The Novel Peptide Drug Conjugate OPDC3 Is Highly Active in Different Hematological Malignancies

Abstract

Background: Peptide drug conjugates (PDCs) are an important emerging class of molecules that allow for targeted delivery of therapeutic agents. Melflufen, which was recently approved by the European Medicines Agency for relapsed refractory multiple myeloma patients, is one such PDC that allows for targeted delivery of the payload drug melphalan. Like melflufen, the novel PDC OPDC3 was designed to target cells with high peptidase activity to deliver toxic payload. In this study, we evaluated the activity of OPDC3 in models of acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), and diffuse large B-cell lymphoma (DLBCL). Since the majority of AML patients eventually relapse, and only a limited set of therapies are available for MDS and DLBCL patients, new treatment options are urgently needed. Methods: The Finnish Hematology Research Biobank provided viably frozen bone marrow mononuclear cells from 29 AML and 6 MDS patients. All 29 AML samples and 1 MDS sample were from relapsed/refractory (R/R) patients, and 5 MDS samples were taken at diagnosis. Multi-parametric flow cytometry-based drug sensitivity and resistance testing (DSRT) was used to assess sample sensitivities to OPDC3, melflufen and venetoclax. Samples were incubated for 72h hours in seven different concentrations ranging from 0.01 nM to 10 000 nM of OPDC3, melflufen and venetoclax. Cells were stained using antibody panels that allowed detection of immature and mature blasts. Cell death and viability were assessed using Annexin V and DRAQ7. Dose response curves were generated for each detected cell subset. Drug sensitivity scores (DSS) and EC50 values were calculated. OPDC3 tumor growth inhibition efficacy was validated on xenografts in ovo initiated from SUDHL-4 cell line. OPDC3 and bendamustine effects as single agents were tested in three different concentrations (8.4; 33.5; 167.5 μM) on DLBCL cell line SUDHL-4. OPDC3 in combination with rituximab and bendamustine in combination with rituximab were also tested. The grafted tumors were quantitatively evaluated by tumor weight using the ChorioAllantoic Membrane (CAM) assay. Toxicity was followed daily by embryonic lethality and final quantitative evaluation was done on day18 after treatment per treatment group. Results: OPDC3 was effective in killing blast cells in samples from R/R AML patients. The most sensitive sample having the highest DSS 33 (IC50: 0.9 nM), least sensitive sample having the lowest DSS 15 (IC50: 19.5 nM), and median DSS being 24.1 (IC50: 8.5 nM) (Figure 1). For venetoclax the highest DSS was 27.9 (IC50: 2 nM), lowest DSS 0 (IC50: >10 000 nM), and median DSS 19.4 (Figure 1). The 3 least sensitive samples to OPDC3 were clearly sensitive to venetoclax (Figure 1). OPDC3 was also able to kill more mature malignant CD14+ cells (median DSS 21.5; median EC50 17.1 nM). OPDC3 was more effective in killing both blast and CD14+ cells than melflufen. Melflufen blast median DSS was 20.6 (EC50: 19.9 nM) and for CD14+ cells median DSS was 16.4 (EC50: 84.7 nM). OPDC3 was also effective in killing MDS blast cells in 4/6 of the patient samples. The highest OPDC3 DSS was 27.2 (IC50: 3.1 nM), lowest DSS 0 (IC50: >10 000), and median DSS 15.3. OPDC3 reduced the DLBCL cell line SUDHL-4 tumor growth at 8.4 μM when compared to the negative control (Figure 2). Bendamustine had little effect on tumor growth at 8.4 μM. At 33.5 μM bendamustine was unable to reduce tumor growth as much as 8.4 μM of OPDC3. OPDC3 also caused less toxicity at 33.5 and 167.5 μM compared to bendumustine at the same concentrations. OPDC3 in combination with rituximab was more effective in reducing tumor growth than both compounds alone, or bendamustine in combination with rituximab. OPDC3 in combination with rituximab caused also the least embryonic toxicity. Conclusions: OPDC3 can efficiently target patient derived AML and MDS blast cells at relatively low nM concentrations. It is also able to kill more differentiated malignant CD14+ AML cells. Especially in R/R AML samples in which the blast cells and CD14+ cells are resistant to venetoclax, OPDC3 was effective at targeting both cell populations. OPDC3 is more effective than bendamustine as a single drug in killing SUDHL-4 tumor cells, and when combined with rituximab compared to bendamustine in combination with rituximab. OPDC3 shows promise as a novel therapeutic for different hematological malignancies. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal