Abstract: PET/CT with both 11 C-choline and 11 C-methionine has recently been reported to offer advantages over 18 F-FDG for imaging in multiple myeloma (MM). The aim of this study was to directly compare the diagnostic performance of both non-FDG radiotracers in MM patients. Methods Nineteen patients with a history of MM (n = 18) or solitary bone plasmacytoma (n = 1) underwent both 11 C-choline and 11 C-methionine PET/CT for diagnostic imaging. In this retrospective analysis, scans were compared on a patient and on a lesion basis. In 12 patients, respective tracer uptake in the iliac crest was correlated with the extent of malignant bone marrow plasma cell infiltration. Results 11 C-methionine detected more intramedullary MM lesions in 8 (42.1%) of 19 patients. In the remainder (11/19 [57.9%]), both 11 C-choline and 11 C-methionine provided equal results. 11 C-methionine demonstrated higher lesion-to-muscle ratios ( P = 0.0001). In the 12 patients in whom a recent bone marrow biopsy was available, SUVmean as well as SUVmax correlated significantly with the degree of malignant plasma cell infiltration for both 11 C-methionine (SUVmean: r = 0.85, P 〈 0.001; SUVmax: r = 0.82, P = 0.001) and 11 C-choline (SUVmean: r = 0.72, P 〈 0.008; SUVmax: r = 0.73; P = 0.006). Conclusions Our data suggest that 11 C-methionine PET/CT might be more sensitive than 11 C-choline PET/CT for the detection of active MM lesions.

Abstract: Cereblon is the direct binding target of the immunomodulatory drugs (IMiDs) that are commonly used to treat multiple myeloma (MM), the second most frequent hematologic malignancy. Patients respond well to initial treatment with IMiDs, but virtually all patients develop drug resistance over time, and the underlying mechanisms are poorly understood. We identified an as yet undescribed DNA hypermethylation in an active intronic CRBN enhancer. Differential hypermethylation in this region was found to be increased in healthy plasma cells, but was more pronounced in IMiD-refractory MM. Methylation significantly correlated with decreased CRBN expression levels. DNA methyltransferase inhibitor (DNTMi) in vitro experiments induced CRBN enhancer demethylation, and sensitizing effects on lenalidomide treatment were observed in 2 MM cell lines. Thus, we provide first evidence that aberrant CRBN DNA methylation is a novel mechanism of IMiD resistance in MM and may predict IMiD response prior to treatment.

Abstract: Introduction: Novel agents are needed for multiple myeloma (MM), which remains incurable with most patients (pts) relapsing or becoming refractory to standard therapies. Talquetamab (Tal) is a bispecific antibody that binds to G protein-coupled receptor family C group 5 member D (GPRC5D), a receptor highly expressed on plasma cells with limited expression in healthy tissue, and CD3 to redirect T cells to GPRC5D-expressing MM cells. Tal monotherapy at the recommended phase 2 dose (RP2D) was well tolerated and yielded an overall response rate of 70% after 6.3 months of follow-up in pts with relapsed/refractory MM (RRMM) in the phase 1 MonumenTAL-1 study; responses were durable and continued to deepen over time. Daratumumab (Dara) is a monoclonal antibody approved for MM treatment that targets CD38 on MM cells, resulting in direct cytotoxicity of MM cells. Dara also impacts immune cell populations, ie, increasing helper and cytotoxic T cells and decreasing suppressive CD38+ immunoregulatory cells. Preclinical studies showed addition of Dara enhanced Tal-mediated lysis of MM cells, suggesting the combination may also increase clinical activity in pts with RRMM. We report initial findings for pts with RRMM who received Tal + Dara in a phase 1b multicohort study (TRIMM-2; NCT04108195). Methods: Eligible pts (aged ≥18 years) were diagnosed with MM and had received ≥3 prior lines of therapy (including a proteasome inhibitor [PI] and immunomodulatory drug [IMiD] ) or were double refractory to a PI and an IMiD. Pts were excluded if they had received an anti-CD38 therapy ≤90 days. Subcutaneous (SC) Tal and Dara were administered in 28-day cycles in different dosing cohorts (with step-up dosing for Tal). The primary objectives were to identify the RP2D of Tal in combination with Dara and to characterize the safety of Tal + Dara at the RP2D. Responses were assessed by IMWG criteria. Adverse events (AEs) were graded per CTCAE v5.0 (cytokine