Tinlarebant-mediated upstream retinol starvation kinetically enables Remofuscin's downstream lysosomal exocytosis to ...

IF a sequential, dual-modality regimen consisting of systemic oral Tinlarebant (LBS-008, target dose achieving ~70% plasma RBP4 reduction, per Phase 2 pharmacokinetics referenced in the evidence set) initiated two weeks prior to, and maintained concurrently with, intravitreal or subretinal Remofuscin (soraprazan/TBS-01, dose range informed by preclinical Abca4-/- mouse studies) is administered to aged (18–24 month) female C57BL/6J mice with established RPE bisretinoid accumulation (confirmed by quantitative fundus autofluorescence, qAF),

THEN the combination will produce a measurably greater net reduction in RPE lysosomal A2E burden — quantified by HPLC bisretinoid extraction and qAF imaging — and superior functional rescue, measured by scotopic electroretinography (ERG) b-wave amplitude and RPE lysosomal membrane integrity (galectin-3 puncta density), compared to either Remofuscin monotherapy or Tinlarebant monotherapy alone, with the combination arm expected to achieve ≥40% greater qAF reduction than Remofuscin alone and restoration of ERG b-wave amplitude toward young-reference levels that Remofuscin monotherapy demonstrably failed to achieve,

BECAUSE the following causal chain is operative:

1. Remofuscin induces lysosomal exocytosis in RPE cells, expelling pre-formed A2E and bisretinoid aggregates into the extracellular space for choroidal clearance. Preclinical evidence in Abca4-/- mice showed significant reductions in intracellular lipofuscin, and Phase 2 clinical data (NCT03951731) confirmed measurable qAF reduction, validating that pharmacological clearance of existing lysosomal A2E is mechanistically achievable. This is the repair mechanism — acting on already-accumulated intracellular junk. (Julien-Schraermeyer et al., Molecular Vision, referenced in Evidence Set)

2. However, Remofuscin monotherapy produced a critical disconnect between structural lipofuscin clearance and functional RPE rescue, as noted explicitly in the Evidence Set. The most parsimonious mechanistic explanation — and the central novel claim of this hypothesis — is that ongoing retinol delivery via the intact RBP4-transthyretin (TTR) complex continuously replenishes A2E substrate. The rate of new A2E biosynthesis from freshly delivered retinol exceeds the rate of Remofuscin-driven exocytotic clearance, re-filling lysosomes faster than they can be emptied, preventing net lysosomal functional recovery. (Visual cycle A2E biosynthesis pathway: Sparrow et al., Progress in Retinal and Eye Research, 2012, referenced in Evidence Set)

3. Tinlarebant, administered upstream and prior to Remofuscin, disrupts the RBP4-TTR complex, facilitating renal clearance of RBP4 and reducing serum retinol delivery to the RPE by approximately 70%. This is validated in Phase 2 clinical data for NCT05244304 (DRAGON trial), where sustained plasma RBP4 and retinol reduction was confirmed. By starving the visual cycle of its retinol substrate, Tinlarebant reduces the ong...

SENS category: LysoSENS