Letrozole sensitizes breast cancer cells to ionizing radiation

Introduction  

Radiotherapy (RT) is considered a standard treatment option after surgery for breast cancer. Letrozole, an aromatase inhibitor, is being evaluated in the adjuvant setting. We determined the effects of the combination of RT and letrozole in the aromatase-expressing breast tumour cell line MCF-7CA, stably transfected with the CYP19 gene.     

The mdm2 proto-oncogene sensitizes human medullary thyroid carcinoma cells to ionizing radiation

We have analysed the radiation response of a human medullary thyroid carcinoma cell line (MTT), characterized by the absence of a functional p53 protein, and the consequences of MDM2 overexpression in this process. We show that the product of the mdm2 proto-oncogene is able to sensitize MTT cells to ionizing radiation. After radiation treatment, MTT cells display histograms consistent with a G2M arrest. MTT cells expressing MDM2 (MTT-mdm2) are unable to respond to DNA damage with G2M arrest, and display a high percentage of apoptosis. MTT-mdm2 cells show high levels of E2F-1 protein, suggesting that the induction of apoptosis observed upon MDM2 overexpression could be dependent on E2F-1. This observation is further supported with assays showing that E2F-1 binding to specific DNA sequences is enhanced in MTT-mdm2 cells. Likewise, transactivation of reporter constructs exclusively dependent on E2F-1 is also elevated after transfection with MDM2. This effect can be reverted by transient transfection with p19ARF. To link the expression of E2F-1 with the induction of apoptosis, we generated clonal cell lines overexpressing E2F-1. Transfection with E2F-1 results in a low number of outgrowing colonies with reduced proliferation rates, indicating that E2F-1 is deleterious for cell growth. This negative regulation correlates with an increase in the percentage of the cell population with DNA content below 2N, suggesting that E2F-1 promotes apoptosis. Finally, overexpression of E2F-1 sensitizes MTT cells to radiation exposure. We conclude that the effects observed by MDM2 overexpression could be mediated by E2F-1.     

Bortezomib sensitizes primary human astrocytoma cells of WHO grades I to IV for tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis.

PURPOSE: Malignant gliomas are the most aggressive human brain tumors without any curative treatment. The antitumor effect of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in gliomas has thus far only been thoroughly established in tumor cell lines. In the present study, we investigated the therapeutic potential of TRAIL in primary human glioma cells. EXPERIMENTAL DESIGN: We isolated primary tumor cells from 13 astrocytoma and oligoastrocytoma patients of all four WHO grades of malignancy and compared the levels of TRAIL-induced apoptosis induction, long-term tumor cell survival, caspase, and caspase target cleavage. RESULTS: We established a stable culture model for isolated primary human glioma cells. In contrast to cell lines, isolated primary tumor cells from all investigated glioma patients were highly TRAIL resistant. Regardless of the tumor heterogeneity, cotreatment with the proteasome inhibitor bortezomib efficiently sensitized all primary glioma samples for TRAIL-induced apoptosis and tremendously reduced their clonogenic survival. Due to the pleiotropic effect of bortezomib-enhanced TRAIL DISC formation upon TRAIL triggering, down-regulation of cFLIP(L) and activation of the intrinsic apoptosis pathway seem to cooperatively contribute to the antitumor effect of bortezomib/TRAIL cotreatment. CONCLUSION: TRAIL sensitivity of tumor cell lines is not a reliable predictor for the behavior of primary tumor cells. The widespread TRAIL resistance in primary glioma cells described here questions the therapeutic clinical benefit of TRAIL as a monotherapeutic agent. Overcoming TRAIL resistance by bortezomib cotreatment might, however, provide a powerful therapeutic option for glioma patients.     

Pharmacological inhibition of AKT sensitizes MCF-7 human breast cancer-initiating cells to radiation

Background

Caner-initiating cells (CICs or cancer stem cells) have been shown both experimentally and clinically to be resistant to radiation. The mechanism underlying radioresistance remains unclear.

Methods

In the present study, we screened 51 genes which are potentially important in mediating radioresistance of breast CICs.

