Citations

3077 Background: ATR protein kinase is activated by replication stress and recruited to stalled forks or single strand DNA defects in various cancers. The topoisomerase-I (Top1) inhibitor irinotecan induces DNA damage. The ATR inhibitor BAY1895344 (elimusertib) has demonstrated cytotoxic potential in SCLC and GI cancer xenografts when combined with Top1 inhibitors . Methods: This phase Ia trial assessed elimusertib in combination with irinotecan in adult patients with refractory advanced solid tumors for whom irinotecan can be considered standard care. Patients with previous irinotecan exposure were excluded. Two dosing schedules were used: 1) Biweekly - irinotecan IV (starting at 150 mg/m2) D1 + elimusertib (starting dose 20 mg PO BID) D1,D2 (cycle=14 days); 2) Weekly - irinotecan (starting at 50 mg/m2) IV on D1,8,15 with elimusertib (starting at 20 mg PO daily) on D2,D3,D9,D10 and D16,D17 (cycle=21 days). Dose escalation utilized a 3+3 design. Primary objectives were to assess safety and tolerability and estimate the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D). Secondary objectives included estimating pharmacokinetic (PK) profiles and assessing anti-tumor activity. Results: A total of 21 patients were enrolled in dose escalation (N=9 [Biweekly] and N=12 [Weekly], median age 58 and 2 lines of prior therapy. For the Biweekly cohort: 3/3 patients enrolled at dose level (DL) 1 experienced hematologic dose-limiting toxicity (DLT); 6 patients received DL-1 without any DLTs. The weekly regimen escalation comprised of 12 patients: 6 enrolled in DL1 with 2/6 having hematologic DLT and 5/6 unable to complete ≥75% of cycle 1 dosing; 6 enrolled in DL-1 with no DLTs observed. Notable grade 3+ treatment-related adverse events and summary best response are summarized (Table 1). The majority of evaluable patients in both schedules had initial disease control (56% [biweekly] and 67% [weekly]). One confirmed partial response was seen in the biweekly RP2D. Median progression-free survival was 2.1 mo [biweekly] and 2.5 mo [weekly]. PK results will be presented at time of meeting. Conclusions: Both RP2D and MTD of elimusertib in combination with irinotecan were reached for both dosing schedules: irinotecan 150 mg/m2 IV D1 + elimusertib 10 mg BID PO D1,D2 (biweekly) and irinotecan 25 mg/m2 IV on D1 + elimusertib (20 mg PO daily) on D2,D3 (weekly). Dose escalation was notably limited by myelotoxicity. Due to sponsor decision, the study was halted prior to planned expansion but the concept of ATR + topo I combination remains scientifically relevant. Clinical trial information: NCT04514497 . [Table: see text]

3076 Background: Ataxia telangiectasia and Rad3-related (ATR) protein kinase is activated by replication stress and recruited to stalled forks or single strand DNA abnormalities in various cancers. The topoisomerase-I (Top1) inhibitor topotecan induces DNA damage. The ATR inhibitor BAY 1895344 (elimusertib) has demonstrated cytotoxic potential in small cell lung cancer and gastrointestinal cancer xenografts when combined with Top1 inhibitors . Methods: This is phase Ia study of elimusertib combined with topotecan in adult patients with refractory advanced solid tumors for whom topotecan can be considered as part of standard care. Patients with previous topotecan exposure were excluded. The study combination was assessed starting at Topotecan 1 mg/m2 IV (D1-D5) plus elimusertib 20 mg BID (D2, D5) (Cycle=21 days). Dose escalation utilized a 3+3 design. Primary objectives were to assess safety and tolerability and estimate the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) of the combination. Secondary objectives included estimating pharmacokinetic (PK) profiles and assessing anti-tumor activity of the combinations. Results: Eight patients were treated in dose escalation. Participants were a median of 63 years old and had received 2 median lines of previous therapy. The initial two patients enrolled into dose level (DL) 1 had dose-limiting toxicities with one of patient experiencing respiratory failure and cardiac arrest in setting of pancytopenia related to study drug. Six patients were subsequently enrolled in and received DL-1 (elimusertib decreased from 20 mg BID to 20 mg Daily) and no DLTs were observed. Notable grade 3+ treatment-related adverse events and summary best response are summarized in Table. Disease control rate was 43% among evaluation patient including one unconfirmed partial response. Median progression-free survival in the RP2D cohort was 3.45 months. PK studies are in process and results will be presented at time of meeting. Conclusions: RP2D and MTD was established for elimusertib in combination with Topotecan: Topotecan 1 mg/m2 IV [D1-D5] plus elimusertib 20 mg Daily [D2, D5] every 3 weeks. Dose escalation was notably limited by myelotoxicity. Due to sponsor decision, the study was halted prior to planned expansions cohorts but the concept of ATR + topo I inhibition remains relevant. Clinical trial information: NCT04514497 . [Table: see text]

The NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for Neuroendocrine and Adrenal Gland Tumors focus on the diagnosis, treatment, and management of patients with neuroendocrine tumors (NETs), adrenal tumors, pheochromocytomas, paragangliomas, and multiple endocrine neoplasia. NETs are generally subclassified by site of origin, stage, and histologic characteristics. Appropriate diagnosis and treatment of NETs often involves collaboration between specialists in multiple disciplines, using specific biochemical, radiologic, and surgical methods. Specialists include pathologists, endocrinologists, radiologists (including nuclear medicine specialists), and medical, radiation, and surgical oncologists. These guidelines discuss the diagnosis and management of both sporadic and hereditary neuroendocrine and adrenal tumors and are intended to assist with clinical decision-making. This article is focused on the 2021 NCCN Guidelines principles of genetic risk assessment and counseling and recommendations for well-differentiated grade 3 NETs, poorly differentiated neuroendocrine carcinomas, adrenal tumors, pheochromocytomas, and paragangliomas.

TPS3161 Background: The p53 pathway has been implicated in antitumor immunity, including antigen presentation and T-cell proliferation. Loss of p53 function can increase resistance to immunotherapy across many tumor types. Eprenetapopt (eprenet) is a small molecule that stabilizes the folded structure of p53, resulting in activation of mutant p53 and stabilization of wild-type (WT) p53. It also targets the cellular redox homeostasis, resulting in induction of apoptosis in tumor cells. In vivo, mice carrying supernumerary copies of the TP53 gene harbor a pro-inflammatory tumor microenvironment, an effect recapitulated in TP53 normal-copy mice treated with eprenetapopt. Combining eprenetapopt and anti-PD1 or anti-CTLA4 therapy resulted in enhanced tumor growth inhibition and improved survival in TP53 WT mice inoculated with B16 melanoma and MC38 colon adenocarcinoma cells . Based on these results, we hypothesized that eprenet-induced p53 stabilization may augment response to immunotherapy. To test this hypothesis, we are conducting a phase 1b/2 study of eprenet in combination with pembrolizumab (eprenet+pembro) in pts with solid tumors. Methods: The primary objectives are to determine the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) and to assess the safety and tolerability of eprenet+pembro in pts with advanced solid tumors. The secondary objectives are to estimate the anti-tumor activity and to describe the pharmacokinetics of the combination. Exploratory objectives include assessing predictive and pharmacodynamic markers of response. The study includes a safety lead-in with a 3+3 dose de-escalation design for pts with advanced solid tumors with known tumor TP53 mutation status ( TP53 WT is acceptable) (max 18 pts), followed by expansion cohorts in pts with NSCLC, gastric/GEJ and urothelial cancer (max 100 pts). In expansion, pts with urothelial and gastric cancers must be naïve to anti-PD-1/ L1 therapy. Eprenet is given IV once daily on Days 1–4 while pembro is administered on Day 3 of each 21-day cycle. The RP2D of eprenet+pembro is considered the dose at which ≤ 1 of 6 pts in a cohort has a dose-limiting toxicity (DLT). Primary endpoints are occurrence of DLTs, adverse events (AEs) and serious AEs with eprenet+pembro. Key secondary endpoints are best objective response, progression free survival and overall survival. Exploratory endpoints include gene mutations by next generation sequencing (including TP53), mRNA expression, multiplex immunohistochemistry and transcriptomics, multiplex flow cytometry on peripheral blood mononuclear cells and cytokines in serum. Continuous monitoring of toxicity will be conducted. The trial opened in May 2020 and is actively enrolling patients. Clinical trial information: NCT04383938.

Abstract Background Immune checkpoint inhibitor (ICI) therapy is highly effective in metastatic mismatch repair-deficient (MMR-D) colorectal cancer (CRC). In this study, we evaluated molecular and clinical predictors of ICI response in MMR-D CRC. Materials and Methods Patient databases at four cancer institutions were queried. The Fisher exact test was performed to test the association of clinical and molecular markers. The Kaplan-Meier method was used to estimate progression-free survival (PFS) and compared by the log-rank test. Twelve- and 24-month PFS rates were compared by the Z test. Results A total of 60 patients with CRC with MMR-D/microsatellite instability-high who previously received ICIs were identified. Patients with liver metastasis had a lower overall response rate as compared with other sites of metastasis (36.4% vs. 68.7%; p = .081). Patients with MLH1/PMS2 loss had worse 1-year and 2-year PFS rates compared with patients with MSH2/MSH6 loss (84.2% vs. 57.8% and 78.2% vs. 54.2%, respectively; p < .001). There were improved 1-year and 2-year PFS rates in patients with wild-type BRAF when compared with patients with BRAF V600E mutation (73.3% vs. 40%, and 73.3% vs. 26.7%; respectively; p < .001). Patients aged >65 had significantly worse PFS rates as compared with patients aged ≤65 (p < .001). Conclusion BRAF V600E mutation, MLH1 and/or PMS2 loss, as well as age >65 years and liver metastasis, may be predictive of duration of ICI response in patients with MMR-D CRC. Larger cohorts are needed to confirm our findings. Implications for Practice The results of this study reveal clinically important biomarkers that potentially predict immune checkpoint inhibitor response in patients with mismatch repair-deficient colorectal cancer.

