Abstract P3-06-08: Imipridone compounds inhibit breast cancer mTORC1 signaling through integrated stress response-mediated upregulation of endogenous mTORC1 inhibitor sestrin2

Breast cancer is a major cause of cancer-related death and there is a need for novel therapies with increased efficacy and decreased toxicity. The small molecule ONC201 was initially identified as a TRAIL pathway inducer. The compound has entered early phase clinical trials and is being tested in a range of solid tumors and hematological malignancies. Our previously published data demonstrate that ONC201 has potent anti-proliferative and pro-apoptotic effects in a broad range of breast cancer subtypes through TRAIL-dependent and TRAIL-independent mechanisms. Analogs of ONC201 with a shared pharmacophore have been developed and form the novel “imipridone” class. When compared with ONC201, imipridones ONC206, ONC212, and ONC213 showed increased potency of anti-proliferative or pro-apoptotic effects in breast cancer cells. We were interested in further defining the previously unstudied anti-proliferative effects of the imipridone compounds. Single agent efficacy of potent imipridone ONC212 in a xenograft model of TNBC was observed in the absence of apoptosis induction. This indicates that the anti-proliferative actions of the compound are sufficient for an in vivo anti-tumor effect. Our lab has previously shown that ONC201 activates an ATF4-dependent integrated stress response (ISR), essential for apoptosis induction in colon cancer cells. In contrast, in breast cancer cells, although ATF4 knockdown did not block cell death induced by ONC201 it did partially abrogate the anti-proliferative effects of the compound. The mammalian target of rapamycin complex 1 (mTORC1) is a well-known regulator of cellular growth and proliferation. mTORC1 signaling is inactivated in breast cancer cells following treatment with ONC201 and its analogs ONC212 and ONC213, regardless of whether the cells undergo apoptosis. Knockdown of ATF4 abrogated ONC201-mediated inhibition of p70 S6 kinase and ribosomal protein S6 phosphorylation, linking ISR induction to mTORC1 inhibition. We hypothesized that sestrin2, an endogenous mTORC1 inhibitor known to be upregulated following cellular stress, might represent a link between induction of ATF4 and inhibition of mTORC1. Treatment with ONC201 and its analogs ONC212 and ONC213 in multiple breast cancer cell lines resulted in sestrin2 upregulation. This was blocked by ATF4 knockdown. Furthermore, knockdown of sestrin2 abrogated the effects of ONC201 on mTORC1 signaling in breast cancers from multiple molecular subtypes. Previous mechanistic studies have focused exclusively on the relevance of ATF4 in the pro-apoptotic effects of ONC201. The novel findings described here help to elucidate the mechanism behind the potent and understudied anti-proliferative effects of the imipridones. Our findings also strengthen the preclinical rationale for testing of imipridone compounds against breast cancers regardless of molecular subtype.

Citation Format: Ralff MD, Kline CLB, El-Deiry WS. Imipridone compounds inhibit breast cancer mTORC1 signaling through integrated stress response-mediated upregulation of endogenous mTORC1 inhibitor sestrin2 [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-06-08.

