APC/PIK3CA mutations and β-catenin status predict tankyrase inhibitor sensitivity of patient-derived colorectal cancer cells.

Aberrant WNT/β-catenin signaling drives carcinogenesis. Tankyrases poly(ADP-ribosyl)ate and destabilize AXINs, β-catenin repressors. Tankyrase inhibitors block WNT/β-catenin signaling and colorectal cancer (CRC) growth. We previously reported that 'short' APC mutations, lacking all seven β-catenin-binding 20-amino acid repeats (20-AARs), are potential predictive biomarkers for CRC cell sensitivity to tankyrase inhibitors. Meanwhile, 'Long' APC mutations, which possess more than one 20-AAR, do not predict inhibitor-resistant cells. Thus, additional biomarkers are needed to precisely predict the inhibitor sensitivity. Using 47 CRC patient-derived cells (PDCs), we examined correlations between the sensitivity to tankyrase inhibitors (G007-LK and RK-582), driver mutations, and the expressions of signaling factors. NOD.CB17-Prkdcscid/J and BALB/c-nu/nu xenograft mice were treated with RK-582. Short APC mutant CRC cells exhibited high/intermediate sensitivities to tankyrase inhibitors in vitro and in vivo. Active β-catenin levels correlated with inhibitor sensitivity in both short and long APC mutant PDCs. PIK3CA mutations, but not KRAS/BRAF mutations, were more frequent in inhibitor-resistant PDCs. Some wild-type APC PDCs showed inhibitor sensitivity in a β-catenin-independent manner. APC/PIK3CA mutations and β-catenin predict the sensitivity of APC-mutated CRC PDCs to tankyrase inhibitors. These observations may help inform the strategy of patient selection in future clinical trials of tankyrase inhibitors.

Chen M ，Mashima T ，Oishi T ，Muramatsu Y ，Seto Y ，Takamatsu M ，Kawata N ，Morino S ，Nakamura A ，Inaba S ，Yuan X ，Maruyama K ，Suzuki M ，Sato A ，Yoshida H ，Jang MK ，Mizutani A ，Takeuchi K ，Yamaguchi K ，Shirai F ，Nagayama S ，Katayama R ，Seimiya H ... -  《-》

APC Mutations as a Potential Biomarker for Sensitivity to Tankyrase Inhibitors in Colorectal Cancer.

In most colorectal cancers, Wnt/β-catenin signaling is activated by loss-of-function mutations in the adenomatous polyposis coli (APC) gene and plays a critical role in tumorigenesis. Tankyrases poly(ADP-ribosyl)ate and destabilize Axins, a negative regulator of β-catenin, and upregulate β-catenin signaling. Tankyrase inhibitors downregulate β-catenin and are expected to be promising therapeutics for colorectal cancer. However, colorectal cancer cells are not always sensitive to tankyrase inhibitors, and predictive biomarkers for the drug sensitivity remain elusive. Here we demonstrate that the short-form APC mutations predict the sensitivity of colorectal cancer cells to tankyrase inhibitors. By using well-established colorectal cancer cell lines, we found that tankyrase inhibitors downregulated β-catenin in the drug-sensitive, but not resistant, colorectal cancer cells. The drug-sensitive cells showed higher Tcf/LEF transcriptional activity than the resistant cells and possessed "short" truncated APCs lacking all seven β-catenin-binding 20-amino acid repeats (20-AARs). In contrast, the drug-resistant cells possessed "long" APC retaining two or more 20-AARs. Knockdown of the long APCs with two 20-AARs increased β-catenin, Tcf/LEF transcriptional activity and its target gene AXIN2 expression. Under these conditions, tankyrase inhibitors were able to downregulate β-catenin in the resistant cells. These results indicate that the long APCs are hypomorphic mutants, whereas they exert a dominant-negative effect on Axin-dependent β-catenin degradation caused by tankyrase inhibitors. Finally, we established 16 patient-derived colorectal cancer cells and confirmed that the tankyrase inhibitor-responsive cells harbor the short-form APC mutations. These observations exemplify the predictive importance of APC mutations, the most common genetic alteration in colorectal cancers, for molecular targeted therapeutics. Mol Cancer Ther; 16(4); 752-62. ©2017 AACR.

Tanaka N ，Mashima T ，Mizutani A ，Sato A ，Aoyama A ，Gong B ，Yoshida H ，Muramatsu Y ，Nakata K ，Matsuura M ，Katayama R ，Nagayama S ，Fujita N ，Sugimoto Y ，Seimiya H ... -  《-》

A novel tankyrase small-molecule inhibitor suppresses APC mutation-driven colorectal tumor growth.

