Efficient transfer of PSA and PSMA cDNAs into DCs generates antibody and T cell antitumor responses in vivo

Development of Spherical Nucleic Acids for Prostate Cancer Immunotherapy

Although the strategy of therapeutic vaccination for the treatment of prostate cancer has advanced to and is available in the clinic (Sipuleucel-T), the efficacy of such therapy remains limited. Here, we develop Immunostimulatory Spherical Nucleic Acid (IS-SNA) nanostructures comprised of CpG oligonucleotides as adjuvant and prostate cancer peptide antigens, and evaluate their antitumor efficacy in syngeneic mouse models of prostate cancer. IS-SNAs with the specific structural feature of presenting both antigen and adjuvant CpG on the surface (hybridized model (HM) SNAs) induce stronger cytotoxic T lymphocyte (CTL) mediated antigen-specific killing of target cells than that for IS-SNAs with CpG on the surface and antigen encapsulated within the core (encapsulated model (EM) SNAs). Mechanistically, HM SNAs increase the co-delivery of CpG and antigen to dendritic cells over that for EM SNAs or admixtures of linear CpG and peptide, thereby improving cross-priming of antitumor CD8⁺ T cells. As a result, vaccination with HM SNAs leads to more effective antitumor immune responses in two prostate cancer models. These data demonstrate the importance of the structural positioning of peptide antigens together with adjuvants within IS-SNAs to the efficacy of IS-SNA-based cancer immunotherapy.

Direct Lymph Node Vaccination of Lentivector/Prostate-Specific Antigen is Safe and Generates Tissue-Specific Responses in Rhesus Macaques

Anti-cancer immunotherapy is emerging from a nadir and demonstrating tangible benefits to patients. A variety of approaches are now employed. We are invoking antigen (Ag)-specific responses through direct injections of recombinant lentivectors (LVs) that encode sequences for tumor-associated antigens into multiple lymph nodes to optimize immune presentation/stimulation. Here we first demonstrate the effectiveness and antigen-specificity of this approach in mice challenged with prostate-specific antigen (PSA)-expressing tumor cells. Next we tested the safety and efficacy of this approach in two cohorts of rhesus macaques as a prelude to a clinical trial application. Our vector encodes the cDNA for rhesus macaque PSA and a rhesus macaque cell surface marker to facilitate vector titering and tracking. We utilized two independent injection schemas demarcated by the timing of LV administration. In both cohorts we observed marked tissue-specific responses as measured by clinical evaluations and magnetic resonance imaging of the prostate gland. Tissue-specific responses were sustained for up to six months-the end-point of the study. Control animals immunized against an irrelevant Ag were unaffected. We did not observe vector spread in test or control animals or perturbations of systemic immune parameters. This approach thus offers an "off-the-shelf" anti-cancer vaccine that could be made at large scale and injected into patients-even on an out-patient basis.

Anti-tumor effect of the alphavirus-based virus-like particle vector expressing prostate-specific antigen in a HLA-DR transgenic mouse model of prostate cancer

The goal of this study was to determine if an alphavirus-based vaccine encoding human Prostate-Specific Antigen (PSA) could generate an effective anti-tumor immune response in a stringent mouse model of prostate cancer. DR2bxPSA F1 male mice expressing human PSA and HLA-DRB1(*)1501 transgenes were vaccinated with virus-like particle vector encoding PSA (VLPV-PSA) followed by the challenge with Transgenic Adenocarcinoma of Mouse Prostate cells engineered to express PSA (TRAMP-PSA). PSA-specific cellular and humoral immune responses were measured before and after tumor challenge. PSA and CD8 reactivity in the tumors was detected by immunohistochemistry. Tumor growth was compared in vaccinated and control groups. We found that VLPV-PSA could infect mouse dendritic cells in vitro and induce a robust PSA-specific immune response in vivo. A substantial proportion of splenic CD8 T cells (19.6 ± 7.4%) produced IFNγ in response to the immunodominant peptide PSA(65-73). In the blood of vaccinated mice, 18.4 ± 4.1% of CD8 T cells were PSA-specific as determined by the staining with H-2D(b)/PSA(65-73) dextramers. VLPV-PSA vaccination also strongly stimulated production of IgG2a/b anti-PSA antibodies. Tumors in vaccinated mice showed low levels of PSA expression and significant CD8+ T cell infiltration. Tumor growth in VLPV-PSA vaccinated mice was significantly delayed at early time points (p=0.002, Gehan-Breslow test). Our data suggest that TC-83-based VLPV-PSA vaccine can efficiently overcome immune tolerance to PSA, mediate rapid clearance of PSA-expressing tumor cells and delay tumor growth. The VLPV-PSA vaccine will undergo further testing for the immunotherapy of prostate cancer.

