The molecular pathogenesis of prostate cancer: focus on the earliest steps.
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DNA, Neoplasm↗
Biomedical subjects
W G Nelson
Publications and source records attributed to W G Nelson.
Relationships among total lipid, lipid classes, and polychlorinated biphenyl concentrations in two indigenous populations of ribbed mussels (Geukensia demissa) over an annual cycle.
Two indigenous ribbed mussel (Geukensia demissa) populations were sampled approximately every four weeks during 1997 to investigate the relationships among concentrations of total lipid, lipid classes, and polychlorinated biphenyls (PCBs). One population was located in a highly contaminated area near a Superfund site (New Bedford Harbor, MA, USA), while the other population was located at a relatively clean site (West Island, Fairhaven, MA, USA). Mussel tissue total PCB concentrations (quantified as the sum of 18 congeners) from the contaminated site were two orders of magnitude greater than those at the clean site. Total lipid and triacylglycerol (TG) also were higher at the contaminated site. No significant relationship (p > 0.05) was observed between total PCBs and total lipid at either location; however, the correlations at both sites increased when total PCBs were compared with total TG or, to a lesser extent, total nonpolar lipid. Principal component analysis and linear discriminatory analysis indicated that the two mussel populations could be distinguished by the proportions of their lipid classes, particularly the concentration of nonpolar lipids, which consisted mainly of TG. These results suggest that the standard method of normalizing organism PCB concentrations to total lipid may not be appropriate as a routine practice, especially when the organism has a relatively low total lipid content (<6% dry wt in this study).
Animals↗
Plasma selenium level before diagnosis and the risk of prostate cancer development.
PURPOSE: Epidemiological studies and a randomized intervention trial suggest that the risk of prostate cancer may be reduced by selenium intake. We investigated whether plasma selenium level before diagnosis correlated with the risk of later developing prostate cancer. MATERIALS AND METHODS: A case control study was performed on men from the Baltimore Longitudinal Study of Aging registry, including 52 with known prostate cancer and 96 age matched controls with no detectable prostatic disease. Plasma selenium was measured at an average time plus or minus standard deviation of 3.83 +/- 1.85 years before the diagnosis of prostate cancer by graphite furnace atomic absorption spectrophotometry. Adjusted odds ratio and 95% confidence interval were computed with logistic regression. RESULTS: After correcting for years before diagnosis, body mass index, and smoking and alcohol use history, higher selenium was associated with a lower risk of prostate cancer. Compared with the lowest quartile of selenium (range 8.2 to 10.7 microg./dl.), the odds ratios of the second (10.8 to 11.8), third (11.9 to 13.2) and fourth (13.3 to 18.2) quartiles were 0.15 (95% confidence interval 0.05 to 0.50), 0.21 (0.07 to 0.68) and 0.24 (0.08 to 0.77, respectively, p =0.01). Furthermore, plasma selenium decreased significantly with patient age (p <0.001). CONCLUSIONS: Low plasma selenium is associated with a 4 to 5-fold increased risk of prostate cancer. These results support the hypothesis that supplemental selenium may reduce the risk of prostate cancer. Because plasma selenium decreases with patient age, supplementation may be particularly beneficial to older men.
Aged↗
Cancer cells engineered to secrete granulocyte-macrophage colony-stimulating factor using ex vivo gene transfer as vaccines for the treatment of genitourinary malignancies.
