Abstract Background: Dying cells play an important role in CD8+ T cell-mediated immunity. While apoptosis is mainly immunologically silent, necroptosis is immunogenic and can more efficiently initiate an adaptive immune response that could be augmented by immune checkpoint inhibition (ICI). Inhibitor of Apoptosis (IAP) proteins are key gatekeepers of how a cell dies, and frequently overexpressed in cancer. ASTX660 (tolinapant) is a triple blocker of cIAP1/2 and XIAP, sensitizing cancer cells to death ligands through ripoptosome formation, activating ‘danger’ co-stimulatory signals and dendritic cell (DC) maturation required to prime a potent antitumor response. Methods: We assessed the safety, pharmacodynamic (PD), and clinical activity of 7 days of oral ASTX660 given prior to pembrolizumab 200 mg (Q3W), in patients (pts) refractory to standard therapy. TITE-CRM was used to explore ASTX660 doses 90-180 mg. Serial paired blood and tumor samples were analyzed to interrogate the effect of ASTX660 on cell death, tumor microenvironment and host immune system. Results: 22 pts have been enrolled; median age 55 years (range 38-81); male:female 5:17; all ECOG PS ≤1; median 4.5 prior therapies. Tumor types included breast, head and neck (HN), hepatocellular, cervical, pancreatic and cholangiocarcinoma. Combination ASTX660-pembrolizumab is currently recruiting at highest dose 180 mg without any dose limiting toxicities (DLT) seen within the 6-week DLT observation period. Most common adverse events (AE) were G1-2 rash, nausea, and asymptomatic increases in amylase, lipase and transaminases; all reversible and easily manageable. Four iRECIST confirmed partial responses were seen in 10 efficacy evaluable pts treated at biologically active dose levels 120 and 150 mg (Overall response rate 40%), including 2 pts with ER+ HER2- breast cancer, 1 cervical adenocarcinoma pt (exceptional response following initial pseudoprogression) and a HN cancer pt refractory to ICI monotherapy. 3/4 responders are ongoing. Efficacy data from pts treated at highest dose level 180 mg is pending. FACS of paired blood samples from responders shows a significant rise in %CD57+/CD3+ cytotoxic effector T cells [mean 11.90% (pre-) vs 14.25% (post-ASTX660); p=.0176]. These changes were not seen in the non-responders group. Full PD from paired blood and tumour sampling will be shared at the meeting. Conclusion: ASTX660-pembrolizumab is is well-tolerated with durable antitumor responses in pts with immunologically cold tumors, providing the first clinical proof-of-concept of immunogenic cell death induction leading to effective adaptive immune response when combined with ICI. Recommended Phase 2 dose optimization and expansion cohorts in immunologically cold cancers are ongoing. Citation Format: Crescens Tiu, Wing Yau, Victoria Sanchez-Perez, Giovanni Codacci-Pisanelli, Ching Leung, Eden S. Andrews, Bristi Basu, Anna Zachariou, Toby Prout, Mona Parmar, Alison Turner, Xiaoran Lai, Zhulin Yin, Karen E. Swales, Syed Haider, Thomas Lund, Diego C. Dos Reis, Tatiany L. Silveira, Alan S. Dunlop, Ann-Marie Baker, Bora Gurel, Ana Ferreira, Claudia Bertan, Nina Tunariu, Edward W. Johnston, Alistair Ring, Tencho Tenev, Tomoko Smyth, Simone Jueliger, Udai Banerji, Johann S. de Bono, Alec Paschalis, Adam Sharp, Anna Minchom, Christina Yap, Pascal Meier, Juanita S. Lopez. Proof-of-concept and preliminary efficacy of triple IAP blockade to maximize immunogenic cell death and induce efficient adaptive immune response: First report on the ASTEROID phase 1 trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT035.

We describe the first-in-human trial of avutometinib (RAF/MEK clamp) and defactinib (FAK inhibitor) in patients with solid tumors. The trial met its primary endpoint and recommended a phase 2 dose/schedule is avutometinib 3.2 mg OD 2/7 days and defactinib 200 mg BID 7/7 days, both drugs administered orally for 3 weeks every 4 weeks. The pharmacokinetics and pharmacodynamics were consistent with previous reports of avutometinib and defactinib used as single agents. Key findings include an objective response rate (ORR) and median progression free survival (mPFS) of 42.3% (11/26; 95% confidence interval (CI): 23.4%-63.1%) and 20.1 months (95% CI: 11.2-43.9) respectively in patients with low grade serous ovarian cancer (LGSOC). This study demonstrates importance of novel combinations of targeted therapies targeting the MAPK and FAK involving intermittent dosing schedules to improve tolerability (NCT03875820/EudraCT number 2017-001035-39).