Role of Dopamine Receptors in the Anticancer Activity of ONC201

ONC201/TIC10 is a first-in-class small molecule inducer of TRAIL that causes early activation of the integrated stress response. Its promising safety profile and broad-spectrum efficacy in vitro have been confirmed in Phase I/II trials in several advanced malignancies. Binding and reporter assays have shown that ONC201 is a selective antagonist of the dopamine D2-like receptors, specifically, DRD2 and DRD3. We hypothesized that ONC201's interaction with DRD2 plays a role in ONC201's anticancer effects. Using cBioportal and quantitative reverse-transcription polymerase chain reaction analyses, we confirmed that DRD2 is expressed in different cancer cell types in a cell type-specific manner. On the other hand, DRD3 was generally not detectable. Overexpressing DRD2 in cells with low DRD2 levels increased ONC201-induced PARP cleavage, which was preceded and correlated with an increase in ONC201-induced CHOP mRNA expression. On the other hand, knocking out DRD2 using CRISPR/Cas9 in three cancer cell lines was not sufficient to abrogate ONC201's anticancer effects. Although ONC201's anticancer activity was not dependent on DRD2 expression in the cancer cell types tested, we assessed the cytotoxic potential of DRD2 blockade. Transient DRD2 knockdown in HCT116 cells activated the integrated stress response and reduced cell number. Pharmacological antagonism of DRD2 significantly reduced cell viability. Thus, we demonstrate in this study that disrupting dopamine receptor expression and activity can have cytotoxic effects that may at least be in part due to the activation of the integrated stress response. On the other hand, ONC201's anticancer activity goes beyond its ability to antagonize DRD2, potentially due to ONC201's ability to activate other pathways that are independent of DRD2. Nevertheless, blocking the dopamine D1-like receptor DRD5 via siRNA or the use of a pharmacological antagonist promoted ONC201-induced anticancer activity.

Cancer stem cell-related gene expression as a potential biomarker of response for first-in-class imipridone ONC201 in solid tumors

Cancer stem cells (CSCs) correlate with recurrence, metastasis and poor survival in clinical studies. Encouraging results from clinical trials of CSC inhibitors have further validated CSCs as therapeutic targets. ONC201 is a first-in-class small molecule imipridone in Phase I/II clinical trials for advanced cancer. We have previously shown that ONC201 targets self-renewing, chemotherapy-resistant colorectal CSCs via Akt/ERK inhibition and DR5/TRAIL induction. In this study, we demonstrate that the anti-CSC effects of ONC201 involve early changes in stem cell-related gene expression prior to tumor cell death induction. A targeted network analysis of gene expression profiles in colorectal cancer cells revealed that ONC201 downregulates stem cell pathways such as Wnt signaling and modulates genes (ID1, ID2, ID3 and ALDH7A1) known to regulate self-renewal in colorectal, prostate cancer and glioblastoma. ONC201-mediated changes in CSC-related gene expression were validated at the RNA and protein level for each tumor type. Accordingly, we observed inhibition of self-renewal and CSC markers in prostate cancer cell lines and patient-derived glioblastoma cells upon ONC201 treatment. Interestingly, ONC201-mediated CSC depletion does not occur in colorectal cancer cells with acquired resistance to ONC201. Finally, we observed that basal expression of CSC-related genes (ID1, CD44, HES7 and TCF3) significantly correlate with ONC201 efficacy in >1000 cancer cell lines and combining the expression of multiple genes leads to a stronger overall prediction. These proof-of-concept studies provide a rationale for testing CSC expression at the RNA and protein level as a predictive and pharmacodynamic biomarker of ONC201 response in ongoing clinical studies.

Abstract 3213: Antagonism of D2-like dopamine receptors plays a role in Onc201’s anticancer effects

ONC201/TIC10 is a first-in-class small molecule inducer of TRAIL that causes early activation of the integrated stress response and inactivates both Akt and ERK. Its promising safety profile and broad spectrum efficacy in vitro has been confirmed in Phase I/II trials in several advanced malignancies. Biochemical and reporter assays have shown that ONC201 is a selective and competitive antagonist of the D2-like receptors, specifically, dopamine receptor D2 (DRD2) and dopamine receptor D3 (DRD3) with a KD value of ~3 µM. The theme that dopamine and dopamine receptors are important in cancer has emerged in the literature. We hypothesize that ONC201’s interaction with DRD2 is critical for ONC201’s anticancer effects. Co-treating HCT116 and RKO colorectal cancer cells with ONC201 and dopamine or the selective D2-like receptor agonist sumanirole partially abrogated ONC201-induced ATF4/CHOP expression and apoptosis. Knocking down DRD2 expression using siRNA negated ONC201’s effects on viable cell count. Overexpressing DRD2 in a cancer cell line that has very low levels of DRD2, increased ONC201-induced PARP cleavage. Quantitative RT-PCR analyses showed that cells that have acquired resistance to ONC201 did not express detectable mRNA levels of the D2-like receptors. To further determine the anti-tumor potential of targeting the D2-like receptor, we treated different cancer cell lines with other D2-like receptor antagonists. Similar to ONC201, the D2-selective antagonist L-741,626 decreased cell viability and induced apoptosis in a number of cancer cell lines. In contrast to ONC201, however, L-741,626 has a poor therapeutic index. Our findings show that the ability of ONC201 to inhibit D2-like receptors contributes to ONC201’s antiproliferative and pro-apoptotic activity. Ongoing work is aimed at elucidating the mechanisms by which antagonism of D2-like receptors can promote apoptotic cell death, especially with regard to ATF4/CHOP/DR5 and Akt/ERK/Foxo3a/TRAIL, which have been shown to be stimulated in ONC201-treated and -sensitive tumor cells.

