Autophagy and Lysosome-Based Targeted Degradation Technologies

Targeted protein degradation (TPD) initially centered on the ubiquitin–proteasome system (UPS). Classical PROTACs demonstrated that small molecules could catalytically eliminate intracellular proteins by recruiting E3 ligases. Yet the proteasome has intrinsic constraints:

• It primarily degrades soluble intracellular proteins
• It struggles with large aggregates and organelles
• It cannot directly eliminate extracellular or membrane proteins
• Its activity can be compromised in stressed or diseased cells

These limitations have catalyzed the rise of lysosome- and autophagy-based targeted degradation technologies — modalities that harness the cell’s broader proteostasis and trafficking machinery.

Unlike the proteasome, the lysosome:

• Degrades membrane proteins and extracellular ligands
• Handles protein aggregates and damaged organelles
• Integrates with endocytosis and macroautophagy
• Provides access to previously “undruggable” spatial compartments

This expansion of degradable target space is reshaping therapeutic strategies in oncology, neurodegeneration, immunology, and rare disease.

LYTACs are bifunctional molecules that bind:

1. An extracellular or membrane-bound target protein
2. A lysosome-shuttling receptor (such as CI-M6PR or ASGPR)

Upon binding, the ternary complex is internalized through endocytosis and trafficked to the lysosome for degradation.

This enables:

• Degradation of secreted cytokines
• Removal of membrane receptors
• Clearance of pathogenic extracellular proteins

Unlike monoclonal antibodies, which typically block function, LYTACs eliminate the target entirely.

• Broad tissue expression
• Established lysosomal trafficking route
• Suitable for systemic applications

• Liver-restricted expression
• Enables hepatocyte-specific degradation
• Valuable for metabolic and liver diseases

Receptor selection determines tissue specificity and therapeutic index.

• Degradation of growth factor receptors
• Removal of immune checkpoint ligands
• Targeting shed extracellular drivers

• Eliminating profibrotic secreted proteins

LYTACs extend TPD into compartments previously inaccessible to small molecules.

Beyond classical LYTACs, newer modalities refine surface protein degradation strategies.

LYMTACs expand lysosome-directed degradation by targeting lysosomal membrane proteins or alternative internalization routes.

Key differentiators:

• Exploit distinct lysosomal membrane trafficking pathways
• Potentially bypass limitations of CI-M6PR dependency
• Broaden receptor options

LYMTACs increase flexibility in receptor biology and tissue targeting.

PROTABs are antibody-based constructs designed to induce degradation of cell-surface targets.

Mechanistic logic:

• Antibody binds membrane target
• Engages endogenous ubiquitination or internalization machinery
• Drives lysosomal degradation

Unlike classical antibodies that merely block receptor function, PROTABs induce complete target removal.

Advantages over mAbs:

• Sustained target depletion
• Reduced compensatory signaling
• Potential to overcome resistance to receptor blockade

While LYTACs operate via endocytic–lysosomal pathways, other technologies harness macroautophagy, the cell’s bulk degradation system.

Autophagy normally clears:

• Protein aggregates
• Damaged mitochondria
• Intracellular pathogens

Selective autophagy can be induced through engineered proximity strategies.

ATTECs are small molecules that bind both:

• A target protein
• LC3 (a core autophagosome protein)

By tethering the target to LC3, ATTECs promote selective autophagic engulfment and degradation.

• Proteasome-independent
• Effective against aggregate-prone proteins
• Promising in neurodegenerative diseases

• Dependence on autophagic flux
• Potential off-target autophagy activation

AUTACs function differently from ATTECs.

AUTACs mimic S-guanylation signals that induce K63-linked ubiquitination. This modification marks the target for selective autophagic degradation.

• Ubiquitin-dependent autophagy engagement
• Broader compatibility with cellular degradation signals
• Potential organelle targeting applications

AUTACs have been explored for mitochondrial clearance and damaged organelle removal.

