5048 Background: Dickkopf-1 (DKK1) is a secreted Wnt signaling modulator that is upregulated in prostate cancers with low androgen receptor (AR) expression and co-occurring mutations in Wnt signaling family genes. DKN-01, a potent humanized monoclonal antibody (IgG4) with neutralizing activity against DKK1, delays prostate cancer growth in pre-clinical DKK1-expressing models in an NK cell dependent manner. These data provided the rationale for a prospective clinical trial testing DKN-01 in patients with mCRPC and elevated DKK1. Here, we report the safety and efficacy results of the phase 1 dose escalation cohorts. Methods: This is an investigator-initiated parallel-arm non-randomized phase 1/2 clinical trial testing DKN-01 alone or in combination with docetaxel 75 mg/m2 for men with mCRPC who progressed on ≥1 AR signaling inhibitor. Eligible patients who had progressed on or were intolerant of docetaxel were assigned to the monotherapy cohort whereas taxane-naïve patients were assigned to the DKN-01 plus docetaxel combination cohort. DKK1 status was determined by RNA in-situ expression. The primary endpoint of the phase 1 dose escalation cohorts was safety, characterized by dose-limiting toxicity (DLT). A secondary endpoint of the study was to correlate anti-tumor activity, DKK1 expression (cutoff H-score ≥ 1), and clinical evidence of aggressive variant prostate cancer (AVPC). Results: 13 pts were enrolled in the completed phase 1 portion of this study – 7 patients in the monotherapy cohort and 6 patients in the combination cohort. No DLTs were observed at DKN-01 300mg or 600mg dose levels as monotherapy or in combination with docetaxel. No treatment-related serious adverse events occurred in either cohort. A best overall response of stable disease occurred in 2 out of 7 patients in the monotherapy cohort. In the combination cohort, all 5 evaluable patients had a partial response (PR) – 3 confirmed and 2 unconfirmed. All evaluable combination patients had ≥ 50% reduction in either PSA or CEA. Confirmed PRs in the combination cohort were observed in both DKK1 low (DKK1 H-score < 1) and high expressing tumors (H-score ≥1), including in 2 out of 3 patients with AVPC. Conclusions: DKN-01 600mg was well tolerated and selected as the recommended phase 2 dose as monotherapy and in combination with docetaxel. DKN-01 in combination with docetaxel showed promising clinical activity in prostate cancers regardless of DKK1 expression and was particularly promising in patients with AVPC. Further accrual into the phase 2 portion of this study is ongoing alongside preclinical and correlative studies aiming to investigate the mechanism of action of this combination therapeutic strategy. Clinical trial information: NCT03837353.

PURPOSEThe outcomes of anti-PD-1 agents plus fluoropyrimidine/platinum in frontline advanced gastroesophageal adenocarcinomas (aGEAs) remain poor. We investigated the safety, tolerability, and activity of fluoropyrimidine/oxaliplatin and tislelizumab with the DKK1-neutralizing antibody DKN-01 in aGEAs in a phase IIa open-label study.PATIENTS AND METHODSPatients had untreated human epidermal growth factor receptor 2-negative aGEAs, RECIST v1.1 measurable disease, Eastern Cooperative Oncology Group (ECOG) performance status 0-1, and adequate organ function. Patients received intravenous DKN-01 300 mg once every 2 weeks, tislelizumab 200 mg once every 3 weeks, oxaliplatin 130 mg/m2 once every 3 weeks, and capecitabine 1,000 mg/m2 twice daily on days 1-15 of each 21-day cycle. The primary end point was safety and tolerability. Key secondary end points included objective response rate (ORR) by RECISTv1.1, progression-free survival (PFS), and overall survival (OS).RESULTSBetween September 18, 2020, and April 8, 2021, 25 patients were enrolled. All patients who received at least one dose of DKN-01 were included in the safety analysis. Most patients had gastroesophageal junction tumors, median age was 61 years, 76% were male, and 55% were ECOG of 0. All patients reported at least one treatment-emergent adverse event. The ORR was 73% (95% CI, 49.8 to 89.3), with a disease control rate of 95%. The ORR was 90% (95% CI, 55.5 to 99.7) in the DKK1-high tumor patients and 67% (95% CI, 29.9 to 92.5) in the DKK1-low tumor patients. The median PFS was 11.3 months (95% CI, 5.8 to 12.0) and the 12-month PFS rate was 33%. The median OS was 19.5 months (95% CI, 15.2 to 24.4) with a 12-month OS rate of 76% and an 18-month OS rate of 55%.CONCLUSIONDKN-01 can be safely combined with frontline fluoropyrimidine/oxaliplatin and tislelizumab and demonstrates encouraging activity independent of PD-L1 expression levels. A randomized phase II trial is ongoing (ClinicalTrials.gov identifier: NCT04363801).

