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Melphalan flufenamide (melflufen), a first-in-class alkylating peptide-drug conjugate, plus dexamethasone demonstrated superior progression-free survival (PFS), but not overall survival (OS), versus pomalidomide plus dexamethasone in relapsed/refractory multiple myeloma in the OCEAN study. Time to progression (TTP) <36 months after a prior autologous stem cell transplantation (ASCT) was a negative prognostic factor for OS with melflufen. This post hoc exploratory analysis evaluated patients refractory to prior alkylators (e.g., cyclophosphamide and melphalan) in OCEAN. In 153 patients refractory to prior alkylators (melflufen, n = 78; pomalidomide, n = 75), the melflufen and pomalidomide arms had similar median PFS (5.6 months [95% CI, 4.2-8.3] vs. 4.7 months [95% CI, 3.1-7.3]; hazard ratio [HR], 0.92 [95% CI, 0.63-1.33]) and OS (23.4 months [95% CI, 14.4-31.7] vs. 20.0 months [95% CI, 12.0-28.7]; HR, 0.92 [95% CI, 0.62-1.38]). Among alkylator-refractory patients with a TTP ≥ 36 months after a prior ASCT or no prior ASCT (melflufen, n = 54; pomalidomide, n = 53), the observed median PFS and OS were longer in the melflufen arm than the pomalidomide arm. The safety profile of melflufen was consistent with previous reports. These results suggest that melflufen is safe and effective in patients with alkylator-refractory disease, suggesting differentiated activity from other alkylators.

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INTRODUCTION: Melphalan flufenamide (melflufen), a first-in-class alkylating peptide-drug conjugate, plus dexamethasone demonstrated superior progression-free survival (PFS) but directionally different overall survival (OS) favoring pomalidomide (hazard ratio [HR], 1.10) in OCEAN. METHODS: These analyses further investigated prognostic subgroups impacting survival in updated data from the randomized, phase 3 OCEAN study (NCT03151811; date: February 3, 2022) and the phase 2 HORIZON study (NCT02963493; date: February 2, 2022). RESULTS: In OCEAN, subgroups prognostic for OS were age (P = .011; <65 years favored pomalidomide) and no previous autologous stem cell transplant (ASCT) or progression >36 months after ASCT (P = .001; favored melflufen). Overall, 245 of 495 (49%) patients randomized had received a previous ASCT, of which 202 (82%) had progressed within 36 months following their ASCT. When excluding patients who had progressed <36 months post-ASCT (melflufen group, n = 145; pomalidomide group, n = 148), median OS was 23.6 months with melflufen and 19.8 months with pomalidomide (HR, 0.83 [95% CI, 0.62-1.12]; P = .22). Among patients with triple-class refractory disease in HORIZON, patients who had progressed <36 months post-ASCT (n = 58) had a lower response rate and shorter duration of response and PFS than the remaining patients (n = 52). Safety was consistent with previous reports. CONCLUSION: These analyses demonstrate a consistent benefit for melflufen and dexamethasone in patients with relapsed/refractory multiple myeloma who have not received an ASCT or progressed >36 months after receiving an ASCT (ClinicalTrials.gov identifier: NCT03151811).

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Despite therapeutic advances and improved patient outcomes in recent years, multiple myeloma (MM) remains a mostly incurable hematologic malignancy. Patients with relapsed/refractory MM (RRMM), especially those with triple-class-refractory disease or poor-prognostic features, have substantially unmet needs for new therapies with novel mechanisms of action. Melphalan flufenamide (melflufen) is the first alkylating peptide-drug conjugate that targets aminopeptidases to show efficacy and manageable safety, in combination with dexamethasone, in patients with RRMM who had received at least 4 prior lines of therapy, including at least 1 immunomodulatory drug, at least 1 proteasome inhibitor and at least 1 anti-CD38 monoclonal antibody, and received accelerated approval by the U.S. Food and Drug Administration (FDA) in early 2021 for use in this patient population. Initial analyses of the phase III OCEAN study data led to melflufen being voluntarily withdrawn from the U.S. market in late 2021, but subsequent analyses have prompted the manufacturer to rescind its voluntary withdrawal to allow further discussions with the U.S. FDA and the regulatory review with the European Medicines Agency (EMA) is also ongoing. Here, we provide a review of the novel mechanism of action and pharmacokinetics of melflufen, as well as key efficacy and safety from clinical studies that supported its initial approval, and discuss the nuances of the OCEAN study data. Melflufen demonstrates the potential of novel peptide-drug conjugates to positively impact the treatment landscape in RRMM.