When irradiated and administered intradermally as vaccines, cancer cells engineered to secrete high levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) by gene transfer elicit potent anticancer immune responses in a variety of animal tumor models. Upon vaccination, antigens present in the cancer cells are phagocytosed and processed by skin dendritic cells. These dendritic cells then prime anticancer immune responses by presenting antigenic peptides to T cells. The immune responses generated are capable of eradicating small but lethal cancer cell inocula with minimal toxicity in preclinical animal tumor studies. To develop this vaccination strategy for the treatment of human genitourinary cancers, we have conducted phase I clinical trials using human genitourinary cancer cells as sources of cancer cell antigens. In the first human clinical trial of genetically engineered cancer cell vaccines, a phase I clinical trial of kidney cancer cell vaccines (n = 18), kidney cancer cells were removed at surgery, propagated briefly in vitro, and then genetically modified to secrete high levels of GM-CSF via ex vivo transduction with the retrovirus MFG-GM-CSF. After irradiation, the kidney cancer cells were administered as vaccines to 18 patients with advanced kidney cancers. Vaccine treatment, which caused few side effects, nonetheless appeared to trigger anticancer immune responses manifest as conversion of delayed-type hypersensitivity (DTH) skin responses against irradiated autologous cancer cells after vaccination. Biopsies of vaccine sites yielded findings reminiscent of biopsies from preclinical animal model studies, with evidence of vaccine cell recruitment of dendritic cells, T cells, and eosinophils. One patient with measurable kidney cancer metastases treated at the highest vaccine dose level experienced a partial treatment response. The bioactivity of GM-CSF-secreting autologous cancer cell vaccines was confirmed in a phase I clinical trial for prostate cancer (n = 8). Vaccine cells were prepared from surgically harvested prostate tumors by ex vivo transduction with MFG-GM-CSF in a manner similar to that used for the kidney cancer trial. Vaccine treatment was well tolerated and associated with induction of anticancer immunity as assessed using DTH skin testing. In addition, new antiprostate cancer cell antibodies were detected in serum samples from treated men as a consequence of vaccination. These first clinical trials of GM-CSF-secreting cancer cell vaccines for the treatment of genitourinary cancers have demonstrated both safety and bioactivity, in that very few side effects have been seen and anticancer immune responses have been detected. Future clinical studies will be required to assess vaccine treatment efficacy, refine vaccination dose and schedule, define the appropriate clinical context for the use of such vaccines, and ascertain optimal combinations involving vaccines and other local or systemic anticancer treatments.
Adult↗
GSTP1 CpG island DNA hypermethylation in hepatocellular carcinomas.
Glutathione S-transferases, enzymes that defend cells against damage mediated by oxidant and electrophilic carcinogens, may be critical determinants of cancer pathogenesis. We report here that the pathogenesis of hepatocellular carcinoma (HCC), one of the most common cancers in the world, frequently involves an accumulation of somatic DNA methylation changes at GSTP1, the gene encoding the pi-class glutathione S-transferase. For our study, Hep3B HCC cells and a cohort of 20 HCC tissue specimens were subjected to analysis for GSTP1 expression and for somatic GSTP1 alterations. GSTP1 DNA hypermethylation in HCC DNA was assessed by Southern blot analysis, via a polymerase chain reaction (PCR) assay, and by using a genomic sequencing approach. Hep3B HCC cells failed to express GSTP1 mRNA or GSTP1 polypeptides. Similarly, HCC cells in 19 of 20 HCC cases were devoid of GSTP1 polypeptides. By Southern blot analysis, DNA from Hep3B HCC cells displayed abnormal GSTP1 hypermethylation. Treatment of Hep3B HCC cells in vitro with the DNA methyltransferase inhibitor 5-aza-deoxycytidine both reversed GSTP1 DNA hypermethylation and restored GSTP1 expression. Using a PCR assay, somatic GSTP1 DNA hypermethylation was also detected in HCC DNA from 17 of 20 HCC cases. Genomic sequencing analyses, undertaken to map 5-methyldeoxycytidine nucleotides located at the GSTP1 transcriptional regulatory region, frequently detected somatic DNA hypermethylation near the gene promoter in HCC DNA. The data indicate that GSTP1 DNA hypermethylation changes appear frequently in human HCC. In addition, the data raise the possibility that somatic GSTP1 inactivation, via hypermethylation, may contribute to the pathogenesis of HCC.
Adult↗
Doxorubicin-resistant variants of human prostate cancer cell lines DU 145, PC-3, PPC-1, and TSU-PR1: characterization of biochemical determinants of antineoplastic drug sensitivity.
