A brief history of RAS and the RAS Initiative

In this review, I provide a brief history of the discovery of RAS and the GAPs and GEFs that regulate its activity from a personal perspective. Much of this history has been driven by technological breakthroughs that occurred concurrently, such as molecular cloning, cDNA expression to analyze RAS proteins and their structures, and application of PCR to detect mutations. I discuss the RAS superfamily and RAS proteins as therapeutic targets, including recent advances in developing RAS inhibitors. I also describe the role of the RAS Initiative at Frederick National Laboratory for Cancer Research in advancing development of RAS inhibitors and providing new insights into signaling complexes and interaction of RAS proteins with the plasma membrane.

Machine learning-driven multiscale modeling reveals lipid-dependent dynamics of RAS signaling proteins

RAS is a signaling protein associated with the cell membrane that is mutated in up to 30% of human cancers. RAS signaling has been proposed to be regulated by dynamic heterogeneity of the cell membrane. Investigating such a mechanism requires near-atomistic detail at macroscopic temporal and spatial scales, which is not possible with conventional computational or experimental techniques. We demonstrate here a multiscale simulation infrastructure that uses machine learning to create a scale-bridging ensemble of over 100,000 simulations of active wild-type KRAS on a complex, asymmetric membrane. Initialized and validated with experimental data (including a new structure of active wild-type KRAS), these simulations represent a substantial advance in the ability to characterize RAS-membrane biology. We report distinctive patterns of local lipid composition that correlate with interfacially promiscuous RAS multimerization. These lipid fingerprints are coupled to RAS dynamics, predicted to influence effector binding, and therefore may be a mechanism for regulating cell signaling cascades.

Cost Structures of US Organ Procurement Organizations

BACKGROUND

The goal is to provide a national analysis of organ procurement organization (OPO) costs.

METHODS

Five years of data, for 51 of the 58 OPOs (2013-2017, a near census) were obtained under a FOIA. OPOs are not-for-profit federal contractors with a geographic monopoly. A generalized 15-factor cost regression model was estimated with adjustments to precision of estimates (P) for repeated observations. Selected measures were validated by comparison to IRS forms.

RESULTS

Decease donor organ procurement is a $1B/y operation with over 26 000 transplants/y. Over 60% of the cost of an organ is overhead. Profits are $2.3M/OPO/y. Total assets are $45M/OPO and growing at 9%/y. "Tissue" (skin, bones) generates $2-3M profit/OPO/y. A comparison of the highest with the lower costing OPOs showed our model explained 75% of the cost difference. Comparing costs across OPOs showed that highest-cost OPOs are smaller, import 44% more kidneys, face 6% higher labor costs, report 98% higher compensation for support personnel, spend 46% more on professional education, have 44% fewer assets, compensate their Executive Director 36% less, and have a lower procurement performance (SDRR) score.

CONCLUSIONS

Profits and assets suggest that OPOs are fiscally secure and OPO finances are not a source of the organ shortage. Asset accumulation ($45M/OPO) of incumbents suggests establishing a competitive market with new entrants is unlikely. Kidney-cost allocations support tissue procurements. Professional education spending does not reduce procurement costs. OPO importing of organs from other OPOs is a complex issue possibly increasing cost ($6K/kidney).

CSIG-01. EPIGENETIC REPROGRAMMING DRIVES MALIGNANT PERIPHERAL NERVE SHEATH TUMOR (MPNST) DE-DIFFERENTIATION AND TREATMENT RESISTANCE

