RIP1 protein-dependent assembly of a cytosolic cell death complex is required for inhibitor of apoptosis (IAP) inhibitor-mediated sensitization to lexatumumab-induced apoptosis.

Searching for new strategies to trigger apoptosis in rhabdomyosarcoma (RMS), we investigated the effect of two novel classes of apoptosis-targeting agents, i.e. monoclonal antibodies against TNF-related apoptosis-inducing ligand (TRAIL) receptor 1 (mapatumumab) and TRAIL receptor 2 (lexatumumab) and small-molecule inhibitors of inhibitor of apoptosis (IAP) proteins. Here, we report that IAP inhibitors synergized with lexatumumab, but not with mapatumumab, to reduce cell viability and to induce apoptosis in several RMS cell lines in a highly synergistic manner (combination index <0.1). Cotreatment-induced apoptosis was accompanied by enhanced activation of caspase-8, -9, and -3; loss of mitochondrial membrane potential; and caspase-dependent apoptosis. In addition, IAP inhibitor and lexatumumab cooperated to stimulate the assembly of a cytosolic complex containing RIP1, FADD, and caspase-8. Importantly, knockdown of RIP1 by RNA interference prevented the formation of the RIP1·FADD·caspase-8 complex and inhibited subsequent activation of caspase-8, -9, and -3; loss of mitochondrial membrane potential; and apoptosis upon treatment with IAP inhibitor and lexatumumab. In addition, RIP1 silencing rescued clonogenic survival of cells treated with the combination of lexatumumab and IAP inhibitor, thus underscoring the critical role of RIP1 in cotreatment-induced apoptosis. By comparison, the TNFα-blocking antibody Enbrel had no effect on IAP inhibitor/lexatumumab-induced apoptosis, indicating that an autocrine TNFα loop is dispensable. By demonstrating that IAP inhibitors and lexatumumab synergistically trigger apoptosis in a RIP1-dependent but TNFα-independent manner in RMS cells, our findings substantially advance our understanding of IAP inhibitor-mediated regulation of TRAIL-induced cell death.

Mapatumumab and lexatumumab induce apoptosis in TRAIL-R1 and TRAIL-R2 antibody-resistant NSCLC cell lines when treated in combination with bortezomib.

Mapatumumab and lexatumumab are fully human monoclonal antibodies that bind and activate human tumor necrosis factor-related apoptosis-inducing ligand receptors 1 and 2, respectively. These antibodies induce apoptosis in various tumor cell types, although the degree of sensitivity can vary from highly sensitive to completely resistant. Importantly, tumor cells that are partially or completely resistant to mapatumumab or lexatumumab can often be sensitized when treated in combination with chemotherapeutic drugs. In this regard, the proteasome inhibitor bortezomib has recently shown synergistic activity against established lymphoma cell lines and primary lymphomas when combined with mapatumumab and lexatumumab. Here, we report similar findings using a panel of human non-small cell lung cancer (NSCLC) cell lines. Specifically, we show that bortezomib rapidly induces sensitivity to mapatumumab and lexatumumab in NSCLC cell lines that are completely resistant to antibody alone and that bortezomib concentrations as low as 25 nmol/L sensitize NSCLC cells to the antibodies. Furthermore, bortezomib at the tested concentration has minimal effect on its own, indicating the combination generates synergistic cytotoxicity. Combination treatment induces activation of the caspase cascade and the effect of the combination is caspase dependent. Bortezomib treatment increases the intracellular levels of several important apoptosis regulators that may mediate enhanced sensitivity to mapatumumab and lexatumumab. These results suggest future evaluation of mapatumumab or lexatumumab in combination with bortezomib is warranted in NSCLC patients.

Efficacy of a triple treatment with irradiation, agonistic TRAIL receptor antibodies and EGFR blockade.

