Radiation Biological Toximetry Using Circulating Cell-Free DNA (cfDNA) for Rapid Radiation/Nuclear Triage

Optimal triage biodosimetry would include risk stratification within minutes, and it would provide useful triage despite heterogeneous dosimetry, cytokine therapy, mixed radiation quality, race, and age. For regulatory approval, the U.S. Food and Drug Administration (FDA) Biodosimetry Guidance requires suitability for purpose and a validated species-independent mechanism. Circulating cell-free DNA (cfDNA) concentration assays may provide such triage information. To test this hypothesis, cfDNA concentrations were measured in unprocessed monkey plasma using a branched DNA (bDNA) technique with a laboratory developed test. Therefore, cfDNA concentration measurements are increasingly used in radiation oncology clinics to predict side effect risk. The cfDNA levels, along with hematopoietic parameters, were measured over a 7-day period in Rhesus macaques receiving total body radiation doses ranging from 1 to 6.5 Gy. Low-dose irradiation (0-2 Gy) was easily distinguished from high-dose whole-body exposures (5.5 and 6.5 Gy). Fold changes in cfDNA in the monkey model were comparable to those measured in a bone marrow transplant patient receiving a supralethal radiation dose, suggesting that the lethal threshold of cfDNA concentrations may be similar across species. Average cfDNA levels were 50 ± 40 ng/mL [±1 standard deviation (SD)] pre-irradiation, 120 ± 13 ng/mL at 1 Gy; 242 ± 71 ng/mL at 2 Gy; 607 ± 54 at 5.5 Gy; and 1585 ± 351 at 6.5 Gy (±1 SD). There was an exponential increase in cfDNA concentration with radiation dose. Comparison of the monkey model with the mouse model and the Guskova model, developed using Chernobyl responder data, further demonstrated correlation across species, supporting a similar mechanism of action. The test is available commercially in a Clinical Laboratory Improvement Amendments (CLIA) ready form in the U.S. and the European Union. The remaining challenges include developing methods for further simplification of specimen processing and assay evaluation, as well as more accurate calibration of the triage category with cfDNA concentration cutoffs.

Pancreatic Cancer Derived 3-D Organoids as Clinical Tool to Predict Response to Radiation and Chemo-Radiation Therapy

PURPOSE/OBJECTIVE(S)

Pancreatic cancer (PC) is the fourth leading cause of cancer death in both men and women. The standard of care for patients with locally advanced PC of chemotherapy, stereotactic radiotherapy (RT) or chemo-radiation-therapy has shown highly variable and limited success rates. However, three-dimensional (3D) Pancreatic tumor organoids (PTOs) have shown promise to study tumor response to drugs, and emerging treatments under in vitro conditions. We investigated the potential for using 3D organoids to evaluate the precise radiation and drug dose responses of in vivo PC tumors.

MATERIALS/METHODS

PTOs were created from mouse pancreatic tumor tissues, and their microenvironment was compared to that of in vivo tumors using immunohistochemical staining. The organoids and in vivo PC tumors were treated with fractionated X-ray RT, 3-bromopyruvate (3BP) anti-tumor drug, and with a combination of 3BP + fractionated RT. We quantified treatment response by metabolic imaging and immunofluorescence of αSMA and vimentin markers.

RESULTS

Pancreatic tumor organoids (PTOs) exhibited a similar fibrotic microenvironment and molecular response (as seen by apoptosis biomarker expression) as in vivo tumors. Untreated tumor organoids and in vivo tumor both exhibited proliferative growth of 6 folds the original size after 10 days, whereas no growth was seen for organoids and in vivo tumors treated with 8 (Gray) Gy of fractionated RT. Tumor organoids showed reduced growth rates of 3.2x and 1.8x when treated with 4 and 6 Gy fractionated RT, respectively. Interestingly, combination of 100 µM of 3BP + 4 Gy of RT showed pronounced growth inhibition as compared to 3-BP alone or 4 Gy of radiation alone. Further, we observed overexpression of OCT-4, SOX2, Nanog cancer stem cell markers (CSC) indicated presence of cancer stem cells in tumor organoids which might have some role in resistance to therapies and recurrence in pancreatic cancer.

CONCLUSION

PTOs produced a similar microenvironment and exhibited similar growth characteristics as in vivo tumors following treatment, indicating their potential for predicting in vivo tumor sensitivity and response to RT and combined chemo-RT treatments. Cancer stem cells in pancreatic cancer could be playing a role in resistance to therapies and recurrence in pancreatic cancer.

1H, 13C, and 15N assignments of the mRNA binding protein hnRNP A18

Heterogeneous ribonuclear protein A18 (hnRNP A18) is an RNA binding protein (RBP) involved in the hypoxic cellular stress response and regulation of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) expression in melanoma, breast cancer, prostate cancer, and colon cancer solid tumors. hnRNP A18 is comprised of an N-terminal structured RNA recognition motif (RMM) and a C-terminal intrinsically disordered domain (IDD). Upon cellar stressors, such as UV and hypoxia, hnRNP A18 is phosphorylated by casein kinase 2 (CK2) and glycogen synthase kinase 3β (GSK-3β). After phosphorylation, hnRNP A18 translocates from the nucleus to the cytosol where it interacts with pro-survival mRNA transcripts for proteins such as hypoxia inducible factor 1α and CTLA-4. Both the hypoxic cellular response and modulation of immune checkpoints by cancer cells promote chemoradiation resistance and metastasis. In this study, the ¹ H, ¹³ C, and ¹⁵ N backbone and sidechain resonances of the 172 amino acid hnRNP A18 were assigned sequence-specifically and provide a framework for future NMR-based drug discovery studies toward targeting hnRNP A18. These data will also enable the investigation of the dynamic structural changes within the IDD of hnRNP A18 upon phosphorylation by CK2 and GSK-3β to provide critical insight into the structure and function of IDDs.

Pancreatic cancer derived 3D organoids as a clinical tool to evaluate the treatment response

Background and purpose

Pancreatic cancer (PC) is the fourth leading cause of cancer death in both men and women. The standard of care for patients with locally advanced PC of chemotherapy, stereotactic radiotherapy (RT), or chemo-radiation-therapy has shown highly variable and limited success rates. However, three-dimensional (3D) Pancreatic tumor organoids (PTOs) have shown promise to study tumor response to drugs, and emerging treatments under in vitro conditions. We investigated the potential for using 3D organoids to evaluate the precise radiation and drug dose responses of in vivo PC tumors.

Methods

PTOs were created from mouse pancreatic tumor tissues, and their microenvironment was compared to that of in vivo tumors using immunohistochemical and immunofluorescence staining. The organoids and in vivo PC tumors were treated with fractionated X-ray RT, 3-bromopyruvate (3BP) anti-tumor drug, and combination of 3BP + fractionated RT.

Results

Pancreatic tumor organoids (PTOs) exhibited a similar fibrotic microenvironment and molecular response (as seen by apoptosis biomarker expression) as in vivo tumors. Untreated tumor organoids and in vivo tumor both exhibited proliferative growth of 6 folds the original size after 10 days, whereas no growth was seen for organoids and in vivo tumors treated with 8 (Gray) Gy of fractionated RT. Tumor organoids showed reduced growth rates of 3.2x and 1.8x when treated with 4 and 6 Gy fractionated RT, respectively. Interestingly, combination of 100 µM of 3BP + 4 Gy of RT showed pronounced growth inhibition as compared to 3-BP alone or 4 Gy of radiation alone. Further, positive identification of SOX2, SOX10 and TGFβ indicated presence of cancer stem cells in tumor organoids which might have some role in resistance to therapies in pancreatic cancer.

Conclusions

PTOs produced a similar microenvironment and exhibited similar growth characteristics as in vivo tumors following treatment, indicating their potential for predicting in vivo tumor sensitivity and response to RT and combined chemo-RT treatments.