Intrinsic and acquired antineoplastic drug resistance remain a major problem for advanced prostate cancer treatment. In order to characterize mechanisms of anti-neoplastic drug resistance in human prostate cancer cell lines, resistant sublines of four of the commonly studied prostate cancer cell lines (DU 145, PC-3, PPC-1, and TSU-PR1) were selected following exposure to increasing concentrations of doxorubicin (from 10-1000 nM). Sensitivity patterns of the parent and doxorubicin-resistant sublines to various anti-neoplastic drugs, including adriamycin, amsacrine, etoposide, camptothecin, vinblastine, vincristine, fluorodeoxyuridine, and melphalan, were determined using a sulforhodamine B growth inhibition assay. The expression of three well-described antineoplastic drug resistance proteins, P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), and lung resistance protein (LRP), was assessed using reverse transcriptase-polymerase chain reaction (RT-PCR) assays specific for each of the mRNA species, and using immunocytochemical staining procedures specific for each of the polypeptides. All four of the doxorubicin-selected prostate cancer cell lines exhibited a multidrug resistance phenotype; administration of verapamil restored doxorubicin sensitivity for each of the drug resistant sublines. Although significant MDR1 expression was not detected in any of the parent cell lines before drug exposure by RT-PCR analysis or by immunocytochemistry, both MDR1 mRNA and P-gp protein were expressed by the TSU-PR1 Adr 1000 subline. In contrast, MRP mRNA and protein were present in each of the prostate cancer cell lines before doxorubicin-selection, and an increase in MRP expression appeared to accompany the acquisition of drug resistance in DU 145, PC-3, and PPC-1 doxorubicin-resistant sublines. LRP was variably expressed by each of the parent and resistant cell lines. These data suggest that drug resistance in human prostate cancer may be multifactorial, with MRP and LRP frequently expressed in prostate cancer cells before antineoplastic drug treatment and P-gp expression occasionally acquired after drug exposure.
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Methylation of the neutral endopeptidase gene promoter in human prostate cancers.
Neutral endopeptidase 24.11 (NEP) is a cell surface peptidase expressed by prostatic epithelial cells that cleaves and inactivates neuropeptide growth factors implicated in the growth of androgen-independent prostate cancer (PC). Decreased NEP expression in hormone-refractory metastatic PCs can result from hormonal therapies because NEP transcription is induced by androgens and down-regulated by androgen withdrawal. NEP is encoded by a gene that contains a 5' CpG island spanning a transcriptional regulatory region. In this study, we investigate whether DNA hypermethylation of the NEP promoter accompanies decreased NEP expression in PC cell lines and whether it occurs in human PC tissues in vivo. DNA isolated from PC cell lines and from normal and neoplastic human prostate tissues was restriction-digested with a methylation-sensitive restriction endonuclease and analyzed by Southern blot using a 5' sequence-specific NEP probe. Methylation-specific PCR was performed using PCR primers designed to discriminate between methylated and unmethylated alleles, and reverse transcription-PCR using NEP-specific primers was performed on cDNA extracted from PC cells treated with 5-aza-2'-deoxycytidine. Methylation of the NEP promoter was present in androgen-independent PC cell lines but not in androgen-dependent or small-cell derived PC cell lines and in 3 of 21 (14%) primary PCs from patients with androgen-dependent disease. Exposure of PC cells to the demethylating agent 5-aza-2'-deoxycytidine led to an increase in NEP transcripts in DU-145 and PC-3 cells. These data show that hypermethylation of the 5' CpG NEP island is associated with a loss of NEP expression in PC. Loss of NEP expression via hypermethylation of the NEP promoter may contribute to the development of neuropeptide-stimulated PCs.
Azacitidine↗
No association between the I105V polymorphism of the glutathione S-transferase P1 gene (GSTP1) and prostate cancer risk: a prospective study.
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Case-Control Studies↗
Expression of DNA methyl-transferase (DMT) and the cell cycle in human breast cancer cells.