Background: KRAS mutations (mt) are found in ~30% of non-small cell lung cancers (NSCLC). Despite the approval and development of KRAS G12C and KRAS G12D inhibitors respectively, mechanisms of resistance to MAPK pathway inhibitors are emerging and combination strategies are needed for patients with KRAS mt NSCLC . Avutometinib (VS-6766) is a unique RAF/MEK clamp that inhibits MEK kinase activity and blocks RAF-mediated phosphorylation of MEK. We studied the preclinical and clinical activity of the combination of avutometinib with the mTOR inhibitor everolimus in KRAS mt NSCLC. Methods: A panel of KRAS mt NSCLC cell lines were treated for 1 hour with clinically relevant concentrations of avutometinib and everolimus and changes in phosphoproteins were measured using an antibody array. We then tested for synergy of avutometinib and everolimus in 3D proliferation assays and in the H441 NSCLC xenograft model. A clinical trial is ongoing (NCT02407509) testing the combination of 3.2 mg avutometinib with 5 mg of everolimus administered twice weekly 3 weeks on/1 week off in 28-day cycles (previously defined as the recommended phase 2 dose) in a cohort of patients with KRAS mt NSCLC. Results: Avutometinib inhibited the MAPK pathway (p-MEK, p-ERK, p-90RSK) with an increase in p-PRAS40, suggesting activation of the PI3K pathway as an adaptive resistance mechanism. Everolimus inhibited the PI3K pathway (p-p70S6K and p-RPS6). Among a panel of KRAS mt NSCLC cell lines, avutometinib + everolimus showed synergistic anti-proliferative activity across KRAS G12C, G12V and G12D variants (mean synergy score of ~18). In the H441 KRAS G12V NSCLC xenograft model, there was a significant reduction in tumor volume and increase in survival with the combination of avutometinib and everolimus (87% TGI; 66 days vs 36.5 days in control group) compared to control. In the clinical trial expansion, 16 patients with KRAS mt NSCLC have been treated so far with avutometinib and everolimus (5 G12V, 3 Q61H, 2 G12C, 2 G12A, 2 G12D, 1 G13A, 1 G13D; median prior lines = 2). The current objective response rate (ORR) among the 14 patients who have at least one post assessment scan is 3/14 (21%; 1 G12V, 1 G12A, 1 G13A) with 11/14 showing a reduction in tumor size as best response. The current progression free survival (PFS) is 5.3 months (95% CI 2.8-7.4 months) with 4 patients still on study. Updated data on the planned cohort size of 20 patients will be presented. Conclusion: The combination of avutometinib and everolimus overcomes the activation of the PI3K/AKT/mTOR pathway which is an adaptive resistance mechanism to MAPK pathway inhibition. We have shown that avutometinib and everolimus induce synergistic anti-tumor effects preclinically, and preliminary data suggest clinically meaningful ORR and PFS in patients with KRAS mt NSCLC including non-G12C variants. Citation Format: Simon Rodney, Adam R. Stewart, Victoria Sanchez Perez, Cienne Morton, Lisa A. Pickard, Taleen Shakouri, Toby Prout, Mona Parmar, Alison J. Turner, Silvia Coma, Jonathan Pachter, Laura Finneran, Emma Hall, James Spicer, Anna Minchom, Udai Banerji. Preclinical and clinical evaluation of the RAF/MEK clamp avutometinib (VS-6766) in combination with the mTOR inhibitor everolimus for the treatment of KRAS mutated non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3461.

Inflammation is a hallmark of cancer 1 . In patients with cancer, peripheral blood myeloid expansion, indicated by a high neutrophil-to-lymphocyte ratio, associates with shorter survival and treatment resistance across malignancies and therapeutic modalities 2 – 5 . Whether myeloid inflammation drives progression of prostate cancer in humans remain unclear. Here we show that inhibition of myeloid chemotaxis can reduce tumour-elicited myeloid inflammation and reverse therapy resistance in a subset of patients with metastatic castration-resistant prostate cancer (CRPC). We show that a higher blood neutrophil-to-lymphocyte ratio reflects tumour myeloid infiltration and tumour expression of senescence-associated mRNA species, including those that encode myeloid-chemoattracting CXCR2 ligands. To determine whether myeloid cells fuel resistance to androgen receptor signalling inhibitors, and whether inhibiting CXCR2 to block myeloid chemotaxis reverses this, we conducted an investigator-initiated, proof-of-concept clinical trial of a CXCR2 inhibitor (AZD5069) plus enzalutamide in patients with metastatic CRPC that is resistant to androgen receptor signalling inhibitors. This combination was well tolerated without dose-limiting toxicity and it decreased circulating neutrophil levels, reduced intratumour CD11b + HLA-DR lo CD15 + CD14 − myeloid cell infiltration and imparted durable clinical benefit with biochemical and radiological responses in a subset of patients with metastatic CRPC. This study provides clinical evidence that senescence-associated myeloid inflammation can fuel metastatic CRPC progression and resistance to androgen receptor blockade. Targeting myeloid chemotaxis merits broader evaluation in other cancers.

