Drug Resistance In Pancreatic Cancer Cells Research Articles

Wild type and gain of function mutant TP53 can regulate the sensitivity of pancreatic cancer cells to chemotherapeutic drugs, EGFR/Ras/Raf/MEK, and PI3K/mTORC1/GSK-3 pathway inhibitors, nutraceuticals and alter metabolic properties.

TP53 is a master regulator of many signaling and apoptotic pathways involved in: aging, cell cycle progression, gene regulation, growth, apoptosis, cellular senescence, DNA repair, drug resistance, malignant transformation, metastasis, and metabolism. Most pancreatic cancers are classified as pancreatic ductal adenocarcinomas (PDAC). The tumor suppressor gene TP53 is mutated frequently (50–75%) in PDAC. Different types of TP53 mutations have been observed including gain of function (GOF) point mutations and various deletions of the TP53 gene resulting in lack of the protein expression. Most PDACs have point mutations at the KRAS gene which result in constitutive activation of KRas and multiple downstream signaling pathways. It has been difficult to develop specific KRas inhibitors and/or methods that result in recovery of functional TP53 activity. To further elucidate the roles of TP53 in drug-resistance of pancreatic cancer cells, we introduced wild-type (WT) TP53 or a control vector into two different PDAC cell lines. Introduction of WT-TP53 increased the sensitivity of the cells to multiple chemotherapeutic drugs, signal transduction inhibitors, drugs and nutraceuticals and influenced key metabolic properties of the cells. Therefore, TP53 is a key molecule which is critical in drug sensitivity and metabolism of PDAC.

Co-treatment With Everolimus, an mTOR-Specific Antagonist, or Downregulation of ELK1 Enhances the Sensitivity of Pancreatic Cancer Cells to Genistein.

Genistein is a natural isoflavone with pharmacological or potentially anti-tumor properties. However, the resistance of cancer cells to genistein remains a major obstacle. This study focused on the mechanism implicated in the resistance of pancreatic cancer (PC) cells to genistein and the mechanism of action. First, key molecules and signaling pathways related to genistein resistance in PC cells were explored using bioinformatics tools. DEP domain containing MTOR interacting protein (DEPTOR), a typical inhibitor of the mammalian target of rapamycin (mTOR) signaling, was predicted to be poorly expressed in the genistein-resistant PC cells. Thereafter, genistein-resistant PC cells (Panc-1 and PaCa) were constructed. Altered expression of DEPTOR was introduced in cells, and everolimus (ELM), an mTOR-specific antagonist, was administrated in cells as well to examine their roles in genistein resistance. The cell apoptosis was examined in vitro and in vivo in mouse xenograft tumors. The upstream regulator of DEPTOR was predicted via bioinformatic tools. The bioinformatic analyses showed that the PI3K/AKT/mTOR signaling pathway was activated in the setting of DEPTOR downregulation in genistein-resistant PC cells. DEPTOR overexpression reduced the 50% inhibiting concentration (IC50) of genistein in PC cells and suppressed mTOR phosphorylation, and it increased caspase-3 activity, LDH release and apoptosis in PC cells. ELM treatment enhanced the sensitivity of PC cells to genistein in vitro and it strengthened the tumor-eliminating role of genistein in mice. ETS transcription factor ELK1 (ELK1), a transcription factor that negatively regulated DEPTOR transcription, was suppressed by genistein. Upregulation of ELK1 suppressed DEPTOR transcription and reduced the genistein sensitivity of cells, and it also blocked the genistein-sensitizing roles of ELM in PC cells. In conclusion, this study demonstrated that ELK1 reduces DEPTOR transcription, leading to mTOR phosphorylation and the drug resistance of PC cells.

