Melphalan Flufenamide (Melflufen): First Approval
Melphalan flufenamide (melflufen, Pepaxto®) is a peptide conjugated alkylating drug developed by Oncopeptides for the treat- ment of multiple myeloma (MM) and amyloid light-chain amyloidosis. It is an ethyl ester of a lipophilic dipeptide consisting of melphalan and para-fluoro-L-phenylalanine. Due to its lipophilicity, melphalan flufenamide is rapidly transported across the cell membrane and almost immediately hydrolyzed by aminopeptidases in the cytoplasm to yield more hydrophilic alkylat- ing molecules, such as melphalan and desethyl-melflufen. Like other nitrogen mustard drugs, melphalan flufenamide exerts antitumor activity through DNA crosslinking. In February 2021, melphalan flufenamide, in combination with dexamethasone, received its first approval in the USA for the treatment of adults with relapsed or refractory (r/r) MM who have received at least four prior lines of therapy and whose disease is refractory to at least one proteasome inhibitor (PI), one immunomodulatory agent, and one CD38-directed monoclonal antibody. A multinational clinical study of melphalan flufenamide in amyloid light- chain amyloidosis is underway across several countries, and preclinical studies for various haematological and solid cancers are underway. This article summarizes the milestones in the development of melphalan flufenamide leading to this first approval.
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Sohita Dhillon [email protected]
1 Springer Nature, Private Bag 65901, Mairangi Bay, Auckland 0754, New Zealand
Multiple myeloma (MM) is the second most common haema- tological malignancy . Despite recent advances in therapy and improved clinical outcomes, the majority of patients with MM eventually relapse, with an increasing number of patients becoming refractory to multiple therapies [1, 2]. This high- lights an unmet need for novel therapies for these patients [1, 2]. Several aminopeptidases are overexpressed in malig- nancies, making them potential targets for cancer therapy [3–5]. Various approaches have been used to develop thera- pies targeting these enzymes, including enzyme inhibitors (e.g. bestatin) and peptide-drug conjugates [3, 5, 6]. Recent findings indicate aminopeptidases may play a critical role in the disease progression of MM . Melphalan flufenamide (melflufen, Pepaxto®) is a first-in-class peptide conjugated alkylating drug developed by Oncopeptides for the treatment of MM and amyloid light-chain amyloidosis. It is an active, lipophilic derivative of the chemotherapeutic alkylating agent melphalan that utilizes aminopeptidases to rapidly deliver and release alkylating agents inside tumour cells .
On 26 February 2021 , melphalan flufenamide, in com- bination with dexamethasone, received its first approval in the USA for the treatment of adult patients with relapsed or refractory MM who have received at least four prior lines of therapy and whose disease is refractory to at least one pro- teasome inhibitor, one immunomodulatory agent, and one Key milestones in the development of melphalan flufenamide for the treatment of relapsed or refractory multiple myeloma. FDA US Food and Drug administration, MM multiple myeloma, PDUFA Prescription Drug User Fee Act, RRMM relapsed or refractory multiple myeloma
CD38-directed monoclonal antibody . This indication was approved under accelerated approval based on response rate, and its continued approval may be contingent upon verifica- tion and description of clinical benefit in confirmatory trial(s) . The recommended dosage of melphalan flufenamide is 40 mg administered intravenously over 30 minutes on day 1 in 28-day treatment cycles, in combination with weekly dexamethasone, until disease progression or unacceptable toxicity. Dexamethasone is administered at a dosage of 40 mg (20 mg in patients ≥ 75 years of age) orally or intravenously on days 1, 8, 15 and 22 of each cycle. Dosage adjustment or permanent discontinuation of melphalan flufenamide or dexamethasone therapy may be required because of adverse events (AEs) . A multinational clinical study of melphalan flufenamide in amyloid light-chain amyloidosis is underway across several countries, and preclinical studies for various haematological and solid cancers are underway.
