Citations

Abstract Multiple myeloma (MM) makes up approximately 10% of all hematologic malignancies, with increasing incidence worldwide. Though treatment options for newly diagnosed patients have evolved in recent years, they are not curative, and relapse is common with 2,500-3,000 relapsed or refractory (R/R) MM US patients seeking novel treatments, annually. Cereblon (CRBN)-binding Ikaros and Aiolos (I/A) protein degraders (i.e., lenalidomide (LEN) and pomalidomide (POM)) have had great success in treating MM. However, due to the unstable chiral nature of the CRBN-binding moiety, common to these molecules, many exist as racemic mixtures (1:1 mixture of interconverting (R)- and (S)-enantiomers). A growing body of evidence suggests that the (S)- enantiomer is the active anticancer species, while the (R)-enantiomer is inactive and potentially results in undesired activity. The ability to stabilize the active (S)- enantiomer represents a potential strategy to improve therapeutic outcomes. We are developing SP-3164, the deuterium-stabilized (S)-enantiomer of avadomide (AVA), an I/A-degrading molecular glue which has been studied in over 400 patients, demonstrating safety and activity in hematologic diseases. Our in vitro data demonstrate that SP-3164 more potently and rapidly degrades the cancer-promoting transcription factors, I/A, compared to LEN, POM, and AVA, while the stabilized (R)-enantiomer, SP-3165, neither binds CRBN nor degrades I/A. In preliminary in vivo studies, SP-3164 elicited significant tumor growth inhibition (TGI). Here, we investigate the activity of SP-3164 in MM, compared to established treatment regimens. SP-3164’s potential to degrade Aiolos in MM.1S cells was compared to SP-3165, AVA, and POM. SP-3164 rapidly and robustly degraded Aiolos in a time- and dose-dependent manner, more potently than AVA and POM, while SP-3165 demonstrated minimal Aiolos degradation. To investigate the effect of SP-3164 on cell survival, we treated NCI-H929 cells with SP-3164 (0.1 µM, 1 µM, and 10 µM) and SP-3165 (1 µM) and assessed apoptosis by flow cytometry. SP-3164 induced dose-dependent early and late apoptosis after 72 hours, while SP-3165 showed no induction of apoptosis. SP-3164’s in vivo activity was assessed and compared to SP-3165, LEN, and POM in an NCI-H929 mouse xenograft model. SP-3164 showed significant TGI as a single agent while SP-3165 seemed to support tumor growth. LEN and POM demonstrated minimal TGI. When combined with dexamethasone (DEX), SP-3164 had improved TGI compared to the combination of POM+DEX. These preclinical data demonstrate that SP-3164 is a potent CRBN-binding molecular glue with the ability to rapidly degrade cancer-promoting transcription factors and induce apoptosis in vitro. In vivo, SP-3164 has superior single agent and combination activity compared to approved molecular glues. These data support the continued development as a novel therapy in MM. Citation Format: Aundrietta D. Duncan, Daniela Y. Santiesteban, Nadeem Q. Mirza, Steve Horrigan, Sheila DeWitt, Vincent Jacques, P. Leif Bergsagel. SP-3164, a novel molecular glue degrader with activity in preclinical models of multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6253.

8024 Background: Minimal residual disease (MRD) is prognostic for survival in multiple myeloma (MM). MRD is usually assessed in the bone marrow (BM) by flow cytometry or NGS. MRD by FDG PET/CT provides a global representation of the tumor burden, including response assessment of extramedullary disease. We examined MRD status in MM pts using both BM and PET/CT at Mayo Clinic. Methods: Medical records were reviewed retrospectively for MM pts who received CAR-T between 4/2018 and 12/2022. All PET/CT scans were assessed by radiologists. BM MRD was assessed by flow cytometry with a sensitivity of 10-5. Progression-free survival (PFS) and overall survival (OS) were analyzed by Kaplan-Meier method. Results: Among the 157 CAR-T pts, including 89 pts who received FDA-approved CAR-T, median age was 63 years, 59% (92/157) were males, 42% (66/157) had high risk cytogenetics with median of 5 prior lines of therapy, 36% (57/157) had plasmacytoma. Incidence of CRS was 83%, 5% grade ≥ 3 CRS. Incidence of ICANS was 19%, 4% grade ≥ 3 ICANS. CR/sCR rate was 37%. One hundred and thirty-seven pts (87%) had evaluable BM at month (mo) 1, 85% (117/137) were BM MRDneg at mo 1. Baseline demographics were comparable between the two groups except age, % BM plasma cells and use of bridging therapy. Among the MRDneg pts, CR/sCR rate was 44% (51/117) and 95% (111/117) had sFLC below normal. At median follow-up of 13.8 months, median PFS among pts with BM MRDneg at 1 mo was 12 mo (95% CI: 11, 30) vs 3 mo (95%CI: 2, 7) for BM MRDpos (p<0.001). Median OS among pts with BM MRDneg at 1 mo was 34 mo (95% CI: 24, NR) vs 22 mo (95%CI: 7, NA) for BM MRDpos (p<0.01). At month 1, 112 pts had both BM and PET/CT assessments available, 64/112(57%) were both BM MRDneg/PET MRDneg, 38/112 (34%) were MRDneg for either BM or PET and 10/112 (9%) were positive for both BM and PET (MRDpos/PET MRDpos). Baseline demographics except age were comparable between the 2 groups (Table). Rate of conversion from MRDpos to MRDneg was low. Rate of sustained BM and PET MRDneg at mo 12 was 44% (8/18). The median PFS and OS for BM MRDneg/PET MRDneg was significantly longer as compared to others (Table). Conclusions: Achieving FLC below normal, BM MRDneg and PET MRDneg at 1 month, regardless of IMWG response at that time, is prognostic for both PFS and OS in MM pts receiving CAR-T. Failure to achieve any of these confers poor prognosis. [Table: see text]