225 Background: ICIs induce durable responses in dMMR CRC patients. However, clinical and molecular biomarkers of response to ICIs have not been well-established. In this study, we investigated impact of specific MMR gene loss, BRAF V600E mutation and clinical characteristics of pts on clinical outcomes of ICIs. Methods: Pts were eligible if they had confirmed dMMR CRC by IHC or MSI-H by PCR and received ICIs between 01/01/2012 and 05/01/2019 at Winship Cancer Institute of Emory University, Mayo Clinic, Vanderbilt or Stanford University. Due to the functional dependency, the groups were categorized as protein loss of MLH1+PMS2 vs MSH2+MSH6. Log-rank test, Cox hazard model and Fisher’s exact test were used for survival outcomes, the best response and the distribution of variables among the subgroups. Results: A total of 66 pts with dMMR CRC were identified and BRAF status was available for 41 pts. ORRs in MLH1+PMS2 and MSH2+MSH6 groups were 72.9% and 56.5% respectively (P = 0.189). At 2 years, PFS rates were 55.6% and 78.2% for MLH1+PMS2 and MSH2+MSH6 groups respectively (P < 0.001). Pts with BRAF V600E mutations had significantly worse outcomes as compared to pts with wild-type BRAF (2-year PFS rate of 35.0% and 73.3% respectively; P < 0.001). Notably pts < 65 had better 2-year disease control rates when compared to > 65 (71.1% and 41.5% respectively; P < 0.001). We also observed worse 2-year PFS rates in pts with liver metastases (P = 0.014). CRC side and tumor volume did not impact 2-year PFS rates in our cohort. Conclusions: Our data suggest that pts with loss of function in MSH2+MSH6 may have better 2 year-PFS rates compared pts with MLH1+PMS2 even though ORR favored MLH1+PMS2 group suggesting that ORR may not reflect the durability of ICI response in dMMR CRC patients. Consistently, pts with BRAF V600E mutation which is associated with MLH1 promoter methylation had significantly worse 2-year PFS rates. Overall, our findings suggest that BRAFV600E mutation, the affected MMR proteins, pt age, and site of metastasis may impact durability of ICI response in dMMR CRC patients.

e15029 Background: ICIs induce durable responses in dMMR CRC pts with overall response rates (ORR) of 30-50%. Even though the loss of expression of any MMR gene predicts ICIs response, it is unknown if ORRs are similar across all MMR genes (MLH1, PMS2, MSH2, and MSH6). In this study, we analyzed the impact of each specific MMR gene loss and clinical characteristics of pts with best response to ICIs. Methods: Pts were eligible if they had confirmed dMMR CRC by IHC or microsatellite instability-high (MSI-H) by PCR, and received ICIs between 01/01/2012 and 10/01/2018 at Winship Cancer Institute of Emory University, Mayo Clinic or Vanderbilt University Medical Center. Due to the pattern of frequent concurrent loss and functional dependency, the groups were categorized as MLH1 ±PMS2 vs. MSH2 ±MSH6. Cox proportional hazard model and Fisher’s exact test were used for the best response and the distribution of variable among the subgroups. Results: A total of 45 pts with dMMR CRC were identified. ORRs in MLH1 ±PMS2 and MSH2 ±MSH6 groups were 68% and 57.1% respectively without statistical difference (Table). Pts with age < 50 and 50-65 years old had better ORRs compared to pts with age >65 (58.3%, 85.7% and 42.1% respectively, P=0.036). Left-sided tumors had a trend toward higher ORRs compared to right-sided tumors (83.3% vs 51.5% P=0.086). Gender and BRAF status were not predictors of response. BRAF mutations were more common in right-sided tumors (29.6% vs 11.1% respectively) and in older patients. Conclusions: Our data suggest that MSI-H CRC pts aged 50-65 treated with ICIs, have improved ORR compared to pts > 65; pts with left-sided tumors have a trend toward improved ORR compared to those with right sided tumors. [Table: see text]