Oncogenic Drivers and Therapeutic Vulnerabilities in KRAS Wild-Type Pancreatic Cancer

PURPOSE

Approximately 8% to 10% of pancreatic ductal adenocarcinomas (PDAC) do not harbor mutations in KRAS. Understanding the unique molecular and clinical features of this subset of pancreatic cancer is important to guide patient stratification for clinical trials of molecularly targeted agents.

EXPERIMENTAL DESIGN

We analyzed a single-institution cohort of 795 exocrine pancreatic cancer cases (including 785 PDAC cases) with a targeted multigene sequencing panel and identified 73 patients (9.2%) with KRAS wild-type (WT) pancreatic cancer.

RESULTS

Overall, 43.8% (32/73) of KRAS WT cases had evidence of an alternative driver of the MAPK pathway, including BRAF mutations and in-frame deletions and receptor tyrosine kinase fusions. Conversely, 56.2% of cases did not harbor a clear MAPK driver alteration, but 29.3% of these MAPK-negative KRAS WT cases (12/41) demonstrated activating alterations in other oncogenic drivers, such as GNAS, MYC, PIK3CA, and CTNNB1. We demonstrate potent efficacy of pan-RAF and MEK inhibition in patient-derived organoid models carrying BRAF in-frame deletions. Moreover, we demonstrate durable clinical benefit of targeted therapy in a patient harboring a KRAS WT tumor with a ROS1 fusion. Clinically, patients with KRAS WT tumors were significantly younger in age of onset (median age: 62.6 vs. 65.7 years; P = 0.037). SMAD4 mutations were associated with a particularly poor prognosis in KRAS WT cases.

CONCLUSIONS

This study defines the genomic underpinnings of KRAS WT pancreatic cancer and highlights potential therapeutic avenues for future investigation in molecularly directed clinical trials. See related commentary by Kato et al., p. 4527.

Abstract 1201: ALK amplification and rearrangements are recurrent targetable events in congenital and adult glioblastoma

Purpose: Anaplastic Lymphoma Kinase (ALK) aberrations have been identified in pediatric type infant gliomas, but their occurrence across age groups, functional effects, and treatment response have not been broadly established.

Experimental Design: We performed a comprehensive analysis of ALK expression and genomic aberrations in both newly-generated and retrospective data from 371 glioblastomas (156 adult, 205 infant/pediatric and 10 congenital) with in vitro and in vivo validation of aberrations.

Results: ALK aberrations at the protein or genomic level were detected in 12% of gliomas (45/371) in a wide age range (0-80 years). Recurrent as well as novel ALK fusions (LRRFIP1-ALK, DCTN1-ALK, PRKD3-ALK) were present in 50% (5/10) of congenital/infant, 1.4% (3/205) of pediatric, and 1.9% (3/156) of adult GBMs. ALK fusions were present as the only candidate driver in congenital/infant GBMs, and were sometimes focally amplified. In contrast, adult ALK fusions co-occurred with other oncogenic drivers. No activating ALK mutations were identified in any age group. Novel and recurrent ALK rearrangements promoted STAT3 and ERK1/2 pathways and transformation in vitro and in vivo. ALK-fused GBM cellular and mouse models were responsive to ALK inhibitors, including in patient cells derived from a congenital GBM. Relevant to treatment of infant gliomas, we showed that ALK protein appears minimally expressed in the forebrain at perinatal stages and no gross effects on perinatal brain development was seen in pregnant mice treated with the ALK inhibitor ceritinib.

Conclusions: These findings support expanded evaluation of brain-penetrant ALK inhibitors in clinical trials across infant, pediatric, and adult GBMs.

Citation Format: Anne-Florence Blandin, Ross Giglio, Maya Srikanth Graham, Guadalupe Garcia, Seth Malinowski, Jared K. Woods, Shakti Ramkissoon, Lori Ramkissoon, Frank Dubois, Kate Schoolcraft, Jessica W. Tsai, Dayle K. Wang, Robert Jones, Jayne Vogelzang, Kristine Pelton, Sarah Becker, Fiona Watkinson, Claire Sinai, Elizabeth Cohen, Matthew Booker, Michael Tolstorukov, Veerle Haemels, Liliana Goumnerova, Karen Wright, Mark Kieran, Katie Fehnel, David Reardon, Arnault Tauziede-Espariat, Rishi Lulla, Benjamin Carcamo, Stanley Chaleff, Alain Charest, Frederik De Smet, Azra H. Ligon, Adrian Dubuc, Melanie Pagès, Pascale Varlet, Patrick Wen, Brian Alexander, Susan Chi, Sanda Alexandrescu, Ralf Kittler, Robert Bachoo, Rameen Beroukhim, Pratiti Bandopadhayay, Keith L. Ligon. ALK amplification and rearrangements are recurrent targetable events in congenital and adult glioblastoma [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 1201.

