Cancer peptide vaccines are a promising cancer immunotherapy that can induce cancer-specific cytotoxic T lymphocytes (CTLs) in tumors. However, recent clinical trials of cancer vaccines have revealed that the efficacy of the vaccines is limited. Targeting single antigens and vaccination with short peptides are partly the cause of the poor clinical outcomes. We synthesized a novel multi-epitope long peptide, TAS0314, which induced multiple epitope-specific CTLs in HLA knock-in mice. It also showed superior epitope-specific CTL induction and antitumor activity. We also established a combination treatment model of vaccination with PD-1/PD-L1 blockade in HLA-A*2402 knock-in mice, and it showed a synergistic antitumor effect with TAS0314. Thus, our data indicated that TAS0314 treatment, especially in combination with PD-1/PD-L1 blockade, is a promising therapeutic candidate for cancer immunotherapy.

Background: HER2-targeting antibodies (trastuzumab, pertuzumab) and an antibody-drug conjugate (trastuzumab emtansine: T-DM1) are available for the treatment of HER2 overexpressed breast cancer. TAS0728 is a small molecule, covalent-binding, selective inhibitor of HER2 kinase, and its assessment in humans is ongoing. Although HER2 targeting therapies with trastuzumab/pertuzumab, or T-DM1 initially show clinical activity, those treatments eventually become ineffective due to acquired resistance. Various resistant models to the therapies have been established in vitro to explore novel therapies for resistance. However, those models may not mimic patients’ tumors, because antibody dependent cellular cytotoxicity (ADCC) and/or pharmacokinetics of the drugs were not involved in the establishment of the models. In our previous report, we have established an acquired resistant model to T-DM1 in vivo. The model was sensitive to TAS0728. In the present study, we analyzed the molecular mechanism of T-DM1 resistance and mode of action of TAS0728 in the established model. Furthermore, we established another model with acquired resistance to trastuzumab and pertuzumab in mice, and investigated the sensitivity to TAS0728. Materials and Methods: To establish a resistant model to T-DM1, T-DM1 was administered at 10 mg/kg (q3w, i.v.) in NCI-N87 xenograft model until tumor regression and the subsequent re-growth of tumor were observed. Pharmacodynamics of T-DM1 at 10 mg/kg (q3w, i.v.) or TAS0728 at 60 mg/kg (q.d., p.o.) was evaluated in the tumors. To clarify the resistant mechanisms to T-DM1 and mode of action of TAS0728, molecular profiling of the resistant tumors was conducted by phospho-RTK array, RNA sequencing, and Western blotting. To establish a resistant model to trastuzumab/pertuzumab in vivo, the antibodies were administered concomitantly at 20 mg/kg each (q1w, i.p.) in the NCI-N87 xenograft model until tumor regression and the subsequent re-growth of tumor were observed. The mice were treated with the antibodies at 20 mg/kg each (q1w, i.p.) or TAS0728 at 60 mg/kg (q.d., p.o.) to compare antitumor effects. Results: In the T-DM1 resistant model, TAS0728 exerted antitumor effect associated with HER2 signal inhibition. RNA sequencing revealed that expression level of a candidate gene, which may be involved in the intracellular metabolism of T-DM1, was decreased in the T-DM1 resistant tumor. Alternative RTK activation was not observed. Next, we established a resistant model to trastuzumab/pertuzumab combination therapy in vivo. Although the antibodies initially induced tumor regression in the NCI-N87 xenograft model, ultimately, regrowth of tumors was observed. Once the tumors regrew during the treatment, the antibodies were no longer effective. On the other hand, switching to TAS0728 resulted in significant antitumor effect. Collectively, these results suggested that tumors with acquired resistance to trastuzumab/pertuzumab or T-DM1 are still addicted to the active HER2 signal, and were vulnerable to HER2 inhibition by TAS0728. Conclusion: The acquired resistance models to trastuzumab/pertuzumab or T-DM1 were established in vivo. Selective inhibition of HER2 kinase by TAS0728 is effective in the both resistant models. These results provide a rationale for therapy with TAS0728 in patients refractory to the established anti-HER2 therapy. Citation Format: Hiroki Irie, Rumi Kawabata, Yayoi Fujioka, Fumio Nakagawa, Hideki Nagase, Hiraku Itadani, Kimihiro Ito, Junji Uchida, Shuichi Ohkubo, Kenichi Matsuo, Takeshi Sagara, Teruhiro Utsugi. Acquired resistance to trastuzumab/pertuzumab, or to T-DM1 in vivo can be overcome by HER2 inhibition with TAS0728 [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A126. doi:10.1158/1535-7163.TARG-19-A126

