Functional Interrogation of Ca2+ Signals in Human Cancer Cells In Vitro and Ex Vivo by Fluorescent Microscopy and Molecular Tools

Genetically encoded calcium indicators (GECIs) and high-resolution confocal microscopy enable dynamic visualization of calcium signals in cells and tissues. Two-dimensional and 3D biocompatible materials mimic the mechanical microenvironments of tumor and healthy tissues in a programmable manner. Cancer xenograft models and ex vivo functional imaging of tumor slices reveal physiologically relevant functions of calcium dynamics in tumors at different progression stages. Integration of these powerful techniques allows us to quantify, diagnose, model, and understand cancer pathobiology. Here, we describe detailed materials and methods used to establish this integrated interrogation platform, from generating transduced cancer cell lines that stably express CaViar (GCaMP5G + QuasAr2) to in vitro and ex vivo calcium imaging of the cells in 2D/3D hydrogels and tumor tissues. These tools open the possibility for detailed explorations of mechano-electro-chemical network dynamics in living systems.

Abstract 5431: FGF7 peptide (FGF7p) mimetic mitigates urothelial injury from cyclophosphamide or radiation

Background: Hemorrhagic cystitis from chemical or radiation bladder injury can cause life-threatening bleeding and/or urothelial cancer. Fibroblast growth factor 7 (FGF7) blocks urothelial apoptosis induced by cyclophosphamide (CPP) or radiation, but there are limitations to its use in patients, including an inability to apply it by direct bladder infusion and the high cost due to the large size of the protein (18.8 kDa).

Purpose: We previously identified a small peptide that equaled or exceeded the mitigation effect of full length FGF2 on acute radiation syndrome. Benefits of developing a similar FGF7 biomimetic peptide include lower likelihood of inflammation, longer shelf life, higher purity, and lower cost than the full-length protein.

Methods: Based on the 3-dimensional structure of FGF2 peptide, a corresponding FGF7 peptide (FGF7p) consisting of 19 amino acids was identified and synthesized. FGF7p or vehicle was given subcutaneously (SQ) to female mice subjected to sham injury, intraperitoneal (IP) CPP or external beam radiation over the bladder. One day after injury, bladders were harvested. Slides with paraffin embedded tissues underwent H&E staining, TUNEL and immunofluorescence (IF) assays.

Results: In uninjured control mice, a 20 mg/kg threshold dose of FGF7p induced expression of phosphorylated (activated) FRS2a (pFRS2a) and pAKT in urothelium (consistent with cytoprotective effects of FGF7, albeit at a 4x higher dose than full length FGF7). Unexpectedly, FGF7p activation of urothelial FRS2a and AKT was delayed 24 hours compared to FGF7. FGF7p (20 mg/kg) or vehicle was given at 72 and 48 hours prior to CPP (150 mg/kg). One day after CPP, TUNEL staining revealed an increase in apoptotic and sloughing urothelial cells in vehicle-treated mice compared to in FGF7p-treated mice. IF for pAKT and its targets, pS6K and pBAD, revealed minimal staining in vehicle-treated mice, but strong urothelial staining for all protective markers in FGF7p-treated mice. Using the same dosing strategy, we subjected anesthetized mice to 10 Gy radiation over the bladder. One day after injury, TUNEL staining revealed many more apoptotic urothelial nuclei in control mice, than in FGF7p-treated mice.

Conclusions: FGF7p appears to block bladder urothelial apoptosis via AKT and its targets, in a similar manner to FGF7. FGF7p is 200x less expensive to make vs. FGF7 and is likely to work via direct bladder infusion (avoiding systemic side effects) due to its small size. Our future studies will clarify long term benefits of FGF7p and assess effectiveness of direct bladder infusion.

Citation Format: Sridhar Narla, Lori P. Rice, David Ostrov, Steven G. Swarts, Dietmar W. Siemann, Carlton M. Bates. FGF7 peptide (FGF7p) mimetic mitigates urothelial injury from cyclophosphamide or radiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5431.

Towards an integrative understanding of cancer mechanobiology: calcium, YAP, and microRNA under biophysical forces

An increasing number of studies have demonstrated the significant roles of the interplay between microenvironmental mechanics in tissues and biochemical-genetic activities in resident tumor cells at different stages of tumor progression. Mediated by molecular mechano-sensors or -transducers, biomechanical cues in tissue microenvironments are transmitted into the tumor cells and regulate biochemical responses and gene expression through mechanotransduction processes. However, the molecular interplay between the mechanotransduction processes and intracellular biochemical signaling pathways remains elusive. This paper reviews the recent advances in understanding the crosstalk between biomechanical cues and three critical biochemical effectors during tumor progression: calcium ions (Ca²⁺), yes-associated protein (YAP), and microRNAs (miRNAs). We address the molecular mechanisms underpinning the interplay between the mechanotransduction pathways and each of the three effectors. Furthermore, we discuss the functional interactions among the three effectors in the context of soft matter and mechanobiology. We conclude by proposing future directions on studying the tumor mechanobiology that can employ Ca²⁺, YAP, and miRNAs as novel strategies for cancer mechanotheraputics. This framework has the potential to bring insights into the development of novel next-generation cancer therapies to suppress and treat tumors.

Normal tissue and tumor microenvironment adaptations to aerobic exercise enhance doxorubicin anti-tumor efficacy and ameliorate its cardiotoxicity in retired breeder mice

Aerobic exercise is receiving increased recognition in oncology for its multiple purported benefits. Exercise is known to induce physiologic adaptations that improve patient quality-of-life parameters as well as all-cause mortality. There also is a growing body of evidence that exercise may directly alter the tumor microenvironment to influence tumor growth, metastasis, and response to anticancer therapies. Furthermore, the physiologic adaptations to exercise in normal tissues may protect against treatment-associated toxicity and allow for greater treatment tolerance. However, the exercise prescription required to induce these beneficial tumor-related outcomes remains unclear. This study characterized the aerobic adaptations to voluntary wheel running in normal tissues and the tumor microenvironment. Female, retired breeder BALB/c mice and syngeneic breast adenocarcinoma cells were utilized in primary tumor and metastasis models. Aerobic exercise was found to induce numerous adaptations across various tissues in these mice, although primary tumor growth and metastasis were largely unaffected. However, intratumoral hypoxia and global metabolism were altered in the tumors of exercising hosts relative to non-wheel running controls. Doxorubicin chemotherapy also was found to be more efficacious at delaying tumor growth with adjuvant aerobic exercise. Additionally, doxorubicin-induced cardiac toxicity was ameliorated in exercising hosts relative to non-wheel running controls. Taken together, these data suggest that the normal tissue and tumor microenvironment adaptations to aerobic exercise can improve doxorubicin efficacy while simultaneously limiting its toxicity.

Abstract 905: Investigating the effects of aerobic exercise on preclinical breast cancer outcomes

Aerobic exercise is receiving increased recognition in oncology spheres for its multiple purported benefits. Exercise is known to induce physiologic responses that improve patient quality-of-life parameters as well as all-cause mortality. There is also a growing body of evidence that suggests exercise may directly impact tumor biology and therapy outcomes. Previous studies suggest that exercise can improve tumor perfusion and ameliorate intratumoral hypoxia, increase recruitment of cytotoxic immune cells, and alter metabolic substrate availability. Furthermore, the physiologic adaptations to exercise in normal tissue may protect against treatment-associated toxicity and allow for greater treatment tolerance. With regard to cancer metastasis, reports have been conflicting. The goal of this study was to characterize the effect of exercise on normal tissue adaptations, tumor microenvironment, metastasis, and doxorubicin cardiotoxicity in preclinical breast cancer models. Female, retired breeder BALB/c mice were employed, and aerobic exercise was modeled by singly-housing mice with access to wireless, low-profile voluntary running wheels. Sedentary controls were singly housed with plastic huts. Syngeneic 4T1 or EMT6 breast adenocarcinoma cells were inoculated either intraductally into the 4th mammary duct or intravenously into the tail-vein. In one study, doxorubicin was administered via 3 intraperitoneal (IP) injections over 7 days for a total dose of 11 mg/kg. Exercising mice steadily increased the amount they ran until they reached a plateau of 10-12 km/day from day 10 onward. This exercise regime induced cardiac hypertrophy and oxidative phenotypes in the quadriceps muscle relative to non-wheel running controls. It also prevented the cardiac atrophy and bodyweight loss induced by doxorubicin treatment. In mice bearing intraductal EMT6 tumors, exercise delayed tumor growth and improved survival relative to non-wheel running controls. However, exercise did not alter 4T1 tumor growth or survival. The effect of exercise on metastasis was assessed under three conditions, 1) in mice that ran before and after intravenous 4T1 cell injection, 2) mice that had limited (low exercise) or full (high exercise) access to running wheels after intravenous 4T1 cell injection, and 3) mice than ran after intraductal 4T1 cell injection. Under all three conditions, exercise did not affect the establishment of pulmonary macro-metastases. Taken together, these data suggest that while aerobic exercise may impact tumor growth and metastasis only in some tumor models, the normal tissue adaptations induced by exercise can be sufficient to protect against chemotherapy toxicity, thus warranting further studies of this modality in oncology settings.

Citation Format: Zachary Richard Wakefield, Mai Tanaka, Angela Bundy, Sharon Lepler, Christine Pampo, Lori Rice, Dietmar W. Siemann. Investigating the effects of aerobic exercise on preclinical breast cancer outcomes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 905.

Abstract 3154: Host and neoplastic cell Axl inhibition impair prostate and breast cancer bone metastasis

Prostate and breast cancers are the most prevalent and the second leading causes of cancer-deaths for men and women in the United States. Cancer survival rates generally worsen significantly with advanced and disseminated disease with nearly 90% of all cancer deaths resulting from metastasis. For breast and prostate cancers, bone is the most common site of metastasis. A key signaling pathway involved in metastatic dissemination of tumor cells is the receptor tyrosine kinase Axl. Axl belongs to the Tyro3, Axl, and MerTK (TAM) subfamily, is expressed in a variety of tumor types, including breast and prostate, and is associated with poor prognosis, metastasis, and outcome. The goal of the present study was to characterize the role of Axl signaling in prostate and breast cancer cell dissemination to bone. This was accomplished using Axl knockdown neoplastic cells, a selective small molecule Axl inhibitor (BGB324), and osteoclast progenitor cells in vitro, as well as intracardiac injection of Axl knockdown tumor cells in vivo. The results showed that Axl inhibition significantly decreases tumor cell migration and invasion in vitro, and suppression of Axl signaling in osteoclast precursor cells reduces the formation of mature osteoclasts. In vivo, Axl knockdown in prostate and breast cancer cells significantly suppressed the formation of neoplastic bone lesions. Taken together our findings indicate that therapeutic targeting of Axl may impair tumor metastasis to the bones through neoplastic and host cell signaling axes.

Citation Format: Mai Tanaka, Dietmar W. Siemann. Host and neoplastic cell Axl inhibition impair prostate and breast cancer bone metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3154.