Citation Format: Christina Leah B. Kline, Amriti Lulla, Jessica Wagner, David Dicker, Marie Baumeister, Sophie Oster, Wafik El-Deiry. Antagonism of D2-like dopamine receptors plays a role in Onc201’s anticancer effects [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 3213. doi:10.1158/1538-7445.AM2017-3213

Abstract 2497: ONC201 targets cancer stem cells in colorectal, prostate and glioblastoma multiforme tumors via modulation of stem cell-related gene expression

ONC201 is a first-in-class anti-tumor agent that selectively targets cancer cells without observed toxicity. ONC201 is being tested in phase I/II clinical trials for patients with advanced solid tumors and hematological malignancies. Several tumors contain a rare population of cancer stem cells (CSCs) capable of self-renewal that contribute to tumor maintenance and resistance to therapy. We have previously demonstrated that ONC201 targets self-renewing, chemotherapy-resistant colorectal CSCs (Prabhu et al, Cancer Res, 2015). We hypothesized that anti-CSC effects of ONC201 involve changes in stem-cell related gene expression. A targeted network analysis of gene expression profiles of HCT116 p53-null and RKO human colon cancer cells treated with ONC201 revealed that several stem cell-related pathways and proteins are affected with potential implications for anti-CSC effects in diverse tumor types. Specifically, mRNA levels of ID1 (colon/glioblastoma CSC-regulation, 2.5 fold), ID2 (glioma stem cell regulation, 3.2 fold), ID3 (colon/glioma CSC-regulation, 2.9 fold), ALDH7A1 (prostate CSC marker, 2 fold) were significantly downregulated and KLF9 (glioblastoma stem cell inhibitor, 1.5 fold) was significantly upregulated in HCT116 p53-null cells upon ONC201 treatment. Also, mRNA levels of Wnt pathway related genes such as ligand WNT16 (haematopoietic stem cell/prostate cancer resistance-related, 13.5 fold), receptors FZD2 (2.98 fold), FZD4 (3.9 fold) and transcription factor TCF7L2 (3.55 fold) were significantly downregulated. Validation with qRT-PCR indicated that ID2, WNT16 mRNA levels were significantly downregulated while KLF9 mRNA was significantly upregulated in response to ONC201 treatment in HCT116 p53-null cells. Interestingly, ONC201 downregulated mRNA levels of ID1 (2.1 fold) and FZD4 (1.6 fold) in RKO cells but not in ONC201-resistant RKO cells, indicating that CSC-inhibition could serve as a biomarker of ONC201 response. To functionally validate anti-CSC effects of ONC201 in glioblastoma multiforme (GBM) and prostate cancer we determined effects on self-renewal using tumorsphere formation. ONC201 eradicated CSC-enriched 3-dimensional neurosphere culture models of primary GBM samples, including newly diagnosed and recurrent samples. ONC201 potently inhibited in vitro cell proliferation of all 5 lines, with IC50 values of 433 nM (MGG18), 1.46 μM (MGG4), 1.09 μM (MGG8), 3.97 μM (MGG67R) and 688 nM (MGG152). ONC201 significantly reduced tumorsphere formation of 22Rv1, DU145 and PC3 human prostate cancer cells. Additionally, western blotting revealed that Wnt16 was downregulated in LNCaP and 22Rv1 while CSC marker CD44 was downregulated in 22Rv1 cells. Ongoing studies are further validating these potential anti-CSC molecular targets of ONC201 and determining their contribution to the overall anti-CSC and anti-tumor effect of ONC201.