Abstract Background: Ribonucleotide reductase (RNR) is an essential metabolic enzyme that catalyzes a rate-limiting step for de novo dNTP biosynthesis via converting ribonucleotides to deoxyribonucleotides. dNTPs are also supplied through nucleoside salvage pathway in which dNTP is synthesized from extracellular nucleoside. The salvage pathway is also utilized for conversion of several nucleoside analogues to their active metabolites. Given the previous report showing that the inhibition of de novo pathway activates salvage pathway at least in vitro, RNR is considered as a promising target for combination therapy with nucleoside analogues. However, in vivo efficacy of selective RNR inhibitor in combination with nucleoside analogues has not been clarified yet. Previously, we reported a novel class of RNR inhibitor TAS1553, which is a selective and orally available small molecule abrogating protein-protein interaction between RNR subunits. Here, we evaluated the synergistic activity of TAS1553 and several nucleoside analogues in vitro as well as in vivo studies. Material and methods: Antiproliferative activity was assessed by CellTiter-Glo® 2.0 assay. Intracellular and intratumoral ara-CTP amounts were measured by HPLC analysis. Antitumor efficacy was evaluated in athymic nude mice bearing MV-4-11 (human AML) and CFPAC-1 (human pancreatic cancer) cell line. Results: To examine whether TAS1553 plus nucleoside analogues combination shows synergistic efficacy, we evaluated antiproliferative activity of TAS1553 in combination with some nucleoside analogues (cytarabine, gemcitabine, decitabine, and 2F-ara-A) to calculate the combination index (CI). TAS1553 exhibited synergistic antiproliferative activity (CI < 1) against cancer cell lines in combination with all of the tested nucleoside analogues. Then, to analyze the mechanism underlying the synergistic effect, we asked whether treatment with TAS1553 augments the activity of salvage pathway by measuring ara-CTP, which is an active metabolite of cytarabine. The results showed that treatment with TAS1553 significantly increased ara-CTP accumulation in MV-4-11 cells implying that TAS1553 activates nucleoside salvage pathway by inhibiting de novo nucleotide synthesis. Importantly, when analyzing the timing of treatment for the combination, prior or simultaneous treatment with TAS1553 increased ara-CTP amount more than post treatment. Consistently with in vitro result, co-administration of TAS1553 and cytarabine caused significant increase of intratumoral ara-CTP compared with cytarabine administration in MV-4-11 mouse xenograft model. Following this result, the combination of TAS1553 (100 mg/kg/day, q.d.) and cytarabine (10 mg/kg/day, 5 consecutive days) showed superior antitumor efficacy to MV-4-11 tumor than each monotherapy while the combination did not cause intolerable body weight change. Furthermore, TAS1553 also demonstrated the striking anittumor efficacy in combination with gemcitabine (20 mg/kg/day, q.wk.) on CFPAC-1 mouse xenograft model. Conclusions: TAS1553, a novel class of RNR inhibitor, has synergistic antitumor efficacy in combination with nucleoside analogues. These combination therapy could be promising therapeutic options for cancer patients. Citation Format: Takuya Hoshino, Hiroyuki Ueno, Wakako Yano, Sayaka Tsukioka, Seiji Miyahara, Takamasa Suzuki, Kazutaka Miyadera, Teruhiro Utsugi, Takeshi Sagara. TAS1553, a novel class of RNR inhibitor, demonstrates synergistic antitumor efficacy in combination with nucleoside analogues [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A063. doi:10.1158/1535-7163.TARG-19-A063

