Evolution and current trends in the management of colorectal cancer liver metastasis.

Metastatic colorectal cancer (mCRC) is a major cause of cancer-related death, with a 5-year relative overall survival of up to 20%. The liver is the most common site of distant metastasis in colorectal cancer (CRC), with about 50% of CRC patients metastasizing to their liver over the course of their disease. Complete liver resection is the primary modality of treatment for resectable colorectal cancer liver metastasis (CRLM), with an overall 5-year survival rate of up to 58%. However, only 15% to 20% of patients with CRLM are deemed suitable for resection at presentation. For unresectable diseases, the median survival of patients remains low even with the best chemotherapy. In recent decades, the management of CRLM has continued to evolve with the expansion of resection criteria, novel targeted systemic therapies, and improved locoregional therapies. However, due to the heterogeneity of the CRC patient population, the optimal evaluation of treatment options for CRLM remains complex. Therefore, effective management requires a multidisciplinary team to help define resectability and devise a personalized treatment approach, from the initial diagnosis to the final treatment.

Incorporation of Simulation in Graduate Medical Education: Historical Perspectives, Current Status, and Future Directions.

Technological advancement and improved training strategies have transformed the healthcare practice environment in the last few decades. Simulation has evolved as one of the leading training models for the next generation of healthcare professionals. Simulation-based training enables healthcare professionals to acquire knowledge and skills in a safe and educationally oriented environment and can be a valuable tool for improving clinical practice and patient outcomes. The field of healthcare simulation has been rapidly growing, and various graduate medical education programs around the world have started incorporating this modality into their curricula. In graduate medical education, simulation-based training helps implement an outcome-based curriculum that tests the trainee's actual skill level as the primary factor for the trainee's competency rather than relying on the current model of a predetermined training period. However, the major challenge revolves around developing an educational curriculum incorporating a simulation-based educational model, understanding the value of this new technology, the overall cost factor, and the lack of adequate infrastructure. Hence, embracing the full potential of simulation technology in graduate medical education curricula requires an innovative approach with participation from institutions and stakeholders.

PI3K/Akt/mTOR Signaling Pathway as a Target for Colorectal Cancer Treatment.

In the last decade, pathway-specific targeted therapy has revolutionized colorectal cancer (CRC) treatment strategies. This type of therapy targets a tumor-vulnerable spot formed primarily due to an alteration in an oncogene and/or a tumor suppressor gene. However, tumor heterogeneity in CRC frequently results in treatment resistance, underscoring the need to understand the molecular mechanisms involved in CRC for the development of novel targeted therapies. The phosphatidylinositol 3-kinase/protein kinase B/mammalian target of the rapamycin (PI3K/Akt/mTOR) signaling pathway axis is a major pathway altered in CRC. The aberrant activation of this pathway is associated with CRC initiation, progression, and metastasis and is critical for the development of drug resistance in CRC. Several drugs target PI3K/Akt/mTOR in clinical trials, alone or in combination, for the treatment of CRC. This review aims to provide an overview of the role of the PI3K/Akt/mTOR signaling pathway axis in driving CRC, existing PI3K/Akt/mTOR-targeted agents against CRC, their limitations, and future trends.

Global Cancer Surgery: pragmatic solutions to improve cancer surgery outcomes worldwide.

The first Lancet Oncology Commission on Global Cancer Surgery was published in 2015 and serves as a landmark paper in the field of cancer surgery. The Commission highlighted the burden of cancer and the importance of cancer surgery, while documenting the many inadequacies in the ability to deliver safe, timely, and affordable cancer surgical care. This Commission builds on the first Commission by focusing on solutions and actions to improve access to cancer surgery globally, developed by drawing upon the expertise from cancer surgery leaders across the world. We present solution frameworks in nine domains that can improve access to cancer surgery. These nine domains were refined to identify solutions specific to the six WHO regions. On the basis of these solutions, we developed eight actions to propel essential improvements in the global capacity for cancer surgery. Our initiatives are broad in scope, pragmatic, affordable, and contextually applicable, and aimed at cancer surgeons as well as leaders, administrators, elected officials, and health policy advocates. We envision that the solutions and actions contained within the Commission will address inequities and promote safe, timely, and affordable cancer surgery for every patient, regardless of their socioeconomic status or geographic location.

