 213Bi and 221Fr activities were significantly reduced by furosemide and chlorothiazide treatment (P < 0.0001). The effect on renal 213Bi activity was further enhanced by the combination of DMPS with either chlorothiazide or furosemide (P < 0.0001). Competitive antagonism by bismuth subnitrate moderately reduced the renal uptake of 213Bi. The presence of a higher target-tumor burden significantly prevented the renal 213Bi accumulation (P = 0.003), which was further reduced by DMPS treatment (P < 0.0001). Metal chelation, diuresis with furosemide or chlorothiazide, and competitive metal blockade may be used as adjuvant therapies to modify the renal accumulation of 225Ac daughters.