Abstract 612: ONC212 affects ClpXP complex, impairs mitochondrial bioenergetics and synergizes with glycolysis inhibition in pancreatic cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest human cancers and still represents an unmet clinical need. Survival, proliferation and drug-resistance of pancreatic cancer cells are driven by KRAS mutation, which supports both mitochondrial and glycolytic bioenergetics. ONC212 is a fluorinated imipridone with cytotoxic activity against pancreatic cancer cell lines and patient-derived xenografts. It has been reported to bind to and hyperactivate ClpXP, a mitochondrial protease composed by the regulatory subunit ClpX and the catalytic chamber ClpP, which is involved in the maintenance of respiratory chain function. Here we evaluated the effect of ONC212 on ClpXP expression in a panel of pancreatic cancer cell lines and investigated the metabolic changes occurring in vitro upon ONC212 exposure. Western blot analysis showed that ONC212 destabilized ClpXP complex through the suppression of its regulatory subunit ClpX, while leaving ClpP relatively unaffected. NDUFA12, SDH-A and SDH-B, three ClpP substrates belonging to the respiratory chain complexes I and II, decreased after treatment with ONC212. Moreover, ClpP transient knockdown partially protected cancer cells from ONC212 cytotoxicity. Seahorse XF ATP assay revealed that mitochondrial ATP production was impaired by ONC212, while glycolytic ATP proportionally increased. Accordingly, ONC212 caused a dose-dependent accumulation of lactate in culture supernatant along with the restoration of NAD+, an essential coenzyme fueling glycolytic flux. Interestingly, there was an inverse correlation between basal mitoATP% and ONC212 GI50. Furthermore, AsPC1, one of the most sensitive cell lines, was far less efficient in upregulating glycolysis as compared to the others and suffered a profound decline in ATP production. As a consequence of bioenergy imbalance, AMPK became phosphorylated at Thr172 upon ONC212 treatment in most cell lines. Culturing PDAC cells in galactose-containing medium, favoring mitochondrial metabolism over glycolysis, sensitized them to ONC212. Conversely, hypoxia, which forces cancer cells to generate ATP through glycolysis, rendered them more resistant to the drug. The combination of ONC212 plus 2-Deoxy-d-Glucose, an inhibitor of the first steps of the glycolytic pathway, resulted in highly synergistic loss of cell viability. In addition, the combination treatment, but not ONC212 alone, inhibited ERK1/2 phosphorylation and induced PARP cleavage in PANC1 and BxPC3 cells. Overall, ONC212 targets ClpXP and compromises mitochondrial bioenergetics in pancreatic cancer. Enhancement of glycolytic flux may represent an escape mechanism active in most PDAC cells. Switching metabolic dependence towards mitochondria or combining ONC212 with a glycolytic inhibitor may significantly increase its antineoplastic potential in this highly aggressive malignancy. Citation Format: Isacco Ferrarini, Lanlan Zhou, Wafik S. El-Deiry. ONC212 affects ClpXP complex, impairs mitochondrial bioenergetics and synergizes with glycolysis inhibition in pancreatic cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 612.

Biodegradable nanocarriers for small interfering ribonucleic acid (siRNA) co-delivery strategy increase the chemosensitivity of pancreatic cancer cells to gemcitabine

Ribonucleic acid (RNA) interference (RNAi) therapies are promising cancer treatment modalities that can specifically target abnormal proto-oncogenes, thus improving the therapeutic effect. For the treatment of pancreatic cancer, targeting one mutant proto-oncogene by RNAi usually does not yield the desired therapeutic efficiency. Both K-ras gene mutations and Notch1 overexpression are common symptoms in pancreatic cancer patients, and play a crucial role in pancreatic cancer cell drug resistance. In this study, biodegradable charged polyester-based vectors (BCPVs) were synthesized for the co-delivery of K-ras and Notch1 small interfering ribonucleic acid (siRNA) into MiaPaCa-2 cells (pancreatic cancer cell line) to overcome drug resistance to gemcitabine (GEM), a first-line chemotherapeutic drug used in the clinic. BCPVs could effectively absorb negative siRNA to form a capsule-like structure, prevent siRNA from nuclease digestion in the serum, and promote effective siRNA cell internalization and endosomal escape. Through K-ras and Notch1 gene silencing in MiaPaCa-2 cells, BCPV-siRNAK-ras-siRNANotch1 nanocomplexes effectively reversed the epithelia-mesenchymal transition (EMT) in MiaPaCa-2 cells, thereby greatly enhancing the sensitivity of MiaPaCa-2 cells to GEM. MiaPaCa-2 cell proliferation, migration, and invasion were effectively inhibited, and cell apoptosis was also significantly enhanced by the synergistic antitumor effect of BCPV-siRNAK-ras-siRNANotch1 nanocomplexes and GEM. These results suggest that this combination RNAi therapy can be used to improve cancer cell sensitivity to chemotherapeutic drugs. Specifically, this newly developed strategy has a great potential for treating pancreatic cancer.

