iRGD

iRGD works in two steps. The RGD motif first docks the peptide onto alpha-v-beta-3 and alpha-v-beta-5 integrins, which are selectively upregulated on tumour endothelium and many tumour cells. Proteolysis at the lysine then exposes a C-terminal arginine — a C-end Rule or CendR motif — which binds neuropilin-1 and activates a bulk transport pathway that carries not just the peptide but anything nearby, including co-administered but chemically unlinked drug, across the endothelium and deep into the tumour parenchyma. This is why iRGD is described as a penetration enhancer rather than a targeting ligand: the payload does not have to be conjugated to it. In pancreatic cancer the interest is specifically in defeating the dense desmoplastic stroma that keeps gemcitabine out. The mechanism is well described preclinically and the human data are still early.

Targets: Alpha-v-beta-3 and alpha-v-beta-5 integrins, Neuropilin-1 (NRP-1) via the CendR pathway

• · 3.2 mg/kg IV is the dose carried forward from the first-in-human work; a second cohort tested giving it twice per chemotherapy day. These are trial doses, not a protocol anyone can run outside a study.

Work out your exact syringe units →

• commonInfusion-related reactions— Reported in early-phase work and generally manageable.
• commonNausea and fatigue— Difficult to separate from the accompanying chemotherapy.
• commonAdditive chemotherapy toxicity— The theoretical concern with a penetration enhancer is that it increases drug delivery to healthy tissue too; so far the trials have not shown a marked increase over chemotherapy alone.
• commonUnknown long-term profile— Exposure across all human studies to date is still measured in hundreds of patients.

• Use outside a clinical trial — there is no approved product and no validated dose for self-administration.
• Pregnancy — no reproductive safety data.

• synergyGemcitabine and nab-paclitaxel — The entire clinical programme is built on improving delivery of this chemotherapy backbone in metastatic pancreatic cancer.
• cautionAny co-administered cytotoxic or antibody — By design it increases tissue penetration of whatever else is circulating, which cuts both ways.

• · Standard oncology trial monitoring — counts, chemistry, tumour markers such as CA 19-9 and cross-sectional imaging.
• · Infusion reaction observation on dosing days.
• · There is no established biomarker of iRGD activity in humans.

Investigational worldwide. Not approved anywhere; available only through clinical trials of certepetide.

• Sugahara et al. 2010, coadministration of a tumour-penetrating peptide enhances drug efficacy, Science (preclinical)
• Dean et al. 2022, first-in-human phase 1 of CEND-1 with gemcitabine and nab-paclitaxel in metastatic pancreatic cancer, Lancet Gastroenterology and Hepatology (trial)
• ASCEND phase 2b trial of certepetide in metastatic pancreatic cancer, preliminary cohort reports 2025 (trial)

iRGD is a two-stage molecular machine and understanding the second stage is what makes it interesting. Stage one is conventional: the RGD tripeptide docks onto alpha-v-beta-3 and alpha-v-beta-5 integrins, which are strongly upregulated on angiogenic tumour endothelium and on many tumour cells and are largely quiescent on normal vasculature. That gives tumour selectivity but no penetration — plenty of RGD-conjugated agents stop right there and simply decorate the vessel wall. Stage two is the innovation. Once bound and concentrated at the tumour surface, a protease cleaves the peptide after the lysine at position 5, generating a new C-terminus ending in arginine. A free C-terminal arginine is the C-end Rule motif, and it is a ligand for neuropilin-1. Neuropilin-1 engagement activates a bulk transcytotic transport pathway — a vesicular route that carries fluid-phase cargo from the vessel lumen through the endothelium and onward through the tumour parenchyma. The critical property is that this pathway is non-selective about what it carries. It moves whatever is in the vicinity, including drug that is not chemically attached to the peptide at all. That is why iRGD is described as a penetration enhancer rather than a targeting ligand, and it is what distinguishes it from every antibody-drug conjugate and peptide-drug conjugate in this catalogue: no linker chemistry, no payload attachment, just a temporary permeability window. In pancreatic ductal adenocarcinoma the specific hope is defeating the desmoplastic stroma, a dense collagen and hyaluronan barrier with collapsed vasculature that keeps gemcitabine and nab-paclitaxel out of the tumour core. Two honest caveats. The transport pathway is not tumour-exclusive, so in principle it increases delivery to normal tissue expressing neuropilin-1 too, and the human trials so far have not shown a marked increase in chemotherapy toxicity, which is reassuring but not proof. And there is no validated pharmacodynamic biomarker of iRGD activity in humans — nobody can measure, in a patient, whether the window opened.

