y expressed GST-fused prodomain peptide consisting of the N-terminal half is reported to be more unstable than that consisting of the Cterminal half. We have recently revealed the precise peptide structure of the inhibitory core and its high affinity for the myostatin ligand. Based on these structural data, further modifications of the degradation-competent amino acid architecture and the development of effective delivery methods to target skeletal muscle will advance rational and potent therapies incorporating synthetic myostatin-blocking peptides. ~~ The alkylating agent bendamustine was synthesized in 1963 and developed as an anticancer drug in the German Democratic Republic. In the 1990s bendamustine got into the focus of research again. It is approved for the AEB-071 manufacturer treatment of chronic lymphocytic leukemia , indolent non-Hodgkin lymphoma and multiple myeloma or as second line therapy of refractory diseases in various countries. Current clinical trials suggest beneficial effects in the treatment of solid cancer types such as breast PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19747723 cancer or small-cell lung cancer. Most treatment regimens include bendamustine in combination with other anticancer drugs including biologicals, for instance rituximab. It has been hypothesized that, apart from the alkylating nitrogen mustard group, the benzimidazole scaffold may contribute to the antitumor activity for instance, due to antimetabolite properties, by facilitating nuclear transport or inhibiting DNA repair. Besides the alkylation of DNA, causing strand breaks, bendamustine induces the expression of p53, 
triggers apoptosis and down-regulates mitotic checkpoints, leading to mitotic catastrophe. Recent patent applications aimed at formulations for oral administration. Alkyl esters of bendamustine were reported as potential prodrugs for intravenous application, and biodegradable polyphosphoesters were described as an approach to stabilize bendamustine in solution. Another approach aimed at increasing the cytotoxicity by constructing dimeric and dendrimeric bendamustine derivatives. Exploring the properties of derivatives of bendamustine, esters of bendamustine comprising basic moieties were prepared as potential prodrugs with higher solubility compared to simple esters such as compounds 2 and 3, which were mainly prepared as synthetic intermediates. Very recently, we reported on the stability of the nitrogen mustard and the ester moieties in compounds 27 against hydrolysis and enzymatic cleavage in buffer, in the presence of porcine butyrylcholine esterase as well as in human and murine plasma. The moderately basic morpholinoethyl ester proved to be of particular interest with respect to both solubility and stability. Preliminary data suggested considerably increased cytotoxicity of the esters compared to the parent compound 1, the basic compounds being of particular interest. Based on the assumption that higher antiproliferative activity may result from increased cellular accumulation, additional mechanisms of action or both, we compared compounds 27 with bendamustine regarding cytotoxicity against a panel of 2 / 21 Cytotoxicity of Bendamustine Esters human cancer cell types, representing hematologic and solid malignancies. Additionally, the induction of p53 expression and apoptosis, cellular enrichment and the involvement of PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19748686 the organic cation transporters OCT1 and OCT3 were investigated. Materials and Methods Ethics Statement Human embryonal kidney cells were purchased from the German Collection o
