Different species of relative ceramide level in 4T1.2 or MCF-7 cells measured by LC/MS 48 h after POEG-b-PPPMP or POEG-b-PPPMP/DOX treatments compared to free drug alone or combination. Tumor cells were treated with PPMP, POEG-b-PPPMP, DOX·HCl +PPMP or POEG-b-PPPMP/DOX at the same PPMP concentration of 1.7 μM; DOX·HCl, DOX·HCl +PPMP or POEG-b-PPPMP/DOX at the same DOX concentration of 100 nM. Data are presented as the means ± SD for triplicate samples. P values were generated by one-way ANOVA using the Tukey test for multiple comparisons. *P < 0.05, **P < 0.01, *** P < 0.001.