Ribosomal protein L34 promotes the proliferation, invasion and metastasis of pancreatic cancer cells.

Ribosomal proteins (RPs) are the main components of ribosomes and participate in the self-assembly of ribosomes and protein synthesis. Recent advance has shown that RPs play important roles in the tumorigenesis and drug resistance of various cancers. However, the expression status and function of RPL34 in pancreatic cancer (PC) remains unclear. In this study, we find that RPL34 is overexpressed in PC tissues and cell lines, which is correlated with decreased methylation of its promoter. Knockdown of RPL34 effectively suppresses the proliferation, colony formation, migration and drug-resistance of PC cells, which are accompanied by cell cycle arrest at the G2 phase and induction of apoptosis. In vivo assays demonstrate that RPL34 silencing inhibits PC tumor growth and metastasis. Moreover, gene expression profiling revealed that RPL34 silencing results in alteration of the MAPK and p53 signaling pathways. Clinically, our data indicate a positive association of RPL34 expression with tumor stage and metastasis in PCs. We revealed that RPL34 acts as a potential onco-protein in PC, and RPL34 may be a promising biomarker for prognosis prediction and a potential target for the treatment of PC.

MicroRNA-320a promotes 5-FU resistance in human pancreatic cancer cells.

The drug-resistance of pancreatic cancer cells results in poor therapeutic effect. To predict the therapeutic effect of the chemotherapy drugs to specific patients and to reverse the resistance of pancreatic cancer cells are critical for chemotherapy of pancreatic cancer. MicroRNAs (miRNAs) have been reported to play important roles in the genesis of drug-resistance of various cancer types. There are also many advantages of miRNAs in diagnosis and therapy of disease. Although several miRNAs regulating 5-Fluorouracil (5-FU) resistance in human pancreatic cancer have been reported, the detailed molecular mechanism remains to be determined. In this study, we found that miR-320a was significantly up-regulated in 5-FU resistant pancreatic cancer cells. Over-expression of miR-320a strongly contributed to pathogenesis of pancreatic cancer, which was represented by the increased proliferation, invasion, metastasis, drug-resistance characteristics and the epithelial-to-mesenchymal transition. Furthermore, we demonstrated that miR-320a was able to bind to 3′UTR of PDCD4 mRNA, and mediated its down-regulation in 5-FU resistance of human pancreatic cancer cells. Whereas restoration of PDCD4 expression could partially attenuate the function of miR-320a in pancreatic cancer. Taken together, our study demonstrated that miR-320a played important role in regulating 5-FU resistance by targeting PDCD4 and might be developed as new therapeutic target for pancreatic cancer.

Stromal Carcinoma Associated Fibroblasts Promote Drug Resistance of Human Pancreatic Cancer Cells by Modulation of ROS via CXCR4/CXCL12 Signaling