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INTRODUCTION: Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate that takes advantage of increased aminopeptidase activity inside tumor cells to rapidly release alkylating agents therein. Melflufen in combination with dexamethasone has been evaluated in multiple clinical trials in patients with relapsed/refractory multiple myeloma (MM). AREAS COVERED: This profile covers the unique mechanism of action of melflufen, the preclinical results supporting its activity in cellular models of resistance to chemotherapy, its activity in animal models of MM, and the clinical pharmacokinetics of melflufen. Findings from clinical trials evaluating melflufen, including the pivotal phase II HORIZON study and the phase III OCEAN study, are discussed. EXPERT OPINION: Although MM treatment has improved, patients with disease refractory to multiple standard-of-care drug classes face a dismal prognosis. Melflufen demonstrated efficacy and tolerability in select populations, with an initial approval in the United States in patients with ≥ four previous lines of therapy and triple-class-refractory MM. Results from the phase III OCEAN study - currently under discussion with regulatory agencies in the United States and Europe - are more complex and have been put into context herein. Lastly, melflufen provides a proof-of-concept for the utility of the peptide-drug conjugate platform in relapsed/refractory MM.

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Mesenchymal stem/stromal cells (MSCs) are self-renewing and multipotent progenitors, which constitute the main cellular compartment of the bone marrow stroma. Because MSCs have an important role in the pathogenesis of multiple myeloma, it is essential to know if novel drugs target MSCs. Melflufen is a novel anticancer peptide-drug conjugate compound for patients with relapsed refractory multiple myeloma. Here, we studied the cytotoxicity of melflufen, melphalan and doxorubicin in healthy human bone marrow-derived MSCs (BMSCs) and how these drugs affect BMSC proliferation. We established co-cultures of BMSCs with MM.1S myeloma cells to see if BMSCs increase or decrease the cytotoxicity of melflufen, melphalan, bortezomib and doxorubicin. We evaluated how the drugs affect BMSC differentiation into adipocytes and osteoblasts and the BMSC-supported formation of vascular networks. Our results showed that BMSCs were more sensitive to melflufen than to melphalan. The cytotoxicity of melflufen in myeloma cells was not affected by the co-culture with BMSCs, as was the case for melphalan, bortezomib and doxorubicin. Adipogenesis, osteogenesis and BMSC-mediated angiogenesis were all affected by melflufen. Melphalan and doxorubicin affected BMSC differentiation in similar ways. The effects on adipogenesis and osteogenesis were not solely because of effects on proliferation, seen from the differential expression of differentiation markers normalized by cell number. Overall, our results indicate that melflufen has a significant impact on BMSCs, which could possibly affect therapy outcome.

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From the medical, pharmaceutical, and social perspectives, 2021 has been a year dominated by the COVID-19 pandemic. However, despite this global health crisis, the pharmaceutical industry has continued its endeavors, and 2021 could be considered an excellent year in terms of the drugs accepted by the US Food and Drug Administration (FDA). Thus, during this year, the FDA has approved 50 novel drugs, of which 36 are new chemical entities and 14 biologics. It has also authorized 10 TIDES (8 peptides, 2 oligonucleotides), in addition to 2 antibody-drug conjugates (ADCs) whose structures contain peptides. Thus, TIDES have accounted for about 24% of the approvals in the various drug categories. Importantly, this percentage has surpassed the figure in 2020 (10%), thus reflecting the remarkable success of TIDES. In this review, the approved TIDE-based drugs are analyzed on the basis of their chemical structure, medical target, mode of action, administration route, and adverse effects.

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Relapsed/refractory multiple myeloma (RRMM) is known to have a high burden of disease and complications associated with refractoriness to prior lines of therapy. Severe pain and fatigue symptoms and impairments in physical and emotional functioning have been strongly linked to reduced health-related quality of life (HRQoL) in patients with RRMM. Assessment of patient reported-outcome measures from the pivotal, Phase II HORIZON study (OP-106; NCT02963493) in patients with RRMM (n = 64) demonstrated that melphalan flufenamide (melflufen) plus dexamethasone treatment preserved HRQoL. Patients had clinically meaningful improvements, even after eight treatment cycles, in relevant scales such as global health status/QoL, physical functioning, emotional functioning, pain, and fatigue. Patients with triple-class-refractory disease (n = 50) displayed similar improvements. Patient-reported outcome deterioration was delayed for a substantial amount of time in patients who experienced a response to melflufen plus dexamethasone treatment relative to patients who did not experience a response. These findings support the notion that treatment with melflufen plus dexamethasone may sustain or improve HRQoL over time in patients with RRMM, including in patients with triple-class-refractory disease for whom outcomes are generally worse. The clinical benefits observed in patients from the HORIZON trial are encouraging and supportive of translation into real-world practice.

