نشان دار کردن رادیویی ریتوکسی‌مب (RTX) با 188Re و 99mTc توسط فناوری تری کربنیل

ABSTRACT Radiolabeling of rituximab with 188Re and 99mTc using the tricarbonyl technology

The investigation of novel tumor-targeting radiopharmaceuticals is currently one of the potential fields of interest for researchers for both tumor scintigraphy and/or treatment. Radiolabeled antibodies are important clinical reagents for both tumor imaging and therapy and also for providing an effective evaluation of the pharmacokinetics [1]. Monoclonal antibodies (mAb) have significantly contributed to the success in the treatment of hematological malignancies.

Radioimmunotherapy (RIT) is advantageous compared to unlabeled therapeutic antibodies, given the additive effect of radiation-induced cytotoxicity and the ability of the associated radioactivity to kill tumor cells distant from the bound radiolabeled antibody [2]. In 2002, yttrium-90 ibritumomab tiuxetan (Zevalin; Biogen Idec, Inc., Cambridge, MA, USA) became the first radio immunotherapeutic agent approved by the FDA. In 2003, iodine-131 tositumomab (Bexxar; Corixa Corp, Seattle, WA, USA) received approval by the FDA. Both compounds are used for the treatment of patients with non-Hodgkin’s lymphoma (NHL) [3–5]. Rituximab (RTX), the human IgG1-type chimeric form of the parent murine antibody ibritumomab, is specifically targeted against CD20, a surface antigen expressed by pre-B and mature human B lymphocytes, by N90% of B-cell NHLs, but not by hematopoietic stem cells, pro-B cells, normal plasma cells or other normal tissues [6–9]. Binding affinity of rituximab to CD20 is approximately 5 nM [10]. There is strong evidence that apoptosis, cell-mediated cytotoxicity, complement-dependent cell lysis and cytokine release are primarily responsible for the therapeutic effect of rituximab [7,11].

A number of methods have been proposed for labeling proteins in general and antibodies in particular. 99m Technetium (99mTc) and 188 Rhenium (188Re) represent an attractive pair of radionuclides for biomedical use because of their favorable decay properties for diagnosis (99mTc: 6 h half-life, 140-keV γ-radiation) and therapy (188Re: 17 h half life, 2.12-MeV βmax − radiation) and also due to their onsite availability through the use of 99Mo/99mTc and 188W/188Re generator systems. 188Re and 99mTc can be conjugated to antibodies using similar chemistry methods [12]. Ferro Flores et al. [13] have recently described the development of a freeze-dried kit formulation for the instant preparation of a 188Re-labeled anti-CD20 mAb. Stopar et al. [14] published a study on the radiolabeling of RTX with 99mTc. Furthermore, Torres-García et al. [15] published preliminary studies on the biokinetics of a 188Re-labeled anti-CD20 mAb in patients.

The organometallic fac-[M(CO)3]+ core (M=99mTc, 188Re) was introduced for the development of new target specific radiopharmaceuticals. It has proven to be a versatile synthon for the labeling of different types of bioactive molecules, notably recombinant proteins, peptides and small molecules [16]. The 99mTc synthon can be readily prepared via a one-step kit formulation (IsoLink, Covidien, Petten, The Netherlands) in high yields. A twostep kit preparation for the 188Re-analog is in development [17]. The [M(CO)3]+ core (M=99mTc, 188Re) possesses a high in vivo stability due to the kinetic inertness of the lowvalent, organometallic metal core. The relative high chemical stability of the precursors allows radiolabeling under mild, physiological conditions, suitable for the labeling of temperature-sensitive molecules such as proteins. In fact, [99mTc(CO)3]+ is readily used for direct labeling of recombinant proteins expressing a 6xHis-tag [18–20]. Most recently, Chen et al. [21] described the radiolabeling of trastuzumab (Herceptin) with [188Re (CO)3]+. The study shows for the first time that the use of the tricarbonyl core can be a promising and suitable strategy for the radiolabeling of antibodies with 188Re.

In this study, we present the radiolabeling procedure of the commercial anti-CD20 antibody rituximab with [99mTc (CO)3]+ and [188Re(CO)3]+ as a potential alternative to the 111In/90Y-Zevalin system for diagnosis and therapy of NHL. A comparative preclinical evaluation of the in vitro and the in vivo performances of the 99mTc and the 188Re conjugates is described.