Abstract 1477: Co-targeting c-Met and c-Src pathways to inhibit metastatic cancer cell migration and invasion

Overexpression of tyrosine kinases c-Src and c-Met has been shown to be highly associated with disease progression and poor clinical outcomes in many types of cancers. Although small molecule Src or Met inhibitors are being individually evaluated in clinical trials, patient data suggest that single treatment with any of these inhibitors only yield limited effects. One possibility is that redundant signaling pathways in tumor cells may allow tumor cell functions less interrupted upon inhibition of only one pathway. We therefore propose that c-Src and c-Met are two compensatory pathways that may cooperate to promote cancer metastasis. In order to delineate this hypothesis, we studied treatment effects of combining inhibitors targeting c-Src (dasatinib) and c-Met (ASLAN002) on multiple functional behaviors associated with tumor metastasis in c-Src and c-Met expressing metastatic cancer cells. Combination of Src- and Met-inhibitors was found to strongly inhibit cell colony formation by clonogenic survival assay. In a wound-healing assay, compared to either treatment alone, the combinatorial treatment exhibited greater suppression on cell motility. In addition, using a Matrigel-based Transwell assay, dasatinib plus ASLAN002 resulted in significant reduction of cell invasion in the presence or absence of HGF. Western blot analysis demonstrated that co-targeting Met and Src kinases lead to not only inhibition on c-Met and c-Src autophosphorylation but also multiple downstream kinases such as focal adhesion kinase (FAK), Akt and extracellular signal-regulated kinase (ERK). These data indicate that combined application of small molecule Src and Met inhibitors cause significant impairment on functional behaviors associated with cancer metastasis in vitro including survival, migration and invasion, suggesting that this combination intervention modality may serve as a potential anti-metastatic strategy that could be further tested in metastatic models in vivo.

Citation Format: Yao Dai, Dietmar W. Siemann. Co-targeting c-Met and c-Src pathways to inhibit metastatic cancer cell migration and invasion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1477.

Inhibition of the Axl pathway impairs breast and prostate cancer metastasis to the bones and bone remodeling

Approximately 90% of cancer-related deaths result from cancer metastasis. In prostate and breast cancers, bone is the most common site of cancer cell dissemination. Key steps in the metastatic cascade are promoted through upregulation of critical cell signaling pathways in neoplastic cells. The present study assessed the role of the receptor tyrosine kinase Axl in prostate and breast cancer cell metastasis to bones using (i) Axl knockdown neoplastic cells and osteoclast progenitor cells in vitro, (ii) intracardiac injection of Axl knockdown tumor cells in vivo, and (iii) selective Axl inhibitor BGB324. Axl inhibition in neoplastic cells significantly decreased their metastatic potential, and suppression of Axl signaling in osteoclast precursor cells also reduced the formation of mature osteoclasts. In vivo, Axl knockdown in prostate and breast cancer cells significantly suppressed the formation and progression of bone metastases. Hence, therapeutic targeting of Axl may impair tumor metastasis to the bones through neoplastic and host cell signaling axes.

Using a combination of gangliosides and cell surface vimentin as surface biomarkers for isolating osteosarcoma cells in microfluidic devices

Background

Osteosarcoma (OS) is the most common primary bone tumor and the third leading cause of pediatric cancer deaths. Liquid biopsies are an alternative to current diagnostic imaging modalities that can be used to monitor treatment efficacy and the development of metastases. This study addresses the use of novel biomarkers to detect circulating osteosarcoma cells.

Procedures

Flow cytometry was used to evaluate the relative expression of epithelial cell adhesion molecule (EpCAM), ganglioside 2 and 3 (GD2/3), and cell surface vimentin (CSV) on a panel of OS cell lines. A microfluidic device was used to affirm the efficacy of GD2/3 and CSV to capture CTCs. Once captured, CTCs on the device are enumerated and the capture efficiency for each marker is measured. Patient samples were captured using the LFAM chip.

Results

We report the evaluation of GD2, GD3, and CSV as markers for OS cell capture in cell lines and in patient samples. The results of our capture studies correlate with our flow cytometry data and have shown a low capture efficiency of OS cells using EpCAM antibodies, while showing a moderate capture efficiency of OS cells using the GD2, GD3, and CSV antibodies independently. The combination of biomarkers demonstrate a high capture efficiency of approximately 80%. This is further supported by the detection of 1-1.5 CTCs per mL of blood using GD2 + CSV in OS patient samples.

Conclusions

The combination of GD2 + CSV significantly increased the capture efficacy of OS cells. The detection of CTCs through routine blood sampling may be used clinically for earlier detection of metastases and monitoring the therapeutic effect of treatments in metastatic osteosarcomas.

Bioprinting on Live Tissue for Investigating Cancer Cell Dynamics

A challenge in cancer research is the lack of physiologically responsive in vitro models that enable tracking of cancer cells in tissue-like environments. A model that enables real-time investigation of cancer cell migration, fate, and function during angiogenesis does not exist. Current models, such as 2D or 3D in vitro culturing, can contain multiple cell types, but they do not incorporate the complexity of intact microvascular networks. The objective of this study was to establish a tumor microvasculature model by demonstrating the feasibility of bioprinting cancer cells onto excised mouse tissue. Inkjet-printed DiI⁺ breast cancer cells on mesometrium tissues from C57Bl/6 mice demonstrated cancer cells' motility and proliferation through time-lapse imaging. Colocalization of DAPI⁺ nuclei confirmed that DiI⁺ cancer cells remained intact postprinting. Printed DiI⁺ 4T1 cells also remained viable after printing on Day 0 and after culture on Day 5. Time-lapse imaging over 5 days enabled tracking of cell migration and proliferation. The number of cells and cell area were significantly increased over time. After culture, cancer cell clusters were colocalized with angiogenic microvessels. The number of vascular islands, defined as disconnected endothelial cell segments, was increased for tissues with bioprinted cancer cells, which suggests that the early stages of angiogenesis were influenced by the presence of cancer cells. Bioprinting cathepsin L knockdown 4T1 cancer cells on wild-type tissues or nontarget 4T1 cells on NG2 knockout tissues served to validate the use of the model for probing tumor cell versus microenvironment changes. These results establish the potential for bioprinting cancer cells onto live mouse tissues to investigate cancer microvascular dynamics within a physiologically relevant microenvironment. Impact statement To keep advancing the cancer biology field, tissue engineering has been focusing on developing in vitro tumor biomimetic models that more closely resemble the native microenvironment. We introduce a novel methodology of bioprinting exogenous cancer cells onto mouse tissue that contains multiple cells and systems within native physiology to investigate cancer cell migration and interactions with nearby microvascular networks. This study corroborates the manipulation of different exogenous cells and host microenvironments that impact cancer cell dynamics in a physiologically relevant tissue. Overall, it is a new approach for delineating the effects of the microenvironment on cancer cells and vice versa.

Abstract B02: Combined inhibition of mTOR and Src family kinases enhances treatment effects in prostate cancer cells

Hyperactivated Akt/mTOR pathway and Src family kinases (SFKs) pathway commonly occur in prostate cancer that is highly associated with disease progression and poor prognosis. Therefore, small-molecule inhibitors targeting these pathways have been studied extensively for the treatment of advanced prostate cancer. Nevertheless, clinical observation suggests that individual treatment with either inhibitor only yields limited antitumor effects in patients. One possible interpretation is that these signaling pathways are redundant, such that blocking one pathway is not sufficient to yield considerable efficacies. In this regard, we combined mTOR inhibitor rapamycin and Src inhibitor dasatinib to detect functional behaviors in prostate cancer cells. Cell proliferation was detected by MTT, and clonogenic survival was tested by colony formation assay. Cell migration was assessed by “wound-healing” scratch assay. Protein expression was detected by Western blot analysis. We found that rapamycin plus dasatinib showed greater inhibition on cell proliferation and clonogenic survival than either single agent. Such combination effects were additive in PC-3 and synergistic in DU145 cells, respectively, as reflected by combination index calculation. In addition, cell migration was suppressed to a greater extent by combination treatment than either treatment alone. At the molecular level, co-targeting mTOR and SFKs leads to strong inhibition of not only phosphorylation of these two proteins but also their downstream components such as Akt, focal adhesion kinase (FAK), S6K and 4E-BP1. These data indicate that co-targeting mTOR and Src pathways is able to achieve enhanced tumor-suppressing effects in prostate cancer cells with overexpression of both kinases, suggesting that this combinative intervention modality may serve as a potential anticancer strategy that could be further tested in advanced prostate cancer models in vivo.

Note: This abstract was not presented at the conference.

Citation Format: Yao Dai, Dietmar W Siemann. Combined inhibition of mTOR and Src family kinases enhances treatment effects in prostate cancer cells [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr B02.

Abstract 6114: Host and neoplastic cells utilize Axl for breast cancer bone metastasis

Breast cancer is the most commonly diagnosed malignancy and the second leading cause of cancer-related death for women in the United States. Approximately 90% of cancer-related death results from metastasis, and the bone is the most common site of metastasis for breast cancer. Upregulation of signaling pathways can promote the metastatic phenotypes of neoplastic cells, including cell migration, invasion, proliferation and angiogenesis. In addition, when breast cancer cells disseminate to the bone, neoplastic cells upregulate signaling pathways to activate osteoclast-induced bone resorption. A key pathway involved in metastatic spread of cancer cells is the receptor tyrosine kinase Axl. Genetic and pharmacologic Axl inhibition in both human and rodent breast cancer cell lines (MDA-MB-231 and 4T1) impaired tumor cell migration and invasion. Intracardiac inoculation of Axl knockdown (KD) MDA-MB-231 cells significantly decreased the number of bone metastases compared to the scrambled control MDA-MB-231 cells. Another mechanism by which Axl inhibition impaired bone metastasis is through the modulation of osteoclast maturation and activity. Co-culture of Axl KD breast cancer cells with murine osteoclast precursor cells (Raw264.7) significantly reduced the number of tumor cell-induced osteoclast resorption pits on bone slices. In addition, genetic and pharmacologic inhibition of Axl in Raw264.7 cells as well as bone marrow derived osteoclast precursor cells, significantly reduced osteoclast formation and activity. Scrambled control and Axl KD Raw264.7 cells were cultured in serum free medium for 24 hours, and their conditioned media were collected. The conditioned media of Axl KD Raw264.7 cells revealed significantly decreased levels of monocyte chemoattractant protein 1 (MCP-1), which known to promote osteoclastogenesis, compared to the scrambled control Raw264.7 cells. In summary, we have demonstrated that inhibition of Axl decreases breast cancer metastasis to the bone through modulation of the host and neoplastic cell functions. Collectively, these data indicate that Axl signaling may be a promising therapeutic target to impair tumor progression and metastasis.

Citation Format: Mai Tanaka, Dietmar W. Siemann. Host and neoplastic cells utilize Axl for breast cancer bone metastasis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6114.

Abstract A23: A novel tumor microenvironment model that combines bioprinting and tissue culture to investigate cancer cell and microvascular interactions

A challenge in cancer research is the lack of a physiologically responsive in vitro model that allows for the investigation of cancer cells in a tissue-like environment. A model that enables real-time investigation of cancer cell migration, fate, and function during microvascular network growth does not currently exist. While current models such as 2D in vitro models or microfluidic systems incorporate real-time cell tracking and multiple cell types, they do not mimic the complexity of intact networks and tissue environments. The objective of this study was to establish a novel tumor-microvasculature model by demonstrating the feasibility of bioprinting cancer cells onto excised mouse mesometrium tissues. Prelabeled DiI mouse breast cancer (4T1) cells were inkjet-printed onto mouse mesometrium tissues. The cell ink for printing comprised 2% Na-alginate mixed in minimum essential media with 1% PenStrep (MEM) containing 15 million 4T1 cells. A single cancer cell spot per tissue was created by printing 10 drops of cell ink in the same location. MEM was added on top of tissue 30 seconds after printing and then incubated for 5 minutes before being plated into 6-well plates containing MEM supplemented with 20% serum. Tissues were cultured for 5 days, with media being changed every day. The spot of DiI+ cells was imaged every 24 hours to then quantify cell number and area for Day 0, 1, and 2. At Day 2 or 5, tissues were fixed in methanol and labeled with platelet endothelial cell adhesion molecule (PECAM), and E-cadherin, to identify endothelial cells and cancer cells, respectively. Co-localization of DAPI+ nuclei confirmed that DiI+ cells remained intact post-printing. Printed DiI+ 4T1 cells also remained viable after printing on Day 0 and after culture on Day 5. Time-lapse imaging over 5 days in culture enabled tracking of cell motility and proliferation. The number of cells (Day 0: 159 +/- 40, Day 1: 370 +/- 78, Day 2: 889 +/- 184, Day 5: 18,031 +/- 1,695) and cell area (Day 0: 0.72 +/- 0.19, Day 1: 1.89 +/- 0.33, Day 2: 2.92 +/- 0.44, Day 5: 5.93 +/- 0.75 mm2) were significantly increased over time. Moreover, a proliferation assay of anti-BrdU on Day 2 also highlighted that a subset of E-cadherin+ cells are in the S-phase of the cell cycle, contributing to the increase in cell number and cell area. Also, microvessels in the tissue were angiogenic evident by PECAM+ sprouts. These results corroborate that cancer cells are mobile and proliferative in this novel ex vivo model. Further, they demonstrate the potential for bioprinting cancer cells onto live, intact tissues to investigate cancer dynamics within a physiologically relevant microenvironment.

