C. Jeffrey Smith

Radioactive gold nanoparticles in cancer therapy: therapeutic efficacy studies of GA-198AuNP nanoconstruct in prostate tumor–bearing mice

UNLABELLED Biocompatibility studies and cancer therapeutic applications of nanoparticulate beta-emitting gold-198 (198Au; beta(max) = 0.96 MeV; half-life of 2.7 days) are described. Gum arabic glycoprotein (GA)-functionalized gold nanoparticles (AuNPs) possess optimum sizes (12-18 nm core diameter and 85 nm hydrodynamic diameter) to target individual tumor cells and penetrate through tumor vasculature and pores. We report the results of detailed in vivo therapeutic investigations demonstrating the high tumor affinity of GA-198AuNPs in severely compromised immunodeficient (SCID) mice bearing human prostate tumor xenografts. Intratumoral administration of a single dose of beta-emitting GA-198AuNPs (70 Gy) resulted in clinically significant tumor regression and effective control in the growth of prostate tumors over 30 days. Three weeks after administration of GA-198AuNPs, tumor volumes for the treated animals were 82% smaller as compared with tumor volume of control group. The treatment group showed only transitory weight loss in sharp contrast to the tumor-bearing control group, which underwent substantial weight loss. Pharmacokinetic studies have provided unequivocal evidence for the optimum retention of therapeutic payload of GA-198AuNPs within the tumor site throughout the treatment regimen with minimal or no leakage of radioactivity to various nontarget organs. The measurements of white and red blood cells, platelets, and lymphocytes within the treatment group resembled those of the normal SCID mice, thus providing further evidence on the therapeutic efficacy and concomitant in vivo tolerance and nontoxic features of GA-198AuNPs. FROM THE CLINICAL EDITOR In this study, the biocompatibility and cancer therapeutic applications of glycoprotein (GA) functionalized gold nanoparticles containing b-emitting Au-198 are described in SCID mice bearing human prostate tumor xenografts. The findings of significant therapeutic efficacy, good in vivo tolerance and non-toxic features make these particles ideal candidates for future human applications.

Bombesin Peptide Conjugated Gold Nanocages Internalize via Clathrin Mediated Endocytosis

The nature of interaction and mechanism of internalization of receptor-avid peptide nanoparticles with cells is not yet completely understood. This article describes the cellular internalization mechanism and intracellular trafficking of peptide conjugated receptor targeted porous Gold nanocages (AuNCs) in cancer cells. We synthesized and characterized a library of AuNCs conjugated with bombesin (BBN) peptide. Evidence of selective affinity of AuNC-BBN toward gastrin releasing peptide receptors (GRPR) was obtained using radiolabeled competitive cell binding assay. Endocytic mechanism was investigated using cell inhibitor studies and monitored using optical and transmission electron microscopy (TEM). Results show AuNC-BBN uptake in PC3 cells is mediated by clathrin mediated endocytosis (CME). Indeed, in the presence of CME inhibitors, AuNC-BBN uptake in cells is reduced up to 84%. TEM images further confirm CME characteristic clathrin coated pits and lysosomal release of AuNCs. These results demonstrate that peptide ligands conjugated to the surface of nanoparticles maintain their target specificity. This bolsters the case for peptide robustness and its persisting functionality in intracellular vehicular delivery systems.

Targeted antisense radiotherapy and dose fractionation using a 177Lu-labeled anti-bcl-2 peptide nucleic acid-peptide conjugate