Pancreatic cancer is one of the most aggressive malignancies, with a 5-year overall survival of less than 5%. Tumor drug resistance to conventional chemotherapy, such as Gemcitabine, is often a significant contributor to poor overall survival. One of the common mechanisms of Gemcitabine resistance is activation of cell signaling via increased phosphorylation of mitogen-Activated kinase (MAP) kinases, leading to increased tumor sur- vival and reduced sensitivity to chemotherapeutic agents. A growing body of evidence suggests that the CXCL12/CXCR4 signal transduction axis in the tumor microenvironment is an important mediator of tumor migration, growth, and drug resistance. We hypothesized that stromal cells such as carcinoma-associated fibroblasts (CAFs), an important cellular component of the tumor microenvironment (TME), play a contributory role in the growth, invasiveness, and drug response of pancreatic cancer cells (PCCs) by activating CXCL12/CXCR4-mediated signal transduction. To test this, we used an in vitro model system to study the growth, invasion, and drug response of human PCCs in the presence or absence of in vitro generated CAFs and their precursors, the mesenchymal stem cells (MSCs). Functional studies demonstrated that co-culture of PCCs with CAFs led to signifi- cant increase in tumor cell invasion, which was abrogated by blockade of CXCR4 by plerixafor (AMD3100), a CXCR4 antagonist, and by siRNA- mediated knockdown of CXCR4 in CAFs. Further, we examined the effect of AMD3100 on the chemoresistance of PCCs to Gemcitabine. Our results indicated that AMD3100 reversed Gemcitabine-mediated chemoresistance of PCCs cells in the presence of CAFs or CAFconditioned media. In co- culture with pancreatic cancer cells, CAFs induced activation of MAPK signaling pathways and enhanced transcription of Mn-superoxide dismutase (SOD), glucose 6-phosphate dehydrogenase (G6PD), and catalase, genes involved in reactive oxygen species (ROS) pathways. Using Phloretin (a natural flavonoid found in apple leaves), a ROS inhibitor, we observed attenuation of MAPK signaling, SOD activity, and reversal of drug resistance in CAF-exposed pancreatic cancer cells. Phloretin in combination with Gem- citabine produced remarkable antitumor effects in a tumor xenograft model in immune compromised animals. These findings implicate CXCL12/CXCR4- dependent MAPK signaling and ROS pathways in CAF-mediated modulation of the growth, migration, and drug resistance of PCCs and provide a rationale for developing combination therapies for control of pancreatic cancer.

Abstract A49: Carcinoma-associated fibroblasts in the tumor microenvironment affect growth, invasiveness, and drug response of human pancreatic cancer cells

Abstract Pancreatic cancer is one of the most aggressive malignancies, with a 5-year overall survival of less than 5%. Tumor drug resistance to conventional chemotherapy, such as gemcitabine, is often a significant contributor to poor overall survival. One of the common mechanisms of gemcitabine resistance is activation of cell signaling via increased phosphorylation of Mitogen-Activated kinase (MAP) kinases, leading to increased tumor survival and reduced sensitivity to chemotherapeutic agents. A growing body of evidence suggests that the CXCL12/CXCR4 signal transduction axis in the tumor microenvironment is an important mediator of tumor migration, growth, and drug resistance. We hypothesized that carcinoma-associated fibroblasts (CAFs), an important cellular component of the TME, play a contributory role in the growth, invasiveness, and drug response of pancreatic cancer cells (PCCs) by activating CXCL12/CXCR4-mediated signal transduction. To test this, we used an in vitro model system to study the growth, invasion, and drug response of human PCCs in the presence or absence of in vitro-generated CAFs. Functional studies demonstrated that co-culture of PCCs with CAFs led to significant increase in tumor cell invasion, which was abrogated by blockade of CXCR4 by AMD3100-plerixafor (AMD3100), a CXCR4 antagonist, and by siRNA-mediated knockdown of CXCR4 in CAFs. Increased invasion of PCCs after co-culture with orthotopically derived CAFs was also abrogated by CXCR4 blockade, demonstrating a critical role for this receptor in regulating the tumor-promoting abilities of CAFs. Additionally, we investigated the effect of CAFs on the MAPK Signaling pathway (MEK1/2, p-MEK1/2, ERK1/2, p-ERK1/2, Akt, and p-Akt) via Western blot assays. Further, we examined the effect of AMD3100 on the chemo-resistance of PCCs to gemcitabine. Our results indicated that AMD3100 reversed gemcitabine-mediated chemo-resistance of PCCs cells in the presence of CAFs or CAF-conditioned media. In co-culture with pancreatic cancer cells, CAFs induced activation of MAPK signaling pathways and enhanced transcription of Mn-SOD, G6PD, and catalase, genes involved in reactive oxygen species (ROS) pathways. Using phloretin, a ROS inhibitor, we observed attenuation of MAPK signaling, SOD activity, and reversal of drug resistance in CAF-exposed pancreatic cancer cells. These findings implicate CXCL12/CXCR4-dependent MAPK signaling and ROS pathways in CAF-mediated modulation of the growth, migration, and drug resistance of PCCs. Citation Format: Ahlim Al. Sanani, Brijsh Patel, Alix Duarte, Nitu Bansal, Tushar Bhagat, Yanique Rattigan, Anirban Maitra, Amit Verma, Debabrata Banerjee. Carcinoma-associated fibroblasts in the tumor microenvironment affect growth, invasiveness, and drug response of human pancreatic cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr A49.

