Inhibitor Of Apoptosis Proteins Antagonist Research Articles

Release of P-TEFb from the Super Elongation Complex promotes HIV-1 latency reversal.

The persistence of HIV-1 in long-lived latent reservoirs during suppressive antiretroviral therapy (ART) remains one of the principal barriers to a functional cure. Blocks to transcriptional elongation play a central role in maintaining the latent state, and several latency reversal strategies focus on the release of positive transcription elongation factor b (P-TEFb) from sequestration by negative regulatory complexes, such as the 7SK complex and BRD4. Another major cellular reservoir of P-TEFb is in Super Elongation Complexes (SECs), which play broad regulatory roles in host gene expression. Still, it is unknown if the release of P-TEFb from SECs is a viable latency reversal strategy. Here, we demonstrate that the SEC is not required for HIV-1 replication in primary CD4+ T cells and that a small molecular inhibitor of the P-TEFb/SEC interaction (termed KL-2) increases viral transcription. KL-2 acts synergistically with other latency reversing agents (LRAs) to reactivate viral transcription in several cell line models of latency in a manner that is, at least in part, dependent on the viral Tat protein. Finally, we demonstrate that KL-2 enhances viral reactivation in peripheral blood mononuclear cells (PBMCs) from people living with HIV (PLWH) on suppressive ART, most notably in combination with inhibitor of apoptosis protein antagonists (IAPi). Taken together, these results suggest that the release of P-TEFb from cellular SECs may be a novel route for HIV-1 latency reactivation.

Chimeric antigen receptor dendritic cells targeted delivery of a single tumoricidal factor for cancer immunotherapy

BackgroundChimeric antigen receptor (CAR)-T cells have been used to treat blood cancers by producing a wide variety of cytokines. However, they are not effective in treating solid cancers and can cause severe side-effects, including cytokine release syndrome. TNFα is a tumoricidal cytokine, but it markedly increases the protein levels of cIAP1 and cIAP2, the members of inhibitor of apoptosis protein (IAP) family of E3 ubiquitin ligase that limits caspase-induced apoptosis. Degradation of IAP proteins by an IAP antagonist does not effectively kill cancer cells but enables TNFα to strongly induce cancer cell apoptosis. It would be a promising approach to treat cancers by targeted delivery of TNFα through an inactive adoptive cell in combination with an IAP antagonist.MethodsHuman dendritic cells (DCs) were engineered to express a single tumoricidal factor, TNFα, and a membrane-anchored Mucin1 antibody scFv, named Mucin 1 directed DCs expressing TNFα (M-DCsTNF). The efficacy of M-DCsTNF in recognizing and treating breast cancer was tested in vitro and in vivo.ResultsMucin1 was highly expressed on the surface of a wide range of human breast cancer cell lines. M-DCsTNF directly associated with MDA-MB-231 cells in the bone of NSG mice. M-DCsTNF plus an IAP antagonist, SM-164, but neither alone, markedly induce MDA-MB-231 breast cancer cell apoptosis, which was blocked by TNF antibody. Importantly, M-DCsTNF combined with SM-164, but not SM-164 alone, inhibited the growth of patient-derived breast cancer in NSG mice.ConclusionAn adoptive cell targeting delivery of TNFα combined with an IAP antagonist is a novel effective approach to treat breast cancer and could be expanded to treat other solid cancers. Unlike CAR-T cell, this novel adoptive cell is not activated to produce a wide variety of cytokines, except for additional overexpressed TNF, and thus could avoid the severe side effects such as cytokine release syndrome.

Nanoparticle delivery of Tat synergizes with classical latency reversal agents to express HIV antigen targets.

Limited cellular levels of the HIV transcriptional activator Tat are one contributor to proviral latency that might be targeted in HIV cure strategies. We recently demonstrated that lipid nanoparticles containing HIV tat mRNA induce HIV expression in primary CD4 T cells. Here, we sought to further characterize tat mRNA in the context of several benchmark latency reversal agents (LRAs), including inhibitor of apoptosis protein antagonists (IAPi), bromodomain and extra-Terminal motif inhibitors (BETi), and histone deacetylase inhibitors (HDACi). tat mRNA reversed latency across several different cell line models of HIV latency, an effect dependent on the TAR hairpin loop. Synergistic enhancement of tat mRNA activity was observed with IAPi, HDACi, and BETi, albeit to variable degrees. In primary CD4 T cells from durably suppressed people with HIV, tat mRNA profoundly increased the frequencies of elongated, multiply-spliced, and polyadenylated HIV transcripts, while having a lesser impact on TAR transcript frequencies. tat mRNAs alone resulted in variable HIV p24 protein induction across donors. However, tat mRNA in combination with IAPi, BETi, or HDACi markedly enhanced HIV RNA and protein expression without overt cytotoxicity or cellular activation. Notably, combination regimens approached or in some cases exceeded the latency reversal activity of maximal mitogenic T cell stimulation. Higher levels of tat mRNA-driven HIV p24 induction were observed in donors with larger mitogen-inducible HIV reservoirs, and expression increased with prolonged exposure time. Combination LRA strategies employing both small molecule inhibitors and Tat delivered to CD4 T cells are a promising approach to effectively target the HIV reservoir.

