PARP inhibition is a modulator of anti-tumor immune response in BRCA-deficient tumors

PARP inhibitors are synthetically lethal with BRCA1/2 mutations, and in this setting, accumulation of DNA damage leads to cell death. Because increased DNA damage and subsequent immune activation can prime an anti-tumor immune response, we studied the impact of olaparib ± immune checkpoint blockade (ICB) on anti-tumor activity and the immune microenvironment. Concurrent combination of olaparib, at clinically relevant exposures, with ICB gave durable and deeper anti-tumor activity in the Brca1m BR5 model vs. monotherapies. Olaparib and combination treatment modulated the immune microenvironment, including increases in CD8+ T cells and NK cells, and upregulation of immune pathways, including type I IFN and STING signaling. Olaparib also induced a dose-dependent upregulation of immune pathways, including JAK/STAT, STING and type I IFN, in the tumor cell compartment of a BRCA1m (HBCx-10) but not a BRCA WT (HBCx-9) breast PDX model. In vitro, olaparib induced BRCAm tumor cell–specific dendritic cell transactivation. Relevance to human disease was assessed using patient samples from the MEDIOLA (NCT02734004) trial, which showed increased type I IFN, STING, and JAK/STAT pathway expression following olaparib treatment, in line with preclinical findings. These data together provide evidence for a mechanism and schedule underpinning potential benefit of ICB combination with olaparib.

Abstract 1142: Activity and tolerability of combination of trastuzumab deruxtecan with the next generation PARP1-selective inhibitor AZD5305 in preclinical models

Background: Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate composed of an anti-HER2 antibody, a cleavable tetrapeptide-based linker, and a cytotoxic topoisomerase I inhibitor, approved for HER2+ metastatic breast cancer. Clinically, T-DXd has demonstrated antitumor activity in both HER2+ and HER2-low cancers. Due to the role of PARP1 in resolution of DNA damage induced by topoisomerase I trapping, we tested the combination of the next generation PARP1-selective inhibitor AZD5305 with T-DXd.

Methods: We evaluated the antiproliferative ability of the combination of T-DXd with AZD5305 in a panel of 27 breast cancer cell lines in an in vitro 7-day viability assay. The combination was also evaluated in vivo in two non-HRD HER2+ models, KPL4 (Breast) and NCI-N87 (Gastric) at doses of 3mg/kg and 10mg/kg Q3W for T-DXd combined with 0.01, 0.1, and 1 mg/kg QD of AZD5305. To evaluate the specificity of the combination activity in tumor cells (vs normal tissue), we further evaluated the combination in a human 2D in vitro bone marrow progenitor assay.

Results: We found that the combination had enhanced in vitro cell killing activity over single agents in 8/27 of the models tested. The benefit was present in both Homologous Recombination Deficient (HRD) as well as Homologous Recombination proficient, suggesting it does not depend on HRD (as defined by mutations in DNA damage repair genes). Mechanistically, T-DXd activated PARP and the combination of T-DXd with AZD5305 abrogated PARP1 auto-parylation, leading to enhanced DNA damage (gH2AX, pRPA-S4/8) and cell death (cCasp3). In vivo, the combination was well tolerated and more active than monotherapy of either compound in both KPL4 (at 30 days the growth inhibition was 95% at 10mg/kg T-DXd, 10% at 1mg/kg AZD5305, and 100% TGI with 97% regression with T-DXd + AZD5305) and NCI-N87 (at 41 days TGI of 74% with 10mg/kg T-DXd, 47% with 1mg/kg AZD5305, and 100% TGI with 40% regression for T-DXd + AZD5305; p<0.0001). In an in vitro human bone marrow assay, the combination demonstrated modest enhancement over monotherapy activity (average Loewe Synergy Score of 3.1). We tested alternative doses and schedules of the combination in KPL4 in vivo. We found that reducing the dose of AZD5305 as low as 0.01mg/kg resulted in combination benefit (100% TGI with 78% regression for combination versus 0% TGI for monotherapy on day 30). Further, 7-day delay of 0.01mg/kg AZD5305 in combination with 10mg/kg T-DXd also provided greater activity (>100% TGI with 72% regression on day 30) vs. monotherapy T-DXd alone (95% TGI).

Conclusions: These results suggest that T-DXd combined with the next generation PARP1 inhibitor AZD5305 is a potentially active combination, with preclinical activity demonstrated in HRD and HR proficient models. Further, the dose and scheduling may warrant exploration clinically to optimize therapeutic index.

Citation Format: Yann Wallez, Theresa Proia, Elisabetta Leo, Laura Bradshaw, Zena Wilson, Joe’l Owusu, Azadeh Cheraghchi-Bashi-Astaneh, Anna Staniszewska, Mark O’Connor, Sabina Cosulich, Jerome Mettetal. Activity and tolerability of combination of trastuzumab deruxtecan with the next generation PARP1-selective inhibitor AZD5305 in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1142.

Abstract 1141: Pharmacokinetic and pharmacodynamic evaluation of human tumor xenograft models treated upon administration of trastuzumab deruxtecan

Introduction: Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate comprised of an anti-HER2 antibody, a cleavable tetrapeptide-based linker, and a cytotoxic topoisomerase I inhibitor approved for the treatment of HER2 positive metastatic breast and gastric cancer. T-DXd has demonstrated antitumor activity in both HER2+ and HER2-low patient populations.

Methods: To establish exposure profiles of T-DXd and link with tumor biomarker changes, we administered a single IV dose of T-DXd at 10 mg/kg in human tumor xenograft models representing HER2-positive (NCI-N87; nude) and Her2-low (Capan-1; NOD-SCID) and collected tumor and plasma from 6 h to 336 h post dose. We measured tumor volume in addition to total ADC, total antibody, and free payload in the plasma and assessed biomarkers related to DNA damage in the tumor by western blot (WB) and immunohistochemistry (IHC).

