Synthesis and biological evaluation of podophyllotoxin derivatives as selective antitumor agents

To improve podophyllotoxin's cytotoxicity and selective effect, twenty-two podophyllotoxin derivatives had been designed and synthesized. The cytotoxicity of these compounds was evaluated on A549, MCF-7, HepG2 and L-02 cell lines. As a result, most of the compounds were more potent than the positive drugs Etoposide (VP-16) and Doxorubicin which were widely used in clinical for antitumor. There were no magnitude differences about these de-protected (without Boc group) podophyllotoxin amino acid derivatives' cytotoxicity between three tumor cell lines and normal hepatic L-02 cells. Interestingly, some protected (with Boc group) amino acid derivatives and some ligustrazine derivatives showed high selectivity, especially the compound 2 (sarcosine derivative with Boc group). It exhibited highly selectivity both on the cancer cells and the normal cells. The IC₅₀ of compound 2 was 9.5 ± 0.03 nM, 132.6 ± 24.1 nM, 96.4 ± 1.3 nM and 160.2 ± 4.7 nM against A549, MCF-7, HepG2 and L-02 cells, respectively. The SI (IC₅₀^L-02/IC₅₀^A549) value of compound 2, Doxorubicin and Etoposide was 16.9, 0.2 and 0.5, respectively. Meanwhile, SI (IC₅₀^MCF-7/IC₅₀^A549) value and SI (IC₅₀^HepG2/IC₅₀^A549) value of compound 2 were 14.0 and 10.1, respectively. In summary, compound 2 showed high selectivity especially on A549 cells. Further research on cell apoptosis indicated that compound 2 could induce apoptosis of A549 cells through nuclei fragmentation and had lower toxicity to normal hepatic L-02 cells. The detection of apoptosis and cell cycle analysis indicated that compound 2 induced A549 cells apoptosis and prevented A549 cells transition from S to G₂ phase while there were no obvious changes on L-02 cells. Moreover, the structure-activity relationships of these derivatives were briefly discussed.