Citation Format: Ariana D. Suarez-Martinez, Marc Sole-Gras, Samantha S. Dykes, Zachary R. Wakefield, Kevin Bauer, Arinola Lampejo, Dietmar W. Siemann, Yong Huang, Walter L. Murfee. A novel tumor microenvironment model that combines bioprinting and tissue culture to investigate cancer cell and microvascular interactions [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr A23.

Abstract 2849: Axl: A promising therapeutic target that leads to multimodal inhibition of the metastatic pathway

Cancer is the second leading cause of death in the United States and approximately 90% of cancer-related deaths result from metastasis, the spread of cancer cells to secondary sites. In tumors, the upregulation of certain signaling pathways promotes the metastatic phenotypes of cancer cells characterized by enhanced invasion, migration, survival, proliferation and induction of angiogenesis. A key pathway involved in metastasis is the receptor tyrosine kinase Axl. Axl is expressed in a variety of tumor types and is associated with poor prognosis, metastasis, and outcome. The purpose of the current study was to evaluate the efficacy of genetic and pharmacologic inhibitions of Axl on the metastatic phenotypes, specifically cell migration, invasion and angiogenesis.

Human breast and prostate cancer cell lines (MDA-MB-231 and PC3-ML, respectively), and human lung microvascular endothelial cell (HMVEC-L) were used in this study. Stable Axl short hairpin RNA (shRNA) knockdown MDA-MB-231 and PC3-ML cell lines were generated by Mission Lentiviral transduction particles (Sigma). The efficacy of genetic and pharmacologic inhibition of Axl on tumor cell migration and invasion was evaluated by transwell migration and invasion assays. The effect of Axl knockdown on prostate cancer cell metastasis in vivo was evaluated by an intracardiac bone metastasis model. Conditioned media of Axl knockdown or control MDA-MB-231 cells were analyzed for angiogenic factors using the human angiogenesis array. The effect of Axl knockdown conditioned medium on angiogenic properties in vitro were assessed by endothelial cell tube formation and sprouting. Induction of angiogenesis in vivo was measured by performing intradermal assay.

Genetic and pharmacologic inhibition of Axl decreases tumor cell migration and invasion. Axl knockdown inhibits metastatic disease burden of prostate cancer. Axl knockdown conditioned medium secretes less pro-angiogenic factors compared to its scramble control cells, suggesting that tumor cells utilize Axl pathway to promote the induction of angiogenesis. Axl knockdown conditioned medium impairs angiogenic properties, including endothelial cell tube formation and sprouting. Axl knockdown of tumor cells suppress tumor cell-induced angiogenesis in vivo. Collectively, these data indicate that Axl is involved in multiple steps of the metastatic pathway and that Axl is a promising anti-metastatic agent to inhibit tumor cell dissemination and initiation of angiogenesis. Further studies are ongoing to understand the downstream molecular signaling of Axl.

Citation Format: Mai Tanaka, Dietmar W. Siemann. Axl: A promising therapeutic target that leads to multimodal inhibition of the metastatic pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2849.

Abstract 3914: mTOR pathway components dictate cell response to Src inhibitors in prostate cancer cells

Src inhibitors have been actively evaluated in the clinic for the treatment of advanced prostate cancer however the effects are modest. One interpretation is that oncogenic signaling pathways are redundant and blocking one pathway is not sufficient to yield considerable efficacies. mTOR pathway is commonly hyperactivated in prostate cancer. However, the functional role of mTOR in Src inhibitor-mediated response remains largely unknown. In the current study, we combined mTOR inhibitor rapamycin and Src inhibitor dasatinib to detect functional behaviors in prostate cancer cells. Cell proliferation and clonogenic survival were detected by MTT and colony formation assay, respectively. Wound-healing” scratch assay was conducted to monitor cell migration, and Matrigel-based transwell assay was applied to assess cell invasion. Protein expression was detected by Western blotting. Gene silencing was detected by siRNA transfection. We found that two agents combined together showed greater inhibition on proliferation and clonogenic survival than either agent alone. Such combination effects were additive or synergistic depending on the cell types, as reflected by combination index calculation. In addition, cell migration and invasion were inhibited in a greater extent by rapamycin plus dasatinib, compared to either treatment alone. At the molecular level, co-targeting mTOR and Src lead to clear inhibition of Src and its downstream pathway focal adhesion kinase (FAK), Akt and mTOR downstream components S6RP and 4E-BP1. Interestingly, knockdown 4EBP1, but not S6RP, attenuated dasatinib-mediated functional inhibition. These data indicate that adding mTOR inhibitors to Src-based intervention may achieve better treatment outcomes. Such combination could be evaluated as a novel treatment strategy for prostate cancer patients who are less responsive to Src inhibitors. In addition, 4EBP1 may be used as a candidate predictive biomarker for monitoring clinical effectiveness of Src inhibitors in prostate cancer.

Citation Format: Yao Dai, Dietmar W. Siemann. mTOR pathway components dictate cell response to Src inhibitors in prostate cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3914.

Reliability of blood lactate as a measure of exercise intensity in different strains of mice during forced treadmill running

Exercise has long been known to be beneficial to human health. Studies aimed at understanding the effects of exercise specifically focus on predetermined exercise intensities defined by measuring the aerobic capacity of each individual. Many disease models involving animal training often establish aerobic capacity by using the maximal lactate steady state (MLSS), a widely used method in humans that has frequently been used in rodent studies. The MLSS is defined as the highest exercise intensity at which blood lactate concentration remains constant and is roughly equivalent to 70–80% of maximal aerobic capacity. Due to our up-coming experiments investigating the effect of different exercise intensities in specific strains of tumor-bearing mice, the aim of the present study was to determine the MLSS in athymic nude (NCr nu/nu and NMRI), CDF1, and C3H mice by treadmill running at increasing speeds. However, despite thorough exercise acclimation and the use of different exercise protocols and aversive stimuli, less than half of the experiments across strains pointed towards an established MLSS. Moreover, gently prodding the mice during low to moderate intensity running caused a 30–121% (p<0.05) increase in blood lactate concentration compared to running without stimulation, further questioning the use of lactate as a measure of exercise intensity. Overall, MLSS is difficult to determine and large variations of blood lactate levels were observed depending on the exercise protocol, mice handling strategy and strain. This should be considered when planning experiments in mice using forced exercise protocols.

Prostate cancer cell growth characteristics in serum and prostate-conditioned media from moderate-intensity exercise-trained healthy and tumor-bearing rats

Physical activity is associated with diminished risk of several cancers, and preclinical studies suggest exercise training may alter tumor cell growth in certain tissue(s) (e.g., adipose). From moderate-intensity exercise-trained rats versus sedentary controls, we hypothesized 1) there will be a decreased prostate cancer cell viability and migration in vitro and, within the prostate, a reduced 5α-reductase 2 (5αR2) and increased caspase-3 expression, and 2) that exercise training in tumor-bearing (TB) animals will demonstrate a reduced tumor cell viability in prostate-conditioned media. Serum and prostate were harvested from sedentary or exercise-trained (treadmill running, 10-11 weeks) immune-competent (Copenhagen; n = 20) and -deficient (Nude; n = 18) rats. AT-1 and PC-3 prostate cancer cells were grown in one or more of the following: serum-supplemented media (SSM), SSM from TB rats (SSM-TB), prostate-conditioned media (PCM) or PCM from TB rats (PCM-TB) for 24-96 h under normoxic (18.6% O₂) or hypoxic (5% O₂) conditions. Under normoxic condition, there was a decreased AT-1 cell viability in SSM and PCM from the exercise-trained (ET) immune-competent rats, but no difference in PC-3 cell viability in SSM and PCM from ET Nude rats versus the sedentary (SED) group, or in SSM-TB from ET-TB Nude rats versus the SED-TB group. However, there was a decreased PC-3 cell viability in the PCM-TB of the ET-TB group versus SED-TB group. PC-3 cell viability in all conditioned media types was not altered between groups with hypoxia. In the prostate, exercise training did not alter 5αR2 expression levels, but increased caspase-3 expression levels. In conclusion, prior exercise status reduced prostate cancer cell viability in the serum and prostate of trained rats but did not modify several other key prostate tumor cell growth characteristics (e.g., migration, cell cycle except in S phase of PC-3 cells in PCM-TB). Importantly, once the tumor was established, exercise training reduced tumor cell viability in the surrounding prostate, which may help explain the reduced severity of the disease in patients that exercise.

Failures in preclinical and clinical trials of c-Met inhibitors: evaluation of pathway activity as a promising selection criterion

C-Met is a frequently overexpressed or amplified receptor tyrosine kinase involved in metastatic-related functions, including migration, invasion, cell survival, and angiogenesis. Because of its role in cancer progression and metastasis, many inhibitors have been developed to target this pathway. Unfortunately, most c-Met inhibitor clinical trials have failed to show significant improvement in survival of cancer patients. In these trials tumor type, protein overexpression, or gene amplification are the primary selection criteria for patient inclusion. Our data show that none of these criteria are associated with c-Met pathway activation. Hence, it is conceivable that the majority of c-Met inhibitor clinical trial failures are the consequence of a lack of appropriate patient selection. Further complicating matters, c-Met inhibitors are routinely tested in preclinical studies in the presence of high levels of exogenous Hepatocyte Growth Factor (HGF), its activating ligand. In our studies, several tumor cell lines showed sensitivity to a c-Met inhibitor at high HGF concentrations (50 ng/mL). However, when the tumor lines were tested at HGF levels typically detected in human serum (0.4 to 0.8 ng/mL), inhibitor activity was lost. Thus testing c-Met inhibitors at non-physiological concentrations of HGF may lead to incorrect predictions of drug efficacy in vivo.

Have Clinical Trials Properly Assessed c-Met Inhibitors?

The c-Met/HGF pathway is implicated in cancer progression and dissemination. Many inhibitors have been developed to target this pathway. Unfortunately, most trials have failed to demonstrate efficacy. However, clinical trials have not adequately tested the concept of c-Met pathway inhibition due to the lack of appropriate patient selection criteria.

