Parental PC-3 Cells Research Articles

MR Molecular Imaging of Extradomain-B Fibronectin for Assessing Progression and Therapy Resistance of Prostate Cancer.

Accurate assessment and characterization of the progression and therapy response of prostate cancer are essential for precision healthcare of patients diagnosed with the disease. MRI is a clinical imaging modality routinely used for diagnostic imaging and treatment planning of prostate cancer. Extradomain B fibronectin (EDB-FN) is an oncofetal subtype of fibronectin highly expressed in the extracellular matrix of aggressive cancers, including prostate cancer. It is a promising molecular target for the detection and risk-stratification of prostate cancer with high-resolution MR molecular imaging (MRMI). In this study, we investigated the effectiveness of MRMI with an EDB-FN specific contrast agent MT218 for assessing the progression and therapy resistance of prostate cancer. Low grade LNCaP prostate cancer cells became an invasive phenotype LNCaP-CXCR2 with elevated EDB-FN expression after acquisition of the C-X-C motif chemokine receptor 2 (CXCR2). MT218-MRMI showed brighter signal enhancement in LNCaP-CXCR2 tumor xenografts with a ∼2-fold contrast-to-noise (CNR) increase than in LNCaP tumors in mice. Enzalutamide-resistant C4-2-DR prostate cancer cells were more invasive, with higher EDB-FN expression than parental C4-2 cells. Brighter signal enhancement with a ∼2-fold CNR increase was observed in the C4-2-DR xenografts compared to that of C4-2 tumors in mice with MT218-MRMI. Interestingly, when invasive PC3 prostate cancer cells developed resistance to paclitaxel, the drug-resistant PC3-DR cells became less invasive with reduced EDB-FN expression than the parental PC3 cells. MT218-MRMI detected reduced brightness in the PC3-DR xenografts with more than 2-fold reduction of CNR compared to PC3 tumors in mice. The signal enhancement in all tumors was supported by the immunohistochemical staining of EDB-FN with the G4 monoclonal antibody. The results indicate that MRMI of EDB-FN with MT218 has promise for detection, risk stratification, and monitoring the progression and therapy response of invasive prostate cancer.

Abstract 1678: Docetaxel induces Rac1 and Cdc42 Rho GTPase activation in prostate cancer cells

Abstract Prostate cancer (PCa) is a major health burden that affects the quality of life of men worldwide. In the United States, PCa is the second leading cause of mortality among cancers that affect men. Treatment of advanced PCa aims to suppress androgen signaling and proliferation in cancer cells using anti-androgens and chemotherapy. However, the development of drug resistance is a major limitation to curing advanced prostate cancer and strategies to block mechanisms of therapy resistance would enhance treatment efficacy and potentially improve patient prognosis. Cdc42 and Rac1, members of the family of Rho GTPases, have been associated with the progression of different types of hormone-associated cancer, such as breast, ovary, and prostate, among others. The current study was designed to evaluate the role of Cdc42 and Rac1 in chemoresistant prostate cancer cells, including under castration-resistant and androgen-independent conditions. We did not observe significant differences in active (Rac-GTP) or total Rac1 levels in chemoresistant compared to parental PC3 or DU145 cells; similar findings were observed for Ccd42. Treatment of drug-naïve cells with a sublethal dose of docetaxel (10uM) induced gradual increases in Rac1-GTP up to 30 minutes in 22rv1, 60 minutes in LNCaP and DU145, and 24 hours in PC3 cells. Cdc42-GTP levels also increased with subacute docetaxel treatment up to 24 hours in 22rv1 and DU145. Chemoresistant 22rv1, PC3, and DU145 exhibited similar sensitivity to Rac1 and Ccd42 inhibitors including MB1-167, MBQ-168, EHop-097, with an IC50 of about 1uM for each compound and line. Ongoing studies are evaluating the role of these Rho-GTPases in 3-dimensional growth and survival. Citation Format: Andrea Paola López González, Jessica Colón González, María C. Santa María Fuentes, Surangani Dharmawardhane, Carlos J. Diaz Osterman. Docetaxel induces Rac1 and Cdc42 Rho GTPase activation in prostate cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1678.

EGFR-mediated hyperacetylation of tubulin induced docetaxel resistance by downregulation of HDAC6 and upregulation of MCAK and PLK1 in prostate cancer cells.

