April 11th, 2023
This past weekend saw the induction of the final 300 mice into the study. These mice, which constitute "cohort 4", comprise the last three of the ten treatment groups (numbered 7, 9 and 10 in the full project description), namely:
those receiving everything except senolytic
those receiving everything except blood stem cells
those receiving all four treatments
As I've described in past updates, the first month or so of any group's journey consists of a staggered sequence of injections, starting with mobilisation (or not) of resident HSCs, then injection (or not) of young HSCs, then injection (or not) of vehicle including (or not) senolytic, and finally injection (or not) of virus including (or not) the gene for mTERT. This is a sequence that takes quite a while, especially now that (see update #3) we have introduced a two-week gap between the mobilisation/HSC and the senolytic. So right now we are doing a whale of things in parallel with the different cohorts; cohorts 2 and 3 are midway through things, and cohort 4 is just starting out. I have no words to express my praise for the technicians on the ground at Ichor who are getting this done, as well as their supervisors who are keeping the whole thing under control.
We did have one setback since my last update, which I report in full here. It concerns our senolytic, which (see earlier updates) is galactose-conjugated Navitoclax ("Gal-Nav").
The issue was how to deliver it, which is an issue because Navitoclax is quite hydrophobic and therefore reluctant to solubilise in most common pharmaceutical vehicles. There are several formulations reported in the literature for treating with Navitoclax, and we tried nearly all of them, including variations; unfortunately, all but one of them proved to be inadequate to keep our senolytic in solution. And, while this single exception (Phosal) is fairly commonly used for oral dosing in rodents, it happens to be the only solubiliser of those tested which has little to no published safety record when given as an intraperitoneal injection. Indeed, phosal injections made tester mice quite unhappy - so unhappy that we felt unable to use it for the actual experimental animals via that route.
What to do? Well, it wasn't quite a showstopper. The best solvent we had identified that didn't include Phosal was a cocktail of DMSO, PEG and Tween, and it was actually OK until we tried to push it through a syringe; the drug solubility in this formulation was unfortunately quite marginal, so that forcing the solution through a narrow needle was enough to cause precipitation. As a result, we have retreated to administering the senolytic by oral gavage, using the common Phosal vehicle. This is a lot more work, and we are aware that the bioavailability and pro-drug properties of Gal-Nav may be reduced with oral dosing, but we have decided that it's less bad than having the stuff just clump out of solution, which would pretty much ensure that mice don’t receive a therapeutic dose. Fingers crossed!