Validation and development of MTH1 inhibitors for treatment of cancer

BACKGROUND

Previously, we showed cancer cells rely on the MTH1 protein to prevent incorporation of otherwise deadly oxidised nucleotides into DNA and we developed MTH1 inhibitors which selectively kill cancer cells. Recently, several new and potent inhibitors of MTH1 were demonstrated to be non-toxic to cancer cells, challenging the utility of MTH1 inhibition as a target for cancer treatment.

MATERIAL AND METHODS

Human cancer cell lines were exposed in vitro to MTH1 inhibitors or depleted of MTH1 by siRNA or shRNA. 8-oxodG was measured by immunostaining and modified comet assay. Thermal Proteome profiling, proteomics, cellular thermal shift assays, kinase and CEREP panel were used for target engagement, mode of action and selectivity investigations of MTH1 inhibitors. Effect of MTH1 inhibition on tumour growth was explored in BRAF V600E-mutated malignant melanoma patient derived xenograft and human colon cancer SW480 and HCT116 xenograft models.

RESULTS

Here, we demonstrate that recently described MTH1 inhibitors, which fail to kill cancer cells, also fail to introduce the toxic oxidized nucleotides into DNA. We also describe a new MTH1 inhibitor TH1579, (Karonudib), an analogue of TH588, which is a potent, selective MTH1 inhibitor with good oral availability and demonstrates excellent pharmacokinetic and anti-cancer properties in vivo.

CONCLUSION

We demonstrate that in order to kill cancer cells MTH1 inhibitors must also introduce oxidized nucleotides into DNA. Furthermore, we describe TH1579 as a best-in-class MTH1 inhibitor, which we expect to be useful in order to further validate the MTH1 inhibitor concept.

Reductions in systemic oxygen delivery induce a hypometabolic state in the turtle Trachemys scripta

We investigated the effects of vagal reductions in O(2) delivery on oxygen consumption (VO(2)) in the anesthetized freshwater turtle Trachemys scripta. Specifically, these experiments tested the hypothesis that reductions in arterial oxygen partial pressure (PO(2)) and/or systemic oxygen transport (SOT) trigger a metabolic downregulation. During electric stimulation of the efferent branch of the sectioned right vagus nerve (RVEF), systemic cardiac output decreased 60-70%, systemic PO(2) fell by approximately 30%, and SOT decreased by 60-70%. During RVEF simulation, VO(2) dropped approximately 35%. During control conditions, injection of the metabolic uncoupler 2,4-dinitrophenol (DNP) more than doubled VO(2), reflecting an increase in ATP turnover. RVEF stimulation after DNP injection produced similar cardiovascular and blood gas changes as before DNP, but VO(2) was higher than the VO(2) measured in untreated control animals, indicating that oxygen availability during RVEF stimulation is still sufficient to support VO(2) rates that are even higher than resting rates. We conclude that vagal stimulation triggers metabolic downregulation, primarily through the effects on oxygen transport, although the factor(s) that trigger the hypometabolism remain unknown. The PO(2) may still be an important messenger in metabolic control, but our results suggest that changes in SOT to the metabolically active tissues, rather than changes in PO(2) per se, play an important role in triggering hypometabolism in the freshwater turtle.

Cardiovascular actions of dogfish urotensin I in the dogfish, Scyliorhinus canicula

A synthetic replicate of dogfish urotensin 1 (U-I), a 41-amino-acid residue peptide isolated from an extract of the caudal spinal cord region of the European spotted dogfish Scyliorhinus canicula was prepared in order to study its cardiovascular actions in the species of origin. Bolus intraarterial injections of dogfish U-I (0.3-30 nmol/kg body wt) into the celiac artery of unanesthetized dogfish produced a transient fall in arterial blood pressure (P < 0.05 in the dose range 1-3 nmol/kg) followed by a sustained and dose-dependent rise in pressure (P < 0.05 in the dose range 1-30 nmol/kg). The maximum depressor response (to 3 nmol/kg) was 0.25 +/- 0.08 kPa and the maximum pressor response (to 30 nmol/kg) was 1.08 +/- 0.09 kPa. There was no significant effect on heart rate at any dose tested. Pretreatment of the animals with the alpha-adrenergic receptor antagonist phentolamine significantly (P < 0.05) attenuated the pressor response to injections of dogfish U-I (1 nmol/kg and 10 mol/kg), demonstrating that the effects of the peptide are mediated, at least in part, through release of catecholamines. The data suggest that U-I, released together with potent pressor peptide urotensin II from the caudal neurosecretory system, may play a physiological role in cardiovascular regulation in elasmobranchs.

Purification, structural characterization, and cardiovascular activity of cod bradykinins

Incubation of plasma from the Atlantic cod Gadus morhua with trypsin generated two peptides identified as [Trp5,Leu8]bradykinin (cod BK) and [Arg0,Trp5,Leu8]bradykinin (cod [Arg0]BK). Bolus intraarterial injections of synthetic cod [Arg0]BK (0.1-10 nmol/kg) into conscious cod produced an immediate increase in ventral aortic pressure that was of relatively short duration (<5 min) and an increase in heart rate. Cod [Arg0]BK was approximately 10 times more potent than cod BK, and the maximal pressor response produced by the peptide was significantly (P < 0.05) greater. Bolus intra-arterial injections of either mammalian BK or cod des-Arg9,[Arg0]BK, in doses up to 100 nmol/kg, had no effect on pressure or heart rate. The data indicate that the ligand binding properties of the BK receptors in cod are different from those of the mammalian B1- and B2-receptor subtypes. The pressor response to 1 nmol/kg cod [Arg0]BK was reduced (by 51 +/- 6%; P < 0.05) in prasozin-treated fish, whereas in enalapril-treated fish, the response to the peptide was enhanced (by 42 +/- 12%; P < 0.05). The data indicate an involvement of catecholamines but not an activation of the renin-angiotensin system in mediating the vasopressor action of BK in the cod.