BackgroundBone erosions and cartilage damages are a pathological hallmark of rheumatoid arthritis (RA) and are associated with poor functional outcome1. Aberrant activations of osteoclasts induced by receptor activator of nuclear factor κB ligand (RANKL)2 are involved in the bone erosions of RA. It has also been recently shown that under chronic inflammatory conditions such as RA, inflammatory cytokines in joints induce pathological osteoclast differentiation and cause excessive bone resorption independent of RANKL-RANK signaling3. The Bruton’s tyrosine kinase (BTK) signaling pathway plays a pivotal role in inflammatory response and bone resorption4. Thus, targeting BTK may be efficacious against not only inflammation but also bone erosion by regulating activation of effector cells such as B cells, macrophages and osteoclasts in RA. We have already shown the inhibitory effects of TAS5315 on RANKL-dependent osteoclast activation. However, it remained uncertain whether TAS5315 inhibits osteoclast activation induced by inflammatory cytokines.ObjectivesIn this study, we evaluated the effects of TAS5315 on osteoclast activation induced by inflammatory cytokines (in vitro) and the infiltration of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts in the joint of a mouse CIA model.MethodsIn vitro biochemical assay was performed using available kinase assay panels. The BioMAP® Diversity PLUS panels were used to determine the profile of TAS5315 in primary human cell systems. The effects of TAS5315 on osteoclasts were assessed by examining osteoclast-mediated bone resorption. TAS5315 was orally administrated once a day in an established mouse CIA model. TRAP-positive osteoclasts were counted manually. Bone mineral density (BMD) and bone erosion were assessed using micro-CT analysis. The mechanical properties of the tibia were evaluated by a compression test of proximal metaphysis using a material-testing machine.ResultsTAS5315 selectively inhibited the enzyme activity of BTK and had less off target inhibition against other kinases. In BioMAP® systems, TAS5315 decreased the production of IgG and the expression of cytokines (TNF-α, IL-6, IL-17A). TAS5315 also inhibited osteoclast-mediated bone resorption induced by inflammatory cytokines. On the other hand, anti-RANKL antibody did not inhibit bone resorption induced by inflammatory cytokines. Futhermore, in the mouse CIA model, TAS5315 significantly ameliorated paw swelling and pathological changes. TAS5315 significantly decreased the infiltration of TRAP-positive osteoclasts in the joint and also showed improvement of BMD and bone erosion by time-dependent micro-CT analysis. In vehicle-treated mice, the mechanical strength of tibia was decreased compared with normal mice. TAS5315-treated mice recovered the decreased parameters of the mechanical strength compared with vehicle-treated mice. These data suggests that TAS5315 improves bone erosion in murine model for RA through direct inhibition of osteoclast activation induced by inflammatory cytokines as well as RANKL.ConclusionOur study demonstrates that TAS5315 would be an attractive RA therapeutic drug that could improve bone destruction as well as inflammation.Reference[1] Nat Rev Rheumatol. 2012;8,656-64. 2: Nat Rev Rheumatol. 2015;11,189-94. 3: Arthritis Rheumatol. 2016;68,2889-2900. 4: Drug Discov Today. 2014;19,1200-4.Disclosure of InterestsNone declared

Abstract Background: Patients with unresectable or metastatic endometrial cancer (EMC) have a poor prognosis. Despite the use of platinum-based chemotherapy in the treatment of EMC, more effective therapy is urgently needed for treatment of unresectable or metastatic cancers. We have shown that TAS4464, a highly selective and the most potent inhibitor of NEDD8-activating enzyme (NAE) to date, induced apoptosis in various cancer cell lines. Here, we evaluated the therapeutic potential of TAS4464 in a preclinical EMC xenograft model and delineated how NAE inhibition leads to antitumor activity in EMC. Materials and Methods: The effect of TAS4464 on cell growth was evaluated in twenty-four EMC cell lines. Cytotoxicity to patient-derived EMC cells was examined at Fukushima Medical University (Japan). The effects of TAS4464 on protein expression and phosphorylation status were evaluated by