2.6.3 Phosphatidylinositol-3-phosphate 5-kinase (PIKfyve)
Sophia Gayle et al 69 concluded that apimodal was an
appropriate and selective antitumor agent in opposition to B-NHL. The
PIKfyve lipokinase active site is an apilimod-specific binding site, and
their binding exerts antibody-dependent cell-mediated cytotoxic (ADCC)
effects, thus allowing the use of PIKfyve inhibitors (such as rituximab
and cetuximab) to selectively kill b-cell lymphoma (bcL-NHL) without
damaging normal cells. PIKFYVE knockdown assays confirmed that PIKFYve
inhibition resulted in reduced apilimod activity. In addition, using a
genome-wide CRISPR screen, they discovered that lysosomal dysfunction
significantly contributed to the cytotoxicity of apilimod. Although
PIKfyve activity is lost, endosomal and lysosomal membrane trafficking
is disrupted. Genome-wide loss genetic screening of SU-DHL-10 B-NHL cell
lines using GeCKO library to identify several genes such as TFEB (Major
transcription regulator of lysosomal organisms) and endosomal/lysosomal
genes CLCN7, OSTM1 and SNX10; After knockout OSTM1 and CLCN7, it was
found that apilimod resistance increased, confirming that these genes
affect apilimod sensitivity. CLCN7/OSTM1 and TFEB are downstream factors
of the B-cell receptor (BCR) and key regulators of B-cell development
that can serve as potential therapeutic targets. Knockdown of CLCN7 and
OSTM1 using CRISPR in B-NHL cells resulted in complete apilimod
resistance, while knockdown of TFEB resulted in only partial resistance,
confirming that CLCN7 / OSTM1 is a key factor in apilimod resistance in
B-NHL, while TFEB is a regulator of apilimod resistance mechanisms.
Altogether, these findings introduce a novel therapeutic strategy to
kill B-NHL tumor cells by disrupting lysosomal homeostasis through
apilimod-mediated PIKfyve inhibition.