The honest answer is that we do not yet know, because total human exposure across all studies is still measured in hundreds of patients. What is known: infusion-related reactions occur and are generally manageable, and nausea and fatigue are reported but are hard to separate from the accompanying chemotherapy. The mechanistically predicted problem — increased chemotherapy delivery to healthy tissue — has not materialised as a marked toxicity increase in the trials so far, but 'not seen yet in a few hundred patients' is a much weaker statement than 'does not happen'. The bigger risk is interpretive. Preliminary cohort results from a randomised phase 2, reported through press releases rather than peer review, have circulated as though they were established survival benefits. A median overall survival of 12.7 versus 9.7 months in an interim cohort of a phase 2 is a signal worth pursuing to phase 3, and it is not evidence that the drug works. The specific failure mode for anyone reading about this outside oncology is treating a promising mechanism plus an unpublished interim number as a reason to buy research peptide. The disulfide bond degrades in solution, oxidation and scrambling give an inactive linear peptide, and there is no dose, no route and no monitoring that would make self-administration meaningful.

1. —On each chemotherapy day, investigational only — 3.2 mg per kg intravenously, infused shortly before gemcitabine and nab-paclitaxel so the permeability window is open when the cytotoxics arrive. This is the dose carried forward from the first-in-human phase 1 into the phase 2 programme, expressed per kilogram rather than as a fixed microgram amount.
2. —Alternative schedule tested in a later cohort — The same dose given twice on each chemotherapy day, on the theory that a single infusion's permeability window may close before the chemotherapy has finished distributing. This is a trial question, not established practice.

• Integrin alpha-v-beta-3 — RGD-mediated binding; published affinity figures for the cyclic peptide vary and I did not resolve a primary value

  Stage-one docking on angiogenic tumour endothelium and tumour cells, concentrating the peptide where proteolytic activation can happen.

• Integrin alpha-v-beta-5 — Also RGD-mediated

  Second integrin route to the same docking step.

• Neuropilin-1 (NRP-1), via the CendR motif exposed by proteolysis — The C-end Rule interaction requires a free C-terminal arginine — the intact peptide does not engage it

  Activates a bulk transcytotic transport pathway that carries co-administered, chemically unlinked drug across the endothelium and deep into tumour parenchyma. This is the entire therapeutic idea.

• CEND-1 first-in-human phase 1 in metastatic pancreatic ductal adenocarcinoma Phase 1 · n=31 · 2022

  Safety, tolerability and dose selection of CEND-1 with nab-paclitaxel and gemcitabine. No dose-limiting toxicity attributable to the peptide; encouraging response and survival signals that justified randomised testing.

• ASCEND (NCT05042128) Phase 2 · n=158

  Progression-free survival with gemcitabine and nab-paclitaxel plus certepetide versus placebo in untreated metastatic pancreatic ductal adenocarcinoma. Registered enrolment 158. Preliminary cohort reporting has described a median overall survival advantage and complete responses in the certepetide arm, but these are interim signals from a phase 2, not a definitive readout.

• CEND-1 with neoadjuvant FOLFIRINOX with or without panitumumab (NCT05121038) Phase 1/2 · n=50

  Treatment-related adverse events by CTCAE v5.0 in the neoadjuvant setting. Active, not recruiting at the time of checking.

The permeability window opens within minutes of infusion, which is why the peptide is given immediately before chemotherapy rather than hours ahead. How long it stays open in humans is not established — the preclinical work suggests hours, and the fact that a twice-daily cohort was tested indicates the trialists were not certain either. Plasma clearance of the peptide itself is rapid, on the order of minutes to under an hour. Clinical effects are measured as tumour response and survival over months, exactly as for the chemotherapy backbone. There is no early signal a patient would notice that could be attributed to the peptide.

