Abstract 3909: Potential antitumor effect of a pan-PI3K inhibitor ZSTK474 on human sarcoma cell lines

Phosphatidylinositol-3 kinase (PI3K) is a key signaling molecule for tumor growth and survival, thus the PI3K pathway has been thought to be a promising target for cancer therapy. We previously identified a novel phosphatidylinositol-3 kinase (PI3K) inhibitor, ZSTK474, by its similarity of antiproliferative profile across the JFCR39 cancer cell line panel to a known PI3K inhibitor, LY294002. Since then, ZSTK474 has been evaluated in preclinical models as well as in clinical trials in the US and Japan against a range of advanced solid tumors. The US trial revealed that three of four sarcoma patients exhibited stable disease, suggesting possible clinical benefit in this disease. Treatment of patients with advanced sarcoma remains challenging due to lack of effective medicine. Therefore the results of clinical trial prompted us to examine antitumor activity of this compound in various subtypes of sarcomas. To this end, we developed a sarcoma panel comprising of 17 human sarcoma cell lines from a variety of subtypes and investigated the effect of ZSTK474 across the panel and compare it with those of other molecularly targeted agents and clinically used chemotherapeutic agents for the treatment of sarcoma, such as doxorubicin, paclitaxel and gemcitabine. As a result, ZSTK474 exhibited a unique antiproliferative profile that was similar to other PI3K inhibitor but clearly different from conventional chemotherapeutic drugs examined, as we previously reported using JFCR39 carcinoma cell line panel. Indeed, ZSTK474 inhibited PI3K-downstream pathways, in parallel to growth inhibition, in all the sarcoma cell lines examined, showing proof-of-concept of PI3K inhibition. Of note, ZSTK474 exerted a potent antiproliferative effect on SW684, a fibrosarcoma cell line and MES-SA/Dx5, and a uterine sarcoma cell line that acquired resistance to doxorubicin via overexpression of P-glycoprotein, while both exhibited resistance to most of the chemotherapeutic agents examined. Moreover, ZSTK474 induced extensive apoptosis selectively in Ewing’s sarcoma and alveolar rhabdomyosarcoma cell lines, both of which harbor chromosomal translocations and resulting fusion genes, EWSR1-FLI1 and PAX3-FOXO1, respectively, whereas remaining sarcoma cell lines as well as carcinoma cell lines examined so far hardly underwent apoptosis. Additional cell lines from synovial sarcoma harboring SS18-SSX1/2 fusion gene also underwent apoptosis, suggesting preferential induction of apoptosis in oncogenic chromosomal translocation positive sarcoma cells. Finally, animal experiments using nude mice bearing human sarcoma xenograft confirmed the antitumor activity of ZSTK474 in vivo, with superior efficacy observed in translocation-positive cells. These results suggest that ZSTK474 could be a promising drug candidate for sarcomas, especially those harboring oncogenic chromosomal translocation.

Citation Format: Shingo Dan, Naomi Tamaki, Nachi Namatame, Yuya Yoshizawa, Mutsumi Okamura, Yumiko Nishimura, Kanami Yamazaki, Shin-ichi Yaguchi. Potential antitumor effect of a pan-PI3K inhibitor ZSTK474 on human sarcoma cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3909.

