Fleming, Jason B.

AbstractIt has been challenging to target mutant KRAS (mKRAS) in colorectal cancer (CRC) and other malignancies. Recent efforts have focused on developing inhibitors blocking molecules essential for KRAS activity. In this regard, SOS1 inhibition has arisen as an attractive approach for mKRAS CRC given its essential role as a guanine nucleotide exchange factor for this GTPase. Here, we demonstrated the translational value of SOS1 blockade in mKRAS CRC. We used CRC patient‐derived organoids (PDOs) as preclinical models to evaluate their sensitivity to SOS1 inhibitor BI3406. A combination of in silico analyses and wet lab techniques was utilized to define potential predictive markers for SOS1 sensitivity and potential mechanisms of resistance in CRC. RNA‐seq analysis of CRC PDOs revealed two groups of CRC PDOs with differential sensitivities to SOS1 inhibitor BI3406. The resistant group was enriched in gene sets involving cholesterol homeostasis, epithelial−mesenchymal transition, and TNF‐α/NFκB signaling. Expression analysis identified a significant correlation between SOS1 and SOS2 mRNA levels (Spearman's ρ 0.56, p < 0.001). SOS1/2 protein expression was universally present with heterogeneous patterns in CRC cells but only minimal to none in surrounding nonmalignant cells. Only SOS1 protein expression was associated with worse survival in patients with RAS/RAF mutant CRC (p = 0.04). We also found that SOS1/SOS2 protein expression ratio >1 by immunohistochemistry (p = 0.03) instead of KRAS mutation (p = 1) was a better predictive marker to BI3406 sensitivity of CRC PDOs, concordant with the significant positive correlation between SOS1/SOS2 protein expression ratio and SOS1 dependency. Finally, we showed that GTP‐bound RAS level underwent rebound even in BI3406‐sensitive PDOs with no change of KRAS downstream effector genes, thus suggesting upregulation of guanine nucleotide exchange factor as potential cellular adaptation mechanisms to SOS1 inhibition. Taken together, our results show that high SOS1/SOS2 protein expression ratio predicts sensitivity to SOS1 inhibition and support further clinical development of SOS1‐targeting agents in CRC.

663 Background: GI malignancies continue to be a major cause of cancer related deaths, despite advances in therapy options. In pancreatic cancer, the presence of homologous recombination mutations (HRM) has been shown to confer increased sensitivity to platinum chemotherapy. However, the role of HRM mutations in other GI cancers remains to be determined. The focus of this study is to evaluate the prognostic nature of core and noncore HRM in nonpancreatic GI cancers. Additionally, we aim to understand the predictive nature of these mutations related to platinum exposure. Methods: This was a retrospective review of patients at Moffitt Cancer Center with a primary stage IV nonpancreatic GI cancer treated with platinum therapy. All patients had next generation sequencing and were in the Clinical Genomics Action Committee database between 1/1/2013 and 11/1/2020. All patients had either a core HRM (BRCA1, BRCA2, PALB2) or noncore HRM (such as ATM, ATR, BARD1, BRIP1, FANCA, NBN, and RAD51). Patients were grouped into core HRM vs. noncore HRM. Response was stratified between responders (complete response and partial response) vs. non responders (stable disease and progressive disease), based on RECIST criteria. Progression free survival and overall survival were estimated using Kaplan-Meier method, and the log-rank test was used to assess the difference in progression free survival (PFS) and overall survival (OS) by HRM status and type of platinum therapy used. Results: There were 72 patients included in the study: the majority of patients were male (65.3%) and Caucasian (87.5%). Twenty-one (29.2%) patients had a core HRM and 51 (70.8%) had a noncore HRM. There was no significant difference in response rate between patients with core HRM and patients with noncore HRM for evaluable patients (n = 66): 20.0% of patients with core HRM vs. 21.7% of patients with noncore HRM demonstrated a response to platinum therapy (p = 0.41). An improved OS was noted for patients with core HRM vs. those with noncore HRM at 68.9 vs. 24.3 months (p = 0.019). An improved PFS was also seen in patients with core HRM at 10.4 months vs. 6.3 months with noncore HRM (p = 0.027). There was no difference in PFS based on type of platinum therapy used (oxaliplatin vs. carboplatin vs. cisplatin), while an improved OS was noted for patients treated with oxaliplatin vs. carboplatin vs. cisplatin at 43.1 vs. 28.2 vs. 16.0 months (p = 0.011). Conclusions: Our study demonstrated that in stage IV nonpancreatic GI malignancies treated with platinum therapy, patients with core HRM had a greater OS and PFS compared to those with noncore HRM, suggesting a potential prognostic and predictive role of these mutations. Further studies are needed to confirm our findings.

