ABSTRACT
Background: The surface of the aorta generally does not show motion unless mobile atheroma, thrombi, vegetations, or intimal flaps are present. We previously described unusual mobile filamentous structures in the carotid artery. Here, we describe similar findings in the aorta and their possible cause. Case summary: An 88-year-old female with progressive exertional dyspnoea and severe aortic stenosis had a successful transcatheter aortic valve replacement (TAVR). A filamentous structure was noted on the focused pre-operative 2D transoesophageal echocardiography in the proximal descending aorta and post-TAVR as long strand-like structures attached to the thickened intimal wall with a planar component on 3D imaging. These findings were not associated with symptoms or clinical sequelae on short- and long-term follow-up. Discussion: The mobile structures that we describe are atypical for atheroma, thrombi, vegetations, and dissections in terms of their form and clinical presentation. 2D imaging showed that the filaments had focal thickening and emerged from the aortic surface. These findings suggest a relationship with the intima, perhaps from atherogenesis or injury with disruption or lifting of the intimal surface. No clinical sequelae were detected that may also relate to their position in the descending aorta and not the arch.
ABSTRACT
Impaired polymorphonuclear leukocyte (PMNL) functions contribute to increased infections and cardiovascular diseases in chronic kidney disease (CKD). Uremic toxins reduce hydrogen sulfide (H2S) levels and the anti-oxidant and anti-inflammatory effects of H2S. Its biosynthesis occurs as a side process of transsulfuration and in the disposal of adenosylhomocysteine, a transmethylation inhibitor and proposed uremic toxin. PMNL chemotaxis was measured by the under-agarose method, phagocytosis, and oxidative burst by flow cytometry in whole blood and apoptosis by determining DNA content by flow cytometry and morphological features by fluorescence microscopy. Sodium hydrogen sulfide (NaHS), diallyl trisulphide (DATS) and diallyl disulphide (DADS), cysteine, and GYY4137 were used as H2S-producing substances. Increased H2S concentrations did not affect chemotaxis and phagocytosis. NaHS primed PMNL oxidative burst activated by phorbol 12-myristate 13-acetate (PMA) or E. coli. Both DATS and cysteine significantly decreased E. coli-activated oxidative burst but had no effect on PMA stimulation. While NaHS, DADS, and cysteine attenuated PMNL apoptosis, GYY4137 decreased their viability. Experiments with signal transduction inhibitors suggest that the intrinsic apoptosis pathway is mainly involved in GYY4137-induced PMNL apoptosis and that GYY4137 and cysteine target signaling downstream of phosphoinositide 3-kinase.
Subject(s)
Hydrogen Sulfide , Neutrophils , Cysteine/pharmacology , Cysteine/metabolism , Escherichia coli , Hydrogen Sulfide/pharmacology , Hydrogen Sulfide/metabolism , Phosphatidylinositol 3-Kinases/metabolismABSTRACT
The recruitment of DRP1 to mitochondrial membranes prior to fission is facilitated by the wrapping of endoplasmic reticulum (ER) membranes around the mitochondria. To investigate the complex interplay between the ER membranes and DRP1 in the context of mitochondrial structure and function, we downregulate two key ER shaping proteins, RTN4 and CLIMP-63, and demonstrate pronounced mitochondrial hyperfusion and reduced ER-mitochondria contacts, despite their differential regulation of ER architecture. Although mitochondrial recruitment of DRP1 is unaltered in cells lacking RTN4 or CLIMP-63, several aspects of mitochondrial function, such as mtDNA-encoded translation, respiratory capacity and apoptosis are significantly hampered. Further mechanistic studies reveal that CLIMP-63 is required for cristae remodeling (OPA1 proteolysis) and DRP1-mediated mitochondrial fission, whereas both RTN4 and CLIMP-63 regulate the recruitment of BAX to ER and mitochondrial membranes to enable cytochrome c release and apoptosis, thereby performing novel and distinct roles in the regulation of mitochondrial structure and function.
