Abstract 4971: Quantitative image analysis of androgen receptor (AR) and tubulin biomarker profiles in circulating tumor cells (CTCs) from metastatic castration resistant prostate cancer (mCRPC) patients

Background: CTCs represent a real-time, liquid biopsy for analyses of a variety of molecular biomarkers that offer clinically relevant information. In prostate cancer, the AR pathway controls tumor cell growth and survival and is an important therapeutic target. AR becomes biologically active upon translocation from the cytoplasm to the nucleus in a microtubule dependent fashion, resulting in the activation of numerous genes. Real-time analysis of AR and tubulin status in CTCs may provide insight to therapy response in mCRPC patients.

Methods: Androgen sensitive human prostate cancer cells, LNCaP, were treated with and without a synthetic androgen (R1881; 10 nM, 1 hr) and docetaxel, spiked into healthy donor blood, and captured using a prostate specific microfluidic device (GEDI chip), following the same protocol that we use with patient samples. Cells were fixed and stained (N-terminal AR, CD45, CK, DAPI, and tyr-tubulin) directly on the device and imaged using high resolution multiplex confocal microscopy. AR and tubulin status were analyzed using a quantitative image analysis algorithm. Nuclear AR percentage was calculated by integrating fluorescence intensity within regions defining the entire cell and nucleus. H-Score was calculated by multiplying the nuclear AR percentage by the normalized total cell AR intensity. Tubulin status and microtubule bundling were assessed using a variety of quantitative parameters including measurements of tubulin fluorescence intensity and distribution within the cell.

Results: LNCaP cells in the presence of synthetic androgen exhibited higher nuclear AR percentage (p = 0.0004) and H-score (p = 0.003). Docetaxel treatment led to lower nuclear AR percentage (p = 0.04) and lower H-Score (p = 0.03). Cells treated with docetaxel exhibited higher tubulin intensity range (p = 0.008) and standard deviation (p = 0.03), consistent with docetaxel's mechanism of action. We applied these methods of quantitative image analyses to CTCs isolated from a small cohort of mCRPC patients. Single CTC image analysis revealed heterogeneity in AR status. Quantitative evidence for microtubule bundling was observed in patients receiving docetaxel chemotherapy.

Conclusions: We have developed a high throughput quantitative image analysis algorithm to interrogate mCRPC specific biomarkers, such as AR and tubulin status, in single CTCs. These methods of quantitative image analyses will be prospectively validated with CTCs from mCRPC patients followed longitudinally over the course of treatment with AR inhibitors and taxanes, yielding patient specific, clinically relevant information that can guide physicians’ strategies for the clinical management of cancer.

Citation Format: Daniel Worroll, Giuseppe Galletti, David M. Nanus, Scott T. Tagawa, Paraskevi Giannakakou. Quantitative image analysis of androgen receptor (AR) and tubulin biomarker profiles in circulating tumor cells (CTCs) from metastatic castration resistant prostate cancer (mCRPC) patients. [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 4971.

Abstract 3489: Elucidation of taxane resistance in prostate cancer through RNA-Seq analysis of circulating tumor cells

Prostate cancer is the most commonly diagnosed male cancer in the United States. Taxanes are the only established chemotherapy drugs proven to be effective in improving survival of men with advanced prostate cancer through disruption of the AR-signaling axis downstream of microtubule stabilization. However, there is significant heterogeneity in how patients respond to taxanes and most patients ultimately become refractory due to the development of drug resistance. Currently, the molecular basis of clinical taxane resistance in PC is poorly understood. Prostate cancer circulating tumor cells (P-CTCs) are often found in the peripheral blood of patients suffering from metastatic prostate cancer and have been clinically used as prognostic biomarker for metastatic progression and treatment outcome. The objective of this study is to identify clinically relevant mechanisms of taxane resistance through conducting RNA-Seq analysis in P-CTCs isolated from patients before, during and after they become refractory to taxane chemotherapy.

To show feasibility of RNA-Seq experiments with limiting samples such as CTCs and given the presence of contaminating leucocytes, a pilot experiment was performed in which limiting numbers of prostate cancer cells (LNCaP) either pure or enriched following spiking into healthy donor blood, were analyzed by RNA-Seq. Matching healthy donor blood processed with the same enrichment protocol was used as germline control as well as control for the presence of contaminating leucocytes following CTC enrichment. Trimmed reads were aligned to human reference genome (hg38) using STAR. Determination of Fragments Per Kilobase of exon per Million mapped fragments (FPKM) was performed using Cufflinks and heat map was built based on the value of log10(FPKM+1). Gene expression analysis showed that markers of prostate (such as AR, PSMA, KLK3, KLK2, and AMACR) or epithelial lineage (such as EpCAM, CDH1, KRT8 and KRT18) were detected in both pure LNCaP cells-regardless of amount- as well as limited number of captured LNCaP cells in the presence of contaminating leucocytes. In contrast, healthy donor blood was negative for the prostate and epithelial lineage markers and positive for the leucocyte specific markers (such as CD45 and CD16). Gene set enrichment analysis (GSEA) indicated significant enrichment for Andorgen response, MYC, MTOR and RB related pathways in pure and captured LNCap cells compared with healthy donor blood. These data clearly show that by using RNA-Seq we can detect the prostate and epithelial specific gene signatures of limited number of spiked prostate cancer cells using the microfluidic device. Ongoing work includes RNA-Seq analysis of P-CTCs isolated from patients before and after taxane treatment, in order to detect differentially expressed genes, pathways, and potentially driver somatic mutations associated with clinical taxane resistance.