Docetaxel-based chemotherapy has generally been considered as one of the effective treatments for castration-resistant prostate cancer (PCa). However, clinical treatment with docetaxel often encounters a number of undesirable effects, including drug resistance. Tubulin isoforms have been previously examined for their resistance to docetaxel in many cancers, but their real mechanisms remained unclear. In this study, a series of docetaxel-resistant PC/DX cell sublines were established by chronically exposing PC3 to progressively increased concentrations of docetaxel. Western blotting results showed significantly higher expression of acetyl-tubulin, α-tubulin, β-tubulin, γ-tubulin, and βIII-tubulin in PC/DX25 than in parental PC3 cells. PC/DX25 with greater resistance to docetaxel had higher levels of acetyl-tubulin and mitotic centromere-associated kinesin (MCAK) than PC3 cells. This study found that docetaxel induced the expression of acetyl-tubulin and MCAK in PC3 cells at a dose- and time-dependent manner. Both mRNA and protein levels of histone deacetylase 6 (HDAC6) were significantly decreased in PC/DX25 compared with PC3 cells. PC3 increased the resistance to docetaxel by HDAC6 knockdown and Tubastatin A (HDAC6 inhibitor). Conversely, PC/DX25 reversed the sensitivity to docetaxel by MCAK knockdown. Notably, flow cytometry analysis revealed that MCAK knockdown induced significantly sub G1 fraction in PC/DX cells. Overexpression of polo-like kinase-1 increased the cell survival rate and resistance to docetaxel in PC3 cells. Moreover, epidermal growth factor receptor (EGFR) activation induced the upregulation of acetyl-tubulin in docetaxel-resistant PCa cells. These findings demonstrated that the EGFR-mediated upregulated expression of acetyl-tubulin played an important role in docetaxel-resistant PCa.

Direct cell–cell interaction regulates division of stem cells from PC-3 human prostate cancer cell line

Cancer stem cells (CSCs) are a subpopulation that can drive recurrence and metastasis. Therefore, therapies targeting CSCs are required. Although previous findings have suggested that non-CSCs regulate the proliferation and differentiation of CSCs in the tumor microenvironment, the precise molecular mechanism is largely unknown. In this study, we found that a direct interaction between CSCs and non-CSCs downregulated CSC division in the PC-3 human prostate cancer cell line. We found that the proliferation of PC-3-derived CSCs (PrSCs) was significantly decreased (∼47%) in the presence of non-CSC-rich parental PC-3 cells compared with that in a culture in which they were absent. We observed no differences in PrSC proliferation when we indirectly cocultured them with PC-3 cells across a Transwell insert, and PrSCs that were transiently bound to immobilized PC-3 cells proliferated more slowly than those bound to PrSCs. The frequency of cell division with prior PrSC-PrSC contact was 2.8 times higher in the PrSC monoculture compared with that in the coculture with PC-3 cells. We found that the PrSCs were approximately 1.3 times more closely associated in the monoculture compared with the coculture with PC-3 cells, as determined by a cell proximity assay. The frequency of asymmetric PrSC division was 6.5% in the monoculture compared with 1.0% in the coculture with PC-3 cells (P < 0.045). By analyzing our data, we determined the importance of PrSC–non-CSC contact in regulating the frequency and mode of PrSC division. This regulation might be a valuable target for treating cancer.

SIRT5 Directly Inhibits the PI3K/AKT Pathway in Prostate Cancer Cell Lines.

Prostate cancer (PCa) is the most commonly diagnosed genital cancer in men globally. Among patients who develop advanced PCa, 80% are affected by bone metastasis, with a sharp drop in survival rate. Despite efforts, the details of mechanisms of metastasis of PCa remain unclear. SIRT5, an NAD+-dependent deacylase, is hypothesized to be a crucial regulator of various cancers. The role of SIRT5 in cancer has not been extensively studied compared to other SIRTs. In this study, we showed significantly decreased levels of SIRT5 in PC-3M, a highly aggressive PC-3 cell variant. We characterized the differentially expressed proteins between parental and SIRT5 KO PC-3 cells using quantitative proteomics analysis. A significant increase in expression of interleukin-1β (IL-1β) in SIRT5 KO cells was observed, and the PI3K/AKT/NF-ĸB signaling pathway was found significantly elevated in SIRT5 KO cells by the Gene Ontology annotation and KEGG pathway functional enrichment analysis. Moreover, we confirmed that SIRT5 can bind PI3K by immunoprecipitation analysis. This study is the first to demonstrate a relationship between SIRT5 and PCa metastasis, suggesting that SIRT5-mediated inhibition of the PI3K/AKT/NK-kB pathway is reduced for secondary metastasis from bone to other tissues.

