Evaluation of Preclinical Activity of Isatuximab in Patients with Acute Lymphoblastic Leukemia

This study reports the pharmacologic effects of isatuximab, a CD38 mAb, on T- and B-cell acute lymphoblastic leukemia (ALL). We analyzed CD38 expression in 50-T-ALL and 50 B-ALL clinical samples, and 16 T-ALL and 11 B-ALL cell lines. We primarily focused on in vitro assessments of isatuximab-mediated antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). In vivo assessment of isatuximab activity was performed in several ALL xenograft models, including disseminated and subcutaneous tumor models in female C.B-17 severe combined immunodeficiency mice. Our study reveals that most patients (90%-100%) carried CD38⁺ blasts independent of disease burden. The median CD38 receptor density on abnormal lymphoblasts is 41,026 copies/cell on T-ALL and 28,137 copies/cell on B-ALL, respectively. In patients with T-ALL, there is a significant increase of CD38 expression in abnormal blasts compared with normal T cells. High-level CD38 receptor density (RD) is critical to trigger effective isatuximab-mediated ADCC against target ALL cells. In addition, a correlation between CD38 RD and isatuximab-mediated ADCP is demonstrated. In the disseminated CD38⁺, T-ALL, and B-ALL xenograft models, isatuximab is able to induce robust antitumor activity, even at low doses. This study shows that isatuximab has significant in vitro and in vivo activity against ALL cells with robust ADCC and ADCP effects that are associated with CD38 expression levels in both T-ALL and B-ALL.

Discovery of Selective, Covalent FGFR4 Inhibitors with Antitumor Activity in Models of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) accounts for a majority of primary liver cancer and is one of the most common forms of cancer worldwide. Aberrant signaling of the FGF19-FGFR4 pathway leads to HCC in mice and is hypothesized to be a driver in FGF19 amplified HCC in humans. Multiple small molecule inhibitors have been pursued as targeted therapies for HCC in recent years, including several selective FGFR4 inhibitors that are currently being evaluated in clinical trials. Herein, we report a novel series of highly selective, covalent 2-amino-6,8-dimethyl-pyrido[2,3-d]pyrimidin-7(8H)-ones that potently and selectively inhibit FGFR4 signaling through covalent modification of Cys552, which was confirmed by X-ray crystallography. Correlative target occupancy and pFGFR4 inhibition were observed in vivo, as well as tumor regression in preclinical models of orthotopic and sorafenib-resistant HCC.

Isatuximab Acts Through Fc-Dependent, Independent, and Direct Pathways to Kill Multiple Myeloma Cells

Isatuximab is a monoclonal antibody targeting the transmembrane receptor and ectoenzyme CD38, a protein highly expressed on hematological malignant cells, including those in multiple myeloma (MM). Upon binding to CD38-expressing MM cells, isatuximab is thought to induce tumor cell killing via fragment crystallizable (Fc)-dependent mechanisms, including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC), as well as via direct Fc-independent mechanisms. Here, these mechanisms of action were investigated in MM and diffuse large B-cell lymphoma (DLBCL) cell lines, as well as in peripheral blood mononuclear cells derived from healthy donors, and in MM patient-derived samples. Our findings show that isatuximab-mediated cytotoxicity occurred primarily via ADCC and ADCP in MM cell lines and via ADCC and apoptosis in DLBCL cell lines expressing high levels of CD38. We identified the programmed cell death-1/programmed cell death-ligand 1 (PD-1/PD-L1) pathway and MM cell-secreted transforming growth factor-beta (TGF-β) as tumor cell-related features that could suppress CD38-mediated ADCC. Furthermore, we established that isatuximab can directly activate natural killer (NK) cells and promote NK cell-mediated cytotoxicity via crosslinking of CD38 and CD16. Finally, isatuximab-induced CDC was observed in cell lines with high CD38 receptor density (>250,000 molecules/cell) and limited expression of inhibitory complement regulatory proteins (CD46, CD55, and CD59; <50,000 molecules/cell). Taken together, our findings highlight mechanistic insights for isatuximab and provide support for a range of combination therapy approaches that could be tested for isatuximab in the future.

