Cardiac magnetic resonance imaging for left atrial appendage closure planning.

BACKGROUND: Transesophageal echocardiography (TEE) and cardiac computed tomography angiography (CCTA) are currently utilized for left atrial appendage closure (LAAC) planning. During the recent global iodine contrast media shortage in 2022, cardiac magnetic resonance imaging (CMR) was utilized for the first time for LAAC planning. This study sought to assess the utility of CMR versus TEE for LAAC planning. METHODS: This single center retrospective study consisted of all patients who underwent preoperative CMR for LAAC with Watchman FLX or Amplatzer Amulet. Key measures were accuracy of LAA thrombus exclusion, ostial diameter, depth, lobe count, morphology, accuracy of predicted device size, and devices deployed per case. Bland-Altman Analysis was used to compare CMR versus TEE measurements of LAA ostial diameter and depth. RESULTS: 25 patients underwent preoperative CMR for LAAC planning. A total of 24 (96%) cases were successfully completed with 1.2 ± 0.5 devices deployed per case. Among the 18 patients who underwent intraoperative TEE, there was no significant difference between CMR versus TEE in LAA thrombus exclusion (CMR 83% vs. TEE 100% cases, p = .229), lobe count (CMR 1.7 ± 0.8 vs. TEE 1.4 ± 0.6, p = .177), morphology (p = .422), and accuracy of predicted device size (CMR 67% vs. TEE 72% cases, p = 1.000). When comparing the difference between CMR and TEE measurements, Bland-Altman analysis demonstrated no significant difference in LAA ostial diameter (CMR-TEE bias 0.7 mm, 95% CI [-1.1, 2.4], p = .420), but LAA depth was significantly larger with CMR versus TEE (CMR-TEE bias 7.4 mm, 95% CI [1.6, 13.2], p = .015). CONCLUSIONS: CMR is a promising alternative for LAAC planning in cases where TEE or CCTA are contraindicated or unavailable.

Discovery of Potent, Dual-Inhibitors of Diacylglycerol Kinases Alpha and Zeta Guided by Phenotypic Optimization.

We describe a phenotypic screening and optimization strategy to discover compounds that block intracellular checkpoint signaling in T-cells. We identified dual DGKα and ζ inhibitors notwithstanding the modest similarity between α and ζ relative to other DGK isoforms. Optimized compounds produced cytokine release and T-cell proliferation consistent with DGK inhibition and potentiated an immune response in human and mouse T-cells. Additionally, lead inhibitor BMS-502 demonstrated dose-dependent immune stimulation in the mouse OT-1 model, setting the stage for a drug discovery program.

DGKα/ζ inhibitors combine with PD-1 checkpoint therapy to promote T cell-mediated antitumor immunity.

Programmed cell death protein 1 (PD-1) immune checkpoint blockade therapy has revolutionized cancer treatment. Although PD-1 blockade is effective in a subset of patients with cancer, many fail to respond because of either primary or acquired resistance. Thus, next-generation strategies are needed to expand the depth and breadth of clinical responses. Toward this end, we designed a human primary T cell phenotypic high-throughput screening strategy to identify small molecules with distinct and complementary mechanisms of action to PD-1 checkpoint blockade. Through these efforts, we selected and optimized a chemical series that showed robust potentiation of T cell activation and combinatorial activity with αPD-1 blockade. Target identification was facilitated by chemical proteomic profiling with a lipid-based photoaffinity probe, which displayed enhanced binding to diacylglycerol kinase α (DGKα) in the presence of the active compound, a phenomenon that correlated with the translocation of DGKα to the plasma membrane. We further found that optimized leads within this chemical series were potent and selective inhibitors of both DGKα and DGKζ, lipid kinases that constitute an intracellular T cell checkpoint that blunts T cell signaling through diacylglycerol metabolism. We show that dual DGKα/ζ inhibition amplified suboptimal T cell receptor signaling mediated by low-affinity antigen presentation and low major histocompatibility complex class I expression on tumor cells, both hallmarks of resistance to PD-1 blockade. In addition, DGKα/ζ inhibitors combined with αPD-1 therapy to elicit robust tumor regression in syngeneic mouse tumor models. Together, these findings support targeting DGKα/ζ as a next-generation T cell immune checkpoint strategy.

DGKζ exerts greater control than DGKα over CD8+ T cell activity and tumor inhibition.