Research Progress in the Use of Small Molecule Smac Mimetics in Combination Therapy of Cancer.

Inhibitors of Apoptosis Proteins (IAP) are inhibitors that can block programmed cell death, are expressed at high levels in various cancers, and are recognized as a therapeutic target for cancer therapy. In the past few years, several small molecule IAP protein inhibitors have been designed to mimic the endogenous IAP antagonist, but no IAP inhibitors have been approved for marketing worldwide. Previously, xevinapant has been awarded a breakthrough therapy designation by the FDA. In addition, a combination of Smac-mimetics and chemotherapeutic compounds has been reported to improve anticancer efficacy. According to the phase II clinical data, xevinapant has the potential to significantly enhance the standard therapy for patients with head and neck cancer, which is expected to be approved as an innovative therapy for cancer patients. Therefore, this paper briefly describes the mechanism of IAPs (AT-406, APG-1387, GDC- 0152, TL32711, and LCL161) as single or in combination for cancer treatment, their application status as well as the synthetic pathway, and explores the research prospects and challenges of IAPs antagonists in the tumor combination therapy, with the hope of providing strong insights into the further development of Smac mimics in tumor therapy.

ASTX660-01 Phase 2: A Case Study of Tolinapant-Induced Pseudoprogression in CTCL

Background: Cutaneous T-Cell Lymphomas (CTCL) are rare malignancies that comprise <10% of Non-Hodgkin Lymphoma. Limited treatment options exist for these patients, especially after progression following front-line therapy. Tolinapant is an oral non-peptidomimetic antagonist of the inhibitor of apoptosis proteins (IAPs), cIAP1/2 and XIAP. It plays a role in regulated tumor cell death and immunomodulation (Ferrari et al., Blood Adv. 2021) and has been evaluated in the clinic (ASTX660-01 trial, NCT02503423). Previously, we reported an overall response rate of 28% in CTCL patients treated with tolinapant, with a median duration of response of 8.8 months (Michot et al., EHA 2022). During this trial, in which the patients were given tolinapant on Weeks 1 and 3 in 4-week cycles, clinical investigators have described multiple instances of tumor flare and pseudoprogression, consistent with the described immunomodulatory effects associated with tolinapant treatment. Here, we present one such case, a 58-year-old male, who was diagnosed with mycosis fungoides in 2010, which had previously transformed despite multiple therapies. This subject was selected for a more detailed study due to their clinical course with multiple blood samples and biopsies collected, permitting longitudinal histological and molecular characterization. At enrollment in March 2021, the subject presented with red, scaly plaques and cutaneous tumors scattered on the extremities and trunk. At one-month follow up, the subject had an excellent initial symptomatic response with the visual resolution of several tumors. Moreover, the itch reported as “moderate” at baseline had improved with tolinapant treatment. However, during continued therapy, the remaining plaques and tumors progressively swelled, appearing pink and indurated on dosing, indicative of flare. During off-dosing weeks, these signs of flare were reduced. The subject also reported increased itch during treatment that partly resolved during off-dosing weeks. Considering the disappearance of some tumors and the improved appearance during off-dosing weeks, this was pseudoprogression. Methods: Cell surface phenotype of the lymphoma was determined by flow cytometry (Standard Leukemia/Lymphoma and T-Cell Therapy Panel, NeoGenomics Laboratories) on blood samples collected at screening and during Cycles 1, 3 and 5. To characterize the clinical observations, skin biopsies including tumor tissues were collected at baseline and during Cycles 1, 2, 6, 7 and 10. We used multiplex immunofluorescence analysis (COMET™, Lunaphore Technologies SA), gene expression profiling (PanCancer IO 360™ and Pathways panels, NanoString Technologies, Inc.), genomic profiling (FoundationOne™ Heme, Foundation Medicine, Inc.) and cytokine/chemokine measurements (Human ExplorerMAP™ v. 1.0, xMAP® Technology, Luminex Corporation). Results: Blood samples collected at screening and post-treatment confirmed the presence of lymphoma cells that were CD3 +, CD4 +, CD7 -, CD8 - and CD26 -. Multiplex immunofluorescence analysis of the biopsies was able to detect lymphoma cells as CD4 +, CD7 - and CD8 -. Sparsely distributed CD8 + cells were observed at baseline (screening sample). In the biopsy taken on Cycle 2 Day 1, the level of CD8 + cells was markedly increased. Representative images are shown below (left: baseline; right: post-treatment). Analysis of genes associated with CD8 + T cells, cytotoxic cells, B cells and NK cells showed an increase in gene probe signals for CD8A, CD8B, GZMA, GZMH and PRF1. Post-treatment plasma samples showed an elevation in chemokines involved in leukocyte recruitment, such as, CXCL1, CXCL10 and CCL25. Similarly, consistent systemic changes in CXCL10, the chemokine directing recruitment of CXCR3 + cytotoxic T cells, were also detected in tolinapant-treated peripheral TCL patients in the same trial. Conclusions: Our data offer a cellular and molecular insight into a case of clinical pseudoprogression observed during tolinapant treatment. Understanding pseudoprogression is important for clinical investigators and patients to ensure treatment with tolinapant, or other IAP antagonists, are not discontinued prematurely.

