Antitumor Activity In Preclinical Models Research Articles

DS-7300a, a DNA Topoisomerase I Inhibitor, DXd-Based Antibody-Drug Conjugate Targeting B7-H3, Exerts Potent Antitumor Activities in Preclinical Models.

B7-H3 is overexpressed in various solid tumors and has been considered as an attractive target for cancer therapy. Here, we report the development of DS-7300a, a novel B7-H3-targeting antibody-drug conjugate with a potent DNA topoisomerase I inhibitor, and its in vitro profile, pharmacokinetic profiles, safety profiles, and in vivo antitumor activities in nonclinical species. The target specificity and species cross-reactivity of DS-7300a were assessed. Its pharmacologic activities were evaluated in several human cancer cell lines in vitro and xenograft mouse models, including patient-derived xenograft (PDX) mouse models in vivo. Pharmacokinetics was investigated in cynomolgus monkeys. Safety profiles in rats and cynomolgus monkeys were also assessed. DS-7300a specifically bound to B7-H3 and inhibited the growth of B7-H3-expressing cancer cells, but not that of B7-H3-negative cancer cells, in vitro. Additionally, treatment with DS-7300a and DXd induced phosphorylated checkpoint kinase 1, a DNA damage marker, and cleaved PARP, an apoptosis marker, in cancer cells. Moreover, DS-7300a demonstrated potent in vivo antitumor activities in high-B7-H3 tumor xenograft models, including various tumor types of high-B7-H3 PDX models. Furthermore, DS-7300a was stable in circulation with acceptable pharmacokinetic profiles in monkeys, and well tolerated in rats and monkeys. DS-7300a exerted potent antitumor activities against B7-H3-expressing tumors in in vitro and in vivo models, including PDX mouse models, and showed acceptable pharmacokinetic and safety profiles in nonclinical species. Therefore, DS-7300a may be effective in treating patients with B7-H3-expressing solid tumors in a clinical setting.

A phase 3 randomized, double-blind, placebo-controlled, multicenter, global study of durvalumab with and after chemoradiotherapy in patients with locally advanced, unresectable esophageal squamous cell carcinoma: KUNLUN.

TPS373 Background: Esophageal cancer is the eighth most common cancer type and the sixth leading cause of cancer-related death worldwide, and esophageal squamous cell carcinoma (ESCC) is the most common type of esophageal cancer. For patients with locally advanced, unresectable ESCC (AJCC 8th Stage II–IVA), definitive chemoradiotherapy (dCRT) is the current standard of care; however, up to half of patients will experience disease progression within two years of dCRT, and overall survival rates remain suboptimal. The combination of immune checkpoint inhibitors with CRT has demonstrated synergistic antitumor activity in pre-clinical models, and recent clinical data has demonstrated clinical benefit of combined programmed cell death-1 inhibition and preoperative CRT in patients with locally advanced ESCC. KUNLUN (NCT04550260) is a Phase 3, multicenter, global study evaluating the efficacy and safety of durvalumab, a programmed cell death ligand-1 (PD-L1) inhibitor, given concurrently with, and after, dCRT in patients with locally advanced, unresectable ESCC. Methods: Approximately 600 patients will be randomized 2:1 to receive either durvalumab with dCRT (cisplatin plus fluorouracil or cisplatin plus capecitabine, with a total dose of 50–64 Gy radiation), followed by durvalumab for up to approximately 24 months, or placebo with dCRT, followed by placebo for up to approximately 24 months. Eligible patients will have histologically or cytologically confirmed ESCC, and present with locally advanced, unresectable ESCC that is deemed suitable for dCRT. Patients must have an Eastern Cooperative Oncology Group performance status of 0 or 1, and have not received prior anti-cancer treatment. The co-primary endpoint of the study is progression-free survival according to RECIST v1.1 as assessed by blinded independent central review in all randomized patients and in patients with PD-L1-high tumors. Additional endpoints include overall survival and safety. Study enrollment is ongoing. Funding: This study was sponsored by AstraZeneca.

Evolution of 3-(4-hydroxyphenyl)indoline-2-one as a scaffold for potent and selective anticancer activity.

Development of targeted anticancer modalities has prompted a new era in cancer treatment that is notably different from the age of radical surgery and highly toxic chemotherapy. Behind each effective compound is a rich and complex history from first identification of chemical matter, detailed optimization, and mechanistic investigations, ultimately leading to exciting molecules for drug development. Herein we review the history and on-going journey of one such anticancer scaffold, the 3-(4-hydroxyphenyl)indoline-2-ones. With humble beginnings in 19th century Bavaria, we review this scaffold's synthetic history and anticancer optimization, including its recent demonstration of tumor eradication of drug-resistant, estrogen receptor-positive breast cancer. Compounds containing the 3-(4-hydroxyphenyl)indoline-2-one pharmacophore are emerging as intriguing candidates for the treatment of cancer.

Abstract P020: Schlafen 11 (SLFN11) as a predictive biomarker of the response to TAS1553, a novel small molecule ribonucleotide reductase subunit interaction inhibitor

Abstract Background: Ribonucleotide reductase (RNR) plays a crucial role in dNTP biosynthesis, which is required for DNA synthesis and repair, and is thought to be an attractive cancer therapeutic target. However, the precise significance of RNR inhibition remains to be elucidated, since reported RNR inhibitors exhibit limited pharmacological potency and off-target effects. We have developed a highly potent and novel small molecule RNR inhibitor, TAS1553, and reported that TAS1553 disrupted the protein-protein interaction between RNR subunits and exhibited the broad antiproliferative activity against human cancer cells in both in vitro and in vivo via oral administration. Phase-I study is currently ongoing and the identification of a predictive biomarker is essential to maximize clinical benefit of TAS1553. Here, we report a predictive biomarker of the response to TAS1553, and a clinical development strategy with the biomarker use. Material and methods: TAS1553 was synthesized at Taiho Pharmaceutical Co., Ltd. DNA replication stress, apoptosis, caspase activity and cellular growth inhibition induced by TAS1553 were assessed by western blotting, immunofluorescence staining, Caspase-Glo 3/7 assay and CellTiter-Glo® 2.0 assay, respectively. Cells were transfected with 2 nM siRNAs against SLFN11 (siSLFN11) and used for caspase-3/7 activation assay and cell proliferation assay. Results: TAS1553 induced intracellular pChk1, pRPA2 and γH2AX, followed by cleavage of PARP and caspase-3, suggesting that TAS1553 causes massive DNA replication stress. Then, we explored factors, involved in DNA replication stress, to predict response to TAS1553. Cytotoxicity profiling revealed broad antiproliferative activity of TAS1553 against both human hematological and solid cancer cell lines in a dose-​dependent manner (GI50 = 228-4150 nmol/L), and global gene expression profiling revealed that cells with high SLFN11 mRNA expression showed a higher sensitivity to TAS1553. TAS1553 exerted growth inhibitory activity without any cell killing effect against cells with low SLFN11 expression even at a concentration of 10 μmol/L, but cell killing activity against cells with high SLFN11 expression. Depletion of SLFN11 by siSLFN11 treatment in A673 cells which have high SLFN11 expression suppressed cytotoxic effect but not the growth inhibitory effect of TAS1553. Furthermore, we observed suppression of caspase-3/7 activation induced by TAS1553 in A673 cells transfected with siSLFN11. SLFN11 appeared to sensitize cancer cells to TAS1553 via promoting apoptosis. Conclusions: TAS1553, a novel orally available RNR inhibitor, showed potent antitumor activity in preclinical models of both hematological and solid tumors. Thus, TAS1553 could be a promising therapeutic agent for cancer, and SLFN11 could be a predictive biomarker in order to maximize clinical response to TAS1553. Citation Format: Hiroto Fukushima, Hiroyuki Ueno, Takuya Hoshino, Wakako Yano, Hiraku Itadani, Miki Terasaka, Sayaka Tsukioka, Takamasa Suzuki, Shoki Hara, Yoshio Ogino, Khoon Tee Chong, Tatsuya Suzuki, Yoshihiro Otsu, Satoshi Ito, Nozomu Tanaka, Seiji Miyahara. Schlafen 11 (SLFN11) as a predictive biomarker of the response to TAS1553, a novel small molecule ribonucleotide reductase subunit interaction inhibitor [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P020.