using Western blotting. To identify the factor responsible for TAS4464-induced DNA damage, RNAi knock-down experiment was performed. The antitumor activity of TAS4464 was evaluated in a HEC-59, EMC xenograft mouse model. Results: TAS4464 markedly inhibited cell growth and induced cell death in all of the human EMC cell lines examined. Evaluation of the cytotoxicity of TAS4464 in platinum-refractory patient-derived EMC cells revealed that TAS4464 inhibited growth in these cells. Treatment with TAS4464 at 100 nmol/L for 24 hours resulted in accumulation both in the S phase of the cell cycle and the fraction containing >4N DNA in all the evaluated EMC cells such as HEC-1-B and HEC-59. Further treatment with TAS4464 for additional 48 hours induced sub-G1 accumulation. Because NAE inhibition inactivates cullin-RING ubiquitin ligases (CRLs), TAS4464 treatment induced substrates of CRLs related to cell cycle control such as c-Myc, p21, p27, and Wee1, and DNA replication such as CDT1 and CDC6 within 8 hours accompanied by phosphorylation of DNA checkpoint-related proteins such as RPA32 and CHK1. Phospho-γH2AX and cleaved-caspase 3 were observed at 48 hours treatment with TAS4464. These data indicate that TAS4464 induced single-strand DNA break first, and then caused double-strand DNA break and apoptosis in EMC cells. In RNAi knockdown among TAS4464-induced substrates of CRLs, CDT1 siRNA pretreatment dramatically suppressed appearance of TAS4464-meadiated >4N DNA fraction and DNA double-strand breaks. These data suggest that induced-CDT1, a licensing factor for DNA replication, increase in >4N DNA fraction by DNA rereplication and results in DNA damage in EMC cells. Once- or twice-a-week administration of TAS4464 at a dose of 100 mg/kg for 3 weeks resulted in tumor growth inhibition (TGI) of 79% and 87% in the HEC-59 xenograft model, respectively, compared with single-dose administration of carboplatin at a dose of 100 mg/kg that resulted in a TGI of only 67% with significant weight loss. Conclusion: TAS4464 was broadly active against EMC cell lines accompanied by DNA damage. TAS4464 also inhibited tumor growth in an EMC xenograft model. These results suggest that TAS4464 deserves further research and development as a novel anticancer agent for EMC. Citation Format: Yu Komiya, Chihoko Yoshimura, Hiromi Muraoka, Shuichi Ohkubo, Fumio Nakagawa, Hiroaki Ochiiwa, Hiroshi Sootome, Takashi Mizutani, Kenichi Matsuo, Teruhiro Utsugi, Yoshikazu Iwasawa. NEDD8-activating enzyme inhibitor TAS4464 inhibits tumor growth in endometrial cancer mouse model accompanied by DNA damage response [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B136.

BACKGROUND:About one-third of the Japanese population suffers from Japanese cedar pollinosis, which is frequently accompanied by Japanese cypress pollinosis. Recently, a novel major Japanese cypress pollen allergen, Cha o 3, was discovered. However, whether a Cha o 3 homolog is present in Japanese cedar pollen remains to be determined. METHODS:Western blot analysis was performed using Cha o 3-specific antiserum. In addition, cloning of the gene encoding Cry j 4 was conducted using total cDNA from the male flower of Japanese cedar trees. Allergen potency and cross-reactivity were investigated using a T-cell proliferation assay, basophil activation test, and ImmunoCAP inhibition assay. RESULTS:A low amount of Cha o 3 homolog protein was detected in Japanese cedar pollen extract. The deduced amino acid sequence of Cry j 4 showed 84% identity to that of Cha o 3. Cross-reactivity between Cry j 4 and Cha o 3 was observed at the T cell and IgE levels. CONCLUSIONS:Cry j 4 was discovered as a counterpart allergen of Cha o 3 in Japanese cedar pollen, with a relationship similar to that between Cry j 1-Cha o 1 and Cry j 2-Cha o 2. Our findings also suggest that allergen-specific immunotherapy (ASIT) using Japanese cedar pollen extract does not induce adequate immune tolerance to Cha o 3 due to the low amount of Cry j 4 in Japanese cedar pollen. Therefore, ASIT using Cha o 3 or cypress pollen extract coupled with Japanese cedar pollen extract is required in order to optimally control allergy symptoms during Japanese cypress pollen season.