BACKGROUND AND PURPOSE: : Since the efficacy of a single targeted agent in combination with ionizing radiation is limited by putative treatment resistances, a rationally designed triple treatment consisting of an agonistic antibody targeting either TRAIL-R1 (mapatumumab) or TRAIL-R2 (lexatumumab), radiation and an epidermal growth factor receptor-(EGFR-)inhibiting antibody (cetuximab) was tested. MATERIAL AND METHODS: : Induction of apoptosis after triple treatment was determined in Colo205, HCT116 and FaDu cells by Hoechst 33342 stain. The degree of interaction was determined by isobologram analysis. A knockout variant of HCT116 was used to examine Bax dependence of the triple treatment. The role of Akt/PKB signaling was analyzed using the phosphatidylinositol 3-kinase inhibitor LY294002. Clonogenic assays were performed to examine the effect on clonogenic survival of tumor cells. RESULTS: : A synergistic effect of radiation, cetuximab and agonistic TRAIL-R antibodies was demonstrated in cell lines derived from colorectal tumors or head-and-neck cancers. The efficacy of this multimodal approach was dependent on Bax and inhibition of Akt/PKB in the cell systems used. The results also show a positive impact on clonogenic cell death in several cell lines. CONCLUSION: : These data suggest that rationally designed multimodal therapy approaches integrating radiation with more than one targeted agent will open new perspectives in radiation oncology.

Efficacy of triple therapies including ionising radiation, agonistic TRAIL antibodies and cisplatin.

The detection of molecular targeted agents is a milestone in cancer treatment. Despite the achievements, the efficacy of single targeted agents in combination with radiotherapy is limited by putative treatment resistance. We therefore tested a rationally designed triple therapy consisting of an agonistic antibody against either TRAIL-R1 (mapatumumab/HGS-ETR1) or TRAIL-R2 (lexatumumab/HGS-ETR2) in combination with the established chemotherapeutic drug cisplatin in a panel of solid tumour cell lines derived from head and neck as well as colorectal carcinomas. Induction of apoptosis after monotherapy, double or triple treatment was determined in FaDu (squamous cancer cell line of the head and neck), Colo205 and HCT116 cells (colorectal adenocarcinoma cell lines) by Hoechst 33342 stain. Double and triple therapies were compared using analysis of variance followed by post hoc tests. The degree of interaction was determined by 3D-isobologram analysis. A knockout variant of HCT116 was used to examine Bax-dependence of the triple therapy to gain insight into the underlying molecular signaling pathways possibly responsible for the observed effects. Dose-response relationships revealed different baseline activities of the modalities dependent on cell type. Triple therapy was more effective than double therapy in most cases according to the induction of apoptosis. Furthermore, a synergistic efficacy of the triple therapy was demonstrated in a subset of tumour cell lines. The efficacy of this multimodal approach was highly dependent on the presence of Bax. Our data suggest that targeted agents can be effectively added to existing multimodal therapy approaches which might open new perspectives in radiation oncology.

Histone deacetylase inhibitors enhance lexatumumab-induced apoptosis via a p21Cip1-dependent decrease in survivin levels.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) preferentially induces apoptosis in malignant cells by binding to the death receptors TRAIL-R1 (DR4) and TRAIL-R2 (DR5). Several agents that therapeutically exploit this phenomenon are being developed. We investigated the anticancer activity of two novel, highly specific agonistic monoclonal antibodies to TRAIL-R1 (mapatumumab, HGS-ETR1) and TRAIL-R2 (lexatumumab, HGS-ETR2) in colon cancer cell lines. Our analyses revealed that colon cancer cells display significantly higher surface expressions of TRAIL-R2 than TRAIL-R1, and are more sensitive to lexatumumab-induced apoptosis. The proapoptotic effects of lexatumumab in TRAIL-resistant HCT8 and HT29 cells were dramatically augmented by the histone deacetylase inhibitors trichostatin A or suberoylanilide hydroxamic acid. The presence of p21, but not p53, was critical for the synergy between lexatumumab and histone deacetylase inhibitors. The absence of p21 did not interfere with the formation of the death-inducing signaling complex by lexatumumab, suggesting the involvement of other apoptotic and/or cell cycle regulators. Indeed, treatment with suberoylanilide hydroxamic acid greatly reduced the expression of the inhibitor of apoptosis protein survivin and cdc2 activity in HCT116 p21(+/+) cells but not in the HCT116 p21(-/-) cells. Inhibition of cdc2 activity with flavopiridol decreased survivin expression and sensitized the p21-deficient cells to lexatumumab-induced apoptosis. Similarly, small interfering RNA-mediated knockdown of survivin also enhanced lexatumumab-mediated cell death. Therefore, survivin expression plays a key role in lexatumumab resistance, and reducing survivin expression by inhibiting cdc2 activity is a promising strategy to enhance the anticancer activity of lexatumumab.

Trail receptors: targets for cancer therapy.