release syndrome [CRS] and immune effector cell-associated neurotoxicity syndrome [ICANS] graded per ASTCT guidelines). Results: As of Jul 23, 2021, 23 pts were administered SC Tal + Dara in separate cohorts: Dara 1800 mg + Tal 400 µg/kg weekly (n=8), + Tal 400 µg/kg biweekly (n=5), and + Tal 800 µg/kg biweekly (n=10). Median follow-up across the Tal + Dara cohorts was 2.9 months (range 0.3-11.2). Median age of pts treated with Tal + Dara was 68 years (range 44-81), and 52.2% were male. Pts had received a median of 6 prior lines of therapy (range 3-18); 82.6% were triple-class exposed (82.6% received prior Dara and 8.7% received prior isatuximab) and 73.9% were penta-drug exposed. Any grade AEs were reported in 95.7% of pts and grade 3/4 AEs in 78.3%. The most frequently reported AEs (≥30% across Tal + Dara cohorts) were dysgeusia (52.2%; all grade 1/2), neutropenia (39.1%; grade 3/4 30.4%), thrombocytopenia (39.1%; grade 3/4 21.7%), anemia (34.8%; grade 3/4 21.7%), CRS (34.8%; all grade 1/2), and skin exfoliation (30.4%; all grade 1/2). The median time to CRS onset was 2.5 days (range 2-4), and the median duration was 2 days (range 1-3). Infections occurred in 34.8% of pts (grade 3/4 17.4%). Skin disorders were reported in 65.2% of pts (grade 3/4 13.0%), including nail disorders in 17.4% (all grade 1/2); these events were manageable and did not lead to treatment discontinuation. Two events of ICANS were reported (a grade 1 event [concurrent with CRS] and a grade 3 event), both of which resolved and did not recur. One pt in the Dara 1800 mg + Tal 400 μg/kg biweekly cohort died due to disease progression. Responses in different dosing cohorts are shown in the Table. The median time to first response across Tal + Dara cohorts was 1.0 month (range 0.9-2.4), and median duration of response was not reached. The pharmacokinetic profile of Tal was similar to that observed in the phase 1 monotherapy study. Tal + Dara treatment resulted in proinflammatory cytokine production and T-cell activation, evidenced by interferon-γ and tumor necrosis factor-α induction and PD-1 and CD38 upregulation on peripheral T cells, respectively. Updated data with longer follow-up will be presented at the congress. Conclusions: Tal in combination with Dara was well tolerated, with a safety profile comparable to the monotherapies, and showed promising efficacy in pts with RRMM. These findings support further clinical development of Tal + Dara combination therapy. Figure 1 Figure 1. Disclosures Chari: BMS/Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Secura Bio: Consultancy, Membership on an entity's Board of Directors or advisory committees; Shattuck Labs: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Research Funding; Antengene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Millenium/Takeda: Consultancy, Research Funding; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Research Funding; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi Genzyme: Consultancy, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Consultancy, Research Funding; Karyopharm: Consultancy, Membership on an entity's Board of Directors or advisory committees. Hari: Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding, Speakers Bureau; GSK: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding, Speakers Bureau; Karyopharm: Consultancy; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding, Speakers Bureau; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Adaptive Biotech: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Millenium: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene-BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding, Speakers Bureau. Bahlis: Janssen: Consultancy, Honoraria; Genentech: Consultancy; BMS/Celgene: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; GlaxoSmithKline: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Karyopharm: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Amgen: Consultancy, Honoraria. Mateos: Sea-Gen: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees; Regeneron: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene - Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bluebird bio: Honoraria; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Honoraria; Oncopeptides: Honoraria. van de Donk: Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Adaptive