Subject(s)
Dynamins , Mitochondria , Apoptosis/genetics , Dynamins/metabolism , Energy Metabolism , Mitochondria/metabolism , Mitochondrial Dynamics , Mitochondrial Proteins/genetics , Mitochondrial Proteins/metabolismABSTRACT
BACKGROUND: We previously described percutaneous thrombectomy and right ventricular (RV) mechanical support of a coronavirus disease 2019 (COVID-19) patient with a massive pulmonary embolism. Here, we present a detailed echocardiographic and clinical timeline with 1-year follow-up. CASE SUMMARY: A 57-year-old female with COVID-19 went into shock from a massive pulmonary embolism. After percutaneous removal of a large thrombus burden (AngioVac system; AngioDynamics Inc., Latham, NY, USA), she became severely hypotensive, requiring cardiopulmonary resuscitation, and hemodynamic support with an Impella RP device (Abiomed, Danvers, MA, USA). A paediatric transoesophageal echocardiography (TOE) probe monitored the procedure because an adult probe would not pass (S7-3t-Philips Medical Systems, Andover, MA, USA). Post-thrombectomy, surface imaging documented gradual resolution of RV dysfunction, tricuspid regurgitation, and elevated pulmonary artery pressure. Her course was complicated by renal failure requiring temporary dialysis. She was discharged home on apixaban. Hypercoagulability work-up was negative. Two months later, vocal cord surgery was performed for persistent stridor. Esophagoscopy at that time was prevented by osteophyte obstruction. At 10 months, she received the Pfizer-BioNTech vaccine. At 1 year, the patient remains healthy on apixaban, and her echocardiogram is normal. DISCUSSION: This case illustrates the pivotal role of echocardiography in the diagnosis, percutaneous treatment, and near- and long-term follow-up and management of a patient with massive pulmonary embolism due to COVID-19 with documentation of complete recovery from severe RV dysfunction and haemodynamic collapse. A paediatric TOE probe was a crucial alternative to the adult probe because of possible osteophyte obstruction.
ABSTRACT
In uremic patients, high-density lipoprotein (HDL) loses its anti-inflammatory features and can even become pro-inflammatory due to an altered protein composition. In chronic kidney disease (CKD), impaired functions of polymorphonuclear leukocytes (PMNLs) contribute to inflammation and an increased risk of cardiovascular disease. This study investigated the effect of HDL from CKD and hemodialysis (HD) patients on the CD14 expression on PMNLs. HDL was isolated using a one-step density gradient centrifugation. Isolation of PMNLs was carried out by discontinuous Ficoll-Hypaque density gradient centrifugation. CD14 surface expression was quantified by flow cytometry. The activity of the small GTPase Rac1 was determined by means of an activation pull-down assay. HDL increased the CD14 surface expression on PMNLs. This effect was more pronounced for HDL isolated from uremic patients. The acute phase protein serum amyloid A (SAA) caused higher CD14 expression, while SAA as part of an HDL particle did not. Lipid raft disruption with methyl-ß-cyclodextrin led to a reduced CD14 expression in the absence and presence of HDL. HDL from healthy subjects but not from HD patients decreased the activity of Rac1. Considering the known anti-inflammatory effects of HDL, the finding that even HDL from healthy subjects increased the CD14 expression was unexpected. The pathophysiological relevance of this result needs further investigation.
Subject(s)
Lipopolysaccharide Receptors/genetics , Lipoproteins, HDL/pharmacology , Neutrophils/drug effects , Renal Insufficiency, Chronic/genetics , Uremia/genetics , Aged , Case-Control Studies , Female , Humans , Lipopolysaccharide Receptors/metabolism , Lipoproteins, HDL/isolation & purification , Male , Membrane Microdomains/chemistry , Membrane Microdomains/drug effects , Membrane Microdomains/metabolism , Middle Aged , Neutrophils/metabolism , Neutrophils/pathology , Primary Cell Culture , Renal Dialysis , Renal Insufficiency, Chronic/metabolism , Renal Insufficiency, Chronic/physiopathology , Renal Insufficiency, Chronic/therapy , Serum Amyloid A Protein/genetics , Serum Amyloid A Protein/metabolism , Uremia/metabolism , Uremia/physiopathology , Uremia/therapy , beta-Cyclodextrins/pharmacology , rac1 GTP-Binding Protein/genetics , rac1 GTP-Binding Protein/metabolismABSTRACT
This Special Issue of Toxins focusses on the interconnected factors interfering with the immune response in uremic patients [...].
