Masahiro Inoue

An amino-bisphosphonate targets MMP-9–expressing macrophages and angiogenesis to impair cervical carcinogenesis

A mouse model involving the human papillomavirus type-16 oncogenes develops cervical cancers by lesional stages analogous to those in humans. In this study the angiogenic phenotype was characterized, revealing intense angiogenesis in high-grade cervical intraepithelial neoplasias (CIN-3) and carcinomas. MMP-9, a proangiogenic protease implicated in mobilization of VEGF, appeared in the stroma concomitant with the angiogenic switch, expressed by infiltrating macrophages, similar to what has been observed in humans. Preclinical trials sought to target MMP-9 and angiogenesis with a prototypical MMP inhibitor and with a bisphosphonate, zoledronic acid (ZA), revealing both to be antiangiogenic, producing effects comparable to a Mmp9 gene KO in impairing angiogenic switching, progression of premalignant lesions, and tumor growth. ZA therapy increased neoplastic epithelial and endothelial cell apoptosis without affecting hyperproliferation, indicating that ZA was not antimitotic. The analyses implicated cellular and molecular targets of ZAs actions: ZA suppressed MMP-9 expression by infiltrating macrophages and inhibited metalloprotease activity, reducing association of VEGF with its receptor on angiogenic endothelial cells. Given its track record in clinical use with limited toxicity, ZA holds promise as an unconventional MMP-9 inhibitor for antiangiogenic therapy of cervical cancer and potentially for additional cancers and other diseases where MMP-9 expression by infiltrating macrophages is evident.

VEGF-A has a critical, nonredundant role in angiogenic switching and pancreatic β cell carcinogenesis

In the RIP1-Tag2 mouse model of pancreatic islet carcinoma, angiogenesis is switched on in a discrete premalignant stage of tumor development, persisting thereafter. Signaling through VEGF receptor tyrosine kinases is a well-established component of angiogenic regulation. We show that five VEGF ligand genes are expressed in normal islets and throughout islet tumorigenesis. To begin dissecting their contributions, we produced an islet beta cell specific knockout of VEGF-A, resulting in islets with reduced vascularity but largely normal physiology. In RIP1-Tag2 mice wherein most oncogene-expressing cells had deleted the VEGF-A gene, both angiogenic switching and tumor growth were severely disrupted, as was the neovasculature. Thus, VEGF-A is crucial for angiogenesis in a prototypical model of carcinogenesis, whose loss is not readily compensated.

Progressive vascular changes in a transgenic mouse model of squamous cell carcinoma

Phage display was used to identify homing peptides for blood vessels in a mouse model of HPV16-induced epidermal carcinogenesis. One peptide, CSRPRRSEC, recognized the neovasculature in dysplastic skin but not in carcinomas. Two other peptides, with the sequences CGKRK and CDTRL, preferentially homed to neovasculature in tumors and, to a lesser extent, premalignant dysplasias. The peptides did not home to vessels in normal skin, other normal organs, or the stages in pancreatic islet carcinogenesis in another mouse model. The CGKRK peptide may recognize heparan sulfates in tumor vessels. The dysplasia-homing peptide is identical to a loop in kallikrein-9 and may bind a kallikrein inhibitor or substrate. Thus, characteristics of the angiogenic vasculature distinguish premalignant and malignant stages of skin tumorigenesis.

Tumor hypoxia : A target for selective cancer therapy

Tumor hypoxia has been considered to be a potential therapeutic problem because it renders solid tumors more resistant to sparsely ionizing radiation (IR) and chemotherapeutic drugs. Moreover, recent laboratory and clinical data have shown that tumor hypoxia is also associated with a more malignant phenotype and poor survival in patients suffering from various solid tumors. Therefore, selective targeting of hypoxic tumor cells has been explored, and since severe hypoxia (pO2<0.33%, 2.5 mmHg) does not occur in normal tissue, tumor hypoxia could be exploited for therapeutic advantage. However, the following three characteristics of hypoxic tumor regions present obstacles in targeting hypoxic cells. First, it is difficult to deliver a sufficient amount of drug to a region that is remote from blood vessels. Second, one must specifically target hypoxic tumor cells while sparing normal well‐oxygenated tissue from damage. Finally, the severely hypoxic tumor cells to be attacked have often stopped dividing. Therefore, high delivery efficiency, high specificity and selective cytotoxicity are all necessary to target and combat hypoxic tumor cells. The current review describes progress on the biological aspects of tumor hypoxia and provides a compilation of the recent molecular approaches used to target hypoxic tumors. These approaches include our work with a unique hypoxia‐targeting protein drug, TOP3, with which we have sought to address the above three difficulties.

