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Kinases are the major anticancer drug target class of the 21st century with nearly sixty small molecule kinase inhibitors approved for clinical use in the first two decades. While there are more than 500 kinases encoded by the human genome, currently approved inhibitors act primarily through approximately twenty different targets. Key to the success of kinase inhibitor therapy has been the simultaneous development of biomarker assays to enable the selection of patients most likely to respond. Predictive drug response biomarkers can be identified with cancer cell panel profiling, which is the parallel testing of compounds on a large panel of cancer cell lines. By correlating drug sensitivity with genomic information of the cell lines, strategies for patient stratification or drug repurposing have been developed [1-3]. In two earlier studies [2,3], we compared the kinase selectivity and the cellular inhibition profiles of all kinase inhibitors approved by the FDA until May 2018. Here, we will present the cancer cell panel profiling of all twenty small molecule kinase inhibitors approved since then. Several of these inhibitors act through well-known targets, such as ALK (lorlatinib), BRAF (encorafenib), EGFR (dacomitinib) and MEK1 (binimetinib, selumetinib). Others act through kinases for which no small molecule inhibitors have been approved before, such as CSF1R (pexidartinib), FGFR (erdafitinib, pemigatinib), c-MET (capmatinib), RET (selpercatinib, pralsetinib) and TRK (larotrectinib, entrectinib). All compounds were profiled on a panel of 102 cancer cell lines, known as Oncolines, representing a wide range of solid tumors and hematological malignancies, and harboring mutant and wild-type versions of many major cancer driver genes [3]. To determine similarities in the mechanisms underlying the anti-proliferative activity of the inhibitors, their IC50 fingerprint in the cell proliferation assays were compared by hierarchical clustering [4]. Compounds that act through the same primary kinase clustered together in this analysis. Exceptions were investigated further by profiling of additional cell lines, representing cancer gene alterations that were not present in the 102 cell line panel, such as FLT3 mutation and TRK-gene fusions, which occur in relatively small cancer patient populations. To compare the genomic targeting of kinase inhibitors acting on the same biochemical target, the cancer cell lines were classified as either “mutant” or “wild-type” for specific cancer gene alterations and were grouped per cancer gene. The relationship between drug sensitivity and cancer gene mutation status was examined. Detailed genomic biomarker analyses and comparative profiling results of novel BTK, EGFR, FGFR, FLT3 and TRK kinase inhibitors will be presented.[1] Mol Cancer Ther 2017;26:2609-17; [2] PLoS ONE 2014;9:e92146; [3] Mol Cancer Ther 2019;18:470-81; [4] Mol Cancer Ther 2016;15:3097-109 Citation Format: Jeffrey J. Kooijman, Wilhelmina E. van Riel, Martine B. Prinsen, Jelle Dylus, Jeroen A. de Roos, Yvonne Grobben, Nicole Willemsen-Seegers, Michelle Muller, Jos de Man, Yugo Narumi, Yusuke Kawase, Rogier C. Buijsman, Suzanne J. van Gerwen, Guido J. Zaman. Comparative cancer cell panel profiling of kinase inhibitors approved for clinical use from 2018 to 2020 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1480.

Arginase I (ArgI) is an important small molecule drug target in cancer immunotherapy. Arg1 converts L-arginine into L-ornithine and urea. Recruitment of ArgI-expressing myeloid-derived suppressor cells (MSDCs) at a tumor site results in the depletion of L-arginine, which causes reduced proliferation of T-cells and natural killer cells and inhibition of the antitumor immune response. In patient material, MSDC-induced T-cell suppression can be reverted by arginase inhibitors. ArgI inhibitors work synergistically with checkpoint inhibitor therapy in syngeneic mouse models. In order to find novel inhibitors for ArgI, we developed a set of tools to enable screening and hit validation. The first is an activity assay that enables the high-throughput screening (HTS) of compound libraries. Previously reported arginase assays are poorly compatible with HTS due to the requirement of multiple reactions steps, harsh assay conditions, or the use of low-turnover substrates other than L-arginine. We developed a novel ArgI activity assay, which has a homogenous format and requires only two addition steps before readout. The assay makes use of a fluorescence readout and has a high robustness (Z'-factor > 0.7). Progression of the assay can be followed in real time, allowing for kinetic experiments. To investigate the false positive hit rate, the assay was screened at the Pivot Park Screening Centre with a library consisting of 233 compounds with known interference in other assay formats. Using a simple background signal control, the number of false positives in this library was minimized to below 0.2%. The assay was subsequently used to accurately determine the dissociation constants and binding kinetics of the reference inhibitors ABH, NOHA and CB1158. In order to validate the binding of screening hits to ArgI, we developed a thermal shift assay. We observed a shift in the ArgI melting temperature of up to 3.8°C after addition of the most potent inhibitors. In addition, we developed a Surface Plasmon Resonance binding assay. This showed that ABH and CB1158 have long residence times on ArgI. To allow the development of novel inhibitors through rational drug design, we successfully crystallized human ArgI in a novel space group with higher symmetry (P63) compared to those previously reported (space group P3), and without the presence of hemihedral twinning. We determined a series of high resolution (< 1.7 Å) crystal structures at various pH values and with several ligands. These demonstrate that a series of peptide flips lies at the basis of the pH-dependent symmetry of ArgI and its unusually high pH optimum of 9.0 to 9.5. Finally, to assess the cellular activity of ArgI inhibitors, we examined 102 cancer cell lines for ArgI activity and correlated the results to public gene expression profiles. The novel assay portfolio will help to deliver a new generation of ArgI inhibitors. Citation Format: Yvonne Grobben, Joost C. Uitdehaag, Nicole Willemsen-Seegers, Werner W. Tabak, Martine B. Prinsen, Suzanne J. van Gerwen, Jan van Groningen, Johan Friesen, Helma Rutjes, Jos de Man, Rogier C. Buijsman, Guido J. Zaman. High-throughput fluorescence-based assay for screening of Arginase I inhibitors for cancer immunotherapy [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 1944.