Identification of a novel prostate cancer-associated tumor antigen

Functional analysis of a novel glioma antigen, EFTUD1

BACKGROUND

A cDNA library made from 2 glioma cell lines, U87MG and T98G, was screened by serological identification of antigens by recombinant cDNA expression (SEREX) using serum from a glioblastoma patient. Elongation factor Tu GTP binding domain containing protein 1 (EFTUD1), which is required for ribosome biogenesis, was identified. A cancer microarray database showed overexpression of EFTUD1 in gliomas, suggesting that EFTUD1 is a candidate molecular target for gliomas.

METHODS

EFTUD1 expression in glioma cell lines and glioma tissue was assessed by Western blot, quantitative PCR, and immunohistochemistry. The effect on ribosome biogenesis, cell growth, cell cycle, and induction of apoptosis and autophagy in glioma cells during the downregulation of EFTUD1 was investigated. To reveal the role of autophagy, the autophagy-blocker, chloroquine (CQ), was used in glioma cells downregulating EFTUD1. The effect of combining CQ with EFTUD1 inhibition in glioma cells was analyzed.

RESULTS

EFTUD1 expression in glioma cell lines and tissue was higher than in normal brain tissue. Downregulating EFTUD1 induced G1 cell-cycle arrest and apoptosis, leading to reduced glioma cell proliferation. The mechanism underlying this antitumor effect was impaired ribosome biogenesis via EFTUD1 inhibition. Additionally, protective autophagy was induced by glioma cells as an adaptive response to EFTUD1 inhibition. The antitumor effect induced by the combined treatment was significantly higher than that of either EFTUD1 inhibition or CQ alone.

CONCLUSION

These results suggest that EFTUD1 represents a novel therapeutic target and that the combination of EFTUD1 inhibition with autophagy blockade may be effective in the treatment of gliomas.

Cancer/testis antigens and urological malignancies

Cancer/testis antigens (CTAs) are a group of tumour-associated antigens (TAAs) that display normal expression in the adult testis--an immune-privileged organ--but aberrant expression in several types of cancers, particularly in advanced cancers with stem cell-like characteristics. There has been an explosion in CTA-based research since CTAs were first identified in 1991 and MAGE-1 was shown to elicit an autologous cytotoxic T-lymphocyte (CTL) response in a patient with melanoma. The resulting data have not only highlighted a role for CTAs in tumorigenesis, but have also underscored the translational potential of these antigens for detecting and treating many types of cancers. Studies that have investigated the use of CTAs for the clinical management of urological malignancies indicate that these TAAs have potential roles as novel biomarkers, with increased specificity and sensitivity compared to those currently used in the clinic, and therapeutic targets for cancer immunotherapy. Increasing evidence supports the utilization of these promising tools for urological indications.

Identification of AKAP-4 as a new cancer/testis antigen for detection and immunotherapy of prostate cancer

BACKGROUND

Prostate cancer (PC) is the second most common cancer in older men, after skin cancer. PC is difficult to diagnose because the prostate-specific antigen screening method is associated with many false positives. In addition there is a need to develop new and more effective treatments. Among presently available new treatments, immunotherapy is a promising approach. We investigated the expression of the cancer/testis antigen, AKAP-4, in PC patients to evaluate the possibility of exploiting AKAP-4 as a target for immunotherapy.

METHODS

We analyzed normal prostate tissues, 15 patients with PC and the LnCAP PC cell line by immunohistochemistry. We tested AKAP-4 immunogenicity through indirect ELISA on sera from patients and healthy subjects, and we generated in vitro AKAP-4-specific cytotoxic lymphocytes from peripheral blood mononuclear cells.

RESULTS

AKAP-4 was shown both at the cytoplasmic and surface levels of the LnCAP PC cell line. AKAP-4 was also highly expressed in PC cells from patients. We detected specific anti-AKAP-4 circulating immunoglobulins in AKAP-4 positive subjects. Using recombinant AKAP-4 loaded autologous dendritic cells, we generated AKAP-4-specific and HLA-I-restricted cytotoxic T lymphocytes able to kill PC cells in vitro. Further characterization indicated a Th-1 skewing in the cytokine secretion profile of these cells.