Schwann cell derived tumors comprising schwannomas, neurofibromas, and malignant peripheral nerve sheath tumors are the most common malignancies of the peripheral nervous system. While schwannomas and neurofibromas are benign, MPNSTs are malignant, metastasize, and respond poorly to treatment. Neurofibromas and MPNSTs are associated with loss of NF1, a tumor suppressor that inhibits Ras/MEK signaling, and MPNSTs alone are distinguished by loss of the Polycomb Repressive Complex 2 (PRC2), an epigenetic regulator of methylation. To understand the genomic mechanisms of Schwann cell tumorigenesis and treatment resistance, we performed DNA methylation profiling, RNA-sequencing, and whole exome sequencing of primary Schwann cell tumor resection specimens (n=119 total: n=66 schwannoma, n=13 neurofibroma, n=40 MPNSTs). Hierarchical clustering identified three epigenetic Schwann cell tumor groups with transcriptional differences in PRC2 target genes associated with Schwann cell differentiation. Integrating biochemical and genomic approaches in primary human tumor cell lines from NF1 intact peripheral nerve, NF1 mutant neurofibromas, and MPNSTs, we found MPNST and neurofibroma cell lines with CRISPR knockout SUZ12 or EZH1/2 neurofibroma cell lines demonstrated repression of Schwann cell differentiation genes and induction of Ras signaling target genes. Further, MPNST cells deficient in PRC2 and NF1 exhibited increased basal active Ras-GTP levels, and therapeutically, PRC2 deficient MPNST cell lines were more resistant to the MEK inhibitor selumetinib and radiotherapy when compared to NF1-deficient neurofibroma cells. Single cell RNA sequencing analysis suggested distinct mechanisms of selumetinib resistance in PRC2 intact neurofibroma cells compared to PRC2-deficient MPNST cells. Taken together, our data demonstrate the importance of epigenetic dysregulation in malignant Schwann cell transformation and suggest differentiation status underlies a novel mechanism of MEK inhibitor resistance.

Inhibition of MET Signaling with Ficlatuzumab in Combination with Chemotherapy in Refractory AML: Clinical Outcomes and High-Dimensional Analysis

Acute myeloid leukemia patients refractory to induction therapy or relapsed within one year have poor outcomes. Autocrine production of hepatocyte growth factor by myeloid blasts drives leukemogenesis in pre-clinical models. A phase Ib trial evaluated ficlatuzumab, a first-in-class anti-HGF antibody, in combination with cytarabine in this high-risk population. Dose-limiting toxicities were not observed, and 20 mg/kg was established as the recommended phase II dose. The most frequent treatment-related adverse event was febrile neutropenia. Among 17 evaluable patients, the overall response rate was 53%, all complete remissions. Phospho-proteomic mass cytometry showed potent on-target suppression of p-MET after ficlatuzumab treatment and that attenuation of p-S6 was associated with clinical response. Multiplexed single cell RNA sequencing using prospectively acquired patient specimens identified interferon response genes as adverse predictive factors. The ficlatuzumab and cytarabine combination is well-tolerated with favorable efficacy. High-dimensional analyses at single-cell resolution represent promising approaches for identifying biomarkers of response and mechanisms of resistance in prospective clinical studies.

RAS interaction with Sin1 is dispensable for mTORC2 assembly and activity

RAS proteins are molecular switches that interact with effector proteins when bound to guanosine triphosphate, stimulating downstream signaling in response to multiple stimuli. Although several canonical downstream effectors have been extensively studied and tested as potential targets for RAS-driven cancers, many of these remain poorly characterized. In this study, we undertook a biochemical and structural approach to further study the role of Sin1 as a RAS effector. Sin1 interacted predominantly with KRAS isoform 4A in cells through an atypical RAS-binding domain that we have characterized by X-ray crystallography. Despite the essential role of Sin1 in the assembly and activity of mTORC2, we find that the interaction with RAS is not required for these functions. Cells and mice expressing a mutant of Sin1 that is unable to bind RAS are proficient for activation and assembly of mTORC2. Our results suggest that Sin1 is a bona fide RAS effector that regulates downstream signaling in an mTORC2-independent manner.

