Figure 1. The regressing tumour microenvironment stimulates the outgrowth, infiltration and metastasis of drug-resistant clones.

a, Schematic of the experimental setup. b, Bioluminescent signal of drug-resistant A375^R-TGL cells in vemurafenib-sensitive, A375 tumours, treated with vehicle or vemurafenib for 5 days (vehicle, n = 36; vemurafenib, n = 15 tumours). c, EdU incorporation in A375^R-TGL cells in A375/A375^R-TGL tumours treated with vehicle or vemurafenib for 4 days, as determined by FACS (vehicle, n = 8; vemurafenib, n = 6 tumours). d, Bioluminescent signal of A375^R-TGL tumours alone, treated with vehicle or vemurafenib for 5 days (vehicle, n = 38; vemurafenib, n = 15 tumours). e, Bioluminescent signal of TGL-expressing drug-resistant cancer cells (A375^R, M249^R4, PC9, H2030) in drug-sensitive tumours (Colo800, LOX, UACC62, M249, H3122, HCC827) treated with vehicle or drugs (vemurafenib, crizotinib, erlotinib) for 5 days (n (from left to right on the graph, in this order) = 6, 7, 12, 12, 9, 9, 25, 26, 9, 12, 12, 12, 16, 11 tumours). f, Spontaneous lung metastasis by A375^R cells in mice bearing A375/A375^R-TGL tumours treated with vehicle or vemurafenib (10 days), visualized by BLI (n = 4). g, Seeding of A375^R-TGL cells from the circulation to unlabelled, subcutaneous A375 tumours of mice treated with vehicle or vemurafenib. Signal in the tumour was quantified by BLI (vehicle, n = 30; vemurafenib, n = 34 tumours; three independent experiments combined). h, Treatment response, determined by tumour size, of subcutaneous A375 tumours allowed to be seeded by A375^R−TGL cells from the circulation or mock injected (vehicle, n = 16; vemurafenib, n = 8 tumours). Data in b–e,g,h, are average; error bars represent s.e.m; data in f, center line is median, whiskers are min. to max. P values shown were calculated using a two-tailed Mann-Whitney test (* p<0.05, ** p<0.01, *** p<0.001, n.s.= not significant).