TAXYNERGY (NCT01718353): A randomized phase II trial examining an early switch from first-line docetaxel to cabazitaxel, or cabazitaxel to docetaxel, in men with metastatic castration-resistant prostate cancer (mCRPC)

TPS5100

Background: Docetaxel is the standard 1st-line chemotherapy for mCRPC, while cabazitaxel prolongs survival after docetaxel progression. The activity of cabazitaxel in the 1st-line setting is unknown, while the molecular mechanisms of taxane sensitivity/resistance have been understudied. Clinically, a ≥30% PSA decline within 3 months predicts survival in docetaxel- and cabazitaxel-treated men. Molecularly, emerging evidence suggests that sensitivity/resistance to taxanes relates to the ability of microtubules to traffic AR into the nucleus. Circulating tumor cells (CTCs) represent a real-time biomarker to assess drug-target engagement (DTE) which may be predictive of clinical outcome, and novel enrichment techniques present opportunities for molecular testing. Methods: This is a multicenter phase 2 trial for chemo-naïve mCRPC. 100 men will be randomized (2:1) to 1st-line docetaxel or cabazitaxel. Following 4 cycles, if a ≥30% PSA decline is not achieved, men will switch to the alternative taxane; others will remain on the initial taxane until progression (PCWG2) or unacceptable toxicity. CTCs will be obtained at screening, baseline, after 1 and 4 cycles of chemotherapy, at crossover and at progression to interrogate mechanisms of taxane sensitivity/resistance. CTCs will be enriched via a prostate-specific microfluidic device, enumerated, and analyzed via multiplex confocal microscopy for microtubule bundling and AR localization. TaqMan PCR (and RNA sequencing) will be used to detect AR variants, as preliminary data show that variant ARv567 predicts taxane sensitivity while ARv7 predicts resistance. The primary clinical endpoint of the trial is achievement of a ≥50% PSA reduction during the treatment continuum. The primary molecular endpoint is analysis of DTE in CTCs, and correlation with PSA responses. The study will have 80% power to detect a 25% increase in PSA response rate with tight interclass kappa coefficients for primary biomarkers. Secondary endpoints include radiographic and PSA progression-free survival, objective response rates, overall survival, and safety. Clinical trial information: NCT01718353.

Abstract 2888: Computational analysis of microtubule dynamics for personalized cancer therapy

Metastatic prostate cancer (PC) is treated primarily by means of taxane-based chemotherapy with one of the clinically used taxanes: paclitaxel, docetaxel and cabazitaxel. At the cellular level, the taxanes bind microtubules (MTs), inhibit MT dynamics and alter the spatial organization of the MT network. Thereby the taxanes inhibit the intracellular trafficking of transcription factors critical for tumor survival. In PC, taxanes are the only chemotherapy class shown to improve survival, however, the emergence of clinical taxane resistance hampers their clinical efficacy. In addition, patients resistant to one taxane often respond to another, yet, currently we do not have the ability to match individual patients to a specific taxane. In cells, different taxanes have differential effects on microtubule dynamics which may ultimately pre-determine their efficacy for each individual patient. Thus, we hypothesized that the particular pattern of dynamic behavior of the MT cytoskeleton in individual patients could be exploited therapeutically. Therefore, we looked into dissecting the concrete effects of each of the taxanes for several PC cells lines. Preliminary unpublished data have revealed that PC cells expressing the TMPRSS2-ERG fusion protein exhibit taxane resistance. In addition, we have recently shown that the androgen receptor (AR) binds MTs in order to traffic to the nucleus and that taxane-mediated inhibition of AR nuclear accumulation correlates with patient clinical response to taxane therapy. Moreover, we have shown that the two clinically relevant AR splice variants, ARv567 and ARv7, show differential response to taxane therapy. Therefore, we set out to investigate the hypothesis that ERG fusion and/or AR variants might modulate endogenous microtubule dynamics in a way that determines cellular response to taxane treatment. Xenografts PC models expressing the ARv7 variant exhibit reduced sensitivity to docetaxel treatment. In addition, docetaxel's ability to induce MT stabilization is significantly impaired in ERG+ cells. We have recently established isogenic PC cell line series with inducible ERG (DU145 ERG+ and ERG-), as well as M12 cells without endogenous AR that stably express, wt-AR, ARv567 and ARv7. We then tested in a systematic way endogenous MT dynamics using live cell confocal microscopy of labeled MT tips following EGFP-EB1 lentiviral transduction. We use computer vision algorithms to obtain statistically representative results for the effects of ERG or AR on microtubule homeostasis following treatment with each of the three taxanes. We measure changes in MT behavior as statistically significant shifts in different parameters of MT dynamics measured from >20,000 MTs for each condition. Our preliminary results revealed that the presence of ERG fusion a correlation between MT dynamics and AR variant expression in PC cell lines.

Citation Format: Alexandre Matov, Dragi Kimovski, Giuseppe Galletti, Nancy Chan, Benet Pera, William T. Harkcom, David S. Rickman, Paraskevi Giannakakou. Computational analysis of microtubule dynamics for personalized cancer therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2888. doi:10.1158/1538-7445.AM2013-2888

Abstract 2318: The microtubule cytoskeleton in the dynamic regulation of translation: implications for taxane therapy

Microtubule (MT)-targeting drugs, and in particular the MT-stabilizing drug Taxol, are the most widely used and most effective class of drugs in clinical oncology. However, certain tumor types are refractory to MT-based therapy, and even responsive tumors often acquire drug resistance. Today, 20 years following Taxol's FDA approval we still fail to understand the molecular basis of taxane clinical response. Traditionally, taxane activity has been attributed solely to their anti-mitotic effects; however, we and others have shown that interphase MT functions are the “true” taxane targets mediating clinical activity. In support of this hypothesis we identified a novel mechanism of MT-dependent RNA translation. We found that MTs are intricately involved in regulating hypoxia inducible factor (HIF-1α) translation. Taxol-induced MT stabilization released HIF-1α mRNA from polysomes, and enriched HIF-1α mRNA in Argonaute 2 (Ago2)-containing P-bodes, where HIF-targeting miRNAs were also recruited. MT repolymerization allowed HIF mRNA to re-enter active translation, suggesting that MTs exert a tight control over HIF-1α. Our data have revealed a previously unexplored role for MTs in cancer cell biology and identified an unconventional link between the MT cytoskeleton and HIF protein synthesis. Interestingly, our work suggests that other mRNAs are also regulated in a MT-dependent manner. Polysome profiles in several cancer cell lines consistently showed a striking increase in the 80S monosomal peak following MT disruption, a hallmark of translation inhibition. In addition, taxane treatment resulted in P-body recruitment of two miRNAs not predicted to target HIF-1α, suggesting that other mRNAs are also repressed following MT disruption. Therefore, it is crucial to determine which other mRNAs, important for cancer cell survival, are affected by taxane treatment. To identify MT-dependent messages, we are currently performing polysome profiling coupled with RNA-Seq to identify which mRNAs change translational status following taxane treatment. In parallel, we are also performing RNA-Seq of Ago2-associated mRNAs to identify which mRNAs are enriched in P-bodies following taxane treatment. Preliminary polysome profiling experiments in MDA-MB-231 breast cancer cells yielded 116 transcripts with 2-fold or greater repression of translation upon Taxol treatment, including Aurora A kinase and several cyclin-dependent kinases, which has been validated at the protein level. Importantly, we found that a substantial fraction of the mRNAs that become untranslated are also among those most highly bound by Ago2 upon Taxol treatment, assessed by gene set enrichment analysis (GSEA). Our work has the potential to identify additional mRNAs whose translation is MT-dependent, and therefore lead to novel target discovery whose therapeutic exploitation can synergize with existing taxane-based chemotherapy.