CONCLUSIONS

We demonstrate the aberrant expression of AKAP-4 in PC, which will potentially be developed as a biomarker in PC. We provide evidence that AKAP-4 is a potential target for PC adoptive immunotherapy or anti-tumor vaccination.

Expression of the tumour antigen T21 is up-regulated in prostate cancer and is associated with tumour stage

OBJECTIVES

• To define the expression pattern of the tumour antigen T21 at the protein level in prostate tissues, prostate cell lines and a panel of normal tissues. • To correlate the expression pattern of T21 in prostate cancer with clinical parameters.

PATIENTS AND METHODS

• Tissue samples were collected from 79 patients presenting at clinic with either prostate cancer (63 patients) or benign prostatic hyperplasia (BPH, 16 patients). • A tissue microarray (TMA) was constructed from 44 of the prostate cancer tissues and areas of benign disease (43 patients) from these tissues were also included on the TMA. The remaining tissues (prostate cancer 19 patients and BPH 16 patients) were mounted fresh frozen onto cork boards and sectioned. • Full ethical approval was granted for all aspects of the study and informed patient consent was taken before tissue collection. • Immunohistochemistry was used on the prostate tumour TMA, the normal tissue TMA and the fresh-frozen prostate tissues. Fluorescent microscopy and flow cytometry was performed on prostate cell lines.

RESULTS

• Expression of T21 was highly restricted within normal tissues with only the stomach, ovary, breast and prostate having detectable T21 expression. • T21 was significantly over-expressed in prostate cancer glands compared with benign tissue and was present in >80% of the malignant specimens analysed. • Increased expression was positively correlated to pathological stage of prostate tumours. • Additionally, T21 was associated with Gleason grade and prostate-specific antigen recurrence, although statistical significance was not reached in this restricted cohort of patients.

CONCLUSION

• Taken together these results show that T21 is a potential new biomarker for advanced disease and that elevated levels of T21 appear relevant to prostate cancer development.

Immunotherapy of prostate cancer: should we be targeting stem cells and EMT?

Cancer stem cells have been implicated in a number of solid malignancies including prostate cancer. In the case of localised prostate cancer, patients are often treated with surgery (radical prostatectomy) and/or radiotherapy. However, disease recurrence is an issue in about 30% of patients, who will then go on to receive hormone ablation therapy. Hormone ablation therapy is often palliative in a vast proportion of individuals, and for hormone-refractory patients, there are several immunotherapies targeting a number of prostate tumour antigens which are currently in development. However, clinical responses in this setting are inconsistent, and it is believed that the failure to achieve full and permanent tumour eradication is due to a small, resistant population of cells known as 'cancer stem cells' (CSCs). The stochastic and clonal evolution models are among several models used to describe cancer development. The general consensus is that cancer may arise in any cell as a result of genetic mutations in oncogenes and tumour suppressor genes, which consequently result in uncontrolled cell growth. The cancer stem cell theory, however, challenges previous opinion and proposes that like normal tissues, tumours are hierarchical and only the rare subpopulation of cells at the top of the hierarchy possess the biological properties required to initiate tumourigenesis. Furthermore, where most cancer models infer that every cell within a tumour is equally malignant, i.e. equally capable of reconstituting new tumours, the cancer stem cell theory suggests that only the rare cancer stem cell component possess tumour-initiating capabilities. Hence, according to this model, cancer stem cells are implicated in both tumour initiation and progression. In recent years, the role of epithelial--mesenchymal transition (EMT) in the advancement of prostate cancer has become apparent. Therefore, CSCs and EMT are both likely to play critical roles in prostate cancer tumourigenesis. This review summarises the current immunotherapeutic strategies targeting prostate tumour antigens taking into account the need to consider treatments that target cancer stem cells and cells involved in epithelial--mesenchymal transition.