Immunostimulatory early phenotype of tumor-associated macrophages does not predict tumor growth outcome in an HLA-DR mouse model of prostate cancer

Tumor-associated macrophages (TAM) were shown to support the progression of many solid tumors. However, anti-tumor properties of TAM were also reported in several types of cancer. Here, we investigated the phenotype and functions of TAM in two transgenic mouse models of prostate cancer that display striking differences in tumor growth outcome. Mice expressing prostate-specific antigen (PSA) as a self-antigen specifically in prostate (PSAtg mice) rejected PSA-expressing transgenic adenocarcinoma of mouse prostate (TRAMP) tumors. However, the introduction of HLA-DRB1*1501 (DR2b) transgene presenting PSA-derived peptides in a MHC class II-restricted manner exacerbated the growth of TRAMP-PSA tumors in DR2bxPSA F 1 mice. Despite the difference in tumor growth outcome, tumors in both strains were equally and intensively infiltrated by macrophages on the first week after tumor challenge. TAM exhibited mixed M1/M2 polarization and simultaneously produced pro-inflammatory (TNFα, IL1β) and anti-inflammatory (IL10) cytokines. TAM from both mouse strains demonstrated antigen-presenting potential and pronounced immunostimulatory activity. Moreover, they equally induced apoptosis of tumor cells. In vivo depletion of macrophages in DR2bxPSA F 1 but not PSAtg mice aggravated tumor growth suggesting that macrophages more strongly contribute to anti-tumor immunity when specific presentation of PSA to CD4+ T cells is possible. In summary, we conclude that in the early stages of tumor progression, the phenotype and functional properties of TAM did not predict tumor growth outcome in two transgenic prostate cancer models. Furthermore, we demonstrated that during the initial stage of prostate cancer development, TAM have the potential to activate T cell immunity and mediate anti-tumor effects.

Cancer immunotherapy using virally transduced dendritic cells: animal studies and human clinical trials

The immune system uses a process known as 'immunosurveillance' to help prevent the outgrowth of tumors. In cancer immunotherapy, a major goal is for immunity against tumor-associated antigens to be generated or strengthened in patients. To achieve this goal, several approaches have been tested, including the use of highly potent antigen-presenting cells called dendritic cells (DCs), which can activate T cells efficiently. Presentation of peptides derived from tumor antigens on the surface of DCs can stimulate strong antitumor immunity. Using recombinant viral vectors encoding tumor-associated antigens, DCs can be engineered efficiently to express sustained levels of tumor-antigen peptides. This review discusses the effectiveness of virally transduced DCs in treating tumors and generating antigen-specific T-cell responses. It covers mouse and nonhuman primate studies, preclinical in vitro human cell experiments and clinical trials.

A cytomegalovirus-based vaccine expressing a single tumor-specific CD8+ T-cell epitope delays tumor growth in a murine model of prostate cancer