Citation Format: Jiaren Zhang, Ada Gjyrezi, Prashant Thakkar, Giuseppe Galletti, Akanksha Verma, Olivier Elemento, Paraskevi Giannakakou. Elucidation of taxane resistance in prostate cancer through RNA-Seq analysis of circulating tumor cells. [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 3489.

A SIRT2-Selective Inhibitor Promotes c-Myc Oncoprotein Degradation and Exhibits Broad Anticancer Activity

Targeting sirtuins for cancer treatment has been a topic of debate due to conflicting reports and lack of potent and specific inhibitors. We have developed a thiomyristoyl lysine compound, TM, as a potent SIRT2-specific inhibitor with a broad anticancer effect in various human cancer cells and mouse models of breast cancer. Mechanistically, SIRT2 inhibition promotes c-Myc ubiquitination and degradation. The anticancer effect of TM correlates with its ability to decrease c-Myc level. TM had limited effects on non-cancerous cells and tumor-free mice, suggesting that cancer cells have an increased dependency on SIRT2 that can be exploited for therapeutic benefit. Our studies demonstrate that SIRT2-selective inhibitors are promising anticancer agents and may represent a general strategy to target certain c-Myc-driven cancers.

Cytotoxic chemotherapy in the treatment of advanced renal cell carcinoma in the era of targeted therapy

BACKGROUND

Renal cell carcinoma (RCC) is a heterogeneous disease with regards to histology, progression, and response to treatment. Cytotoxic chemotherapy has been extensively studied in metastatic RCC (mRCC). Responses in most studies are modest and the mechanisms of resistance remain poorly understood. Targeted therapies have significantly improved outcomes in mRCC; however, most patients eventually relapse and die of their disease. Early clinical data suggest that combinations of chemotherapy and targeted agents are clinically active and are well tolerated.

METHODS

We reviewed the available literature for published clinical trials incorporating traditional chemotherapeutic agents in the treatment of mRCC. These papers were identified through a Medline search and were included if they employed at least one chemotherapeutic agent in the treatment of mRCC. The literature was also reviewed for information regarding mechanisms of chemotherapy resistance.

RESULTS

The data regarding the use of cytotoxic chemotherapy in mRCC consist of small, non-randomized phase I and II studies. The major response proportions with single agent chemotherapies are low but combination regimens either with other cytotoxic agents, cytokines, or targeted agents have demonstrated moderate activity. Disparate trial designs and lack of head to head clinical trials make it difficult to compare the efficacy of chemotherapy with that of immunotherapy or targeted agents. Chemotherapy is particularly useful in patients with collecting duct histology and predominantly sarcomatoid differentiation. Chemotherapy resistance may be mediated by overexpression of p-glycoprotein efflux pumps and the dysregulation of the microtubule-hypoxia inducible factor signaling axis.

CONCLUSIONS

The role of cytotoxic chemotherapy in the treatment for clear cell RCC remains poorly defined. Cytotoxic chemotherapy is considered a standard of care in patients with mRCC with predominantly sarcomatoid differentiation and collecting duct RCC variants (Motzer et al., 2014). Early trials combining chemotherapy with targeted therapies are generally well tolerated and show clinical activity. A better understanding of the biology of aggressive subsets of RCC and mechanisms of resistance will help elucidate the role of cytotoxic agents in the current treatment paradigm of RCC.

Abstract 3600: Impaired taxane binding to MTs in intrinsically taxane resistant gastric cancer cells without β-tubulin mutation

The taxanes (i.e., paclitaxel, docetaxel (DTX) and cabazitaxel) are microtubule (MT)-stabilizing drugs widely used to treat solid tumor malignancies. Their success is limited by the presence of intrinsic or acquired drug resistance. Understanding the molecular mechanisms of taxane resistance is a key to significantly improve clinical outcomes of taxane-based chemotherapy. In gastric cancer (GC), retrospective analysis of the TAX-325 trial revealed that the addition of docetaxel (DTX) to standard cisplatin/fluorouracil increased progression-free and overall survival, primarily only in intestinal subtype (INT) GC, suggesting that diffuse (DIF) GC may be intrinsically taxane resistant. In fact, our previous data supported this hypothesis; DIF GC cell lines had higher incidence (63%) of DTX resistance than INT GC cell lines (25%). Flow cytometric analyses showed negligible P-glycoprotein expression on the cell surface of all cell types, and accumulation of C14-labeled DTX in cells was observed in both sensitive and resistant GC cell lines. These results ruled out drug efflux as a possible mechanism that confers taxane resistance in DIF GC cells.

Next, we used fluorescein-conjugated paclitaxel (Flutax) as a probe to investigate the affinity of taxanes to MTs. Live cell imaging showed strong binding of Flutax to MTs in a sensitive cell line at least for 60 minutes. In contrast, Flutax failed to stay bound to MTs in resistant GC cell lines,. In addition, discontinuous decoration of MTs with Flutax was seen in resistant but not in sensitive cell lines. Our observation suggests that MTs of resistant GC cell lines have lower affinity for taxanes, and there might be subtle structural changes of MTs. We are currently conducting the competition of Flutax/DTX to quantify the affinity of DTX in both types of GC cell lines.