Oncogenic mutant RAS signaling activity is rescaled by the ERK/MAPK pathway

Activating mutations in RAS are present in ~ 30% of human tumors, and the resulting aberrations in ERK/MAPK signaling play a central role in oncogenesis. However, the form of these signaling changes is uncertain, with activating RAS mutants linked to both increased and decreased ERK activation in vivo. Rationally targeting the kinase activity of this pathway requires clarification of the quantitative effects of RAS mutations. Here, we use live‐cell imaging in cells expressing only one RAS isoform to quantify ERK activity with a new level of accuracy. We find that despite large differences in their biochemical activity, mutant KRAS isoforms within cells have similar ranges of ERK output. We identify roles for pathway‐level effects, including variation in feedback strength and feedforward modulation of phosphatase activity, that act to rescale pathway sensitivity, ultimately resisting changes in the dynamic range of ERK activity while preserving responsiveness to growth factor stimuli. Our results reconcile seemingly inconsistent reports within the literature and imply that the signaling changes induced by RAS mutations early in oncogenesis are subtle.

Targeted mass spectrometry-based assays enable multiplex quantification of receptor tyrosine kinase, MAP Kinase, and AKT signaling

SUMMARY

A primary goal of the US National Cancer Institute's Ras initiative at the Frederick National Laboratory for Cancer Research is to develop methods to quantify RAS signaling to facilitate development of novel cancer therapeutics. We use targeted proteomics technologies to develop a community resource consisting of 256 validated multiple reaction monitoring (MRM)-based, multiplexed assays for quantifying protein expression and phosphorylation through the receptor tyrosine kinase, MAPK, and AKT signaling networks. As proof of concept, we quantify the response of melanoma (A375 and SK-MEL-2) and colorectal cancer (HCT-116 and HT-29) cell lines to BRAF inhibition by PLX-4720. These assays replace over 60 Western blots with quantitative mass spectrometry-based assays of high molecular specificity and quantitative precision, showing the value of these methods for pharmacodynamic measurements and mechanism of action studies. Methods, fit-for-purpose validation, and results are publicly available as a resource for the community at assays.cancer.gov.

MOTIVATION

A lack of quantitative, multiplexable assays for phosphosignaling limits comprehensive investigation of aberrant signaling in cancer and evaluation of novel treatments. To alleviate this limitation, we sought to develop assays using targeted mass spectrometry for quantifying protein expression and phosphorylation through the receptor tyrosine kinase, MAPK, and AKT signaling networks. The resulting assays provide a resource for replacing over 60 Western blots in examining cancer signaling and tumor biology with high molecular specificity and quantitative rigor.

A Covalent Calmodulin Inhibitor as a Tool to Study Cellular Mechanisms of K-Ras-Driven Stemness

Recently, the highly mutated oncoprotein K-Ras4B (hereafter K-Ras) was shown to drive cancer cell stemness in conjunction with calmodulin (CaM). We previously showed that the covalent CaM inhibitor ophiobolin A (OphA) can potently inhibit K-Ras stemness activity. However, OphA, a fungus-derived natural product, exhibits an unspecific, broad toxicity across all phyla. Here we identified a less toxic, functional analog of OphA that can efficiently inactivate CaM by covalent inhibition. We analyzed a small series of benzazulenones, which bear some structural similarity to OphA and can be synthesized in only six steps. We identified the formyl aminobenzazulenone 1, here named Calmirasone1, as a novel and potent covalent CaM inhibitor. Calmirasone1 has a 4-fold increased affinity for CaM as compared to OphA and was active against K-Ras in cells within minutes, as compared to hours required by OphA. Calmirasone1 displayed a 2.5–4.5-fold higher selectivity for KRAS over BRAF mutant 3D spheroid growth than OphA, suggesting improved relative on-target activity. Importantly, Calmirasone1 has a 40–260-fold lower unspecific toxic effect on HRAS mutant cells, while it reaches almost 50% of the activity of novel K-RasG12C specific inhibitors in 3D spheroid assays. Our results suggest that Calmirasone1 can serve as a new tool compound to further investigate the cancer cell biology of the K-Ras and CaM associated stemness activities.

