The cGAS-STING pathway has become one of the most promising targets in immuno-oncology. By activating the Stimulator of Interferon Genes (STING) receptor, researchers can trigger potent type I interferon responses that reprogram the tumor microenvironment and prime systemic anti-tumor immunity. But translating STING activation from bench to clinic depends heavily on the quality and format of the agonist you start with. Unconjugated small molecules often suffer from rapid clearance, poor tumor retention, and systemic toxicity — problems that PEG-conjugated and linker-ready derivatives are specifically designed to solve. Whether you are screening STING agonists for antibody–drug conjugates (ADCs), nanoparticle formulations, or standalone immunotherapy candidates, this buyer’s guide will help you identify the right reagent for your program.
What to Look For in a STING Agonist Reagent
1. Conjugation-Ready Functional Groups
If your goal is targeted delivery — via an ADC, nanoparticle, or polymer carrier — you need a STING agonist that arrives with a bioconjugation handle already installed. Look for maleimide (Mal), DBCO, or NHS ester reactive groups. Products sold as bare agonists require additional synthetic steps that add cost, time, and batch-to-batch variability.
2. Cleavable Linker Chemistry
For intracellular payload release, a cleavable linker between the agonist and the conjugation handle is critical. Valine-citrulline (Val-Cit or V/C) dipeptide linkers are the gold standard: they are stable in circulation but are rapidly cleaved by cathepsin B inside tumor cells and endosomes. This is the same linker technology used in FDA-approved ADCs.
3. Purity and Monodispersity
STING agonist conjugates are complex molecules. Impurities or polydisperse PEG chains introduce variability in potency assays and pharmacokinetic studies. Prioritize suppliers offering ≥95% purity with defined, monodisperse molecular weights — not broad-distribution polymers.
4. Structural Diversity and Analog Availability
The STING pathway has multiple ligand classes — cyclic dinucleotides (CDNs) like cGAMP, amidobenzimidazole (ABZI) dimers like diABZI, and non-nucleotide small molecules like MSA-2. Having access to multiple structural classes from a single supplier streamlines SAR studies and head-to-head comparisons.
5. Documentation and Supply Reliability
Immunotherapy timelines are aggressive. Choose a supplier that provides certificates of analysis (CoA), ships quickly, and offers custom synthesis for scale-up. Delays in reagent procurement directly delay IND-enabling studies.
The Top 5 STING Agonist Reagents
1. PurePEG STING Agonist Collection (13 Conjugation-Ready Reagents)
Best for: Researchers who need a comprehensive toolkit of conjugation-ready STING agonists
PurePEG’s STING agonist collection is the most versatile catalog of conjugation-ready STING pathway reagents available from a single source. The portfolio spans 13 distinct products, including diABZI derivatives with maleimide, DBCO, and piperazine handles, cleavable Val-Cit linker constructs, the non-nucleotide agonist MSA-2, and Fmoc-protected intermediates for solid-phase synthesis. Unlike most competitors that sell unconjugated agonists, PurePEG provides molecules that are ready for bioconjugation directly out of the vial — eliminating custom synthesis steps. Every product ships with ≥95% purity, defined molecular weight, and a certificate of analysis. Built on the same monodisperse PEG and linker chemistry platform used in FDA-approved ADCs, this collection gives immuno-oncology teams a single procurement source for screening, hit-to-lead, and preclinical studies. Next-day shipping is available from PurePEG’s San Diego facility.
→ [Browse the full STING agonist collection at PurePEG](https://purepeg.com/product-category/sting/)
2. PurePEG diABZI-V/C-DBCO (DBCO-Val-Cit-PABC-diABZI)
Best for: Click-chemistry-based ADC and nanoparticle conjugation
diABZI-V/C-DBCO (SKU 81101, CAS 3035557-60-6, MW 1500.66) is a fully assembled STING agonist–linker–payload construct designed for strain-promoted azide-alkyne cycloaddition (SPAAC) click chemistry. The DBCO handle reacts selectively with azide-functionalized antibodies, polymers, or nanoparticles under physiological conditions — no copper catalyst required. The Val-Cit-PABC cleavable linker ensures that the active diABZI payload is released only after cathepsin B cleavage inside the target cell. This is the architecture of choice for researchers building next-generation STING-agonist ADCs or targeted nanomedicine platforms. Available in 5 mg ($890) and 10 mg ($1,600) quantities at ≥95% purity, this product is one of very few commercially available STING agonist–DBCO conjugates on the market.
→ [View diABZI-V/C-DBCO product details](https://purepeg.com/product/diabzi-v-c-dbco/)
3. PurePEG diABZI-V/C-Mal
Best for: Thiol-maleimide conjugation to antibodies and cysteine-engineered proteins
diABZI-V/C-Mal (SKU 81104, CAS 3035557-55-9, MW 1378.52) pairs the potent diABZI STING agonist with a maleimide conjugation handle via the same Val-Cit-PABC cleavable linker system. Maleimide–thiol chemistry remains the most widely used bioconjugation strategy in ADC development, making this reagent the natural choice for teams working with reduced interchain disulfides or engineered cysteine residues on monoclonal antibodies. The product arrives as a white solid at ≥95% purity, stored at −18°C. Like all PurePEG STING products, diABZI-V/C-Mal is manufactured with monodisperse linker chemistry — meaning every molecule has an identical, defined structure, which is essential for reproducible drug-to-antibody ratio (DAR) control and regulatory submissions. Available in 5 mg units at $1,803.
