Discovery of Selective, Covalent FGFR4 Inhibitors with Antitumor Activity in Models of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) accounts for a majority of primary liver cancer and is one of the most common forms of cancer worldwide. Aberrant signaling of the FGF19-FGFR4 pathway leads to HCC in mice and is hypothesized to be a driver in FGF19 amplified HCC in humans. Multiple small molecule inhibitors have been pursued as targeted therapies for HCC in recent years, including several selective FGFR4 inhibitors that are currently being evaluated in clinical trials. Herein, we report a novel series of highly selective, covalent 2-amino-6,8-dimethyl-pyrido[2,3-d]pyrimidin-7(8H)-ones that potently and selectively inhibit FGFR4 signaling through covalent modification of Cys552, which was confirmed by X-ray crystallography. Correlative target occupancy and pFGFR4 inhibition were observed in vivo, as well as tumor regression in preclinical models of orthotopic and sorafenib-resistant HCC.

Abstract 2790: The anti-TGFβ neutralizing antibody, SAR439459, blocks the immunosuppressive effects of TGFβ and inhibits the growth of syngeneic tumors in combination with anti-PD1

TGFβ may act as a tumor suppressor early in tumorigenesis; however, TGFβ is also known to support tumor growth via multiple mechanisms, including promotion of epithelial-mesenchymal transition, fibroblast recruitment, ECM deposition, neovascularization, and immunosuppression of both adaptive and innate immune cells. SAR439459 is pan-neutralizing TGFβ antibody that is being developed for the treatment of solid tumors. In this study, we investigated the effect of SAR439459 on the immune system in primary human immune cells in vitro and in murine syngeneic tumor models in vivo. Exogenous TGFβ inhibited proliferation of CD8pos primary human T cells and suppressed the production of inflammatory cytokines such as IFNγ. The addition of SAR439459 blocked these effects. Additionally, TGFβ enhanced the development of inducible Tregs by approximately 4-fold, while the inclusion of SAR439459 abrogated this effect. The effects of exogenous TGFβ and SAR439459 were next examined in the context of T Cell Receptor signaling in a co-culture system of Jurkat cells expressing luciferase reporter under the control of NFAT-responsive promoter and PD-L1pos APCs. The addition of anti-PD1 stimulated TCR signaling in this system, while the addition of TGFβ inhibited anti-PD1-mediated response. SAR439459 restored the ability of anti-PD1 to stimulate the TCR signaling. These data support the notion that TGFβ neutralization could positively impact T effector cells and inhibit Tregs development. Therefore, combining a TGFβ-neutralizing antibody with anti-PD1 could enhance T cell responsiveness. Compared to checkpoint inhibitors, which are suggested to cause the reactivation and de-repression of exhausted T cells, the effects of TGFβ on the immune system are thought to be distinct. To test this, the combination of anti-PD1 and SAR439459 was examined in syngeneic mouse models. Established MC38 tumors were treated with anti-PD1, SAR439459 or the combination of both antibodies. In tumor-bearing mice treated with either anti-PD1 or SAR439459 alone, neither Ab resulted in significant tumor growth inhibition. However, the combination of anti-PD-1 and SAR439459 led to tumor regression in the majority of tumor-bearing mice. These results provide the rationale for combining TGF-β neutralization with checkpoint inhibitors, specifically anti-PD1, for the treatment of human cancers.

Citation Format: Richard C. Gregory, Rita Greco, Hongjing Qu, Natalia Malkova, Mikhail Levit, Keli Perron, Waldemar Racki, Fangxian Sun, Gary Shapiro, Christopher Winter, Dmitri Wiederschain, Tun Tun Lin, Jack Pollard. The anti-TGFβ neutralizing antibody, SAR439459, blocks the immunosuppressive effects of TGFβ and inhibits the growth of syngeneic tumors in combination with anti-PD1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2790.

Peginterferon Beta-1a Shows Antitumor Activity as a Single Agent and Enhances Efficacy of Standard of Care Cancer Therapeutics in Human Melanoma, Breast, Renal, and Colon Xenograft Models

Because of its tumor-suppressive effect, interferon-based therapy has been used for the treatment of melanoma. However, limited data are available regarding the antitumor effects of pegylated interferons, either alone or in combination with approved anticancer drugs. We report that treatment of human WM-266-4 melanoma cells with peginterferon beta-1a induced apoptotic markers. Additionally, peginterferon beta-1a significantly inhibited the growth of human SK-MEL-1, A-375, and WM-266-4 melanoma xenografts established in immunocompromised mice. Peginterferon beta-1a regressed large, established WM-266-4 xenografts in nude mice. Treatment of SK-MEL-1 tumor-bearing mice with a combination of peginterferon beta-1a and the MEK inhibitor PD325901 ((R)-N-(2,3-dihydroxypropoxy)-3,4-difluoro-2-(2-fluoro-4-iodophenylamino)benzamide) significantly improved tumor growth inhibition compared with either agent alone. Examination of the antitumor activity of peginterferon beta-1a in combination with approved anticancer drugs in breast and renal carcinomas revealed improved antitumor activity in these preclinical xenograft models, as did the combination of peginterferon beta-1a and bevacizumab in a colon carcinoma xenograft model.

