in this context, the aim of the “ shock - and - kill ” strategy is to reactivate latently infected cells with latency reversal agents ( lras ) and render them vulnerable to cell death or clearance by the immune system. 7, 8 previously reported approaches to hiv reactivation, including protein kinase c ( prkc ) agonists, histone deacetylase ( hdac ) inhibitors ( hdaci ), and toll - like receptor ( tlr ) agonists, 9 have been highly effective in in vitro models of latency, but their efficacy is only moderate when tested in vivo. 10, 11, 12, 13 moreover, by broadly activating cellular pathways, these compounds elicit significant proinflammatory effects or alter the function and fate of specific immune effector cells, 14, 15 hence limiting their use in clinical settings. 16, 17, 18, 19 similarly, promising candidates such as bryostatin - 1 and analogs, phorbol esters, and phosphatidylethanolamine binding protein 1 ( pebp1 ) agonists reactivate hiv via activation of the canonical nuclear factor kappa b ( nfkb ) pathway, 13, 20 inadvertently leading to uncontrolled cytokine release and overt t cell activation. 21, 22 consequently, there is a need to develop alternative approach ( es ) that can reactivate latent reservoirs and eliminate infected cells without triggering systemic activation, inflammation, or impairment of immune clearance mechanisms. in this regard, small molecules known as mimetics of the second mitochondrial activator of caspases ( smac mimetics [ sms ] ) were originally developed as cancer therapeutics. they have received increasing recognition because they specifically activate the non - canonical nfkb pathway, 23, 24, 25 which naturally exhibits higher functional selectivity and more confined proinflammatory effects compared to the canonical nfkb pathway. 24, 26 engagement of the non - canonical nfkb pathway by smac leads to degradation of cellular inhibitor of apoptosis ( ciap ), accumulation of nfkb - inducing kinase ( nik ), and activation of component of inhibitor of nfkb kinase complex ( chuk ) homodimer, culminating in cleavage of inactive nfkb2 p100 to active p52. 26 an association between relb and p52 induces expression of target genes27 and, in the context of hiv, the pathway reactivates latently infected vrs. 20 the non - canonical nfkb pathway can also be triggered by signaling intermediates of the apoptosis cascade. in fact, cleavage of smac / diablo exposes the n - terminal motif ala - val - pro - ile, which binds specifically to baculovirus intermediate repeat domains 2 and 3 of iap proteins. these proteins in turn trigger downstream events that ultimately lead to degradation of baculoviral iap repeat containing 2 ( birc2, also known as ciap1 ) and baculoviral iap repeat containing 3 ( birc3, also known as ciap2 ) 28 and potentiation of apoptosis. 29 the unique ability of smac to degrade iaps and activate apoptosis pathway ( s ) makes sms interesting candidates in the field of hiv cure research30, 31 because latently infected cd4 + t cells display aberrant expression of cell survival factors, including xiap, birc2 and bcl2. 8, 32 pharmacological activation of the non - canonical nfkb pathway by sms was recently found to induce on - art plasma viremia in animal models of hiv latency, 24, 25 underscoring the potential of this class of molecules as lras. however, it remains unclear whether induction of hiv expression by sms leads to a reduction of vrs in lymphoid and non - lymphoid tissues of animal models. in this study, we show that bivalent apg - 1387, currently in clinical development in the oncology field, activates the non - canonical nfkb pathway and hence, is a potent lra. by degrading iaps, this compound also induces the expression of active caspase 3 ( casp3 ), a key component of the execution phase of apoptosis, in latently infected cells. likewise, in primary cd4 + t cells infected with a dual reporter - encoded hiv, apg - 1387 reduces the level of latent cells without notably affecting the productively infected pool. accordingly, in vivo treatment with apg - 1387 could reactivate expression of latent viruses and was found to meaningfully reduce the integrated hiv - dna level in tissues of art - suppressed humanized bone marrow liver thymus ( blt ) mice, without assessable immunotoxicity. upon art interruption, apg - 1387 - treated mice rebounded more slowly and to a lower set point. overall, the study demonstrates that apg - 1387 has the capacity to not only reverse hiv latency but also potentiate cell apoptosis, thus supporting the notion that bivalent sms could be harnessed to reduce vrs without causing generalized t cell activation. results discussion several lras have shown their biological activity both in vitro and in vivo but are clinically unsafe for further evaluations. 46, 47 the most potent lras, including hdaci and protein kinase c ( prkc ) agonist bryostatin - 1, activate the canonical nfkb pathway, 46 causing explicit t cell activation and broad cytotoxicity, and hence eliciting significant collateral damage on host cells. reactivation of latent hiv by prkc agonists has recently been demonstrated to induce resistance to apoptosis, a phenomenon often associated with phosphorylation and activation of the antiapoptotic protein bcl2. 48 thus, the failure of common lras such as prkc agonists and hdaci to safely purge hiv and effectively reduce vrs in people living with hiv necessitate s the development of clinical approaches to achieve an hiv cure. in this study, we demonstrate that apg - 1387, a bivalent sm initially developed as a cancer therapy, can efficiently reactivate hiv in cd4 + t cell line models of hiv - 1 latency via a process that involves activation of the noncanonical nfkb pathway. although this iap antagonist modestly increases hiv rna detection in virally suppressed hu - mice, it has the capability to reduce both the frequency of latently infected cells and the level of viral rebound upon art treatment interruption. indeed, apg - 1387 treatment enhances the expression of caspase - 3, a marker of apoptosis, in latently infected cells from t cell lines or in t cells from certain tissues of virally suppressed hu - mice. in the context of productive infection, in vitro stimulation with apg - 1387 also enhanced cleavage of casp3. iaps are overly expressed in various cancers, enabling prolonged survival of cancerous cells [ as reviewed by49 ]. consequently, their antagonists are thought to either directly induce or sensitize cancerous cells to death by triggering proapoptotic pathways. 50, 51 interestingly, iaps such as birc2 have recently been shown to be negative regulators of hiv transcription, and their expression is found to be correlated with viral latency. 23, 31, 32 indeed, both birc2 / 3 and xiap are overexpressed in hiv latently infected cd4 + t and myeloid cells, and the sms which induce the degradation of these iaps can reactivate hiv. we demonstrate herein that various monov alent and bivalent sms can induce efficient viral reactivation in different t cell models of latency and that some are more potent than others. bivalent sms are more effective than their monov alent counterparts, probably because of the presence of dimers that may contribute to a more stable and enhanced activation via interactions with the two adjacent binding domains of iaps. 52 among the bivalent sms we examined, apg - 1387 is most effective at degrading iaps, facilitating a conversion of nfkb p100 to p52, and reactivating hiv expression through an nik - dependent process, a hallmark of an activated non - canonical nfkb pathway. 23, 24 in cd4 + t cell models of hiv latency, apg - 1387 treatment is associated with remarkable viral reactivation. however, in primary cd4 + t cells infected with hi. fate.