Results: In HER2+ NCI-N87 tumor-bearing mice, T-DXd plasma AUC was 342.6ug/ml*day and T1/2 was 3.5 days, while in the HER2-low Capan-1 tumor-bearing mice, T-DXd plasma AUC was 297.2ug/ml*day and T1/2 was 1.4 days. Plasma exposures of free payload (DXd) were less than 1 ng/mL. Both models responded to T-DXd, demonstrating regression over the 14 day study (T/C =-6.08%, NCI-N87 and -96.1%, Capan-1). In NCI-N87, we observed rapid and sustained increases in gamma H2AX (gH2AX), with a 3.5-fold increase in % positive staining by IHC (H-score p<0.001) with gH2AX foci as early as 24h post treatment, and sustained out to 96h. Western blot analysis and quantification of gH2AX revealed a 4.3-fold increase at 48h (p<0.0001), which was sustained out to 96h. Further, we observed significant increases in pRAD50 at 24h (3.6-fold increase by IHC, H-score p<0.001) which was sustained out to 96h. In Capan-1, we observed more diffuse staining of gH2AX and non-significant 1.4-fold increase in gH2AX at 24h. pRAD50 increases were delayed in the Capan-1 model with a 2.8-fold increase observed at 48h and sustained out to 168h post treatment.

Conclusions: Plasma exposure of T-DXd in NCI-N87 tumor bearing mice was prolonged compared to Capan-1, possibly due to mouse strain differences. The increased systemic exposure resulted in more rapid and sustained DNA damage as measured by gH2AX and pRAD50 in the NCI-N87 tumor compared to Capan-1. This profile suggests exploration of combinations with DNA damage response inhibitors to inform design of dose and schedule of combination therapy may be warranted.

Citation Format: Theresa Proia, Jelena Urosevic, Christina Vasalou, Rebecca Sargeant, Matthew Griffin, Jiaqi Yuan, Anton I. Rosenbaum, Jerome Mettetal. Pharmacokinetic and pharmacodynamic evaluation of human tumor xenograft models treated upon administration of trastuzumab deruxtecan [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1141.

Abstract P2-13-23: Activity and tolerability of combination of trastuzumab deruxtecan with the pan-AKT inhibitor capivasertib in preclinical HER2+ and HER2-low breast cancer models

Background: Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate composed of an anti-HER2 antibody, a cleavable tetrapeptide-based linker, and a cytotoxic topoisomerase I inhibitor approved for HER2+ metastatic breast and gastric cancer. Clinically, T-DXd has demonstrated significant antitumor activity in both HER2+ and HER2-low (IHC 1+ & 2+/ISH-) breast cancer patients. The PI3K/AKT pathway is frequently activated in breast cancer, and mediates signals downstream of HER2. T-DXd has been shown to inhibit downstream AKT signaling driven by HER2. Capivasertib, a potent, selective inhibitor of all three AKT isoforms (AKT1/2/3) has shown clinical activity in breast cancer trials. Given the clinical activity of both agents, the anti-tumor activity of combined treatment with T-DXd with capivasertib, was explored preclinically in HER2+ and HER2-low models. Methods: The antiproliferative activity of the combination of T-DXd with capivasertib was assessed in a panel of 27 breast cancer cell lines using a 7 day viability assay. To determine whether the combination also translates in vivo, T-DXd (3 and 10mg/kg Q3W) and capivasertib (130mg/kg BID 4 days on/3 days off) were tested in KPL4 (HER2+). To determine whether the combination of T-DXd and capivasertib has a negative impact on normal tissue integrity, we further evaluated the combination in a human 2D in vitro bone marrow progenitor assay. Results: The combination treatment was more effective than each single agent in 6/27 of the models tested in vitro, resulting in increased cell kill in the viability assay. Two of these positive cell lines, HCC1569 (HER2+) and AU565 (HER2+) were PTEN altered, KPL4 (HER2+) and EFM19 (ER+) were mutant in PIK3CA, and HCC1419 (HER2+) and ZR-75-30 (ER+/HER2+) were neither PTEN or PIK3CA altered. In KPL4 xenografts, the combination of T-DXd and capivasertib showed modest increased activity over monotherapy T-DXd or capivasertib at 28d (Tumor Growth Inhibition (TGI) of T-DXd = 76%, capivasertib = 25%, and T-DXd+Capivasertib = 83%; p=0.3 combo vs. mono T-DXd) and more markedly at 46d (TGI of the combination vs T-DXd monotherapy was 65%). Importantly, the combination showed enhanced durability of response (stasis) in 100% mice while 38% (3/8) mice in the T-DXd mono therapy treatment group were actively re-growing at 46d. In the in vitro bone marrow assay, the combination demonstrated no increased interaction over monotherapy activity (average Loewe Synergy Score of -0.2). Conclusions: These results suggest combining T-DXd with capivasertib has potential to be active in breast cancer patients, with activity likely to be enriched in tumours with mutations in PIK3CA and PTEN, but also in tumours with no PI3K pathway activating mutations.

Citation Format: Azadeh Cheraghchi Bashi, Theresa Proia, Suzanne Randle, Mark Anderton, Zeshaan Rasheed, J. Elizabeth Pease, Simon Barry, Danielle Carroll, Jerome Mettetal. Activity and tolerability of combination of trastuzumab deruxtecan with the pan-AKT inhibitor capivasertib in preclinical HER2+ and HER2-low breast cancer models [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-13-23.