Most colorectal cancers (CRC) are initiated by mutations of APC, leading to increased β-catenin-mediated signaling. However, continued requirement of Wnt/β-catenin signaling for tumor progression in the context of acquired KRAS and other mutations is less well-established. To attenuate Wnt/β-catenin signaling in tumors, we have developed potent and specific small-molecule tankyrase inhibitors, G007-LK and G244-LM, that reduce Wnt/β-catenin signaling by preventing poly(ADP-ribosyl)ation-dependent AXIN degradation, thereby promoting β-catenin destabilization. We show that novel tankyrase inhibitors completely block ligand-driven Wnt/β-catenin signaling in cell culture and display approximately 50% inhibition of APC mutation-driven signaling in most CRC cell lines. It was previously unknown whether the level of AXIN protein stabilization by tankyrase inhibition is sufficient to impact tumor growth in the absence of normal APC activity. Compound G007-LK displays favorable pharmacokinetic properties and inhibits in vivo tumor growth in a subset of APC-mutant CRC xenograft models. In the xenograft model most sensitive to tankyrase inhibitor, COLO-320DM, G007-LK inhibits cell-cycle progression, reduces colony formation, and induces differentiation, suggesting that β-catenin-dependent maintenance of an undifferentiated state may be blocked by tankyrase inhibition. The full potential of the antitumor activity of G007-LK may be limited by intestinal toxicity associated with inhibition of Wnt/β-catenin signaling and cell proliferation in intestinal crypts. These results establish proof-of-concept antitumor efficacy for tankyrase inhibitors in APC-mutant CRC models and uncover potential diagnostic and safety concerns to be overcome as tankyrase inhibitors are advanced into the clinic.

Lau T ，Chan E ，Callow M ，Waaler J ，Boggs J ，Blake RA ，Magnuson S ，Sambrone A ，Schutten M ，Firestein R ，Machon O ，Korinek V ，Choo E ，Diaz D ，Merchant M ，Polakis P ，Holsworth DD ，Krauss S ，Costa M ... -  《-》

RK-287107, a potent and specific tankyrase inhibitor, blocks colorectal cancer cell growth in a preclinical model.

Aberrant activation of Wnt/β-catenin signaling causes tumorigenesis and promotes the proliferation of colorectal cancer cells. Porcupine inhibitors, which block secretion of Wnt ligands, may have only limited clinical impact for the treatment of colorectal cancer, because most colorectal cancer is caused by loss-of-function mutations of the tumor suppressor adenomatous polyposis coli (APC) downstream of Wnt ligands. Tankyrase poly(ADP-ribosyl)ates (PARylates) Axin, a negative regulator of β-catenin. This post-translational modification causes ubiquitin-dependent degradation of Axin, resulting in β-catenin accumulation. Tankyrase inhibitors downregulate β-catenin and suppress the growth of APC-mutated colorectal cancer cells. Herein, we report a novel tankyrase-specific inhibitor RK-287107, which inhibits tankyrase-1 and -2 four- and eight-fold more potently, respectively, than G007-LK, a tankyrase inhibitor that has been previously reported as effective in mouse xenograft models. RK-287107 causes Axin2 accumulation and downregulates β-catenin, T-cell factor/lymphoid enhancer factor reporter activity and the target gene expression in colorectal cancer cells harboring the shortly truncated APC mutations. Consistently, RK-287107 inhibits the growth of APC-mutated (β-catenin-dependent) colorectal cancer COLO-320DM and SW403 cells but not the APC-wild (β-catenin-independent) colorectal cancer RKO cells. Intraperitoneal or oral administration of RK-287107 suppresses COLO-320DM tumor growth in NOD-SCID mice. Rates of tumor growth inhibition showed good correlation with the behavior of pharmacodynamic biomarkers, such as Axin2 accumulation and MYC downregulation. These observations indicate that RK-287107 exerts a proof-of-concept antitumor effect, and thus may have potential for tankyrase-directed molecular cancer therapy.

Mizutani A ，Yashiroda Y ，Muramatsu Y ，Yoshida H ，Chikada T ，Tsumura T ，Okue M ，Shirai F ，Fukami T ，Yoshida M ，Seimiya H ... -  《-》

Tankyrase-selective inhibitor STP1002 shows preclinical antitumour efficacy without on-target toxicity in the gastrointestinal tract.

Tankyrase inhibition stabilises AXINs and antagonises the Wnt/β-catenin pathway in adenomatous polyposis coli (APC)-mutated colorectal cancer (CRC), suggesting that tankyrase is a potential therapeutic target for APC-mutated CRC. However, clinical trials on reported tankyrase inhibitors have been severely limited by on-target toxicity in the gastrointestinal (GI) tract. Herein, we report a new tankyrase-selective inhibitor, STP1002, having preclinical antitumour efficacy without on-target toxicity in APC-mutated CRC models. STP1002 was developed and characterised using in vitro and in vivo functional studies; its pharmacokinetics, antitumour efficacy and toxicity were evaluated in vivo. STP1002 showed potent, selective inhibition of tankyrase 1/2 but not of members of the poly (ADP-ribose) polymerase 1/2 (PARP1/2). STP1002 exerted antitumour activity by stabilising AXINs and antagonising the Wnt/β-catenin pathway in a subset of APC-mutated CRC cell lines but not in inhibitor-resistant cells and APC-wild-type CRC cell lines. STP1002 showed favourable pharmacokinetic profiles for oral administration once daily. STP1002 inhibited tumour growth of APC-mutated CRC xenograft animal models but not of APC-wild type models in a dose-dependent manner. The antitumour efficacy of STP1002 was confirmed using APC-mutated CRC patient-derived tumour xenograft models. STP1002 showed no significant on-target toxicity in the GI tract compared to G007-LK, which shows severe ileum toxicity in preclinical animal models. These results demonstrate that STP1002, a novel, orally active tankyrase inhibitor, shows preclinical antitumour efficacy without on-target toxicity in the GI tract. Our data provide a rationale for a clinical trial on STP1002 as a potential tankyrase-targeted drug in patients with APC-mutated CRC.

Kim DY ，Kwon YJ ，Seo WY ，Kim UI ，Ahn S ，Choi SM ，Bang HT ，Kim K ，Kim JS ... -  《-》