Illustrative ion-trapping model
A one-unit pH shift changes the trapping hypothesis
For a hypothetical monoprotic weak base with pKa 8.1, hold cytoplasmic pH at 7.2 and compare lysosomal pH 4.8 with 5.8. BioTwin’s equilibrium ion-trapping calculation changes the modeled lysosome-to-cytoplasm concentration ratio from about 223 to about 22.
- pKa 8.1Same hypothetical molecule
A monoprotic weak base; cytoplasmic pH stays at 7.2.
- ≈223:1Lysosomal pH 4.8
Stronger modeled trapping in the more acidic compartment.
- ≈22:1Lysosomal pH 5.8
A higher pH substantially reduces the modeled ratio.
- Make the operation inspectable · The ratio is (1 + 10^(pKa − lysosomal pH)) divided by (1 + 10^(pKa − cytoplasmic pH)). BioTwin uses this established equilibrium calculation to make a candidate’s compartment assumption explicit and test its sensitivity before a more detailed model.
- Choose a compartment-specific measurement · For a lysosomal target, test whether the candidate reaches that compartment under the relevant pH conditions. For a cytoplasmic target, investigate whether sequestration could make a whole-cell concentration misleading. Pair compartment concentration with a target-engagement readout.
- Know which effects this example leaves open · Membrane permeability, active transport, binding, multiple ionization sites and drug-induced pH changes can alter accumulation. Published models such as Trapp and colleagues’ include additional transport and partitioning terms. This simple ratio is a hypothesis generator for a small molecule.
Ask where the molecule accumulates
A whole-cell measurement gives a useful total. A compartment model asks how that total could be distributed under the specified conditions. The aim is to identify whether the intended target may see a different exposure from the bulk cellular estimate.
Treat accumulation as a hypothesis to measure
Current support is computational partitioning analysis. Results depend on the molecule, compartment assumptions and calibration. Modeled accumulation does not establish physical target access or engagement, and the method is not a general delivery model for mRNA, vectors or other large modalities.
Separate the next two questions
First, can the program establish relevant tissue and cellular exposure? Then, does the compartment distribution support the proposed target mechanism? Keeping those questions separate can reveal which measurement is missing before a distribution model becomes a design claim.
- Barrier and exposure modeling · Investigate the route into the relevant tissue. Barrier and exposure modeling
- Local effect · See how exposure and target response can be assessed together in a defined setting. Local effect