Abstract 1813: The genetic makeup of patient-derived xenografts shapes the immune landscape of humanized mice tumors

The complex interplay between the immune system and cancer cells is challenging to model in preclinical species. Many commonly mutated genes that influence tumorigenesis actively participate in the activation, recruitment or suppression of the immune system. A growing body of clinical findings indicates that defined oncogenic driver mutations correlate with immune contexture and associated immunotherapy responses. The goal of this study was to generate a hematopoietic stem cells (HSCs) transplanted humanized mice model using patient-derived xenografts with defined mutations to understand whether genetic alterations in the cancer cells can influence the tumor's immune landscape.

Loss of function in the tumor suppressor gene STK11/LKB1 are observed in 5-30% of NSCLC. Patients with STK11 mutations do not typically respond to immune checkpoint blockade, and analysis of patient tumor biopsies indicates that these tumors are poorly infiltrated by immune cells such as T cells and dendritic cells, but with higher density of suppressive myeloid cells and associated cytokines. Therefore, there is an interest to understand ways to improve IO responses in these patients. To determine whether we could recapitulate this biology in a preclinical model, we implanted three STK11mut and one wild type PDX on humanized mice generated from six cord blood donors, and compared the immune infiltration in these tumors.

Our results demonstrate efficient engraftment of human immune cells in the peripheral blood (53.1%), spleen (64.2%), and bone marrow (59.3%) of humanized mice (n=29, animals). Along with T and B cells, myeloid immune populations such as monocytes, macrophages and dendritic cells, which are absent in the previous generation of humanized mice, were present in the peripheral blood (monocytes 4.7%, dendritic cells 7.2% ) and bone marrow (macrophage 27.8%, neutrophils 21.6% and 10.2% dendritic cells ) of humanized mice. Tumor human immune subpopulation cells were significantly different (One-way Anova analysis) between the STK11mut (n=3) vs. wild type (n=1) humanized PDXs models (n=7 animals/PDX model). Three STK11mut tumors had low percentage of human CD45+ leukocytes infiltration (STK11mut; 0.9, 1.1 and 2.3% vs. wt; 6.6%) We also found a significantly reduced percentage of CD8+ cytotoxic T cells (STK11mut; 5.6, 3.2, 3.1% vs. wt; 9.6%) and dendritic cells subsets (STK11mut; 3.6, 2.2, 3.1% vs. wt; 5.6%) in the STK11mut PDXs implanted on humanized mice.

We have shown efficient engraftment of a multilineage human immune system in immunodeficient mice and a selective infiltration of human immune cells subsets in PDXs representing a key genetic segment of NSCLC. Our novel humanized PDX model can recapitulate human tumor immune reconstitution, providing a valuable opportunity to evaluate the benefit of immunomodulatory therapies and personalize immune intervention strategies.

Citation Format: Maneesh Singh, Laura Bradshaw, Laura B. Prickett, Griffin Matthew, Maryann San Martin, Noel Monks, Lisa Drew, Simon T. Barry, Corinne Reimer, Theresa Proia. The genetic makeup of patient-derived xenografts shapes the immune landscape of humanized mice tumors [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 1813.

Abstract 1664: Inhibition of arginase in combination with radiation therapy shows increased immune-activation and anti-tumor activity in syngeneic tumor models

The tumor microenvironment (TME) has multiple mechanisms of immune-suppression including recruitment of arginase (ARG) expressing myeloid cells. ARG is an enzyme that catalyzes hydrolysis of L-arginine into urea and L-ornithine. Given L-arginine is essential for optimal function of both T cells and natural killer (NK) cells, inhibition of ARG has been recognized as a potential therapeutic approach to reverse immune-suppression and optimize anti-tumor immunity. We recently presented development of a novel ARG inhibitor, AZD0011, and demonstrated immune activation and anti-tumor activity as single agent and in combination with a-PD-L1 in various tumor models. We now expand these findings demonstrating combination benefit with radiation therapy. Radiation therapy (5 gray on day 6 and 9 after tumor cell implant) demonstrated an increase of both the number of arginase expressing myeloid cells, and NK cells in the TME of Lewis Lung (LL) tumors. Immuno-histochemistry also demonstrated a redistribution of the location of ARG positive myeloid cells with a marked increase at the edge of the tumor. LL tumor bearing mice receiving either AZD0011 (30 mg/kg twice daily), or radiation therapy as monotherapy did not show a significant anti-tumor response reaching 0.3% and 28% tumor growth inhibition (TGI) respectively (p>0.05 versus vehicle). In contrast, combination treatment showed a marked increased efficacy averaging 60% TGI (p<0.05 versus either monotherapy). Combination treatment also further increased several markers of immune activation including a doubling of the number of IL2+ or IFNg+ CD4+ and CD8+ T-cells in tumor draining lymph nodes. In summary, our pre-clinical data demonstrates that radiation therapy increases the number and location of intra-tumoral ARG expression myeloid cells and increased anti-tumor activity when combining the ARG inhibitor AZD0011 with radiation therapy.

Citation Format: Alwin Schuller, Aatman Doshi, Susan Cantin, Matt Griffin, Maryann San Martin, Theresa Proia, Corinne Reimer, Scott Mlynarski, Ray Finlay, Wenlin Shao. Inhibition of arginase in combination with radiation therapy shows increased immune-activation and anti-tumor activity in syngeneic tumor models [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 1664.