Citation Format: Varun Vijay Prabhu, Joshua E. Allen, Dan Zhao, Amriti R. Lulla, Christina Leah B. Kline, A. Pieter J. van den Heuvel, Avital Lev, Tracy T. Batchelor, David T. Dicker, Andrew S. Chi, Wafik S. El-Deiry. ONC201 targets cancer stem cells in colorectal, prostate and glioblastoma multiforme tumors via modulation of stem cell-related gene expression. [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 2497.

Abstract 3014: ONC201 anti-cancer effects against solid tumors are mediated through eIF2α kinases HRI and PKR but are PERK-independent

ONC201 is a first-in-class small molecule inducer of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway. We recently reported that ONC201-mediated induction of the TRAIL pathway is largely promoted by a preceding early activation of the integrated stress response pathway (ISR) (Kline et al., Sci. Sig., in press, 2015). ONC201 engages the ISR to exert its broad-spectrum anti-cancer effects through pro-apoptotic and anti-proliferative activities. ONC201 upregulates ATF4, the key indicator of ISR activation, in a manner that is dependent on two eIF2α kinases: heme-regulated inhibitor (HRI) and double-stranded RNA activated protein kinase (PKR). Of note, the activation of ATF4 and downstream cell death signaling by ONC201 is PERK-independent. We now further elucidate how the novel dual engagement of HRI and PKR by ONC201 contributes to the anti-cancer effects of ONC201. ONC201 treatment results in early phosphorylation of eIF2α in a manner that is dependent on HRI. On the other hand, we have shown that ONC201-induced downregulation of cyclin D1 is dependent, at least in part, on PKR, but not on eIF2 α phosphorylation per se. This occurs potentially via PKR-mediated ubiquitination and subsequent proteasome degradation of cyclin D1. Treating cells with ONC201 and the proteasome inhibitor MG132 prevents ONC201-induced decrease of cyclin D1. Despite distinctions in their regulatory protein domains, HRI and PKR have both been shown to respond to oxidative stress. Treating cells with ONC201 in the presence of the antioxidant N-acetylcysteine abrogated ATF4 induction. Our findings document a unique activity of ONC201 on protein translation, via activation of HRI and PKR, as well as effects on protein stability through the proteasome leading to anti-cancer effects.

Citation Format: Christina Leah B. Kline, Wafik S. El-Deiry. ONC201 anti-cancer effects against solid tumors are mediated through eIF2α kinases HRI and PKR but are PERK-independent. [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 3014.

Small-Molecule NSC59984 Restores p53 Pathway Signaling and Antitumor Effects against Colorectal Cancer via p73 Activation and Degradation of Mutant p53

The tumor-suppressor p53 prevents cancer development via initiating cell-cycle arrest, cell death, repair, or antiangiogenesis processes. Over 50% of human cancers harbor cancer-causing mutant p53. p53 mutations not only abrogate its tumor-suppressor function, but also endow mutant p53 with a gain of function (GOF), creating a proto-oncogene that contributes to tumorigenesis, tumor progression, and chemo- or radiotherapy resistance. Thus, targeting mutant p53 to restore a wild-type p53 signaling pathway provides an attractive strategy for cancer therapy. We demonstrate that small-molecule NSC59984 not only restores wild-type p53 signaling, but also depletes mutant p53 GOF. NSC59984 induces mutant p53 protein degradation via MDM2 and the ubiquitin-proteasome pathway. NSC59984 restores wild-type p53 signaling via p73 activation, specifically in mutant p53-expressing colorectal cancer cells. At therapeutic doses, NSC59984 induces p73-dependent cell death in cancer cells with minimal genotoxicity and without evident toxicity toward normal cells. NSC59984 synergizes with CPT11 to induce cell death in mutant p53-expressing colorectal cancer cells and inhibits mutant p53-associated colon tumor xenograft growth in a p73-dependent manner in vivo. We hypothesize that specific targeting of mutant p53 may be essential for anticancer strategies that involve the stimulation of p73 in order to efficiently restore tumor suppression. Taken together, our data identify NSC59984 as a promising lead compound for anticancer therapy that acts by targeting GOF-mutant p53 and stimulates p73 to restore the p53 pathway signaling.

