Hi Alpharius,
Thanks for the link. They also discuss FISETIN but are not clear in the abstract whether it was studied together with the two selective BCL-XL inhibotors A1331852 and A1155463, or independently? One would need to read the full article to establish that naturally occurring fruit flavone FISETIN would possibly be a relatively safe senolytic substance?
They tested all 3 substances independently. A1331852 and A1155463 are selective inhibitors of Bcl-XL.
They did not explain how Fisetin kills senescent cells, but there are some cancer cell studies with Fisetin which suggest BCL-2 inhibition:
https://www.ncbi.nlm...pubmed/25840992
Fisetin binds directly to Bcl-2: https://www.ncbi.nlm...pubmed/28264627
But it seems to hit other Bcl-2 family members like Mcl-1, Bcl-xL and Bcl-w (other name Bcl2L2), either by lowering the protein level or by binding to the antiapoptotic proteins.
https://www.ncbi.nlm...pubmed/20510331
Ok so to me it seems Fisetin inhibits probably not selectively the Bcl-2 antiapoptotic proteins.
Thats maybe a problem. Why? Please stay with me here.
Because Navitoclax does the same it binds not selective but strong to Bcl-2, Bcl-XL and Bcl-w.
But do we need the Bcl-2 inhibition really or is it just causing side effects like neutrophils toxicity? It seems that the selective Bcl-2 inhibitor TW-37 is not senolytic.
On the other side the selective Bcl-XL inhibitors A1331852 and A1155463 are senolytic. They do not bind to Bcl-2.
So it seems Bcl-2 is not so important in senescent cells but its inhibition could kill other healthy cells.
So from the proteins discussed here, it would be interesting to know if Bcl-w or Mcl-1 inhibition is needed to kill senescent cells. Or maybe even the Bcl-2 inhibition could be needed in some cells or maybe we just need a little bit supression, who knows. We are experimenting here.
Fisetin is probably like a natural version of Navitoclax and inhibits all Bcl-2 family members not selectively.
Is it better or worse then Navitoclax, I can`t tell.
Maybe it does not even matter because we would just use Navitoclax 1 time in 2-3 months and the positive effects would outweigh the negatives, but this is also speculation.