Phyllis R. Wachsberger

Epigenetic modulation of endogenous tumor suppressor expression in lung cancer xenografts suppresses tumorigenicity

Epigenetic changes involved in cancer development, unlike genetic changes, are reversible. DNA methyltransferase and histone deacetylase inhibitors show antiproliferative effects in vitro, through tumor suppressor reactivation and induction of apoptosis. Such inhibitors have shown activity in the treatment of hematologic disorders but there is little data concerning their effectiveness in treatment of solid tumors. FHIT, WWOX and other tumor suppressor genes are frequently epigenetically inactivated in lung cancers. Lung cancer cell clones carrying conditional FHIT or WWOX transgenes showed significant suppression of xenograft tumor growth after induction of expression of the FHIT or WWOX transgene, suggesting that treatments to restore endogenous Fhit and Wwox expression in lung cancers would result in decreased tumorigenicity. H1299 lung cancer cells, lacking Fhit, Wwox, p16INK4a and Rassf1a expression due to epigenetic modifications, were used to assess efficacy of epigenetically targeted protocols in suppressing growth of lung tumors, by injection of 5‐aza‐2‐deoxycytidine (AZA) and trichostatin A (TSA) in nude mice with established H1299 tumors. High doses of intraperitoneal AZA/TSA suppressed growth of small tumors but did not affect large tumors (200 mm3); lower AZA doses, administered intraperitoneally or intratumorally, suppressed growth of small tumors without apparent toxicity. Responding tumors showed restoration of Fhit, Wwox, p16INKa, Rassf1a expression, low mitotic activity, high apoptotic fraction and activation of caspase 3. These preclinical studies show the therapeutic potential of restoration of tumor suppressor expression through epigenetic modulation and the promise of re‐expressed tumor suppressors as markers and effectors of the responses.

Rejoining of DNA double-strand breaks in Ku80-deficient mouse fibroblasts

The role of Ku80 in the repair of DNA double-strand breaks (DSBs) was examined in fibroblasts derived from a Ku80 knockout mouse model described by Nussenzweig et al. (Nature 382, 551-555, 1996). Primary fibroblasts from Ku80+/+ and Ku80-/- mice were immortalized by transfection with plasmids containing either the human MYC proto-oncogene or the Simian virus 40 (SV40) T antigen and were used to measure induction and rejoining of DSBs after exposure to ionizing radiation. The number of DSBs in the cells was quantified by either asymmetric field-inversion gel electrophoresis (AFIGE) or clamped homogeneous electrical-field gel electrophoresis (CHEF). The latter method was introduced for a more reliable quantification of repair even when DNA degradation occurs in a fraction of the irradiated cell population during the postirradiation incubation time. The results confirm that Ku80-deficient mouse fibroblasts are sensitive to ionizing radiation and demonstrate that the increased radiosensitivity may result from a deficiency in DSB rejoining. The results further indicate that unless techniques are employed that allow for distinction between DNA degradation and DNA repair, erroneous conclusions may be drawn regarding the potential of cells to repair DSBs.

Mammalian cells adapted to growth at pH 67 have elevated HSP27 levels and are resistant to cisplatin

HSP27 levels are elevated in two Chinese hamster cell lines and in a human melanoma cell line adapted to growth at pH 6.7. The level of HSP72 is elevated in the melanoma cell line but not in the hamster cell lines adapted to growth at pH 6.7. HSC73 levels are not elevated in any of the adapted cell lines. Low pH adapted cells from all cell lines are resistant to cisplatin. It is proposed that elevated HSP27 levels in low pH-adapted cells may play a role in resistance to hyperthermia and resistance to cisplatin.

Effects of hyperthermia on the cytoskeleton and cell survival in G1 and S phase Chinese hamster ovary cells

The effects of acute hyperthermia on three cytoskeletal systems (microtubules (MT), microfilaments (MF), and vimentin intermediate filaments (VIMF] were observed in G1 and S phase Chinese hamster ovary (CHO) 10B cells using immunofluorescence microscopy and compared to cell survival. A scoring system was devised to express the degree of cytoskeletal collapse induced by heat and the degree of recovery 20 h following heat treatments. A positive correlation was found between recovery from heat-induced cytoskeletal disruption and surviving fractions (SF) of cells heated in G1 but not with SF of cells heated in S phase. Recovery of MT arrays, for example, averaged 96.5%, 71.6% and 20.3% for heat doses of 5 min, 15 min and 25 min, 45 degrees C, respectively. The corresponding SF (means) were 0.92, 0.68 and 0.23, respectively. However, in S phase cells, where restoration of MT and VIMF patterns averaged 94.2%, 83.8% and 33.0% for heat doses of 5 min, 15 min and 25 min, 45 degrees C respectively, SF were 0.70, 0.09 and 0.02. These results suggest that heat-induced cytoskeletal alterations may play a role in the death of cells heated in G1, and that these alterations do not significantly influence death of cells heated in S phase. This work is in agreement with previous studies showing that cells heated in G1 or S phase appear to die by different mechanisms, and further emphasizes the need to use synchronous populations of cells in order to understand the mechanisms whereby cells die following hyperthermia.