Small molecules inhibitors of the heterogeneous ribonuclear protein A18 (hnRNP A18): a regulator of protein translation and an immune checkpoint

We have identified chemical probes that simultaneously inhibit cancer cell progression and an immune checkpoint. Using the computational Site Identification by Ligand Competitive Saturation (SILCS) technology, structural biology and cell-based assays, we identify small molecules that directly and selectively bind to the RNA Recognition Motif (RRM) of hnRNP A18, a regulator of protein translation in cancer cells. hnRNP A18 recognizes a specific RNA signature motif in the 3′UTR of transcripts associated with cancer cell progression (Trx, VEGF, RPA) and, as shown here, a tumor immune checkpoint (CTLA-4). Post-transcriptional regulation of immune checkpoints is a potential therapeutic strategy that remains to be exploited. The probes target hnRNP A18 RRM in vitro and in cells as evaluated by cellular target engagement. As single agents, the probes specifically disrupt hnRNP A18–RNA interactions, downregulate Trx and CTLA-4 protein levels and inhibit proliferation of several cancer cell lines without affecting the viability of normal epithelial cells. These first-in-class chemical probes will greatly facilitate the elucidation of the underexplored biological function of RNA Binding Proteins (RBPs) in cancer cells, including their effects on proliferation and immune checkpoint activation.

Investigating chemopotentiation by low-dose fractionated radiation therapy for disseminated intra-abdominal gastric cancer

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Background: Treatment options are rather limited for gastrointestinal cancer patients whose disease has disseminated into the intra-abdominal cavity. There is currently no modality that has been shown to prolong survival of this patient sub-population. Here, we designed pre-clinical studies to evaluate the potential application of chemopotentiation by Low Dose Fractionated Radiation Therapy (LDFRT) for disseminated gastric cancer and evaluate the role of a likely biomarker, the Dual Oxidase 2 (DUOX2) enzyme. Methods: Nude mice were injected orthotopically with human gastric cancer cells expressing endogenous or lower levels of DUOX2 and randomly assigned to four treatment groups: 1; vehicle alone, 2; chemotherapy consisting of a modified regimen of docetaxel, cisplatin and 5’-fluorouracil (mDCF) for three consecutive days, 3; Low Dose- Whole Abdomen Radiation Therapy (LD-WART) (5 fractions of 15 cGy in three days), 4; mDCF and LD-WART. Blood was harvested at day 14 and 45 and cancer progression was evaluated by fluorescence imaging (Xenogen). Results: The combined regimen was well tolerated in all animals and led to DUOX2 upregulation, increased serum protein oxidation and reduced cancer progression in the DUOX2 positive tumors. Tumors expressing lower DUOX2 levels were more sensitive to chemotherapy but no additional benefit was obtained with LD-WART. The potential clinical significance of these findings is exemplified by a tumor microarray demonstrating that only about 46% of human gastric tumors expressed DUOX2. The molecular mechanisms underlying DUOX2 effects in response to the combined regimen include NF-kB upregulation and VEGF down regulation. Moreover, the combined regimen of mDCF and LDFRT was also effective on a Cancer Stem Cell (CSC)-Like subpopulation of mouse gastric cancer cells. Conclusions: Taken together these data suggest that DUOX2 could be used as a potential biomarker for patient stratification for chemopotentiation by LD-WART for positive tumors while chemotherapy alone would be more effective for DUOX2 negative tumors. The absence of added toxicity suggests that these cycles could be repeated.

A Combination of Radiotherapy, Hyperthermia, and Immunotherapy Inhibits Pancreatic Tumor Growth and Prolongs the Survival of Mice

Background: Pancreatic cancer (PC) is the fourth-most-deadly cancer in the United States with a 5-year survival rate of only 8%. Unfortunately, only 10–20% of PC patients are candidates for surgery, with the vast majority of patients with locally-advanced disease undergoing chemotherapy and/or radiation therapy (RT). Current treatments are clearly inadequate and novel strategies are crucially required. We investigated a novel tripartite treatment (combination of tumor targeted hyperthermia (HT), radiation therapy (RT), and immunotherapy (IT)) to alter immunosuppressive PC-tumor microenvironment (TME). (2). Methods: In a syngeneic PC murine tumor model, HT was delivered before tumor-targeted RT, by a small animal radiation research platform (SARRP) followed by intraperitoneal injections of cytotoxic T-cell agonist antibody against OX40 (also known as CD134 or Tumor necrosis factor receptor superfamily member 4; TNFRSF4) that can promote T-effector cell activation and inhibit T-regulatory (T-reg) function. (3). Results: Tripartite treatment demonstrated significant inhibition of tumor growth (p < 0.01) up to 45 days post-treatment with an increased survival rate compared to any monotherapy. Flow cytometric analysis showed a significant increase (p < 0.01) in cytotoxic CD8 and CD4+ T-cells in the TME of the tripartite treatment groups. There was no tripartite-treatment-related toxicity observed in mice. (4). Conclusions: Tripartite treatment could be a novel therapeutic option for PC patients.

Abstract 4434: Contribution of heterogenous ribonucleoprotein A18 in prostate cancer progression

Prostate cancer is the third leading cause of cancer deaths among men in the United States, with recurrent metastasis being the predominant cause of mortality. In spite of the significant progress made in the past half century with hormonal therapy for metastatic prostate cancer, a majority eventually progresses to a lethal stage of the disease commonly known as castration-resistant prostate cancer. New treatment strategies are therefore needed. Previous work from our lab has identified the RNA-binding protein heterogenous ribonucleoprotein A18 (hnRNP A18) as a new regulator of protein translation in cancer cells. While its localization is predominantly nuclear, hnRNP A18 translocates out to the cytosol in response to cellular stress like hypoxia. Immunohistochemistry data from tissue microarrays reveals increased expression of hnRNP A18 in prostate hyperplasia, and even greater overexpression in prostate adenocarcinoma as compared to the surrounding normal tissue. Furthermore, a greater percentage of hnRNP A18 is seen to shift from the nucleus to the cytosol as the disease progresses. In the cytosol, hnRNP A18 recognizes and binds to a specific 51 nucleotide RNA motif in the 3' untranslated region of targeted transcripts, stabilizing them and enhancing their translation. Transcripts targeted by hnRNP A18 confer tumor growth advantages. The down-regulation of hnRNP A18 was seen to reduce cancer cell proliferation, migration, and invasion. Moreover, down-regulation of hnRNP A18 significantly reduces prostate cancer growth in a mouse tumor xenograft model. Taken together, our data suggests that hnRNP A18 could be a potentially new target to stop or limit prostate cancer progression.

Citation Format: Elizabeth Tsuying Chang, Eun Yong Choi, Palak R. Parekh, France Carrier. Contribution of heterogenous ribonucleoprotein A18 in prostate cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4434.

Exploring the Concept of Radiation "Booster Shot" in Combination with an Anti-PD-L1 mAb to Enhance Anti-Tumor Immune Effects in Mouse Pancreas Tumors

Radiotherapy (RT) has long been known to be immunogenic. Mounting preclinical data demonstrate a synergistic anti-tumor effect when RT is used in combination with immune check point inhibitors (ICI). However, it is unclear how to best integrate RT with an ICI (i.e. dose fractionation, sequence, etc.). Here we explored the concept that RT delivered as an in situ tumor vaccine sequentially to separate tumors over time might stimulate more potent and rapid antitumor immune response than RT delivered to only one tumor. In essence, radiation to a second tumor could be likened to giving a vaccine "booster shot". Mice bearing pancreatic tumors in three different sites were injected with anti-PD-L1 antibody and exposed to three daily consecutive fractions of 4 Gy each at one or two sites with a one week interval. Our data indicate that delivering an RT to one tumor followed by an RT "booster shot" to a second tumor, compared to treating only one tumor with RT, significantly reduced tumor growth at a third non-irradiated site. This abscopal effect to the non-irradiated site was observed earlier (day 9) in mice that received RT to two tumors versusa single tumor (day 17). Decreased growth of the non-irradiated tumor correlated with a transient increase of the CD4/CD8 ratio in the tumor, increase myeloid-derived suppressor cells and tumor associated macrophages in the draining lymph nodes. These data warrant further exploration of sequentially treating multiple lesions with RT and ICI with the intent of generating a robust anti-tumor immune response.

