The IC50 of TRAIL in these cells was about 125 ng ml. the SRC inhibitor, PP2, by itself did not affect cell viability at 10 uM, but the sensitivity of the cell line to TRAIL was significantly enhanced in the presence of PP2 with an IC50 for TRAIL of approximately 32 ng ml in selleck chem inhibitor the presence of PP2. The inactive compound, PP3, had little or no effect alone or in combination with TRAIL. Previously we showed that TNBC cells are more sensi tive to TRAIL than are other subtypes of breast Inhibitors,Modulators,Libraries cancer. We next investigated whether SRC inhibition would sensitize TRAIL resistant cells to TRAIL by testing the combination of TRAIL PP2 on a panel of breast cancer cell lines representing ER positive, HER2 amplified, TNBC basal A, and TNBC basal B subtypes.

The combination of TRAIL and PP2 was more effect ive than TRAIL alone in all cell lines tested and was more effective than PP2 alone in all cell lines except the HER2 amplified cell line BT474. When the inhibition of viability by the combined treat ment was compared with the sum of the inhibition seen with Inhibitors,Modulators,Libraries TRAIL alone and PP2 alone, Inhibitors,Modulators,Libraries a significant difference was seen in the TNBC basal B cell lines MB231 and Hs578t, and the TNBC basal B cell line HCC1937. Although the combination appeared more active than the sum of the two agents alone in the TNBC basal B cell line MB157, these data did not reach statistical sig nificance, in part because of the high sensitivity to TRAIL alone in this cell line. In the other cell lines, although the combination was more toxic than either treatment alone, the effects were relatively modest and not greater than the sum of the individual treatments.

Inhibitors,Modulators,Libraries Our primary screen identified BCL2L1 and BCL2L2, known negative regulators of the mito chondrial apoptosis pathway, as putative nega tive regulators of TRAIL induced apoptosis in MB231 cells. Further, BCL2L1 was identified as a node in the gene interaction network generated by using our Inhibitors,Modulators,Libraries RNAi screening data. Silencing of BCL2L1 enhanced TRAIL induced caspase activation in three of the four cell lines tested at high stringency and in all four lines if a lower stringency was used. Expression of BCL2L1 protein was measured in the four cell lines assayed in the secondary screen. BCL XL was expressed in the four cell lines tested, but it was expressed at higher levels in the TRAIL resistant T47D and SKBR3 cell lines.

We con firmed the enhancement of TRAIL induced caspase 3 7 ac tivity by using five different selleck inhibitor BCL2L1 siRNAs in the four cell lines used for in the secondary screen. All five siRNAs enhanced TRAIL induced caspase 3 7 activation by more than 2 standard deviations in the TNBC cell lines MB231 and MB468 and four of the five enhanced TRAIL induced caspase 3 7 activation by more than 2 standard devia tions in the ER positive cell line T47D and in the HER2 amplified cell line SKBR3.