Netrin-1 feedforward mechanism promotes pancreatic cancer liver metastasis via hepatic stellate cell activation, retinoid, and ELF3 signaling

The biology of metastatic pancreatic ductal adenocarcinoma (PDAC) is distinct from that of the primary tumor due to changes in cell plasticity governed by a distinct transcriptome. Therapeutic strategies that target this distinct biology are needed. We detect an upregulation of the neuronal axon guidance molecule Netrin-1 in PDAC liver metastases that signals through its dependence receptor (DR), uncoordinated-5b (Unc5b), to facilitate metastasis in vitro and in vivo. The mechanism of Netrin-1 induction involves a feedforward loop whereby Netrin-1 on the surface of PDAC-secreted extracellular vesicles prepares the metastatic niche by inducing hepatic stellate cell activation and retinoic acid secretion that in turn upregulates Netrin-1 in disseminated tumor cells via RAR/RXR and Elf3 signaling. While this mechanism promotes PDAC liver metastasis, it also identifies a therapeutic vulnerability, as it can be targeted using anti-Netrin-1 therapy to inhibit metastasis using the Unc5b DR cell death mechanism.

Abstract 1286: UNC5B promotes EMT and metastasis of pancreatic adenocarcinomas and expresses different isoforms that impact sensitivity to Netrin-1 blockade

The axonal guidance receptor UNC5B is considered to be a tumor suppressor because it promotes apoptosis in the absence of its protein ligand, NTN1. But we find that UNC5B is not a tumor suppressor of pancreatic ductal adenocarcinomas (PDAC), and instead promotes metastasis. In TCGA data, UNC5B expression associates with poor patient outcome. In vivo, pancreatic cancer metastasis was completely eliminated by knocking out UNC5B from the genetically engineered KPC mouse model of PDACs, and was reduced upon knockout of UNC5B in a splenectomy model of liver metastasis. An inhibitor of NTN1, NP137, also reduced metastasis in vivo. In vitro, knockout of UNC5B from mesenchymal pancreatic cell lines was sufficient to reduce many metastatic traits including invasiveness, EMT, and aerobic glycolysis. YAP1 is a known target of UNC5B and was overexpressed in high UNC5B expressing cell lines, which were sensitive to the YAP1 inhibitor CA3. NP137 is currently in clinical trial for several tumor types and we have been investigating which patients might respond best to this drug. Using an antibody (D9M7Z) that recognizes an epitope in UNC5B that overlaps with the caspase-3 cleavage site that is critical for UNC5B's apoptotic functions, we found two isoforms in murine and human PDACs: one isoform that contains the caspase-3-containing epitope as well as a previously-unreported isoform that to lack it. Cells expressing the caspase-3 site were much more sensitive to NP137. We also discovered genetic alterations in patient samples that induce expression of UNC5B. For instance, UNC5B was recurrently amplified in PDACs and these amplifications were highly focal to the UNC5B locus; also, UNC5B expression was increased by mutations of ARID1A, a component of the SWI/SNF transcription complex that is recurrently mutated in pancreatic adenocarcinomas. ARID1A mutations caused cell lines to become mesenchymal, but the cells returned to an epithelial phenotype upon knockout of UNC5B. In current and future clinical trials, NP137 may particularly benefit patients with tumors that harbor mutations in ARID1A or ARID1B, focal amplifications of UNC5B, and/or high expression of the caspase-3-containing isoform of UNC5B.

Citation Format: Chris R. Harris, Orjola Prela, Lan Wang, Anthony Casabianca, Wade Narrow, Zachary Sechrist, Tracy Withers, Cory Shields, Asra Asad, Aram Hezel, Darren Carpizo. UNC5B promotes EMT and metastasis of pancreatic adenocarcinomas and expresses different isoforms that impact sensitivity to Netrin-1 blockade [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 1286.