A human tumor cell's ability to avoid the normal regulatory mechanisms of cell growth, division, and death are the hallmarks of transformation and cancer. Numerous novel therapeutic agents currently in preclinical or clinical evaluation aim to revive the normal regulation or evade these regulatory defects and induce growth arrest and cell death. One of the cell death pathways that has garnered significant interest, as a potential target for therapeutic intervention, is the programmed cell death pathway regulated by the tumor necrosis factor-related apoptosis-inducing ligand receptors (TRAIL-RS). Receptor agonist molecules including forms of the native ligand and monoclonal antibodies are being developed and tested as therapeutics in the treatment of human cancer.

Quality improvement initiative to improve inpatient outcomes for Neonatal Abstinence Syndrome.

OBJECTIVES: To improve Neonatal Abstinence Syndrome (NAS) inpatient outcomes through a comprehensive quality improvement (QI) program. DESIGN: Inclusion criteria were opioid-exposed infants ≥36 weeks. QI methodology including stakeholder interviews and plan-do-study-act (PDSA) cycles were utilized. We compared pre- and post-intervention NAS outcomes after a QI initiative that included: A non-pharmacologic care bundle, function-based assessments consisting of symptom prioritization and then the "Eat, Sleep, Console" (ESC) Tool; and a switch to methadone for pharmacologic treatment. RESULTS: Pharmacologic treatment decreased from 87.1 to 40.0%; adjunctive agent use from 33.6 to 2.4%; hospitalization length from a mean 17.4 to 11.3 days, and opioid treatment days from 16.2 to 12.7 (p < 0.001 for all). Total hospital charges decreased from $31,825 to $20,668 per infant. Parental presence increased from 55.6 to 75.8% (p < 0.0001). No adverse events were noted. CONCLUSIONS: A comprehensive QI program focused on non-pharmacologic care, function-based assessments, and methadone resulted in significant sustained improvements in NAS outcomes. These findings have important implications for establishing potentially better practices for opioid-exposed newborns.

Novel in vivo imaging shows up-regulation of death receptors by paclitaxel and correlates with enhanced antitumor effects of receptor agonist antibodies.

Susceptibility to apoptosis by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is mediated through cognate death receptor signaling. We hypothesized that auto-amplification of this apparatus would enhance antitumor effects in vivo and could be optimized using the results obtained from novel imaging techniques. We therefore imaged mice bearing human colorectal cancer (Colo205) tumor xenografts with HGS-ETR1 and HGS-ETR2 agonist antibodies to TRAIL receptor-1 (TRAIL-R1) and TRAIL-R2, respectively, after radiolabeling the antibodies. Paclitaxel significantly increased in vivo expression of TRAIL-R1 and TRAIL-R2 in a time-dependent manner. The imaging results were confirmed by immunoblots for steady-state protein levels (>20-fold increase in TRAIL-R1 and TRAIL-R2 levels in tumor xenografts by 48 h after paclitaxel administration). TRAIL-R1 and TRAIL-R2 mRNA expression did not change, suggesting that these effects were posttranscriptional. Sequential treatment with paclitaxel followed by HGS-ETR1 or HGS-ETR2 after 48 h resulted in markedly enhanced antitumor activity against Colo205 mouse xenografts. Our experiments suggest that sequential taxane treatment followed by TRAIL-R agonist antibodies could be applied in the clinic, and that novel imaging techniques using radiolabeled receptor antibodies may be exploitable to optimize sequence timing and patient selection.

Enhanced apoptosis and tumor regression induced by a direct agonist antibody to tumor necrosis factor-related apoptosis-inducing ligand receptor 2.

PURPOSE: Substantial evidence indicates that supraoligomerization of the death receptors for Fas ligand and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is necessary for efficient activation of the apoptotic pathway. Bivalent IgG antibodies can induce the efficient apoptosis by mimicking the natural ligands but only after these antibodies are further oligomerized by cross-linking. In this study, we generated a novel agonist antibody to TRAIL receptor 2 (TRAIL-R2) capable of inducing apoptosis without cross-linking and elucidated its mode of action and efficacy. EXPERIMENTAL DESIGN: A fully human antibody to TRAIL-R2, KMTR2, was generated from KM Mouse immunized with TRAIL-R2 ectodomain. Apoptosis-inducing activities of unfractionated or purified monomeric IgG of KMTR2 was evaluated in the presence or absence of cross-linkers, secondary antibodies or Fc receptor-expressing effector cells, against human colorectal adenocarcinoma Colo205. Oligomerization of TRAIL-R2 was analyzed by size exclusion chromatography and confocal microscopy, and in vivo efficacy was examined in Colo205 xenograft model. RESULTS: KMTR2 specifically recognized TRAIL-R2 and induced apoptosis with or without cross-linking. Size exclusion chromatography showed that the apoptosis activity coeluted with monomeric IgG and was effective independent of secondary antibody or Fc receptor-expressing effector cells. The antibody formed supracomplexes with soluble recombinant and membrane-anchored TRAIL-R2 and enhanced clustering of TRAIL-R2 on cell surface without cross-linking. KMTR2 was dramatically efficacious in reducing established human tumor. CONCLUSION: Our findings indicate that novel agonist antibody KMTR2 can direct antibody-dependent oligomerization of TRAIL-R2 and initiates efficient apoptotic signaling and tumor regression independent of host effector function. Thus, the direct agonist would be a lead candidate for cancer therapeutics.

