Cellular senescence promotes meibomian gland dysfunction in a chronic graft-versus-host disease mouse model

PURPOSE

Aging is a well-established risk factor for meibomian gland dysfunction (MGD). We previously reported an accelerated cellular senescence phenomenon in the lacrimal glands of a murine model of chronic graft-versus-host disease (cGVHD). Herein, we aimed to elucidate the relationship between cellular senescence and MGD in cGVHD mice, utilizing the senolytic agent ABT-263.

METHODS

A cGVHD mouse model was established through allogeneic bone marrow transplantation (BMT) from B10.D2 to BALB/c mice. Subsequently, cGVHD mice were treated with either ABT-263 or vehicle. The eyelids of recipients were analyzed at 4-week intervals post-BMT in both groups.

RESULTS

Meibomian gland (MG) area was significantly smaller in cGVHD mice than in syngeneic control mice. ABT-263-treated mice retained a significantly larger MG area than their vehicle-treated counterparts. Pathological and immunohistochemical examinations revealed significant reductions in eyelid tissue inflammation and pathological fibrosis in the ABT-263 group compared to that in the vehicle-treated group. Additionally, expression of DNA damage markers, senescent cell markers, and senescence-associated secretory phenotype (SASP) factors was elevated in the eyelids of cGVHD mice compared with that in syngeneic mice. The expression of these cellular senescence-associated molecules was considerably suppressed in ABT-263-treated eyelids compared to that in vehicle-treated ones.

CONCLUSIONS

Cellular senescence, along with expression of SASP factors, exhibited increased activity in the eyelids, particularly in the MGs of cGVHD mice. ABT-263 mitigated the severity of MGD. These findings highlight the potential of targeting cellular senescence as an effective approach for MGD treatment in cGVHD.

Phase 1 trial of navitoclax and sorafenib in patients with relapsed or refractory solid tumors with hepatocellular carcinoma expansion cohort

Navitoclax (ABT-263) is an oral BCL2 homology-3 mimetic that binds with high affinity to pro-survival BCL2 proteins, resulting in apoptosis. Sorafenib, an oral multi kinase inhibitor also promotes apoptosis and inhibits tumor angiogenesis. The efficacy of either agent alone is limited; however, preclinical studies demonstrate synergy with the combination of navitoclax and sorafenib. In this phase 1 study, we evaluated the combination of navitoclax and sorafenib in a dose escalation cohort of patients with refractory solid tumors, with an expansion cohort in hepatocellular carcinoma (HCC). Maximum tolerated dose (MTD) was determined using the continual reassessment method. Navitoclax and sorafenib were administered continuously on days 1 through 21 of 21-day cycles. Ten patients were enrolled in the dose escalation cohort and 15 HCC patients were enrolled in the expansion cohort. Two dose levels were tested, and the MTD was navitoclax 150 mg daily plus sorafenib 400 mg twice daily. Among all patients, the most common grade 3 toxicity was thrombocytopenia (5 patients, 20%): there were no grade 4 or 5 toxicities. Patients received a median of 2 cycles (range 1-36 cycles) and all patients were off study treatment at data cut off. Six patients in the expansion cohort had stable disease, and there were no partial or complete responses. Drug-drug interaction between navitoclax and sorafenib was not observed. The combination of navitoclax and sorafenib did not increase induction of apoptosis compared with navitoclax alone. Navitoclax plus sorafenib is tolerable but showed limited efficacy in the HCC expansion cohort. These findings do not support further development of this combination for the treatment of advanced HCC. This phase I trial was conducted under ClinicalTrials.gov registry number NCT01364051.

m6A-related lncRNAs as potential biomarkers and the lncRNA ELFN1-AS1/miR-182-5p/BCL-2 regulatory axis in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoid subtype. However, unsatisfactory survival outcomes remain a major challenge, and the underlying mechanisms are poorly understood. N6-methyladenosine (m6A), the most common internal modification of eukaryotic mRNA, participates in cancer pathogenesis. In this study, m6A-associated long non-coding RNAs (lncRNA) were retrieved from publicly available databases. Univariate, LASSO, and multivariate Cox regression analyses were performed to establish an m6A-associated lncRNA model specific to DLBCL. Kaplan-Meier curves, principal component analysis, functional enrichment analyses and nomographs were used to study the risk model. The underlying clinicopathological characteristics and drug sensitivity predictions against the model were identified. Risk modelling based on the three m6A-associated lncRNAs was an independent prognostic factor. By regrouping patients using our model-based method, we could differentiate patients more accurately for their response to immunotherapy. In addition, prospective compounds that can target DLBCL subtypes have been identified. The m6A-associated lncRNA risk-scoring model developed herein holds implications for DLBCL prognosis and clinical response prediction to immunotherapy. In addition, we used bioinformatic tools to identify and verify the ceRNA of the m6A-associated lncRNA ELFN1-AS1/miR-182-5p/BCL-2 regulatory axis. ELFN1-AS1 was highly expressed in DLBCL and DLBCL cell lines. ELFN1-AS1 inhibition significantly reduced the proliferation of DLBCL cells and promoted apoptosis. ABT-263 inhibits proliferation and promotes apoptosis in DLBCL cells. In vitro and in vivo studies have shown that ABT-263 combined with si-ELFN1-AS1 can inhibit DLBCL progression.

ABT-263 exerts a protective effect on upper urinary tract damage by alleviating neurogenic bladder fibrosis

This study investigated the mechanism of action of ABT-263 in the treatment of neurogenic bladder fibrosis (NBF)and its protective effects against upper urinary tract damage (UUTD). Sixty 12-week-old Sprague-Dawley (SD) rats were randomly divided into sham, sham + ABT-263 (50 mg/kg), NBF, NBF + ABT-263 (25 mg/kg, oral gavage), and NBF + ABT-263 (50 mg/kg, oral gavage) groups. After cystometry, bladder and kidney tissue samples were collected for hematoxylin and eosin (HE), Masson, and Sirius red staining, and Western Blotting (WB) and qPCR detection. Primary rat bladder fibroblasts were isolated, extracted, and cultured. After co-stimulation with TGF-β1 (10 ng/mL) and ABT-263 (concentrations of 0, 0.1, 1, 10, and 100 µmol/L) for 24 h, cells were collected. Cell apoptosis was detected using CCK8, WB, immunofluorescence, and annexin/PI assays. Compared with the sham group, there was no significant difference in any physical parameters in the sham + ABT-263 (50 mg/kg) group. Compared with the NBF group, most of the markers involved in fibrosis were improved in the NBF + ABT-263 (25 mg/kg) and NBF + ABT-263 (50 mg/kg) groups, while the NBF + ABT-263 (50 mg/kg) group showed a significant improvement. When the concentration of ABT-263 was increased to 10 µmol/L, the apoptosis rate of primary bladder fibroblasts increased, and the expression of the anti-apoptotic protein BCL-xL began to decrease.ABT-263 plays an important role in relieving NBF and protecting against UUTD, which may be due to the promotion of myofibroblast apoptosis through the mitochondrial apoptosis pathway.

The Bcl-2/Bcl-xL Inhibitor ABT-263 Attenuates Retinal Degeneration by Selectively Inducing Apoptosis in Senescent Retinal Pigment Epithelial Cells

Age-related macular degeneration (AMD) is one of the leading causes of blindness in elderly individuals. However, the currently used intravitreal injections of anti-vascular endothelial growth factor are invasive, and repetitive injections are also accompanied by a risk of intraocular infection. The pathogenic mechanism of AMD is still not completely understood, but a multifactorial mechanism that combines genetic predisposition and environmental factors, including cellular senescence, has been suggested. Cellular senescence refers to the accumulation of cells that stop dividing due to the presence of free radicals and DNA damage. Characteristics of senescent cells include nuclear hypertrophy, increased levels of cell cycle inhibitors such as p16 and p21, and resistance to apoptosis. Senolytic drugs remove senescent cells by targeting the main characteristics of these cells. One of the senolytic drugs, ABT-263, which inhibits the antiapoptotic functions of Bcl-2 and Bcl-xL, may be a new treatment for AMD patients because it targets senescent retinal pigment epithelium (RPE) cells. We proved that it selectively kills doxorubicin (Dox)-induced senescent ARPE-19 cells by activating apoptosis. By removing senescent cells, the expression of inflammatory cytokines was reduced, and the proliferation of the remaining cells was increased. When ABT-263 was orally administered to the mouse model of senescent RPE cells induced by Dox, we confirmed that senescent RPE cells were selectively removed and retinal degeneration was alleviated. Therefore, we suggest that ABT-263, which removes senescent RPE cells through its senolytic effect, has the potential to be the first orally administered senolytic drug for the treatment of AMD.

Treatment of advanced atherosclerotic mice with the senolytic agent ABT-263 is associated with reduced indices of plaque stability and increased mortality

The use of senolytic agents to remove senescent cells from atherosclerotic lesions is controversial. A common limitation of previous studies is the failure to rigorously define the effects of senolytic agent ABT-263 (Navitoclax) on smooth muscle cells (SMC) despite studies claiming that they are the major source of senescent cells. Moreover, there are no studies of the effect of ABT-263 on endothelial cells (EC), which along with SMC comprise 90% of α-SMA+ myofibroblast-like cells in the protective fibrous cap. Here we tested the hypothesis that treatment of advanced atherosclerotic mice with the ABT-263 will reduce lesion size and increase plaque stability. SMC (Myh11-CreERT2-eYFP) and EC (Cdh5-CreERT2-eYFP) lineage tracing Apoe-/- mice were fed a WD for 18 weeks, followed by ABT-263 100mg/kg/bw for six weeks or 50mg/kg/bw for nine weeks. ABT-263 treatment did not change lesion size or lumen area of the brachiocephalic artery (BCA). However, ABT-263 treatment reduced SMC by 90% and increased EC-contributions to lesions via EC-to-mesenchymal transition (EndoMT) by 60%. ABT-263 treatment also reduced α-SMA+ fibrous cap thickness by 60% and increased mortality by >50%. Contrary to expectations, treatment of WD-fed Apoe-/- mice with the senolytic agent ABT-263 resulted in multiple detrimental changes including reduced indices of stability, and increased mortality.