Potentiation of apoptosis in drug-resistant mantle cell lymphoma cells by MCL-1 inhibitor involves downregulation of inhibitor of apoptosis proteins

Bruton’s tyrosine kinase inhibitors (BTKi) and CAR T-cell therapy have demonstrated tremendous clinical benefits in mantle cell lymphoma (MCL) patients, but intrinsic or acquired resistance inevitably develops. In this study, we assessed the efficacy of the highly potent and selective MCL-1 inhibitor AZD5991 in various therapy-resistant MCL cell models. AZD5991 markedly induced apoptosis in these cells. In addition to liberating BAK from the antiapoptotic MCL-1/BAK complex for the subsequent apoptosis cascade, AZD5991 downregulated inhibitor of apoptosis proteins (IAPs) through a BAK-dependent mechanism to amplify the apoptotic signal. The combination of AZD5991 with venetoclax enhanced apoptosis and reduced mitochondrial oxygen consumption capacity in MCL cell lines irrespective of their BTKi or venetoclax sensitivity. This combination also dramatically inhibited tumor growth and prolonged mouse survival in two aggressive MCL patient-derived xenograft models. Mechanistically, the augmented cell lethality was accompanied by the synergistic suppression of IAPs. Supporting this notion, the IAP antagonist BV6 induced dramatic apoptosis in resistant MCL cells and sensitized the resistant MCL cells to venetoclax. Our study uncovered another unique route for MCL-1 inhibitor to trigger apoptosis, implying that the pro-apoptotic combination of IAP antagonists and apoptosis inducers could be further exploited for MCL patients with multiple therapeutic resistance.

Abstract PO-050: Preliminary results from an early-phase, open-label study of tolinapant and radiation in cisplatin-ineligible patients with previously untreated, locally advanced head and neck cancer

Abstract Background: Genomic alterations in NF-kB and inhibitor of apoptosis protein (IAP) pathways are common in head and neck cancer (HNC). IAP antagonists have shown activity in HNC, especially when paired with radiation therapy (RT), in both preclinical and early clinical studies. Our preclinical studies suggest that the combination of tolinapant and RT works in part by enhancing T cell activation, dendritic cell maturation, immunogenic cell death, and other aspects of the anti-tumor immune response. However, the safety and efficacy of IAPi combined with definitive RT, without platinum chemotherapy, has not been explored clinically. Methods: This is an open-label, early-phase study to determine the safety of the IAPi tolinapant combined with definitive or adjuvant RT. Eligible patients have previously untreated, locally advanced HNC, ECOG ≤1, with plan for definitive or adjuvant RT but are ineligible for treatment with cisplatin. Patients are treated with intensity-modulated radiation therapy (IMRT) or proton therapy (IMPT) to 60-70 Gy with tolinapant 180 mg (the single-agent recommended phase 2 dose) daily by mouth or feeding tube for 7 days during weeks 1, 3, 5, and 7 of RT, with the option of tolinapant dose reduction to 90 mg daily for toxicity. In the adjuvant setting, patients are treated for 6 weeks with 3 cycles of tolinapant. Blood is collected for research at baseline and during weeks 2 and 7. Tissue biopsies at baseline and during week 2 are optional. Results: Eight patients have been consented, including 3 screen failures and 5 enrolled (accrual target = 10 enrolled). All enrolled patients to date received definitive RT; four patients were treated with IMPT. Tumor sites included nasopharynx (1), oropharynx (one HPV+, one HPV-), and larynx (2). The most common reason for cisplatin ineligibility was hearing loss. The median age was 70 (range, 64-81). One patient had a grade 2 rash with pruritis that persisted for several weeks after treatment; other AEs included one treatment interruption during week 1, attributed to RT. Dose reduction of tolinapant was not required for any patients. Three patients have been evaluated by imaging and clinical exam 3 months after treatment, with no evidence of residual disease. Flow cytometry of peripheral blood samples showed a decrease in the proportion of CD4+CD25+ T cells (3/5 patients) and increase of differentiation markers on CD8+ T cells (4/5 patients) from baseline to week 2; these trends were more pronounced at week 7. The one patient who experienced a persistent grade 2 rash with pruritis had a >10-fold increase in activated (HLA-DR+CD38+) CD8+ T cells by week 7. Conclusions: Based on preliminary safety and tolerability data reviewed at this interim analysis, tolinapant at 180 mg appears to be a safe dose for combination with definitive RT. Additional studies will further characterize the dynamics of the peripheral immune response and provide longer follow up on a larger cohort of patients. This study was supported by Astex Pharmaceuticals, Inc. with a research grant to NCS and NFS. Citation Format: Nicole C. Schmitt, William A. Stokes, James E. Bates, Madison Stallings, Brendan L. C. Kinney, Mark W. McDonald, Soumon Rudra, Jill Remick, Zachary S. Buchwald, Dong M. Shin, Azeem S. Kaka, Mihir R. Patel, Nabil F. Saba. Preliminary results from an early-phase, open-label study of tolinapant and radiation in cisplatin-ineligible patients with previously untreated, locally advanced head and neck cancer [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Innovating through Basic, Clinical, and Translational Research; 2023 Jul 7-8; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2023;29(18_Suppl):Abstract nr PO-050.