Abstract 1802: Small molecule compound NCI-8 induces mutant p53 degradation via inhibition of the MDM2-Hsp90 axis

The tumor suppressor p53 prevents cancer development via regulating cell cycle arrest, cell death, or repair processes. Over 50% of human cancers harbor mutant p53. Mutations in p53 not only abrogate its tumor suppressor function, but also endow mutant p53 with a gain-of-function (GOF), creating a proto-oncogene that contributes to tumorigenesis, tumor progression and chemotherapeutic resistance. Thus, targeting mutant p53 to restore wild-type p53 pathway signaling is an attractive strategy for cancer therapy. We previously reported a novel small molecular compound, NCI-8, which not only restores wild-type p53 signaling, but also depletes mutant p53 protein (Zhang S, Zhou L, Hong B, et al. Cancer Res 2013;73(8 Suppl):Abstract 2171). In this study, we further elucidate the mechanism of the small molecular compound NCI-8-mediated degradation of mutant p53 protein. We found that the small molecule NCI-8 induces mutant p53 protein degradation via the MDM2-ubiquitin-proteasome pathway. NCI-8 exposure leads to phosphorylation of p53 at Thr55. Dephosphorylation of p53 at Thr55 rescues mutant p53 protein from degradation in cells treated with Apigenin, suggesting that phosphorylation at Thr55 is required for mutant p53 protein degradation induced by NCI-8. Hsp90 and hsp70 are two molecular chaperones that stabilize mutant p53 protein by affecting the MDM2 mediated turnover of mutant p53, therefore, we investigated the effect of NCI-8 on the MDM2-hsp chaperone axis. We found that less HSP90 but more MDM2 were bound to mutant p53 in cells treated with NCI-8, suggesting that NCI-8 induces mutant p53 protein degradation through disturbing the MDM2-hsp chaperone axis. Correlated to the degradation of mutant p53 protein, the p73 pathway was activated in response to NCI-8 treatment specifically in mutant p53-expressing colorectal cancer cells. Our results provide a possible mechanism of NCI-8-mediated p73-dependent restoration of the p53 pathway via mutant p53 protein degradation.

Citation Format: Shengliang Zhang, Lanlan Zhou, Christina Leah B. Kline, David T. Dicker, Wafik S. El-Deiry. Small molecule compound NCI-8 induces mutant p53 degradation via inhibition of the MDM2-Hsp90 axis. [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 1802. doi:10.1158/1538-7445.AM2014-1802

Personalized dosing via pharmacokinetic monitoring of 5-fluorouracil might reduce toxicity in early- or late-stage colorectal cancer patients treated with infusional 5-fluorouracil-based chemotherapy regimens

INTRODUCTION

Therapeutic plasma 5-fluorouracil (5-FU) levels are achieved in only 20% to 30% of patients with the current practice of administering 5-FU doses based on body surface area (BSA). Alternatively, 5-FU doses can be adjusted based on 5-FU pharmacokinetic (PK) monitoring. Although benefits of PK monitoring of 5-FU in metastatic colorectal cancer (CRC) have been reported, its utility among patients with early stage disease has not been reported.

