Harnessing the Potential of Real-World Evidence in the Treatment of Colorectal Cancer: Where Do We Stand?

OPINION STATEMENT

Treatment guidelines for colorectal cancer (CRC) are primarily based on the results of randomized clinical trials (RCTs), the gold standard methodology to evaluate safety and efficacy of oncological treatments. However, generalizability of trial results is often limited due to stringent eligibility criteria, underrepresentation of specific populations, and more heterogeneity in clinical practice. This may result in an efficacy-effectiveness gap and uncertainty regarding meaningful benefit versus treatment harm. Meanwhile, conduct of traditional RCTs has become increasingly challenging due to identification of a growing number of (small) molecular subtypes. These challenges-combined with the digitalization of health records-have led to growing interest in use of real-world data (RWD) to complement evidence from RCTs. RWD is used to evaluate epidemiological trends, quality of care, treatment effectiveness, long-term (rare) safety, and quality of life (QoL) measures. In addition, RWD is increasingly considered in decision-making by clinicians, regulators, and payers. In this narrative review, we elaborate on these applications in CRC, and provide illustrative examples. As long as the quality of RWD is safeguarded, ongoing developments, such as common data models, federated learning, and predictive modelling, will further unfold its potential. First, whenever possible, we recommend conducting pragmatic trials, such as registry-based RCTs, to optimize generalizability and answer clinical questions that are not addressed in registrational trials. Second, we argue that marketing approval should be conditional for patients who would have been ineligible for the registrational trial, awaiting planned (non) randomized evaluation of outcomes in the real world. Third, high-quality effectiveness results should be incorporated in treatment guidelines to aid in patient counseling. We believe that a coordinated effort from all stakeholders is essential to improve the quality of RWD, create a learning healthcare system with optimal use of trials and real-world evidence (RWE), and ultimately ensure personalized care for every CRC patient.

Lung Mean Dose Prediction in Transarterial Radioembolization (TARE): Superiority of [166Ho]-Scout Over [99mTc]MAA in a Prospective Cohort Study

PURPOSE

Radiation pneumonitis is a serious complication of radioembolization. In holmium-166 ([166Ho]) radioembolization, the lung mean dose (LMD) can be estimated (eLMD) using a scout dose with either technetium-99 m-macroaggregated albumin ([99mTc]MAA) or [166Ho]-microspheres. The accuracy of eLMD based on [99mTc]MAA (eLMDMAA) was compared to eLMD based on [166Ho]-scout dose (eLMDHo-scout) in two prospective clinical studies.

MATERIALS AND METHODS

Patients were included if they received both scout doses ([99mTc]MAA and [166Ho]-scout), had a posttreatment [166Ho]-SPECT/CT (gold standard) and were scanned on the same hybrid SPECT/CT system. The correlation between eLMDMAA/eLMDHo-scout and LMDHo-treatment was assessed by Spearman's rank correlation coefficient (r). Wilcoxon signed rank test was used to analyze paired data.

RESULTS

Thirty-seven patients with unresectable liver metastases were included. During follow-up, none developed symptoms of radiation pneumonitis. Median eLMDMAA (1.53 Gy, range 0.09-21.33 Gy) was significantly higher than median LMDHo-treatment (0.00 Gy, range 0.00-1.20 Gy; p < 0.01). Median eLMDHo-scout (median 0.00 Gy, range 0.00-1.21 Gy) was not significantly different compared to LMDHo-treatment (p > 0.05). In all cases, eLMDMAA was higher than LMDHo-treatment (p < 0.01). While a significant correlation was found between eLMDHo-scout and LMDHo-treatment (r = 0.43, p < 0.01), there was no correlation between eLMDMAA and LMDHo-treatment (r = 0.02, p = 0.90).

CONCLUSION

[166Ho]-scout dose is superior in predicting LMD over [99mTc]MAA, in [166Ho]-radioembolization. Consequently, [166Ho]-scout may limit unnecessary patient exclusions and avoid unnecessary therapeutic activity reductions in patients eligible for radioembolization.

TRAIL REGISTRATION

NCT01031784, registered December 2009. NCT01612325, registered June 2012.