BackgroundThe family of Janus kinases (JAKs) plays important roles in signalling pathway mediated by various cytokine receptors. An aberrant activation of JAK-STAT signalling has been reported to be involved in the pathogenesis of autoimmune diseases1. Pan-JAK inhibitors have shown a good efficacy in patient with rheumatoid arthritis (RA)2. However, their use is limited due to safety concerns, including severe herpes zoster infection, by inhibiting JAK1-mediated interferon signaling3. Therefore, a selective JAK3 inhibitor would provide a better balance between efficacy and safety than pan-JAK inhibitors.ObjectivesWe identified the characteristics of TAS8274, a novel highly selective inhibitor of JAK3, using in vitro assays, a mouse model of collagen-induced arthritis (CIA), and a mouse model of herpes simplex virus (HSV)−1 infection.MethodsIn vitro biochemical assay was performed using available kinase assay panels. The effects on anti-inflammatory responses were assessed by examining cytokine productions. IL-2, IL-3, and IFN-α–induced phosphorylation of STAT proteins in peripheral blood mononuclear cells (PBMCs) were analysed by a flow cytometry method. NK cell cytotoxicity in the presence of IFN-α was evaluated by Cr51 release assay. In a mouse skin HSV-1 infection model, TAS8274 and tacrolimus were administered for 7 days before inoculation of the virus on the back skin, and then were administered for another ten consecutive days. At the end of this experiment, the number of papules on the back was counted. To evaluate the therapeutic efficacy using mouse CIA model, TAS8274 was orally administered to CIA mice after the disease onset. Disease severity was evaluated by clinical score of paw swelling, and the scores of inflammation, pannus, cartilage, and bone damage were performed using a modified Mankin score system.ResultsTAS8274 inhibited the enzymatic activity of JAK3 (IC50=0.16 nM), and showed more than 1000-fold selectivity against other JAK kinases. In the cell-based assays, TAS8274 strongly inhibited IL-17 production from differentiated Th17 cells. TAS8274 also suppressed the IL-2-induced STAT5 phosphorylation in PBMCs, but had much lower inhibitory effects on the IFN-α-induced STAT1 phosphorylation. In contrast, Tofacitinib and Baricitinib had robust inhibitory effects on the IFN-α-induced STAT1 phosphorylation. Furthermore, Tofacitinib and Baricitinib dose-dependently reduced the NK cell cytotoxicity, while TAS8274 had little effect on that. Tacrolimus-treated group significantly increased the number of papules compared with vehicle-treated group in a mouse HSV-1 infection model, but TAS8274-treated group did not increase the number of papules. In an established mouse CIA model, TAS8274 dose-dependently reduced the severity of arthritis and histopathological scores compared with vehicle-treated mice.ConclusionsTAS8274 did not inhibit the JAK3-independent STAT signalling pathway in vitro and showed potent efficacy at dose range without exacerbation of the risk of HSV-1 infection. Our study demonstrates that TAS8274 would be an attractive therapeutic agent with excellent balance between efficacy and safety.References[1] Immunity2012;36,542–50. [2] Ann Rheum Dis. 2013;72,111–5. [3] Arthritis Rheumatol2014;66:2675–84.Disclosure of InterestNone declared

298 Background: Recent reports suggest that AR aberrations are involved in the development of metastatic castration-resistant prostate cancer and in resistance to AR-targeted therapies. These aberrations include point mutations, copy number gain, and alternatively spliced AR forms. TAS3681 has demonstrated activity as a pure AR antagonist against several AR mutations and has shown an antitumor effect in an AR-v7 positive xenograft model. In order to further characterize the properties of TAS3681, we investigated its effects in cell-based AR overexpression/stabilization models and assessed the subcellular localization of FL-AR and AR-v7 in enzalutamide (Enz) -resistant cells. Methods: The Nano-bit assay was performed to analyze dimerization of FL-AR and AR-v7 proteins. Prostate cancer (PCa) cells expressing AR-v7 were treated with TAS3681, and nuclear and cytoplasmic fractions were prepared. Then the levels of FL-AR and AR-v7 protein in each fraction were determined by