2 Scientific Summary
Melphalan flufenamide is an ethyl ester of a dipeptide con- sisting of melphalan and para-fluoro-L-phenylalanine [6, 10]. With the use of a simple peptide bond, the activity of melphalan flufenamide is enabled via aminopeptidases, such as aminopeptidase N (also known as CD13), resulting in a peptidase-potentiated effect . Melphalan flufenamide is rapidly transported across the cell membrane, most prob- ably by passive diffusion of the lipophilic molecule, and almost immediately hydrolyzed by aminopeptidases in the cytoplasm to yield more hydrophilic alkylating molecules, such as melphalan and desethyl-melflufen [6, 10]. The rapid transport of melphalan flufenamide and slow transport of
melphalan out of cells results in a high intracellular concen- tration of melphalan in cells expressing high levels of amin- opeptidases [6, 11, 12]. Like other nitrogen mustard drugs, melphalan flufenamide exerts antitumor activity through DNA crosslinking .
Melphalan flufenamide demonstrated antitumour activity in MM, lymphoma and acute myeloid leukaemia cell lines, and primary tumour cells, as well as in xenograft models of these Chemical structure of melphalan flufenamide
diseases [13–15]. It inhibited proliferation and induced apop- tosis of several haematopoietic and solid tumour cells [6, 13]. Melphalan flufenamide triggered myeloma cell death regard- less of p53 status, thereby overcoming p53 deficiency-mediated melphalan resistance . Melphalan flufenamide also demon- strated antitumour activity in amyloidosis patient-derived light chain producing cells, and eliminated amyloidogenic clones and reduced the levels of toxic serum light chain in an adoptive trans- fer mouse model of amyloidosis . Melphalan flufenamide was shown to be a highly effective against human tumour cell lines and primary cultures of various malignancies in vitro and in vivo , including breast cancer models . Importantly, activity is also observed in bortezomib-resistant MM cell lines [13, 19]. It was also more effective than bortezomib, lenalido- mide, pomalidomide or bendamustine in abrogating clonogenic outgrowth of malignant plasma cells from the bone marrow of patients with relapsed or refractory MM . Furthermore, the combination of melphalan flufenamide and lenalidomide, bort- ezomib or dexamethasone demonstrated synergistic cytotoxic activity in melphalan-resistant and -sensitive MM cell lines .
Peak plasma concentration (Cmax) of melphalan flufena- mide is reached slightly before the end of a 30-min infu- sion of melphalan flufenamide 40 mg and that of the active metabolite melphalan is reached 4–15 minutes after the end
of the infusion [9, 10]. Melphalan flufenamide disappeared rapidly from plasma because of distribution to peripheral tissues, with no late redistribution back to plasma . Over the 30-min infusion, Cmax and area under the concentration- time curve values for melphalan were larger than those for melphalan flufenamide, indicating rapid conversion of mel- phalan flufenamide to the active metabolite . The mean volume of distribution of melphalan flufenamide after a sin- gle dose was 35 L and that of melphalan was 76 L .
Melphalan flufenamide is metabolized in tissues to dese- thyl-melphalan flufenamide and melphalan. Melphalan, in turn, is metabolized primarily by spontaneous hydrolysis to monohydroxy-melphalan, dihydroxy-melphalan and para- fluoro-phenylalanine. After the end of infusion of melphalan flufenamide 40 mg, the mean elimination half-life of the parent compound was 2.1 minutes and that of melphalan was 70 minutes. The mean clearance of melphalan flufenamide and melphalan was 692 and 23 L/h, respectively, following infusion of a melphalan flufenamide 40 mg dose .
Patients with lower body surface area were observed to have higher exposure to melphalan . The pharmacokinet- ics of melphalan were not affected by age (35–85 years), renal impairment (creatinine clearance 45–89 mL/min) or mild hepatic impairment [total bilirubin ≤ upper limit of normal (ULN) and aspartate aminotransferase (AST) > ULN, or total bilirubin 1–1.5 × the ULN and any AST] to a clinically meaningful extent .