Because tubulin mutations have been reported in many taxane-resistant cell lines, we sequenced the different tubulin isotypes in GC cell lines using both Sanger and next generation sequencing. No mutations were identified. In addition, we did not see any significant changes in the expression of βIII-tubulin or tubulin post-translational modifications between the sensitive and resistant cell lines. Pathway analyses on the RNA-Seq datasets derived from the panels of sensitive and resistant cell lines before and after taxane treatment is ongoing to identify the key molecular events underlying taxane resistance.Taken together, our data indicate that new molecular pathway(s) or change of overall MT structure and/or function may contribute to the impaired taxane binding to MTs in resistant GC cells. Our study will lead us to novel mechanistic insights in intrinsic drug resistance, and will ultimately allow us to target key molecule(s) to overcome chemo-resistance, the key determinant to improve overall survival of patients.

Citation Format: Katsuhiro Kita, Giuseppe Galletti, Kyle Cleveland, Prashant V. Thakkar, Ada Gjyrezi, Chao Zhang, Isabel Barasoain, J. Fernando Díaz, Doron Betel, Manish A. Shah, Paraskevi Giannakakou. Impaired taxane binding to MTs in intrinsically taxane resistant gastric cancer cells without β-tubulin mutation. [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 3600. doi:10.1158/1538-7445.AM2015-3600

Abstract 2121: Microtubule-regulated mRNA translation signaling and therapeutic implications in cancer

Drugs that affect microtubule dynamics and function, both those that stabilize microtubules (e.g. taxanes) and those that depolymerize them (e.g. vincas, Eribulin) are widely used in cancer chemotherapy. However, their mechanism of action at the molecular level and the signaling pathways regulated by microtubule dynamics are not fully understood, precluding chemotherapy customization to the individuals. Previously, we have reported that microtubule dynamics control the translation of HIF-1α mRNA. We showed that treatment with microtubule-targeting drugs (MTDs) shifts HIF-1α mRNA from actively translating polysomes to non-translating ribosomes resulting in inhibition of HIF-1α transcriptional activity. Using cell lines with acquired mutations at different MTD binding sites we conclusively showed that microtubule disruption was required for the inhibition of HIF translation. However, additional mRNAs susceptible to MTD treatment or the exact signaling pathway that senses microtubule disruption and leads to inhibition of translation are not known. Polysome RNA-Seq analyses of untreated and drug treated cells has identified additional mRNAs whose polysome association is shifted towards inactive translation similar to HIF-1α mRNA. We are using bioinformatics analyses to identify a common microtubule-susceptibility motif in addition to validation experiments at the protein and pathway level. The polysome analysis showed that protein synthesis is inhibited at the stage of translation initiation. In an effort to better understand the underlying mechanism of translation inhibition of HIF-1α mRNA and additional microtubule-dependent mRNAs, we assessed 4E-BP1 protein as its phosphorylation is a key regulator of cap dependent mRNA translation. We observed that taxanes or Eribulin treatment hyper-phosphorylates 4E-BP1 without affecting ribosomal protein S6 (rpS6) phosphorylation. Using the taxane-resistant breast cancer cell line MB-231/K20T which harbors an acquired mutation at the taxane binding site of β-tubulin we showed that Taxol treatment has no effect on 4E-BP1 hyper- phosphorylation, consistent with its lack of microtubule activity. In contrast, Eribulin, which has a distinct binding site on tubulin, is able to overcome taxol-resistance by fully engaging the microtubule-4E-BP1 axis. Interestingly, in renal cell carcinoma (RCC) cells, for which treatment with microtubule inhibitors has no clinical benefit, we didn't observe 4E-BP1 hyper-phosphorylation after taxane or Eribulin treatment, even though microtubules were affected. These results suggest that the microtubule-4E-BP1 axis is compromised in RCC and that there is a link between 4E-BP1 phosphorylation and MTD efficacy. Hence, we propose that identifying the link of 4E-BP1 dependent signaling with microtubules will have important therapeutic implications in MTD chemotherapy.

Citation Format: Prashant Khade, Paraskevi Giannakakou. Microtubule-regulated mRNA translation signaling and therapeutic implications in cancer. [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 2121. doi:10.1158/1538-7445.AM2015-2121

Abstract 4311: Molecular basis of interaction between ERG and microtubule inhibitors in CRPC patients

Microtubules (MTs) are cytoskeletal polymer of α/β tubulin heterodimers that are involved in several cellular functions including mitosis, cell shape and intracellular trafficking. Due to their fundamental role in the maintenance of cell homeostasis, MTs are the target of several chemotherapeutic drugs that act by either stabilizing (taxanes, epothilones) or destabilizing (vinca alkaloids, Eribulin) the MT network.

Taxanes (docetaxel and cabazitaxel) are currently used for first or second line treatment of patients with metastatic castration-resistant prostate caner (CRPC) and are the only class of chemotherapy drugs that improve survival. Despite taxane clinical success, there is significant heterogeneity in how patients respond to taxane therapy and most of CRPC patients eventually become refractory and develop resistance to the treatment. The molecular basis underlying this heterogeneity in treatment response is still to be determined.