P10.22.B COMBINATION OF ARTS MIMETICS WITH AUTOPHAGY INHIBITORS AS A NOVEL THERAPEUTIC STRATEGY TO OVERCOME APOPTOSIS RESISTANCE IN GLIOBLASTOMA

Abstract BACKGROUND Glioblastoma (GBM) is the most common malignant brain tumour in adults. The current standard of care for GBM patients consists of maximal surgical resection followed by chemotherapy and radiation. Despite such an aggressive treatment approach, the average 5-year survival rate for GBM patients is approximately 5%. One of the main reasons for poor therapy response in the GBM is resistance to programmed cell death, otherwise known as apoptosis. One of the mechanisms behind apoptosis resistance relies on the upregulation of inhibitor of apoptosis proteins (IAPs) which are known to hinder pro-apoptotic proteins and allow cell survival under abnormal conditions such as severe DNA damage. However, there are natural IAP antagonists such as ARTS which are capable of stimulating cell death by promoting the degradation of IAPs. To harness the pro-apoptotic function of IAP antagonists, small peptide mimetics of ARTS have been developed. This project investigates the efficacy of utilizing ARTS mimetics as a novel strategy to overcome apoptosis resistance in the GBM treatment. MATERIAL AND METHODS This study utilizes patient-derived cells with exogenous gain-of-function (GOF) overexpression to introduce full-length ARTS protein as well as pharmacological small peptide mimetics of ARTS to evaluate the response of GBM cells following the promotion of ARTS activity. We also employ a patient-derived orthotopic xenograft mouse model to test novel combinatorial strategies in vivo, where we used a nanoparticle drug delivery system to ensure treatment delivery across the blood-brain barrier (BBB). RESULTS We found that patient-derived GBM cells were highly resistant to ARTS-induced apoptosis. Further molecular investigation unveiled a novel role of ARTS in the upregulation of autophagy as a resistance mechanism. A combination of ARTS GOF or mimetic peptides with autophagy inhibitors mitigated resistance to ARTS-mediated apoptosis and drastically decreased GBM cell proliferation. This combination was further tested in the patient-derived xenograft mouse model, which demonstrated the successful delivery of ARTS mimetic peptides and autophagy inhibitors through the BBB via nanoparticle lipid carriers. Animals treated with a combination of the autophagy inhibitor Spautin-1 and ARTS mimetic peptides demonstrated significantly prolonged survival, confirming the therapeutic potential of such combinatorial approach for GBM treatment. CONCLUSION Altogether, these findings uncover a previously unknown role of ARTS in autophagy regulation and provide evidence that the combination of IAP-antagonist mimetics with autophagy inhibitors can be an effective strategy against highly aggressive GBM brain tumours. This work was supported by the Health Sciences Centre Foundation (HSCF).

BV6, AN ANTAGONIST OF INHIBITOR OF APOPTOSIS PROTEINS, SENSITIZES RESISTANT MANTLE CELL LYMPHOMA CELLS TO VENETOCLAX

Introduction: Although Bruton’s tyrosine kinase inhibitors (BTKi) and CAR T-cell therapy have achieved remarkable efficacy in the treatment of mantle cell lymphoma (MCL), it remains incurable due to the inevitable development of therapeutic resistance. The BCL-2 inhibitor venetoclax is effective in many relapsed MCL patients, including those who progressed on BTKi, but subsequent relapse to venetoclax yields poor clinical outcomes. Hence, novel therapeutics and combination therapies are required to tackle the clinical challenges. Here, we investigated BV6, an antagonist of inhibitor of apoptosis proteins (IAPs), alone and in combination with venetoclax in multiple therapy-resistant MCL models. Methods: We performed single-cell RNA-seq to assess gene expression in ibrutinib-sensitive, ibrutinib-resistant, and dual ibrutinib-/CAR T-resistant MCL patients. Cell lines with acquired resistance to ibrutinib or venetoclax, as well as primary tumor cells from patients who relapsed after multiple therapies, were used as models of MCL resistance. CellTiter-Glo® luminescent assay was used to measure cell viability; annexin V/PI staining was used to measure the induction of apoptosis; and western blotting was used to assess IAP and apoptosis signaling protein expression across MCL cell lines after drug treatment. Results: The single-cell RNA-seq analysis demonstrated that IAP gene expression was not influenced by patient response to ibrutinib and CAR T-cell therapy, and western blotting showed that IAP proteins were broadly expressed across all MCL cell lines. To determine the on-target effects of BV6, we treated JeKo-1, JeKo-IBN-R, Mino, and Mino-VEN-R cells with BV6 and examined the expression of IAPs. BV6 treatment for 4h markedly reduced c-IAP1 and c-IAP2 expression, and moderately reduced XIAP expression. BV6 inhibited cell viability in both ibrutinib- and venetoclax-resistant cell lines, and BV6 treatment for 24 h dose-dependently induced apoptosis in MCL cells, including not only cell lines with acquired resistance but also patient primary cells, independent of their resistance to ibrutinib, venetoclax, and CAR T-cell therapy. We observed a striking and significant synergy in the cell viability assay when ibrutinib- or venetoclax-resistant cells were treated with BV6 combined with venetoclax (combination index < 1), and a dramatic enhancement of apoptosis (p < 0.001). The combination eradicated c-IAP1 and c-IAP2 expression, while XIAP was synergistically diminished. This was accompanied by strong caspase-3 activation and PARP cleavage. This combination therapy is currently under evaluation in venetoclax-resistant mouse model in vivo. Conclusions: Our findings indicate that a combination of IAP antagonists with apoptosis inducers can be exploited as a rational strategy to overcome therapeutic resistance in MCL. This study was supported by philanthropic funds from the Kimmel Research fund and various donor funds. Keywords: Aggressive B-cell non-Hodgkin lymphoma, Combination Therapies, Molecular Targeted Therapies No conflicts of interests pertinent to the abstract.