Abstract 1844: A CD70 antibody-drug conjugate is highly active and induces long term remission in patient-derived xenograft mouse models of cutaneous T cell lymphoma

Cutaneous T cell lymphoma (CTCL) is a type of non-Hodgkin's lymphoma in which malignant T cells initially home to the skin followed by systemic dissemination as the disease progresses. CD70 is rarely expressed in normal tissues but is overexpressed in activated T and B lymphocytes. From archival diagnostic specimens of 37 patients, we demonstrate that CD70 is highly expressed in subtypes of mature TCL, especially CTCL. SGNCD70A is a new anti-CD70 antibody-drug conjugate combining a monoclonal antibody to CD70 with a DNA-damaging agent. SGNCD70A inhibited cell growth and induced apoptosis of CD70+ CTCL cell lines and primary tumors from patient-derived xenograft (PDX) mice, but had no inhibitory effect on CD70- lymphoblastic TCL cells and normal T cells. Next, we examined the anti-tumor activity of SGNCD70A in CTCL PDX model. One week after tumor inoculation, mice were treated intraperitoneally with single-dosing of PBS, 100 μg/kg (SGN70A100) or 300 μg/kg (SGN70A300) of SGN-CD70A. SGN-CD70A prolonged survival of treated mice in a dose-dependent fashion compared to untreated mice. Median survival was 21 days, 27.5 days (P=0.041), and 57 days (p<0.01) for the PBS control, SGN70A100 and SGN70A300 group, respectively. To confirm that survival was dictated by disease progression, rather than drug toxicity of SGN-CD70A, we measured tumor burden by cell-free DNA (cfDNA) throughout the course of treatment. We demonstrated that cfDNA paralleled the disease progression and peaked before death of the animals. In contrast, in surviving mice, cfDNA remained at the background level. Importantly, we discovered relapse occurred in SGN70A300 group (3 of 4, 75%) due to persistent disease, not due to acquired resistance to SGN-CD70A. Thus, we investigated whether multiple dosing could lead to complete regression of tumors in PDX model. We treated PDX mice with SGN70A300 weekly (SGN70A300x3) for 3 consecutive weeks. In the SGN70A300x3 group, three of four mice survived beyond day 90 (median >85 days), resulting in markedly prolonged survival compared to the single-dose- and PBS-treated mice with a median survival of 39 days, (P<0.01) and 20 days (P<0.01), respectively. Compared to PBS group, both SGN70A300 and SGN70A300x3 treated mice had delayed tumor growth and cfDNA rise. Furthermore, in SGN70A300 group, cfDNA started to rise seven days before the endpoint of the mice in a range of 30-42 days, while three surviving mice in SGN70A300x3 remained at background cfDNA levels until day 85, indicating that multiple doses of SGN-CD70A decreased overall tumor burden and the occurrence of relapse in CTCL. Our results showed that CD70 is highly expressed in mature TCL, especially in CTCL. Using CTCL PDX models, SGN-CD70A has marked anti-tumor activity, leading to long-term survival of treated mice. Our results provide a rationale for clinical investigation of SGN-CD70A in patients with TCL.

Citation Format: Chi-Heng Wu, Chen-Yen Yang, Linlin Wang, Ryan Gill, Frank McCormick, Weiyun Z. Ai. A CD70 antibody-drug conjugate is highly active and induces long term remission in patient-derived xenograft mouse models of cutaneous T cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1844.

Ancient DNA, lipid biomarkers and palaeoecological evidence reveals construction and life on early medieval lake settlements

Direct evidence of ancient human occupation is typically established through archaeological excavation. Excavations are costly and destructive, and practically impossible in some lake and wetland environments. We present here an alternative approach, providing direct evidence from lake sediments using DNA metabarcoding, steroid lipid biomarkers (bile acids) and from traditional environmental analyses. Applied to an early Medieval Celtic settlement in Ireland (a crannog) this approach provides a site chronology and direct evidence of human occupation, crops, animal farming and on-site slaughtering. This is the first independently-dated, continuous molecular archive of human activity from an archeological site, demonstrating a link between animal husbandry, food resources, island use. These sites are under threat but are impossible to preserve in-situ so this approach can be used, with or without excavation, to produce a robust and full site chronology and provide direct evidence of occupation, the use of plants and animals, and activities such as butchery.