Cytomegalovirus (CMV) is a highly immunogenic virus that results in a persistent, life-long infection in the host typically with no ill effects. Certain unique features of CMV, including its capacity to actively replicate in the presence of strong host CMV-specific immunity, may give CMV an advantage compared with other virus-based vaccine delivery platforms. In the present study, we tested the utility of mouse CMV (mCMV)-based vaccines expressing human prostate-specific antigen (PSA) for prostate cancer immunotherapy in double-transgenic mice expressing PSA and HLA-DRB1*1501 (DR2bxPSA F1 mice). We assessed the capacity of 2 mCMV-based vectors to induce PSA-specific CD8 T-cell responses and affect the growth of PSA-expressing Transgenic Adenocarcinoma of the Mouse Prostate tumors (TRAMP-PSA). In the absence of tumor challenge, immunization with mCMV vectors expressing either a H2-D(b)-restricted epitope PSA(65-73) (mCMV/PSA(65-73)) or the full-length gene for PSA (mCMV/PSA(FL)) induced comparable levels of CD8 T-cell responses that increased (inflated) with time. Upon challenge with TRAMP-PSA tumor cells, animals immunized with mCMV/PSA(65-73) had delay of tumor growth and increased PSA-specific CD8 T-cell responses, whereas animals immunized with mCMV/PSA(FL) showed progressive tumor growth and no increase in number of splenic PSA(65-73)-specific T cells. The data show that a prototype CMV-based prostate cancer vaccine can induce an effective antitumor immune response in a "humanized" double-transgenic mouse model. The observation that mCMV/PSA(FL) is not effective against TRAMP-PSA is consistent with our previous findings that HLA-DRB1*1501-restricted immune responses to PSA are associated with suppression of effective CD8 T-cell responses to TRAMP-PSA tumors.

Cancer immunotherapy: a paradigm shift for prostate cancer treatment

Prostate cancer remains a significant health problem for men in the Western world. Although treatment modalities are available, these do not confer long-term benefit and are accompanied by deleterious side effects. Immunotherapy represents a valuable alternative to conventional treatments by inducing tumour-specific immune responses that control the growth of cancer cells. Sipuleucel-T is approved by the FDA as an immunotherapeutic agent for the treatment of patients with asymptomatic or minimally symptomatic castration-resistant prostate cancer (CRPC). Although this approval has raised cost-versus-benefit issues, it has provided proof of concept for the therapeutic potential of active immunotherapy approaches for metastatic CRPC. Numerous clinical studies have demonstrated clinical benefit using immunotherapy compared to traditional chemotherapy and several active immunotherapy approaches (at various developmental stages)have demonstrated the potential to change the face of prostate cancer treatment.

Dual antigen target-based immunotherapy for prostate cancer eliminates the growth of established tumors in mice

AIMS

We have previously shown that immunization with an adenovirus vector carrying an individual antigen induces antigen-specific CD8 T cells actively engaged in the destruction of tumor cells expressing the cognate antigen. In order to expand the range of antitumor responses beyond an individual antigen, we designed a recombinant adenovirus type 5 (rAd5) carrying a fusion construct of two full-length antigens. We used this adenovirus vector to test the concept that multiantigenic effector T cells could be generated simultaneously following a single immunization.

METHOD

To perform the rAd5 constructs, we selected a combination of prostate-specific antigen (PSA) and prostate stem cell antigen (PSCA) genes based on their restricted distribution within the prostate tissue and their association with the development and progression of prostate cancer.

RESULTS

Immunization of mice with rAd5 vector carrying a fusion construct of PSA and PSCA (Ad5-PSA/PSCA) simultaneously induced the expansion of anti-PSA and anti-PSCA CD8 T cells, as measured by intracellular cytokine staining for IFN-γ. The antigen-specific T-cell responses that developed were efficient in eliminating the target cells expressing cognate antigens measured by an in vivo cytotoxic T-cell assay. The in vivo tumor growth study showed that immunization of mice with Ad5-PSA/PSCA vaccine induced strong antitumor immunity when challenged with mouse prostate tumor cell lines (RM11) expressing human PSA (RM11/PSA). To further analyze the impact on therapeutic efficacy of Ad5-PSA/PSCA vaccine against the tumor cells expressing PSA and PSCA (RM11-PSA/PSCA) antigens, we injected mice with Ad5-PSA/PSCA vaccine. The vaccine inhibited the growth of established tumors with 80% of the mice becoming tumor free. These data provide useful information that antigen-specific effector T cells can be generated simultaneously and that their additive antitumor effect has the potential to eliminate the growth of established tumors. Therefore, the immunotherapy approach of using the simultaneous targeting of dual antigens associated with prostate cancer may have important implications for human clinical trials.

