Imatinib Mesylate Exerted Antitumor Effect by Promoting Infiltration of Effector T Cells in Tumor.

Imatinib mesylate is a potent tyrosine kinase inhibitor that may induce immunological effects, such as inhibition of immune suppressive cells; but, how it modulates the immune system remains to be completely elucidated. In this study, we showed that cell proliferation of CT26 colon cancer and Lewis lung carcinoma (3LL) lung cancer cells was not inhibited by imatinib in vitro, although its administration significantly suppressed the growth of CT26, but not 3LL, subcutaneous tumors, and prolonged survival in CT26 tumor-bearing mice. Further, we examined the expression of immune cell-related molecules in the tumors to elucidate the differences in imatinib-mediated antitumor effects between CT26 and 3LL tumors. The nCounter assay showed that the expression of CD8 and CD8+ T cell-recruiting chemokine genes was significantly elevated in imatinib-treated CT26 tumors than that in control tumors; however, the gene expression remained unchanged in imatinib-treated or control 3LL tumors. Furthermore, frequency of interferon-γ+ (IFN-γ+) CD8+ T cells was increased in imatinib-treated CT26 tumors than control tumors, indicating induction of antitumor immunity by imatinib. The analysis indicates that imatinib promotes infiltration of effector T cells in tumors by upregulating expression of cytokines that recruit CD8+ T cells in the tumor microenvironment, which may lead to a strong antitumor effect.

Local Administration of GITR Agonistic Antibody Induces a Stronger Antitumor Immunity than Systemic Delivery.

An anti-glucocorticoid induced TNF receptor (GITR) agonistic antibody (Ab) induces an antitumor immunity with both stimulation of effector T cells and inhibition of regulatory T cell activity. To enhance GITR Ab-mediated tumor immunity, we focused on the intratumoral route, since a tumor-localized high concentration of Ab would confer activation of only tumor-infiltrating T cells. First, in a murine colon cancer model, we showed that the intratumoral delivery of Ab significantly increased the number of effector T cells infiltrated into tumors, and suppressed tumor growth more effectively than the intraperitoneal and intravenous injections did. Then, we found that the injection of Ab into the peritumoral area induced a systemic antitumor immunity at a similar level to the intratumoral injection. Therefore, we hypothesized that the transfer of locally administrated Ab into tumor-draining lymph nodes (TDLNs) plays an important role in inducing an effective immunity. In fact, intratumorally or peritumorally injected Ab was detected in TDLNs, and resection of Ab-injected TDLNs significantly reduced GITR Ab-mediated systemic tumor immunity. Intratumoral injection showed less number of auto-reactive T cells in the spleen than the intraperitoneal injection did. Intratumoral delivery of GITR Ab is a promising approach to induce an effective immunity compared to the systemic delivery.

Pre-immunization of donor lymphocytes with GITR agonistic antibody enhances antitumor immunity in autologous hematopoietic stem cell transplantation.

The lymphopenic condition following autologous hematopoietic stem cell transplantation (HSCT) enhances the proliferation of T cells by engaging tumor-associated antigens, leading to the alteration of the T-cell repertoire towards antitumor immunity. However, cure by autologous HSCT alone have rarely occurred in the clinical setting. Since tumor-reactive lymphocytes preferentially proliferate during reconstitution of the immune system, we examined whether the priming of donor lymphocytes can strengthen the antitumor effect by HSCT in a CT26 murine colon cancer model. The systemic administration of an anti-glucocorticoid-induced TNF receptor (GITR) agonistic antibody (Ab) significantly increased the number of CT26-responsive T cells but not that of auto-reactive lymphocytes in donor mice. The infusion of non-primed and GITR Ab-primed donor lymphocytes suppressed the CT26 tumor growth, and only the primed lymphocytes eliminated tumors in all the treated mice. The frequency of CT26-responsive T cells was elevated in recipient mice infused with both primed and non-primed lymphocytes until 4 weeks after transplantation, while the frequency in recipients with primed lymphocytes was markedly elevated compared with that in mice harboring non-primed lymphocytes at 2 weeks. The frequencies of regulatory T cells and myeloid-derived suppressor cells were elevated in recipient mice infused with primed and non-primed lymphocytes 2 weeks after transplantation, and returned to normal levels by week 4. The combination of autologous HSCT with pre-immunization of donor lymphocytes is a promising strategy to induce strong antitumor immunity.

Strong antitumor efficacy of a pancreatic tumor-targeting oncolytic adenovirus for neuroendocrine tumors.

Although oncolytic adenoviruses are promising cancer therapy agents, for effective oncolytic activity, viruses need to specifically infect and effectively replicate in cancer cells but not in normal cells. We have previously identified a pancreatic cancer-targeting ligand, SYENFSA (SYE), by screening an adenovirus library displaying random peptides against human pancreatic cancer cells and reported that a survivin promoter-regulated adenovirus, displaying the SYE ligand (AdSur-SYE), provided effective oncolysis of pancreatic ductal adenocarcinoma (PDAC) in a preclinical study. As we examined the infectivity of AdSur-SYE in human surgical specimens of various pancreatic tumors, we unexpectedly found that AdSur-SYE showed high gene transduction efficiency for pancreatic neuroendocrine tumors (PNETs) as well as for PDAC, 9.1- and 6.2-fold, respectively, compared to that of the nontargeting virus (AdSur). The infectivity of both vectors was almost the same in other cancers and organs such as the pancreas. Immunostaining indicated that the cells infected with AdSur-SYE were PNET cells but not stromal cells. AdSur-SYE showed a significantly higher oncolytic potency than that of AdSur in human PNET cell lines, and intratumoral infection with AdSur-SYE completely diminished subcutaneous tumors in a murine model, in which AdSur-SYE effectively proliferated and spread. AdSur-SYE exerted a stronger oncolytic effect in primary PNET cells cocultured with mouse embryonic fibroblasts than AdSur did. Thus, AdSur-SYE shows promise as a next-generation therapy for PNET.

A Tumor-targeting Adenovirus with High Gene-transduction Efficiency for Primary Pancreatic Cancer and Ascites Cells.

BACKGROUND: Optimizing targeting strategies for vectors in order to enhance antitumor activity and secure patient safety is important for cancer gene therapy. We previously identified two pancreatic cancer-targeting ligands (PFWSGAV: PFW and SYENFSA: SYE) by screening an adenovirus library in vivo and in vitro, respectively. MATERIALS AND METHODS: To examine clinical usefulness, we assessed gene-transduction efficiency using surgically-resected pancreatic cancer specimens and ascites cells. RESULTS: For surgical specimens, vectors displaying PFW and SYE improved transduction efficiency by 4.4- and 4.3-fold, respectively. The SYE-displaying vector was >2-fold more efficient for all seven cases, whereas the PFW-displaying vector increased efficiency in two out of four cases. For ascites samples, both vectors increased gene-transduction efficiency of epithelial cell adhesion molecule (EpCAM)-positive ascites cells by >2-fold in two out of five cases. CONCLUSION: Both vectors enhanced adenovirus infectivity of pancreatic cancer cells and have potential for gene therapy of pancreatic cancer; therefore they should be further evaluated in clinical studies.