Citation Format: Marisa Carbonaro, Duane Hassane, Paraskevi Giannakakou. The microtubule cytoskeleton in the dynamic regulation of translation: implications for taxane therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2318. doi:10.1158/1538-7445.AM2013-2318

Abstract 1467: Development of a HER2-based GEDI microfluidic device for the molecular characterization of CTCs from metastatic breast cancer patients

Microtubule targeting drugs (MTDs) constitute the mainstay of the most active chemotherapy regimens against breast cancer (BC) and have been standard therapy for locally advanced and metastatic disease for the last 20 years. However, metastatic BC (MBC) is still incurable mainly because of acquired drug resistance. The molecular basis of clinical drug resistance is not well understood which together with the lack of predictive biomarkers in the clinical setting prevents us from personalizing MTD-based therapy.

Isolation of Circulating Tumor Cells (CTCs) from the blood of metastatic patients has emerged as a valid source of tumor tissue in the form of liquid biopsy that is being used as prognostic biomarker based on CTC enumeration. To be able to perform molecular CTC analyses we have developed a BC specific microfluidic device that operates on the principle of geometrically enhanced differential immunocapture (GEDI), using antibody-coated microposts. We selected HER2 as BC selective surface antigen to isolate CTCs from MBC patients as it is expressed in 90% of breast tumors and overexpressed in 30%, while it is minimally affected by epithelial-to-mesenchymal transition (EMT) often occurring in metastasis. We previously demonstrated that the ability of the HER2 GEDI microfluidic device to capture BC cells expressing high and intermediate to low levels of HER2 expression confirming its suitability for BC patients with highly heterogeneous HER2 levels.

We have tested the HER2-based GEDI in MBC patients and have confirmed CTC capture. To test the performance of our device we are currently comparing it to the FDA approved CellSearch using blood from the same patient where CTCs are enumerated by both Cell Search and our device.

Importantly, the retained viability of GEDI-captured CTCs provides us the opportunity to functionally test CTC response to chemotherapy directly on the device, in an effort to develop an assay predictive of clinical response so that we can tailor chemotherapy to the individual. In this assay, we are treating the GEDI-captured CTCs with physiologically relevant concentrations of MTDs and are subsequently assaying drug-induced target modifications. As a proof of principle, we have demonstrated that taxane sensitive BC cell lines captured on the GEDI device showed evidence of effective drug-target engagement by the presence of microtubule bundling following Docetaxel treatment. We are currently evaluating the response of GEDI-captured BC taxane-resistant cells to ex-vivo drug treatment to evaluate the dynamic range of our assay.

We are currently conducting a clinical trial that characterizes GEDI-captured CTCs isolated from MTD treated MBC patients where we will monitor the molecular characteristics of the CTCs during chemotherapy treatment and at disease relapse. This approach will give us significant insight of the mechanisms of resistance of MTDs.

Citation Format: Giuseppe Galletti, Brian Kirby, Linda T. Vahdat, Paraskevi Giannakakou. Development of a HER2-based GEDI microfluidic device for the molecular characterization of CTCs from metastatic breast cancer patients. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1467. doi:10.1158/1538-7445.AM2013-1467

Abstract 3492: Using CTCs to interrogate mechanisms of taxane resistance in the prospective TAXYNERGY clinical trial in prostate cancer

Prostate cancer progression into castration-resistant prostate cancer (CRPC) is driven by continued androgen receptor (AR) signaling despite surgical and chemical androgen ablation. The taxanes represent the only class of chemotherapy that improves overall survival in CRPC patients. Despite their success, CRPC patients do progress on taxane treatment rendering taxane-resistant tumors. The molecular mechanisms underlying clinical taxane resistance in CRPC have not been well elucidated due to the lack of available tumor tissue to study. Circulating tumor cells (CTCs) represent a liquid biopsy of the original tumor and isolation of them can lead to their molecular characterization potentially revealing predictive biomarkers for taxane sensitivity or resistance. Here, we use a geometrically enhanced differential immunocapture (GEDI) microfluidic device that couples an anti-prostate specific membrane antigen (PSMA) antibody with optimized 3D geometry to capture and isolate live CTCs from whole blood of CRPC patients. The GEDI-microfluidic device was shown to have a 2-400 fold higher sensitivity for CTC capture than the FDA-approved CellSearch® system. We have previously shown that CRPC patient CTCs can be used to derive functional information that correlates to clinical response to taxane chemotherapy, namely AR subcellular localization status. We have developed a suite of other functional assays that can be performed on live GEDI-captured CTCs that enable their molecular characterization and allow us to test specific mechanistic hypotheses based on our extensive preclinical data. Included, and herein described, are the determination of AR subcellular localization, extent of effective drug-target engagement assessed by microtubule bundling, identification of RNA species relevant to the mechanism of taxane resistance and computer vision algorithms that will allow for enriched and automated analysis of high-volume image sets of GEDI-captured CTCs. In addition, we will be testing the hypothesis that distinct AR splice variants may affect patient sensitivity to taxane-based chemotherapy. This suite of assays are being rigorously applied in a phase II clinical trial in which chemotherapy-naïve CRPC patients will be initially treated with either docetaxel or cabazitaxel and clinically evaluated for an early switch to the other taxane following disease progression. This prospective, randomized, multi-site clinical trial will enroll 100 CRPC patients within one year. Patients will be followed until relapse and each patient will have 15 independent GEDI assays performed across five time points from baseline to chemotherapy crossover to relapse. The depth of coverage this suite of assays provides will offer unique insights for potential mechanisms of clinical taxane resistance and predictive biomarkers for taxane sensitivity in CRPC patient CTCs.