Alternative names CK-1535; J1; Melflufen; Melphalan flufenamide hydrochloride-Oncopeptides; Melphalan-prodrug-Oncopep- tides; PEPAXTO; Ygalo
Class Amides; amines; antineoplastics; chlorinated hydrocarbons; esters; fluorobenzenes; peptide drug conjugates Mechanism of Action Exerts antitumour activity through crosslinking of DNA
Route of Administration Intravenous
Pharmacodynamics Inhibited proliferation and induced apoptosis of several haematopoietic and solid tumour cells
When combined with lenalidomide, bortezomib or dexamethasone, it demonstrated synergistic cytotoxic activity in melphalan-resistant and -sensitive multiple myeloma cell lines
Pharmacokinetics Cmax of melphalan flufenamide reached slightly before the end of 30-min infusion; Cmax of the active metabolite melphalan reached 4–15 min after the infusion
Mean volume of distribution of melphalan flufenamide after a single dose 35 L Metabolized in tissues to desethyl-melphalan flufenamide and melphalan
Mean t1/2 of melphalan flufenamide 2.1 minutes; mean t1/2 of melphalan 70 minutes
Most common adverse events
Haematological Neutropenia, thrombocytopenia, anaemia
Non-haematological Fatigue, nausea, diarrhoea, pyrexia and respiratory tract infection Grade ≥ 3 Neutropenia, thrombocytopenia, anaemia
WHO ATC code L01AA10 (melphalan) EphMRA ATC code L1A (alkylating Agents)
Chemical name Ethyl (2S)-2-[[(2S)-2-amino-3-[4-[bis(2chloroethyl)amino]phenyl]propanoyl]amino]-3-(4-fluorophenyl)pro- panoate hydrochloride
Cmax peak plasma drug concentration, t1/2 elimination half-life
2.3 Therapeutic Trials
2.3.1 HORIZON Phase 2 Study
Melphalan flufenamide in combination with dexamethasone demonstrated clinical efficacy in heavily pretreated patients with relapsed or refractory MM (median age 65 years) who were participating in the pivotal, single-arm, multicentre, phase 2 HORIZON study (NCT02963493) . Patients enrolled had received at least two prior lines of therapy (including ≥ 1 immunomodulatory agent and ≥ 1 protea- some inhibitor) and were refractory to pomalidomide and/or an anti-CD38 monoclonal antibody. As of 14 January 2020, 157 patients had been treated with the recommended dos- age of melphalan flufenamide plus dexamethasone (median duration of treatment 3.8 months). The investigator-assessed overall response rate (ORR; primary endpoint), per Inter- national Myeloma Working Group criteria, was 29% (one
stringent complete response, 17 very good partial responses and 28 partial responses) and the clinical benefit rate was 45% (including 25 minimal responses). The median duration of response (DOR) was 5.5 months, median progression- free survival (PFS) was 4.2 months, and the median overall survival (OS) was 11.6 months. A pre-planned subgroup analysis demonstrated the efficacy of melphalan flufenamide
plus dexamethasone in patients with high-risk features, including in patients with triple-class refractory MM (i.e. refractory to or intolerant of ≥ 1 immunomodulatory drug,
≥ 1 one proteasome inhibitor and ≥ 1 anti-CD38 monoclo- nal antibody; n = 119). In this subgroup of patients, the ORR was 26% (13 very good partial responses and 18 partial responses), the clinical benefit rate was 39% (including 16 minimal responses), the median DOR was 4.4 months, the median PFS was 3.9 months and the median OS was 11.2 months . Melphalan flufenamide demonstrated efficacy in patients refractory to an alkylator in one previous line of therapy (n = 60) with an ORR of 28%; however, in patients refractory to alkylators in two or more previous lines the ORR was 6% (n = 32), according to a subgroup analysis .
2.3.2 O‑12‑M1 Phase 1/2 Study
The clinical activity of melphalan flufenamide was dem- onstrated in patients with relapsed or refractory MM who were participating in the open-label, multicentre, phase 1/2 dose-confirmation and dose-expansion O-12-M1 study (NCT01897714) . In phase 1, patients (n = 23) received many, Greece, Israel, Italy, Norway, Poland, Spain, US, UK
AL immunoglobulin light chain, DMX dexamethasone, melphalan flufenamide melflufen, RRMM relapsed or refractory multiple myeloma
intravenous melphalan flufenamide 15, 25, 40 or 55 mg on day 1 in 21-day cycles plus oral dexamethasone 40 mg/week. The primary objectives were to determine the maximum tolerated dose (phase 1) and the ORR and clinical benefit rates (phase 2). In phase 1, the maximum tolerated dose of melphalan flufenamide was determined to be 40 mg in combination with dexamethasone 40 mg weekly, with an optimal cycle length of 28 days.