CD4+ T Cell-Mediated Antigen-Specific Immunotherapy in a Mouse Model of Cervical Cancer

A major agenda for tumor immunology is the generation of specific immune responses leading to the destruction of incipient and frank neoplasia. In this report, we show that a novel HPV16 E7 fusion protein can produce objective therapeutic responses against incipient cervical cancer in genetically engineered mice that express in the cervix the HPV16 early region genes implicated as causative agents in human cervical cancer. Although nonresponsive toward the HPV16 E7 oncoprotein in the CD8+ T-cell compartment by virtue of MHC haplotype, the mice were capable of mounting an induced CD4+ T-cell response against E7, and in addition developed spontaneous anti-E7 antibodies. HPV16/CD4-/- mice showed increased tumor burden indicative of CD4-mediated immune surveillance. Seeking to enhance the CD4 response, we immunized mice bearing incipient cervical cancer with a recombinant protein fusing E7 with a mycobacterial heat shock protein. The incidences of cervical carcinoma and of high-grade dysplasia (CIN 3) were consequently reduced by comparison to control mice. Thus, an HPV16 E7 immunogen holds promise for noninvasive treatment and prevention of human cervical cancer.

Inactivation of Rho GTPases by p190 RhoGAP reduces human pancreatic cancer cell invasion and metastasis

A number of small GTPases are involved in cancer cell proliferation, migration and invasion, acting as molecular switches that cycle between GTP‐ and GDP‐bound states. GTPase‐activating proteins (GAPs) have been established as a major class of negative regulators of Rho GTPase signaling. To investigate the biological function of p190 RhoGAP toward RhoA in cancer cell invasion and metastasis, we generated a chimera made of the RhoGAP domain of p190 and the C‐terminus of RhoA (p190‐RhoA chimera), and transfected it into human pancreatic cancer cells, AsPC‐1. Epidermal growth factor (EGF)‐induced activation of RhoA, as well as RhoB and RhoC, to a lesser extent, was significantly inhibited in p190‐RhoA chimera‐transfected AsPC‐1 cells compared with that of control cells (mock‐infected), when assessed by pull‐down assay for GTP‐bound RhoA, RhoB, and RhoC, respectively. EGF‐induced invasion of p190‐RhoA chimera transfectants was significantly inhibited compared with that of mock‐infected cells in a modified Boyden chamber assay. Furthermore, the mice injected intrasplenically with AsPC‐1 cells that overexpressed the p190‐RhoA chimera had a marked reduction in the number and size of metastatic nodules in the liver. These data suggest that the inhibitory action of p190 RhoGAP toward RhoA offers a novel approach to the treatment of invasion and metastasis of cancer cells. (Cancer Sci 2006; 97: 848–853)

Selective inhibition of cancer cell invasion by a geranylgeranyltransferase-I inhibitor

A number of small GTPases are involved in cancer cell proliferation, migration and invasion. They need to be prenylated for full biological functions. We have recently reported that 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors, which block the biosynthesis of farnesylpyrophosphate and geranylgeranylpyrophosphate, inhibit in vitro invasion of human pancreatic cancer cells. In the present study, we examined the effects of two selective inhibitors of prenylation, a farnesyltransferase inhibitor (FTI-277) and a geranylgeranyltransferase type I inhibitor (GGTI-298), on in vitro invasion of cancer cells in a modified Boyden chamber assay. The invasion of COLO 320DM human colon cancer cells was inhibited potently by HMG-CoA reductase inhibitor lovastatin and GGTI-298 but weakly by FTI-277. The treatment of cancer cells with GGTI-298 markedly caused RhoA to decrease in the membrane fraction and accumulate in the cytosolic fraction, whereas it had almost no effect on the translocation of Ras. FTI-277 markedly inhibited membrane localization of Ras, but its inhibitory effect on cancer cell invasion occurred only at doses that affected membrane localization of RhoA. FTI-277 and GGTI-298 decreased the growth potential of COLO 320DM cells, but the inhibitory effect of GGTI-298 was rather selective toward invasion in association with changes in cell morphology and RhoA localization. These results suggest that geranylgeranylation of RhoA by geranylgeranyltransferase type I is critical for cancer cell invasion, and inhibition of geranylgeranyltransferase type I activity should offer a novel approach to the treatment of invasion and metastasis of cancer cells resistant to farnesyltransferase inhibitors.

Cross talk between apoptosis and invasion signaling in cancer cells through caspase-3 activation.

In solid tumors, cancer cells are exposed to various microenvironmental stresses such as hypoxia, nutritional depletion, and low pH. Cancer cells adapt to these stresses and circumvent cell death. When the antiapoptotic signals overcome the stress, cancer cells might acquire physiologic functions, such as invasiveness, instead of cell death. Here, we report that tumor cells acquire an invasive capacity from apoptotic signals through caspase activation. We treated rat ascites hepatoma MM1 cells with an apoptosis-inducing drug, etoposide, or hypoxia, and assessed the invasion capacity with an in vitro bioassay. Although MM1 cells hardly showed invasiveness in serum-free medium, under stress conditions, invasive capacity accompanied with morphologic change was induced with caspase-3 activation. Such stress-induced invasion as well as morphologic change was suppressed by blocking caspase-3 activity with caspase inhibitors or by RNA interference of caspase-3. In contrast, lysophosphatidic acid-induced invasiveness was not affected by caspase-3 inhibition. These results suggest that caspase-3 activation contributes to the stress-induced invasive capacity of these cancer cells.