The expanding role of IAP antagonists for the treatment of head and neck cancer.

Inhibitors of apoptosis proteins (IAPs) inhibit the intrinsic and extrinsic cell death pathways, promoting cell survival. Antagonists of these pathways are under study as anti-cancer therapeutics. A high proportion of head and neck squamous cell carcinomas (HNSCCs) have genomic alterations in IAP pathways, resulting in the dysregulation of cell death pathways and rendering them susceptible to IAP antagonist therapy. Preclinical studies suggest IAP antagonists, also known as second mitochondria-derived activator of caspases mimetics, may be effective treatments for HNSCC, especially when combined with radiation. Mechanistic studies have shown both molecular mechanisms (i.e., enhanced cell death) and immune mechanisms (e.g., immunogenic cell death and T-cell activation), underlying the efficacy of these drugs in preclinical models. Phase I/II clinical trials have shown promising results, portending a future where this class of targeted therapies becomes incorporated into the treatment paradigm for head and neck cancers. IAP antagonists have shown great promise for head and neck cancer, especially in combination with radiation therapy. Here, we review recent preclinical and clinical studies on the use of these novel targeted agents for head and neck cancer.

Inhibitor of Apoptosis Proteins Antagonist Induces T-cell Proliferation after Cross-Presentation by Dendritic Cells.

Cross-presentation of tumor antigens by dendritic cells (DC) is crucial to prime, stimulate and restimulate CD8+ T cells. This process is important in initiating and maintaining an antitumor response. Here, we show that the presence of conventional type 1 DCs (cDC1), a DC subtype that excels in cross-presentation, in the tumor correlated with response to neoadjuvant immune checkpoint blockade (ICB) in melanoma. This led us to hypothesize that patients failing to respond to ICB could benefit from enhanced cross-presentation of tumor antigens. We therefore established a cross-presentation assay to screen over 5,500 compounds for enhancers of DC cross-presentation using induced T-cell proliferation as the readout. We identified 145 enhancers, including AZD5582, an antagonist of inhibitor of apoptosis proteins (IAP) cIAP1, cIAP2, and XIAP. AZD5582 treatment led to DC activation of the noncanonical NF-kB pathway, enhanced antigen import from endolysosomes into the cytosol, and increased expression of genes involved in cross-presentation. Furthermore, it upregulated expression of CD80, CD86, MHC class II, CD70 and secretion of TNF by DCs. This enhanced DC activation and maturation program was observed also in tumor-bearing mice upon AZD5582 treatment, culminating in an increased frequency of systemic tumor antigen-specific CD8+ T cells. Our results merit further exploration of AZD5582 to increase antigen cross-presentation for improving the clinical benefit of ICB in patients who are unlikely to respond to ICB.

The IAP antagonist birinapant enhances chimeric antigen receptor T cell therapy for glioblastoma by overcoming antigen heterogeneity

Antigen heterogeneity that results in tumor antigenic escape is one of the major obstacles to successful chimeric antigen receptor (CAR) Tcell therapies in solid tumors including glioblastoma multiforme (GBM). To address this issue and improve the efficacy of CAR Tcell therapy for GBM, we developed an approach that combines CAR Tcells with inhibitor of apoptosis protein (IAP) antagonists, a new class of small molecules that mediate the degradation of IAPs, to treat GBM. Here, we demonstrated that the IAP antagonist birinapant could sensitize GBM cell lines and patient-derived primary GBM organoids to apoptosis induced by CAR Tcell-derived cytokines, such as tumor necrosis factor. Therefore, birinapant could enhance CAR Tcell-mediated bystander death of antigen-negative GBM cells, thus preventing tumor antigenic escape in antigen-heterogeneous tumor models invitro and invivo. In addition, birinapant could promote the activation of NF-κB signaling pathways in antigen-stimulated CAR Tcells, and with a birinapant-resistant tumor model we showed that birinapant had no deleterious effect on CAR Tcell functions invitro and invivo. Overall, we demonstrated the potential of combining the IAP antagonist birinapant with CAR Tcells as a novel and feasible approach to overcoming tumor antigen heterogeneity and enhancing CAR Tcell therapy forGBM.