Abstract 2966: Isatuximab-induced multiple myeloma cell killing through effector functions is dependent on CD38 expression and complement inhibitors

Isatuximab (Isa) is an IgG1 monoclonal antibody (Ab) that specifically recognizes human CD38. Once Isa engages multiple myeloma (MM) cells expressing a high level of CD38, it can induce tumor cell killing via Fc-dependent mechanisms including Ab-dependent cell-mediated cytotoxicity (ADCC), Ab-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC). To better understand the mechanism of Isa-mediated cytotoxicity, we studied CD38 levels in 16 established MM lines and measured Isa-mediated ADCC, ADCP, and CDC in tumor cell killing. The cytotoxic functions of Isa were dependent on CD38 receptor density (RD) in most cell lines. Isa-mediated ADCC was observed in a subset (7/16) of MM cell lines that displayed CD38 RD &gt;100,000 molecules/cell. Similarly, the same subset of MM cells, with 1 exception, were sensitive to Isa-mediated ADCP, indicating a similar CD38 RD is also required for this killing effect. A much higher CD38 RD (&gt;250,000 molecules/cell) alone was insufficient for Isa-mediated CDC. Cell lines MOLP-8 and MOLP-2 have CD38 RD &gt;250,000 molecules/cell, but are resistant to Isa-mediated CDC. Overexpression of CD38 in cell lines with low endogenous CD38 expression did not always sensitize the cells to Isa-mediated CDC. These results suggest that additional mechanisms are involved in the regulation of such cytotoxic effects. We further investigated the expression of complement-cascade inhibitors CD46, CD55, and CD59. High-level expression of at least one of these molecules was associated with resistance to Isa-mediated CDC, even when cells were CD38 high (hi). By comparing 4 selected MM cell lines, we found that a minimal RD level of 50,000 molecules/cell for CD46, CD55 or CD59 appears to be an important threshold to suppress Isa-mediated CDC. When CD59 function was neutralized by an anti-CD59 antibody, we were able to re-sensitize the cells to Isa-mediated CDC in CD38hi MOLP-8 cells. Neutralizing CD59 function alone did not rescue Isa-mediated CDC in CD38-low expressing NCI-H929 cells. However, overexpressing CD38 and inhibiting CD59 rendered NCI-H929 cells sensitive to CDC. Taken together, the high-level of CD38 expression and low-level of CD59 (and perhaps other inhibitors) expression are important for Isa-mediated CDC in killing of target tumor cells. In conclusion, the main immune effector mechanisms involved in Isa-mediated killing of MM cells include ADCC and ADCP. These effects are dependent on high levels of CD38 RD in MM cell lines in vitro. Further confirmation is under way using samples from MM patients.

Citation Format: Zhili Song, Guang Yang, Anlai Wang, Rita Greco, Joachim Theilhaber, Elvis Shehu, Daniel Ajona, Bruno Paiva, Chen Zhu, Dmitri Wiederschain, Marielle F. Chiron Blondel, Francisco Adrian. Isatuximab-induced multiple myeloma cell killing through effector functions is dependent on CD38 expression and complement inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2966.

Multiple ulcers in primary syphilis with negative rapid plasma reagin and Venereal Disease Research Laboratory tests: an unusual presentation during the re-emergence of syphilis in Albania

Since 1995 infectious syphilis has re-emerged in Albania. As syphilis has become more common, more unusual presentations are being recognized. We present a case of an HIV-negative man with primary syphilis presenting with multiple penile ulcers and negative rapid plasma reagin and Venereal Disease Research Laboratory tests. The case illustrates the challenges of diagnosing early syphilis and the importance of not relying on non-treponemal tests.