Hodgkin's Lymphoma Cell Lines Have up-Regulated IL-3 Receptor α (IL-3Rα) Expression and Are Sensitive to SL-401, An IL-3Rα Targeted Drug,

Abstract

3737 Background: Hodgkin lymphoma (HL) is among the most curable lymphomas, however 20%-30% of patients relapse after initial chemotherapy, or have primary refractory disease. While 30–50% of these patients may be cured with second line chemotherapy and autologous stem cell transplant, patients who do not obtain a complete response (CR) prior to transplantation, or who relapse after second line therapy have few effective therapeutic options. Novel treatment strategies for these patients are needed. It has been previously shown that in patients with classical HL the malignant Hodgkin Reed-Sternberg cells (HRS) express a high level of the Interleukin-3 receptor (IL-3R). Therefore, we hypothesized that SL-401, a novel biologic conjugate consisting of IL-3 linked to diphtheria toxin, which targets IL-3R, may be an effective approach for selectively targeting and killing HRS cells. Methods: We first assessed the expression of the IL-3R α-chain (CD123) on two nodular sclerosing (HDLM-2 and L-428) and two mixed cellularity (KM:H2 and L-1236) HL cell lines by flow cytometry. Cells were washed with PBS and stained with CD123 PE (BD Pharmingen) as well as other antibodies, including CD15 FITC (BD Pharmingen), for 20 minutes at 4°C and again washed with PBS. Stained cells were acquired using the LSR II (BD) and data were analyzed using Flow Jo (Tree Star). We then tested the sensitivity of these cell lines to SL-401 using a CellTiter Glo in vitro cytotoxicity assay. A CD123 positive eyrthroleukemic cell line (TF-1/H-ras) with known sensitivity to SL-401 was used as a positive control. The cell lines were cultured in the presence or absence of SL-401 for 48 h and assessed for cell viability at concentrations ranging from 3×10−7 to 1.3 μg/ml. Results: We found high expression of CD123 on HDLM-2 and L-428 HL lines (99% and 89%, respectively) and low-to-moderate expression of the receptor on the L1236 and KM-H2 lines (19.5% and 1%, respectively). Based on CD123 expression, we assessed the sensitivity of these cell lines to SL-401. The L428 and HDLM2 cell lines, which exhibited a high expression of CD123, showed sensitivity to SL-401 relative to control starting at approximately 0.3 ng/ml. Cell viability was reduced to 64.8 ± 5% for L-428 and 68.2 ± 8% for HDLM2 when incubated at the highest concentration of drug (1 μg/ml (L428) and 0.7 μg/ml (HDLM2)). The low CD123 expressing cell lines L1236 and KM:H2 were less sensitive to SL-401 and did not exhibit a significant reduction in cell viability even at the highest concentration of SL-401 tested (1.3 ug/ml; 100 ± 2% and 88.4 ± 6%, respectively). Other lymphoid malignant cell lines with CD123 expression reported in the literature were also tested. Interestingly, the T Acute Lymphocytic Leukemia (T-ALL) cell lines DND41 and P12 showed marked sensitivity to SL-401, with a reduction in cell viability to 55.9 ± 4% and 47.9 ± 6%, respectively, in the presence of 1.3 μg/ml of drug. Conclusion: These results suggest that CD123 expression may vary as a function of HL histology, and that sensitivity to SL-401 may correlate with CD123 expression. Based on these results, SL-401, which is currently being evaluated in clinical trials of patients with acute myeloid leukemia, myelodysplastic syndrome, and chronic myeloid leukemia, may be a potential treatment strategy in refractory HL, and warrants further exploration in T-ALL. Exploration of CD123 expression in primary and relapsed/refractory patients with lymphoid malignancies as well as in vivo studies with SL-401 in this setting is currently underway. Disclosures: Brooks: Stemline Therapeutics, Inc: Employment, equity options. Cirrito:Stemline Therapeutics Inc.: Employment, Equity Ownership, Patents & Royalties. Bergstein:Stemline Therapeutics Inc.: Employment, Equity Ownership, Patents & Royalties. O'Connor:Merck: Research Funding; Spectrum: Research Funding; Novartis: Research Funding; Celgene: Consultancy, Research Funding.

The Hodgkin Lymphoma Immune Microenvironment: Turning Bad News into Good

“…These discrepancies may have arisen because the samples were too small, or because there are more pDC variants, with different abilities to induce T cell proliferation and to produce cytokines [ 91 ]. In addition, CD123 is used as a specific marker of pDCs, but it must be remembered that HRS cells also express it in 90% of cHL cases [ 94 ], especially in NS cHL, and overexpress IL3 receptors [ 95 ]. Other data suggest that CD123 expression also occurs in M2-like macrophages in the TME of cHL [ 96 ].…”

CD123 as a Biomarker in Hematolymphoid Malignancies: Principles of Detection and Targeted Therapies

“…CD123 is expressed on Hodgkin–Reed–Sternberg cells in 90% of Hodgkin lymphoma (HL), and IL-3 is capable of inducing Hodgkin cell line growth in vitro [ 57 ]. CD123 overexpression appears to be highest in nodular sclerosis HL [ 58 ]. Other data suggest that CD123 expression is also present on macrophages in the microenvironment of HL, suggesting that targeting CD123 might impact both the neoplastic cells as well as the tumor microenvironment [ 59 ].…”