Estrogen receptor (ER)-negative breast cancer cells display extensive methylation of the ER gene CpG island and elevated DNA methyltransferase (DMT) expression compared to ER-positive cells. The present study demonstrates that DMT protein levels tightly correlate with S phase fraction in ER-positive cells, whereas ER-negative cells express DMT throughout the cell cycle. In addition, levels of p21CIP1, which disrupts DMT binding to PCNA, are inversely correlated with DMT levels. Therefore increased DMT expression in ER-negative cells is not simply due to elevated S-phase fraction, but rather to more complex changes that allow cells to escape normal cell cycle-dependent controls on DMT expression. Because ER-negative breast tumors often have activated growth factor pathways, the impact of these pathways on DMT expression was examined in ER-positive cells. Stable transfection with fibroblast growth factors (FGFs) 1 and 4 led to increased DMT expression that could not be accounted for by a shift in S phase fraction. Elevated DMT protein expression in FGF-transfectants was accompanied by a significant decrease in p21, again suggesting a reciprocal relationship between these two proteins. However, acquisition of an estrogen-independent phenotype, even in conjunction with elevated DMT levels, was not sufficient to promote ER gene silencing via methylation. These results indicate that multiple steps are required for de novo methylation of the ER CpG island.
Amino Acid Sequence↗
Induction of immunity to prostate cancer antigens: results of a clinical trial of vaccination with irradiated autologous prostate tumor cells engineered to secrete granulocyte-macrophage colony-stimulating factor using ex vivo gene transfer.
Vaccination with irradiated granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting gene-transduced cancer vaccines induces tumoricidal immune responses. In a Phase I human gene therapy trial, eight immunocompetent prostate cancer (PCA) patients were treated with autologous, GM-CSF-secreting, irradiated tumor vaccines prepared from ex vivo retroviral transduction of surgically harvested cells. Expansion of primary cultures of autologous vaccine cells was successful to meet trial specifications in 8 of 11 cases (73%); the yields of the primary culture cell limited the number of courses of vaccination. Side effects were pruritus, erythema, and swelling at vaccination sites. Vaccine site biopsies manifested infiltrates of dendritic cells and macrophages among prostate tumor vaccine cells. Vaccination activated new T-cell and B-cell immune responses against PCA antigens. T-cell responses, evaluated by assessing delayed-type hypersensitivity (DTH) reactions against untransduced autologous tumor cells, were evident in two of eight patients before vaccination and in seven of eight patients after treatment. Reactive DTH site biopsies manifested infiltrates of effector cells consisting of CD45RO+ T-cells, and degranulating eosinophils consistent with activation of both Th1 and Th2 T-cell responses. A distinctive eosinophilic vasculitis was evident near autologous tumor cells at vaccine sites, and at DTH sites. B-cell responses were also induced. Sera from three of eight vaccinated men contained new antibodies recognizing polypeptides of 26, 31, and 150 kDa in protein extracts from prostate cells. The 150-kDa polypeptide was expressed by LNCaP and PC-3 PCA cells, as well as by normal prostate epithelial cells, but not by prostate stromal cells. No antibodies against prostate-specific antigen were detected. These data suggest that both T-cell and B-cell immune responses to human PCA can be generated by treatment with irradiated, GM-CSF gene-transduced PCA vaccines.
Antigens, Neoplasm↗
Abnormal regulation of DNA methyltransferase expression during colorectal carcinogenesis.
