Pancreatic tumors exhibit myeloid-driven amino acid stress and upregulate arginine biosynthesis
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Curated by eLife
Evaluation Summary:
This study builds on previous observations of arginine depletion in the pancreatic tumor microenvironment, with the goal of developing and using a cell culture medium (TIFM) that better recapitulates nutrient levels in the TME. With this system, the authors identify arginine biosynthesis as an adaptation of pancreatic cancer cells to arginine starvation. This work reinforces a timely message that builds upon the push for optimizing and reformulating cell culture media, so as to improve fidelity, and better recapitulation of physiological/pathophysiological cellular behavior. The latter is in turn critical for translational and therapeutic applications. The work will be of interest to tumor biologists.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1 and Reviewer #2 agreed to share their names with the authors.)
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Abstract
Nutrient stress in the tumor microenvironment requires cancer cells to adopt adaptive metabolic programs for survival and proliferation. Therefore, knowledge of microenvironmental nutrient levels and how cancer cells cope with such nutrition is critical to understand the metabolism underpinning cancer cell biology. Previously, we performed quantitative metabolomics of the interstitial fluid (the local perfusate) of murine pancreatic ductal adenocarcinoma (PDAC) tumors to comprehensively characterize nutrient availability in the microenvironment of these tumors. Here, we develop T umor I nterstitial F luid M edium (TIFM), a cell culture medium that contains nutrient levels representative of the PDAC microenvironment, enabling us to study PDAC metabolism ex vivo under physiological nutrient conditions. We show that PDAC cells cultured in TIFM adopt a cellular state closer to that of PDAC cells present in tumors compared to standard culture models. Further, using the TIFM model, we found arginine biosynthesis is active in PDAC and allows PDAC cells to maintain levels of this amino acid despite microenvironmental arginine depletion. We also show that myeloid derived arginase activity is largely responsible for the low levels of arginine in PDAC tumors. Altogether, these data indicate that nutrient availability in tumors is an important determinant of cancer cell metabolism and behavior, and cell culture models that incorporate physiological nutrient availability have improved fidelity to in vivo systems and enable the discovery of novel cancer metabolic phenotypes.
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Evaluation Summary:
This study builds on previous observations of arginine depletion in the pancreatic tumor microenvironment, with the goal of developing and using a cell culture medium (TIFM) that better recapitulates nutrient levels in the TME. With this system, the authors identify arginine biosynthesis as an adaptation of pancreatic cancer cells to arginine starvation. This work reinforces a timely message that builds upon the push for optimizing and reformulating cell culture media, so as to improve fidelity, and better recapitulation of physiological/pathophysiological cellular behavior. The latter is in turn critical for translational and therapeutic applications. The work will be of interest to tumor biologists.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also …
Evaluation Summary:
This study builds on previous observations of arginine depletion in the pancreatic tumor microenvironment, with the goal of developing and using a cell culture medium (TIFM) that better recapitulates nutrient levels in the TME. With this system, the authors identify arginine biosynthesis as an adaptation of pancreatic cancer cells to arginine starvation. This work reinforces a timely message that builds upon the push for optimizing and reformulating cell culture media, so as to improve fidelity, and better recapitulation of physiological/pathophysiological cellular behavior. The latter is in turn critical for translational and therapeutic applications. The work will be of interest to tumor biologists.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1 and Reviewer #2 agreed to share their names with the authors.)