Results

The expression of AKT1 and AKT2 at protein and mRNA levels was dramatically increased among the screened genes by 8 Gy radiation treatment in MCF-7 mammosphere cells (predominantly CD24^–/low/CD44⁺ CICs), but not in the bulk population of MCF-7 cells (predominantly CD24⁺/CD44⁺). Using apoptosis and clonogenic survival assays, we found pharmacological inhibition of AKT with selective inhibitors of AKT sensitized MCF-7 mammosphere cells, but not MCF-7 monolayer cells to radiation.

Conclusion

The present findings suggest that treatment with AKT inhibitors prior to ionizing radiation treatment may be a potential benefit to patients with breast cancer, in particular to eradiate breast CICs.     

Bortezomib sensitizes human head and neck carcinoma cells SQ20B to radiation

The proteasome inhibitor bortezomib was tested in a cell screen as a single agent with good efficacy in multiple hematologic and solid cancer cell lines. Phase II/III studies have supported the use of bortezomib in hematologic malignancies. In solid tumors, however, the results have been poor. There is data that bortezomib can induce PTEN expression resulting in down-regulation of PI3K-Akt signaling. We and others have shown that down-regulation of Akt results in radiation sensitization. We therefore evaluated the use of bortezomib in the head and neck cancer cell line SQ20B as a radiation sensitizer. SQ20B have a constitutively active mutation in EGFR resulting in a robust Akt response. We found that 10 nM of bortezomib decreased Akt signaling to almost undetectable. This same concentration decreased the surviving fraction after 2 Gy (SF2) from 0.77 to 0.45. Given that radiation is usually given at 2 Gy increments daily for 30 or more treatments, the exponential difference in log kill could be as high as 7 logs. The dose of bortezomib is also 2 logs less as a sensitizer than that required for single agent efficacy. Further studies should be done to explore this model in vivo.     

siRNA-mediated MDM2 inhibition sensitizes human lung cancer A549 cells to radiation

MDM2 (murine double minute 2) is well-documented to play a key role in radiation response and tumor radiosensitivity, thus offering an attractive clinic drug target to enhance tumor sensitivity to anti-cancer radiotherapy. In this study, we designed and tested two siRNA fragments against human MDM2 in non-small cell human lung cancer A549 cells. Transfection of mammalian expression vector pUR/U6 containing either MDM2 siRNA1 or siRNA2 fragment was shown to reduce MDM2 mRNA levels by 72% and 31%, respectively. Western blotting detected a similar inhibition of MDM2 protein levels in cells transfected with MDM2 siRNA1. A549 cells transfected with the expression vector for siRNA1 significantly decreased cell proliferation and rendered cells more sensitive to radiation. The basal apoptotic and necrotic cells, 1% and 2%, respectively, detected among A549 cells were increased to 2.6% and 14.4% after gamma-irradiation with 5 Gy. Transfection of MDM2 siRNA1 induced 30.1% apoptosis and 12.7% necrosis while combined treatment of siRNA1 and 5-Gy radiation increased apoptosis and necrosis to 45.9% and 15.2%, respectively. These data provide the first evidence that specific siRNA fragment (MDM2 siRNA1) targeting human MDM2 mRNA is able to enhance lung cancer radiosensitivity.     

Phenylbutyrate sensitizes human glioblastoma cells lacking wild-type p53 function to ionizing radiation

