Aldo-keto reductase 1C3 may be a new radioresistance marker in non-small-cell lung cancer

Human aldo-keto reductase 1C3, type 2 3α-hydroxysteroid dehydrogenase (HSD)/type 5 17β-HSD (AKR1C3) is known to be involved in steroid, prostaglandin and lipid aldehyde metabolism. The role of AKR1C3 in the radiosensitivity to X-rays of human non-small-cell lung cancer (NSCLC) cells was explored. In this study, a specific small interfering RNA (siRNA) to target the AKR1C3 gene was used. A suite of readouts including cell survival were determined using a colony formation assay; apoptosis evaluated by Annexin V expression levels, irradiation-induced cytotoxicity established using a MTT cell viability assay and cell cycle distribution measured by flow cytometry were used in characterizing the role of the AKR1C3 gene. Although AKR1C3 was significantly overexpressed in both our radioresistant subclone cells and NSCLC tissues, a specific AKR1C3 siRNA significantly enhanced cell radiosensitivity and was concomitant with decreased expression of this gene. Furthermore, reduced interleukin-6 (IL-6)-mediated radioresistance was observed when siRNA was used to knock down AKR1C3 activity. This AKR1C3-mediated radioresistance was correlated with an arrest in the G2/M cell cycle and a decreased induction of apoptosis. AKR1C3 may present a potential therapeutic target in addressing radioresistance of NSCLC, and in particular in IL-6-mediated radioresistance.

Administration of PLGA nanoparticles carrying shRNA against focal adhesion kinase and CD44 results in enhanced antitumor effects against ovarian cancer

The two membrane-bound proteins, focal adhesion kinase (FAK) and CD44, are involved in processes critical to cancer progression. FAK has an active role in angiogenesis, cell proliferation and cell apoptosis, whereas the heavily glycosylated CD44 has been implicated in cancer metastasis. Here, using short hairpin RNA (shRNA) against FAK and CD44, we demonstrate that simultaneous knockdown of both these genes inhibits cancer growth more efficiently than knockdown of either gene individually. Plasmids targeting these genes or non-relative control sequences were constructed and delivered to ovarian cancer targets by biodegradable poly D,L-lactide-co-glycolide acid nanoparticles (PLGANPs). Nude mice were utilized in an intraperitoneal model of ovarian carcinomatosis to assess antitumor efficacy in vivo. Single gene knockdown resulted in significantly smaller tumors than those observed in the empty-vector control (P's<0.001). More importantly, knockdown of both genes resulted in tumors smaller than both the empty-vector group (P<0.0001) and the single gene knockdown groups (P's<0.001). Knockdown of both FAK and CD44 resulted in tumors with inhibited angiogenesis, reduced proliferation and increased apoptosis as compared with controls (P's<0.001) and single knockdown groups (P's<0.05). These results indicate that dual knockdown of FAK and CD44 in the tumors of patients with ovarian cancer may have an enhanced therapeutic effect, and point toward a mechanism involving the inhibition of angiogenesis, cellular proliferation and the induction of apoptosis.

ANXA2 remodels the microstructures of caco2 cells

ANXA2 was reported as a multiple tumors relevant gene expressed excessively in many tumor tissue types, especially in the cancers from digestion system, and its aberrant expression enhances the malignant properties of cancer cells. We suppose that the microstructure heterogeneity is important to maintain the malignancy of cancer cells, and excessive ANXA2 expression enhance the malignancy by remodeling the microstructures of cancer cells. To validate the proposal, the ANXA2-/-caco2 cell line was generated and the changes of the microstructures in the ANXA2 deleted and wild type caco2 cells were observed under fluorescence microscope, laser scanning confocal microscope and electron microscope. We found that ANXA2 deletion induced the pseudopodia shorted and spared, non-stained areas increased, mitochondria decreased, and the expression and polymerization of F-actin and β-tubulin changed. By the findings above, it is firstly reported in this paper that the ANXA2 excessive expression induces the significant changes of the microstructures in cancer cells. Combining our previous data together, our results indicate that ANXA2 excessive expression enhances the malignancy of cancers partially by remodeling the cell microstructures.