Possibility of paclitaxel to induce the stemness-related characteristics of prostate cancer cells.

Drug resistance poses a crucial problem in the treatment of prostate cancer. Recent studies have shown that chemotherapy agents may cause cancer cells to acquire stem cell-like properties, resulting in drug resistance and, eventually, treatment failure. To evaluate whether long-term paclitaxel exposure causes an increase in the stem cell-like properties of prostate cancer cells. Paclitaxel-resistant PC-3 cells were generated from parental PC-3 cells by treating them with increasing concentrations of paclitaxel. The expression levels of the stem cell markers NANOG, C-MYC, CD44, and ABCG2 were evaluated using quantitative real-time polymerase chain reaction (RT-qPCR). A sphere formation assay was performed to test the potential of the cells to behave as stem cells, and a wound healing assay was carried out to evaluate migration ability of the cells. The expression levels of C-MYC and NANOG were significantly higher in paclitaxel-resistant PC-3 cells compared to the parental PC-3 cells. However, there was no significant increase in the expression of CD44 or ABCG2. In addition, the sphere-forming capacity and migration ability of resistant PC-3 cells were increased. The results of the current study indicate that paclitaxel exposure may increase the stem cell-like properties of PC-3 prostate cancer cells.

SLX4IP N-terminus dictates telomeric localization in ALT-like castration-resistant prostate cancer cell lines.

To ensure replicative immortality in cancer, telomeres must be maintained through activation of telomere maintenance mechanisms (TMMs) that are dependent on telomerase or the alternative lengthening of telomeres (ALT) pathway. Although TMM pathways have traditionally been considered to be mutually exclusive, ALT hallmarks have been identified in cancers defined as being telomerase-positive, supporting TMM coexistence. In castration-resistant prostate cancer (CRPC), in vitro models were thought to be universally dependent on telomerase as the primary TMM; however, CRPC models with androgen receptor (AR) loss demonstrate ALT hallmarks with limited telomerase activity and require ALT-associated PML bodies (APBs) for sustained telomere maintenance. The TMM coexistence in AR-negative CRPC is reliant on the ALT regulator protein, SLX4IP. To identify the regions of SLX4IP responsible for the induction of APBs and telomere preservation in CRPC models, five 3xFLAG-tagged SLX4IP constructs were designed and stably introduced into parental C4-2B, DU145, and PC-3 cells. Once generated, these cell lines were interrogated for APB abundance and SLX4IP construct localization via immunofluorescence-fluorescence in situ hybridization (IF-FISH) and coimmunoprecipitation experiments for telomeric localization. Similarly, PC-3 cells with endogenous SLX4IP knockdown and SLX4IP construct introduction were interrogated for APB abundance, telomere length preservation, and senescent rescue. Here, we define the N-terminus of SLX4IP as being responsible for the promotion of the ALT-like phenotype of AR-negative CRPC models. Specifically, the N-terminus of SLX4IP was sufficient for promoting APB formation to a similar degree as full-length SLX4IP across CRPC cell lines. Additionally, APB promotion by the N-terminus of SLX4IP rescued telomere shortening and senescent induction triggered by SLX4IP knockdown in AR-negative CRPC cells. Moreover, APB formation and telomere maintenance were dependent on the ability of the N-terminus to direct SLX4IP localization at telomeres and APBs. These findings identify the role of the uncharacterized ALT regulator SLX4IP in the promotion of TMM coexistence to perpetuate replicative immortality in CRPC in vitro.

GLUT5 (SLC2A5) enables fructose-mediated proliferation independent of ketohexokinase