Citation Format: Matthew S. Sung, Ada Gjyrezi, Guang Yu Lee, Alexandre Matov, Giuseppe Galletti, Matthew Loftus, Yusef Syed, Timothy Lannin, Atanas Hristov, Christopher Mason, Scott Tagawa, Brian Kirby, David Nanus, Paraskevi Giannakakou. Using CTCs to interrogate mechanisms of taxane resistance in the prospective TAXYNERGY clinical trial in prostate cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3492. doi:10.1158/1538-7445.AM2013-3492

Abstract 4081: Taxane sensitivity in prostate cancer is determined by androgen receptor splice variants

Although its pivotal role in prostate cancer care, androgen deprivation therapy (ADT) is not curative as many patients progress to a castration-resistant stage (CRPC) which remains driven by pathologic reactivation of androgen receptor (AR). Taxanes represent the only chemotherapy class that improves survival in CRPC and as such Docetaxel (DTX) and Cabazitaxel (CTX) are standard of care.

Recent evidence revealed the presence of several AR splice variants lacking the ligand binding domain and thus constitutively active in CRPC. Previous data from our lab showed that taxanes impair the ligand-induced nuclear accumulation and transcriptional activity of full-length AR (AR-FL) in taxane treated human prostate cancer cells and CRPC patients. Indeed we showed that AR cytoplasmic sequestration in patient's circulating tumour cells (CTCs) was significantly correlated with clinical response to taxane chemotherapy. This is due to AR binding microtubules (MTs) and using them for nuclear accumulation supported by the dynein motor protein. However, the effect of taxane on the nuclear accumulation and activity of the AR variants is unknown. Thus, we set out to investigate the mechanism underlying AR variant nuclear accumulation and the impact of taxane treatment on AR variant function focusing on the two clinically relevant AR splice variants ARv567 and AR-V7.

A microtubule co-sedimentation assay revealed that ARv567 is associated with MTs, in contrast to AR-V7. Serial AR mutagenesis demonstrated that the MT binding domain comprises a region aa 559 - 663 which is missing in AR-V7. Dynamitin overexpression inhibited the nuclear accumulation of AR-FL and ARv567 but had no effect on AR-V7, suggesting that AR-V7’s nuclear translocation is independent of dynein-based MT transport. To examine the impact of taxane treatment on variant activity we microinjected GFP-tagged AR-FL, or AR variants into the nucleus of PC3 cells and monitored the dynamics of AR nuclear translocation using live-cell confocal microscopy. Moreover we stably transfected M12 cells with AR-FL, AR-V7 and AR-v567 and assessed AR's nuclear translocation in response to R1881 and in the presence or absence of DTX. Our data showed that taxanes significantly inhibited the nuclear accumulation and activity of AR-FL and ARv567 but not that of AR-V7 and that this effect is androgen independent. We are currently elucidating the effect of taxanes on AR variant transcriptional activity using luciferase reporter and specific genes expression assays. Taken together our data revealed that functional MTs are required for AR's nuclear transport in a ligand independent manner, as in the case of ARv567. However, this does not apply to AR-V7 which is not under MT control and thus insensitive to taxane treatment. These data suggest that impairment of AR variant expression might be predictive of clinical taxane sensitivity in CRPC.

Citation Format: Luigi Portella, Maria Thadani-Mulero, Alexandre Matov, David M. Nanus, Stephen R. Plymate, Paraskevi Giannakakou. Taxane sensitivity in prostate cancer is determined by androgen receptor splice variants. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4081. doi:10.1158/1538-7445.AM2013-4081

Abstract LB-59: ERG induces taxane resistance in castration-resistant prostate cancer

Taxanes are the only chemotherapies to prolong survival for patients with metastatic castration-resistant prostate cancer (CRPC), and both docetaxel (doc) and cabazitaxel (cab) are FDA approved for this indication. Despite the initial efficacy of taxanes in treating CRPC, all patients ultimately fail due to the development of drug resistance. In this study we show that ERG over-expression, which occurs in roughly 50% of prostate cancers, is associated with both doc and cab resistance using in vitro and in vivo models of CRPC. Using either tetracycline-inducible or constitutively active expression systems in multiple prostate cancer cell lines, we found that ERG over-expression leads to at least a 10 fold increase in IC50 doses of doc or cab based on cell viability assays and inhibition of taxane-induced apoptosis. Similarly, ERG over-expressing prostate cancer xenografts were reproducibly more resistant to cab compared to the cab-sensitive control xenografts. Based on a biochemical and cell biological characterization, we observed that ERG binds directly to tubulin in the cytoplasm of prostate cancer cells, as well as in circulating tumor cells from patients treated with doc, and prevents taxane-induced microtubule stabilization. ERG over-expression affects several parameters of microtubule dynamics and inhibits effective drug-target engagement of doc or cab with tubulin, either directly via its tubulin interaction or indirectly by affecting transcription of genes that modulate microtubule homeostasis. In addition, ERG induces and binds to clusterin, a molecular chaperone also associated with taxane resistance. Clusterin knock-down with siRNA abrogates ERG-induced taxane resistance. Altogether, this data suggests that ERG, an oncogenic transcription factor, plays a novel role beyond regulating gene expression and functions outside the nucleus to cooperate with clusterin and tubulin in promoting taxane resistance. Determining ERG status in patient tumors may aid in patient selection for doc or cab therapy and/or influence co-targeting approaches using the clusterin antisense inhibitor OGX-011.

Citation Format: Giuseppe Galletti, Himisha Beltran, Alexandre Matov, Jacqueline Fontugne, Juan Miguel Mosquera, Ladan Fazli, Scott Tagawa, David Nanus, Martin Gleave, Mark Rubin, Paraskevi Giannakakou, David S. Rickman. ERG induces taxane resistance in castration-resistant prostate cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-59. doi:10.1158/1538-7445.AM2013-LB-59

Clinical and preclinical evaluation of taxane sensitivity in gastric cancer (GC): Relevance of GC histology