Response to radiotherapy in pancreatic ductal adenocarcinoma is enhanced by inhibition of myeloid-derived suppressor cells using STAT3 anti-sense oligonucleotide

Pancreatic ductal adenocarcinoma (PDAC) has a heterogeneous tumor microenvironment (TME) comprised of myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages, neutrophils, regulatory T cells, and myofibroblasts. The precise mechanisms that regulate the composition of the TME and how they contribute to radiotherapy (RT) response remain poorly understood. In this study, we analyze changes in immune cell populations and circulating chemokines in patient samples and animal models of pancreatic cancer to characterize the immune response to radiotherapy. Further, we identify STAT3 as a key mediator of immunosuppression post-RT. We found granulocytic MDSCs (G-MDSCs) and neutrophils to be increased in response to RT in murine and human PDAC samples. We also found that RT-induced STAT3 phosphorylation correlated with increased MDSC infiltration and proliferation. Targeting STAT3 using an anti-sense oligonucleotide in combination with RT circumvented RT-induced MDSC infiltration, enhanced the proportion of effector T cells, and improved response to RT. In addition, STAT3 inhibition contributed to the remodeling of the PDAC extracellular matrix when combined with RT, resulting in decreased collagen deposition and fibrotic tissue formation. Collectively, our data provide evidence that targeting STAT3 in combination with RT can mitigate the pro-tumorigenic effects of RT and improve tumor response.

Discovery of AZD4573, a Potent and Selective Inhibitor of CDK9 That Enables Short Duration of Target Engagement for the Treatment of Hematological Malignancies

A CDK9 inhibitor having short target engagement would enable a reduction of Mcl-1 activity, resulting in apoptosis in cancer cells dependent on Mcl-1 for survival. We report the optimization of a series of amidopyridines (from compound 2), focusing on properties suitable for achieving short target engagement after intravenous administration. By increasing potency and human metabolic clearance, we identified compound 24, a potent and selective CDK9 inhibitor with suitable predicted human pharmacokinetic properties to deliver transient inhibition of CDK9. Furthermore, the solubility of 24 was considered adequate to allow i.v. formulation at the anticipated effective dose. Short-term treatment with compound 24 led to a rapid dose- and time-dependent decrease of pSer2-RNAP2 and Mcl-1, resulting in cell apoptosis in multiple hematological cancer cell lines. Intermittent dosing of compound 24 demonstrated efficacy in xenograft models derived from multiple hematological tumors. Compound 24 is currently in clinical trials for the treatment of hematological malignancies.

Frontiers in cancer immunotherapy-a symposium report

Cancer immunotherapy has dramatically changed the approach to cancer treatment. The aim of targeting the immune system to recognize and destroy cancer cells has afforded many patients the prospect of achieving deep, long-term remission and potential cures. However, many challenges remain for achieving the goal of effective immunotherapy for all cancer patients. Checkpoint inhibitors have been able to achieve long-term responses in a minority of patients, yet improving response rates with combination therapies increases the possibility of toxicity. Chimeric antigen receptor T cells have demonstrated high response rates in hematological cancers, although most patients experience relapse. In addition, some cancers are notoriously immunologically "cold" and typically are not effective targets for immunotherapy. Overcoming these obstacles will require new strategies to improve upon the efficacy of current agents, identify biomarkers to select appropriate therapies, and discover new modalities to expand the accessibility of immunotherapy to additional tumor types and patient populations.

Abstract 4523: Inhibition of arginase in combination with anti-PDL1 leads to increased infiltration and activation of CD8+ T cells, NK cells, and CD103+ dendritic cells in mouse syngeneic tumor models

The tumor microenvironment (TME) has multiple mechanisms of immune-suppression, one being recruitment of arginase (ARG) expressing myeloid cells. ARG is an enzyme that catalyzes hydrolysis of L-arginine into urea and L-ornithine. L-arginine is a semi-essential amino acid required for optimal function of T cells and natural killer (NK) cells. Arginine depletion in the TME inhibits T cell and NK cell function. Therefore, inhibition of ARG can reverse immune-suppression and optimize anti-tumor immunity. To determine the dependence to arginine, we cultured human T- and NK cells in arginine concentrations ranging from 0 to 150 µM. Both human CD8+ T cells and NK cells showed decreased proliferation with decreased L-arginine concentration, and a complete proliferation arrest in the absence of L-arginine. L-arginine threshold for optimal proliferation was determined to be ~30 µM for CD8+ T cells and ~ 9 µM for NK cells. Furthermore, both CD8+ T cells and NK cells showed decreases in cytotoxic molecules (e.g. granzyme A, granzyme B, perforin) when cultured under reduced arginine conditions. In addition, NK cells showed a decreased ability to kill target cells in low arginine conditions. We next explored whether arginase inhibition could reverse the immune-suppressive environment in vivo. Administration of arginase inhibitor to tumor bearing mice resulted in a dose dependent increase in both plasma (up to 4 fold) and tumor arginine (up to 12 fold) in all models tested including MC38-ova, CT26, and Lewis Lung. In addition, ARG inhibitor showed signs of in vivo immune cell activation including ~doubling of the number of CD8+ T cells, NK cells, and CD103+ dendritic cells in the tumor microenvironment. Combining with anti PD-L1 further increased the number of CD8+ T cells to ~4-fold of control levels. Arginase inhibitor also increased the activation state of CD8 T cell as determined by percent of granzyme, IFNg, and Ki67 positivity. Moreover, ARG inhibitor resulted in an increase of IFNg and TNFa producing CD8+ T cells in tumor draining lymph nodes. Treatment of tumor bearing mice with ARG inhibitor as monotherapy resulted in modest, but consistent, tumor growth inhibition (TGI) of ~30% in multiple syngeneic models (LL, MC38-ova, CT26). Combining ARG inhibitor with anti-PDL1 significantly improved efficacy reaching ~87% TGI in the MCA38-ova model, with 7/10 mice showing tumor regression. In summary, our pre-clinical data demonstrates that an ARG inhibitor in combination with a checkpoint inhibitor can increase plasma and tumor arginine levels and reverse tumor immune-suppression leading to strong immune activation and anti-tumor responses, suggesting arginase inhibitors could provide an opportunity to increase activity of checkpoint inhibitors clinically.