western blotting. AR-overexpressing PCa cells transfected with a wild-type AR expression vector were treated with TAS3681 in the presence of androgen. AR-stabilized PCa cells were transfected with a Speckle-type POZ protein (SPOP) mutant expression vector and then were treated with TAS3681. Results: AR antagonism by TAS3681 caused dose-dependent inhibition of FL-AR homodimerization (HD) and FL-AR/AR-v7 heterodimer formation in the presence of androgen. TAS3681 had no direct inhibitory effect on HD of AR-v7. However, AR downregulation by TAS3681 reduced nuclear AR-v7 protein in Enz-resistant cells under castration conditions. In AR-overexpressing PCa cells, TAS3681 reduced the AR protein and effectively suppressed both AR transactivation and cell proliferation. In contrast to Enz, TAS3681 also effectively reduced the AR protein in AR-stabilized PCa cells harboring SPOP mutation. Conclusions: TAS3681 suppresses aberrant AR activation, including AR overexpression and expression of constitutively active nuclear localized AR-v7, via downregulation of AR/AR-v7. These findings suggest that TAS3681 has the potential to overcome resistance to current AR-targeted therapies.

Abstract Background: Activating mutations in the EGFR gene are important targets in cancer therapy because they are key drivers of NSCLC. EGFR-TKIs (gefitinib, erlotinib and afatinib) are eligible for first-line therapy in NSCLC patients with EGFR activating mutations such as exon 19 deletions and L858R. However, NSCLC driven by EGFR exon 20 insertions, the third most common mutation in the EGFR gene, are associated with poor clinical response to the existing EGFR-TKI therapies, suggesting an unmet medical need for these patients. TAS6417 (previously termed TPC-064) is a novel EGFR inhibitor that has a potent inhibitory activity against exon 20 insertions while sparing wild-type (WT) EGFR, and could be an efficacious treatment option for these patients without the risk of severe diarrhea associated with inhibition of WT EGFR. Materials and Methods: Tumor growth analysis was conducted in athymic nude mice or nude rats bearing a patient-derived xenograft (PDX) (LXF2478, an NSCLC harboring EGFR V769_D770insASV mutation), or genetically engineered cells expressing EGFR exon 20 insertions (NCI-H1975 EGFR D770_N771insSVD and NIH-3T3 EGFR H773_V774insNPH). The protein and phosphoprotein expression level in tumors were determined by Western blot analysis. Results: TAS6417 was discovered as a more potent and selective inhibitory activity on the EGFR harboring exon 20 insertions compared to WT. The effect of TAS6417 on antitumor activity was evaluated in subcutaneously implantation model in nude mice and nude rats, and also in orthotopic lung implantation in nude mice. In sc mouse models, once-daily dosing of TAS6417 at 50 mg/kg or more inhibited tumor growth of genetically engineered cell lines, NCI-H1975 EGFR D770_N771insSVD (expressing exon 20 insertion mutation instead of endogenous L858R/T790M mutations) and NIH-3T3 EGFR N773_V774insNPH. Furthermore, a PDX harboring EGFR V769_D770insASV showed a striking response to TAS6417, resulting in tumor regression at 100 mg/kg. In nude rats bearing NCI-H1975 EGFR D770_N771insSVD xenografts, TAS6417 inhibited tumor growth at 10 mg/kg or more, and tumor shrinkage was observed at 40 mg/kg without any effect on body weight gain. Furthermore, TAS6417 provided a survival benefit with good tolerability in lung orthotopic implantation mouse model. Pharmacodynamics marker analysis revealed that TAS6417 inhibited EGFR signaling including both AKT and ERK pathways in tumors, leading to caspase activation with an increase in Bim protein expression. Conclusions: These findings demonstrated that TAS6417 had potent antitumor activity with good tolerability in not only genetically engineered xenografts but also in a PDX harboring EGFR exon 20 insertions, suggesting a promising therapeutic option for patients with NSCLC harboring EGFR exon 20 insertions. Citation Format: Shinichi Hasako, Miki Terasaka, Ryoto Fujita, Naomi Abe, Akihiro Hashimoto, Kenichi Matsuo, Teruhiro Utsugi, Yoshikazau Iwasawa. Characterization of antitumor activity of TAS6417, a novel EGFR-TKI targeting exon 20 insertions [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A158.