Somatic changes in CpG dinucleotide methylation occur quite commonly in human cancer cell DNA. Relative to DNA from normal human colonic cells, DNA from human colorectal cancer cells typically displays regional CpG dinucleotide hypermethylation amid global CpG dinucleotide hypomethylation. The role of the maintenance DNA methyltransferase (DNMT1) in the acquisition of such abnormal CpG dinucleotide methylation changes in colorectal cancer cells remains controversial; in one study, 60-200-fold increases in DNMT1 mRNA expression were detected in colorectal polyps and cancers relative to normal colonic tissue [W. S. El-Deiry et al., Proc. Natl. Acad. Sci. USA, 88: 3470-3474, 1991], whereas in another study, only small increases in DNMT1 mRNA expression, commensurate with differences in cell proliferation accompanying colonic tumorigenesis, were observed [P. J. Lee et al., Proc. Natl. Acad. Sci. USA, 93: 10366-10370, 1996]. To definitively ascertain whether abnormal DNMT1 expression might accompany human colorectal carcinogenesis, we subjected a series of normal and neoplastic colonic tissues to immunohistochemical staining using a polyclonal antiserum raised against a DNMT1 polypeptide. A concordance of DNMT1 expression with the expression of PCNA and other cell proliferation markers, such as Ki-67 and DNA topoisomerase IIalpha, was observed in normal colonic epithelial cells and in cells comprising other normal epithelia and lymphoid tissues. The polypeptide p21, which has been reported to undermine DNMT1 binding to proliferating cell nuclear antigen at DNA replication sites, was not expressed by normal colonic cells containing DNMT1 and other cell proliferation markers. In adenomatous polyps, although DNMT1 expression coincided with the expression of other cell proliferation markers, many DNMT1-expressing cells also expressed p21. The fidelity of DNMT1 expression was further undermined in colorectal carcinomas, in which a striking heterogeneity in DNMT1 expression, with some carcinoma cells containing very high DNMT1 levels and others containing very low DNMT1 levels, was observed. These results indicate that human colorectal carcinogenesis is accompanied by a progressive dysregulation of DNMT1 expression and suggest that abnormalities in DNMT1 expression may contribute to the abnormal CpG dinucleotide methylation changes characteristic of human colorectal carcinoma cell DNA.
Colon↗
Proliferative inflammatory atrophy of the prostate: implications for prostatic carcinogenesis.
Proliferation in the setting of longstanding chronic inflammation appears to predispose to carcinoma in the liver, large bowel, urinary bladder, and gastric mucosa. Focal prostatic atrophy, which is associated with chronic inflammation, is highly proliferative (Ruska et al, Am J Surg Pathol 1998, 22:1073-1077); thus the focus of this study was to more fully characterize the phenotype of the atrophic cells to assess the feasibility of the proposal that they may be targets of neoplastic transformation. The pi-class glutathione S-transferase (GSTP1), a carcinogen-detoxifying enzyme, is not expressed in >90% of prostate carcinomas (CaPs). GSTP1 promoter hypermethylation, which appears to permanently silence transcription, is the most frequently detected genomic alteration in CaP (Lee et al, Proc Natl Acad Sci USA 1994, 91:11733-11737; >90% of cases). In high-grade prostatic intraepithelial neoplasia (PIN), this alteration is present in at least 70% of cases (Brooks et al, Cancer Epidemiol Biomarkers Prev, 1998, 7:531-536). Although normal-appearing prostate secretory cells rarely express GSTP1, they remain capable of expression, inasmuch as GSTP1 promoter hypermethylation is not detected in normal prostate. Fifty-five lesions from paraffin-embedded prostatectomy specimens (n = 42) were stained for GSTP1, using immunohistochemistry. Adjacent sections were stained for p27(Kip1), Ki-67, androgen receptor (AR), prostate-specific antigen (PSA), prostate-specific acid phosphatase (PSAP), Bcl-2, and basal cell-specific cytokeratins (34betaE12). With normal prostate epithelium as the internal standard, staining was scored for each marker in the atrophic epithelium. The lesions showed two cell types, basal cells staining positive for 34betaE12, and atrophic secretory-type cells staining weakly negative for 34betaE12. All lesions showed elevated levels of Bcl-2 in many of the secretory-type cells. All lesions had an elevated staining index for the proliferation marker Ki-67 in the secretory layer and decreased expression of p27(Kip1), a finding reminiscent of high-grade PIN (De Marzo et al, Am J Pathol 1998, 153:911-919). Consistent with partial secretory cell differentiation, the luminal cells showed weak to moderate staining for androgen receptor and the secretory proteins PSA and PSAP. All atrophic lesions showed elevated GSTP1 expression in many of the luminal secretory-type cells. Because all lesions are hyperproliferative, are associated with inflammation, and have the distinct morphological appearance recognized as prostatic atrophy, we suggest the term "proliferative inflammatory atrophy" (PIA). Elevated levels of GSTP1 may reflect its inducible nature in secretory cells, possibly in response to increased electrophile or oxidant stress. Elevated Bcl-2 expression may be responsible for the very low apoptotic rate in PIA and is consistent with the conclusion that PIA is a regenerative lesion. We discuss our proposal to integrate the atrophy and high-grade PIN hypotheses of prostate carcinogenesis by suggesting that atrophy may give rise to carcinoma either directly, as previously postulated, or indirectly by first developing into high-grade PIN.
