Virulizin(R) - A review of its antineoplastic activity

Virulizin induces production of IL-17E to enhance antitumor activity by recruitment of eosinophils into tumors

Virulizin has demonstrated strong antitumor efficacy in a variety of human tumor xenograft models including melanoma, pancreatic cancer, breast cancer, ovarian cancer and prostate cancer. Our previous studies have demonstrated that macrophages, NK cells, and cytokines are important in the antitumor mechanism of Virulizin. Virulizin treatment of tumor bearing mice results in the expansion as well as increased activity of monocytes/macrophages and production of cytokines IL-12 and TNFalpha and activation of NK cells. In this study we show that the inflammatory cytokine IL-17E (IL-25) is induced by Virulizin treatment and is part of its antitumor mechanism. IL-17E is a proinflammatory cytokine, which induces a T(H)2 type immune response, associated with eosinophil expansion and infiltration into mucosal tissues. IL-17E was increased in sera of Virulizin-treated mice bearing human melanoma xenografts, compared to saline-treated controls, as shown by 2D gel electrophoresis and ELISA. Treatment of splenocytes in vitro with Virulizin resulted in increased IL-17E mRNA expression, which peaked between 24 and 32 h post-stimulation. Both in vitro and in vivo experiments demonstrated that B cells produced IL-17E in response to Virulizin treatment. Furthermore, Virulizin treatment in vivo resulted in increased blood eosinophilia and eosinophil infiltration into tumors. Finally, injection of recombinant IL-17E showed antitumor activity towards xenografted tumors, which correlated with increased eosinophilia in blood and tumors. Taken together, these results support another antitumor mechanism mediated by Virulizin, through induction of IL-17E by B cells, leading to recruitment of eosinophils into tumors, which may function in parallel with macrophages and NK cells in mediating tumor destruction.

Virulizin, a novel immunotherapy agent, stimulates TNFalpha expression in monocytes/macrophages in vitro and in vivo

Virulizin, a novel biological response modifier, has demonstrated broad antitumor efficacy in a variety of human tumor xenograft models including melanoma, pancreatic cancer, breast cancer, ovarian cancer and prostate cancer. Previous studies have demonstrated a significant role of macrophages and NK cells in the antitumor mechanism of Virulizin. Increased activity and expansion of macrophages and NK cells has been observed in mice treated with Virulizin. In the present study, the effects of Virulizin on TNFalpha expression were investigated in vitro and in vivo. CD-1 nude mice were treated with Virulizin daily for 5 days. Quantitative RT-PCR demonstrated that the level of TNFalpha mRNA increased in peritoneal macrophages isolated from Virulizin-treated mice as compared to the control group. An increase in TNFalpha protein expression was also observed, as assessed by flow cytometric analysis. Increased levels of TNFalpha mRNA were seen in human tumor xenografts following treatment of tumor-bearing mice with Virulizin. In the presence of LPS, Virulizin also stimulated TNFalpha protein secretion and mRNA expression in human monocytic U937 cells and mouse macrophage RAW264.7 cells in vitro in a time- and dose-dependent manner. U937 cells treated with Virulizin showed a significantly enhanced cytotoxicity that was eliminated upon neutralization of TNFalpha. Virulizin also induced the phosphorylation of IkappaB, suggesting that induction of TNFalpha expression by Virulizin is mediated by activation of NFkappaB. The results indicate that Virulizin-induced TNFalpha expression contributes to modulation of immune responses and antitumor activities.

Efficacy of systemic therapy in advanced pancreatic carcinoma

With a worldwide incidence of more than 200,000 cases and almost as many deaths, pancreatic carcinoma (PC) remains one of the leading causes of cancer deaths, especially in the Western world. Due to the late onset of symptoms, almost all patients suffer from disseminated disease at the time of diagnosis and only a minority will ever be candidates for radical surgery. Only about one tenth of the operated patients remain disease free. For these reasons, development of effective palliative systemic therapy is important. Almost a decade ago, gemcitabine replaced 5-Fu as the gold standard in systemic treatment of advanced PC. Since then, a number of trials have investigated the potential additional effect of several cytotoxic or targeted agents in combination with gemcitabine. As shown in this review, nearly all these trials have proved disappointing. This review provides an overview of the results of current phase III trials of gemcitabine based systemic therapy. Furthermore, we discuss the role of systemic therapy compared to BSC only and the potential future role of targeted therapies.