INTRODUCTION The overall goal of these studies was to test the hypothesis that simultaneous down-regulation of a tumor survival gene and delivery of internally emitted cytotoxic radiation will be more effective than either treatment modality alone. The objectives were to evaluate the therapeutic efficacy of a (177)Lu-labeled anti-bcl-2-PNA-Tyr(3)-octreotate antisense conjugate in a mouse model bearing human non-Hodgkins lymphoma (NHL) tumor xenografts and to optimize targeted antisense radiotherapy by dose fractionation. METHODS In the initial therapy studies, tumor-bearing mice were given saline, nonradioactive DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate, (177)Lu-DOTA-Tyr(3)-octreotate, (177)Lu-DOTA-PNA-peptide alone, or (177)Lu-DOTA-PNA-peptide followed by a chase dose of nonradioactive PNA-peptide. The MTD of (177)Lu-DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate was then determined. Subsequently single dose MTD and four weekly fractionated doses were directly compared, followed by histopathologic evaluation. RESULTS Antisense radiotherapy using 4.44 MBq of the (177)Lu-DOTA-PNA-peptide followed by nonradioactive PNA-peptide was significantly more effective than other low dose treatment regimens. A dose of 18.5 MBq of (177)Lu-DOTA-PNA-peptide was determined to be the approximate maximum tolerated dose (MTD). The median times to progression to a 1cm(3) tumor volume were 32 and 49 days for single dose MTD and fractionated dose (4 × 4.63 MBq) groups, respectively. Histopathology revealed metastases in the single dose groups, but not in the dose fractionation group. CONCLUSIONS Targeted antisense radiotherapy using (177)Lu-DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate and DOTA-PNA-peptide conjugate effectively inhibited tumor progression in a mouse model of NHL. Furthermore, a dose fractionation regimen had a significant advantage over a single high dose, in terms of tumor growth inhibition and prevention of metastasis. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE Down-regulating bcl-2, an anti-apoptotic proto-oncogene, is a mechanism to reverse chemotherapy resistance or failure in humans with NHL. We have developed a (177)Lu-DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate conjugate for targeted antisense radiotherapy, in which down-regulation of bcl-2 and delivery of cytotoxic radiation occur simultaneously. Our previous studies have shown highly specific inhibition of bcl-2 protein, additive in vitro cytotoxic effects on human lymphoma cells, and favorable biodistribution and dosimetric properties. Lutetium-177 targeted antisense radiotherapy demonstrates a significant advantage over conventional (177)Lu-peptide receptor radionuclide therapy in a mouse model of NHL. Our preclinical studies identified an effective combination of antisense and radionuclide therapy, with the goal of future clinical trials in patients.

Molecular Imaging of Breast Cancer Tissue via Site-Directed Radiopharmaceuticals

The American Cancer Society reports that ~261,100 new cases of invasive and in situ breast cancer were diagnosed in 2010, and nearly 40,000 fatalities were attributed to this disease (American Cancer Society, 2010). Although death rates have steadily decreased since 1990, breast cancer currently ranks second in cancer deaths among women. Improvements in detection, treatment, and prevention education contribute to slow the incidence rate, and rapidly evolving nuclear medicine techniques have emerged as a formidable opponent to female breast cancer. The involvement of nuclear medicine imaging modalities in both the detection and diagnosis of breast cancer has increased in recent years (Gopalan et al., 2002). In contrast to earlier imaging methods, in which the transmission of various forms of energy through tissue is employed to generate an image, nuclear medicine imaging techniques are based on detection of the energy emitted from radioactive tracers that are injected into the body and subsequently accumulate locally in specific tissues (Nass et al., 2001). The classification of these techniques as either positron emission tomography (PET) or single photon emission computed tomography (SPECT) imaging modalities is determined by the radionuclide that is utilized to synthesize a given radiotracer. The theory behind nuclear medicine imaging techniques to detect and diagnose breast cancer is founded on preferential radiopharmaceutical uptake by cancerous cells as a result of alterations in metabolic rate, vascularity, or receptor expression which are associated with malignancy. Although both PET and SPECT are commonly employed to detect a variety of malignancies, neither imaging technique has achieved clinical acceptance as a method of imaging breast cancer due to the lack of sensitivity and specificity demonstrated by available radiotracers (Gopalan et al., 2002; Nass et al., 2001; Rosen et al., 2008). Presently, there is only one radiopharmaceutical, the SPECT imaging agent technetium-99m methoxy-isobutyl-isonitrile (99mTc-sestamibi, Miraluma®), that has received FDA approval for use as a diagnostic adjunct to mammography (Gopalan et al., 2002; Nass et al., 2001; Rosen et al., 2008). Although the mechanism governing the concentration of 99mTc-sestamibi in cancer cells is not fully understood, it may be related to the degree of cellular proliferation and vascular permeability (Nass et al., 2001). Once inside malignant cells, 99mTc-sestamibi is

New advances in the synthesis of a water-soluble triphosphine and the development of tripodally coordinated rhodium(I) and platinum(II) complexes

A new water-soluble triphosphine PhP[CH2CH2P-(CH2OH)2]2 is produced via the formylation of PhP(CH2CH2PH2)2; this triphosphine, upon interaction with [Rh(cod)Cl]2 and Pt(cod)Cl2(cod = cycloocta-1,5-diene) under biphasic (water/CH2Cl2) conditions, produced water-soluble rhodium(I) and platinum(II) complexes respectively; 31P and 195Pt NMR spectroscopic data confirm the tripodal coordination of RhI and PtII involving > PPh and the two –P(CH2OH)2 functionalities.