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Reviewer #1 (Public Review):
In this study, Apiz-Saab et al. build up prior work by the Muir lab, which examined the metabolite composition in the tumor microenvironment and found that some metabolites like arginine are present in very different levels from that in our standard culture media. In this study, the authors have formulated a custom media based on the composition of the tumor interstitial fluid (TIF media or TIFM) and found that pancreatic cancer cells cultured in this media have a metabolic state more like tumors in vivo. This is primarily driven by very low levels of arginine, which induces arginine biosynthesis is the cancer cells to cope with this nutrient limited state. Using genetic and pharmacological approaches, the authors demonstrate that arginase expression within tumor-infiltrating myeloid cells drives tumor …
Reviewer #1 (Public Review):
In this study, Apiz-Saab et al. build up prior work by the Muir lab, which examined the metabolite composition in the tumor microenvironment and found that some metabolites like arginine are present in very different levels from that in our standard culture media. In this study, the authors have formulated a custom media based on the composition of the tumor interstitial fluid (TIF media or TIFM) and found that pancreatic cancer cells cultured in this media have a metabolic state more like tumors in vivo. This is primarily driven by very low levels of arginine, which induces arginine biosynthesis is the cancer cells to cope with this nutrient limited state. Using genetic and pharmacological approaches, the authors demonstrate that arginase expression within tumor-infiltrating myeloid cells drives tumor microenvironmental arginine depletion in vivo.
Strengths:
This is a very rigorous, well-designed study and the findings are broadly interesting for the metabolism, immunometabolism, and pancreatic cancer communities. The methods are comprehensive and the experimental details in the legends are complete. The discussion is particularly well developed and does an excellent job of putting the findings in the context of the field.
Weaknesses:
The claim that arginine biosynthesis is an adaptation to myeloid arginine depletion could be further supported in vivo.
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Reviewer #2 (Public Review):
In this manuscript, Muir et al. build on their previous observation that arginine is depleted in the microenvironment of pancreatic ductal adenocarcinoma (PDAC), which they detected after performing an assay for quantification of metabolites in the tumor interstitial fluid (TIF) of murine PDAC models (Sullivan et al., elife 2019). Here, they develop and use a cell culture medium (TIFM) comprising nutrients at levels equivalent to those in the PDAC TIF or tumor microenvironment (TME) and identify arginine biosynthesis as an adaptation of PDAC cells to arginine starvation. They further point at tumor-infiltrating myeloid cells, which express arginase 1 (Arg1), as the cause of arginine depletion in PDAC TME.
Strengths:
1- The manuscript is well-written and reinforces a timely message that has previously been …
Reviewer #2 (Public Review):
In this manuscript, Muir et al. build on their previous observation that arginine is depleted in the microenvironment of pancreatic ductal adenocarcinoma (PDAC), which they detected after performing an assay for quantification of metabolites in the tumor interstitial fluid (TIF) of murine PDAC models (Sullivan et al., elife 2019). Here, they develop and use a cell culture medium (TIFM) comprising nutrients at levels equivalent to those in the PDAC TIF or tumor microenvironment (TME) and identify arginine biosynthesis as an adaptation of PDAC cells to arginine starvation. They further point at tumor-infiltrating myeloid cells, which express arginase 1 (Arg1), as the cause of arginine depletion in PDAC TME.
Strengths:
1- The manuscript is well-written and reinforces a timely message that has previously been provided by other groups under different contexts (Cantor et al., 2017; Vande Voorde et al., 2019), that is the push for optimizing and reformulating cell culture media, so as to improve fidelity by better recapitulating physiological /pathophysiological cellular behavior. The latter, in turn is critical for translational and therapeutic applications.
2- Use of this novel medium allowed the authors to identify a mechanism used by PDAC cells to cope with arginine starvation (that is induction of arginine biosynthesis). They also point at a potential cause of this starvation, namely the myeloid cell expression of Arginase1 (Arg1) which can breakdown and deplete arginine in the TME.
Weaknesses:
3- The myeloid part does not seem to be the main focus of this manuscript, as it is not deeply dissected; yet the title includes "myeloid-driven" amino acid stress. No evidence is provided for decreased arginine biosynthesis in tumors with myeloid-specific depletion of Arg1 where arginine levels are increased in the TME.
4- Statistical significance is only shown for a few selected figure panels and is lacking in the vast majority of figures. Importantly, sample number is low throughout the manuscript, decreasing the robustness of the conclusions and weakening statistical assessment.
6- There are some inaccuracies with regards to tracing the incorporation of the glutamine nitrogen into synthesis of arginine; and some figure legends could be more specifically written so as to better explain/clarify the data.
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