Novel Antibody-Drug Conjugate with Anti-CD26 Humanized Monoclonal Antibody and Transcription Factor IIH (TFIIH) Inhibitor, Triptolide, Inhibits Tumor Growth via Impairing mRNA Synthesis.

Here, we report a novel antibody drug conjugate (ADC) with the humanized anti-CD26 monoclonal antibody YS110 and triptolide (TR-1). YS110 has an inhibitory activity against the CD26-positive tumor growth via the immunological and direct pathway, such as intra-nuclear transportation of CD26 and YS110, and suppressed transcription of RNA polymerase II (Pol II) subunit POLR2A. The ADC conjugated with YS110 and an antitumor compound triptolide (TR-1), which is an inhibitor for TFIIH, one of the general transcription factors for Pol II was developed. YS110 and triptolide were crosslinked by the heterobifunctional linker succinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate (SMCC) and designated Y-TR1. Antitumor efficacy of Y-TR1 against malignant mesothelioma and leukemia cell lines were assessed by the in vitro cell viability assay and in vivo assay using xenografted mouse models. Y-TR1 showed significant cytotoxicity against CD26-positive cell lines but not CD26-negative counterparts in a dose-dependent manner via suppression of mRNA synthesis by impairment of the Pol II activity. The tumors in xenografted mice administered Y-TR1 was smaller than that of the unconjugated YS110 treated mice without severe toxicity. In conclusion, the novel compound Y-TR1 showed antitumor properties against CD26-positive cancer cell lines both in vitro and in vivo without toxicity. The Y-TR1 is a unique antitumor ADC and functions against Pol II.

Development of novel monoclonal antibodies with specific binding affinity for denatured human CD26 in formalin-fixed paraffin-embedded and decalcified specimens.

A 110-kDa type II transmembrane glycoprotein with dipeptidyl peptidase IV (DPPIV) activity in its extracellular region, CD26 has a multitude of biological functions and plays an important role in the regulation of inflammatory responses and tumor biology. Our work has focused on CD26 as a novel therapeutic target for various tumors and immune disorders, and we have recently developed a humanized anti-CD26 monoclonal antibody (mAb), YS110, which has promising safety profile and clinical activity in patients with malignant pleural mesothelioma. The development of an anti-human CD26 mAb that can clearly and reliably detect the denatured CD26 molecule in formalin-fixed paraffin-embedded (FFPE) tissues in the clinical setting is therefore of the utmost importance. To develop novel anti-CD26 mAbs capable of binding to denatured CD26, we immunized mice with urea-treated CD26 protein. Hybridoma supernatants were screened for specific reactivity with human CD26 by immunostaining through the use of a set of FFPE human CD26-positive or negative tumor cell lines. This screening method enables us to develop novel anti-human CD26 mAbs suitable for immunohistochemical staining of CD26 in FFPE non-tumor and tumor tissue sections with reliable clarity and intensity. Specifically, these mAbs display strong binding affinity to denatured human CD26 rather than undenatured human CD26, and are capable of detecting denatured human CD26 in decalcified specimens. These novel anti-CD26 mAbs are potentially useful for the analysis of CD26 expression in cancer patients with bony metastasis, and may help decide the appropriateness of YS110 therapy for future cancer patients.

A humanized anti-CD26 monoclonal antibody inhibits cell growth of malignant mesothelioma via retarded G2/M cell cycle transition.

BACKGROUND: Malignant Mesothelioma (MM) is a highly aggressive tumor with poor prognosis. Multimodal treatments and novel molecular targeted therapies against MM are in high demand in order treat this disease effectively. We have developed a humanized monoclonal antibody YS110 against CD26 expressed in 85 % of MM cases. CD26 is thought to be involved in tumor growth and invasion by interacting with collagen and fibronectin, or affecting signal transduction processes. METHODS: We evaluated the direct anti-tumor effect of YS110 against MM cell lines, NCI-H2452 and JMN, and investigated its effects on cell cycle and on the cell cycle regulator molecules. In addition, we investigated synergistic effects of YS110 and anti-tumor agent pemetrexed (PMX) against MM cell line both in vitro and in vivo. RESULTS: YS110 suppressed the proliferation of NCI-H2452 cells by approximately 20 % in 48 h. Based on cell cycle analysis, percentage of cells in G2/M phase increased 8.0 % on the average after YS110 treatment; in addition, cell cycle regulator p21 cip/waf1 was increased and cyclin B1 was decreased after YS110 treatment. Inhibitory phosphorylation of both cdc2 (Tyr15) and cdc25C (Ser216) were elevated. Furthermore, activating phosphorylation of p38 MAPK (Thr180/Tyr182) and ERK1/2 (Thr202/Tyr204) were augmented at 24 h after YS110 treatment. PMX rapidly induced CD26 expression on cell surface and the treatment with both YS110 and PMX inhibited in vivo tumor growth accompanied by a synergistic reduction in the MIB-1 index. CONCLUSION: This is a first report of a novel anti-proliferative mechanism of the humanized anti-CD26 monoclonal antibody YS110, which resulted in G2/M cell cycle delay through regulation of quantity and activity of various cell cycle regulating molecules.