Abstract B021: The axon guidance receptor UNC5B is a driver of pancreatic cancer metastasis

Axon guidance pathways have often been linked to tumorigenesis by informatics analyses, but their roles in tumorigenesis are not well understood at a functional level. Here we show that axon guidance receptor UNC5B and its ligand, NTN1, promote the metastasis of pancreatic ductal adenocarcinomas (PDACs) by reducing anoikis and by promoting a mesenchymal phenotype. In vivo, removal of two floxed UNC5B alleles eliminated PDAC metastasis in the genetically engineered KPC mouse model, and also reduced metastasis by xenografted PDAC cell lines. PDAC metastasis also decreased upon treatment of animals with NP137, an antibody that targets NTN1. In vitro, deletion of UNC5B from pancreatic adenocarcinoma cell lines reduced invasiveness, and was sufficient to convert PDAC cell lines from an epithelial to a mesenchymal state. UNC5B also increased YAP1 expression but decreased anoikis; anoikis could then be restored by treatment with the YAP1 inhibitor CA3. Clinically, UNC5B expression associated with poor outcomes in patients with pancreatic adenocarcinomas. UNC5B and NTN1 expression increased upon truncation of the SWI/SNF component ARID1A, which is recurrently mutated in PDACs. Highly focal amplifications of UNC5B were also observed in some patient samples, and were mutually exclusive with mutations in ARID1A or ARID1B. NP137 is currently in clinical trials for various cancers, and may benefit pancreatic adenocarcinoma patients, particularly those with UNC5B amplifications or with ARID1A/ARID1B mutations.

Citation Format: Chris Harris, Anthony Casabianca, Zach Sechrist, Cory Shields, Wade Narrow, Tracy Withers, Crissy Dudgeon, Mike O'Dell, Aram Hezel, Darren Carpizo. The axon guidance receptor UNC5B is a driver of pancreatic cancer metastasis [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B021.

Abstract B058: The lincRNA Neat1 controls SWI/SNF occupancy to retain ductal cell identity in the pancreas

Pancreatic ductal adenocarcinoma (PDAC) is the 4th leading cause of cancer deaths in the US and among the most fatal. Cancer originating from the ductal compartment often leads to the emergence of the highly aggressive basal subtype of PDAC. Defining the cellular and molecular origins of basal subtype PDAC would greatly improve our ability to devise strategies to treat patients with this aggressive form of PDAC. Towards this end, we have discovered that loss of the long intergenic non-coding RNA (lincRNA) Neat1 promotes ductal cell plasticity, dramatically inducing the formation of duct-derived preneoplastic lesions known as intraductal papillary mucinous neoplasms (IPMNs), and increasing the likelihood of basal subtype PDAC. Neat1 deficiency has a profound impact on chromatin organization and on the distribution of the SWI/SNF chromatin remodeling complex at the chromatin, suggesting that Neat1 maintains ductal cell identity via impacting SWI/SNF function. Probing for Brg1, a core component of the SWI/SNF complex, we demonstrated that Neat1 loss leads to decreased SWI/SNF binding at enhancer regions. This idea is further supported by the phenotypic similarities between mice deficient for Neat1 and Arid1a. We thus hypothesize that Neat1 and SWI/SNF are critical for the maintenance of ductal cell identity in the pancreas via controlling SWI/SNF-dependent enhancer activity and that loss of Neat1 increases ductal cell transformation and thus facilitates IPMN formation and progression to basal subtype PDAC. These studies will reveal both the biological role and mechanistic underpinnings of the lincRNA Neat1 in relationship with the SWI/SNF chromatin remodeling complexes. Our data suggest that Neat1 or SWI/SNF loss-of-function predisposes pancreatic ductal cells towards the most aggressive subtype of PDAC, laying critical groundwork for development of new diagnostic tools and therapeutic targets.

Citation Format: Emily Berry, Zamira Guerra Soares, Jennifer Twardowski, Wenjia Wang, Aram Hezel, Stephano S. Mello. The lincRNA Neat1 controls SWI/SNF occupancy to retain ductal cell identity in the pancreas [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B058.

Prevalence of and factors associated with treatment modification at first cycle in older adults with advanced cancer receiving palliative treatment

INTRODUCTION

Treatment toxicities are common in older adults with cancer and consequently, treatment modifications are sometimes considered. We evaluated the prevalence and factors associated with treatment modifications at the first cycle in older patients receiving palliative systemic treatment.