Stromal localization of inactive CD8+ T cells in metastatic mismatch repair deficient colorectal cancer

BACKGROUND

The determinants of metastasis in mismatch repair deficiency with high levels of microsatellite instability (MSI-H) in colorectal cancer (CRC) are poorly understood. Here, we hypothesized that distinct immune and stromal microenvironments in primary tumors may discriminate between non-metastatic MSI-H CRC and metastatic MSI-H CRC.

METHODS

We profiled 46,727 single cells using high-plex imaging mass cytometry and analyzed both differential cell type abundance, and spatial distribution of fibroblasts and immune cells in primary CRC tumors with or without metastatic capacity. We validated our findings in a second independent cohort using immunohistochemistry.

RESULTS

High-plex imaging mass cytometry and hierarchical clustering based on microenvironmental markers separated primary MSI-H CRC tumors with and without metastatic capacity. Primary tumors with metastatic capacity displayed a high stromal content and low influx of CD8+ T cells, which expressed significantly lower levels of markers reflecting proliferation (Ki67) and antigen-experience (CD45RO) compared to CD8+ T cells in non-metastatic tumors. CD8+ T cells showed intra-epithelial localization in non-metastatic tumors, but stromal localization in metastatic tumors, which was validated in a second cohort.

CONCLUSION

We conclude that localization of phenotypically distinct CD8+ T cells within stroma may predict metastasis formation in MSI-H CRC.

Comparison of NTRK fusion detection methods in microsatellite-instability-high metastatic colorectal cancer

Tropomyosin receptor kinase (TRK) inhibitors have been approved for metastatic solid tumors harboring NTRK fusions, but the detection of NTRK fusions is challenging. International guidelines recommend pan-TRK immunohistochemistry (IHC) screening followed by next generation sequencing (NGS) in tumor types with low prevalence of NTRK fusions, including metastatic colorectal cancer (mCRC). RNA-based NGS is preferred, but is expensive, time-consuming, and extracting good-quality RNA from FFPE tissue is challenging. Alternatives in daily clinical practice are warranted. We assessed the diagnostic performance of RNA-NGS, FFPE-targeted locus capture (FFPE-TLC), fluorescence in situ hybridization (FISH), and the 5'/3' imbalance quantitative RT-PCR (qRT-PCR) after IHC screening in 268 patients with microsatellite-instability-high mCRC, the subgroup in which NTRK fusions are most prevalent (1-5%). A consensus result was determined after review of all assay results. In 16 IHC positive tumors, 10 NTRK fusions were detected. In 33 IHC negative samples, no additional transcribed NTRK fusions were found, underscoring the high sensitivity of IHC. Sensitivity of RNA-NGS, FFPE-TLC, FISH, and qRT-PCR was 90%, 90%, 78%, and 100%, respectively. Specificity was 100% for all assays. Robustness, defined as the percentage of samples that provided an interpretable result in the first run, was 100% for FFPE-TLC, yet more limited for RNA-NGS (85%), FISH (70%), and qRT-PCR (70%). Overall, we do not recommend FISH for the detection of NTRK fusions in mCRC due to its low sensitivity and limited robustness. We conclude that RNA-NGS, FFPE-TLC, and qRT-PCR are appropriate assays for NTRK fusion detection, after enrichment with pan-TRK IHC, in routine clinical practice.

Trends in Use and Perceptions About Triplet Chemotherapy Plus Bevacizumab for Metastatic Colorectal Cancer

Importance

Triplet chemotherapy with fluorouracil, folinic acid, oxaliplatin, and irinotecan plus bevacizumab (FOLFOXIRI-B) is an effective first-line treatment option for patients with metastatic colorectal cancer (mCRC). However, the degree of implementation of FOLFOXIRI-B in daily practice is unknown.

Objectives

To evaluate the current adoption rate of FOLFOXIRI-B in patients with mCRC and investigate the perspectives of medical oncologists toward this treatment option.

Design, Setting, and Participants

This 1-week, multicenter, cross-sectional study in the Netherlands used a flash mob design, which facilitates ultrafast data generation (flash) through the engagement of numerous researchers (mob). During the study week (March 1-5, 2021), patient data were retrieved from electronic health records of 47 hospitals on patients with mCRC who were referred to a medical oncologist between November 1, 2020, and January 31, 2021. Interviews were simultaneously conducted with 101 medical oncologists from 52 hospitals who regularly treat patients with mCRC.