104 Background: CRC is characterized by hyperactivation of the Wnt pathway where DKK1 plays a critical regulatory role. DKN-01 is an IgG4 monoclonal antibody that potently neutralizes DKK1. DKN-01 has immunomodulatory activity and stimulates a pro-inflammatory tumor microenvironment. Elevated DKK1 expression has been shown to correlate with fluorouracil (5FU) resistance in CRC tumors. 5FU-based combination therapies have demonstrated promising clinical activity in combination with DKN-01 in gastric cancer. In pre-clinical models of 5FU-resistant CRC, DKN-01 showed potent anti-tumor effects. Methods: DeFianCe (NCT05480306) is a Phase 2 randomized, open-label, two-part, multicenter study to evaluate efficacy and safety of DKN-01 plus FOLFIRI/FOLFOX and bevacizumab versus standard of care (SOC) [FOLFIRI/FOLFOX and bevacizumab] as 2L treatment of advanced MSS CRC patients (pts). The primary endpoint of the single arm Part A (DKN-01 + SOC) was safety and tolerability with secondary endpoints including overall response rate (ORR), progression-free survival (PFS) and overall survival. Retrospective analysis of tumoral DKK1 mRNA expression was measured centrally by in situ hybridization. Results: Thirty-three pts enrolled in Part A between Sept 2022-April 2023. As of 21 Aug 2023, median age 56 years (35, 84); 20 males. 29 pts had tumors with evaluable baseline DKK1 expression; 55% were DKK1-expressing (≥1% tumor cells). All patients had received prior 5FU-based therapies, 30 pts (91%) with oxaliplatin in combination and 17 pts (52%) had prior bevacizumab. 24 pts (73%) had RAS mutations (22 KRAS, 2 NRAS) and 23 pts (70%) had liver metastasis. 30 pts (91%) received DKN-01 + bevacizumab + FOLFIRI. 17 pts (52%) had ≥grade 3 treatment related adverse events (TRAE) with neutrophil count decreased, anemia and fatigue representing the most common. No pt discontinued DKN-01 due to a TRAE. Of the 27 response evaluable pts the ORR was 30% and the DCR was 93%: 8 PR, 17 SD and 2 PD. The median PFS has not been reached. Conclusions: DKN-01 in combination with SOC was well tolerated with promising preliminary activity (ORR 30% and DCR 93%) in the single arm Part A. PFS has not been reached and survival follow up is ongoing. Part B randomized expansion phase has begun and is enrolling an additional 130 pts. Tumoral DKK1 expression and correlation with clinical outcomes will be evaluated as an exploratory efficacy endpoint. Clinical trial information: NCT05480306 .

Biliary tract cancers demonstrate profound therapeutic resistance, and broadly effective therapies for refractory disease are lacking. We conducted a single-arm, second-line phase II trial combining DKN-01, a humanized monoclonal antibody targeting Dickkopf-1 (DKK-1), and nivolumab to treat patients with advanced biliary tract cancer (NCT04057365). No objective responses were seen. To identify mechanisms of treatment failure, we analyzed paired pre-treatment and on-treatment biopsies using scRNA-seq and constructed a detailed molecular classification of malignant and immune cells. We annotated five biliary tract cancer malignant cell states: classical, basal, mesenchymal, neural-like, and endothelial-like. Neural-like and endothelial-like states, which drive therapeutic resistance in other cancers, have not previously been described in BTC. Malignant cell states co-varied with distinct immune cell states, revealing diverse mechanisms of myeloid and T-cell mediated immune suppression, including M2 myeloid and terminally exhausted T cell programs that were induced by DKN-01/nivolumab. Here, we provide the first systematic classification of functionally annotated cell states in biliary tract cancer and provide new insight into resistance mechanisms to an immunotherapy combination that can inform the next generation of trials.