Two isoforms of diacylglycerol kinases (DGKs), DGKα and DGKζ, are primarily responsible for terminating DAG-mediated activation of Ras and PKCθ pathways in T cells. A direct comparison of tumor growth between mice lacking each isoform has not been undertaken. We evaluated the growth of three syngeneic tumor cell lines in mice lacking either DGKα or DGKζ in the presence or absence of treatment with anti-PD1 and determined that (i) mice deficient in DGKζ conferred enhanced control of tumor relative to mice deficient in DGKα and (ii) deficiency of DGKζ acted additively with anti-PD1 in tumor control. Consistent with this finding, functional and RNA-sequencing analyses revealed greater changes in stimulated DGKζ-deficient T cells compared with DGKα-deficient T cells, which were enhanced relative to wildtype T cells. DGKζ also imparted greater regulation than DGKα in human T cells. Together, these data support targeting the ζ isoform of DGKs to therapeutically enhance T cell anti-tumor activity.

Discovery of Pyridazinone and Pyrazolo[1,5-a]pyridine Inhibitors of C-Terminal Src Kinase.

C-terminal Src kinase (CSK) functions as a negative regulator of T cell activation through inhibitory phosphorylation of LCK, so inhibitors of CSK are of interest as potential immuno-oncology agents. Screening of an internal kinase inhibitor collection identified pyridazinone lead 1, and a series of modifications led to optimized compound 13. Compound 13 showed potent activity in biochemical and cellular assays in vitro and demonstrated the ability to increase T cell proliferation induced by T cell receptor signaling. Compound 13 gave extended exposure in mice upon oral dosing and produced a functional response (decrease in LCK phosphorylation) in mouse spleens at 6 h post dose.

Inhibition of poly(ADP-ribose) polymerase enhances cell death and improves tumor growth delay in irradiated lung cancer models.

PURPOSE: Poly(ADP-ribose) polymerase-1 (PARP-1) is the founding member of a family of enzymes that catalyze the addition of ADP-ribose units to proteins that mediate DNA repair pathways. Ionizing radiation induces DNA strand breaks, suggesting that PARP-1 inhibition may sensitize tumor cells to radiation. EXPERIMENTAL DESIGN: We investigated the combination of PARP-1 inhibition with radiation in lung cancer models. ABT-888, a novel potent PARP-1 inhibitor, was used to explore the effects of PARP-1 inhibition on irradiated tumors and tumor vasculature. RESULTS: ABT-888 reduced clonogenic survival in H460 lung cancer cells, and inhibited DNA repair as shown by enhanced expression of DNA strand break marker histone gamma-H2AX. Both apoptosis and autophagy contributed to the mechanism of increased cell death. Additionally, ABT-888 increased tumor growth delay at well-tolerated doses in murine models. For a 5-fold increase in tumor volume, tumor growth delay was 1 day for ABT-888 alone, 7 days for radiation alone, and 13.5 days for combination treatment. Immunohistochemical staining of tumor sections revealed an increase in terminal deoxyribonucleotide transferase-mediated nick-end labeling apoptotic staining, and a decrease in Ki-67 proliferative staining after combination treatment. Matrigel assay showed a decrease in in vitro endothelial tubule formation with ABT-888/radiation combination treatment, and von Willebrand factor staining of tumor sections revealed decreased vessel formation in vivo, suggesting that this strategy may also target tumor angiogenesis. CONCLUSIONS: We conclude that PARP-1 inhibition shows promise as an effective means of enhancing tumor sensitivity to radiation, and future clinical studies are needed to determine the potential of ABT-888 as a radiation enhancer.

Vascular endothelial growth factor tyrosine kinase inhibitor AZD2171 and fractionated radiotherapy in mouse models of lung cancer.