Abstract 4478: Characterization of the biochemical interaction of hnRNP A18 to thioredoxin transcript

Introduction: The RNA-binding protein heterogenous ribonucleoprotein A18 (hnRNP A18) is a protein translation regulator found to be elevated in many cancers. Previous work from our lab has shown that under stress conditions, hnRNP A18 is able to bind and regulate the translation of a group of mRNAs, including thioredoxin (TRX), a redox-regulating protein implicated in promoting tumor progression. Additionally, the formation of functional hnRNP A18:TRX complexes increases de novo protein synthesis of TRX through the stabilization of its mRNA transcript. It has been reported that like most RNA-binding proteins, hnRNP A18 is a modular protein and is uniquely composed of a single N-terminal RNA binding domain (RBD) and a C-terminal arginine-glycine rich (RGG) domain. The RBD is able to dictate specificity and affinity of substrate binding, while methylation of the arginine residues in the RGG domain contributes to its RNA binding capability. The observed translational regulation of TRX by hnRNP A18 merits further studies into understanding the physical interaction between the two molecules.

Methods/Results: To determine the region which hnRNP A18 interacts with thioredoxin, stable cell lines overexpressing the RBD, RGG or full length (FL) domains of hnRNP A18 were generated in human melanoma cells. Ribonucleoprotein immunoprecipitation assays were performed using specific antibodies to either the RBD or RGG domain epitope. Reverse transcription PCR data reveals the presence of TRX mRNA in the resultant immunoprecipitated materials, indicating that both the RBD and RGG domain of hnRNP A18 protein is able to independently bind TRX mRNA. Maximum binding was observed when both RBD and RGG regions were present. Furthermore, hnRNP A18-GST recombinant proteins were engineered to determine the exact region which hnRNP A18 binds to on its target mRNAs. TRX mRNA was systematically deleted and increasing amounts of hnRNP A18-GST protein was added to determine binding capability. Northwestern analysis reveals that hnRNP A18 binds to its consensus motif in the TRX 3’UTR and to a new 19 nucleotide motif downstream of the consensus site.

Conclusion: Heterogenous ribonucleoprotein A18 is a stress-activated RNA-binding protein that functions in the translational regulation of TRX. Although the RBD and RGG domains are each independently able to physically interact with TRX, both regions are necessary for maximal binding. Furthermore, a new 19 nucleotide motif located downstream of the hnRNP A18 consensus motif was also found to be sufficient for binding. The binding interface between RNA-binding proteins and their target mRNAs hold significant importance in understanding how the two molecules interact and will offer new insights into developing novel drug therapeutics that disrupt ribonucleoprotein formation.

Citation Format: Elizabeth Tsuying Chang, Palak Parekh, Eun Yong Choi, Ruiqing Yang, France Carrier. Characterization of the biochemical interaction of hnRNP A18 to thioredoxin transcript [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4478. doi:10.1158/1538-7445.AM2017-4478

Abstract 5852: DUOX2, a key player for chemopotentiation by low-dose fractionated radiation therapy in gastric cancer cells

One of the most conventional therapy for solid tumors is radiotherapy. Still, this modality presents a challenge when it comes to managing highly disseminated gastrointestinal cancers due to increased toxicity to surrounding tissues. Recent laboratory and clinical data indicate that Low Dose Fractionated Radiation Therapy (LDFRT) can potentiate systemic chemotherapy and presents the possibility to revisit the concept of Whole Abdominal Radiotherapy (WART) for disseminated intra-abdominal gastric cancers. Earlier work considered LDFRT ineffective for tumor removal but we now know that LDFRT induces hyper-radiosensitivity (HRS) in a number of proliferating cells. We have recently shown that dual oxidase (DUOX2) is a major contributor to induce HRS at radiation doses as low as 0.15 Gy and sensitize human gastric cancer cells to chemotherapy. The aim of our study is to determine the utility of DUOX2 as a potential biomarker for the clinical application of chemopotentiation by LDFRT. First, we performed immunohistochemistry (IHC) on 48 human gastric samples with progressive grades. Our data indicate that only about 50% of human gastric cancers are positive for DUOX2. The reason for DUOX2 variability of expression is not clear but may be linked to inflammation since six of the seven (86%) gastritis samples we examined expressed strong levels of DUOX2 in the surface of epithelial cells. Our data also indicate that expression of DUOX2 significantly increases the levels of macrophages infiltration in tissue expressing DUOX2 as well as in the stroma surrounded by cells expressing DUOX2. This suggests that expression of DUOX2 could impact on the dynamic of the tumor microenvironment. Expression of DUOX2 in response to LDFRT is conserved since we also observed this in mice primary gastric cancer cells as well as cancer stem cells. Furthermore, as a first step to develop DUOX2 as an accessible biomarker, we studied DUOX2 activity by measuring the accumulation of oxidative serum proteins in gastric cancer cells media. Our data indicate that down regulation of DUOX2 significantly reduces the levels of serum protein oxidation. Taken together these data suggest that DUOX2 could potentially be used as a biomarker to stratify patients and follow the efficiency of clinical application of chemopotentiation by LDFRT.

Citation Format: Palak R. Parekh, Elizabeth Chang, Navesh K. Sharma, France Carrier. DUOX2, a key player for chemopotentiation by low-dose fractionated radiation therapy in gastric cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5852. doi:10.1158/1538-7445.AM2017-5852

Crystal structure of the human heterogeneous ribonucleoprotein A18 RNA-recognition motif

The heterogeneous ribonucleoprotein A18 (hnRNP A18) is upregulated in hypoxic regions of various solid tumors and promotes tumor growth via the coordination of mRNA transcripts associated with pro-survival genes. Thus, hnRNP A18 represents an important therapeutic target in tumor cells. Presented here is the first X-ray crystal structure to be reported for the RNA-recognition motif of hnRNP A18. By comparing this structure with those of homologous RNA-binding proteins (i.e. hnRNP A1), three residues on one face of an antiparallel β-sheet (Arg48, Phe50 and Phe52) and one residue in an unstructured loop (Arg41) were identified as likely to be involved in protein-nucleic acid interactions. This structure helps to serve as a foundation for biophysical studies of this RNA-binding protein and structure-based drug-design efforts for targeting hnRNP A18 in cancer, such as malignant melanoma, where hnRNP A18 levels are elevated and contribute to disease progression.

Heterogenous ribonucleoprotein A18 (hnRNP A18) promotes tumor growth by increasing protein translation of selected transcripts in cancer cells

The heterogenous ribonucleoprotein A18 (hnRNP A18) promotes tumor growth by coordinating the translation of selected transcripts associated with proliferation and survival. hnRNP A18 binds to and stabilizes the transcripts of pro-survival genes harboring its RNA signature motif in their 3′UTRs. hnRNP A18 binds to ATR, RPA, TRX, HIF-1α and several protein translation factor mRNAs on polysomes and increases de novo protein translation under cellular stress. Most importantly, down regulation of hnRNP A18 decreases proliferation, invasion and migration in addition to significantly reducing tumor growth in two mouse xenograft models, melanoma and breast cancer. Moreover, tissue microarrays performed on human melanoma, prostate, breast and colon cancer indicate that hnRNP A18 is over expressed in 40 to 60% of these malignant tissue as compared to normal adjacent tissue. Immunohistochemistry data indicate that hnRNP A18 is over expressed in the stroma and hypoxic areas of human tumors. These data thus indicate that hnRNP A18 can promote tumor growth in in vivo models by coordinating the translation of pro-survival transcripts to support the demands of proliferating cells and increase survival under cellular stress. hnRNP A18 therefore represents a new target to selectively inhibit protein translation in tumor cells.

Abstract 5081: hnRNP A18: an emerging novel target for cancer therapy

Heterogenous ribonucleoprotein A18 (hnRNP A18) increases de novo protein translation during cellular stress. Although hnRNP A18 has recently been associated with several cancers, the exact role of it during the multifactorial process of cancer growth and progression is still unknown. Accordingly, we examined the dependability of various malignant cancer cell lines on hnRNP A18. Down-regulation of hnRNP A18 impaired the proliferative, invasive and migratory properties of melanoma and triple negative breast cancer cell lines in vitro, while overexpression of hnRNP 18 caused an increase in invasiveness. Consistent with these observations, we detected remarkable reduction of tumor growth in two mouse xenograft models, melanoma and breast cancer. Moreover, down-regulation of hnRNP A18 increased the sensitivity of melanoma cells and breast cancer cells to paclitaxel and 5-fluoro uracil, respectively. In conclusion, hnRNP A18 plays a key role in tumor growth and progression. It may serve as a novel target for the treatment of cancer.

Citation Format: Palak R. Parekh, Elizabeth Chang, Qingyuan Yang, France Carrier. hnRNP A18: an emerging novel target for cancer therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5081.