Exposure

First-line systemic treatment as determined by the treating physician.

Main Outcomes and Measures

The FOLFOXIRI-B prescription rate was the main outcome. Current practice was compared with prescription rates in 2015 to 2018. Eligibility for treatment with FOLFOXIRI-B was estimated. An exploratory outcome was medical oncologists' reported perspectives on FOLFOXIRI-B.

Results

A total of 5948 patients in the Netherlands (median age [interquartile range], 66 [57-73] years; 3503 [59%] male; and 3712 [62%] with left-sided or rectal tumor) were treated with first-line systemic therapy for synchronous mCRC. A total of 282 patients with mCRC underwent systemic therapy during the study period (2021). Of these 282 patients, 199 (71%) were treated with intensive first-line therapy other than FOLFOXIRI-B, of whom 184 (65%) were treated with oxaliplatin doublets with or without bevacizumab; 14 (5%) with irinotecan doublets with or without bevacizumab, panitumumab, or cetuximab; and 1 (0.4%) with irinotecan with bevacizumab. Fifty-four patients (19%) were treated with fluoropyrimidine monotherapy with or without bevacizumab, 1 patient (0.4%) with panitumumab monotherapy, and 3 (1%) with immune checkpoint inhibitors. In total, 25 patients (9%; 95% CI, 6%-12%) were treated with first-line FOLFOXIRI-B compared with 142 (2%; 95% CI, 2%-3%) in 2015 to 2018. During the study period, 21 of 157 eligible patients (13.4%) in the Netherlands were treated with FOLFOXIRI-B. A total of 87 medical oncologists (86%) reported discussing FOLFOXIRI-B as a treatment option with eligible patients. A total of 47 of 85 (55%) generally communicated a preference for a chemotherapy doublet to patients. These oncologists reported a significantly lower awareness of guidelines and trial results. Toxic effects were the most reported reason to prefer an alternative regimen.

Conclusions and Relevance

The findings of this study suggest that FOLFOXIRI-B prescription rates have marginally increased in the last 5 years. Considering that most medical oncologists discuss this treatment option, the prescription rate found in this study was below expectations. Awareness of guidelines and trial data seems to contribute to the discussion of available treatment options by medical oncologists, and the findings of this study suggest a need for repeated and continuing medical education.

Targeting RNA helicase DDX3 in stem cell maintenance and teratoma formation

DDX3 is an RNA helicase that has antiapoptotic properties, and promotes proliferation and transformation. Besides the role of DDX3 in transformed cells, there is evidence to indicate that DDX3 expression is at its highest levels during early embryonic development and is also expressed in germ cells of adults. Even though there is a distinct pattern of DDX3 expression during embryonic development and in adults, very little is known regarding its role in embryonic stem cells and pluripotency. In this work, we examined the relationship between DDX3 and human embryonic stem cells and its differentiated lineages. DDX3 expression was analyzed by immunohistochemistry in human embryonic stem cells and embryonal carcinoma cells. From the data obtained, it was evident that DDX3 was overexpressed in undifferentiated stem cells compared to differentiated cells. Moreover, when DDX3 expression was abrogated in multiple stem cells, proliferation was decreased, but differentiation was facilitated. Importantly, this resulted in reduced potency to induce teratoma formation. Taken together, these findings indicate a distinct role for DDX3 in stem cell maintenance.

Nuclear DDX3 expression predicts poor outcome in colorectal and breast cancer

Purpose

DEAD box protein 3 (DDX3) is an RNA helicase with oncogenic properties that shuttles between the cytoplasm and nucleus. The majority of DDX3 is found in the cytoplasm, but a subset of tumors has distinct nuclear DDX3 localization of yet unknown biological significance. This study aimed to evaluate the significance of and mechanisms behind nuclear DDX3 expression in colorectal and breast cancer.

Methods

Expression of nuclear DDX3 and the nuclear exporter chromosome region maintenance 1 (CRM1) was evaluated by immunohistochemistry in 304 colorectal and 292 breast cancer patient samples. Correlations between the subcellular localization of DDX3 and CRM1 and the difference in overall survival between patients with and without nuclear DDX3 were studied. In addition, DDX3 mutants were created for in vitro evaluation of the mechanism behind nuclear retention of DDX3.