Silencing of MBD1 reverses pancreatic cancer therapy resistance through inhibition of DNA damage repair

High resistance to traditional chemo- and radiotherapies contributes to the poor prognosis of pancreatic cancer (PC). Methyl-CpG binding domain protein 1 (MBD1), which plays an important role in disease progression, contributes to the drug resistance of PC cells; however, the mechanism underlying the drug resistance endowed by MBD1 remains unknown. In this study, we found that MBD1 was recruited to DNA damage sites under DNA damage conditions. Silencing of MBD1 significantly impaired activation of the DNA damage checkpoint response and inhibited DNA repair capacity. MBD1 binds mediator of DNA damage checkpoint protein 1 (MDC1), which is induced by radiation and regulates NBS1 activation in the presence of DNA damage repair. Knockdown of MBD1 significantly increased the sensitivity of cells to radiation and cisplatin (diamindichloridoplatin, DDP) in vitro. Importantly, the function of MBD1 in regulating chemoradioresistance is also partially dependent on DNA damage repair. Thus, we hypothesize that MBD1 may promote PC chemoradioresistance by regulating PC cell fate in the presence of DNA damage. Collectively, these findings reveal an important function of MBD1 in DNA repair and mediation of chemoradioresistance of cancer cells. Moreover, this study suggests that MBD1 is a promising molecular target for sensitizing resistant PC tumor cells to chemoradiotherapy.

Abstract LB-348: Chemoresistance in pancreatic cancer is conferred by MUC1 cytoplasmic tail binding to the promoter region of the ABCC1 (MRP-1) gene

Abstract Introduction: The high mortality rate of pancreatic cancer (PC) is in part, due to their high propensity for metastasis and multidrug resistance. The three most common ways by which cancer cells acquire chemoresistance is via deregulation of apoptotic pathways, upregulation of survival pathways and upregulation of multi-drug resistance (MDR) genes. The MDR genes encode for ATP-binding cassette (ABC) membrane transporters, which extrudes chemotherapeutic drugs from cancer cells. However, the mechanisms behind the up-regulation of the MDR genes are not entirely understood. More than 90% of metastatic PC patients overexpress MUC1 (CD227), a membrane tethered mucin glycoprotein that has been linked to increased metastatic phenotype and drug resistance. The cytoplasmic tail (CT) of MUC1 has seven conserved tyrosine residues which are important for the signal transduction role of MUC1. The aim of this study was to understand the underlying mechanism by which MUC1 induces drug resistance in PC cells. Method: We used a panel of PC cells lines that endogenously express low or high levels of MUC1. The cells lines expressing low endogenous MUC1 were stably infected with the retroviral vector containing empty plasmid (Neo), or plasmid carrying full-length MUC1 (MUC1 WT), or full length MUC1 with the tyrosine residues of MUC1 CT mutated to phenylalanine (MUC1 Y0). The cells were treated with three commonly used chemotherapeutic/preventive drugs (Gemcitabine, Etoposide and Celecoxib). The level of dead cells was evaluated by H3 incorporation assay and Annexin V staining. We also checked for the activation of prosurvival pathways Erk1/2 and PI3K by Western Blot. The mRNA level of MDR genes were determined by RTPCR. CHIP (Chromatin Immunoprecipitation) was performed to determine the localization of MUC1 CT to the promoter region of ABCC1 gene (MRP1). Results: Our results indicate that PC cells expressing MUC1 WT or MUC1 Y0 have intrinsic resistance to chemotherapeutic, compared to cells expressing low levels of MUC1. We observed an enhanced activation of the prosurvival pathways Erk1/2 and PI3K in MUC1 high PC cells, compared to cells expressing low MUC1 or MUC1 Y0. Upon inhibition of the PI3K/Akt pathway, a partial loss in the chemoresistance was seen, indicating that this pathway is partially responsible for the chemoresistance. DNA microarray and RT PCR showed that the expression of MDR genes (ABCC1, ABCC3, ABCC5 and ABCB1) was significantly higher in PC cells expressing MUC1 WT or MUC1 Y0. Most importantly, for the first time, we showed that MUC1 CT localizes to the promoter region of a MDR gene, ABCC1. This suggests that MUC1 directly drives the transcription and expression of ABCC1 gene. The implications of the data are clinically significant as small molecule inhibitors can be designed to specifically block MUC1 CT signaling and transcriptional activity. 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 LB-348. doi:1538-7445.AM2012-LB-348