Virulizin, a novel immunotherapy agent, activates NK cells through induction of IL-12 expression in macrophages

Virulizin, a novel biological response modifier, has demonstrated significant antitumor efficacy in a variety of human tumor xenograft models including melanoma, pancreatic cancer, breast cancer, ovarian cancer and prostate cancer. The significant role of macrophages and NK (Natural killer) cells was implicated in the antitumor mechanism of Virulizin where expansion as well as increased activity of macrophages and NK cells were observed in mice treated with Virulizin. Depletion of macrophages compromised Virulizin-induced NK1.1+ cell infiltration into xenografted tumors and was accompanied by reduced antitumor efficacy. In the present study, involvement of macrophages in NK cell activation was investigated further. We found that depletion of NK cells in CD-1 nude mice by anti-ASGM1 antibody significantly compromised the antitumor activity of Virulizin. Cytotoxicity of NK cells isolated from Virulizin-treated mice was enhanced against NK-sensitive YAC-1 cells and C8161 human melanoma cells, but not against NK-insensitive P815 cells. An increased level of IL-12beta was observed in the serum of mice treated with Virulizin. IL-12 mRNA and protein levels were also increased in peritoneal macrophages isolated from Virulizin-treated mice. Moreover, Virulizin-induced cytotoxic activity of NK cells isolated from the spleen was abolished when an IL-12 neutralizing antibody was co-administered. In addition, depletion of macrophages in mice significantly impaired Virulizin-induced NK cell cytotoxicty. Taken together, the results suggest that Virulizin induces macrophage IL-12 production, which in turn stimulates NK cell-mediated antitumor activity.

NK cell activation and tumor infiltration are involved in the antitumor mechanism of Virulizin

Previous studies have demonstrated antitumor efficacy of Virulizin in several human tumor xenograft models and a critical role for macrophages in the antitumor mechanism of Virulizin. Although there is growing support for an immune stimulatory mechanism of action for Virulizin, the details remain to be elucidated. The aim of this study was to determine whether infiltration of natural killer (NK) cells into xenografted tumors is altered by Virulizin treatment, and whether such alterations contribute to the antitumor activity of Virulizin. Immunohistochemical analysis demonstrated that xenografted tumors from Virulizin-treated mice had an increase in infiltration of F4/80(+) (macrophages) and NK1.1(+) (NK) cells. The increase in NK1.1(+) cell infiltration occurred at an early stage of Virulizin treatment, which correlated with an early sign of apoptosis. In addition, Virulizin resulted in an increase in the number of NK cells in the spleens, and NK cells isolated from the spleen exhibited increased cytotoxicity to tumor cells in vitro. In NK cell-deficient SCID-beige mice, the antitumor activity of Virulizin was compromised, providing additional support to the hypothesis that NK cells are necessary for inhibition of tumor growth by Virulizin. Finally, depletion of macrophages resulted in the loss of Virulizin-induced increase in NK1.1(+) cell infiltration into xenografted tumors, suggesting the involvement of macrophages in NK cell infiltration into tumors. Taken together, these results strongly support a mechanism in which Virulizin stimulates a sustained expansion and infiltration of NK cells and macrophages into tumors with subsequent activation of NK cells that is responsible for the observed antitumor activity.

Preclinical efficacy of Virulizin in human breast, ovarian and prostate tumor models