Abstract A001: Clinical-genomic analysis of KRAS wild-type pancreatic cancer confirms alternative targetable drivers and provides insight for age and risk related clinical stratification

Approximately 8-10% of pancreatic cancers do not harbor mutations in KRAS. Understanding the unique molecular and clinical features of this subset of pancreatic cancer (PC) is important to guide patient stratification for clinical trials of molecularly targeted agents. To this end we investigated a cohort of 795 PC patients from Dana-Farber Cancer Institute who had undergone somatic genomic characterization with OncoPanel, a targeted next-generation sequencing panel with coverage of more than 400 cancer-associated genes. A total of 9.2% (73/795) of cases in our cohort were KRAS WT. The KRAS WT cohort was statistically enriched for MSI-H PC and acinar cell carcinomas (p = 0.0035, p < 0.0001 respectively). Actionable alterations in alternative MAPK drivers were identified in 44% (32/73) of KRAS WT cases. BRAF alterations accounted for 56% (18/32) of detected alternative MAPK drivers, the majority of which (72%) were Class II which exhibit dimer-dependent constitutive activity. Receptor Tyrosine Kinase (RTK) fusion events in BRAF, NTRK1, NRG1, NTRK3, ROS1, and FGFR2 accounted for 25% (8/32) of detected alternative MAPK drivers in KRAS WT tumors. BRAF in-frame deletions showed increased sensitivity to dual pan-RAF and MEK inhibition in organoid models and one patient with a ROS1 fusion received prolonged clinical benefit from targeted therapy. In addition to alternative MAPK drivers, mutations in GNAS (p = 0.0014) and ARID2 (p = 0.045) were significantly enriched in KRAS WT PC, whereas TP53 mutations were significantly less frequent in KRAS WT cases. Interestingly, although not statistically significant, rates of mutation in the other canonical tumor suppressor genes (CDKN2A, SMAD4) were also lower in KRAS WT PC. Clinically, KRAS Mutant (MUT) PC were associated with a decreased overall survival (OS) compared to the KRAS WT cohort [median OS 17.5 vs 24.0 months, HR 1.38, p = 0.036], however this relationship was no longer significant after accounting for other clinical factors. For patients with KRAS WT PC, those with SMAD4 alterations had a significantly decreased OS (HR 6.24, p < 0.001), whereas presence of TP53 or CDKN2A mutations had no significant impact. Lastly, we found that KRAS WT PC was associated with a younger age of onset. Interestingly, we noted that KRAS WT PC patients with a younger age of onset had tumors with few oncogenic alterations whereas no such association was seen in KRAS MUT patients. Validation of this finding in a separate dataset is required and is currently ongoing. In summary, our clinical and genomic characterization of KRAS WT PC identifies a high prevalence of alternative MAPK drivers that are amenable to targeted therapies. Our cohort also recapitulates the previously reported clinical characteristics of KRAS WT PC and identifies the presence of SMAD4 alterations as significantly associated with decreased overall survival in KRAS WT PC. Additional analysis from multiple sources will be critical to risk stratify these patients further and to validate age-related findings.

Citation Format: Harshabad Singh, Rachel B. Keller, Kevin S. Kapner, Julien Dilly, Srivatsan Raghavan, Chen Yuan, Eizabeth Cohen, Michael Tolstorukov, Emma Hill, Elizabeth Andrews, Lauren K. Brais, Annacarolina Da Silva, Kimberly Perez, Douglas A. Rubinson, Benjamin L. Schlechter, Michael H. Rosenthal, Jason L. Hornick, Valentina Nardi, Yvonne Li, Hersh Gupta, Andrew Cherniack, Mathew L. Meyerson, James M. Cleary, Jonathan A. Nowak, Brian M. Wolpin, Andrew A. Aguirre. Clinical-genomic analysis of KRAS wild-type pancreatic cancer confirms alternative targetable drivers and provides insight for age and risk related clinical stratification [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 A001.

Association of a very high tumor mutational load with increased CD8+ and PD-1+ T-cell infiltration and improved clinical outcomes to PD-(L)1 blockade across different PD-L1 expression levels in non-small cell lung cancer

