Authors :
Brittany Spitznagel, PhD, PharmD – Biohaven Pharmaceuticals
Alexander Komarov, PhD – Biohaven Pharmaceuticals
Ulrike DeMarco, MS – Biohaven Pharmaceuticals
Kelly Smith, PhD – Biohaven Pharmaceuticals
Ling-Xin Wang, PhD – Biohaven Pharmaceuticals
Lynn Resnick, PhD – Biohaven Pharmaceuticals
Kelly Picchione, PhD – Biohaven Pharmaceuticals
Jason Lerner, MD – Biohaven Pharmaceuticals
Presenting Author: David Weaver, PhD – Biohaven Pharmaceuticals
Steven Dworetzky, PhD – Biohaven Pharmaceuticals
Michael Bozik, MD – Biohaven Pharmaceuticals
Rationale:
Mutations in the gene, KCNQ2, encoding the Kv7.2 protein are known to cause a severe neonatal developmental and epileptic encephalopathy (DEE). Recently, an 8-year-old boy with KCNQ2 DEE was successfully transitioned from a first-generation Kv7 channel activator to opakalim (BHV-7000), a third generation Kv7 channel activator, under a compassionate use IND. Prior attempts to wean the first-generation activator resulted in episodes of status epilepticus and severe dystonia and irritability. The child is heterozygous for a mutation resulting in a Kv7.2 protein where glycine at amino acid position 281 is replaced by a glutamate (G281E). To better understand the antiseizure effects of opakalim and the first-generation activator in this patient, we sought to determine whether Kv7.2 G281E, expressed in combination with WT Kv7.2 and WT Kv7.3, forms active channels and whether these channels can be activated by the first-generation activator and/or opakalim.
Methods:
To control the stoichiometry of Kv7.2/Kv7.3 subunit assembly, an expression construct was made where Kv7.2 and Kv7.3 subunits were concatenated as shown below (Figure 1). A construct was made to achieve one copy of Kv7.2 WT and one copy of Kv7.2 G281E. The concatenated construct, in addition to unconcatenated Kv7.2 WT/Kv7.3 WT subunits, were expressed in CHO-K1 cells and evaluated in the presence and absence opakalim or the first-generation activator using whole-cell voltage-clamp electrophysiology.
Results:
The construct containing one copy of Kv7.2 G281E produced active channels with ½-maximal voltage of activation like unconcatenated Kv7.2 WT/Kv7.3 WT channels indicating voltage sensitivity remains intact in the channel containing one mutant Kv7.2 G281E subunit. When treated with either opakalim or the first-generation activator, the voltage-dependence of activation for channels containing WT Kv7.2/Kv7.3 subunits or one copy of Kv7.2 G281E was shifted toward negative potentials to a similar degree although the potency of opakalim and the first-generation activator for potentiating channels containing one copy of Kv7.2 G281E was lower compared to channels containing only WT Kv7.2/Kv7.3 subunits.Conclusions:
Since the patient is heterozygous for Kv7.2 G218E, it is likely that the channel population is comprised of ~25% WT channels, 50% channels containing one copy of Kv7.2 G281E, and 25% channels containing two copies of Kv7.2 G281E. Since both the first-generation activator and opakalim could activate the Kv7.2 G281E-containing channels and the patient responded favorably to replacement of the first-generation activator with opakalim, it is likely that therapeutic benefit arises from potentiation of both WT and Kv7.2 G281E-containing channels and underscores the potential value of opakalim for treatment of other patients with Kv7.2 mutant-associated DEE.
Funding:
Biohaven Pharmaceuticals