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OBJECTIVE: The objective of this article was to review existing data of melflufen (Pepaxto) as an additional treatment option for heavily pretreated relapsed and refractory multiple myeloma. DATA SOURCES: A PubMed search was completed using the search terms melphalan flufenamide; melflufen; melflufen AND relapsed refractory multiple myeloma; melphalan flufenamide and relapsed refractory multiple myeloma between January 1, 2013, and October 18, 2021. Additional information was obtained from the National Institutes of Health Clinical Trial Registry, Federal Drug Administration (FDA) web updates, and Pepaxto prescribing information. STUDY SELECTION/DATA EXTRACTION: Clinical trials including melflufen in relapsed refractory multiple myeloma and trials related to safety and clinical pharmacology were included. DATA SYNTHESIS: The findings of this review show melflufen in combination with dexamethasone can be used as a treatment option for patients with relapsed and refractory multiple myeloma who have previously received greater than 4 previous lines of therapy, and documented resistance to a proteosome inhibitor, an anti-CD38 monoclonal antibody, and an immunomodulator. RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE: Melflufen in combination with dexamethasone is a reasonable option for patients with relapsed and refractory multiple myeloma who have received at least 4 previous lines of therapy and considered ineligible for autologous stem cell transplant. Further clinical utilization in earlier lines of therapy is under review, pending the in-depth safety analysis by the FDA. CONCLUSIONS: The FDA approval of melflufen in combination with dexamethasone provides an additional therapy option for patients with heavily pretreated relapsed and refractory multiple myeloma.

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Despite recent therapeutic advances, multiple myeloma (MM) patients experience relapses as they become resistant to various classes and combinations of treatment. Melphalan (L-PAM) is an ageless drug. However, its use in the autologous stem cell transplantation (ASCT) setting and the innovative quadruplet regimen as well as daratumumab, bortezomib, and prednisone make this old drug current yet. Melflufen is a peptide-conjugated alkylator belonging to a novel class of compounds, representing an overcoming of L-PAM in terms of mechanism of action and effectiveness. The improved melflufen cytotoxicity is related to aminopeptidase activity, notably present in normal and neoplastic cells and remarkably heavily overexpressed in MM cells. Upon entering a cell, melflufen is cleaved by aminopeptidases, ultimately releasing the L-PAM payload and eliciting further the inflow and cleavage of the conjugated peptide. This virtuous loop persists until all extracellular melflufen has been utilized. The aminopeptidase-driven accumulation results in a 50-fold increase in L-PAM cell enrichment as compared with free alkylator. This condition produces selective cytotoxicity, increased on-target cell potency, and decreased off-target cell toxicity, ultimately overcoming resistance pathways triggered by previous treatments, including alkylators. Due to its distinct mechanism of action, melflufen plus dexamethasone as a doublet, and in combination with other novel drugs, has the potential to be beneficial for a broad range of patients with relapsed/refractory (RR) MM in third- or even in second-line therapy. The safety profile of melflufen has been consistent across studies, and no new safety concerns have been identified when melflufen was administered in doublet and triplet combinations. Based on growing clinical evidence, melflufen could be not only a good addition in the fight against RRMM but also a drug with a very favorable tolerability profile.

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An updated survival analysis was conducted for the Phase II study O-12-M1 of melphalan flufenamide (melflufen) plus dexamethasone in patients with relapsed/refractory multiple myeloma (RRMM) with two or more prior lines of therapy (including bortezomib and lenalidomide). Partial response or better was seen in 31%. After a 46-month median overall survival (OS) follow-up, melflufen plus dexamethasone had a median OS of 20·7 months (75th percentile OS, 47·5 months). The median time-to-next treatment for melflufen plus dexamethasone was 7·9 months. In summary, melflufen plus dexamethasone resulted in sustained long-term clinical benefit in patients with RRMM.

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Despite the availability of new therapies that have led to improved outcomes for patients with multiple myeloma, most patients will eventually relapse. With triplet and even quadruplet combination therapies becoming standard in the first and second line, many patients will have few treatment options after second-line treatment. Melflufen (melphalan flufenamide) is a first-in-class peptide-drug conjugate (PDC) that targets aminopeptidases and rapidly releases alkylating agents into tumor cells. Once inside the tumor cells, melflufen is hydrolyzed by peptidases to release alkylator molecules, which become entrapped. Melflufen showed anti-myeloma activity in myeloma cells that were resistant to bortezomib and the alkylator melphalan. In early phase studies (O-12-M1 and HORIZON [OP-106]), melflufen plus dexamethasone has demonstrated encouraging clinical activity and a manageable safety profile in heavily pretreated patients with relapsed/refractory multiple myeloma, including those with triple-class refractory disease and extramedullary disease. The Phase III OCEAN study (OP-104) is further evaluating melflufen plus dexamethasone in patients with relapsed/refractory multiple myeloma. The safety profile of melflufen is characterized primarily by clinically manageable hematologic adverse events. Melflufen, with its novel mechanism of action, has the potential to provide clinically meaningful benefits to patients with relapsed/refractory multiple myeloma, including those with high unmet needs.