Dominant Expression of PVRIG and TIGIT Inhibitory Pathways in Bone Marrow of Multiple Myeloma Patients

IntroductionBlocking inhibitory immune checkpoints holds promise to treat multiple myeloma (MM) patients. However, currently available checkpoint inhibitors have not shown significant clinical benefits for MM patients, warranting the need for alternative checkpoint blockers. The immune checkpoint TIGIT was recently shown to be the most upregulated immune inhibitory receptor on CD8+ T cells in MM patients' bone marrow (BM), compared to other checkpoints (Guillerey C., Blood. 2018). Preclinical models demonstrated the dominant effects of TIGIT blockade or depletion, by significantly improving mice survival, reducing myeloma cell numbers and exhausted T cell hallmarks (Minnie S., Blood. 2018). As a result, several clinical trials using anti-TIGIT monoclonal antibodies have been recently initiated in MM patients.The DNAM-1 family, in addition to TIGIT, also includes the inhibitory receptor PVRIG, that competes with the co-activating receptor DNAM-1 for the binding to the shared ligand PVRL2, similarly to the TIGIT/PVR/DNAM-1 interaction. Accordingly, TIGIT and PVRIG co-blockade were shown to synergize in enhancing T cell activity and anti-tumor activity in preclinical models (Whelan S., Cancer Immunol. Res. 2019). PVRL2 together with PVR (ligand of TIGIT) were shown to be highly expressed on plasma cells and on CD14+ cells in BM of MM patients (Lozano E., Clin. Cancer Res. 2020). This study aimed at evaluating DNAM-1 axis receptors expression in MM patients' BM.MethodsFresh BM aspirates were collected from 21 MM patients with progressive disease (PD) or in complete response (CR) after obtaining IRB approval. BM mononuclear cells were isolated and single cell suspensions were obtained followed by staining with anti-human antibodies to evaluate DNAM-1 axis members and PD-1 expression. BM biopsies from 6 MM patients (each patient had 4 core on the Tissue Micro-Array T291 USBiomax) were stained for PVRL2 expression by immuno-histochemistry (IHC).ResultsFlow cytometry analysis of PD-1 and DNAM-1 axis receptors revealed a significant lower fraction of PD1+ cells among cell populations examined compared with other receptors. TIGIT expression was the highest on NK, CD8+ and NKT cells compared to CD4+ T cells, which is in line with previous published data (Lozano E. Clin. Cancer Res. 2020). In contrast, DNAM-1 was expressed on CD8+ T, NK and NKT cells with prominent high expression on CD4+ T cells (Fig 1A). The highest expression among the receptors was of PVRIG on all lymphoid populations, except CD4+ where DNAM-1 was more highly expressed. Importantly, 50% of CD8+ T cells co-expressed TIGIT and PVRIG, supporting a combinatorial therapeutic approach (Fig. 1B).Additionally, the expression of the PVRL2 ligand on MM plasma and endothelial cells was demonstrated by IHC. FACS analysis further supported PVRL2 expression on plasma cells in MM BM (Fig 2).A higher expression of PVRIG, TIGIT and PD-1 was present on DNAM-1 negative CD8+ T cells (Fig 3A, B), suggesting accumulation of exhausted cells in MM tumor microenvironment (TME) as previously described (Minnie S., Blood. 2018). PVRIG had significantly higher expression on DNAM+ cells, compared to PD-1 and TIGIT (Fig 3C), suggesting the potential of its blockade to enhance DNAM-1 activation and subsequent proliferation of earlier differentiated memory cells in MM TME. Finally, CR patients had a trend for higher DNAM-1 expression on CD8+ T cells compared to those with PD (Fig 3D). This is consistent with other reports in mice showing that the expression of DNAM-1 negatively correlates with BM myeloma cell numbers (Minnie S., Blood. 2018).ConclusionsDNAM-1 axis receptors are dominantly expressed on lymphocytes in BM of MM patients, with PVRIG exhibiting the most prominent expression. The reduced expression of DNAM-1 in PD patients' TME, compared to CR patients, suggests a link between DNAM-1 axis and clinical outcomes. Recent data suggest TIGIT is an attractive target for blockade in MM. Our new findings highlight for the first time the dominant expression of PVRIG, as well as TIGIT, and suggest that combined blockade of TIGIT with PVRIG may potentially benefit MM patients, placing the DNAM-1 axis as a dominant pathway in MM therapy. [Display omitted] DisclosuresFrenkel: Compugen Ltd.: Current Employment, Other: in the event of frontal participation, I will be reimbursed for my travel expenses by Compugen Ltd.. Alteber: Compugen Ltd.: Current Employment. Cojocaru: Compugen Ltd.: Current Employment. Ophir: Compugen Ltd.: Current Employment.