iRGD has no standalone activity, so 'stacking' is the entire concept rather than an optional extra. The established pairing is with gemcitabine and nab-paclitaxel in metastatic pancreatic cancer, infused immediately before the cytotoxics so the permeability window is open when they arrive. Timing is the whole game — give it too early and the window has closed, too late and the chemotherapy has already distributed. A FOLFIRINOX combination with and without panitumumab is in earlier trials. The theoretically interesting extension is with antibodies and immune checkpoint inhibitors, because the same transcytotic route should carry large molecules and because opening a stromal barrier may also let T cells in, but that is preclinical reasoning rather than trial data. The caution that follows directly from the mechanism is that iRGD increases tissue penetration of whatever else is circulating, so it should be assumed to modify the pharmacology of every co-administered drug rather than only the intended one. There is no legitimate consumer product here. Research-grade iRGD sold as a peptide has no clinical dosing basis, no purity guarantee for a molecule whose entire activity depends on one correctly-formed disulfide bond, and no human safety data outside a trial.

Against the peptide-drug conjugates elsewhere in this class — melphalan flufenamide, zoptarelin doxorubicin — iRGD is the opposite design. Those attach a payload to a homing peptide and depend on the linker and the target enzyme. iRGD attaches nothing and depends on opening a transport route that carries free drug. That is more elegant and also harder to verify, because there is no conjugate to measure and no biomarker of the effect. Against stromal-depletion strategies in pancreatic cancer — hyaluronidase with PEGPH20, hedgehog pathway inhibitors — the history is sobering: several approaches that plausibly should have improved drug delivery either failed or made outcomes worse, in some cases because the stroma turned out to be partly restraining the tumour rather than only shielding it. iRGD has to be read against that record. Against the enhanced permeability and retention effect that nanomedicine relied on for two decades, iRGD is an attempt to create an active transport route rather than depend on passive leakiness, which is a genuine conceptual advance whether or not this particular molecule succeeds.

Not characterised, and there is no price because there is no product. Certepetide is investigational worldwide and supplied only through clinical trials. Research-grade peptide sold online has a price but no relationship to a therapeutic dose.

• ?No published human pharmacokinetics worth quoting — no tmax, volume of distribution, clearance, protein binding or elimination data are given here because I could not source them.
• ?The duration of the tumour permeability window in humans is unknown. The twice-daily dosing cohort exists because the trialists did not know either.
• ?Integrin binding affinities are not quoted because published figures vary and I did not resolve a primary source.
• ?The ASCEND efficacy figures circulating publicly — median overall survival of 12.7 versus 9.7 months and four complete responses versus none — come from preliminary cohort reporting rather than a peer-reviewed publication. I verified that the trial exists, its phase, its enrolment and its primary endpoint through the registry, but not those specific numbers.
• ?The trial year for ASCEND is left null because the registry status was listed as unknown at the time of checking and no primary publication has appeared.
• ?Whether the transcytotic route is sufficiently tumour-selective in humans is unresolved. The absence of increased toxicity so far is reassuring but the sample is small.
• ?There is no validated pharmacodynamic biomarker of iRGD activity in humans, which means no trial so far can confirm that the mechanism engaged in the patients who did or did not respond.
• ?Blood-brain barrier penetration is unknown, though neuropilin-1-mediated transport into brain tumours has been explored preclinically.

• Coadministration of a tumor-penetrating peptide enhances the efficacy of cancer drugs Sugahara KN, Teesalu T, Karmali PP, et al., Science, 2010 · PMID 20378772

  The foundational paper. Established that iRGD improves the efficacy of drugs it is not chemically attached to, which is the counterintuitive claim the whole programme rests on.

• Dual αV-integrin and neuropilin-1 targeting peptide CEND-1 plus nab-paclitaxel and gemcitabine for the treatment of metastatic pancreatic ductal adenocarcinoma: a first-in-human, open-label, multicentre, phase 1 study Dean A, Gill S, McGregor M, et al., The Lancet Gastroenterology & Hepatology, 2022 · PMID 35803294

  The first-in-human study. Source of the 3.2 mg/kg dose and the safety picture that justified randomised testing.

• The ASCEND Study: Gemcitabine and Nab-Paclitaxel With LSTA1 (Certepetide) or Placebo in Patients With Untreated Metastatic Pancreatic Ductal Adenocarcinoma (NCT05042128) Australasian Gastro-Intestinal Trials Group / Lisata Therapeutics, ClinicalTrials.gov registry record

  Registry record confirming the trial exists, is phase 2, enrols 158 and has progression-free survival as its primary endpoint. The efficacy numbers circulating in press releases are not yet a peer-reviewed publication.