A laboratory model of the hypoxic tumour microenvironment
Dr Giles Best - Royal North Shore Hospital, Sydney, Australia
The work that I presented this morning was focussing on an inhibitor of two protein kinases called PIM kinase and PI3 kinase and it’s a pan-inhibitor of both families of kinases. We showed preliminary data that combining a single agent PIM inhibitor with idelalisib, the PI3 kinase delta inhibitor, that the combination was highly synergistic. So through an MTA with a company based in Ireland called Inflection Biosciences we have been testing their dual inhibitor, called IBL202, as I say it’s a pan PIM and PI3 kinase inhibitor, and shown that under conditions that mimic the CLL tumour microenvironment it’s highly effective and even more so than either their PIM inhibitor alone or the PI3 kinase inhibitor, idelalisib. Our model of the tumour microenvironment really incorporates a co-culture of the primary CLL, patient derived CLL, cells with a CD40 ligand expressing fibroblast layer. We culture this model under normoxic conditions, so 21% oxygen, and hypoxic conditions, 3% oxygen, and in the Kolling Institute we have a dedicated piece of apparatus that allows us to tightly regulate the oxygen that these cells are exposed to. Under those conditions we see that the sensitivity to both the PIM alone inhibitor and the dual PIM/PI3 kinase inhibitor, the sensitivity of the leukemic cells is reduced but particularly with the PIM alone inhibitor, but the cells are still very sensitive to the dual PIM/PI3 kinase inhibitor IBL202. Certainly under the hypoxic co-culture conditions the cells, at least in our hands, were completely insensitive to the PI3 kinase delta inhibitor idelalisib. So at least in our in vitro modelling we think that the dual inhibitor is significantly more effective than either of the single inhibitors.
So what will the next steps be in this research?
The next steps will be to expand our cohort of primary samples that we’re testing. One of the limitations of CLL as a disease is that there are very few, if any, very good cell line models. Even the mouse models of CLL are limited in their applicability to the human condition so we think that the use of primary material takes into the heterogeneity of CLL patients in general. So our aim is to look at disease subgroups that we know currently there’s an unmet need for treatment. At least our preliminary data has shown that there is no difference in sensitivity of patient samples, particularly patients with deletions or mutations in p53, there's no difference in the sensitivity to IBL202 compared to patients from a more favourable prognostic subgroup.
And for CLL patients down the track, where do you think this could lead?
The emerging data certainly presented at this conference suggests that single agent therapy is effective but that relapse rates are still high. So inhibition of more than one target protein in more than one survival pathway is going to avoid the ability of the leukemic cells to avoid cell death and that the pathways that you target, certainly our agent targets, are complementary to each other. So by inhibiting both pathways simultaneously with a single agent we believe that we’ll get a better rate of leukemic cell kill in the first treatment and that may well lead to a better response and better remission rates, durable remissions in CLL patients.