ASH 2021 | Targeting amyloidosis with botulinum toxin

AL amyloidosis is a rare and very debilitating disease, that remains incurable. And unlike multiple myeloma, that is a tumor part in disease, amyloidosis is related to the expansion of a limited amount of plasma cell clones, that secrete an incredible amount of free light chains. And importantly, these free light chains have chemical physical properties that make them amyloidogenic. So they form these insoluble fibers in circulation, and precipitate in target organs, inducing organ damage, and eventual patient demise.

The current therapies for AL targeted the bone marrow plasma-cell clone, using approaches that are employed in myeloma. But however, there are no therapies that really target the pathogenic component of this disorder, that is the free light chain secretion. And also surprisingly, there is limited amount of data that show the mechanisms of free light chain and immunoglobulin secretion in plasma cells.

When we started this study, there were only two works that showed a colocalization between intact immunoglobulin and SNARE proteins, specific SNARE proteins. So SNAREs are a large family of proteins that by coating secretory vesicles, mediate the secretion of immunoglobulin, extracellularly. And it’s well known that SNAREs are the main target of botulinum neurotoxin.

Here at ASH, we present our work, where we targeted free light chain secretion by delivering botulinum neurotoxin to, plasma cells. And we tested seven different serotypes of botulinum with a distinct SNARE specificity. And we showed that all serotypes of botulinum, except for the B, that behaved like the control vector, induced cytotoxicity at 24 hours. Further, we observed that upon botulinum neurotoxin administration, there was a decrease in free light chain secretion extracellularly, in the cells that undergo apoptosis, but not in the cells that survive, consistent with our hypothesis.

Also, we wanted to identify, what are the potential SNARE targets of these cytotoxic botulinum neurotoxin. And we looked at the SNARE cleavage, that is a readout of the catalytic activity of botulinum neurotoxin. And we showed that the clones that undergo apoptosis, have also a dual cleavage of SNAP23 and VAMP-3, that are potentially two SNARE targets, SNARE proteins that modulate the free light chain secretion in plasma cells.

Also, it pertains to molecular mechanisms. We showed the retention of free light chains intracellularly, and used unfolded protein response, with the induction of CHOP and GADD34. That is the molecular mechanisms that will drive the apoptosis in these cytotoxic clones.

So overall, our preliminary data show really, the proof of concept, that it is really feasible to target immunoglobulin and free light chain secretion in plasma cells. And this is a potential translatability of this approach in AL amyloidosis, and clinical application, potentially, in the future.