Gallium-67-citrate imaging in nuclear oncology

Measuring oncogenic signaling pathways in cancer with PET: an emerging paradigm from studies in castration-resistant prostate cancer

As parallel advances in cancer biology and drug development continue to elevate the role of targeted therapies in oncology, the need for imaging biomarkers that systematically measure the biology associated with therapeutic intervention has become more urgent. Although the molecular imaging community has a commitment to develop technologies to this end, few investigational radiotracers directly measure the biology of common oncogenic signaling pathways often addressed by targeted therapies. Visible progress has been achieved with a handful of radiotracers rationally designed to intercalate the pathobiology of prostate cancer, a molecularly heterogeneous disease nevertheless broadly defined by a fairly small repertoire of recurrent oncogenic lesions.

SIGNIFICANCE

That variable treatment responses or emergent resistance phenotypes are often documented in humans argues strongly for diagnostic technologies that can be realistically applied posttherapy to capture the dynamic patterns of disease response. The purpose of this review is to describe a collection of radiotracers developed to measure the pathobiology of prostate cancer for improved treatment monitoring, placing particular emphasis on the biologic rationale for their preparation. A chronologic description of radiotracer development programs is outlined, primarily to stress how an ongoing dialectic between earlier and more contemporary imaging technologies has accelerated discovery.

Clinical impact of serum proteins on drug delivery

Among serum proteins albumin and transferrin have attracted the most interest as drug carriers in the past two decades. Prior to that, their potential use was overshadowed by the advent of monoclonal antibodies that was initiated by Milstein and Koehler in 1975. Meanwhile intensive pursuit of exploiting transferrin, but above all albumin as an exogenous or endogenous carrier protein for treating various diseases, primarily cancer, rheumatoid arthritis, diabetes and hepatitis has resulted in several marketed products and numerous clinical trials. While the use of transferrin has clinically been primarily restricted to immunotoxins, albumin-based drug delivery systems ranging from albumin drug nanoparticles, albumin fusion protein, prodrugs and peptide derivatives that bind covalently to albumin as well as physically binding antibody fragments and therapeutically active peptides are in advanced clinical trials or approved products. For treating diabetes, Levemir and Victoza that are myristic acid derivatives of human insulin or glucagon-like peptide 1 (GLP-1) act as long-acting peptides by binding to the fatty acid binding sites on circulating albumin to control glucose levels. Levemir from Novo Nordisk has already developed into a blockbuster since its market approval in 2004. Abraxane, an albumin paclitaxel nanoparticle as a water-soluble galenic formulation avoiding the use of cremophor/ethanol, transports paclitaxel through passive targeting as an albumin paclitaxel complex to the tumor site and is superior to conventional Taxol against metastatic breast cancer. INNO-206, an albumin-binding doxorubicin prodrug that also accumulates in solid tumors due to the enhanced permeability and retention (EPR) effect but releases the parent drug through acid cleavage, either intra- or extracellularly, is entering phase II studies against sarcoma. An expanding field is the use of albumin-binding antibody moieties which do not contain the fragment crystallizable (Fc) portion of, conventional immunoglobulin G (IgG) but are comprised of monovalent or bivalent light and/or heavy chains and incorporate an additional albumin-binding peptide or antibody domain. The most advanced antibody of this kind is ATN-103 (Ozoralizumab), a trivalent albumin-binding nanobody that neutralizes the pro-inflammatory tumor necrosis factor alpha (TNF-α) as a causative agent for exacerbating rheumatoid arthritis. ATN-103 is currently in multi-center phase II trials against this debilitating disease. In summary, because albumin as the most abundant circulating protein cannot only be used to improve the pharmacokinetic profile of therapeutically relevant peptides and the targeting moiety of antibodies but also for peptide-based targeting as well as low-molecular weight drugs to inflamed or malignant tissue, it is anticipated that R&D efforts of academia and the pharmaceutical industry in this field of drug delivery will prosper.