Abstract 1805: DUOX2: The key player for hyper-radiosensitivity in gastric cancer cells with low dose fractionation radio therapy (LDFRT)

The most conventional therapy for solid tumors is radiotherapy. Still there is a challenge when it comes to managing highly disseminated gastrointestinal cancers because of the toxicity issues. Earlier, low dose fractionated radiotherapy (LDFRT) was considered to be ineffective for tumor removal, rather believed to cause cancer. There are few improvements with the use of novel approach in few cases of solid malignancy. This paradigm exploits the advantage of LDFRT with the combination of chemotherapy. Because now it's known that LDFRT causes hyper-radiosensitivity (HRS). The aim of our study is to determine the efficacy of LDFRT in combination with modified regimen of docetaxel, cisplatin and 5′-fluorouracil (mDCF) and their mechanism of action in gastric cancer cells. Our data indicate that consecutive three days radiation with daily fraction of 0.15 Gy produced HRS in gastric cancer cells and potentiated the effect of chemotherapeutic drugs (mDCF). Colony survival assays showed only 10% of gastric cancer cell survival when LDFRT was combined with mDCF while ten times higher dose (1.35 Gy) of radiation alone was required to achieve the same results. RT2-PCR profiler array analysis showed marked upregulation of dual oxidase-2 (DUOX2), an enzyme of NADPH- oxidase family, without inducing the genes involved in DNA repair. This was evident from 3.5 fold increase in reactive oxygen species (ROS) in cells exposed to LDFRT and mDCF. Further, this was confirmed by increase in cancer cell survival hence radioresistance with downregulation of DUOX2 expression. In addition to this inhibition of DUOX2 activity also abrogated the efficacy of the combination therapy. Taken together these data suggest that chemopotentiation by LDFRT in gastric cancer cells may be partly due to increased ROS production by DUOX2 without inducing the DNA repair machinery. These data thus provide a rationale for further explorations of potential clinical applications of LDFRT as a chemopotentiator for advanced and metastatic gastric cancers. (* = Equally Contributed)

Citation Format: Duc Nguyan, Palak R. Parekh, Elizabeth T. Chang, Navesh Sharma, France Carrier. DUOX2: The key player for hyper-radiosensitivity in gastric cancer cells with low dose fractionation radio therapy (LDFRT). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1805. doi:10.1158/1538-7445.AM2015-1805

Abstract 2116: HDAC9 and 11 contribute to UV resistance in melanoma cells

We have previously shown that the Histone Deacetylase Inhibitor (HDACi) trichostatin A (TSA) can sensitize cancer cells to UV radiation by facilitating the formation of Cyclobutane pyrimidine dimers (CPD) without increasing the levels of HDAC1. Here we show that HDAC9 and HDAC11 are upregulated in response to UV radiation in a number of human melanoma cell lines. Both HDAC9 and HDAC11 have an hnRNP A18 signature motif in their 3′UTR. hnRNP A18 is a new regulator of protein translation that can confer growth advantages to tumor cells by specifically increasing the stability and translation of mRNA transcripts harboring its signature motif. Our data indicate that HDAC9 and 11 levels correspond to hnRNP A18 level in response to UV radiation in several melanoma cell lines while hnRNP A18 and HDAC 9 and 11 are not upregulated in response to UV radiation in the normal human fibroblasts Malme cells or the normal melanocytes HEMa-LP. Moreover, clonogenic colony survival assays indicate that melanoma cells expressing higher hnRNP A18 endogenous levels are more resistant to UV radiation than cells expressing lower hnRNP A18 levels. In addition, down regulation of hnRNP A18 prevents HDAC 9 and 11 upregulation in response to UV radiation. Furthermore, overexpression of hnRNP A18 increases further the levels of HDAC 9 and 11 in response to UV radiation. These data suggest that upregulation of HDAC9 and 11 in response to hnRNP A18 activation contribute to UV resistance and may increase sensitization to UV-induced cell killing by HDACi.

Citation Format: Elizabeth T. Chang, Palak R. Parekh, Qingyuan Yang, France Carrier. HDAC9 and 11 contribute to UV resistance in melanoma cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2116. doi:10.1158/1538-7445.AM2015-2116

Abstract 3307: Chemopotentiation by low dose fractionated radiation therapy in colon cancer cells

Response rates for patients with primary and metastatic colorectal cancer treated with modern chemotherapy regimens such as 5-FU, leucovorin, oxaliplatin (FOLFOX) have routinely exceeded 50% and are frequently as high as 60-70%. However, as in most chemotherapy regimens, toxicity to normal cells is often a significant limitation. Tumors of the gastrointestinal (GI) track are also sensitive to radiation but the inability to combine radiation therapy (RT) with full-dose chemotherapy can be detrimental to patients, particularly those that may have disseminated micrometastatic disease. Therefore, new treatment strategies that incorporate chemotherapy that could increase tumor response without increasing toxicity are highly desirable. Laboratory and clinical data suggest that using low-dose fractionated radiation therapy (LDFRT) as a chemopotentiator may allow for full-dose chemotherapy with improved efficacy without adding to the toxicity of the systemic treatment. Here we show that twice daily radiation doses as low as 0.15 Gy for three consecutive days can significantly increase FOLFOX killing efficiency in human colon cancer RKO cells. In addition, our data indicate that the chemopotentiation by LDFRT may be mediated by the stress inducible hnRNP A18 protein. Down regulation of hnRNP A18 sensitizes RKO cells to LDFRT and FOLFOX independently and increases further the chemopotentiation by LDFRT. Moreover, overexpression of hnRNP A18 increases radio-resistance and chemo-resistance to FOLFOX. hnRNP A18 is a new regulator of protein translation in cancer cells that specifically targets transcripts devoted to confer growth advantages. This data suggest that hnRNP A18 could be targeted to increase further the systemic effect of chemopotentation by LDFRT. The identification of hnNRP A18 as a new cellular pathway responsive to low dose radiation and its contribution to chemopotentiation provide a novel opportunity for better measurement of the therapeutic response and could contribute to the rationale designs of new mechanism based clinical trials.

Citation Format: Teresa Smith, Palak R. Parekh, Elizabeth T. Chang, Michael Chuong, France Carrier. Chemopotentiation by low dose fractionated radiation therapy in colon cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3307. doi:10.1158/1538-7445.AM2015-3307

Contribution of Dual Oxidase 2 (DUOX2) to Hyper-Radiosensitivity in Human Gastric Cancer Cells

Whole-abdominal radiotherapy (WART) is a primary method for managing gastrointestinal cancers that have disseminated into intra-abdominal tissues. While effective, this approach is limited because of the increased toxicity to normal tissue associated with combined WART and full-dose chemotherapy regimens. Recent studies have demonstrated a survival advantage in a novel treatment paradigm that allows for the safe use of full-dose systemic chemotherapy in combination with low-dose fractionated radiotherapy (LDFRT). Traditionally, radiation doses greater than 120 cGy have been used in radiotherapy because lower doses were thought to be ineffective for tumor therapy. However, we now know that LDFRT can produce hyper-radiosensitivity (HRS), a phenomenon where cells undergo apoptosis at radiation doses as low as 15 cGy, in a number of proliferating cells. The objectives of our current study were to determine whether LDFRT can induce HRS in gastrointestinal cancer cells and to identify biomarkers of chemopotentiation by LDFRT. Our data indicate that three consecutive daily fractions of 15 cGy produced HRS in gastric cancer cells and potentiated a modified regimen of docetaxel, cisplatin and 5'-fluorouracil (mDCF). Colony survival assays indicated that 15 cGy was sufficient to kill 90% of the cells when LDFRT was combined with mDCF whereas a dose almost 10 times higher (135 cGy) was needed to achieve the same rate when using conventional radiotherapy alone. RT(2) PCR Profiler™ array analysis indicated that this combined regimen upregulated dual oxidase 2 (DUOX2), an enzyme functioning in the production of hydrogen peroxide, without upregulating genes involved in DNA repair. Moreover, downregulation of DUOX2 increased radioresistance at every radiation dose tested. In addition, our data indicate that reactive oxygen species (ROS) increase up to 3.5-fold in cells exposed to LDFRT and mDCF. Furthermore, inhibition of NADPH oxidase abrogated the killing efficiency of this combined regimen. Taken together these data suggest that chemopotentiation by LDFRT in gastric cancer cells may be due, at least in part, to increased ROS production (DUOX2) without upregulation of the DNA repair machinery. These data thus provide a rationale for further explorations of potential clinical applications of LDFRT, such as in WART, as a chemopotentiator for advanced and metastatic gastric cancers.