Navitoclax (ABT-263) Rejuvenates Human Skin by Eliminating Senescent Dermal Fibroblasts in a Mouse/Human Chimeric Model

Chronic senescence, such as aging, contributes to age-related tissue dysfunction and disease development. The accumulation of senescent fibroblasts and the senescence-associated secretory phenotype is particularly implicated in this process. Removal of senescent cells has been reported to prevent tissue dysfunction and to extend the life span during aging. ABT-263 (navitoclax), which inhibits antiapoptotic proteins, is a leading antiaging drug; however, its role in human skin aging is unclear. This study aimed to determine the rejuvenating effects of ABT-263 on aging skin using a human skin graft mouse model. We assessed the viability of ABT-263-treated skin fibroblasts after inducing senescence. Aged human skin was transplanted under the back skin of nude mice and injected intraperitoneally with the drug or control. Analysis of the skin specimens revealed that ABT-263 induced selective elimination of senescent dermal fibroblasts. Senescent human skin treated with ABT-263 exhibited a decrease in the number of senescent cells and in the expression of aging-related secretory phenotype molecules, such as matrix metalloproteinases and interleukins and an increase in collagen density. Our results indicate that selective removal of senescent skin cells with ABT-263 can improve the aging phenotype of human skin without side effects. ABT-263 is, thus, a novel potential therapeutic agent for skin aging.

Clearance of senescent cells by navitoclax (ABT263) rejuvenates UHMWPE-induced osteolysis

Periprosthetic osteolysis is the leading cause of prosthesis failure and subsequent total joint revision. Wear particles produced by prosthetic materials are the main biological factors that cause periprosthetic osteolysis. Reducing the inflammatory response induced by the phagocytosis of wear particles by macrophages, blocking the activation of osteoclastogenesis, and promoting bone regeneration are essential for preventing the aseptic loosening of prostheses. In this study, we demonstrated that cellular senescence played a vital role during the process of ultra-high molecular weight polyethylene (UHMWPE) particle-induced osteolysis. Administration of the senolytic drug navitoclax (ABT263) could eliminate senescent cells and inhibit the secretion and inflammatory state of the senescence-associated secretory phenotype (SASP). We also discovered that ABT263 inhibited the formation of osteoclasts and had a significant therapeutic effect on UHMWPE particle-induced osteolysis based on the results of UHMWPE-induced mouse cranial osteolysis. Therefore, our research provided innovative strategies and ideas for the prevention and treatment of periprosthetic osteolysis.

Synergistic activity of ABT-263 and ONC201/TIC10 against solid tumor cell lines is associated with suppression of anti-apoptotic Mcl-1, BAG3, pAkt, and upregulation of pro-apoptotic Noxa and Bax cleavage during apoptosis

A major underlying cause of the resistance of solid tumor cells to cancer therapy is the evasion of cell death following anti-cancer drug treatment. We explored the combination of TRAIL-inducing compound ONC201/TIC10 and Bcl-xL/Bcl-2 inhibitor ABT-263 to target the extrinsic and intrinsic apoptotic pathways, respectively, in solid tumor cell lines (N = 13) derived from different tissues (colon, prostate, lung, breast, ovary, bladder). We found an IC50 range of 0.83-20.10 μM for ONC201 and 0.06-14.75 μM for ABT-263 among the 13 cancer cell lines. We show that combination of ONC201 and ABT-263 produces a strong synergistic effect leading to tumor cell death, and that the combination is not toxic to human fibroblast cells. In OVCAR-3 ovarian cancer cells, 2.5 μM ONC201 and 1.25 μM ABT-263 yielded 37% and 27% inhibition of viability, respectively, while the combination of the two agents yielded 92% inhibition of viability, resulting in a high synergy score of 52; conversely, the same combination in the HFF-1 human fibroblast cells yielded 2.45% inhibition of viability and a synergy score of 6.92 (synergy scores were calculated using SynergyFinder; scores greater than 10 are considered synergistic). We also found that the combination of these two agents resulted in synergistic caspase activation and PARP cleavage consistent with induction of apoptosis. Combination therapy-induced cell death correlated with decreased levels of Mcl-1, BAG3, pAkt, and upregulation of Noxa along with Bax cleavage during apoptosis at 48 hours, and ATF4, TRAIL, and DR5 induction at 24 hours. There was some heterogeneity in the cell lines with regard to these responses. Our data provide evidence for synergy from the combination of ONC201 and ABT-263 against human solid tumor cell lines associated with alterations in cell death and pro-survival mediators. The combination of ONC201 and ABT-263 merits further exploration in vivo and in clinical trials against a variety of solid malignancies.

Clearance of senescent cells with ABT-263 improves biological functions of synovial mesenchymal stem cells from osteoarthritis patients

BACKGROUND

Osteoarthritis (OA) is an age-related joint disease characterized by progressive cartilage loss. Synovial mesenchymal stem cells (MSCs) are anticipated as a cell source for OA treatment; however, synovial MSC preparations isolated from OA patients contain many senescent cells that inhibit cartilage regeneration through their senescence-associated secretory phenotype (SASP) and poor chondrogenic capacity. The aim of this study was to improve the biological function of OA synovial MSCs by removing senescent cells using the senolytic drug ABT-263.

METHODS

We pretreated synovial MSCs derived from 5 OA patients with ABT-263 for 24 h and then evaluated senescence-associated beta-galactosidase (SA-β-gal) activity, B cell lymphoma 2 (BCL-2) activity, apoptosis, surface antigen expression, colony formation ability, and multipotency.

RESULTS

The ABT-263 pretreatment significantly decreased the percentage of SA-β-gal-positive cells and BCL-2 expression and induced early- and late-stage apoptosis. Cleaved caspase-3 was expressed in SA-β-gal-positive cells. The pretreated MSCs formed greater numbers of colonies with larger diameters. The expression rate of CD34 was decreased in the pretreated cells. Differentiation assays revealed that ABT-263 pretreatment enhanced the adipogenic and chondrogenic capabilities of OA synovial MSCs. In chondrogenesis, the pretreated cells produced greater amounts of glycosaminoglycan and type II collagen and showed lower expression of senescence markers (p16 and p21) and SASP factors (MMP-13 and IL-6) and smaller amounts of type I collagen.

CONCLUSION

Pretreatment of synovial MSCs from OA patients with ABT-263 can improve the function of the cells by selectively eliminating senescent cells. These findings indicate that ABT-263 could hold promise for the development of effective cell-based OA therapy.

Effects and Related Mechanisms of the Senolytic Agent ABT-263 on the Survival of Irradiated A549 and Ca9-22 Cancer Cells

Senolytic agents eliminate senescent cells and are expected to reduce senescent cell-mediated adverse effects in cancer therapy. However, the effects of senolytic agents on the survival of irradiated cancer cells remain unknown. Here, the effects of the senolytic agent ABT-263 on the survival of irradiated A549 and Ca9-22 cancer cells were investigated. ABT-263 was added to the culture medium after irradiation. SA-β-gal activity and cell size, which are hallmarks of cell senescence, were evaluated using a flow cytometer. The colony-forming assay and annexin V staining were performed to test cell survival. We first confirmed that radiation increased the proportion of cells with high SA-β-gal activity and that ABT-263 decreased it. Of note, ABT-263 decreased the survival of irradiated cancer cells and increased the proportion of radiation-induced annexin V⁺ cells. Furthermore, the caspase inhibitor suppressed the ABT-263-induced decrease in the survival of irradiated cells. Intriguingly, ABT-263 decreased the proportion of SA-β-gal low-activity/large cells in the irradiated A549 cells, which was recovered by the caspase inhibitor. Together, these findings suggest that populations maintaining the ability to proliferate existed among the irradiated cancer cells showing senescence-related features and that ABT-263 eliminated the population, which led to decreased survival of irradiated cancer cells.

Selective therapeutic benefit of X-rays and inhibitors of EGFR, PI3K/mTOR, and Bcl-2 in breast, lung, and cervical cancer cells

Cancer continues to be a growing burden, especially in the resource limited regions of the world, and more effective and affordable therapies are highly desirable. In this study, the effect of X-ray irradiation and four inhibitors, viz. those against epidermal growth factor receptor (EGFR), phosphatidylinositol 3-kinase (PI3K), mammalian target of rapamycin (mTOR) and B-cell lymphoma 2 (Bcl-2) was evaluated in lung, breast, and cervical cancer cell lines, including normal cell lines to determine and compare the potential therapeutic benefit of these treatment modalities. A clonogenic survival assay was used to determine the radiosensitivity and cytotoxicity of inhibitors of EGFR, PI3K/mTOR, and Bcl-2 in the cell lines. From the data, the equivalent dose at which 50% of the cell populations were killed, for cancer and normal cells, was used to determine the relative cellular sensitivity to X-ray irradiation and inhibitor treatment. It was found that breast cancer cell lines were more sensitive to X-ray irradiation, whilst cervical and lung cancer cell lines were more sensitive to EGFR and PI3K/mTOR inhibitor therapy. These data suggest that patients with breast cancer possessing similar characteristics to MDA-MB-231 and MCF-7 cells may derive therapeutic benefit from X-ray irradiation, whilst EGFR and PI3K/mTOR inhibitor therapy may potentially benefit cancer patients possessing cancers similar to HeLa and A549 cells.

Protective role of cytoplasmic p21Cip1/Waf1 in apoptosis of CDK4/6 inhibitor-induced senescence in breast cancer cells

Inhibition of CDK4/6 slows the cell cycle and induces senescence in breast cancer cells. However, senescent cancer cells promote invasion and metastasis. Several drugs reportedly target senescent cells, including ABT‐263 (navitoclax). We examined the effects of the CDK4/6 inhibitor abemaciclib and ABT‐263 on two human breast cancer cell lines. The abemaciclib and ABT‐263 combination additively decreased the viability of MDA‐MB‐231 cells, but not MCF‐7 cells. Also, the combination therapy‐induced caspase‐dependent apoptosis in MDA‐MB‐231 cells. Combination therapy with abemaciclib and ABT‐737, an ABT‐263 analog, significantly suppressed the in vivo growth of MDA‐MB‐231 with transient body‐weight loss. Given that p16^Ink4a and p21^Cip1/Waf1 are key factors in senescence and that both cell lines were negative for p16, the role of p21 in apoptosis of treated breast cancer cells was investigated. Although abemaciclib increased the cytoplasmic p21 level in both cell lines as a hallmark of senescence, the abemaciclib and ABT‐263 combination decreased it only in MDA‐MB‐231 cells. This decrease of p21 expression was relieved by caspase inhibition, and p21 was colocalized with caspase‐3 in the cytoplasm of MDA‐MB‐231 cells. Alternatively, small interfering RNA‐mediated knockdown of p21 rendered caspase‐3‐negative MCF‐7 cells susceptible to abemaciclib and ABT‐263, as well as TNF‐related apoptosis‐inducing ligand. Furthermore, a clinical database analysis showed that p21^high breast cancer patients had a poorer prognosis compared to p21^low patients. These results suggest that cytoplasmic p21 plays a protective role in apoptosis of CDK4/6 inhibitor‐induced senescent breast cancer cells.

