Long-Acting Peptide Depot Formulations as an Injection-Reduction Strategy

Long-acting peptide depot formulations reduce how often patients need injections, but they are not non-injectable alternatives for people who fear needles. Their central trade-off is fewer injections in exchange for new constraints on release, stability and administration. Nanoparticle-enabled intranasal delivery is still being developed and could remove the injection and help the drug reach the brain, but those hopes still need to be borne out in treatment.

Why patients abandon peptide therapy before it can work

Patients who cannot stay on a treatment cannot get the long-term benefit it is meant to provide. In peptide therapy, the injection schedule is a structural part of that problem. Native GLP-1 has a plasma half-life measured in minutes, which helps explain why drugs in this class have long needed to be given often through an invasive route. Moving from daily to weekly dosing was a meaningful advance. Yet a weekly injection still asks patients to accept an indefinite commitment to an invasive route.

Some abandon approved prescriptions at the pharmacy before taking a dose, while others stop soon after the first fill or within the first year. Cost and insurance barriers are leading drivers, with gastrointestinal side effects and access problems adding further pressure. A formulation can change how a patient takes a drug without changing whether they can get it or pay for it.

Within that broader problem, nausea, vomiting and diarrhea give formulation scientists a specific target. These effects are pharmacokinetically linked to peak drug concentrations after injection, making the exposure curve a potential design lever. Sustained release could spread exposure over time and reduce the gastrointestinal events caused by peaks. Lionbio is pursuing a different route toward that objective through nanoparticle-based nasal-spray delivery, with the potential to reduce nausea without a bolus injection. The adherence problem includes nontechnical barriers and engineering problems in its injection and exposure components.

What depot formulations actually do to a drug's time-in-body profile

A depot converts one injection from a bolus event into a controlled-release reservoir. Instead of making the administration schedule closely track the drug’s short lifetime, it releases the peptide over an extended period. The depot is intended to maintain a therapeutically relevant plasma concentration between injections. This separates how often the patient receives treatment from how long the body remains exposed to it.

The release profile describes how that exposure changes over time. Its peak is the highest concentration, also called Cmax, while its trough is the low point before the next dose. An excessive early peak can produce unwanted pharmacological effects, whereas a trough near zero can leave the patient underexposed. A useful depot must therefore do more than keep releasing measurable drug. It must maintain enough active peptide across the intended dosing interval without an excessive initial surge.

A biodegradable polymer matrix can protect the peptide against enzymatic and hydrolytic degradation while controlling its release. Polymer properties, including molecular weight, end group and lactide-to-glycolide ratio, affect encapsulation efficiency, particle size, release profile and preserved bioactivity. Those properties connect the material’s design to the drug’s time-in-body profile. However, the peptide must also remain stable inside the matrix during storage and after injection. Every mechanism that slows release introduces another set of engineering constraints.

Three platform technologies and the distinct trade-offs each carries

The main approaches are PLGA/PLA biodegradable microspheres, in-situ forming hydrogel depots and albumin-binding peptide conjugates. The first two control release through a material placed at the injection site. The third extends the peptide’s lifetime in circulation without forming a depot, making it a useful comparator. The comparison turns on where each approach places the work of prolonging exposure. That choice determines both its use case and its residual burden.

PLGA/PLA microspheres are the most established platform in this group. Encapsulating peptides in biodegradable polymer can increase bioavailability and extend release, with the aim of maintaining a constant plasma concentration. Liraglutide-loaded PLGA microspheres have shown sustained in-vitro release over multiple weeks, and exenatide PLGA microspheres have been investigated for controlled release. These findings demonstrate the platform’s relevance to peptide therapeutics, although in-vitro release is not itself evidence of a usable clinical dosing interval. The practical task is to translate a long release period into reliable therapeutic exposure.

Microspheres make that task demanding because the formulation must control both the initial burst and the end-of-interval decline. They can also be hard to reconstitute before injection, while aggregation and degradation limit how well they hold up in storage. Manufacturing must coordinate drug loading, peptide integrity, microsphere characteristics, release kinetics and reproducibility. Changing one of these variables can affect the others. A formulation that extends release still has to preserve the active ingredient and remain reproducible enough to manufacture.

In-situ forming gels offer a simpler preparation process than microspheres, which can make industrialization more manageable. Xiong et al. (2024) developed a water-free in-situ depot gel for ACTY116 that avoided high temperatures, high shear mixing and homogenization to preserve peptide chemical stability. Coulter et al. (JACS, 2024) describe a further refinement in enzyme-responsive peptoid-peptide hydrogels. These systems modulate release in response to local enzymatic activity rather than relying solely on diffusion or bulk erosion. The gel approach therefore offers more than one way to tune the reservoir.

Hydrogel formulations using semaglutide as a model have shown the potential to sustain exposure for over six weeks, with reduced peak-to-trough variation and comparable total bioavailability relative to daily dosing. The supplied work is a preprint involving rodent studies, so its implications for quarterly dosing in humans remain a development prospect. Physical administration also remains consequential. In-situ forming depots may require 18–19-gauge needles, while injectable microspheres typically use 20–23-gauge needles, compared with 27–31 gauge for standard subcutaneous peptide injections. A longer interval can thus come with a larger needle.

