Melflufen

melphalan flufenamide, Pepaxto (US, withdrawn), Pepaxti (EU), Ygalo (development name)

Oncology & imaging

Awaiting medical reviewEN ES DE FR PT ZH+ Follow for updates

Note on this profile. Melflufen is a hospital-administered chemotherapy agent, authorised in the European Union and withdrawn from the United States market. It is not a research-only compound and has no self-directed use of any kind. This page explains the published science and the regulatory split.

Summary

Class: Peptide-drug conjugate: a lipophilic dipeptide (para-fluoro-L-phenylalanine ethyl ester) linked to melphalan, an alkylating chemotherapy agent. Strictly a peptide-conjugated small molecule, not a peptide drug
Mechanism: The lipophilic peptide carries melphalan rapidly into cells, where aminopeptidases cleave it and trap a high concentration of active alkylator inside — especially in myeloma cells, which are rich in those enzymes
Routes studied: Intravenous infusion, given with dexamethasone
Half-life: Very short in plasma — minutes — because it is taken up and cleaved rapidly; the active melphalan released intracellularly is the pharmacologically relevant species
Storage: Lyophilised vial reconstituted and diluted by hospital pharmacy for infusion under cytotoxic handling procedures
Regulatory status: EU-authorised (Pepaxti) for relapsed/refractory multiple myeloma in defined circumstances; voluntarily withdrawn from the US market in 2021 after the OCEAN survival finding, FDA approval formally withdrawn †

Doses are as reported in studies or by the community — never recommendations.

1What it is

Melflufen is a peptide-drug conjugate, which in this case means something specific and clever: the peptide is not the drug and not merely a carrier to a receptor. Melphalan is a decades-old alkylating chemotherapy that damages DNA. Attached to a short lipophilic dipeptide ester, it becomes highly fat-soluble and diffuses into cells very rapidly. Once inside, intracellular aminopeptidases — which multiple myeloma cells express at high levels — cleave the peptide off, releasing hydrophilic melphalan that is then effectively trapped inside the cell. The result is a much higher intracellular alkylator concentration than infusing melphalan itself would give, with the enrichment biased toward cells rich in those peptidases.

Its story is also a caution. The FDA granted accelerated approval in February 2021 on the basis of the single-arm HORIZON trial. The confirmatory randomised trial, OCEAN, met its progression-free survival endpoint but showed worse overall survival than the comparator in part of the population. The sponsor withdrew the product from the US market in October 2021 and the approval was ultimately withdrawn. The EMA, assessing the same data, authorised it in 2022 with a restricted indication. Same evidence, opposite conclusions — a useful illustration of how accelerated approval and confirmatory trials interact.

2How it's thought to work

Lipophilicity drives rapid uptake. The dipeptide ester makes the molecule far more membrane-permeable than melphalan, so it enters cells within seconds to minutes rather than relying on amino-acid transporters.

Aminopeptidase cleavage traps the payload. Intracellular aminopeptidases hydrolyse the peptide, releasing melphalan and the related alkylating metabolite. These are hydrophilic and cannot easily leave, so they accumulate.

Enrichment in peptidase-rich cells. Multiple myeloma cells express high levels of aminopeptidases, giving a degree of selectivity — a pharmacological bias, not a targeting mechanism in the antibody sense.

DNA damage and apoptosis. Alkylation produces DNA cross-links, including in cells that have become resistant to melphalan itself in preclinical models, possibly because of the much higher intracellular concentration achieved.

The peptide's role. is delivery and intracellular trapping. There is no receptor binding and no signalling activity; this is why it belongs in the peptide-drug conjugate category rather than among peptide therapeutics proper. Compare ANG1005 (#249), where the peptide targets a specific receptor for transport.

A peptide-drug conjugate that is inert until it is inside a cell. Aminopeptidases, abundant in myeloma cells, cut the carrier away and release an alkylating warhead next to the DNA — the arming step happens where the damage is wanted.Schematic — not to scale

3What the research shows

Relapsed/refractory multiple myeloma, single-arm

HORIZON (n=157) gave melflufen plus dexamethasone to heavily pretreated patients, most with triple-class-refractory disease. Overall response rate was about 29% with median progression-free survival around 4 months (Richardson 2021, J Clin Oncol). Single-arm; this is what the accelerated approval rested on. [1]

Relapsed/refractory multiple myeloma, randomised

OCEAN (n=495) randomised melflufen plus dexamethasone against pomalidomide plus dexamethasone. Progression-free survival favoured melflufen (median roughly 6.8 versus 4.9 months), meeting the primary endpoint, but overall survival was shorter in the melflufen arm (Schjesvold 2022, Lancet Haematol). Subgroup analysis suggested the overall survival disadvantage was concentrated in patients who had previously undergone autologous stem cell transplant, with the non-transplanted subgroup performing better — the basis of the sponsor's continued argument and of the EU indication wording. Subgroup findings from a trial with an adverse primary survival signal are hypothesis-generating, not conclusive. [2]

Combination work

Studies have combined melflufen with daratumumab, bortezomib and other agents (ANCHOR and related trials), reporting response signals in small cohorts. Community use: essentially none documented. This is an intravenous cytotoxic given in hospital. There is no community or self-directed context, and the handling requirements alone put it outside any such setting.