The vascular endothelial growth factor receptor (VEGFR) tyrosine kinases are being explored as targets for antiangiogenic cancer therapy. Radiotherapy also inhibits tumor growth and affects vasculature. We investigated the combination of the potent VEGFR tyrosine kinase inhibitor AZD2171 and ionizing radiation in cell culture and mouse models of lung cancer. We show that ionizing radiation induces expression of phosphorylated VEGFR-2 (Flk-1) in endothelial cells and that this phosphorylation is inhibited by AZD2171. Human umbilical vascular endothelial cells become more sensitive to radiation after treatment with AZD2171 as determined by clonogenic assay. Matrigel assay showed a decrease in in vitro endothelial tubule formation with AZD2171/radiation combination treatment. When similar combination was applied to the H460 lung cancer xenograft model in nude mice, loss of radiation-induced phosphorylated Flk-1 was observed in the combination treatment group, which also showed a large decrease in tumor vascular density by staining of the von Willebrand factor. H460 tumor growth delay was enhanced in the combination treatment group compared with the groups treated with AZD2171 or radiation alone. Additionally, after therapy, Ki67 index showed >4-fold reduction of tumor proliferation in the combination therapy group, which also showed increased intratumoral apoptotic index by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining. In conclusion, AZD2171 sensitizes lung tumor xenografts to radiation and inhibits angiogenesis both in vitro and in vivo. When used as a radiation enhancer, AZD2171 has the potential to improve tumor growth delay by inhibiting tumor proliferation and promoting apoptosis. Clinical trials are needed to determine the potential of this combination therapy in patients with locally advanced lung cancer.

Inhibition of mammalian target of rapamycin or apoptotic pathway induces autophagy and radiosensitizes PTEN null prostate cancer cells.

The phosphatidylinositol 3-kinase/Akt pathway plays a critical role in oncogenesis, and dysregulation of this pathway through loss of PTEN suppression is a particularly common phenomenon in aggressive prostate cancers. The mammalian target of rapamycin (mTOR) is a downstream signaling kinase in this pathway, exerting prosurvival influence on cells through the activation of factors involved in protein synthesis. The mTOR inhibitor rapamycin and its derivatives are cytotoxic to a number of cell lines. Recently, mTOR inhibition has also been shown to radiosensitize endothelial and breast cancer cells in vitro. Because radiation is an important modality in the treatment of prostate cancer, we tested the ability of the mTOR inhibitor RAD001 (everolimus) to enhance the cytotoxic effects of radiation on two prostate cancer cell lines, PC-3 and DU145. We found that both cell lines became more vulnerable to irradiation after treatment with RAD001, with the PTEN-deficient PC-3 cell line showing the greater sensitivity. This increased susceptibility to radiation is associated with induction of autophagy. Furthermore, we show that blocking apoptosis with caspase inhibition and Bax/Bak small interfering RNA in these cell lines enhances radiation-induced mortality and induces autophagy. Together, these data highlight the emerging importance of mTOR as a molecular target for therapeutic intervention, and lend support to the idea that nonapoptotic modes of cell death may play a crucial role in improving tumor cell kill.

Inhibition of survivin and aurora B kinase sensitizes mesothelioma cells by enhancing mitotic arrests.

PURPOSE: Survivin, a member of the inhibitor of apoptosis gene family, has also been shown to regulate mitosis. It binds Aurora B kinase and the inner centromere protein to form the chromosome passenger complex. Both Aurora B and survivin are overexpressed in many tumors. In this study, we examined whether irradiation affected survivin and Aurora B expression in mesothelioma cells, and how inhibition of these molecules affected radiosensitivity. METHODS AND MATERIALS: ZM447439 and survivin antisense oligonucleotides were used to inhibit survivin and Aurora B kinase respectively. Western blot was performed to determine the expression of survivin, Aurora B, phosphorylated-histone H3 (Ser 10), and caspase cleavage. Multinucleated cells were counted using flow cytometry, and cell survival after treatment was determined using clonogenic assay. RESULTS: At 3-Gy irradiation an increase was observed in levels of survivin and Aurora B as well as the kinase activity of Aurora B, with an increase in G2/M phase. The radiation-induced upregulation of these molecules was effectively attenuated by antisense oligonucleotides against survivin and a small-molecule inhibitor of Aurora B, ZM447439. Dual inhibition of survivin and Aurora B synergistically radiosensitized mesothelioma cells with a dose enhancement ratio of 2.55. This treatment resulted in increased formation of multinucleated cells after irradiation but did not increase levels of cleaved caspase 3. CONCLUSION: Inhibition of survivin and Aurora B induces mitotic cell arrest in mesothelioma cells after irradiation. These two proteins may be potential therapeutic targets for the enhancement of radiotherapy in malignant pleural mesothelioma.

Targeting the Akt/mammalian target of rapamycin pathway for radiosensitization of breast cancer.