Circulating tumor DNA dynamics as a surrogate of efficacy

Abstract Background PTEN loss of function is frequent in GBM correlating with poor prognosis, impaired antitumor responses and reduced efficacy of Immune Checkpoint Inhibitors (ICI). Ipat is a potent, selective, small-molecule inhibitor of Akt. Ipat efficiently depletes FOXP3+ regulatory T cells from the tumor microenvironment (TME) resulting in increased infiltration of effector T cells in solid tumors (Lopez 2020, AACR). We hypothesize that Akt inhibition in PTEN loss glioblastomas may deplete the TME of suppressive immune cells, and render malignant brain tumors more responsive to ICIs. Methods Relapsed WHO grade IV GBM pts with stable neurological symptoms ≥5 days prior to enrollment, requiring <3mg Dexamethasone were recruited into a dose determination cohort (A2; n=12) and an expansion cohort (B3; n=11) of this early phase, open-label trial studying the combination of Ipat and A. Primary objectives were to determine the safety and tolerability of the combination (A2) and preliminary efficacy (B3). Results 23 recurrent GBM pts (median age 55 yrs (25-71 yrs; 74% male) were enrolled. Median ECOG PS 1. All pts had surgery followed by radical-chemoradiotherapy. Median prior lines of therapy 1 (range 1-4). 15 pts had PTEN loss by IHC (H<30) indicative of biallelic loss of function, 1 had deleterious PTEN mutations detected by next generation sequencing. No DLTs, no significant treatment-related (TR) serious adverse events (SAEs), or immune-related AEs were observed. Most common TR AEs were G1-2 diarrhea (61%), rash (26%) and mucositis (22%). Clinical benefit rate (CR, PR and SD> 6 cycles) in 19 efficacy evaluable pts was 32% (6/19 overall) and 28.6% (4/14) for pts with PTEN loss. Multiplex IHC of archival samples (n=19) showed PTEN loss tumors had significantly greater numbers of CD3+ infiltrating T-lymphocytes within the TME compared to PTEN wild type tumors (median 53.64/mm2 vs 1.94/mm2; p=0.0021). Within the PTEN loss cohort (n=13), pts with clinical benefit had significantly higher baseline number of CD8+ effector T cells as compared to non-responders (median 46.50/mm2 vs 8.21/mm2; p=0.0336). Two pts with PTEN loss proceeded to re-resection on trial. One exceptional responder, a 58yr male refractory to radical chemo-radiotherapy and Bevacizumab had a resection of enhancing disease after 5 cycles that showed >70% depletion of CD4+ T regulatory cells with an increase in CD8+ lymphocyte infiltration and no residual evidence of tumor (pathological CR). In contrast, a non-responding patient who proceeded to debulking surgery had no change in infiltration of CD8+ lymphocytes, but a marked increase (>27-fold) in CD4+ regulatory T cells. Conclusion The RP2D of 400mg Ipa OD + 1200mg A Q3W was well tolerated in GBM pts. Early efficacy signals were detected with PTEN loss being a promising predictive biomarker for response to combination. Citation Format: Crescens Tiu, Wing Hing Yau, Liam C. Welsh, Timothy L. Jones, Anna Zachariou, Toby Prout, Mona Parmar, Alison J. Turner, Robert W. Daly, Christina Yap, Mateus Crespo, Bora Gurel, Ruth M. Riisnaes, Shaun A. DeCordova, Karen E. Swales, Udai Banerji, Anna R. Minchom, Adam Sharp, Johann S. de Bono, Juanita S. Lopez. Preliminary evidence of antitumor activity of Ipatasertib (Ipat) and Atezolizumab (A) in glioblastoma (GBM) patients (pts) with PTEN loss in the Phase 1 Ice-CAP trial (NCT03673787) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT093.

Progression free survival by baseline ESR1

Escalation phase dose levels and final recruitment

Despite improved understanding of effector T-cell trafficking into the central nervous system, initial trials with anti-PD1/PD-L1 immune checkpoint inhibitors (ICIs) have failed to meet their primary endpoints. PTEN loss of function is frequent in GBM and has been correlated with not only poor overall prognosis, but also impaired antitumour responses, including reduced T cell infiltration into tumour and reduced efficacy of ICIs. Ipatasertib is a novel, potent, selective, small-molecule inhibitor of Akt. We have shown that Ipatasertib efficiently depletes FOXP3+ regulatory T cells from the tumour microenvironment (TME) resulting in increased infiltration of effector T cells in solid tumours (Lopez 2020, AACR). We hypothesize that the use of AKT inhibition in PTEN glioblastomas may deplete the TME of suppressive immune cells, and render malignant brain tumours more responsive to ICIs. We present updated data for the combination of Ipat+ATZ in patients with glioblastoma. Patients with relapsed WHO grade IV GBM with stable neurological symptoms ≥5 days prior to enrolment, requiring <3mg Dexamethasone were recruited into two cohorts of this early phase, open-label, single-centre trial studying the combination of Ipatasertib (Ipat) and Atezolizumab (ATZ): a dose finding cohort (A2; n=9) and an expansion cohort (B3; n=7, recruitment ongoing). The Ice-CAP A2 cohort assessed safety, pharmacodynamic, and preliminary clinical activity of Ipat (200mg or 400mg OD) + ATZ (1200mg Q3W) in pts with potentially resectable relapsed WHO Grade IV GBM. Pts had a 14-21-day run-in phase of Ipat then surgical tumour resection. Combination Ipat+ATZ commenced post surgery. Patients who declined surgery or who were deemed high risk for surgery proceeded directly to combination. Patients in the expansion cohort B3 commenced directly on Ipat+ATZ at the RP2D of 400mg Ipat with ATZ. 16 evaluable recurrent GBM pts were enrolled across two cohorts. Median age 56 yrs (25-71 yrs). Median ECOG PS 1. Median lines of prior therapy 1 (range 1-4). 10 pts had PTEN loss by IHC (H<30) and/or PTEN mutations on next generation sequencing. No DLTs, treatment-related (TR) serious adverse events (AEs), or immune-related AEs were observed. Most common TR AEs were G1 diarrhoea (44%), mucositis (17%), rash (28%). Clinical benefit rate (CR, PR and SD> 6 cycles) at clinical cutoff date (23/02/21) in patients with PTEN aberration was 30% (3/10). A 58-year-old man with PTEN loss had MRI at Cycle 5 showing worsening enhancement suggestive of disease progression. Resection of the lesion showed intense lymphocyte infiltration and pathological CR. He is currently on Cycle 22 with no evidence of disease. Two other patients with PTEN loss with radiological stable disease per RANO criteria remain well on study for >6 cycles. Combination Ipat+ATZ appears safe and tolerable in GBM pts, with 400mg Ipatasertib OD + 1200mg ATZ Q3W declared as RP2D. Early efficacy signals were detected with PTEN loss being a promising predictive biomarker for response to combination. An expansion cohort enriched with pts with PTEN loss is ongoing.