Supplementary Table from Phase IB Study of GITR Agonist Antibody TRX518 Singly and in Combination with Gemcitabine, Pembrolizumab, or Nivolumab in Patients with Advanced Solid Tumors

4027 Background: DKN-01 is an anti-DKK1 mAb which has demonstrated anti-tumor activity in patients with advanced GEA with low tumor PD-L1 expression, a subset with very limited therapeutic options. DKN-01 has immunomodulatory activity, stimulates a pro-inflammatory tumor microenvironment, and upregulates PD-L1 levels. Here we present 2-year survival data for 1L advanced GEA patients who received combination treatment with DKN-01, the Fc-optimized anti-PD-1 tislelizumab, and CAPOX chemotherapy. The ORR was previously reported (68% in ITT and 79% in PD-L1-low populations). Methods: This Phase 2, multi-center, single arm Part A of the DisTinGuish (NCT04363801) study investigated DKN-01 + tislelizumab + CAPOX as 1L therapy in advanced HER2(-) GEA, regardless of DKK1 and PD-L1 expression levels. Tumor DKK1 and PD-L1 were assessed by central laboratories. The primary endpoint was ORR in a modified intent to treat population (>1 dose DKN-01); secondary endpoints included PFS and OS in the ITT population. Results: Twenty-five patients were enrolled from September 2020 to April 2021. As of 23 January 2023: Median age was 61 years (22, 80); 17 patients had GEJ adenocarcinoma; 8 had gastric cancer. Twenty-one patients had tumors with evaluable DKK1 expression. Twenty-two patients had tumors with evaluable PD-L1 expression; the majority (73%) were low expressors (vCPS <5%). Median (m) duration on treatment is 11.3 months (mo). Seven patients remain on study, with 4 on-treatment beyond 2 years. The mPFS is 11.3 mo in the overall ITT population and 10.7 mo in patients with low tumor PD-L1 expression. The mOS is 19.5 mo in the overall ITT population and 18.7 mo in the patients with low tumor PD-L1 expression. Treatment related adverse events (TRAEs) were mild with most G1/2. The most common AEs related to the study drug regimen were nausea (72%), diarrhea (64%) and fatigue (60%). Five patients experienced G3 DKN-01-TRAEs including decreased neutrophil count (1), diarrhea (1), vomiting (1), hypophosphatemia (2), and pulmonary embolism (1). Conclusions: At 2-years of follow-up, 1L treatment of advanced GEA patients with DKN-01 in combination with tislelizumab and CAPOX resulted in a prolongation of PFS and OS compared with the modern SOC regimen of nivolumab plus chemotherapy, both in the overall population (mPFS 11.3 vs 7.7 mo; mOS 19.5 vs 13.8 mo) and in the PD-L1 low subgroup (mPFS 10.7 vs 7.5 mo; mOS 18.7 vs 12.4 mo), alongside a manageable safety profile. The prolonged PFS and OS observed in the current study are notable, especially in our trial population dominated by patients with tumors of low PD-L1 expression, where the known benefit of anti-PD-1 therapy is limited. The ongoing Part C of this study is evaluating mFOLFOX6/CAPOX plus tislelizumab with or without DKN-01 in the same 1L GEA patient population. Further evaluation of biomarkers is also ongoing. Clinical trial information: NCT04363801 .