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Background: Docetaxel (D) is a standard treatment for advanced gastric cancer based on the TAX-325 study (van Cutsem, JCO 2006). We asked the question, do all subtypes of GC benefit equally from D therapy? Methods: We performed a post-hoc analysis of the TAX-325 study. We classified randomized patients as diffuse or non-diffuse histology and correlated histology with clinical outcomes using a Cox proportional hazards model. Preclinical studies involved 13 GC cell lines (4 intestinal subtype, 7 diffuse subtype, 2 unknown), assessed for D sensitivity using the Sulforhodamine B (SRB) cytotoxicity assay, microtubule bundling, mitotic arrest by immunofluorescence as evidence of drug-target engagement, and apoptosis assessment by Caspase 8, Caspase 3, and PARP cleavage by Western Blot. Results: In post hoc analysis of TAX-325, patients were classified as diffuse (n=206) or non-diffuse (n=239). Non-diffuse GC showed a significant improvement in overall survival with the addition of D (12.1 v 8.8 mo, p=0.002), whereas diffuse histology was not associated with an improvement in survival (8.3 v 8.5 mo, p=0.66). Preclinical studies similarly reveal that 5/7 diffuse GC cell lines were resistant to D by SRB assay compared with 1/4 intestinal GC cell lines (IC50 > 600 nM). To examine drug target engagement, a dynamic measure of D activity, 4/6 diffuse GC cell lines showed lack of D engagement on the microtubule network at physiologic D concentrations (0-100 nM). 5/6 diffuse cell lines demonstrated no apoptosis. Additionally, we found that 0/9 GC cell lines expressed P-glycoprotein, ruling out multidrug resistance as an etiology for diffuse GC resistance to D. Conclusions: In exploratory analysis, we observed diffuse GC to be resistant to the addition of D to standard chemotherapy in a random assignment phase III clinical trial. In vitro analyses support these clinical findings and demonstrate intrinsic D resistance in diffuse GC, unrelated to multidrug resistance. Ongoing mechanistic studies focus on the molecular basis of taxane sensitivity in GC to predict treatment efficacy. These findings will inform future clinical studies aimed at individualized therapy.

Androgen receptor on the move: boarding the microtubule expressway to the nucleus

Recent studies have shown that the microtubule-stabilizing drug paclitaxel, which is commonly used for the treatment of prostate cancer, inhibits signaling from the androgen receptor by inhibiting its nuclear accumulation downstream of microtubule stabilization. This mechanism is independent of paclitaxel-induced mitotic arrest and could provide an alternative mechanism of drug action that can explain its clinical activity. In this review, we highlight the importance of signaling and trafficking pathways that depend on intact and dynamic microtubules, and, as such, they represent downstream targets of microtubule inhibitors. We showcase prostate cancer, which is driven by the activity of the androgen receptor, as recent reports have revealed a connection between the microtubule-dependent trafficking of the androgen receptor and the clinical efficacy of taxanes. Identification and further elucidation of microtubule-dependent tumor-specific pathways will help us better understand the molecular basis of clinical taxane resistance as well as to identify individual patients more likely to respond to treatment.

The beta 1 tubulin R307H single nucleotide polymorphism is associated with treatment failures in immune thrombocytopenia (ITP)

Predictive biomarkers are needed in immune thrombocytopenia (ITP). Single nucleotide polymorphisms (SNPs) in beta 1 tubulin are potential candidates, as beta 1 tubulin is integral for platelet production and function, and SNPs in beta 1 tubulin have been associated with distinct phenotypes in platelets. We investigated the most prevalent beta 1 tubulin SNP (R307H) as a biomarker in patients with ITP via a retrospective chart review. Allelic frequencies between a group of 191 ITP patients and a healthy control group showed no difference, suggesting no direct aetiological role for the SNP in ITP. However, over similar periods of follow-up, both heterozygote and homozygote minor allele ITP patients were treated with significantly more treatment modalities and had significantly higher risk of failure to immune-modulatory therapies [relative risk (RR) = 1·5, 95% confidence interval (CI) = 1·1-2·1; P = 0·01]; with rituximab, in particular, ITP patients with the SNP experienced a 58% failure rate (RR = 1·6, 95%CI = 1·03-2·5; P = 0·04). Analysis of the absolute immature platelet fraction (A-IPF) as a marker of platelet production showed that SNP patients had significantly higher median A-IPFs compared to non-SNP patients when complete responses were achieved using immune modulatory therapies. The data suggest that the beta 1 tubulin R307H SNP has potential for use as a biomarker in ITP and may affect platelet turnover.

Isolation and characterization of circulating tumor cells in prostate cancer

Circulating tumor cells (CTCs) are tumor cells found in the peripheral blood that putatively originate from established sites of malignancy and likely have metastatic potential. Analysis of CTCs has demonstrated promise as a prognostic marker as well as a source of identifying potential targets for novel therapeutics. Isolation and characterization of these cells for study, however, remain challenging owing to their rarity in comparison with other cellular components of the peripheral blood. Several techniques that exploit the unique biochemical properties of CTCs have been developed to facilitate their isolation. Positive selection of CTCs has been achieved using microfluidic surfaces coated with antibodies against epithelial cell markers or tumor-specific antigens such as EpCAM or prostate-specific membrane antigen (PSMA). Following isolation, characterization of CTCs may help guide clinical decision making. For instance, molecular and genetic characterization may shed light on the development of chemotherapy resistance and mechanisms of metastasis without the need for a tissue biopsy. This paper will review novel isolation techniques to capture CTCs from patients with advanced prostate cancer, as well as efforts to characterize the CTCs. We will also review how these analyzes can assist in clinical decision making.

CONCLUSION

The study of CTCs provides insight into the molecular biology of tumors of prostate origin that will eventually guide the development of tailored therapeutics. These advances are predicated on high yield and accurate isolation techniques that exploit the unique biochemical features of these cells.

Computer assisted analysis of microtubule dynamics in living cells

Microtubules are dynamic polymers that rapidly transition between states of growth, shortening, and pause. These dynamic events are critical for basic cellular processes, especially cell division. Typically, these events are quantified by imaging microtubule movements over time, which results in large data sets that require rigorous quantitative analysis. In most cases, these analyses are performed manually by the researcher. This process is both tedious and prone to error; thus an efficient and reliable computer-assisted quantification system would provide a rapid approach, suitable for high-throughput data analysis. In this paper, we describe methods to automatically segment and track microtubule movements. Our method is a snake based method [1]. Instead of a closed contour, we use an open contour to track individual microtubule. We redefine some of the internal energy terms specifically for open snake. A new external energy term for locating the end points of a microtubule is also defined. Testing is done using simulated images and untreated MCF-7 breast cancer cell lines as well as cells treated with the microtubule-targeting chemotherapeutic agent, Taxol.

Integrating image analysis algorithms in a web interface for the quantification of microtubule dynamics

We present improvements to a web interface and an integrated computational tracking algorithm for quantitative analysis of microtubule dynamics in live-cell microscopy images. Based on a previously implemented system, more new functionalities have been added to the interface. The system also integrates a computational tracking algorithm to aid the analysis. The analysis workflow of the proposed interface is made similar to the current manual analysis workflow in order to make the interface intuitive to use. We show the workflow of the computer analysis algorithm and how it is used to aid the existing analysis workflow. We also demonstrate how to re-evaluate existing data in a case study using real imaging data. Lastly, we show the added functionalities of the interface including how to share image data and analysis results.