Efficacy of doublet palbociclib plus taselesib in advanced solid tumors

Baseline tissue biomarker analysis

Background: Low-grade serous ovarian cancer (LGSOC) constitutes up to 10% of all ovarian cancer and has clinical and molecular characteristics (resistance to chemotherapy, presence of RAS/RAF mutations, lack of TP53 mutations) distinct from high-grade serous ovarian cancer. Here, we characterized the effects of the dual RAF/MEK inhibitor VS-6766 and the FAK inhibitor defactinib on signal transduction and viability in LGSOC cell lines and patient-derived organoids. To correlate molecular characteristics with clinical response, we characterized genomic alterations in archival tumor samples from patients with LGSOC treated with the combination of VS-6766 and defactinib on a clinical trial (FRAME). Material and Methods: We exposed 5 LGSOC cell lines to clinical Cmax concentrations adjusted for protein binding of VS-6766 and defactinib. We quantified phospho- and total proteins (n=66) with an antibody-bead based assay normalized to GAPDH. We also studied growth inhibitory effects of the combination on KRAS mutant (mt) LGSOC patient-derived organoids. We performed next generation sequencing on archival samples from LGSOC patients treated with VS-6766 in combination with defactinib. Results: Signal transduction changes at 1 hr included reduction of p-FAK in 5/5 cell lines in response to defactinib. Cells exposed to VS-6766 showed a reduction in p-ERK and p-p90-RSK in 4/5 cell lines. Additionally, VS-6766 decreased p-cJUN and increased p-IκB in 4/5 cell lines, changes correlated with apoptosis. At 24 hrs, p-ERK and p-p90-RSK inhibition were maintained in 3/5 cell lines. Both drugs increased cleaved PARP in 4/5 cell lines and VS-6766 increased p-SMAD3 and BIM levels, indicating an increase in cell death/apoptosis. The combination of VS-6766 + defactinib showed synergistic growth inhibition in a KRAS mt LGSOC organoid model (combination index 0.51). The clinical combination of VS-6766 and defactinib (September 2021 cut-off) has shown an objective response rate (ORR) of 11/24 (46%) across all patients with LGSOC, and an ORR of 64% (7/11) for patients with KRAS mt LGSOC (n=11). In addition to mutations in KRAS, emerging data may suggest a correlation of U2AF1 and MED12 mutations with response. Conclusions: VS-6766, the dual RAF/MEK inhibitor, induces significant inhibition of ERK pathway signaling in addition to perturbations in TNF/NFκB signaling. Both defactinib and VS-6766 induce apoptosis in LGSOC models. The results provide mechanistic insights into the encouraging response rates observed in patients with LGSOC treated with VS-6766 and defactinib (NCT03875820). These data support the ongoing randomized phase II ENGOTov60/GOG3052/RAMP201 study (NCT04625270). Citation Format: Adam R. Stewart, Lisa Pickard, Ekta Paranjape, Victoria Sanchez Perez, Sanjib Chowdhury, Stephanie Lustgarten, Silvia Coma, Jonathan A. Pachter, Mark S. Carey, Gabriel DiMattia, Hannah C. Badham, Toby Prout, Mona Parmar, Muneeb Mahmud, Christina Yap, Matthew G. Krebs, Susana Banerjee, Udai Banerji. Mechanistic evaluation of VS-6766 (dual RAF/MEK inhibitor) and defactinib (FAK inhibitor) in low-grade serous ovarian cancer models with correlations to clinical response [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 3476.

Supplementary Table from A Phase I Trial of CT900, a Novel α-Folate Receptor–Mediated Thymidylate Synthase Inhibitor, in Patients with Solid Tumors with Expansion Cohorts in Patients with High-Grade Serous Ovarian Cancer

