Novel small molecule STAT3 inhibitors in cancer therapy.

Karolina Dzwonek, Filip Stefaniak, Paweł Gunerka, Monika Lamparska-Przybysz

Cancer cell proliferation, invasion and metastasis are regulated by an interconnecting signaling pathways involving extracellular ligands, transmembrane receptors, protein kinases and transcription factors. Insights into this complicated signaling network have revealed many novel cancer targets for which chemotherapeutic agents may be developed. On contrary to traditional cancer drugs which interfere with DNA synthesis and repair system, a new class of agents has been developed to aim directly at specific molecular targets involved in oncogenesis (e.g. EGFR). Due to their selective activity they are characterized by significantly different toxicity profile from traditional cancer drugs. However, many cancer therapeutic agents elicit resistance that makes them ineffective and often produce cross-resistance to other drugs. Therefore, we aim to obtain innovative target specific drugs, able to breakdown the cancer cells’ resistance and to improve cancer therapy efficiency.
Among recently investigated potential targets for selective cancer treatment are signal transducers and activators of transcription (STATs). STATs are transcription factors activated in response to cytokines and growth factors and are involved in different cellular processes including proliferation, differentiation and inflammation. Of the seven known mammalian STAT proteins STAT3 was shown to be constitutively activated in many human malignancies. Aberrant STAT3 activity promotes tumor progression through transcriptional activation of genes encoding apoptosis inhibitors, cell-cycle regulators and inducers of angiogenesis. Available data indicate that inhibition of STAT3 signaling leads to an attenuation of cancer cell growth and the induction of apoptosis.

The aim of our investigation was to design a novel STAT3 small molecule inhibitor that would selectively inhibit STAT3 activity, reducing expression of its downstream genes. Thus, we performed computational modeling and small molecule docking simulations using X-ray structure of STAT3beta homodimer. Once the model was established and validated we performed a virtual screening of the library of over 3000 compounds. As a result we have chosen 38 promising structures which were then synthesized and their biological activity against STAT3 was tested. We have applied in vitro luciferase activity assay exploiting stably transfected cell line with luciferase gene under the control of promoter containing STAT3 binding motif. One of drug candidates - CPL-402-003 showed significant inhibitory effect on STAT3 transcription activity resulting in decreased luciferase expression. Moreover, the same compound revealed low toxicity on non-malignant cells displaying no constitutive STAT3 activation. We are currently investigating CPL-402-003 and its derivatives on different cancer cell lines to establish its anti-proliferative/pro-apoptotic activity. Results of the in vitro studies will be subsequently confirmed in mouse xenograft model.