METHODS

Patients (n = 369) from the GAP 70+ Trial (NCT02054741; PI: Mohile) usual care arm were included. Enrolled patients were aged 70+ with advanced cancer and ≥ 1 Geriatric Assessment (GA) domain impairment. Treatment modification was defined as any change from National Comprehensive Cancer Network guidelines or published clinical trials. Baseline variables included: 1) sociodemographic factors; 2) clinical variables; 3) GA domains; and 4) physician beliefs about life expectancy. Bivariate analyses and multivariable cluster-weighted generalized estimating equation model were conducted to assess the association of baseline variables with cycle 1 treatment modifications.

RESULTS

Mean age was 77.2 years (range: 70-94); 62% had lung or gastrointestinal cancers, and 35% had treatment modifications at cycle 1. Increasing age by one year (odds ratio (OR) 1.1, 95% confidence interval [CI] 1.0-1.2), receipt of ≥second line of chemotherapy (OR 1.8, CI 1.1-3.0), functional impairment (OR 1.6, CI 1.1-2.3) and income ≤$50,000 (OR 1.7, CI 1.1-2.4) were independently associated with a higher likelihood of cycle 1 treatment modification.

CONCLUSION

Treatment modifications occurred in 35% of older adults with advanced cancer at cycle 1. Increasing age, receipt of ≥second line of chemotherapy, functional impairment, and lower income were independently associated with treatment modifications. These findings emphasize the need for evidence-based regimens in older adults with cancer and GA impairments.

Abstract PR-006: Spatially resolved, single cell assessment of pancreatic ductal adenocarcinoma expression subtypes reveals mixed and hybrid basal-classical marker expression with prognostic significance and discrete spatial localization

Background: Pancreatic adenocarcinoma (PDAC) is a rapidly progressive disease, with few molecular markers that stratify patients for survival time or treatment response. Bulk transcriptional analyses of PDAC have identified two major transcriptional subtypes, classical and basal, the latter of which is associated with worse overall survival and limited sensitivity to chemotherapy. However, spatial localization and classical-basal heterogeneity are incompletely understood at the individual cell level within a bulk tumor. Design: We built and validated a multiplex immunofluorescence assay that employs three classical and two basal subtype markers to measure subtype composition at spatially resolved, single cell resolution in a multi-institutional cohort of formalin-fixed paraffin-embedded primary pancreatic cancer resection specimens. Using digital image analysis, supervised machine learning, and Cox proportional hazards regression, we analyzed protein-level classical-basal subtype landscape, cell localization, and outcome associations. Results: Subtyping data were successfully generated for 1.2 million tumor cells across 290 resected tumor specimens (median 3579 cells/tumor). Tumor level analysis of cellular composition revealed that 88% of tumors are “mixed”, harboring any number of both classical and basal cells, whereas tumors composed only of classical or basal cells represented 11% and 1.4% of cases, respectively. In addition to pure classical and basal cells, we identified “hybrid cells” co-expressing basal and classical markers in 79% of cases, ranging in abundance from <1% to 41% of cells within a given tumor. Spatial analysis at an individual gland level revealed that 62% of hybrid cells are located within glands harboring a mixture of both classical and basal cells, even though such mixed glands are substantially less common than purely basal or classical glands. As shown with previous bulk RNAseq datasets, multivariable Cox proportional hazard regression demonstrated that increasing basal cell composition was associated with worse disease-free survival (DFS) (Q4 vs Q1: hazard ratio [HR] 2.04, 95% CI: 1.27-3.30, PTREND 0.0007) and overall survival (OS) (Q4 vs. Q1: HR 1.83, 95% CI: 1.14-2.94, PTREND 0.01), whereas increasing classical cell composition was associated with improved DFS (Q4 vs Q1: HR 0.63, 95% CI: 0.39-1.01, PTREND 0.01). Compared to tumors with few or no hybrid cells, tumors with high hybrid cell composition exhibited worse DFS (High vs Low: HR 1.43, 95% CI: 1.04-1.95, PTREND 0.03). Conclusion: Multiplexed, protein-based expression analysis using a panel of classical and basal subtype markers reveals that most PDACs are composed of a mix of classical and basal cells. Furthermore, a substantial proportion of cases contain “hybrid” cells that harbor prognostic significance and may represent a transitional or plastic cell state based upon their gland-level distribution.