Minor intron retention drives clonal hematopoietic disorders and diverse cancer predisposition

Most eukaryotes harbor two distinct pre-mRNA splicing machineries: the major spliceosome, which removes >99% of introns, and the minor spliceosome, which removes rare, evolutionarily conserved introns. Although hypothesized to serve important regulatory functions, physiologic roles of the minor spliceosome are not well understood. For example, the minor spliceosome component ZRSR2 is subject to recurrent, leukemia-associated mutations, yet functional connections among minor introns, hematopoiesis and cancers are unclear. Here, we identify that impaired minor intron excision via ZRSR2 loss enhances hematopoietic stem cell self-renewal. CRISPR screens mimicking nonsense-mediated decay of minor intron-containing mRNA species converged on LZTR1, a regulator of RAS-related GTPases. LZTR1 minor intron retention was also discovered in the RASopathy Noonan syndrome, due to intronic mutations disrupting splicing and diverse solid tumors. These data uncover minor intron recognition as a regulator of hematopoiesis, noncoding mutations within minor introns as potential cancer drivers and links among ZRSR2 mutations, LZTR1 regulation and leukemias.

Sensitivity of Oncogenic KRAS-Expressing Cells to CDK9 Inhibition

Oncogenic forms of KRAS proteins are known to be drivers of pancreatic, colorectal, and lung cancers. The goal of this study is to identify chemical leads that inhibit oncogenic KRAS signaling. We first developed an isogenic panel of mouse embryonic fibroblast (MEF) cell lines that carry wild-type RAS, oncogenic KRAS, and oncogenic BRAF. We validated these cell lines by screening against a tool compound library of 1402 annotated inhibitors in an adenosine triphosphate (ATP)-based cell viability assay. Subsequently, this MEF panel was used to conduct a high-throughput phenotypic screen in a cell viability assay with a proprietary compound library. All 126 compounds that exhibited a selective activity against mutant KRAS were selected and prioritized based on their activities in secondary assays. Finally, five chemical clusters were chosen. They had specific activity against SW620 and LS513 over Colo320 colorectal cancer cell lines. In addition, they had no effects on BRAF^V600E, MEK1, extracellular signal-regulated kinase 2 (ERK2), phosphoinositide 3-kinase alpha (PI3Kα), AKT1, or mammalian target of rapamycin (mTOR) as tested in in vitro enzymatic activity assays. Biophysical assays demonstrated that these compounds did not bind directly to KRAS. We further identified the mechanism of action and showed that three of them have CDK9 inhibitory activity. In conclusion, we have developed and validated an isogenic MEF panel that was used successfully to identify RAS oncogenic or wild-type allele-specific vulnerabilities. Furthermore, we identified sensitivity of oncogenic KRAS-expressing cells to CDK9 inhibitors, which warrants future studies of treating KRAS-driven cancers with CDK9 inhibitors.

Estimated impact of novel coronavirus-19 and transplant center inactivity on end-stage renal disease-related patient mortality in the United States

To predict whether the COVID‐19 pandemic and transplant center responses could have resulted in preventable deaths, we analyzed registry information of the US end‐stage renal disease (ESRD) patient population awaiting kidney transplantation. Data were from the Organ Procurement and Transplantation Network (OPTN), the US Centers for Disease Control and Prevention, and the United States Renal Data System. Based on 2019 OPTN reports, annualized reduction in kidney transplantation of 25%–100% could result in excess deaths of wait‐listed (deceased donor) transplant candidates from 84 to 337 and living donor candidate excess deaths from 35 to 141 (total 119–478 potentially preventable deaths of transplant candidates). Changes in transplant activity due to COVID‐19 varied with some centers shutting down while others simply heeded known or suspected pandemic risks. Understanding potential excess mortality for ESRD transplant candidates when circumstances compel curtailment of transplant activity may inform policy and procedural aspects of organ transplant systems allowing ways to best inform patients and families as to potential risks in shuttering organ transplant activity. Considering that more than 700 000 Americans have ESRD with 100 000 awaiting a kidney transplant, our highest annual estimate of 478 excess total deaths from postponing kidney transplantation seems modest.

