Birinapant (TL32711)

Birinapant, also called TL32711, is a potent antagonist for XIAP with Kd value of 45 nM and cIAP1 with Kd value <1 nM [1].
Birinapant not only binds to the isolated BIR3 domains of cIAP1, cIAP2, XIAP but the single BIR domain of ML-IAP with high affinity and degrades TRAF2-bound cIAP1 and cIAP2 rapidly accordingly inhibiting the activation of TNF-mediated NF- kB. Additionally, birinapantcan promote the formation of caspase-8: RIPK1 complex in response to TNF stimulation, which result in downstream caspasesactivation [4].
In the inorganic SUM149- and SUM190-derived cells, which with differential XIAP expression (SUM149 wtXIAP, SUM190 shXIAP) and other high cIAP1/2 but low XIAP binding affinity bivalent Smac mimetic GT13402, XIAP inhibition are needed for increasing TRAIL potency. Opposite, single agent efficacy of Birinapant is owing to pan-IAP antagonism. Rapid cIAP1 degradation was caused by birinapant, as well as NF-κB activation, PARP cleavage andcaspase activation. While combined withTNF-α, showing strong combination activity, the combination was more effective than individual. The response in spheroid models was conserved, whereas in vivo birinapant inhibited tumor growth without adding TNF-α in vitro to resistant cell lines. In a parental cell line, TNF-αcombined withbirinapantinhibited the growth of a melanoma cell line with acquired resistance to the same extent of BRAF inhibition [1, 2].
Drug treatment increased the mean [18F]ICMT-11 tumor uptake with a peak at 24 hours for CPA (40 mg/kg; AUC40-60: 8.04 ± 1.33 and 16.05 ± 3.35 %ID/mL × min at baseline and 24 hours, respectively) and 6 hours for birinapant (15 mg/kg; AUC40-60: 20.29 ± 0.82 and 31.07 ± 5.66 %ID/mL × min, at baseline and 6 hours, respectively). Voxel-based spatiotemporal analysis of tumor-intrinsic heterogeneity showed that [18F] ICMT-11 could detect the discrete pockets of caspase-3 activation. Caspase-3 activation that measured ex vivo associated with the increased tumor [18F] ICMT-11, and early radiotracer uptake predicted apoptosis, distinct from the glucose metabolism with [18F] fluorodeoxyglucose-PET, which depicted the continuous loss of cell viability [3].
References:
1.Allensworth JL, Sauer S, Lyerly HK, et al. Smac mimetic Birinapant induces apoptosis and enhances TRAIL potency in inflammatory breast cancer cells in an IAP-dependent and TNF-a-independent mechanism. Breast Cancer Research, 2013, 137:359-371.
2.Krepler C, Chunduru SK, Halloran MB, et al. The novel SMAC mimetic birinapant exhibits potent activity against human melanoma cells. Clinical Cancer Research, 2013, 19 (7): 1784-1794.
3.Nguyen QD, Lavdas I, Gubbins J, et al. Temporal and Spatial Evolution of Therapy-Induced Tumor Apoptosis Detected by Caspase-3–Selective Molecular Imaging. Clinical Cancer Research, 2013, 19 (14): 3914-3924.
4.Benetatos CA, Mitsuuchi Y, Burns JM, et al. Birinapant (TL32711), a Bivalent SMAC Mimetic, Targets TRAF2-Associated cIAPs, Abrogates TNF-Induced NF-kB Activation, and Is Active in Patient-Derived Xenograft Models. 2014, 13(4):867-879.

Birinapant (TL32711) Improves Responses to GEM/AZD7762 Combination Therapy in Triple-negative Breast Cancer Cell Lines.[Pubmed:27272773]

Anticancer Res. 2016 Jun;36(6):2649-57.

BACKGROUND: Triple-negative breast cancer (TNBC) is an aggressive form of breast cancer currently lacking targeted therapies. Our previous work demonstrated a therapeutic synergism with gemcitabine (GEM) and the CHK1 inhibitor (AZD7762) combination treatment in a TNBC cell line. We hypothesized that the response to this combination therapy would differ among heterogeneous TNBC patients and that addition of a SMAC mimetic (TL32711) could improve efficacy. MATERIALS AND METHODS: Therapeutic responses to GEM, GEM/AZD7762, and GEM/AZD7762/TL32711 combinations were investigated by XTT assays and western blotting of cell cycle and apoptosis-related proteins in ten TNBC cell lines. RESULTS: TNBC cell lines harboring low levels of endogenous CHK1, cIAP1 and cIAP2 were responsive to GEM alone, whereas cell lines demonstrating a minimal increase in phospho-S345 CHK1 after treatment were responsive to GEM/AZD7762 or GEM/AZD7762/TL32711 combination. CONCLUSION: The response of TNBC cells to particular therapies varies and will require development of predictive biomarkers.