Photodynamic Therapy Combined with Bcl-2/Bcl-xL Inhibition Increases the Noxa/Mcl-1 Ratio Independent of Usp9X and Synergistically Enhances Apoptosis in Glioblastoma

Simple Summary

Glioblastoma represents one of the most common malignant brain tumors in adults and is associated with a poor clinical outcome despite current therapeutic measures. Therefore, novel strategies for the treatment of this disease are urgently needed. In this work, we examined the antineoplastic effects of a combined treatment with photodynamic therapy and ABT-263 on different glioblastoma cells. Photodynamic therapy uses the selective uptake of a photosensitive molecule followed by activation by light of a specific wavelength to kill cancer cells. ABT-263 is a small molecule inhibitor that targets cancer cells by facilitating programmed cell death. This novel combinatorial therapeutic strategy synergistically killed glioblastoma cells. These results indicate that a combination of the two treatment modalities may be of benefit for the treatment of glioblastoma supporting further studies.

Abstract

The purpose of this study was to assess in vitro whether the biological effects of 5-aminolevulinic acid (5-ALA)-based photodynamic therapy are enhanced by inhibition of the anti-apoptotic Bcl-2 family proteins Bcl-2 and Bcl-xL in different glioblastoma models. Pre-clinical testing of a microcontroller-based device emitting light of 405 nm wavelength in combination with exposure to 5-ALA (PDT) and the Bcl-2/Bcl-xL inhibitor ABT-263 (navitoclax) was performed in human established and primary cultured glioblastoma cells as well as glioma stem-like cells. We applied cell count analyses to assess cellular proliferation and Annexin V/PI staining to examine pro-apoptotic effects. Western blot analyses and specific knockdown experiments using siRNA were used to examine molecular mechanisms of action. Bcl-2/Bcl-xL inhibition synergistically enhanced apoptosis in combination with PDT. This effect was caspase-dependent. On the molecular level, PDT caused an increased Noxa/Mcl-1 ratio, which was even more pronounced when combined with ABT-263 in a Usp9X-independent manner. Our data showed that Bcl-2/Bcl-xL inhibition increases the response of glioblastoma cells toward photodynamic therapy. This effect can be partly attributed to cytotoxicity and is likely related to a pro-apoptotic shift because of an increased Noxa/Mcl-1 ratio. The results of this study warrant further investigation.

Effect of ABT-263 on Intestinal Fibrosis in Human Myofibroblasts, Human Intestinal Organoids, and the Mouse Salmonella typhimurium Model

BACKGROUND

Intestinal fibrosis and subsequent intestinal obstruction are common complications of Crohn's disease (CD). Current therapeutics combat inflammation, but no pharmacological therapy exists for fibrostenotic disease. Pathological persistence of activated intestinal myofibroblasts is a key driver of fibrosis in CD. In other organ systems, BH-3 mimetic drugs that affect Bcl-2 apoptotic pathways induce apoptosis in activated myofibroblasts and reduce fibrogenic gene expression, thereby reducing fibrosis.

METHODS

We evaluated the proapoptotic and antifibrotic efficacy of several classes of BH-3 mimetics in 2 in vitro fibrogenesis models. The candidate molecule, ABT-263, was advanced to a 3-dimensional human intestinal organoid (HIO) model. Finally, the therapeutic efficacy of ABT-263 was evaluated in the mouse Salmonella typhimurium intestinal fibrosis model.

RESULTS

The BH-3 mimetics induced apoptosis, repressed fibrotic protein expression, and reduced fibrogenic gene expression in normal human intestinal myofibroblasts. The BH-3 mimetics that target Bcl-2 and Bcl-xl demonstrated the greatest efficacy in vitro. The ABT-199 and ABT-263 induced apoptosis and ameliorated fibrogenesis in the in vitro myofibroblast models. In the HIO model, ABT-263 inhibited fibrogenesis and induced apoptosis. In the mouse S. typhimurium model, dose-dependent reduction in macroscopic pathology, histological inflammation, inflammatory and fibrotic gene expression, and extracellular matrix protein expression indicated ABT-263 may reduce intestinal fibrosis.

CONCLUSIONS

In vitro, the antifibrotic efficacy of BH-3 mimetics identifies the Bcl-2 pathway as a druggable target and BH-3 mimetics as putative therapeutics. Reduction of inflammation and fibrosis in the mouse intestinal fibrosis model by ABT-263 indicates BH-3 mimetics as potential, novel antifibrotic therapeutics for Crohn's disease.

The Cancer SENESCopedia: A delineation of cancer cell senescence

Cellular senescence is characterized as a stable proliferation arrest that can be triggered by multiple stresses. Most knowledge about senescent cells is obtained from studies in primary cells. However, senescence features may be different in cancer cells, since the pathways that are involved in senescence induction are often deregulated in cancer. We report here a comprehensive analysis of the transcriptome and senolytic responses in a panel of 13 cancer cell lines rendered senescent by two distinct compounds. We show that in cancer cells, the response to senolytic agents and the composition of the senescence-associated secretory phenotype are more influenced by the cell of origin than by the senescence trigger. Using machine learning, we establish the SENCAN gene expression classifier for the detection of senescence in cancer cell samples. The expression profiles and senescence classifier are available as an interactive online Cancer SENESCopedia.

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Senescent cancer cells respond differently to senolytic ABT-263

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SASP expression in cancer is heterogeneous and influenced by cell origin

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The SENCAN classifier detects cancer cell senescence in vitro

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The Cancer SENESCopedia contains transcriptome data from 37 senescence models

A Phase I study of the safety, pharmacokinetics and efficacy of navitoclax plus docetaxel in patients with advanced solid tumors

Aim: This Phase I study investigated safety of navitoclax and docetaxel in patients (n = 41) with advanced solid tumors. Patients & methods: Two navitoclax plus docetaxel dosing schedules (21 and 28 days) were evaluated. Maximum tolerated dose, dose-limiting toxicities and preliminary antitumor activity were assessed. Results: Ten (24%) patients experienced dose-limiting toxicities; dose-escalation cohorts: n = 7 (21-day schedule: n = 5; 28-day schedule: n = 2) and 21-day expanded safety cohort: n = 3. Navitoclax 150-mg days 1-5 every 21 days with docetaxel 75 mg/m² day 1 was the maximum tolerated dose and optimal schedule. Adverse events included thrombocytopenia (63%), fatigue (61%), nausea (59%) and neutropenia (51%). Four confirmed partial responses occurred. Conclusion: Navitoclax 150-mg orally once/day was safely administered with docetaxel. Myelosuppression limited dose escalation; antitumor activity was observed. Clinical trial registration: NCT00888108 (ClinicalTrials.gov).

Senolytics for Cancer Therapy: Is All That Glitters Really Gold?

Simple Summary

Senescence is an essential component of tumor cell biology and is a primary cell stress response to therapy. While the long-term impact of senescence in cancer therapy is not yet fully understood, the use of senolytics, drugs that selectively kill senescent cells, is an area of active investigation in cancer treatment. Several challenges and unanswered questions have arisen from the current preclinical literature, indicating the need to re-evaluate some of the basic premises and experimental approaches, as well as the potential utility for translating to the clinic the application of senolytics as adjuvants to current cancer therapy.

Abstract

Senolytics represent a group of mechanistically diverse drugs that can eliminate senescent cells, both in tumors and in several aging-related pathologies. Consequently, senolytic use has been proposed as a potential adjuvant approach to improve the response to senescence-inducing conventional and targeted cancer therapies. Despite the unequivocal promise of senolytics, issues of universality, selectivity, resistance, and toxicity remain to be further clarified. In this review, we attempt to summarize and analyze the current preclinical literature involving the use of senolytics in senescent tumor cell models, and to propose tenable solutions and future directions to improve the understanding and use of this novel class of drugs.

Synergistic Effects of TW-37 and ABT-263 on Renal Cell Carcinoma Cells

Background

Renal cell carcinoma (RCC) is a common urological system malignancy lack of effective therapeutic options. Upregulation of the Bcl-2 proteins was correlated with poor prognosis of RCC, suggesting that BH-3 mimetics may be a promising treatment option. ABT-263 is a BH3 mimetic that possesses anti-tumor effects. TW-37 is another inhibitor of Bcl-2 family protein with potential anti-tumor activities. However, since their effect as single agent is limited, combination treatment represents a strategy to improve the efficiency. We studied the ABT-263 in combination with TW-37 and analyzed the molecular mechanisms of action in RCC cells.

Methods

MTT and colony formation assays were used to measure the proliferation of RCC cells. Transwell assay was used to assay the migration and invasion of RCC cells. Cell cycle distribution and apoptosis were measured using the flow cytometry and apoptotic nucleosome assay, respectively. Western blotting was performed to measure the change of proteins. The anti-tumor effects of ABT-263, TW-37 and their combination were also evaluated in vivo.

Results

Cotreatment of TW-37 and ABT-263 synergistically repressed the proliferation of RCC cells. TW-37 and ABT-263 also synergistically inhibited the migration and invasion of RCC cells It was also showed that TW-37 and ABT-263 synergistically induced cell cycle arrest at the G2/M phase. Furthermore, increased apoptosis was observed after exposure to TW-37 and ABT-263. Mechanism investigation showed that TW-37 and ABT-263 synergistically induced apoptosis via the mitochondrial pathway and relied on the activation of Bax and caspases. Furthermore, ERK signaling pathway activation was detected after treated with TW-37 and ABT-263. Finally, TW-37 and ABT-263 also synergistically repressed the growth of RCC cells in xenograft mice.