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is known to be activated by radiation. The mammalian target of rapamycin (mTOR) is downstream of Akt, and we investigated the effects of radiation on Akt/mTOR signaling in breast cancer cell models. RAD001 (everolimus), a potent derivative of the mTOR inhibitor rapamycin, was used to study the effects of mTOR inhibition, as the role of mTOR inhibition in enhancing radiation remains unexplored. RAD001 decreased clonogenic cell survival in both breast cancer cell lines MDA-MB-231 and MCF-7, although the effect is greater in MDA-MB-231 cells. Irradiation induced Akt and mTOR signaling, and this signaling is attenuated by RAD001. The radiation-induced signaling activation is mediated by PI3K because inhibition of PI3K with LY294002 inhibited the increase in downstream mTOR signaling. Additionally, caspase-dependent apoptosis is an important mechanism of cell death when RAD001 is combined with 3 Gy radiation, as shown by induction of caspase-3 cleavage. An increase in G(2)-M cell cycle arrest was seen in the combination treatment group when compared with controls, suggesting that cell cycle arrest may have been a contributing factor in the increased radiosensitization seen in this study. We conclude that RAD001 attenuates radiation-induced prosurvival Akt/mTOR signaling and enhances the cytotoxic effects of radiation in breast cancer cell models, showing promise as a method of radiosensitization of breast cancer.

Radiosensitization of lung cancer by nutlin, an inhibitor of murine double minute 2.

p53 plays a critical role in cell cycle arrest and induction of apoptosis. Certain malignancies carry wild-type p53, which is frequently down-regulated by murine double minute 2 (MDM2) overexpression. Availability of a small-molecule inhibitor against MDM2, nutlin, has made it feasible to evaluate the anti-MDM2-based therapeutic strategies. The rationale for the current study is that functional p53 has been linked with improved responses to radiation treatment. Hence, this study evaluates the use of nutlin, a small-molecule inhibitor that blocks the interaction of p53 and MDM2, in sensitizing cancer cells to radiation. Expression of MDM2, p53, and p21 in both p53 wild-type and p53-defective lung cancer cell lines was examined. Clonogenic and 7-amino-actinomycin D studies were used to determine possible mechanisms of cell death. The combined effect of MDM2 inhibition and radiation on cell cycle was also studied. We found that radiosensitization by nutlin occurs in lung cancer cells with wild-type p53. There were increased apoptosis and cell cycle arrest following administration of nutlin and radiation. Furthermore, the combination of nutlin and radiation decreased the ability of endothelial cells to form vasculature, as shown by Matrigel assays. Our data suggest that nutlin is an effective radiosensitizer of p53 wild-type cells. The radiosensitizing effect seems to be at least partially due to induction of apoptosis and cell cycle arrest. In addition, nutlin may be an effective radiosensitizer of tumor vasculature.

Inhibition of signal transducer and activator of transcription 3 activity results in down-regulation of Survivin following irradiation.

Signal transducer and activator of transcription 3 (Stat3) and Survivin are constitutively up-regulated in various human tumor cells. We previously found Survivin to be significantly reduced in response to radiation in human umbilical vein endothelial cells (HUVEC) but not in tumor cell lines. In this study, we examined the effect of Stat3 on Survivin expression in irradiated HUVECs and breast cancer cells. We also studied how inhibition of Stat3 and Survivin activity affects cell survival and angiogenesis following irradiation. We determined that Survivin was significantly increased by overexpression of an active Stat3 (Stat3-C). Following irradiation, the level of phospho-Stat3 Tyr(705), but not phospho-Stat3 Ser(727), was reduced in HUVECs, whereas it remained unchanged in irradiated breast cancer cells. Correspondingly, Stat3 DNA-binding activity following irradiation was specifically down-regulated in HUVECs but not in breast cancer cells. Mutation of Tyr(705) abolished radiation-induced down-regulation of Survivin. Clonogenic and endothelial cell morphogenesis assays suggested that DN-Stat3 and DN-Survivin together resulted in the greatest radiosensitization of MDA-MB-231, decreasing angiogenesis and cell survival. In summary, Stat3 modulates Survivin, and both are potential therapeutic targets for radiation sensitization in breast cancer.

Enhanced radiation damage of tumor vasculature by mTOR inhibitors.