BackgroundFructose is an abundant source of carbon and energy for cells to use for metabolism, but only certain cell types use fructose to proliferate. Tumor cells that acquire the ability to metabolize fructose have a fitness advantage over their neighboring cells, but the proteins that mediate fructose metabolism in this context are unknown. Here, we investigated the determinants of fructose-mediated cell proliferation.MethodsLive cell imaging and crystal violet assays were used to characterize the ability of several cell lines (RKO, H508, HepG2, Huh7, HEK293T (293T), A172, U118-MG, U87, MCF-7, MDA-MB-468, PC3, DLD1 HCT116, and 22RV1) to proliferate in fructose (i.e., the fructolytic ability). Fructose metabolism gene expression was determined by RT-qPCR and western blot for each cell line. A positive selection approach was used to “train” non-fructolytic PC3 cells to utilize fructose for proliferation. RNA-seq was performed on parental and trained PC3 cells to find key transcripts associated with fructolytic ability. A CRISPR-cas9 plasmid containing KHK-specific sgRNA was transfected in 293T cells to generate KHK-/- cells. Lentiviral transduction was used to overexpress empty vector, KHK, or GLUT5 in cells. Metabolic profiling was done with seahorse metabolic flux analysis as well as LC/MS metabolomics. Cell Titer Glo was used to determine cell sensitivity to 2-deoxyglucose in media containing either fructose or glucose.ResultsWe found that neither the tissue of origin nor expression level of any single gene related to fructose catabolism determine the fructolytic ability. However, cells cultured chronically in fructose can develop fructolytic ability. SLC2A5, encoding the fructose transporter, GLUT5, was specifically upregulated in these cells. Overexpression of GLUT5 in non-fructolytic cells enabled growth in fructose-containing media across cells of different origins. GLUT5 permitted fructose to flux through glycolysis using hexokinase (HK) and not ketohexokinase (KHK).ConclusionsWe show that GLUT5 is a robust and generalizable driver of fructose-dependent cell proliferation. This indicates that fructose uptake is the limiting factor for fructose-mediated cell proliferation. We further demonstrate that cellular proliferation with fructose is independent of KHK.

The role of S100A4 for bone metastasis in prostate cancer cells

BackgroundProstate cancers frequently metastasize to bone, where the best microenvironment for distant colonization is provided. Since osteotropic metastasis of prostate cancer is a critical determinant of patients’ survival, searches for preventive measures are ongoing in the field. Therefore, it is important to dissect the mechanisms of each step of bone metastasis, including the epithelial-mesenchymal transition (EMT) and cross-talk between metastatic niches and cancer cells.MethodsIn this study, we established a highly bone-metastatic subline of human prostate cancer cells by selecting bone-homing population of PC3 cells after cardiac injection of eight-week-old male BALB/c-nude mice. Then we assessed the proliferation, EMT characteristics, and migration properties of the subline (mtPC3) cells in comparison with the parental PC3 cells. To investigate the role of S100A4, we performed gene knock-down by lentiviral transduction, or treated cells with recombinant S100A4 protein or a S100A4-neutralizing antibody. The effect of cancer cells on osteoclastogenesis was evaluated after treatment of pre-osteoclasts with conditioned medium (CM) from cancer cells.ResultsThe mtPC3 cells secreted a markedly high level of S100A4 protein and showed elevated cell proliferation and mesenchymal properties. The increased proliferation and EMT traits of mtPC3 cells was inhibited by S100A4 knock-down, but was not affected by exogenous S100A4. Furthermore, S100A4 released from mtPC3 cells stimulated osteoclast development via the cell surface receptor RAGE. Down-regulation or neutralization of S100A4 in the CM of mtPC3 cells attenuated cancer-induced osteoclastogenesis.ConclusionAltogether, our results suggest that intracellular S100A4 promotes cell proliferation and EMT characteristics in tumor cells, and that secreted S100A4 activates osteoclastogenesis, contributing to osteolytic bone metastasis. Thus, S100A4 upregulation in cancer cells highly metastatic to bone might be a key element in regulating bone metastasis.

Protein Disulfide Isomerase 4 Drives Docetaxel Resistance in Prostate Cancer

Background: Protein disulfide isomerase 4 (PDIA4) has been reported to be closely associated with chemoresistance in several types of malignancies. But the pathogenic mechanisms of PDIA4 involved in docetaxel (DTX) resistance in prostate cancer (PCa) are still unknown. Hence, this study was conducted to evaluate the potential effect of PDIA4 on chemoresistance to DTX in PCa cells and to investigate the underlying mechanisms. Methods: Two types of DTX-resistant PCa cells, that is, DTX-resistant PC-3 cells (PC-3/DTXR) and C4-2B cells (C4-2B/DTXR) were developed, as well as the parental PC-3 and C4-2B cells were obtained to investigate these issues. Short hairpin RNAs targeting human PDIA4 to knockdown the expression of PDIA4 or PDIA4-expressing adenoviral vectors to overexpress the PDIA4 were transfected into PCa cells to study the underlying mechanisms of PDIA4 involving in PCa DTX resistance. Results: Results showed that PDIA4 exhibited a dramatic overexpression in PC-3/DTXR and C4-2B/DTXR cells. Down-regulation of PDIA4 by infecting PC-3/DTXR and C4-2B/DTXR cells with shPDIA4 lentivirus stimulated cell death by prompting apoptosis. Up-regulation of PDIA4 by infecting PC-3 and C4-2B cells with PDIA4-expressing adenovirus showed severer resistance to DTX. In addition, PDIA4 up-regulation induced phosphorylated protein kinase B (Akt) expression, while PDIA4 knockdown significantly inhibited the expression in PCa cells. Conclusions: Our study indicates that PDIA4 is a negative regulator of PCa cell apoptosis and plays a critical role in PCa DTX resistance by activating the Akt-signaling pathway. Thereby, it implies that targeting PDIA4 could be a potential adjuvant therapeutic approach against DTX resistance in PCa.