Conclusion

In summary, our data demonstrated that combined treatment with TW-37 and ABT-263 exhibited synergistic RCC cell death and this combination may be applied as an effective therapeutic strategy against RCC.

Senolytic Targeting of Bcl-2 Anti-Apoptotic Family Increases Cell Death in Irradiated Sarcoma Cells

Simple Summary

Limited volumetric change after pre-operative radiotherapy (RT) suggests that sarcomas generally do not undergo cell death. Senolytic drugs represent a highly promising field as a new therapy approach to drive senescent cancer cells towards cell death to enhance treatment response. Here, we demonstrate that the Bcl-2 family of anti-apoptotic proteins in irradiated senescent sarcoma cells represents a senotherapeutic target to improve the cell death response in RT. This study paves the way for new treatment options in soft tissue sarcoma management.

Abstract

Radiotherapy (RT) is a key component of cancer treatment. Most of the time, radiation is given after surgery but for soft-tissue sarcomas (STS), pre-surgical radiation is commonly utilized. However, despite improvements in RT accuracy, the rate of local recurrence remains high and is the major cause of death for patients with STS. A better understanding of cell fates in response to RT could provide new therapeutic options to enhance tumour cell killing by RT and facilitate surgical resection. Here, we showed that irradiated STS cell cultures do not die but instead undergo therapy-induced senescence (TIS), which is characterized by proliferation arrest, senescence-associated β-galactosidase activity, secretion of inflammatory cytokines and persistent DNA damage. STS-TIS was also associated with increased levels of the anti-apoptotic Bcl-2 family of proteins which rendered cells targetable using senolytic Bcl-2 inhibitors. As oppose to radiation alone, the addition of senolytic agents Venetoclax (ABT-199) or Navitoclax (ABT-263) after irradiation induced a rapid apoptotic cell death in STS monolayer cultures and in a more complex three-dimensional culture model. Together, these data suggest a new promising therapeutic approach for sarcoma patients who receive neoadjuvant RT. The addition of senolytic agents to radiation treatments may significantly reduce tumour volume prior to surgery and thereby improve the clinical outcome of patients.

ABT-263 Reduces Hypertrophic Scars by Targeting Apoptosis of Myofibroblasts

Background: Inhibiting proliferation and inducing apoptosis of myofibroblasts is becoming one of the promising and effective ways to treat hypertrophic scar. ABT-263, as an orally bioavailable BCL-2 family inhibitor, has showed great antitumor characteristics by targeting tumor cell apoptosis. The objective of this study was to explore whether ABT-263 could target apoptosis of overactivated myofibroblasts in hypertrophic scar. Methods: In vivo, we used ABT-263 to treat scars in a rabbit ear scar model. Photographs and ultrasound examination were taken weekly, and scars were harvested on day 42 for further Masson trichrome staining. In vitro, the expression levels of BCL-2 family members, including prosurvival proteins, activators, and effectors, were detected systematically in hypertrophic scar tissues and adjacent normal skin tissues, as well as in human hypertrophic scar fibroblasts (HSFs) and human normal dermal fibroblasts (HFBs). The roles of ABT-263 in apoptosis and proliferation of HSFs and HFBs were determined by annexin V/PI assay, CCK-8 kit, and cell cycle analysis. Mitochondrial membrane potential was evaluated by JC-1 staining and the expression of type I/III collagen and α-SMA was measured by PCR, western blotting, and immunofluorescence staining. Furthermore, immunoprecipitation was performed to explore the potential mechanism. Results: In vivo, ABT-263 could significantly improve the scar appearance and collagen arrangement, decrease scar elevation index (SEI), and induce cell apoptosis. In vitro, the expression levels of BCL-2, BCL-XL, and BIM were significantly higher in scar tissues and HSFs than those in normal skin tissues and HFBs. ABT-263 selectively induced HSFs apoptosis by releasing BIM from binding with prosurvival proteins. Moreover, ABT-263 inhibited HSFs proliferation and reduced the expression of α-SMA and type I/III collagen in a concentration- and time- dependent manner. Conclusion: HSFs showed increased mitochondrial priming with higher level of proapoptotic activator BIM and were primed to death. ABT-263 showed great therapeutic ability in the treatment of hypertrophic scar by targeting HSFs.

Navitoclax enhances the effectiveness of EGFR-targeted antibody-drug conjugates in PDX models of EGFR-expressing triple-negative breast cancer

BACKGROUND

Targeted therapies for triple-negative breast cancer (TNBC) are limited; however, the epidermal growth factor receptor (EGFR) represents a potential target, as the majority of TNBC express EGFR. The purpose of these studies was to evaluate the effectiveness of two EGFR-targeted antibody-drug conjugates (ADC: ABT-414; ABBV-321) in combination with navitoclax, an antagonist of the anti-apoptotic BCL-2 and BCL-XL proteins, in order to assess the translational relevance of these combinations for TNBC.

METHODS

The pre-clinical efficacy of combined treatments was evaluated in multiple patient-derived xenograft (PDX) models of TNBC. Microscopy-based dynamic BH3 profiling (DBP) was used to assess mitochondrial apoptotic signaling induced by navitoclax and/or ADC treatments, and the expression of EGFR and BCL-2/XL was analyzed in 46 triple-negative patient tumors.

RESULTS

Treatment with navitoclax plus ABT-414 caused a significant reduction in tumor growth in five of seven PDXs and significant tumor regression in the highest EGFR-expressing PDX. Navitoclax plus ABBV-321, an EGFR-targeted ADC that displays more effective wild-type EGFR-targeting, elicited more significant tumor growth inhibition and regressions in the two highest EGFR-expressing models evaluated. The level of mitochondrial apoptotic signaling induced by single or combined drug treatments, as measured by DBP, correlated with the treatment responses observed in vivo. Lastly, the majority of triple-negative patient tumors were found to express EGFR and co-express BCL-XL and/or BCL-2.

CONCLUSIONS

The dramatic tumor regressions achieved using combined agents in pre-clinical TNBC models underscore the abilities of BCL-2/XL antagonists to enhance the effectiveness of EGFR-targeted ADCs and highlight the clinical potential for usage of such targeted ADCs to alleviate toxicities associated with combinations of BCL-2/XL inhibitors and systemic chemotherapies.

Single Agent and Synergistic Activity of Maritoclax with ABT-263 in Nasopharyngeal Carcinoma (NPC) Cell Lines

The BCL-2 anti-apoptotic proteins are over-expressed in many cancers and hence are attractive therapeutic targets. In this study, we tested the sensitivity of two Nasopharyngeal Carcinoma (NPC) cell lines HK1 and C666-1 to Maritoclax, which is reported to repress anti-apoptotic protein MCL-1 and BH3 mimetic ABT-263, which selectively inhibits anti-apoptotic proteins BCL-2, BCL-XL and BCL-w. We investigated the sensitisation of the NPC cell lines to these drugs using the SYBR Green I assay and 3D NPC spheroids. We report that Maritoclax repressed anti-apoptotic proteins MCL-1, BCL-2, and BCL-XL in a dose- and time-dependent manner and displayed a single agent activity in inhibiting cell proliferation of the NPC cell lines. Moreover, combination of Maritoclax and ABT-263 exhibited synergistic antiproliferative effect in the HK1 cells. Similar results were obtained in the 3D spheroids generated from the HK1 cells. More notably, 3D HK1 spheroids either treated with single agent Maritoclax or combination with ABT-263, over 10 days, did not develop resistance to the treatment rapidly. Collectively, the findings illustrate that Maritoclax as a single agent or combination with BH3 mimetics could be potentially useful as treatment strategies for the management of NPC.

Targeting antioxidant enzymes enhances the therapeutic efficacy of the BCL-XL inhibitor ABT-263 in KRAS-mutant colorectal cancers

Cancer chemotherapeutic drugs exert cytotoxic effects by modulating intracellular reactive oxygen species (ROS) levels. However, whether ROS modulates the efficacy of targeted therapeutics remains poorly understood. Previously, we reported that upregulation of the anti-apoptotic protein, BCL-X_L, by KRAS activating mutations was a potential target for KRAS-mutant colorectal cancer (CRC) treatment. Here, we demonstrated that the BCL-X_L targeting agent, ABT-263, increased intracellular ROS levels and targeting antioxidant pathways augmented the therapeutic efficacy of this BH3 mimetic. ABT-263 induced expression of genes associated with ROS response and increased intracellular ROS levels by enhancing mitochondrial superoxide generation. The superoxide dismutase inhibitor, 2-methoxyestradiol (2-ME), exhibited synergism with ABT-263 in KRAS-mutant CRC cell lines. This synergistic effect was attributed to the inhibition of mTOR-dependent translation of the anti-apoptotic MCL-1 protein via caspase 3-mediated cleavage of AKT and S6K. In addition, combination treatment of ABT-263 and 2-ME demonstrated a synergistic effect in in vivo patient-derived xenografts harboring KRAS mutations. Our data suggest a novel role for ROS in BH3 mimetic-based targeted therapy and provide a novel strategy for treatment of CRC patients with KRAS mutations.

Clearance of therapy-induced senescent tumor cells by the senolytic ABT-263 via interference with BCL-XL -BAX interaction

Tumor cells undergo senescence in response to both conventional and targeted cancer therapies. The induction of senescence in response to cancer therapy can contribute to unfavorable patient outcomes, potentially including disease relapse. This possibiliy is supported by our findings that tumor cells induced into senescence by doxorubicin or etoposide can give rise to viable tumors in vivo. We further demonstrate sensitivity of these senescent tumor cells to the senolytic ABT-263 (navitoclax), therefore providing a "two-hit" approach to eliminate senescent tumor cells that persist after exposure to chemotherapy or radiation. The sequential combination of therapy-induced senescence and ABT-263 could shift the response to therapy toward apoptosis by interfering with the interaction between BCL-XL and BAX. The administration of ABT-263 after either etoposide or doxorubicin also resulted in marked, prolonged tumor suppression in tumor-bearing animals. These findings support the premise that senolytic therapy following conventional cancer therapy may improve therapeutic outcomes and delay disease recurrence.