573 Background: Pre-operative radiotherapy (RT) for PA has the potential to reduce positive surgical margin rates and increase pathologic tumor response, which has been associated with improved survival. Increasing the BED can improve local control and overall survival for patients with unresectable PA. Use of stereotactic body radiation therapy (SBRT) to achieve a higher BED has been limited by toxicity to adjacent radiosensitive structures, but this can be mitigated by MRgRT. We describe our use of MRgRT prior to potentially curative resection of localized PA. Methods: We performed a single institution retrospective analysis of all patients with localized PA who received high BED SBRT on the MR Linac followed by surgical resection with curative intent. Toxicity was evaluated according to Common Terminology Criteria for Adverse Events, version 5.0. Tumor response was evaluated according to the College of American Pathologists tumor regression grading criteria (CAP-TRG), ranging from CAP 0 indicating pathologic complete response to CAP grade 3 indicating no response. Ordinal logistic regression model was used to assess the association between time from RT to surgery and TRG. Follow up included MRI or CT scans at least every three months. Results: We analyzed 26 patients with borderline resectable (80.8%), locally advanced (11.5%), and resectable (7.7%) tumors who received high BED MRgRT followed by surgical resection. Median age at diagnosis was 68 years (34 - 86). Most patients received chemotherapy (80.8%) prior to RT, with 81% of these receiving FOLFINIRNOX and 19% receiving gemcitabine/nab-paclitaxel. All patients received MR-guided high BED SBRT to a median dose of 50 Gy (40 - 50) in 5 fractions. On-table adaptive replanning was performed in 88% of patients, with 74% having all 5 fractions adapted. No acute grade 2+ toxicity associated with RT was observed. The median time to resection was 50 days (37 – 115), and the procedure types included: Whipple (69%), distal (23%), or total pancreatectomy (8%). The R0 resection rate was 96% and no perioperative deaths occurred within 90 days. Complete (0) or near-complete (1) pathologic response was observed in 35% of cases and the time from RT to surgery was positively associated with TRG (R2= 0.22, p = 0.0003). The median follow-up after RT was 16.5 months (3.9- 26.2) during which 9 patients recurred, and 3 patients died of disease. The derived median progression-free survival from RT was 13.2 months. Conclusions: These initial pathology outcomes following high BED MR-guided SBRT are encouraging and suggest that the time from SBRT to surgical resection is associated with response. This finding is consistent with results from other preoperative GI tumor sites and results from prospective studies using high BED SBRT with MRI guidance in combined modality therapy against PA are eagerly awaited.

174 Background: Colorectal cancer (CRC), while one of the most common cancer diagnoses, can behave heterogeneously based on molecular characteristics. A subset of patients (pts) with CRC are characterized with mismatch repair deficiency (MMR-d), these pts exhibit encouraging responses to immunotherapy. The predictive nature of various factors, such as BRAF status, age, and MMR-D protein loss type, have been investigated in pts with MMR-d CRC. However, the prognostic role of these factors has not been well established. The purpose of this study was to identify characteristics that influence survival in MMR-d mCRC. Methods: This study evaluated pts with MMR-d mCRC in the Flatiron database. Overall survival (OS) was determined from date of diagnosis of stage IV disease to date of death and stratified based on age greater than or less than 50 years, BRAF mutation status, RAS mutation status, and type of MMR gene loss. For statistical analysis, the Chi-Square test was implemented to determine the prognostic significance of clinical and molecular features. Univariate and multivariate analyses were determined through the Cox regression model. Results: There were 1,101 pts in the study. The majority of pts were older than 50 (79.7%), Caucasian (75%), and had ECOG 0-1 (83.4%). Among the 803 pts with known BRAF status, 44.3% (n=356) had BRAF V600E mutation and 55.7% (n=447) were BRAF wildtype. Pts with BRAF V600E mutation had OS of 18.9 months vs. 33.2 months for pts with wild type BRAF (HR 1.52, 95% CI: 1.25-1.86, p<0.001). Pts older than 50 had a lower median OS vs. those who were ≤50 at 21.4 months vs. 38.7 months (HR 1.66, 95% CI: 1.33-2.07, p<0.001). When comparing MSH2/MSH6 mutations to MLH1/PMS2, a trend towards improved OS was seen with median survival of 35.2 months vs. 22.7 months, respectively (HR 0.79, 95% CI: 0.61-1.02, p=0.067). On multivariate analysis, BRAF mutation and older age continued to be associated with differences in survival, while KRAS mutation and specific MMR gene loss did not. Conclusions: BRAF V600E mutation and age greater than 50 are associated with decreased survival for pts with MMR-D mCRC. KRAS mutations and specific MMR alterations are not associated with differences in survival.

