Anti-PTN antibody inhibits MM growth and induces apoptosis in vitro, and affects total cell recovery and the total viable cell recovery. (A) The myeloma cell lines MM-1S and U266 and BM cells from a MM patient were assessed for cell viability, proliferation, and apoptosis. MM cells were incubated with anti-PTN antibody or control IgG for 24 hours and cellular viability assessed by MTT assay. 300 μg/mL anti-PTN reduced the viability of all MM cells tested here, compared with cells incubated without antibody (media) or with control IgG. To assess cell proliferation, MM cells were treated with increasing concentrations of anti-PTN antibody and then measured for BrdU incorporation by flow cytometry. All 3 MM samples treated with anti-PTN antibody showed decreased BrdU levels compared with cells treated with control antibody. Apoptosis was measured using Annexin V/PI staining followed by flow cytometry. The anti-PTN antibody at all 3 concentrations induced apoptosis in these 3 MM samples in a concentration-dependent fashion. (B) For the evaluation of inhibition of cell growth, an aliquot of each of these cell suspensions was mixed with an equal volume of trypan blue dye and total number of viable cells recovered was determined using light microscopy. Untreated (control) cells were considered as 100%. The samples were set up in triplicates. The results shown are the means of data from triplicate samples. P values were based on comparing results with IgG control antibody vs anti-PTN antibody.