PURPOSE: Histone deacetylase (HDAC) inhibitors induce growth arrest, differentiation, and apoptosis in cancer cells. Phenylbutyrate (PB) is a HDAC inhibitor used clinically for treatment of urea cycle disorders. Because of its low cytotoxicity, cerebrospinal fluid penetration, and high oral bioavailability, we investigated PB as a potential radiation sensitizer in human glioblastoma cell lines. METHODS AND MATERIALS: Four glioblastoma cell lines were selected for this study. Phenylbutyrate was used at a concentration of 2 mM, which is achievable in humans. Western blots were used to assess levels of acetylated histone H3 in tumor cells after treatment with PB. Flow cytometry was used for cell cycle analysis. Clonogenic assays were performed to assess the effect of PB on radiation sensitivity. We used shRNA against p53 to study the role of p53 in radiosensitization. RESULTS: Treatment with PB alone resulted in hyperacetylation of histones, confirmed by Western blot analysis. The PB alone resulted in cytostatic effects in three cell lines. There was no evidence of G(1) arrest, increase in sub-G(1) fraction or p21 protein induction. Clonogenic assays showed radiosensitization in two lines harboring p53 mutations, with enhancement ratios (+/- SE) of 1.5 (+/- 0.2) and 1.3 (+/- 0.1), respectively. There was no radiopotentiating effect in two cell lines with wild-type p53, but knockdown of wild-type p53 resulted in radiosensitization by PB. CONCLUSIONS: Phenylbutyrate can produce p21-independent cytostasis, and enhances radiation sensitivity in p53 mutant human glioblastoma cells in vitro. This suggests the potential application of combined PB and radiotherapy in glioblastoma harboring mutant p53.     

Ouabain sensitizes tumor cells but not normal cells to radiation

Ouabain is a cardiac glycoside that blocks the sodium, potassium-pump (Na,K-Pump). When A549 human lung adenocarcinoma cells were treated with 10(-6) M ouabain for 4 hr starting 1 hr before irradiation, they were sensitized (enhancement ratio at 1% survival 1.46 +/- .07, N = 5). Ouabain affected radiation repair because it decreased the shoulder of the cell survival curve and it sensitized cells when added after radiation. CCL-210 normal human lung fibroblasts were not radiosensitized by ouabain concentrations from 10(-8) M to 10(-5) M. These results suggest that it may be possible to exploit differences in the Na,K-pumps of normal cells and tumor cells to improve the therapeutic index of radiation.     

Neutral metoclopramide sensitizes cytotoxicity induced by ionizing radiation in SCID mice xenografted with a human brain astrocytoma

A formulation of metoclopramide (MCA) conformationally altered by neutralization of pH (nMCA, Neu-Sensamide) has been shown to have the same efficacy of enhancing the cytotoxicity of a single dose of 1 Gy radiation as acidic formulations (e.g., Primperan, Sensamide) in a human lung adenocarcinoma (H2981) xenografted into SCID mice. In the present study, 2 × 1 Gy radiation was combined with 2 × 2 mg nMCA/kg body weight injected 2 hr before radiation treatment for evaluation of radiosensitization in SCID mice xenografted with a human brain astrocytoma (T24). Given in this treatment schedule, nMCA alone at 2 mg/kg showed no cytotoxic effect on tumor growth in vivo. When combined with 2 × 1 Gy of radiation, however, the cytotoxicity was significantly increased as measured by tumor growth delay over the radiation-only-treated group. Furthermore, nMCA was absorbed into brains of mice and rats as efficiently as acidic MCA (aMCA) when analyzed 45 min after i.m. injection by high-performance liquid chromatography. Int. J. Cancer 73:871–874, 1997. © 1997 Wiley-Liss, Inc.     

Berberine sensitizes human glioma cells, but not normal glial cells, to ionizing radiation in vitro

The identification of nontoxic agents that can enhance the efficacy of postoperative radiotherapy for patients with glioblastoma multiforme (GBM) remains a challenge in oncology. We evaluated human GBM cell lines for their responsiveness to berberine, an alkaloid compound used commonly in Asia as an antibiotic. In experiments measuring clonogenic survival, treatment with a nontoxic dose of berberine rendered GBM cells more sensitive than vehicle-treated control cells to x-rays. Such radiosensitization was not observed in parallel experiments with primary human glial cultures. These data suggest that berberine could be integrated with postoperative radiotherapy to selectively promote residual GBM tumor cell death     

Gimeracil sensitizes cells to radiation via inhibition of homologous recombination

Background and purpose

5-Chloro-2,4-dihydroxypyridine (Gimeracil) is a component of an oral fluoropyrimidine derivative S-1. Gimeracil is originally added to S-1 to yield prolonged 5-FU concentrations in tumor tissues by inhibiting dihydropyrimidine dehydrogenase, which degrades 5-FU. We found that Gimeracil by itself had the radiosensitizing effect.

