In vitro and in vivo multidrug resistance reversal activity by a Betti-base derivative of tylosin.

The multidrug resistance (MDR) proteins are present in a majority of human tumours. Their activity is important to understand the chemotherapeutic failure. A search for MDR-reversing compounds was conducted among various Betti-base derivatives of tylosin. Here, we evaluate the in vitro and in vivo P-glycoprotein (P-gp)-modulating activity of the most promising compound N-tylosil-1-alpha-amino-(3-bromophenyl)-methyl-2-naphthol (TBN) using human MDR1 gene-transfected and parental L5178 mouse lymphoma cell lines. In vitro experiments showed that TBN dramatically increased the P-gp-mediated cellular uptake of the fluorescent substrate rhodamine 123. Similarly, TBN was found to act as a very potent enhancer of the cytotoxicity of doxorubicin on the resistant cell line. We also provide in vivo evidence using DBA/2 mice in support for an increased tumoural accumulation of doxorubicin, without affecting its tissue distribution, resulting in an enhanced antitumoural effect. Our results suggest that TBN is a potent modulator of the P-gp membrane pump and that the compound could be of clinical relevance to improve the efficacy of chemotherapy in MDR cancers.