Functional characterization of circulating tumor cells with a prostate-cancer-specific microfluidic device

Cancer metastasis accounts for the majority of cancer-related deaths owing to poor response to anticancer therapies. Molecular understanding of metastasis-associated drug resistance remains elusive due to the scarcity of available tumor tissue. Isolation of circulating tumor cells (CTCs) from the peripheral blood of patients has emerged as a valid alternative source of tumor tissue that can be subjected to molecular characterization. However, issues with low purity and sensitivity have impeded adoption to clinical practice. Here we report a novel method to capture and molecularly characterize CTCs isolated from castrate-resistant prostate cancer patients (CRPC) receiving taxane chemotherapy. We have developed a geometrically enhanced differential immunocapture (GEDI) microfluidic device that combines an anti-prostate specific membrane antigen (PSMA) antibody with a 3D geometry that captures CTCs while minimizing nonspecific leukocyte adhesion. Enumeration of GEDI-captured CTCs (defined as intact, nucleated PSMA+/CD45- cells) revealed a median of 54 cells per ml identified in CRPC patients versus 3 in healthy donors. Direct comparison with the commercially available CellSearch® revealed a 2-400 fold higher sensitivity achieved with the GEDI device. Confocal microscopy of patient-derived GEDI-captured CTCs identified the TMPRSS2:ERG fusion protein, while sequencing identified specific androgen receptor point mutation (T868A) in blood samples spiked with only 50 PC C4-2 cells. On-chip treatment of patient-derived CTCs with docetaxel and paclitaxel allowed monitoring of drug-target engagement by means of microtubule bundling. CTCs isolated from docetaxel-resistant CRPC patients did not show any evidence of drug activity. These measurements constitute the first functional assays of drug-target engagement in living circulating tumor cells and therefore have the potential to enable longitudinal monitoring of target response and inform the development of new anticancer agents.

Abstract 3634: Molecular determinants of taxane activity using CTCs from CRPC patients

Androgen receptor (AR) signaling drives castration resistant prostate cancer (CRPC) disease progression. The taxanes (TXN) represent the only class of chemotherapy agents that improve survival in CRPC. Our recent work revealed that TXNs work by blocking AR nuclear accumulation and signaling downstream of microtubule (MT) stabilization. Moreover, we showed that AR cytoplasmic sequestration in CRPC patients’ circulating tumor cells (CTCs) significantly correlated with clinical response to TXN therapy. Our data, suggest that TXN-induced blockade of AR nuclear accumulation partly underlies the clinical activity of TXNs in CRPC. Recently several AR splice variants, lacking the ligand binding domain, have been identified in CRPC. These variants are constitutively active in the nucleus and likely to be insensitive to current therapies targeting either ligand biosynthesis or ligand-receptor interactions. Currently, the role of AR splice variants on TXN chemotherapy response in CRPC is unknown. Our preliminary data in preclinical PC models suggest that certain AR variants depend on MTs for nuclear accumulation and are TXN sensitive while others are MT-independent and TXN-insensitive. In this study we are prospectively evaluating whether the presence of AR splice variants and the integrity of the MT-AR axis in CTCs can predict clinical response to TXN chemotherapy in CRPC. CTCs are captured by the geometrically enhanced differential immunocapture (GEDI) microfluidic device that uses PSMA-based immunocapture and size-selective cell transport for maximum specificity of CRPC-derived CTCs. We captured viable CTCs from CRPC patients (median 54 CTC/ml) and performed molecular and functional analyses. Comparison of CTCs captured by CellSearch or GEDI, using same day blood draw from 30 CRPC patients, revealed a 2-400 fold increase in CTC numbers with the GEDI. GEDI-capture of live CTCs allowed us to evaluate ex-vivo TXN sensitivity and determine drug-target-engagement (DTE) by MT bundling. CTCs isolated from docetaxel (DTX)-resistant CRPC patients did not show any evidence of DTX activity in this assay suggesting that it can be used to monitor patient's response in real time. In addition, we have miniaturized RNA sequencing (RNA-Seq) to enable molecular analyses of GEDI-captured CTCs. RNA-Seq of 50 GEDI-captured LNCap 86.2 cells spiked into 1 ml healthy donor blood, detected both the T868A AR point mutation and ARv567 splice variant. In an ongoing prospective clinical study, we are capturing CTCs from CRPC patients treated with TXNs and are evaluating the integrity of the MT-AR signaling axis, in relation to clinical response to therapy. Our CTC analyses include RNA-Seq for the detection of AR splice variants, alterations in tubulin isotypes and MT related proteins, and multiplex confocal microscopy of DTE and AR localization. These analyses are performed longitudinally and may identify biomarkers predictive of clinical TXN efficacy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3634. doi:1538-7445.AM2012-3634

Abstract 2376: Development of a novel microfluidic device for the capture and molecular characterization of circulating tumor cells from metastatic breast cancer patients

Breast cancer (BC) is the most commonly diagnosed malignancy and the second leading cause of cancer death among women in the United States. Microtubule targeting drugs (MTDs) represent the most active chemotherapy against BC and are standard therapy for locally advanced and metastatic disease. However, metastatic BC (MBC) remains an incurable disease due to acquired drug resistance. The molecular basis of clinical resistance to MTD therapy is not well understood, primarily due to the lack of readily accessible BC tissue during therapy and at the time of relapse precluding the development of rational approaches to overcome it. Circulating Tumor Cells (CTCs) have emerged as a reliable and accessible source of tumor tissue enabling molecular analysis of CTCs during disease progression. However, the extremely low purity associated with the use of the commercially available EpCAM-based CTC capture technology, precludes accurate CTC molecular analyses. To overcome this limitation, we are developing a novel BC-specific microfluidic device that operates on the principle of geometrically enhanced differential immunocapture (GEDI), using antibody-coated microposts. This innovative design achieves capture of viable CTCs using only 1 ml of blood and minimizes leucocyte contamination. We selected HER2 as an alternative to EpCAM-based capture, as HER2 is expressed in 90% of breast tumors and overexpressed in 30%, whereas it is absent from leucocytes. In addition, our preliminary data suggest that EpCAM can be downregulated during epithelial-to-mesenchymal transition (EMT) that often precedes dissemination of cancer cells to the circulation. HER2, on the other hand, is expressed in EMT cells further indicating its suitability for CTC capture from most of the clinically relevant BC subtypes. We tested the performance of various HER-2 antibodies using immunoblot and confocal microscopy analyses of 10 different BC cell lines with varying HER2 expression levels. Surprisingly, the antibody that provided the best dynamic range of HER2 detection in these assays, exhibited poor capture efficiency and lack of discrimination between HER2-positive and negative cell lines. Next, we tested antibody performance using flow cytometry and live-cell imaging in order to preserve the native conformation of HER2 extracellular epitope. These assays identified a different HER2 antibody that showed high capture efficiency and specificity for HER2 positive cells when applied to the GEDI microfluidic device. Currently, we are using the HER2-based GEDI to isolate CTCs from MBC patients receiving MTD-based chemotherapy. In this prospective study, we are characterizing the GEDI-captured CTCs isolated from MBC patients at baseline (before chemotherapy), during the course of therapy and at disease progression in order to gain insights into mechanisms of MTD-resistance.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2376. doi:1538-7445.AM2012-2376

