Gene-based therapy of malignant melanoma

Ret mouse very large tumors (VLTs) display altered ratios of infiltrating memory to naive T cells: Roles in tumor expansion

Melanoma is an aggressive skin cancer, however it is immunogenic. The size of the primary tumor is associated with the nodal metastases. Our goals were to characterize melanoma-associated antigens (MAAs) and tumor-infiltrating T-lymphocytes (TILs) subsets in the few very large tumors (VLTs) developing in ret transgenic mice of melanoma. Tumors >700mg (VLTs) were investigated for MAAs and subsets of TILs. Immunohistochemistry and flow cytometry-based studies were performed to determine the infiltration patterns of T-lymphocytes in VLTs. It was observed that zinc fixative restores the antigenicity of the cell-surface markers of lymphocyte subpopulations without the need of antigen retrieval, whereas formalin-based fixative fails to restore the antigenicity in the presence of antigen retrieval in the immunohistochemistry. VLTs from ret mice express MAAs, such as Tyrosinase, TRP-1, TRP-2 and gp-100. The mean±standard deviation (S.D.) T-cell infiltration per 400 times-high power field in VLTs; CD4(+) (2.33±1.3), CD8(+) (2.00±1.0), and CD4(+) Foxp3(+) (2.5±0.5) regulatory T cells infiltration was exclusively restricted to the tumor stroma. Moreover, our flow cytometry-based data reveal that % mean±S.D. naive CD3(+) CD4(+) T cell infiltration (32.8±4.0%) was significantly larger than effector (25.8±2.8%, p<0.01) and central memory cells (16.1±3.7%, p<0.001) in VLTs. Similarly, between CD3(+) CD8(+) T cells, naive cells infiltrate (57.7±2.3%) in a significantly larger frequency than effector (5.0±0.4%, p<0.0001) and central memory cell (4.8±1.7%, p<0.0001) subsets. These results suggest that the VLTs from ret mice display lowered infiltration ratios between memory and naive T cells, which could be associated with the relatively large growth of VLTs.

New approaches in metastatic melanoma: biological and molecular targeted therapies

Classical metastatic melanoma therapy is disappointing but important progress has been made in the understanding of melanoma biology. Genetic lesions and several intracellular signaling pathways that could serve as targets for novel therapy have been identified and a number of new agents are under evaluation. Promising tumor cell targets were identified in the cell membrane, cytoplasm and nucleus. New therapeutic approaches, besides monoclonal antibodies and vaccination, include an increasing number of small molecules that have been shown to interfere restrictively with intracellular signaling pathways in melanoma and decrease proliferation, survival, migration or invasion. Other agents can interfere with stromal components of melanoma, such as angiogenesis and components of the immune system.

The mechanism of exogenous B7.1-enhanced IL-12-mediated complete regression of tumors by a single electroporation delivery

Electroporation-based mono-gene therapy has received great interest in recent years but coadministration of different therapeutic genes for treatment of tumors has not been well explored. We hypothesize that electroporation is capable of delivering multiple genes that induce an additive or synergistic antitumor effect. To test this hypothesis, we used mice that were bearing SCCVII or TRAMP tumors. Established tumors with a diameter of 4-5 mm were injected with control plasmid DNA or plasmid DNA encoding B7.1, IL-12 or both via electroporation. Tumor regression, CTL activity and the level of B7.1, IL-12 and Stat1 expression were determined in both wild-type mice and in mice with a knock-out of the Stat1 gene. Remarkably, a single coadministration of the plasmids that encoded IL-12 and B7.1 eradicated tumors in 80% of mice. The therapeutic effect was associated with high levels of endogenous B7.1 expression, activity of cytotoxic lymphocytes, and activation of Stat1. Both exogenous B7.1 and IL-12 were required for inducing a high level of Stat1 activation in tumors, which occurred through a mechanism that was independent of the host Stat1. Both stimulators were also required for inducing the strong cytotoxic lymphocyte activity and for increasing the level and extending the duration of endogenous B7.1 expression. We therefore propose a 2-signal stimulation model to explain the synergistic effect of the coadministration of IL-12 and B7.1 on the regression of the tumors.

Regulatory elements of the melanocortin 1 receptor

Among more than 120 genes that are now known to regulate mammalian pigmentation, one of the key genes is MC1R, which encodes the melanocortin 1 receptor, a seven transmembrane G protein-coupled receptor expressed on the surface of melanocytes. Since the monoexonic sequence of the gene was cloned and characterized more than a decade ago, tremendous efforts have been dedicated to the extensive genotyping of mostly red-haired populations all around the world, thus providing allelic variants that may or may not account for melanoma susceptibility in the presence or absence of ultraviolet (UV) exposure. Soluble factors, such as proopiomelanocortin (POMC) derivatives, agouti signal protein (ASP) and others, regulate MC1R expression, leading to improved photoprotection via increased eumelanin synthesis or in contrast, inducing the switch to pheomelanin. However, there is an obvious lack of knowledge regarding the numerous and complex regulatory mechanisms that govern the expression of MC1R at the intra-cellular level, from gene transcription in response to an external stimulus to the expression of the mature receptor on the melanocyte surface.

