β-tan and Sal A inhibit promoter-induced proliferation and transformation of JB6P + cells. At 50–60% confluency, JB6P + cells were treated with the indicated concentrations of β-tan and Sal A, with or without TPA co-treatment. (A) Cell growth was determined at 48 h and expressed as percentage of control (Ct) treated cells using the MTT Cell Proliferation Kit. Significance from TPA treatment is indicated by ††† at p < 0.001 while significance from control treatment is indicated by *** at p < 0.001. Results represent the averages (± SEM) of at least two independent experiments done in triplicate wells. (B, C) In the anchorage-independent growth assay, JB6P + cells were suspended in 0.4% soft agar over 0.6% base agar layers, with the indicated β-tan and Sal A concentrations (μg/ml) and TPA co-treatment. Treatments were replenished every three days, where the co-treatment of 2.5 μg/ml β-tan or Sal A with TPA and colony growth was photographed at 200X magnification (B) and quantified at 9 ± 1 day post-seeding using the CytoSelectTM Transformation Assay (C). Colony growth is expressed as percentage of TPA only-treated cells and plotted as mean colony growth (± SEM) of two independent experiments done in triplicate wells (C). Significance from TPA control is indicated by ††† at p < 0.001.