Discovery of pan-IAP degraders via a CRBN recruiting mechanism

Inhibitors of apoptosis proteins (IAPs), defined by the presence of baculovirus IAP repeat (BIR) protein domain, are critical regulators of cell survival and cell death processes. Cellular IAP 1/2 (cIAP1/2) and X-linked IAPs (XIAPs) regulate the innate immune signaling pathway through their E3 ubiquitin ligase activity. Peptidomimetics or small-molecule IAP antagonists have been developed to treat various diseases, such as cancer, infection, and inflammation. In this study, we synthesized and characterized IAP–cereblon (CRBN) heterodimerizing proteolysis-targeting chimera (PROTAC), which induces the degradation of cIAP1/2 and XIAP but not CRBN. We demonstrated that this PROTAC inhibits tumor necrosis factor alpha (TNFα)-induced innate immune response and cancer cell migration and invasion, leading to apoptotic cell death. Our study is the first to demonstrate that both cIAPs and XIAP are degradable when applied to the PROTAC strategy.

Lipopolysaccharide sensitizes the therapeutic response of breast cancer to IAP antagonist.

Inhibitor of apoptosis protein (IAP) is a class of E3 ubiquitin ligases functioning to support cancer survival and growth. Many small-molecule IAP antagonists have been developed, aiming to degrade IAP proteins to kill cancer. We have evaluated the effect of lipopolysaccharide (LPS), a component of the bacterial outer membrane, on IAP antagonists in treating breast cancer in a mouse model to guide future clinical trials. We show that LPS promotes IAP antagonist-induced regression of triple-negative breast cancer (TNBC) from MDA-MB-231 cells in immunodeficient mice. IAP antagonists such as SM-164, AT-406, and BV6, do not kill MDA-MB-231 cells alone, but allow LPS to induce cancer cell apoptosis rapidly. The apoptosis caused by LPS plus SM-164 is blocked by toll-like receptor 4 (TLR4) or MyD88 inhibitor, which inhibits LPS-induced TNFα production by the cancer cells. Consistent with this, MDA-MB-231 cell apoptosis induced by LPS plus SM-164 is also blocked by the TNF inhibitor. LPS alone does not kill MDA-MB-231 cells because it markedly increases the protein level of cIAP1/2, which is directly associated with and stabilized by MyD88, an adaptor protein of TLR4. ER+ MCF7 breast cancer cells expressing low levels of cIAP1/2 undergo apoptosis in response to SM-164 combined with TNFα but not with LPS. Furthermore, TNFα but not LPS alone inhibits MCF7 cell growth in vitro. Consistent with these, LPS combined with SM-164, but not either of them alone, causes regression of ER+ breast cancer from MCF7 cells in immunodeficient mice. In summary, LPS sensitizes the therapeutic response of both triple-negative and ER+ breast cancer to IAP antagonist therapy by inducing rapid apoptosis of the cancer cells through TLR4- and MyD88-mediated production of TNFα. We conclude that antibiotics that can reduce microbiota-derived LPS should not be used together with an IAP antagonist for cancer therapy.

Abstract 3443: The IAP antagonist xevinapant, in combination with high-dose cisplatin chemoradiotherapy, induces NF-kB and apoptotic pathway biomarkers in patients with high-risk locally advanced squamous cell carcinoma of the head and neck

Abstract Introduction: Inhibitor of Apoptosis Proteins (IAPs) regulate apoptosis and modulate NF-kB signaling, which in turn drives the expression of genes involved in immune and inflammatory responses. Xevinapant (XVT) (a.k.a Debio 1143) is an orally available IAP antagonist shown to enhance tumor response to radiation through the proapoptotic cytokine TNFα and caspase activation. Results from a double-blind, multicenter, randomized, phase II trial in patients with high-risk locally advanced squamous cell carcinoma of the head and neck (LA-SCCHN) revealed significant improvement in overall survival (OS), progression free survival (PFS) and duration of response with XVT in combination with high-dose cisplatin chemoradiotherapy (CRT) vs CRT alone (NCT02022098). We analyzed XVT pharmacodynamic (PD) biomarker time-concentration profiles and explored the association of PD changes over time with clinical efficacy and safety parameters. Methods: Three serum PD biomarkers were measured during cycle 1: caspase-cleaved cytokeratin 18 fragment (CKM30), a biomarker of epithelial apoptosis, MCP1 and TNFα, both NF-kB target genes. Time course changes in PD biomarker exposure, measured by their Area Under the Curve (AUC), were tested for association with clinical efficacy and safety endpoints, by linear, logistic, and Cox Proportional Hazard models. Clinical response parameters included locoregional control (LRC) at 18 months from end of treatment (EOT), PFS, duration of LRC, time to distant relapse (TTDR), OS and complete response (CR) 6 months after EOT. Results: The biomarker analysis set was composed of all patients with baseline PD assessments and at least one post-baseline measurement and included 35 and 40 patients in the XVT and placebo (PBO) arms, respectively. All three serum PD biomarkers increased upon administration of CRT + XVT during cycle 1. The increase in CKM30 and MCP1 levels was significantly higher in the CRT + XVT arm vs the CRT + PBO arm, as tested by linear mixed effect models (CKM30: p = 0.0167; MCP1: p = 0.0135). Interestingly, CKM30 AUC appeared to be correlated with response in CRT + XVT but not CRT + PBO (based on LRC at month 18 or CR at month 6). No associations between any of the three biomarkers were observed with the safety endpoints explored. Conclusions: Xevinapant has demonstrated promising activity in combination with CRT in LA-SCCHN. The outcome of the exploratory PD analyses indicates that XVT modulates NF-kB signaling, leading to serum increases in MCP1 and TNFα while further augmenting CRT-induced apoptotic marker CKM30. Our findings further characterize the mechanism of action of XVT and how it may ultimately result in enhanced clinical responses to CRT. Citation Format: Luke Piggott, Bruno Gavillet, Franck Brichory, Kathrin Gollmer, Florilene Bouisset, Gregoire Vuagniaux. The IAP antagonist xevinapant, in combination with high-dose cisplatin chemoradiotherapy, induces NF-kB and apoptotic pathway biomarkers in patients with high-risk locally advanced squamous cell carcinoma of the head and neck [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3443.