An artificial PAP gene breaks self-tolerance and promotes tumor regression in the TRAMP model for prostate carcinoma

Prostate cancer (PCa) is the most commonly diagnosed type of cancer in men in western industrialized countries. As a public health burden, the need for the invention of new cost-saving PCa immunotherapies is apparent. In this study, we present a DNA vaccine encoding for the prostate-specific antigen prostatic acid phosphatase (PAP) linked to the J-domain and the SV40 enhancer sequence. The PAP DNA vaccine induced a strong PAP-specific cellular immune response after electroporation (EP)-based delivery in C57BL/6 mice. Splenocytes from mice immunized with PAP recognized the naturally processed PAP epitopes, indicating that vaccination with the PAP-J gene broke its self-tolerance against PAP. Remarkably, DNA vaccination with PAP-J inhibited tumor growth in the Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) mouse model that closely resembled human PCa. Therefore, this study highlights a novel cancer immunotherapy approach with the potential to control PCa in clinical settings.

Gene therapy for prostate cancer

Cancer remains a leading cause of morbidity and mortality. Despite advances in understanding, detection, and treatment, it accounts for almost one-fourth of all deaths per year in Western countries. Prostate cancer is currently the most commonly diagnosed noncutaneous cancer in men in Europe and the United States, accounting for 15% of all cancers in men. As life expectancy of individuals increases, it is expected that there will also be an increase in the incidence and mortality of prostate cancer. Prostate cancer may be inoperable at initial presentation, unresponsive to chemotherapy and radiotherapy, or recur following appropriate treatment. At the time of presentation, patients may already have metastases in their tissues. Preventing tumor recurrence requires systemic therapy; however, current modalities are limited by toxicity or lack of efficacy. For patients with such metastatic cancers, the development of alternative therapies is essential. Gene therapy is a realistic prospect for the treatment of prostate and other cancers, and involves the delivery of genetic information to the patient to facilitate the production of therapeutic proteins. Therapeutics can act directly (eg, by inducing tumor cells to produce cytotoxic agents) or indirectly by upregulating the immune system to efficiently target tumor cells or by destroying the tumor's vasculature. However, technological difficulties must be addressed before an efficient and safe gene medicine is achieved (primarily by developing a means of delivering genes to the target cells or tissue safely and efficiently). A wealth of research has been carried out over the past 20 years, involving various strategies for the treatment of prostate cancer at preclinical and clinical trial levels. The therapeutic efficacy observed with many of these approaches in patients indicates that these treatment modalities will serve as an important component of urological malignancy treatment in the clinic, either in isolation or in combination with current approaches.

Optimised electroporation mediated DNA vaccination for treatment of prostate cancer

BACKGROUND

Immunological therapies enhance the ability of the immune system to recognise and destroy cancer cells via selective killing mechanisms. DNA vaccines have potential to activate the immune system against specific antigens, with accompanying potent immunological adjuvant effects from unmethylated CpG motifs as on prokaryotic DNA. We investigated an electroporation driven plasmid DNA vaccination strategy in animal models for treatment of prostate cancer.

METHODS

Plasmid expressing human PSA gene (phPSA) was delivered in vivo by intra-muscular electroporation, to induce effective anti-tumour immune responses against prostate antigen expressing tumours. Groups of male C57 BL/6 mice received intra-muscular injections of phPSA plasmid. For phPSA delivery, quadriceps muscle was injected with 50 microg plasmid. After 80 seconds, square-wave pulses were administered in sequence using a custom designed pulse generator and a custom-designed applicator with 2 needles placed through the skin central to the muscle. To determine an optimum treatment regimen, three different vaccination schedules were investigated. In a separate experiment, the immune potential of the phPSA vaccine was further enhanced with co- administration of synthetic CpG rich oligonucleotides. One week after last vaccination, the mice were challenged subcutaneously with TRAMPC1/hPSA (prostate cancer cell line stably expressing human PSA) and tumour growth was monitored. Serum from animals was examined by ELISA for anti-hPSA antibodies and for IFN gamma. Histological assessment of the tumours was also carried out. In vivo and in vitro cytotoxicity assays were performed with splenocytes from treated mice.

RESULTS

The phPSA vaccine therapy significantly delayed the appearance of tumours and resulted in prolonged survival of the animals. Four-dose vaccination regimen provided optimal immunological effects. Co - administration of the synthetic CpG with phPSA increased anti-tumour responses, preventing tumour occurrence in 54% of treated animals. Vaccination with phPSA resulted in anti-hPSA Abs production and a significant production of IFN gamma was observed in immunised animals (p < 0.05). Immune responses were tumour specific and were transferable in adoptive T cell transfer experiments.