Methods and materials

We used various cell lines deficient in non-homologous end-joining (NHEJ) or homologous recombination (HR) as well as DLD-1 and HeLa in clonogenic assay. γ-H2AX focus formation and SCneo assay was performed to examine the effects of Gimeracil on DNA double strand break (DSB) repair mechanisms.

Results

Results of γ-H2AX focus assay indicated that Gimeracil inhibited DNA DSB repair. It did not sensitize cells deficient in HR but sensitized those deficient in NHEJ. In SCneo assay, Gimeracil reduced the frequency of neo-positive clones. Additionally, it sensitized the cells in S-phase more than in G0/G1.

Conclusions

Gimeracil inhibits HR. Because HR plays key roles in the repair of DSBH caused by radiotherapy, Gimeracil may enhance the efficacy of radiotherapy through the suppression of HR-mediated DNA repair pathways.     

Pemetrexed sensitizes human lung cancer cells to cytotoxic immune cells

Pemetrexed (PEM) is a useful drug that can be combined with immune checkpoint blockade therapy for treatment of patients with advanced non–small‐cell lung cancer (NSCLC). However, its effects on anti–cancer immunity, especially the sensitivity of NSCLC cells to cytotoxic immune cells, have not been fully investigated. In this study, we examined the effects of PEM on the sensitivity of human NSCLC cells to two different types of cytotoxic immune cells. Pre‐treatment with PEM increased the sensitivity of two NSCLC cell lines, PC9 and A549, to activated T cells and natural killer (NK) cells, and decreased the expression of anti–apoptotic proteins, including XIAP and Mcl‐1. In addition, PEM treatment increased the cell surface expression of programmed death‐ligand 1 (PD‐L1) on PC9 cells. PEM‐induced upregulation of PD‐L1 on PC9 cells was at least partially ascribed to activation of ERK and the NFκB pathway. In contrast, PEM treatment increased the expression of UL16‐binding proteins (ULBP), ligands for the NKG2D NK receptor, on PC9 and A549 cells, as well as the induction of senescence. Although the addition of anti–programmed cell death 1 antibody showed no effect on the sensitivity of PEM‐treated PC9 and A549 cells to activated T cells, that of anti–NKG2D antibody decreased the enhanced sensitivity of PEM‐treated A549 cells to NK cells. These results indicate that PEM can effectively sensitize human NSCLC cells to cytotoxic immune cells while modulating the expression of immune‐regulatory molecules.     

Adenovirus-mediated antisense ATM gene transfer sensitizes prostate cancer cells to radiation

Treatment failure after radiation therapy of prostate cancer (PC) could be a significant problem. Our objective is to design genetic radiosensitizing strategies for the treatment of PC. Cells from individuals with the genetic disorder ataxia telangiectasia (AT) are hypersensitive to ionizing radiation. Therefore, we examined whether attenuation of the AT gene product, AT mutated (ATM), in PC cells could result in an increased intrinsic radiosensitivity. A p53-mutant PC cell line, PC-3 was infected with adenoviral vectors, expressing antisense ATM RNA to various domains of the ATM gene. Immunoblot analyses of cellular extracts from antisense ATM-transfected PC-3 cells showed attenuated expression of the ATM protein within 2 days of viral infection. Compared with cells infected with an adeno-beta-galactosidase vector, antisense ATM-transfected PC-3 cells showed aberrant control of S-phase cell-cycle checkpoints after exposure to ionizing radiation. Under these conditions, the intrinsic radiosensitivity of the PC-3 cells was enhanced. Consequently antisense ATM gene therapy could serve as a paradigm for strategies that target the cellular survival mechanisms of an irradiated tumor cell and may provide therapeutic benefit to patients undergoing radiation therapy for PC.     

Taxol, vincristine or nocodazole induces lethality in G1-checkpoint-defective human astrocytoma U373MG cells by triggering hyperploid progression.