Abstract Dendritic cells (DC) are essential for the long term survival of plasma cells (PC) in the bone marrow and for the maintenance of persistent antibody titers. But the molecular basis for these interactions is not very clear. Both normal and malignant PC (like myeloma) express the T-cell co-stimulatory molecule CD28. Our data show that CD28 expressed on PC play a major role in CD80/CD86 (B7) mediated DC induction of growth factors such as IL-6 and immunosuppressive enzyme indoleamine 2,3 dioxygenase (IDO) as well as in antibody or DC mediated protection of PC in vitro. While IL-6 protected PC in vitro, IDO induced the formation of regulatory T cells in culture. Use of myeloma drug lenalidomide to inhibit DC-B7 expression or anti-CD28(Fab)2 fragments to block CD28-B7 interactions reduced DC ability to protect MM cells or produce IL-6/IDO. Moreover, just like in T-cell models, CD28 activation in malignant PC triggers similar molecular events such as tyrosine phosphorylation and association of p85. We believe that downstream of CD28, while PI3K/Akt governs survival, the Vav1/SLP76 pathway regulate PC proliferation and these form the molecular basis for a bi-directional molecular bridge between the PC and bone marrow microenvironment. Targeting this bridge could form the basis for future therapeutic strategies. Our data suggests a role for CD28-B7 in plasma cell survival by modulating the bone marrow microenvironment.

Abstract We have previously shown (AAI2009) that dendritic cells (DC) contribute to the survival of long lived plasma cells in the bone marrow, which are important to maintain persistent antibody titres. What is not clear are the molecular interactions that are involved. Both normal and malignant plasma cells(like myeloma cells) express the T-cell co-stimulatory molecule CD28, and both interact with DCs in the bone marrow microenvironment. CD28 activation on MM triggers similar molecular partners downstream as observed in T-cells. Gene expression analysis of normal and malignant plasma cells shows that CD28 expression correlates with poor prognostic subgroups that are associated with specific genetic lesions. In our data, while activation of CD28 with antibodies or DC-CD80/CD86 (B7) protects myeloma cells against cell death, the ligation of B7 on DCs induces DC production of plasma cell survival factor IL-6, and immunosuppressive factor indoleamine 2,3-dioxygenase (IDO). Use of Lenalidomide (a common myeloma drug) to inhibit DC-B7 expression or anti-CD28(Fab)2 fragments to block CD28-B7 interactions reduced DC ability to protect MM cells. Experiments with αCD28(Fab)2 or inhibitors of notch pathway suggest a cross talk that regulates IL-6 production. IDO activity in DC-MM cocultures, suppressed T-cell proliferation in MLRs while an IDO inhibitor alleviated this. Our data suggests a role for CD28-B7 in plasma cell survival by modulating the bone marrow microenvironment.

Abstract Bone marrow (BM) niche plays critical roles in promoting progression and chemoresistance of multiple myeloma (MM), but the iron metabolism bridging the malignant plasma cells and BM stromal cells (BMSCs) has not been well elucidated. Using in vitro and in vivo models of interaction of MM and BMSCs, we identified that iron level was augmented due to the elevated expression of transferrin in MM cells, and the accumulation of iron desensitized MM cells to proteasome inhibitors (PIs) treatment and promoted productions of cholesterol and lanosterol. Simultaneously, direct contact with BMSCs remarkably upregulated the protein level of GPX4, a ROS eraser, to obviate ferroptosis in MM cells. Mechanistic studies revealed that CD40/CD40 ligand (CD40L) signaling promoted the expressions of transferrin and SUMO-specific protease 3 (SENP3), and SENP3 stabilized GPX4 protein via deSUMOylation modification. GPX4 inhibitor induced ferroptosis was cell-cell contact dependent, since blocking CD40/CD40L interaction, or depletion of Cd40l in BMSCs from Cd40lfl/fl;Prx1Cre/+ mice, eliminated the anti-MM efficacy of RSL3 in the Vk*MYC mouse model of myeloma, but not in the patient-derived xenografts (PDX) model. Our study deciphers mechanism of iron metabolism in regulating MM chemoresistance, and clarifies the therapeutic potential of non-apoptosis strategies in managing refractory or relapsed MM patients.