Results

DDX3 was present in the nucleus of 35% of colorectal and 48% of breast cancer patient samples and was particularly strong in the nucleolus. Nuclear DDX3 correlated with worse overall survival in both colorectal (hazard ratio [HR] 2.34, P<0.001) and breast cancer (HR 2.39, P=0.004) patients. Colorectal cancers with nuclear DDX3 expression more often had cytoplasmic expression of the nuclear exporter CRM1 (relative risk 1.67, P=0.04). In vitro analysis of DDX3 deletion mutants demonstrated that CRM1-mediated export was most dependent on the N-terminal nuclear export signal.

Conclusion

Overall, we conclude that nuclear DDX3 is partially CRM1-mediated and predicts worse survival in colorectal and breast cancer patients, putting it forward as a target for therapeutic intervention with DDX3 inhibitors under development in these cancer types.

Combination treatment using DDX3 and PARP inhibitors induces synthetic lethality in BRCA1-proficient breast cancer

Triple-negative breast cancers have unfavorable outcomes due to their inherent aggressive behavior and lack of targeted therapies. Breast cancers occurring in BRCA1 mutation carriers are mostly triple-negative and harbor homologous recombination deficiency, sensitizing them to inhibition of a second DNA damage repair pathway by, e.g., PARP inhibitors. Unfortunately, resistance against PARP inhibitors in BRCA1-deficient cancers is common and sensitivity is limited in BRCA1-proficient breast cancers. RK-33, an inhibitor of the RNA helicase DDX3, was previously demonstrated to impede non-homologous end-joining repair of DNA breaks. Consequently, we evaluated DDX3 as a therapeutic target in BRCA pro- and deficient breast cancers and assessed whether DDX3 inhibition could sensitize cells to PARP inhibition. High DDX3 expression was identified by immunohistochemistry in breast cancer samples of 24% of BRCA1 (p = 0.337) and 21% of BRCA2 mutation carriers (p = 0.624), as compared to 30% of sporadic breast cancer samples. The sensitivity to the DDX3 inhibitor RK-33 was similar in BRCA1 pro- and deficient breast cancer cell lines, with IC50 values in the low micromolar range (2.8-6.6 μM). A synergistic interaction was observed for combination treatment with RK-33 and the PARP inhibitor olaparib in BRCA1-proficient breast cancer, with the mean combination index ranging from 0.59 to 0.62. Overall, we conclude that BRCA pro- and deficient breast cancers have a similar dependency upon DDX3. DDX3 inhibition by RK-33 synergizes with PARP inhibitor treatment, especially in breast cancers with a BRCA1-proficient background.

RK-33 Radiosensitizes Prostate Cancer Cells by Blocking the RNA Helicase DDX3

Despite advances in diagnosis and treatment, prostate cancer is the most prevalent cancer in males and the second highest cause of cancer-related mortality. We identified an RNA helicase gene, DDX3 (DDX3X), which is overexpressed in prostate cancers, and whose expression is directly correlated with high Gleason scores. Knockdown of DDX3 in the aggressive prostate cancer cell lines DU145 and 22Rv1 resulted in significantly reduced clonogenicity. To target DDX3, we rationally designed a small molecule, RK-33, which docks into the ATP-binding domain of DDX3. Functional studies indicated that RK-33 preferentially bound to DDX3 and perturbed its activity. RK-33 treatment of prostate cancer cell lines DU145, 22Rv1, and LNCaP (which have high DDX3 levels) decreased proliferation and induced a G₁ phase cell-cycle arrest. Conversely, the low DDX3-expressing cell line, PC3, exhibited few changes following RK-33 treatment. Importantly, combination studies using RK-33 and radiation exhibited synergistic effects both in vitro and in a xenograft model of prostate cancer demonstrating the role of RK-33 as a radiosensitizer. Taken together, these results indicate that blocking DDX3 by RK-33 in combination with radiation treatment is a viable option for treating locally advanced prostate cancer. Cancer Res; 76(21); 6340-50. ©2016 AACR.

