Molecular Characterization of Acquired Tolerance of Tumor Cells to Picropodophyllin (PPP)

Abstract

BackgroundPicropodophyllin (PPP) is a promising novel anti-neoplastic agent that efficiently kills tumor cells in vitro and causes tumor regression and increased survival in vivo. We have previously reported that PPP treatment induced moderate tolerance in two out of 10 cell lines only, and here report the acquired genomic and expression alterations associated with PPP selection over 1.5 years of treatment.Methodology/Principal FindingsCopy number alterations monitored using metaphase and array-based comparative genomic hybridization analyses revealed largely overlapping alterations in parental and maximally tolerant cells. Gain/ amplification of the MYC and PVT1 loci in 8q24.21 were verified on the chromosome level. Abnormalities observed in connection to PPP treatment included regular gains and losses, as well as homozygous losses in 10q24.1-q24.2 and 12p12.3-p13.2 in one of the lines and amplification at 5q11.2 in the other. Abnormalities observed in both tolerant derivatives include amplification/gain of 5q11.2, gain of 11q12.1-q14.3 and gain of 13q33.3-qter. Using Nexus software analysis we combined the array-CGH data with data from gene expression profilings and identified genes that were altered in both inputs. A subset of genes identified as downregulated (ALDH1A3, ANXA1, TLR4 and RAB5A) or upregulated (COX6A1, NFIX, ME1, MAPK and TAP2) were validated by siRNA in the tolerant or parental cells to alter sensitivity to PPP and confirmed to alter sensitivity to PPP in further cell lines.ConclusionsLong-term PPP selection lead to altered gene expression in PPP tolerant cells with increase as well as decrease of genes involved in cell death such as PTEN and BCL2. In addition, acquired genomic copy number alterations were observed that were often reflected by altered mRNA expression levels for genes in the same regions.

The dichotomy of the Insulin-like growth factor 1 receptor: RTK and GPCR: friend or foe for cancer treatment?

“…Among the second category of the IGF-1R kinase inhibitors (TKIs), the cyclolignan picropodophyllin (PPP), originally described as inhibiting the IGF-1R [38] and inducing tumour regression in xenografted mice [3,10,21,[29][30][31]37,54,59,68,89,92,94,110,116,134,143,146,155], also triggers IGF-1R downregulation [144] raising the question of how the receptor is downregulated when its kinase activity is inhibited via either strategy? This contradiction was recently investigated for the case of anti-IGF-1R antibody (Figitumumab) induced receptor degradation [157].…”

Long non-coding RNAs in colorectal cancer: implications for pathogenesis and clinical application

“…[44][45][46] It is now well known that some CRC cases are linked to some factors, such as environment, 47 inflammation, 48,49 immunity, 50 and epigenetic alterations 51,52 rather than heritable genetic changes. An interesting thing is that these factors can influence each other, for instance, epigenetic aberrations induced by environmental factors contribute to cancer processes; 53 interaction of drug and molecular characteristics can influence lncRNAs and clinical outcome; 46,54,55 and epigenetic factors such as lncRNAs can also coordinate cellular responses to environment in turn. 56 The significance of lncRNAs in human CRC was realized in 2001 when Tanaka et al 57 determined that a loss of imprinting of long QT intronic transcript 1 (LIT1/KCNQ1OT1) was frequently observed in CRC patients, suggesting a link between lncRNAs and CRC.…”

Alternative Cytotoxic Effects of the Postulated IGF-IR Inhibitor Picropodophyllin In Vitro

“…Interestingly, genomic arrays of cells selected for PPP resistance show commonly altered expression of tubulin or microtubule-associated genes including overexpression of MARK1 and TUBA4A and underexpression of EML5 and MICAL2 (40), although other changes in gene expression was also found.…”