KLK4 Induces Anti-Tumor Effects in Human Xenograft Mouse Models of Orthotopic and Metastatic Prostate Cancer.

Simple SummaryThe serine protease kallikrein-related peptidase 4 (KLK4) has been reported to potentially play a role in the progression of prostate cancer and other cancer types. However, most of these reports have been limited to in vitro studies. In vivo cancer models offer greater complexity to mimic the characteristics of cancer growth and metastasis in humans. In this study, we used in vivo models of prostate cancer and demonstrated that KLK4 can strongly inhibit the growth of primary prostate tumors as well as bone metastases. To our knowledge, this is the first report of an anti-tumor effect of KLK4 in prostate cancer in vivo.Recent reports have suggested the role of kallikrein-related peptidase 4 (KLK4) to be that of remodeling the tumor microenvironment in many cancers, including prostate cancer. Notably, these studies have suggested a pro-tumorigenic role for KLK4, especially in prostate cancer. However, these have been primarily in vitro studies, with limited in vivo studies performed to date. Herein, we employed an orthotopic inoculation xenograft model to mimic the growth of primary tumors, and an intracardiac injection to induce metastatic dissemination to determine the in vivo tumorigenic effects of KLK4 overexpressed in PC3 prostate cancer cells. Notably, we found that these KLK4-expressing cells gave rise to smaller localized tumors and decreased metastases than the parent PC-3 cells. To our knowledge, this is the first report of an anti-tumorigenic effect of KLK4, particularly in prostate cancer. These findings also provide a cautionary tale of the need for in vivo analyses to substantiate in vitro experimental data.

CD44v8-10 mRNA contained in serum exosomes as a diagnostic marker for docetaxel resistance in prostate cancer patients

BackgroundDocetaxel is first-line chemotherapy for castration-resistant prostate cancer (CRPC), but most patients acquire docetaxel resistance. CD44 has been shown to be involved in drug resistance of cancers including prostate cancer. We hypothesized that CD44 in serum exosomes could be a diagnostic marker for docetaxel resistance in CRPC patients. In this study, we examined CD44 protein and mRNA expression in cell lysates and exosomes isolated from prostate cancer cells, evaluated the effect of CD44v8-10 knockdown on docetaxel sensitivity and measured CD44 mRNA copy numbers contained in serum exosomes in prostate cancer patients. Materials and methodsDocetaxel-sensitive PC-3 prostate cancer cells and docetaxel-resistant PC-3R cells established previously from parental PC-3 cells were used. CD44v8-10 knockdown was performed by siRNA transfection. Blood was collected from 50 docetaxel-naïve and 10 docetaxel-resistant patients and 15 control males. CD44 protein expression was evaluated by Western blotting. CD44 mRNA expression was measured by RT-digital PCR. ResultsThe levels of CD44v8-10 protein and mRNA in cell lysates and exosomes were higher in PC-3R cells than in PC-3 cells. CD44v8-10 knockdown significantly increased docetaxel sensitivity of PC-3R cells. The CD44v8-10 mRNA copy numbers in serum exosomes were higher in docetaxel-resistant patients than in docetaxel-naïve patients and control males (median 46, 12 and 17 copies/mL serum, respectively, P = 0.032). In contrast, the serum exosomal mRNA copy numbers of CD44 standard isoform (CD44s) were not different among 3 groups (median 25, 14 and 13 copies/mL serum, respectively, P = 0.150). ConclusionsCD44v8-10 may be involved in docetaxel resistance in prostate cancer and serum exosomal CD44v8-10 mRNA could be a diagnostic marker for docetaxel-resistant CRPC.

Suppressing PARylation by 2',5'-oligoadenylate synthetase 1 inhibits DNA damage-induced cell death.