History of surgery for cerebrovascular disease in children. Part II. Vein of Galen malformations.

Vein of Galen aneurysmal malformations are a mixed group of lesions characterized by an abnormal fistula between abnormal distal branches of the choroidal and/or posterior cerebral arteries and the great vein of Galen. In this paper the authors trace the historical evolution of the current approach to diagnosis and treatment, and the literature is reviewed comprehensively. During the historical era, vein of Galen malformations were described in individual case reports and an early classification system was developed. In the early era of treatment, open surgery was the preferred approach, although morbidity and mortality rates were high. The development of neurointerventional techniques allowed the introduction of occlusive materials into the fistula, with pronounced improvements in clinical outcome.

History of surgery for cerebrovascular disease in children. Part III. Arteriovenous malformations.

Arteriovenous malformations (AVMs) are the most common cause of intracerebral hemorrhage in children. In this paper the authors trace the historical evolution of the recognition, diagnosis, and treatment of pediatric intracerebral AVMs, and they summarize the contemporary approach and current controversies surrounding treatment of these lesions. Important distinctions between adult and pediatric AVMs are emphasized.

History of surgery for cerebrovascular disease in children. Part I. Intracranial arterial aneurysms.

Intracranial aneurysms are rare in children, and their origins and treatment methods tend to be different from those in these same entities in adults. These lesions tend to be congenital or to have an infectious or traumatic origin. In the current paper the authors trace the historical evolution of the diagnosis and treatment of intracranial aneurysms in children. Based on the literature, these lesions appear to occur in children in less than 3% of all series. The literature also supports the suggestion that symptoms from these aneurysms are often from mass effect and that giant aneurysms and lesions in the posterior cranial fossa are relatively more common in children than in adults. The termination of the carotid artery and the anterior cerebral artery seem to be disproportionately common sites of aneurysm formation in this cohort. Interestingly, surgical outcomes in children appear to be moderately better than in adults. Based on the literature, the claim can be made that a multidisciplinary approach to the management of such aneurysms can yield good outcomes in a very high percentage of children treated.

Revision of Breastfeeding Guidelines in the Setting of Maternal Opioid Use Disorder: One Institution's Experience.

Breastfeeding is recommended for women with opioid use disorder who are treated with methadone or buprenorphine. Infants with neonatal abstinence syndrome (NAS) secondary to in-utero opioid exposure have unique challenges related to breastfeeding but also have significant benefits including improved NAS symptoms with a decreased need for pharmacotherapy. Poor understanding of substance use disorder and treatment, lack of evidence-based recommendations, and vague guidelines from national academies create controversy about breastfeeding eligibility for these women. Defining breastfeeding guidelines is often difficult, particularly in large institutions with multiple providers caring for the mother-infant dyad. Based on the available evidence and review of our institutional data, we revised our breastfeeding guidelines for mothers with opioid use disorder. The aims of our new guidelines are (a) to safely promote breastfeeding in all mothers with opioid use disorder who are in recovery, (b) to improve NAS outcomes through use of breastfeeding as a key nonpharmacologic treatment modality, and (c) to improve staff communication and consistency on the subject of breastfeeding in this patient population.

Children and television tipovers: a significant and preventable cause of long-term neurological deficits.