In phase 2, patients received melphalan flufenamide 40 mg plus dexamethasone; those who were unable to toler- ate dexamethasone could continue treatment with single agent melphalan flufenamide. Overall, 45 patients received melphalan flufenamide in combination with dexamethasone and 13 patients received single agent melphalan flufenamide. In patients treated with combination therapy (n = 45), at a median follow-up of 27.9 months, the ORR was 31% (five very good partial responses and nine partial responses), the clinical benefit rate was 49%, the median DOR was 8.4 months, the median PFS was 5.7 months and the median OS was 20.7 months. In patients who received single agent mel- phalan flufenamide, the ORR was 8% (one partial response), clinical benefit rate was 23%, median PFS was 4.4 months and median OS was 15.5 months at a median follow-up of
17.3 months . In a survival follow-up of the phase 2 study at a median of 46 months, the median PFS and OS in patients who received melphalan flufenamide plus dexa- methasone (n = 45) were unchanged at 5.7 and 20.7 months, respectively, and the median time-to-next treatment was 7.9 months .
2.3.3 ANCHOR Phase 1/2 Study
Melphalan flufenamide plus dexamethasone in combination with bortezomib or daratumumab showed clinical activity in heavily pretreated patients with relapsed or refractory MM who were participating in the ongoing (recruiting), phase 1/2 ANCHOR study (NCT03481556) . Patients treated with daratumumab could not have received prior anti-CD38 anti- body and those treated with bortezomib could not be pro- teasome inhibitor-refractory. At the time of the most recent data cutoff (6 April 2020), 33 patients had been treated with melphalan flufenamide (20, 30 or 40 mg on day 1 of a 28-day cycle), dexamethasone plus daratumumab (median age 64 years), and 10 patients had been treated with melphalan flufenamide, dexamethasone plus bortezomib (median age 71 years). In the daratumumab group, the ORR was 70%, including one stringent complete response, one complete response, 10 very good partial responses and 11 partial responses. At a median follow-up of 11.9 months the median PFS was 11.5 months; the median duration of response was
12.5 months. In the bortezomib group, the ORR was 60%, including three very good partial responses and three partial
responses; PFS data were immature at the time of analysis. No dose limiting toxicities were observed in this group .
2.4 Adverse Events
Melphalan flufenamide had a manageable tolerability profile in patients with relapsed or refractory MM based on data from the pivotal phase 2 HORIZON study (NCT01897714) . Treatment-emergent AEs occurred in all patients, with 95% of patients reporting at least one melphalan flufena- mide-related AE. The most common treatment-emergent AEs with melphalan flufenamide were haematological adverse events, which were generally reversible and man- ageable with dose adjustments, dose delays, use of growth factors, platelet transfusions and appropriate supportive care. The most common haematological treatment-emergent AEs and grade ≥ 3 AEs were neutropenia (82%; grade ≥ 3 79%), thrombocytopenia (82%; grade ≥ 3 76%) and anaemia
(71%; grade ≥ 3 43%). Any-grade and grade 3 or 4 bleeding events with concurrent grade 3 or 4 thrombocytopenia were reported in 16% and 3% of patients, respectively. The most common (incidence > 25%) non-haematological treatment- emergent AEs were nausea (32%), fatigue (29%), asthenia (27%) and diarrhoea (27%). The most common grade 3 or 4 non-haematological treatment-emergent AEs included pneu- monia (10%) and hypophosphatemia (5%); 11% of patients had grade 3 or 4 neutropenia with concurrent infections, of which 7% of patients had pneumonia .
Serious treatment-emergent AEs occurred in 49% of patients with pneumonia (9%) and febrile neutropenia (5%) reported most commonly . Five patients had second primary malignancies, with four patients developing malig- nancies with cutaneous manifestations [basal cell carcinoma (n = 2); squamous cell carcinoma (n = 1); basal cell carci- noma, squamous cell carcinoma and malignant melanoma (n = 1)], and myelodysplasia reported in one patient after 17 cycles of study medication (this patient had received multiple prior cycles of alkylator-based therapy, including stem-cell transplant prior to study entry). Ten patients died because of treatment-emergent AEs, none of which were considered related to melphalan flufenamide treatment . The average monthly dose of melphalan flufenamide was
37.8 mg . Treatment-emergent AEs resulted in dose reductions in 27% of patients [most commonly because of thrombocytopenia (14%) and neutropenia (3%)], treat- ment discontinuations in 22% of patients [most commonly because of thrombocytopenia (10%) and neutropenia (3%)] and dose delays in 61% of patients (the median number of treatment cycles with a dose delay was one). Concomitant red blood cell or platelet transfusions were required in 65% of patients, platelet transfusions only were required in 43% of patients and concomitant growth factor support was required in 68% of patients .