The Metabolic Landscape of RAS-Driven Cancers from biology to therapy

Our understanding of how the RAS protein family, and in particular mutant KRAS promote metabolic dysregulation in cancer cells has advanced significantly over the last decade. In this Review, we discuss the metabolic reprogramming mediated by oncogenic RAS in cancer, and elucidating the underlying mechanisms could translate to novel therapeutic opportunities to target metabolic vulnerabilities in RAS-driven cancers.

Promoting Ethical Payment in Human Infection Challenge Studies

To prepare for potential human infection challenge studies (HICS) involving SARS-CoV-2, we convened a multidisciplinary working group to address ethical questions regarding whether and how much SARS-CoV-2 HICS participants should be paid. Because the goals of paying HICS participants, as well as the relevant ethical concerns, are the same as those arising for other types of clinical research, the same basic framework for ethical payment can apply. This framework divides payment into reimbursement, compensation, and incentives, focusing on fairness and promoting adequate recruitment and retention as counterweights to concerns about undue inducement. Within the basic framework, several factors are especially salient for HICS, and for SARS-CoV-2 HICS in particular, including the nature of participant confinement, anticipated discomfort, risks and uncertainty, participant motivations, and trust. These factors are reflected in a payment worksheet created to help sponsors, researchers, and ethics reviewers systematically develop and assess ethically justifiable payment amounts.

DoMY-Seq: A yeast two-hybrid-based technique for precision mapping of protein-protein interaction motifs

Interactions between proteins are fundamental for every biological process and especially important in cell signaling pathways. Biochemical techniques that evaluate these protein-protein interactions (PPIs), such as in vitro pull downs and coimmunoprecipitations, have become popular in most laboratories and are essential to identify and validate novel protein binding partners. Most PPIs occur through small domains or motifs, which are challenging and laborious to map by using standard biochemical approaches because they generally require the cloning of several truncation mutants. Moreover, these classical methodologies provide limited resolution of the interacting interface. Here, we describe the development of an alternative technique to overcome these limitations termed "Protein Domain mapping using Yeast 2 Hybrid-Next Generation Sequencing" (DoMY-Seq), which leverages both yeast two-hybrid and next-generation sequencing techniques. In brief, our approach involves creating a library of fragments derived from an open reading frame of interest and enriching for the interacting fragments using a yeast two-hybrid reporter system. Next-generation sequencing is then subsequently employed to read and map the sequence of the interacting fragment, yielding a high-resolution plot of the binding interface. We optimized DoMY-Seq by taking advantage of the well-described and high-affinity interaction between KRAS and CRAF, and we provide high-resolution domain mapping on this and other protein-interacting pairs, including CRAF-MEK1, RIT1-RGL3, and p53-MDM2. Thus, DoMY-Seq provides an unbiased alternative method to rapidly identify the domains involved in PPIs by advancing the use of yeast two-hybrid technology.

SPRED proteins and their roles in signal transduction, development, and malignancy

The roles of SPRED proteins in signaling, development, and cancer are becoming increasingly recognized. SPRED proteins comprise an N-terminal EVH-1 domain, a central c-Kit-binding domain, and C-terminal SROUTY domain. They negatively regulate signaling from tyrosine kinases to the Ras-MAPK pathway. SPRED1 binds directly to both c-KIT and to the RasGAP, neurofibromin, whose function is completely dependent on this interaction. Loss-of-function mutations in SPRED1 occur in human cancers and cause the developmental disorder, Legius syndrome. Genetic ablation of SPRED genes in mice leads to behavioral problems, dwarfism, and multiple other phenotypes including increased risk of leukemia. In this review, we summarize and discuss biochemical, structural, and biological functions of these proteins including their roles in normal cell growth and differentiation and in human disease.