NL-201, a De Novo Agonist of IL-2 and IL-15 Receptors, Demonstrates Synergistic Antitumor Activity with Anti-PD-1 Checkpoint Inhibitor Therapy in a Preclinical Non-Hodgkin Lymphoma Model

NL-201 is a potent, selective, and long-acting computationally designed alpha-independent agonist of the IL-2 and IL-15 receptors that is being developed as an immunotherapy for cancer. NL-201 binds to the beta and gamma subunits, selectively stimulating dose-dependent expansion and tumor infiltration of cytotoxic CD8+ T cells and natural killer (NK) cells, thereby enhancing the immune response to the tumor. Absence of binding to the IL-2 alpha subunit reduces the undesirable effects of traditional IL-2 therapies, such as vascular leak syndrome and expansion of immunosuppressive regulatory T cells. In this abstract, we demonstrate that NL-201, alone or in combination, demonstrates robust antitumor activity in preclinical models of non-Hodgkin lymphoma (NHL).We have previously demonstrated that NL-201 has marked antitumor activity in multiple syngeneic tumor models, including the A20 lymphoma model. These observations in lymphoma have been extended to explore the effects of NL-201 in combination with anti-mPD-1 checkpoint inhibitor therapy in vivo. In this model, NL-201 and anti-mPD-1 demonstrated tumor growth inhibition and increased median survival (21 days each vs 17 days as observed in control) when given alone. In combination, NL-201 and anti-mPD-1 resulted in increased antitumor activity and significant prolongation of survival (>51 days). We have also demonstrated that NL-201 does not directly induce signaling or cell death in B cell−derived NHL, suggesting that the observed antitumor activity is due to activation of non-malignant host immune cells.Additional in vitro and in vivo NHL models are being tested to enhance understanding of the interaction between NL-201 and other approved therapies within the hematopoietic tumor microenvironment. These data will be used to design future clinical trials of NL-201 in novel regimens to treat hematological malignancies. DisclosuresHuard: Neoleukin Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company, Patents & Royalties. Tatalick: Neoleukin Therapeutics, Inc.: Consultancy, Current equity holder in publicly-traded company, Other: Independent paid nonclinical consultant for Neoleukin. Walkey: Neoleukin Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company, Current holder of stock options in a privately-held company. Swanson: Neoleukin Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company, Patents & Royalties.

Co-Expression of an shRNA Targeting MICA/Micb Improves the Clinical Activity of a NKG2D-Based CAR T in Patients with Relapsed / Refractory AML/MDS

While CAR T cell therapy has delivered impressive clinical efficacy in B cell malignancies, similar levels of clinical activity have not been demonstrated in acute myeloid leukemia (AML). One underlying reason for this lack of translation is the relative paucity of validated CAR T targets. Major Histocompatibility Complex Class 1 related proteins MICA and MICB along with the UL16 binding proteins 1-6 (ULBP1-6) are frequently over-expressed on AML and myelodysplastic syndrome (MDS) blasts. The Natural Killer Group 2D (NKG2D) is a single receptor able to bind MICA, MICB and ULBP1-6, thus providing a potentially powerful approach that could be exploited to target this family of targets thereby providing a novel CAR T approach for AML/MDS.Expressing the NKG2D receptor fused to the human CD3z cytoplasmic domain generates a CAR that, when expressed in primary T cells, generates a CAR T product (termed CYAD-01) that showed good anti-tumor activity in preclinical models. In clinical trials, CYAD-01 showed a good tolerability profile but with a disappointing level of clinical activity when combined with cyclophosphamide / fludarabine preconditioning (DEPLETHINK trial, NCT03466320).We hypothesised that the transient expression of MICA/MICB on the CAR T itself may inhibit the activity of the NKG2D CAR through self-targeting and consequent fratricide. We developed a single shRNA able to knockdown both MICA and MICB. Co-expression of this shRNA with the NKG2D CAR generated a second generation CAR T product termed CYAD-02 which was examined in a highly similar AML/MDS patient population and preconditioning regimen as employed in the DEPLETHINK trial.CYAD-02 was evaluated in the the first-in-human CYCLE-1 trial (NCT04167696) in patients with r/r AML/MDS. The dose-escalation phase evaluated three dose-levels (DL) (1x10 8, 3x10 8 and 1x10 9 total cells per infusion), administered as a single infusion after standard preconditioning chemotherapy (cyclophosphamide 300 mg/m²/day and fludarabine 30 mg/m²/day, daily for 3 days) according to a classic 3+3 design.As of July 2021, 11 patients have been treated with CYAD-02 at the different dose-levels (3 at each DL1 and 2 and 5 at DL3). In terms of safety and tolerability, there was no evidence of a differential safety profile of CYAD-02 within the CYCLE-1 trial as compared to that observed in the CYAD-01 clinical trial. Of note, five patients enrolled in all 3 DLs experienced Grade ≥ 3 adverse events (AE) at least possibly related to CYAD-02 (cytokine release syndrome, febrile neutropenia, white blood cell count decreased, infusion related reaction).With respect to clinical activity, seven patients in total achieved stable disease (2 at DL1, 3 at DL2 and 2 at DL3) with 4 demonstrating evidence of transient blast reduction or anti-leukemic activity (decrease of at least 50% of the bone marrow blasts). In addition, two MDS patients at DL3 achieved a marrow complete response. Overall, this suggests dose dependent response to CYAD-02. Furthermore, patients receiving CYAD-02 cells seem to display a greater duration of response and stronger blast reduction as compared to patients who received CYAD-01 in DEPLETHINK.Interestingly, peak engraftment levels were higher for CYAD-02 compared to CYAD-01 at the same dose (DEPLETHINK trial). At DL3, CYAD-02 cells could be readily detected in peripheral blood of 4/5 patients through month 2. In addition, and unlike what is reported in B cell CAR T-cells trials, there was very limited evidence of elevated homeostatic cytokines (IL-7/IL-15) following CyFlu administration with IL-15 not detected in any of the patients and IL-7 showing only a minor increase in 2 patients.The knockdown of MICA/MICB appears to have a positive contribution to the initial clinical activity of CYAD-02 as compared to that achieved with the first generation CYAD-01 CAR T, together with good safety and tolerability. The lack of homeostatic cytokines after preconditioning, likely limiting the engraftment and activity of CAR T cells, may be related to the biology of myeloid malignancies. One approach to further drive the potency of NKG2D-based CAR T cells would likely be armoring the CAR T through using the T cell as a vehicle to secrete cytokines alongside the CAR. Overall, shRNA knockdown technology provides a means to modify CAR T function and here shows that single shRNA can target two independent genes to enhance the phenotype of the CAR Ts. DisclosuresDeeren: Alexion: Consultancy; BMS: Consultancy; Incyte: Consultancy; Novartis: Consultancy; Sanofi: Consultancy, Research Funding; Sobi: Consultancy; Takeda: Consultancy. Lin: AbbVie, Aptevo Therapeutics, Astellas Pharma, Bio-Path Holdings, Celgene, Celyad, Genentech-Roche, Gilead Sciences, Incyte, Jazz Pharmaceuticals, Novartis, Ono Pharmaceutical, Pfizer, Prescient Therapeutics, Seattle Genetics, Tolero, Trovagene: Research Funding. Alcantar-Orozco: Celyad Oncology: Current Employment. Dheur: Celyad Oncology: Current Employment. Breman: Celyad Oncology: Current Employment. Braun: Celyad Oncology: Current Employment. Lonez: Celyad Oncology: Current Employment. Gilham: Celyad Oncology: Current Employment. Flament: Celyad Oncology: Current Employment. Lehmann: Celyad Oncology: Current Employment.