A viral vaccine encoding prostate-specific antigen induces antigen spreading to a common set of self-proteins in prostate cancer patients

PURPOSE

We previously reported a randomized phase II clinical trial combining a poxvirus-based vaccine encoding prostate-specific antigen (PSA) with radiotherapy in patients with localized prostate cancer. Here, we investigate whether vaccination against PSA induced immune responses to additional tumor-associated antigens and how this influenced clinical outcome.

EXPERIMENTAL DESIGN

Pretreatment and posttreatment serum samples from patients treated with vaccine + external beam radiation therapy (EBRT) versus EBRT alone were evaluated by Western blot and serologic screening of a prostate cancer cDNA expression library (SEREX) to assess the development of treatment-associated autoantibody responses.

RESULTS

Western blotting revealed treatment-associated autoantibody responses in 15 of 33 (45.5%) patients treated with vaccine + EBRT versus 1 of 8 (12.5%) treated with EBRT alone. SEREX screening identified 18 antigens, which were assembled on an antigen array with 16 previously identified antigens. Antigen array screening revealed that 7 of 33 patients (21.2%) treated with vaccine + EBRT showed a vaccine-associated autoantibody response to four ubiquitously expressed self-antigens: DIRC2, NDUFS1, MRFAP1, and MATN2. These responses were not seen in patients treated with EBRT alone, or other control groups. Patients with autoantibody responses to this panel of antigens had a trend toward decreased biochemical-free survival.

CONCLUSIONS

Vaccine + EBRT induced antigen spreading in a large proportion of patients. A subset of patients developed autoantibodies to a panel of four self-antigens and showed a trend toward inferior outcomes. Thus, cancer vaccines directed against tumor-specific antigens can trigger autoantibody responses to self-proteins, which may influence the efficacy of vaccination.

A novel plant homeodomain finger 10-mediated antiapoptotic mechanism involving repression of caspase-3 in gastric cancer cells

The mechanisms governing tumorigenesis of gastric cancer have been an area of intense investigation. Currently, plant homeodomain (PHD) finger (PHF) proteins have been implicated in both tumor suppression and progression. However, the function of PHF10 has not been well characterized. Here, we show that various levels of PHF10 protein were observed in gastric cancer cell lines. Alteration of PHF10 expression, which is associated with tumor cell growth, may result in apoptosis in gastric cancer cells both in vitro and in vivo. Knockdown of PHF10 expression in gastric cancer cells led to significant induction of caspase-3 expression at both the RNA and protein levels and thus induced alteration of caspase-3 substrates in a time-dependent manner. Moreover, results from luciferase assays indicated that PHF10 acted as a transcriptional repressor when the two PHD domains contained in PHF10 were intact. Combined with previous findings, our data suggest that PHF10 transcriptionally regulates the expression of caspase-3. Finally, by using systematic reporter deletion and chromatin immunoprecipitation assays, we localized a region between nucleotides -270 and -170 in the caspase-3 promoter that was required for the efficient inhibition of caspase-3 promoter activity by PHF10. Collectively, our findings show that PHF10 repressed caspase-3 expression and impaired the programmed cell death pathway in human gastric cancer at the transcriptional level.

Clinical proteomics: discovery of cancer biomarkers using mass spectrometry and bioinformatics approaches--a prostate cancer perspective

Prostate cancer (PCa) is an intractable disease, where diagnosis and clinical prediction of the disease course and response to treatment is compromised by the lack of objective and robust biomarker assays. In late stage metastatic disease, treatment options are limited, although it is recognized that some patients may benefit from immunotherapy and in particular vaccine therapy. However, research into biomarkers that correlate with the clinical outcome of immunotherapy has lagged behind vaccine development. Thus, proteomic tools are increasingly being utilized for the discovery of biomarkers which will allow us to make clinical decisions about patient treatment at an earlier stage and should aid in shortening the development time for vaccines. In this review we will summarize the various proteomic platforms used to investigate new biomarkers in PCa for better patient diagnosis, prognosis, patient stratification, treatment monitoring and clinical surrogate endpoints. We will discuss method limitations and highlight the key areas of research required for understanding the etiology of PCa.