Citation Format: Hannah L. Williams, Jinming Zhang, Srivatsan Raghavan, Peter S. Winter, Kevin Kapner, Sara Vayrynen, Andressa Dias Costa, Chen Yuan, Mai Chan Lau, Vicente Morales-Oyarvide, Douglas Rubinson, Lauren Brais, Emma Reilly, Margaret Kozak, David Linehan, Richard Dunne, Daniel Chang, Albert Koong, Aram Hezel, William C. Hahn, Alek K. Shalek, Andrew J. Aguirre, Jonathan A. Nowak, Brian M Wolpin. Spatially resolved, single cell assessment of pancreatic ductal adenocarcinoma expression subtypes reveals mixed and hybrid basal-classical marker expression with prognostic significance and discrete spatial localization [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PR-006.

Durvalumab With or Without Tremelimumab for Patients With Metastatic Pancreatic Ductal Adenocarcinoma: A Phase 2 Randomized Clinical Trial

Importance

New therapeutic options for patients with metastatic pancreatic ductal adenocarcinoma (mPDAC) are needed. This study evaluated dual checkpoint combination therapy in patients with mPDAC.

Objective

To evaluate the safety and efficacy of the anti-PD-L1 (programmed death-ligand 1) antibody using either durvalumab monotherapy or in combination with the anticytotoxic T-lymphocyte antigen 4 antibody using durvalumab plus tremelimumab therapy in patients with mPDAC.

Design, Setting, and Participants

Part A of this multicenter, 2-part, phase 2 randomized clinical trial was a lead-in safety, open-label study with planned expansion to part B pending an efficacy signal from part A. Between November 26, 2015, and March 23, 2017, 65 patients with mPDAC who had previously received only 1 first-line fluorouracil-based or gemcitabine-based treatment were enrolled at 21 sites in 6 countries. Efficacy analysis included the intent-to-treat population; safety analysis included patients who received at least 1 dose of study treatment and for whom any postdose data were available.

Interventions

Patients received durvalumab (1500 mg every 4 weeks) plus tremelimumab (75 mg every 4 weeks) combination therapy for 4 cycles followed by durvalumab therapy (1500 mg every 4 weeks) or durvalumab monotherapy (1500 mg every 4 weeks) for up to 12 months or until the onset of progressive disease or unacceptable toxic effects.

Main Outcomes and Measures

Safety and efficacy were measured by objective response rate, which was used to determine study expansion to part B. The threshold for expansion was an objective response rate of 10% for either treatment arm.

Results

Among 65 randomized patients, 34 (52%) were men and median age was 61 (95% CI, 37-81) years. Grade 3 or higher treatment-related adverse events occurred in 7 of 32 patients (22%) receiving combination therapy and in 2 of 32 patients (6%) receiving monotherapy; 1 patient randomized to the monotherapy arm did not receive treatment owing to worsened disease. Fatigue, diarrhea, and pruritus were the most common adverse events in both arms. Overall, 4 of 64 patients (6%) discontinued treatment owing to treatment-related adverse events. Objective response rate was 3.1% (95% CI, 0.08-16.22) for patients receiving combination therapy and 0% (95% CI, 0.00-10.58) for patients receiving monotherapy. Low patient numbers limited observation of the associations between treatment response and PD-L1 expression or microsatellite instability status.

Conclusion and Relevance

Treatment was well tolerated, and the efficacy of durvalumab plus tremelimumab therapy and durvalumab monotherapy reflected a population of patients with mPDAC who had poor prognoses and rapidly progressing disease. Patients were not enrolled in part B because the threshold for efficacy was not met in part A.

Trial Registration

ClinicalTrials.gov identifier: NCT02558894.