Citation Format: Alwin Schuller, Aatman Doshi, Susan Cantin, Michael Secinaro, Yanjun Wang, Laura Prickett, Sharon Tentarelli, Eric Gangl, Horma Ghadially, Kristina Ilieva, Theresa Proia, Scott Mlynarski, Ray Finlay, Wenlin Shao. Inhibition of arginase in combination with anti-PDL1 leads to increased infiltration and activation of CD8+ T cells, NK cells, and CD103+ dendritic cells in mouse syngeneic tumor models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4523.

Abstract 967: Anti-tumor and immune effects of olaparib +/- anti-PD-L1 in preclinical BRCA1mut tumor models

PARP inhibitor treatments are synthetically lethal with BRCA1/2 mutations and, in this setting, accumulation of DNA damage leads ultimately to cell death. Increases in DNA damage are also associated with increased levels of cytosolic DNA and consequently signalling through the cGAS-STING pathway, which can lead to increased inflammatory gene expression and Type I interferon response.

We sought to evaluate the benefit of combining the PARP inhibitor olaparib with immune checkpoint blockade (ICB) in a mouse syngeneic ovarian model, BR5, which lacks BRCA1. We show that olaparib combination with anti-PD-L1 prolonged duration of anti-tumor response vs. either monotherapy. The combination increased durable complete responses (CRs) with 6/10 animals tumor free at 77 days, compared with 1/9 and 2/9 tumor-free animals for olaparib and anti-PD-L1 monotherapies, respectively. Similar results were observed for combination of olaparib with anti-CTLA-4. Furthermore, mice treated with olaparib + ICB demonstrated immunological memory, with 100% of mice with CRs successfully rejecting tumor growth upon rechallenge with BR5. Olaparib treatment of human T cells in vitro and mouse T cells in vitro and in vivo did not show inhibition of T cell activation or proliferation. Moreover, olaparib treatment led to changes in tumor immune infiltrate in the BR5 tumors, including approximately 2-fold increased CD8 T cells and 1.5-fold increased NK cells relative to vehicle.

Differential gene expression analysis of olaparib or anti-PD-L1treated BR5 tumors revealed broad upregulation of immune pathways. Interestingly, type I IFN and STING pathways showed a more pronounced upregulation with Olaparib than with anti-PD-L1 treatment. Moreover, a dose-dependent upregulation of immune pathways, including JAK-STAT, STING and type I IFN was observed in a tumor cell-centric analysis from a BRCA1mut breast PDX model treated with olaparib. In contrast, no significant upregulation of STING or type I IFN pathways is observed in response to olaparib in a BRCAwt breast PDX model.

In vitro mechanistic studies demonstrated that co-culture of olaparib-treated human BRCA1mut MDA-MB-436 tumor cells with human dendritic cells (DC) resulted in an approximately 2-fold upregulation of CD86 expression on DCs. Comparison of isogenic DLD-1 tumor cells showed CD86 upregulation on DCs only following co-culture with olaparib-treated BRCA2-/- DLD-1 cells, but not wt DLD-1 cells. Similarly, increased PD-L1 expression was only observed in BRCA2-/- DLD-1 cells treated with olaparib and following co-culture with DC. These observations suggest a basis for increased immune priming following olaparib treatment of BRCAmut tumors, which can be consolidated with ICB, such as anti-PD-L1, treatment.

Citation Format: Anna Staniszewska, Joshua Armenia, Matthew King, Chrysiis Michaloglou, Maneesh Singh, Maryann San Martin, Zena Wilson, Theresa Proia, Oona Delpuech, Mark O'Connor, Elisabetta Leo, Viia Valge-Archer. Anti-tumor and immune effects of olaparib +/- anti-PD-L1 in preclinical BRCA1mut tumor models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 967.

Targeting melanoma's MCL1 bias unleashes the apoptotic potential of BRAF and ERK1/2 pathway inhibitors

BRAF and MEK1/2 inhibitors are effective in melanoma but resistance inevitably develops. Despite increasing the abundance of pro-apoptotic BIM and BMF, ERK1/2 pathway inhibition is predominantly cytostatic, reflecting residual pro-survival BCL2 family activity. Here, we show that uniquely low BCL-XL expression in melanoma biases the pro-survival pool towards MCL1. Consequently, BRAF or MEK1/2 inhibitors are synthetic lethal with the MCL1 inhibitor AZD5991, driving profound tumour cell death that requires BAK/BAX, BIM and BMF, and inhibiting tumour growth in vivo. Combination of ERK1/2 pathway inhibitors with BCL2/BCL-w/BCL-XL inhibitors is stronger in CRC, correlating with a low MCL1:BCL-XL ratio; indeed the MCL1:BCL-XL ratio is predictive of ERK1/2 pathway inhibitor synergy with MCL1 or BCL2/BCL-w/BCL-XL inhibitors. Finally, AZD5991 delays acquired BRAFi/MEKi resistance and enhances the efficacy of an ERK1/2 inhibitor in a model of acquired BRAFi + MEKi resistance. Thus combining ERK1/2 pathway inhibitors with MCL1 antagonists in melanoma could improve therapeutic index and patient outcomes.