Subject(s)
Gastrointestinal Microbiome , Immune System Diseases , Renal Insufficiency, Chronic/immunology , Toxins, Biological , Uremia/immunology , Humans , Inflammasomes , Oxidative StressABSTRACT
BACKGROUND: Late antibody-mediated rejection (AMR) is a major cause of transplant failure. Potential therapeutic targets are plasma cells and natural killer (NK) cells, both expressing high levels of CD38. METHODS: Here, we report the use of CD38 monoclonal antibody daratumumab (9-mo course) in a kidney allograft recipient diagnosed with smoldering myeloma and anti-HLA class II donor-specific antibody-positive chronic active AMR 13 years after transplantation. Patient monitoring included serial HLA single-antigen testing, peripheral blood immune cell phenotyping, as well as follow-up allograft and bone marrow biopsies at 3 and 9 months, including analyses of rejection-related gene expression patterns. RESULTS: Daratumumab led to persistent CD138+ cell depletion in the bone marrow and blood and substantially decreased NK cells counts in blood and graft tissue. At the same time, donor-specific antibody in serum disappeared, and in vitro alloantibody production by CD138+ cells enriched from bone marrow aspirates was abrogated. A 3-month follow-up biopsy revealed a complete resolution of microcirculation inflammation (g+ptc: 3 to 0) and molecular AMR activity (AMR score: 0.79 to <0.2). The same biopsy showed (subclinical) tubulointerstitial inflammation, which prompted steroid treatment. Over an observation period of 12 months, graft function stabilized. CONCLUSIONS: Targeting CD38 for plasma cell and NK cell depletion may be an effective strategy to counteract AMR. Our results may encourage the design of future trials to clarify the role of this innovative treatment concept in organ transplantation.
Subject(s)
Antibodies, Monoclonal/therapeutic use , Graft Rejection/drug therapy , HLA Antigens/immunology , Immunosuppressive Agents/therapeutic use , Isoantibodies/blood , Kidney Transplantation/adverse effects , Killer Cells, Natural/drug effects , Plasma Cells/drug effects , Chronic Disease , Graft Rejection/blood , Graft Rejection/immunology , Graft Survival/drug effects , Humans , Immunity, Cellular/drug effects , Immunity, Humoral/drug effects , Killer Cells, Natural/immunology , Killer Cells, Natural/metabolism , Male , Middle Aged , Plasma Cells/immunology , Plasma Cells/metabolism , Treatment OutcomeABSTRACT
Measuring the economy during COVID-19 has created a set of hurdles and prospects for the U.S. statistical agencies, the private sector, and academia. This included how to deal with unprecedented movements in economic variables while ensuring data quality. At the same time, new entrants released data that are sometimes at odds with gold standard releases. Given the multitude of data, this article focuses on both existing and new ways to track the employment statistics. The results leave more questions than answers.
ABSTRACT
Cardiovascular disease and infections are major causes for the high incidence of morbidity and mortality of patients with chronic kidney disease. Both complications are directly or indirectly associated with disturbed functions or altered apoptotic rates of polymorphonuclear leukocytes, monocytes, lymphocytes, and dendritic cells. Normal responses of immune cells can be reduced, leading to infectious diseases or pre-activated/primed, giving rise to inflammation and subsequently to cardiovascular disease. This review summarizes the impact of kidney dysfunction on the immune system. Renal failure results in disturbed renal metabolic activities with reduced renin, erythropoietin, and vitamin D production, which adversely affects the immune system. Decreased kidney function also leads to reduced glomerular filtration and the retention of uremic toxins. A large number of uremic toxins with detrimental effects on immune cells have been identified. Besides small water-soluble and protein-bound compounds originating from the intestinal microbiome, several molecules in the middle molecular range, e.g., immunoglobulin light chains, retinol-binding protein, the neuropeptides Met-enkephalin and neuropeptide Y, endothelin-1, and the adipokines leptin and resistin, adversely affect immune cells. Posttranslational modifications such as carbamoylation, advanced glycation products, and oxidative modifications contribute to uremic toxicity. Furthermore, high-density lipoprotein from uremic patients has an altered protein profile and thereby loses its anti-inflammatory properties.