Abstract 3397: Rational targeting of protein translation for cancer treatments

Deregulation of protein translation is associated with a growing number of human diseases including tumorigenesis. New anti cancer therapies targeting the protein translation regulator mammalian Target Of Rapamycin (mTOR) highlight the importance of this signaling pathway. However, feedback mechanisms that can compensate for this general protein translation pathway limit the clinical efficiency of this approach. New drugs that could rationally target protein translation in cancer cells are therefore needed. We have identified the heterogenous ribonucleoprotein A18 (hnRNP A18) as a new regulator of protein translation in cancer cells. hnRNP A18 is up regulated in several human tumors including prostate, breast, colon and as shown here in melanoma tumors. hnRNP A18 regulates protein translation of its targeted transcripts by binding to a specific RNA signature motif in their 3’UTRs. Our data indicate that the hypoxia mimetic agent CoCl2 increases hnRNP A18 protein levels in melanoma cells but not in normal melanocytes. In addition, down regulation of hnRNP A18 sensitizes melanoma cells to CoCl2 and Temozolimide. The functional significance of this effect was evaluated in a mouse xenograft model where hnRNP A18 down regulation reduced melanoma tumor growth by more than 70%. RNA immunoprecipitation assay indicate that hnRNP A18 binds to a number of transcripts associated with tumor growth including the Hypoxia Inducible Factor 1α (HIF-1α). Levels of hnRNP A18 also directly affect HIF-1α protein levels in response to CoCl2. Taken together these data indicate that hnRNP A18 is a new regulator of protein translation that could be targeted to develop new mechanism based therapy for the rational inhibition of protein translation in cancer cells.

Citation Format: Elizabeth Chang, Duc Nguyen, Qingyuan Yang, France Carrier. Rational targeting of protein translation for cancer treatments. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3397. doi:10.1158/1538-7445.AM2014-3397

Abstract 844: Contribution of dual oxidase 2 (DUOX2) to hyper radiosensitivity in human gastric cancer cells

Whole abdominal radiotherapy (WART) is a primary method for managing gastrointestinal cancers that have disseminated into intra-abdominal tissues. While effective, this approach is limited since combination of WART with full-dose chemotherapy regimens increase toxicity to normal tissue. Recent studies have demonstrated a survival advantage in a novel treatment paradigm that allows for the safe use of full-dose systemic chemotherapy in combination with Low Dose Fractionated Radiotherapy (LDFRT). Traditionally, radiotherapy used doses greater than 120 cGy because it was thought that lower radiation doses would be ineffective for tumor therapy. We now know that LDFRT can produce hyper-radiosensitivity (HRS), a phenomenon where cells undergo apoptosis at radiation doses as low as 15 cGy, in a number of proliferating cells. Here we aimed at determining whether LDFRT can induce HRS in gastrointestinal cancer cells and at identifying biomarkers of chemopotentiation by LDFRT. Our data indicate that three consecutive daily fractions of 15 cGy produced HRS in gastric cancer cells and potentiated a modified regimen of Docetaxel, Cisplatin, and 5’-fluorouracil (mDCF). Colony survival assays indicated that 15 cGy was sufficient to kill 90% of the cells when LDFRT was combined with mDCF whereas an almost ten times higher dose (135 cGy) was needed to achieve the same rate when using conventional radiotherapy alone. RT2 PCR Profiler Array analysis indicated that this combined regimen up-regulated dual oxidase 2 (DUOX2), an enzyme functioning in the production of hydrogen peroxide, without up-regulating genes involved in DNA repair. Moreover, down regulation of DUOX2 increased radiation resistance at every radiation doses tested. In addition, a subset of genes known to be activated by Reactive Oxygen Species were specifically upregulated by LDFRT when combined with mDCF. Taken together these data suggest that chemopotentiation by LDFRT in gastric cells may be due, at least in part, to increased ROS production (DUOX2) without upregulation of the DNA repair machinery. These data thus provide a rationale for further explorations of potential clinical applications of LDFRT, such as in WART, as chemopotentiator for advanced and metastatic gastric cancers.

Citation Format: Duc Nguyen, Elizabeth Chang, Navesh Sharma, France Carrier. Contribution of dual oxidase 2 (DUOX2) to hyper radiosensitivity in human gastric cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 844. doi:10.1158/1538-7445.AM2014-844

VorinostatSAHA Promotes Hyper-Radiosensitivity in Wild Type p53 Human Glioblastoma Cells

Glioblastoma multiforme (GBM) is a very aggressive and locally invasive tumor. The current standard of care is partial brain radiation therapy (60 Gy) concurrently with the alkylating agent temozolomide (TMZ). However, patients' survival remains poor (6-12 months) mainly due to local and diffuse (distant) recurrence. The possibility to promote hyper radiosensitivity (HRS) with low dose radiation may contribute to improve outcome. Here, we evaluated the effect of Vorinostat^SAHA and TMZ on glioblastoma cells' sensitivity to low dose radiation. Clonogenic survivals were performed on D54 (p53 and PTEN wild type) and U118 (p53 and PTEN mutants) cells exposed to clinically relevant doses of Vorinostat^SAHA and TMZ and increasing radiation doses. Apoptosis was measured by the activation of caspase-3 and the role of p53 and PTEN were evaluated with the p53 inhibitor pifithrin α and the PI3K/AKT pathway inhibitor LY29002. Vorinostat^SAHA promoted HRS at doses as low as 0.25 Gy in the D54 but not the U118 cells. Killing efficiency was associated with caspase-3 activation, delayed H2AX phosphorylation and abrogation of a radiation -induced G2 arrest. Inhibiting p53 function with pifithrin α prevented the promotion of HRS by Vorinostat^SAHA. Moreover, LY29002, a PI-3K inhibitor, restored promotion of HRS by Vorinostat^SAHA in the p53 mutant U118 cells to levels similar to the p53 wild type cells. TMZ also promoted HRS at doses as low as 0.15 Gy. These finding indicate that HRS can be promoted in p53 wild type glioblastoma cells through a functional PTEN to delay DNA repair and sensitize cells to low dose radiation. Promotion of HRS thus appears to be a viable approach for GBM that could be used as a basis to develop new Phase I/II studies.

Translational phase I trial of vorinostat (suberoylanilide hydroxamic acid) combined with cytarabine and etoposide in patients with relapsed, refractory, or high-risk acute myeloid leukemia

PURPOSE

To determine the maximum-tolerated dose (MTD) of the histone deacetylase inhibitor vorinostat combined with fixed doses of cytarabine (ara-C or cytosine arabinoside) and etoposide in patients with poor-risk or advanced acute leukemia, to obtain preliminary efficacy data, describe pharmacokinetics, and in vivo pharmacodynamic effects of vorinostat in leukemia blasts.

EXPERIMENTAL DESIGN

In this open-label phase I study, vorinostat was given orally on days one to seven at three escalating dose levels: 200 mg twice a day, 200 mg three times a day, and 300 mg twice a day. On days 11 to 14, etoposide (100 mg/m(2)) and cytarabine (1 or 2 g/m(2) twice a day if ≥65 or <65 years old, respectively) were given. The study used a standard 3+3 dose escalation design.

RESULTS

Eighteen of 21 patients with acute myelogenous leukemia (AML) treated on study completed planned therapy. Dose-limiting toxicities [hyperbilirubinemia/septic death (1) and anorexia/fatigue (1)] were encountered at the 200 mg three times a day level; thus, the MTD was established to be vorinostat 200 mg twice a day. Of 21 patients enrolled, seven attained a complete remission (CR) or CR with incomplete platelet recovery, including six of 13 patients treated at the MTD. The median remission duration was seven months. No differences in percentage S-phase cells or multidrug resistance transporter (MDR1 or BCRP) expression or function were observed in vivo in leukemia blasts upon vorinostat treatment.

CONCLUSIONS

Vorinostat 200 mg twice a day can be given safely for seven days before treatment with cytarabine and etoposide. The relatively high CR rate seen at the MTD in this poor-risk group of patients with AML warrants further studies to confirm these findings.