Abstract 5337: Tolinapant (ASTX660) enhances the anti-leukemic activity of Venetoclax and Dexamethasone in T cell acute lymphoblastic leukemia (T-ALL)

Abstract Background: Inhibitors of apoptosis proteins (IAPs) are overexpressed in ALL leading to resistance to apoptosis and chemo-resistance. Tolinapant, a non-peptidomimetic antagonist of the cellular and X-linked inhibitors of apoptosis (cIAP1/2 and XIAP) being evaluated in Phase 1/2 clinical trial [NCT02503423] showed single-agent activity in T-cell lymphoma. Objectives: Herein, we analyzed the preclinical activity of tolinapant in combination with ABT199 and Dexamethasone (DEX) in T-ALL (in vitro and ex-vivo patient derived xenografts (PDX). Results: Using a panel of 8 T-ALL cell lines we analyzed the single agent activity of tolinapant. Loucy and SUP-T11 were most sensitive (IC50 = 190-309 nM). CCRF-CEM and ALL-SIL showed moderate sensitivity (IC50 = 10-18 µM) while Jurkat, MOLT16, MOLT4 and PF382 were resistant. Western blotting (WB) showed decreased levels of cIAP1and cIAP2 with no change in XIAP in response to tolinapant as a single agent. We next investigated the efficacy of tolinapant with Bcl2 inhibitor ABT199. The combination of ABT199 and ASTX660 was synergistic in Loucy cell line with combination index (CI) of 0.14. Cell death was increased to 64±3% in combination v/s 27±0.9% in ABT199. WB showed decreased cIAP2 and increased levels of cleaved caspase 7 and cleaved caspase 9 in combination compared to single agents, suggesting increased apoptosis. Treatment of PDX-derived cells with tolinapant and ABT199 was more effective than monotherapy in inducing apoptosis in CD45+ bulk (46±0.7% to 63±6%, p&amp;lt;0.0001) and leukemia initiating cells (LICs, CD45+ CD7+ CD19- CD34+) (39±3% to 54±8%, p=0.003). Next, we checked the effect of combination of DEX with tolinapant in T-ALL cell lines. CCRF-CEM cell line is from a relapsed patient and is resistant to DEX. The combination was synergistic with CI of 0.26 and cell death of 50±4% compared to 20±3% by DEX. A triple combination of DEX, ABT199 and tolinapant increased apoptotic response to 82.9±1%, compared to DEX+ABT199 dual combination where apoptosis was induced to 52.4±2%. Strong synergy in terms of both cytoreduction as well as apoptosis induction was observed in SUP-T11 cells. Tolinapant sensitized SUP-T11 cells to DEX with ED50 value of 542 nM in combination compared to ~2 µM with DEX treatment. Simultaneous analysis of cell proliferation, stress response and DNA damage using single-cell proteomics analysis showed downregulation of proliferation (Ki-67), stress response (ATF4, LC3B) and increased levels of cleaved PARP, cleaved caspase 3 suggesting increased apoptosis in combination of tolinapant with DEX. Treatment of PDX-derived cells with tolinapant enhanced the cytotoxic effect of DEX in CD45+ bulk (58±2% to 71±0.1%, p&amp;lt;0.0001) and LICs (62±2% to 78±0.9%, p&amp;lt;0.0001). Conclusion: Tolinapant synergizes with the anti-leukemic activity of ABT199 and DEX, establishing a therapeutic rationale for IAP antagonist in T-ALL. Citation Format: Priyanka Sharma, Sujan Piya, Huaxian Ma, Natalia Baran, Muharrem Muftuoglu, Mahesh Basyal, Vivian Ruvolo, George Ward, Tomoko Smyth, Martin J. Sims, Michael Andreeff, Gautam Borthakur. Tolinapant (ASTX660) enhances the anti-leukemic activity of Venetoclax and Dexamethasone in T cell acute lymphoblastic leukemia (T-ALL) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5337.

A validated liquid chromatography-tandem mass spectroscopy method for the quantification of tolinapant in human plasma.