Subject(s)
Cardiovascular Diseases/immunology , Communicable Diseases/immunology , Immune System/immunology , Renal Insufficiency, Chronic/immunology , Uremia/immunology , Animals , Cardiovascular Diseases/metabolism , Cardiovascular Diseases/mortality , Cardiovascular Diseases/physiopathology , Communicable Diseases/metabolism , Communicable Diseases/mortality , Communicable Diseases/physiopathology , Glomerular Filtration Rate , Humans , Immune System/metabolism , Immune System/physiopathology , Kidney/metabolism , Kidney/physiopathology , Renal Insufficiency, Chronic/metabolism , Renal Insufficiency, Chronic/mortality , Renal Insufficiency, Chronic/physiopathology , Toxins, Biological/metabolism , Uremia/metabolism , Uremia/mortality , Uremia/physiopathologyABSTRACT
BACKGROUND: The coronavirus disease 2019 (COVID-19) has caused a global pandemic with an unprecedented burden on health and the economy worldwide. Although it primarily involves the respiratory tract system, cardiovascular complications, particularly arterial and venous thrombosis, are frequently reported and are associated with adverse outcomes. CASE SUMMARY: We describe the case of a 57-year-old female who presented with acute hypoxic respiratory failure and shock. She was found to have left lower extremity deep vein thrombosis and a suspected pulmonary embolism. A large mobile right atrial mass was found on echocardiogram. Given the large thrombus burden that portended an extremely high risk for embolization to the pulmonary arteries, emergent percutaneous aspiration of an organized thrombus (rather than thrombolysis) was performed using the AngioVac system (Angiodynamics Inc., Latham, NY, USA) complicated by haemodynamic collapse due to acute right ventricular failure. An Impella RP (Abiomed, Danvers, MA, USA) was then placed, with rapid stabilization of haemodynamics. The patient tested positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). She was treated with antimicrobial and systemic anticoagulation therapy. She was successfully weaned off the Impella RP on post-operative day 4 and was extubated on day 5. She was discharged on day 16 in a stable condition. DISCUSSION: Incident venous thrombo-embolism is frequently encountered in COVID-19 patients. We report the first case of a large intracardiac thrombus associated with SARS-CoV-2 infection managed successfully with percutaneous thrombectomy and right ventricular mechanical circulatory support.
ABSTRACT
Squamous cell carcinoma of the head and neck (SCCHN) is the sixth most common cancer worldwide, with overall survival of less than 50%. Current therapeutic strategies involving a combination of surgery, radiation, and/or chemotherapy are associated with debilitating side effects, highlighting the need for more specific and efficacious therapies. Inhibitors of BCL-2 family proteins (BH3 mimetics) are under investigation or in clinical practice for several hematological malignancies and show promise in solid tumors. In order to explore the therapeutic potential of BH3 mimetics in the treatment of SCCHN, we assessed the expression levels of BCL-2, BCL-XL, and MCL-1 via Western blots and immunohistochemistry, in cell lines, primary cells derived from SCCHN patients and in tissue microarrays containing tumor tissue from a cohort of 191 SCCHN patients. All preclinical models exhibited moderate to high levels of BCL-XL and MCL-1, with little or no BCL-2. Although expression levels of BCL-XL and MCL-1 did not correlate with patient outcome, a combination of BH3 mimetics to target these proteins resulted in decreased clonogenic potential and enhanced apoptosis in all preclinical models, including tumor tissue resected from patients, as well as a reduction of tumor volume in a zebrafish xenograft model of SCCHN. Our results show that SCCHN is dependent on both BCL-XL and MCL-1 for apoptosis evasion and combination therapy targeting both proteins may offer significant therapeutic benefits in this disease.
Subject(s)
Peptide Fragments/chemistry , Proto-Oncogene Proteins/chemistry , Squamous Cell Carcinoma of Head and Neck/drug therapy , Animals , Antineoplastic Agents/pharmacology , Antineoplastic Agents/therapeutic use , Apoptosis/drug effects , Cell Line, Tumor , Cisplatin/pharmacology , Cisplatin/therapeutic use , Female , Humans , Kaplan-Meier Estimate , Male , Middle Aged , Neoplasm Proteins/metabolism , Squamous Cell Carcinoma of Head and Neck/pathology , Treatment Outcome , Xenograft Model Antitumor Assays , ZebrafishABSTRACT
Graphic communication (GC) is useful for continuous quality improvement (CQI), education, and patient care when in-person discussion is not possible because of geographic and schedule constraints. In echocardiography, these constraints can be mitigated by (a) capturing screenshots and device photos or videos and sharing them by email or text message, (b) simultaneous viewing of images on digital displays, and (c) broadcasting the study real time during acquisition to other mobile or stationary devices. Screenshots are useful for CQI and education and can be acquired, annotated, and shared with minimal impact on the flow of clinical echo interpretation. Providers at different locations can employ GC for shared clinical decision making by viewing echo studies from the same server, video conferencing or accessing real-time broadcast from a device. Which GC tool is selected is determined by its ease of use, the provider's goals and whether immediate image review is needed.