9018 Background: VS-6766 is a small molecule RAF/MEK clamp that results in the reduction of p-MEK and p-ERK. Preclinical data show synergy of VS-6766 with the mTOR inhibitor everolimus across a panel of KRAS mutated (mt) NSCLC cell lines. This clinical trial evaluated the safety and efficacy of a novel intermittent regimen of VS-6766 and everolimus with an expansion in KRAS mt NSCLC (NCT02407509). Methods: The trial used a 3+3 dose escalation design with an intermittent once a week schedule A, and if tolerated, twice a week schedule B (Mon-Thu or Tue-Fri) for both drugs on a 3 weeks on/1 week off, 28 day cycle. Patients with RAS or RAF mt cancers were eligible for the dose escalation cohort, and 20 patients with KRAS mt NSCLC will be treated in the dose expansion cohort. Toxicity was evaluated by NCI CTC V4 and efficacy was evaluated using RECIST 1.1. Results: A total of 28 patients have been treated; median age 60 yrs (range 36-78), and median lines of previous treatment 3 (range 0-7). Sixteen patients have been treated in the dose escalation (3 in schedule A and 13 in the schedule B). The doses of 4 mg of VS-6766 and 5 mg everolimus (once weekly) were tolerated with no dose limiting toxicities (DLTs) and the dose intensity escalated to schedule B (twice weekly). At 4 mg VS-6766 twice weekly, DLTs were observed in two out of six patients and included grade 4 CPK elevation and grade 3 rash. Thus, the dose in schedule B (twice weekly) was de-escalated to 3.2 mg VS-6766 and the dose of everolimus was kept at 5 mg. No DLTs were reported in 6 patients and thus this was declared as the recommended phase 2 dose (RP2D). At the RP2D, the grade 3-4 drug related AE were rash (18%) and pruritus (7%). In the dose escalation cohorts, 3 partial responses (PRs) were reported (2 KRAS G12D low grade serous ovarian cancer and 1 NRAS Q61K mt thyroid cancer). In the KRAS mt NSCLC expansion cohort, 10 patients are evaluable for efficacy and 2 confirmed responses were reported ( KRAS mutations G12V and G13A) with an objective response rate (ORR) 20% to date. The disease control rate (PR + SD) at the first scheduled evaluation was 90%. The median progression free survival (PFS) in the KRAS mt NSCLC cohort is 6.35 months (95% CI 3.52 – not reached). Updated ORR and PFS data will be presented. Conclusions: A tolerable intermittent dosing schedule targeting both the MAPK and PI3K pathways has been established. The combination of VS-6766 with everolimus has shown activity in patients with a variety of KRAS mutation variants including responses in KRAS mt NSCLC.

Background Data suggest that immunomodulation induced by DNA hypomethylating agents can sensitize tumors to immune checkpoint inhibitors. We conducted a phase 1 dose-escalation trial (NCT02998567) of guadecitabine and pembrolizumab in patients with advanced solid tumors. We hypothesized that guadecitabine will overcome pembrolizumab resistance. Methods Patients received guadecitabine (45 mg/m2 or 30 mg/m2, administered subcutaneously on days 1–4), with pembrolizumab (200 mg administered intravenously starting from cycle 2 onwards) every 3 weeks. Primary endpoints were safety, tolerability and maximum tolerated dose; secondary and exploratory endpoints included objective response rate (ORR), changes in methylome, transcriptome, immune contextures in pre-treatment and on-treatment tumor biopsies. Results Between January 2017 and January 2020, 34 patients were enrolled. The recommended phase II dose was guadecitabine 30 mg/m2, days 1–4, and pembrolizumab 200 mg on day 1 every 3 weeks. Two dose-limiting toxicities (neutropenia, febrile neutropenia) were reported at guadecitabine 45 mg/m2 with none reported at guadecitabine 30 mg/m2. The most common treatment-related adverse events (TRAEs) were neutropenia (58.8%), fatigue (17.6%), febrile neutropenia (11.8%) and nausea (11.8%). Common, grade 3+ TRAEs were neutropaenia (38.2%) and febrile neutropaenia (11.8%). There were no treatment-related deaths. Overall, 30 patients were evaluable for antitumor activity; ORR was 7% with 37% achieving disease control (progression-free survival) for ≥24 weeks. Of 12 evaluable patients with non-small cell lung cancer, 10 had been previously treated with immune checkpoint inhibitors with 5 (42%) having disease control ≥24 weeks (clinical benefit). Reduction in LINE-1 DNA methylation following treatment in blood (peripheral blood mononuclear cells) and tissue samples was demonstrated and methylation at transcriptional start site and 5’ untranslated region gene regions showed enriched negative correlation with gene expression. Increases in intra-tumoural effector T-cells were seen in some responding patients. Patients having clinical benefit had high baseline inflammatory signature on RNAseq analyses. Conclusions Guadecitabine in combination with pembrolizumab is tolerable with biological and anticancer activity. Reversal of previous resistance to immune checkpoint inhibitors is demonstrated.