TPS275 Background: Colorectal cancer is the third most prevalent cancer, and the prognosis of patients with advanced metastatic (mCRC) is poor. The efficacy of standard of care (SOC) second-line chemotherapy combinations with anti-vascular endothelial growth factor (VEGF) therapies remains modest. Previously treated advanced mCRC that is microsatellite stable (MSS/pMMR) represents nearly 95% of the metastatic population and remains a high unmet medical need. DKN-01 is a humanized IgG4 monoclonal antibody (mAb) targeted against Dickkopf-related protein 1 (DKK1), a regulator of the Wnt signaling pathway. DKK1 has been identified as a potential oncogenic driver in CRC and has been correlated with 5FU resistance. Therefore, DKK1 expression is a potential predictive biomarker for chemotherapeutic resistance in CRC. Methods: This is a phase 2 randomized, open-label, two-part, multicenter study with a safety run-in to evaluate safety and efficacy of DKN-01 plus FOLFIRI/FOLFOX and bevacizumab versus SOC [FOLFIRI/FOLFOX and bevacizumab] as second-line treatment of advanced mCRC patients. In Parts A and B, approximately 150 advanced MSS, BRAF Wild Type mCRC patients with radiographic progression during or following 1 prior line of systemic treatment will be enrolled in the study. Part A is a safety run-in with DKN-01 plus FOLFIRI/FOLFOX and bevacizumab in at least 20 safety evaluable patients. In Part B, approximately 130 patients will be randomized 1:1 to either the experimental (DKN-01 plus FOLFIRI/FOLFOX and bevacizumab) or control arm (FOLFIRI/FOLFOX and bevacizumab), using a central stratified block randomization scheme and stratified based on DKK1 RNAscope tumor percentage score (TPS) (≥1% vs <1%). Primary endpoint is progression free survival and secondary endpoints include overall response rate, duration of response, overall survival and incidence of ≥Grade 3 related treatment-related adverse events (TRAEs). Exploratory endpoints will include evaluation of efficacy outcomes based upon tumoral DKK1 expression. Recruitment is ongoing. Clinical trial information: NCT05480306 .

PURPOSE:Dickkopf-1 (DKK1) is a Wnt signaling modulator promoting tumor growth, metastasis, angiogenesis, and immunosuppression by regulating innate immunity. DKK1 is over-expressed in gynecologic cancers and is associated with shortened survival. DKN-01 is a humanized monoclonal antibody with DKK1 neutralizing activity that may provide clinical benefit to patients whose tumors have overexpression of DKK1 or Wnt genetic alterations. METHODS:We conducted an open-label, Phase 2 basket study with 2-stage design in patients with endometrial carcinoma (EC) and platinum-resistant/refractory epithelial ovarian cancer. DKN-01 was administered either as monotherapy or in combination with weekly paclitaxel at investigator's discretion. All patients underwent NGS testing prior to enrollment; tumor tissue was also tested for DKK1 expression by RNAscope pre-treatment and after cycle 1 if available. At least 50% of patients were required to have a Wnt signaling alteration either directly or tangentially. This publication reports results from the EC population overall and by DKK1-expression. RESULTS:DKN-01 monotherapy and in combination with paclitaxel was more effective in patients with high DKK1-expressing tumors compared to low-expressing tumors. DKN-01 monotherapy demonstrated an objective response rate [ORR] of 25.0% vs. 0%; disease control rate [DCR] of 62.5% vs. 6.7%; median progression-free survival [PFS] was 4.3 vs. 1.8 months, and overall survival [OS] was 11.0 vs. 8.2 months in DKK1-high vs DKK1-low patients. Similarly, DKN-01 in combination with paclitaxel demonstrated greater clinical activity in patients with DKK1-high tumors compared to DKK1-low tumors: DCR was 55% vs. 44%; median PFS was 5.4 vs. 1.8 months; and OS was 19.1 vs. 10.1 months. Wnt activating mutations correlated with higher DKK1 expression. DKN-01 was well tolerated as a monotherapy and in combination with paclitaxel. CONCLUSIONS:Collectively, data demonstrates promising clinical activity of a well-tolerated drug, DKN-01, in EC patients with high tumoral DKK1 expression which frequently corresponded to the presence of a Wnt activating mutation. Future development will focus on using DKN-01 in DKK1-high EC patients in combination with immunotherapy.

