Bacterial l‐asparaginases are enzymes that catalyze the hydrolysis of l‐asparagine to aspartic acid. For the past 30 years, these enzymes have been used as therapeutic agents in the treatment of acute childhood lymphoblastic leukemia. Their intrinsic low‐rate glutaminase activity, however, causes serious side‐effects, including neurotoxicity, hepatitis, coagulopathy, and other dysfunctions. Erwinia carotovora asparaginase shows decreased glutaminase activity, so it is believed to have fewer side‐effects in leukemia therapy. To gain detailed insights into the properties of E. carotovora asparaginase, combined crystallographic, thermal stability and cytotoxic experiments were performed. The crystal structure of E. carotovoral‐asparaginase in the presence of l‐Asp was determined at 2.5 Å resolution and refined to an R_cryst of 19.2 (R_free = 26.6%) with good stereochemistry. Cytotoxicity measurements revealed that E. carotovora asparaginase is 30 times less toxic than the Escherichia coli enzyme against human leukemia cell lines. Moreover, denaturing experiments showed that E. carotovora asparaginase has decreased thermodynamic stability as compared to the E. coli enzyme and is rapidly inactivated in the presence of urea. On the basis of these results, we propose that E. carotovora asparaginase has limited potential as an antileukemic drug, despite its promising low glutaminase activity. Our analysis may be applicable to the therapeutic evaluation of other asparaginases as well.

Poly(lactic-co-glycolic acid) (PLGA) is a biodegradable and biocompatible polymer which is widely used as a matrix to incorporate therapeutic agents. The anticancer activity of targeted folate-modified docetaxel-loaded PLGA nanoparticles (F–NP–Doc) was studied in vitro. Nanoparticles were prepared by a single-emulsion solvent-evaporation technique and characterized by physico-chemical methods. Cell survival was measured by the MTT assay and the sulforhodamine B assay. Folate receptor α expression, particle uptake and apoptosis were assessed by flow cytometry. Folate-modified docetaxel-loaded PLGA nanoparticles showed high anticancer activity in vitro against HeLa cervical carcinoma cells and MCF7 breast adenocarcinoma cells overexpressing folate receptors. Targeted F–NP–Doc nanoparticles were more active compared to free docetaxel and non-targeted NP–Doc nanoparticles; in contrast, the activity of targeted nanoparticles against human fibroblasts (negative control) was significantly lower. F–NP–Doc particles, like free docetaxel, induced apoptosis in cancer cells. F–NP–Doc, but not unmodified docetaxel-loaded PLGA nanoparticles, reversed multidrug resistance of MCF7R breast adenocarcinoma cells. High antitumor activity of F–NP–Doc has also been proven in in vivo experiments. The summarized experimental data brought us to the conclusion that the incorporation of docetaxel into the targeted PLGA nanoparticles dramatically improves its selectivity against cancer cells.

Polyamidoamine (PAMAM) dendrimers of the second generation (G2) are branched polymers containing 16 surface amino groups that allow them to be used as universal carriers on creating systems for drug delivery. G2 labeled with fluorescein isothiocyanate (FITC) efficiently bound with the surface of tumor cells at 4°C and was absorbed by the cells at 37°C. The covalent binding to G2-FITC of a vector protein, a recombinant fragment of the human alpha-fetoprotein receptor-binding domain (rAFP3D), increased the binding and endocytosis efficiency more than threefold. Covalent conjugates of G2 with doxorubicin (Dox) obtained by acid-labile linking of cis-aconitic anhydride (CAA) without the vector protein (G2-Dox) and with the vector protein rAFP3D (rAFP3D-G2-Dox) were accumulated by the tumor cells with high efficiency. However, a selective effect was observed only in rAFP3D-G2-Dox, which also demonstrated high cytotoxic activity against the human ovarian adenocarcinoma SKOV3 cells and low cytotoxicity against human peripheral blood lymphocytes. Based on these results, rAFP3D-G2 conjugate is promising for selective delivery of antitumor drugs.

The specific receptor of alpha-fetoprotein (AFP) is a universal tumor marker, being expressed on the surface of many tumor cells, but not in normal human tissues. AFP enters the cell by receptor-mediated endocytosis; its receptor-binding site is hypothetically localized in the third domain of AFP. A recombinant C-terminal AFP fragment, which contains all the third and a part of the second domains of hAFP, was produced. This AFP fragment was bound specifically to the AFP receptor on the surface of tumor cells and was accumulated by them with the same efficiency as the full-size hAFP. Similar to hAFP, the recombinant C-terminal fragment inhibited the estradiol-induced growth of hormone-dependent MCF-7 cells in vitro. Hence, the recombinant C-terminal AFP fragment can be used as a protein vector for the targeted delivery of cytostatic drugs to tumor cells.