It is known that radiation activates the phosphoinositol-3 kinase (PI3K)/Akt pathway and that inhibition of PI3K or Akt sensitizes tumor vasculature to radiotherapy. Mammalian target of rapamycin (mTOR) is a downstream target of Akt, and we hypothesized that irradiation activates mTOR signaling in both glioma and endothelial cells (ECs) and that radiosensitization results from inhibiting mTOR signaling. mTOR inhibitors, rapamycin and RAD001 (everolimus) were found to radiosensitize vascular ECs, but failed to sensitize glioma cells as determined by clonogenic assay. Therefore, we investigated the anti-angiogenic effects of mTOR inhibitors. Increased phospho-mTOR protein was detected in irradiated human umbilical vein endothelial cells (HUVEC), but not in GL261 glioma cells. Phospho-S6, a biomarker for mTOR signaling, was also found to be induced following irradiation in HUVEC and this effect was inhibited by PI3K or mTOR inhibitors. Significant increase in cleaved caspase 3 was detected when Rad001 was combined with radiation. Endothelial tube formation was significantly diminished following treatment with rapamycin and 3 Gy of radiation. Histological sections of GL261 tumors from mice showed a greatly reduced vascular density when treated with RAD001 and radiation. Power Weighted Doppler of glioma xenografts in mice showed a significant reduction in vasculature and blood flow compared with mice treated with 3 Gy or RAD001 alone. We conclude that irradiation activates mTOR signaling in vascular endothelium and that rapamycin and RAD001 increased apoptosis of ECs in response to radiation. To the authors' best knowledge this is the first study which demonstrates that mTOR inhibitors may be a way to target the vasculature by radiosensitizing the vascular endothelium resulting in better tumor control as seen in experiments demonstrating increased tumor growth delay in mice treated with rapamycin with radiation compared with mice treat with either treatment alone. We conclude that mTOR inhibitors have increased efficacy as antiangiogenics when combined with radiation.

Integrin alpha v beta 3 antagonist Cilengitide enhances efficacy of radiotherapy in endothelial cell and non-small-cell lung cancer models.

PURPOSE: Integrins alpha v beta 3 and alpha v beta 5 are important in tumor growth and angiogenesis and have been recently explored as targets for cancer therapy. Radiotherapy also inhibits tumor growth and affects vasculature. We explored the combination of integrin antagonist Cilengitide (EMD 121974) and ionizing radiation. METHODS AND MATERIALS: Levels of alpha v beta 3 were determined for human umbilical vein endothelial cells (HUVEC), as well as H157 and H460 human non-small-cell lung cancer cells, using FACS analysis and immunofluorescence imaging. Clonogenic assays, Western immunoblots probed for cleaved caspase 3, and Annexin-V probing were used to evaluate cell survival and apoptosis. A cell detachment assay and matrigel assay were used to further examine the effects of treatment. RESULTS: Human umbilical vein endothelial cells had the highest alpha v beta 3 level, followed by H157, and H460. Interestingly, we found that 5 Gy irradiation induced expression of alpha v beta 3 in all cell lines. Clonogenic assays showed a radiosensitizing effect with Cilengitide, and calculation of the dose enhancement ratio showed that the effect was highest in HUVECs (1.38), followed by H157 (1.19), and H460 (1.10), corresponding to the levels of target expression. There was an increase in apoptotic cells after combination treatment with Cilengitide and radiation, and there was an increase in detached cells after treatment with Cilengitide. Additionally, there was decreased endothelial tubule formation after combination treatment. CONCLUSIONS: We conclude that radiation induces expression of alpha v beta 3 integrin in endothelial and non-small-cell lung cancer models, and that integrin antagonist Cilengitide is a radiosensitizer in proportion to the levels of target integrin expression.

E-cadherin promoter polymorphisms are not associated with the aggressiveness of prostate cancer in Caucasian patients.

BACKGROUND: -160C-->A and -347G-->GA polymorphisms in the promoter region decrease E-cadherin gene transcription. Decreased E-cadherin expression predicts poor outcome among patients with cancer. We sought to investigate whether -160C-->A and/or -347G-->GA polymorphisms were associated with the aggressiveness of prostate cancer. METHODS: TaqMan single nucleotide polymorphism genotyping assay (Applied Biosystems, Foster City, CA) was used to detect -160C-->A and -347G-->GA polymorphisms in deoxyribonucleic acid from the paraffin-embedded prostate tissues of 98 Caucasian patients. RESULTS: The genotype frequencies were -160C/C: 48% (47 of 98); -160C/A: 44% (43 of 98); -160A/A: 8% (8 of 98); -347G/G: 68% (67 of 98); -347G/GA: 28% (27 of 98); and -347GA/GA: 4% (4 of 98). Using the chi-square test, we found that the polymorphisms -160C-->A and -347G-->GA were not related to other clinical and pathologic parameters (i.e., age, prostate-specific antigen level, Gleason grade, and clinical stage) (P > 0.05). In combination analysis, there was no significant relationship between patients with both -160C/C and -347G/G, and these same parameters (P > 0.05). Using the log-rank test, we found no significant difference in relapse-free survival and overall survival between patients with -160C/C and those with -160A/C or -160A/A (P = 0.0764 and 0.2746, respectively), and also no significant difference between patients with -347G/G and those with -347GA/G or -347GA/GA (P = 0.9416 and 0.7367, respectively). There was also no significant difference in relapse-free survival and overall survival between patients with homozygosities of -160C/-347G and patients with other genotypes (P = 0.1418 and 0.2434, respectively). CONCLUSION: We conclude that E-cadherin -160C-->A and/or -347G-->GA polymorphisms are not associated with the aggressiveness of prostate cancer in Caucasian patients.