Combination of Loncastuximab Tesirine and Polatuzumab Vedotin Shows Increased Anti-Tumor Activity in Pre-Clinical Models of Non-Hodgkin Lymphoma

Loncastuximab tesirine-lpyl (formerly ADCT-402) is an antibody-drug conjugate (ADC) comprising a humanised anti-CD19 monoclonal antibody conjugated to the pyrrolobenzodiazepine (PBD) dimer-based payload tesirine. Once bound to CD19 on the cell membrane, loncastuximab tesirine is rapidly internalised and the released PBD dimer warhead causes interstrand DNA crosslinks which ultimately trigger cell death. Pre-clinically, loncastuximab tesirine has shown potent and specific anti-tumor activity in lymphoma models both as single agent and in combination with other approved drugs, like venetoclax, idelalisib and bendamustine (Zammarchi, Corbett et al. 2018, Tarantelli, Spriano et al. 2019). Loncastuximab tesirine has been recently approved by the United States Food and Drug Administration (FDA) for the treatment of relapsed or refractory (r/r) diffuse large B-cell lymphoma (DLBCL) and it is currently being tested in multiple clinical trials, either as monotherapy or in combination with other anti-lymphoma drugs.Polatuzumab vedotin is an ADC composed of a humanized anti-CD79b monoclonal antibody conjugated to monomethyl auristatin E (vcMMAE) and it is approved by the FDA for treatment of r/r DLBCL when used in combination with bendamustine and rituximab.Here, we investigated the in vitro and in vivo anti-tumor activity of loncastuximab tesirine combined with polatuzumab vedotin in pre-clinical models of non-Hodgkin lymphoma (NHL).In vitro, the combination of loncastuximab tesirine and polatuzumab vedotin was tested in three human-derived, CD19 and CD79b-positive NHL cell lines (WSU-DLCL2, TMD8 and Ramos) and it resulted in synergistic (TMD8 and Ramos) and additive (WSU-DLCL2) activity, as assessed by the Chou-Talalay method.Quantification of cell viability (propidium iodide [PI]-negative and Annexin V-negative) and early/late apoptosis (Annexin V-positive and PI-negative/ Annexin V-positive and-PI positive) on TMD8 and Ramos cells treated with loncastuximab tesirine, polatuzumab vedotin or the combination of the two agents showed a significant reduction of viable cells accompanied by an increase in apoptotic cells in the combination setting compared to the single agents.In vivo, loncastuximab tesirine was tested either alone (0.25 or 0.5 mg/kg, single dose) or in combination with polatuzumab vedotin (1 mg/kg, single dose) in the WSU-DLCL2 xenograft model. At the highest dose of loncastuximab tesirine, combination with polatuzumab vedotin resulted in improved anti-tumor activity and superior response rate compared to the 2 agents in monotherapy. All treatment regimens were well tolerated by the mice, as assessed by body weight measurements and frequent observation for signs of treatment-related side effects.In conclusion, the combination of loncastuximab tesirine and polatuzumab vedotin resulted in improved anti-tumor activity both in vitro and in vivo in lymphoma preclinical models and it was well tolerated. Altogether, these novel pre-clinical data warrant translation of the combination of loncastuximab tesirine and polatuzumab vedotin into the clinic for the treatment of NHL. DisclosuresSachini: ADC Therapeutics: Current Employment, Current equity holder in publicly-traded company. Jabeen: ADC Therapeutics: Current Employment, Current equity holder in publicly-traded company. van Berkel: ADC Therapeutics: Current Employment, Current equity holder in publicly-traded company, Patents & Royalties. Zammarchi: ADC Therapeutics: Current Employment, Current equity holder in publicly-traded company, Patents & Royalties.

10P DS-6000a, a novel CDH6-targeting antibody-drug conjugate with a novel DNA topoisomerase I inhibitor DXd, demonstrates potent antitumor activity in preclinical models

Human Cadherin 6 (CDH6) is a single transmembrane protein consisting of 790 amino acids classified into the type 2 cadherin family. Human CDH6 is specifically expressed in the brain and kidneys during the development phase and has been reported to systemically decrease CDH6 expression in the adult body. CDH6 expression is increased specifically in renal cell carcinoma (RCC) and ovarian cancer (OVC). Therefore, CDH6 could be an attractive target for cancer therapy. We created DS-6000a, a CDH6-targeting antibody-drug conjugate (ADC) using an enzymatically cleavable tetrapeptide-based linker, and a high drug-to-antibody ratio (DAR 7 to 8) with a novel DNA topoisomerase I inhibitor (DXd).

13P SY-5609, a highly potent and selective oral CDK7 inhibitor, exhibits robust antitumor activity in preclinical models of KRAS mutant cancers as a single agent and in combination with chemotherapy

Mutational KRAS activation drives oncogenic processes including aberrant cell cycle progression. CDK7 inhibition has been shown to target two fundamental processes in cancer: transcription and cell cycle control. SY-5609 is a CDK7 inhibitor in development in patients with solid tumors including pancreatic and lung cancers (NCT04247126). Here we report on SY-5609 preclinical activity in models of KRAS-mutant pancreatic ductal adenocarcinoma (PDAC) and non-small-cell lung cancer (NSCLC).

Cytolytic Activity of CAR T Cells and Maintenance of Their CD4+ Subset Is Critical for Optimal Antitumor Activity in Preclinical Solid Tumor Models.

Simple SummaryAdoptively transferred T cells expressing recombinant chimeric antigen receptors (CAR T cells) have been approved for the therapy of hematological malignancies of the B cell lineage. However, CAR T cell therapy for patients with solid tumors so far has shown limited benefits. Correlative clinical studies of patients with hematological malignancies have suggested that less differentiated CAR T cells have improved anti-leukemic activity. We have therefore investigated the role of differentiation on the anti-tumor activity of CAR T cells targeting the solid tumor antigen HER2 in preclinical models. We utilized different activation/expansion protocols, and explored whether different co-stimulatory domains in the CAR construct influence the short- and long-term efficacy of HER2-CAR T cells. We demonstrate that the CAR T cell product with the highest proportion of effector cells and maintaining a good balance of CD4+/CD8+ cells is the most effective against solid tumors both in vitro and in vivo.Correlative clinical studies of hematological malignancies have implicated that less differentiated, CD8+-dominant CAR T cell products have greater antitumor activity. Here, we have investigated whether the differentiation status of CAR T cell products affects their antitumor activity in preclinical models of solid tumors. We explored if different activation/expansion protocols, as well as different co-stimulatory domains in the CAR construct, influence the short- and long-term efficacy of CAR T cells against HER2-positive tumors. We generated T cell products that range from the most differentiated (CD28.z; OKT3-antiCD28/RPMI expansion) to the least differentiated (41BB.z; OKT3-RetroNectin/LymphoONE expansion), as judged by cell surface expression of the differentiation markers CCR7 and CD45RA. While the effect of differentiation status was variable with regard to antigen-specific cytokine production, the most differentiated CD28.z CAR T cell products, which were enriched in effector memory T cells, had the greatest target-specific cytolytic activity in vitro. These products also had a greater proliferative capacity and maintained CD4+ T cells upon repeated stimulation in vitro. In vivo, differentiated CD28.z CAR T cells also had the greatest antitumor activity, resulting in complete response. Our results highlight that it is critical to optimize CAR T cell production and that optimal product characteristics might depend on the targeted antigen and/or cancer.

