MET-independent lung cancer cells evading EGFR kinase inhibitors are therapeutically susceptible to BH3 mimetic agents.

Targeted therapies for cancer are inherently limited by the inevitable recurrence of resistant disease after initial responses. To define early molecular changes within residual tumor cells that persist after treatment, we analyzed drug-sensitive lung adenocarcinoma cell lines exposed to reversible or irreversible epidermal growth factor receptor (EGFR) inhibitors, alone or in combination with MET-kinase inhibitors, to characterize the adaptive response that engenders drug resistance. Tumor cells displaying early resistance exhibited dependence on MET-independent activation of BCL-2/BCL-XL survival signaling. Further, such cells displayed a quiescence-like state associated with greatly retarded cell proliferation and cytoskeletal functions that were readily reversed after withdrawal of targeted inhibitors. Findings were validated in a xenograft model, showing BCL-2 induction and p-STAT3[Y705] activation within the residual tumor cells surviving the initial antitumor response to targeted therapies. Disrupting the mitochondrial BCL-2/BCL-XL antiapoptotic machinery in early survivor cells using BCL-2 Homology Domain 3 (BH3) mimetic agents such as ABT-737, or by dual RNAi-mediated knockdown of BCL-2/BCL-XL, was sufficient to eradicate the early-resistant lung-tumor-cells evading targeted inhibitors. Similarly, in a xenograft model the preemptive cotreatment of lung tumor cells with an EGFR inhibitor and a BH3 mimetic eradicated early TKI-resistant evaders and ultimately achieved a more durable response with prolonged remission. Our findings prompt prospective clinical investigations using BH3-mimetics combined with targeted receptor kinase inhibitors to optimize and improve clinical outcomes in lung-cancer treatment.

Nitrosylcobalamin potentiates the anti-neoplastic effects of chemotherapeutic agents via suppression of survival signaling.

BACKGROUND: Nitrosylcobalamin (NO-Cbl) is a chemotherapeutic pro-drug derived from vitamin B12 that preferentially delivers nitric oxide (NO) to tumor cells, based upon increased receptor expression. NO-Cbl induces Apo2L/TRAIL-mediated apoptosis and inhibits survival signaling in a variety of malignant cell lines. Chemotherapeutic agents often simultaneously induce an apoptotic signal and activation of NF-kappaB, which has the undesired effect of promoting cell survival. The specific aims of this study were to 1) measure the anti-tumor effects of NO-Cbl alone and in combination with conventional chemotherapeutic agents, and to 2) examine the mechanism of action of NO-Cbl as a single agent and in combination therapy. METHODOLOGY: Using anti-proliferative assays, electrophoretic mobility shift assay (EMSA), immunoblot analysis and kinase assays, we demonstrate an increase in the effectiveness of chemotherapeutic agents in combination with NO-Cbl as a result of suppressed NF-kappaB activation. RESULTS: Eighteen chemotherapeutic agents were tested in combination with NO-Cbl, in thirteen malignant cell lines, resulting in a synergistic anti-proliferative effect in 78% of the combinations tested. NO-Cbl pre-treatment resulted in decreased NF-kappaB DNA binding activity, inhibition of IkappaB kinase (IKK) enzymatic activity, decreased AKT activation, increased caspase-8 and PARP cleavage, and decreased cellular XIAP protein levels. CONCLUSION: The use of NO-Cbl to inhibit survival signaling may enhance drug efficacy by preventing concomitant activation of NF-kappaB or AKT.

Effect of inositol hexakisphosphate kinase 2 on transforming growth factor beta-activated kinase 1 and NF-kappaB activation.

We previously showed that inositol hexakisphosphate kinase 2 (IHPK2) functions as a growth-suppressive and apoptosis-enhancing kinase during cell stress. Overexpression of IHPK2 sensitized ovarian carcinoma cell lines to the growth-suppressive and apoptotic effects of interferon beta (IFN-beta), IFN-alpha2, and gamma-irradiation. Expression of a kinase-dead mutant abrogated 50% of the apoptosis induced by IFN-beta. Because the kinase-dead mutant retained significant response to cell stressors, we hypothesized that a portion of the death-promoting function of IHPK2 was independent of its kinase activity. We now demonstrate that IHPK2 binds to tumor necrosis factor (TNF) receptor-associated factor (TRAF) 2 and interferes with phosphorylation of transforming growth factor beta-activated kinase 1 (TAK1), thereby inhibiting NF-kappaB signaling. IHPK2 contains two sites required for TRAF2 binding, Ser-347 and Ser-359. Compared with wild type IHPK2-transfected cells, cells expressing S347A and S359A mutations displayed 3.5-fold greater TAK1 activation following TNF-alpha. This mutant demonstrated a 6-10-fold increase in NF-kappaB DNA binding following TNF-alpha compared with wild type IHPK2-expressing cells in which NF-kappaB DNA binding was inhibited. Cells transfected with wild type IHPK2 or IHPK2 mutants that lacked S347A and S359A mutations displayed enhanced terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling staining following TNF-alpha. We believe that IHPK2-TRAF2 binding leads to attenuation of TAK1- and NF-kappaB-mediated signaling and is partially responsible for the apoptotic activity of IHPK2.