Intracellular levels of reactive oxygen species correlate with ABT-263 sensitivity in non-small-cell lung cancer cells

ABT‐263 (Navitoclax) is a BH3‐mimetic drugs targeting anti‐apoptotic B‐cell lymphoma‐2 (BCL‐2) family proteins, including BCL‐2, BCL‐xL, and BCL‐w, thereby inducing apoptosis. In small‐cell lung cancer (SCLC) cells, the response to ABT‐263 is associated with the expression of myeloid cell leukemia‐1 (MCL‐1) protein, however the efficacy of ABT‐263 in non‐small‐cell lung cancer (NSCLC) has not been thoroughly evaluated. There are currently no established biomarkers for predicting the efficacy of ABT‐263 treatment in NSCLC. We screened a panel of different NSCLC cell lines and found that ABT‐263 inhibited cell proliferation and induced apoptosis in Calu‐1, Calu‐3, and BID007 cells. Inconsistent with previous reports on SCLC, low levels of MCL‐1 did not predict the response to ABT‐263 in NSCLC cells, however we found that intracellular levels of reactive oxygen species (ROS) in cancer cells were associated with sensitivity to ABT‐263 in NSCLC cells. We also showed that increasing the level of intracellular ROS could enhance the sensitivity to ABT‐263 in NSCLC cells. In summary, we propose that the intracellular levels of ROS could be used as a potential novel biomarker for predicting a response to ABT‐263 in NSCLC. Furthermore, we show some evidence supporting the further assessment of ABT‐263 as a new therapeutic strategy in patients with NSCLC combined with agents regulating ROS levels. We believe that our findings and follow‐up studies on this matter would lead to novel diagnostic and treatment strategies in patients with NSCLC.

Inhibition of EGFR pathway promotes the cytotoxicity of ABT-263 in human leukemia K562 cells by blocking MCL1 upregulation

ABT-263 induces MCL1 upregulation in cancer cells, which confers resistance to the drug. An increased understanding of the mechanism underlying ABT-263-induced MCL1 expression may provide a strategy to improve its tumor-suppression activity. The present study revealed that ABT-263 reduced the turnover of MCL1 mRNA, thereby upregulating MCL1 expression in human K562 leukemia cells. Furthermore, ABT-263-induced EGFR activation promoted AGO2 phosphorylation at Y393 and reduced miR-125b maturation. Treatment with EGFR inhibitors mitigated MCL1 upregulation induced by ABT-263. Additionally, lithium chloride (LiCl) alleviated ABT-263-induced MCL1 upregulation through EGFR-AGO2 axis-modulated miR-125b suppression. Ectopic expression of dominant negative AGO2(Y393F) or transfection with miR-125b abolished ABT-263-induced upregulation of MCL1 mRNA and protein levels. Co-treatment with either EGFR inhibitors or LiCl collaboratively enhanced ABT-263 cytotoxicity, while MCL1 overexpression eliminated this synergistic effect. Collectively, our data reveal that ABT-263 increases EGFR-mediated AGO2 phosphorylation, which in turn suppresses miR-125b-mediated MCL1 mRNA degradation in K562 cells. The suppression of this signaling pathway results in the synergistic cytotoxic effect of EGFR inhibitors or LiCl and ABT-263.

EMT-inducing transcription factor ZEB1-associated resistance to the BCL-2/BCL-XL inhibitor is overcome by BIM upregulation in ovarian clear cell carcinoma cells

Ovarian clear cell carcinoma (OCCC) is an aggressive subtype of epithelial ovarian cancer, which generally exhibits chemoresistance. Effective therapy for OCCC is currently unavailable, requiring the development of new therapeutic strategies. ABT-263 (navitoclax), an inhibitor of the anti-apoptotic BCL-2/BCL-X_L, has a potent ability of inducing death in cancer cells; however, the therapeutic effect of ABT-263 in OCCC remains unclear. Epithelial cells undergo epithelial-mesenchymal transition (EMT) to acquire a mesenchymal phenotype, which is known to contribute to the development of resistance against therapeutic agents. In this study, we revealed that the sensitivity of OCCC cells to ABT-263 was associated with the epithelial/mesenchymal status of the cells. While the OCCC cells with an epithelial phenotype were ABT-263-sensitive, those with a mesenchymal phenotype were ABT-263-resistant, which was accompanied by an insufficient expression of the pro-apoptotic BH3 protein BIM. Mechanistically, the EMT-inducing transcription factor, ZEB1 down-regulated BIM transcription by binding to BIM promoter, resulting in resistance to ABT-263. It is noteworthy that ZEB1-associated ABT-263 resistance was overcome by an HDAC inhibitor, FK228 (romidepsin), through the up-regulation of BIM. In summary, our study provides evidence for a mechanism for ABT-263 resistance in OCCC cells as well as a potential therapeutic strategy to overcome it.

Apoptosis signaling molecules as treatment targets in head and neck squamous cell carcinoma

OBJECTIVES

To evaluate BCL-2 family signaling molecules in head and neck squamous cell carcinoma (HNSCC) and examine the ability of therapeutic agents with variable mechanisms of action to induce apoptosis in HNSCC cells.

METHODS

messenger ribonculeic acid (mRNA) expression of BAK, BAX, B-cell lymphoma (Bcl-2), BCL2 Like 1 (BCL2L1), and MCL1 were measured in The Cancer Genome Atlas (TCGA) head and neck cancer dataset, as well as in a dataset from a cohort at Montefiore Medical Center (MMC). Protein expression was similarly evaluated in a panel of HNSCC cell lines (HN30, HN31, HN5, MDA686LN, UMSCC47). Cell viability and Annexin V assays were used to assess the efficacy and apoptotic potential of a variety of agents (ABT-263 [navitoclax], A-1210477, and bortezomib.

RESULTS

Expression of BAK, BAX, BCL2L1, and MCL1 were each significantly higher than expression of BCL2 in the TCGA and MMC datasets. Protein expression demonstrated the same pattern of expression when examined in HNSCC cell lines. Treatment with combined ABT-263 (navitoclax)/A-1210477 or with bortezomib demonstrated apoptosis responses that approached or exceeded treatment with staurospaurine control.

CONCLUSION

HNSCC cells rely on inhibition of apoptosis via BCL-xL and MCL-1 overexpression, and induction of apoptosis remains a potential therapeutic option as long as strategies overcome redundant anti-apoptotic signals.

LEVEL OF EVIDENCE

NA Laryngoscope, 130:2643-2649, 2020.

Controlled induction and targeted elimination of p16INK4a-expressing chondrocytes in cartilage explant culture

Cellular senescence is a phenotypic state that contributes to age-related diseases through the secretion of matrix-degrading and inflammatory molecules. An emerging therapeutic strategy for osteoarthritis (OA) is to selectively eliminate senescent cells by initiating apoptosis. This study establishes a cartilage explant model of senescence induction and senolytic clearance using p16^Ink4a expression as a biomarker of senescence. Growth-factor stimulation of explants increased the expression of p16^Ink4a at both the mRNA and protein levels. Applying this culture system to cartilage from p16tdTom reporter mice (a knockin allele with tdTomato fluorescent protein regulated by the endogenous p16Ink4a promoter) demonstrated the emergence of a p16-high population that was quantified using flow cytometry for tdTomato. Cell sorting was used to separate chondrocytes based on tdTomato fluorescence and p16-high cells showed higher senescence-associated β-galactosidase activity and increased gene expression of the senescence-associated secretory phenotype as compared with p16-low cells. The potential for effective senolysis within the cartilage extracellular matrix was assessed using navitoclax (ABT-263). Navitoclax treatment reduced the percentage of p16-high cells from 17.9 to 6.1% (mean of 13 matched pairs; P < 0.001) and increased cleaved caspase-3 confirmed apoptotic activity. Together, these findings establish a physiologically relevant cartilage explant model for testing the induction and elimination of senescent chondrocytes, which will support investigations of senolytic therapy for OA.-Sessions, G. A., Copp, M. E., Liu, J.-Y., Sinkler, M. A., D'Costa, S., Diekman, B. O. Controlled induction and targeted elimination of p16^INK4a-expressing chondrocytes in cartilage explant culture.

BH3 mimetic ABT-263 enhances the anticancer effects of apigenin in tumor cells with activating EGFR mutation

Background

Mutated epidermal growth factor receptor (EGFR) is one of the most successful targets in cancer targeted therapy. While this treatment has benefited many patients with an activating EGFR mutation (EGFRm), almost all those who initially benefited will eventually develop acquired drug resistance (ADR) after a certain period of time. New therapeutic strategies need to be explored to treat EGFRm tumors and overcome or minimize this recurring ADR.

Results

Our data showed that apigenin alone has only mild inhibitory effects on EGFRm tumor cells. By drug screening, we found that ABT-263 can significantly enhance the antitumor activities of apigenin in tumor cells harbouring an activating EGFR mutation and AZD9291-resistant H1975 cells. Mechanistically, apigenin upregulated the expression of Noxa in EGFRm tumor cells by targeting the AKT-FoxO3a pathway, thereby synergizing with ABT-263 to suppress tumor cell growth and proliferation in vitro and in vivo.

Conclusions

Our study provides a rationale for the clinical application of the combination treatment of apigenin and BH3 mimetics in the treatment of EGFRm tumors.

Electronic supplementary material

The online version of this article (10.1186/s13578-019-0322-y) contains supplementary material, which is available to authorized users.

The ratio of Bcl-2/Bim as a predictor of cisplatin response provides a rational combination of ABT-263 with cisplatin or radiation in small cell lung cancer

BACKGROUND

Cisplatin-based chemotherapy and radiotherapy are the most commonly used treatments for small cell lung cancer (SCLC). However, despise initially dramatic response, the response duration of SCLC patients is variable and resistance to chemo- and radio-therapy inevitably develops.

OBJECTIVE

The aim of the study is to investigate the role of Bcl-2 family proteins in predicting SCLC sensitivity to cisplatin treatment, and to identify the potential sensitizer of cisplatin or ratiation treatment in SCLC.

METHODS

We collected cisplatin sensitivity data from public available database, and evaluated its possible association with mRNA or protein expression of Bcl-2 family members in SCLC cell lines.