9018

Background: Although high TMB correlates with improved outcomes to immune checkpoint inhibitors (ICI) in patients (pts) with non-small cell lung cancer (NSCLC), an optimal TMB cutoff to discriminate cancers most likely to respond to ICI has not been identified. Whether TMB impacts outcomes to ICI in different PD-L1 levels subgroups is also unclear. Methods: Unbiased recursive partitioning (URP) was used to identify an optimal TMB cutoff for objective response rate (ORR) in two independent cohorts of pts with NSCLC treated with ICI at DFCI and MSKCC. TCGA was interrogated to find differences in tumor immune cell subsets according to the TMB cutoff identified. Multiplexed immunofluorescence (IF) for CD8, PD-1, PD-L1, Foxp3, and CK7 was also performed on NSCLC samples at the DFCI. Results: In the DFCI (N=686) and MSKCC (N=672) cohorts, URP found an optimal TMB cutoff for ORR at 19 mutations/megabase (mut/Mb), corresponding to the ̃90th percentile in each cohort. Median progression-free (PFS) and overall survival (OS) were significantly longer in NSCLCs with TMB ≥19 mut/Mb vs <19 mut/Mb, in both cohorts (Table). After harmonizing TMB between DFCI OncoPanel and MSK-IMPACT NGS platforms, URP confirmed an optimal TMB cutoff for ORR at the 90th percentile in the combined cohort, which also associated with longer PFS/OS to ICI (Table). A TMB ≥90th percentile correlated with longer PFS/OS to ICI among NSCLCs with PD-L1 levels ≥50% and 1-49%, and longer PFS among those with PD-L1 <1% (Table). Cell subset transcriptome analysis from the TCGA showed higher proportions of CD8+ T cells (P=0.02) and M1 macrophages (P<0.01) among NSCLCs with a TMB ≥ vs <90th percentile. IF confirmed increased CD8+, CD8+ PD1+ T-cell infiltration (P<0.01), and increased CD8+/Foxp3+ ratio in NSCLC with very high TMB Conclusions: A very high TMB is associated with better outcomes to ICI and a distinct immunophenotype in NSCLC. Rational integration of TMB and PD-L1 expression may identify NSCLCs most likely to respond to ICI.[Table: see text]

TMOD-03. PAN-CANCER ANALYSIS OF ORTHOTOPIC PATIENT DERIVED XENOGRAFTS FROM BRAIN METASTASES

Brain metastases (BM) are a leading cause of cancer death and prognosis remains poor despite treatment advances at other sites. Models are central to therapeutic development, but few orthotopic patient-derived xenograft (PDX) models of BM exist. To represent diversity across BM types, we established a program to create orthotopic PDX at scale from all BM patients. To date BM were received from 100 patients and PDX attempted by direct brain injection (PDX, n=89) or injection of low passage patient-derived cell lines (PDCLX, n=11). We created 65 successful BM PDX from 13 cancers: 17 lung (55% take), 15 breast (68%), 6 melanoma (75%), 5 CNS lymphoma (83%), 3 gastrointestinal (75%), 2 esophageal (40%), 2 ovarian (67%), 1 sarcoma (100%), 1 laryngeal (100%), 1 prostate (100%), 1 pancreatic (100%), 1 uterine adenosarcoma (100%), and 1 yolk sac tumor (100%). Take rate was similar for models derived from patients with prior chemotherapy-only versus immune/targeted therapy-only (63 vs 58%). Fifteen patients had live tumor and matching PBMCs archived for modeling in vitro immunotherapy responses. Mean time to moribund among different cancer types ranged from 27 days (yolk sac tumor) to 177.5 days (ovarian). BM PDX had a favorable timeline for preclinical study (90% moribund at 180 days). All PDX retained high fidelity to the patient driver SNVs and copy aberrations, even at &gt;P4. No significant differences noted by immunodeficient strain (SCID versus NSG) or injection site (orthotopic versus heterotopic). Explants from BM PDX were able to generate long-term cell lines (60%) or short-term cultures with qualitative concordance of model-to-patient responses to targeted therapy (Osimertinib, EGFRi) and immunotherapy (Pembrolizumab, PD1i). Genomic and clinical data were used to create the DFCI BM PDX cBioPortal for public release and models distribution will be available through the DFCI Center for Patient Derived Models.

Enhanced chromatin accessibility of the dosage compensated Drosophila male X-chromosome requires the CLAMP zinc finger protein

The essential process of dosage compensation is required to equalize gene expression of X-chromosome genes between males (XY) and females (XX). In Drosophila, the conserved Male-specific lethal (MSL) histone acetyltransferase complex mediates dosage compensation by increasing transcript levels from genes on the single male X-chromosome approximately two-fold. Consistent with its increased levels of transcription, the male X-chromosome has enhanced chromatin accessibility, distinguishing it from the autosomes. Here, we demonstrate that the non-sex-specific CLAMP (Chromatin-linked adaptor for MSL proteins) zinc finger protein that recognizes GA-rich sequences genome-wide promotes the specialized chromatin environment on the male X-chromosome and can act over long genomic distances (~14 kb). Although MSL complex is required for increasing transcript levels of X-linked genes, it is not required for enhancing global male X-chromosome chromatin accessibility, and instead works cooperatively with CLAMP to facilitate an accessible chromatin configuration at its sites of highest occupancy. Furthermore, CLAMP regulates chromatin structure at strong MSL complex binding sites through promoting recruitment of the Nucleosome Remodeling Factor (NURF) complex. In contrast to the X-chromosome, CLAMP regulates chromatin and gene expression on autosomes through a distinct mechanism that does not involve NURF recruitment. Overall, our results support a model where synergy between a non-sex-specific transcription factor (CLAMP) and a sex-specific cofactor (MSL) creates a specialized chromatin domain on the male X-chromosome.