Chromatin Modulation by Histone Deacetylase Inhibitors: Impact on Cellular Sensitivity to Ionizing Radiation

It is well established that cells are more sensitive to ionizing radiation during the G₂/M phase of the cell cycle when their chromatin is highly compacted. However, highly compacted chromatin is less susceptible to DNA Double Strand Breaks (DSBs) than relaxed chromatin. Therefore, it is now becoming apparent that it is the cell capacity to repair its damaged DNA and refold its chromatin into its original compacted status that primarily affects the overall cellular sensitivity to ionizing radiation. The Histone Deacetylase Inhibitors (HDACIs) are a new class of anticancer agents that relax chromatin structure by increasing the levels of histone acetylation. The effect of HDACIs on normal and cancer cells sensitivity to ionizing radiation differs. Reports have indicated that HDACIs can protect normal cells while simultaneously sensitize cancer cells to ionizing radiation. This difference may stem from the individual characteristic of the normal and cancer cells chromatin structure. This review discusses this possibility and addresses the role of HDACIs in radiation therapy.

Nucleolin inhibits G4 oligonucleotide unwinding by Werner helicase

BACKGROUND

The Werner protein (WRNp), a member of the RecQ helicase family, is strongly associated with the nucleolus, as is nucleolin (NCL), an important nucleolar constituent protein. Both WRNp and NCL respond to the effects of DNA damaging agents. Therefore, we have investigated if these nuclear proteins interact and if this interaction has a possible functional significance in DNA damage repair.

METHODOLOGY/PRINCIPAL FINDINGS

Here we report that WRNp interacts with the RNA-binding protein, NCL, based on immunoprecipitation, immunofluorescent co-localization in live and fixed cells, and direct binding of purified WRNp to nucleolin. We also map the binding region to the C-terminal domains of both proteins. Furthermore, treatment of U2OS cells with 15 µM of the Topoisomerase I inhibitor, camptothecin, causes the dissociation of the nucleolin-Werner complex in the nucleolus, followed by partial re-association in the nucleoplasm. Other DNA damaging agents, such as hydroxyurea, Mitomycin C, and aphidicolin do not have these effects. Nucleolin or its C-terminal fragment affected the helicase, but not the exonuclease activity of WRNp, by inhibiting WRN unwinding of G4 tetraplex DNA structures, as seen in activity assays and electrophoretic mobility shift assays (EMSA).

CONCLUSIONS/SIGNIFICANCE

These data suggest that nucleolin may regulate G4 DNA unwinding by WRNp, possibly in response to certain DNA damaging agents. We postulate that the NCL-WRNp complex may contain an inactive form of WRNp, which is released from the nucleolus upon DNA damage. Then, when required, WRNp is released from inhibition and can participate in the DNA repair processes.

Cancer cells' epigenetic composition and predisposition to histone deacetylase inhibitor sensitization

Normal cells are up to ten times more resistant to histone deacetylase inhibitors (HDACis)-induced cell death compared with transformed cells. The molecular processes underlying this selectivity for cancer cells are still not well understood. Although a differential response to oxidative stress and capacity to repair damaged DNA have been described in some systems, these cannot fully account for the sensitivity of cancer cells to HDACis since the heterogeneity of cancer cells prompts differential sensitivities to reactive oxygen species and generates a panoply of defective DNA repair mechanisms within given histologies, cancer cell lines and tumor xenografts. It seems also unlikely that the influence of HDACis on cancer treatments reside primarily on gene transcription, since gene-expression profiling aimed at defining correlation with response to HDACis in cancer cells indicates that less than 5% to approximately 20% of transcribed genes are altered by HDACis treatment. Moreover, the altered genes vary from cell line to cell line and between different HDACis. Therefore, no consistent picture of a target(s) or pathway(s) modulated by HDACis has emerged. One consistent parameter that has however been observed in peripheral blood mononuclear cells of patients treated with HDACi is the accumulation of acetylated histones. Because one of the primary functions of histone acetylation is to increase chromatin accessibility, this article will explore the possibility that intrinsic molecular and structural characteristics of cancer cells provide a selective advantage for HDACis sensitivity.

Abstract 1852: Identification of the UV-inducible RNA binding protein hnRNP A18 as a new target for melanoma progression

Melanoma is the most dangerous form of skin cancer. If recognized and treated early, it is nearly 100 percent curable. However, invasive melanoma is hard to treat and consequently presents an extremely poor prognosis with a 5-year survival of about 6% and a median survival duration of 7.5 months. We have identified the UV-inducible RNA binding protein hnRNP A18 as a new target for melanoma progression and responses to anticancer drugs treatments. hnRNP A18 basal levels are up-regulated in melanoma cells as compared to normal melanocytes and UV radiation increases hnRNP A18 levels in 5 of the 6 melanoma cell lines we studied. More over, down regulation of hnRNP A18 reduced by more than 80% melanoma tumor growth in mice xenograft and sensitized melanoma cells to Temozolimide (TMZ) and the hypoxic mimetic agent CoCl2. In addition, levels of hnRNP A18 expression in response to UV radiation are proportional to melanoma cells capacity to survive UV-induced cellular damage. We have identified an hnRNP A18 RNA binding signature motif in the 3′ UTR of key regulatory proteins such as HDAC 8, 9, 11, HIF-1α and ATR that can confer resistance to UV induced DNA damage and hypoxic conditions. Therefore by targeting of a single molecule, hnRNP A18, it may be possible to shut down an entire network of protective proteins conferring melanoma cells, and potentially other solid tumors, growth advantage and resistance to conventional therapies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1852. doi:1538-7445.AM2012-1852

Enhanced translation by Nucleolin via G-rich elements in coding and non-coding regions of target mRNAs

RNA-binding proteins (RBPs) regulate gene expression at many post-transcriptional levels, including mRNA stability and translation. The RBP nucleolin, with four RNA-recognition motifs, has been implicated in cell proliferation, carcinogenesis and viral infection. However, the subset of nucleolin target mRNAs and the influence of nucleolin on their expression had not been studied at a transcriptome-wide level. Here, we globally identified nucleolin target transcripts, many of which encoded cell growth- and cancer-related proteins, and used them to find a signature motif on nucleolin target mRNAs. Surprisingly, this motif was very rich in G residues and was not only found in the 3'-untranslated region (UTR), but also in the coding region (CR) and 5'-UTR. Nucleolin enhanced the translation of mRNAs bearing the G-rich motif, since silencing nucleolin did not change target mRNA stability, but decreased the size of polysomes forming on target transcripts and lowered the abundance of the encoded proteins. In summary, nucleolin binds G-rich sequences in the CR and UTRs of target mRNAs, many of which encode cancer proteins, and enhances their translation.

The calcium-binding protein S100B down-regulates p53 and apoptosis in malignant melanoma

The S100B-p53 protein complex was discovered in C8146A malignant melanoma, but the consequences of this interaction required further study. When S100B expression was inhibited in C8146As by siRNA (siRNA(S100B)), wt p53 mRNA levels were unchanged, but p53 protein, phosphorylated p53, and p53 gene products (i.e. p21 and PIDD) were increased. siRNA(S100B) transfections also restored p53-dependent apoptosis in C8146As as judged by poly(ADP-ribose) polymerase cleavage, DNA ladder formation, caspase 3 and 8 activation, and aggregation of the Fas death receptor (+UV); whereas, siRNA(S100B) had no effect in SK-MEL-28 cells containing elevated S100B and inactive p53 (p53R145L mutant). siRNA(S100B)-mediated apoptosis was independent of the mitochondria, because no changes were observed in mitochondrial membrane potential, cytochrome c release, caspase 9 activation, or ratios of pro- and anti-apoptotic proteins (BAX, Bcl-2, and Bcl-X(L)). As expected, cells lacking S100B (LOX-IM VI) were not affected by siRNA(S100B), and introduction of S100B reduced their UV-induced apoptosis activity by 7-fold, further demonstrating that S100B inhibits apoptosis activities in p53-containing cells. In other wild-type p53 cells (i.e. C8146A, UACC-2571, and UACC-62), S100B was found to contribute to cell survival after UV treatment, and for C8146As, the decrease in survival after siRNA(S100B) transfection (+UV) could be reversed by the p53 inhibitor, pifithrin-alpha. In summary, reducing S100B expression with siRNA was sufficient to activate p53, its transcriptional activation activities, and p53-dependent apoptosis pathway(s) in melanoma involving the Fas death receptor and perhaps PIDD. Thus, a well known marker for malignant melanoma, S100B, likely contributes to cancer progression by down-regulating the tumor suppressor protein, p53.