Subject(s)
Echocardiography , Patient Care , Quality Assurance, Health Care , Radiology Information Systems , Telemedicine/trends , User-Computer Interface , HumansABSTRACT
Maintenance of mitochondrial integrity is critical for normal cellular homoeostasis. Most cells respond to stress stimuli and undergo apoptosis by perturbing mitochondrial structure and function to release proteins, such as cytochrome c, which are essential for the execution of the intrinsic apoptotic cascade. Cancer cells evade these events by overexpressing the anti-apoptotic BCL-2 family of proteins on mitochondrial membranes. Inhibitors of the anti-apoptotic BCL-2 family proteins, also known as BH3 mimetics, antagonise the pro-survival functions of these proteins and result in rapid apoptosis. Although the precise mechanism by which BH3 mimetics induce apoptosis has been well characterised, not much is known in terms of the structural changes that occur in mitochondria during apoptosis. Using a panel of highly selective BH3 mimetics and a wide range of cell lines, we demonstrate that BH3 mimetics induce extensive mitochondrial fission, accompanied by swelling of the mitochondrial matrix and rupture of the outer mitochondrial membrane. These changes occur in a BAX/ BAK-dependent manner. Although a major mitochondrial fission GTPase, DRP-1, has been implicated in mitochondrial apoptosis, our data demonstrate that DRP-1 might function independently/downstream of BH3 mimetic-mediated mitochondrial fission to facilitate the release of cytochrome c and apoptosis. Moreover, downregulation of DRP-1 prevented cytochrome c release and apoptosis even when OPA1, a protein mediating mitochondrial fusion, was silenced. Although BH3 mimetic-mediated displacement of BAK and other BH3-only proteins from BCL-XL and MCL-1 was unaffected by DRP-1 downregulation, it prevented BAK activation significantly, thus placing DRP-1 as one of the most critical players, along with BAX and BAK, that governs BH3 mimetic-mediated cytochrome c release and apoptosis.
ABSTRACT
The endoplasmic reticulum (ER) with its elaborate network of highly curved tubules and flat sheets interacts with several other organelles, including mitochondria, peroxisomes and endosomes, to play vital roles in their membrane dynamics and functions. Previously, we identified structurally diverse chemicals from different pharmacological classes, which induce a reversible reorganisation of ER membranes. Using apogossypol as a prototypic tool compound, we now show that ER membrane reorganisation occurs at the level of ER tubules but does not involve ER sheets. Reorganisation of ER membranes prevents DRP-1-mediated mitochondrial fission, thereby antagonising the functions of several mitochondrial fission-inducing agents. Previous reports have suggested that ER membranes mark the constriction sites of mitochondria by localising DRP-1, as well as BAX on mitochondrial membranes to facilitate both mitochondrial fission and outer membrane permeabilisation. Following ER membrane reorganisation and subsequent exposure to an apoptotic stimulus (BH3 mimetics), DRP-1 still colocalises with the reorganised ER membranes but BAX translocation and activation, cytochrome c release and phosphatidylserine externalisation are all inhibited, thereby diminishing the ability of BH3 mimetics to induce the intrinsic apoptotic pathway. Strikingly, both ER membrane reorganisation and its resulting inhibition of apoptosis could be reversed by inhibitors of dihydroorotate dehydrogenase (DHODH), namely teriflunomide and its active metabolite, leflunomide. However, neither genetic inhibition of DHODH using RNA interference nor metabolic supplementation with orotate or uridine to circumvent the consequences of a loss of DHODH activity rescued the effects of DHODH inhibitors, suggesting that the effects of these inhibitors in preventing ER membrane reorganisation is most likely independent of their ability to antagonise DHODH activity. Our results strengthen the hypothesis that ER is fundamental for key mitochondrial functions, such as fusion-fission dynamics and apoptosis.