Intraperitoneal oxygen microbubble therapy: A novel approach to enhance systemic oxygenation in a smoke inhalation model of acute hypoxic respiratory failure.

Background: Patients suffering from severe acute respiratory distress syndrome (ARDS) face limited therapeutic options and alarmingly high mortality rates. Refractory hypoxemia, a hallmark of ARDS, often necessitates invasive and high-risk treatments. Oxygen microbubbles (OMB) present a promising approach for extrapulmonary oxygenation, potentially augmenting systemic oxygen levels without exposing patients to significant risks. Methods: Rats with severe, acute hypoxemia secondary to wood smoke inhalation (SI) received intraperitoneal (IP) bolus injections of escalating weight-by-volume (BW/V) OMB doses or normal saline to determine optimal dosage and treatment efficacy. Subsequently, a 10 % BW/V OMB bolus or saline was administered to a group of SI rats and a control group of healthy rats (SHAM). Imaging, vital signs, and laboratory studies were compared at baseline, post-smoke inhalation, and post-treatment. Histological examination and lung tissue wet/dry weight ratios were assessed at study conclusion. Results: Treatment with various OMB doses in SI-induced acute hypoxemia revealed that a 10 % BW/V OMB dose significantly augmented systemic oxygen levels while minimizing dose volume. The second set of studies demonstrated a significant increase in partial pressure of arterial oxygen (PaO2) and normalization of heart rate with OMB treatment in the SI group compared to saline treatment or control group treatment. Conclusions: This study highlights the successful augmentation of systemic oxygenation following OMB treatment in a small animal model of severe hypoxemia. OMB therapy emerges as a novel and promising treatment modality with immense translational potential for oxygenation support in acute care settings.

Colonic oxygen microbubbles augment systemic oxygenation and CO2 removal in a porcine smoke inhalation model of severe hypoxia.

Inhalation injury can lead to pulmonary complications resulting in the development of respiratory distress and severe hypoxia. Respiratory distress is one of the major causes of death in critically ill patients with a reported mortality rate of up to 45%. The present study focuses on the effect of oxygen microbubble (OMB) infusion via the colon in a porcine model of smoke inhalation-induced lung injury. Juvenile female Duroc pigs (n = 6 colonic OMB, n = 6 no treatment) ranging from 39 to 51 kg in weight were exposed to smoke under general anesthesia for 2 h. Animals developed severe hypoxia 48 h after smoke inhalation as reflected by reduction in SpO2 to 66.3 ± 13.1% and PaO2 to 45.3 ± 7.6 mmHg, as well as bilateral diffuse infiltrates demonstrated on chest X-ray. Colonic OMB infusion (75-100 mL/kg dose) resulted in significant improvements in systemic oxygenation as demonstrated by an increase in PaO2 of 13.2 ± 4.7 mmHg and SpO2 of 15.2 ± 10.0% out to 2.5 h, compared to no-treatment control animals that experienced a decline in PaO2 of 8.2 ± 7.9 mmHg and SpO2 of 12.9 ± 18.7% over the same timeframe. Likewise, colonic OMB decreased PaCO2 and PmvCO2 by 19.7 ± 7.6 mmHg and 7.6 ± 6.7 mmHg, respectively, compared to controls that experienced increases in PaCO2 and PmvCO2 of 17.9 ± 11.7 mmHg and 18.3 ± 11.2 mmHg. We conclude that colonic delivery of OMB therapy has potential to treat patients experiencing severe hypoxemic respiratory failure.

Competency-Based Medical Education (CBME): an Overview and Relevance to the Education of Future Surgical Oncologists.