Abstract 2951: The tumor microenvironment in cholangiocarcinoma is dominated by an immunosuppressive infiltrate

Purpose: To characterize the dynamics of the immune response to cholangiocarcinoma (CCA) in a genetically engineered mouse model of CCA in order to identify immune pathways susceptible to targeted immunotherapies.

Experimental Design: Genetically modified mice with targeted Kras activation and loss of p53 (Alb-Cre/LSL-KRASG12D /p53Lox/+) in the liver spontaneously develop CCA recapitulating the histopathologic features of human disease. To evaluate the in vivo immune response to CCA, tumors from Kras-p53 mice and normal livers were excised and processed for histologic examination, flow cytometry, and gene expression analysis. Immunohistochemistry (IHC) and flow cytometry were performed on myeloid and T cell markers to distinguish immune cell subsets. Cell lines established from isolated CCA tumors were used to assess the functional impact between the immune system and tumor cells in co-culture in-vitro studies.

Results: Kras-p53 murine hepatic tumors were highly desmoplastic with a heavy fibrotic stromal compartment. IHC analysis demonstrated a prominent inflammatory leukocyte infiltrate compared to normal liver. Flow cytometry of single cell tumor suspensions showed the immune reaction was dominated by CD11b+ monocytic (Ly6C+) and granulocytic (Ly6G+) myeloid cells, and Foxp3+ regulatory T cells (T reg). In vitro studies revealed tumor educated myeloid cells expressed higher levels of genes associated with an immunosuppressive phenotype, including Arginase 1 (p=<0.007). Invasion assays analyzing the migration potential of CCA cell lines co-cultured with CD11b+ cells showed increased invasive properties in these tumor cells when compared to naive controls (p=<0.0001). Additionally, increased tumor-initiating properties were seen by qRT-PCR in tumor cell lines having undergone similar co-culture experiments. These data suggest the immune response to CCA is predominantly immunosuppressive and tumor supportive.

Conclusion: CCA tumors from Alb-Cre/LSL-KRASG12D /p53Lox/+ mice have a prominent immunosuppressive infiltrate recapitulating features of the immune reaction in human disease. Thus, Kras-p53 mice provide an ideal model to test targeted immunotherapy for the treatment of CCA.

Citation Format: Nathania M. Figueroa, Brian Belt, Ankit Patel, Booyeon Han, Margaret Hill, William Alexander, Michael O'Dell, Aditi Murthy, Kelli Connolly, Scott A. Gerber, Aram Hezel, David Linehan. The tumor microenvironment in cholangiocarcinoma is dominated by an immunosuppressive infiltrate [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2951. doi:10.1158/1538-7445.AM2017-2951

Abstract B24: Pharmacokinetic and pharmacodynamic profile of the novel, oral and selective CCR2 inhibitor CCX872-B in a Phase 1B pancreatic cancer trial

Introduction: The monocyte chemoattractant protein-1/ chemokine receptor 2 (CCR2) axis regulates the recruitment of inflammatory monocytes to sites of inflammation and cancer. CCR2 inhibition in preclinical models has resulted in diminished numbers of tumor-infiltrating immuno-suppressive macrophages and decreased pancreatic tumor size. Recently, a clinical trial with a different CCR2 inhibitor, PF-4136309, reported increased response rate from 28% historically (FOLFIRINOX alone, fluorouracil [5-FU], leucovorin, irinotecan, oxaliplatin) to 48% (FOLFIRINOX plus CCR2 inhibitor) at 12 weeks. CCX872-B is a potent, oral CCR2 inhibitor with a favorable PK profile compared to PF-4136309. In a Phase 1 healthy volunteer study, single and multiple doses of CCX872-B ranging from 3 to 300 mg were explored. CCX872-B was well-tolerated, with a dose-linear pharmacokinetic (PK) profile and dose-dependent blockade of CCR2 on circulating monocytes in receptor occupancy (RO) and internalization (RI) assays.