PATIENTS AND METHODS

We retrospectively examined the effect of 5-FU PK monitoring in 84 CRC patients (49 stage IV and 35 stage II/III) receiving mFOLFOX6 (modifiedFOLFOX6; modified 5-fluorouracil, leucovorin, oxaliplatin protocol) or mFOLFIRI (modified 5-fluorouracil, leucovorin, irinotecan protocol). Forty-six of the 84 patients received 5-FU doses based on BSA and 38 received doses that were adjusted with PK monitoring. 5-FU plasma levels were measured using a nanoparticle immunoassay method.

RESULTS

5-fluorouracil PK monitoring significantly improved disease-free survival in stage II/III patients (P = .0429). There was also a trend towards improved progression-free survival among stage IV patients who had their 5-FU levels PK-monitored (P = .16). Moreover, 5-FU PK monitoring significantly reduced (P = .0437) and delayed (P = .0144) adverse effects in stage II/III patients. Toxicity occurred after the second 5-FU dose in the BSA group and after the sixth to seventh dose in the PK monitoring group. In stage IV patients, the onset of toxicities was also delayed with PK monitoring (P = .0605).

CONCLUSION

We provide evidence that PK monitoring of 5-FU is potentially beneficial for late stage and early stage CRC. These results contribute to the growing body of evidence regarding patient benefit when treatment decisions are based on the individual patient characteristics, in this case, a patients' 5-FU levels.

Personalizing colon cancer therapeutics: targeting old and new mechanisms of action

The use of pharmaceuticals for colon cancer treatment has been increasingly personalized, in part due to the development of new molecular tools. In this review, we discuss the old and new colon cancer chemotherapeutics, and the parameters that have been shown to be predictive of efficacy and safety of these chemotherapeutics. In addition, we discuss how alternate pharmaceuticals have been developed in light of a potential lack of response or resistance to a particular chemotherapeutic.

Abstract 1176: Pharmacokinetic monitoring of 5-FU appears beneficial in stage II-IV colorectal cancer patients treated with different 5-FU-based chemotherapeutic regimens

The mainstay of colorectal cancer chemotherapy has been 5-fluorouracil (5-FU) alone or in combination with other agents. Unfortunately, therapeutic plasma 5-FU levels are achieved in only 20-30% of patients, in response to administration of 5-FU doses calculated from the patient's body surface area. Pharmacokinetic (PK) monitoring of 5-FU has been found to be beneficial for metastatic colorectal cancer patients. However, its utility among Stage II and III patients has not been reported. Purpose: We examined the impact of pharmacokinetic monitoring of 5-FU in colorectal patients with Stage II- Stage IV disease, receiving different 5-FU-based chemotherapy regimens, in terms of therapeutic response and safety. Methods: The study involved 73 colorectal cancer patients. The patients received different 5-FU based regimens; namely, FOLFOX6, mFOLFOX, FOLFIRI, and capecitabine. Thirty-five patients received 5-FU doses based on the traditional body surface area (BSA) method, which takes into account the patient's height and weight. On the other hand, in 38 patients, their 5-FU dose was adjusted based on their plasma 5-FU levels from their previous cycle. 5-FU plasma levels were measured using the commercially available OnDose test (Myriad Genetic Laboratories Inc., Salt Lake City, UT). The 5-FU levels were monitored per cycle and administered doses were adjusted accordingly until a target plasma AUC level of 20-24 mg.h/L was achieved. Results: Pharmacokinetic monitoring among Stage IV patients (n=17) had a trend toward improved survival. Out of the 8 patients that needed at least one dose adjustment, 7 of them involved increasing the 5-FU dose. 5-FU doses were not increased in the patients that did not have their 5-FU levels monitored. The ability to maximize the 5-FU dose administered without risking toxicity with PK monitoring may explain at least in part the trend towards prolonged survival in patients that underwent pharmacokinetic dose adjustment. Among Stage II and III patients, toxicities were markedly reduced by pharmacokinetic dose adjustment of 5-FU. In patients that had their doses adjusted by the BSA method, 38% experienced (7 out of 18 patients) dose-limiting toxicities, that included Grade III diarrhea, fatigue, nausea and vomiting, and cardiotoxicity. In contrast, none of the patients (n=19) that underwent pharmacokinetic monitoring experienced dose-limiting toxicity (Fisher's exact test, p=0.0031). The toxicities observed in the BSA group were not among the patients that received capecitabine. Conclusions: 5-FU dose adjustment in response to pharmacokinetic monitoring results in a trend towards improved survival of Stage IV patients. Moreover, dose-limiting toxicities are reduced in Stage II and III patients. The results presented point to the benefits of pharmacokinetic dose adjustment of 5-FU in clinical practice.