Subject(s)
Apoptosis/drug effects , Endoplasmic Reticulum/metabolism , Gossypol/analogs & derivatives , Mitochondrial Dynamics/drug effects , Crotonates/pharmacology , Cytochromes c/metabolism , Endoplasmic Reticulum/drug effects , Endoplasmic Reticulum/ultrastructure , Gossypol/pharmacology , HeLa Cells , Humans , Hydroxybutyrates , Intracellular Membranes/drug effects , Intracellular Membranes/metabolism , Leflunomide/pharmacology , Mitochondria/drug effects , Mitochondria/metabolism , Models, Biological , Nitriles , Protein Transport/drug effects , Toluidines/pharmacology , bcl-2-Associated X Protein/metabolismABSTRACT
The anti-inflammatory properties of high-density lipoproteins (HDL) are lost in uremia. These HDL may show pro-inflammatory features partially as a result of changed protein composition. Alterations of polymorphonuclear leukocytes (PMNLs) in chronic kidney disease (CKD) may contribute to chronic inflammation and high vascular risk. We investigated if HDL from uremic patients is related to systemic inflammation by interfering with PMNL function. PMNL apoptosis was investigated by assessing morphological features and DNA content. CD11b surface expression was quantified by flow cytometry. Oxidative burst was measured via cytochrome c reduction assay. Chemotaxis was assessed by using an under-agarose migration assay. We found that HDL from CKD and hemodialysis (HD) patients significantly attenuated PMNL apoptosis, whereas HDL isolated from healthy subjects had no effect on PMNL apoptosis. The use of signal transduction inhibitors indicated that uremic HDL exerts anti-apoptotic effects by activating pathways involving phosphoinositide 3-kinase and extracellular-signal regulated kinase. Healthy HDL attenuated the surface expression of CD11b, whereas HDL from CKD and HD patients had no effect. All tested isolates increased the stimulation of oxidative burst, but did not affect PMNL chemotactic movement. In conclusion, HDL may contribute to the systemic inflammation in uremic patients by modulating PMNL functions.
Subject(s)
Lipoproteins, HDL/immunology , Neutrophils/immunology , Renal Insufficiency, Chronic/immunology , Uremia/immunology , Adult , Aged , Apoptosis , CD11b Antigen/immunology , Female , Humans , Male , Middle Aged , Renal DialysisABSTRACT
Induction of apoptosis by selective BH3-mimetics is currently investigated as a novel strategy for cancer treatment. Here, we report that selective BH3-mimetics induce apoptosis in a variety of hematological malignancies. Apoptosis is accompanied by severe mitochondrial toxicities upstream of caspase activation. Specifically, the selective BH3-mimetics ABT-199, A-1331852 and S63845, which target BCL-2, BCL-XL and MCL-1, respectively, induce comparable ultrastructural changes including mitochondrial swelling, a decrease of mitochondrial matrix density and severe loss of cristae structure. These shared effects on mitochondrial morphology indicate a similar function of these anti-apoptotic BCL-2 proteins in maintaining mitochondrial integrity and function.
Subject(s)
Mitochondria/drug effects , Molecular Mimicry , Myeloid Cell Leukemia Sequence 1 Protein/drug effects , Proto-Oncogene Proteins c-bcl-2/drug effects , bcl-X Protein/drug effects , Apoptosis , Caspases/metabolism , Enzyme Activation , Humans , Mitochondria/metabolism , Myeloid Cell Leukemia Sequence 1 Protein/metabolism , Proto-Oncogene Proteins c-bcl-2/metabolism , bcl-X Protein/metabolismABSTRACT
The impressive selectivity and efficacy of BH3 mimetics for treating cancer has largely been limited to BCL-2 dependent hematological malignancies. Most solid tumors depend on other anti-apoptotic proteins, including MCL-1, for survival. The recent description of S63845 as the first specific and potent MCL-1 inhibitor represents an important therapeutic advance, since MCL-1 is not targeted by the currently available BH3 mimetics, Navitoclax or Venetoclax, and is commonly associated with chemoresistance. In this study, we confirm a high binding affinity and selectivity of S63845 to induce apoptosis in MCL-1-dependent cancer cell lines. Furthermore, S63845 synergizes with other BH3 mimetics to induce apoptosis in cell lines derived from both hematological and solid tumors. Although the anti-apoptotic BCL-2 family members in these cell lines interact with a spectrum of pro-apoptotic BH3-only proteins to regulate apoptosis, these interactions alone do not explain the relative sensitivities of these cell lines to BH3 mimetic-induced apoptosis. These findings necessitated further investigation into the requirement of BH3-only proteins in BH3 mimetic-mediated apoptosis. Concurrent inhibition of BCL-XL and MCL-1 by BH3 mimetics in colorectal HCT116 cells induced apoptosis in a BAX- but not BAK-dependent manner. Remarkably this apoptosis was independent of all known BH3-only proteins. Although BH3-only proteins were required for apoptosis induced as a result of BCL-XL inhibition, this requirement was overcome when both BCL-XL and MCL-1 were inhibited, implicating distinct mechanisms by which different anti-apoptotic BCL-2 family members may regulate apoptosis in cancer.