CONCLUSIONS

This phPSA plasmid electroporation vaccination strategy can effectively activate tumour specific immune responses. Optimisation of the approach indicated that a four-dose regimen provided highest tumour protection. In vivo electroporation mediated vaccination is a safe and effective modality for the treatment of prostate cancer and has a potential to be used as a neo-adjuvant or adjuvant therapy.

A changing world for DCvax: a PSMA loaded autologous dendritic cell vaccine for prostate cancer

BACKGROUND

Northwest Therapeutics' DCvax-prostate consists of autologous dendritic cells (DCs) loaded with prostate-specific membrane antigen (PSMA) peptides, administered intravenously. Phase I-II testing, a decade ago, showed clinical benefit and immunological response in some patients. More recently DCvax brain, a product using a similar DC platform showed encouraging Phase I-II results and sipleucel-T, a prostatic acid phosphatase (PAP)-directed DC immunotherapy had positive Phase III results.

OBJECTIVE

Features of the clinical setting into which a new immunotherapy could be introduced are discussed, to refine a perspective on DCvax-prostate in the context of evolving prostate cancer therapeutics. PSMA-directed therapeutics and immune anticancer technologies are reviewed, and the clinical and immunological correlative testing of DCvax-prostate is discussed.

METHODS

Clinical and preclinical data from peer-reviewed literature, meetings proceedings and manufacturer-provided information are considered.

CONCLUSION

DCvax-prostate had encouraging early-phase trial results, but development and testing had stalled. As a more detailed understanding of patient-selection for capacity for anticancer immune response, the quantitation of immunological correlates, and the changing marketplace develop, it is appealing to consider a well tolerated, PSMA-directed autologous dendritic cell therapeutic product. Further clinical trial development of DCvax-prostate is warranted, and required if it is to find a relevant clinical application.

Cutting edge: permissive MHC class II allele changes the pattern of antitumor immune response resulting in failure of tumor rejection

We studied the growth of transgenic adenocarcinoma of mouse prostate (TRAMP)-C1 tumor cells expressing human prostate-specific Ag (PSA) in HLA-DRB1*1501 (DR2b) transgenic mice. TRAMP-PSA tumors were frequently rejected by HLA-DR2b(-) mice but had increased incidence in HLA-DR2b(+) littermates. The levels of PSA-specific CD8 T cell responses were significantly higher in the HLA-DR2b(-) mice that rejected TRAMP-PSA tumors compared with HLA-DR2b(+) tumor-bearing littermates. In contrast, Ab responses to PSA were strong in HLA-DR2b(+) mice bearing TRAMP-PSA tumors and were virtually undetectable in HLA-DR2b(-) littermates. The analysis of CD4 T cell responses to PSA revealed the presence of several CD4 T cell epitopes in HLA-DR2b(+) mice but failed to identify strong I-A(b)-restricted epitopes in HLA-DR2b(-) mice. Our data demonstrate that the expression of a permissive HLA class II allele can change the pattern of the immune response to a tumor Ag, resulting in the failure of tumor rejection.

Retrovirally transduced murine T lymphocytes expressing FasL mediate effective killing of prostate cancer cells

Adoptively transferred T cells possess anticancer activities partially mediated by T-cell FasL engagement of Fas tumor targets. However, antigen-induced T-cell activation and clonal expansion, which stimulates FasL activity, is often inefficient in tumors. As a gene therapy approach to overcome this obstacle, we have created oncoretroviral vectors to overexpress FasL or non-cleavable FasL (ncFasL) on murine T cells of a diverse T-cell receptor repertoire. Expression of c-FLIP was also engineered to prevent apoptosis of transduced cells. Retroviral transduction of murine T lymphocytes has historically been problematic, and we describe optimized T-cell transduction protocols involving CD3/CD28 co-stimulation of T cells, transduction on ice using concentrated oncoretrovirus, and culture with IL-15. Genetically modified T cells home to established prostate cancer tumors in vivo. Co-stimulated T cells expressing FasL, ncFasL and ncFasL/c-FLIP each mediated cytotoxicity in vitro against RM-1 and LNCaP prostate cancer cells. To evaluate the compatibility of this approach with current prostate cancer therapies, we exposed RM-1, LNCaP, and TRAMP-C1 cells to radiation, mitoxantrone, or docetaxel. Fas and H-2(b) expression were upregulated by these methods. We have developed a novel FasL-based immuno-gene therapy for prostate cancer that warrants further investigation given the apparent constitutive and inducible Fas pathway expression in this malignancy.

