Abstract 677: Effective depletion of M2 macrophages by CD206-NAMPT-ADCs

Introduction/ Purpose of study Targeting M2 macrophages as an immunosuppressive cell population within the tumor-microenvironment has become an important effort within preclinical research to achieve and enhance anti-tumor efficacy. In contrast to reprogramming approaches, we focused on effective and specific depletion of M2 macrophages (Mphs) by a new antibody-drug-conjugate (ADC) comprising a CD206-binding antibody conjugated to a nicotinamide phosphoribosyl transferase (NAMPT) toxophore which was proved to be very potent in cell killing.

Description of procedures Human (hu) and mouse (ms) cross-reactive CD206 antibodies were identified by phage display using recombinant hu/ms CD206-extracellular domains. Selected clones showing strong CD206 binding by ELISA were reformatted into huIgG1 format and cellular targeting confirmed by FACS binding and internalization using CD206-transfected HEK cells. Antibodies were conjugated to a NAMPT toxophore by Cys-conjugation using two different non-cleavable linkers. Murine peritoneal Mphs collected after thioglycolate stimulation were polarized to M1 (LPS + IFNγ) or M2 (IL4 + IL13 + PGE2) within 24h and characterized for cytokines and typical markers via FACS (CD206, CD163, CD80/MHCII) and qPCR (iNOS, TGFβ, ARG1). After 96h treatment with either CD206- or isotype-NAMPT-ADCs, viability of Mphs was determined. In vivo pharmacokinetics (PK) of unconjugated antibodies were analyzed in plasma of female BALB/c mice for up to 72h.

Summary of data Of the resulting 57 hu/ms cross-reactive CD206-binding antibodies, TPP-17829 and TPP-17836 were identified with single-digit nanomolar binding affinity and strong internalization in CD206-transfected cells as a prerequisite for an ADC approach. Conjugation of the antibodies to NAMPT toxophores yielded drug-antibody-ratios of 4-7 as determined by SEC-UV without significant aggregation. These two CD206-NAMPT-ADCs successfully depleted polarized M2-Mphs characterized by high CD206 expression, whereas isotype-NAMPT-ADC controls had no effect. While the unconjugated NAMPT toxophore was potent in depleting primary low-proliferating M1/M2 Mphs, by comparison, the anti-proliferative toxophore KSP (kinesin-spindle-protein inhibitor) was completely ineffective. PK analysis of TPP-17829 and TPP-17836, however, revealed a rapid plasma clearance within the first hours, most likely target-mediated via the liver, rendering them unacceptable for in vivo efficacy testing as NAMPT-ADCs.

Conclusions CD206-NAMPT-ADCs demonstrated proof of concept for specific depletion of M2-Mphs in vitro. However, specific in vivo depletion of M2 Mphs from tumors will be challenging with respect to fast plasma clearance observed for anti-CD206 antibodies.

Citation Format: Sandra Berndt, Katharina Filarsky, Patrick Smith, Niels Boehnke, Markus Berger, Fionnuala McAleese Eser, Hans-Georg Lerchen, Phillip Ellinger, Mathias Gehrmann, Jim Wu, Dominic Hildebrand, Bertolt Kreft, Uwe Gritzan. Effective depletion of M2 macrophages by CD206-NAMPT-ADCs [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 677.

NFATC1 activation by DNA hypomethylation in chronic lymphocytic leukemia correlates with clinical staging and can be inhibited by ibrutinib

B cell receptor (BCR) signaling is a key for survival of chronic lymphocytic leukemia (CLL) cells, and BCR signaling inhibitors are clinically active. However, relapse and resistance to treatment require novel treatment options. To detect novel candidate therapeutic targets, we performed a genome-wide DNA methylation screen with custom arrays and identified aberrant promoter DNA methylation in 2,192 genes. The transcription factor NFATC1 that is a downstream effector of BCR signaling was among the top hypomethylated genes and was concomitantly transcriptionally upregulated in CLL. Intriguingly, NFATC1 promoter DNA hypomethylation levels were significantly variant in clinical trial cohorts from different disease progression stages and furthermore correlated with Binet disease staging and thymidine kinase levels, strongly suggesting a central role of NFATC1 in CLL development. Functionally, DNA hypomethylation at NFATC1 promoter inversely correlated with RNA levels of NFATC1 and dysregulation correlated with expression of target genes BCL-2, CCND1 and CCR7. The inhibition of the NFAT regulator calcineurin with tacrolimus and cyclosporin A and the BCR signaling inhibitor ibrutinib significantly reduced NFAT activity in leukemic cell lines, and NFAT inhibition resulted in increased apoptosis of primary CLL cells. In summary, our results indicate that the aberrant activation of NFATC1 by DNA hypomethylation and BCR signaling plays a major role in the pathomechanism of CLL.

Active human nucleolar organizer regions are interspersed with inactive rDNA repeats in normal and tumor cells

AIM

The synthesis of rRNA is a key determinant of normal and malignant cell growth and subject to epigenetic regulation. Yet, the epigenomic features of rDNA arrays clustered in nucleolar organizer regions are largely unknown. We set out to explore for the first time how DNA methylation is distributed on individual rDNA arrays.

MATERIALS & METHODS

Here we combined immunofluorescence detection of DNA modifications with fluorescence hybridization of single DNA fibers, metaphase immuno-FISH and methylation-sensitive restriction enzyme digestions followed by Southern blot.

RESULTS

We found clustering of both hypomethylated and hypermethylated repeat units and hypermethylation of noncanonical rDNA in IMR90 fibroblasts and HCT116 colorectal carcinoma cells. Surprisingly, we also found transitions between hypo- and hypermethylated rDNA repeat clusters on single DNA fibers.

CONCLUSION

Collectively, our analyses revealed co-existence of different epialleles on individual nucleolar organizer regions and showed that epi-combing is a valuable approach to analyze epigenomic patterns of repetitive DNA.