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INTRODUCTION: The overall survival of patients with multiple myeloma has improved with the advent of novel agents; however, multiple myeloma remains incurable. Combinations of standard-of-care agents such as immunomodulators, proteasome inhibitors, and anti-CD38 monoclonal antibodies are increasingly used in earlier lines of therapy. Patients with disease that is refractory to multiple novel agents represent a population with high unmet medical need and for whom therapies with new mechanisms of action could be beneficial. Melphalan flufenamide (melflufen) has demonstrated encouraging activity in patients with relapsed and refractory multiple myeloma. AREAS COVERED: This review provides an overview of the mechanism of action of melflufen, a first-in-class peptide-drug conjugate that targets aminopeptidases and rapidly delivers alkylating agents into tumor cells. It reviews key Phase I and II clinical trial data for melflufen in combination with dexamethasone as well as in triplet combinations with daratumumab or bortezomib. The safety profile of melflufen, which is characterized primarily by clinically manageable hematologic adverse events, is described. EXPERT OPINION: Melflufen has potential to fill a gap in the myeloma treatment landscape by providing a new mechanism of action with clinically meaningful efficacy and a favorable safety profile in patients refractory to multiple novel agents.

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BACKGROUND: Chemotherapy options in advanced urothelial carcinoma (UC) remain limited. Here we evaluated the peptide-based alkylating agent melphalan-flufenamide (mel-flufen) for UC. METHODS: UC cell lines J82, RT4, TCCsup and 5637 were treated with mel-flufen, alone or combined with cisplatin, gemcitabine, dasatinib or bestatin. Cell viability (MTT assay), intracellular drug accumulation (liquid chromatography) apoptosis induction (apoptotic cell nuclei morphology, western blot analysis of PARP-1/caspase-9 cleavage and Bak/Bax activation) were evaluated. Kinome alterations were characterized by PathScan array and phospho-Src validated by western blotting. Aminopeptidase N (ANPEP) expression was evaluated in UC clinical specimens in relation to patient outcome. RESULTS: In J82, RT4, TCCsup and 5637 UC cells, mel-flufen amplified the intracellular loading of melphalan in part via aminopeptidase N (ANPEP), resulting in increased cytotoxicity compared to melphalan alone. Mel-flufen induced apoptosis seen as activation of Bak/Bax, cleavage of caspase-9/PARP-1 and induction of apoptotic cell nuclei morphology. Combining mel-flufen with cisplatin or gemcitabine in J82 cells resulted in additive cytotoxic effects and for gemcitabine also increased apoptosis induction. Profiling of mel-flufen-induced kinome alterations in J82 cells revealed that mel-flufen alone did not inhibit Src phosphorylation. Accordingly, the Src inhibitor dasatinib sensitized for mel-flufen cytotoxicity. Immunohistochemical analysis of the putative mel-flufen biomarker ANPEP demonstrated prominent expression levels in tumours from 82 of 83 cystectomy patients. Significantly longer median overall survival was found in patients with high ANPEP expression (P = 0.02). CONCLUSION: Mel-flufen alone or in combination with cisplatin, gemcitabine or Src inhibition holds promise as a novel treatment for UC.

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PURPOSE: Melflufen (melphalan flufenamide, previously designated J1) is an optimized and targeted derivative of melphalan, hydrolyzed by aminopeptidases overexpressed in tumor cells resulting in selective release and trapping of melphalan, and enhanced activity in preclinical models. METHODS: This was a prospective, single-armed, open-label, first-in-human, dose-finding phase I/IIa study in 45 adult patients with advanced and progressive solid tumors without standard treatment options. Most common tumor types were ovarian carcinoma (n = 20) and non-small-cell lung cancer (NSCLC, n = 11). RESULTS: In the dose-escalating phase I part of the study, seven patients were treated with increasing fixed doses of melflufen (25-130 mg) Q3W. In the subsequent phase IIa part, 38 patients received in total 115 cycles of therapy at doses of 30-75 mg. No dose-limiting toxicities (DLTs) were observed at 25 and 50 mg; at higher doses DLTs were reversible neutropenias and thrombocytopenias, particularly evident in heavily pretreated patients, and the recommended phase II dose (RPTD) was set to 50 mg. Response Evaluation Criteria In Solid Tumors (RECIST) evaluation after 3 cycles of therapy (27 patients) showed partial response in one (ovarian cancer), and stable disease in 18 patients. One NSCLC patient received nine cycles of melflufen and progressed after 7 months of therapy. CONCLUSIONS: In conclusion, melflufen can safely be given to cancer patients, and the toxicity profile was as expected for alkylating agents; RPTD is 50 mg Q3W. Reversible and manageable bone marrow suppression was identified as a DLT. Clinical activity is suggested in ovarian cancer, but modest activity in treatment of refractory NSCLC.

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