Abstract C32: Characterization of molecular targets of the novel platinum agent PT-112 in human colon cancer cells
Authors: Wang Justin Q. , Ames Tyler , Arciero Emily , Hehenberger Marie-Therese , Chatterjee Devasis 
Published: May 2016

Background: The purpose of this study was to delineate differences in the mechanism of action (MOA) and to identify unique molecular targets responsible for the antineoplastic effects of PT-112 when compared to oxaliplatin. PT-112 is a novel platinum-based chemotherapeutic agent currently under clinical development that has demonstrated superior efficacy in resistant cell lines and xenograft models. In this study we focus on the differential mechanistic effects of PT-112 and oxaliplatin treatment of HCT-116 colon cancer cells and report data derived from multiple cancer signaling pathways.

Results: Treatment of HCT-116 with the IC50 dose of PT-112 and oxaliplatin for 24 and 48h resulted in growth inhibition and apoptosis induction as measured by MTT assay, pro-caspase 8 and PARP cleavage. At equipotent doses, oxaliplatin treatment resulted in greater DNA damage as measured by H2A.X serine phosphorylation when compared to PT-112, whereas PT-112 induced markedly greater degrees of expression of several proteins in multiple pathways, including p53, p16, and FasL. PT-112's activity may derive more directly from p53 expression, when compared to oxaliplatin, as revealed by growth inhibition assays using and a p53-null HCT-116 cell line. Additionally, PT-112 triggered the cleavage of executioner pro-caspases 3, 6 and 7 to a greater extent vs oxaliplatin.

When compared to oxaliplatin, PT-112 treatment resulted in the significant inhibition of gp130 and JAK/STAT signaling and transcriptional activation mediated by IL-6. A decrease, relative to oxaliplatin, in TNF-mediated NF-κB signaling and expression of cell-cycle factors E2F3, CDK4 and CDK1, as well as cell survival protein c-FLIPshort were also observed. PT-112 was more potent than oxaliplatin in inducing the release of High-mobility group protein B1, a marker for immunogenic cell death (ICD) processes. Additionally, the inhibition of the malignant phenotype, as assessed by anchorage independent growth, was significantly greater in cells incubated with PT-112 when compared to oxaliplatin.

When treating non-malignant 1459 colon cells or biopsied benign normal colon tissue grown in culture, PT-112 did not result in apoptosis at concentrations much higher than those that were used in the HCT-116 experiments. In contrast, oxaliplatin remained equivalently potent in the non-malignant cell lines.

Conclusions: PT-112's ability to affect numerous intracellular proteins, and the evidence of extracellular initiation of anticancer signaling, along with the apparent reduced dependence on DNA-damage, makes it an attractive and versatile compound, particularly as it relates to potential drug resistance mechanisms. PT-112's inhibition of STAT3 activation and induction of ICD also offers the intriguing proposition of downstream immune-potentiating therapeutic effects. These results underline a unique rationale for further clinical evaluation of PT-112. In conclusion, our study has demonstrated that PT-112 treatment simultaneously regulates multiple cellular targets including apoptosis, cell survival, tumor suppressor and cell cycle proteins and pathways in a manner that is clearly differentiated from oxaliplatin.

Citation Format: Justin Q. Wang, Tyler Ames, Emily Arciero, Marie-Therese Hehenberger, Devasis Chatterjee. Characterization of molecular targets of the novel platinum agent PT-112 in human colon cancer cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C32.