Antiviral activity and mode of action of extracts from neem seed kernel against duck plague virus in vitro1

Four fractions obtained from alcohol extracts of neem (Azadirachta indica) seed kernel by column chromatography were investigated for antivirus activity against the duck plague virus (DPV) in vitro. Duck embryo fibroblasts (DEF) infected with DPV were treated with the neem seed kernel extracts, and the effect of antivirus was judged by 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide colorimetric method assay and direct immunofluorescence assay. The mode of action was tested by the plaque reduction assay. The results showed that fractions 1 to 3 were inactive. The median inhibitory concentration (IC(50)) of fraction 4 was 10.9 μg/mL and inhibited the virus protein expression in the direct immunofluorescence assay. In the plaque reduction assay, fraction 4 could significantly reduce the number of plaques compared with the negative control (P < 0.01) in all modes of action. This study indicated that the fourth fraction obtained from neem seed kernel could improve the viability of infected cells, and reduce the cytopathic effects caused by DPV and the amount of the virus protein expressed in virus-infected cells. The antiviral activity works in the whole process of virus infecting the normal cells.

Abstract P2-11-10: Prospective memory impairment in early breast cancer survivors: Finally homing in on the real deficit?

Background There is still much debate about the impact of early breast cancer (EBC) treatment on memory functioning. One limitation of existing studies is that they are based on neuropsychological testing procedures which may not be sensitive enough to detect memory problems as encountered in daily life. In fact, no study has objectively assessed everyday memory performance in EBC. One crucial aspect of using memory in daily activities is to remember to do something at an appropriate time in the future without being asked to do so-defined as “prospective memory” (PM). Despite its importance for daily functioning, little is known about PM in EBC patients. Thus, we investigated whether EBC survivors who were within 1 year of having completed adjuvant chemotherapy have PM impairment in comparison to age-matched healthy controls. In addition, we evaluated the contributions of fatigue and depression to PM functioning.

Methods We undertook a cross sectional quantitative case-control study (n = 80) comparing EBC patients from the Ottawa Hospital Regional Cancer Centre with age and education-matched healthy controls from the community. A standardized test of PM (Memory for Intention Screening Test) was administered to both groups. Impairment was defined as a score that fell 2 standard deviations below the mean performance of the control group. Standardized measures of depression (CESD) and fatigue (Fact-F) were also completed.

Results Age was well balanced between the groups (case and control mean age 54y, p = .84). EBC patients performed more poorly than controls on the PM test (p &lt; .001) and had a significantly higher rate of impairment (23% vs. 5%, McNemar χ2, p &lt;.01, odds ratio=5.5, 95% CI=1.7745 to 17.1473). A series of hierarchical regressions showed that patients PM performance was affected by fatigue (p &lt;.05), but not depression (p = .51).

Conclusions The results demonstrate reduced memory performance in EBC survivors, with a specific impact on PM. Women who complain of ‘chemo fog’ should be evaluated carefully for PM deficits and their concerns should be acknowledged. An important finding from this study is the demonstration that fatigue is associated with memory deficits when memory as used in everyday life is evaluated. This finding which is suggestive of a common mechanism involved in fatigue symptoms and everyday memory disturbances raises the possibility that interventions targeted at improving fatigue may also improve memory functioning and quality of life in EBC survivors. Further longitudinal studies should be conducted to critically evaluate the role of chemotherapy by assessing PM before the initiation of chemotherapy and in EBC patients receiving only adjuvant hormonal therapy.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-11-10.

