Abstract 5480: Effect of the Smac Mimetic TL32711 in Combination with TRAIL or TNF Alpha on a Panel of Melanoma Cell Lines

Abstract Although major advances have been made recently in the treatment of malignant melanoma, it remains an incurable disease when not surgically excised at a very early stage. This is due to the development of resistance to targeted compounds currently being tested in patients. In addition, the genetic heterogeneity of melanoma often limits the effects of those therapies to specific subsets of patients. New targets that are exploitable in multiple genetic subgroups of melanoma and that can overcome resistance are therefore still urgently needed. IAP's (inhibitor of apoptosis proteins) have been described as major players in conferring resistance to therapy by blocking the apoptotic cascade in a high percentage of melanomas. Thus, the sensitivity to apoptotic stimuli, such as TNF alpha or TRAIL, could be restored in melanomas using the novel Smac (second mitochondria-derived activator of caspases) mimetic, TL32711. A panel of patient-derived human melanoma cell lines was clustered according to mutational status, representing all major genetic subgroups of cutaneous melanoma. Cells were treated with TL32711 as a single agent or in combination with TRAIL or TNF-α for 72h. Cell viability was assessed by MTS assay. Target inhibition and initiation of apoptosis were also evaluated. To more accurately predict in vivo efficacy, cells were grown as three dimensional spheroids in a collagen matrix and treated as described above. Treatment effects on spheroids were assessed through confocal microscopy using live/ dead immune fluorescent staining, as well as alamar blue cell viability assay for objective quantification.We observed that seventeen out of eighteen cell lines tested were resistant to TL32711 as a single agent in vitro, even at high doses of the compound. Similarly, treatment with TRAIL or TNF-α alone did not show any significant increase in apoptosis. However, when TL32711 was combined with either TRAIL or TNF-α, a strong synergistic activity was observed in twelve out of eighteen cell lines at low doses, resulting in a dramatic increase in cell death of adherent and three dimensional cultures (spheroids). In all treated cell lines, degradation of the target IAP proteins was observed. However, only in sensitive cell lines, activation of apoptotic cascade was observed.In conclusion, the Smac mimetic TL32711 exhibits strong synergistic activity in combination with TRAIL or TNF-α leading to apoptosis in the majority of the genetically diverse cell lines tested. Since TNF-α and TRAIL are present in a high percentage of melanoma tumors in vivo, single agent activity of TL32711 may be observed in vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5480. doi:10.1158/1538-7445.AM2011-5480