Targeting DDX3 with a small molecule inhibitor for lung cancer therapy

Lung cancer is the most common malignancy worldwide and is a focus for developing targeted therapies due to its refractory nature to current treatment. We identified a RNA helicase, DDX3, which is overexpressed in many cancer types including lung cancer and is associated with lower survival in lung cancer patients. We designed a first-in-class small molecule inhibitor, RK-33, which binds to DDX3 and abrogates its activity. Inhibition of DDX3 by RK-33 caused G1 cell cycle arrest, induced apoptosis, and promoted radiation sensitization in DDX3-overexpressing cells. Importantly, RK-33 in combination with radiation induced tumor regression in multiple mouse models of lung cancer. Mechanistically, loss of DDX3 function either by shRNA or by RK-33 impaired Wnt signaling through disruption of the DDX3-β-catenin axis and inhibited non-homologous end joining-the major DNA repair pathway in mammalian somatic cells. Overall, inhibition of DDX3 by RK-33 promotes tumor regression, thus providing a compelling argument to develop DDX3 inhibitors for lung cancer therapy.

Abstract 3812: Targeting BRCA1-deficient breast cancer by inhibition of the DEAD box RNA helicase DDX3X

Introduction: The DEAD box RNA helicase DDX3X (DDX3) has been demonstrated to have a pro-oncogenic role in breast cancer. Thus, abrogating DDX3 activity was explored as a viable anti-cancer strategy using a small molecule inhibitor of DDX3, referred to as RK-33. RK-33 was found to inhibit non-homologous end joining (NHEJ), a DNA double strand break (DSB) repair mechanism. Therefore, we set out to determine the utility of RK-33 in breast cancers of BRCA1 mutation carriers, as they exhibit deficiencies in homologous recombination, an additional DSB repair mechanism. We hypothesized that BRCA1-deficient breast cancers would be more dependent on NHEJ to maintain genomic stability and thus inhibiting DDX3 activity by RK-33 would be an efficacious treatment strategy.

Methods: We evaluated DDX3 protein expression levels by immunohistochemistry in 102 BRCA1 and 29 BRCA2 germline mutation carriers and compared these to those of 345 sporadic breast cancer patients. In addition, DDX3 expression in two BRCA1-deficient (SUM149PT and HCC1937) and two BRCA1-proficient breast cancer cell lines (MCF-7 and MDA-MB-231) was quantified by immunoblotting. Furthermore, we compared the cell killing abilities of RK-33 in these BRCA1 pro- and deficient cell lines, as well as in MCF-7 cells before and after knockdown of BRCA1 by shRNA.

Results: High cytoplasmic DDX3 expression is less frequent in BRCA1 (24.5%) and BRCA2 (20.7%) related breast cancer, when compared to sporadic breast cancer (34.2%; OR 0.63; 95% CI 0.38-1.03; P = 0.065). This difference is statistically significant when correcting for higher grade and basal-like subtype in the group of BRCA1 mutation carriers (OR 0.33; 95% CI 0.14-0.77; P = 0.01). The BRCA1 pro- and deficient cell lines expressed similar levels of DDX3 and had a comparable sensitivity to RK-33 with IC-50 values ranging between 2 and 7 uM. Knockdown of BRCA1 in MCF-7 did not result in an increased sensitivity to RK-33.

Conclusion: DDX3 expression is lower in breast cancer in BRCA1 mutation carriers, when compared to sporadic breast cancers of similar grade and molecular subtype. BRCA1 pro- and deficient breast cancer cell lines are equally sensitive to inhibition of DDX3 by RK-33. This indicates that abrogating NHEJ activity by RK-33 results in cell death irrespective of additional deficiencies in the DNA repair pathway. Given that RK-33 showed good in vitro efficacy to kill all breast cancer cell lines, additional research is required to evaluate the use of RK-33 as a targeted chemotherapy agent for breast cancer.

Citation Format: Marise R. Heerma van Voss, Farhad Vesuna, Guus M. Bol, Paul J. van Diest, Venu Raman. Targeting BRCA1-deficient breast cancer by inhibition of the DEAD box RNA helicase DDX3X. [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 3812. doi:10.1158/1538-7445.AM2014-3812

Expression of the RNA helicase DDX3 and the hypoxia response in breast cancer

Aims

DDX3 is an RNA helicase that has antiapoptotic properties, and promotes proliferation and transformation. In addition, DDX3 was shown to be a direct downstream target of HIF-1α (the master regulatory of the hypoxia response) in breast cancer cell lines. However, the relation between DDX3 and hypoxia has not been addressed in human tumors. In this paper, we studied the relation between DDX3 and the hypoxic responsive proteins in human breast cancer.