Background Elevated tumoral DKK1 expression is seen in approximately one third of previously treated GEA and has been associated with more aggressive disease and shorter overall survival. DKN-01 (D) is a targeted anti-DKK1 mAb which has demonstrated improved clinical outcomes in previously treated GEA pts with elevated tumoral DKK1 expression when used in combination with an anti-PD1 antibody. Methods DisTinGuish (NCT04363801) is a Phase 2a single arm 2-part trial; Part A is reported separately; Part B investigated two dosing cohorts of D (300 mg and 600 mg) + tislelizumab (TS) as 2L therapy for DKK1-high GEA pts. Primary objective was to examine safety and tolerability and secondary objectives evaluated multiple efficacy endpoints including overall response rate (ORR) and disease control rate (DCR) in a modified intent to treat (mITT) population (>1 dose D). Results 52 pts enrolled between 27 Oct 2020 and 7 Jun 2022; (D-300 mg, 24 pts; D-600 mg 28 pts). Median age was 63 (29, 76); 41 males (79%). 18 pts (35%) had gastroesophageal junction (GEJ) adenocarcinoma; 34 pts (65%) had gastric cancer (GC). 22 pts from US, 30 pts from Republic of Korea. 49 pts have PD-L1 visually-estimated combined positive score (vCPS) results: <1 n=13 (27%); 1-<10 n=22 (45%); ≥10 n=14 (29%). 38 pts with genomic profiling: Wnt activating mutations in 12 pts, no MSI-H. 4 pts were IO experienced. Median number of cycles 2 (1, 19). 12 pts remain on therapy. 19 pts (37%) experienced D-related adverse events (AE); 74% were G1/2. Most common regimen related AEs: fatigue, nausea, AST increased. 3 pts (6%) had serious D-related AEs [vomiting, fatigue, dehydration]. No G5 TRAEs. No D-related AE led to D-dose reduction or discontinuation. Preliminary ORR in response evaluable IO naive mITT (n=36) was 25% and DCR 44%. mITT ORR by vCPS (figure 1): <1: [n=11; PR-3 (27%), SD-1, PD-7]; 1-<10: [n=12; PR-1 (8%), SD-3, PD-8 (1 PD pt -> irPR)]; ≥10: [n=11; PR-5 (45%), SD-3, PD-3]. 6 of 9 responders remain on therapy, median DoR not reached. Median PFS: 1.4 mos (vCPS <1: 1.4 mos, 1-<10: 1.4 mos, ≥10: 2.9 mos). Conclusions The combination of D + TS represents a well-tolerated, active chemotherapy-free combination in previously treated DKK1-high IO naïve GEA pts. Encouraging durable activity was observed particularly in DKK1 high/vCPS≥10 cohort: ORR 45%, DCR 73%. Updated ORR, DoR, PFS and additional correlative biomarker evaluation will be reported. Acknowledgements Diane Piper and Mathis Thoma, Leap Therapeutics, Inc. biometrics support Trial Registration NCT04363801

is the preva-lent of cancer-related worldwide. CRC has elevated Wnt signaling activity in which DKK1 plays a regulatory role. DKN-01 is an IgG4 clinical stage antibody that specifically neutralizes DKK1. Fluo-rouracil (5FU)-based therapies are the standard backbone treatment for CRC and have demonstrated clinical activity in combination with DKN-01 in gastroesophageal adenocarci-noma (GEA). DKK1 expression has been shown to correlate with 5FU resistance in CRC tumors and cell lines. We eval-uated the efficacy of DKN-01 alone and in combination with 5FU in parental and 5FU-resistant HCT116 and SW480 xenograft models. Further, given the established role of DKK1 on TME modulation, we also explored treatment with DKN-01 as a monotherapy and in combination with anti-PD-1 in a CT26 syngeneic CRC model. DKN-01 (mDKN-01), anti-PD-1, or the combination. Results In the parental HCT116 model, 30%, 39%, and 55% tumor growth inhibition (TGI) were observed in the DKN-01, 5FU, and combination treatment groups compared to isotype controls. Strikingly, in the HCT116 5FU-resistant model, 5FU had a negligible effect on TGI compared to DKN-01 monotherapy; and combination treatment groups in both 5FU-resist-ant models experienced 100% tumor regression. In the CT26 syngeneic model, mDKN-01 monotherapy resulted in 71% TGI with 47% of the group experiencing tumor regression at study termination unlike the anti-PD-1 monotherapy which had negligible TGI. The effect of mDKN-01 was further enhanced the combination resulting in additional 58% TGI of group experiencing tumor regression.