Apoptosis↗
New concepts in tissue specificity for prostate cancer and benign prostatic hyperplasia.
Of the hundreds of species of mammals, all of which have prostate glands, only humans and dogs are known to suffer from benign prostatic hyperplasia (BPH) and prostate carcinoma. In humans, prostate carcinoma is common, yet carcinomas of other sex accessory tissues are rare. In addition, different anatomic regions within the prostate gland have very different rates of BPH and carcinoma. In this article, we explore ideas and potential mechanisms relating to these paradoxical findings that may help explain the species, organ, and zone specificity of BPH and prostate cancer. We present an evolutionary argument that attempts to relate a high-fat diet, with its potential for generating oxidative DNA damage, to the species selectivity of prostate cancer. In addition, we outline an argument based on our preliminary studies indicating that chronic inflammation and the associated increase in cell turnover in the setting of increased oxidative stress may help to account for the organ selectivity of genitourinary carcinomas.
Animals↗
Prostate cancer vaccines: current status.
Recent insights into cell-mediated immunotherapy have led to a wave of new trials involving immunotherapy for prostate cancer. Vaccines have evolved from nonspecific immune stimulants like Bacillus Calmette-Guerin (BCG) to much more specific and potent strategies. Techniques currently being investigated include passive immunotherapy with monoclonal antibodies, adoptive transfer of activated effector T cells, and active immunotherapy involving immunization with whole-cell or antigen-specific vaccines. These therapies are being modified with cytokines and other immune modulating agents. Understanding the mechanisms of antitumor immunity and identifying relevant tumor-specific antigens will likely improve these vaccine strategies and provide them with a niche in the future of prostate cancer therapy.
Adjuvants, Immunologic↗
Mouse embryonic stem cells carrying one or two defective Msh2 alleles respond abnormally to oxidative stress inflicted by low-level radiation.
Chronic oxidative stress may play a critical role in the pathogenesis of many human cancers. Here, we report that mouse embryonic stem (ES) cells deficient in DNA mismatch repair responded abnormally when exposed to low levels of ionizing radiation, a stress known to generate oxidative DNA damage. ES cells derived from mice carrying either one or two disrupted Msh2 alleles displayed an increased survival following protracted exposures to low-level ionizing radiation as compared with wild-type ES cells. The increases in survival exhibited by ES cells deficient in DNA mismatch repair appeared to have resulted from a failure to efficiently execute cell death (apoptosis) in response to radiation exposure. For each of the ES cell types, prolonged low-level radiation treatment generated oxidative genome damage that manifested as an accumulation of oxidized bases in genomic DNA. However, ES cells from Msh2(+/-) and Msh2(-/-) mice accumulated more oxidized bases as a consequence of low-level radiation exposure than ES cells from Msh2(+/+) mice. The propensity for normal cells with mismatch repair enzyme deficiencies, including cells heterozygous for inactivating mismatch repair enzyme gene mutations, to survive promutagenic genome insults accompanying oxidative stresses may contribute to the increased cancer risk characteristic of the hereditary nonpolyposis colorectal cancer syndrome.
Alleles↗
CD4+ T cell tolerance to parenchymal self-antigens requires presentation by bone marrow-derived antigen-presenting cells.