Nitrosylcobalamin promotes cell death via S nitrosylation of Apo2L/TRAIL receptor DR4.

We have previously demonstrated that nitrosylcobalamin (NO-Cbl), an analogue of vitamin B12 that delivers nitric oxide (NO), had potent antiproliferative activity against several human cancer cell lines. NO-Cbl induced apoptosis via a death receptor/caspase-8 pathway. In this study, we demonstrate that a functional Apo2L/TRAIL receptor was necessary for the induction of cell death by NO-Cbl. Furthermore, the Apo2L/TRAIL death receptor DR4 (TRAIL R1) was S nitrosylated following NO-Cbl treatment. Human melanoma (A375), renal carcinoma (ACHN), and ovarian carcinoma (NIH-OVCAR-3) cells were treated with NO-Cbl and subjected to the biotin switch assay; S-nitrosylated DR4 was detected in all three cell lines. NO-Cbl treatment did not cause S nitrosylation of DR5. The seven cysteine residues located in the cytoplasmic domain of DR4 were individually point mutated to alanines. NIH-OVCAR-3 cells expressing the DR4 C336A mutation lacked S nitrosylation following NO-Cbl treatment. Overexpression of wild-type DR4 sensitized cells to growth inhibition by NO-Cbl. Cells expressing the DR4 C336A mutant were more resistant to NO-Cbl and Apo2L/TRAIL than were the other six C-A mutations or wild-type cells. The C336A mutant also displayed blunted caspase-8 enzymatic activity following NO-Cbl treatment compared to the other mutants. Thus, DR4 residue C336 becomes S nitrosylated and promotes apoptosis following NO-Cbl treatment.

Apo2L/TRAIL induction and nuclear translocation of inositol hexakisphosphate kinase 2 during IFN-beta-induced apoptosis in ovarian carcinoma.

Previously, we have reported that overexpression of IHPK2 (inositol hexakisphosphate kinase 2) sensitized NIH-OVCAR-3 ovarian carcinoma cell lines to the growth-suppressive and apoptotic effects of IFN-beta (interferon-beta) treatment and gamma-irradiation. In the present study, we demonstrate that Apo2L/TRAIL (Apo2L/tumour-necrosis-factor-related apoptosis-inducing ligand) is a critical mediator of IFN-induced apoptosis in these cells. Compared with IFN-alpha2, IFN-beta is a more potent inducer of Apo2L/TRAIL and IHPK2 activity. Overexpression of IHPK2 converts IFN-alpha2-resistant cells into cells that readily undergo apoptosis in response to IFN-alpha2. In untreated cells transfected with IHPK2-eGFP (where eGFP stands for enhanced green fluorescent protein), the fusion protein is localized to the cytoplasm and perinuclear region. After treatment with IFN-beta, IHPK2-eGFP translocated to the nucleus. In cells transfected with mutant IHPK2-NLS-eGFP (where NLS stands for nuclear localization sequence), containing point mutations in the NLS, the fusion protein remained trapped in the cytoplasm, even after IFN-beta treatment. Cells expressing mutant NLS mutation were more resistant to IFN-beta. The IC50 value of IHPK2-expressing cells was 2-3-fold lower than vector control. The IC50 value of NLS-mutant-expressing cells was 3-fold higher than vector control. Blocking antibodies to Apo2L/TRAIL or transfection with a dominant negative Apo2L/TRAIL receptor (DR5Delta) inhibited the antiproliferative effects of IFN-beta. Thus overexpression of IHPK2 enhanced apoptotic effects of IFN-beta, and expression of the NLS mutant conferred resistance to IFN-beta. Apo2L/TRAIL expression and nuclear localization of IHPK2 are both required for the induction of apoptosis by IFN-beta in ovarian carcinoma.

