Penetratin Improves Tumor Retention of Single-Chain Antibodies: A Novel Step toward Optimization of Radioimmunotherapy of Solid Tumors

Abstract

Single-chain Fv (scFv) antibody fragments exhibit improved pharmacokinetics and biodistribution compared with intact IgG. The tumor uptake of scFvs is rapid, and the serum half-life is shorter than IgG. However, scFvs exhibit lower net dose deposition in the tumor due to a shorter residence time that limits their use in radioimmunotherapy. To improve the tumor uptake and retention of scFvs, we investigated the utility of cell-penetrating peptides, penetratin and transactivator of transcription (TAT). Biodistribution studies were done in LS174T tumor-bearing mice with divalent scFv derived from anti-tumor-associated glycoprotein 72 monoclonal antibody (mAb) CC49. Penetratin increased the tumor retention of scFvs without affecting the peak dose accumulation. The percentage of doses retained in tumors at 24 hours postadministration with a control (no peptide), penetratin, and TAT were 27.25%, 79.84%, and 48.55%, respectively, of that accumulated at 8 hours postinjection. The tumor-to-blood ratios at 24 hours postadministration were 7.14, 19.53, and 16.48 with control, penetratin, and TAT treatment, respectively, whereas the pharmacokinetics were unaltered. Coinjection with TAT, however, resulted in increased uptake of the radioconjugate by the lungs. Autoradiography of the excised tumors indicated a more homogenous distribution of the radiolabeled scFv with both penetratin and TAT in comparison with the control treatment. Real-time whole-body imaging of the live animals confirmed improved tumor localization with penetratin without any increase in the uptake by normal tissues. In conclusion, a significant improvement in the tumor retention of sc(Fv) 2 was achieved by administration of penetratin. Therefore, the combination of penetratin and scFvs has the potential of improving the utility of mAb-based radiopharmaceuticals. (Cancer Res 2005; 65(17): 7840-6)

Cell-penetrating and cell-targeting peptides in drug delivery

“…This study revealed that the higher the number of CPP copies grafted on a cell-specific monoclonal antibody (Mab), the lower was the specificity of the Mab for the native cell. Significant localization and retention of CPP-Mab fragments in non-targeted tissues in vivo have been confirmed more recently by Jain et al, especially with a high peptide to antibody ratio [19]. In this study, the cell-penetrating "driving force" predominated over the specific antigen binding of the Mab fragments.…”

“…In another study, Tat or Antennapedia peptides were co-administrated with sc(Fv) 2 fragments [19]. In such a situation, there was no stable link between the CPPs and the sc(Fv) 2 fragment.…”

“…However, a higher tumor retention was observed with the Antennapedia peptide and, to a lower extent, with the Tat CPP than with the sc(Fv) 2 fragment alone. However, the Tat peptide used in this study lacked one arginine residue [19]. Therefore, the lower tumor retention observed with Tat in this work should be reconsidered as the replacement of just a single cationic residue in Tat can greatly decrease its cell uptake [11,13].…”

“…Most of them are fundamental studies mainly about the entry mechanism of CPPs or the biological evaluation of a coupled drug, whereas only a little number concerns clinical applications. It is noteworthy to consider that a stable covalent linkage has to be formed between CPP and cargo to allow translocation, at least for Tat, Antennapedia, or poly-Arg peptides, although a couple of publications also reported a surprising efficacy upon simple mixing with the cargo entities [18,19]. Similarly, another CPP, Pep-1, which has been marketed as "Chariot" [20], can induce internalization of a cargo molecule just by being mixed with it [21].…”

Protective effects of anti-ricin A-chain antibodies delivered intracellularly against ricin-induced cytotoxicity

“…Many other cationic and hydrophobic cell penetrating peptides (CPPs) have been reported to perform intracellular delivery of proteins into cultured cells [22] , as well as in vivo delivery of enzymes such as galactosidase and Cre recombinase to tissues [23,24] . Also CPPs significantly enhanced retention of the antibody by tumors [25] . More importantly, most CPPs are nontoxic when used at low doses [26] .…”