Helena Dzojic

Adenovirus CD40 Ligand Gene Therapy Counteracts Immune Escape Mechanisms in the Tumor Microenvironment

Tumors exhibit immune escape properties that promote their survival. These properties include modulation of Ag presentation, secretion of immunosuppressive factors, resistance to apoptosis, and induction of immune deviation, e.g., shifting from Th1- to Th2-type responses. These escape mechanisms have proven to hamper several immunotherapeutic strategies, and efforts need to be taken to revert this situation. We have studied the immunological effects of introducing CD40 ligand (CD40L), a potent dendritic cell activation molecule, into the tumor micromilieu by adenoviral gene transfer. For this purpose, a murine bladder cancer model (MB49) was used in C57BL/6 mice. The MB49 cells are known to induce IL-10 in the tumor environment. IL-10 potently inhibits the maturation of dendritic cells and thereby also the activation of CTLs. In this paper we show that CD40L immunogene therapy suppresses IL-10 and TGF-β production (2-fold decrease) and induces a typical Th1-type response in the tumor area (200-fold increase in IL-12 production). The antitumor responses obtained were MB49 cell specific, and the cytotoxicity of the stimulated CD8+ cells could be blocked by IL-10. Adenovirus CD40L therapy was capable of regressing small tumors (five of six animals were tumor free) and inhibiting the progression of larger tumors even in the presence of other escape mechanisms, such as apoptosis resistance. Furthermore, CD40L-transduced MB49 cells promoted the maturation of dendritic cells (2-fold increase in IL-12) independently of IL-10. Our results argue for using adenovirus CD40L gene transfer, alone or in combination with other modalities, for the treatment of Th2-dominated tumors.

A Novel Chromogranin-A Promoter-Driven Oncolytic Adenovirus for Midgut Carcinoid Therapy

Purpose: The use of replication-selective oncolytic adenoviruses is an emerging therapeutic approach for cancer, which thus far has not been employed for carcinoids. We therefore constructed Ad[CgA-E1A], a novel replication-selective oncolytic adenovirus, where the chromogranin A (CgA) promoter controls expression of the adenoviral E1A gene. Experimental Design: The Ad[CgA-E1A] virus was evaluated for E1A protein expression, replication ability, and cytolytic activity in various cell lines. It was also evaluated for treatment of xenografted human carcinoid tumors in nude mice. To use Ad[CgA-E1A] for the treatment of carcinoid liver metastases, it is important that normal hepatocytes do not support virus replication to minimize hepatotoxicity. We therefore evaluated CgA protein expression in normal hepatocytes. We also evaluated CgA gene expression in normal hepatocytes and microdissected tumor cells from carcinoid metastases. Results: We found that Ad[CgA-E1A] replicates similarly to wild-type virus in tumor cells with neuroendocrine features, including the BON carcinoid cell line and the SH-SY-5Y neuroblastoma cell lines, whereas it is attenuated in other cell types. Thus, cells where the CgA promoter is active are selectively killed. We also found that Ad[CgA-E1A] is able to suppress fast-growing human BON carcinoid tumors in nude mice. Furthermore, CgA is highly expressed in microdissected cells from carcinoid metastases, whereas it is not expressed in normal hepatocytes. Conclusion: Ad[CgA-E1A] is an interesting agent for the treatment of carcinoid liver metastases in conjunction with standard therapy for these malignancies.

An oncolytic conditionally replicating adenovirus for hormone-dependent and hormone-independent prostate cancer

The use of conditionally replicating adenoviruses offers an attractive complementary treatment strategy for localized prostate cancer. We have produced a replicating adenovirus, Ad[I/PPT-E1A], where E1A gene expression is controlled by a recombinant regulatory sequence designated PPT. The PPT sequence comprises a PSA enhancer, a PSMA enhancer and a T-cell receptor γ-chain alternate reading frame protein promoter, and it is shielded from transcriptional interference from adenoviral backbone sequences by an H19 insulator. Ad[I/PPT-E1A] yields prostate-specific E1A protein expression, viral replication and cytolysis in vitro. Furthermore, Ad[I/PPT-E1A] considerably regresses the growth of subcutaneous LNCaP prostate cancer tumors in nude mice. Importantly, the viral replication and cytolytic effect of Ad[I/PPT-E1A] are independent of the testosterone levels in the prostate cancer cells. This may be beneficial in a clinical setting since many prostate cancer patients are treated with androgen withdrawal. In conclusion, Ad[I/PPT-E1A] may prove to be useful in the treatment of localized prostate cancer.