In the next two decades, the global cancer burden is expected to rise by 47%, and the demand for global cancer surgery will increase by 52%. At present, only 25% of the estimated 80% of patients needing surgical intervention have access to timely surgical care. The shortage of a trained workforce of surgical oncologists is one of the main barriers to providing the optimal surgical intervention needed for cancer patients. Some of the contributing factors to the shortage of trained surgical oncologists are variations in the current global educational platforms, long training programs, and physician burnout. Therefore, the availability of a credible training framework and a sustainable certification pipeline for future surgical oncologists is critical to meet the global demand for an adequate healthcare workforce. The current surgical oncology educational program is a time-based construct that trains surgeons to function seamlessly in the multidisciplinary care of cancer patients. However, there is a lack of flexibility in the training framework and timeline despite differences in trainees' abilities. Developing a globally acceptable standard curriculum for surgical oncology training based on the competency-based medical education (CBME) framework and tailoring it to local needs can increase the surgical oncology workforce ready to tackle the rising cancer burden. However, successful implementation of the global CBME-based surgical oncology training curriculum requires an innovative approach to ensure that this framework produces a competent surgical oncologist that meets the local needs.

Colorectal cancer: Review of signaling pathways and associated therapeutic strategies.

Tumor profiling and targeted therapy revolutionized the treatment strategies of metastatic colorectal cancer (mCRC) in the last decade. The heterogeneity of CRC tumors plays a critical role in the development of treatment resistance, which underscores the need to understand the molecular mechanism involved in CRC to develop novel targeted therapeutic strategies. This review provides an overview of the signaling pathways driving CRC, the existing targeted agents, their limitations, and future trends.

A novel large animal model of smoke inhalation-induced acute respiratory distress syndrome.

BACKGROUND: Acute respiratory distress syndrome (ARDS) is multifactorial and can result from sepsis, trauma, or pneumonia, amongst other primary pathologies. It is one of the major causes of death in critically ill patients with a reported mortality rate up to 45%. The present study focuses on the development of a large animal model of smoke inhalation-induced ARDS in an effort to provide the scientific community with a reliable, reproducible large animal model of isolated toxic inhalation injury-induced ARDS. METHODS: Animals (n = 21) were exposed to smoke under general anesthesia for 1 to 2 h (median smoke exposure = 0.5 to 1 L of oak wood smoke) after the ultrasound-guided placement of carotid, pulmonary, and femoral artery catheters. Peripheral oxygen saturation (SpO2), vital signs, and ventilator parameters were monitored throughout the procedure. Chest x-ray, carotid, femoral and pulmonary artery blood samples were collected before, during, and after smoke exposure. Animals were euthanized and lung tissue collected for analysis 48 h after smoke inhalation. RESULTS: Animals developed ARDS 48 h after smoke inhalation as reflected by a decrease in SpO2 by approximately 31%, PaO2/FiO2 ratio by approximately 208 (50%), and development of bilateral, diffuse infiltrates on chest x-ray. Study animals also demonstrated a significant increase in IL-6 level, lung tissue injury score and wet/dry ratio, as well as changes in other arterial blood gas (ABG) parameters. CONCLUSIONS: This study reports, for the first time, a novel large animal model of isolated smoke inhalation-induced ARDS without confounding variables such as cutaneous burn injury. Use of this unique model may be of benefit in studying the pathophysiology of inhalation injury or for development of novel therapeutics.

Rat model of smoke inhalation-induced acute lung injury.

BACKGROUND: Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a lethal disease with limited therapeutic options and an unacceptably high mortality rate. Understanding the complex pathophysiological processes involved in the development of ALI/ARDS is critical for developing novel therapeutic strategies. Smoke inhalation (SI) injury is the leading cause of morbidity and mortality in patients with burn-associated ALI/ARDS; however, to our knowledge few reliable, reproducible models are available for pure SI animal model to investigate therapeutic options for ALI/ARDS without the confounding variables introduced by cutaneous burn or other pathology. OBJECTIVE: To develop a small animal model of pure SI-induced ALI and to use this model for eventual testing of novel therapeutics for ALI. METHODS: Rats were exposed to smoke using a custom-made smoke generator. Peripheral oxygen saturation (SpO2), heart rate, arterial blood gas, and chest X-ray (CXR) were measured before and after SI. Wet/dry weight (W/D) ratio, lung injury score and immunohistochemical staining of cleaved caspase 3 were performed on harvested lung tissues of healthy and SI animals. RESULTS: The current study demonstrates the induction of ALI in rats after SI as reflected by a significant, sustained decrease in SpO2 and the development of diffuse bilateral pulmonary infiltrates on CXR. Lung tissue of animals exposed to SI showed increased inflammation, oedema and apoptosis as reflected by the increase in W/D ratio, injury score and cleaved caspase 3 level of the harvested tissues compared with healthy animals. CONCLUSION: We have successfully developed a small animal model of pure SI-induced ALI. This model is offered to the scientific community as a reliable model of isolated pulmonary SI-induced injury without the confounding variables of cutaneous injury or other systemic pathology to be used for study of novel therapeutics or other investigation.

