Table 1:

Tools for the study and manipulation of innervation of the tumour microenvironment

Tool	Mechanism of action	Application	Ref
Mouse line
Advillin-Cre transgenic mouse	Peripheral sensory nerve-specific Cre recombinase (not expressed in CNS)	Enables specific deletion of genes in sensory nerves, or nerve depletion when crossed with DTA or DTR knock-in mice	192,193
Ngf knock-in mouse	Ngf gene preceded by a stop codon inserted into the ROSA26 locus	When crossed to a Cre-expressing mouse strain (e.g. epithelial or stromal expressed Cre), increases NGF production and tissue innervation	4,59
Nav1.8 Cre knock-in mouse	Express Cre recombinase from the endogenous sodium channel Scn10a locus.	Enables selective deletion of genes in nociceptive nerves, or nociceptive neuron depletion when crossed with DTA or DTR knock-in mice.	194
TrkAF592A or TrkBF616A knock-in mice	Trk knock-in alleles with modified kinase domains allowing pharmacological inhibition with nanomolar concentrations of the ligands 1NMPP1 or 1NaPP1	Temporal pharmacological inhibition of nerve recruitment in the TME	118,195
Trkb-CreERT2 knock-in mouse	Tamoxifen-inducible sensory nerve-specific Cre recombinase	Enables temporal control over gene expression specifically in sensory nerves or nerve depletion when crossed with DTA or DTR knock-in mice.	82
Neurotoxin
6-hydroxy dopamine (6OHDA)	Polar monoamine mimetic that is taken up in the periphery by post-synaptic adrenergic nerves causing free radical destruction of nerve terminals	When given neonatally, it induces permanent global sympathectomy (as well as off-target CNS effects), whereas in the adult, it only causes temporary peripheral sympathectomy (as it is unable to cross the BBB)	2,5,30,31
RTX	A super agonist of sensory neuron-expressed calcium channel TRPV1, causing calcium-mediated neuronal death	When given neonatally, it induces permanent global sensory denervation, whereas in the adult, it causes temporary peripheral sensory denervation	10,196
Capsaicin	TRPV1 agonist causing cytotoxicity at high doses	Less potent than RTX requiring repeated injections or incorporation into daily mouse feeds to induce lasting sensory denervation.	7,11,38,197
Botulinum toxin	Bacterium-derived protease that is taken up by endocytosis in the axonal terminal, and which selectively cleaves synaptic proteins preventing acetylcholine release	When injected into a tissue of interest causes temporary denervation of cholinergic synapses	3,18,32,198
Surgical denervation
Mechanical neurectomy	Mechanical transection of axonal process, or removal of ganglionic cell body	Physical disruption of tissue innervation	3–5,8,9,16,18,43
Genetic vector
AAV	Replication inactivated viral vector that stably and predictably integrates desired engineered genetic information into neurons with minimal neurotoxicity	When injected peripherally in a tissue of interest, it travels in a retrograde manner to an innervating ganglion with the neuronal cell type selectivity determined by an engineered promoter (e.g. tyrosine hydroxylase for adrenergic specific expression)	26,199
Neuro modulation
Optogenetic ion channels	Light activated microbial ion channels with high fidelity spatial and temporal activation and inactivation	When expressed in peripheral nerves in vivo, it enables precise spatiotemporal control of nerve firing and neurotransmitter release	200
Chemogenetic receptors	Engineered G-protein coupled receptors activated by biologically inert drugs that modulate neuronal firing via altering intracellular levels of second messengers such as cAMP and calcium	When expressed in nerves in vivo, it enables temporal (and to a degree spatial) control of nerve firing and neurotransmitter release	199,201
Long-acting ion channels (NaChBac)	Voltage-gated prokaryotic sodium ion channel with prolonged inactivation kinetics	When expressed in nerves in vivo, it enables increased nerve firing and neurotransmitter release	26,202

AAV, adeno-associated virus; BBB, blood-brain barrier; CNS, central nervous system; DTA, diphtheria toxin antigen; DTR, diphtheria toxin receptor; NGF, nerve growth factor; RTX, resiniferatoxin; Trk, tropomyosin receptor kinase; TRPV1, transient receptor potential cation channel subfamily V member 1.