Abstract Purpose: TRX518 is a mAb engaging the glucocorticoid-induced TNF receptor−related protein (GITR). This open-label, phase I study (TRX518-003) evaluated the safety and efficacy of repeated dose TRX518 monotherapy and in combination with gemcitabine, pembrolizumab, or nivolumab in advanced solid tumors. Patients and Methods: TRX518 monotherapy was dose escalated (Part A) and expanded (Part B) up to 4 mg/kg loading, 1 mg/kg every 3 weeks. Parts C–E included dose-escalation (2 and 4 mg/kg loading followed by 1 mg/kg) and dose-expansion (4 mg/kg loading) phases with gemcitabine (Part C), pembrolizumab (Part D), or nivolumab (Part E). Primary endpoints included incidence of dose-limiting toxicities (DLT), serious adverse events (SAE), and pharmacokinetics. Secondary endpoints were efficacy and pharmacodynamics. Results: A total of 109 patients received TRX518: 43 (Parts A+B), 30 (Part C), 26 (Part D), and 10 (Part E), respectively. A total of 67% of patients in Parts D+E had received prior anti–PD(L)1 or anti–CTLA-4. No DLTs, treatment-related SAEs, and/or grade 4 or 5 AEs were observed with TRX518 monotherapy. In Parts C–E, no DLTs were observed, although TRX518-related SAEs were reported in 3.3% (Part C) and 10.0% (Part E), respectively. Objective response rate was 3.2%, 3.8%, 4%, and 12.5% in Parts A+B, C, D, and E, respectively. TRX518 affected peripheral and intratumoral regulatory T cells (Treg) with different kinetics depending on the combination regimen. Responses with TRX518 monotherapy+anti–PD1 combination were associated with intratumoral Treg reductions and CD8 increases and activation after treatment. Conclusions: TRX518 showed an acceptable safety profile with pharmacodynamic activity. Repeated dose TRX518 monotherapy and in combination resulted in limited clinical responses associated with immune activation. See related commentary by Hernandez-Guerrero and Moreno, p. 3905

292 Background: Despite recent approval of anti-PD-1 antibodies as 1L therapy in HER2(-) advanced GEA, benefit remains modest and limited largely to PD-L1(+) patients (pts), primarily those with combined positive scores (CPS) ≥5. Thus novel therapeutic approaches are needed for this pt population. DKN-01 is a targeted anti-DKK1 mAb which has demonstrated improved clinical outcomes in pts with elevated tumoral DKK1 expression, a subset of pts with more aggressive disease and shorter overall survival. Methods: DisTinGuish (NCT04363801) is a Phase 2a single arm 2-part trial; Part A investigated DKN-01 (D) + tislelizumab (TS) + CAPOX as 1L therapy for pts with advanced HER2(-) GEA regardless of DKK1 status; Part B investigated two dosing cohorts of D (300 mg and 600 mg) + TS as 2L therapy for DKK1-high advanced GEA pts. Primary objective was to examine safety and tolerability and secondary objectives evaluated multiple efficacy endpoints including overall response rate (ORR) in a modified intent to treat (mITT) population (>1 dose D). Results: Forty-nine pts enrolled between 01 Sept 2020 and 15 Sept 2021; 25 pts in Part A and 24 pts in Part B (D-300 mg). Key clinicopathologic features and efficacy outcomes are shown in Table. The most common D-related AEs were low grade (G1/2) fatigue, nausea, and diarrhea. Nine pts had D-related ≥G3 toxicities, elevated AST/ALT, elevated alkaline phosphatase, hypophosphatemia, hyponatremia, lymphopenia, neutropenia, diarrhea, vomiting, fatigue all occurring in 1 pt and pulmonary embolism in 2 pts (one G5 event). No new safety signals were observed in Part A or B1. Duration of response (DoR), median PFS and median OS have not been reached for Part A. Last pt enrolled in Part B1 on 15 Sept 2021. Conclusions: The combination of D/TS + CAPOX represents a well-tolerated, active 1L combination, particularly for DKK1-high patients consistent with the proposed mechanism of action. Activity appears to be independent of PD-L1 status. Part B1 is aligned with biomarker enrichment and efficacy and biomarker data will be presented along with updated Part A efficacy data. Clinical trial information: NCT04363801. [Table: see text]

Targeted therapies are being increasingly used in clinical practice and trials. However, tumor heterogeneity among sites of metastatic disease can occur creating a conundrum when utilizing biomarker directed therapies. Here we demonstrate a patient with recurrent uterine carcinosarcoma whose local recurrence and metastatic recurrence had a varied response to paclitaxel in combination with DKN-01, a monoclonal antibody against DKK1, a modulator of Wnt/β-catenin and PI3K/AKT signaling pathways. This may be explained by differences in mutational profile found between the two sites. Our findings highlight the importance of analyzing tissue from the primary tumor as well as metastatic lesions, especially if there is a discrepancy in their response to treatment.