ERG (ETS-related gene) is over-expressed by 30-80 fold in at least 50% of prostate cancers as a result of gene fusion with the 5′ promoter of the AR-induced TMPRSS2 gene. ERG rearrangement is an early event in prostate cancer tumorigenesis and represents the most frequent recurrent genetic alteration in prostate cancer. We recently showed that ERG over-expression is associated with decreased taxane sensitivity in prostate cancer cell lines, in vivo xenograft models, and in ERG-positive CRPC patients. Mechanistically, we demonstrated that ERG contributes to taxane resistance by binding tubulin in the cytoplasm, altering MT dynamics towards increased catastrophe rate thereby shifting the dynamic equilibrium between MT polymers (preferred taxane substrate) and soluble tubulin dimers (preferred substrate for MT-depolymerizing drugs) towards soluble tubulin. Tiling mutant co-immunoprecipitation showed that ERG-tubulin physical interaction is mediated by ERG PNT domain, which has been also implicated with ERG homo-oligomerization and heterodimerization. Moreover, MT-cosedimentation assay elucidated that ERG predominantly interacts with tubulin dimers instead of MT-polymers. Finally, we demonstrated that treatment with the MT-depolymerizing drugs nocodazole or Eribulin is associated with lack of resistance or even enhanced sensitivity in ERG-positive cells.

We are currently investigating the molecular basis of the interaction between Eribulin and ERG in CRPC models, in order to elucidate the potential role of Eribulin in the treatment of ERG+ CRPC patients.

Overall, our data strongly suggest a new role for ERG as MT-destabilizing MAP, with significant therapeutic implications in CRPC patients. ERG status could emerge as biomarker predictive of response to MT-inhibitors, driving clinical decisions for patient selection to appropriate therapies.

Citation Format: Giuseppe Galletti, Cynthia Cheung, David S. Rickman, Paraskevi Giannakakou. Molecular basis of interaction between ERG and microtubule inhibitors in CRPC patients. [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 4311. doi:10.1158/1538-7445.AM2015-4311

Abstract 1667: Targeting acute myelogenous leukemia with novel combrestatin analogs and development of predictors of response

Introduction: Most adult acute myelogenous leukemia (AML) patients relapse and die of the disease. AML stem cells (AML-SCs) have been postulated to resist standard chemotherapeutic agents and thus give rise to relapse. Combretastatin A-4 (CA-4), a natural product isolated from the South African tree Combretum caffrum, has been reported to possess anti-leukemic activity in AML cell lines. To increase the repertoire of combretastatin analogs with potent anti-leukemic activity, about 100 CA-4 analogs were tested in AML cells, and studied the mechanism that AML cells resist to such microtubule (MT) inhibitors.

Methods: Cell viability/apoptosis was determined by annexin V and 7-AAD staining and flow cytometry. Cellular ROS production was measured by CellROX. Cell cycle was determined by DAPI staining and flow cytometry. Stem cell function was evaluated by colony assay and mouse xenograft assays. Tubulin depolymerization was measured by immunofluorescence or immunoblotting for microtubule fraction. Interaction of tubulin with BTAN or p38 MAPK was determined by pull down assays.

Results: One of the most potent analogs, BTAN, was further investigated in a panel of leukemic cell lines and primary AML samples. Similar to CA-4, BTAN inhibited tubulin polymerization in vitro and induced MT depolymerization and cell cycle arrest at G2/M in AML cells. BTAN induced cell death of AML blast, progenitor and stem cells via caspase activation regardless of their proliferating status and level of intracellular reactive oxygen species (ROS). In addition, BTAN impaired the physical contact of AML with stromal cells. To further identify the mechanism of resistance to BTAN, we investigated several signal transduction pathways including AKT, JAK-STAT, ERK1/2, JNK and p38. p38 MAPK inhibitor sensitized leukemia cells to BTAN treatment, and the sensitivity of AML cells to BTAN correlated with the basal level of active/phosphorylated p38 MAPK, suggesting p38 MAPK may interfere with the sensitivity to BTAN in AML. We demonstrated that tubulin interacted with p38 MAPK, especially its phosphorylated form, which was disrupted by treatment with a p38 MAPK inhibitor. In addition, in the presence of p38 inhibitor, the accumulation of BTAN was potentiated in AML cells, suggesting activated p38 may interfere with the interaction between BTAN and its tubulin targets.

Conclusion: Our data demonstrated that BTAN is a newly identified anti-AML-SC agent that works by disrupting the MT cytoskeleton and inducing caspase activation. These data suggest that the MT network is involved in the regulation of pro-survival signaling pathways even in quiescent AML-SCs, and that p38 MAPK is a key modulator for the response of AML blasts to microtubule inhibitors and that co-treatment with p38 MAPK inhibitors could be beneficial to microtubule destabilizing agents in AML.

Note: This abstract was not presented at the meeting.

