Selective Alpha-Particle Mediated Depletion of Tumor Vasculature with Vascular Normalization

BACKGROUND: Abnormal regulation of angiogenesis in tumors results in the formation of vessels that are necessary for tumor growth, but compromised in structure and function. Abnormal tumor vasculature impairs oxygen and drug delivery and results in radiotherapy and chemotherapy resistance, respectively. Alpha particles are extraordinarily potent, short-ranged radiations with geometry uniquely suitable for selectively killing neovasculature. METHODOLOGY AND PRINCIPAL FINDINGS: Actinium-225 ((225)Ac)-E4G10, an alpha-emitting antibody construct reactive with the unengaged form of vascular endothelial cadherin, is capable of potent, selective killing of tumor neovascular endothelium and late endothelial progenitors in bone-marrow and blood. No specific normal-tissue uptake of E4G10 was seen by imaging or post-mortem biodistribution studies in mice. In a mouse-model of prostatic carcinoma, (225)Ac-E4G10 treatment resulted in inhibition of tumor growth, lower serum prostate specific antigen level and markedly prolonged survival, which was further enhanced by subsequent administration of paclitaxel. Immunohistochemistry revealed lower vessel density and enhanced tumor cell apoptosis in (225)Ac-E4G10 treated tumors. Additionally, the residual tumor vasculature appeared normalized as evident by enhanced pericyte coverage following (225)Ac-E4G10 therapy. However, no toxicity was observed in vascularized normal organs following (225)Ac-E4G10 therapy. CONCLUSIONS: The data suggest that alpha-particle immunotherapy to neovasculature, alone or in combination with sequential chemotherapy, is an effective approach to cancer therapy

PET Imaging of Soluble Yttrium-86-Labeled Carbon Nanotubes in Mice

The potential medical applications of nanomaterials are shaping the landscape of the nanobiotechnology field and driving it forward. A key factor in determining the suitability of these nanomaterials must be how they interface with biological systems. Single walled carbon nanotubes (CNT) are being investigated as platforms for the delivery of biological, radiological, and chemical payloads to target tissues. CNT are mechanically robust graphene cylinders 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. In order to evaluate the potential usefulness of this CNT scaffold, we undertook an imaging study to determine the tissue biodistribution and pharmacokinetics of prototypical DOTA-functionalized CNT labeled with yttrium-86 and indium-111 ((86)Y-CNT and (111)In-CNT, respectively) in a mouse model.The (86)Y-CNT construct was synthesized from amine-functionalized, water-soluble CNT by covalently attaching multiple copies of DOTA chelates and then radiolabeling with the positron-emitting metal-ion, yttrium-86. A gamma-emitting (111)In-CNT construct was similarly prepared and purified. The constructs were characterized spectroscopically, microscopically, and chromatographically. The whole-body distribution and clearance of yttrium-86 was characterized at 3 and 24 hours post-injection using positron emission tomography (PET). The yttrium-86 cleared the blood within 3 hours and distributed predominantly to the kidneys, liver, spleen and bone. Although the activity that accumulated in the kidney cleared with time, the whole-body clearance was slow. Differential uptake in these target tissues was observed following intravenous or intraperitoneal injection.The whole-body PET images indicated that the major sites of accumulation of activity resulting from the administration of (86)Y-CNT were the kidney, liver, spleen, and to a much less extent the bone. Blood clearance was rapid and could be beneficial in the use of short-lived radionuclides in diagnostic applications

²²⁵Ac-E4G10 therapy inhibits the growth of LnCap prostate tumors.

<p>A, Flow cytometric analysis depicting the lack of E4G10 binding to LnCap cells; J591, mouse-anti prostate specific membrane antigen is the positive control. Mouse and rat isotype controls were also evaluated. B, Photographs of in situ (left) and excised tumor (right) in a representative dual control and ²²⁵Ac-E4G10 treated animal. C, Tumor volume in various treatment groups at described time-points. D, Serum prostate specific antigen (PSA) levels in the three treatment groups at 22 days post-implantation with 5 million LnCap cells. E, Kaplan Meier curve showing enhancement of survival with ²²⁵Ac-E4G10 treatment. Data in C, D are mean ± S.E.M. <i>Scale bar</i>, 1 cm.</p

A combination of ²²⁵Ac-E4G10 with paclitaxel enhances the anti-tumor response.

<p>A, Tumor volume in the four treatment groups over time. Data are mean ± S.E.M. B, Kaplan Meier survival curve of treated animals showing significant enhancement of animal survival when ²²⁵Ac-E4G10 therapy is followed by a course of paclitaxel. C, Absence of histopathologic damage in normal organs, assessed 10 days after cessation of ²²⁵Ac-E4G10 treatment.</p

²²⁵Ac-E4G10 treatment results in a relatively normal remaining tumor vasculature.

<p>A, Greater coverage of tumor blood vessels (CD31 positive) by pericytes (α-SMA-positive cells) in ²²⁵Ac-E4G10 treated tumor relative to dual control. B, Transmission electron micrographs of blood vessels in dual control and ²²⁵Ac-E4G10 treated tumor. The dual control tumor contains extravasated RBC-filled vascular spaces that are not lined with endothelial cells, whereas blood vessels in ²²⁵Ac-E4G10 treated tumor display a continuous endothelial lining (arrow) resting on a basement membrane (BM) that is shared with the surrounding pericyte. Scale bar, 50 µm</p

Effect of ²²⁵Ac-E4G10 therapy on tumor histology, vascularity and apoptosis.

<p>A, Light microscopy depicting numerous RBC-filled vascular spaces (arrows) in dual control tumor and fewer, but relatively normal-looking vessels (arrowheads) in the ²²⁵Ac-E4G10 treated tumor. B, Top: Immunohistochemical staining of tumor-sections for vWF, an endothelial cell marker (top). TUNEL staining of tumor sections to detect apoptosis (bottom). Quantification of vWF staining (C) and apoptosis (D) in 4 randomly selected fields. Data are mean ± S.E.M.</p

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