Gene Expression Profiling of Adenosine Triphosphate-Binding Cassette Transporters in Response to K-ras Activation and Hypoxia in Human Pancreatic Cancer Cell Cultures

Pancreatic cancer (PC) is hypoxic and highly resistant to conventional chemotherapy. We sought to determine whether K-ras oncogene and/or hypoxia can induce expression of drug resistance-promoting adenosine triphosphate-binding cassette (ABC) transporters in human PC cell lines. Immortalized near-normal human pancreatic ductal epithelial(HPDE) cells, HPDE cells expressing K-rasG12V oncogene, and PCcell lines (MIA PaCa-2, PANC-1, BxPC-3) were subjected to hypoxia and examined for messenger RNA expression of 48 ABC transporters. Mutant K-ras activation and/or hypoxia of HPDE cells led to induction of various ABC transporters. In the case of PC cell lines, no clear correlation was found between expression of constitutively active K-ras and global ABC transporter expression. Moreover, hypoxic treatment of PC cell lines had different effects on ABC transporter expression.Importantly, PC cell lines did not express the multidrug resistance 1 ABC transporter, a major mechanism of drug resistance. However, multi drug resistance 1 expression in the cells was up-regulated in response to continuous exposure to low doses of vincristine, indicating that drug resistance could be induced. Expression of K-ras oncogene and hypoxia, as well as exposure to drugs, can contribute to drug resistance in PC cells.

Gemcitabine, docetaxel, and capecitabine (GTX) in the treatment of metastatic pancreatic cancer (PC): A prospective phase II study

14024 Background: We have found that the combination of gemcitabine, docetaxel, and capecitabine (GTX), when administered in a specific sequence, will induce a p53 independent pathway of cell death through the MAP kinase pathway. The sequence overcomes drug resistance in PC cells in vitro. We have begun a prospective, phase II trial of GTX in patients with metastatic PC as first-line therapy. Methods: 23 patients with metastatic PC, ECOG 0–2 were enrolled at either Columbia or a community practice. Each cycle was administered over a 21 days. Capecitabine was administered at 750 mg/m2 twice daily for 14 days. Gemcitabine (750 mg/m2 over 75 minutes) and docetaxel (30 mg/m2) were administered on days 4 and 11. Responses were measured by CT (RECIST) and PET after every three cycles. A response by PET was defined as a 50% reduction in SUV while a CR was an absence of uptake. Results: Median age was 61, including 8 men and 15 women. Metastatic sites included liver (87%), abdomen (65%), and lung (17%). 70% of liver positive patients had at least five metastases. 22% had malignant ascites. 16 patients remain alive and 7 have progressive disease. Median survival has not yet been reached. Progression occurred at a median of 5.1 months. By CT, the response rate at metastatic sites was 39% (17% CR / 22% PR). Stable disease was observed in 48% at metastatic sites. PET showed a 53% response rate at metastatic sites. At the primary site, CT showed a 30% response rate including 17% complete responses. By PET criteria, there was a 31% response rate and a 26% CR rate at the primary site. In three patients, a PET response heralded a CT response by three cycles. In one patient, progressive disease on PET preceded progression on CT by two months. Toxicity: Grade 3 leukopenia and thrombocytopenia were 13% and 9%, respectively. There was no grade four hematologic toxicity. One patient experienced lung disease related to gemcitabine and withdrew from the study. A second patient experienced grade 4 mucositis, thrush, and sepsis which was presumed due to DPD deficiency. Grade 3–4 toxicities: HFS: 9%. There was no grade 3–4 diarrhea. Conclusions: GTX, elicits a promising response rate when used in metastatic P.C. PET detects a response and failure of chemotherapy earlier than CT scans. [Table: see text]