OBJECT: Television tipover has recently been recognized as a significant cause of injury in children, and head injury accounts for most of the associated deaths. The authors reviewed their experience with children who sustained head injury from falling televisions. METHODS: Children admitted with the diagnosis of head injury related to falling televisions since 1992 were identified from the authors' trauma database, and a retrospective review of the medical records was performed. Eighteen patients were identified: 13 boys and five girls whose ages ranged from 12 months to 10 years (mean 44 months). The admission Glasgow Coma Scale (GCS) score was 15 in 10 patients. Only three patients had a GCS score of 8 or less (one patient had a score of 4). Neurological examinations were normal in 10 patients; three had cranial nerve deficits and three had otorrhea, otorrhagia, or hemotympanum. Radiological abnormalities included 16 skull fractures, three epidural hematomas, three small subdural hematomas, one intracranial hemorrhage, and three venous obstructions of the transverse-sigmoid sinus. The mean hospital stay was 8.9 days (range 2-39 days). Follow up at 0.2 to 68 months (mean 13.4 months) revealed severe neurological deficits in one patient and cranial nerve deficits of cranial nerves six, seven, or eight in six patients. CONCLUSIONS: Falling televisions result in significant head injuries in children, with substantial short- and long-term sequelae. This injury is easily preventable through simple measures taken by both the manufacturers and caregivers.

Induction of potent NK cell-dependent anti-myeloma cytotoxic T cells in response to combined mapatumumab and bortezomib.

There is increasing evidence that some cancer therapies can promote tumor immunogenicity to boost the endogenous antitumor immune response. In this study, we used the novel combination of agonistic anti-TRAIL-R1 antibody (mapatumumab, Mapa) with low dose bortezomib (LDB) for this purpose. The combination induced profound myeloma cell apoptosis, greatly enhanced the uptake of myeloma cell apoptotic bodies by dendritic cell (DC) and induced anti-myeloma cytotoxicity by both CD8+ T cells and NK cells. Cytotoxic lymphocyte expansion was detected within 24 h of commencing therapy and was maximized when myeloma-pulsed DC were co-treated with low dose bortezomib and mapatumumab (LDB+Mapa) in the presence of NK cells. This study shows that Mapa has two distinct but connected modes of action against multiple myeloma (MM). First, when combined with LDB, Mapa produced powerful myeloma cell apoptosis; secondly, it promoted DC priming and an NK cell-mediated expansion of anti-myeloma cytotoxic lymphocyte (CTL). Overall, this study indicates that Mapa can be used to drive potent anti-MM immune responses.

Deletion of Stat3 blocks mammary gland involution and extends functional competence of the secretory epithelium in the absence of lactogenic stimuli.

The transcription factor Stat3 is activated through tyrosine phosphorylation by many cytokines and is a fundamental mediator of their signals. In the mammary gland, Stat3 activity increases sharply shortly after weaning, and involution is delayed in mice, that contain a mutant Stat3 lacking 33 amino acids including the key tyrosine residue. We have now generated a more extensive mutation of Stat3 through the deletion of exons 15-21 in mammary epithelium. This resulted in the loss of 245 amino acids including the DNA binding and SH2 domains, and Stat3 protein was undetectable. Pregnancy-mediated mammary development and lactation were normal in these mice. Involution was delayed and, remarkably, Stat3-null mammary epithelium maintained its functional integrity and competence even 6 d after weaning, whereas control mammary tissue was rendered nonfunctional within 2 d. The lack of remodeling and functional stasis of the epithelium correlated with the disruption of proteinase activity. Our data demonstrate that mammary tissue can retain its functional competence in the absence of external lactogenic stimuli and demonstrate a delay in the initiation of the irreversible stage of involution.

Measuring the health status of children with hydrocephalus by using a new outcome measure.

OBJECT: In the preceding article, the authors described the Hydrocephalus Outcome Questionnaire (HOQ), a simple, reliable, and valid measure of health status in children with hydrocephalus. In the present study, they present their initial experience in using the HOQ to quantify the health status in a typical cohort of children with hydrocephalus. METHODS: The mothers of children with hydrocephalus completed the HOQ and, with the child's attending surgeon, provided a global rating of their children's health. An exploratory analysis was performed using a multivariate analysis of variance (ANOVA) to determine which variables might be associated with worse health status. The mothers of 80 children, ranging in age from 5 to 17 years, participated in the study. The mean HOQ Overall Health score was 0.68, a value estimated to be equivalent to a mean health utility score of 0.77. The global health ratings provided by the mothers and the surgeons were moderately correlated with the HOQ scores (Pearson correlations 0.58 and 0.57, respectively). Results of the multivariate ANOVA indicated that the presence of epilepsy was strongly associated with a worse health status (p < 0.0001, F-test). CONCLUSIONS: The health status of a typical sample of children with hydrocephalus was measured using the HOQ. The only consistently significant association with health status found was the presence of epilepsy.