Abstract P3-04-11: Systemic treatment decision making for patients with stage I and II, hormone receptor positive, her2/neu negative breast cancer

Background: Oncotype DX is a clinically validated risk stratification tool that can predict the risk of recurrence and the benefit of adjuvant chemotherapy in women with hormone receptor positive (HR+), HER2/neu negative early stage breast cancer (EBC). This tool has been available to oncologists in Ontario since April 2010 at significant cost, yet no guidelines exist regarding their use. This retrospective chart review examined the factors that were associated with use of Oncotype DX at a tertiary care cancer centre.

Materials and methods: One hundred patients (pts) diagnosed with HR+, HER2/neu negative EBC (stage I-II), who underwent Oncotype DX testing between April 1, 2010, and June 30, 2011 were included in the study. A second control group of 100 patients with similar disease characteristics but who did not receive Oncotype DX testing were randomly selected. Data collection included demographics, tumor grade and stage, and Adjuvant! Online recurrence risk scores. The distribution of patients in each category was compared using the chi-square test to detect statistically significant differences between distributions.

Results: Median age in the Oncotype DX group was 58 years (r: 26–77) and 63 years (r: 30–81) in the control group. 20 patients in the Oncotype DX group were aged 35–49, 57 patients were aged 50–64, and 23 patients were aged 65 or older, while the control group had 16, 43, and 41 patients, respectively (p = 0.02). The Oncotype DX group had 72 pre- and perimenopausal pts and 28 postmenopausal patients, while the control group had 81 and 19 patients, respectively (p = 0.13). 20, 56, and 24 pts in the Oncotype DX group had grade 1, 2, and 3 histology, respectively, vs. 44, 44, and 12, respectively in the control group (p &lt; 0.01). The Oncotype DX group had 7 patients with tumors between 1–10 mm, 55 between 10.1–20 mm, 34 between 20.1–50 mm, and 4 greater than 50 mm, vs. 29, 42, 23, and 1, respectively in the control group (p &lt; 0.01). When 10-year Adjuvant Online recurrence scores were calculated using tamoxifen, 17, 67, and 16 patients in the Oncotype DX group had risk scores of &lt;15, 15–25, and &gt;25, respectively, vs. 62, 33, and 5 in the control group (p &lt; 0.01). When the scores were calculated using tamoxifen plus an aromatase inhibitor, 49, 42, and 9 patients in the Oncotype DX group, and 75, 24, and 1 patients in the control group fell into these categories, respectively (p &lt; 0.01). Median Oncotype DX recurrence score was 17 (r: 0–70), with 10-year recurrence risk of 11% (r:3–34%).

Conclusions: This single-centre series is aimed at identifying potential clinical and pathological factors which can influence physicians' decision to request Oncotype DX testing for pts with EBC. Physicians were more likely to request Oncotype DX testing for patients that were younger, had larger and higher grade tumors, and higher Adjuvant! Online recurrence risk scores. These results will be used to design a prospective study evaluating these factors and how Oncotype DX testing may influence treatment decision making.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P3-04-11.

Abstract P5-01-01: Predicting OncoDX Recurrence Scores with Immunohistochemical Markers

Background: Standard immunohistochemistry (IHC) performed for invasive breast carcinoma includes ER, PR and Her2/Neu status, and these markers are used in conjunction with other patient and tumour factors to determine prognosis and guide treatment. Many, but not all, low stage, lymph node (LN) negative, ER positive patients have a good prognosis without chemotherapy. Thus a demand exists for predictive tools to stratify patient risk within this subgroup. It has been reported that, for a subset of ER positive Her2/Neu negative patients, the 21 gene OncotypeDX recurrence score (Onco-RS) adds independent prognostic information to that obtained from these standard IHC markers (1). As several genes analyzed for the Onco-RS relate to ER, PR, HER2/neu and proliferative status, it is reasonable to try to incorporate clinical-pathological variables and these IHC scores into a predictive model. Indeed, recent studies suggest that most of the additional information provided by the OncoDX-RS may be obtained more cost effectively using the Ki-67 IHC based proliferation percentage combined with a semi-quantitative assessment of standard IHC markers including ER and PR and Her2/neu (2). The aim of this study is to assess the ability of a simple combined IHC recurrence score (IHC-RS) to predict Onco-RS. The IHC-RS was derived from a simple semi-quantitative assessment of ER and PR combined with Ki-67 proliferation percentage.