RESULTS

The IC50 value of cisplatin was significantly correlated with the ratio of Bcl-2/Bim mRNA expression in 33 SCLC cell lines (P= 0.041) as well as the ratio of Bcl-2/Bim protein expression in 7 SCLC cell lines (P= 0.0252). Furthermore, a BH3-mimetic ABT-263 was found to be able to sensitize SCLC cells to cisplatin or radiation. The synergistic and additive antitumor activity of ABT-263 combined with cisplatin or radiation was associated with the enhanced apoptosis, which may be caused by the disruption of Bcl-2 binding to Bim by ABT-263.

CONCLUSIONS

Our study indicates that the ratio of Bcl-2/Bim could be a SCLC response predictor to cisplatin, and ABT-263 addition could be an effective strategy to improve the activity of chemo- or radio-therapy in SCLC.

Allosteric modulation of sigma receptors by BH3 mimetics ABT-737, ABT-263 (Navitoclax) and ABT-199 (Venetoclax)

ABT-737, ABT-263 (Navitoclax) and ABT-199 (Venetoclax) are under intensive preclinical and clinical investigation as treatments for hematologic and other malignancies. These small molecules mimic pro-death B-cell lymphoma-2 (Bcl-2) Homology 3 (BH3) domain-only proteins. They also bear a structural resemblance to certain sigma (σ) receptor ligands. Moreover, the Bcl-2 and σ receptor protein families are both located primarily at the endoplasmic reticulum, mediate cell death and survival through protein-protein interactions, and physically associate. Accordingly, we examined the ability of the ABT series of BH3 mimetics to interact with σ receptors using radioligand-binding techniques. Negative allosteric modulation of [3H](+)-pentazocine, an agonist, binding to σ1 receptors in guinea pig brain membranes was observed for ABT-737, ABT-263 and ABT-199. Findings included reduction of specific binding to distinct plateaus in concentration-dependent fashion, significant slowing of radioligand dissociation kinetics, and decreases in radioligand affinity with no or modest changes in maximal receptor densities. Using a ternary complex model, dissociation constants (KX) for modulator binding to the σ1 receptor ranged from 1 to 2.5 μM, while negative cooperativity factors (α), representing the changes in affinity of ligand and modulator when bound as a ternary complex with the receptor, ranged from 0.15 to 0.42. These observations were extended and reinforced by studies using intact small cell (NCI-H69) and non-small cell (NCI-H23) lung cancer cells, and by using an antagonist σ1 receptor radioligand, E-N-1-(3'-[125I]iodoallyl)-N'-4-(3″,4″-dimethoxyphenethyl)piperazine, in mouse brain membranes. By contrast, exploratory studies indicate marked enhancement of the σ2 receptor binding of [3H]1,3-di-(o-tolyl)guanidine/(+)-pentazocine in NCI-H23 cells and guinea pig brain membranes. These findings raise intriguing questions regarding mechanism and potential functional outcomes.

ABT-263 exhibits apoptosis-inducing potential in oral cancer cells by targeting C/EBP-homologous protein

PURPOSE

ABT-263 is a potent BH3 mimetic that possesses anticancer potential against various types of cancer. In general, this potential is due to its high binding affinity to anti-apoptotic proteins in the Bcl-2 family that disrupt sequestration of pro-apoptotic proteins. In the present study, we sought to identify an alternative regulatory mechanism responsible for ABT-263-mediated anticancer activity in human oral cancer.

METHODS

We investigated the in vitro anti-cancer effects of ABT-263 using a trypan blue exclusion assay, Western blotting, DAPI staining, immunofluorescence staining, a live/dead assay, microarray-based expression profiling, and quantitative real-time PCR. In vivo anti-tumorigenic effects of ABT-263 were examined using a nude mouse tumor xenograft model, a TUNEL assay, and immunohistochemistry.

RESULTS

We found that ABT-263 suppressed viability and induced apoptosis in human oral cancer-derived cell lines HSC-3 and HSC-4. Subsequent microarray-based gene expression profiling revealed 55 differentially expressed genes in the ABT-263-treatead group, including 12 genes associated with "endoplasmic reticulum stress and apoptosis." Consistent with the microarray results, the mRNA expression levels of the top four genes (CHOP, TRB3, ASNS, and STC2) were found to be significantly increased. In addition, we found that ABT-263 considerably enhanced the expression levels of the C/EBP-homologous protein (CHOP) and its mRNA, resulting in apoptosis induction in four other human oral cancer-derived cell lines (MC-3, YD-15, HN22, and Ca9.22). Extending our in vitro findings, we found that ABT-263 reduced the growth of HSC-4 cells in vivo at a dosage of 100 mg/kg/day without any change in body weight. TUNEL-positive cells were also found to be increased in tumors of ABT-263-treated mice without any apparent histopathological changes in liver or kidney tissues.

CONCLUSIONS

These results provide evidence that ABT-263 may serve as an effective therapeutic agent for the treatment of human oral cancer.

Targeting sphingosine kinase 2 suppresses cell growth and synergizes with BCL2/BCL-XL inhibitors through NOXA-mediated MCL1 degradation in cholangiocarcinoma

Sphingosine kinase 2 (SPHK2) is a key factor within sphingolipid metabolism, responsible for the conversion of pro-apoptotic sphingosine to the pro-survival sphingosine-1-phosphate. We have previously shown that ABC294640, a first-in-class SPHK2 inhibitor, inhibits growth of cholangiocarcinoma cells. In a Phase I study of ABC294640 in tumors, the best response was achieved in a cholangiocarcinoma patient. These data suggest SPHK2 as a novel therapeutic target of cholangiocarcinoma. However, the antitumor mechanism of ABC294640 in cholangiocarcinoma remains not clear. In the current study, we found that ABC294640 upregulated expression of pro-apoptotic NOXA. In cholangiocarcinoma patients, high NOXA mRNA expression was associated with better overall survival. Also, SPHK2 mRNA expression was negatively correlated with NOXA mRNA expression. NOXA is known to degrade MCL1, an anti-apoptotic BCL2 protein. We showed that ABC294640 directed MCL1 for proteasome degradation. Knockdown of NOXA prevented ABC294640-induced MCL1 degradation and apoptosis. In addition, ABC294640 had a synergistic effect with BCL2/BCL-XL inhibitors ABT-263 and Obatoclax in inhibiting cell growth. Combined treatment with ABC294640 and BCL2/BCL-XL inhibitors induced potent apoptosis. Silencing of MCL1 also potentiated ABT-263-induced cytotoxicity. Furthermore, we found that both SPHK2 and MCL1 protein expression were significantly higher in cholangiocarcinoma than that in nontumoral bile ducts. SPHK2 expression correlated significantly with MCL1 expression. Our study reveals that ABC294640 inhibits cholangiocarcinoma cell growth and sensitizes the antitumor effect of BCL2/BCL-XL inhibitors through NOXA-mediated MCL1 degradation. Combinations of ABC294640 with BCL2/BCL-XL inhibitors may provide novel strategies for the treatment of cholangiocarcinoma.

Selective BCL-XL inhibition promotes apoptosis in combination with MLN8237 in medulloblastoma and pediatric glioblastoma cells

Background

CNS tumors, including medulloblastoma and pediatric glioblastoma (pGBM) account for the majority of solid pediatric malignancies. There remains an unmet need to identify novel treatment approaches in poor prognosis and relapsed pediatric brain tumors, where therapeutic options are limited. Small-molecule B-cell lymphoma 2 (BCL-2) family inhibitors may enhance tumor cell killing when combined with conventional and targeted chemotherapeutic agents. We investigated the effect of disrupting BCL-2 and B cell lymphoma-extra large (BCL-XL) protein function using ABT-263, ABT-199 and WEHI-539 in medulloblastoma and pGBM cells following treatment with MLN8237, an Aurora kinase inhibitor under investigation as a novel agent for the treatment of malignant brain tumors.

Methods

Tumor cell growth and viability were determined by MTT/WST-1 assays and flow cytometry. Effects on cell phenotype, cell cycle progression, and ploidy were determined by live cell imaging and DNA content analysis. Apoptosis was determined by annexin V/propidium iodide staining and time-lapse microscopy and confirmed by measuring caspase-3/7 activity and western blotting and by short interfering RNA (siRNA) knockdown of BCL-2 associated X protein/BCL-2 antagonist killer (BAX/BAK).

Results

ABT-263, in combination with MLN8237, reduced mitotic slippage and polyploidy and promoted the elimination of mitotically defective cells via a BAX/BAK-dependent, caspase-mediated apoptotic pathway. The BCL-XL antagonist, WEHI-539, significantly augmented tumor cell killing when used in combination with MLN8237, as well as sensitized resistant brain tumor cells to a novel BAX activator, SMBA1. In addition, siRNA-mediated knockdown of BCL-XL sensitized pGBM and medulloblastoma cells to MLN8237 and mimicked the effect of combination drug treatment.

Conclusion

Selective small-molecule inhibitors of BCL-XL may enhance the efficacy of MLN8237 and other targeted chemotherapeutic agents.

Targeting Mcl-1 and other Bcl-2 family member proteins in cancer therapy

Regulation of both the extrinsic and the mitochondria-dependent intrinsic apoptotic pathways plays a key role in the development of the hematopoietic system, for sustaining cell survival during generation of various cell types, in eliminating cells with dual identities such as CD4/CD8 double-positive cells (Hettmann, Didonato, Karin, & Leiden, 1999; Ogasawara, Suda, & Nagata, 1995), for sustaining cells during the rapid clonal expansion phase (Schirmer, Vallejo, Weyand, & Gronzy, 1998), as well as eliminating cells during the contraction phase (Yajima et al., 2006). The anti-apoptotic protein Mcl-1 is necessary for sustaining hematopoietic stem cells (HPS) (Akashi et al., 2003; Akashi, Traver, Miyamoto, & Weissman, 2000). The anti-apoptotic factors Mcl-1, Bcl-2, and Bcl-xL were also found to be over-expressed in acute myeloid leukemia (AML) (Kaufmann et al., 2016) and acute lymphocytic leukemia (ALL) (Findley, Gu, Yeager, & Zhou, 1997), suggesting that dis-regulated apoptotic processes could be a factor in the instigation of leukemia and/or its relapse. Molecules targeting these proteins were used as single agents to treat leukemia. However, by using a set of recently developed specific molecule inhibitors targeting anti-apoptotic proteins, distinct roles are being discovered for these anti-apoptotic proteins during hematopoietic and tumor development. Furthermore, using these inhibitors in proper combinations can effectively induce apoptosis in various solid tumors, even though each agent on its own cannot induce apoptosis in them. These new findings suggest that inhibiting anti-apoptotic elements can induce apoptosis without external stimuli in most cells, but it comes with a risk that some combinations could also trigger apoptosis in healthy cells. One way to address the safety issue is by limiting exposure to all the agents to only cancer cells, thus making the combination safe and effective. In this article, we review this rapidly developing idea in cancer research.

