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Melphalan Flufenamide is a peptide-drug conjugate composed of a peptide conjugated, via an aminopeptidase-targeting linkage, to the alkylating agent melphalan, with potential antineoplastic and anti-angiogenic activities. Upon administration, the highly lipophilic melphalan flufenamide penetrates cell membranes and enters cells. In aminopeptidase-positive tumor cells, melphalan flufenamide is hydrolyzed by peptidases to release the hydrophilic alkylating agent melphalan. This results in the specific release and accumulation of melphalan in aminopeptidase-positive tumor cells. Melphalan alkylates DNA at the N7 position of guanine residues and induces DNA intra- and inter-strand cross-linkages. This results in the inhibition of DNA and RNA synthesis and the induction of apoptosis, thereby inhibiting tumor cell proliferation. Peptidases are overexpressed by certain cancer cells. The administration of melphalan flufenamide allows for enhanced efficacy and reduced toxicity compared to melphalan.1,2,3

Summary 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.

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.

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. The authors received medical editorial support for the development of this manuscript, which was funded by Oncopeptides AB.

Background: Low survival rates in metastatic high-grade osteosarcoma (HGOS) have remained stagnant for the last three decades. This study aims to investigate the role of aminopeptidase N (ANPEP) in HGOS progression and its targeting with a novel lipophilic peptidase-enhanced cytotoxic compound melphalan flufenamide (melflufen) in HGOS. Methods: Meta-analysis of publicly available gene expression datasets was performed to determine the impact of ANPEP gene expression on metastasis-free survival of HGOS patients. The efficacy of standard-of-care anti-neoplastic drugs and a lipophilic peptidase-enhanced cytotoxic conjugate melflufen was investigated in patient-derived HGOS ex vivo models and cell lines. The kinetics of apoptosis and necrosis induced by melflufen and doxorubicin were compared. Anti-neoplastic effects of melflufen were investigated in vivo. Results: Elevated ANPEP expression in diagnostic biopsies of HGOS patients was found to significantly reduce metastasis-free survival. In drug sensitivity assays, melflufen has shown an anti-proliferative effect in HGOS ex vivo samples and cell lines, including those resistant to methotrexate, etoposide, doxorubicin, and PARP inhibitors. Further, HGOS cells treated with melflufen displayed a rapid induction of apoptosis and this sensitivity correlated with high expression of ANPEP. In combination treatments, melflufen demonstrated synergy with doxorubicin in killing HGOS cells. Finally, Melflufen displayed anti-tumor growth and anti-metastatic effects in vivo. Conclusion: This study may pave the way for use of melflufen as an adjuvant to doxorubicin in improving the therapeutic efficacy for the treatment of metastatic HGOS.