Stathmin expression in metastatic colorectal cancer.

OBJECTIVES: To evaluate the relationship between stathmin expression and clinical outcome in colorectal cancer (CRC). BACKGROUND: Stathmin is a phosphoprotein involved in the regulation of microtubule dynamics and integration of intracellular signaling pathways. Stathmin has been implicated in the tumorigenesis of several cancers and is a potential therapeutic target. METHODS: Stathmin expression was evaluated in 25 metastatic CRC (mCRC) patients by immunohistochemistry (IHC). Ki67 IHC and TUNEL assay were also evaluated in mCRC for cell proliferation and apoptosis. RESULTS: High expression of stathmin was correlated with CRC metastasis (p = .0084), and significantly worse overall survival (OS) in CRC patients (p = .036). There was a significant increase in cell proliferation and a decrease in apoptosis in liver metastasis compared with CRC primary tumors as determined by Ki67 IHC and TUNEL assay (p < .0001). We also observed a significant positive correlation between stathmin level and cell proliferation in both CRC primary tumor and liver metastasis (p = .0429 to 0.0451; r = .4236 to .4288). CONCLUSION: Stathmin expression correlated with worse patient prognosis in mCRC patients and positively correlated with increased cell proliferation. Together, our findings indicate stathmin as a novel potential marker for increased risk of CRC-specific mortality and identify stathmin as an attractive therapeutic target for the treatment of mCRC.

Correlation of PRL3 expression with colorectal cancer progression.

OBJECTIVES: To evaluate the relationship between phosphatase of regenerating liver 3 (PRL3) expression and clinical outcome in colorectal cancer (CRC). BACKGROUND: PRL3, a protein tyrosine phosphatase functions as one of the key regulatory enzymes of various signal transduction pathways. PRL3 is highly expressed in a majority of cancers and is a novel potential therapeutic target. METHODS: PRL3 expression was evaluated by immunohistochemistry in 167 patients with CRC, 37 patients with no disease, and 26 patients with metastatic CRC (mCRC). Phosphorylated Akt at serine 473 (p-Akt S473) expression was also evaluated by immunohistochemistry in mCRC patients. RESULTS: High expression of PRL3 was correlated with CRC progression, and every one unit increase in PRL3 level contributed to an increase in the rate of death by 1%-1.7%. PRL3 expression was significantly higher in liver metastases compared with primary tumors and showed a significant positive correlation with the expression level of p-Akt S473. CONCLUSION: PRL3 expression levels associated with CRC progression and metastasis, and positively correlated with activated Akt level in mCRC. Together, these findings indicated that PRL3 might be a potential marker for increased risk of CRC-specific tumor burden and identify PRL3 as an attractive therapeutic target for mCRC treatment.

Prognostic and therapeutic implications of NHERF1 expression and regulation in colorectal cancer.