High expression of 2',5'-oligoadenylate synthetase 1 (OAS1), which adds AMP residues in 2',5' linkage to a variety of substrates, is observed in many cancers as a part of the interferon-related DNA damage resistance signature (IRDS). Poly(ADP-ribose) (PAR) is rapidly synthesized from NAD+ at sites of DNA damage to facilitate repair, but excessive PAR synthesis due to extensive DNA damage results in cell death by energy depletion and/or activation of PAR-dependent programmed cell death pathways. We find that OAS1 adds AMP residues in 2',5' linkage to PAR, inhibiting its synthesis invitro and reducing its accumulation in cells. Increased OAS1 expression substantially improves cell viability following DNA-damaging treatments that stimulate PAR synthesis during DNA repair. We conclude that high expression of OAS1 in cancer cells promotes their ability to survive DNA damage by attenuating PAR synthesis and thus preventing cell death.

Arctigenin induces necroptosis through mitochondrial dysfunction with CCN1 upregulation in prostate cancer cells under lactic acidosis.

Arctigenin, a mitochondrial complex I inhibitor, has been identified as a potential anti-tumor agent, but the involved mechanism still remains elusive. Herein, we studied the underlying mechanism(s) of action of arctigenin on acidity-tolerant prostate cancer PC-3AcT cells in the lactic acid-containing medium. At concentration showing no toxicity on normal prostate epithelial RWPE-1 and HPrEC cells, arctigenin alone or in combination with docetaxel induced significant cytotoxicity in PC-3AcT cells compared to parental PC-3 cells. With arctigenin treatment, reactive oxygen species (ROS) levels, annexin V-PE positive fractions, sub-G0/G1 peak in cell cycle analysis, mitochondrial membrane depolarization, and cell communication network factor 1 (CCN1) levels were increased, while cellular ATP content and phospho (p)-Akt level were decreased. Pretreatment with ROS scavenger N-acetylcysteine effectively reversed the series of phenomena caused by arctigenin, suggesting that ROS served as upstream molecules of arctigenin-driven cytotoxicity. Meanwhile, arctigenin increased the levels of p-receptor-interacting serine/threonine-protein kinase 3 (p-RIP3) and p-mixed lineage kinase domain-like pseudokinase (p-MLKL) as necroptosis mediators, and pretreatment with necroptosis inhibitor necrostatin-1 restored their levels and cell viability. Treatment of spheroids with arctigenin resulted in necroptotic cell death, which was prevented by N-acetylcysteine. The siRNA-based knockdown of CCN1 suppressed the levels of MLKL, B-cell lymphoma 2 (Bcl-2), and induced myeloid leukemia cell differentiation (Mcl-1) with increased cleavage of Bcl-2-associated X (Bax) and caspase-3. Collectively, these results provide new insights into the molecular mechanisms underlying arctigenin-induced cytotoxicity, and support arctigenin as a potential therapeutic agent for targeting non-Warburg phenotype through induction of necroptosis via ROS-mediated mitochondrial damage and CCN1 upregulation.

Heme oxygenase-1 in osteosarcoma.

The present study was planned to analyze serum heme oxygenase-1 levels in osteosarcoma patients. Twenty five histopathologically confirmed cases of osteosarcoma localized without metastasis of all the ages attending the Orthopedic Clinics were included in the study group and twenty five patients having musculoskeletal pain (age and sex matched) served as control. Five ml of venous blood was collected aseptically from antecubital vein and serum was be separated by centrifugation and analyzed the same day. Routine biochemistry investigations were performed as per standard enzymatic methods by autoanalyzer. Serum Heme oxygenase-1 was analyzed by enzyme-linked immunosorbent assay. In osteosarcoma patients, serum HO-1 levels were increased as compared to patients having musculoskeletal pain (P < 0.05). Workers have found that HO-1 induction in prostate cancer cell lines (PC3) cells restored the proliferation of osteoblasts, which was inhibited during co-culture with parental prostate cancer cell line PC3 cells. However, no concrete data are available on blood levels of HO in osteosarcoma. Major role of HO-1 is the protection against oxidative injury, additionally, it regulates cell proliferation, modulates inflammatory response and facilitates angiogenesis. Findings of the present study suggests that pharmacological agents that regulate HO activity or HO-1 gene silencing may become powerful tools for preventing the onset or progression of various cancers and sensitize them to anticancer therapies.