Abstract 3215: STAT3 antisense oligonucleotide (ASO) reverses immunosuppression and enhances cytotoxic cell function to enhance PDL1 blockade

Danvatirsen (AZD9150) is a therapeutic antisense oligonucleotide that selectively targets human STAT3, a ubiquitously expressed transcription factor and master regulator of immune suppression in the tumor microenvironment (TME). Danvatirsen has shown clinical benefit alone and combined with durvalumab (anti-PDL1) in Phase 1/2 clinical studies. To further our mechanistic understanding, we conducted (1) immunophenotyping, (2) ex vivo stimulation/cytokine assays, and (3) single-cell RNA sequencing (scRNASeq) analysis using murine surrogate drugs at three timepoints (following one (1W), two (2W), or three (3W) weeks of mouse surrogate STAT3 ASO, vehicle, or control ASO treatment alone, or anti-PDL1 alone or combined with STAT3 ASO (combo) in W2 and W3) in Balb/c mice bearing syngeneic CT26 tumors. Consistent with clinical data and previous findings (Ref 1, 2), tumor growth inhibition was observed in both monotherapy (STAT3 mean TGI 56%; anti-PDL1 mean TGI 54%) and combo treated (mean TGI >100%) groups. Consistent with the robust anti-tumor activity, significant (p<0.05) immunophenotypic changes were observed following 3W of STAT3 ASO or combo treatment. Fewer changes were observed with anti-PDL1 monotherapy. As reported previously, M-MDSC decreased (60%) and neutrophil/G-MDSC increased (8-fold) in both STAT3 ASO and combo treated at 3W. We also discovered significant changes in NK, NK T, and CD11b NK cells, which increased >5-fold after 3W combo treatment. Both STAT3 ASO and combo enhanced expression of GZB in CD11b NK cells, supporting their role in NK cytotoxicity. Combo treatment also increased cross-presenting CD8+CD103+ DCs (4-fold) and inflammatory DCs (3-fold). Further, CD8+ cells had reduced levels of T cell exhaustion marker TIM3 and increased CD69 and GZB in the combo, suggesting enhanced CD8 T cell effector function.

Although few immunophenotypic changes were observed following 2W of treatment, preliminary data on cytokines (IFNγ, TNFα, IL2) at 2W suggest cytokine changes precipitate the immunophenotypic changes seen at 3 weeks.

These findings expand our understanding of the mechanism by which STAT3 ASO treatment as monotherapy and in combination with anti-PDL1 modifies the TME to produce significant anti-tumor effects. The results are in accord with previously reported increases in IFNg and Type I IFN signatures and decreases in a suppressive gene signature in paired pre- and on-treatment biopsies from danvatirsen-treated patients (Ref 2) and suggest STAT3 ASO treatment modulates both innate and adaptive immune responses. Studies are ongoing to perform further subtyping of drug-elicited cell population changes using single cell RNA Sequencing (results to be presented).

References

1. Woessner et al (2017) Cancer Research 77(13 Supplement):3684-3684

2. Cohen et al (2018) Annals Oncology 29, Supplement 8: viii372-viii399.

Citation Format: Srimathi Srinivasan, Yang Xu, Theresa Proia, Nanhua Deng, J. Carl Barrett, Alexandra-Chloe Villani, Patricia E. McCoon. STAT3 antisense oligonucleotide (ASO) reverses immunosuppression and enhances cytotoxic cell function to enhance PDL1 blockade [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 3215.

Abstract 2500: Transient CDK9 inhibition with AZD4573 modulates Bfl-1 in preclinical lymphoma models

AZD4573 is a selective cyclin-dependent kinase 9 (CDK9) inhibitor under clinical development in patients with hematological malignancies. Transient CDK9 inhibition serves as an orthogonal approach for targeting Mcl-1, a labile anti-apoptotic protein essential for the survival of cancer cells. Across-broad hematological cancer models, anti-tumor responses with AZD4573 strongly correlate with selective Mcl-1 inhibitors, such as AZD5991 (R2=0.8). Despite compelling evidence for an Mcl-1 dependent mechanism of action, we also observed a subset of lymphoma models more sensitive to CDK9 inhibition compared to Mcl-1 inhibition, suggesting acute CDK9 inhibition could be targeting other labile proteins beyond Mcl-1 to induce apoptosis. We identified Bfl-1 as one such potential target and demonstrate lymphoma models expressing Bfl-1 are highly sensitive to CDK9 inhibition.

Bfl-1 belongs to the Bcl-2 family of anti-apoptotic proteins and was detected in over 20% of lymphoma cell lines evaluated (n=33). Cycloheximide experiments indicate Bfl-1 has a short protein half-life (<1h), similar to Mcl-1. Therefore, treatment with 100nM of AZD4573 in diffuse large B-cell lymphoma cell lines OCILY10 and TMD8 caused rapid down-regulation of both Mcl-1 and Bfl-1 by 4h, resulting in caspase cleavage by 6h. Evaluation of caspase activation following 6h treatment revealed an average maximum effect of 87% for AZD4573 compared to 45% with Mcl-1 inhibition, suggesting these cell lines are not exclusively Mcl-1-dependent. The hypothesis that survival of lymphoma cells may be co-dependent on both Mcl-1 and Bfl-1 was evaluated by siRNA knockdown. Following a dose-dependent suppression of Bfl-1 protein (>80%) in OCILY10 and TMD8 cells, viability loss was minimal (<30% reduction relative to control). However, when Bfl-1 knockdown cells were treated for 6h with an Mcl-1 inhibitor, the maximum caspase activation increased to over 90% in both cell lines, phenocopying a similar magnitude achieved with AZD4573-mediated CDK9 inhibition. In these models, depletion of both Bfl-1 and Mcl-1 was necessary to induce maximum apoptosis, with studies ongoing to evaluate single-gene Bfl-1 dependency in additional lymphoma models.

Consistent with the in vitro phenotype, intermittent dosing of the ABC-DLBCL xenografts OCILY10 and TMD8 with AZD4573 caused robust tumor regressions (198 and 184% TGI, respectively). AZD4573-mediated anti-tumor activity was associated with pharmacodynamic reductions of pSer2-RNAPII, Mcl-1 and Bfl-1, followed by caspase activation. Collectively, these findings support the ability to target Bfl-1 via CDK9 inhibition. Given the current absence of clinical small molecule Bfl-1 inhibitors and expanded monotherapy activity compared to selective Mcl-1 inhibition in a subset of preclinical models, CDK9 inhibitors have tremendous therapeutic potential in the treatment of patients with Bfl-1-expressing lymphoma.