Selective Inhibition of the Second Bromodomain of BET Family Proteins Results in Robust Antitumor Activity in Preclinical Models of Acute Myeloid Leukemia.

Dual bromodomain BET inhibitors that bind with similar affinities to the first and second bromodomains across BRD2, BRD3, BRD4, and BRDT have displayed modest activity as monotherapy in clinical trials. Thrombocytopenia, closely followed by symptoms characteristic of gastrointestinal toxicity, have presented as dose-limiting adverse events that may have prevented escalation to higher dose levels required for more robust efficacy. ABBV-744 is a highly selective inhibitor for the second bromodomain of the four BET family proteins. In contrast to the broad antiproliferative activities observed with dual bromodomain BET inhibitors, ABBV-744 displayed significant antiproliferative activities largely although not exclusively in cancer cell lines derived from acute myeloid leukemia and androgen receptor positive prostate cancer. Studies in acute myeloid leukemia xenograft models demonstrated antitumor efficacy for ABBV-744 that was comparable with the pan-BET inhibitor ABBV-075 but with an improved therapeutic index. Enhanced antitumor efficacy was also observed with the combination of ABBV-744 and the BCL-2 inhibitor, venetoclax compared with monotherapies of either agent alone. These results collectively support the clinical evaluation of ABBV-744 in AML (Clinical Trials.gov identifier: NCT03360006).

Abstract 1260: First-in-class, orally bioavailable KRASG12V(ON) tri-complex inhibitors, as single agents and in combinations, drive profound anti-tumor activity in preclinical models of KRASG12V mutant cancers

Abstract KRASG12V mutant cancers represent a significant unmet medical need with nearly 44,000 new diagnoses annually in the US. The KRASG12V mutation occurs frequently in multiple tumor histotypes; the incidence in NSCLC, CRC and pancreatic cancers is 6%, 10% and 26%, respectively. RAS proteins are small GTPases that drive cell proliferation and survival when bound to GTP. Mutant RAS proteins exist predominantly in the GTP-bound (RAS(ON)) state, leading to excessive downstream signaling via interaction with effectors such as RAF. The intrinsic GTP hydrolysis rate of KRASG12V is significantly lower than that of either KRASG12C or KRASG12D. Therefore, targeting the KRASG12V(ON) state will be critical for maximal suppression of this oncogenic driver. No targeted, direct inhibitors of KRASG12V(ON) have been described to date. We have built a pipeline of small molecule inhibitors targeting multiple oncogenic RAS(ON) mutants. Here we describe the preclinical profile of KRASG12V(ON) inhibitors that promote a tri-complex between the inhibitor, the immunophilin cyclophilin A (CypA), and the active GTP-bound state of KRASG12V. In cancer cell lines bearing KRASG12V mutations, KRASG12V(ON) inhibitors trigger an immediate disruption of RAS-effector interactions, leading to attenuation of RAS pathway signaling, potent (sub-nM EC50) growth suppression, and apoptosis. KRASG12V(ON) inhibitors produce deep, durable, and dose-dependent suppression of tumor RAS pathway activation in vivo following oral administration. An extended duration of tumor pharmacodynamic activity, relative to plasma exposure, is observed that likely reflects retention of the inhibitors in tumor tissue due to high affinity binding to CypA. In human tumor xenograft models of KRASG12V mutant NSCLC, CRC and pancreatic cancers, oral administration of KRASG12V(ON) inhibitors is well-tolerated and drives profound and durable tumor regressions, with complete responses in some animals. KRASG12V(ON) inhibitors also downregulate immune checkpoint proteins PD-L1 and CD73 on KRASG12V mutant cancer cells, changes which can support enhanced anti-tumor immunity. The ability to target the GTP-bound form of mutant KRASG12V permits a broad array of combination opportunities in cancer types where single agent KRASG12V(ON) inhibition may be insufficient, for example with agents targeting pathway nodes both upstream (e.g. SHP2, SOS1) and downstream (e.g. MEK, ERK) of RAS, as well as parallel pathways (e.g. mTORC1). Tri-complex inhibitors that target KRASG12V(ON) are predicted to combat escape mechanisms in RAS-addicted cancer cells characterized by an increased pool of activated KRASG12V(ON). These inhibitors may lead to an attractive, targeted therapeutic option for the treatment of RAS-addicted cancers with a very high unmet medical need. Citation Format: Elena Koltun, Jim Cregg, Meghan A. Rice, Dan M. Whalen, Rebecca Freilich, Jingjing Jiang, Richard Hansen, Alun Bermingham, John E. Knox, Jay Dinglasan, Kyle Seamon, Cristina Blaj, Stephanie S. Chang, Yang Liu, Jun Huang, Kang-Jye Chou, Laura McDowell, Bianca J. Lee, David Wildes, Zhengping Wang, Mallika Singh, Adrian L. Gill, Jacqueline A. Smith. First-in-class, orally bioavailable KRASG12V(ON) tri-complex inhibitors, as single agents and in combinations, drive profound anti-tumor activity in preclinical models of KRASG12V mutant cancers [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 1260.

Abstract 981: BCL-2 inhibitor APG-2575 and homoharringtonine (HHT) synergistically induces apoptosis and inhibits tumor growth in preclinical models of acute myeloid leukemia and myelodysplastic syndromes (AML/MDS)

Abstract The AML treatment landscape has improved dramatically in the past decade, with improved objective response rates and overall survival after treatment with newly approved targeted therapies. BCL-2 inhibition combined with a hypomethylating agent or low-dose cytosine arabinoside (Ara-C) is also effective in previously untreated elderly patients who are not candidates for standard induction therapy. However, the effect of BCL-2 inhibition is commonly weakened when tumor cells upregulate antiapoptotic protein MCL-1 to escape apoptosis. Thus, combination therapy is introduced to suppress MCL-1 levels. HHT (omacetaxine mepesuccinate) has been widely used in Chinese patients with AML for 30 years. As an inhibitor of protein synthesis, HHT decreases MCL-1. This study investigated the effect of combining clinical stage BCL-2 selective inhibitor APG-2575 with HHT in AML and MDS cells, as well as murine xenograft tumor models. In AML (MV-4-11, OCI-AML-3) and MDS (SKM-1) cell lines, single-agent HHT exerted stronger antiproliferative and apoptogenic activities compared to APG-2575 (as assessed by Cell Titer Glo assay or flow cytometry). When combined, these treatments synergistically inhibited cellular proliferation and induced apoptosis. In a mouse xenograft tumor model derived from MV-4-11 cells, APG-2575 demonstrated limited antitumor activity, with a T/C (Treated/Control tumor volume %) value of 63% whereas HHT showed stronger activity, with T/C equal to 30%. Most importantly, these antitumor effects were potentiated when APG-2575 and HHT were combined, yielding a T/C value of 3% and partial regression in all treated tumors. Mechanistically, BCL-2 inhibition with APG-2575 decreased BCL-2:BIM complexes and but increased MCL-1:BIM complexes, as liberated BIM was re-sequestered by MCL-1. On the other hand, concomitant treatment with HHT abolished induction of MCL-1:BIM complexes. Besides BIM complexes, MCL-1:PUMA and MCL-1:BAK pairings also decreased after exposure to HHT. The decrease in MCL-1 complex coincided with its downregulation at protein levels. Thus, under such an MCL-1-supressed condition facilitated by HHT treatment, the freed proapoptotic proteins (BIM, PUMA, BAK) more potently manifested apoptotic signals triggered by APG-2575. In summary, APG-2575 synergizes with HHT to potentiate antitumor activity in preclinical models of AML/MDS. HHT suppresses MCL-1 protein, preventing or abolishing formation of MCL-1:BIM, MCL-1:PUMA, and MCL-1:BAK complexes, and hence allowing prodeath proteins to fully engage in tumor cell apoptosis induction. Our results provide scientific rationale for clinical development of APG-2575 plus HHT in patients with AML/MDS. Citation Format: Douglas D. Fang, Qiuqiong Tang, Yanhui Kong, Tao Rong, Qixin Wang, Jing Deng, Dajun Yang, Yifan Zhai. BCL-2 inhibitor APG-2575 and homoharringtonine (HHT) synergistically induces apoptosis and inhibits tumor growth in preclinical models of acute myeloid leukemia and myelodysplastic syndromes (AML/MDS) [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 981.