Abstract 5448: PTK7 as a potential therapeutic target in ovarian cancer

The identification of proteins that selectively discriminate between tumor cells and normal adult cells allows for the specific targeting of diseased cells with antibody therapeutics. One such recently identified protein, PTK7, is an onco-fetal membrane protein which exhibits limited expression and function in adults. PTK7 was identified as a member of the RTK super family but lacks a functional kinase domain. Normally, PTK7 is expressed early in development and its loss is associated with severe defects in neural tube closure and sensory hair cell bundle formation. Functionally, little is known about the signaling involving PTK7, but it has been linked to both the canonical and noncanonical WNT pathways. Recently, PTK7 expression has been shown to be upregulated in a number of cancers including: ovarian, melanoma, leukemia, lung, pancreatic, colon, renal and breast. In vitro and in vivo studies support a role in regulating angiogenesis, invasion & survival. To further validate PTK7 as a potential cancer target that may be required for tumor maintenance and progression, we analyzed the expression of PTK7 in normal and tumor samples, and validated an in vitro and in vivo role of PTK7 on cell growth in ovarian cancer cell lines using both genetic tools and polyclonal antibodies. Silencing PTK7 with stably expressed inducible shRNAs is shown to inhibit the growth of ovarian cancer cell lines in vitro and to lead to delayed tumor growth upon PTK7 knockdown in murine tumor xenograft models. Further supporting the role of PTK7 as a potential antibody target, polyclonal antibodies to PTK7 are shown to inhibit the growth of SKOV3 and OVCAR8 cells in vitro. Although 4 human antibodies derived from phage display failed to inhibit in vitro cell growth, these results suggest that functionally blocking PTK7 may lead to the inhibition of ovarian tumor growth and is a potential target for antibody therapies.

Citation Format: Zhihu Ding, Amanda Lennon, Keli Perron, David Harper, Hui Su, Meredith Wolfram, Joshua Murtie, Stuart Licht, Jason Pinckney, Helene Simonds-Mannes, Kimberly Bishop, Julie-Ann Gavigan, Dinesh Bangari, Maureen Magnay, William Weber, David Reczek, William Brondyk, Vicky Drewett, Marc Trombe, Dietmar Hoffmann, Raffaele Baffa, Serena Silver, Victoria Richon, Christopher Winter, Venkat Reddy, Richard C. Gregory. PTK7 as a potential therapeutic target in ovarian cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5448. doi:10.1158/1538-7445.AM2014-5448

Combination of two insulin-like growth factor-I receptor inhibitory antibodies targeting distinct epitopes leads to an enhanced antitumor response

The insulin-like growth factor-I receptor (IGF-IR) is a cell surface receptor tyrosine kinase that mediates cell survival signaling and supports tumor progression in multiple tumor types. We identified a spectrum of inhibitory IGF-IR antibodies with diverse binding epitopes and ligand-blocking properties. By binding distinct inhibitory epitopes, two of these antibodies, BIIB4 and BIIB5, block both IGF-I and IGF-II binding to IGF-IR using competitive and allosteric mechanisms, respectively. Here, we explored the inhibitory effects of combining BIIB4 and BIIB5. In biochemical assays, the combination of BIIB4 and BIIB5 improved both the potency and extent of IGF-I and IGF-II blockade compared with either antibody alone. In tumor cells, the combination of BIIB4 and BIIB5 accelerated IGF-IR downregulation and more efficiently inhibited IGF-IR activation as well as downstream signaling, particularly AKT phosphorylation. In several carcinoma cell lines, the antibody combination more effectively inhibited ligand-driven cell growth than either BIIB4 or BIIB5 alone. Notably, the enhanced tumor growth-inhibitory activity of the BIIB4 and BIIB5 combination was much more pronounced at high ligand concentrations, where the individual antibodies exhibited substantially reduced activity. Compared with single antibodies, the BIIB4 and BIIB5 combination also significantly further enhanced the antitumor activity of the epidermal growth factor receptor inhibitor erlotinib and the mTOR inhibitor rapamycin. Moreover, in osteosarcoma and hepatocellular carcinoma xenograft models, the BIIB4 and BIIB5 combination significantly reduced tumor growth to a greater degree than each single antibody. Taken together, our results suggest that targeting multiple distinct inhibitory epitopes on IGF-IR may be a more effective strategy of affecting the IGF-IR pathway in cancer.

Post-transcriptional steps involved in the assembly of photosystem I in Chlamydomonas

Assembly of the PSI (photosystem I) complex in eukaryotic photosynthetic organisms depends on the concerted interactions of the nuclear and chloroplast genetic systems. We have identified several nucleus-encoded factors of Chlamydomonas reinhardtii that are specifically required for the synthesis of the two large chloroplast-encoded reaction-centre polypeptides, PsaA and PsaB, of photosystem I and that function at plastid post-transcriptional steps. Raa1, Raa2 and Raa3 are required for the splicing of the three discontinuous psaA precursor transcripts; they are part of large RNA-protein complexes that are reminiscent of spliceosomal particles. Tab1 and Tab2 are involved in the initiation of translation of the psaB mRNA and are localized in the membrane and stromal phases of the chloroplast, where they are associated with high-molecular-mass complexes. Moreover, two chloroplast-encoded proteins, Ycf3 and Ycf4, are required for the primary steps of assembling the photosystem I subunits into a functional complex.

A factor related to pseudouridine synthases is required for chloroplast group II intron trans-splicing in Chlamydomonas reinhardtii

In Chlamydomonas reinhardtii, the psaA mRNA is assembled by a process involving two steps of trans-splicing that remove two group II introns and give rise to the mature mRNA. The products of at least 14 nuclear genes and one chloroplast gene (tscA) are necessary for this process. We have cloned Maa2, one of the nuclear genes involved in trans-splicing of the second intron. Maa2 encodes a protein with similarity to conserved domains of pseudouridine synthases, but mutagenesis of putative catalytic residues showed that this activity may not be required for trans-splicing of psaA RNA. Although it is not clear whether the pseudouridine synthase activity has been maintained in Maa2, it is possible that this enzyme was recruited during evolution as an RNA chaperone for folding or stabilizing the psaA intron. The Maa2 protein appears to be associated through ionic interactions with a low density membrane system in the chloroplast that also contains RNA-binding proteins involved in translation.