Antitumor profile of the PI3K inhibitor ZSTK474 in human sarcoma cell lines

Treatment of patients with advanced sarcoma remains challenging due to lack of effective medicine, with the development of novel drugs being of keen interest. A pan-PI3K inhibitor, ZSTK474, has been evaluated in clinical trials against a range of advanced solid tumors, with clinical benefit shown in sarcoma patients. In the present study, we developed a panel of 14 human sarcoma cell lines and investigated the antitumor effect of 24 anticancer agents including ZSTK474, other PI3K inhibitors, and those clinically used for sarcoma treatment. ZSTK474 exhibited a similar antiproliferative profile to other PI3K inhibitors but was clearly different from the other drugs examined. Indeed, ZSTK474 inhibited PI3K-downstream pathways, in parallel to growth inhibition, in all cell lines examined, showing proof-of-concept of PI3K inhibition. In addition, ZSTK474 induced apoptosis selectively in Ewing's sarcoma (RD-ES and A673), alveolar rhabdomyosarcoma (SJCRH30) and synovial sarcoma (SYO-1, Aska-SS and Yamato-SS) cell lines, all of which harbor chromosomal translocation and resulting oncogenic fusion genes, EWSR1-FLI1, PAX3-FOXO1 and SS18-SSX, respectively. Finally, animal experiments confirmed the antitumor activity of ZSTK474 in vivo, with superior efficacy observed in translocation-positive cells. These results suggest that ZSTK474 could be a promising drug candidate for treating sarcomas, especially those harboring chromosomal translocation.

Basal expression of insulin-like growth factor 1 receptor determines intrinsic resistance of cancer cells to a phosphatidylinositol 3-kinase inhibitor ZSTK474

Drug resistance often critically limits the efficacy of molecular targeted drugs. Although pharmacological inhibition of phosphatidylinositol 3-kinase (PI3K) is an attractive therapeutic strategy for cancer therapy, molecular determinants for efficacy of PI3K inhibitors (PI3Kis) remain unclear. We previously identified that overexpression of insulin-like growth factor 1 receptor (IGF1R) contributed to the development of drug resistance after long-term exposure to PI3Kis. In this study, we examined the involvement of basal IGF1R expression in intrinsic resistance of drug-naïve cancer cells to PI3Kis and whether inhibition of IGF1R overcomes the resistance. We found that cancer cells highly expressing IGF1R showed resistance to dephosphorylation of Akt and subsequent antitumor effect by ZSTK474 treatment. Knockdown of IGF1R by siRNAs facilitated the dephosphorylation and enhanced the drug efficacy. These cells expressed tyrosine-phosphorylated insulin receptor substrate 1 at high levels, which was dependent on basal IGF1R expression. In these cells, the efficacy of ZSTK474 in vitro and in vivo was improved by its combination with the IGF1R inhibitor OSI-906. Finally, we found a significant correlation between the basal expression level of IGF1R and the inefficacy of ZSTK474 in an in vivo human cancer panel, as well as in vitro. These results suggest that basal IGF1R expression affects intrinsic resistance of cancer cells to ZSTK474, and IGF1R is a promising target to improve the therapeutic efficacy. The current results provide evidence of combination therapy of PI3Kis with IGF1R inhibitors for treating IGF1R-positive human cancers.

Efficient delivery of small interfering RNA to bone-metastatic tumors by using atelocollagen in vivo

Silencing of gene expression by small interfering RNAs (siRNAs) is rapidly becoming a powerful tool for genetic analysis and represents a potential strategy for therapeutic product development. However, there are no reports of systemic delivery for siRNAs toward treatment of bone-metastatic cancer. Accordingly, we report here that i.v. injection of GL3 luciferase siRNA complexed with atelocollagen showed effective reduction of luciferase expression from bone-metastatic prostate tumor cells developed in mouse thorax, jaws, and/or legs. We also show that the siRNA/atelocollagen complex can be efficiently delivered to tumors 24 h after injection and can exist intact at least for 3 days. Furthermore, atelocollagen-mediated systemic administration of siRNAs such as enhancer of zeste homolog 2 and phosphoinositide 3'-hydroxykinase p110-alpha-subunit, which were selected as candidate targets for inhibition of bone metastasis, resulted in an efficient inhibition of metastatic tumor growth in bone tissues. In addition, upregulation of serum IL-12 and IFN-alpha levels was not associated with the in vivo administration of the siRNA/atelocollagen complex. Thus, for treatment of bone metastasis of prostate cancer, an atelocollagen-mediated systemic delivery method could be a reliable and safe approach to the achievement of maximal function of siRNA.