Antitumoral effect of interleukin-12-secreting fibroblasts in a mouse model of ovarian cancer: implications for the use of ovarian cancer biopsy-derived fibroblasts as a vehicle for regional gene therapy

Preclinical and Clinical Immunotherapeutic Strategies in Epithelial Ovarian Cancer

In the past 20 years, the immune system has increasingly been recognized as a major player in tumor cell control, leading to considerable advances in cancer treatment. While promising with regards to melanoma, renal cancer and non-small cell lung cancer, immunotherapy provides, for the time being, limited success in other cancers, including ovarian cancer, potentially due to insufficient immunogenicity or to a particularly immunosuppressive microenvironment. In this review, we provide a global description of the immune context of ovarian cancer, in particular epithelial ovarian cancer (EOC). We describe the adaptive and innate components involved in the EOC immune response, including infiltrating tumor-specific T lymphocytes, B lymphocytes, and natural killer and myeloid cells. In addition, we highlight the rationale behind the use of EOC preclinical mouse models to assess resistance to immunotherapy, and we summarize the main preclinical studies that yielded anti-EOC immunotherapeutic strategies. Finally, we focus on major published or ongoing immunotherapy clinical trials concerning EOC.

Development of a prosaposin-derived therapeutic cyclic peptide that targets ovarian cancer via the tumor microenvironment

The vast majority of ovarian cancer-related deaths are caused by metastatic dissemination of tumor cells, resulting in subsequent organ failure. However, despite our increased understanding of the physiological processes involved in tumor metastasis, there are no clinically approved drugs that have made a major impact in increasing the overall survival of patients with advanced, metastatic ovarian cancer. We identified prosaposin (psap) as a potent inhibitor of tumor metastasis, which acts via stimulation of p53 and the antitumorigenic protein thrombospondin-1 (TSP-1) in bone marrow-derived cells that are recruited to metastatic sites. We report that more than 97% of human serous ovarian tumors tested express CD36, the receptor that mediates the proapoptotic activity of TSP-1. Accordingly, we sought to determine whether a peptide derived from psap would be effective in treating this form of ovarian cancer. To that end, we developed a cyclic peptide with drug-like properties derived from the active sequence in psap. The cyclic psap peptide promoted tumor regression in a patient-derived tumor xenograft model of metastatic ovarian cancer. Thus, we hypothesize that a therapeutic agent based on this psap peptide would have efficacy in treating patients with metastatic ovarian cancer.

Phase-I clinical trial of IL-12 plasmid/lipopolymer complexes for the treatment of recurrent ovarian cancer

A phase-I trial to assess the safety and tolerability of human interleukin-12 (IL-12) plasmid (phIL-12) formulated with a synthetic lipopolymer, polyethyleneglycol-polyethyleneimine-cholesterol (PPC), was conducted on women with chemotherapy-resistant recurrent ovarian cancer. A total of 13 patients were enrolled in four dose-escalating cohorts and treated with 0.6, 3, 12 or 24 mg m(-2) of the formulated plasmid once every week for 4 weeks. Administration of phIL-12/PPC was generally safe and well-tolerated. Common side effects included low-grade fever and abdominal pain. Stable disease and reduction in serum CA-125 levels were clinically observed in some patients. Measurable levels of IL-12 plasmid were detectable in PF samples collected throughout the course of phIL-12/PPC treatment. In comparison, serum samples either did not contain detectable amounts of plasmid DNA or contained <1% of the amount found in the corresponding PF samples. Treatment-related increases in IFN-gamma levels were observed in PF but not in serum. These data demonstrate that IL-12 gene delivery with a synthetic delivery system is feasible for ovarian cancer patients.

The development of gene therapy: from monogenic recessive disorders to complex diseases such as cancer

During the last 4 decades, gene therapy has moved from preclinical to clinical studies for many diseases ranging from monogenic recessive disorders such as hemophilia to more complex diseases such as cancer, cardiovascular disorders, and human immunodeficiency virus (HIV). To date, more than 1,340 gene therapy clinical trials have been completed, are ongoing, or have been approved in 28 countries, using more than 100 genes. Most of those clinical trials (66.5%) were aimed at the treatment of cancer. Early hype, failures, and tragic events have now largely been replaced by the necessary stepwise progress needed to realize clinical benefits. We now understand better the strengths and weaknesses of various gene transfer vectors; this facilitates the choice of appropriate vectors for individual diseases. Continuous advances in our understanding of tumor biology have allowed the development of elegant, more efficient, and less toxic treatment strategies. In this introductory chapter, we review the history of gene therapy since the early 1960s and present in detail two major recurring themes in gene therapy: (1) the development of vector and delivery systems and (2) the design of strategies to fight or cure particular diseases. The field of cancer gene therapy experienced an "awkward adolescence." Although this field has certainly not yet reached maturity, it still holds the potential of alleviating the suffering of many individuals with cancer.