Experimental Procedures: This ongoing clinical trial consists of a single-dose CCX872-B regimen in Part A which has been completed in 4 patients with pancreatic adenocarcinoma, followed by a multiple dose Part B regimen in up to 50 additional patients, in combination with FOLFIRINOX therapy for up to 12 cycles. Each patient in Part A received one dose of 150 mg CCX872-B. PK, pharmacodynamics (PD), and safety were evaluated on Days 1, 4, and 8. PD was assessed via blockade of CCR2 by CCX872-B. Patient plasma obtained pre-dose, 2 hr, and 12 hr post dose was mixed with human CD14+ monocytes, and was used to measure monocyte migration at EC50 and EC90 of MCP-1, the principal ligand for CCR2, in a chemotaxis assay. Patient plasma obtained as above and mixed with human monocytes was used to measure Alexa Fluor ®-labeled MCP-1 in RO (4°C) and RI (37 °C) assays via flow cytometry.

Results: CCX872-B was well tolerated by all subjects. Mean Cmax was 8580 ng/mL, AUClast was 164,000 hr*ng/mL, and terminal t1/2 was 35h. Mean% CCR2 coverage, based on migration, RO, and RI assays, respectively, was 95%, 98%, and 95% at 2h post dose, and 86%, 84%, and 73% at 12h post dose. With an expected 4-5 fold accumulation at steady state dosing, CCR2 coverage of ≥90% is anticipated with a twice daily (BID) dosing regimen.

Conclusions: The safety, PK, and PD data of CCX872-B in pancreatic cancer patients, consistent with healthy volunteer data, support BID dosing of 150 mg CCX872-B to provide excellent CCR2 blockade in Part B of this ongoing trial. Currently, 4 patients with non-resectable pancreatic cancer have been enrolled in Part B. All patients will receive either 150 mg CCX872-B once daily or BID for at least 12 weeks combined with FOLFIRINOX for up to 12 cycles. Patients with stable disease may continue treatment beyond 12 weeks. The primary endpoint of this study is the progression free survival at week 24, aiming to improve this rate from 50% with FOLFIRINOX alone historically to at least 60%.

Citation Format: Aram Hezel, Ferry Eskens, Stefan Sleijfer, Marcus Noel, Andrea Wang-Gillam, Sabrina Cheng, Antonia Potarca, Bin Zhao, Lisa Lohr, Shichang Miao, Israel Charo, Pirow Bekker, Thomas J. Schall. Pharmacokinetic and pharmacodynamic profile of the novel, oral and selective CCR2 inhibitor CCX872-B in a Phase 1B pancreatic cancer trial. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B24.

Abstract PR09: Plac8 links oncogenic mutations to regulation of autophagy and is critical to pancreatic cancer progression

A) Pancreatic ductal adenocarcinoma (PDA) depends on a marked reprogramming of metabolic pathways, including the acquisition of autophagy dependence, for survival and growth. How common mutations in PDA cause autophagy dependence as well as the timing of autophagy activation in the course of cancer progression, have not been established. Here we show how Plac8, a gene synergistically up-regulated in response to the common cooperating oncogenic mutations found in PDA (RAS activation and functional loss of p53), is critical to the growth of PDA by sustaining autophagy via facititating autophagosome-lysosome fusion. Furthermore, we delineate that Kras and p53 mutations cooperate to induce autophagic flux. B) To establish Plac8’s role in PDA growth and autophagy we use murine cell lines and human PDA cell lines to determine 1) the lysosomal localization of Plac8, 2) its role in regulating autophagy using both loss of function and gain of function approaches, 3) the impact on lysosomal biology, and 4) the relationship between Plac8 and other genetic pathways governing autophagy. Using genetically engineered models of PDA we determine the timing of autophagy activation in PDA progression and the impact of Plac8 mutation. C) We identify Plac8 as a novel regulator of autophagosome-lysosome fusion required for PDA growth, thus providing a mechanistic link between oncogenic mutations and the activation of autophagy in cancer. Plac8 expression is required for growth of human PDA cells as xenografts in mice, as well as activation of autophagy. We find that concurrent mutation of KRAS and p53 is critical for maximal induction of autophagy in vitro. Correspondingly, using genetically engineered mouse models of PDA (Pdx1-Cre; LSL-KrasG12D; p53L/+), in which loss of p53 function occurs in a step-wise manner relying on the spontaneous loss of a heterozygous WT p53 allele, we see a step-wise incremental increase in LC3 puncta in vivo with each histological stage through the course of PDA progression. Thus, we find that the cooperative effects of KRAS and p53 drive activation of autophagy rather than either mutation alone. The overall survival of a Pdx1-Cre; LSL-KrasG12D; p53L/+; Plac8null murine cohort (OS 27.9 wks) was significantly longer than a Pdx1-Cre; LSL-KrasG12D; p53L/+; Plac8wt cohort (OS 17.0 wks, p=0.0006) demonstrating in vivo that genetic inactivation of Plac8 impedes cancer progression and resulting death. Our data suggest that the role of Plac8 in facilitating autophagy is critical to cancer, as the requirement of Plac8 for both tumorigenicity and autophagy can be compensated by over-expression of Atg12, a gene critical for autophagosome formation or by constitutively activated Rab7, a gene encoding a GTP-binding protein stimulating autophagosome-lysosome fusion. D) We conclude that Plac8 may offer a potential therapeutic window and point of intervention, as Plac8 mutation in the engineered PDA model inhibits cancer progression and significantly improves survival while having a minimal impact on the overall fitness of the animals. In fact, Plac8, and regulation of autophagosome-lysosome fusion, has specific relevance to regulation of autophagy during malignant cell transformation as Plac8 and the processes it regulates, appear to be largely dispensable to many normal physiologic processes.

