MUC1 Story: Great Expectations, Disappointments and the Renaissance.

In the course of studying human mucin MUC1, the attitude towards this molecule has been changing time and again. Initially, the list of presumable functions of MUC1 was restricted to protecting and lubricating epithelium. To date, it is assumed to play an important role in cell signaling as well as in all stages of oncogenesis, from malignant cell transformation to tumor dissemination. The story of MUC1 is full of hopes and disappointments. However, the scientific interest to MUC1 has never waned, and the more profoundly it has been investigated, the clearer its hidden potential turned to be disclosed. The therapeutic potential of mucin MUC1 has already been noted by various scientific groups at the early stages of research. Over forty years ago, the first insights into MUC1 functions became a strong ground for considering this molecule as potential target for anticancer therapy. Therefore, this direction of research has always been of particular interest and practical importance. More than 200 papers on MUC1 were published in 2016; the majority of them are dedicated to MUC1-related anticancer diagnostics and therapeutics. Here we review the history of MUC1 studies from the very first attempts to reveal its functions to the ongoing renaissance.

RGD-based Therapy: Principles of Selectivity.

Design of selective anticancer drugs that are targeting RGD-binding integrin receptors which are known to be one of the perspective directions in the field of oncology. Significant progress in the development and application of these types compounds is already demonstrated. The accumulating body of basic and clinical evidence demonstrates potential significant effects on both in vitro and in vivo experimental models. However, the specific mechanism of action of these compounds is generally not a fully elucidated or the exact target responsible for the achievement of stated effects hasn't yet been defined sufficiently. To date eight types of integrin receptors, which are capable to recognize RGD-motif in natural ligands, has in fact been identified as (namely αIIbß3, αvß1, αvß3, αvß5, αvß6, αvß8, α5ß1, α8ß1). Even so, the estimation of the affinity of one particular RGD-bearing anticancer agent is often based on the determination of the binding efficacy to only one or rarely two integrin receptors. Traditionally the range of targets is restricted by the integrins, which are known to be highly expressed in a particular model system. While potential interactions of such an agent with other RGD-recognizing receptors usually remain beyond the research. Nonetheless, such interactions may also affect the viability and behavior of cancer cells. In this review we attempt to critically analyze the principles of selectivity achievement in the case of RGD-bearing natural ligands and the applicability of these principles in the context of the anticancer drug design.

Preparation and functional evaluation of RGD-modified streptavidin targeting to integrin-expressing melanoma cells.

The vertical growth stage is the most dangerous stage of melanoma and is often associated with a poor prognosis. The increased invasiveness and metastasis that is typical for vertically growing melanoma are mediated by the molecules of cell adhesion (particularly, integrins). Integrin αvß3, which is abundantly expressed on melanoma cells with high metastatic potentials and is characterized by low expression levels in normal melanocytes, is potentially an attractive target for melanoma diagnostics and therapy. Integrin αvß3 is known to recognize the arginine-glycine-aspartic (RGD) sequence, which has been found in a wide variety of its natural ligands. Here expression vectors bearing the genes of fusion proteins have been constructed for producing these proteins in Escherichia coli. Such fusion proteins consist of a peptidic 'address,' targeting the integrins on melanoma cells, linked to an 'adaptor' for the attachment of a diagnostic or toxic agent. The peptidic 'address' contains the RGD motif, which is stabilized by a disulfide bond to achieve the optimal receptor binding conformation. The 'adaptor' is a tetrameric protein, namely, streptavidin, that is able to achieve high-affinity binding of d-biotin (K(d) = 10(-15) M) and confer avidity to the address peptide. This binding ability facilitates the generation of anti-melanoma diagnostic and therapeutic agents using the appropriate biotin derivatives. These recombinant proteins were purified from the periplasm of E.coli using columns with 2-iminobiotin agarose and demonstrated an ability to adhere to the surface of murine and human melanoma cells.