Lymphomas of the anterior mediastinum

Lymphomas are the most common cause of masses in the pediatric mediastinum. More than 50% of children with lymphoblastic lymphoma present with an anterior mediastinal mass, and more than one third of all patients with non-Hodgkin's lymphoma have their primary sites in the mediastinum. Hodgkin's disease also frequently involves this anatomic compartment with approximately two thirds of all pediatric cases manifesting mediastinal adenopathy. Although surgical resection generally is not involved in the primary treatment of these diseases, surgeons often play a key role in obtaining adequate tissue for proper diagnostic analysis. Surgical access to the mediastinum often is required in the acquisition of a specimen.

An investigation of the physical characteristics of 66Ga as an isotope for PET imaging and quantification

Isotopes commonly used for PET imaging and quantification have a straightforward decay scheme involving "pure" positron (beta +) emission, i.e., 95%-100% beta + abundance, with no additional gamma rays. 66Ga (Emax = 4.2 MeV, T1/2 = 9.5 h) is a member of a category of isotopes with a lower abundance of beta +'s (57%) and a more complicated spectrum involving combinations of gamma rays that are emitted in cascade. These additional gamma rays tend to cause a higher singles rate, resulting in more random coincidence events. The most abundant positron (51.5%) in the spectrum has one of the highest energies considered for PET imaging. For the purpose of monoclonal antibody dosimetry using 66Ga, it is important to verify the quantification in phantoms prior to initiating human studies. A series of quantitative phantom measurements were performed on the PC4600, a head-optimized BGO based scanner with multiple detector rings. Count rate linearity was verified over concentrations ranging from 4.0 kBq/cc to 37 kBq/cc (0.11-1.0 microCi/cc); resolution averaged 16 mm full width half-maximum in the x and y directions in both the direct and cross planes. Axial resolution was 14 mm. The range of the energetic positrons (up to 4.153 MeV, range 7.6 mm in tissue) was verified as a primary source of resolution degradation. Within the limits outlined above, 66Ga is a suitable isotope for use as 66Ga citrate or with monoclonal antibodies in the detection and staging of tumors and other lesions. In addition, the energetic positrons have possible therapeutic applications when used as a monoclonal antibody label.

Gallium and Indium Complexes of Bis(amino thiol) (N(2)S(2)) Ligands

Three methods have been developed to prepare gallium and indium complexes of three tetradentate N(2)S(2) ligands of the general formula M(N(2)S(2))R (M = Ga, In; R = Cl, Br, SCN, O(2)CC(6)H(5)-O,O'). The ancillary ligand (Cl, SCN, O(2)CC(6)H(5)-O,O') was varied with the tetradentate ligand BAT-TM. X-ray crystallography shows that the coordination geometry about the d(10) metal ion is influenced by the steric requirements of the ligands. X-ray crystallography of four molecules results in the following data: GaCl(BAT-TM) (1), formula = C(10)H(22)ClGaN(2)S(2), space group = Pnma, a = 12.387(4) Å, b = 21.116(6) Å, c = 5.986(2) Å, V = 1565.8(9) Å(3), Z = 4; InCl(BAT-TM) (2), formula = C(10)H(22)ClInN(2)S(2), space group = Pnma, a = 12.968(9) Å, b = 29.29(1) Å, c = 5.866(2) Å, V = 1620(2) Å(3), Z = 4; InNCS(BAT-TM) (3), formula = C(11)H(24)ClInN(3)S(3), space group = Pbca, a = 11.812(3) Å, b = 11.679(3) Å, c = 24.238(9) Å, V = 3449.7 (17) Å(3), Z = 8; In(O,O'-O(2)CC(6)H(5))(BAT-TM) (4), formula = C(19)H(29)O(2)InN(2)S(2), space group = P2(1)/n, a = 10.783(2) Å, b = 18.708(4) Å, c = 12.335(4) Å, V = 2321.7(9) Å(3), Z = 4. Proton NMR studies show that the complexes are stable in solution; in polar solvents such as acetonitrile, for certain molecules, two metal-ligand complexes are observed. Similarly, two metal-ligand complexes are seen in NMR data taken in 80% acetonitrile/20% D(2)O (pD = 4.6) mixture. HPLC studies (acetonitrile/50 mM sodium acetate, pH = 4.6) show that the lipophilicity of the ligand determines the retention time of the complex.