BACKGROUND: Na+ /H+ exchanger regulatory factor 1 (NHERF1) has been implicated in the tumorigenesis of several cancer types and is a potential therapeutic target. The current study evaluated the relationship between NHERF1 expression and clinical outcome in colorectal cancer (CRC). METHODS: NHERF1 expression was evaluated by immunohistochemistry in 167 patients with CRC primary tumors, 37 patients with no disease, and 27 patients with metastatic CRC (mCRC); and in the orthotopically implanted tumors in mice. NHERF1 expression was manipulated in CRC cells using inducible short hairpin RNAs to determine its biological functions. RESULTS: High expression of NHERF1 correlated with CRC progression and metastasis, as well as significantly worse overall survival, recurrence-free survival, and disease-specific survival. Orthotopic implantation studies demonstrated increased NHERF1 expression in liver metastases. Treatment of CRC xenografts with insulin-like growth factor 1 receptor (IGF1R) inhibitors downregulated NHERF1 expression, indicating NHERF1 is downstream of IGF1R signaling. Knockdown of NHERF1 increased apoptosis and reduced X-linked inhibitor of apoptosis protein (XIAP) and survivin expression, indicating NHERF1 is critical for CRC cell survival. CONCLUSION: NHERF1 expression levels correlated with worse prognosis in patients with CRC and plays a critical role in CRC cell survival. Together, our findings establish NHERF1 as a novel potential marker for increased risk of CRC-specific mortality and identify NHERF1 as an attractive therapeutic target for mCRC treatment.

Role of keratan sulfate expression in human pancreatic cancer malignancy.

Keratan sulfate (KS) is a sulfated linear polymer of N-acetyllactosamine. Proteoglycans carrying keratan sulfate epitopes were majorly observed in cornea, cartilage and brain; and mainly involved in embryonic development, cornea transparency, and wound healing process. Recently, expression of KS in cancer has been shown to be highly associated with advanced tumor grade and poor prognosis. Therefore, we aimed to identify the expression of KS epitope in human pancreatic cancer primary and metastatic tumor lesions. Immunohistochemical analysis of KS expression was performed on primary pancreatic tumors and metastatic tissues. We observed an increased expression of KS epitope on primary tumor tissues compared to uninvolved normal and tumor stroma; and is associated with worse overall survival. Moreover, lung metastatic tumors show a higher-level expression of KS compared to primary tumors. Interestingly, KS biosynthesis specific glycosyltransferases expression was differentially regulated in metastatic pancreatic tumors. Taken together, these results indicate that aberrant expression of KS is predictive of pancreatic cancer progression and metastasis and may serve as a novel prognostic biomarker for pancreatic cancer.

TGFß and IGF1R signaling activates protein kinase A through differential regulation of ezrin phosphorylation in colon cancer cells.

Aberrant cell survival plays a critical role in cancer progression and metastasis. We have previously shown that ezrin, a cAMP-dependent protein kinase A-anchoring protein (AKAP), is up-regulated in colorectal cancer (CRC) liver metastasis. Phosphorylation of ezrin at Thr-567 activates ezrin and plays an important role in CRC cell survival associated with XIAP and survivin up-regulation. In this study, we demonstrate that in FET and GEO colon cancer cells, knockdown of ezrin expression or inhibition of ezrin phosphorylation at Thr-567 increases apoptosis through protein kinase A (PKA) activation in a cAMP-independent manner. Transforming growth factor (TGF) ß signaling inhibits ezrin phosphorylation in a Smad3-dependent and Smad2-independent manner and regulates pro-apoptotic function through ezrin-mediated PKA activation. On the other hand, ezrin phosphorylation at Thr-567 by insulin-like growth factor 1 receptor (IGF1R) signaling leads to cAMP-dependent PKA activation and enhances cell survival. Further studies indicate that phosphorylated ezrin forms a complex with PKA RII, and dephosphorylated ezrin dissociates from the complex and facilitates the association of PKA RII with AKAP149, both of which activate PKA yet lead to either cell survival or apoptosis. Thus, our studies reveal a novel mechanism of differential PKA activation mediated by TGFß and IGF1R signaling through regulation of ezrin phosphorylation in CRC, resulting in different cell fates. This is of significance because TGFß and IGF1R signaling pathways are well-characterized tumor suppressor and oncogenic pathways, respectively, with important roles in CRC tumorigenesis and metastasis. Our studies indicate that they cross-talk and antagonize each other's function through regulation of ezrin activation. Therefore, ezrin may be a potential therapeutic target in CRC.

Akt inhibitor MK-2206 promotes anti-tumor activity and cell death by modulation of AIF and Ezrin in colorectal cancer.