Abstract Obesity is a risk factor for Pancreatic Ductal Adenocarcinoma (PDAC), but the molecular mechanisms involved are unclear. Oncogenic mutation of K-Ras occurs early and nearly universally in patients with this disease. However, recent evidence indicates that oncogenic Ras is not fully active and for activity to surpass the threshold required to engage a Ras-inflammation feed-forward loop, it requires a stimulus. We hypothesized that high-fat intake acts as an inflammatory stimulus, increasing K-Ras activity and that cyclooxygenase -2 (COX2) expression is required in the inflammatory loop. LSL-K-Ras mice were crossed with elastase-CreER (acinar cell-specific) or Pdx1-Cre (pancreatic cell-specific) to “knock-in” expression of oncogenic K-Ras. Additionally, acinar cell-specific -Ras mice were crossed with COX2 conditional knockout mice. All mice were fed isocaloric diets with different amounts of fat and a COX2 inhibitor was administered to some acinar cell-specific -Ras mice. Pancreata were analyzed for Ras activity, Phospho-ERK levels, inflammation, fibrosis, PanIN and PDAC development. We observed that consumption of a high fat diet (HFD) led to increased K-Ras activity, PanIN formation, fibrotic stroma and PDAC development compared to a control diet. Additionally, we observed a significant reduction in the survival of mice fed a HFD. Genetic deletion of COX2 in acinar cells and COX2 systemic inhibition prevented the HFD-induced effects in acinar cell-specific -Ras mice. These findings indicated that a HFD stimulates activation of oncogenic K-Ras and initiates an inflammatory feed-forward loop requiring the expression of COX2 leading to pancreatic inflammation, fibrosis, PanINs and PDAC. This mechanism may explain the PDAC risks associated with consumption of a HFD. Citation Format: Bincy Philip, Christina L. Roland, Jarek Daniluk, Yan Liu, Deyali Chatterjee, Sobeyda Berenice Gomez, Baoan Ji, Huang Haojie, Huamin Wang, Jason B. Fleming, Craig D. Logsdon, Zobeida Cruz-Monserrate. High fat triggers oncogenic K-Ras activity and a COX2 dependent feed-forward loop to induce pancreatic ductal adenocarcinoma development. [abstract]. In: Proceedings of the Twelfth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2013 Oct 27-30; National Harbor, MD. Philadelphia (PA): AACR; Can Prev Res 2013;6(11 Suppl): Abstract nr C61.

Abstract Purpose: Pancreatic ductal adenocarcinoma (PDAC) is lethal cancer whose primary tumor is characterized by dense composition of cancer cells, stromal cells, and extracellular matrix (ECM) composed largely of collagen. Within the PDAC tumor microenvironment, activated pancreatic stellate cells (PSC) are the dominant stromal cell type and responsible for collagen deposition. Lumican is a secreted proteoglycan that regulates collagen fibril assembly. We have previously identified that the presence of lumican in the ECM surrounding PDAC cells is associated with improved patient outcome after multimodal therapy and surgical removal of localized PDAC. Experimental Design: Lumican expression in PDAC from 27 patients was determined by IHC and quantitatively analyzed for colocalization with PSCs. In vitro studies examined the molecular mechanisms of lumican transcription and secretion from PSCs (HPSCs and HPaSteC), and cell adhesion and migration assays examined the effect of lumican on PSCs in a collagen-rich environment. Results: Here we identify PSCs as a significant source of extracellular lumican production through quantitative IHC analysis. We demonstrate that the cytokine, TGF-β, negatively regulates lumican gene transcription within HPSCs through its canonical signaling pathway and binding of SMAD4 to novel SBEs identified within the promoter region. In addition, we found that the ability of HPSCs to produce and secrete extracellular lumican significantly enhances HPSCs adhesion and mobility on collagen. Conclusions: Our results demonstrate that activated pancreatic stellate cells within PDAC secrete lumican under the negative control of TGF-β; once secreted, the extracellular lumican enhances stellate cell adhesion and mobility in a collagen-rich environment. Clin Cancer Res; 22(19); 4934–46. ©2016 AACR.

Abstract Purpose: To evaluate the relevance between lumican expression patterns and the clinical course of patients with pancreatic ductal adenocarcinoma (PDAC), and to investigate the role of lumican in PDAC progression. Experimental Design: One hundred thirty-one patient tumors were chosen for tissue microarray staining, and Cox regression analysis was used to test the associations between lumican expression and clinical, pathologic, and oncologic outcomes in all patients. Primary PDAC cells and recombinant human lumican protein were used to establish a working model to mimic the in vivo interactions between stromal lumican and PDAC cells. Using this model, we tested the effects of lumican on EGFR signaling via Akt and hypoxia-inducible factor-1α (HIF1α) and its subsequent influence on glucose consumption, lactate production, intracellular ATP, and apoptotic cell death. Results: Lumican was present in the stroma surrounding PDAC cells in roughly one-half of primary tumors and the direct xenografts. Patients with stromal lumican were associated with a profound reduction in metastatic recurrence after surgery and 3-fold longer survival than patients without stromal lumican. In PDAC cells, extracellular lumican reduced EGFR expression and phosphorylation through enhanced dimerization and internalization of EGFR and the resultant inhibition of Akt kinase activity. Lumican also reduced HIF1α expression and activity via Akt. PDAC cells with enhanced HIF1α activity were resistant to lumican-induced inhibition of glucose consumption, lactate production, intracellular ATP, and apoptosis. Conclusions: There is a positive association between stromal lumican in primary PDAC tumors and prolonged survival after tumor resection. Lumican plays a restrictive role in EGFR-expressing pancreatic cancer progression. Clin Cancer Res; 20(24); 6529–40. ©2014 AACR.