Effects of senolytic drugs on human mesenchymal stromal cells

Background

Senolytic drugs are thought to target senescent cells and might thereby rejuvenate tissues. In fact, such compounds were suggested to increase health and lifespan in various murine aging models. So far, effects of senolytic drugs have not been analysed during replicative senescence of human mesenchymal stromal cells (MSCs).

Methods

In this study, we tested four potentially senolytic drugs: ABT-263 (navitoclax), quercetin, nicotinamide riboside, and danazol. The effects of these compounds were analysed during long-term expansion of MSCs, until replicative senescence. Furthermore, we determined the effect on molecular markers for replicative senescence, such as senescence-associated beta-galactosidase staining (SA-β-gal), telomere attrition, and senescence-associated DNA methylation changes.

Results

Co-culture experiments of fluorescently labelled early and late passages revealed that particularly ABT-263 had a significant but moderate senolytic effect. This was in line with reduced SA-β-gal staining in senescent MSCs upon treatment with ABT-263. However, none of the drugs had significant effects on the maximum number of population doublings, telomere length, or epigenetic senescence predictions.

Conclusions

Of the four tested drugs, only ABT-263 revealed a senolytic effect in human MSCs—and even treatment with this compound did not rejuvenate MSCs with regard to telomere length or epigenetic senescence signature. It will be important to identify more potent senolytic drugs to meet the high hopes for regenerative medicine.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0857-6) contains supplementary material, which is available to authorized users.

Synergistic anti-proliferative effects of combination of ABT-263 and MCL-1 selective inhibitor A-1210477 on cervical cancer cell lines

OBJECTIVE

There are number of studies which report that BCL-2 anti-apoptotic proteins (e.g. BCL-2, BCL-XL, and MCL-1) are highly expressed in cervical cancer tissues compared to the normal cervical epithelia. Despite these reports, targeting these proteins for cervical cancer treatment has not been explored extensively. BH3-mimetics that inhibit specific BCL-2 anti-apoptotic proteins may hold encouraging treatment outcomes for cervical cancer management. Hence, the aim of this pilot study is to investigate the sensitivity of cervical cancer cell lines to combination of two BH3-mimetics namely ABT-263 which selectively inhibits BCL-2, BCL-XL and BCL-w and A-1210477, a selective MCL-1 inhibitor.

RESULTS

We report that combination of A-1210477 and ABT-263 exhibited synergistic effects on all cervical cancer cell lines tested. Drug sensitization studies revealed that A-1210477 sensitised the cervical cancer cell lines SiHa and CaSki to ABT-263 by 11- and fivefold, respectively. Sensitization also occurred in the opposite direction whereby ABT-263 sensitised SiHa and CaSki to A-1210477 by eightfold. This report shows that combination of ABT-263 and A-1210477 could be a potential treatment strategy for cervical cancer. Extensive drug mechanistic studies and drug sensitivity studies in physiological models are necessary to unleash the prospect of this combination for cervical cancer therapy.

Dihydroartemisinin suppresses STAT3 signaling and Mcl-1 and Survivin expression to potentiate ABT-263-induced apoptosis in Non-small Cell Lung Cancer cells harboring EGFR or RAS mutation

Non-small cell lung cancer (NSCLC) is the most common malignancy worldwide. A significant fraction of NSCLC carries activating mutations in epidermal growth factor receptor (EGFR) or RAS oncogene. Dihydroartemisinin (DHA) is a semisynthetic derivative of the herbal antimalarial drug artemisinin that has been recently reported to exhibit anti-cancer activity. To develop new therapeutic strategies for NSCLC, we investigated the interactions between DHA and ABT-263 in NSCLC cells harboring EGFR or RAS mutation. Our data indicated that DHA synergized with ABT-263 to trigger Bax-dependent apoptosis in NSCLC cells in culture. DHA treatment antagonized ABT-263-induced Mcl-1 upregulation and sensitized NSCLC cells to ABT-263-triggered apoptosis. Additionally, DHA treatment caused downregulation of Survivin and upregulation of Bim, which also contribute to cotreatment-induced cytotoxicity. Moreover, DHA effectively suppressed STAT3 phosphorylation, and STAT3 inactivation resulted in the downregulation of Mcl-1 and Survivin, functioning to enhance ABT-263-induced cytotoxicity. Finally, cotreatment of DHA and ABT-263 significantly inhibited xenograft growth in nude mice. Together, DHA effectively inhibits STAT3 activity and modulates expression of Mcl-1, Survivin and Bim, thereby synergizing with ABT-263 to trigger apoptosis in NSCLC cells harboring EGFR or RAS mutation. Our data provide a novel therapeutic strategy for EGFR or RAS mutant NSCLC treatment.

JQ1 synergizes with the Bcl-2 inhibitor ABT-263 against MYCN-amplified small cell lung cancer

Small cell lung cancer (SCLC) is a clinically aggressive cancer with very poor prognosis. Amplification of MYC family genes and overexpression of Bcl-2 protein are common in SCLC, and they are likely therapeutic targets for SCLC. Previous clinical study showed that single agent targeting Bcl-2 with ABT-263 was of limited efficacy in SCLC. In this study, we demonstrated for the first time that co-targeting of N-Myc and Bcl-2 resulted in marked synergistic antitumor effects in MYCN-amplified SCLC. We found that MYCN-amplified SCLC cells were highly sensitive to a Bromodomain and Extra-Terminal domain (BET) inhibitor JQ1, which was able to inhibit N-Myc protein expression. The inhibition of N-Myc by JQ1 induced the expression of Bim, and thereby sensitizing MYCN-amplified SCLC cells to ABT-263. The knockdown on Bim by siRNA reduced this JQ1/ABT-263 induced cell death. ABT-263 and JQ1 co-treatment in MYCN-amplified SCLC cells markedly disrupted Bim/Bcl-2 interaction, and prevented Bim's interaction with Mcl-1. Importantly, this JQ1/ABT-263 co-targeting substantially inhibited the growth of MYCN-amplified SCLC xenografts in vivo. Our study demonstrates a new JQ-1/ABT-263 co-targeting strategy that can be employed for MYCN-amplified SCLC with high efficacy.

The role of apoptosis repressor with a CARD domain (ARC) in the therapeutic resistance of renal cell carcinoma (RCC): the crucial role of ARC in the inhibition of extrinsic and intrinsic apoptotic signalling

Background

Renal cell carcinomas (RCCs) display broad resistance against conventional radio- and chemotherapies, which is due at least in part to impairments in both extrinsic and intrinsic apoptotic pathways. One important anti-apoptotic factor that is strongly overexpressed in RCCs and known to inhibit both apoptotic pathways is ARC (apoptosis repressor with a CARD domain).

Methods

Expression and subcellular distribution of ARC in RCC tissue samples and RCC cell lines were determined by immunohistochemistry and fluorescent immunohistochemistry, respectively. Extrinsic and intrinsic apoptosis signalling were induced by TRAIL (TNF-related apoptosis-inducing ligand), ABT-263 or topotecan. ARC knock-down was performed in clearCa-12 cells using lentiviral transduction of pGIPZ. shRNAmir constructs. Extrinsic respectively intrinsic apoptosis were induced by TRAIL (TNF-related apoptosis-inducing ligand), ABT263 or topotecan. Potential synergistic effects were tested by pre-treatment with topotecan and subsequent treatment with ABT263. Activation of different caspases and mitochondrial depolarisation (JC-1 staining) were analysed by flow cytometry. Protein expression of Bcl-2 family members and ARC in RCC cell lines was measured by Western blotting. Statistical analysis was performed by Student’s t-test.

Results

Regarding the extrinsic pathway, ARC knockdown strongly enhanced TRAIL-induced apoptosis by increasing the activation level of caspase-8. Regarding the intrinsic pathway, ARC, which was only weakly expressed in the nuclei of RCCs in vivo, exerted its anti-apoptotic effect by impairing mitochondrial activation rather than inhibiting p53. Topotecan- and ABT-263-induced apoptosis was strongly enhanced following ARC knockdown in RCC cell lines. In addition, topotecan pre-treatment enhanced ABT-263-induced apoptosis and this effect was amplified in ARC-knockdown cells.

Conclusion

Taken together, our results are the first to demonstrate the importance of ARC protein in the inhibition of both the extrinsic and intrinsic pathways of apoptosis in RCCs. In this context, ARC cooperates with anti-apoptotic Bcl-2 family members to exert its strong anti-apoptotic effects and is therefore an important factor not only in the therapeutic resistance but also in future therapy strategies (i.e., Bcl-2 inhibitors) in RCC. In sum, targeting of ARC may enhance the therapeutic response in combination therapy protocols.

Discovery of piperlongumine as a potential novel lead for the development of senolytic agents

Accumulating evidence indicates that senescent cells play an important role in many age-associated diseases. The pharmacological depletion of senescent cells (SCs) with a "senolytic agent", a small molecule that selectively kills SCs, is a potential novel therapeutic approach for these diseases. Recently, we discovered ABT-263, a potent and highly selective senolytic agent, by screening a library of rationally-selected compounds. With this screening approach, we also identified a second senolytic agent called piperlongumine (PL). PL is a natural product that is reported to have many pharmacological effects, including anti-tumor activity. We show here that PL preferentially killed senescent human WI-38 fibroblasts when senescence was induced by ionizing radiation, replicative exhaustion, or ectopic expression of the oncogene Ras. PL killed SCs by inducing apoptosis, and this process did not require the induction of reactive oxygen species. In addition, we found that PL synergistically killed SCs in combination with ABT-263, and initial structural modifications to PL identified analogs with improved potency and/or selectivity in inducing SC death. Overall, our studies demonstrate that PL is a novel lead for developing senolytic agents.