The antiangiogenic agent SU5416 down-regulates phorbol ester-mediated induction of cyclooxygenase 2 expression by inhibiting nicotinamide adenine dinucleotide phosphate oxidase activity.

Increased expression of cyclooxygenase (COX) 2 and the production of PGs appear to provide a survival advantage to transformed cells through the inhibition of apoptosis, increased attachment to extracellular matrix, increased invasiveness and the stimulation of angiogenesis. The purpose of this study was to determine whether an angiogenic antagonist, SU5416, could inhibit endogenous and phorbol 12-myristate 13-acetate (PMA)-mediated induction of COX-2 expression. SU5416 (5 micro M) inhibited endogenous as well as PMA-mediated induction of COX-2 expression when analyzed by immunoblot and Northern blot analysis. However, COX-1 expression remained unchanged under similar conditions. PMA is a potent inducer of reactive oxygen species that can play an important role during the induction of COX-2 expression. Our results demonstrated that PMA-mediated induction of COX-2 expression was found to be dependent on NADPH oxidase activity. An inhibitor of NADPH oxidase (diphenyleneiodonium chloride) blocked the PMA-mediated induction of COX-2 expression. The oxidase complex exhibited a temporal pattern of activation after exposure to PMA in which maximum activation was observed at 30 min after the addition of PMA. Activation of NADPH oxidase was also inhibited by SU5416, whereas an inhibitor of epidermal growth factor receptor signaling was unable to prevent the PMA-mediated induction of NADPH oxidase activity. When we blocked the PMA-mediated production of reactive oxygen species by blocking NADPH oxidase with SU5416, COX-2 expression and PGE(2) synthesis were also inhibited. Our results suggest that inhibition of NADPH oxidase activity, blocking of COX-2 expression, and PGE(2) synthesis may represent novel targets for SU5416.

Survivin as a therapeutic target for radiation sensitization in lung cancer.

Expression of survivin is elevated in most malignancies, especially in radiation-resistant cell lines. In this study, we investigated how radiation affects survivin expression in primary endothelial cells as well as in malignant cell lines. We found that 3 Gy significantly reduced survivin protein level in human umbilical vein endothelial cells (HUVECs) but not in tumor cell lines. Flow cytometry studies suggest that the down-regulation of survivin is independent of cell cycle. In addition, survivin mRNA level was also down-regulatable by irradiation. However, it was abrogated by actinomycin D-mediated inhibition of gene transcription. Luciferase reporter gene assays suggest that irradiation suppressed the survivin promoter. p53 overexpression reduced survivin expression, but overexpression of a p53 mutant failed to abolish the radiation-induced down-regulation in HUVECs. Alteration of p53 status in Val138 lung cancer cell line also failed to restore the radiation-inducible down-regulation. Overexpression of survivin in 293 cells prevented apoptosis induced by irradiation and increased cell viability after irradiation. The inhibition of survivin using antisense oligonucleotides caused a significant decrease in cell viability of irradiated H460 lung cancer cells. These data suggest that radiation transcriptionally down-regulates survivin in HUVECs. This regulatory mechanism is defective in malignancies and is not mediated by p53. Survivin overexpression may lead to resistance to radiotherapy by inhibiting apoptosis and enhancing cell viability. The inhibition of survivin results in sensitization of H460 lung cancer cells to radiation. These studies suggest that survivin may be a target for cancer therapy.

Murine double minute 2 as a therapeutic target for radiation sensitization of lung cancer.