Design: A cohort of 159 women aged 27–78 with ER positive, HER2/neu negative breast cancer completed Oncodx testing between March 2010 and May 2012. This sample reflects the population selected at our institution for Oncotype testing. The variables investigated for inclusion in a model to predict RS score included tumor grade, stage, patient age, Allred ER & PR and Ki-67 percentage.

Results and Discussion: A predictive model was developed to generate a recurrence score (IHC-RS) using stepwise multiple regression incorporating Allred ER score, Allred PR score and Ki-67 percentage. The best subset model (Schwartz BIC) accounted for 60.7% of the Onco-RS variability (adjusted R2 = 60.7, p = 0.05).

In addition, analysis of individual cases where the IHC-RS was not in agreement with the Onco-RS reveals that the Onco-RS, although technically highly reproducible, may suffer from sampling error. The IHC-RS is more robust with respect to sampling error, owing to the retention of tumor architecture inherent in IHC. IHC, however, can lack the technical reproducibility and transportability inherent in the Onco-RS methodology. There are clearly advantages to an ICH derived multi-score such as IHC-4 (3) or the simpler IHC-RS proposed in this study. Full utility of any IHC-based recurrence score will require standardization of testing and scoring both within and across different testing laboratories. In addition, full utility of any IHC based model will require direct correlation to patient outcome, rather than to a surrogate marker such as the Onco-RS used in this study.

1. M Dowsett et al. J Clin Oncol. 2010 Apr 10; 1829–1834 2. Cuzick J et al. J Clin Oncol. 2011 Nov 10;4273-8. 3. S Barton et al. British Journal of Cancer (2012) 106, 1760–1765.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-01-01.

Abstract P3-13-05: Evaluating efficacy of de-escalated bisphosphonate therapy in metastatic breast cancer patients at low-risk of skeletal related events. TRIUMPH: A pragmatic multicentre trial

Background: Optimal bisphosphonate (BP) dosing intervals for breast cancer patients (pts) with bone metastases (BM) remain unknown. BP are usually prescribed q3-4 wk regardless of individual pt risk for skeletal related events (SREs). Recent evidence (Amadori J Clin Oncol, 2012 suppl; abstr 9005) shows that q12 wk BP is as effective as q4 wk in pts previously treated with &gt;9 cycles of q4 wk therapy. Hence, further evaluation of modified BP dosing strategies is warranted. The objective of the current study was to show in women with biochemically defined low-risk bone disease that IV BP use every q12 wk for 1 year is sufficient to maintain stability of the bone turnover [measured by serum c-telopeptide (CTx) or bone specific alkaline phosphatase (BSAP)].

Methods: Eligible pts with BM, who had received &gt;3 months of q3-4 wk IV BP and no systemic treatment change within 4 wks of study entry were enrolled. Low risk was defined as serum CTx &lt;600 ng/L. Biochemical failure was defined as CTx levels &gt;600 ng/L at baseline, weeks 6, 12, 24, 36 or 48. Evaluation of palliative benefit of 12-wk IV BP therapy was measured by SREs, analgesic use, and self-reported pain (BPI and FACT-BP).