Abstract 186: Small-molecule inhibition of cathepsins L and K as potential therapeutics for macrophage-driven breast cancer

Tumor-associated macrophages secrete many factors including proteases and growth factors, which ultimately promote the metastatic phenotype of mammary tumors. Due to their numerous pro-tumor functions, tumor-associated macrophages represent an attractive cell population for stromal-targeted anti-cancer therapies. Interleukin-4 stimulation promotes macrophage differentiation from a baseline M0 state to a more pro-tumorigenic M2 phenotype, which is often associated with increased expression of proteases including the lysosomal cathepsin L. Cathepsin L is important in both macrophage and tumor cell invasion, whereby secreted cathepsin L degrades the extracellular matrix allowing for cell infiltration. M0 to M2 differentiation was not accompanied by an overall increase in the protein expression of cathepsin L, however, secreted cathepsin L was increased in the M2 macrophage population. The present study examined the role of cathepsin L in M0 to M2 differentiation and macrophage-mediated tumor cell invasion using the novel cathepsin L/K inhibitors KGP94 and KGP207 [Dr. Kevin Pinney, Baylor University]. Boyden chamber assays revealed that KGP94 and KGP207 prevented in vitro M2 macrophage invasion and reduced macrophage-stimulated invasion of 4T1 murine breast cancer cells. KGP94 and KGP207 treatment also partially prevented IL-4-stimulated M0 to M2 differentiation of macrophages as determined by a decrease in the IL-4-induced expression of the M2 marker Arginase-1 upon drug treatment. Furthermore, exogenous recombinant cathepsin L partially stimulated the expression of Arginase-1 in M0 macrophages. Together, these data suggest that cathepsin L may play a role in macrophage M0 to M2 differentiation. In summary, the novel cathepsin L/K inhibitors KGP94 and KGP207 altered M0 to M2 differentiation, reduced macrophage invasion, and reduced macrophage-stimulated invasion of breast cancer cells. These data highlight the importance of cathepsin L in macrophage functions and suggest that cathepsin inhibition strategies may be therapeutically beneficial by impairing the progression of tumors, particularly those with high recruitment of M2 macrophages.

Citation Format: Samantha S. Dykes, Dietmar W. Siemann. Small-molecule inhibition of cathepsins L and K as potential therapeutics for macrophage-driven breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 186.

Abstract 2507: Axl suppression inhibits cell migration, invasion and survival in breast and prostate cancer cell lines

Cancer is the second leading cause of death in the United States with approximately 90% of cancer-related deaths resulting from metastatic disease. In tumor cells, upregulation of certain signaling pathways promote metastatic phenotypes characterized by enhanced invasion, migration, survival, proliferation and induction of angiogenesis. One pathway of considerable interest involves the receptor tyrosine kinase Axl that is expressed in a variety of tumor types and is associated with poor prognosis and metastasis. Furthermore,

Axl's ligand, Growth arrest specific 6 (Gas6) protein, can activate a number of downstream signaling pathways that promote metastatic phenotypes. The purpose of the current study was to characterize Axl and Gas6 in a number of human tumor cell lines and to determine the effect of Axl suppression on the metastatic phenotypes, specifically cell migration, invasion and survival. A panel of human tumor cell lines, including prostate, breast, colorectal, renal, and osteosarcoma, were characterized for Axl expression by Western blot and qPCR. Gas6 expression was assessed by qPCR and Gas6 secretion was determined in conditioned media by ELISA. Axl was genetically inactivated by shRNA

in prostate (DU145) and breast (MDA-MB-231) cancer cell lines. The efficiency of knockdown was determined by Western blot. The effect of Axl knockdown on the migratory and invasive potentials of these cell lines was evaluated by transwell migration and invasion assays. A clonogenic cell survival assay was used to assess the impact of Axl knockdown on tumor cell viability. Axl-expressing tumor cells expressed and secreted its ligand Gas6, suggesting that Axl is co-expressed with Gas6, and may be mediated by autocrine regulation. Genetic inactivation of Axl (shRNA) inhibited cell migration, invasion and reduced clonogenic cell survival in both the MD-MB-231 breast and DU145 prostate cancer cell lines. These findings suggest that Axl may be a novel therapeutic target to inhibit the dissemination of tumor cells. Ongoing experiments are evaluating the impact of the Axl-targeting agent R428 on Axl signaling and metastatic phenotype.

Citation Format: Mai Tanaka, Samantha S. Dykes, Dietmar W. Siemann. Axl suppression inhibits cell migration, invasion and survival in breast and prostate cancer cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2507.

Tumor oxygenation and cancer therapy-then and now

In 2012, cancer affected 14.1 million people worldwide and was responsible for 8.2 million deaths. The disease predominantly affects aged populations and is one of the leading causes of death in most western countries. In tumors, the aggressive growth of the neoplastic cell population and associated overexpression of pro-angiogenic factors lead to the development of disorganized blood vessel networks that are structurally and functionally different from normal vasculature. A disorganized labyrinth of vessels that are immature, tortuous and hyperpermeable typifies tumor vasculature. Functionally, the ability of the tumor vasculature to deliver nutrients and remove waste products is severely diminished. A critical consequence of the inadequate vascular networks in solid tumors is the development of regions of hypoxia [low oxygen tensions typically defined as oxygen tensions (pO₂ values) < 10 mm Hg]. Tumor cells existing in such hypoxic environments have long been known to be resistant to anticancer therapy, display an aggressive phenotype, and promote tumor progression and dissemination. This review discusses the physiological basis of hypoxia, methods of detection, and strategies to overcome the resulting therapy resistance.

Treatment with Src inhibitor Dasatinib results in elevated metastatic potential in the 4T1 murine mammary carcinoma model

Introduction

The src inhibitor Dasatinib has been widely studied as an anti-metastatic agent. The aims of this study were to examine the effect of Src inhibition on the metastatic potential of the 4T1 murine mammary carcinoma.

Context

Src is a non-receptor tyrosine kinase well-known to contribute to the metastatic potential of tumour cells. It does so through alteration of signalling pathways important to metastasis. Elevated levels of Src are common in many cancer types, and have been correlated with tumour progression and poor patient prognosis.

Aims

This study examined whether disruption of the Src signalling pathway could inhibit metastases formation.

Settings and Design

The Src inhibitor Dasatinib was evaluated in vitro and in vivo using the highly metastatic 4T1 murine mammary adenocarcinoma cell line.

Methods and Material

In vitro assays included growth curve, western blot, migration, and invasion assays. In vivo assays included intradermal and tail vein injection models.

Statistical analysis used

In vitro data were analysed using one-way ANOVA with Dunnett's multiple comparisons in GraphPad Prism 6.0. In vivo data were analysed using GraphPad Prism 6.0, using the Wilcoxon matched pairs test.

Results

Dasatinib is effective at inhibiting in vitro phosphorylation of Src, migration and invasion in the 4T1 cell line, as well as angiogenesis in vivo. In vitro treatment with Dasatinib impaired the metastatic ability of tumour cells as assessed by a tail vein injection model. However, both the syngeneic BALB/c and the athymic nu/nu mice receiving oral doses of the drug developed significantly higher numbers of 4T1 lung metastases. This effect was not seen in a different breast carcinoma cell line, the MDA-MB-231-4175-LM2, nor was this effect seen in the murine fibrosarcoma KHT cell line.

Conclusions

The 4T1 cell line is not an appropriate model to study Src inhibition.

Exercise and the Tumor Microenvironment: Potential Therapeutic Implications

An imbalance in oxygen delivery to demand in solid tumors results in local areas of hypoxia leading to poor prognosis for the patient. We hypothesize that aerobic exercise increases tumor blood flow, recruits previously nonperfused tumor blood vessels, and thereby augments blood-tumor O2 transport and diminishes tumor hypoxia. When combined with conventional anticancer treatments, aerobic exercise can significantly improve the outcomes for several types of cancers.

Abstract 3063: Predicting efficacy of c-Met targeting therapy in autocrine and paracrine tumor cell lines

Tumor cells frequently harbor abnormalities in signaling pathways, leading to increased migration, invasion, survival, angiogenesis, and proliferation. C-Met is one such commonly aberrant pathway. Because of its effects on tumor cells, c-Met has been a target of interest for anti-metastatic therapies. Clinical trials of c-Met inhibition select patients based on total Met expression, or amplification of the Met gene. However, c-Met inhibitors target the activated pathway. We therefore predict that phospho-Met will be a better marker for patient sensitivity to, and hence selection for, c-Met inhibitor trials. C-Met is activated by the endogenous ligand Hepatocyte Growth Factor (HGF). In order to mimic the paracrine signaling during in vitro experiments, many studies add exogenous HGF at concentrations of 25-50 ng/mL. However, these concentrations may not be representative of in vivo conditions. HGF serum levels of healthy humans is 0.4 ng/mL. While HGF levels do rise in cancer patients, it is unusual to see serum levels higher than 1 ng/mL. Conditioned media from several cell lines (MDA-MB-231, PC-3, DU145, LNCaP, OS156, OS521, U87, U118, RKO, KHT, SCC7, and RIF) was collected to analyze for secretion of HGF in conditioned media. These cells were then examined for basal phosphorylation of Met. The cell lines that secreted HGF also had higher levels of phospho-Met in comparison to non-HGF-secreting cell lines. Importantly, levels of total Met did not predict for levels of phospho-Met. In migration and invasion assays, the HGF-secreting cell line KHT was found to be sensitive to the c-Met inhibitor BMS-777607.The non-HGF-secreting cell line DU145 only became sensitive to the inhibitor when high, non-physiologic exogenous levels of HGF (25-50 ng/mL) were added.These results suggest that autocrine activation of the c-Met pathway may be a factor in predicting sensitivity to c-Met inhibition. This may indicate the existence of a subset of patients most likely respond to c-Met inhibition therapy. Furthermore, consideration of exogenous HGF concentration should be considered when conducting preclinical trials of c-Met inhibitors, as addition of exogenous HGF may change the apparent efficacy of the inhibitor.

Citation Format: Veronica S. Hughes, Dietmar W. Siemann. Predicting efficacy of c-Met targeting therapy in autocrine and paracrine tumor cell lines [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 3063. doi:10.1158/1538-7445.AM2017-3063

Abstract 2952: The novel cathepsin L/K inhibitors KGP94 and KGP207 prevent M0 to M2 macrophage differentiation and macrophage-mediated pro-tumor functions

Tumor-associated macrophages play many important roles in tumor progression, including facilitating tumor cell invasion and angiogenesis. Due to their numerous pro-tumor functions, tumor-associated macrophages represent an important cell population in the design of targeted anti-cancer therapies. Interleukin-4-mediated activation of macrophages resulted in an M2-like, or pro-tumor macrophage phenotype, often associated with increased expression of proteases including the lysosomal cathepsin L. Cathepsin L is important in both macrophage and tumor cell invasion, whereby secreted cathepsin L degrades the extracellular matrix, allowing for cell infiltration. The present study examined the role of cathepsin L in M0 to M2 differentiation and macrophage-mediated tumor cell invasion using the novel cathepsin L/K inhibitors KGP94 and KGP207 [Dr. Kevin Pinney, Baylor University]. KGP94 and KGP207 prevented M2 macrophage motility and invasion in in vitro migration and invasion assays. Moreover, KGP94 and KGP207 reduced macrophage-stimulated invasion of 4T1 murine breast cancer cells. Together, these data suggested that cathepsin L was necessary for macrophage invasion and motility and for macrophage-mediated invasion of breast cancer cells. KGP94 and KGP207 treatment partially prevented IL-4-stimulated M0 to M2 differentiation of macrophages as determined by a decrease in the IL-4-induced expression of the M2 marker Arginase-1 upon drug treatment. Additionally, exogenous recombinant cathepsin L partially stimulated the expression of Arginase-1 in M0 macrophages. Together, these data suggest that cathepsin L plays a role in macrophage M0 to M2 differentiation. In conclusion, the novel cathepsin L/K inhibitors KGP94 and KGP207 prevented M0 to M2 differentiation, macrophage invasion, and macrophage-stimulated invasion of breast cancer cells. These data highlight the importance of cathepsin L in macrophage functions and suggest that cathepsin L inhibition is a viable approach for the treatment of tumors associated with high macrophage infiltration.

