Evidence of drug-response heterogeneity rapidly generated from a single cancer cell

Abstract

One cancer cell line is believed to be composed of numerous clones with different drug sensitivity. We sought to investigate the difference of drug-response pattern in clones from a cell line or from a single cell. We showed that 22 clones derived from 4T1 cells were drastically different from each other with respect to drug-response pattern against 11 anticancer drugs and expression profile of 19 genes associated with drug resistance or sensitivity. Similar results were obtained using daughter clones derived from a single 4T1 cell. Each daughter clone showed distinct drug-response pattern and gene expression profile. Similar results were also obtained using Bcap37 cells. We conclude that a single cancer cell can rapidly produce a population of cells with high heterogeneity of drug response and the acquisition of drug-response heterogeneity is random.

Keywords: cancer; drug-response; heterogeneity.

Figure 1. Relative drug sensitivity of clones from 4T1 cells

For each drug, there was a clone that had the smallest IC₅₀, which was used to divide IC₅₀ of this clone and of all other clones (x axis) to derive the value of fold change (y axis).

Figure 2. Each clone derived from 4T1 cells exhibits drug-response pattern distinct from others

The IC₅₀s of 4T1 cells toward 11 drugs (x axis) were used to divide IC₅₀s of 4T1 cells and of all other clones to derive fold change values (y axis).

Figure 3. Relative levels of gene expression of clones from 4T1 cells

For each gene, there was a clone that had the lowest expression level. The fold change is based on the formula 2^{-[(ΔCT)clone(i)-(ΔCT)clone(a)]} according to the method previously described [39], where, clone(i) denote any one of the 22 clones, and clone(a) denotes the one with lowest expression of a given gene. ΔCT was derived as described in Materials and Methods.

Figure 4. Each clone derived from 4T1 cells exhibits gene expression pattern distinct from others

Taking 4T1 as a reference, The relative expression level of the 19 genes in each clone is based on the formula 2^{-[(ΔCT)clone(i)-(ΔCT)4T1]} according to the method previously described [39], where, clone(i) denote any one of the 22 clones. ΔCT was derived as described in Materials and Methods.

Figure 5. Relative drug sensitivity of subclones from monoclonal N1 (a clone from 4T1)

For each drug, there was a clone that had the smallest IC₅₀, which was used to divide IC₅₀ of this subclone and of all other subclones (x axis) to derive the value of fold change (y axis).

Figure 6. Each subclone derived from monoclonal N1 exhibits drug-response pattern distinct from others

The IC₅₀s of monoclonal N1 toward 10 drugs (x axis) were used to divide IC₅₀s of the monoclonal N1 and of all other subclones to derive fold change values (y axis).

Figure 7. Relative levels of gene expression of subclones from monoclonal N1

For each gene, there was a subclone that had the lowest expression level. The fold change is based on the formula 2^{-[(ΔCT)subclone(i)-(ΔCT)subclone(a)]} according to the method previously described [39], where, subclone(i) denote any one of the 14 subclones, and subclone(a) denotes the one with lowest expression of a given gene. ΔCT was derived as described in Materials and Methods.

Figure 8. Each subclone derived from monoclonal N1 exhibits gene expression pattern distinct from others

Taking N1 as a reference, the relative expression level of the 19 genes in each subclone is based on the formula 2^{-[(ΔCT)subclone(i)-(ΔCT)N1]} according to the method previously described [39], where, subclone(i) denote any one of the 14 clones. ΔCT was derived as described in Materials and Methods.