The tolerability profile of melphalan flufenamide in combination with dexamethasone plus daratumumab (n = 33) or dexamethasone plus bortezomib (n = 10) in the ANCHOR study (NCT03481556) was generally simi- lar to that observed with melphalan flufenamide plus dexa- methasone. The most common grade 3 or 4 treatment-related AEs were cytopenias, with neutropenia, thrombocytopenia and anaemia occurring most frequently both in the daratu- mumab group (incidence 58%, 55% and 24%, respectively)
and the bortezomib group (incidence 80%, 60% and 40%,
respectively) . Grade 3 or 4 non-haematological AEs were uncommon in both combination therapy groups. Seri- ous treatment-emergent AEs were reported in 12 (36%) patients in the daratumumab group, with influenza (9%), pneumonia, parainfluenza virus infection and febrile neutro- penia (6% each) occurring most commonly. Two patients in this group experienced fatal AEs, sepsis (treatment-related) and myeloma progression. In the bortezomib group, seri- ous treatment-emergent AEs occurred in six (60%) patients, with pneumonia (20%) reported most frequently; there were no deaths in this group .
Melphalan flufenamide has not been studied in the high- dose setting of myeloablation with stem cell support.
2.5 Ongoing Clinical Trials
In addition to the ongoing phase 2 HORIZON (NCT02963493) and phase 1/2 ANCHOR (NCT03481556)
studies, the randomized, open-label, superiority, phase 3 OCEAN study (NCT03151811) is underway. The OCEAN study will evaluate the efficacy and safety of melphalan flufenamide plus dexamethasone versus pomalidomide plus dexamethasone in 495 patients with MM who have received 2–4 prior therapies . The primary endpoint is PFS and the secondary endpoints include ORR, DOR and OS . Recruitment is underway for the randomized, open-label, phase 3 LIGHTHOUSE study (NCT04649060), which will evaluate the efficacy and safety of melphalan flufenamide and dexamethasone in combination with subcutaneous dara- tumumab versus daratumumab alone in ≈ 240 patients with relapsed or refractory MM who were previously treated with an immunomodulatory agent and proteasome inhibitor . The primary endpoint of the study is PFS and secondary endpoints include ORR, clinical benefit rate, DOR and OS .
Patients are also being recruited in the open-label, mul- ticentre phase 2 BRIDGE study (NCT03639610), which is assessing the pharmacokinetics of melphalan flufenamide plus dexamethasone in ≈ 35 patients with relapsed or refrac- tory MM and impaired renal function. The randomized, two- period, cross-over phase 2 PORT study (NCT04412707) is recruiting ≈ 20 patients to compare the pharmacokinet- ics, and safety and tolerability of peripheral versus central
intravenous administration of melphalan flufenamide in relapsed or refractory patients with MM. In addition, the Expanded Access Program sEAPort (NCT04534322) will provide early treatment access to melphalan flufenamide and assess its safety in patients with triple class refractory MM. The open-label, phase 1 / 2 ASCENT study (NCT04115956) is recruiting ≈ 46 patients to evaluate the safety and efficacy of melphalan flufenamide plus dexameth- asone in patients with immunoglobulin light chain amyloi-
dosis following at least one prior line of therapy .
3 Current Status
On 26 February 2021 , melphalan flufenamide, in com- bination with dexamethasone, received its first approval in the USA for the treatment of adult patients with relapsed or refractory multiple myeloma who have received at least four prior lines of therapy and whose disease is refractory to at least one proteasome inhibitor, one immunomodulatory agent, and one CD38-directed monoclonal antibody .
Funding The preparation of this review was not supported by any external funding.
Authorship and Conflict of interest During the peer review process the manufacturer of the agent under review was offered an opportunity to comment on the article. Changes resulting from any comments received were made by the authors on the basis of scientific completeness and accuracy. Sohita Dhillon is a contracted employee of Adis International Ltd/Springer Nature and declares no relevant conflicts of interest. All authors contributed to the review and are responsible for the article content.
Ethics approval, Consent to participate, Consent to publish, Availability of data and material, Code availability Not applicable.
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