Results: Between Oct. 2010-Sept. 2011, 85 pts consented to screening, with 13 found ineligible. In the 71 accrued pts baseline characteristics were: mean age 60 (SD 13), median time from breast cancer diagnosis to development of bone metastases 4 months (IQR 82), median duration of prior BP therapy 14 months (IQR 19), and mean number of SREs/yr prior to entering study 0.35 (SD 0.76). Baseline median CTx was 120 ng/L (IQR 240) and BSAP 9.2 IU/L (IQR 3). To date: 26/71 pts (36%) remain on study. Reasons for coming off study include; study completion (18), elevation of CTx &gt;600ng/L (10), or on study SRE (3). An elevation of CTx between baseline and wk 6 was significantly associated with coming off study early (p = 0.008). For pts who had had an SRE before study entry the odds ratios for coming off study early due to an on study SRE or elevated CTx was 1.005 (CI 1.002–1.009; p = 0.007) and for coming off early for an SRE was 0.0245 (CI 0.061–0.094; p = 0.046) respectively. Of the 8/13 pts who were ineligible due to baseline CTx &gt;600ng/L, 6 had an SRE within 1 year of screening.

Conclusion: De-escalating BP therapy to 12 weekly in low risk pts has advantages for both the pt and the health care system. Individual risk of SREs is highly variable, however baseline serum CTx levels &lt;600 ng/L is associated with a low risk of subsequent SREs. While larger trials are required to assess whether increasing CTx with de-escalated therapy will lead to higher rates of SREs or not (Coleman et al. J Clin Oncol 2012 suppl; abstr 511). However, the results of this study and Amadori et al. would suggest that de-escalated BP treatment will likely become a new standard of care after a limited period of q 4wk treatment.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P3-13-05.

Mitochondrial bioenergetic deficits in the hippocampi of rats with chronic ischemia-induced vascular dementia

Vascular dementia (VD), defined as a loss of memory and cognitive function resulting from vascular lesions in the brain, is the second-most-common cause of dementia in the elderly, after Alzheimer's disease. In recent years, research has focused on the pathogenesis of VD, and mitochondrial bioenergetic deficits have been suggested to contribute to VD onset. To further investigate the role of mitochondria in VD, we used a rat model of VD, which involved permanent bilateral occlusion of the common carotid arteries (with a 1-week interval between artery occlusion to avoid an abrupt reduction in cerebral blood flow) leading to chronic cerebral hypoperfusion. Prior to occlusion, male Wistar rats underwent 7 days of Morris water maze training. Only animals that could swim and passed the Morris water maze test were chosen for the study. After 5 days of Morris water maze training, mitochondria from the hippocampi of rats, which were randomly selected from animals that could complete the Morris water maze test, were isolated for functional assessment. Mitochondria isolated from the hippocampi of rats from the ischemia group had decreased pyruvate dehydrogenase protein levels, and increased oxidative stress, as manifested by increased hydrogen peroxide production. The ischemia group mitochondria also exhibited decreased respiration coupled to decreased expression and activity of the electron transport chain complex IV (cytochrome c oxidase). These results indicate that the mitochondrial oxidative metabolism is inhibited in the hippocampi of rats following chronic ischemia-induced VD. As the mitochondrial oxidative metabolism deficits, namely mitochondrial bioenergetic deficits directly affect the functions of neurons, it may contribute to VD onset.

Continuity clinics in oncology training programs in Canada

PURPOSE

Continuity clinics (ccs) give trainees an opportunity for longitudinal follow-up of a patient cohort. Trainees can function in a semi-autonomous manner and prepare for independent practice. Data about such clinics in Canada are limited. Our objective was to assess the utility of ccs in Canadian oncology training programs.

METHODS

Surveys were developed by the authors for medical and radiation oncology program directors (pds) and trainees, to assess the utility of ccs in Canadian oncology training programs.oncology patients, to assess their attitudes toward ccs. The pds were contacted by e-mail, using the Web site of the Canadian Resident Matching Service; the trainees were contacted by e-mail through the pds and their administrative assistants. Surveys were distributed electronically using SurveyMonkey. Patients were approached by staff oncologists during follow-up visits at The Ottawa Hospital Cancer Centre.

