The discovery and structure-activity relationships of pyrano[3,4-b]indole-based inhibitors of hepatitis C virus NS5B polymerase.

We describe the structure-activity relationship of the C7-position of pyrano[3,4-b]indole-based inhibitors of HCV NS5B polymerase. Further exploration of the allosteric binding site led to the discovery of the significantly more potent compounds 13 and 14.

N-(3,3a,4,4a,5,5a,6,6a-Octahydro-1,3-dioxo-4,6- ethenocycloprop[f]isoindol-2-(1H)-yl)carboxamides: Identification of novel orthopoxvirus egress inhibitors.

A series of novel, potent orthopoxvirus egress inhibitors was identified during high-throughput screening of the ViroPharma small molecule collection. Using structure--activity relationship information inferred from early hits, several compounds were synthesized, and compound 14 was identified as a potent, orally bioavailable first-in-class inhibitor of orthopoxvirus egress from infected cells. Compound 14 has shown comparable efficaciousness in three murine orthopoxvirus models and has entered Phase I clinical trials.

Electrophilic Oxidation and [1,2]-Rearrangement of the Biindole Core of Birinapant.

Birinapant/TL32711 (1) is a bivalent antagonist of the inhibitor of apoptosis (IAP) family of proteins and was designed to mimic AVPI, the N-terminal tetrapeptide of the second mitochondria-derived activator of caspases (Smac/DIABLO). Birinapant bound to the BIR3 domains of cIAP1, cIAP2, and XIAP with K i values of 1, 36, and 45 nM, respectively. Birinapant-mediated activation of cIAP1 resulted in cIAP1 autoubiquitylation and degradation and correlated with inhibition of TNF-mediated NF-κB activation, induction of tumor cell death in vitro, and tumor regression in vivo. Birinapant is being evaluated in Phase 1/2 trials for the treatment of cancer and hepatitis B virus (HBV) infection. After one year at accelerated storage conditions, a formulation of 1 afforded four degradants in >0.1% abundance by HPLC analysis. The primary degradants (2 and 3) were formed via oxidation of the biindole core, while the secondary degradants (5 and 6) arose via [1,2]-rearrangement of 3 and 2, respectively. Forced degradation conditions were developed, which allowed the isolation of 2 and 3 in multigram quantities. Novel deuterated analogues of 1 were prepared to determine the site of oxidation, and NMR experiments confirmed the chemical structures of 5 and 6. The de novo synthesis of 2, 3, 5, and 6 confirmed these experimental findings.

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

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-κB 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, a smac-mimetic with improved tolerability for the treatment of solid tumors and hematological malignancies.

Birinapant (1) is a second-generation bivalent antagonist of IAP proteins that is currently undergoing clinical development for the treatment of cancer. Using a range of assays that evaluated cIAP1 stability and oligomeric state, we demonstrated that 1 stabilized the cIAP1-BUCR (BIR3-UBA-CARD-RING) dimer and promoted autoubiquitylation of cIAP1 in vitro. Smac-mimetic 1-induced loss of cIAPs correlated with inhibition of TNF-mediated NF-κB activation, caspase activation, and tumor cell killing. Many first-generation Smac-mimetics such as compound A (2) were poorly tolerated. Notably, animals that lack functional cIAP1, cIAP2, and XIAP are not viable, and 2 mimicked features of triple IAP knockout cells in vitro. The improved tolerability of 1 was associated with (i) decreased potency against cIAP2 and affinity for XIAP BIR3 and (ii) decreased ability to inhibit XIAP-dependent signaling pathways. The P2' position of 1 was critical to this differential activity, and this improved tolerability has allowed 1 to proceed into clinical studies.