the tumour microenvironment in cancer Last updated April 2020 Introduction This chapter provides An overview of the regulatory processes involved in angiogenesis
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Slide1
Targeting angiogenesis and the tumour microenvironment in cancer
Last updated: April 2020
Slide2IntroductionThis chapter provides:An overview of the regulatory processes involved in angiogenesis in normal physiology and cancer, and explains the role of abnormal vasculature
in tumour progressionA discussion of angiogenesis and immunosuppression in the TME and how the key angiogenic factors VEGF and Ang2 can both promote immunosuppressionA rationale for vascular normalisation as a therapeutic strategy, including dual targeting of VEGF and Ang2, as well as combination therapy with PD-1 blockade
Ang2, angiopoietin 2
;
PD-1, programmed
cell death protein
1; TME
, tumour microenvironment;
VEGF, vascular
endothelial growth
factor.
Slide3Regulation of angiogenesis in normal physiology and cancer
Slide4Tip cell
Stalk cell
Physiological angiogenesis occurs in embryonic development and wound healing
Angiogenesis is the
formation of new blood vessels from pre-existing
vessels and is controlled by a
balance of endogenous stimulators and inhibitors
. During embryonic development and wound healing, various stimuli can
tip the balance
in favour of angiogenesis
1,2
1. Ramjiawan RR, et al. Angiogenesis 2017;20(2):185–204. 2.
Albini
A. et al.
Nat Rev Clin Oncol
2012;9:498–509;
3. Lugano R, et al. Cell
Mol Life
Sci 2019 [Epub
ahead of print
].
Sprouting angiogenesis
3
Intussusceptive
angiogenesis
3
Stimulators
of angiogenesis
1,2
VEGF; PIGF; Ang1/2; Tie2; FGF; PDGF; EGF; MMP-2; MMP-9; COX-2;
mTOR
; ROS; calories; glucose
,
fat; pH
, oxygen
levels
Inhibitors of angiogenisis
1,2
TSP-1; PF-4; angiostatin; endostatin; tumstatin; interferon
α
,
β
,
γ
; TIMPs; AMPK; tight junctions; integrins (ligated)
AMPK, 5' AMP-activated protein
kinase; Ang1/2, angiopoietin 1/2;
COX-2,
cyclooxygenase 2;
EGF, epidermal growth
factor; FGF
, fibroblast growth
factor
;
MMP-2/9, matrix metallopeptidase 2/9; mTOR,
mammalian target of
rapamycin;
PD-1, programmed cell death protein 1; PDGF,
platelet-derived
growth
factor; PF-4
,
platelet
factor
4;
PIGF, placental growth factor; ROS,
reactive
oxygen
species;
TIMP, tissue inhibitor of
metalloproteinase; TME, tumour microenvironment
; TSP-1, thrombospondin
1; VEGF, vascular endothelial growth factor.
In
sprouting angiogenesis
, outgrowing tip cells fuse with an existing vessel or newly formed sprout, whereas in
intussusceptive
angiogenesis
a pre-existing vessel splits into two
3
Slide5In cancer, angiogenesis is critical for tumour growth and metastasis1. Zimna A, Kurpisz M. Biomed Res Int 2015;2015:549412; 2. Tocris Bioscience. Angiogenesis. https://www.tocris.com/cell-biology/angiogenesis (Accessed: February 2020).
1. Hypoxia induces the release of pro-angiogenic factors 2. Hypoxia also upregulates protease expression, leading to basement membrane degradation and pericyte detachment3. Tip cells migrate along the angiogenic factor gradient4. Endothelial cells differentiate into proliferative stalk cells
5
. VEGF stimulates DLL4 secretion, which binds to Notch-1 receptors, thereby downregulating VEGFR suppressing proliferation
As
a tumour develops, its size is limited by the diffusion of nutrients, oxygen and metabolites from existing blood
vessels.
