Tankyrase inhibition in personalized cancer medicine – defining patient inclusion criteria

In the work we used a panel of cell lines (colorectal cancer, non-small cell lung cancer, renal cancer, ovarian cancer and melanoma) to identify factors that enhanced (acting additive or synergistic) or disabled tankyrase inhibition. The factors were validated in vivo in xenografts or syngeneic/immunocompetent mouse models. The tankyrase inhibitor was tested both as single agent ,and in combination treatments, in cell culture and against in vivo tumors. Line Mygland, the PhD candidate, will submit her thesis when paper III is submitted, summer 2019. We plan that her defence to take place in the autumn 2019. In paper I, “Tankyrase Inhibition Enhances the Antiproliferative Effect of PI3K and EGFR Inhibition, Mutually Affecting beta-catenin and AKT Signaling in Colorectal Cancer” (Solberg NT et al 2018), a combinatorial therapeutic approach combining a TNKS inhibitor (G007-LK) with PI3K (BKM120) and EGFR (erlotinib) inhibitors in colorectal cancer was investigated. The data demonstrated that PI3K and EGFR inhibition enhanced the effect of TNKS inhibition in the TNKS inhibitor-sensitive colorectal cancer cell line COLO320DM, and in the non-sensitive colorectal cancer cell line HCT-15. In both cell lines, combined TNKS/PI3K/EGFR inhibition was more effective at reducing growth than a dual TNKS/MEK inhibition. TNKS/PI3K/EGFR inhibition affected in a context-dependent manner components of the WNT/β-catenin, AKT/mTOR, EGFR, and RAS signaling pathways. TNKS/PI3K/EGFR inhibition also efficiently reduced growth of both COLO320DM and HCT-15 tumor xenografts in vivo. In paper II, “Tankyrase inhibition sensitizes melanoma to PD-1 immune checkpoint blockade in syngeneic mouse models” Waaler J, Mygland L et al ([shared first authorship], under revision, 2019), we report that a specific small-molecule tankyrase inhibitor, G007-LK, attenuates WNT/β-catenin and YAP signaling pathways in the syngeneic murine B16-F10 melanoma model enabling sensitivity to anti-PD-1 immune checkpoint therapy. Monotherapy with tankyrase inhibiton did not affect tumor growth. RNA sequencing of 18 tankyrase inhibitor-treated human melanoma cell lines and B16-F10 cells revealed a transcriptional response profile for a subpopulation. This cell line sub-group displayed elevated baseline YAP signaling activity and was susceptible to reduce melanocyte inducing transcription factor (MITF) expression upon tankyrase inhibition. Abnormal regulation of WNT signaling is a common denominator in a major fraction of cancers and is associated directly with tumor progression. As there is at current no viable anti-cancer WNT inhibitor drug in clinical practice, at Oslo University Hospital we have developed a WNT inhibitor innovation program and identified small molecules that block tankyrase (patented by OUH and Invent2), a novel central biotarget in the WNT signaling pathway. We were for the first time able to efficiently reduce WNT signaling in some tumor cells by selective tankyrase inhibition. This effect is strongly context dependent and we needed to learn the rules and principles of this context dependency. Furthermore, the effect of tankyrase mediated WNT inhibition can be strongly enhanced by second pathway inhibitors and we wanted to establish which second pathway inhibitors that could enhance tankyrase mediated WNT inhibition and in what context. The intention for the results was to define guidelines for patient inclusion data for tankyrase inhibition as either single agent or in combination with a second inhibitor. Currently, together with our industry partner Mercachem (Nijmegen, NL), we are broadening the target product profile of our existing tankyrase inhibitor leads (funded by BIOTEK2021). Complete ADME testing, along with safety and tox studies (FORNY-NFR funded), for the clinical I stage candidate drug OM-153 (IND) is expected to be finalized in 2020. For paper I, “Tankyrase Inhibition Enhances the Antiproliferative Effect of PI3K and EGFR Inhibition, Mutually Affecting beta-catenin and AKT Signaling in Colorectal Cancer”, we discovered that combining TNKS inhibitors with PI3K and EGFR inhibition may expand the therapeutic arsenal against colorectal cancers. Currently there exist FDA-approved drugs against both PI3K and EGFR signaling. A process towards combination studies in clinical trials, using the combinations, can be initiated following reached IND for our tankyrase inhibitor. For paper II, “Tankyrase inhibition sensitizes melanoma to PD-1 immune checkpoint blockade in syngeneic mouse models”, we obtained strong proof-of-concept data demonstrating that, in an immune competent mouse melanoma model, checkpoint inhibitors in combination with inhibition of the WNT signaling pathway using G007-LK, show robust therapeutic efficacy. This has to our knowledge not been shown before and comprises a new therapeutic principle with the potential to improve treatment at least in selected melanoma patient groups. Currently, there are no therapeutic strategies available for targeting WNT/β-catenin signaling to counteract checkpoint inhibitor resistance in melanoma. Again, initiation of clinical trials must follow a tankyrase inhibitor IND.