Normalization help

I need help determining how to properly normalize to cell number in my assay. My project is to measure how different compounds degrade a protein. I have an assay designed that has a luminescence endpoint, the greater the degradation the lower the luminescence reading. The way l've set up this test run is with compounds on an eight point dose titration with a vehicle control. I understand that normally I can take my vehicle control divided by the reading for my dose of interest and that will give me a percent of control degradation, however, I'm concerned that these compounds are causing cell death. Cells dying would also decrease the luminescence reading. So l set up in parallel another assay that measures cell death laid out in the same format also with a luminescence endpoint, more living cells = more luminescent signal. It turns out that at these high doses where l'm seeing protein degradation I am also seeing cell death. Can you help me come up with an equation to determine percent degradation taking into account that some of these compounds cause cell death. I feel like l've been thinking about this too long and I'm over complicating it.