Abstract 2202: Tarloxotinib exhibits potent activity in NRG1 fusion and rearranged cancers
Authors: Tirunagaru Vijaya G. , Estrada-Bernal Adriana , Yu Hui , Rivard Chris , Hirsch Fred , Bull Matthew , Abbatista Maria , Smaill Jeff , Patterson Adam V. , Doebele Robert C. , Vellanki Avanish 
Published: August 2019

Abstract
Background: NRG1 fusions and rearrangements are oncogenic drivers that have been observed in a variety of tumor types and enriched in invasive mucinous adenocarcinomas (IMA) of the lung. The oncoprotein binds HER3-HER2 heterodimers and activates downstream signaling, supporting a therapeutic paradigm of ERBB3/ERBB2 inhibition. While patient responses have been observed with Afatinib, durable responses have largely been absent. Tarloxotinib, a clinical-stage prodrug that releases a potent, irreversible EGFR/HER2 inhibitor (Tarloxotinib-E) selectively in severely hypoxic regions of tumours has been shown to overcome the intrinsic resistance of EGFR exon 20 insertion mutations and HER2 activating mutations to existing TKIs in vitro and in vivo.
Results: NRG1 altered cell lines (MDA-MB-175 with DOC4-NRG fusion, HCC95 with NRG gene amplification and H1793 with increased NRG1 mRNA) showed high sensitivity to Tarloxotinib-E whereas Tarloxotinib prodrug was &gt;45 fold less potent under normoxic conditions, consistent with lower sensitivity of the prodrug and the requirement of hypoxia for activation. Tarloxotinib-E inhibited HER2, HER3, Akt and ERK phosphorylation between 10-100 nM whereas afatinib was 10-fold less potent. In vivo activity of Tarloxotinib was evaluated using the CLU-NRG1 patient-derived xenograft model. Nude mice bearing OV-10-0050 tumors implanted subcutaneously were treated with vehicle, the human equivalent dose (HED) of afatinib (6 mg/kg, qd, p.o.) and two doses of tarloxotinib (26 and 48 mg/kg, qw, i.p.) corresponding to Tarloxotinib HED of 75 and 150 mg/m2. Afatinib showed initial activity that reduced over time and was ineffective. In contrast, Tarloxotinib elicited a profound, durable and dose dependent anti-tumor response. Tarloxotinib dosed at 48 mg/kg showed dramatic tumor regression in all the mice while Tarloxotinib dosed at 26 mg/kg showed significant dose dependent tumor regression. Efforts are underway to define the PK/PD correlation by measuring Tarloxotinib and Tarloxotinib-E exposure in plasma and tumor along with the evaluation of hypoxia and the expression of STEAP4 reductase. Tarloxotinib mediated on-target and signaling effects in OV-10-0050 tumors will be presented at the meeting.
Conclusions: Tarloxotinib, a prodrug of a potent irreversible inhibitor of EGFR/HER2 in clinical development demonstrated significant activity in CLU-NRG1 patient-derived xenograft model. NRG1 fusions and rearrangements represent an emerging actionable driver alteration in a variety of cancers. Clinical development of Tarloxotinib in NRG1 altered cancers presents an attractive opportunity.
Citation Format: Vijaya G. Tirunagaru, Adriana Estrada-Bernal, Hui Yu, Chris Rivard, Fred Hirsch, Matthew Bull, Maria Abbatista, Jeff Smaill, Adam V. Patterson, Robert C. Doebele, Avanish Vellanki. Tarloxotinib exhibits potent activity in NRG1 fusion and rearranged cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2202.