Effect of a Smac Mimetic (TL32711, Birinapant) on the Apoptotic Program and Apoptosis Biomarkers Examined with Validated Multiplex Immunoassays Fit for Clinical Use.[Pubmed:26446940]

Clin Cancer Res. 2016 Feb 15;22(4):1000-10.

PURPOSE: To support clinical pharmacodynamic evaluation of the Smac mimetic TL32711 (birinapant) and other apoptosis-targeting drugs, we describe the development, validation, and application of novel immunoassays for 15 cytosolic and membrane-associated proteins indicative of the induction, onset, and commitment to apoptosis in human tumors. EXPERIMENTAL DESIGN: The multiplex immunoassays were constructed on the Luminex platform with apoptosis biomarkers grouped into three panels. Panel 1 contains Bak, Bax, total caspase-3, total lamin-B (intact and 45 kDa fragment), and Smac; panel 2 contains Bad, Bax-Bcl-2 heterodimer, Bcl-xL, Bim, and Mcl1; and panel 3 contains active (cleaved) caspase-3, Bcl-xL-Bak heterodimer, Mcl1-Bak heterodimer, pS99-Bad, and survivin. Antibody specificity was confirmed by immunoprecipitation and Western blot analysis. RESULTS: Two laboratories analytically validated the multiplex immunoassays for application with core-needle biopsy samples processed to control preanalytical variables; the biologic variability for each biomarker was estimated from xenograft measurements. Studies of TL32711 in xenograft models confirmed a dose-dependent increase in activated caspase-3 6 hours after dosing and provided assay fit-for-purpose confirmation. Coincident changes in cytosolic lamin-B and subsequent changes in Bcl-xL provided correlative evidence of caspase-3 activation. The validated assay is suitable for use with clinical specimens; 14 of 15 biomarkers were quantifiable in patient core-needle biopsies. CONCLUSIONS: The validated multiplex immunoassays developed for this study provided proof of mechanism data for TL32711 and are suitable for quantifying apoptotic biomarkers in clinical trials.

Birinapant (TL32711), a bivalent SMAC mimetic, targets TRAF2-associated cIAPs, abrogates TNF-induced NF-kappaB activation, and is active in patient-derived xenograft models.[Pubmed:24563541]

Mol Cancer Ther. 2014 Apr;13(4):867-79.

The acquisition of apoptosis resistance is a fundamental event in cancer development. Among the mechanisms used by cancer cells to evade apoptosis is the dysregulation of inhibitor of apoptosis (IAP) proteins. The activity of the IAPs is regulated by endogenous IAP antagonists such as SMAC (also termed DIABLO). Antagonism of IAP proteins by SMAC occurs via binding of the N-terminal tetrapeptide (AVPI) of SMAC to selected BIR domains of the IAPs. Small molecule compounds that mimic the AVPI motif of SMAC have been designed to overcome IAP-mediated apoptosis resistance of cancer cells. Here, we report the preclinical characterization of Birinapant (TL32711), a bivalent SMAC-mimetic compound currently in clinical trials for the treatment of cancer. Birinapant bound to the BIR3 domains of cIAP1, cIAP2, XIAP, and the BIR domain of ML-IAP in vitro and induced the autoubiquitylation and proteasomal degradation of cIAP1 and cIAP2 in intact cells, which resulted in formation of a RIPK1:caspase-8 complex, caspase-8 activation, and induction of tumor cell death. Birinapant preferentially targeted the TRAF2-associated cIAP1 and cIAP2 with subsequent inhibition of TNF-induced NF-kappaB activation. The activity of a variety of chemotherapeutic cancer drugs was potentiated by birinapant both in a TNF-dependent or TNF-independent manner. Tumor growth in multiple primary patient-derived xenotransplant models was inhibited by birinapant at well-tolerated doses. These results support the therapeutic combination of birinapant with multiple chemotherapies, in particular, those therapies that can induce TNF secretion.

Birinapant (TL32711), a bivalent Smac mimetic, is a potent antagonist for XIAP and cIAP1 with Kds of 45 nM and less than 1 nM, respectively. Birinapant (TL32711) induces the autoubiquitylation and proteasomal degradation of cIAP1 and cIAP2 in intact cells, which results in formation of a RIPK1: caspase-8 complex, caspase-8 activation, and induction of tumor cell death. Birinapant (TL32711) targets TRAF2-associated cIAPs and abrogates TNF-induced NF-κB activation.

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