Biotechnologies: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees; Cellectis: Research Funding. Dholaria: Janssen: Research Funding; Takeda: Research Funding; Jazz: Speakers Bureau; MEI: Research Funding; Angiocrine: Research Funding; Poseida: Research Funding; Celgene: Speakers Bureau; Pfizer: Research Funding. Garfall: Janssen: Honoraria, Research Funding; GSK: Honoraria; Novartis: Research Funding; Tmunity Therapeutics: Research Funding; Amgen: Honoraria. Goldschmidt: Novartis: Honoraria, Research Funding; Dietmar-Hopp-Foundation: Other: Grant; Sanofi: Consultancy, Honoraria, Other: Grants and/or Provision of Investigational Medicinal Product, Research Funding; Takeda: Consultancy, Research Funding; MSD: Research Funding; Mundipharma: Research Funding; Molecular Partners: Research Funding; Johns Hopkins University: Other: Grant; Janssen: Consultancy, Honoraria, Other: Grants and/or Provision of Investigational Medicinal Product, Research Funding; Incyte: Research Funding; GSK: Honoraria; Chugai: Honoraria, Other: Grants and/or Provision of Investigational Medicinal Product, Research Funding; BMS: Consultancy, Honoraria, Other: Grants and/or Provision of Investigational Medicinal Product, Research Funding; Celgene: Consultancy, Honoraria, Other: Grants and/or Provision of Investigational Medicinal Product, Research Funding; Adaptive Biotechnology: Consultancy; Amgen: Consultancy, Honoraria, Other: Grants and/or Provision of Investigational Medicinal Product, Research Funding. Krishnan: City of Hope Cancer Center: Current Employment; JANSSEN: Consultancy, Research Funding; BMS: Consultancy, Current equity holder in publicly-traded company, Speakers Bureau; MAGENTA: Consultancy; REGENERON: Consultancy; SANOFI: Consultancy; GSK: Consultancy; Amgen: Speakers Bureau. Martin: Janssen: Research Funding; Amgen: Research Funding; Oncopeptides: Consultancy; Sanofi: Research Funding; GlaxoSmithKline: Consultancy. Morillo Giles: Janssen: Honoraria; Takeda: Honoraria; Abbvie: Honoraria. Oriol: Oncopeptides: Consultancy, Membership on an entity's Board of Directors or advisory committees; Karyopharm: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS/Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Reece: BMS: Honoraria, Research Funding; GSK: Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria; Millennium: Research Funding; Karyopharm: Consultancy, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Sanofi: Honoraria. Rodriguez: Takeda: Consultancy, Speakers Bureau; Karyopharm: Consultancy, Speakers Bureau; Janssen: Consultancy, Speakers Bureau; Amgen: Consultancy, Speakers Bureau; Oncopeptides: Consultancy, Honoraria; BMS: Consultancy, Speakers Bureau. Rodriguez-Otero: Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene-BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Kite: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria; Regeneron: Honoraria; Clínica Universidad de Navarra: Current Employment. San-Miguel: AbbVie, Amgen, Bristol-Myers Squibb, Celgene, GlaxoSmithKline, Janssen, Karyopharm, Merck Sharpe & Dohme, Novartis, Regeneron, Roche, Sanofi, SecuraBio, Takeda: Consultancy, Other: Advisory board. Usmani: Array BioPharma: Consultancy, Research Funding; GSK: Consultancy, Research Funding; Celgene/BMS: Consultancy, Research Funding, Speakers Bureau; Abbvie: Consultancy; Amgen: Consultancy, Research Funding, Speakers Bureau; Janssen: Consultancy, Research Funding, Speakers Bureau; EdoPharma: Consultancy; Merck: Consultancy, Research Funding; Sanofi: Consultancy, Research Funding, Speakers Bureau; Pharmacyclics: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding; SkylineDX: Consultancy, Research Funding; Janssen Oncology: Consultancy, Research Funding; Takeda: Consultancy, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Research Funding. Verona: Janssen: Current Employment. Wang Lin: Janssen: Current Employment, Current holder of individual stocks in a privately-held company. Prior: Janssen: Current Employment, Current holder of individual stocks in a privately-held company. Wade: Janssen: Current Employment, Current holder of individual stocks in a privately-held company. Weiss: Janssen: Current holder of individual stocks in a privately-held company, Ended employment in the past 24 months. Goldberg: Janssen: Current Employment, Current holder of individual stocks in a privately-held company. Askari: Janssen: Research Funding.