Abstract Background: Hyperactivation of the PI3K/AKT pathway correlates with impaired antitumour response, including reduced T cell infiltration into tumour and reduced efficacy of immune checkpoint inhibitors (ICIs). PTEN loss of function, often observed in GBM, may contribute to refractoriness of ICIs in this disease. Methods: The Ice-CAP A2 cohort assessed safety, pharmacodynamic, and preliminary clinical activity of Ipa (200mg or 400mg OD) + A (1200mg Q3W) in pts with potentially resectable relapsed WHO Grade IV GBM. Key inclusion criteria were stable neurological symptoms ≥5 days prior to enrolment, steroid requirement <3mg Dexamethasone. Pts had a 14-21-day run-in phase of Ipa then surgical tumour resection. Combination Ipa+A commenced post surgery. Dose-limiting toxicity (DLT) period included run-in phase to Cycle 1 completion (≤11 wks). Results: 10 evaluable pts were enrolled (3 had Ipa at 200mg, 7 at 400mg); median age 58 (range 25-70y), ECOG score 1; median duration of treatment 8 wks. 2 remain on treatment. No DLTs, treatment-related (TR) serious adverse events (AEs), or immune-related AEs were observed. Most common TR AEs were G1 diarrhoea (60%), mucositis (30%), rash (20%). 7 pts had PTEN loss and/or PTEN mutations. Clinical benefit rate in pts with PTEN aberration was 2/7 (29%): 1 pCR and 1 SD >12wks, both on 400mg Ipa. A 58-year-old man with PTEN loss had MRI at Cycle 5 showing worsening enhancement suggestive of disease progression. Resection of the lesion showed intense lymphocyte infiltration and pathological CR. He is currently on Cycle 18 with no evidence of disease. Conclusion: Combination Ipa+A appears safe and tolerable in GBM pts, with 400mg Ipa OD + 1200mg A Q3W declared as RP2D. PTEN loss may be a promising predictive biomarker for response to combination. An expansion cohort enriched with pts with PTEN loss is ongoing. Cytokine and FACS data will be presented at AACR Table 1.Clinical Benefit Rate of glioblastoma patients stratified according to PTEN aberrationsPTEN statusnBest responseClinical Benefit RatePTEN loss on IHC (H<30)51 pCRa2/7 (29%)1 SD >12 wks, ongoingb3 PDPTEN aberration on NGS but PTEN protein expression pending11 PDcPTEN loss of heterozygozity on PCR11 PDWild type PTEN on NGS or IHC (H≥30)33 PDLegend: IHC = immunohistochemistry; NGS = next generation sequencing; PCR = polymerase chain reaction;pCR = pathologic complete response; SD = stable disease; PD = progressive diseaseaExceptional responder with PTEN H=5 on IHC and splice site 75_79+2delGACCTGT on NGSb PTENY68*; c PTENQ298* Citation Format: Crescens Tiu, Andrea Biondo, Liam C. Welsh, Timothy L. Jones, Anna Zachariou, Toby Prout, Alison J. Turner, Robert Daly, Igor Vivanco, Christina Yap, Ben Jenkins, Mateus Crespo, Ruth Riisnaes, Suzanne Carreira, Bora Gurel, Nina Tunariu, Anna Minchom, Udai Banerji, Johann S. de Bono, Juanita S. Lopez. Results of the glioblastoma multiforme (GBM) cohort of phase 1 trial Ice-CAP (NCT03673787): Preliminary evidence of antitumour activity of Ipatasertib (Ipa) and Atezolizumab (A) in patients (pts) with PTEN loss [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 CT120.

AbstractCyclin-dependent kinase 4/6 (CDK4/6) and PI3K inhibitors synergize in PIK3CA-mutant ER-positive HER2-negative breast cancer models. We conducted a phase Ib trial investigating the safety and efficacy of doublet CDK4/6 inhibitor palbociclib plus selective PI3K inhibitor taselisib in advanced solid tumors, and triplet palbociclib plus taselisib plus fulvestrant in 25 patients with PIK3CA-mutant, ER-positive HER2-negative advanced breast cancer. The triplet therapy response rate in PIK3CA-mutant, ER-positive HER2-negative cancer was 37.5% [95% confidence interval (CI), 18.8–59.4]. Durable disease control was observed in PIK3CA-mutant ER-negative breast cancer and other solid tumors with doublet therapy. Both combinations were well tolerated at pharmacodynamically active doses. In the triplet group, high baseline cyclin E1 expression associated with shorter progression-free survival (PFS; HR = 4.2; 95% CI, 1.3–13.1; P = 0.02). Early circulating tumor DNA (ctDNA) dynamics demonstrated high on-treatment ctDNA association with shorter PFS (HR = 5.2; 95% CI, 1.4–19.4; P = 0.04). Longitudinal plasma ctDNA sequencing provided genomic evolution evidence during triplet therapy.SIGNIFICANCE:The triplet of palbociclib, taselisib, and fulvestrant has promising efficacy in patients with heavily pretreated PIK3CA-mutant ER-positive HER2-negative advanced breast cancer. A subset of patients with PIK3CA-mutant triple-negative breast cancer derived clinical benefit from palbociclib and taselisib doublet, suggesting a potential nonchemotherapy targeted approach for this population.This article is highlighted in the In This Issue feature, p. 1