Citation Format: Samantha S. Dykes, Dietmar W. Siemann. The novel cathepsin L/K inhibitors KGP94 and KGP207 prevent M0 to M2 macrophage differentiation and macrophage-mediated pro-tumor functions [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 2952. doi:10.1158/1538-7445.AM2017-2952

Abstract 4518: Impact of hypoxia on SFK activities in prostate cancer cells

Background: Metastasis is the major reason of disease progression and poor prognosis in prostate cancer. Src family kinases (SFKs), including c-Src, Lyn and Fyn, are non-receptor tyrosine kinases that have been shown to play an essential role in local invasion, castration resistance, and metastasis in prostate cancer. Hypoxia is able to promote metastasis-associated functions by activating various signaling molecules, including SFKs. However, whether all SFK members are upregulated by hypoxia is unclear. In the current study, the effects of hypoxia on cell functions and SFK activities are determined. Further, genetic approaches are applied to identify the typical SFK member that is mostly activated by hypoxia.

Methods: For hypoxic exposure, prostate cancer cells were exposed to low oxygen tensions (1% O2) for varied durations (0, 2, 6, 24 h). For drug treatment, cells were treated with saracatinib (0, 100, 500, 1000 nM) for indicated time periods. To test cell migration, “wound-healing” assay was used by making a scratch on confluent monolayers. Cells that have migrated to the denuded area were imaged. Cell invasion was detected by seeding cells into Matrigel-coated transwell chamber and cells on the bottom membranes were counted after treatment. Clonogenic assay was performed to test cell survival. At the molecular level, SFKs phosphorylation was detected by Western blotting, and gene knockdown was accomplished by siRNA transfection. To investigate expression of p-SFK and HIF-1α in patients, tumor tissues from prostate cancer patients were probed with desired antibody by immunohistochemical staining.

Results: Both p-SFK and HIF-1α were highly expressed in patient tissues with advanced stage, with HIF-1 expression significantly associated with tumor grade and Gleason score. At the cellular level, while short term hypoxic exposure (2-6 h) induced greater cell migration, invasion and survival than prolonged hypoxia (24 h) in PC-3ML and C4-2B, these behaviors were increased under hypoxia with a period of 24 h in TRAMP-C1 cells. Further, hypoxia enhanced SFK phosphorylation in the pattern that was consistent with cell functions. Knockdown SRC, but not LYN, abolished hypoxia-induced invasion and p-SFK expression. Lastly, SFK inhibitor saracatinib showed stronger inhibition on functional behaviors facilitated under hypoxia than normal conditions.

Conclusions: Our data show that hypoxia, particularly short-term exposure, is able to enhance metastatic phenotypes by activating SFKs, predominantly c-Src, in prostate cancer cells, suggesting c-Src may be the most important signaling molecule of hypoxia-mediated behaviors. These findings have clarified the exact SFK member that is typically activated under hypoxia at least in prostate cancer model in vitro. More importantly, SFK inhibitors are able to impair cell functions driven by hypoxia, suggesting their therapeutic potential by suppressing tumor metastasis that is driven by hypoxia in prostate cancer.

Citation Format: Yao Dai, Dietmar W. Siemann. Impact of hypoxia on SFK activities in prostate cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4518. doi:10.1158/1538-7445.AM2017-4518

Abstract 5180: Effects of soy isoflavones and SRC inhibitors on metastatic activity in prostate cancer

Background: In advanced prostate cancer (PCa), cells escape from the primary tumor and enter the bloodstream, preferentially targeting the bone. This results in weakened bones, spinal compressions, fractures and intense pain. Efforts to interfere with early steps in the metastatic cascade by affecting the tumor microenvironment have led to the development of promising small molecule targeting agents. The tyrosine kinase inhibitors, saracatinib and dasatinib, have been shown to inhibit activation of Src and downstream effectors thought to be involved in cancer cell dissemination. Soy-derived isoflavones (ISFs) have been shown to have cytostatic effects on PCa cells without toxicity.

Aim: The aim of these studies was to determine if ISFs enhance the effects of Src inhibitors on PCa cells, resulting in lower doses of these agents needed to produce optimum results.

Methods: PC-3 ML and LNCaP cells were treated with either a Src inhibitor (dasatinib or saracatinib), a soy isoflavone extract (ISFs), or a combination. Modified Boyden transwell chambers were used to evaluate migration and invasion. Cell cycle and proliferation were measured using FACS analyses and trypan blue staining, respectively.

Results: ISFs and Src inhibitors did not cause cytotoxicity or reduce proliferation. However, Src inhibitors produced an increase in cells in G1 phase, while ISFs increased cells in G2/M phase. When ISFs were combined with Src inhibitors, both phases were increased with a concomitant decrease in S phase cells. In transwell migration studies, all agents significantly decreased the number of cells found on the bottom of the membrane: dasatinib&gt;saracatinib&gt;ISFs. Lower doses of Src inhibitors were needed to produce inhibition of migration when ISFs were added to the treatment. Invasion studies with PC-3 ML and LNCaP cells suggest that ISFs can reduce metastatic activity by 39% and 35%, respectively. Therefore, by adding ISFs, lower doses of inhibitors might be used to achieve optimal response and decrease toxicity.

Conclusions: In vitro studies suggested that a combination of a Src inhibitors and ISFs, at non-cytotoxic doses, results in greater inhibition of metastatic or invasion activity than either alone. Further studies are needed to determine if this strategy could be used clinically to treat patients with lower doses of small molecule inhibitors by including soy isoflavone concentrates in the treatment regimen.

Citation Format: Lori P. Rice, Dietmar W. Siemann. Effects of soy isoflavones and SRC inhibitors on metastatic activity in prostate cancer [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 5180. doi:10.1158/1538-7445.AM2017-5180

Epithelial-to-mesenchymal transition confers pericyte properties on cancer cells

Carcinoma cells can acquire increased motility and invasiveness through epithelial-to-mesenchymal transition (EMT). However, the significance of EMT in cancer metastasis has been controversial, and the exact fates and functions of EMT cancer cells in vivo remain inadequately understood. Here, we tracked epithelial cancer cells that underwent inducible or spontaneous EMT in various tumor transplantation models. Unlike epithelial cells, the majority of EMT cancer cells were specifically located in the perivascular space and closely associated with blood vessels. EMT markedly activated multiple pericyte markers in carcinoma cells, in particular PDGFR-β and N-cadherin, which enabled EMT cells to be chemoattracted towards and physically interact with endothelium. In tumor xenografts generated from carcinoma cells that were prone to spontaneous EMT, a substantial fraction of the pericytes associated with tumor vasculature were derived from EMT cancer cells. Depletion of such EMT cells in transplanted tumors diminished pericyte coverage, impaired vascular integrity, and attenuated tumor growth. These findings suggest that EMT confers key pericyte attributes on cancer cells. The resulting EMT cells phenotypically and functionally resemble pericytes and are indispensable for vascular stabilization and sustained tumor growth. This study thus proposes a previously unrecognized role for EMT in cancer.

Targeting the Angiopoietin-2/Tie-2 axis in conjunction with VEGF signal interference

Anti-angiogenic therapies target the tumor vasculature, impairing its development and growth. It was hypothesized over 40 years ago by the late Judah Folkman and Julie Denekamp that depriving a tumor of oxygen and nutrients, by targeting the tumor vasculature, could have therapeutic benefits. Identification of growth factors and signaling pathways important in angiogenesis subsequently led to the development of a series of anti-angiogenic agents that over the past decade have become part of the standard of care in several disease settings. Unfortunately not all patients respond to the currently available anti-angiogenic therapies while others become resistant to these agents following prolonged exposure. Identification of new pathways that may drive angiogenesis led to the development of second-generation anti-angiogenic agents such as those targeting the Ang-2/Tie2 axis. Recently, it has become clear that combination of first and second generation agents targeting the blood vessel network can lead to outcomes superior to those using either agent alone. The present review focuses on the current status of VEGF and Ang-2 targeted agents and the potential utility of using them in combination to impair tumor angiogenesis.

Abstract 4102: Effect of HGF concentrations on c-Met inhibition investigation

Tumor cells frequently harbor abnormalities in signaling pathways, leading to increased migration, invasion, survival, angiogenesis, and proliferation. C-Met is a receptor tyrosine kinase critical for embryogenesis and liver repair, and protein levels are often elevated in a large variety of tumors. C-Met is activated by the endogenous ligand Hepatocyte Growth Factor (HGF). HGF is produced by mesenchymal cells and stimulates the c-Met protein, leading to a variety of downstream signaling pathways that result in increased migration, proliferation, survival, and angiogenesis.

While many tumor cells express the c-Met receptor, a number of tumor types, including glioblastoma and osteosarcoma, have been observed to co-express both HGF and c-Met. The purpose of the current study was to measure tumor cell HGF secretion in vitro, to determine HGF concentrations in vivo, and study how HGF concentrations affect tumor cell response to c-Met inhibition. Over forty cell lines were investigated for HGF secretion via ELISA of conditioned media. The small molecule c-Met inhibitor BMS-777607 was used to interrupt the c-Met axis in a select number of tumor cell lines. C3H/HeJ, nude, and Balb/c mice, were measured for serum levels of HGF.

Data obtained using ELISA of conditioned media show that about one quarter of the cell lines tested secreted HGF. Cell lines tested include, but are not limited to, glioblastoma, prostate, breast, fibrosarcoma, and osteosarcoma. Migration assays were performed on several of these cell lines to determine sensitivity to BMS-777607. HGF-secreting cell lines, including the KHT, U87, U118, and OS156, are sensitive to BMS-777607 at 0.1, 1, and 10 μM. Non-HGF-secreting cell lines, such as PC-3 and MDA-MB-231, are insensitive to BMS-777607 at the same concentrations. A migration assay was performed with the PC-3 cells, with cells exposed to 0.1, 1, and 10 uM BMS-777607 while in the presence of 0, 5, 10, and 25 ng/mL HGF. These cells are not sensitive to the c-Met inhibitor at low concentrations of HGF, yet become sensitive at higher concentrations. These results indicate that sensitivity to c-Met inhibition may be dependent on both HGF-secretion status and levels of exogenous HGF. Furthermore, our findings suggest that in vitro investigations of c-Met inhibition should be done at physiologically relevant HGF concentrations.

In order to properly perform c-Met inhibition experiments in vitro, a better understanding of in situ HGF concentration is needed. Serum levels of HGF were measured in the C3H/HeJ, nude, and Balb/c mice. The average serum HGF concentration in these mice was between 3 and 5 ng/mL. Still, it is ultimately the local concentration of HGF within the tumor microenvironment that is critical, but no intra-tumor values for HGF have been reported. Consequently measurements of HGF levels within tumors by microdialysis are ongoing.

Citation Format: Veronica S. Hughes, Dietmar W. Siemann. Effect of HGF concentrations on c-Met inhibition investigation. [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 4102.

Evaluations of the Renal Cell Carcinoma Model Caki-1 Using a Silicon Based Microvascular Casting Technique

The vascular development of orthotopically grown human renal cell carcinoma (Caki-1) was examined using a silicon based casting technique in nude mice. Images taken of these vascular casts showed Caki-1 tumors to be highly vascularized and invasive. The spread of the tumor within the cortex of the kidney revealed that Caki-1 recruits the kidney's own vasculature, destroying the functional glomeruli in the process. The loss of these glomeruli was further highlighted by the presence of enlarged glomeruli resulting from the development of super nephrons. Vessel size and density measurements were then made in this model. This was done using both computer-based and manual measurement methods. In the vessel size studies the computer-based method tended to overestimate the number of larger diameter vessels whereas the vessels density assessment showed good agreement between the two techniques. Nevertheless, both methods showed that Caki-1 tumors possessed a higher proportion of larger diameter vessels and a lower vessel density than normal kidney cortex.