Abstract: Introduction: Proteasome inhibition is the backbone of various Multiple Myeloma (MM) treatment regimens, leading to durable responses and high quality remissions. However, under prolonged therapy patients eventually develop drug resistance and the underlying mechanisms have been poorly understood. Proteasome inhibitor resistant cell lines were generated by continuous exposure to proteasome inhibiting drugs. In these cell line models a number of variants within the PSMB5 gene were observed. This includes single point mutations, leading to conformational changes of the _5 subunit within the 20S proteolytic core of the proteasome, impairing its chymotryptic catalytic function and the binding of inhibitory drugs. However, no PSMB5 mutations could, so far, be identified in human disease, leaving the functional relevance of such mutations to be determined. Methods: We applied the MM Mutation Panel (M3P) and used the Personal Genome Machine (Life Technologies) to sequence CD138+ purified bone marrow plasma cells and peripheral blood germ line control from a MM patient in third relapse that had been previously treated by various proteasome inhibitor containing therapies (VTD-PACE, VCD, PAD-Rev). This patient was subsequently treated with a pomalidomide, bortezomib, adriamycin and dexamethasone combination therapy (Pom-PAD) and achieved a partial remission after 4 cycles of therapy. When being exposed to VCD at earlier relapse a complete remission was induced within 6 cycles of therapy, demonstrating excellent response to proteasome inhibition at this earlier disease stage. Results: We identified clonal missense mutations in this patient at known NRAS hotspot location (p.Gln61Arg) and in MAX (p.Arg35His). Most notably we found and validated four subclonal single point mutations in PSMB5, each of them in subclonal frequencies with variant reads (VR) ranging from 1.9%- 5.9% (average read depth 750X). All PSMB5 mutations occurred in a highly conserved region in exon 2 of the gene (p.Cys122Tyr, p.Met104Ile, p.Ala86Pro, p.Ala79Thr), with three of them being located within the proteasome inhibitor drug binding site. Our 400bp amplicon design allowed us to observe that each mutation identified in PSMB5 is exclusively present on a different sequencing read and no reads are shared between the mutations. This implies that the mutations are present on different subclones of the tumor, which means that, despite low VR frequencies of the single mutation, in sum more than a quarter of the whole tumor might be affected by mutated PSMB5. At a disease stage when the patient was well responsive to proteasome inhibitor treatment (at diagnosis and at first relapse), of note, none of the mutations in PSMB5 is detectable. Conclusion: Here we report the first in human PSMB5 mutation in a MM patient. These mutations evolved in parallel within different subclones of the disease under the selective pressure of bortezomib- containing treatment regimens, representing branching evolution. It is to speculate whether previous investigations negating the existence of PSMB5 mutations in proteasome inhibitor treated patients might not have sequenced deep enough or did set up a sensitivity cut-off too rigid to detect such subclonal mutations. Our finding suggests that the mutations identified may contribute to the development of proteasome inhibitor resistance, emphasizing the need for more detailed genomic characterization of tumors, including minor subclonal mutation detection. Functional analysis of the mutations is ongoing and results will be presented at the meeting. Figure Figure. Disclosures No relevant conflicts of interest to declare.