Abstract Background: Methylation is reported to support cancer immune tolerance. We conducted a phase 1 dose-escalation trial [NCT02998567] of combination guadecitabine (G; DNA hypomethylating agent) and pembrolizumab (P) in patients (pts) with advanced cancers. We hypothesized that G can normalize the expression of epigenetically suppressed immune genes, increase interferon producing tumor-infiltrating lymphocytes (TILs), and enhance the anticancer activity of P. Methods: In dose escalation (Es), pts received G (45 mg/m2 or 30 mg/m2, administered SC on days 1-4) with P (200 mg, administered IV starting from cycle 2 onwards) as outpatient Q3W; in expansion (Ex), the RP2D of G (30 mg/m2) with P (200 mg) Q3W was administered. Pre-treatment and on-treatment tumor biopsies were evaluated for PD-L1 expression, tumor infiltrating lymphocytes, gene expression by RNAseq and methylome studies. Longitudinal analyses of peripheral blood CD3, CD4 and CD8 lymphocytes by flow cytometry were performed. Results: Overall, 34 pts (Es, n = 14; Ex, n = 20) were evaluable for safety. The most common treatment-related adverse events (TRAEs) were neutropenia (n = 21), fatigue (n = 6) and thrombocytopenia (n = 3), diarrhea (n = 2). G3+ TRAEs were neutropenia (n = 14), febrile neutropenia (n = 4), raised ALP (n = 1), raised AST (n=1), colitis (n = 1), diarrhoea (n = 1) and lung infection (n = 1). Two DLTs (neutropenia, febrile neutropenia) were reported at G 45mg/m2 with none reported at G 30mg/m2. There were no treatment-related deaths. In total, 28 pts (Es, n = 12; Ex, n = 16) were evaluable for antitumor activity studies (≥2 scans); ORR (CR+PR) and DCR (CR+PR+SD) were 3% and 57%; 10/15 pts with non-small cell lung cancer (13 pts resistant/refractory to PD-1/PD-L1 targeting agents) were evaluable, with a DCR of 80% and 5 pts having DCR > 6 months with 8 pts remaining on study treatment. Overall, 25 paired biopsies were obtained. Using LINE1 sequences to study global methylation, both tumor biopsies and peripheral blood showed reduced methylation post-G treatment. Preliminary data on tumor-infiltrating lymphocytes assessed by multicolor immunofluorescence in 9 paired biopsies showed a numerical increase in median values of T-helper (CD4+FOXP3-) (10.20 to 19.70, p = 0.5469), T-regulatory (CD4+FOXP3+) (5.1 to 6.7, p=0.8438), and T-cytotoxic (CD8+) cell densities (2.7 to 7.4, p=0.6523) . Comparing with matched pre-treatment, on treatment tumor had numerical increases in interferon alpha and gamma response pathway activation in serial biopsy RNAseq analyses but did not reach significance. Conclusions: G plus P resulted in no unexpected toxicities with evidence suggestive of biological and anti-cancer activity. Citation Format: Dionysis Papadatos-Pastos, Abhijit Pal, Melek Akay, Malaka Ameratunga, Sanjena Mithra, Joo-Ern Ang, Sofia Levva, Reece Caldwell, Ruth Riisnaes, Mateus Crespo, Wei Yuan, George Seed, Bora Gurel, Ines Figueiredo, Rita Pereira, Susana Miranda, Anna Ferreira, Suzanne Carreira, Claudia Bertan, Chloe Baker, Ricardo Morilla, Robert Brown, Nahal Masrour, Toby Prout, Anna Zachariou, Alison Turner, Mona Parmar, Mark Van de Velde, Ben Jenkins, Christina Yap, Nina Tunariu, Udai Banerji, Juanita Lopez, Anna Minchom, Johann De Bono. HyPeR: A phase 1, dose escalation and expansion trial of guadecitabine (SGI-110), a second-generation hypomethylating agent in combination with pembrolizumab (MK3475) in patients with refractory solid tumors [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 CT129.

6043 Background: CT900 (BTG945/ONX-0801) is a novel small molecule that binds to folate receptor alpha (FRα), is internalized and causes cytotoxicity by thymidylate synthase inhibition. Methods: The aims of the expansion cohorts were to determine toxicity, response rates and correlation of the response to FRα expression in patients with HGSOC (NCT02360345). Four expansion cohorts were studied which included: schedule A (6 mg/m2/q every 2 weeks), schedule B (12 mg/m2/q every 2 weeks), schedule C (12 mg/m2/q every 2 weeks with 12 mg dexamethasone IV and 8 mg of dexamethasone for 2 days) and schedule D (12 mg/m2/q every 3 weeks). Response rates were assessed by RECIST V1.1 and GCIG CA125 response criteria. Patients who were withdrawn for reasons other than toxicity within 8 weeks (cohorts A, B, C) and 12 weeks (cohort D) were not assessable for efficacy. FRα expression was quantified using immunohistochemistry. Results: A total of 67 patients were treated in the 4 cohorts (14, 25, 15 and 13 for cohorts A, B, C and D). The median age was 62 (IQR 57 - 68) and the median lines of previous treatment was 5 (range 1 to 13). A majority of patients were platinum resistant. The most common toxicities across all expansion cohorts were: fatigue (51%), nausea (36%), anemia (27%), fever (25%), AST elevation (21%), most of which were grade 1 - 2. Toxicity of special interest included radiological changes of pneumonitis and was 15% in all cohorts (7%, 16%, 27% and 8% in cohorts A, B, C and D, respectively). These changes were grade 1 - 2 in all but one case. RECIST response rates in evaluable patients across the different cohorts were: A 1/8 (13%), B 6/21 (29%), C 5/12 (42%) and D 2/12 (17%). FRα expression in archival tumor tissue was measured in 59/67 patients. Expression was found to be high/medium in 43/59 (73%), low in 7/59 (12%) and negative/very low in 9/59 (15%). In patients with high/medium FRα expression, the RECIST response rates in different cohorts were: A 0/9 (0%), B 6/16 (38%), C 4/12 (33%) and D 1/6 (17%). The CA125 response rate in all patients within cohort B was 13/25 (52%) and 10/16 (63%) in patients with high/medium FRα expression. Conclusions: CT900 has shown clinical activity in patients with heavily pre-treated platinum-resistant, high/medium FRα expressing HGSOC. Based on toxicity and efficacy, the schedule of 12 mg/m2/q2 weekly (schedule B) is the recommended phase II dose for further evaluation in patients with relapsed high/medium FRα expressing HGSOC. Clinical trial information: NCT02360345.

