PowerShell read from file search for string and remove unwanted text

working on a script to backup DNS settings from a NIC and changing them back after some other actions.

$BACKUP = Get-DnsClientServerAddress -InterfaceAlias WLAN* >>c:tmpdns.txt

contents of dns.txt

InterfaceAlias               Interface Address ServerAddresses                                                                          
                             Index     Family                                                                                           
--------------               --------- ------- ---------------                                                                          
WLAN 2                               6 IPv4    {1.1.1.1, 8.8.8.8}                                                                  
WLAN 2                               6 IPv6    {}

now for restoring i just need the 2 IP’s between the {} so im starting with

$OLD = Get-Content C:tmpdns.txt | Select-String -Pattern 'ipv4' -SimpleMatch

what leaves me with

WLAN 2                               6 IPv4    {1.1.1.1, 8.8.8.8}

but how do i get rid of the rest to get just the 2 IP’s left in $Old

thx for help