T cell tolerance to parenchymal self-antigens is thought to be induced by encounter of the T cell with its cognate peptide-major histocompatibility complex (MHC) ligand expressed on the parenchymal cell, which lacks appropriate costimulatory function. We have used a model system in which naive T cell receptor (TCR) transgenic hemagglutinin (HA)-specific CD4+ T cells are adoptively transferred into mice expressing HA as a self-antigen on parenchymal cells. After transfer, HA-specific T cells develop a phenotype indicative of TCR engagement and are rendered functionally tolerant. However, T cell tolerance is not induced by peptide-MHC complexes expressed on parenchymal cells. Rather, tolerance induction requires that HA is presented by bone marrow (BM)-derived cells. These results indicate that tolerance induction to parenchymal self-antigens requires transfer to a BM-derived antigen-presenting cell that presents it to T cells in a tolerogenic fashion.
Animals↗
Sensitivity of human prostatic carcinoma cell lines to low dose rate radiation exposure.
PURPOSE: Low dose rate radioemitters, such as 125I, 103Pd, and 89Sr, have been used both for local and systemic treatment of prostate cancer. Most normal cells exposed to ionizing radiation characteristically activate cell cycle checkpoints, resulting in cell cycle arrest at the G1/S and G2/M transition points. Cancer cells are typically quite sensitive to radiation killing late in the G2 phase of the replicative cell cycle. Furthermore, most cancer cells accumulating at the G2/M transition point as a result of low dose rate radiation exposure appear to become sensitive to further low dose rate irradiation. For this reason, protracted exposure of cancer cells to low dose rate radiation has been proposed to result in increased cancer cell killing as compared with brief exposures of cancer cells to high dose rate radiation. Since many human prostatic carcinomas contain somatic genome alterations targeting genes which affect the cell cycle and radiation-associated cell cycle checkpoints, we evaluated the effects of low dose rate radiation exposure on the cell cycle and on clonogenic survival for various human prostatic carcinoma cell lines. MATERIALS AND METHODS: Human prostatic carcinoma cells from the LNCaP, DU 145, PC-3, PPC-1, and TSU-Pr1 cell lines were exposed to low dose rate (0.25 Gy/hour) or high dose rate (60 Gy/hour) radiation in vitro and then assessed for radiation cytotoxicity by clonogenic survival assay. Cell cycle perturbations following protracted exposure to low dose rate radiation were evaluated using flow cytometry. RESULTS: For LNCaP cells, low dose rate radiation exposure resulted in an accumulation of cells at both the G1/S and the G2/M cell cycle transition points. For DU 145, PC-3, PPC-1, and TSU-Pr1 cells, treatment with low dose rate radiation triggered G2/M cell cycle arrest, but not G1/S arrest. Unexpectedly, the cell cycle redistribution pattern phenotypes observed, G1/S and G2/M cell cycle arrest versus G2/M arrest alone, appeared to have little effect on low dose rate radiation survival. Furthermore, while PC-3, PPC-1, and TSU-Pr1 cells exhibited increased cytotoxic sensitivity to low dose rate versus fractionated high dose rate radiation treatment, DU 145 and LNCaP cells did not. CONCLUSIONS: Radiation-associated pertubations in replicative cell cycle progression were not dominant determinants of low dose rate radiation killing efficacy in human prostate cancer cell lines in vitro.
Humans↗
Serum vascular endothelial growth factor is a candidate biomarker of metastatic tumor response to ex vivo gene therapy of renal cell cancer.
We report the close correlation between changes in serum immunoreactive vascular endothelial growth factor 165 (iVEGF165) levels and metastatic tumor burden measured by computed tomography scan before treatment, during the antitumor response, and during early progression in a patient treated with ex vivo gene therapy for renal cell carcinoma. With the researcher blinded to outcome, iVEGF levels were measured in archived serum samples from a patient with metastatic renal cell carcinoma who demonstrated a 7-month partial remission to treatment with autologous, irradiated human GM-CSF gene transduced tumor vaccine. Although a spontaneous regression could not be formally excluded in this patient, the appearance of 20 new pulmonary metastases on computed tomography scan after nephrectomy and before vaccination indicates that if spontaneous regression occurred, it took place at the start of vaccine treatment.
Biomarkers, Tumor↗