→ [View diABZI-V/C-Mal product details](https://purepeg.com/product/diabzi-v-c-mal/)
4. InvivoGen STING Agonists (diABZI, cGAMP, DMXAA)
Best for: Early-stage pathway validation and in vitro screening
InvivoGen offers a well-established catalog of unconjugated STING agonists spanning multiple structural classes. Their diABZI compound (marketed as diABZI STING agonist-1) is a potent human STING activator, while 2’3′-cGAMP serves as the natural endogenous ligand for pathway validation experiments. DMXAA (also known as ASA404) is a murine-selective STING agonist frequently used in syngeneic mouse tumor models. These reagents are research-grade and well-cited in the literature, making them reliable tools for initial pathway screening and mechanism-of-action studies. However, InvivoGen’s STING agonists are sold as unconjugated small molecules — they do not include bioconjugation handles, cleavable linkers, or PEG spacers. Researchers who need to attach these agonists to antibodies, nanoparticles, or polymers will need to perform custom linker synthesis in-house, adding weeks of chemistry effort and introducing batch variability.
5. MedChemExpress MSA-2 and SR-717
Best for: Oral STING agonist screening and in vivo mouse studies
MedChemExpress (MCE) supplies MSA-2 and SR-717, two non-nucleotide small-molecule STING agonists that have gained traction for their oral bioavailability in preclinical models. MSA-2 is a non-covalent human STING agonist with a unique binding mode, while SR-717 is a closed-form, cell-permeable agonist with demonstrated anti-tumor activity in murine models. Both compounds are useful for in vivo proof-of-concept studies where systemic STING activation — rather than targeted delivery — is the goal. Like InvivoGen’s offerings, these are unconjugated molecules without conjugation handles or linker architectures. They are best suited for pharmacology studies rather than conjugate development. Note that PurePEG also offers MSA-2 (SKU 81301, CAS 129425-81-6, MW 294.32) for researchers who want to source this compound from a supplier with broader STING conjugate expertise and consolidated ordering.
How to Choose the Right STING Agonist
Your choice depends on where you are in the development pipeline:
- Building STING-agonist ADCs or targeted conjugates? Start with PurePEG’s diABZI-V/C-DBCO (for click chemistry) or diABZI-V/C-Mal (for thiol conjugation). These arrive conjugation-ready and eliminate the need for custom linker synthesis.
- Screening multiple STING agonist classes for SAR? The PurePEG STING collection gives you 13 analogs — nucleoside and non-nucleoside, conjugated and unconjugated — from a single vendor with consistent purity standards.
- Running early-stage pathway validation? InvivoGen’s unconjugated diABZI and cGAMP are well-cited starting points for in vitro STING activation assays.
- Testing oral STING agonists in mice? MedChemExpress’s SR-717 and MSA-2 are designed for systemic delivery in preclinical animal models.
For any program that will eventually require targeted delivery via PEG linkers or nanocarriers, starting with conjugation-ready reagents from the outset saves months of chemistry optimization downstream.
Frequently Asked Questions
What is a STING agonist and how does it work in cancer immunotherapy?
A STING agonist is a compound that activates the Stimulator of Interferon Genes (STING) receptor, a cytosolic innate immune sensor. Activation triggers production of type I interferons and pro-inflammatory cytokines, which reprogram the tumor microenvironment from immunosuppressive to immunostimulatory. This primes dendritic cells to cross-present tumor antigens and activates cytotoxic T cells against the tumor. STING agonists are being developed as standalone immunotherapies, vaccine adjuvants, and payloads for antibody–drug conjugates.
Why conjugate a STING agonist to PEG or an antibody?
Unconjugated small-molecule STING agonists often suffer from rapid systemic clearance, off-target inflammation, and poor tumor accumulation. Conjugating the agonist to an antibody (via ADC technology) or a PEG-based nanocarrier enables targeted delivery to the tumor, improving the therapeutic index. Cleavable linkers like Val-Cit ensure the active agonist is released only inside tumor cells or tumor-associated immune cells. PEG linkers also improve solubility and circulation half-life.
What is the difference between diABZI and cGAMP as STING agonists?
cGAMP (cyclic GMP-AMP) is the natural endogenous STING ligand produced by the cGAS enzyme. It is a cyclic dinucleotide (CDN) and is widely used as a reference agonist. diABZI (dimeric amidobenzimidazole) is a synthetic non-CDN agonist that binds STING at a different site and is significantly more potent than cGAMP in many assays. diABZI-based compounds are the preferred scaffold for most ADC and conjugate programs due to their superior potency and favorable drug-like properties.
Can I get custom STING agonist conjugates?
Yes. PurePEG offers custom synthesis services from their San Diego facility. If you need a specific PEG length, alternative linker chemistry, or a STING agonist conjugated to a functional group not currently in the catalog, their chemistry team can design and produce it. Contact PurePEG directly for custom synthesis inquiries and volume pricing.
Start Your STING Agonist Program with the Right Reagents
PurePEG’s STING agonist collection is the only commercial source offering a full panel of conjugation-ready diABZI derivatives with cleavable linkers, click-chemistry handles, and maleimide groups — all manufactured to monodisperse, ≥95% purity standards. Whether you are building ADCs, formulating nanoparticles, or screening agonist analogs, start with reagents that are ready for the next step. Browse the complete collection and request a quote today.