Angiogenesis
acts as a checkpoint
that permits further tumour
growth
1,2
Pathological
angiogenesis
provides the
vascular supply
for proliferating
cells1,2
Steps involved in tumour vascularisation
2
In cancer, angiogenesis is driven by hypoxia
2
DLL4,
delta-like canonical Notch ligand 4; PDGFβ, platelet-derived growth factor beta; VEGF, vascular endothelial growth factor; VEGFR, vascular endothelial growth factor receptor.Endothelial cellPericyte detachmentBasement membrane degradationEndothelialprogenitor cellBasementmembraneHypoxicenvironmentstabilisesexpressionof HIF-1VEGFR2, EGFR and FGFRVEGFEGFFGFTGFβIGF1MMPTip cellVEGFR2Stalk cellVEGFR2Notch 1DLL4PDGFPericyte recruitmentHypersprouting6. PDGFβ stimulates pericyte attachment and reduces proliferation and VEGF sensitivity. The blood supply stimulates further tumour growth
Slide6Angiogenesis
Oncogenic angiogenesis and the resulting abnormal vasculature is one of the hallmarks of cancer
1
1. Hanahan D, et al. Cell 2011;144(5);646–74; 2. Ramjiawan RR, et al. Angiogenesis 2017;20(2):185–204
.
Pathological angiogenesis leads to vasculature with
abnormal structure and function
2
Blood vessels supplying solid tumours are often
tortuous and
disorganised
,
and are often
excessively leaky
2
This leads to
changes in the TME
2
TME
, tumour
microenvironment
.
Slide7↑ Adhesion
molecules
TGF
β
, adenosine
IL-10
↓ Phagocytosis
↓
Antitumour
M1
phenotype
↑ Pro-tumour
M2
phenotype
↑ T
reg
Cell
EC
DC
TAM
↓ Maturation
↓ Antigen
presentation↑ PD-L1↑ PD-L1↑ PD-L1↓ T-cell Infiltration↑ FASLLow O2Low pHTumour↑ PD-L1CTLAbnormal vasculature promotes tumour progressionAbnormal vasculature contributes to tumour progression by impairing perfusion, resulting in tumour hypoxia and low intratumoural pH1The leaky nature of tumour blood vessels in combination with dysfunctional lymphatic drainage also leads to elevated interstitial fluid pressure in the TME1Abnormal vessels and impaired perfusion can restrict entry of cytotoxic drugs and immune cells from the circulation into tumours1Factors in the TME can also impair the function of CD8+ cytotoxic lymphocytes, and limit their penetration into the tumour1Furthermore, abnormal and leaky tumour blood vessels facilitate the intravasation of cancer cells into the systemic circulation, promoting metastasis11. Fukumura D, et al. Nat Rev Clin Oncol 2018;15(5):325‒40.Abnormal vasculature↑ Immunity suppression↓ Adaptive immunityCD, cluster of differentiation; CTL, cytotoxic T lymphocyte; DC, dendritic cell; EC, endothelial cell; FASL, Fas ligand; IL-10, interleukin-10; PD-1, programmed cell death protein 1; PD-L1; programmed death ligand 1; TAM, tumour-associated macrophage; TGFβ, transforming growth factor beta; TME, tumour microenvironment; Treg, regulatory T cell.
Slide8The tumour microenvironment contributes to resistance to immunotherapy1. Jenkins RW, et al. Br. J. Cancer 2018;118:9–16; 2.Topalian
SL, et al. Cancer Cell 2015;27(4):450–61.
Arg1, arginase-1; CD, cluster of differentiation; CTLA-4, cytotoxic T lymphocyte-associated protein 4; IDO, indoleamine-pyrrole 2,3-dioxygenase; JAK1,2; Janus kinase 1, 2; LAG3, lymphocyte-activation gene 3; MDSC, myeloid-derived suppressor cell; PD-L1; programmed death ligand 1; PD-1, programmed cell death protein 1; PGE
2
, prostaglandin
E
2
;
TCR, T-cell receptor; TIM3, T-cell immunoglobulin and mucin domain 3; TME, tumour microenvironment; T
reg
, regulatory T cell; VISTA, V-domain Ig suppressor of T-cell activation;
α
PD-L1, anti-PD-L1 antibody;
α
PD-1, anti-PD-1 antibody;
Β2
M, beta-2 microglobulin.