Citation Format: Christina Leah B. Kline, Angelique Schiccitano, Jay Zhu, Cheryl Beachler, Hassan Sheikh, Harold Harvey, Heath Mackley, Walter Koltun, Kevin McKenna, Lisa Poritz, Evangelos Messaris, David Stewart, Jeffrey Sivik, Wafik El-Deiry. Pharmacokinetic monitoring of 5-FU appears beneficial in stage II-IV colorectal cancer patients treated with different 5-FU-based chemotherapeutic regimens. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1176. doi:10.1158/1538-7445.AM2013-1176

Prostate apoptosis response protein 4 sensitizes human colon cancer cells to chemotherapeutic 5-FU through mediation of an NF kappaB and microRNA network

Background

Diminished expression or activity of prostate apoptosis response protein 4 (Par-4) has been demonstrated in a number of cancers, although reports on Par-4 expression during colon cancer progression are lacking. An understanding of the molecular events in conjunction with the genetic networks affected by Par-4 is warranted.

Results

Colon cancer specimens derived from patients have significantly diminished expression of Par-4 mRNA relative to paired normal colon. Hence, the functional consequences of reintroducing Par-4 into HT29 colon cancer cells were assessed. Overexpression augmented the interaction of Par-4 with NFκB in the cytosol but not nucleus, and facilitated apoptosis in the presence of 5-fluorouracil (5-FU). Analogous findings were obtained when AKT1 pro-survival signaling was inhibited. Transcriptome profiling identified ~700 genes differentially regulated by Par-4 overexpression in HT29 cells. Nearly all Par-4-regulated genes were shown by promoter analysis to contain cis-binding sequences for NFκB, and meta-analysis of patient expression data revealed that one-third of these genes exist as a recurrent co-regulated network in colon cancer specimens. Sets of genes involved in programmed cell death, cell cycle regulation and interestingly the microRNA pathway were found overrepresented in the network. Noteworthy, Par-4 overexpression decreased NFκB occupancy at the promoter of one particular network gene DROSHA, encoding a microRNA processing enzyme. The resulting down-regulation of DROSHA was associated with expression changes in a cohort of microRNAs. Many of these microRNAs are predicted to target mRNAs encoding proteins with apoptosis-related functions. Western and functional analyses were employed to validate several predictions. For instance, miR-34a up-regulation corresponded with a down-regulation of BCL2 protein. Treating Par-4-overexpressing HT29 cells with a miR-34a antagomir functionally reversed both BCL2 down-regulation and apoptosis by 5-FU. Conversely, bypassing Par-4 overexpression by direct knockdown of DROSHA expression in native HT29 cells increased miR-34a expression and 5-FU sensitivity.

Conclusion

Our findings suggest that the initiation of apoptotic sensitivity in colon cancer cells can be mediated by Par-4 binding to NFκB in the cytoplasm with consequential changes in the expression of microRNA pathway components.