Methods and Results

DDX3 expression was investigated by immunohistochemistry in breast cancer in comparison with hypoxia related proteins HIF-1α, GLUT1, CAIX, EGFR, HER2, Akt1, FOXO4, p53, ERα, COMMD1, FER kinase, PIN1, E-cadherin, p21, p27, Transferrin receptor, FOXO3A, c-Met and Notch1. DDX3 was overexpressed in 127 of 366 breast cancer patients, and was correlated with overexpression of HIF-1α and its downstream genes CAIX and GLUT1. Moreover, DDX3 expression correlated with hypoxia-related proteins EGFR, HER2, FOXO4, ERα and c-Met in a HIF-1α dependent fashion, and with COMMD1, FER kinase, Akt1, E-cadherin, TfR and FOXO3A independent of HIF-1α.

Conclusions

In invasive breast cancer, expression of DDX3 was correlated with overexpression of HIF-1α and many other hypoxia related proteins, pointing to a distinct role for DDX3 under hypoxic conditions and supporting the oncogenic role of DDX3 which could have clinical implication for current development of DDX3 inhibitors.

Epigenetic biomarkers in the diagnosis of ovarian cancer

INTRODUCTION

Current diagnostic methods for ovarian cancer have limited performance. Recent advances within the field of epigenetics have shifted the clinical implementation of epigenetic biomarkers as a diagnostic approach from a dream for the future to a present-day consideration. Patients could potentially benefit greatly from this novel diagnostic approach.

AREAS COVERED

Epigenetic mechanisms in cancer are discussed, with a focus on potential diagnostic epigenetic biomarkers in ovarian cancer in tissue and body fluids. A literature search was undertaken (on 22-09-2011) for these subjects using the search syntax ((((((((((((((("ovarian") OR "ovary") OR "ovarian cancer") OR "ovarian cancers") OR "cancer of the ovary") OR "tumour of the ovary") OR "ovarian tumor") OR "ovarian tumors") OR "ovarian tumour") OR "ovarian tumours") OR "ovarian neoplasm") OR "ovarian neoplasms" OR "ovarian carcinoma") OR "ovarian carcinomas") OR "carcinoma of the ovary")) AND ((((((((("epigenetics") OR "epigenetic") OR "epigenome") OR "methylation") OR "hypermethylation") OR "chromatin modification") OR "histone") OR "histones") OR "acetylation")

EXPERT OPINION

To date no single epigenetic biomarker is able to accurately detect early ovarian cancer in either tissue or body fluids. A panel of epigenetic biomarkers based on aberrant DNA methylation in body fluids, especially blood, has the best chance of being implemented in clinical practice, as it is semi-invasive. However, progression toward clinical use is hampered by the lack of detection techniques combining high throughput and accuracy with low cost, by difficulties in establishing reliable reference values and by the heterogeneous nature of ovarian cancer. Until addressed, implementation as a diagnostic measure complimenting current techniques in select cases seems a far way to go, and implementation as a primary screening tool is yet even farther away.

Abstract 5720: RK-33, a novel small molecule for lung cancer therapy via inhibition of NHEJ