Inadequate tumour-specific T-cell function is
a putative
mechanism
of resistance to
immunotherapy that is driven by the TME
1
An immunosuppressive TME is characterised by:1,2High levels of immune-suppressing cytokines and/or metabolitesRecruitment of immune suppressive cells such as MDSCs and TregsMutations in key effector pathwaysHigh levels of PD-L1 expressionPreclinical models have shown an association between elevation of immune-suppressive cell types (including Tregs, MDSCs, Th2 CD4+ T cells, and M2-polarised tumour-associated macrophages) in the TME and impaired immunotherapy efficacy1These cell types promote an immunosuppressive TME that inhibits antitumour cytotoxic and Th1-directed T-cell activities, primarily through the release of cytokines, chemokines, and other soluble mediators1
Slide9Angiogenesis and immunosuppression in the TME
Slide10Angiogenesis and immunosuppression are interconnected processesPreclinical and clinical evidence suggests that angiogenesis and immunosuppression have shared
regulators1Molecules that regulate angiogenesis can affect immune cells and their interaction with tumours through direct effects on immune cells, as well as indirect effects on the endothelium and through vascular normalisation2Pro-angiogenic molecules are associated with immunosuppressive effects on antigen presentation, T-cell priming, T-cell trafficking and T-cell tumour infiltration21. Campesato LF, Merghoub T. Ann Transl Med 2017;5(24):
497;
2.
Fukumura D, et al. Nat Rev Clin Oncol 2018;15(5):325‒40
.
VEGF
Ang2
(others)
Angiogenic factors
Angiogenesis
Immunosuppression
Ang2, angiopoietin 2
;
VEGF, vascular
endothelial growth
factor.
Slide11Excessive VEGF in the TME promotes immunosuppression
In addition to its key role in angiogenesis, excessive
VEGF in the TME induces immunosuppression via the following
mechanisms:
1
Increased VEGF directly
inhibits CTL trafficking, proliferation and effector function
VEGF
inhibits dendritic cell maturation and antigen presentation
, hampering
T-cell
activation and reducing the T cell-mediated immune response
VEGF increases the
number and
enhances the function
of
immunosuppressive
T
reg
cells
,
TAMs and/or
monocytesVEGF promotes angiogenesis, resulting in abnormal tumour vasculature, hypoxia, and low pH in the TME1. Fukumura D, et al. Nat Rev Clin Oncol 2018;15(5):325‒40.Ang2, angiopoietin 2; CTL, cytotoxic T lymphocyte; DC, dendritic cell; MDSC, myeloid-derived suppressor cell; TAM, tumour-associated macrophage; TME, tumour microenvironment; Treg, regulatory T cell; VEGF, vascular endothelial growth factor. ↓ Adaptive immunity↓ Innate immunity TumourCells known to produce VEGFCells known to produce ANG2
Slide12Ang2 signalling can also induce immunosuppressionThe immuno-modulatory role of Ang2, another regulator of angiogenesis, is not as well understood as that of VEGF. However, activated Ang2 promotes
immunosuppression in tumours through the following mechanisms:11. Fukumura D, et al. Nat Rev Clin Oncol 2018;15(5):325‒40.Increasing leukocyte–endothelial interactions via upregulation of adhesion molecules, facilitating recruitment of immunosuppressive cells, e.g. MDSCs, Tregs and Tie2-expressing monocytes
Disrupting
EC–pericyte
contacts, facilitating
migration of immune cells
out of the vasculature and into the TME
Modulating the function
of
monocytes
by suppressing the secretion
of
TNF, thus restricting their anticancer activity
Ang2, angiopoietin 2
; EC, endothelial
cell; MDSC
, myeloid-derived suppressor
cell
; TAM, tumour-associated
macrophage;
TME
, tumour microenvironment;
TNF, tumour
necrosis factor; Treg, regulatory T cell; VEGF, vascular endothelial growth factor.
Slide13The VEGF/Ang2 signalling axis facilitates tumour cell migration and metastasis1. Fukumura D, et al. Nat Rev Clin Oncol 2018;15(5):325‒40
.Overexpression of VEGF and Ang2 may mediate metastasis through a variety of mechanisms:1
Furthermore,
high
levels of Ang2 expression
in patients with breast cancer
have been shown to correlate with
the
presence of metastatic
disease
1
Inducing structural
and biochemical
abnormality of
tumour-associated
blood vessels
In animal models, VEGF also exerts pro-metastatic effects through activation of the
calcineurin–nuclear
factor of activated cell
dissemination
Preclinical evidence
in models of breast cancer suggests
that a high level of Ang2 pathway activation results in lymph node invasion and metastasis
Ang2, angiopoietin 2; VEGF, vascular endothelial growth factor.
