Enhancement of Mitochondrial Membrane Potential and Pro-Survival Pathways with Azole Compound C7 Resulting in Expansion of Hematopoietic Stem and Progenitor Cells

Ex-vivo expansion of hematopoietic stem & progenitor cells (HSPC) could improve hematopoietic recovery and reduce post-transplant complications, especially for umbilical cord blood (UCB) grafts where limited total cell numbers result in delayed engraftment.

Freshly-thawed UCB mononucleated cells (MNCs) or purified CD34 ⁺ cells were cultured in animal component free medium supplemented with C7 and a basal cytokine cocktail. The effects of the expansion protocol were measured with phenotypic, in-vitro, and in-vivo functional assays. A range of molecular techniques were also performed to elucidate the mechanisms of action of C7.

In previous studies, expansion cultures initiated with UCB-MNCs and supplemented with C7 resulted in significant expansions of UCB HSPC over 11 days and these grafts demonstrated elevated and sustained multi-lineage engraftment of human cells in primary NSG mice (Bari et al., 2018). In UCB-CD34+ enriched cultures, the addition of C7 to a basal cytokine cocktail also boosted absolute CD45+CD34(BR)+CD38-CD45RA- progenitor expansion by 283±29.4 fold over 11 days which was 1.86±0.12 fold higher than control cultures (p<0.001; n=6). Furthermore, C7 induced significant expansion of primitive HSPC in UCB-MNC defined by phenotype CD45+CD34(BR)+CD38-CD45RA-CD90+CD49f+ by more than 633±8.5 fold, which is 7.5±0.16 fold higher compared to control cultures (p<0.01; n=3). The addition of C7 to CD34+ cells from mobilized peripheral blood (PB) and bone marrow (BM) also resulted in a significant expansion of HSPCs (p<0.05; n=3) (Fig 1A).

When expanded UCB-CD34+ were engrafted in NSG mice, NSG PB analysis at week 3 and week 28 post-transplantation showed significantly higher (p<0.01) human CD45+ cell engraftment in C7 expanded graft (16.4%±2.6) than cytokine expanded graft (7.8%±0.9). NSG BM analysis at week 31 also exhibited similar trends for human CD45+ cell engraftment in C7 expanded grafts with multilineage reconstitution (p<0.01; n=6).

Significantly enhanced CD45+ cell viability (p<0.01; n=3) was observed in C7 cultures compared to control cultures. Mitochondrial health was also improved as confirmed by lower mitochondrial superoxides and higher mitochondrial membrane potential in C7-cultured UCB-MNCs (p<0.05; n=3) that is reflective of reduced reactive oxygen species (ROS) (Fig 1B). As C7 is a chemical analogue of a p38 inhibitor (SB203580), p-p38 (T180/Y182) was significantly reduced in C7-expanded CD34+ culture compared to controls. Significant increases in HIF-1α in C7 expanded CD34+ cells were also observed, potentially indicative of a hypoxic state induced by C7 to benefit HSPC together with reduced levels of ROS.

Kinase inhibition profiling studies on C7 identified CK1δ, a kinase involved in Wnt and p53 signalling pathways, as one of the activation targets directly activated by C7. CK1δ was boosted in C7-expanded cells and this was further validated with western blots on C7 expanded pooled CD34+. CK1δ plays a putative role in p53 activation which is stipulated to promote HSC quiescence favouring long-term maintenance of HSPCs. Western blot analysis also revealed that p53 and BCL-2 were increased with C7 expanded CD34+. GSK3β was also boosted in C7 expanded pooled CD34+ cultures possibly as a result of CK1δ signalling leading to increased proliferation via the Wnt signalling pathway.

Multiple safety studies were conducted on C7 to ensure its safety in clinical applications. This included the BIOMAP phenotypic safety and toxicology tests on human primary cells, AMES test and fluctuation assays for bacteria and SAFETYscan47 ^TM In Vitro Pharmacological Profiling for biochemical safety, all of which were negative for any cytotoxicity or off-targets associated with acute toxicity. No changes were detected in cytogenetics and fluorescence in situ hybridization with UCB-MNC for major leukemia-related genetics as well when they were cultured with C7.

As a small molecule capable of significant HSPC expansion from both UCB and PB sources, C7 is promising for the future of HSPC transplantation. The mechanism behind C7 is likely to be a multi-pronged one with p38 inhibition, increase in HIF-1α, CK1δ activation, improved mitochondrial health, and induction of pro-survival pathways for expanding HSPC populations.