Key Highlights

  • Xaranetide inhibited all three ion channel types tested in cell-line experiments: an NMDA receptor subtype, CaV2.2 and ASIC1a
  • CaV2.2 and ASIC1a inhibition is reported for the first time, from testing at ApconiX in the United Kingdom
  • With 14 nM xaranetide present, raising glutamate from 100 µM to 1 mM did not overcome inhibition of GluN1/GluN2A receptors
  • Mean current at -80 mV came back from about 50% to 83% of the initial response after a step to +40 mV

Argenica Therapeutics Limited (ASX:AGN), a Perth-based clinical-stage biotechnology company, reported laboratory results on xaranetide, its lead drug candidate. In cell-line experiments, the compound inhibited three types of ion channel linked to brain injury: a subtype of the NMDA receptor, CaV2.2 and ASIC1a. Argenica said its CaV2.2 and ASIC1a results are being reported for the first time. ApconiX in the United Kingdom and B'SYS in Switzerland ran the work.

Study Design and Channels Tested

Researchers measured electrical currents in HEK (Human Embryonic Kidney) cell lines that stably express each full-length channel, and ran a reference control in parallel for every channel. For the NMDA receptor, the experiments looked at how potent xaranetide is, how quickly it acts, by what mechanism and how that depends on membrane voltage. The three channels were the NMDA receptor, ASIC1a (acid-sensing ion channel 1a) and CaV2.2, a voltage-gated calcium channel, each associated with glutamate-related excitotoxicity. Argenica describes that process as glutamate building up, over-activating receptors on neurons and letting calcium accumulate inside them, which can damage mitochondria and trigger processes that end in neuronal death.

NMDA Receptor Results

Xaranetide lowered activity in both NMDA receptor subunits examined, and the inhibition grew as the concentration rose. With 1.2 µM applied, onset time constants were near five seconds in both subtypes. B'SYS then studied GluN1/GluN2A receptors exposed to 0.014 µM (14 nM) xaranetide while glutamate was stepped up through 100 µM, 300 µM and 1 mM; inhibition remained throughout. Argenica said this pattern is consistent with an effect that does not depend on competing for the glutamate binding site. Additional tests on the NMDA 1/2A subtype were reported as supporting a voltage-dependent, non-competitive open-channel blocking mechanism.

Partial Reversibility

Argenica also examined whether the NMDA effect can be undone. Following xaranetide exposure and a step in membrane voltage to +40 mV, the average current recorded at -80 mV came back from about 50% of the starting response to 83%, a partial reversal under that protocol. The company linked this to the role of NMDA receptors in normal signalling, noting that they help strengthen links between neurons, which supports learning and adaptation during recovery. Its stated therapeutic aim is to restrain excess receptor activity during acute injury while leaving the signalling needed for recovery.

CaV2.2 and ASIC1a Findings

The ApconiX testing recorded currents through CaV2.2, ASIC1a and an NMDA receptor subtype, and xaranetide inhibited each of them. Argenica says CaV2.2 helps regulate calcium entry and the discharge of chemical messengers, glutamate among them, between brain cells. ASIC1a reacts to acidity: the company states that tissue can turn acidic when oxygen supply and blood flow fall, and that this channel adds to the ensuing damage. These results follow earlier published work by Professor Bruno Meloni and colleagues (Edwards et al., 2018, Molecular Brain), in which R18D, identified by Argenica as xaranetide, reduced calcium accumulation induced by glutamate in cultured neurons and protected them from excitotoxic injury.

Company Commentary

Argenica states that acute ischaemic stroke and traumatic brain injury set off damaging biological processes that can start within minutes and continue for hours to days. In stroke, it says the aim is to protect tissue that is still viable but under threat in the penumbra surrounding the infarct core, while blood flow returns. It adds that glutamate can build up and over-activate NMDA channels when blood flow is reduced.

Chief Executive Officer and Managing Director Dr Liz Dallimore said the proposed mechanism acts on NMDA channels after they open, potentially limiting calcium entry, and that activity at ASIC1a and CaV2.2 could be relevant in more severe strokes. She described this as a possible explanation for findings in Argenica's exploratory Phase 2 analyses of more severely affected patients. Argenica also cited a Stroke Treatment Academic Industry Roundtable (STAIR) recommendation to prioritise therapies that act on multiple injury pathways.

Summing Up

Argenica Therapeutics reported in vitro results in which xaranetide inhibited an NMDA receptor subtype, CaV2.2 and ASIC1a in HEK cell line experiments at ApconiX and B'SYS. The NMDA inhibition persisted as glutamate rose from 100 µM to 1 mM and was partly reversible, with mean current recovering from approximately 50% to 83%. The CaV2.2 and ASIC1a results are reported for the first time.