Tolerability of obinutuzumab therapy in patients with rituximab-relapsed/refractory B-cell malignancies - a retrospective single center cohort study

SIRPα Suppresses Response to Therapeutic Antibodies by Nurse Like Cells From Chronic Lymphocytic Leukemia Patients

Targeted antibody therapies improve outcomes for chronic lymphocytic leukemia (CLL) patients. However, resistance often develops. We have previously shown that resistance to therapeutic antibodies, by monocyte derived macrophages (referred to as nurse like cells, NLCs), from CLL patients is characterized by suppression of antibody dependent phagocytosis (ADP). The mechanism(s) contributing to the muted ADP responses remain unresolved. In this regard, an innate immune checkpoint was recently described that uses the CD47:SIRPα axis to suppress phagocytic responses by macrophages. In this study we examine whether the SIRPα axis regulates ADP responses to the anti-CD20 antibody, obinutuzumab, by NLCs. Using siRNA depletion strategies we show that SIRPα is a suppressor of ADP responses. Moreover, we show that this innate immune checkpoint contributes to the resistance phenotype in NLCs derived from CLL patients. Finally, we show that SIRPα suppression is mediated via the phosphatase, Shp1, which in turn suppresses SYK-dependent activation of ADP. Thus, we identify a druggable pathway that could be exploited to enhance sensitivity to existing therapeutic antibodies used in CLL. This is the first study to show that activation of the CD47:SIRPα innate immune checkpoint contributes to ADP resistance in NLCs from CLL patients.

Helping the Released Guardian: Drug Combinations for Supporting the Anticancer Activity of HDM2 (MDM2) Antagonists

The protein p53, known as the “Guardian of the Genome”, plays an important role in maintaining DNA integrity, providing protection against cancer-promoting mutations. Dysfunction of p53 is observed in almost every cancer, with 50% of cases bearing loss-of-function mutations/deletions in the TP53 gene. In the remaining 50% of cases the overexpression of HDM2 (mouse double minute 2, human homolog) protein, which is a natural inhibitor of p53, is the most common way of keeping p53 inactive. Disruption of HDM2-p53 interaction with the use of HDM2 antagonists leads to the release of p53 and expression of its target genes, engaged in the induction of cell cycle arrest, DNA repair, senescence, and apoptosis. The induction of apoptosis, however, is restricted to only a handful of p53^wt cells, and, generally, cancer cells treated with HDM2 antagonists are not efficiently eliminated. For this reason, HDM2 antagonists were tested in combinations with multiple other therapeutics in a search for synergy that would enhance the cancer eradication. This manuscript aims at reviewing the recent progress in developing strategies of combined cancer treatment with the use of HDM2 antagonists.