Increased therapeutic efficacy of the prostate-specific oncolytic adenovirus Ad[I/PPT-E1A] by reduction of the insulator size and introduction of the full-length E3 region

Conditionally replicating adenoviruses are developing as a complement to traditional cancer therapies. Ad[I/PPT-E1A] is an E1B/E3-deleted virus that replicates exclusively in prostate cells, since the expression of E1A is controlled by the recombinant 1.4 kb prostate-specific PPT promoter. The transcriptional integrity of PPT is maintained by the 3.0 kb mouse H19 insulator that was introduced directly upstream of the PPT sequence. In order to increase the cloning capacity to be able to reintroduce E3 sequences in the 35.7 kb Ad[I/PPT-E1A] genome, various shorter insulators were examined in a luciferase reporter gene assay. It was found that the 1.6 kb core H19 insulator (i) improves the activity of PPT, compared to the 3.0 kb full-length insulator, while still maintaining prostate cell specificity and releasing 1.4 kb of space for insertion of additional sequences. To improve the ability of the virus to efficiently lyse infected cells and persist in vivo, we inserted the adenovirus death protein (ADP) or the full-length adenovirus E3 region. The oncolytic activity of PPT-E1A-based viruses was studied using MTS, crystal violet and replication assays. The virus with the reintroduced full-length E3-region (Ad[i/PPT-E1A, E3]) showed the highest cytopathic effects in vitro. Furthermore, this virus suppressed the growth of aggressively growing prostate tumors in vivo. Therefore, we conclude that Ad[i/PPT-E1A, E3] is a prostate-specific oncolytic adenovirus with a high potential for treating localized prostate cancer.

Two-step amplification of the human PPT sequence provides specific gene expression in an immunocompetent murine prostate cancer model

The recombinant prostate-specific PPT sequence comprises a prostate-specific antigen enhancer, a PSMA enhancer and a TARP promoter. It is transcriptionally active in human prostate cancer cells both in the presence and absence of testosterone. However, in experimental murine prostate cancer, it has no detectable transcriptional activity. Herein, we describe that the PPT sequence in combination with a two-step transcriptional amplification (TSTA) system becomes active also in murine prostate cancer cells. An adenovirus with TSTA-amplified PPT-controlled expression of the luciferase reporter gene, Ad[PPT/TSTA-Luc], has up to 100-fold higher prostate-specific transcriptional activity than a non-amplified PPT-based adenovirus, Ad[PPT-Luc], in human cells. In addition, Ad[PPT/TSTA-Luc] confers prostate-specific transgene expression in murine cells, with an activity that is approximately 23% of Ad[CMV-Luc] in the transgenic adenocarcinoma of the mouse prostate (TRAMP)-C2 cells. Moreover, to visualize luciferase expression in living mice a charge-coupled device camera was used. Ad[PPT/TSTA-Luc] yielded approximately 30-fold higher transgene expression than Ad[PPT-Luc] in LNCaP tumor xenografts. Importantly, Ad[PPT/TSTA-Luc] also showed activity in murine TRAMP-C2 tumors, whereas Ad[PPT-Luc] activity was undetectable. These results highlight that the recombinant PPT sequence is active in murine prostate cancer cells when augmented by a TSTA system. This finding opens up for preclinical studies with prostate-specific therapeutic gene expression in immunocompetent mice.

281. Adenovirus-Mediated CD40 Ligand Therapy Induces Tumor Cell Apoptosis and Systemic Immunity in the TRAMP-C2 Mouse Prostate Cancer Model

Ligation of CD40 by its ligand (CD40L) can generate a variety of responses depending on the cell types that express CD40. The interaction between CD40L and CD40 on antigen presenting cells is essential for the initiation of antigen specific T cell responses, whereas CD40L stimulation on CD40 positive tumor cells can induce cellular apoptosis. We have investigated whether CD40L gene transfer is a feasible therapy for prostate cancer. An adenoviral vector expressing murine CD40L (AdCD40L) induced apoptosis and yielded reduced viability in murine prostate cancer, TRAMP-C2, cells. In animal studies, CD40L-expressing TRAMP-C2 cells were rejected and vaccination with CD40L-expressing TRAMP-C2 cells induced anti- tumor immunity against challenges with parental tumors at a distant site. Furthermore, peritumoral injections of AdCD40L in preestablished subcutanous TRAMP-C2 tumors induced tumor growth suppression. In order to increase the therapeutic effects even further we pretreated cells with the histone deacetylase inhibitor FK228, a drug known to increase coxsackie-adenovirus receptor (CAR) expression. Pretreatment of prostate cancer cells with FK228 before adenoviral transduction resulted in a dramatic increase in transgene expression and improved therapeutic potentials. The use of AdCD40L offers an attractive option for prostate cancer gene therapy.

1024. An Oncolytic Conditionally Replicating Adenovirus for Hormone-Dependent and Hormone-Independent Prostate Cancer

The use of conditionally replicating adenoviruses offers an attractive complementary treatment strategy for localized prostate cancer. We have produced a replicating adenovirus, Ad[I/PPT-E1A], where E1A gene expression is controlled by a recombinant regulatory sequence designated PPT. The PPT sequence comprises a PSA enhancer, a PSMA enhancer and a TARP promoter and it is shielded from transcriptional interference from adenoviral backbone sequences by an H19 insulator. Ad[I/PPT-E1A] yields prostate-specific E1A protein expression, viral replication and cytolysis in vitro. Furthermore, Ad[I/PPT-E1A] considerably regresses the growth of subcutaneous LNCaP prostate tumors in nude mice. Importantly, viral replication and cytolytic effect of Ad[I/PPT-E1A] are independent on the testosterone levels in the prostate cancer cell. This may be beneficial in a clinical setting since many prostate cancer patients are treated with androgen withdrawal. In conclusion, Ad[I/PPT-E1A] may prove to be useful in the treatment of localized prostate cancer.