Tolinapant (ASTX660), a pan-selective inhibitor of apoptosis protein antagonist with dual cIAP/XIAP activity, was identified as a clinical candidate in preclinical efficacy, pharmacokinetic and safety studies. In order to assess tolinapant in first-in-human Phase I/II clinical trials, a validated bioanalytical method was required to determine plasma pharmacokinetics. Tolinapant and d4-tolinapant were extracted from human plasma using liquid-liquid extraction. Separation chromatography was performed on a Acquity BEH C18 1.7 µM, 50 mm × 2.1mm i.d. column, using a mobile phase of 0.1% formic acid in water and 0.1% formic acid in acetonitrile. Mass spectrometry detection was performed by positive turbo ion spray ionisation, in multiple reaction monitoring mode. The method was validated according to the US Food and Drug Administration (FDA) guidelines. The method has a quantifiable linear range of 1-500ng/mL (r 2=0.999). The intra- and inter-day coefficients of variation were <11.4%. Dilution QC samples agreed with prepared concentrations, with a precision of 1.5% and accuracy of 101%. Tolinapant mean recoveries ranged from 85.1-94.4 % with negligible matrix effects. A highly sensitive and selective LC-MS/MS bioanalytical method was developed and validated. The method was successfully applied in Phase 1/2 clinical trials to determine the human pharmacokinetic profile of tolinapant.

Suppressed XIAP and cIAP expressions in human brain cancer stem cells using BV6- and GDC0152-encapsulated nanoparticles

BackgroundSmac mimetics functioned against inhibitors of apoptosis proteins (IAP) often fail to achieve sufficient ability in glioblastoma multiforme (GBM) treatment due to the obstruction of the blood-brain barrier (BBB). MethodsBV6- and GDC0152-encapsulated solid lipid nanoparticles (SLNs) with surface transferrin (Tf) and folic acid (FA) (BV6-GDC0152-Tf-FA-SLNs) were developed to downregulate IAP in U87MG cells and human brain cancer stem cells (HBCSCs) for GBM treatment. Significant findingsAn increase in stearic acid (SA) level enlarged SLNs with improved entrapment of BV6 and GDC0152. 1H NMR study revealed hydrogen bonding between SA and the two IAP antagonists, supporting controlled release of BV6 and GDC0152 from SLNs. Increasing sodium dodecyl sulfate concentration reduced the size of SLNs, and raised the particle stability. Conjugated Tf and FA on SLNs favored permeating the BBB as corroborated from decreased transendothelial electrical resistance, and raised BBB permeability of propidium iodide, BV6 and GDC0152. The ability of BV6-GDC0152-Tf-FA-SLNs to target IAP in U87MG cells and HBCSCs was validated from the downregulated XIAP and cIAP-1 expressions and upregulated caspase-3 expression in immunofluorescence staining, flow cytometry and western blot analysis. Hence, Tf- and FA-grafted SLNs can be an effective colloidal delivery system to deliver BV6 and GDC0152 across the BBB, facilitate IAP targeting, and enhanced drug bioavailability of the two Smac mimetics in GBM cells for potential clinical trials.

DCAF12 promotes apoptosis and inhibits NF-κB activation by acting as an endogenous antagonist of IAPs

Members of the Inhibitor of Apoptosis Protein (IAP) family are essential for cell survival and appear to neutralize the cell death machinery by binding pro-apoptotic caspases. dcaf12 was recently identified as an apoptosis regulator in Drosophila. However, the underlying molecular mechanisms are unknown. Here we revealed that human DCAF12 homolog binds multiple IAPs, including XIAP, cIAP1, cIAP2, and BRUCE, through recognition of BIR domains in IAPs. The pro-apoptotic function of DCAF12 is dependent on its capacity to bind IAPs. In response to apoptotic stimuli, DCAF12 translocates from the nucleus to the cytoplasm, where it blocks the interaction between XIAP and pro-apoptotic caspases to facilitate caspase activation and apoptosis execution. Similarly, DCAF12 suppresses NF-κB activation in an IAP binding-dependent manner. Moreover, DCAF12 acts as a tumor suppressor to restrict the malignant phenotypes of cancer cells. Together, our results suggest that DCAF12 is an evolutionarily conserved IAP antagonist.

Combined noncanonical NF-κB agonism and targeted BET bromodomain inhibition reverse HIV latency ex vivo.

Latency reversal strategies for HIV cure using inhibitor of apoptosis protein (IAP) antagonists (IAPi) induce unprecedented levels of latent reservoir expression without immunotoxicity during suppressive antiretroviral therapy (ART). However, full targeting of the reservoir may require combinatorial approaches. A Jurkat latency model screen for IAPi combination partners demonstrated synergistic latency reversal with bromodomain (BD) and extraterminal domain protein inhibitors (BETi). Mechanistic investigations using CRISPR-CAS9 and single-cell RNA-Seq informed comprehensive ex vivo evaluations of IAPi plus pan-BET, bD-selective BET, or selective BET isoform targeting in CD4+ T cells from ART-suppressed donors. IAPi+BETi treatment resulted in striking induction of cell-associated HIV gag RNA, but lesser induction of fully elongated and tat-rev RNA compared with T cell activation–positive controls. IAPi+BETi resulted in HIV protein induction in bulk cultures of CD4+ T cells using an ultrasensitive p24 assay, but did not result in enhanced viral outgrowth frequency using a standard quantitative viral outgrowth assay. This study defines HIV transcriptional elongation and splicing as important barriers to latent HIV protein expression following latency reversal, delineates the roles of BET proteins and their BDs in HIV latency, and provides a rationale for exploration of IAPi+BETi in animal models of HIV latency.