RESULTS

Completed surveys were received from 33% of trainees and 63% of pds contacted; patient surveys were completed by 95 patients. Participation in a cc was reported by 47% of responding pds and 37% of responding trainees. Among respondents, 80% rated the ccs as "important" or "very important" to training. The biggest challenge identified by trainees and pds was lack of clinic space. Most pds (57%) and trainees (59%) felt that the staff oncologist should review the patient only if the trainee has concerns, but only 37% of patients shared that view (p = 0.0002). However, many patients expressed the desire to participate in trainee education.

CONCLUSIONS

Continuity clinics are considered beneficial by pds and trainees. Patients desire more trainee supervision than the trainees themselves and the pds do, a factor that should be considered when implementing a cc.

Diabetes self-risk assessment questionnaires coupled with a multimedia health promotion campaign are cheap and effective tools to increase public awareness of diabetes in a large Chinese population

AIMS

To evaluate costs and effectiveness of implementing a diabetes self-risk assessment (Diabetes Risk Score) questionnaire coupled with a multimedia health promotion campaign on changes in diabetes awareness in a large diabetes prevention programme.

METHODS

Between 2007 and 2010, a multimedia health promotion campaign was conducted targeting the 1.94 million population of Qingdao, China, using newspapers, radio programmes, distribution of free booklets and Diabetes Risk Score flyers. Diabetes awareness questionnaires filled out by people first interviewed in 2006 (survey A), before the initiation of the campaign, were compared with those first interviewed between 2007 and 2010 during the campaign period (survey B). The rates of diabetes awareness in both surveys were studied amongst adults aged 35-74 years without a prior history of diabetes, but with a Diabetes Risk Score of ≥ 14.

RESULTS

In survey B, 85, 82 and 76% of the urban participants correctly recognized obesity, family history of diabetes and physical inactivity, respectively, as important risk factors for diabetes; while the awareness rates were 43, 46 and 25%, respectively, in survey A (P < 0.001). The corresponding figures among rural participants were 65, 63 and 53% in survey B and 29, 22 and 11% in survey A (P < 0.001). To cover 1000 individuals, the programme spent €5.4 on the use of the Diabetes Risk Score flyer, €31.3 on the education booklet, €7.7 on the newspaper campaign and €37.5 on radio programmes.

CONCLUSIONS

The combination of a Diabetes Risk Score questionnaire with a multimedia health promotion campaign is a cheap and effective health promotion tool to raise public awareness of diabetes.

Frailty in relation to the risk of falls, fractures, and mortality in older Chinese adults: results from the Beijing Longitudinal Study of Aging

OBJECTIVES

Falls are well known to be associated with adverse health outcomes, especially when complicated by fracture. Falls are more common in people who are frail and readily related to several items in the frailty phenotype. Less is known about the relationship between falls and frailty defined as deficit accumulation. Our objective was to investigate the relationship between falls, fractures, and frailty based on deficit accumulation.

DESIGN

Representative cohort study, with 8 year follow-up.

SETTING

The Beijing Longitudinal Study of Aging (BLSA).

PARTICIPANTS

3,257 Chinese people aged 55+ years at baseline.

MEASUREMENTS

A frailty index (FI) was constructed using 33 health deficits, but excluding falls and fractures. The rates of falls, fractures and death as a function of age and the FI were analyzed. Multivariable models evaluated the relationships between frailty and the risk of recurrent falls, fractures, and mortality adjusting for age, sex, and education. Self or informant reported fall and fracture data were verified against participants' health records.

RESULTS

Of 3,257 participants at baseline (1992), 360 people (11.1%) reported a history of falls, and 238 (7.3%) reported fractures. By eight years, 1,155 people had died (35.3%). The FI was associated with an increased risk of recurrent falls (OR=1.54; 95% confidence interval (CI)=1.34-1.76), fractures (OR=1.07; 95% CI=0.94-1.22), and death (OR=1.50, 95% CI=1.41-1.60). The FI showed a significant effect on mortality in a multivariate Cox regression model (Hazard Rate=1.29, 95% CI=1.25-1.33). When adjusted for the FI, neither falls nor fractures were associated with mortality.