Background: HER2 is a well-established therapeutic target in breast and gastric cancer. Although HER2-targeting therapies are available for HER2-overexpressed breast and gastric cancer, the combination with chemotherapy is still necessary. Recent preclinical and clinical studies suggest that combination therapies of HER2-targeting agents without chemotherapy may be effective. Therefore, the dual HER2-targeting approaches as well as a single-agent HER2-targeting therapy are desired. TAS0728 (former name TPC-107) is an orally available, HER2-selective covalent inhibitor that has a high kinase specificity excluding EGFR. In previous studies, TAS0728 showed potent inhibitory activities for both activated mutations of HER2 and overexpressed HER2, while sparing EGFR activity in cells. Here, we report that TAS0728 demonstrates potent antitumor activity for HER2-amplified tumor models both as a single agent and in combination with HER2-targeting antibodies. Materials and Methods: TAS0728 was administered for 14 days to nude mice and the plasma concentration profile and PK parameters of TAS0728 were determined. For pharmacodynamic (PD) evaluation, TAS0728 was administered to mice bearing N87 xenografts as a single dose and PD markers in tumor were examined by Western blot analysis. BT-474 or N87 xenograft models were used for in vivo antitumor evaluation of TAS0728 as a single agent. The 4-1ST xenograft model was used to investigate the combination of TAS0728 with trastuzumab or trastuzumab emtansine (T-DM1). In this model, TAS0728 (q.d., p.o.) was administered in combination with trastuzumab (q1w, i.v.) or T-DM1 (Day 1, i.v.). Tumor volumes and body weights were measured twice a week. Results: TAS0728 demonstrated favorable oral PK properties in mice, and exhibited a robust inhibition of PD markers including phosphorylation of HER2 and HER3 in tumor tissues of N87 xenografts. Consistent with the results of the PD study, TAS0728 showed significant antitumor effect in the N87 and BT474 xenograft models at PD effective doses (30 and 60 mg/kg/day) with minimum body weight changes. In the 4-1ST xenograft model, TAS0728 at 15 mg/kg/day strongly enhanced the antitumor effect of trastuzumab (20 mg/kg) or T-DM1 (7.5 mg/kg). Conclusion: TAS0728 was effective both as a single agent and in combination with HER2-targeting antibodies including trastuzumab and T-DM1. These studies provide a rationale for both a single-agent therapy of TAS0728 and a dual HER2 blockade with TAS0728 and HER2-targeting antibodies for the therapy of HER2-overexpressed tumors. Citation Format: Hiroki Irie, Kei Oguchi, Kimihiro Ito, Yayoi Fujioka, Yuichi Kawai, Tadashi Shimamura, Hikari Araki, Akio Fujioka, Fumio Nakagawa, Rumi Kawabata, Hideki Nagase, Takeshi Sagara, Junji Uchida, Kenichi Matsuo, Teruhiro Utsugi, Yoshikazu Iwasawa. TAS0728, a HER2-selective covalent inhibitor, demonstrates potent antitumor effect as a single agent and in combination with anti-HER2 antibodies in HER2-overexpressed tumor models [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B179.