Investigations on bendamustine esters as new antitumor agents and the role of ABCG2 as a surrogate marker of breast cancer initiating cells
ABC-transporter expression is a crucial mechanism of tumor resistance and was recently also associated with cancer initiating cells (CIC). Flow cytometry was applied to detect the expression of CIC-markers, ABCB1 and ABCG2 in human brain- and breast cancer cell lines and to examine possible correlations between ABC-transporter expression and CICs. Only one of the investigated brain tumor cell lines (Daoy) comprised cells expressing CIC-markers which revealed increased clonogenicity in vitro.
... investigations on the correlation between CICs and ABCG2, MCF-7 breast cancer cells were treated with topotecan (Topo) to induce ABCG2 expression. Topo treatment led to increased resistance against cytostatic drugs, which are substrates of ABCG2. Concurrently, Topo treatment induced a reversible decrease in the expression of the CIC-markers CD24 and EpCAM, but did not result in increased clonogenicity in vivo. In contrast, Topo treated cells revealed decreased tumorigenicity, most probably due to the down-regulation of CD24 and EpCAM. Nevertheless, further investigations are necessary to determine whether ABCG2 induction and CD24/EpCAM down-regulation are interrelated or independent processes. The nitrogen mustard (N-Lost) derivative bendamustine (BM) has been approved as an anticancer drug for the treatment of hematopoietic malignancies for decades. Nevertheless, as becomes obvious from a series of recent publications and patent applications, there is increasing interest in this cytostatic with respect to, for example, improved oral bioavailability of BM by optimized formulations. Following a different approach, in this thesis the potential of esters of BM was explored, with a focus on representative aminoalkyl esters. Alkyl- and various aminoalkyl (e.g. 2-morpholinoethyl or 2-pyrrolidinoethyl) esters of BM were investigated for stability in various media and cytotoxicity in vitro against a broad panel of human malignancies. For this purpose, a fast, selective RP-HPLC method using fluorescence detection was established a [...]