BACKGROUND: There is extensive evidence for the role of aberrant cell survival signaling mechanisms in cancer progression and metastasis. Akt is a major component of cell survival-signaling mechanisms in several types of cancer. It has been shown that activated Akt stabilizes XIAP by S87 phosphorylation leading to survivin/XIAP complex formation, caspase inhibition and cytoprotection of cancer cells. We have reported that TGFß/PKA/PP2A-mediated tumor suppressor signaling regulates Akt phosphorylation in association with the dissociation of survivin/XIAP complexes leading to inhibition of stress-dependent induction of cell survival. METHODS: IGF1R-dependent colon cancer cells (GEO and CBS) were used for the study. Effects on cell proliferation and cell death were determined in the presence of MK-2206. Xenograft studies were performed to determine the effect of MK-2206 on tumor volume. The effect on various cell death markers such as XIAP, survivin, AIF, Ezrin, pEzrin was determined by western blot analysis. Graph pad 5.0 was used for statistical analysis. P < 0.05 was considered significant. RESULTS: We characterized the mechanisms by which a novel Akt kinase inhibitor MK-2206 induced cell death in IGF1R-dependent colorectal cancer (CRC) cells with upregulated PI3K/Akt signaling in response to IGF1R activation. MK-2206 treatment generated a significant reduction in tumor growth in vivo and promoted cell death through two mechanisms. This is the first report demonstrating that Akt inactivation by MK-2206 leads to induction of and mitochondria-to-nuclear localization of the Apoptosis Inducing Factor (AIF), which is involved in caspase-independent cell death. We also observed that exposure to MK-2206 dephosphorylated Ezrin at the T567 site leading to the disruption of Akt-pEzrin-XIAP cell survival signaling. Ezrin phosphorylation at this site has been associated with malignant progression in solid tumors. CONCLUSION: The identification of these 2 novel mechanisms leading to induction of cell death indicates MK-2206 might be a potential clinical candidate for therapeutic targeting of the subset of IGF1R-dependent cancers in CRC.

Ezrin expression and cell survival regulation in colorectal cancer.

Colorectal cancer (CRC) is the second largest cause of cancer deaths in the United States. A key barrier that prevents better outcomes for this type of cancer as well as other solid tumors is the lack of effective therapies against the metastatic disease. Thus there is an urgent need to fill this gap in cancer therapy. We utilized a 2D-DIGE proteomics approach to identify and characterize proteins that are differentially regulated between primary colon tumor and liver metastatic deposits of the IGF1R-dependent GEO human CRC xenograft, orthotopically implanted in athymic nude mice that may serve as potential therapeutic targets against CRC metastasis. We observed increased expression of ezrin in liver metastasis in comparison to the primary colonic tumor. Increased ezrin expression was further confirmed by western blot and microarray analyses. Ezrin, a cytoskeletal protein belonging to Ezrin-Radixin-Moesin (ERM) family plays important roles in cell motility, invasion and metastasis. However, its exact function in colorectal cancer is not well characterized. Establishment of advanced GEO cell lines with enhanced liver-metastasizing ability showed a significant increase in ezrin expression in liver metastasis. Increased phosphorylation of ezrin at the T567 site (termed here as p-ezrin T567) was observed in liver metastasis. IHC studies of human CRC patient specimens showed an increased expression of p-ezrin T567 in liver metastasis compared to the primary tumors of the same patient. Ezrin modulation by siRNA, inhibitors and T567A/D point mutations significantly downregulated inhibitors of apoptosis (IAP) proteins XIAP and survivin that have been linked to increased aberrant cell survival and metastasis and increased cell death. Inhibition of the IGF1R signaling pathway by humanized recombinant IGF1R monoclonal antibody MK-0646 in athymic mouse subcutaneous xenografts resulted in inhibition of p-ezrin T567 indicating ezrin signaling is downstream of the IGF1R signaling pathway. We identified increased expression of p-ezrin T567 in CRC liver metastasis in both orthotopically implanted GEO tumors as well as human patient specimens. We report for the first time that p-ezrin T567 is downstream of the IGF1R signaling and demonstrate that ezrin regulates cell survival through survivin/XIAP modulation.