Abstract 2077: Activity of DHODH inhibitor BAY2402234 in subcutaneous and intracranial models of SCLC

Abstract Introduction: BAY2402234 is a potent and specific orally administered inhibitor of dihydroorotate dehydrogenase (DHODH) which showed anti-tumor activity in preclinical models of AML and is under clinical evaluation in myeloid malignancies (NCT03404726). Small cell lung cancer (SCLC) is a highly metastatic malignancy (the brain being a frequent metastatic site), which carries a dismal clinical prognosis. Previous preclinical research indicated that SCLC was particularly sensitive to DHODH inhibition, and in the current investigation the activity of BAY2402234 in this tumor indication was evaluated. Experimental Procedures: A variety of in vivo models derived from human SCLC samples were evaluated: (1) cell-line derived xenograft (CDX) subcutaneous models; (2) a CDX intracranial model; and (3) patient-derived xenograft (PDX) subcutaneous models. As is typical for SCLC, most of these models harbored mutations in both p53 and Rb1. BAY2402234 was administered orally either once daily or on an intermittent schedule (4 days on/3 days off). Standard-of-care (SoC) therapies were included in some experiments. Tumor tissue and plasma were collected for pharmacodynamic analyses. Results: In subcutaneous CDX models, BAY2402234 exhibited robust anti-tumor activity, including tumor regressions in some models. Strong anti-tumor activity was also observed in various subcutaneous PDX models, including activity in a model resistant to SoC therapy. In an intracranial tumor model, BAY2402234 significantly enhanced survival compared to the vehicle-treated cohort. Both dosing schedules tested were well-tolerated and highly active. Pharmacodynamic analyses to quantify the level of target inhibition observed in the various models are ongoing. Conclusions: The results of this investigation confirm and extend previous preclinical results and indicate that BAY2402234 may represent a novel treatment for SCLC, including patients with brain metastases. RESTRICTED Citation Format: Stefan Kaulfuss, Andreas Janzer, Gerhard Siemeister, Renan Borowicz, Katrin Jaensch, Katrin Gutberlet, Ricarda Schlenz, Andrea Triller, Ashley Eheim, Michael Jeffers, Sven Christian. Activity of DHODH inhibitor BAY2402234 in subcutaneous and intracranial models of SCLC [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 2077.

Abstract LB118: Mechanisms underlying synergistic activity in MYD88MTDLBCL of KT-413, a targeted degrader of IRAK4 and IMiD substrate

Abstract Relapsed/refractory DLBCL remains an incurable disease, and single-agent therapies typically show low response rates and/or transient clinical responses. Oncogenic MYD88 mutations occur in ~25% of DLBCL and drive constitutive NFkB activation, promoting proliferation and survival. Despite its role in tumor biology, targeting MYD88MT by inhibiting or degrading IRAK4 alone, a key component of the MYD88 complex, does not drive significant antitumor activity in preclinical models. One potential reason is the frequent redundant NFkB pathway activation by co-mutations, highlighting the need for combination therapies to effectively target the NFkB pathway in DLBCL. To address this challenge, we have developed IRAKIMiDs, heterobifunctional degraders that simultaneously degrade both IRAK4 and IMiD substrates, as a rational therapeutic combination in a single molecule. IRAKIMiDs show increased antitumor activity in vitro and in vivo in MYD88MT cells as compared to IMiD or IRAK4-targeting alone, highlighting suggesting their potential as single agents in R/R DLBCL.Our lead IRAKIMiD, KT-413, is a potent degrader of IRAK4 (DC50 6nM) and IMiD substrates (Ikaros/Aiolos DC50 2nM), inducing rapid and potent cell killing in vitro and complete and sustained tumor regressions in vivo in MYD88MT models of DLBCL. This activity is superior to the IMiD CC-220, which has similar activity against IMiD substrates (Ikaros/Aiolos DC50 1 nM), supporting the synergistic role of IRAK4 degradation in the context of IMiD biology. We show here that the combined activity of these 2 mechanisms drives a synergistic effect on NFkB and IRF4 signaling with greater downstream effect on NFkB and type 1 interferon (IFN) signaling and cell cycle gene expression than either mechanism alone. In THP1 cells engineered with NFkB and IRF4 reporters, KT-413 but not CC-220 inhibits TLR-stimulated NFkB and IRF4 transcription, supporting a role for IRAK4 but not IMiDs in MYD88-driven survival and proliferation signals. IMiDs have previously been shown to modulate type1 IFN signaling through downregulation of IRF4. We propose that simultaneous targeting of both NFkB and type 1 IFN signaling with KT-413 drives synergistic cell killing in MYD88MT cells. In MYD88MT OCI-Ly10 cells, KT-413 leads to greater IRF4 downregulation, increased type 1 IFN signaling, and preferential downregulation of NFkB pathway and cell cycle transcripts when compared to CC-220. These data support the hypothesis that the synergistic activity of targeting IRAK4 and IMiD substrates by KT-413 in MYD88MT DLBCL is a result of dual targeting of NFkB and IRF4/Type1 IFN through degradation of both IRAK4 and IMiD substrates,driving significantly greater cell killing as compared to either mechanism alone, supporting the potential for the first single agent targeted therapy in MYD88MT DLBCL. KT-413 is on track for initiation of a Phase 1 trial in B cell lymphoma in 2H 2021. Citation Format: Christine R. Klaus, Scott F. Rusin, Kirti Sharma, Samyabrata Bhaduri, Matthew M. Weiss, Alice A. McDonald, Michele F. Mayo, Duncan Walker, Rahul Karnik. Mechanisms underlying synergistic activity in MYD88MTDLBCL of KT-413, a targeted degrader of IRAK4 and IMiD substrate [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 LB118.