Abstract 339: Mechanisms of resistance to poly (ADP-ribose) polymerase inhibitors in prostate cancer

Abstract Background: Poly (ADP-ribose) polymerase inhibitors (PARPi) have demonstrated promise in treating cancers with DNA damage repair (DDR) gene abnormalities. As a result, olaparib and more recently, rucaparib have been given Breakthrough Therapy designation by the FDA for use in metastatic castration resistant prostate cancer (mCRPC) with BRCA1/2 and ATM mutations. One of the problems encountered with PARPi is drug resistance which generally limits drug efficacy. Mechanistic studies on PARPi resistance have shown one of the main mechanisms of acquired resistance to be a reversion mutation of BRCA1/2. However, this is likely more applicable to cancers in which impaired BRCA1/2 function is due to a mutation rather than in prostate cancer (PC) where BRCA2 tends to be frequently deleted. Therefore, we hypothesize that mechanisms of resistance to PARPi in PC may involve alternative molecular mechanisms rather than a reversion mutation. Methods: We used human castration-resistant PC cell lines that harbor genomic deletions of BRCA2, PC-3 and LnCaP-Abl, and performed cell viability (MTT) assays to determine the inhibitory growth (IG) concentrations of these cell lines with talazoparib and olaparib. We cultured parental PC-3 cells in sublethal concentrations (IG 50% and IG 90%) of talazoparib-supplemented media to develop talazoparib-resistant cells. RNA sequencing followed by gene-set enrichment analysis (GSEA) of hallmark gene sets was performed on the talazoparib-resistant PC-3 cells to understand the underlying molecular mechanisms. Results: We observed that the talazoparib-resistant PC-3 cells exhibited significantly enhanced cell growth compared to parental cells when cultured in the IG 90% concentration of olaparib. However, interestingly, the talazoparib-resistant cells grew much slower in 2D compared to parental PC-3 cells when cultured in the PARPi-free media. Our transcriptomic analysis showed significant enrichment of various inflammatory response pathways, including TNF-α and IFNα/γ signaling pathways, in the talazoparib-resistant cells and even in the parental PC-3 cells transiently treated with talazoparib. Conclusion: We hypothesize that resistance to PARPi in PC may be related to upregulation of inflammatory signaling. Therefore, further exploration of TNF-α and IFNα/γ and their role in PARPi resistance mechanisms may lead to the identification of targets that allow for overcoming PARPi resistance in PC. Citation Format: Mohammad Atiq, Goutam Chakraborty, Subhiksha Nandakumar, Ying Z. Mazzu, Konrad Stopsack, Yuki Yoshikawa, Nabeela Khan, Gwo-Shu Mary Lee, Philip W. Kantoff. Mechanisms of resistance to poly (ADP-ribose) polymerase inhibitors in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 339.

Targeting checkpoint kinases in prostate cancer cells resistant to poly ADP-ribose polymerase inhibitors.

e16543 Background: The identification of DNA damage response (DDR) gene abnormalities in various cancers has provided potential therapeutic targets including the poly ADP-ribose polymerase enzyme (PARP). PARP inhibitors are now approved for use in ovarian, breast, and prostate cancer (PC). Olaparib and rucaparib have been given Breakthrough Therapy designation by the FDA for use in patients with metastatic castration-resistant prostate cancer and germline BRCA1/2 or ATM mutations. However, drug resistance limits the efficacy of PARPi. Somatic reversion mutations of BRCA1/2 have been described as one potential mechanism of resistance to PARPi in patients with germline BRCA1/2 mutations. However, in PC, the BRCA2 gene is frequently deleted, in contrast to other cancers, where it is mutated. Thus, we hypothesize that resistance to PARPi in PC may involve alternative molecular mechanisms. Methods: We performed cell viability assays to determine the inhibitory growth (IG) concentrations of olaparib and talazoparib on human castration-resistant PC cell lines (PC-3 and LNCaP-Abl) that have heterozygous genomic deletions of BRCA2. Parental PC-3 cells were cultured in sublethal concentrations (IG 50% and IG 90%) of talazoparib-supplemented media for approximately 2 months to develop talazoparib-resistant cells. We then performed an analysis of phosphorylation status in untreated and treated parental PC-3 and talazoparib-resistant clones with a phosphokinase array. We confirmed this with Western blot. Results: Talazoparib-resistant PC-3 clones showed significantly enhanced cell growth compared to parental cells when cultured in media supplemented with the IG 90% concentration of talazoparib or olaparib. The phosphokinase array revealed a significant increase in the phosphorylation of CHEK2 in talazoparib-resistant clones compared to parental PC-3 cells. Interestingly, a similar increase was seen after 72 hours of treatment with talazoparib, indicating an early connection between PARP inhibition and CHEK2 phosphorylation in PC cells. Moreover, a pan-CHEK inhibitor, prexasertib, led to significant cell growth inhibition in talazoparib-resistant PC-3 clones and a significantly lower IG 50% concentration compared to parental PC-3 cells. Conclusions: We speculate that early activation of CHEK2 may be a primary mechanism of resistance to PARPi in PC cells with deletion of BRCA2. Furthermore, our preliminary data showed that CHEK inhibition can overcome PARPi resistance, indicating a potential for CHEK inhibitor-based therapy for PC patients.