Introduction Melphalan flufenamide (Melflufen; Oncopeptides AB) is a novel enzyme-activated analogue of melphalan that enables a more rapid and higher intracellular accumulation of melphalan in tumor cells than is achievable by direct exposure to equimolar doses of melphalan. Our preclinical study showed that melflufen is a more potent anti-myeloma (MM) agent than melphalan, overcomes drug-resistance, and induces synergistic anti-MM activity in combination with bortezomib, lenalidomide, or dexamethasone (Chauhan et al, Clinical Cancer Res 2013;19:3019). However, the effect of melflufen on the immunosuppressive and tumor-promoting MM-host bone marrow (BM) accessory cells such as immunologically dysfunctional plasmacytoid dendritic cells (pDCs; CD123/IL-3Rα) remains unclear. Here, we utilized our coculture models of pDCs, T-, and NK cells with autologous patient MM cells to examine whether a combination of melflufen and immune checkpoint inhibitor anti-PD-L1 Ab, or daratumumab (anti-CD38 Ab), restores anti-MM immunity. Methods MM patient BM and PB samples (N=10; obtained after informed consent), and cell lines were used for the study. Minimally cytotoxic concentration of melflufen (0.1 µM) was used to assess immune functions. CTL/NK activity assays MM CD8 + T- or NK-cells were cultured with autologous pDCs (1:10 pDC:T/NK ratio) with melflufen (0.1 μM) alone, and with anti-PD-L1 (5 μg/ml) or anti-CD38 (0.5 μg/ml) Abs for 3-5 days; cells were washed to remove the drugs, and then cultured for another 24h with pre-stained target MM cells (10:1 E/T ratio; T/NK:MM), followed by quantification of viable MM cells by flow. Results 1) Both MM tumor cells and pDCs showed higher PD-L1 and CD38 levels vs normal plasma cells; 2) Treatment of MM patient total BM mononuclear cells or purified MM cells with melflufen (0.1 µM) increased PD-L1 expression on MM cells (1.84-fold, treated vs untreated; p Conclusions The combination of melflufen and anti-PD-L1 increases pDC-induced T- and NK cell-mediated cytolytic activities against MM. Moreover, combined melflufen and anti-CD38 Abs modestly enhance pDC-induced NK cell-mediated MM-specific cytolytic activity. Our preclinical data suggest targeting PD-L1 in combination with melflufen as well as support an ongoing clinical trial of melflufen with anti-CD38 Abs to enhance anti-MM immunity. Disclosures Nupponen: Oncopeptides AB: Consultancy. Lehmann: Oncopeptides AB: Current Employment. Lindberg: Oncopeptides: Current Employment, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months, Other: Travel, Accommodations, Expenses; Camurus: Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses; Affibody: Membership on an entity's Board of Directors or advisory committees. Gullbo: Oncopeptides AB: Consultancy. Richardson: Takeda: Consultancy, Research Funding; Celgene/BMS: Consultancy, Research Funding; Janssen: Consultancy; Sanofi: Consultancy; Protocol Intelligence: Consultancy; Karyopharm: Consultancy, Research Funding; GlaxoSmithKline: Consultancy; Regeneron: Consultancy; AstraZeneca: Consultancy; Secura Bio: Consultancy; AbbVie: Consultancy; Oncopeptides: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy, Research Funding. Chauhan: C4 Therapeutics: Current equity holder in publicly-traded company; Oncopeptides: Consultancy; Stemline Therapeutics: Consultancy. Anderson: Janssen: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Sanofi-Aventis: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Millenium-Takeda: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Scientific Founder of Oncopep and C4 Therapeutics: Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Mana Therapeutics: Membership on an entity's Board of Directors or advisory committees.

8037 Background: Development of resistance to standard treatments for RRMM highlights the need for novel therapies. Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate (PDC) that leverages aminopeptidases and rapidly releases alkylating agents inside tumor cells. Melflufen + dex showed clinical activity and an acceptable safety profile in HORIZON (Richardson et al. J Clin Oncol. 2020 Dec 9 [Epub]). This is an update of the BTZ arm of the phase 1/2a ANCHOR study (NCT03481556). Methods: Patients (pts) with RRMM were intolerant or refractory to a prior IMiD, with 1-4 prior lines of therapy (LoTs). Prior treatment with a proteasome inhibitor (PI) was allowed, but pts could not be refractory to PIs in the last LoT. Melflufen (30, 40, or 20 mg intravenously; d 1 of each 28-d cycle) was administered with BTZ (1.3 mg/m2 subcutaneous) + oral dex (20 mg on d 1, 4, 8, and 11 and 40 mg on d 15 and 22; dex dose reduced if aged ≥ 75 y). The primary objective in phase 1 was to determine the optimal phase 2 dose of melflufen for this combination. Results: As of the data cutoff date (October 19, 2020), 13 pts received melflufen (30 mg, n = 6; 40 mg, n = 7) + dex and BTZ. In the 30 mg and 40 mg cohorts, respectively, median age was 78.5 y (range, 70-82) and 70.0 y (range, 61-76); median prior LoTs was 3.5 (range, 2-4) and 2.0 (range, 1-4); 33% and 50% of evaluable pts had high-risk cytogenetics; 83% and 71% were refractory to last LoT; 100% and 86% received a prior PI; 33% and 14% were refractory to PIs. In the 30 mg and 40 mg cohorts, respectively, median treatment duration was 6.5 mo (range, 1.4-29.0) and 8.7 mo (range, 2.1-19.6); 4 (67%) and 4 pts (57%) were still on treatment; 2 and 3 pts discontinued (30 mg: progressive disease [PD] and other [1 pt each]; 40 mg: adverse event [AE], lack of efficacy, and PD [1 pt each]). Confirmed overall response rate in the 30 mg and 40 mg cohorts, respectively, was 50% (1 very good partial response [VGPR] and 2 partial response [PR]) and 71% (1 complete response, 3 VGPR, and 1 PR). Most common grade 3/4 treatment-related AEs (TRAEs) were thrombocytopenia (30 mg: 50%; 40 mg: 100%) and neutropenia (30 mg: 33%; 40 mg: 71%); grade 3/4 nonhematologic TRAEs were infrequent; 3 pts discontinued study treatment due to treatment-emergent AEs (30 mg: cardiac failure chronic and osteolysis [1 pt each]; 40 mg: thrombocytopenia [1 pt]). Serious TRAEs occurred in 2 pts (33%) in the 30 mg cohort (neutropenia and pneumonia [1 pt], syncope [1 pt]) and 1 pt (14%) in the 40 mg cohort (thrombocytopenia and neutropenia). No dose-limiting toxicities occurred at either dose level. Fatal AEs occurred in 1 pt in the 30 mg cohort (cardiac failure chronic; unrelated to study treatment). Conclusions: ANCHOR determined that the optimal dose of melflufen is 30 mg + dex and BTZ; results showed clinical activity in heavily pretreated pts. Recruitment is ongoing; updated data will be presented. Clinical trial information: NCT03481556.