Abstract CT029: Pediatric phase 2 trial of the WEE1 inhibitor adavosertib (AZD1775) and irinotecan: A Children's Oncology Group Study (ADVL1312)

Abstract Background: Inhibition of the WEE1 kinase by adavosertib (AZD1775) potentiates replicative stress from genomic instability or chemotherapy, and demonstrated anti-tumor activity in preclinical models of pediatric cancer. This study reports the phase 2 expansion of the ADVL1312 phase I/II trial combining irinotecan and adavosertib in children and adolescents with relapsed/refractory solid and CNS tumors. Methods: Patients (< 21 yrs old) with measurable or MIBG-evaluable relapsed/refractory neuroblastoma (Part B), medulloblastoma/CNS embryonal tumors (Part C) or rhabdomyosarcoma (Part D) were treated with irinotecan (90 mg/m2/dose) and adavosertib (85 mg/m2/dose) orally for 5-days every 21-days. Any patient who received at least one dose was considered evaluable for response. Using a Simon's two stage design the combination was considered effective if there were three out of twenty responses in parts B and D or six out of nineteen responses in part C. Tumor tissue was analyzed for ATRX deficiency by multiplex immunofluorescence of ultrabright telomere foci and ATRX, and where available, prior tumor genomic analyses. Results: Twenty eligible patients with neuroblastoma, with a median age of nine years old (6-19) were included in Part B. They had a median of three prior chemotherapy regimens (1-7); nineteen patients (95%) had prior irinotecan and seventeen (85%) received prior radiation therapy. The combination therapy resulted in three objective responses confirmed by central review (estimated response rate of 16.7%) meeting the protocol defined efficacy endpoint for Part B. The responses included a measurable partial response (11 cycles), MIBG evaluable complete response (9 cycles) and MIBG and marrow evaluable partial response (18 cycles). In addition, there were three patients with prolonged stable disease of 8, 11 and 13 cycles. Two of the three patients with objective responses had tumors with predicted ATRX deficiency, while the third did not have available archival tumor. Of the nine neuroblastoma patient tumors with predicted ATRX deficiency, 4 (44%) had objective responses or prolonged stable disease. In part C, of 9 patients eligible for response, 1 patient with pineoblastoma had a confirmed partial response (9 cycles) and another with medulloblastoma had prolonged stable disease (11 cycles). In part D, of 10 eligible patients, 2 had stable disease of 8 and 10 cycles. Part C and D did not meet the protocol defined efficacy endpoint. The combination was well tolerated with one patient experiencing a dose limiting toxicity that resolved with dose reduction. Conclusion: This the first phase 2 clinical trial of adavosertib in pediatrics and the first in combination with irinotecan. The combination was of sufficient activity to support further study in neuroblastoma, and possibly other pediatric tumor types with recurrent ATRX mutation. Citation Format: Kristina A. Cole, Heba Ijaz, Lea Surrey, Mariarita Santi-vicini, Xiaowei Liu, Charles G. Minard, John M. Maris, Stephan Voss, Elizabeth Fox, Brenda Weigal. Pediatric phase 2 trial of the WEE1 inhibitor adavosertib (AZD1775) and irinotecan: A Children's Oncology Group Study (ADVL1312) [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 CT029.

Abstract 1530: Anti-HER2 CAR monocytes demonstrate targeted anti-tumor activity and enable a single day cell manufacturing process

Abstract Recent advances in cell therapy have led to significant efficacy in hematologic malignancies, but solid tumors remain an intractable challenge. We have previously developed a CAR macrophage (CAR-M) adoptive cell therapy platform and demonstrated potent anti-tumor activity in pre-clinical models. CAR-M overcome several of the barriers to efficacy in the solid tumor setting - trafficking, immunosuppression, lymphocyte exclusion, and antigen heterogeneity. Currently, CAR-M are generated via ex vivo differentiation of peripheral blood monocytes into macrophages prior to genetic manipulation. In order to streamline the manufacturing process, improve cell yields, and potentially improve tumor infiltration, we sought to evaluate the feasibility of directly engineering CD14+ monocytes to express CAR. Using the chimeric adenoviral vector Ad5f35, we engineered primary human CAR-monocytes to target tumors overexpressing HER2. CAR expression and viability both exceeded 90%. Anti-HER2 CAR-monocytes produced pro-inflammatory cytokines in response to antigen, specifically phagocytosed HER2 overexpressing target cells, and eradicated HER2-overexpressing tumor cells in a time and dose-dependent manner. CAR-monocytes efficiently differentiated into CAR-expressing macrophages in response to various maturation factors and cytokines within 3-5 days. Adenoviral based gene modification resulted in the upregulation of several pro-inflammatory markers on CAR-monocytes and pre-conditioned these cells to differentiate into M1 macrophages in the absence of exogenous M1 polarization factors. The M1 phenotype was maintained when CAR-monocytes were challenged with immunosuppressive cytokines in vitro. These cells demonstrated potent effector function after differentiation into macrophages, regardless of exposure to GM-CSF, M-CSF, or immunosuppressive factors. Anti-HER2 CAR monocytes carried broadly expressed myeloid chemokine receptors and responded to a panel of chemotactic factors. In order to optimize the cell manufacturing process associated with CAR-M, we established a closed-system, ultra-rapid CAR monocyte process. This process enabled same day manufacturing of the final CAR monocyte cell product, significantly reducing the cost of goods associated with autologous cell therapy as well as “vein to vein” time. This study demonstrated the successful development of CAR-monocytes with direct anti-tumor activity and capacity to differentiate into M1 polarized CAR-M. In addition, we established an ultra-rapid same-day CAR monocyte manufacturing process. The CAR-monocyte platform represents an advance in the field of adoptive cell therapy. Citation Format: Linara Gabitova, Brett Menchel, Rashid Gabbasov, Stefano Pierini, Andrew Best, Kayleigh Ross, Yumi Ohtani, Daniel Blumenthal, Sascha Abramson, Thomas Condamine, Michael Klichinsky. Anti-HER2 CAR monocytes demonstrate targeted anti-tumor activity and enable a single day cell manufacturing process [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 1530.

