Fueled by the development of technologies enabling clonal selection-by-binding from vast libraries of in vitro generated genotype-phenotype-linked polypeptides, several groups have been inspired to develop novel binding proteins via protein-engineering routes. Bypassing the need for recruitment of an immune system for their generation, such binders have been developed and built on a diverse set of frameworks, differing in size and structural organization compared with the immunoglobulin
Molecular imaging in vivo has the potential to improve the diagnosis of many diseases by defining relevant aberrant cellular alterations and to indicate adequate treatment. In cancer diagnosis, molecular imaging can, in contrast to a biopsy, provide a global view of potentially all metastatic lesions in the body. Radionuclide molecular imaging of therapeutic targets is a non-invasive procedure that can be easily repeated multiple times to, for example, follow the effects of a treatment regimen
Guiding surgical incisions with fluorescent probes has been demonstrated in individual clinical trials for decades, but the scientific and commercial prerequisites have now reached a level that indicates a dramatic increase in its clinical value [53]. In a pioneering study, a fluorescently near-IR-labeled EGFR-binding affibody molecule was administered intravenously to nude rats with xenografted glioma tumors that were clearly visualized 1 h pi, providing excellent potential for increased
For therapeutic applications based solely on blocking the activity of disease-related target proteins as a mechanism of action (MOA), the Fragment crystallizable (Fc) portion of mAbs, mediating, for example, antibody-dependent cell-mediated cytotoxicity (ADCC) and complement activation, is not required and might even be undesired. Similar to non-Fc-containing antibody derivatives, such as scFv, Fab, Fv, and domain antibodies, affibody molecules with high affinity and specificity are attractive
Arming affibody molecules with a cytotoxic payload appears to be a seemingly straightforward and efficient way to direct the action of the payload to desired cell populations. The concept has been evaluated in different preclinical studies and, so far, the payload has been a cytotoxic substance (biologically derived toxin, cytotoxic drug, or therapeutic radionuclide) intended for cancer therapy.
One approach is to construct fusion proteins comprising a potent toxin of plant or bacterial origin
It is a challenge to achieve sufficient therapeutic effect while maintaining off-target toxicity at a manageable level when potent cytotoxic agents or therapeutic radionuclides are used as payloads.
Lessons learned from in vivo imaging experiments have shown that, similarly to other scaffold proteins, affibody molecules may accumulate in kidneys and liver in addition to the tumor, and such off-target accumulation of cytotoxic molecules may cause off-target toxicity. One way to potentially reduce
Affibody molecules conjugated to various nanoparticles have been evaluated for several different purposes, such as targeted drug delivery 115, 116, 117 and molecular imaging 47, 52, 118. One interesting application is theranostics, combining diagnostic imaging with the delivery of therapeutic drugs. Lu and colleagues engineered thioether-bridged organosilica nanoparticles conjugated with a near-IR dye and HER2-specific affibody molecules [119]. The particles were also loaded with doxorubicin.
The small size and module-like characteristics of affibody molecules has inspired several groups to use them as gene fusion or conjugation partners to obtain a variety of different molecular tools.
Using an in-house and highly complex (5 × 1013) mRNA-displayed affibody library, Wang and coworkers selected binders to LOV2, a photosensitive protein from Avena sativa (wild oats) [7]. Upon irradiation with light, LOV2 undergoes a change in conformation from the so-called ‘dark state’ to the ‘light
In conclusion, affibody molecules represent a class of affinity proteins that have been investigated for a multitude of applications over the past 20 years. Many binders have been explored for biotechnological use [130], and several affibody molecules with different specificities have been evaluated for in vivo purposes. By direct or chelator-mediated conjugation of suitable radionuclides, affibody-based PET and/or SPECT tracers have been generated and evaluated preclinically for imaging of
F.Y.F. is an employee of Affibody Medical AB. S.S., T.G., A.E.K., P-Å.N., and J.L. are members of the Technical Advisory Board at Affibody Medical AB. Will small and disulfide-free affinity proteins become an alternative to conventional small organic drugs for certain intracellular therapeutic applications? Is the affibody scaffold also suitable for the generation of binders to nonprotein targets, such as haptens, P-tyrosine peptides, and carbohydrates? Is the small size of affibody molecules
We would like to thank Vladimir Tolmachev and Anna Orlova for valuable input on the section describing the use of affibody-based tracers in medical imaging.