4Reported side effects and interactions

Literature-reported

Literature. Myelosuppression dominates — thrombocytopenia, neutropenia and anaemia are very common and frequently severe, with bleeding and infection as the downstream risks. Also reported: fatigue, nausea, diarrhoea, pyrexia, infusion-related reactions, and secondary malignancy risk as with alkylating agents generally. The EU label carries the cytotoxic-class warnings.

Serious. severe cytopenias requiring transfusion and growth-factor support; serious infections including pneumonia; the overall survival signal from OCEAN in previously transplanted patients is itself the most consequential safety finding.

Community-reported

none; no community use exists.

Theoretical. alkylating agents damage stem-cell reserve, which is why prior transplant status plausibly matters and why secondary myelodysplasia is a long-term concern.

Interactions. additive myelosuppression with other cytotoxic or myelosuppressive drugs; live vaccines are contraindicated during treatment; dexamethasone co-administration brings its own interaction set (CYP3A4, glucose, infection risk).

Markers researchers commonly monitor

These follow the label and the trial protocols:

Marker	Why it's watched
Full blood count with platelets, neutrophils and haemoglobin	the dose-limiting toxicity; checked before each dose and frequently between cycles.
Serum and urine paraprotein, free light chains	the disease response measures in myeloma.
Bone marrow assessment	for depth of response and for secondary myelodysplasia over time.
Renal function (creatinine, eGFR)	myeloma commonly damages kidneys and clearance affects tolerability.
Liver enzymes and bilirubin	routine with any cytotoxic.
Infection markers and clinical surveillance	neutropenic infection is the main cause of serious harm.
Calcium and LDH	disease activity and tumour burden.
Prior autologous transplant status	not a lab marker, but the single most important stratifying variable in the OCEAN analysis and in the EU indication.

Free for everyone. Safety information is never behind a paywall.

5Formulation and administration context

Supplied as a powder for and dilution by hospital pharmacy, then given as a 30-minute intravenous infusion through a central venous catheter in a cycle with dexamethasone. It is a cytotoxic agent subject to the full set of preparation, containment and disposal requirements, prepared only by trained pharmacy staff. There is no outpatient self-administration route, no self-preparation guidance, and nothing in this section translates to any other setting.

6Commonly studied alongside

Dexamethasone (mandatory partner in all pivotal work), pomalidomide (comparator in OCEAN), daratumumab and bortezomib (combination studies). Cross-link: ANG1005 (#249) and the peptide-drug conjugate concept generally; motixafortide as another peptide used in myeloma care, for stem cell mobilisation.

Informational cross-links. Not stack recommendations.

7Regulatory status by region

Region	Status (checked —)
United States	Not available. FDA granted accelerated approval February 2021 (Pepaxto); product voluntarily withdrawn from the market October 2021 after OCEAN, and the approval was subsequently withdrawn following FDA proceedings †
European Union	EMA-authorised 2022 as Pepaxti, in combination with dexamethasone, for adults with relapsed/refractory multiple myeloma who have had at least three prior lines of therapy, are refractory to defined classes, and — per the indication wording — have either not had autologous stem cell transplant or had a time to progression of more than 3 years after it †
United Kingdom	Status to be confirmed; not assumed to follow the EU authorisation post-Brexit †
Australia	Not approved †
South Africa	Not registered †
Sport	Not relevant; cytotoxic chemotherapy is not a doping agent and is not listed. Not prohibited

8Open questions

Whether the overall survival disadvantage in OCEAN is genuinely confined to previously transplanted patients, or whether the subgroup finding is noise.
Why the EMA and FDA reached opposite conclusions on identical data, and what that implies for accelerated approval generally.
Whether the peptide-conjugate approach to alkylator delivery has a future with a better-chosen patient population or combination.
Whether aminopeptidase expression could be used prospectively to select patients.

9References

1Richardson PG et al. (2021). Melflufen plus dexamethasone in relapsed/refractory multiple myeloma (HORIZON): a Phase 2 study. J Clin Oncol. PubMed
2Schjesvold FH et al. (2022). Melflufen or pomalidomide plus dexamethasone for patients with multiple myeloma refractory to lenalidomide (OCEAN): a randomised, head-to-head, open-label, Phase 3 study. Lancet Haematol. PubMed
3Chauhan D et al. (2013). In vitro and in vivo antitumor activity of a novel alkylating agent, melphalan-flufenamide, against multiple myeloma cells. Clin Cancer Res. PubMed · DOI
4Wickström M et al. (2017). Melflufen — a peptidase-potentiated alkylating agent in clinical trials. Oncotarget. PubMed · DOI
5FDA (2021). Oncopeptides withdraws Pepaxto from the US market; subsequent withdrawal of approval proceedings. PubMed
6EMA (2022). Pepaxti: EPAR and summary of product characteristics. PubMed

References are being resolved to PubMed/DOI identifiers; links search PubMed for the citation until then.

† Being confirmed by our reviewers against current sources.

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11Page history

31 Oct 2026Profile published — awaiting medical review

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