It had previously been reported that isolated PA (1) induces cellular apoptosis . Indeed, we observe that fully synthetic PA (1) also induces apoptosis, as does Ph-DA and PA-DA , at low nanomolar concentrations, as determined by caspase-3 activation in Jurkat cells, however controls ePA and ePA-DA (35-1) do not (Fig. and Fig. ). Further investigation also revealed that PA (1) and PA-DA (35-2) markedly increased the proportion of Jurkat cells in G1 phases (Fig. and Fig. ), but not in ePA and ePA-DA (35-1) treated cells. Notably, we observe that PA (1) and Ph-PA display minimal effects on cell viability in freshly isolated human peripheral blood mononuclear cells (PBMCs) as well as no obvious effects on caspase activation (Fig. and Fig. ), suggesting that their toxicity mechanisms are selective to rapidly proliferating cells.