Citation Format: Hongliang Zong, Narsimha R. Penthala, Vijayakumar N. Sonar, Paraskevi Giannakakou, Gail J. Roboz, Peter A. Crooks, Monica L. Guzman. Targeting acute myelogenous leukemia with novel combrestatin analogs and development of predictors of response. [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 1667. doi:10.1158/1538-7445.AM2015-1667

Abstract 5096: ALIBI: a novel, truncated tubulin isotype in AML and stem cells

Tubulin isotype expression is tissue restricted, with β-1 tubulin (TUBB1) restricted to hematopoietic tissues. Using the TCGA database, we found that β-1 is highly expressed in acute myeloid leukemia (AML) among all hematologic malignancies. β-1 may therefore be an attractive target for the development of novel therapeutics for AML. Analysis of a panel of AML cell lines using a polyclonal antibody against the C-terminus of β-1 revealed the presence of a band at 35kD, distinct from the canonical tubulin molecular weight of 50kD. This 35kD band, which we call Acute Leukemia Isoform β1 (ALIBI), was present in 10 of the 19 AML cell lines tested of various molecular and morphologic subtypes. In addition, we analyzed 12 AML primary AML patient blast samples and found ALIBI expression in six patient samples, suggesting that ALIBI is clinically relevant and prevalent Immunofluorescent analysis of ALIBI's subcellular localization revealed that ALIBI is present in distinct cytoplasmic aggregates not co-localizing with native microtubules as well as in the nucleus. Interestingly, ALIBI was also enriched in AML patient CD34+/CD38- cells containing leukemia stem cells. Using a murine β-1 antibody in a mouse model of acute leukemia (HOXA9-NUP98/BCR-ABL) we found that ALIBI expression was significantly higher in the leukemic marrow as compared to normal mouse marrow. As leukemia stem cells share features with embryonic stem cells (ESCs) we next investigated ALIBI expression in mouse ESCs after differentiation along megakaryocytic and erythroid lineages. ALIBI, but not canonical β-1, was expressed in ESCs, while hematopoietic differentiation led to loss of ALIBI and expression of only canonical β-1 tubulin, suggesting that expression of canonical β-1 and ALIBI are differentially regulated and that ALIBI expression is associated with stemness. RNASeq and 5′RACE of cell lines and patient samples revealed that ALIBI mRNA is missing exons 1 and 2 of canonical β-1 RNA, while it retains part of exon 3, exon 4 and the intervening intron. These results suggest that ALIBI mRNA is alternatively spliced, leading to the use of a cryptic translational start site in exon 4 flanked by a strong Kozak sequence. Exogenous expression of the putative coding region of ALIBI in ALIBI-negative cell lines produced a protein product with similar molecular weight and subcellular localization as endogenous ALIBI. Studies of ALIBI function using genome editing are currently underway. In conclusion, ALIBI is a novel truncated isoform of tubulin that has unique biologic features never previously described for tubulins. While the exact function of ALIBI within leukemic cells is still being uncovered, it nevertheless is a highly attractive target of novel therapeutic development based on its high expression in AML and its unique biologic properties.

Citation Format: Paul Basciano, Xi Li, Jason Matakas, Susanna Liu, Silvana Di Giandomenico, Siddhartha Sen, Todd Evans, Joseph Scandura, Monica Guzman, Paraskevi Giannakakou. ALIBI: a novel, truncated tubulin isotype in AML and stem 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 5096. doi:10.1158/1538-7445.AM2015-5096

β-1 tubulin R307H SNP alters microtubule dynamics and affects severity of a hereditary thrombocytopenia

BACKGROUND

Single nucleotide polymorphisms (SNPs) in platelet-associated genes partly explain inherent variability in platelet counts. Patients with monoallelic Bernard Soulier syndrome due to the Bolzano mutation (GPIBA A156V) have variable platelet counts despite a common mutation for unknown reasons.

OBJECTIVES

We investigated the effect of the most common SNP (R307H) in the hematopoietic-specific tubulin isotype β-1 in these Bernard Soulier patients and potential microtubule-based mechanisms of worsened thrombocytopenia.

PATIENTS/METHODS

Ninety-four monoallelic Bolzano mutation patients were evaluated for the R307H β-1 SNP and had platelet counts measured by three methods; the Q43P SNP was also evaluated. To investigate possible mechanisms underlying this association, we used molecular modeling of β-1 tubulin with and without the R307H SNP. We transfected SNP or non-SNP β-1 tubulin into MCF-7 and CMK cell lines and measured microtubule regrowth after nocodazole-induced depolymerization.

RESULTS

We found that patients with at least one R307H SNP allele had significantly worse thrombocytopenia; manual platelet counting revealed a median platelet count of 124 in non-SNP patients and 76 in SNP patients (both ×10(9)  L(-1) ; P < 0.01). The Q43P SNP had no significant association with platelet count. Molecular modeling suggested a structural relationship between the R307H SNP and microtubule stability via alterations in the M-loop of β tubulin; in vitro microtubule recovery assays revealed that cells transfected with R307H SNP β-1 had significantly impaired microtubule recovery.

CONCLUSIONS

Our data show that the R307H SNP is significantly associated with the degree of thrombocytopenia in congenital and acquired platelet disorders, and may affect platelets by altering microtubule behavior.