This abstract is also presented as Poster B36.

Citation Format: Vijaya Balakrishnan, Kinsey Conan, Michael O'Dell, Jing Li Huang, Laurel Newman, Christa Whitney-Miller, Hartmut Land, Aram Hezel. Plac8 links oncogenic mutations to regulation of autophagy and is critical to pancreatic cancer progression. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr PR09.

Safety and effectiveness of oxaliplatin-based chemotherapy regimens in adults 75 years and older with colorectal cancer

Although the safety and efficacy of oxaliplatin-based chemotherapy regimens for colorectal cancer (CRC) have been demonstrated in adults > 75 years of age enrolled in clinical trials, safety and effectiveness outside the trial setting are less established. In this comparative effectiveness study, we note that older adults with stage III and metastatic CRC treated outside of a clinical trial experienced safety and effectiveness of oxaliplatin-based chemotherapy regimens comparable to that of younger adults.

BACKGROUND

Although the safety and efficacy of oxaliplatin-based chemotherapy regimens for colorectal cancer (CRC) have been demonstrated in adults ≥ 75 years of age who are enrolled in clinical trials, safety and effectiveness outside the trial setting are less established.

METHODS

We retrospectively collected cases of patients ≥ 75 years of age who were diagnosed with stage III and metastatic CRC and initiated treatment between January 2000 and January 2007 at 2 academic hospitals in Boston, MA. Cases were matched in a 1:2 ratio to controls who were < 75 years of age by hospital site, stage of disease (stage III vs. metastatic) and line of therapy (first- or second-line or beyond). The primary study endpoints were grade ≥ 3 treatment-associated toxicities and intolerance (number of dose delays/reductions and hospital/facility admissions during treatment). The secondary endpoint was overall survival.

RESULTS

We identified 84 patients ≥ 75 years of age (25% ≥ 80 years) and 168 controls. In the cohort, 77% had colon cancer, 75% had metastatic disease, and 60% were receiving oxaliplatin as first-line therapy. There was no significant difference in grade ≥ 3 treatment-associated toxicities between the patients and the controls (71.4% vs. 68.5%, respectively; P = .63). Further there was no statistically significant difference between patients and controls for combined endpoints of any grade ≥ 3 toxicity or hospital/facility admission (P = .92). With a median follow-up of 52 months, 2-year overall survival was similar between patients and controls (43% vs. 52%, respectively; P = .87).

CONCLUSION

Older adults with stage III and metastatic CRC treated outside of a clinical trial experienced safety and effectiveness of oxaliplatin-based chemotherapy regimens that was comparable to that of younger adults.

