Expression of the Sonic Hedgehog Embryonic Signalling Pathway Components in Matched Pre-Treatment and Relapsed Small Cell Lung Cancer Biopsies

Cancer stem cells may be responsible for tumour regrowth and acquisition of resistance in small cell lung cancer (SCLC). The Hedgehog pathway regulates survival and proliferation of tissue progenitor and stem cell populations, promoting the expression of stem cell related and proliferative genes. We evaluated the Sonic Hedgehog (Shh) embryonic signalling pathway in relapsed SCLC. Expression levels of Shh related genes GLI1, SMO, SUFU, PTCH1, HHIP, BCL2, BMI, ZEB1, ZEB2, N-MYC, Twist1 were analysed by qRT-PCR in matched pre-treatment and relapsed tumour fresh frozen biopsies of three SCLC patients. Expression of each gene was compared using the paired samples t-test, as well as comparison of mean expression levels was done. Data were statistically interpreted using the MedCalc version 10.2.0.0 software. 2.9-fold lower mean mRNA expression of the major Hedgehog activation indicator GLI1 was observed in relapsed samples (p = 0.0529). Mean expression of six Shh inducible genes, PTCH1, HHIP, N-MYC, ZEB2, Twist1, ZEB1, was also downregulated by 2.6-, 2.2-, 1.9-, 1.8-, 1.2-, 1.1-fold, respectively (p = 0.4252, p = 0.1268, p = 0.2480, p = 0.1169, p = 0.1480, p = 0.7595, respectively). 1.8-fold mean expression decrease was found for Gli activator Smo (p = 0.4111). Only the Shh pathway inhibitor SUFU and two other examined Hedgehog signalling inducible genes BCL2 and BMI in relapsed SCLC showed 0.8-, 0.9-,and 0.8-fold increase of expression, respectively (p = 0.3074, p = 0.7921, and p = 0.3822, respectively). To our knowledge, this is the first report of comparison of Shh signalling in matched pre-treatment and relapsed SCLC biopsies. Our data show decreased activity for majority of Shh pathway components in relapsed SCLC, although difference did not reach statistical significance.