Citation Format: Scott Boiko, Theresa Proia, Maryann San Martin, Lisa Drew, Wenlin Shao, Justin Cidado. Transient CDK9 inhibition with AZD4573 modulates Bfl-1 in preclinical lymphoma models [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 2500.

Abstract 297: AZD4573: Mechanistic PKPD model linking CDK9 inhibition to Mcl1 depletion and induction of apoptosis in preclinical AML model

Cyclin-dependent kinase 9 (CDK9) regulates elongation of transcription through phosphorylation of RNA polymerase II (pSer2-RNAPII), and its short-term inhibition results in the selective downregulation of genes with short-lived transcripts and labile proteins - including the anti-apoptotic protein Mcl1. AZD4573 is a selective inhibitor of CDK9 with short pharmacokinetic (PK) half-life. Intermittent dosing of AZD4573 in mouse MV411 (AML cell line) xenograft models results in progressive reduction in tumor volume with the mechanism of action believed to be via induction of apoptosis following depletion of Mcl1. The aim of this work was to derive a quantitative understanding of the relationships between extent and duration of CDK9 inhibition, depletion of Mcl1 and rate of induction of apoptosis in MV411 tumor cells.

A mechanistic model has been established that quantitatively and dynamically connects AZD4573 plasma and tumor PK to the rate and extent of modulation of pSer2-RNAPII and Mcl1 in the tumor and rate of induction of cell death (as measured by reduction in tumor volume). Tumor pSer2-RNAPII and Mcl1 pharmacodynamics were modeled using a series of linked indirect response models. Production rate of pSer2-RNAPII was modeled as being directly inhibited by AZD4573 concentration in the tumor. Production rate of Mcl1 was linked to pSer2-RNAPII via a series of transit compartments to capture the transcription/translation driven delay in onset of response. Induction of intrinsic apoptosis in the MV411 tumor cells was modelled as being inhibited by Mcl1.

Tumor pSer2-RNAPII exhibited a rapid, dose-dependent decrease following IP dosing of AZD4573 in mice. The free concentration of AZD4573 that resulted in half-maximal inhibition of pSer2-RNAPII production rate was estimated to be in the range 11-21 nM. Following a brief delay, tumor Mcl1 also exhibited a relatively rapid decrease that was proportional to the pSer2-RNAPII response. Mcl1 protein half-life was estimated to be 0.3 hr. Rate of induction of apoptosis could be decribed as a saturable first-order process (Kmax ~ 0.2 hr-1) and appeared to exhibit a steep response to the depletion of Mcl1, with reduction of Mcl1 to 25% (of the baseline value) being estimated to result in half-maximal rate of induction of apoptosis in the MV411 cells.

The described MV411 PKPD/efficacy model has been assumed to be representative of AML in human patients and was used to derive preliminary predictions of clinical efficacy at a range of possible IV dosing regimens.

Citation Format: Douglas Ferguson, Theresa Proia, Justin Cidado, Scott Boiko, Maryann San Martin, Steven Criscione, Wenlin Shao, Lisa Drew. AZD4573: Mechanistic PKPD model linking CDK9 inhibition to Mcl1 depletion and induction of apoptosis in preclinical AML model [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 297.

Abstract B112: Synergistic anti-lymphoma activity of ibrutinib and dual mTORC1/2 inhibitors in diffuse large B cell lymphoma is maintained in vivo on an intermittent schedule

Diffuse large B cell lymphoma (DLBCL) is the most common type of aggressive non Hodgkins lymphoma. The Activated B-Cell (ABC) subtype of DLBCL is driven by chronic active BCR signaling and remains the most difficult to treat. Resistant ABC-DLBCL occurs in as many as 40% of patients following treatment with R-CHOP. To identify additional treatment options, we performed a combination screen in DLBCL cell lines using a panel of drugs known to target survival and proliferation pathways in DLBCL, and uncovered a drug combination with highly synergistic activity that included the BTK inhibitor, ibrutinib, with the dual mTORC1/2 inhibitor, AZD2014. Ibrutinib is known to have activity in ABC-DLBCL; in a recent Phase I/II clinical trial of relapsed/refractory ABC-DLBCL, ibrutinib treatment resulted in 55% response rate in patients with B cell receptor mutations (Wilson et al, Nature Medicine 2015). In ABC-DLBCL cell lines, combination of AZD2014 with ibrutinib resulted in cell death, induction of cleaved caspase 3, and potent inhibition of c-myc and p-4EBP1. In vivo, combination of ibrutinib with AZD2014 was well tolerated and resulted in potent anti-tumor activity in OCI-Ly10 that was greater than either agent alone, with greater than 100% tumor growth inhibition as well as synergistic inhibition of p-4EBP1 (Ezell et al, Oncotarget 2014). This work was evaluated using a continuous daily dosing schedule of AZD2014 and ibrutinib. More recently, both continuous and intermittent dosing schedules (2 days on, 5 off) have been explored in patients with other solid tumours and was found to be better tolerated. We evaluated an intermittent schedule of AZD2014 in our preclinical ABC-DLBCL model, OCI-Ly10, in combination with ibrutinib and demonstrated that the synergistic combination activity was maintained, with 60% regression compared to only 36% regression with the daily dosing schedule combination. In addition to p-4EBP1 inhibition, we also observed synergistic inhibition of p-pRAS40, p-AKT, p-NDRG1, c-myc, survivin and HMGSC1. Ongoing preclinical work is focused on understanding whether more significant suppression of relevant pathways was achieved with intermittent compared to continuous dosing. Collectively, our data support a rationale for combining BTK and dual mTORC1/2 inhibitors for an effective and alternative treatment option in ABC-DLBCL.