Blood pressure control by the renin-angiotensin system and its interaction with the sympathetic nervous system in fish

The renin-angiotensin system (RAS) is from an evolutionary viewpoint a well-preserved regulatory system with many morphological and physiological similarities in all vertebrate groups from fish to mammals. Regulation by the RAS is often complicated, involving several other control systems and blood pressure is just one of many parameters controlled by this system. Control of cardiovascular functions by the RAS in fish has received some attention and both a direct action and modulation of adrenergic nerves by angiotensin II have been reported in most species studied. The interaction between the RAS and the adrenergic system in fish is not fully understood, but the facilitation of catecholamine release by angiotensin II is probably one of the more important mechanisms.

Isolation, localization, and cardiovascular activity of tachykinins from the stomach of the bowfin Amia calva

The bowfin is an extant representative of an ancient group of ray-finned fish with evolutionary connections to modern teleosts. A peptide with substance P-like immunoreactivity was isolated from an extract of bowfin stomach and its primary structure was established as Ser-Lys-Ser-His-Gln-Phe-Tyr-Gly-Leu-Met-NH2. This amino acid sequence resembles mammalian substance P only in the COOH-terminal region of the peptide. A second tachykinin with neurokinin A-like immunoreactivity isolated from the extract comprises 23 amino acid residues and shows limited structural similarity to mammalian neuropeptide-gamma. A randomly distributed population of cells in the gastric glands of the bowfin were immunostained with an antiserum raised against substance P, but no immunopositive structures were identified in the surface epithelium, lamina propria, or the nerve plexuses of the submucosa. Bolus injections of synthetic bowfin substance P (0.1-10 nmol/kg) into the bulbus arteriosus of unanesthetized bowfin resulted in a significant and dose-dependent rise in vascular resistance and arterial blood pressure (P < 0.01) and a fall in cardiac output (P < 0.05) without change in heart rate. After 5-10 min, arterial pressure and vascular resistance returned to preinjection levels, but cardiac output significantly (P < 0.05) increased over baseline values. The response to the peptide was unaffected by pretreatment of the animals with phentolamine. The study has shown that the stomach of the bowfin synthesizes tachykinins with novel structural features that display cardiovascular activity in this species.

Isolation and biological activity of [Trp5]bradykinin from the plasma of the phylogenetically ancient fish, the bowfin and the longnosed gar

The holostean fish occupy an important position in vertebrate phylogeny as extant representatives of a ancient group of ray-finned fish with evolutionary connections to present-day teleosts. Incubation of heat-denatured plasma from the bowfin Amia calva with trypsin generated bradykinin-like immunoreactivity. The primary structure of bowfin bradykinin was established as Ala-Pro-Pro-Gly-Trp-Ser-Pro-Phe-Arg. This amino acid sequence contains one amino acid substitution (Phe5 --> Trp) compared with mammalian bradykinin. The same peptide was generated in heat-denatured plasma from the longnosed gar Lepisosteus osseus. Treatment of plasma from either the bowfin or gar with glass beads under conditions previously shown to activate Factor XII in the plasma of mammals and reptiles did not generate bradykinin. Bolus injections of synthetic bowfin bradykinin (0.1, 0.3, and 1.0 nmol/kg) into the bulbus arteriosus of unanesthetized bowfin resulted in an immediate fall in arterial blood pressure of 5-10 min duration that was followed by a dose-dependent rise in pressure that was sustained for 30-60 min. There was no change in heart rate following bradykinin administration. The data suggest that the kallikrein-kinin system may predate the appearance of teleosts and may play a role in cardiovascular regulation in holosteans.

THE RENIN-ANGIOTENSIN SYSTEM IN BLOOD PRESSURE CONTROL DURING EXERCISE IN THE COD GADUS MORHUA

The effects of angiotensin I, angiotensin II and exercise on ventral and dorsal aortic blood pressure and heart rate were investigated in the Atlantic cod, Gadus morhua. Both angiotensins produced a marked increase in blood pressure. After injection of the angiotensin-converting enzyme (ACE) inhibitor enalapril, both ventral and dorsal blood pressures decreased significantly and the effect of angiotensin I was abolished. This demonstrates that ACE activity is necessay for conversion of angiotensin I to angiotensin II in the cod, as in other teleosts investigated, and provides a tool for further study of angiotensin function. During swimming exercise at 2/3 body lengths per second, ventral and dorsal aortic blood pressures increased, but this exercise hypertension was absent in fish pretreated with the alpha-adrenoceptor antagonist prazosin. Instead, an increase in both ventral and dorsal aortic blood pressures occurred immediately after the exercise period. This post-exercise hypertension could be abolished by injection of enalapril, suggesting that the angiotensin system is the responsible ‘anti-drop’ factor activated in the absence of a functional adrenergic vasomotor control. We conclude that the angiotensin system provides a major contribution to the resting blood pressure regulation in the cod, and that this system can be activated to offset a decrease in arterial blood pressure.