In this report, we describe a novel lytic mechanism exploited by antimicrotubule drugs (AMDs) such as Taxol which are frequently used to treat multiple human cancers including breast and ovarian cancers. In cells lacking the G1-arresting capacity due to the defect in retinoblastoma or p53 gene function, AMDs trigger hyperploid progression and death. The hyperploid progression occurs via continued cell-cycle progression without cell division. Blocking hyperploid progression through hydroxyurea or ectopically expressed p27(Kip1), a G1-specific Cdk inhibitor, abrogates AMD cytotoxicity. Thus, AMDs induce lethality in G1-checkpoint-defective cells by triggering hyperploid progression. The phenomenon is reminiscent of that observed previously with bub-1 yeast mutant. The potential significance of this finding lies in that hyperploid progression-mediated death may be exploited to develop a therapy with tumor-specificity at the genetic level. As a large fraction of human cancers are mutated in p53 gene, it may have a wide therapeutic applicability.     

Combined inhibition of extracellular signal-regulated kinases and HSP90 sensitizes human colon carcinoma cells to ionizing radiation

Indomethacin, a common nonsteroidal anti-inflammatory drug, has been shown to enhance radiation-mediated cell-killing effect through the activation of p38 mitogen-activated protein kinase (MAPK). We found that indomethacin strongly reduced the basal level of extracellular signal-regulated kinases 1 and 2 (ERK1/2) in HT-29 human colon carcinoma cells. The inhibition of ERK1/2 by indomethacin was only observed in cells with high basal activities of ERK1/2 such as HT-29 cells, but not in cells with low basal activities, such as HeLa. Cell cycle analysis of HT-29 cells exposed with indomethacin showed a partial G1/S arrest and slow DNA synthesis. However, the treatment with NS398, a specific COX-1/2 inhibitor, failed to show any effect on cell cycle, indicating that the inhibition of COX-1/2 is not responsible for cell cycle arrest. Since U0126, a specific inhibitor for MEK1/2, also induced a partial G1/S arrest, the G1/S arrest induced by indomethacin is, at least in part, caused by the inhibition of ERK1/2. Cell proliferation of HT-29 was inhibited by the treatment of U0126 but not in HeLa cells, and the treatment of HT-29 cells with U0126 enhanced radiation sensitivity possibly due to the accumulation of cells in G1 phase. We found that 17-allylamino-17-demethoxygeldanamycin, a geldanamycin delivative, radiosensitized HT-29 cells at a relatively low dose of irradiation, and indomethacin and U0126 further enhanced this effect. Therefore, tumor cells with elevated ERK1/2 activity can be effectively sensitized to radiation treatment by a combinational inhibition of HSP90 and MAPK activity.     

Bortezomib sensitizes primary human esthesioneuroblastoma cells to TRAIL-induced apoptosis

TNF-related apoptosis-inducing ligand (TRAIL), a promising novel anti-cancer cytokine of the TNF superfamily, and Bortezomib, the first-in-class clinically used proteasome inhibitor, alone or in combination have been shown to efficiently kill numerous tumor cell lines. However, data concerning primary human tumor cells are very rare. Using primary esthesioneuroblastoma cells we analyzed the anti-tumor potential and the mechanism employed by Bortezomib in combination with TRAIL for the treatment of this rare but aggressive tumor. Expression of components of the TRAIL pathway was analyzed in tumor specimens and isolated primary tumor cells at the protein level. Cells were treated with TRAIL, Bortezomib, and a combination thereof, and apoptosis induction was quantified. Clonogenicity assays were performed to elucidate the long-term effect of this treatment. Despite expressing all components of the TRAIL pathway, freshly isolated primary esthesioneuroblastoma cells were completely resistant to TRAIL-induced apoptosis. They could, however, be very efficiently sensitized by subtoxic doses of Bortezomib. The influence of Bortezomib on the TRAIL pathway was analyzed and showed upregulation of TRAIL death receptor expression, enhancement of the TRAIL death-inducing signaling complex (DISC), and downregulation of anti-apoptotic proteins of the TRAIL pathway. Of clinical relevance, TRAIL-resistant primary tumor cells could be repeatedly sensitized by Bortezomib, providing the basis for repeated clinical application schedules. This is the first report on the highly synergistic induction of apoptosis in primary esthesioneuroblastoma cells by Bortezomib and TRAIL. This combination, therefore, represents a promising novel therapeutic option for esthesioneuroblastoma.