In vivo analysis of insulin-like growth factor type 1 receptor humanized monoclonal antibody MK-0646 and small molecule kinase inhibitor OSI-906 in colorectal cancer.

The development and characterization of effective anticancer drugs against colorectal cancer (CRC) is of urgent need since it is the second most common cause of cancer death. The study was designed to evaluate the effects of two IGF-1R antagonists, MK-0646, a recombinant fully humanized monoclonal antibody and OSI-906, a small molecule tyrosine kinase inhibitor on CRC cells. Xenograft study was performed on IGF-1R-dependent CRC cell lines for analyzing the antitumor activity of MK-0646 and OSI-906. Tumor proliferation and apoptosis were assessed using Ki67 and TUNEL assays, respectively. We also performed in vitro characterization of MK-0646 and OSI-906 treatment on CRC cells to identify mechanisms associated with drug-induced cell death. Exposure of the GEO and CBS tumor xenografts to MK-0646 or OSI-906 led to a decrease in tumor growth. TUNEL analysis showed an increase of approximately 45-55% in apoptotic cells in both MK-0646 and OSI-906 treated tumor samples. We report the novel finding that treatment with IGF-1R antagonists led to downregulation of X-linked inhibitor of apoptosis (XIAP) protein involved in cell survival and inhibition of cell death. In conclusion, IGF-1R antagonists (MK-0646 and OSI-906) demonstrated single agent inhibition of subcutaneous CRC xenograft growth. This was coupled to pro-apoptotic effects resulting in downregulation of XIAP and inhibition of cell survival. We report a novel mechanism by which MK-0646 and OSI-906 elicits cell death in vivo and in vitro. Moreover, these results indicate that MK-0646 and OSI-906 may be potential anticancer candidates for the treatment of patients with IGF-1R-dependent CRC.

Differential PKA activation and AKAP association determines cell fate in cancer cells.

BACKGROUND: The dependence of malignant properties of colorectal cancer (CRC) cells on IGF1R signaling has been demonstrated and several IGF1R antagonists are currently in clinical trials. Recently, we identified a novel pathway in which cAMP independent PKA activation by TGFß signaling resulted in the destabilization of survivin/XIAP complex leading to increased cell death. In this study, we evaluated the effect of IGF1R inhibition or activation on PKA activation and its downstream cell survival signaling mechanisms. METHODS: Small molecule IGF1R kinase inhibitor OSI-906 was used to test the effect of IGF1R inhibition on PKA activation, AKAP association and its downstream cell survival signaling. In a complementary approach, ligand mediated activation of IGF1R was performed and AKAP/PKA signaling was analyzed for their downstream survival effects. RESULTS: We demonstrate that the inhibition of IGF1R in the IGF1R-dependent CRC subset generates cell death through a novel mechanism involving TGFß stimulated cAMP independent PKA activity that leads to disruption of cell survival by survivin/XIAP mediated inhibition of caspase activity. Importantly, ligand mediated activation of the IGF1R in CRC cells results in the generation of cAMP dependent PKA activity that functions in cell survival by inhibiting caspase activity. Therefore, this subset of CRC demonstrates 2 opposing pathways organized by 2 different AKAPs in the cytoplasm that both utilize activation of PKA in a manner that leads to different outcomes with respect to life and death. The cAMP independent PKA activation pathway is dependent upon mitochondrial AKAP149 for its apoptotic functions. In contrast, Praja2 (Pja2), an AKAP-like E3 ligase protein was identified as a key element in controlling cAMP dependent PKA activity and pro-survival signaling. Genetic manipulation of AKAP149 and Praja2 using siRNA KD had opposing effects on PKA activity and survivin/XIAP regulation. CONCLUSIONS: We had identified 2 cytoplasmic pathways dependent upon the same enzymatic activity with opposite effects on cell fate in terms of life and death. Understanding the specific mechanistic functions of IGF1R with respect to determining the PKA survival functions would have potential for impact upon the development of new therapeutic strategies by exploiting the IGF1R/cAMP-PKA survival signaling in cancer.