Abstract 5498: Prognostic tools to predict the efficacy of anticancer drug treatment targeting Chromatin DNA or enzymes acting on DNA

There is currently no prognostic tool that can predict or monitor a cancer patient's response to anticancer drugs targeting chromatin DNA or enzymes acting on DNA. Cancer patients generally receive chemotherapy without the possibility to determine a priori whether the proposed regimen will be effective. We have developed a simple quantitative assay to measure the efficiency of Topoisomerase 2 (Topo2) inhibitors on genomic DNA (gDNA). The technique combines PCR-stop assay to real time PCR (RT-PCR). Prior reports have demonstrated that Topo2 poisons such as VP16 (etoposide) and Doxorubicin, induce prominent DNA cleavage in the P2 promoter of the c-myc gene. Therefore, we have optimized the design of primers complimentary to the sequence of Topo2 sites in the c-myc locus to suit the sensitivity of real time PCR detection. In PCR-Stop assay, the extent of locus-specific DNA damage sustained by the cells is inversely proportional to the levels of DNA amplification. The PCR-stop-RT-PCR assay was first carried out on gDNA isolated from normal and cancer cells that were either untreated or treated with a combination of Histone Deacetylase and Topo2 inhibitors. Our data indicate that the levels of DNA damage correlate with the levels of histone H2AX phosphorylation and are proportional to the efficiency of the drug combination as measured by survival assays. The potential clinical application of the assay was tested on PBMC of two leukemia patients treated with oral VorinostatSAHA (400 mg/day for three days). Our data indicate that Vorinostat increased the sensitivity of both patients PBMC to VP-16 by about 40%. One main advantage of this technique is that it uses small amounts of sample DNA (50-100 ng) to assess the efficiency of a particular drug or drug regimen. This assay could be used as a diagnostic tool for pre-clinical or clinical assessment of drug efficiency, evaluation of regimen suitability for a given patient and determination of optimal drug doses.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5498.

Abstract 1312: Functional significance for an hnRNP A18 signature RNA motif in the 3'UTR of Ataxia Telangiectasia and RAD3 related (ATR) transcript

The predominantly nuclear hnRNP A18 translocates to the cytosol in response to cellular stress and increases translation by specifically binding to the 3'untranslated region (UTR) of several mRNA transcripts and the eukaryotic Initiation Factor 4G. Here, we identified a 51 nucleotides motif that is present 11.49 times more often in the 3'UTR of hnRNP A18 mRNA targets than in the unigene data base. This motif was identified by computational analysis of primary sequences and secondary structures of hnRNP A18 mRNA targets against the unaligned sequences. Band shift analyses indicate that the motif is sufficient to confer binding to hnRNP A18. A search of the entire unigene data base indicates that the hnRNP A18 motif is also present in the 3'UTR of the Ataxia Telangiectasia and Rad3 related (ATR) mRNA. Validation of the predicted hnRNP A18 motif is provided by hnRNP A18 binding to ATR 3'UTR and amplification of endogenous ATR transcript on polysomal fractions immunoprecipitated with hnRNP A18 antibodies. Moreover, over expression of hnRNP A18 results in increased ATR protein levels and increased phosphorylation of Chk1, a preferred ATR substrate, in response to UV radiation. To our knowledge, this constitutes the first demonstration of a post-transcriptional regulatory mechanism for ATR activity. hnRNP A18 could thus become a new target to trigger ATR activity as back up stress-response mechanisms to functionally compensate for absent or defective genotoxic stress responders.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1312.

Functional significance for a heterogenous ribonucleoprotein A18 signature RNA motif in the 3'-untranslated region of ataxia telangiectasia mutated and Rad3-related (ATR) transcript

The predominantly nuclear heterogenous ribonucleoprotein A18 (hnRNP A18) translocates to the cytosol in response to cellular stress and increases translation by specifically binding to the 3'-untranslated region (UTR) of several mRNA transcripts and the eukaryotic initiation factor 4G. Here, we identified a 51-nucleotide motif that is present 11.49 times more often in the 3'-UTR of hnRNP A18 mRNA targets than in the UniGene data base. This motif was identified by computational analysis of primary sequences and secondary structures of hnRNP A18 mRNA targets against the unaligned sequences. Band shift analyses indicate that the motif is sufficient to confer binding to hnRNP A18. A search of the entire UniGene data base indicates that the hnRNP A18 motif is also present in the 3'-UTR of the ataxia telangiectasia mutated and Rad3-related (ATR) mRNA. Validation of the predicted hnRNP A18 motif is provided by amplification of endogenous ATR transcript on polysomal fractions immunoprecipitated with hnRNP A18. Moreover, overexpression of hnRNP A18 results in increased ATR protein levels and increased phosphorylation of Chk1, a preferred ATR substrate, in response to UV radiation. In addition, our data indicate that inhibition of casein kinase II or GSK3beta significantly reduced hnRNP A18 cytosolic translocation in response to UV radiation. To our knowledge, this constitutes the first demonstration of a post-transcriptional regulatory mechanism for ATR activity. hnRNP A18 could thus become a new target to trigger ATR activity as back-up stress response mechanisms to functionally compensate for absent or defective responders.

The Nucleolus Takes Control of Protein Trafficking Under Cellular Stress

The nucleolus is a highly dynamic nuclear substructure that was originally described as the site of ribosome biogenesis. The advent of proteomic analysis has now allowed the identification of over 4500 nucleolus associated proteins with only about 30% of them associated with ribogenesis (1). The great number of nucleolar proteins not associated with traditionally accepted nucleolar functions indicates a role for the nucleolus in other cellular functions such as mitosis, cell-cycle progression, cell proliferation and many forms of stress response including DNA repair (2). A number of recent reviews have addressed the pivotal role of the nucleolus in the cellular stress response (1, 3, 4). Here, we will focus on the role of Nucleolin and Nucleophosmin, two major components of the nucleolus, in response to genotoxic stress. Due to space constraint only a limited number of studies are cited. We thus apologize to all our colleagues whose works are not referenced here.

Over Expression of Nucleophosmin and Nucleolin Contributes to the Suboptimal Activation of a G2/M Checkpoint in Ataxia Telangiectasia Fibroblasts

Ataxia Telangiectasia (AT) cells exhibit suboptimal activation of radiation-induced cell cycle checkpoints despite having a wild type p53 genotype. Reducing or eliminating this delay could restore p53 function and reinstate normal cellular response to genotoxic stress. Here we show that the levels of Nuclephosmin (NPM), NPM phosphorylated at Serine 125, p53, p53 phosphorylated at Serine 15 and Serine 392 and the levels of Nucleolin (NCL) are high in AT fibroblasts compared to normal cells. Transfection of a functional ATM into AT fibroblasts reduced p53, phospo-p53, phospho-NPM and NCL levels to wild type fibroblasts levels. Our data indicate that ATM regulates phospho-NPM and NCL indirectly through the Protein Phosphatase 1 (PP1). Both, NPM and NCL interact with p53 and hinder its phosphorylation at Serine 15 in response to bleomycin. Moreover, NPM and NCL are phosphorylated by several of the same kinases targeting p53 and could potentially compete with p53 for phosphorylation in AT cells. In addition, our data indicate that down regulation of NCL and to a lesser extent NPM increase the number of AT cells arrested in G2/M in response to bleomycin. Together this data indicate that the lack of PP1 activation in AT cells result in increased NPM and NCL protein levels which prevents p53 phosphorylation in response to bleomycin and contributes to a defective G2/M checkpoint.