Cell signaling associated with internalization of 67 kDa laminin receptor (67LR) by soluble laminin and its implication for protection against neurodegenerative diseases.

Cell signaling associated with internalization of 67 kDa laminin receptor (67LR) by soluble laminin and its implication for protection against neurodegenerative diseases.

Arctigenin shows preferential cytotoxicity to acidity-tolerant prostate carcinoma PC-3 cells through ROS-mediated mitochondrial damage and the inhibition of PI3K/Akt/mTOR pathway

Extracellular acidity in the tumor microenvironment contributes to chemoresistance of malignant tumors. The objective of this study was to determine anticancer effects of arctigenin, a novel anti-inflammatory lignan extracted from seeds of Arctium lappa, on acidity-tolerant prostate cancer PC-3AcT cells. The PC-3AcT cells manifested increased tolerance to low-pH media with enhanced percent cell viability and increased resistance to docetaxel compared to their parental PC-3 cells. Arctigenin alone or in combination with docetaxel induced potent cytotoxicity. Preferential sensitization of PC-3AcT cells to arctigenin was accompanied by increased cell fractions with sub-G0/G1 peak and annexin V-PE(+), increased ROS levels, decreased mitochondrial membrane potential and cellular ATP content, and inhibition of PI3K/Akt/mTOR pathway. A series of changes caused by arctigenin were efficiently reversed through reducing ROS levels by radical scavenger N-acetylcysteine, thus placing ROS upstream of arctigenin-driven cytotoxicity. Collectively, these results demonstrate that arctigenin can increase oxidative stress-mediated mitochondrial damage of acidity-tolerant PC-3AcT cells, suggesting that arctigenin might be a potential therapeutic candidate to overcome acidic-microenvironment-associated chemotherapeutic resistance in prostate cancer.

Abstract 5896: Downregulation of calcium-sensing receptor enhances MET-mediated prostate cancer chemosensitivity

Abstract Chemoresistance, in various types of cancer including prostate cancer (PCa), is one of the major challenges in cancer therapy. Others and our lab have reported that the epithelial-to-mesenchymal transition (EMT) plays critical roles in development of chemoresistance and metastasis. The calcium-sensing receptor (CaSR) plays important roles in maintenance of calcium homeostasis and altered CaSR expression, and functional changes are involved in certain diseases, including tumorigenesis and its development. However, the mechanism of CaSR in PCa chemoresistance remains unclear. In current study, the CaSR expression level was detected in parental PC3 and DU145 cells and their chemoresistant PC3-TxR and DU145-TxR cells. We found the CaSR was highly expressed in chemoresistant PC3-TxR and DU145-TxR cells. Then by using siRNA technique, CaSR expression was transiently knocked down in chemoresistant cells. The tumor cell migration, invasion, and colony formation were evaluated by wound healing, transwell, and colony formation assays, respectively. The drug sensitivity was evaluated using MTS assay. We observed that the abilities of tumor cell migration and invasion were significantly diminished in CaSR knockdown PC3-TxR and DU145-TxR cells. The ability of colony formation was also reduced. Interestingly, the sensitivity to paclitaxel was reactivated in CaSR knockdown PC3-TxR and DU145-TxR cells. We finally observed that E-cadherin expression was increased in CaSR knockdown chemoresistant cells, and Snail, Vimentin and β-catenin were decreased; these results are consistent with EMT phenotypic alterations. Taken together, we conclude that downregulation of CaSR enhances MET-mediated prostate cancer chemosensitivity. Supported by NSFC Key Project 81130046; NSFC projects 81773146,81272415; JCYJ20170412152943794, JCYJ20170412154619484, JCYJ20170307105128101, JCYJ2017030711041760; Guangxi Key Projects 2013GXNSFEA053004. Citation Format: Luying Huang, Fuhao Wang, Haibo Tong, Atsushi Mizokami, Evan T. Keller, Yi Lu, Jian Zhang. Downregulation of calcium-sensing receptor enhances MET-mediated prostate cancer chemosensitivity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5896.