Tumor protection following vaccination with low doses of lentivirally transduced DCs expressing the self-antigen erbB2

Gene therapy strategies may accelerate the development of prophylactic immunotherapy against cancer. We synthesized a lentiviral (LV) vector encoding a kinase-deficient form of erbB2 (erbB2tr) to transduce murine dendritic cells (DCs) efficiently. Murine erbB2 models a clinically relevant tumor-associated self-antigen; its human homolog (HER-2/neu) is overexpressed in breast cancer and in 80% of metastatic prostate cancers. Following one infection, approximately 47% of DCs overexpressed erbB2tr. To determine whether low doses of transduced DCs could protect mice from prostate cancer cells, we performed prime/boost vaccinations with 2 x 10(3) or 2 x 10(5) erbB2tr-transduced DCs. Six weeks after vaccination, mice were simultaneously bilaterally challenged with the aggressive RM-1 prostate cancer cell line and an erbB2tr-expressing variant (RM-1-erbB2tr). Whereas control mice developed both tumors, all recipients of 2 x 10(5) erbB2tr-transduced DCs developed only wild-type RM-1 tumors. One-third of mice vaccinated with just 2 x 10(3) erbB2tr-transduced DCs also demonstrated erbB2tr-specific tumor protection. Protection against RM-1-erbB2tr tumors was associated with sustained levels of anti-erbB2tr antibody production and also correlated with erbB2tr-specific Th1 cytokine secretion. Depletion of CD4(+), CD8(+), or natural killer (NK) cells prior to tumor challenge underscored their role in mediating tumor protection. We conclude that administration of DCs expressing a self-antigen through efficient LV-based gene transfer activates cellular and humoral immunity, protecting host animals against specific tumor challenge.

Generation of robust cytotoxic T lymphocytes against prostate specific antigen by transduction of dendritic cells using protein and recombinant adeno-associated virus

Prostate cancer is the most common male cancer and there is an urgent need for adjuvant therapy such as immunotherapy. Recombinant adeno-associated virus type 2 (rAAV) vectors are useful for antigen gene-loading of human dendritic cells (DC) and for the rapid generation of cytotoxic T lymphocytes (CTL). In this study, we report a protocol for AAV-loading of DC with the AAV-loading of self-antigen prostate specific antigen (PSA) resulting in generation of CTL. PSA and cytokine expression, Cell surface marker analysis of DC and CTL cells were done using a FACScalibur flow cytometer. Chromium-51 release assay was used to analyze the killing activity of CTL. It was found that AAV-loading of DC with the PSA gene is superior to PSA protein loading of the same antigen for generating effective CTL. AAV/PSA-loading of DC was found to result in: (1) strong, rapid PSA-specific, MHC Class I-restricted CTL, (2) PSA expression in DC, (3) high CD80, CD83, and CD86 expression on DC, (4) high level of IL-12 and low level of IL-10 in DC, (5) T cell populations with significant interferon gamma (IFNgamma) expression, but low IL-4 expression, (6) high proliferation of T cell populations, (7) high CD8:CD4 and CD8:CD56 T cell ratios. The reason for generation of robust CTL is partly explained by the characteristics of DC and CTL described. This protocol may be useful for adoptive immunotherapy against self antigens such as PSA for prostate cancer.

Engineered human tmpk/AZT as a novel enzyme/prodrug axis for suicide gene therapy

Gene therapy and stem cell transplantation safety could be enhanced by control over the fate of therapeutic cells. Suicide gene therapy uses enzymes that convert prodrugs to cytotoxic entities; however, heterologous moieties with poor kinetics are employed. We describe a novel enzyme/prodrug combination for selectively inducing apoptosis in lentiviral vector-transduced cells. Rationally designed variants of human thymidylate kinase (tmpk) that effectively phosphorylate 3'-azido-3'-deoxythymidine (AZT) were efficiently delivered. Transduced Jurkat cell lines were eliminated by AZT. We demonstrate that this schema targeted both dividing and non-dividing cells, with a novel killing mechanism involving apoptosis induction via disruption of the mitochondrial inner membrane potential and activation of caspase-3. Primary murine and human T cells were also transduced and responded to AZT. Furthermore, low-dose AZT administration to non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice injected with transduced K562 cells suppressed tumor growth. This novel suicide gene therapy approach can thus be integrated as a safety switch into therapeutic vectors.