Combination with vorinostat overcomes ABT-263 (navitoclax) resistance of small cell lung cancer

Small cell lung cancer (SCLC) is an aggressive tumor type with high mortality. One promising approach for SCLC treatment would be to utilize agents targeting molecular abnormalities regulating resistance to apoptosis. BH3 mimetic antagonists, such as ABT-737 and its orally available derivative ABT-263 (navitoclax) have been developed to block the function of pro-survival BCL-2 family members. The sensitivity of SCLC to these drugs varies over a broad range in vitro and in clinical trials. We have previously shown that the expression of Noxa, a BH3-only pro-apoptotic BCL-2 family protein, is a critical determinant of sensitivity to ABT-737. Thus, pharmacological up-regulation of Noxa could enhance cell death induced by the BH3 mimetics. We find that the combination of ABT-263 and a HDAC inhibitor, vorinostat, efficiently induces apoptosis in a variety of SCLC cell lines, including ABT-263 resistant cell lines. Cell death induced by combined treatment is Noxa- and/or BIM-dependent in some cell lines but in others appears to be mediated by down-regulation of BCL-XL and release of BAK from BCL-XL and MCL-1. These results suggest that combination of HDAC inhibitors and BCL-2 inhibitors could be an alternative and effective regimen for SCLC treatment.

PMCA2 silencing potentiates MDA-MB-231 breast cancer cell death initiated with the Bcl-2 inhibitor ABT-263

PMCA2 overexpression in some breast cancers suggests that this calcium pump isoform may play a role in breast pathophysiology. To investigate PMCA2 as a potential drug target for breast cancer therapy, we assessed the functional consequence of PMCA2 silencing on cell death pathways and calcium signals in the basal-like MDA-MB-231 breast cancer cell line. Silencing PMCA2 expression alone has no effect on MDA-MB-231 cell viability, however, PMCA2 silencing promotes calcium-induced cell death initiated with the calcium ionophore ionomycin. Assessment of cytoplasmic calcium responses generated with various agents including ionomycin demonstrates that in MDA-MB-231 cells, PMCA2 does not play a major role in shaping global calcium signals. We also examined the ability of PMCA2 silencing to modulate caspase-dependent cell death triggered by a Bcl-2 inhibitor that is in clinical development for the treatment of various cancers, ABT-263 (Navitoclax). Despite the lack of effect on global calcium responses, PMCA2 silencing augmented Bcl-2 inhibitor (ABT-263)-mediated MDA-MB-231 breast cancer cell death. These studies provide evidence that PMCA2 inhibitors could sensitize PMCA2-positive breast cancers to cell death initiators that work through mechanisms involving the Bcl-2 survival pathway.

VHL-deficient renal cancer cells gain resistance to mitochondria-activating apoptosis inducers by activating AKT through the IGF1R-PI3K pathway

We previously developed (2-deoxyglucose)-(ABT-263) combination therapy (2DG-ABT), which induces apoptosis by activating Bak in the mitochondria of highly glycolytic cells with varied genetic backgrounds. However, the rates of apoptosis induced by 2DG-ABT were lower in von Hippel-Lindau (VHL)-deficient cancer cells. The re-expression of VHL protein in these cells lowered IGF1R expression in a manner independent of oxygen concentration. Lowering IGF1R expression via small interfering RNA (siRNA) sensitized the cells to 2DG-ABT, suggesting that IGF1R interfered with the activation of apoptosis by the mitochondria. To determine which of the two pathways activated by IGF1R, the Ras-ERK pathway or the PI3K-AKT pathway, was involved in the impairment of mitochondria activation, the cells were treated with a specific inhibitor of either PI3K or ERK, and 2DG-ABT was added to activate the mitochondria. The apoptotic rates resulting from 2DG-ABT treatment were higher in the cells treated with the PI3K inhibitor, while the rates remained approximately the same in the cells treated with the ERK inhibitor. In 2DG-ABT-sensitive cells, a 4-h 2DG treatment caused the dissociation of Mcl-1 from Bak, while ABT treatment alone caused the dissociation of Bcl-xL from Bak without substantially reducing Mcl-1 levels. In 2DG-ABT-resistant cells, Mcl-1 dissociated from Bak only when AKT activity was inhibited during the 4-h 2DG treatment. Thus, in VHL-deficient cells, IGF1R activated AKT and stabilized the Bak-Mcl-1 complex, thereby conferring cell resistance to apoptosis.

ABT-263 induces apoptosis and synergizes with chemotherapy by targeting stemness pathways in esophageal cancer

Activation of cancer stem cell signaling is central to acquired resistance to therapy in esophageal cancer (EC). ABT-263, a potent Bcl-2 family inhibitor, is active against many tumor types. However, effect of ABT-263 on EC cells and their resistant counterparts are unknown. Here we report that ABT-263 inhibited cell proliferation and induced apoptosis in human EC cells and their chemo-resistant counterparts. The combination of ABT-263 with 5-FU had synergistic lethal effects and amplified apoptosis that does not depend fully on its inhibition of BCL-2 family proteins in EC cells. To further explore the novel mechanisms of ABT-263, proteomic array (RPPAs) were performed and gene set enriched analysis demonstrated that ABT-263 suppresses the expression of many oncogenes including genes that govern stemness pathways. Immunoblotting and immunofluorescence further confirmed reduction in protein expression and transcription in Wnt/β-catenin and YAP/SOX9 axes. Furthermore, ABT263 strongly suppresses cancer stem cell properties in EC cells and the combination of ABT-263 and 5-FU significantly reduced tumor growth in vivo and suppresses the expression of stemness genes. Thus, our findings demonstrated a novel mechanism of ABT-263 antitumor effect in EC and indicating that combination of ABT-263 with cytotoxic drugs is worthy of pursuit in patients with EC.

Identification of a novel senolytic agent, navitoclax, targeting the Bcl-2 family of anti-apoptotic factors

Clearing senescent cells extends healthspan in mice. Using a hypothesis‐driven bioinformatics‐based approach, we recently identified pro‐survival pathways in human senescent cells that contribute to their resistance to apoptosis. This led to identification of dasatinib (D) and quercetin (Q) as senolytics, agents that target some of these pathways and induce apoptosis preferentially in senescent cells. Among other pro‐survival regulators identified was Bcl‐xl. Here, we tested whether the Bcl‐2 family inhibitors, navitoclax (N) and TW‐37 (T), are senolytic. Like D and Q, N is senolytic in some, but not all types of senescent cells: N reduced viability of senescent human umbilical vein epithelial cells (HUVECs), IMR90 human lung fibroblasts, and murine embryonic fibroblasts (MEFs), but not human primary preadipocytes, consistent with our previous finding that Bcl‐xl siRNA is senolytic in HUVECs, but not preadipocytes. In contrast, T had little senolytic activity. N targets Bcl‐2, Bcl‐xl, and Bcl‐w, while T targets Bcl‐2, Bcl‐xl, and Mcl‐1. The combination of Bcl‐2, Bcl‐xl, and Bcl‐w siRNAs was senolytic in HUVECs and IMR90 cells, while combination of Bcl‐2, Bcl‐xl, and Mcl‐1 siRNAs was not. Susceptibility to N correlated with patterns of Bcl‐2 family member proteins in different types of human senescent cells, as has been found in predicting response of cancers to N. Thus, N is senolytic and acts in a potentially predictable cell type‐restricted manner. The hypothesis‐driven, bioinformatics‐based approach we used to discover that dasatinib (D) and quercetin (Q) are senolytic can be extended to increase the repertoire of senolytic drugs, including additional cell type‐specific senolytic agents.

BAX-BAK1-independent LC3B lipidation by BH3 mimetics is unrelated to BH3 mimetic activity and has only minimal effects on autophagic flux

Inhibition of prosurvival BCL2 family members can induce autophagy, but the mechanism is controversial. We have provided genetic evidence that BCL2 family members block autophagy by inhibiting BAX and BAK1, but others have proposed they instead inhibit BECN1. Here we confirm that small molecule BH3 mimetics can induce BAX- and BAK1-independent MAP1LC3B/LC3B lipidation, but this only occurred at concentrations far greater than required to induce apoptosis and dissociate canonical BH3 domain-containing proteins that bind more tightly than BECN1. Because high concentrations of a less-active enantiomer of ABT-263 also induced BAX- and BAK1-independent LC3B lipidation, induction of this marker of autophagy appears to be an off-target effect. Indeed, robust autophagic flux was not induced by BH3 mimetic compounds in the absence of BAX and BAK1. Therefore at concentrations that are on target and achievable in vivo, BH3 mimetics only induce autophagy in a BAX- and BAK1-dependent manner.

Glucose availability and glycolytic metabolism dictate glycosphingolipid levels

Cancer therapeutics has seen an emergence and re-emergence of two metabolic fields in recent years, those of bioactive sphingolipids and glycolytic metabolism. Anaerobic glycolysis and its implications in cancer have been at the forefront of cancer research for over 90 years. More recently, the role of sphingolipids in cancer cell metabolism has gained recognition, notably ceramide's essential role in programmed cell death and the role of the glucosylceramide synthase (GCS) in chemotherapeutic resistance. Despite this knowledge, a direct link between these two fields has yet to be definitively drawn. Herein, we show that in a model of highly glycolytic cells, generation of the glycosphingolipid (GSL) glucosylceramide (GlcCer) by GCS was elevated in response to increased glucose availability, while glucose deprivation diminished GSL levels. This effect was likely substrate dependent, independent of both GCS levels and activity. Conversely, leukemia cells with elevated GSLs showed a significant change in GCS activity, but no change in glucose uptake or GCS expression. In a leukemia cell line with elevated GlcCer, treatment with inhibitors of glycolysis or the pentose phosphate pathway (PPP) significantly decreased GlcCer levels. When combined with pre-clinical inhibitor ABT-263, this effect was augmented and production of pro-apoptotic sphingolipid ceramide increased. Taken together, we have shown that there exists a definitive link between glucose metabolism and GSL production, laying the groundwork for connecting two distinct yet essential metabolic fields in cancer research. Furthermore, we have proposed a novel combination therapeutic option targeting two metabolic vulnerabilities for the treatment of leukemia.