Immune killing activity of lymphocytes on Hela cells expressing interleukin-12 in vitro

The killing effects of lymphocytes on Hela cells expressing interleukin-12 (IL-12) in vitro were explored. By using gene transfection technique, full length IL-12 gene was transfected into Hela cells. The expression of IL-12 in Hela cells was detected quantitatively by ELISA; Changes in killing effects of lymphocytes on Hela cells expressing IL-12 were observed by MTT. It was found that Hela cells could express IL-12 between 24 h and 72 h after transfection. Killing activity of lymphocytes on Hela cells expressing IL-12 was significantly enhanced. It was concluded by cell transfection technique, Hela cells could express IL-12 and were more easily killed by lymphocytes.

Angiogenesis meets immunology: Cytokine gene therapy of cancer

Delivery of cytokine genes at the tumor site in pre-clinical models has been shown to recruit host inflammatory cells followed by inhibition of tumor growth. This local effect is often accompanied by systemic protection mediated by the immune system, mainly by CD8(+) T and NK cells. On this basis, cytokine gene-transduced tumor cells have widely been used as vaccines in clinical trials, which have shown good safety profiles and some local responses but substantial lack of systemic efficacy. Are these findings the end of the story? Possibly not, if major improvements will be attained in the coming years. These should be directed at the level of gene selection and delivery, in order to identify the optimal cytokine and achieve efficient and durable cytokine expression, and at the level of improving immune stimulation, i.e. by co-administration of co-stimulatory molecules including B7 and CD40, or boosting the expression of tumor antigens or MHC class I molecules. Interestingly, some of the cytokines which have shown encouraging anti-tumor activity, including IFNs, IL-4, IL-12 and TNF-alpha, are endowed with anti-angiogenic or vasculotoxic effects, which may significantly contribute to local tumor control. Therapeutic exploitation of this property may result in the design of novel approaches which, by maximizing immune-stimulating and anti-angiogenic effects, could possibly lead to starvation of established tumors in patients.

Gene therapy of ovarian cancer with IFN-alpha-producing fibroblasts: comparison of constitutive and inducible vectors

Ovarian cancer represents a malignancy suitable for cell and gene therapy approaches owing to its containment within the peritoneal cavity, even at advanced tumor stages. As regulation of transgene expression would be preferable for conducting clinical trials for reasons of safety, we investigated whether intraperitoneal (i.p.) administration of retroviral vector-transduced fibroblasts encoding murine interferon-alpha (IFN-alpha) could have therapeutic activity, and compared its effect with the antitumor effects of fibroblasts producing IFN-alpha under a rapamycin analogue (AP21967)-inducible promoter. Human and murine fibroblasts were recruited into the solid component of transplantable ovarian cancer-grown i.p. in severe combined immunodeficiency mice. Multiple administrations of fibroblasts producing IFN-alpha in a constitutive manner showed therapeutic efficacy, leading to significant prolongation of survival in the majority of animals, associated with inhibition of tumor angiogenesis. Compared to cells transduced by the constitutive vector, fibroblasts transduced by the inducible vector released twofold higher IFN-alpha levels in vitro, following induction by AP21967, and production of the cytokine was under pharmacologic control both in vitro and in vivo. However, these cells elicited only modest therapeutic effects in vivo. Overall, these findings indicate that intracavitary IFN-alpha gene therapy using engineered fibroblasts requires sustained production of IFN-alpha to achieve durable antitumor effects.