Auto-antibodies in prostate cancer: humoral immune response to antigenic determinants coded by the differentially expressed transcripts FLJ23438 and VAMP3

BACKGROUND

Here we evaluate auto-antibody response against two potential antigenic determinants of genes highly expressed in low Gleason Score prostate cancer (PC) tumor samples, namely FLJ23438 and VAMP3.

METHODS

RT-PCR assays were used to analyze mRNA expression profiles of FLJ23438 and VAMP3 transcripts. The auto-antibody response against FLJ23438 and VAMP3 recombinant proteins was tested by immunoblot assays using PC, benign prostate hyperplasia (BPH), healthy donors (HD), and other human cancers plasma samples.

RESULTS

Our data showed that 37% (10/27) and 7.4% (2/27) of PC plasma samples presented auto-antibodies against FLJ23438 and VAMP3, respectively. Only 8.3% (1/12) of BPH plasma samples were reactive for both auto-antibodies, while none (0/12) of HD plasma samples tested were reactive.

CONCLUSIONS

The prevalence of 37% of positive PC plasma samples for anti-FLJ23438 antibodies suggests that humoral immune response against this antigenic determinant could be a potential serum marker for this cancer.

Gene therapy for prostate cancer: current strategies and new cell-based approaches

Prostate cancer is the most commonly diagnosed cancer in adult males in the Western world. It accounts for one in ten cancer cases and is the second leading cause of cancer death in men, after lung cancer. A number of curative treatments are available for patients with localized prostate cancer such as radical prostatectomy, radiotherapy, or brachytherapy. However, a proportion of these men will develop progressive disease, and some will present de novo with advanced and metastatic prostate cancer, which is amenable to palliation only with androgen-withdrawal therapy. Most of these patients will eventually develop hormone refractory disease which is incurable, and for whom gene therapy, if feasible may develop as an alternative treatment option. In this review we discuss the gene therapy vectors and strategies that are currently in use, new cell-based approaches, discuss their advantages and disadvantages, and review the potential or proven pre-clinical and clinical efficacy in prostate cancer models/patients.

H2 relaxin overexpression increasesin vivo prostate xenograft tumor growth and angiogenesis

Our study reports a preliminary investigation into the role of human H2 relaxin in prostate tumor growth. A luciferase-expressing human prostate cancer cell line, PC-3, was generated and termed PC3-Luc. PC3-Luc cells were transduced with lentiviral vectors engineering the expression of either enhanced green fluorescent protein (eGFP) or both H2 relaxin and eGFP in a bicistronic format. These transduced cells were termed PC3-Luc-eGFP and PC3-Luc-H2/eGFP, respectively. To gauge effects, PC3-Luc-H2/eGFP and PC3-Luc-eGFP cells were injected into NOD/SCID mice and monitored over 6 weeks. PC-3 tumor xenografts overexpressing H2 relaxin exhibited greater tumor volumes compared to control tumors. Circulating H2 relaxin levels in sera increased with the relative size of the tumor, with moderately elevated H2 relaxin levels in mice bearing PC3-Luc-H2/eGFP tumors compared to PC3-Luc-eGFP tumors. Zymographic analysis demonstrated that proMMP-9 enzyme activity was significantly downregulated in H2 relaxin-overexpressing tumors. An advanced angiogenic phenotype was observed in H2 relaxin-overexpressing tumors indicated by greater intratumoral vascularization by immunohistochemical staining of endothelial cells with anti-mouse CD31. Moreover, PC3-Luc-H2/eGFP tumors exhibited increased VEGF transcript by reverse-transcription PCR, compared to basal levels in control animals. Taken together, our study provides the first account of a potential role of H2 relaxin in prostate tumor development.