Blockade of CD26 signaling inhibits human osteoclast development.

Bone remodeling is maintained by the delicate balance between osteoblasts (OBs) and osteoclasts (OCs). However, the role of CD26 in regulating bone remodeling has not yet been characterized. We herein show that CD26 is preferentially expressed on normal human OCs and is intensely expressed on activated human OCs in osteolytic bone alterations. Macrophage-colony stimulating factor (M-CSF) and soluble receptor activator of NF-κB ligand (sRANKL) induced human OC differentiation, in association with CD26 expression on monocyte-macrophage lineage cells. CD26 expression was accompanied by increased phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK), which is crucial for early human OC differentiation. The humanized anti-CD26 monoclonal antibody, huCD26mAb, impaired the formation and function of tartrate-resistant acid phosphatase (TRAP)/CD26 positive multi-nucleated (nuclei > 3) OCs with maturation in the manner of dose-dependency. It was revealed that huCD26mAb inhibits early OC differentiation via the inactivation of MKK3/6, p38 MAPK and subsequent dephosphorylation of microphthalmia-associated transcription factor (mi/Mitf). These inhibitions occur immediately after RANKL binds to RANK on the human OC precursor cells and were demonstrated using the OC functional assays. huCD26mAb subsequently impaired OC maturation and bone resorption by suppressing the expression of TRAP and OC fusion proteins. In addition, p38 MAPK inhibitor also strongly inhibited OC formation and function. Our results suggest that the blockade of CD26 signaling impairs the development of human functional OCs by inhibiting p38 MAPK-mi/Mitf phosphorylation pathway and that targeting human OCs with huCD26mAb may have therapeutic potential for the treatment of osteolytic lesions following metastasis to alleviate bone destruction and reduce total skeletal-related events (SREs).

Nuclear localization of CD26 induced by a humanized monoclonal antibody inhibits tumor cell growth by modulating of POLR2A transcription.

CD26 is a type II glycoprotein known as dipeptidyl peptidase IV and has been identified as one of the cell surface markers associated with various types of cancers and a subset of cancer stem cells. Recent studies have suggested that CD26 expression is involved in tumor growth, tumor invasion, and metastasis. The CD26 is shown in an extensive intracellular distribution, ranging from the cell surface to the nucleus. We have previously showed that the humanized anti-CD26 monoclonal antibody (mAb), YS110, exhibits inhibitory effects on various cancers. However, functions of CD26 on cancer cells and molecular mechanisms of impaired tumor growth by YS110 treatment are not well understood. In this study, we demonstrated that the treatment with YS110 induced nuclear translocation of both cell-surface CD26 and YS110 in cancer cells and xenografted tumor. It was shown that the CD26 and YS110 were co-localized in nucleus by immunoelectron microscopic analysis. In response to YS110 treatment, CD26 was translocated into the nucleus via caveolin-dependent endocytosis. It was revealed that the nuclear CD26 interacted with a genomic flanking region of the gene for POLR2A, a subunit of RNA polymerase II, using a chromatin immunoprecipitation assay. This interaction with nuclear CD26 and POLR2A gene consequently led to transcriptional repression of the POLR2A gene, resulting in retarded cell proliferation of cancer cells. Furthermore, the impaired nuclear transport of CD26 by treatment with an endocytosis inhibitor or expressions of deletion mutants of CD26 reversed the POLR2A repression induced by YS110 treatment. These findings reveal that the nuclear CD26 functions in the regulation of gene expression and tumor growth, and provide a novel mechanism of mAb-therapy related to inducible translocation of cell-surface target molecule into the nucleus.