Impact of sequencing depth in ChIP-seq experiments

In a chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-seq) experiment, an important consideration in experimental design is the minimum number of sequenced reads required to obtain statistically significant results. We present an extensive evaluation of the impact of sequencing depth on identification of enriched regions for key histone modifications (H3K4me3, H3K36me3, H3K27me3 and H3K9me2/me3) using deep-sequenced datasets in human and fly. We propose to define sufficient sequencing depth as the number of reads at which detected enrichment regions increase <1% for an additional million reads. Although the required depth depends on the nature of the mark and the state of the cell in each experiment, we observe that sufficient depth is often reached at <20 million reads for fly. For human, there are no clear saturation points for the examined datasets, but our analysis suggests 40–50 million reads as a practical minimum for most marks. We also devise a mathematical model to estimate the sufficient depth and total genomic coverage of a mark. Lastly, we find that the five algorithms tested do not agree well for broad enrichment profiles, especially at lower depths. Our findings suggest that sufficient sequencing depth and an appropriate peak-calling algorithm are essential for ensuring robustness of conclusions derived from ChIP-seq data.

Multiplexed Illumina sequencing libraries from picogram quantities of DNA

Background

High throughput sequencing is frequently used to discover the location of regulatory interactions on chromatin. However, techniques that enrich DNA where regulatory activity takes place, such as chromatin immunoprecipitation (ChIP), often yield less DNA than optimal for sequencing library preparation. Existing protocols for picogram-scale libraries require concomitant fragmentation of DNA, pre-amplification, or long overnight steps.

Results

We report a simple and fast library construction method that produces libraries from sub-nanogram quantities of DNA. This protocol yields conventional libraries with barcodes suitable for multiplexed sample analysis on the Illumina platform. We demonstrate the utility of this method by constructing a ChIP-seq library from 100 pg of ChIP DNA that demonstrates equivalent genomic coverage of target regions to a library produced from a larger scale experiment.

Conclusions

Application of this method allows whole genome studies from samples where material or yields are limiting.

Loss of the tumor suppressor Snf5 leads to aberrant activation of the Hedgehog-Gli pathway

Aberrant activation of the Hedgehog (Hh) pathway can drive tumorigenesis. To investigate the mechanism by which glioma-associated oncogene family zinc finger-1 (GLI1), a crucial effector of Hh signaling, regulates Hh pathway activation, we searched for GLI1-interacting proteins. We report that the chromatin remodeling protein SNF5 (encoded by SMARCB1, hereafter called SNF5), which is inactivated in human malignant rhabdoid tumors (MRTs), interacts with GLI1. We show that Snf5 localizes to Gli1-regulated promoters and that loss of Snf5 leads to activation of the Hh-Gli pathway. Conversely, re-expression of SNF5 in MRT cells represses GLI1. Consistent with this, we show the presence of a Hh-Gli-activated gene expression profile in primary MRTs and show that GLI1 drives the growth of SNF5-deficient MRT cells in vitro and in vivo. Therefore, our studies reveal that SNF5 is a key mediator of Hh signaling and that aberrant activation of GLI1 is a previously undescribed targetable mechanism contributing to the growth of MRT cells.

A mutant spacer sequence between -35 and -10 elements makes the Plac promoter hyperactive and cAMP receptor protein-independent

To determine whether the spacer region between the -35 and -10 elements plays any sequence-specific role, we randomized the GC-rich sequence ((-20)CCGGCTCG(-13)) within the spacer region of the cAMP-dependent lac promoter and selected an activator-independent mutant, which showed extraordinarily high intrinsic activity. The hyperactive promoter is obtained by incorporation of a specific 10-bp-long AT-rich DNA sequence within the spacer, referred to as the -15 sequence, which must be juxtaposed to the upstream end of the -10 sequence for the hyperactivity. The transcription enhancement functions only in the presence of a -35 element. The spacer sequence enhanced both RNA polymerase binding and open complex formation. Isolated in the lac promoter, it also enhanced transcription when placed at two other unrelated promoters. Sequence analysis shows a low GC content and an abundance of stereochemically flexible TG:CA and TA:TA dimeric steps in the -18/-9 region and a strong correlation between the presence of flexible dimeric steps in this region and the intrinsic strength of the promoter.