TPS8051 Background: Melphalan flufenamide (melflufen) is a first-in-class peptide-drug conjugate (PDC) that leverages aminopeptidases and rapidly releases alkylating agents inside tumor cells. Melflufen + dex showed clinical efficacy and was well tolerated in pts with heavily pretreated RRMM (HORIZON; Richardson et al. J Clin Oncol. 2020 Dec 9 [Epub]). The ongoing phase 1/2 ANCHOR study (OP-104) established the optimal dose for melflufen + dex and dara, showing meaningful clinical activity and manageable safety at both melflufen doses tested in pts with RRMM (Ocio et al. ASH 2020. Oral 417). The aim of this study (OP-108; NCT04649060) is to evaluate the efficacy and safety of melflufen + dex and dara vs dara in pts with RRMM previously treated with an IMiD and a proteasome inhibitor (PI), similar to the indication for dara monotherapy. Methods: Pt enrollment has begun (N = 240 planned). Pts must be ≥ 18 y, double refractory to (or intolerant of) an IMiD and a PI or had ≥ 3 prior lines of therapy (LoTs) including an IMiD and a PI, have measurable disease, and Eastern Cooperative Oncology Group performance status ≤ 2. Pts with primary refractory disease and refractoriness to an anti-CD38 antibody are excluded. Pts will be randomized 1:1 to open-label melflufen + dex and dara (Arm A) or single-agent dara (Arm B) until progressive disease [PD] or unacceptable toxicity, stratified by prior LoT number. Pts in Arm B with PD can opt to receive Arm A triplet therapy. Arm A: melflufen 30 mg intravenously on d 1 of each 28-d cycle; dex 40 mg/wk orally (20 mg if aged ≥ 75 y); dara 1800 mg subcutaneously on d 1, 8, 15, and 22 of cycle 1 and 2, d 1 and 15 of cycles 3-6, and d 1 of cycles 7+. Arm B: dara at the same dosage as Arm A. Primary objective: superiority ( P value from the 2-sided statistical test < 0.05; upper limit of the 2-sided 95% CI for the hazard ratio < 1) of progression-free survival (PFS) in pts treated with triplet therapy vs dara. An estimated sample of 240 pts with 160 expected events (PD or death) and 15% assumed dropout rate would provide 90% power at a 2-sided log rank test at 5% significance level to detect a hazard ratio for death of 0.6. Key secondary endpoints: overall response rate (ORR; ≥ partial response [PR]), duration of response, and safety. Response will be assessed by a blinded independent review committee based on International Myeloma Working Group criteria. Other secondary endpoints: clinical benefit rate (≥ minimal response), time to response, time to progression, time to next treatment, and overall survival. Exploratory endpoints include: minimal residual disease in pts achieving ≥ very good PR, PFS following next line of treatment (PFS-2), pt-reported outcomes, pharmacokinetics, translational biomarkers, response rate in pts with extramedullary disease, and efficacy (including ORR) in Arm B pts who receive Arm A triplet therapy after PD. Clinical trial information: NCT04649060.