CONCLUSION

Falls and fractures were common in older Chinese adults, and associated with frailty. Only frailty was independently associated with death.

Anti-DLL4 has broad spectrum activity in pancreatic cancer dependent on targeting DLL4-Notch signaling in both tumor and vasculature cells

PURPOSE

We previously showed that targeting Delta-like ligand 4 (DLL4) in colon and breast tumors inhibited tumor growth and reduced tumor initiating cell frequency. In this report, we have extended these studies to pancreatic cancer and probed the mechanism of action in tumor and stromal cells involved in antitumor efficacy.

EXPERIMENTAL DESIGN

Patient-derived pancreatic xenograft tumor models were used to evaluate the antitumor effect of anti-DLL4. To investigate the mechanism of action, we compared the activity of targeting DLL4 in tumor cells with an anti-human DLL4 antibody (anti-hDLL4) and in the host stroma/vasculature with an anti-mouse DLL4 antibody (anti-mDLL4). The effect of these antibodies on cancer stem cell frequency was examined by in vivo limiting dilution assays.

RESULTS

The combination of anti-hDLL4 and anti-mDLL4 was efficacious in a broad spectrum of pancreatic tumor xenografts and showed additive antitumor activity together with gemcitabine. Treatment with either anti-hDLL4 or anti-mDLL4 delayed pancreatic tumor recurrence following termination of gemcitabine treatment, and the two together produced an additive effect. Anti-hDLL4 had a pronounced effect in reducing the tumorigenicity of pancreatic cancer cells based on serial transplantation and tumorsphere assays. In contrast, disruption of tumor angiogenesis with anti-mDLL4 alone or with anti-VEGF had minimal effects on tumorigenicity. Gene expression analyses indicated that anti-DLL4 treatment regulated genes that participate in Notch signaling, pancreatic differentiation, and epithelial-to-mesenchymal transition.

CONCLUSIONS

Our findings suggest a novel therapeutic approach for pancreatic cancer treatment through antagonism of DLL4/Notch signaling.

Basic anatomy and tumor biology of the RPS6KA6 gene that encodes the p90 ribosomal S6 kinase-4

The RPS6KA6 gene encodes the p90 ribosomal S6 kinase-4 (RSK4) that is still largely uncharacterized. In this study we identified a new RSK4 transcription initiation site and several alternative splice sites with a 5’RACE approach. The resulting mRNA variants encompass four possible first start codons. The first 15 nucleotides (nt) of exon 22 in mouse and the penultimate exon in both human (exon 21) and mouse (exon 24) RSK4 underwent alternative splicing, although the penultimate exon deleted variant appeared mainly in cell clines, but not in most normal tissues. Demethylation agent 5-azacytidine inhibited the deletion of the penultimate exon whereas two indolocarbazole-derived inhibitors of cyclin dependent kinase 4 or 6 induced deletion of the first 39 nt from exon 21 of human RSK4. In all human cancer cell lines studied, the 90-kD wild type RSK4 was sparse but, surprisingly, several isoforms at or smaller than 72-kD were expressed as detected by seven different antibodies. On immunoblots, each of these smaller isoforms often appeared as a duplet or triplet and the levels of these isoforms varied greatly among different cell lines and culture conditions. Cyclin D1 inhibited RSK4 expression and serum starvation enhanced the inhibition, whereas c-Myc and RSK4 inhibited cyclin D1. The effects of RSK4 on cell growth, cell death and chemoresponse depended on the mRNA variant or the protein isoform expressed, on the specificity of the cell lines, as well as on the anchorage-dependent or -independent growth conditions and the in vivo situation. Moreover, we also observed that even a given cDNA might be expressed to multiple proteins; therefore, when using a cDNA, one needs to exclude this possibility before attribution of the biological results from the cDNA to the anticipated protein. Collectively, our results suggest that whether RSK4 is oncogenic or tumor suppressive depends on many factors.