Exploitation of the HIF axis for cancer therapy

Hypoxia, a reduction in the normal level of tissue oxygen tension, occurs in most solid tumors in regions where tumor growth outstrips new blood vessel formation. Hypoxic cancer cells are resistant to both chemotherapy and radiation and are a major reason for the failure of cancer therapy. The cellular response to hypoxia is mediated through the hypoxia-inducible transcription factor-1 (HIF-1). HIF-1 is critically important for tumor progression and angiogenesis. In fact, HIF-1alpha is overexpressed in 70% of human cancers and their metastases. Thus, agents that inhibit angiogenesis and tumor growth via inhibition of HIF-1 represent an attractive yet unexplored new modality for cancer treatment. We will overview inhibitors of HIF-1alpha and will discuss their potential use for cancer therapy.

Abstract 2112: AR splice variants ARv7 and ARv567 utilize different mechanisms of cytoplasmic trafficking and nuclear translocation: Therapeutic implications for PC

Prostate cancer (PC) is one of the most prevalent cancers among men worldwide. While androgen deprivation therapy (ADT) is initially effective in the treatment of PC, resistance emerges resulting in castration-resistant prostate cancer (CRPC) disease, which is driven by continuous signaling from the androgen receptor (AR). Several new drugs designed to inhibit AR signaling (abiraterone and enzalutamide) have been recently approved for PC treatment. However resistance to these next-generation AR inhibitors inevitably occurs and is mediated by adaptive mechanisms that restore AR function. Overexpression of AR splice variants (ARv567 and ARv7), which lack the ligand-binding domain (LBD), was shown to mediate resistance to abiraterone and enzalutamide. Following ADT resistance, CRPC patients are treated with the taxanes Docetaxel (DTX) and Cabazitaxel as first and second line chemotherapy.

Our recent work showed that AR binds to microtubules (MTs) utilizing them as tracks for its nuclear translocation, and that taxanes inhibit AR signaling by sequesting AR in the cytoplasm downstream of MT stabilization. We showed that MT binding is mediated by the Hinge region of AR, which is present in ARv567 but missing in ARv7 variant. In contrast to ARv567, ARv7 does not bind MTs and its nuclear localization is not affected by taxane treatment and its expression confers taxane resistance in vitro and in vivo.

Since the main nuclear localization signal (NLS) of AR is in the hinge region we hypothesized that ARv7 has a different nuclear translocation mechanism than Arv567 or AR-WT. Co-immunoprecipitation experiments revealed that AR-WT and ARv567 interact with importin-α, and that DTX treatment inhibits this interaction. In contrast, ARv7 does not interact with importin-α and is insensitive to DTX. To monitor the dynamics of AR variant nuclear accumulation we performed live cell confocal microscopy using PC3 cells microinjected with GFP-AR-WT, -ARv7 or -ARv567. Our results showed that both AR-WT and AR-v567 were sensitive to inhibition of the importin pathway, using the importin-β inhibitor importazole, while ARv7 was unaffected. FRAP experiments of M12 cells stably expressing GFP-tagged AR-WT, or ARvs revealed that the recovery after photobleaching of ARv7 nuclear fraction was much faster than that of ARv567 or AR-WT, suggesting enhanced motility of ARv7. FRAP experiments in DTX or importazole treated cells further confirmed the insensitivity of ARv7 to perturbations of the MT network and importin pathway. Taken together our results show that AR-WT and ARv567 utilize MTs and, the importin-α/β pathway for nuclear translocation; while ARv7 is MTs and importin independent. Elucidation of the mechanisms of cytoplasmic trafficking and nuclear translocation of ARv7 variant will allow us to identify new druggable targets in order to revert resistance to taxanes and next generation AR targeting drugs.

Citation Format: Luigi Portella, Paraskevi Giannakakou. AR splice variants ARv7 and ARv567 utilize different mechanisms of cytoplasmic trafficking and nuclear translocation: Therapeutic implications for PC. [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 2112. doi:10.1158/1538-7445.AM2014-2112

Abstract 1158: Microtubule perturbation regulates remodeling of tumor microenvironment by modulating the composition of tumor cell secretome

Microtubules (MTs) represent one of the most effective targets in cancer chemotherapy. However, MT-targeting drugs, such as the taxanes, often fail in the metastatic setting and mechanisms underlying drug resistance are poorly elucidated. An important process during tumor development and metastasis involves the dynamic remodeling of the 3D microenvironment surrounding the tumor cells which enables them to successfully proliferate and metastasize. We hypothesized that tumor cell MTs may regulate the cellular signaling process that controls tumor-mediated remodeling of the microenvironment by paracrine activation of fibroblasts. To assess the role of MT dynamics in the secretion of factors from the tumor cells that mediate communication with the microenvironment, we collected conditioned medium (CM) from untreated or paclitaxel (PTX)-pre-treated metastatic breast cancer MDA-MB-231 cells and applied it to HMF3S human mammary fibroblasts. We observed that CM from untreated 231 cells resulted in fibroblast activation as evidenced by their increased directional 3D cell motility towards a serum gradient. CM from PTX-pretreated 231 cells, at concentrations that suppress MT dynamics, but not from the PTX-resistant β-tubulin mutation 231 clone, 231K20T cells, did not result in activation of fibroblasts' 3D motility, suggesting that MT-mediated secretion of soluble factor(s) (secretome) underlies fibroblast activation. Mass-spectrometry analysis of CM derived from untreated or PTX-pretreated 231 cells identified proteins whose secretion was diminished following suppression of MT dynamics and which are involved in cell motility, cell-cell communication, or ECM remodeling, such as TGFβ, CTGF, c-Met, fibronectin, and lysyl oxidase 2. Treatment of 231-derived CM with an anti-TGFβ blocking antibody diminished HMF3S fibroblast motility in 3D, suggesting that the presence of TGFβ in the tumor cell secretome mediated the activation of tumor associated fibroblasts. To further probe the MT-dependent regulation of TGFβ secretion we showed that PTX treatment prevented trafficking of intracellular TGFβ to the cell surface in 231 cells, likely underlying its reduced secretion. Confocal reflectance and two-photon microscopic imaging revealed that CM treatment of HMF3S fibroblasts induced significant collagen remodeling comparable to treatment with exogenous TGFβ alone. Our findings point to a novel role of interphase MTs in tumor cell secretome and raise the possibility that MTs may regulate secretion of distinct soluble factors in different types of tumor cells, which then mediate the communication between tumor cell compartment and the tumor microenvironment. These novel insights have significant implications for the mechanism of action and resistance to MT inhibitors.