Tumor Oxygenation and Acidification are Increased in Melanoma Xenografts after Exposure to Hyperglycemia and meta-Iodo-benzylguanidine

Abstract Burd, R., Lavorgna, S. N., Daskalakis, C., Wachsberger, P. R., Wahl, M. L., Biaglow, J. E., Stevens, C. W. and Leeper, D. B. Tumor Oxygenation and Acidification are Increased in Melanoma Xenografts after Exposure to Hyperglycemia and meta-Iodo-benzylguanidine. Radiat. Res. 159, 328–335 (2003). Tumor oxygen tension and extracellular pH (pHe) are physiological parameters that can be manipulated to improve current cancer therapies. Many human tumors consist of cells that are chronically exposed to low pHe. Exposure of tumor cells in culture to glucose decreases oxygen consumption (oxygen sparing or Crabtree effect), and while this effect is absent in low pH-adapted tumor cells, it can be restored by combining the respiratory inhibitor meta-iodo-benzylguanidine (MIBG) with glucose (Burd et al., Cancer Res. 61, 5630–5635, 2001). The effects of hyperglycemia and MIBG on tumor oxygen tension and on pHe were investigated in human melanoma xenografts in SCID mice. An oral gavage of 1 M glucose (2 g/kg) increased the average blood glucose concentration from <140 mg/dl to ∼400 mg/dl. Although tumor pHe decreased from pH 6.7 to pH 6.5 (P < 0.01) after about 60 min, no change in tumor oxygen tension was observed. However, when oral glucose and MIBG (15 mg/kg) were administered together, oxygen tension increased from 2.8 mmHg to ∼17 mmHg, and tumor pHe decreased from pH 6.7 to pH 6.3 (P < 0.01) after about 115 min. In conclusion, administration of glucose together with MIBG increases tumor oxygen tension and also increases the magnitude and duration of acidification. Hyperglycemia plus MIBG has the potential to improve response to radiation therapy as well as to hyperthermia and some chemotherapies.

Betulinic acid sensitization of low pH adapted human melanoma cells to hyperthermia.

Betulinic acid is a known inducer of apoptosis in human melanoma that is most effective under conditions of low pH. It was hypothesized that betulinic acid, in combination with acute acidification and/or hyperthermia, would induce higher levels of apoptosis and cytotoxicity in low pH-adapted human melanoma cells than in cells grown at pH 7.3. DB-1 human melanoma cells, adapted to a tumour-like growth pH of 6.7, were exposed to hyperthermia (2h at 42°C) and/or betulinic acid (4-10 µg/ml) and compared with cells grown at a physiological pH of 7.3 or after acute acidification from pH 7.3-6.3 or pH 6.7-6.3. Betulinic acid induced higher levels of apoptosis and cytotoxicity in low pH-adapted cells than in cells grown at pH 7.3, as measured by the terminal deoxynucleotidyl transferase (TdT) DNA fragmentation assay (TUNEL), the MTS cell viability assay, and single cell survival. Acute acidification of low pH adapted cells rendered them more susceptible to betulinic acid-induced apoptosis and cytotoxicity. In the presence of hyperthermia at 42°C for 2h, cells grown at pH 7.3 were not sensitized to heat killing by betulinic acid, whereas cells grown at pH 7.3 and acutely acidified to pH 6.3, cells adapted to growth at pH 6.7 and cells adapted to growth at pH 6.7 and acutely acidified to pH 6.3 were all similarly sensitized to heat killing by betulinic acid, with survival values of 5, 9 and 2%, respectively. It is concluded that betulinic acid may be useful in potentiating the therapeutic efficacy of hyperthermia as a cytotoxic agent in acidotic areas of tumours with minimal effect in normal tissues growing at pH 7.3.

Quercetin Selectively Inhibits Bioreduction and Enhances Apoptosis in Melanoma Cells That Overexpress Tyrosinase