Albumin-binding conjugates change the mechanism by attaching a fatty-acid linker to the peptide. When the peptide binds to albumin in circulation, its terminal half-life increases without the need for a polymer matrix or gel. Yu et al. (2026) report TE-8214, a fully aqueous, depot-free dual-fatty-acid-conjugated octreotide analog administered through a fine 30-gauge needle without reconstitution. In Phase 1, it was well-tolerated across the doses tested, with no serious or Grade ≥3 treatment-emergent adverse events. At the highest dose, IGF-1 remained suppressed through Day 28.

That biomarker response should not be confused with a demonstrated monthly dosing schedule. Albumin binding extends half-life to days, while microsphere and gel reservoirs aim to extend it to weeks. The molecules may need more engineering to allow doses a month or a quarter apart. Frequency is exchanged for constraints elsewhere, including needle gauge, reconstitution complexity or the dosing-interval ceiling.

What depot technology does not solve about delivery-site burden and stability

The clearest demonstration of this distinction comes from long-acting somatostatin analogs. Yu et al. (2026) note that octreotide LAR, lanreotide Autogel and pasireotide LAR permit monthly dosing but require 18–22 gauge injections, frequently causing pain, nodules and inflammation. Nodules can be mistaken for metastatic lesions during imaging, adding anxiety to the physical burden. Repeated injections can also produce localized induration and tissue hardening.

Tissue changes can complicate future administrations and create variable drug release, connecting local injury to pharmacokinetic reliability. This makes the patient-facing and formulation-facing problems inseparable. A release profile designed in the formulation must still perform in tissue that may change over repeated treatment. Counting injections alone misses that interaction.

Stability imposes a separate ceiling because a longer-lasting reservoir is useful only while its peptide remains active. Protection during manufacture, storage and residence in the body cannot be treated as the same task. The water-free ACTY116 formulation illustrates how even preparation conditions must be chosen around a sensitive payload. Even when a reservoir lasts longer, exposure can still fall too low near the end of release.

These are reasonable targets for further engineering. The albumin-conjugate approach already shows that some needle and preparation burdens can be reduced by changing the mechanism. Intranasal nanoparticle strategies, including Lionbio’s, go further in one specific respect by avoiding the subcutaneous reservoir and its polymer-stability problem altogether. Nasal delivery changes which stability constraints matter. A longer-lived subcutaneous depot also leaves central nervous system delivery unsolved.

Why reaching the brain through a subcutaneous depot remains out of reach

Sustained plasma exposure and adequate brain exposure are different pharmacological objectives. A subcutaneous depot can improve the first without establishing the second because the blood-brain barrier still separates systemic circulation from central targets. More time in circulation does not by itself establish an effective concentration in the brain.

That distinction matters as interest in neurological applications of GLP-1 receptor agonists expands. Preclinical studies report neuroprotective effects, including reduced protein aggregation, improved mitochondrial function and suppression of neuroinflammation. Epidemiological analyses also suggest that people who use these drugs long term have a lower incidence of dementia and Parkinson’s disease. These signals make central delivery scientifically important, but they do not establish a neurological treatment benefit. Observational associations and preclinical mechanisms leave a clinical question open.

Randomized Alzheimer’s disease trials have so far not demonstrated clinically meaningful cognitive improvement. That gap between biological promise and trial outcomes cannot be assigned to brain delivery alone from the evidence given. Nevertheless, limited brain penetration creates a clear pharmacological tension. Raising systemic doses to compensate can increase peripheral exposure and the gastrointestinal burden that smoother depot release was intended to reduce.

The resulting research directions include earlier intervention, biomarker-guided patient selection and brain-penetrant formulations. Extending a subcutaneous release interval changes when the drug enters circulation, while brain-targeted delivery changes where it can go. Neither objective substitutes for the other. The unmet need is thus not simply a longer-lasting depot, but a formulation designed for brain access.

The nose-to-brain route as a structurally different answer to the delivery problem

Intranasal delivery offers access through olfactory and trigeminal nerve pathways that can bypass the blood-brain barrier. Its logic is therefore different from holding a peptide beneath the skin and releasing it into circulation. In principle, the route could produce higher brain concentrations with lower systemic exposure. Lower peripheral Cmax could also address the gastrointestinal side-effect mechanism from a different direction. These potential advantages require evidence to establish.

The nasal route has its own barriers, including mucociliary clearance, enzymatic degradation and epithelial permeability. Nanocarriers, mucoadhesive systems and cell permeation enhancers are being studied to address them. A 2025 King’s College London study led by Han et al., published in Small, found that intranasal acyl-ghrelin conjugated to gold nanoparticles reached the brain and produced neuroprotective effects in an animal model. Compared with free peptide, the nanoparticle formulation improved stability and brain uptake. The result supports the delivery mechanism without establishing human efficacy.

Winterdahl et al. (2025) used [¹³N]-labeled oxytocin to track intranasal peptide distribution in six healthy human volunteers, providing the first human PET evidence for nose-to-brain peptide transport. Transport evidence still leaves questions about therapeutic dose, clinical benefit and repeatable delivery. Rodents have larger olfactory epithelia relative to body size than humans, making translation a genuine anatomical challenge. Sex-based dosing dimorphism adds another variable for clinical investigation. These constraints make formulation design central.

Built on more than 30 years of biomedical innovation from Columbia University, Lionbio’s nanoparticle platform is designed to address clearance, peptide stability and epithelial transport. It belongs within this broader effort to turn nose-to-brain delivery into a clinically useful route, rather than serving as evidence that the translational work is complete. A depot reduces injection frequency, whereas an effective intranasal formulation could remove the injection itself. Evidence for each route is still needed to show when patients can move from fewer injections to none.