AUTOTACs directly recruit the autophagy receptor p62/SQSTM1 to a target.

p62 recognizes ubiquitinated proteins and links them to LC3 on autophagosomes. AUTOTACs bypass ubiquitination complexity by directly engaging p62.

• Simplified recruitment logic
• Potentially more direct autophagy initiation

ULKTACs recruit ULK1, the kinase that initiates autophagosome formation.

Instead of tagging the target for existing autophagy, ULKTACs locally activate autophagy machinery near the target protein.

• Spatially confined autophagy
• Greater control of degradation initiation
• Potential to overcome autophagic flux limitations

Many diseases (e.g., neurodegeneration) involve impaired autophagy. Therapeutic success depends on:

• Baseline flux levels
• Lysosomal integrity
• mTOR signaling state

Biomarker development is essential.

Lysosome and autophagy components vary across tissues. Leveraging:

• Receptor-restricted expression (ASGPR)
• Tissue-specific autophagy regulators
• Delivery vectors

can optimize therapeutic index.

Non-selective autophagy induction risks:

• Muscle wasting
• Immune dysregulation
• Metabolic disturbance

Precision recruitment is therefore critical.

Challenges include:

• Large molecular weight
• Cell permeability
• Endosomal escape (for extracellular targeting systems)
• Maintaining ternary complex stability

Structure-guided design and high-content imaging screens are increasingly central.

Autophagy-based degraders are especially promising in:

• Aggregate-prone protein diseases
• Huntington’s disease
• Tauopathies
• Parkinson’s disease

Proteasome systems often struggle with large fibrillar aggregates; autophagy excels in this domain.

In cancer, autophagy plays dual roles:

• Tumor suppression (via proteostasis maintenance)
• Tumor survival under stress

Targeted autophagic degradation can:

• Eliminate oncogenic drivers
• Remove immune evasion proteins
• Target metabolic dependencies

Selective clearance of:

• Cytokines
• Surface immune checkpoints
• Secreted inflammatory mediators

could reshape autoimmune and inflammatory disease treatment.

Diseases caused by:

• Toxic gain-of-function proteins
• Organelle accumulation
• Protein misfolding

may benefit from selective autophagy recruitment strategies.

Biotech companies are rapidly expanding into lysosomal and autophagy platforms, often positioning themselves as:

• “Beyond PROTAC” companies
• Extracellular degradome specialists
• Autophagy-first drug discovery platforms

Key differentiators include:

• Receptor libraries
• Autophagy receptor selectivity
• Tissue-targeting technologies
• Biomarker development capabilities

Pharmaceutical interest is growing due to:

• Access to membrane proteins
• Potential first-in-class opportunities
• Synergy with antibody platforms

As with proteasomal degradation, resistance can emerge through:

• Receptor downregulation
• Lysosomal dysfunction
• Autophagy pathway mutations
• Compensatory signaling pathways

Combination strategies (e.g., mTOR modulation + targeted autophagy) may improve durability.

The next phase of innovation will likely focus on:

• Organelle-specific degradation (mitophagy-targeting chimeras)
• Condensate-associated autophagy
• Tissue-restricted lysosomal receptors
• Small-molecule modulators of autophagy selectivity
• Multi-functional chimeras integrating degradation and signaling control

Integration with:

• Synthetic lethality frameworks
• Spatial pharmacology
• AI-guided ternary complex modeling

will further refine precision.

Autophagy- and lysosome-based targeted degradation technologies represent a decisive expansion of the druggable proteome.

They enable:

• Extracellular protein elimination
• Aggregate clearance
• Organelle removal
• Context-dependent degradation

Where classical PROTACs opened the door to catalytic protein elimination, lysosomal and autophagy modalities unlock the broader spatial architecture of cellular proteostasis.

The field is evolving from simply degrading intracellular proteins to programming cellular disposal systems.

In doing so, drug discovery is transitioning from blocking disease drivers to orchestrating their controlled removal across compartments — inside, outside, and across organelles.

The proteasome was just the beginning.