Citation Format: Theresa Proia, Nanhua Deng, Urzsula Polanska, Deborah Lawson, Vasu Sah, Maryann San Martin, Corinne Reimer, Sabina Cosulich. Synergistic anti-lymphoma activity of ibrutinib and dual mTORC1/2 inhibitors in diffuse large B cell lymphoma is maintained in vivo on an intermittent schedule. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B112.

23814, an Inhibitory Antibody of Ligand-Mediated Notch1 Activation, Modulates Angiogenesis and Inhibits Tumor Growth without Gastrointestinal Toxicity

Dysregulation of Notch signaling has been implicated in the development of many different types of cancer. Notch inhibitors are being tested in the clinic, but in most cases gastrointestinal and other toxicities have limited the dosage and, therefore, the effectiveness of these therapies. Herein, we describe the generation of a monoclonal antibody against the ligand-binding domain of the Notch1 receptor that specifically blocks ligand-induced activation. This antibody, 23814, recognizes both human and murine Notch1 with similar affinity, enabling examination of the effects on both tumor and host tissue in preclinical models. 23814 blocked Notch1 function in vivo, inhibited functional angiogenesis, and inhibited tumor growth without causing gastrointestinal toxicity. The lack of toxicity allowed for combination of 23814 and the VEGFR inhibitor tivozanib, resulting in significant growth inhibition of several VEGFR inhibitor-resistant tumor models. Analysis of the gene expression profiles of an extensive collection of murine breast tumors enabled the successful prediction of which tumors were most likely to respond to the combination of 23814 and tivozanib. Therefore, the use of a specific Notch1 antibody that does not induce significant toxicity may allow combination treatment with angiogenesis inhibitors or other targeted agents to achieve enhanced therapeutic benefit.

Abstract 2990: Notch1 monoclonal antibody inhibits tumor growth and modulates angiogenesis

AVEO Oncology has developed a series of inducible mouse models of cancer, which through the preservation of critical tumor/stromal interactions, facilitate identification of cell-surface and secreted proteins that represent viable targets for therapeutic antibodies and other biologics. Functional genetic screens performed in vivo in these models identified the Notch pathway as a critical regulator of tumor maintenance. This finding was consistent with emerging evidence that activation of Notch signaling via receptor point mutation, receptor amplification, and elevated receptor and ligand expression, plays a key role in various human cancers. Moreover, the Notch pathway controls diverse aspects of tumorigenesis and tumor maintenance, regulating tumor autonomous processes and interactions with the microenvironment, including angiogenesis. To further understand the role of the Notch pathway in tumor maintenance, and to assess the therapeutic potential of targeting the Notch pathway in cancer, we have generated monoclonal antibodies that inhibit the Notch1 receptor. Characterization of monoclonal antibodies targeting Notch1 through cell-based and biochemical studies demonstrated that the Notch1 monoclonal antibody bound with high affinity and high specificity to the Notch1 receptor, prevented ligand-mediated activation of the target receptor, and specifically repressed Notch-dependent signaling with high potency. Significantly, specific inhibition by the Notch1 monoclonal antibody did not result in the dose-limiting gut toxicity observed with Notch1 mAb resulted in tumor inhibition that was accompanied by increased vascular density, inhibition of Notch target gene expression, and increased expression of angiogenesis-related genes, consistent with expected changes resulting from Notch1/Dll4 pathway inhibition. In addition, several tumor models treated in combination with Notch1 mAb and an investigational VEGF pathway inhibitor, tivozanib, demonstrated increased tumor inhibition compared to either agent alone. Interestingly, combination treatment resulted in decreased vascular density and downregulated expression of angiogenesis genes, similar to treatment with VEGF inhibitor alone. Collectively, our work suggests that combination therapy of Notch1 antibodies with VEGF inhibitors should be evaluated as a potential viable therapeutic option for VEGF-resistant tumors.

Citation Format: Heidi Okamura, Theresa Proia, Alisa Bell, Qing Liu, Zakir Siddiquee, Jie Lin, Jeno Gyuris. Notch1 monoclonal antibody inhibits tumor growth and modulates angiogenesis. [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 2990. doi:10.1158/1538-7445.AM2014-2990

Cell-state transitions regulated by SLUG are critical for tissue regeneration and tumor initiation

Perturbations in stem cell activity and differentiation can lead to developmental defects and cancer. We use an approach involving a quantitative model of cell-state transitions in vitro to gain insights into how SLUG/SNAI2, a key developmental transcription factor, modulates mammary epithelial stem cell activity and differentiation in vivo. In the absence of SLUG, stem cells fail to transition into basal progenitor cells, while existing basal progenitor cells undergo luminal differentiation; together, these changes result in abnormal mammary architecture and defects in tissue function. Furthermore, we show that in the absence of SLUG, mammary stem cell activity necessary for tissue regeneration and cancer initiation is lost. Mechanistically, SLUG regulates differentiation and cellular plasticity by recruiting the chromatin modifier lysine-specific demethylase 1 (LSD1) to promoters of lineage-specific genes to repress transcription. Together, these results demonstrate that SLUG plays a dual role in repressing luminal epithelial differentiation while unlocking stem cell transitions necessary for tumorigenesis.

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SLUG promotes stem cell-state transitions necessary for tumorigenesis

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Loss of SLUG in mice leads to luminal differentiation of basal/myoepithelial cells

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In vitro quantitative modeling can accurately predict epithelial plasticity in vivo

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A SLUG/LSD1 complex epigenetically regulates mammary epithelial cell differentiation