Phase 2 trial of interferon-beta as second-line treatment of ovarian cancer, fallopian tube cancer, or primary carcinoma of the peritoneum.

OBJECTIVE: The protocol was designed to examine the biological effects and clinical activity of interferon-beta in patients with platinum/taxane-resistant ovarian cancer. METHODS: Patients with resistant ovarian and fallopian tube cancers and primary peritoneal carcinoma were treated with recombinant human interferon-beta (Rebif, Serono International) at doses ranging from 6 to 24 million international units (MIU)/day, based on their tolerance to therapy. Levels of IP-10, an interferon-inducible protein, were measured in the serum to evaluate the biological effects of the drug. Also, the peripheral blood mononuclear cells and serum were examined for the induction of previously described novel regulators of interferon-induced death. RESULTS: Eighteen patients were treated, of whom 9 (50%) could be treated at the highest dose level (24 MIU). The major toxicities were fever, chills and fatigue. The median duration of therapy was 6 weeks (range 1-22). No objective responses were observed. IP-10 levels were significantly increased, compared with baseline, at 2, 4, and 6 weeks after initiation of therapy (p < 0.01). CONCLUSIONS: Recombinant human interferon-beta produced a definite biological effect in the serum of treated patients, but this outcome was not translated into any clinically observable or meaningful impact on the disease process.

Suppression of NF-kappa B survival signaling by nitrosylcobalamin sensitizes neoplasms to the anti-tumor effects of Apo2L/TRAIL.

We have previously demonstrated the anti-tumor activity of nitrosylcobalamin (NO-Cbl), an analog of vitamin B12 that delivers nitric oxide (NO) and increases the expression of tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) and its receptors in human tumors. The specific aim of this study was to examine whether NO-Cbl could sensitize drug-resistant melanomas to Apo2L/TRAIL. Antiproliferative effects of NO-Cbl and Apo2L/TRAIL were assessed in malignant melanomas and non-tumorigenic melanocyte and fibroblast cell lines. Athymic nude mice bearing human melanoma A375 xenografts were treated with NO-Cbl and Apo2L/TRAIL. Apoptosis was measured by TUNEL and confirmed by examining levels and activity of key mediators of apoptosis. The activation status of NF-kappa B was established by assaying DNA binding, luciferase reporter activity, the phosphorylation status of I kappa B alpha, and in vitro IKK activity. NO-Cbl sensitized Apo2L/TRAIL-resistant melanoma cell lines to growth inhibition by Apo2L/TRAIL but had minimal effect on normal cell lines. NO-Cbl and Apo2L/TRAIL exerted synergistic anti-tumor activity against A375 xenografts. Treatment with NO-Cbl followed by Apo2L/TRAIL induced apoptosis in Apo2L/TRAIL-resistant tumor cells, characterized by cleavage of caspase-3, caspase-8, and PARP. NO-Cbl inhibited IKK activation, characterized by decreased phosphorylation of I kappa B alpha and inhibition of NF-kappa B DNA binding activity. NO-Cbl suppressed Apo2L/TRAIL- and TNF-alpha-mediated activation of a transfected NF-kappa B-driven luciferase reporter. XIAP, an inhibitor of apoptosis, was inactivated by NO-Cbl. NO-Cbl treatment rendered Apo2L/TRAIL-resistant malignancies sensitive to the anti-tumor effects of Apo2L/TRAIL in vitro and in vivo. The use of NO-Cbl and Apo2L/TRAIL capitalizes on the tumor-specific properties of both agents and represents a promising anti-cancer combination.

IFN-alpha2b and thalidomide synergistically inhibit tumor-induced angiogenesis.

Angiogenesis is an absolute requirement for tumor growth and metastasis. The purpose of this study was to evaluate the antiangiogenic activity of interferon-alpha2b (IFN-alpha2b) and thalidomide, as single agents and in combination. The murine dermis model was used to assess tumor-induced angiogenesis in nude mice. Human ACHN (renal), NIH-OVCAR-3 (ovarian), LNCaP (prostate), and SK-Mel-1 (melanoma) tumor cells were inoculated intradermally into the flanks of nude mice. IFN-alpha2b and thalidomide, administered daily, were effective inhibitors of angiogenesis induced by all four tumor types. The combination of IFN-alpha2b and thalidomide caused a synergistic decrease in mean vessel count in tumors that were resistant to the antiproliferative effects of IFN-alpha2b and thalidomide in vitro. This enhanced suppression of angiogenesis translated into synergistic antitumor activity in a xenograft model. Pegylated IFN-alpha (PEG-IFN-alpha2b) (10(6) U) administered once in 10 days was as effective as daily IFN-alpha2b treatment (10(6) U x 10 days). IFN-alpha2b and thalidomide have potentiated antiangiogenic activity when used in combination. A single dose of PEG-IFN-alpha2b (10(6) U) was as effective at suppressing vessel growth as an equivalent dose of IFN-alpha2b given daily for 10 days.