Transcriptional targeting of RGD fiber-mutant adenovirus vectors can improve the safety of suicide gene therapy for murine melanoma

Since RGD fiber-mutant adenovirus vector (AdRGD), which contains an alphav-integrin tropism, is highly efficient in gene transduction to melanoma, the AdRGD-mediated herpes simplex virus thymidine kinase (HSVtk)/ganciclovir (GCV) system is an attractive approach for melanoma treatment. However, the intratumoral injection of AdRGD causes limited transgene expression in healthy normal tissue, due to unwanted vector spread. Herein, we describe our attempt to overcome this limitation related to the safety of HSVtk/GCV treatment by using AdRGD carrying either melanoma-specific tyrosinase (Tyr) promoter or tumor-specific telomerase reverse transcriptase (TERT) promoter instead of universal cytomegalovirus promoter. Our in vitro study revealed that Tyr promoter-regulated AdRGD exhibited high transgene expression specificity for melanoma cells, and that TERT promoter-regulated AdRGD could induce efficient gene expression in tumor cells, but was relatively quiescent in normal cells. Anti-B16BL6 melanoma effects in mice injected intratumorally with AdRGD-Tyr/HSVtk or AdRGD-TERT/HSVtk, after which GCV was injected intraperitoneally for 10 days, were comparable to those in mice injected with AdRGD-CMV/HSVtk at 10 times less vector dosage. On the other hand, AdRGD-Tyr/HSVtk and AdRGD-TERT/HSVtk did not induce severe adverse effects even when they were intravenously injected into mice at 10(9) plaque-forming units (PFU), whereas mice injected with AdRGD-CMV/HSVtk at 10(8) PFU exhibited body weight reduction and serum level increase of biochemical enzymes for hepatotoxicity. These results indicate that AdRGD combined with transcriptional regulation using Tyr or TERT promoter is a potentially useful and safe vector system for suicide gene therapy for melanoma.

Evaluation of combined gene regulatory elements for transcriptional targeting of suicide gene expression to malignant melanoma

Selective killing of tumors can be achieved by targeting the transcription of suicide genes via specific DNA control elements to malignant cells. Three different enhancer-promoter systems were constructed and evaluated for their capability to direct gene expression to melanoma. Two tissue-specific (tyrosine and MIA) promoters and one weak viral promoter were fused to multiple tandem copies of a melanocyte-specific enhancer element. Reporter gene assays revealed a maximum increase in transcription by combining each promoter with 3-4 copies of the enhancer and demonstrated that all enhancer-promoter combinations exhibited tissue-specific activity. Though this activity was still significantly less than that of the strong but unspecific cytomegalovirus (CMV) promoter. In contrast, when those combinations were employed to drive the expression of two suicide genes, encoding the diptheria toxin A chain (DT-A) and the prodrug-activating herpes simplex virus thymidine kinase (TK), respectively, only those constructs in which transcription was under control of tissue-specific promoter elements mediated selective killing of melanoma cells. This killing was in the range of cell death induced by CMV promoter activity. Our data indicate that the enhancer/tyrosinase and enhancer/MIA promoter constructs but not the viral promoter constructs can provide a valuable tool for selective suicide gene expression in melanoma.

Humoral immune response against melanoma antigens induced by vaccination with cytokine gene-modified autologous tumor cells

Although the existence of a humoral response against tumor-associated antigens is well appreciated, a systematic analysis of its possible induction by the tumor remains missing. We compared the specific IgG response of Stage IV melanoma patients during vaccination. Patients had been treated within 2 clinical trials with autologous tumor cells gene-modified for IL-7 or IL-12. A panel of 27 tumor-associated antigens (HD-MM-01 to HD-MM-27) was isolated by a SEREX screening of a testis cDNA library using a pool of 5 sera from patients after vaccination. All antigens were retested with individual sera of 12 patients both pre- and post-vaccination. A serological response was induced during vaccination against 18 antigens. Remarkably, induction was detected only in patients included in the screening pool. The low overlap between sero-reactivity of the 12 patients suggested a very individualized immunological reaction. Two of 5 sera included in the screening pool exhibited a high frequency of induced humoral responses. The same patients had been shown to have a high Karnovsky index and had generated lytic cytotoxic T cells against the tumor. Besides 2 known cancer-germline genes (SCP-1 and PLU-1), the other isolated antigens were expressed in a non-tumor-specific fashion as analyzed by virtual Northern blot or RT-PCR. The properties of homologues to several of the identified tumor-antigens, especially PLU-1, SCP-1, DNEL2, CLOCK, and PIASx-alpha, suggest further investigation of their possible function in malignant melanoma. We conclude that a strong humoral response against tumor-associated antigens is inducible by tumor cells and that this response is very individual.