Abstract 1502: Microtubule stabilization alters tumor secretome and fibroblast activation

Microtubules (MTs) represent one of the most effective targets in cancer chemotherapy. However, drugs that target MTs, like the taxanes, often fail in the metastatic setting. Therefore it is of utmost importance to fully understand the roles of MTs and MT-targeting agents in tumor biology. An important process for tumor development and metastasis involves the remodeling of the 3D microenvironment surrounding tumor cells. In order to successfully proliferate and metastasize, tumor cells need to dynamically respond to, manipulate, and remodel their surrounding microenvironment. We hypothesized that MTs, as a dynamic cytoskeletal component, regulates the cellular signaling process that controls tumor-mediated remodeling of the microenvironment. To test this hypothesis, we assessed the MT-dependence of metastatic MDA-MB-231 (231) breast cancer cell activation of HMF3S human mammary fibroblasts. We collected media conditioned by vehicle- or paclitaxel (PTX)-pretreated 231 cells and then applied this conditioned media to HMF3S fibroblasts. Application of 231-derived conditioned media activated HMF3S fibroblasts as evidenced by their enhanced directional 3D motility towards a serum gradient. However, application of conditioned media from PTX-pretreated 231 cells to HMF3S fibroblasts inhibited their 3D directional motility. Importantly, we demonstrated that this effect was due to PTX-induced MT stabilization as conditioned media from PTX-treated 231 cells resistant to PTX did not inhibit fibroblasts’ 3D motility. Together, these results suggest that the composition of the tumor secretome changes upon MT stabilization by PTX, which in turn affects the ability of tumor cells to communicate with fibroblasts. In order to identify the factors responsible for this MT-dependent cell-cell communication we performed a differential proteomic analysis of the conditioned media from vehicle- and PTX-pretreated 231 cells. Using splitless nanoflow chromatography coupled with quadrupole time-of-flight mass spec, we identified a total of 2124 proteins within these tumor secretomes. Using a 2-fold change threshold, we identified 78 under-represented and 31 over-represented proteins in the secretome of PTX- versus vehicle-pretreated cells. We focused our analysis on under-represented proteins based on the hypothesis that MT stabilization would inhibit their secretion. From this analysis we have identified proteins involved in cell motility, cell-cell communication, or ECM remodeling. TGFβ, CTGF, cMet, fibronectin, and lysyl oxidase 2 were key down-regulated proteins identified in the tumor secretome upon PTX-induced MT stabilization. Currently we are investigating the mechanisms by which stabilization of the MT cytoskeleton results in the down-regulation of these factors. These findings point to a novel role of interphase MTs in tumor biology and can possibly enhance our understanding of taxane clinical efficacy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1502. doi:1538-7445.AM2012-1502

Abstract 285: Androgen receptor splice variants determine taxane sensitivity in prostate cancer

Androgen ablation therapy is the mainstay for prostate cancer (PC) treatment, however, it is not curative, as many patients progress to a castration-resistant stage (CRPC). CRPC remains driven by active androgen receptor (AR) signaling. Several AR splice variants lacking the ligand binding domain were recently identified in PC. These variants are constitutively active in the nucleus, rise in response to castration, and are thought to mediate disease progression in CRPC. Taxane chemotherapy improves survival in CRPC. We have recently shown that taxanes impair the ligand-induced nuclear accumulation and transcriptional activity of full-length AR (AR-FL), downstream of microtubule (MT) stabilization. This is due to AR binding MTs and using them for its nuclear accumulation with the aid of the dynein motor protein. However, the effect of taxane treatment on the nuclear accumulation and activity of the AR variants is not known. As the variants are expressed in CRPC, we sought to examine the mechanism underlying AR variant nuclear accumulation and the impact of taxane treatment on their function. We have focused our studies on two clinically relevant AR splice variants ARv567 and AR-V7 and assessed their ability to bind MTs, translocate to the nucleus with dynein and response to taxane treatment. Our data showed that the two variants behave differently on all aspects. Microtubule co-sedimentation revealed that ARv567 is associated with MTs, in contrast to the significantly reduced association displayed by AR-V7. Dynamitin overexpression inhibited the nuclear accumulation of AR-FL and ARv567 but had no effect on AR-V7, suggesting that AR-V7's nuclear translocation is independent of dynein-based MT transport. To examine the impact of taxane treatment on variant activity we microinjected GFP-tagged AR-FL, or variants into the nucleus of PC3 cells and monitored the dynamics of AR nuclear translocation using live-cell confocal microscopy and AR transcriptional activity using ARE luciferase reporter assay. Our data showed that taxanes significantly inhibited the nuclear accumulation and activity of AR-FL and ARv567 but not that of AR-V7. Human xenograft models expressing the ARv567 exhibited greater tumor volume decreases in response to taxane treatment as compared with xenografts expressing either AR-FL or other variants. Taken together our data reveal that functional MTs are required for AR's nuclear transport in a ligand independent manner, as in the case of ARv567. However, this does not apply to AR-V7 which is not under MT control and thus, remains insensitive to taxane treatment. We are currently narrowing down the MT binding domain on the AR by serial mutagenesis and are testing their MT binding abilities. These data suggest that inhibition of AR nuclear accumulation underlies, in part, the activity of taxanes in CRPC and that the presence of the variants may determine the clinical efficacy of taxane chemotherapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 285. doi:1538-7445.AM2012-285

Microtubules regulate hypoxia-inducible factor-1α protein trafficking and activity: implications for taxane therapy