In summary, silicon based vascular casting proved to be a simple and effective tool for the study of tumor vasculature. In particular this technique could readily be used to examine the invasion of tumor into normal tissue. The computer-based technique for evaluating vessel number and vascular density was found to have merit in both normal and tumor tissues, particularly in the vascular density studies. However, in both settings this technique did tend to overestimate the number of larger diameter vessels.

Hypoxia regulates SOX2 expression to promote prostate cancer cell invasion and sphere formation

SOX2 is an embryonic stem cell marker that in prostate cancer has been associated not only with tumorigenesis but also metastasis. Furthermore hypoxia in primary tumors has been linked to poor prognosis and outcomes in this disease. The goal of the present study was to investigate the impact of hypoxia on SOX2 expression and metastasis-associated functions in prostate cancer cells. A tissue microarray of 80 samples from prostate cancer patients or healthy controls was employed to examine the expression of HIF-1α and its correlation with SOX2. The role of SOX2 and HIF-1/2α in the regulation of cell invasion and sphere formation capacity under hypoxic conditions was investigated in vitro using short hairpin RNA (shRNA)-mediated knockdown in three human prostate cancer cell lines. HIF-1α expression was significantly elevated in malignant prostate tissue compared to benign or normal tissue, and in tumor samples its expression was highly correlated with SOX2. In prostate cancer cells, acute and chronic exposures to hypoxia that resulted in elevated expression levels of HIF-1α and HIF-2α, respectively, also induced SOX2. Genetic depletion of SOX2 attenuated hypoxia-induced cell functions. Knockdown of HIF-1α, but not HIF-2α, decreased acute hypoxia-mediated cell invasion and SOX2 up-regulation, whereas only HIF-2α gene silencing reduced sphere formation capacity and chronic hypoxia-mediated SOX2 up-regulation. Enhanced SOX2 expression and HIF-1α or HIF-2α associated phenotypes are dependent on the time duration of exposure to hypoxia. The present results indicate that SOX2 may be a key mediator of hypoxia-induced metastasis-associated functions and hence may serve as a potential target for therapeutic interventions for metastatic prostate cancer.

Cathepsin L in tumor angiogenesis and its therapeutic intervention by the small molecule inhibitor KGP94

A significant proportion of breast cancer patients harbor clinically undetectable micrometastases at the time of diagnosis. If left untreated, these micro-metastases may lead to disease relapse and possibly death. Hence, there is significant interest in the development of novel anti-metastatic agents that could also curb the growth of pre-established micrometastases. Like primary tumor, the growth of metastases also is driven by angiogenesis. Although the role of cysteine protease Cathepsin L (CTSL) in metastasis associated tumor cell functions such as migration and invasion is well recognized, its role in tumor angiogenesis remains less explored. The present study examines the contribution of CTSL to breast cancer angiogenesis and evaluates the anti-angiogenic efficacy of CTSL inhibitor KGP94. CTSL semi-quantitative RT-PCR analysis on breast tissue panels revealed significant upregulation of CTSL in breast cancer patients which strongly correlated with increased relapse and metastatic incidence and poor overall survival. Preclinically, CTSL ablation using shRNA or KGP94 treatment led to a significant reduction in MDA-MB-231 tumor cell induced angiogenesis in vivo. In-vitro assessments demonstrated a significant decrease in various angiogenic properties such as endothelial cell sprouting, migration, invasion, tube formation and proliferation in the presence of KGP94. Microarray analyses revealed a significant upregulation of cell cycle related genes by CTSL. Western blot analyses further confirmed upregulation of members of the cyclin family by CTSL. Collectively, these data indicate that CTSL is an important contributor to tumor angiogenesis and that the CTSL inhibition may have therapeutic utility in the treatment of breast cancer patients.

Chemosensitizing AML cells by targeting bone marrow endothelial cells

Refractory disease is the greatest challenge in treating patients with acute myeloid leukemia (AML). Blood vessels may serve as sanctuary sites for AML. When AML cells were co-cultured with bone marrow endothelial cells (BMECs), a greater proportion of leukemia cells were in G0/G1. This led us to a strategy of targeting BMECs with tubulin-binding combretastatins, causing BMECs to lose their flat phenotype, degrade their cytoskeleton, cease growth, and impair migration despite unchanged BMEC viability and metabolism. Combretastatins also caused downregulation of BMEC adhesion molecules known to tether AML cells, including vascular cell adhesion molecule (VCAM)-1 and vascular endothelial (VE)-cadherin. When AML-BMEC co-cultures were treated with combretastatins, a significantly greater proportion of AML cells dislodged from BMECs and entered the G2/M cell cycle, suggesting enhanced susceptibility to cell cycle agents. Indeed, the combination of combretastatins and cytotoxic chemotherapy enhanced additive AML cell death. In vivo mice xenograft studies confirmed this finding by revealing complete AML regression after treatment with combretastatins and cytotoxic chemotherapy. Beyond highlighting the pathologic role of BMECs in the leukemia microenvironment as a protective reservoir of disease, these results support a new strategy for using vascular-targeting combretastatins in combination with cytotoxic chemotherapy to treat AML.

Cathepsin L inactivation leads to multimodal inhibition of prostate cancer cell dissemination in a preclinical bone metastasis model

It is estimated that approximately 90% of patients with advanced prostate cancer develop bone metastases; an occurrence that results in a substantial reduction in the quality of life and a drastic worsening of prognosis. The development of novel therapeutic strategies that impair the metastatic process and associated skeletal adversities is therefore critical to improving prostate cancer patient survival. Recognition of the importance of Cathepsin L (CTSL) to metastatic dissemination of cancer cells has led to the development of several CTSL inhibition strategies. The present investigation employed intra-cardiac injection of human PC-3ML prostate cancer cells into nude mice to examine tumor cell dissemination in a preclinical bone metastasis model. CTSL knockdown confirmed the validity of targeting this protease and subsequent intervention studies with the small molecule CTSL inhibitor KGP94 resulted in a significant reduction in metastatic tumor burden in the bone and an improvement in overall survival. CTSL inhibition by KGP94 also led to a significant impairment of tumor initiated angiogenesis. Furthermore, KGP94 treatment decreased osteoclast formation and bone resorptive function, thus, perturbing the reciprocal interactions between tumor cells and osteoclasts within the bone microenvironment which typically result in bone loss and aggressive growth of metastases. These functional effects were accompanied by a significant downregulation of NFκB signaling activity and expression of osteoclastogenesis related NFκB target genes. Collectively, these data indicate that the CTSL inhibitor KGP94 has the potential to alleviate metastatic disease progression and associated skeletal morbidities and hence may have utility in the treatment of advanced prostate cancer patients.

Abstract B59: Dual mTOR kinase inhibitor reverses rapamycin resistance in prostate cancer cells

The mTOR pathway is frequently over-activated in human cancers. However, classic allosteric mTOR inhibitors rapamycin and its analogs only exert limited clinical benefits in patients. It has been shown that many tumors either fail to respond to rapamycin initially or are able to acquire resistance after the initial treatment of rapamycin. Such primary and secondary resistances remain as major concerns in rapamycin-based anti-cancer therapies that may inevitably lead to therapeutic failure. We have previously shown that the ATP-competitive dual mTOR kinase inhibitor AZD8055 can significantly inhibit malignant behaviors in parental cells however its functional efficacies in the rapamycin-resistance setting remains unclear.

Cancer cells with wildtype PTEN were selected as models of primary rapamycin resistance since the mTOR pathway is usually less abnormal in these cells. To establish cells with acquired rapamycin resistance, PTEN-null prostate cancer PC-3 cells were gradually treated with increasing concentrations of rapamycin (up to 10 μM) until the cells were completely unresponsive to rapamycin (PC-3RR). Cell proliferation was determined by MTT assay and clonogenic survival was tested by colony formation assay. m7G pull-down assay was employed to detect the cap-dependent translation. mTOR downstream pathways were detected by Western blotting.

PTEN wildtype and PC-3RR cells essentially failed to respond to rapamycin; IC50 values were greater than 100 nM in PTEN wildtype cells and 1 μM in PC-3RR cells, respectively. However, for both cell types AZD8055 suppressed proliferation at the nanomolar level in a dose dependent manner, with IC50 values less than 30 nM. Similarly, cellular clonogenic capacity was impaired by AZD8055 to a greater extent than was the case for rapamycin. At the molecular level, AZD8055, but not rapamycin, strongly prevents the dissociation of 4E-BP1 from eIF4E, therefore blocking cap-dependent translation. Further, while the p-S6K (T389) and p-S6 (S235/236) pathway was potently inhibited by both agents, AZD8055 displayed more striking inhibition on p-4E-BP1 (T37/46) and p-Akt (S473) than did rapamycin in all cells tested.

Interestingly, similar to rapamycin, AZD8055 slightly increased p-Akt (T308), suggesting the existence of the PI3K-mediated feedback loop. However, the PI3K inhibitor wortmannin failed to sensitize cell response to AZD8055, implying such feedback-dependent activation has little impact on the drug efficacy.

These findings indicate that dual mTOR kinase inhibitor AZD8055 significantly inhibits malignant functions in cancer cells that are highly resistant to rapamycin. Such effects are likely to be associated with deactivation of rapamycin-insensitive mTOR downstream components such as Akt and 4E-BP1, but not the upstream feedback pathway. These data provide in vitro evidence in support of future evaluation of ATP-competitive mTOR inhibitors in cancer models that are resistant to rapamycin analogs.

Citation Format: Yao Dai, Li Zhao, Dietmar W. Siemann. Dual mTOR kinase inhibitor reverses rapamycin resistance in prostate cancer cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B59.

Abstract B24: Impact of aerobic exercise on tumor oxygenation and perfusion in breast cancer

The purpose of this study is to evaluate the effects of low to moderate aerobic exercise on tumor vasculature, perfusion and oxygenation in breast cancer. Poor perfusion and hypoxia are common features of solid tumors that are a result of abnormal tumor angiogenesis. Both chemo- and radiation therapies are negatively affected by tumor hypoxia, with the presence of hypoxia associated with treatment failure and poor outcomes in cancer patients. While strategies to enhance tumor oxygenation and perfusion have been developed, their success in the clinic has been limited. A potential method to increase oxygenation and decrease hypoxia that is safe and well-tolerated is aerobic exercise. The benefits of exercise as a palliative measure are well documented, however the effects of exercise on tumor blood flow and oxygenation have not been extensively characterized.

Histological analysis of vessel density (MECA-32), vessel perfusion (Hoechst-33342) and hypoxia (EF5) were quantified in tumor bearing mice subjected to low to moderate intensity treadmill running and compared to sedentary control mice. In a separate model, a murine dorsal skinfold window chamber model and in vivo microscopy of microvessel function was utilized to characterize changes in tumor vascular structure and function in real time. In these studies, the combination of hyperspectral imaging of hemoglobin (Hb) saturation and first-pass fluorescence (FPF) imaging of blood transit time were used. Hb saturation imaging reveals the oxygenation of blood within microvessels while FPF imaging gives information regarding blood flow and network connections by recording a fluorescent contrast agent as it is injected into circulation.

Spectroscopic analysis was performed in female nude mice with surgically installed titanium window chambers. Mammary tumors were initiated in the windows and once tumors reached a specified volume, animals were subjected to daily treadmill running for up to a week. As a sedentary control, mice were placed on a stationary treadmill for equivalent periods of time. Combination imaging was performed daily to monitor microvessel oxygenation and blood flow. Preliminary results indicate that following one bout of exercise, tumor perfusion is increased, however there was no significant correlation between exercise and tumor microvessel oxygenation.