Phase II trial of mapatumumab, a fully human agonist monoclonal antibody to tumor necrosis factor-related apoptosis-inducing ligand receptor 1 (TRAIL-R1), in combination with paclitaxel and carboplatin in patients with advanced non-small-cell lung cancer.

BACKGROUND: This phase II study examined the efficacy of mapatumumab in combination with paclitaxel and carboplatin in patients with non-small-cell lung cancer (NSCLC). PATIENTS AND METHODS: Patients with stage IIIB or stage IV advanced primary NSCLC were randomly assigned (1:1:1) to receive up to 6 courses of standard-dose paclitaxel and carboplatin or a combination of paclitaxel, carboplatin, and mapatumumab (10 mg/kg or 30 mg/kg). Primary efficacy end points were overall response rate and median progression-free survival (PFS). Secondary efficacy end points included disease control rate, overall survival (OS), time to response, and duration of response. Exploratory studies included evaluation of historical biopsy materials for TRAIL-R1 expression by immunohistochemical analysis and serum levels of M30, a marker of apoptosis, before and after the first 2 doses of mapatumumab. Safety parameters, including adverse events (AEs), laboratory tests, and immunogenicity, were assessed. RESULTS: The majority of patients had stage IV disease (79%) and an Eastern Cooperative Oncology Group (ECOG) performance status of 0 (58%); baseline characteristics were similar across treatment arms. No improvements in response or disease control rates, PFS, or OS were gained from the addition of mapatumumab. Adverse events in the mapatumumab arms were generally consistent with toxicities seen in the carboplatin and paclitaxel control arm. Levels of M30 were highly variable, and consistent patterns were not seen across treatment arms. CONCLUSION: This study showed no clinical benefit from adding mapatumumab to carboplatin and paclitaxel in unselected patients with NSCLC. The combination was generally well tolerated. The possibility of subgroups sensitive to mapatumumab is discussed.

Sorafenib sensitizes solid tumors to Apo2L/TRAIL and Apo2L/TRAIL receptor agonist antibodies by the Jak2-Stat3-Mcl1 axis.

BACKGROUND: Approximately half of tumor cell lines are resistant to the tumor-selective apoptotic effects of tumor necrosis factor-related apoptosis-inducing ligand (Apo22L/TRAIL). Previously, we showed that combining Apo2L/TRAIL with sorafenib, a multikinase inhibitor, results in dramatic efficacy in Apo2L/TRAIL-resistant tumor xenografts via inhibition of Mcl-1. Soluble Apo2L/TRAIL is capable of binding to several surface receptors, including the pro-apoptotic death receptors, DR4 and DR5, and decoy receptors, DcR1 and DcR2. Monoclonal antibodies targeting either of these death receptors are being investigated as antitumor agents in clinical trials. We hypothesized that sorafenib and Apo2L/TRAIL or Apo2L/TRAIL death receptor agonist (TRA) antibodies against DR4 (mapatumumab) and DR5 (lexatumumab) will overcome resistance to Apo2L/TRAIL-mediated apoptosis and as increase antitumor efficacy in Apo2L/TRAIL-sensitive solid tumors. METHODOLOGY/PRINCIPAL FINDINGS: We found that Apo2L/TRAIL or TRA antibodies combined with sorafenib synergistically reduce cell growth and increase cell death across a panel of solid tumor cell lines in vitro. This panel included human breast, prostate, colon, liver and thyroid cancers. The cooperativity of these combinations was also observed in vivo, as measured by tumor volume and TUNEL staining as a measure of apoptosis. We found that sorafenib inhibits Jak/Stat3 signaling and downregulates their target genes, including cyclin D1, cyclin D2 and Mcl-1, in a dose-dependent manner. CONCLUSIONS/SIGNIFICANCE: The combination of sorafenib with Apo2L/TRAIL or Apo2L/TRAIL receptor agonist antibodies sensitizes Apo2L/TRAIL-resistant cells and increases the sensitivity of Apo2L/TRAIL-sensitive cells. Our findings demonstrate the involvement of the Jak2-Stat3-Mcl1 axis in response to sorafenib treatment, which may play a key role in sorafenib-mediated sensitization to Apo2L/TRAIL.