Disruption of the microtubule cytoskeleton impairs tumor angiogenesis by inhibiting the hypoxia-inducible factor (HIF-1α) pathway. However, the signaling cascade linking microtubule disruption to HIF-1α inactivation has not been elucidated. Here, we show that microtubule-targeting drug (MTD) treatment impaired HIF-1α protein nuclear translocation, which significantly down-regulated HIF transcriptional activity. We provide strong evidence that HIF-1α protein associates with polymerized microtubules and traffics to the nucleus, with the aid of the dynein motor protein. Together, these data suggest that microtubules are critically involved in the nuclear trafficking and transcriptional activity of HIF-1α. We also show that the connection between the microtubule cytoskeleton and HIF-1α regulation is lost in renal cell carcinoma (RCC), where HIF-1α is overexpressed because of mutations in the von Hippel Lindau (VHL) tumor suppressor protein. Specifically, we show that MTD treatment of RCC cells did not impair HIF-1α nuclear accumulation or transcriptional activity, and had no effect on the polysome association profile of HIF-1α. Interestingly, we found that HIF-1α protein did not bind microtubules in RCC. Moreover, restoration of VHL function failed to restore the ability of MTDs to inhibit HIF-1α, suggesting that VHL does not contribute to this phenotype. Together, these results suggest that HIF-1α regulation is microtubule-independent, and likely contributes to the chemoresistant nature of RCCs. Further understanding of the microtubule-dependent HIF-1α regulation, and lack thereof in RCC, is essential given the importance of HIF-1α in tumor biology, and the widespread use of MTDs in clinical oncology.

Prospective analysis of prostate cancer (PC) circulating tumor cells (CTCs) to predict response to docetaxel (DOC) chemotherapy

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Background: Taxane chemotherapy induces cellular microtubule stabilization (bundling) leading to mitotic arrest and apoptotic cell death. We recently reported that in castration-resistant PC, stabilizing of microtubules by taxanes inhibits ligand-induced androgen receptor (AR) nuclear translocation and activation of ARE-gene transcription (Cancer Res 2011;71:6019). This suggests the clinical activity of DOC results from inhibition of AR signaling. A pilot analysis of CTCs from 14 CRPC pts receiving taxanes revealed that predominant cytoplasmic AR and decreased total AR intensity each was associated with increased odds of response (P<0.001). We initiated a prospective trial to determine if CTC analysis could predict DOC response.

Methods: Eligibility: Patients (pts) receiving DOC q21 days for CRPC with >5 CTCs determined by CellSearch. On cycle 1 d1 + d8, CTCs are isolated by ficoll tube separation and by CellSearch enrichment. Cells are stained for expression of prostate specific membrane antigen (PSMA), CD45, AR and acetylated tubulin (AcTub) as a marker of microtubule stabilization. AR localization and total fluorescence intensity, and AcTub intensity are quantitated by confocal microscopy and correlated with response to DOC using PCWG2 criteria. 72 pts are planned to provide 80% power to detect an association.

Results: 28 of 72 pts have been prospectively enrolled to assess AR and AcTub as a biomarker of response. 20 pts have discontinued DOC. Day 1 samples were obtained from 27 pts and day 8 on 22 (5 pts on days 9 to 21). Immunofluorescence staining and evaluation of PSMA, CD45, and acetylated tubulin was performed successfully in 8 pts analyzed to date. CTCs can be identified in all pts. Cells are scored for AR and AcTub intensity (scale 1- 4) and AR nuclear vs cytoplasmic localization.

Conclusions: Our results to date indicate that PC CTCs can be readily isolated from men receiving DOC chemotherapy in a multicenter fashion and assayed for AR localization and AcTub. Preliminary results suggest that monitoring AR subcellular localization and microtubule bundling in CTCs may predict clinical responses to DOC chemotherapy, warranting further study, including our prospective trial.

A folate receptor-targeting nanoparticle minimizes drug resistance in a human cancer model

Resistance to chemotherapy is a major obstacle in cancer therapy. The main purpose of this study is to evaluate the potential of a folate receptor-targeting nanoparticle to overcome/minimize drug resistance and to explore the underlying mechanisms. This is accomplished with enhanced cellular accumulation and retention of paclitaxel (one of the most effective anticancer drugs in use today and a well-known P-glycoprotein (P-gp) substrate) in a P-gp-overexpressing cancer model. The folate receptor-targeted nanoparticle, HFT-T, consists of a heparin-folate-paclitaxel (HFT) backbone with an additional paclitaxel (T) loaded in its hydrophobic core. In vitro analyses demonstrated that the HFT-T nanoparticle was superior to free paclitaxel or nontargeted nanoparticle (HT-T) in inhibiting proliferation of P-gp-overexpressing cancer cells (KB-8-5), partially due to its enhanced uptake and prolonged intracellular retention. In a subcutaneous KB-8-5 xenograft model, HFT-T administration enhanced the specific delivery of paclitaxel into tumor tissues and remarkably prolonged retention within tumor tissues. Importantly, HFT-T treatment markedly retarded tumor growth in a xenograft model of resistant human squamous cancer. Immunohistochemical analysis further indicated that increased in vivo efficacy of HFT-T nanoparticles was associated with a higher degree of microtubule stabilization, mitotic arrest, antiangiogenic activity, and inhibition of cell proliferation. These findings suggest that when the paclitaxel was delivered as an HFT-T nanoparticle, the drug is better retained within the P-gp-overexpressing cells than the free form of paclitaxel. These results indicated that the targeted HFT-T nanoparticle may be promising in minimizing P-gp related drug resistance and enhancing therapeutic efficacy compared with the free form of paclitaxel.

Taxane-induced blockade to nuclear accumulation of the androgen receptor predicts clinical responses in metastatic prostate cancer

Prostate cancer progression requires active androgen receptor (AR) signaling which occurs following translocation of AR from the cytoplasm to the nucleus. Chemotherapy with taxanes improves survival in patients with castrate resistant prostate cancer (CRPC). Taxanes induce microtubule stabilization, mitotic arrest, and apoptotic cell death, but recent data suggest that taxanes can also affect AR signaling. Here, we report that taxanes inhibit ligand-induced AR nuclear translocation and downstream transcriptional activation of AR target genes such as prostate-specific antigen. AR nuclear translocation was not inhibited in cells with acquired β-tubulin mutations that prevent taxane-induced microtubule stabilization, confirming a role for microtubules in AR trafficking. Upon ligand activation, AR associated with the minus-end-microtubule motor dynein, thereby trafficking on microtubules to translocate to the nucleus. Analysis of circulating tumor cells (CTC) isolated from the peripheral blood of CRPC patients receiving taxane chemotherapy revealed a significant correlation between AR cytoplasmic sequestration and clinical response to therapy. These results indicate that taxanes act in CRPC patients at least in part by inhibiting AR nuclear transport and signaling. Further, they suggest that monitoring AR subcellular localization in the CTCs of CRPC patients might predict clinical responses to taxane chemotherapy.