For histological analysis, mammary tumors were initiated in the fat pad of female nude mice. Once tumors nodules were established, animals were subjected to either a single bout or daily bouts of exercise for 1 to 5 weeks. Sedentary controls were exposed to a stationary treadmill for equivalent periods of time. Following exercise protocols, tumors were harvested and sectioned for immunohistochemical analysis. Staining analysis revealed an improvement in tumor oxygenation and an increase in the number of perfused vessels in tumors of exercising animals in comparison to sedentary controls.

Our results demonstrate aerobic exercise can increase tumor oxygenation and perfusion in breast cancer, suggesting that exercise can potentially be used as an adjunctive therapy to overcome tumor hypoxia and enhance the efficacy of chemo- and radiation therapy.

Citation Format: Jennifer A. Lee, Jennifer Wiggins, Dietmar W. Siemann. Impact of aerobic exercise on tumor oxygenation and perfusion in breast cancer. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Angiogenesis and Vascular Normalization: Bench to Bedside to Biomarkers; Mar 5-8, 2015; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl):Abstract nr B24.

Abstract A04: Is the lack of clinical success with antiangiogenic therapy due to vascular normalization not being a universal phenomenon?

Introduction: Pre-clinical studies have demonstrated that combining angiogenesis inhibitors (AIs) with conventional radiation and chemotherapy treatments can be an effective anti-tumor therapy. However, clinical benefits from such combinations have been more modest. A principal mechanism by which AIs are believed to increase tumor sensitivity to radiation and chemotherapy is vascular normalization, a process which should improve tumor blood perfusion and oxygenation. Here we review the universality of this concept by examining those pre-clinical studies that directly determined the effect of AI treatment on tumor oxygenation.

Methods: This review was based on searching the PubMed database using the criteria angiogenesis inhibitors combined with one of each of the following: oxygenation, hypoxia, or normalization coupled with our own knowledge within the fields of tumor hypoxia and vascular targeting. A total of 51 pre-clinical studies were identified. The techniques used to monitor hypoxia/oxygenation included immunohistochemical analysis of hypoxia marker binding (pimonidazole and EF5) or hypoxia gene expression (CA9 and HIF-1alpha), direct oxygenation measurements (Eppendorf electrode, EPR oximetry, Oxylite probe or phosphorous quenching), or radiation response. The AIs included the two principal classes of inhibitors, those targeting VEGF (bevacizumab, DC101) and tyrosine kinase (vandetanib, sunitinib, sorafanib, axitinib, pazopanib, AG-013736, PTK787/ZK222584, SU5416), as well as a variety of other agents (TNP-470, suramin, endostatin, thrombospondin, thalidomide, anginex, arginine deiminase, nucleolin antagonist, nelfinavir).

Results: 19 studies demonstrated significant improvements in tumor oxygenation status. These included a decrease in hypoxia marker labelling (bevacizumab, DC101, suramin, endostatin, nucleolin antagonist); an increase in oxygenation determined using the Eppendorf electrode (TNP-470 and an anti-VEGF antibody), EPR oximetry (thalidomide, vandetanib, SU5416), and Oxylite probe (bevacizumab); an increase in hypoxia regulated gene expression (endostatin and SU5416); and enhanced radiation response (thrombospondin). In contrast, 21 studies found a significant decrease in tumor oxygenation using hypoxic markers measured by immunohistochemistry (bevacizumab, DC101, sunitinib, pazopanib, AG-013736, nelfinavir) or PET activity (PTK787/ZK222584), and increased expression of HIF-1alpha (bevacizumab). Moreover, 9 studies reported no change in tumor oxygenation as measured with hypoxic markers (endostatin and SU5416), direct oxygen measurements (anti-VEGF antibody, DC101, arginine deiminase), or radiation response (DC101). Finally, two studies actually reported both increases and decreases when using direct oxygen measurements depending on the time after treatment with bevacizumab or DC101.

Conclusions: While there is clear evidence that tumor oxygenation can improve following AI treatment, consistent with vascular normalization occurring, this is clearly not a universal finding. Importantly the effects on tumor hypoxia/oxygenation status show no relationship to either the specific AI or the assay used to monitor these parameters. These findings suggest that for the combination of AIs with conventional anti-cancer therapies to be most effective it will be important to establish the impact the AI has on the tumor vasculature and associated tumor pathophysiology in a given treatment setting.

Citation Format: Michael R. Horsman, Dietmar W. Siemann. Is the lack of clinical success with antiangiogenic therapy due to vascular normalization not being a universal phenomenon? [abstract]. In: Proceedings of the AACR Special Conference: Tumor Angiogenesis and Vascular Normalization: Bench to Bedside to Biomarkers; Mar 5-8, 2015; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl):Abstract nr A04.

Synthesis and biochemical evaluation of benzoylbenzophenone thiosemicarbazone analogues as potent and selective inhibitors of cathepsin L

Upregulation of cathepsin L in a variety of tumors and its ability to promote cancer cell invasion and migration through degradation of the extracellular matrix suggest that cathepsin L is a promising biological target for the development of anti-metastatic agents. Based on encouraging results from studies on benzophenone thiosemicarbazone cathepsin inhibitors, a series of fourteen benzoylbenzophenone thiosemicarbazone analogues were designed, synthesized, and evaluated for their inhibitory activity against cathepsins L and B. Thiosemicarbazone inhibitors 3-benzoylbenzophenone thiosemicarbazone 1, 1,3-bis(4-fluorobenzoyl)benzene thiosemicarbazone 8, and 1,3-bis(2-fluorobenzoyl)-5-bromobenzene thiosemicarbazone 32 displayed the greatest potency against cathepsin L with low IC50 values of 9.9 nM, 14.4 nM, and 8.1 nM, respectively. The benzoylbenzophenone thiosemicarbazone analogues evaluated were selective in their inhibition of cathepsin L compared to cathepsin B. Thiosemicarbazone analogue 32 inhibited invasion through Matrigel of MDA-MB-231 breast cancer cells by 70% at 10 μM. Thiosemicarbazone analogue 8 significantly inhibited the invasive potential of PC-3ML prostate cancer cells by 92% at 5 μM. The most active cathepsin L inhibitors from this benzoylbenzophenone thiosemicarbazone series (1, 8, and 32) displayed low cytotoxicity toward normal primary cells [in this case human umbilical vein endothelial cells (HUVECs)]. In an initial in vivo study, 3-benzoylbenzophenone thiosemicarbazone (1) was well-tolerated in a CDF1 mouse model bearing an implanted C3H mammary carcinoma, and showed efficacy in tumor growth delay. Low cytotoxicity, inhibition of cell invasion, and in vivo tolerability are desirable characteristics for anti-metastatic agents functioning through an inhibition of cathepsin L. Active members of this structurally diverse group of benzoylbenzophenone thiosemicarbazone cathepsin L inhibitors show promise as potential anti-metastatic, pre-clinical drug candidates.

Cathepsin L targeting in cancer treatment

Proteolytic enzymes may serve as promising targets for novel therapeutic treatment strategies seeking to impede cancer progression and metastasis. One such enzyme is cathepsin L (CTSL), a lysosomal cysteine protease. CTSL upregulation, a common occurrence in a variety of human cancers, has been widely correlated with metastatic aggressiveness and poor patient prognosis. In addition, CTSL has been implicated to contribute to cancer-associated osteolysis, a debilitating morbidity affecting both life expectancy and the quality of life. In this review, we highlight the mechanisms by which CTSL contributes to tumor progression and dissemination and discuss the therapeutic utility of CTSL intervention strategies aimed at impeding metastatic progression and bone resorption.

Abstract 777: Effects of Src inhibitors and soy isoflavones on human prostate cancer cells

Background: Src family kinases are often over-expressed and highly active in solid tumors, including prostate cancer. This phenotype is associated with a poor prognosis partly because Src is a key factor in important signaling pathways involved in cell proliferation, angiogenesis, and initiation of metastasis. As a result, several promising small molecule targeting agents have been developed to prevent phosphorylation of key tyrosine residues that produce Src activation. However, these agents are not without side effects. The purpose of this study was to determine if adding a cytostatic soy isoflavone extract (ISF) to the treatment would produce optimal results at lower doses of the Src inhibitor. The ISF used in these studies has been shown to inhibit tumor growth in mice carrying human prostate cancer cell xenografts without causing toxicity to the host.

Methods: Aggressive PC-3ML cells (a gift from A. Fatatis, Drexel University), and weakly tumorigenic LNCaP cells were treated for 24 hr with various concentrations of Src inhibitors (dasatinib, saracatinib), ISF (200 ug/ml, NovaSoy), or a combination. To evaluate effects on the metastatic potential of the cells, functional assays of cell growth and motility were performed, including those that assess clonogenic cell survival, cell cycle progression, and transwell migration and invasion activity.

Results: Src inhibitors and ISF alone produced very little reduction in cell viability, but significant cytostatic effects, as determined by a reduction in clonogenicity, the number of cells able to form 50-cell colonies. This was likely due, in part, to changes in cell cycle progression. Both dasatinib and saracatinib caused an accumulation of cells in the G1 phase. As expected, ISF treatment resulted in higher numbers of cells in the G2/M phase. When the treatments were combined, cells exposed to dasatinib were observed to accumulate in both phases, with a significant decrease in S-phase cells. The results were not significant for saracatinib-treated cells. Exposure to either a Src inhibitor or ISF significantly reduced the migration of cells in a transwell chamber and their ability to invade through a Matrigel-coated 8 micron-pore membrane towards a chemoattractant (media containing 10% FBS). Dasatinib produced much greater effects, and at lower concentrations, than saracatinib. When combined with ISF, the effects were enhanced, particularly with dasatinib.

Conclusions: In vitro studies suggested that combining a Src inhibitor and ISF resulted in greater inhibition of metastatic potential than either alone. This may indicate that including ISF in treatment regimens may allow a lower dose of the targeting agent to be used to achieve optimal response and also decrease toxicity.

Citation Format: Lori P. Rice, Christine Pampo, Sharon Lepler, Dietmar W. Siemann. Effects of Src inhibitors and soy isoflavones on human prostate cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 777. doi:10.1158/1538-7445.AM2015-777

Abstract 4122: C-Met inhibition sensitivity in vitro: Autocrine vs. paracrine activation of the c-Met pathway

Tumor cells frequently harbor abnormalities in signaling pathways, leading to increased migration, invasion, survival, angiogenesis, and proliferation. C-Met is one such commonly aberrant pathway. C-Met is a receptor tyrosine kinase critical for embryogenesis and liver repair, and protein levels are often elevated in a large variety of tumors. C-Met is activated by the endogenous ligand Hepatocyte Growth Factor (HGF). HGF is produced by mesenchymal cells and stimulates the c-Met protein, leading to a variety of downstream signaling pathways that result in increased migration, proliferation, survival, and angiogenesis.

While many tumor cells express the c-Met receptor, a number of tumor types, including glioblastoma and osteosarcoma, have been observed to co-express both HGF and c-Met, and activate the pathway in an autocrine manner. The purpose of the current study was to determine whether tumor cells utilizing autocrine c-Met signaling would more sensitive to c-Met inhibition than those relying on the paracrine pathway. Experimental procedures include ELISA, western, migration, invasion, and clonogenic cell survival. Cell lines investigated include: two glioblastoma cell lines (U87 and U118), two osteosarcoma cell lines (OS156 and OS521), two fibrosarcoma cell lines (KHT and RIF), a breast (MDA-MB-231) and a prostate cancer cell line (PC-3). The small molecule c-Met inhibitor BMS-777607 and an HGF-neutralizing antibody were used to compare the effects interrupting the c-Met axis in these tumor cell lines.