Citation Format: Katsuhiro Kita, Andy Tran, Lewis M. Brown, Duane C. Hassane, Shawn Carey, Alexandre Matov, Cynthia A. Reinhart-King, Paraskevi Giannakakou. Microtubule perturbation regulates remodeling of tumor microenvironment by modulating the composition of tumor cell secretome. [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 1158. doi:10.1158/1538-7445.AM2014-1158

Abstract 923: Analysis of microtubule perturbations and androgen receptor localization in circulating tumor cells from castration resistant prostate cancer patients as predictive biomarkers of clinical response to docetaxel chemotherapy

Although the recent availability of novel treatment for castration resistant prostate cancer (CRPC) has shown improvements in overall survival, CRPC is incurable and lethal disease. It has been recognized that tumor progression despite castrate levels of androgens is still associated with active signaling from the androgen receptor (AR) which affects gene transcription following its nuclear accumulation. Taxanes bind to and stabilize cellular microtubules (MTs) perturbing the fine and intricate organization of the microtubule network thus, impairing MT-based cell processes like cell division and intracellular trafficking. Our recent work showed that AR translocation from the cytoplasm to the nucleus is MT-dependent and that taxane treatment sequesters AR into the cytoplasm inhibiting the receptors transcriptional activity. While this novel mechanism of taxane activity may explain the clinical efficacy of taxanes in CRPC, clinically we still fail to understand the molecular basis of patient response or resistance to taxanes. We hypothesized that engagement of the MT-AR pathway by the taxanes can be used as read-out of effective drug-target engagement in cancer cells and can be used as biomarker predictive of taxane activity in CRPC patients.

To assess the predictive role of these biomarkers, we are currently conducting a prospective clinical study in which we isolate circulating tumor cells (CTCs) from the peripheral blood of CRPC patient undergoing docetaxel treatment. We have enrolled 50 of the 80 total patients, from which we isolated CTCs before (at baseline) and during docetaxel treatment (at day 8 of first cycle of docetaxel and upon relapse) using two different approaches: the EpCAM-based immunomagnetic enrichment (CellSearch) and the ficolling technique to isolate unenriched PBMCs inclusive of CTCs. To avoid issues with leucocyte contamination we subject the EpCAM captured cells are to staining for DAPI , PSMA, CD-45, AR and Tubulin and image them by confocal microscopy. CTCs are defined as nucleated, PSMA+, CD-45- cells. The unenriched PBMC population is also subjected to the same multiplex confocal microscopy protocol. Microtubule network morphology and AR subcellular localization in then assessed in CTCs and each biomarker alone and in combination is correlated with clinical response to docetaxel treatment defined by PCWG2 recommendation. So far we have collected and analyzed baseline and cycle 1-Day 8 samples from all 50 patients and relapse samples from 31 patients.

Determination of effective drug-target engagement on C1D8 may allow early detection of molecular response to treatment, or lack of molecular response, which will ultimately allow for chemotherapy customization for the individual patient.

Citation Format: Shinsuke Tasaki, Matthew Sung, Alexandre Matov, Giuseppe Galletti, Elan Diamond, Neil Bander, Kathy Zhou, Scott Tagawa, David Nanus, Paraskevi Giannakakou. Analysis of microtubule perturbations and androgen receptor localization in circulating tumor cells from castration resistant prostate cancer patients as predictive biomarkers of clinical response to docetaxel chemotherapy. [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 923. doi:10.1158/1538-7445.AM2014-923

Circulating tumor cells in prostate cancer diagnosis and monitoring: an appraisal of clinical potential

Circulating tumor cells (CTCs) have emerged as a viable solution to the lack of tumor tissue availability for patients with a variety of solid tumors, including prostate cancer. Different approaches have been used to capture this tumor cell population and several of these techniques have been used to assess the potential role of CTCs as a biological marker to predict treatment efficacy and clinical outcome. CTCs are now considered a strong tool to understand the molecular characteristics of prostate cancer, and to be used and analyzed as a 'liquid biopsy' in the attempt to grasp the biological portrait of the disease in the individual patient.