Abstract Background: Hyperactivation of the PI3K/AKT pathway correlates with impaired anti-tumor responses, including reduced T cell infiltration into tumor, and reduced efficacy of immune checkpoint inhibitors. Blockade of this pathway synergizes with PD-L1/PD-1 axis blockade preclinically. Methods: This Phase I clinical trial (NCT03673787) assessed the safety, pharmacodynamic, and preliminary clinical activity of Ipa (200mg or 400mg OD) given in combination with A 1200mg q3 wk in refractory pts. Serial paired blood and tumor samples were analysed to interrogate the effect of Ipa on the tumor micro-environment and host immune system prior to the addition of the immune check point inhibitor, A. Results: 18 adult pts were treated in dose escalation. Median age 49 yrs. All pts had ECOG PS 0-1 and median 7 prior therapies. Most common TRAEs (>15%) were mild Gr1-2 diarrhea (56%), rash (50%), fatigue (33%), nausea (33%), raised ALT/AST (33%), headache (28%) and arthralgia (22%). 1 pt had G2 systemic immune activation; 2 pts had G3 rash, both rapidly reversible. 1 DLT of G3 raised ALT seen at 200mg (1 DLT/9 evaluable pts) but none at 400mg (0 DLT/6). Of 14 RECIST evaluable patients, there were 2 confirmed PRs, and 5 SD (clinical benefit rate 50%). Reductions of CD4+FOXP3+ Tregs in tumor microenvironment were seen after 2wks of single agent Ipa, regardless of PIK3/AKT somatic mutation status (Table 1). Responding pts had a >400% median increase in intra-tumoral CD8+ Teff cell infiltration, effectively switching from a desert phenotype to an inflamed phenotype. Paired changes in FACS, transcriptome and cytokine will also be presented.Conclusions: The RP2D of Ipa 400mg OD combination with A was well tolerated with early efficacy signals. Further biomarker work is ongoing and will be evaluated in expansion cohorts. Table 1:Changes in immune cell populations as assessed by multicolour Immunofluorescence in paired biopsies of breast/gynae patients, % change in cell number/mm2 from baseline (median [min,max$])&Post 2 weeks single agent Ipatasertib(n=9)Post 1 cycle of combination Ipatasertib and Atezolizumab(n=7)CD4+FOXP3+Tregs cellsCD 8+ Teff cellsCD4+FOXP3+Tregs cellsCD 8+ Teff cellsIntra-tumourstromaIntra-tumourstromaIntra-tumourstromaIntra-tumourstromaAll patients-23.9*[-89.7, BL0]-30.0*[-91.6, BL0]-37.7*[-84.4, -24.5]-28.4[-92.4, 259.8]335.9[-44.0,BL0]45.4[-51.0, BL0]59.6[-60.6,493.3]64.7[-51.7,293.3]Stratified by somatic PI3K/AKT/PTEN mutational statusPathogenic mutations (mt)11.1[-82.2, BL0]#-10.7[-91.6, BL0]Φnsnsnsns-30.5[-60.6,-0.5]11.3[-51.7,50.0]Wildtype (wt)-63.1[-89.7,19.0]#-47.5[-77.0,11.1]Φnsnsnsns426.5[59.6,493.3]126.7[79.4,293.3]Stratified by responseResponders (PR + SD>4 cycles). 1 ER+ HER2+ breast cancer (wt), 1 ER+ HER2- breast cancer (wt)459.9[426.5,493.3]@103.1[79.4,126.7]Non-responders (PD at 4 cycles) 1 cervical cancer, 4 ER+ breast cancer-0.5[-60.6, 59.6]@30.6[-51.7,293.3]*significant change (p≤0.05; Wilcoxon sign-rank test) from baseline, $maximum values denoted by BL0indicate that the baseline value was zero, and so percentage change from baseline is not defined. For the analysis, the baseline value has been replaced by a nominal value of 0.1 so that a large percentage increase is associated with these cases. Note that these large percentage increases do not affect the non-parametric statistical tests used.#no significant difference in distribution of reduction in intra-tumoural CD4+ FOXP3+Tregsbetween pts with pathogenic mutations in PI3K/AKT and those without (p=0.30; Wilcoxon rank-sum test)Φno significant difference in distribution of reduction in stromal CD4+FOXP3+Tregsbetween pts with pathogenic mutations in PI3K/AKT and those without (p=0.44; Wilcoxon rank-sum test) @ difference between responders and non-responders p=0.083; Wilcoxon rank-sum test)mt pathogenic mutations in PI3K/AKT and PTEN as per COSMIC database present in tumour or PTEN loss by IHC. wt no pathogenic mutations in PI3K/AKT and PTEN as per COSMIC database detected in tumour and intact PTEN expression by IHC. &exploratory analyses with no adjustment for multiple testing Citation Format: Juanita S. Lopez, Andrea Biondo, Crescens Tiu, Mariana Scaranti, Malaka Ameratunga, Anna Zachariou, Alison Turner, Nina Tunariu, Toby Prout, Mona Parmar, Hannah Badham, Karen Swales, Wei Yuan, Ricardo Morilla, Mateus Crespo, Rob Daly, Ines Figueiredo, Bora Gurel, Rita Pereira, Ruth Riisnaes, Igor Vivanco, Anna Minchom, Ben Jenkins, Christina Yap, Udai Banerji, Johann De Bono. Proof-of-concept evidence of immune modulation by blockade of the phosphatidylinositol 3-kinase (PI3K)-AKT signaling pathway in the phase I dose escalation study of Ipatasertib (Ipa) in combination with atezolizumab (A) in patients (pts) with advanced solid tumors (Ice-CAP) [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 CT140.