Effects of interferon beta on transcobalamin II-receptor expression and antitumor activity of nitrosylcobalamin.

BACKGROUND: The ubiquitous plasma membrane transcobalamin II receptor (TC II-R) mediates uptake of cobalamin (Cbl; vitamin B12), an essential micronutrient. Tumors often require more Cbl than normal tissue, and increased Cbl uptake may result from increased TC II-R expression. To examine whether Cbl could therefore be used as a carrier molecule to target a chemotherapy drug, we tested an analogue of Cbl with nitric oxide as a ligand, nitrosylcobalamin (NO-Cbl). Because interferon beta (IFN-beta) has antitumor effects and increases expression of some membrane receptors, we examined whether it may enhance the effects of NO-Cbl. METHODS: Antiproliferative effects of NO-Cbl were assessed in 24 normal and cancer cell lines. Xenograft tumors of human ovarian cancer NIH-OVCAR-3 cells were established in athymic nude mice, and tumor growth was monitored after treatment with NO-Cbl and IFN-beta, both individually and concomitantly. TC II-R expression and apoptosis was monitored in vitro and in vivo. RNA protection assays and mitochondrial membrane potential assays were used to distinguish the extrinsic and intrinsic apoptotic pathways, respectively. RESULTS: Cancer cell lines were more sensitive to NO-Cbl (with ID(50)s [the dose that inhibits growth by 50%] as low as 2 microM) than normal cell lines (with ID(50)s of 85-135 microM). Single-agent NO-Cbl and IFN-beta treatment of NIH-OVCAR-3 xenografts induced tumor regression, whereas combination treatment induced tumor eradication. IFN-beta treatment increased TC II-R expression in vitro and uptake of [(57)Co]cobalamin in vivo. Compared with NIH-OVCAR-3 cells treated with NO-Cbl, cells treated with NO-Cbl and IFN-beta were more apoptotic and expressed higher mRNA levels of various apoptosis-associated genes. No changes in mitochondrial membrane potential were observed in cells treated with NO-Cbl. CONCLUSION: NO-Cbl inhibited tumor growth in vivo by activating the extrinsic apoptotic pathway. The increased expression of TC II-R induced by IFN-beta resulted in enhanced antitumor effects with NO-Cbl both in vitro and in vivo.

Inositol hexakisphosphate kinase 2 sensitizes ovarian carcinoma cells to multiple cancer therapeutics.

We recently identified inositol hexakisphosphate kinase 2 (IP6K2) as a positive regulator of apoptosis. Overexpression of IP6K2 enhances apoptosis induced by interferon-beta (IFN-beta) and cytotoxic agents in NIH-OVCAR-3 ovarian carcinoma cells. In this study, we contrast and compare IFN-beta and radiation-induced death, and show that IP6K2 expression sensitizes tumor cells. Unirradiated NIH-OVCAR-3 cells transfected with IP6K2 formed fewer colonies compared to unirradiated vector-expressing cells. IP6K2 overexpression caused increased radiosensitivity, evidenced by decreased colony forming units (CFU). Both IFN-beta and radiation induced caspase 8. IFN-beta, but not gamma-irradiation, induced TRAIL in NIH-OVCAR-3 cells. Gamma irradiation, but not IFN-beta, induced DR4 mRNA. Apoptotic effects of IFN-beta or gamma-irradiation were blocked by expression of a dominant negative mutant death receptor 5 (DR5Delta) or by Bcl-2. Caspase-8 mRNA induction was more pronounced in IP6K2-expressing cells compared to vector-expressing cells. These data suggest that overexpression of IP6K2 enhances sensitivity of some ovarian carcinomas to radiation and IFN-beta. IP6K2 may function to enhance the expression and/or function of caspase 8 and DR4 following cell injury. Both IFN-beta and gamma-irradiation induce apoptosis through the extrinsic, receptor-mediated pathway, IFN-beta through TRAIL, radiation through DR4, and both through caspase 8. The function of both death inducers is positively regulated by IP6K2.