Androgen receptor splice variants determine taxane sensitivity in prostate cancer

Prostate cancer growth depends on androgen receptor signaling. Androgen ablation therapy induces expression of constitutively active androgen receptor splice variants that drive disease progression. Taxanes are a standard of care therapy in castration-resistant prostate cancer (CRPC); however, mechanisms underlying the clinical activity of taxanes are poorly understood. Recent work suggests that the microtubule network of prostate cells is critical for androgen receptor nuclear translocation and activity. In this study, we used a set of androgen receptor deletion mutants to identify the microtubule-binding domain of the androgen receptor, which encompasses the DNA binding domain plus hinge region. We report that two clinically relevant androgen receptor splice variants, ARv567 and ARv7, differentially associate with microtubules and dynein motor protein, thereby resulting in differential taxane sensitivity in vitro and in vivo. ARv7, which lacks the hinge region, did not co-sediment with microtubules or coprecipitate with dynein motor protein, unlike ARv567. Mechanistic investigations revealed that the nuclear accumulation and transcriptional activity of ARv7 was unaffected by taxane treatment. In contrast, the microtubule-interacting splice variant ARv567 was sensitive to taxane-induced microtubule stabilization. In ARv567-expressing LuCap86.2 tumor xenografts, docetaxel treatment was highly efficacious, whereas ARv7-expressing LuCap23.1 tumor xenografts displayed docetaxel resistance. Our results suggest that androgen receptor variants that accumulate in CRPC cells utilize distinct pathways of nuclear import that affect the antitumor efficacy of taxanes, suggesting a mechanistic rationale to customize treatments for patients with CRPC, which might improve outcomes.

Isolation of breast cancer and gastric cancer circulating tumor cells by use of an anti HER2-based microfluidic device

Circulating tumor cells (CTCs) have emerged as a reliable source of tumor cells, and their concentration has prognostic implications. CTC capture offers real-time access to cancer tissue without the need of an invasive biopsy, while their phenotypic and molecular interrogation can provide insight into the biological changes of the tumor that occur during treatment. The majority of the CTC capture methods are based on EpCAM expression as a surface marker of tumor-derived cells. However, EpCAM protein expression levels can be significantly down regulated during cancer progression as a consequence of the process of epithelial to mesenchymal transition. In this paper, we describe a novel HER2 (Human Epidermal Receptor 2)-based microfluidic device for the isolation of CTCs from peripheral blood of patients with HER2-expressing solid tumors. We selected HER2 as an alternative to EpCAM as the receptor is biologically and therapeutically relevant in several solid tumors, like breast cancer (BC), where it is overexpressed in 30% of the patients and expressed in 90%, and gastric cancer (GC), in which HER2 presence is identified in more than 60% of the cases. We tested the performance of various anti HER2 antibodies in a panel of nine different BC cell lines with varying HER2 protein expression levels, using immunoblotting, confocal microscopy, live cells imaging and flow cytometry analyses. The antibody associated with the highest capture efficiency and sensitivity for HER2 expressing cells on the microfluidic device was the one that performed best in live cells imaging and flow cytometry assays as opposed to the fixed cell analyses, suggesting that recognition of the native conformation of the HER2 extracellular epitope on living cells was essential for specificity and sensitivity of CTC capture. Next, we tested the performance of the HER2 microfluidic device using blood from metastatic breast and gastric cancer patients. The HER2 microfluidic device exhibited CTC capture in 9/9 blood samples. Thus, the described HER2-based microfluidic device can be considered as a valid clinically relevant method for CTC capture in HER2 expressing solid cancers.

Circulating tumor cells from prostate cancer patients interact with E-selectin under physiologic blood flow

Hematogenous metastasis accounts for the majority of cancer-related deaths, yet the mechanism remains unclear. Circulating tumor cells (CTCs) in blood may employ different pathways to cross blood endothelial barrier and establish a metastatic niche. Several studies provide evidence that prostate cancer (PCa) cell tethering and rolling on microvascular endothelium via E-selectin/E-selectin ligand interactions under shear flow theoretically promote extravasation and contribute to the development of metastases. However, it is unknown if CTCs from PCa patients interact with E-selectin expressed on endothelium, initiating a route for tumor metastases. Here we report that CTCs derived from PCa patients showed interactions with E-selectin and E-selectin expressing endothelial cells. To examine E-selectin-mediated interactions of PCa cell lines and CTCs derived from metastatic PCa patients, we used fluorescently-labeled anti-prostate specific membrane antigen (PSMA) monoclonal antibody J591-488 which is internalized following cell-surface binding. We employed a microscale flow device consisting of E-selectin-coated microtubes and human umbilical vein endothelial cells (HUVECs) on parallel-plate flow chamber simulating vascular endothelium. We observed that J591-488 did not significantly alter the rolling behavior in PCa cells at shear stresses below 3 dyn/cm(2). CTCs obtained from 31 PCa patient samples showed that CTCs tether and stably interact with E-selectin and E-selectin expressing HUVECs at physiological shear stress. Interestingly, samples collected during disease progression demonstrated significantly more CTC/E-selectin interactions than samples during times of therapeutic response (p=0.016). Analysis of the expression of sialyl Lewis X (sLe(x)) in patient samples showed that a small subset comprising 1.9-18.8% of CTCs possess high sLe(x) expression. Furthermore, E-selectin-mediated interactions between prostate CTCs and HUVECs were diminished in the presence of anti-E-selectin neutralizing antibody. CTC-Endothelial interactions provide a novel insight into potential adhesive mechanisms of prostate CTCs as a means to initiate metastasis.