Abstract 1236: Subclinical doses and choice of replication stress inducer in combination with CHK1 inhibitors for optimal tumor control and immune responses in vitro and in vivo

Abstract

Abstract Background: Lung cancer and melanoma are responsible for almost 25% of cancer deaths in Australia. Despite recent progress with targeted and immuno-therapies, the 5 year survival rate in late stage patients is still<20%. CHK1 inhibitors are being investigated as chemosensitizing agents with agents that increase replication stress, primarily Gemcitiabine. Clinical trials of this combination have shown some good responses but high levels of normal tissue toxicity. Materials and methods: Here we have investigated the molecular basis of sensitivity to CHK1 inhibitors as combinations with subclinical doses of hydroxyurea (HU) in melanoma and non-small cell lung cancer (NSCLC) tumor spheres and cell lines in 2% O2 conditions and xenograft models in immune compromised mice and with humanized immune systems. Results: We report that low dose HU increased the sensitivity of >70% of both melanoma and NSCLC cell lines to CHK1 inhibitor (GDC-0575) triggered apoptosis, with complete loss of viability found with clinically achievable doses of this combination. Similar sensitivity was observed in xenograft models of both melanoma and NSCLC. We also demonstrate that a low dose of Gemcitabine combination with CHK1 inhibitor results in complete loss of proliferative potential in normal tissue, whereas normal tissue retaining proliferative potential after treatment with even high doses of hydroxyurea in combination with CHK1 inhibitor. In vivo, this translates to minimal effect on lymphocyte populations in the blood. The combination also triggers an inflammatory response involving the recruitment of macrophages, associated with increased HMGB1 nuclear staining. Immune responses were also assessed in humanized mouse models. Discussion: These data indicate that the combination of low dose HU and CHK1 inhibitor have strong anti-cancer activity in the setting of melanoma and NSCLC cancer, and triggers an inflammatory response, and is likely to be better tolerated than current combinations with Gemcitabine. Our data suggest a significant proportion of melanoma and lung cancer patients could benefit from treatment with this drug combination, and this appears to include an immune response to the tumor. Citation Format: Zay Yar Oo, Martina Proctor, Alex Stevenson, Deborah Nazareth, Jill Larsen, Nikolas Haass, Brian G. Gabrielli. Subclinical doses and choice of replication stress inducer in combination with CHK1 inhibitors for optimal tumor control and immune responses in vitro and in vivo [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 1236.