Therapeutic combinations targeting innate and adaptive immunity and predictive biomarkers of response in esophagogastric cancer (EGC) are needed. We assessed safety and clinical utility of DKN-01 (a novel DKK1-neutralizing IgG4 antibody) combined with pembrolizumab and retrospectively determined DKK1 tumoral expression as a biomarker. Patients with advanced EGC received intravenous DKN-01 (150 or 300 mg) on days 1 and 15 with pembrolizumab 200 mg on day 1 in 21-day cycles. Clinical response was assessed by RECIST v1.1. Association of tumoral DKK1 mRNA expression (H-score: high ≥ upper-tertile, low < upper-tertile) with response was assessed with PD-L1 levels as a covariate. Sixty-three patients received DKN-01 150 mg (n = 2) or 300 mg (n = 61) plus pembrolizumab. Common adverse events were fatigue, anemia, blood alkaline phosphatase elevation, aspartate aminotransferase elevation, and hyponatremia. Among evaluable anti-PD-1/PD-L1-naïve patients receiving DKN-01 300 mg and pembrolizumab, objective response rate (ORR) was 11.4% (5/44) and 18.5% (5/27) in patients with gastroesophageal junction or gastric cancer (GEJ/GC). Among response-evaluable anti-PD-1/PD-L1-naïve patients with GEJ/GC and known tumoral DKK1 expression, ORR was 50% in DKK1-high and 0% in DKK1-low patients, median PFS was 22.1 vs. 5.9 weeks (HR, 0.24; 95% CI, 0.08-0.67), respectively, and median OS was 31.6 weeks vs. 17.4 weeks (HR, 0.41; 95% CI, 0.16-1.07), respectively. Association of DKK1 expression with PFS was independent of PD-L1 expression (adjusted HR, 0.21; 95% CI, 0.06-0.69). DKN-01 combined with pembrolizumab was well tolerated with no new safety signals. Antitumor activity was enriched in anti-PD-1/PD-L1-naïve patients with GEJ/GC whose tumors expressed high DKK1.

Objectives: Dickkopf-1 (DKK1) modulates Wnt signaling, promotes tumor growth through a CKAP4-AKT signaling pathway and contributes to an immune suppressive tumor microenvironment. DKN-01 (D), a neutralizing DKK1 antibody has demonstrated safety and clinical activity in advanced gynecologic malignancies. Prior literature has reported an association of CTNNB1 mutations and an aggressive biology and shorter survival in endometrioid endometrial cancer. We previously demonstrated Wnt activating mutations were associated with higher DKK1 tumoral expression in advanced gynecologic malignancies. Methods: Pts with recurrent gynecologic cancers [endometrial (EEC), ovarian (EOC) and carcinosarcoma (MMMT)] were treated with D as monotherapy (mono) or in combination with paclitaxel (pac) in a phase 2 basket trial (NCT03395080) whereby ≥50% must have had a Wnt signaling alteration. Here we report on the subgroup of pts with Wnt activating mutations (CTNNB1, RNF43, APC). Clopper-Pearson confidence intervals were used to study the association of Wnt activating mutations with clinical benefit (CR, PR or SD); Kaplan-Meier estimates/Cox-PH models were used for analyses of progression free survival (PFS) and overall survival (OS). Results: Conclusions: D has single agent activity in a subgroup of pts with Wnt activating mutations, historically identified as a poor prognostic group, whereby they experienced greater clinical benefit and longer survival compared with pts without Wnt activating mutations. A notable finding was that all responding pts had PIK3CA mutations. This study is ongoing and updated results will be presented. Dickkopf-1 (DKK1) modulates Wnt signaling, promotes tumor growth through a CKAP4-AKT signaling pathway and contributes to an immune suppressive tumor microenvironment. DKN-01 (D), a neutralizing DKK1 antibody has demonstrated safety and clinical activity in advanced gynecologic malignancies. Prior literature has reported an association of CTNNB1 mutations and an aggressive biology and shorter survival in endometrioid endometrial cancer. We previously demonstrated Wnt activating mutations were associated with higher DKK1 tumoral expression in advanced gynecologic malignancies. Pts with recurrent gynecologic cancers [endometrial (EEC), ovarian (EOC) and carcinosarcoma (MMMT)] were treated with D as monotherapy (mono) or in combination with paclitaxel (pac) in a phase 2 basket trial (NCT03395080) whereby ≥50% must have had a Wnt signaling alteration. Here we report on the subgroup of pts with Wnt activating mutations (CTNNB1, RNF43, APC). Clopper-Pearson confidence intervals were used to study the association of Wnt activating mutations with clinical benefit (CR, PR or SD); Kaplan-Meier estimates/Cox-PH models were used for analyses of progression free survival (PFS) and overall survival (OS). D has single agent activity in a subgroup of pts with Wnt activating mutations, historically identified as a poor prognostic group, whereby they experienced greater clinical benefit and longer survival compared with pts without Wnt activating mutations. A notable finding was that all responding pts had PIK3CA mutations. This study is ongoing and updated results will be presented.