K-ras activation generates an inflammatory response in lung tumors

Activating mutations in K-ras are one of the most common genetic alterations in human lung cancer. To dissect the role of K-ras activation in bronchial epithelial cells during lung tumorigenesis, we created a model of lung adenocarcinoma by generating a conditional mutant mouse with both Clara cell secretory protein (CC10)-Cre recombinase and the Lox-Stop-Lox K-ras(G12D) alleles. The activation of K-ras mutant allele in CC10 positive cells resulted in a progressive phenotype characterized by cellular atypia, adenoma and ultimately adenocarcinoma. Surprisingly, K-ras activation in the bronchiolar epithelium is associated with a robust inflammatory response characterized by an abundant infiltration of alveolar macrophages and neutrophils. These mice displayed early mortality in the setting of this pulmonary inflammatory response with a median survival of 8 weeks. Bronchoalveolar lavage fluid from these mutant mice contained the MIP-2, KC, MCP-1 and LIX chemokines that increased significantly with age. Cell lines derived from these tumors directly produced MIP-2, LIX and KC. This model demonstrates that K-ras activation in the lung induces the elaboration of inflammatory chemokines and provides an excellent means to further study the complex interactions between inflammatory cells, chemokines and tumor progression.

Dual inactivation of RB and p53 pathways in RAS-induced melanomas

The frequent loss of both INK4a and ARF in melanoma raises the question of which INK4a-ARF gene product functions to suppress melanoma genesis in vivo. Moreover, the high incidence of INK4a-ARF inactivation in transformed melanocytes, along with the lack of p53 mutation, implies a cell type-specific role for INK4a-ARF that may not be complemented by other lesions of the RB and p53 pathways. A mouse model of cutaneous melanoma has been generated previously through the combined effects of INK4a(Delta2/3) deficiency (null for INK4a and ARF) and melanocyte-specific expression of activated RAS (tyrosinase-driven H-RAS(V12G), Tyr-RAS). In this study, we made use of this Tyr-RAS allele to determine whether activated RAS can cooperate with p53 loss in melanoma genesis, whether such melanomas are biologically comparable to those arising in INK4a(Delta2/3-/-) mice, and whether tumor-associated mutations emerge in the p16(INK4a)-RB pathway in such melanomas. Here, we report that p53 inactivation can cooperate with activated RAS to promote the development of cutaneous melanomas that are clinically indistinguishable from those arisen on the INK4a(Delta2/3) null background. Genomewide analysis of RAS-induced p53 mutant melanomas by comparative genomic hybridization and candidate gene surveys revealed alterations of key components governing RB-regulated G(1)/S transition, including c-Myc, cyclin D1, cdc25a, and p21(CIP1). Consistent with the profile of c-Myc dysregulation, the reintroduction of p16(INK4a) profoundly reduced the growth of Tyr-RAS INK4a(Delta2/3-/-) tumor cells but had no effect on tumor cells derived from Tyr-RAS p53(-/-) melanomas. Together, these data validate a role for p53 inactivation in melanomagenesis and suggest that both the RB and p53 pathways function to suppress melanocyte transformation in vivo in the mouse.

Accelerated accumulation of somatic mutations in mice deficient in the nucleotide excision repair gene XPA

Inheritable mutations in nucleotide excision repair (NER) genes cause cancer-prone human disorders, such as xeroderma pigmentosum, which are also characterized by symptoms of accelerated ageing. To study the impact of NER deficiency on mutation accumulation in vivo, mutant frequencies have been determined in liver and brain of 2-16 month old NER deficient XPA-/-, lacZ hybrid mice. While mutant frequencies in liver of 2-month old XPA-/-, lacZ mice were comparable to XPA+/-, lacZ and the lacZ parental strain animals, by 4 months of age mutant frequencies in the XPA-deficient mice were significantly increased by a factor of two and increased further until the age of 16 months. In brain, mutant frequencies were not found to increase with age. These results show that a deficiency in the NER gene XPA causes an accelerated accumulation of somatic mutations in liver but not in brain. This is in keeping with a higher incidence of spontaneous liver tumors reported earlier for XPA-/- mice after about 15 months of age.