Src activity alters alpha3 integrin expression in colon tumor cells

Src kinase has been linked to increased motility in the progression and metastasis of human colon cancer, although the mechanisms are not fully understood. Integrins are involved in metastasis by mediating attachment and migration of cells, as well as through transducing signals. This study examines the link between Src and integrin activity in the metastatic process in colon cancer cells. To determine Src involvement in integrin expression, the human colon cancer cell line, HCT116, was transfected with an activated Src construct and assayed for its ability to attach to and migrate across collagen and laminin. These cells attached more readily and migrated less rapidly on the extracellular matrix (ECM) than did cells transfected with empty vector. Examination of integrin levels showed a decrease in the alpha3 subunit in Src transfected cells as well as decreased cell surface localization of alpha3 integrin. The downregulation of alpha3 integrin was reversed by inhibition of Src and by inhibition of MAP kinase. Inhibition of alpha3 integrin using shRNA resulted in decreased MMP7 secretion, a possible cause of decreased invasion with low alpha3 integrin expression. This study shows that Src overexpression downregulates alpha3 integrin total protein expression and localization to the cell surface of HCT116 colon cancer cells. This indicates that Src activity may enhance metastasis by altering alpha3 integrin expression.

Src kinase induces tumor formation in the c-SRC C57BL/6 mouse

Src kinase has been linked as a causative agent in the progression of a number of cancers including colon, breast, lung and melanoma. Src protein and activity levels are increased in colorectal cancer and liver metastases arising secondary to colon cancer. However, although Src protein is increased in colon cancer as early as the adenomatous polyp stage, a role for Src in carcinogenesis has not been established. We developed the c-SRC transgenic mouse in the C57BL/6 strain to address the issue of carcinogenesis in cells with high levels of Src expression. The transgene was constructed with the human c-SRC gene downstream of the mouse metallothionein promoter to create zinc inducible gene expression. In these C57BL/6 mice, Src protein was increased in a number of tissues both with and without zinc induction. No additional carcinogenic agent was administered. After 20 months, mice were assessed for tumor development in the liver and GI tract, as well as other organs. Of the mice with the transgene, 15% developed tumors in the liver while no tumors were detected in wild type C57BL/6 mice. A further study was conducted by crossing c-SRC C57BL/6 mice with p21 nullizygous mice to determine the effect of oncogene expression combined with inactivation of the tumor suppressor gene, p21. Addition of the c-SRC transgene to the p21-/- background increased tumor formation almost 3-fold, while it increased metastasis 6-fold. The data from our study show, for the first time, that Src kinase may play a role in carcinogenesis.

Glucosamine-induced phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 is mediated by the protein kinase R-like endoplasmic-reticulum associated kinase

In diabetic animals, enhanced production of vascular endothelial growth factor is thought to be a major contributor to the development of diabetic retinopathy. In the present study, glucosamine-treated R28 retinal neuronal cells were used as an experimental model system to explore the possible involvement of the hexosamine biosynthetic pathway in the diabetes-induced changes in mRNA translation. Glucosamine treatment enhanced vascular endothelial growth factor production subsequent to changes in phosphorylation of the alpha-subunit of eukaryotic initiation factor 2, with no change in vascular endothelial growth factor mRNA content. Possible mechanisms through which glucosamine might act to increase eukaryotic initiation factor 2alpha phosphorylation include enhanced O-linked glycosylation of protein kinase or phosphatase regulatory proteins and/or induction of oxidative stress. However, increasing global protein O-glycosylation through inhibition of O-beta-N-acetylglucosaminidase did not mimic the effect of glucosamine on eukaryotic initiation factor 2alpha phosphorylation. Likewise, attenuating glucosamine-induced oxidative stress with two different antioxidants did not reduce glucosamine-induced eukaryotic initiation factor 2alpha phosphorylation. Glucosamine treatment was also found to promote eukaryotic initiation factor 2alpha phosphorylation in wild-type mouse embryonic fibroblasts, but not in mouse embryonic fibroblasts lacking the eukaryotic initiation factor 2alpha kinase referred to as RNA-dependent protein kinase-like endoplasmic-reticulum associated kinase, implicating the kinase in the glucosamine-induced increase in eukaryotic initiation factor 2alpha phosphorylation. Overall, the results are consistent with glucosamine causing activation of RNA-dependent protein kinase-like endoplasmic-reticulum associated kinase, which phosphorylates eukaryotic initiation factor 2alpha and consequently upregulates translation of mRNAs encoding specific proteins, such as vascular endothelial growth factor.