Slide14Targeting angiogenesis and the TME in cancerTherapeutic strategies
Slide15Tumour perfusion
and oxygenation
Vasogenic oedema
Interstitial pressure
Drug delivery
Cancer cell shedding
Invasiveness
Metastasis
Drug and/ or radiation
sensitivity
Immune regulatory cells
Immune effector cells
Anti-angiogenic treatment
Vascular
normalisation
Progression
Response
Immunosuppressive
microenvironment
Immunosupportive
microenvironment
TAM
CTL
Vascular normalisation converts an immunosuppressive TME to an immunosupportive one
Treatment with anti-angiogenic agents can
renormalise tumour vasculature
. Vascular normalisation
converts an immunosuppressive microenvironment to an immunosupportive one by improving blood perfusion and oxygenation, thereby enabling increased infiltration of immune effector cells1Vascular normalisation also enhances the delivery and effectiveness of chemotherapy and immunotherapy1A challenge with anti-VEGF therapies is that vascular normalisation may only be transient (i.e. lasting days to weeks), and not sustained1Preclinical evidence suggests that dual inhibition of Ang2 and VEGF may extend the window of normalisation compared with inhibition of either pathway alone11. Fukumura D, et al. Nat Rev Clin Oncol 2018;15(5):325‒40.Ang2, angiopoietin 2; CTL, cytotoxic T lymphocyte; TAM, tumour-associated macrophage; TME, tumour microenvironment; VEGF, vascular endothelial growth factor.
Slide16Endothelial
cell membrane
Inhibition of
angiogenesis and
metastasis
Tie2
Ang2
VEGFR2
VEGF
Dual blockade
Dual targeting of VEGF and Ang2 may be more effective than targeting either pathway alone
VEGF
and Ang2 signalling have different but
complementary functions
in tumour
angiogenesis:
1–3
Ang2
destabilises established blood vessels
through interruption of vascular tyrosine protein kinase receptor Tie2 signalling, which promotes vessel remodelling – a prerequisite for sprouting angiogenesis
Signalling via VEGF
regulates endothelial cell proliferation and migration, and vessel
sprouting
Tumours might escape anti-VEGF therapies through alternative modes of vascularisation, e.g. upregulation of alternative angiogenic pathways such as Ang2–Tie2 signalling1Preclinical studies in mouse models of various solid tumours have shown that combined VEGF/Ang2 blockade prolongs survival compared with blockade of either pathway alone1Dual VEGF/Ang2 inhibition was also associated with a reduced frequency of metastatic dissemination compared with anti-VEGF therapy alone in models of breast cancer11. Fukumura D, et al. Nat Rev Clin Oncol 2018;15(5):325‒40; 2. Gerald D, et al. Cancer Res 2013;73(6):1649–57; 3. Huang H, et al. Nat Rev Cancer 2010;10(8):575–85. Targeting angiogenesis by inhibiting VEGF and Ang2 signallingAng2, angiopoietin 2; VEGF, vascular endothelial growth factor; VEGFR(2), vascular endothelial growth factor receptor (2).
Slide17VEGF/Ang2 inhibition in combination with PD-1 blockade could further improve therapeutic efficacyDual inhibition of VEGF and Ang2 enhances the TME to support T-cell trafficking and function
in the tumour, providing a rationale for their use in combination with a PD-1 inhibitor1‒5The triple combination of VEGF, Ang2 and PD-1 inhibition may further drive T cell-mediated tumour cell death1‒51. Hofmann I, et al. Poster presentation at the 8th Euro Global Summit on Cancer Therapy 2015; 2. Fukumura D, et al. Nat Rev Clin Oncol 2018;15(5):325‒40; 3. Gerald D, et al. Cancer Res 2013;73(6):1649–57; 4. Huang H, et al. Nat Rev Cancer 2010;10(8):575–85; 5. Boehringer Ingelheim. Data on file.
Ang2, angiopoietin 2
; CD, cluster of differentiation; PD-1, programmed cell death protein 1; TME, tumour
microenvironment; VEGF, vascular
endothelial growth
factor
, VEGFR(2), vascular endothelial growth factor receptor (2).
Slide18Summary
Slide19SummaryPathological angiogenesis in cancer can result in abnormal vasculature and an immunosuppressed TME, which can fuel tumour progression
Angiogenesis and immunosuppression are interconnected processes, both regulated by VEGF and Ang2Vascular normalisation with antiangiogenic agents can convert an immunosuppressive TME to an immunosupportive oneVEGF/Ang2 inhibition in combination with PD-1 blockade represents a rational therapeutic strategy to normalise tumour vasculature, reprogramme the TME and maximise the effectiveness of immunotherapy
Ang2, angiopoietin 2
;
PD-1, programmed
cell death protein
1; TME
, tumour microenvironment;
VEGF, vascular
endothelial growth
factor.