Cellular vehicles for cancer gene therapy: current status and future potential

Cancer is a difficult target for any therapeutic strategy; therefore, there is a continuous search for new therapeutic modalities, for application either alone or in combination. In this regard, gene-based therapy is a new approach that offers hope of improved control of tumors. Intensive research to apply gene therapy for cancer treatment has led to identification of the most important technical and theoretical barriers that need to be overcome for clinical success. One of the central unresolved challenges remains the issue of specific and efficient delivery of genes to target cells or tissues, emphasizing the importance of the gene carrier. Along with different viral and non-viral vector systems, mammalian cells have also been considered as vehicles for delivery of anti-cancer therapeutics. The cell-based delivery approach was introduced as the first attempt to apply gene therapy to cancer treatment, and in general, has followed most of the ups and downs of gene therapy applications, progressing alongside new knowledge gained in this field. As a result, significant progress has been made in some aspects of the cell-based approach, while the development of other essential issues is only just gaining speed. It appears that the initial phase of development of cell-based protocols - the achievement of efficient ex vivo cell loading with therapeutics - has largely been fulfilled. However, the desired efficacy of cell-based strategies in general has not yet been reached, and specificity of tumor homing needs to be improved considerably. There is hope that advances in related scientific fields will promote the utilization of cells as powerful and versatile vehicles for cancer gene therapy.

Retroviral gene transfer of interferon-inducible protein 10 inhibits growth of human melanoma xenografts

Interferon-inducible protein 10 (IP-10) is an immunomodulatory chemokine recently recognized to have potent antiangiogenic activity in vivo. Due to difficulties in the stability, manufacture and chronic administration of recombinant forms of endogenous antiangiogenic proteins, antiangiogenic gene therapy has emerged as a promising new form of cancer treatment. We retrovirally transduced A375 human melanoma cells with the human IP-10 gene and injected cells subcutaneously into nude mice. IP-10-transduced cells also were mixed with null-transduced cells in varying proportions before injection. In vivo growth of IP-10-transduced melanoma cells was markedly diminished compared to parental or null-transduced cells (p = 0.0002, Kruskal-Wallis test). This growth inhibition was associated with a marked reduction in microvessel density. The degree of growth inhibition of tumors following injection of a mixed population of null- and IP-10-transduced cells was directly associated with the fraction of IP-10-transduced cells present. We conclude that retroviral transduction of human melanoma cells with the IP-10 gene leads to sufficient protein secretion to inhibit angiogenesis and tumor growth. These findings suggest that IP-10 gene therapy might be an effective therapy in patients with cancer.

Effect of retroviral endostatin gene transfer on subcutaneous and intraperitoneal growth of murine tumors

BACKGROUND

Inhibiting tumor angiogenesis is a promising new strategy for treating cancer. Difficulties with the stability, manufacture, and long-term administration of recombinant antiangiogenic proteins have prompted investigators to use gene therapy to generate these proteins in vivo. We investigated whether transfer of the gene encoding the angiogenesis inhibitor endostatin into the murine liver cell line NMuLi could inhibit tumor growth in vivo.

METHODS

NMuLi cells were transduced with retroviral vectors containing the murine endostatin gene. The presence and function of endostatin in transduced cell supernatants were confirmed by competitive enzyme immunoassay and endothelial cell proliferation assays. Nude mice were given a subcutaneous or intraperitoneal injection with NMuLi cells, control transduced cells (NEF-null), or endostatin-transduced clones (NEF-Endo1 to 4) and were monitored for tumor growth. All statistical tests were two-sided.

RESULTS

Supernatants from the clone secreting the lowest amount of endostatin (NEF-Endo4, 28 ng/mL) inhibited endothelial cell proliferation by 6% (95% confidence interval [CI] = 0% to 12%), and those from the clone secreting the highest amount (NEF-Endo1, 223 ng/mL) inhibited endothelial cell proliferation by 20% (95% CI = 13% to 27%). Increased levels of endostatin were detected in tumor lysates, but not serum, of mice given a subcutaneous injection of NEF-Endo1 cells. After 63 days, mice given a subcutaneous injection of parental NMuLi or NEF-null cells had tumor volumes of 2400 mm(3) (95% CI = 1478 mm(3) to 3300 mm(3)) and 2700 mm(3) (95% CI = 2241 mm(3) to 3144 mm(3)), respectively, compared with mean tumor volumes of less than 30 mm(3) in mice given an injection of NEF-Endo clones, a statistically significant difference (P<.001). After 123 days, all 16 mice given an intraperitoneal injection of parental NMuLi or NEF-null cells had died, compared with only three (9%) of 32 mice given an injection of NEF-Endo clones.

CONCLUSIONS

Retroviral endostatin gene transfer leads to secretion of functional endostatin that is sufficiently active to inhibit tumor growth. Further studies of retroviral endostatin gene transfer for the treatment of cancer are warranted.