Figure 2. Potent and selective activity of CD46-ADC on MM cells compared with BM stromal cells, with potentiation of ADC effect in the context of MM-stromal interactions.

(A) Confocal immunocytochemistry of MM1.R after 4 (left) and 18 (right) hours of incubation with anti-CD46 antibody (red). Late lysosomes shown with anti-LAMP1 antibody (green), and partial colocalization shown in merged panel (yellow). (B) Dose response for CD46-ADC inhibition of viability of MM cells compared with HS5 and BM61 BM stromal cells after 96-hour incubation (n = 3). NR: EC₅₀ not reached due to lack of killing at the highest concentration tested. (C) Lack of effect of nonbinding control ADC until approximately 100 nM (n = 3). (D) Annexin V and PI staining of MM cell line INA-6 for 0–10 nM CD46-ADC, with apoptosis and death by 48 hours (representative data, n = 3). (E) Sensitivity of MM1.S cell line to CD46-ADC is increased in the presence of HS5, BM61, or HS27A BM stromal cells. EC₅₀ was 2.25 nM on MM1.S alone and 0.77 nM, 0.92 nM, and 1.05 nM for MM1.S in the presence of HS5, HS27A, and BM61, respectively (data represent mean ± SEM, n = 3).