Virulizin is a novel biological response modifier (BRM) approved for the treatment of melanoma and is currently in a phase III clinical trial against advanced pancreatic cancer. The purpose of this study was to define the anti-cancer activity of Virulizin against a number of solid human tumors. The therapeutic effect of Virulizin was evaluated in mouse xenograft models, and the results demonstrate that Virulizin has high efficacy against breast, ovarian and prostate tumor xenografts. Seventy-seven percent inhibition, with an optimal T/C value of 24.8%, was observed in human beast MDA-MB-231 xenografts treated with Virulizin as compared to saline-treated controls (p=0.0004). In human ovarian SK-OV-3 tumor xenografts, administration of Virulizin inhibited tumor growth by 77.6% compared to saline controls (p=0.0439). Furthermore, high anti-tumor activity was also demonstrated in DU145 and PC-3 prostate tumor xenografts, as indicated by 72.6 and 49.1% suppression of tumor growth (versus saline controls, p=0.0007 or p=0.0049), respectively. Direct comparisons with the anti-tumor activities of conventional drugs demonstrated that Virulizin has higher or equal efficacy against all four tumors tested. Finally, addition of Virulizin into co-cultures of tumor cells and macrophages stimulated the cytolytic activity of the macrophages against the tumor cells in a dose-dependent manner. This result suggests that stimulation of immune cells is at least part of the anti-tumor mechanism of action of Virulizin. These results clearly demonstrate that Virulizin inhibits the growth of human breast, ovarian and prostate tumors, indicating great potential for expansion of the clinical indications for this novel BRM.

Antitumor activity of Virulizin, a novel biological response modifier (BRM) in a panel of human pancreatic cancer and melanoma xenografts

PURPOSE

To define the anticancer efficacy of Virulizin in vivo as a single agent or in combination with conventional drugs in human pancreatic tumor and melanoma xenografts.

METHODS

The therapeutic effect of Virulizin was evaluated in a series of human tumor xenografts in athymic nude mice.

RESULTS

Virulizin had a high level of antitumor activity against all the pancreatic tumors (BxPC-3, SU 86.86. and Mia-PaCa-2) and melanomas (C8161 and A2058), as indicated by suppression of tumor growth with an optimal T/C value of <or=40% when administered as a single agent. No significant changes in Virulizin antitumor activity were observed when different schedules (3 days/week vs 7 days/week) or routes of administration (i.p. vs i.m.) were used. In combination therapy, Virulizin significantly enhanced the antitumor activity of gemcitabine and 5-fluorouracil against pancreatic tumors and of dacarbazine against metastatic melanomas, as reflected by a further decrease in tumor growth as compared to tumors in animals treated with the conventional drugs alone.

CONCLUSION

These studies suggest that Virulizin effectively inhibits the growth of solid human pancreatic tumors and melanomas in the xenograft model.

A critical review of T cell targeting immunotherapy in pancreatic cancer: only a hypothesis or a real hope for the patients?

T cell targeting immunotherapy is now being investigated in patients with pancreatic carcinomas. Until recently this therapeutic strategy has been used as a single specific treatment and clinical studies have demonstrated that tumour-specific T cell responses can be induced in a subset of patients and even in patients with advanced disease. However, it remains to be demonstrated whether these T cell responses can mediate clinically relevant antitumour reactivity. Furthermore, in vitro studies of cancer cell susceptibility to antitumour T cell reactivity are often limited to cancer cell lines because native tumour cells are frequently not available from patients. It is therefore still a hypothesis that T cell targeting immunotherapy can be developed into an efficient therapeutic strategy in patients with inoperable pancreatic cancer. Future investigations of this therapeutic strategy should probably focus on its incorporation into treatment regimens that also include other newer treatment strategies, for example tumour-reactive antibodies coupled with toxins or cytotoxic drugs, improved vaccination procedures probably including the use of dendritic cells and enhancement of antigenic presentation in the tumour microenvironment. T cell targeting immunotherapy will contribute to the hope of curative treatment in patients with inoperable tumours if such combinatory approaches can be developed.

Novel treatments and therapies in development for pancreatic cancer

Until recently, 5-fluorouracil was the most widely used treatment for non-resectable pancreatic cancer. This treatment, however, only resulted in a median survival time of approximately 4 months. In the last few years, gemcitabine has rapidly become the new treatment benchmark, due more to its superior clinical benefit rather than to it conferring an increased median survival (approximately 5-6 months). Thus, the outlook for patients with pancreatic cancer is still relatively bleak. A number of new treatment options are presently being investigated. Some of these are combination therapies involving gemcitabine and other chemotherapeutic agents or radiation. Other novel treatment strategies are also already being evaluated in clinical studies. Some of the more promising treatments in development are discussed and evaluated in this article.