Abstract
Background:Multiple myeloma (MM) is the second most common hematologic malignancy in the United States, with over 30,000 new cases diagnosed annually. The development of novel therapies and immunotherapies has improved the 5-year relative survival rate from 54% in 2020 to 62% in 2025. However, relapsed and refractory MM (RRMM) continues to be a major barrier to further survival gains.
Personalized treatment strategies that integrate multi-omics profilings with drug sensitivity testing offer promise for improving RRMM outcomes. Yet, implementation of such approaches remains limited, particularly in community hospitals serving underrepresented and rural populations. A key obstacle is the lack of efficient ex vivo drug screening platforms for identifying effective therapies tailored to individual patients. Existing ex vivo MM culture systems are complex, costly, and labor-intensive. They often rely on co-culture with mixed cell types using expensive devices, supplemented with cytokines and antibodies over 5–7 days, introducing bias and limiting scalability. Thus, we established a simplified ex vivo protocol for drug sensitivity testing that can be feasibly implemented in community hospital settings.
Methods: Our two versions of simplified ex vivo protocol were published with detailed instructions (PMID: 40654055 and 38977990). Briefly, CD138⁺ plasma cells were enriched from patient bone marrow samples and cultured for 18 hours in RPMI-1640 supplemented with 20% heat-inactivated autologous serum, maintaining approximately 80% cell viability. The protocol does not require high-end instrumentation or PhD-level expertise. This streamlined approach enables drug sensitivity testing in a 96-well plate format using primary patient cells.
Aims: This study aims to adapt the existing 1-day ex vivo drug sensitivity testing protocol from a 96-well plate format to 384-well and/or 1,536-well plate formats. Additionally, the study seeks to apply the protocol to assess the efficacy of current treatment regimens in primary multiple myeloma samples.
Results: We successfully adapted the protocol for use in a 384-well plate format by seeding 50 µL of CD138⁺ cells at 0.3 × 10⁶/mL per well. Ongoing efforts are focused on enhancing cell viability by fine tuning of these conditions and integrating robotic process automation using cost-effective BioTek instrumentation.
Using this protocol, we also evaluated residual MM cells from a patient undergoing treatment. < 1% cell viability was detected after 18 hours of culture, and a follow-up bone marrow biopsy confirmed a reduction of MM cells to undetectable level. We are currently collecting additional residual samples to assess whether this approach can reliably measure treatment effectiveness.
Implications for Clinical Practice: Adapting the protocol to 384- and 1,536-well plate formats enables drug sensitivity testing of over 300 FDA-approved anti-tumor agents at multiple concentrations, considering that the myeloma cell number in patient samples is limited. Consistent results across multiple specimens may support the protocol's use for evaluating therapeutic effectiveness alongside minimal residual disease (MRD) assays.
Significance & Conclusion: We are establishing a practical, accessible protocol for ex vivo drug sensitivity testing and treatment evaluation that can be implemented in community hospital settings, particularly in rural and under-represented areas. This approach has the potential to improve clinical decision-making and advance personalized myeloma care in underserved populations.