Peloruside- and laulimalide-resistant human ovarian carcinoma cells have βI-tubulin mutations and altered expression of βII- and βIII-tubulin isotypes

Peloruside A and laulimalide are potent microtubule-stabilizing natural products with a mechanism of action similar to that of paclitaxel. However, the binding site of peloruside A and laulimalide on tubulin remains poorly understood. Drug resistance in anticancer treatment is a serious problem. We developed peloruside A- and laulimalide-resistant cell lines by selecting 1A9 human ovarian carcinoma cells that were able to grow in the presence of one of these agents. The 1A9-laulimalide resistant cells (L4) were 39-fold resistant to the selecting agent and 39-fold cross-resistant to peloruside A, whereas the 1A9-peloruside A resistant cells (R1) were 6-fold resistant to the selecting agent while they remained sensitive to laulimalide. Neither cell line showed resistance to paclitaxel or other drugs that bind to the taxoid site on β-tubulin nor was there resistance to microtubule-destabilizing drugs. The resistant cells exhibited impaired peloruside A/laulimalide-induced tubulin polymerization and impaired mitotic arrest. Tubulin mutations were found in the βI-tubulin isotype, R306H or R306C for L4 and A296T for R1 cells. This is the first cell-based evidence to support a β-tubulin-binding site for peloruside A and laulimalide. To determine whether the different resistance phenotypes of the cells were attributable to any other tubulin alterations, the β-tubulin isotype composition of the cells was examined. Increased expression of βII- and βIII-tubulin was observed in L4 cells only. These results provide insight into how alterations in tubulin lead to unique resistance profiles for two drugs, peloruside A and laulimalide, that have a similar mode of action.

Abstract 4911: Molecular investigation of the FTI/Taxol synergy using an integrated framework of transcriptome analysis

Farnesyltransferase inhibitors (FTIs) are a class of anticancer drugs that have exhibited modest activity in the clinic as single agents, but were found to have promising activity in combination with the microtubule-stabilizing drug Taxol (TX), both in vitro and in vivo. Clinical trials with an FTI/TX combination have demonstrated a clinical benefit for a subset of patients refractory to previous taxane-treatment. However, the precise cellular machinery underlying the FTI/TX synergistic drug combination still needs to be elucidated. To this end, we undertook an unbiased experimental/computational approach designed to identify the key cellular components that either contribute to or drive the therapeutic synergy of this drug combination. The approach combined (i) measurements of drug-mediated changes on tubulin biomarkers and overall survival; (ii) whole-genome transcriptome analysis using the combination index drug synergy algorithm; (iii) utilization of interaction and functional databases to identify pathway connections and (iv) a reverse-engineering forward simulation (REFS) approach to identify genes that drive synergy.

Drug-induced transcriptome changes were examined using whole-genome Affymetrix HGU133 Plus 2 microarrays. Gene changes deemed significant using a fold change criterion, identified as synergistic with the combination index analysis, and their biological relevance was assessed by experimental validation by qPCR and siRNA studies. Also, the transcriptome changes unique to the LNF/TX combination were evaluated in the context of detailed molecular interaction maps and groups of biological function. Our analyses identified several major network hubs that include: (i) overexpression of the class II β-tubulin isotype TUBB2A and of several heat shock protein such as HSP40 and HSP70 and (ii) synergistic overexpression of cell cycle genes CDKN1A and MDM2 (iii) through REFS modeling, prosaposin and granulin were identified as drivers of drug synergy (iv) induction of the focal adhesion molecule paxillin (PXN). Interestingly, stable knockdown of protein farnesyltransferase mimicked the effects of FTI treatment and resulted in strong substratum attachment and migration defects suggesting that PXN could be regulated by farnesyltransferase and its pharmacologic inhibitors. Ultimately, we plan to check the expression levels of the key genes in tumor biopsies from patients enrolled in the Phase 1 FTI/Taxotere clinical trial and correlate their expression in pre- and post-treatment biopsies with clinical response to the combination chemotherapy.

Herein, we demonstrate a combined experimental and computational approach that includes functional analysis, data-driven simulation and experimental validation, and its power to identify key cellular components, both known and novel, in the anticancer activity of drug combinations exhibiting therapeutic synergy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4911. doi:10.1158/1538-7445.AM2011-4911

Abstract 435: MT regulation of tumor-dependent microenvironment remodeling

Microtubules (MTs) represent one of the most effective targets in cancer chemotherapy. However, drugs that target MTs, like the taxanes, often fail in the metastatic setting. Most studies are performed in a two-dimensional monoculture thus, overlook the complexity of the tumor microenvironment. Therefore, to gain a better understanding of tumor MT biology within a physiological context we studied the role of MT dynamics in 3D co-cultures closer mimicking the tumor microenvironment. Since tumor cells need to remodel their ECM in order to metastasize we hypothesized that the interphase MT cytoskeleton, through the coordination of cellular signaling regulates this process. To test this hypothesis we first assessed the MT-dependence of tumor-mediated ECM remodeling, using a floating collagen gel contraction assay. In this assay, breast cancer cells were embedded into a floating collagen gel and monitored for their ability to contract the gel as a result of cell generated traction force. We observed that the MDA-MB-231 metastatic breast cancer cells exhibited greater contractility as compared with the MCF-7 non-metastatic breast cancer cells or the non-tumorigenic human breast epithelial cell line MCF10A. However upon disruption of MTs with paclitaxel (PTX), tumor cell contractility was severely inhibited at drug concentrations that did not affect cell number, suggesting that dynamic MTs are essential for cell traction force generation. In addition, we observed that human mammary fibroblasts when co-cultured with breast cancer cells in 3D exhibited increased motility as compared to 3D fibroblast monocultures. Interestingly, fibroblast activation was inhibited in co-cultures with breast cancer cells previously treated with a taxane, suggesting that tumor MT stabilization negatively affects fibroblast activation. To investigate the factors that mediated the tumor cell communication with surrounding fibroblasts we monitored fibroblast motility in 3D monocultures following incubation with conditioned medium collected from either untreated or Taxol pre-treated breast cancer cells. In agreement with our 3D co-culture results, fibroblast 3D motility was inhibited following exposure to conditioned medium from the Taxol-pretreated cells.

These results suggest that the composition of the tumor secretome changes upon MT stabilization, which in turn affects the ability of tumor cells to communicate with stromal fibroblasts. Currently, we are performing proteomic analysis of the conditioned media to identify soluble factors whose secretion is dependent on dynamic microtubules. In addition, to determine whether the effects of taxane treatment is solely due to microtubule stabilization we are performing the 3D co-culture experiments using a Taxol-resistant β-tubulin mutant breast cancer cell line. These findings point to a novel role of interphase MTs in tumor biology and can possibly lead to new avenues for taxane clinical efficacy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 435. doi:10.1158/1538-7445.AM2011-435