Nucleolin Binds to the Proliferating Cell Nuclear Antigen and Inhibits Nucleotide Excision Repair

Nucleolin is over-expressed in malignant tumors and is used as a marker for cell proliferation and to reliably predict tumor growth rate. However, it is not known whether nucleolin expression is directly involved in or is a consequence of carcinogenesis. Using GST-pull down assays, we have determined that the recombinant nucleolin interacts with the Proliferating Cell Nuclear Antigen (PCNA). Co-immunoprecipitation assays indicate that the nucleolin-PCNA interaction also occurs in intact cells and this interaction increases after exposure of colon carcinoma RKO cells to UV radiation. Moreover, our data indicate that PCNA and nucleolin co-localize in some areas within the RKO cell nuclei. The functional significance of this interaction is evaluated on Nucleotide Excision Repair (NER) since PCNA is a primary mediator of this cellular function. Our data indicate that overexpression of nucleolin decreases the repair efficiency of UV damaged plasmid DNA in RKO cells. Co-transfection with PCNA can rescue this effect in vivo. Furthermore, reduction of nucleolin protein levels increases DNA repair efficiency in RKO and CHO cells and consequently increases cell survival. These data indicate that the direct interaction of nucleolin with PCNA inhibits NER efficiency of UV damaged DNA. This effect could contribute to carcinogenesis and aging in cells over-expressing nucleolin.

Recognition of the tumor suppressor protein p53 and other protein targets by the calcium-binding protein S100B

S100B is an EF-hand containing calcium-binding protein of the S100 protein family that exerts its biological effect by binding and affecting various target proteins. A consensus sequence for S100B target proteins was published as (K/R)(L/I)xWxxIL and matches a region in the actin capping protein CapZ (V.V. Ivanenkov, G.A. Jamieson, Jr., E. Gruenstein, R.V. Dimlich, Characterization of S-100b binding epitopes. Identification of a novel target, the actin capping protein, CapZ, J. Biol. Chem. 270 (1995) 14651-14658). Several additional S100B targets are known including p53, a nuclear Dbf2 related (NDR) kinase, the RAGE receptor, neuromodulin, protein kinase C, and others. Examining the binding sites of such targets and new protein sequence searches provided additional potential target proteins for S100B including Hdm2 and Hdm4, which were both found to bind S100B in a calcium-dependent manner. The interaction between S100B and the Hdm2 and/or the Hdm4 proteins may be important physiologically in light of evidence that like Hdm2, S100B also contributes to lowering protein levels of the tumor suppressor protein, p53. For the S100B-p53 interaction, it was found that phosphorylation of specific serine and/or threonine residues reduces the affinity of the S100B-p53 interaction by as much as an order of magnitude, and is important for protecting p53 from S100B-dependent down-regulation, a scenario that is similar to what is found for the Hdm2-p53 complex.

Determination of the vertical distribution of radioelements (K, U, Th, Cs) in soils from portable HP-Ge spectrometer measurements: A tool for soil erosion studies

Soil erosion studies, based on the 137Cs technique, require a lot of time-consuming cores to determine soil loss or gain. We show that portable HP-Ge spectrometer can be used to determine the content and the distribution in the soil of natural and artificial radionuclides. Simulations of gamma-rays transport throughout the soil profile used a Monte Carlo code. The methodology requires a unique undisturbed coring site to build the models, calibrate the spectrometer readings and derive soil denudation or accumulation thickness.

Post-transcriptional regulation of thioredoxin by the stress inducible heterogenous ribonucleoprotein A18

Thioredoxin (TRX) is a key protein of the cellular redox metabolism, which expression is increased in several tumors especially gastric tumors. Even though ultraviolet (UV) and hypoxia specifically induce TRX, the mechanisms that lead to increased TRX levels are still ill defined. Here, we show that the heterogenous ribonucleoprotein A18 (hnRNP A18) RNA Binding Domain (RBD) and the arginine, glycine (RGG) rich domain can bind TRX 3′-untranslated region (3′-UTR) independently but both domains are required for maximal binding. Immunoprecipitation (IP) of hnRNP A18-mRNAs complexes and co-localization of hnRNP A18 and TRX transcripts on ribosomal fractions confirm the interaction of hnRNP A18 with TRX transcripts in cells. Moreover, down regulation of hnRNP A18 correlates with a significant reduction of TRX protein levels. In addition, hnRNP A18 increases TRX translation and interacts with the eukaryotic Initiation Factor 4G (eIF4G), a component of the general translational machinery. Furthermore, hnRNP A18 phosphorylation by the hypoxia inducible GSK3β increases hnRNP A18 RNA binding activity in vitro and in RKO cells in response to UV radiation. These data support a regulatory role for hnRNP A18 in TRX post-transcriptional expression possibly through a kissing loop model bridging TRX 3′- and 5′-UTRs through eIF4G.

Charon's size and an upper limit on its atmosphere from a stellar occultation

Pluto and its satellite, Charon (discovered in 1978; ref. 1), appear to form a double planet, rather than a hierarchical planet/satellite couple. Charon is about half Pluto's size and about one-eighth its mass. The precise radii of Pluto and Charon have remained uncertain, leading to large uncertainties on their densities. Although stellar occultations by Charon are in principle a powerful way of measuring its size, they are rare, as the satellite subtends less than 0.3 microradians (0.06 arcsec) on the sky. One occultation (in 1980) yielded a lower limit of 600 km for the satellite's radius, which was later refined to 601.5 km (ref. 4). Here we report observations from a multi-station stellar occultation by Charon, which we use to derive a radius, R(C) = 603.6 +/- 1.4 km (1sigma), and a density of rho = 1.71 +/- 0.08 g cm(-3). This occultation also provides upper limits of 110 and 15 (3sigma) nanobar for an atmosphere around Charon, assuming respectively a pure nitrogen or pure methane atmosphere.

Design of Inhibitors for S100B

S100B interacts with the p53 protein in a calcium-dependent manner and down-regulates its function as a tumor suppressor. Therefore, inhibiting the S100B-p53 interaction represents a new approach for restoring functional wild-type p53 in cancers with elevated S100B such as found in malignant melanoma. A discussion of the biological rational for targeting S100B and a description of methodologies relevant to the discovery of compounds that inhibit S100B-p53 binding, including computational techniques, structural biology techniques, and cellular assays, is presented.

Sensitization to UV-induced apoptosis by the histone deacetylase inhibitor trichostatin A (TSA)

UV-induced apoptosis is a protective mechanism that is primarily caused by DNA damage. Cyclobutane pyrimidine dimers (CPD) and 6-4 photoproducts are the main DNA adducts triggered by UV radiation. Because the formation of DNA lesions in the chromatin is modulated by the structure of the nucleosomes, we postulated that modification of chromatin compaction could affect the formation of the lesions and consequently apoptosis. To verify this possibility we treated human colon carcinoma RKO cells with the histone deacetylase inhibitor trichostatin A (TSA) prior to exposure to UV radiation. Our data show that pre-treatment with TSA increased UV killing efficiency by more than threefold. This effect correlated with increased formation of CPDs and consequently apoptosis. On the other hand, TSA treatment after UV exposure rather than before had no more effect than UV radiation alone. This suggests that a primed (opened) chromatin status is required to sensitize the cells. Moreover, TSA sensitization to UV-induced apoptosis is p53 dependent. p53 and acetylation of the core histones may thus contribute to UV-induced apoptosis by modulating the formation of DNA lesions on chromatin.

Identification and Characterization of Small Molecule Inhibitors of the Calcium-Dependent S100B−p53 Tumor Suppressor Interaction

The binding of S100B to p53 down-regulates wild-type p53 tumor suppressor activity in cancer cells such as malignant melanoma, so a search for small molecules that bind S100B and prevent S100B-p53 complex formation was undertaken. Chemical databases were computationally searched for potential inhibitors of S100B, and 60 compounds were selected for testing on the basis of energy scoring, commercial availability, and chemical similarity clustering. Seven of these compounds bound to S100B as determined by steady state fluorescence spectroscopy (1.0 microM < or = K(D) < or = 120 microM) and five inhibited the growth of primary malignant melanoma cells (C8146A) at comparable concentrations (1.0 microM < or = IC(50) < or = 50 microM). Additionally, saturation transfer difference (STD) NMR experiments confirmed binding and qualitatively identified protons from the small molecule at the small molecule-S100B interface. Heteronuclear single quantum coherence (HSQC) NMR titrations indicate that these compounds interact with the p53 binding site on S100B. An NMR-docked model of one such inhibitor, pentamidine, bound to Ca(2+)-loaded S100B was calculated using intermolecular NOE data between S100B and the drug, and indicates that pentamidine binds into the p53 binding site on S100B defined by helices 3 and 4 and loop 2 (termed the hinge region).