Lung cancer is the leading cause of cancer mortality worldwide. More importantly, only about 30% of non-small-cell lung cancer patients respond to current combination therapy, which includes radiation and platinum based compounds. Currently, there are limited molecular targets that can be drugable for lung cancer treatment. Our investigation in cancer biogenesis has identified an RNA helicase, DDX3, being dysregulated in many cancer types including lung cancer. DDX3 is a member of the DEAD-box RNA helicase family and contributes to cancer by promoting proliferation, cell growth, transformation and inhibition of apoptosis. Importantly, knockdown of DDX3 in the highly aggressive lung cancer cell line, A549, abrogated its colony forming abilities. In our efforts to abrogate DDX3 functions in vivo, we synthesized a tricyclic 5:7:5-fused diimidazodiazepine ring (RK-33) to fit into the ATP binding domain of DDX3. Initial results confirmed the binding of RK-33 to DDX3 using a streptavidin pull down assay. Subsequently, we demonstrated the effects of RK-33 in vitro and found a synergy between radiation and RK-33 in lung cancer cells. Also, treatment with RK-33 caused a cell cycle arrest in G1 phase and decreased Cyclin D1 levels in A549 and H1299 lung cancer cells. Furthermore, treatment with RK-33 resulted in decreased radiation induced DNA break repair demonstrated by immunofluorescent staining of A549 lung cancer cells with γH2AX and 53BP1 antibodies. In addition, we showed that the non-homologous end joining (NHEJ) activity in cancer cells was decreased by treatment with RK-33. However, homologues recombination activity was not affected by RK-33. Impaired NHEJ is known to increase radiation sensitivity hence inhibiting NHEJ by RK-33 could improve radiation therapy. Following these encouraging results observed in vitro, we initiated in vivo studies, using a lung cancer model with immune competent mice by expressing Twist1 and Kras selectively in the alveolar type II pneumocytes, which confers lung tissue specificity. Following tumor development, confirmed by micro-CT, the animals were treated with RK-33 (20 mg/kg) and different doses of stereotactic radiation (15 Gy) using a small animal radiation platform. Four weeks following treatment, tumor volumes were determined by micro-CT and H&E staining after necroscopy. A 72% reduction of tumor load was accomplished after treatment with RK-33 and radiation (15 Gy) compared to 28% tumor volume reduction in the radiation alone group. Interestingly, there was less tumor reduction when RK-33 was used in combination with 3 Gy x 10 radiation treatment. No evident toxicity became apparent during the treatment with RK-33. All experiments were done in replicates. Conclusion: These in vitro and in vivo results indicate that RK-33 is a promising and safe radiosensitizer, via inhibition of NHEJ, and could be a promising new drug in combination with stereotactic radiotherapy for lung cancer treatment.

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 5720. doi:1538-7445.AM2012-5720

Expression of DDX3 is directly modulated by hypoxia inducible factor-1 alpha in breast epithelial cells

DEAD box protein, DDX3, is aberrantly expressed in breast cancer cells ranging from weakly invasive to aggressive phenotypes and functions as an important regulator of cancer cell growth and survival. Here, we demonstrate that hypoxia inducible factor-1α is a transcriptional activator of DDX3 in breast cancer cells. Within the promoter region of the human DDX3 gene, we identified three putative hypoxia inducible factor-1 responsive elements. By luciferase reporter assays in combination with mutated hypoxia inducible factor-1 responsive elements, we determined that the hypoxia inducible factor-1 responsive element at position -153 relative to the translation start site is essential for transcriptional activation of DDX3 under hypoxic conditions. We also demonstrated that hypoxia inducible factor-1 binds to the DDX3 promoter and that the binding is specific, as revealed by siRNA against hypoxia inducible factor-1 and chromatin immunoprecipitation assays. Thus, the activation of DDX3 expression during hypoxia is due to the direct binding of hypoxia inducible factor-1 to hypoxia responsive elements in the DDX3 promoter. In addition, we observed a significant overlap in the protein expression pattern of hypoxia inducible factor-1α and DDX3 in MDA-MB-231 xenograft tumors. Taken together, our results demonstrate, for the first time, the role of DDX3 as a hypoxia-inducible gene that exhibits enhanced expression through the interaction of hypoxia inducible factor-1 with hypoxia inducible factor-1 responsive elements in its promoter region.

Novel, Broad Spectrum Anti-Cancer Agents Containing the Tricyclic 5:7:5-Fused Diimidazodiazepine Ring System

Synthesis of a series of novel, broad-spectrum anti-cancer agents containing the tricyclic 5:7:5-fused diimidazo[4,5-d:4',5'-f][1,3]diazepine ring system is reported. Compounds 1, 2, 8, 11, and 12 in the series show promising in vitro antitumor activity with low micromolar IC(50)'s against prostate, lung, breast, and ovarian cancer cell lines. Some notions about structure-activity relationships and a possible mechanism of biological activity are presented. Also presented are preliminary in vivo toxicity studies of 1 using SCID mice.