Abstract Tyrosinase is expressed in melanoma cells and catalyzes the formation of 3,3′,4′,5,7-pentahydroxyflavone (quercetin) into reactive quinone species and subsequent glutathionyl adducts. Therefore, we examined the effect of quercetin metabolism on the glutathione (GSH) bioreduction pathway and cell viability in DB-1 melanoma cells that express varying levels of tyrosinase (Tyr+). In a cell-free system, GSH was significantly decreased by quercetin, which coincided with the formation of glutathionyl adducts. In Tyr+ clones, quercetin decreased bioreduction capacity and increased reactive oxygen species (ROS) to a greater degree compared to control cells. The antioxidant/electrophile response element-induced enzymes, glutathione-S-transferase (GST), and nicotinamide adenine dinucleotide phosphate:quinone oxidoreductase 1 were expressed at high levels in Tyr+ cells and contributed to pro-oxidant quercetin metabolism. The basal level of ROS and apoptosis was higher in Tyr+ cells and were selectively increased after exposure to quercetin. The increase in apoptosis following quercetin exposure was p53/Bax mediated and correlated with a decrease in GST-driven bioreduction capacity and an increase in ROS. In conclusion, quercetin can selectively sensitize Tyr+ expressing melanoma cells to apoptosis and may serve as an adjuvant to chemotherapy by enhancing cell death and interfering with GST-mediated drug resistance.

Hsp90 inhibition enhances PI-3 kinase inhibition and radiosensitivity in glioblastoma.

AbstractPurpose Combined targeting with a PI3-kinase inhibitor, BKM120, and an Hsp90 inhibitor, HSP990, was investigated as a multi-targeted approach to potentiate cell death in glioblastoma (GBM). Additionally, the effect of dual drug treatment combined with cytotoxic stress (radiation therapy) was examined.MethodsFour human GBM cell lines containing wild-type or mutated PTEN and/or p53 were studied. The effects of drug treatments on cell viability, apoptosis induction, pAKt activity, cell cycle arrest, clonogenicity, and tumor growth delay were studied.ResultsCombined concurrent treatment with both drugs produced more cell killing in cell viability and apoptosis assays than either drug alone. BKM120 plus HSP990 induced suppression of baseline Akt signaling as well as radiation (RT)-induced pAkt signaling in all cell lines. Cell cycle analysis revealed that HSP990 and BKM120, singly or combined, induced G2/M arrest leading to apoptosis/necrosis and polyploidy. Additionally, the drugs radiosensitized GBM cells in clonogenic assays. In vivo tumor growth delay studies demonstrated the effectiveness of combined drug treatment with HSP990 and BKM120 over single drug treatment, as well as the effectiveness of combined drug treatment in enhancing the effectiveness of radiation therapy.ConclusionsIn conclusion, HSP990 and BKM120, with and without RT, are active agents against glioma tumors. The sensitivity to these agents does not appear to depend on PTEN/p53status in the cell lines tested. We suggest that the combined action of both drugs is a viable multi-targeted strategy with the potential to improve clinical outcome for patients with high-grade glioma.

Effects of androgen suppression and radiation on prostate cancer suggest a role for angiogenesis blockade

Antiandrogen therapy is an important modality in the treatment of prostate cancer. Recent research into the role of angiogenesis in tumour growth and metastasis has uncovered links between antiandrogen therapy, radiation therapy and angiogenesis, which have exciting implications for the treatment of prostate cancer. Angiogenic cytokines such as vascular endothelial growth factor (VEGF) have been identified in prostate cancer cells and tumours, and androgens appear to stimulate VEGF. This article assesses the antiangiogenic effects of hormonal therapy and assesses the role that angiogenesis may play in the observed cooperation between hormonal and radiation therapies for prostate cancer.

Hyperthermia does not affect rejoining of DNA double-strand breaks in a cell-free assay

Purpose : Heat radiosensitization is poorly understood but is believed to be caused by an inhibition in the repair of radiation-induced DNA lesions. This inhibition in DNA repair may be caused either by direct heat inactivation of repair enzymes, or by heat-induced protein denaturation that leads to their precipitation onto nuclear chromatin structures, generating a barrier that prevents repair enzymes from reaching the damage sites. Material and methods : A previously described (Ganguly and Iliakis, Int J Radiat Biol 1995, 68, 447-457) cell-free assay was introduced to evaluate rejoining of radiation-induced DNA double-strand breaks (dsb) in heated (45.5°C, 20 min) nuclei prepared from A549 cells, in reactions assembled with extracts of non-heated and non-irradiated HeLa cells. The assay allowed the functional evaluation of the effect of precipitated nuclear protein on dsb rejoining. By combining heated nuclei with extracts of non-heated cells the assay avoided complications that would otherwise arise when intact cells are studied, where both nuclear structures and repair factors are heated and therefore potentially altered. Results : It was observed that exposure of A549 cells to 45.5°C for 20 min caused a 50% increase in the relative protein content of isolated nuclei but had no effect on the in vitro rejoining of dsb. In agreement with earlier reports, a greatly reduced rate of dsb rejoining was observed either in intact A549 or HeLa cells after exposure to heat. Conclusions : The results indicate that an increased retention of proteins in heated nuclei is not necessarily associated with an inhibition of dsb rejoining. While the in vitro system may only reproduce certain aspects of the in vivo conditions, the results suggest that protein accretion as a mechanism of heat radiosensitization requires further testing using functional assays.