NEW YORK – The novel NF-kB inhibitor IT-901 appears active against Richter syndrome, according to in vitro analyses of primary leukemic cells and in vivo analyses in patient-derived xenograft models.
The findings suggest that NF-kB inhibition should be considered as a therapeutic strategy for Richter syndrome patients, Tiziana Vaisitti, PhD, said at the annual International Workshop on Chronic Lymphocytic Leukemia.
Several factors have been shown to be associated with the development of Richter syndrome (RS), including somatic and germline genetic characteristics, biologic and clinical features, and certain CLL therapies. Recent studies have identified a critical role of mutations in specific genes, such as CKN2A, TP53, and NOTCH1 in the transformation of CLL to RS, which ultimately results in the aberrant activation of selected pathways – including NF-kB, Dr. Vaisitti of the University of Turin and the Italian Institute for Genomic Medicine, Turin, Italy explained.
In an ongoing study on the effects of IT-901 in CLL, she and her colleagues showed that “this compound was able to interfere with NF-kB transcriptional activity.”
That effect is followed by rapid and marked reduction in “the oxidative phosphorylation capacity of CLL cells, determined also by the transcriptional regulation of genes that control this process.”
“Moreover, this compound induces a significant increase and release of mitochondrial reactive oxygen species,” she said, adding: “The final result of this cascade of events is that IT-901 is able to rapidly induce apoptosis selectively in primary CLL cells, independently of the clinical subgroup of patients we are considering, and with very little toxicity on normal lymphocytes.”
The experimental data indicated that IT-901 is effective not only on the leukemic side, but it also acts on the stromal bystander component of the disease, mainly on nurse-like cells, by modulating the expression of molecules critical for CLL survival, she said.
Those findings were reported at the 2016 American Society of Hematology annual meeting (Blood. 2016;128:304).
For the current analyses, she and her colleagues tested the effects of IT-901 in RS, which affects up to 10% of patients with CLL, and for which there is an unmet therapeutic need. They looked at the mechanisms of action of the compound in leukemic cells both in vitro and in vivo.
In line with previous data, NF-kB was “constitutively highly active in RS cells freshly isolated from patients,” she reported.
Exposure to IT-901 at a 5 microM dose for 6 hours significantly decreased binding of p50 and p65 to DNA, and western blotting analyses on nuclear extracts indicated impaired translocation of those subunits in the nucleus, and compromised expression of the whole NF-kB complex, she said.
IT-901 also induced apoptosis in primary RS cells in a dose- and time-dependent manner; significant efficacy was seen after 24 hours of treatment, with more than half of the cells dead.
These results were then confirmed in an RS cell line established in the lab from a patient-derived xenograft (PDX) model, and even in the presence of a protective stromal layer IT-901 was able to induce apoptosis, she said.
The effects of IT-901 treatment were then analyzed in vivo using 3 different PDX models established from primary cells of RS patients and characterized by different molecular and genetic features. RS cells obtained from the PDX-tumor mass, were subcutaneously injected in severely immune-compromised mice and left to engraft until a palpable mass was present. IT-901 was then administered at a dose of 15 mg/kg, every day for 2 weeks, with a 2 day break after 5 days of administration.
Tumor size was significantly reduced, and as was demonstrated in vitro, immune-histochemical analyses of the tumor mass showed diminished expression and localization of the p65 subunit into the nucleus of tumor cells and increased cleavage of Caspase-3 in the treated mice as compared with vehicle-treated mice.
The findings provide proof-of-principle that IT-901 is effective in RS cells, diminishing NF-kB transcriptional activity and expression, and finally inducing apoptosis, Dr. Vaisitti said.
Dr. Vaisitti has received research funding from Immune Target.