Murine double minute 2 (MDM2) inhibits p53-mediated functions, which are essential for therapies using DNA-damaging agents. The purpose of this study was to determine whether MDM2 inhibition enhances the radiosensitivity of a lung cancer model. The effects of MDM2 inhibition on tumor vasculature were also studied. Transient transfection of H460 lung cancer cells and human umbilical vascular endothelial cells (HUVEC) with antisense oligonucleotides (ASODN) against MDM2 resulted in a reduced level of MDM2 and increased levels of p21 and p53. Clonogenic assays showed that inhibition of MDM2 greatly decreased cell survival following irradiation. Quantification of apoptotic cells by 7-aminoactinomycin D staining and of senescent cells by X-gal staining showed that both processes were significantly increased in H460 cells treated with MDM2-specific ASODN and radiation. H460 xenografts that were treated with MDM2 ASODN plus radiotherapy also showed significant growth delay (P < 0.001) and increased apoptosis by terminal deoxynucleotidyl transferase-mediated nick end labeling staining. HUVECs transfected with MDM2-specific ASODN showed impaired viability and migration with decreased tube formation. Doppler studies showed that tumor blood flow was compromised when H460 xenografts were treated with MDM2-specific ASODN and radiation. A combination of radiotherapy and inhibition of MDM2 through the antisense approach results in improved tumor control in the H460 lung cancer model. This implies that a similar strategy should be investigated among patients with locally advanced lung cancer, receiving thoracic radiotherapy.

XIAP and survivin as therapeutic targets for radiation sensitization in preclinical models of lung cancer.

Survivin and XIAP are members of inhibitors of apoptosis (IAPs) family. They are upregulated in various malignancies. Inactivation of these molecules has resulted in chemosensitization. The purpose of this study was to determine whether inhibition of survivin, XIAP, or both enhances radiotherapy in a lung cancer model. Transient transfection of H460 cells with antisense oligonucleotides (ASOs) against either molecule has specifically reduced their expression, by Western analysis. Results from 3-(4,5-methylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide and clonogenic assays suggest that inhibition of survivin or XIAP greatly decreased cell survival following irradiation. A significantly increased number of apoptotic cells were detected when H460 cells were treated with either antisurvivin, anti-XIAP or both ASOs (P=0.03, 0.0003 and 0.01, respectively) plus irradiation. H460 xenografts that were treated with ASOs plus radiotherapy demonstrated growth delay beyond 15 days. Growth delay in the groups of combined treatment was greater than that in other groups. However, treatment with ASOs alone did not affect tumor growth delay in mice, but decreased the survival of H460 cells in culture. Antisense treatment did not cause any mortality or weight loss during the 32 days of study. These data suggest that inhibition of survivin or XIAP radiosensitizes H460 lung cancer cells by upregulating apoptosis and downregulating cell survival. Combination of radiotherapy and inhibition of survivin and XIAP through the antisense approach results in improved tumor control by radiotherapy in a mouse model of lung cancer.

Clusterin as a therapeutic target for radiation sensitization in a lung cancer model.

PURPOSE: Clusterin plays important roles in cell survival and death. Inactivation of clusterin enhances the therapeutic efficacy of chemotherapy in lung cancer models. The purpose of this study was to determine whether inhibition of clusterin by an antisense-based investigative drug enhances radiation sensitization in a lung cancer model. METHODS AND MATERIALS: Cells were transfected with an antisense oligonucleotide (ASO) against clusterin (OGX-011). Apoptosis was determined by 7-aminoactinomycin D staining. Cell survival was examined by 3-(4, 5-methylthiazol-2-yl)-2, 5-diphenyl-tetrazolium bromide (MTT) and clonogenic assay. Xenograft model was used to demonstrate tumor growth and tumor blood flow. RESULTS: OGX-011 specifically attenuated the expression of secreted clusterin (prosurvival), with no apparent effect on the expression of nuclear clusterin (proapoptotic). Apoptosis was significantly increased when H460 lung cancer cells were treated with OGX-011 plus radiation. Inhibition of clusterin followed by radiation greatly decreased cell survival. H460 xenografts that were treated with OGX-011 plus radiotherapy demonstrated growth delay beyond 17 days. Doppler studies showed that tumor blood flow was compromised when mice bearing H460 xenografts were treated with OGX-011 and radiation. CONCLUSION: A combination of radiotherapy and OGX-011 improved control of tumor growth and vascular regression in the H460 lung cancer model.