Abstract 2786: A FcgR IIB tumor enriching anti-CD137 novel antibody to avoid liver Immuno-toxicity

Abstract CD137 (4-1BB/TNFRSF9) is a costimulatory T-cell receptor belonging to the TNF receptor superfamily which is transiently expressed on T cell and NK cells. Targeting CD137 or its natural ligand 4-1BB ligand (4-1BBL) has important implications in many clinical conditions, including cancer. Anti-CD137 agonistic anti-CD137 antibodies have shown potent, often curative anti-tumor activity in preclinical models. In depth analysis revealed that 4-1BB-mediated anti-cancer effects are based on its ability to induce activation of cytotoxic T lymphocytes and high amounts of cytokines, including IFN-γ. However, this approach has suffered significant setback in the clinic due to either dose-dependent severe liver toxicity (e.g. Urelumab), or lack of single agent activity in the case of Utomilumab. Multiple therapeutics that attempt to restrict 4-1BB agonism to the tumor microenvironment and minimize systemic exposure have emerged. Here we present a novel antibody targeting 4-1BB receptor, named HLX25 with engineered Fc region to enhance the binding to FcγR IIB. In vitro, HLX25 induces comparable or superior CD137 activation and IL-2 release compared to Urelumab and Utomilumab, suggesting potentially a better safety profile. We showed that HLX25 binds to unique non-ligand competing epitope, which is different from both Urelumab and Utomilumab. In vivo, HLX25 shows potent dose-dependent single agent anti-tumor activity as low as 0.3mg/kg in MC38 model without sign of liver toxicity up to 20 mg/kg, suggesting superior efficacy and better safety profile. Citation Format: Jie Xue, Jen-Kuan Chang, Chen Dong, Yi-Ting Mao, Pallavi Raghavendra, Ou Li, Hassan Issafras, Wenfeng Xu, Weidong Jiang. A FcgR IIB tumor enriching anti-CD137 novel antibody to avoid liver Immuno-toxicity [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 2786.

Sy-1365, a Potent and Selective CDK7 Inhibitor, Exhibits Anti-Tumor Activity in Preclinical Models of Hematologic Malignancies, and Demonstrates Interactions with the BCL-XL/BCL2 Mitochondrial Apoptosis Signaling Pathway in Leukemia

Introduction: The transcriptional kinase CDK7 has been implicated in the pathogenesis of multiple malignancies, including hematologic malignancies, and may play important roles in regulation of oncogenic transcriptional dependencies and in regulation of the mitochondrial apoptosis machinery in tumors. SY-1365, a selective inhibitor of CDK7, was developed to exploit tumor dependencies driven by CDK7 and is in clinical development in patients with advanced solid tumors. We have previously reported that SY-1365 selectively induces apoptosis in leukemic cells relative to non-malignant cells in vitro, and demonstrates anti-tumor activity in AML xenografts. Here we report that SY-1365 has potent inhibitory activity against a broad panel of hematologic malignancies in vitro and ex vivo, induces regressions in AML xenografts using a clinically relevant dosing regimen, and demonstrates synergy with the BCL2 inhibitor venetoclax in AML cells in vitro.Methods: SY-1365 dose-response curves were measured using the ATP-lite assay in a panel of 85 leukemia and lymphoma cell lines in vitro, and in a panel of 226 patient-derived tumor samples from 5 leukemic indications cultured ex vivo. In vivo tumor inhibitory activity was evaluated using once weekly (QW) and twice weekly (BIW) dosing regimens in ML-2 and Kasumi-1 AML xenografts. Growth-rate (GR) adjusted dose response curves were used to classify cell lines into low and high sensitivity groups, and were evaluated relative to RNA expression data to identify markers predictive of sensitivity to SY-1365. Synergy between SY-1365 and venetoclax was evaluated in vitro using KG-1 AML cells.Results: In 42 leukemia lines, SY-1365 had a median IC50 of 11nM (range 1-79nM), with 48% (20/42) demonstrating particularly low IC50s (<10nM). In 43 lymphoma lines, the median IC50 was 6nM (range 1-39nM), with 59% (27/46) demonstrating low IC50s (<10nM). Similarly, SY-1365 demonstrated potent inhibitory activity against patient-derived leukemia samples cultured ex vivo (median IC50 of 28nM), with 82% (185/226) of the samples showing IC50 below 100nM and 8% (19/226) under 10nM. Furthermore, analysis of growth rate (GR) in hematologic tumor cell lines showed that <10nM SY-1365 induced cytotoxicity (GR<0) in 19% (8/42) of leukemia and 21% (9/43) of lymphoma lines. To evaluate SY-1365 anti-tumor activity in vivo, 2 AML cell lines that demonstrate cytotoxic responses to SY-1365 in vitro (Kasumi-1 and ML-2) were grown as subcutaneous xenografts in mice. QW and BIW dosing of 40mg/kg SY-1365 induced tumor regressions in Kasumi-1 xenografts, and BIW dosing induced tumor stasis in ML-2 xenografts. Tumor growth inhibition was detected with a 20mg/kg BIW dosing regimen in both models. Comparison of SY-1365 sensitivity with RNA expression in hematologic tumor cell lines revealed that lower expression of BCL2L1, which encodes the mitochondrial apoptosis inhibitor BCL-XL, was highly predictive of sensitivity in leukemia cell lines (Accuracy=89%, FDR<0.05); no such relationship was observed in lymphoma lines. Considering the established role of BCL2 and the mitochondrial apoptosis pathway in leukemia, we reasoned that BCL-XL low-expressing leukemias, in addition to being sensitive to SY-1365, would also be reliant on BCL2 for survival. Indeed, in vitro combination studies demonstrated synergistic inhibitory activity of SY-1365 with the BCL2 inhibitor venetoclax in KG-1 AML cells. A potential synergistic interaction with SY-1365 and venetoclax is currently being explored in vivo with AML xenografts.Conclusions: SY-1365 shows potent in vitro inhibitory activity in multiple hematological indications and can induce AML xenograft tumor regression in mice. In vitro exploratory biomarker and tumor cell inhibitory combination studies in AML suggest a role for mitochondrial apoptosis signaling in mediating sensitivity to SY-1365 and support the evaluation of a combination with venetoclax. SY-1365 is currently being assessed in a phase 1 trial in adult patients with advanced solid tumors (NCT03134638). The results described here support the potential for additional exploration in patients with hematological malignancies. DisclosuresHodgson:Syros Pharmaceuticals: Employment, Equity Ownership. Johannessen:Syros Pharmaceuticals: Employment, Equity Ownership. Rajagopal:Syros Pharmaceuticals: Employment, Equity Ownership. Hu:Syros Pharmaceuticals: Employment, Equity Ownership. Orlando:Syros Pharmaceuticals: Employment, Equity Ownership. Eaton:Syros Pharmaceuticals: Employment, Equity Ownership. McKeown:Syros Pharmaceuticals: Employment. Tyner:Takeda Pharmaceutical Company: Research Funding; Agios Pharmaceuticals: Research Funding; Incyte Corporation: Research Funding; Gilead: Research Funding; Janssen Pharmaceutica: Research Funding; Syros: Research Funding; Aptose Biosciences: Research Funding; Seattle Genetics: Research Funding; Constellation Pharmaceuticals: Research Funding; Genentech: Research Funding; Array Biopharma: Research Funding; AstraZeneca: Research Funding; Leap Oncology: Consultancy. Sprott:Syros Pharmaceuticals: Employment, Equity Ownership. Fritz:Syros Pharmaceuticals: Employment, Equity Ownership. Di Tomaso:Syros Pharmaceuticals: Employment.