Abstract Background: Dickkopf-1 (DKK1) modulates Wnt signaling, promotes tumor growth through a CKAP4-AKT signaling pathway and contributes to an immune suppressive tumor microenvironment. DKN-01, a neutralizing DKK1 antibody has demonstrated safety and clinical activity in advanced gynecologic malignancies. We report response and survival outcomes in EEC patients (pts) treated with DKN-01 monotherapy by tumor genetics (Wnt signaling alterations and PI3K/AKT mutations). Methods: Pts with recurrent EEC were treated with DKN-01 as monotherapy (mono) or in combination with paclitaxel in a phase 2 basket trial (NCT03395080) whereby ≥50% must have had a Wnt signaling alteration. Here we report on EEC mono group only. Clopper-Pearson confidence intervals and logistic regression were used to study the association of Wnt signaling alterations with clinical benefit (CR, PR or SD) following DKN-01 monotherapy; Kaplan-Meier estimates/Cox-PH models were used for analyses of progression free survival (PFS) and overall survival (OS). Results: As of 30 December 2019, 29 EEC pts enrolled; 21 pts (72%) had Wnt signaling alterations [ARID1A most common (11 pts, 38%)] and 25 (86%) had PI3K/AKT mutations [PIK3CA in 13 pts (45%)]. Median number of prior therapies was 4 (range 1, 9); 20 pts (69%) had endometrioid histology and 19 pts (66%) had G2/G3 tumor grade at diagnosis. 26 pts were evaluable, 20 pts Wnt altered and 6 pts non-Wnt altered; 24 pts with and 2 pts without PI3K/AKT mutations. In the Wnt altered group, there was 1 cCR, 1 cPR, 8 SD (6 durable SD >120 days) and 10 PD compared with 0 responders, 1 SD and 5 PD in the non-Wnt altered group. In the 24 pts with PI3K/AKT mutations there was 1 cCR, 1 cPR, 8 SD (6 durable SD >120 days) and 14 PD compared with 1 SD and 1 PD in the 2 pts without PI3K/AKT mutations. The 2 responding pts had PI3KCA mutations in common. Probability of 6 month PFS/OS was 30% (95% CI:12.3, 50.1) and 70% (95% CI: 45.1, 85.3) for Wnt altered pts vs 18% (95% CI: 0.8, 53.8) and 50% (95% CI: 11.1, 80.4) for non-Wnt altered, respectively. Conclusions: DKN-01 has single agent activity in heavily pretreated EEC pts. EEC pts frequently had Wnt signaling alterations and PIK3/AKT mutations; greater clinical benefit was demonstrated in pts whose tumors had Wnt signaling alterations. This study is ongoing and updated results will be presented. Citation Format: Rebecca Arend, Cesar Castro, Erica Hamilton, Kristopher LyBarger, Linda Duska, Michael Kagey, William Bradley, Jasgit Sachdev, Cynthia A. Sirard, David M. O'Malley. Patients with recurrent epithelial endometrial cancers (EEC) and Wnt signaling alterations demonstrated greater clinical benefit when treated with DKN-01 monotherapy [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr PO036.

Dickkopf-1 (DKK1) modulates Wnt signaling and contributes to an immune suppressive tumor microenvironment. DKN-01 (D), a neutralizing DKK1 antibody, in combination with an anti-PD1 antibody, has demonstrated safety and clinical activity in advanced previously treated DKK1-high GEA. We report response and survival outcomes in GEA patients (pts) treated with D + tislelizumab (T) + capecitabine/oxaliplatin (CAPOX) as a first line therapy.