Data obtained using ELISA of conditioned media show that the glioblastoma (U87 and U118) and fibrosarcoma (KHT) cells secrete HGF, while the breast and prostate cells (MDA-MB-231; PC-3) do not. Furthermore western blot analysis showed higher basal levels of phospho-c-Met among the HGF-secreting cell lines in comparison to the non-HGF secreting cell lines, indicating that the KHT, U87, and U118 models activate c-Met in an autocrine manner, while the MDA-MB-231 and PC-3 lines activate c-Met in a paracrine manner. Importantly preliminary assessments indicate the autocrine glioblastoma and fibrosarcoma cell lines to be more sensitive to small molecule c-Met inhibition than the paracrine breast and prostate cancer cell lines. Investigations of additional cancer models are ongoing but our findings to date support the notion that cancer cells that autocrine activate the c-Met pathway may more susceptible to c-Met inhibition than those utilizing primarily paracrine activation of this pathway.

Citation Format: Veronica Hughes, Dietmar W. Siemann. C-Met inhibition sensitivity in vitro: Autocrine vs. paracrine activation of the c-Met pathway. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4122. doi:10.1158/1538-7445.AM2015-4122

Modulation of the tumor vasculature and oxygenation to improve therapy

The tumor microenvironment is increasingly recognized as a major factor influencing the success of therapeutic treatments and has become a key focus for cancer research. The progressive growth of a tumor results in an inability of normal tissue blood vessels to oxygenate and provide sufficient nutritional support to tumor cells. As a consequence the expanding neoplastic cell population initiates its own vascular network which is both structurally and functionally abnormal. This aberrant vasculature impacts all aspects of the tumor microenvironment including the cells, extracellular matrix, and extracellular molecules which together are essential for the initiation, progression and spread of tumor cells. The physical conditions that arise are imposing and manifold, and include elevated interstitial pressure, localized extracellular acidity, and regions of oxygen and nutrient deprivation. No less important are the functional consequences experienced by the tumor cells residing in such environments: adaptation to hypoxia, cell quiescence, modulation of transporters and critical signaling molecules, immune escape, and enhanced metastatic potential. Together these factors lead to therapeutic barriers that create a significant hindrance to the control of cancers by conventional anticancer therapies. However, the aberrant nature of the tumor microenvironments also offers unique therapeutic opportunities. Particularly interventions that seek to improve tumor physiology and alleviate tumor hypoxia will selectively impair the neoplastic cell populations residing in these environments. Ultimately, by combining such therapeutic strategies with conventional anticancer treatments it may be possible to bring cancer growth, invasion, and metastasis to a halt.

VEGFR inhibitors upregulate CXCR4 in VEGF receptor-expressing glioblastoma in a TGFβR signaling-dependent manner

The failure of standard treatment for patients diagnosed with glioblastoma (GBM) coupled with the highly vascularized nature of this solid tumor has led to the consideration of agents targeting VEGF or VEGFRs, as alternative therapeutic strategies for this disease. Despite modest achievements in survival obtained with such treatments, failure to maintain an enduring survival benefit and more invasive relapsing tumors are evident. Our study suggests a potential mechanism by which anti-VEGF/VEGFR therapies regulate the enhanced invasive phenotype through a pathway that involves TGFβR and CXCR4. VEGFR signaling inhibitors (Cediranib and Vandetanib) elevated the expression of CXCR4 in VEGFR-expressing GBM cell lines and tumors, and enhanced the in vitro migration of these lines toward CXCL12. The combination of VEGFR inhibitor and CXCR4 antagonist provided a greater survival benefit to tumor-bearing animals. The upregulation of CXCR4 by VEGFR inhibitors was dependent on TGFβ/TGFβR, but not HGF/MET, signaling activity, suggesting a mechanism of crosstalk among VEGF/VEGFR, TGFβ/TGFβR, and CXCL12/CXCR4 pathways in the malignant phenotype of recurrent tumors after anti-VEGF/VEGFR therapies. Thus, the combination of VEGFR, CXCR4, and TGFβR inhibitors could provide an alternative strategy to halt GBM progression.

Abstract 4030: In-vivo evaluation of the anti-metastatic efficacy of small molecule Cathepsin L inhibitor KGP94 in a prostate cancer model

It is estimated that ∼85% of patients with advanced prostate cancer develop skeletal metastases; an occurrence that results in a substantial reduction in the quality of life and a drastic worsening of the prognosis. The development of novel therapeutic strategies that impair the metastatic process and associated skeletal adversities is therefore critical to improving prostate cancer patient survival.

Tumor cells rely on proteolytic enzymes for successful establishment of metastases. Cathepsin L (CTSL) is a lysosomal cysteine protease that is up regulated in a wide range of human cancers including prostate cancer. The elevated secretion of CTSL by aggressively metastasizing tumor cells plays a key role in metastatic spread of tumor cells through proteolytic degradation of extracellular matrix and basement membrane components. In addition, tumor secreted cytokines have been shown to increase osteoclastic secretion of CTSL to promote bone resorption. Intervention strategies targeting CTSL may therefore serve a dual purpose by inhibiting both metastatic dissemination as well as bone resorption. The goal of present studies was to evaluate the anti-metastatic and anti-bone resorptive efficacy of CTSL inhibition using the small molecule CTSL inhibitor 3-bromophenyl-3-hydroxyphenyl-ketone thiosemicarbazone (KGP94).

KGP94 treatment significantly impaired the metastatic phenotype of highly metastatic prostate cancer PC-3ML cells. Treatment with 25µM KGP94 decreased the migratory and invasive capacities of PC-3ML cells by 78 and 53% respectively. To validate the anti-metastatic efficacy of KGP94 in-vivo, luciferase labelled PC-3ML cells were injected into the left ventricle of male nu/nu mice followed by daily treatment with 20mg/kg KGP94. Metastatic progression was monitored by weekly bioluminescence imaging using firefly luciferase reporter system. KGP94 treatment led to a significant reduction in metastatic tumor burden (65% reduction) and a reduction in metastatic incidence. Histological assessment of bones further confirmed the reduction in metastatic burden upon KGP94 treatment. CTSL inhibition also led to a significant increase in overall survival of tumor bearing mice (p=0.01). In vitro assessment of anti-resorptive function of KGP94 was performed using osteoclastogenesis and pit formation assays. KGP94 treatment of RAW264.7 osteoclast precursor cells led to a significant decrease (72%) in osteoclast formation as demonstrated by a decrease in the number of TRAP+ multinucleate cells. KGP94 also inhibited the bone resorptive activity of osteoclasts as indicated by a significant reduction in the number of resorptive pits formed by osteoclasts on bone slices.

In conclusion, our findings suggest that CTSL inhibition using small molecule KGP94 can significantly impair metastatic dissemination of prostate cancer cells and alleviate bone resorption.

Citation Format: Dhivya R. Sudhan, Dietmar W. Siemann. In-vivo evaluation of the anti-metastatic efficacy of small molecule Cathepsin L inhibitor KGP94 in a prostate cancer model. [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 4030. doi:10.1158/1538-7445.AM2014-4030

Abstract 4037: Combining tyrosine kinase inhibitors and isoflavones to target metastatic activity in prostate cancer cells

Background: Efforts to impede early steps in the metastatic cascade have led to the development of promising small molecule targeting agents. The purpose of this study was to evaluate the use of Src tyrosine kinase inhibitors known to interfere with cell migration and invasion, in combination with a cytostatic soy isoflavone extract (ISFs) on metastatic activity in prostate cancer cells. Methods: PC-3ML cells (a gift from A. Fatatis, Drexel University), and LNCaP cells treated with a Src inhibitor, ISFs, or a combination, were evaluated for clonogenic cell survival, cell cycle progression, and transwell migration and invasion activity. Results: Src inhibitors and ISFs induced an accumulation of cells in the G1 and G2/M phases of the cell cycle, respectively, with little change in cell viability or survival. Invasion studies with PC-3 ML and LNCaP cells suggest that ISFs can reduce metastatic activity by 39% and 35%, respectively. In addition, ISFs enhance the effectiveness of the Src inhibitors to reduce invasiveness. This may indicate that including ISFs in treatment regimens may allow a lower dose of the targeting agent to be used to achieve optimal response and decrease toxicity. Conclusions: In vitro studies suggested that combining a Src inhibitor and ISFs resulted in greater inhibition of metastatic activity than either alone.

Citation Format: Lori P. Rice, Christine Pampo, Sharon Lepler, Dietmar W. Siemann. Combining tyrosine kinase inhibitors and isoflavones to target metastatic activity in prostate cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4037. doi:10.1158/1538-7445.AM2014-4037

Abstract 1816: Assessment of anti-tumor activity of the cathepsin L inhibitor, KGP94

Purpose: The cysteine cathepsin proteases are known to play an important role in tumor progression, invasion and angiogenesis. The present study evaluated the anti-tumor activity and pharmacokinetics of the small-molecule cathepsin L inhibitor KGP94.

Materials and Methods: Male CDF1 or C3H/HeNHsd mice were inoculated on the right rear foot with a C3H mammary carcinoma or a SCCVII carcinoma, respectively. A solution of KGP94 was prepared each day by dissolving in a mixture of 10% Tween 80 and 90% HEPES-buffer. It was intraperitoneally injected at 0.01 ml/g mouse bodyweight. Various doses (1-20 mg/kg) were administered between 1-20 days, starting from the day of tumor inoculation. Anti-tumor activity was assessed by determining the tumor growth time, which was the time in days to reach a volume of 500 mm3 (TGT500). Pharmacokinetics of KGP94 were investigated by drawing blood samples before, and up to 24 hours after KGP94 injection. Results are listed as Mean (± Standard Error). One-way ANOVA comparison of group means was performed, and a P&lt;0.05 was considered significant.

Results: The TGT500 for control animals was 18.0 days (± 0.3) for the C3H mammary carcinoma and 13.6 days (± 0.7) for the SCCVII carcinoma. Treating tumors with KGP94 significantly increased the TGT500 for both tumor models to around 21 and 17 days respectively, when doses were at 10.0 mg/kg or higher. At a dose of 5.0 mg/kg the TGT500 of the C3H mammary carcinoma was significantly increased to 21.4 days (± 1.1), whereas the TGT500 of the SCCVII carcinoma was unchanged at 13.8 (± 0.2). At lower KGP94 doses neither tumor model showed significant growth delay. Additional experiments with the C3H mammary carcinoma model showed that treatment was most effective when started immediately after tumor inoculation, and that treatment for 5 days was just as effective as 20 days. Pharmacokinetic analysis of KGP94 levels in mouse plasma is ongoing.

Conclusion: In the C3H mammary carcinoma KGP94 significantly delayed tumor growth, but the effect was primarily on the early phase following tumor cell inoculation. This suggests that KGP94 may have a more significant role in inhibiting the establishment of metastasis rather than influencing the growth of established tumors. Significant growth delay was also observed in the SCCVII tumor model. However, it occurred with higher doses of KGP94 compared to the C3H mammary carcinoma. The higher dose could be explained by the more aggressive nature of the SCCVII tumor model.

Supported by The Danish Cancer Society, The Danish Council for Independent Research: Medical Sciences, and OXiGENE Inc.

Citation Format: Thomas R. Wittenborn, Michael Stratford, Mary Lynn Trawick, Kevin G. Pinney, David J. Chaplin, Dietmar W. Siemann, Michael R. Horsman. Assessment of anti-tumor activity of the cathepsin L inhibitor, KGP94. [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 1816. doi:10.1158/1538-7445.AM2014-1816