Cancer immunotherapy with TLR9 agonists – Combination with checkpoint inhibitors in tumor models
Manuel Schmidt1, Barbara Volz1, Kerstin Kapp1, Detlef Oswald1, Burghardt Wittig2, Mariola Söhngen1
1Mologen AG, Berlin, Germany; 2Foundation Institute Molecular Biology and Bioinformatics, Freie Universitaet Berlin, Germany
TLR9 agonists are developed as anti-cancer therapies based on their broad activation of the innate/adaptive immune system. Previously, chemical modification of DNA-based TLR9 agonists was used to prevent their degradation by exonucleases. To avoid off-target effects observed with these modifications, new TLR9 agonists containing only natural DNA were stabilized by structural components. The dSLIM® family is protected from exonucleolytic degradation by its covalently-closed dumbbell-shaped structure. The linear single-stranded EnanDIM® family is protected by L-deoxyribonucleotides (natural enantiomers of the D-form) at their 3’-ends. The dSLIM® family member lefitolimod is currently evaluated in an ongoing Phase 3 clinical IMPALA trial in mCRC, whereas dSLIM-B and EnanDIM-A are in preclinical development. The checkpoint inhibitor (CPI) aPD-1 has the potential to revert immune escape of tumor cells by restoring T cell function of especially cytotoxic T cells. Since the targets of TLR9 agonists are upstream of that of aPD-1, the immune surveillance reactivation (ISR) via TLR9 provides a basis to increase efficacy of CPI. Combining i.tu. injection of dSLIM-B with i.p. injection of aPD-1 resulted in a clearly reduced tumor growth and statistically significant prolonged survival in the CT26 colon carcinoma model compared to the single agents. In the A20 lymphoma model the combinatory effect of i.p. aPD-1 and i.tu. lefitolimod led to an even more pronounced tumor growth inhibition and, consequently, significantly prolonged survival. Finally, subcutaneous injection of EnanDIM-A with aPD-1 in the CT26 model generated an improved anti-tumor effect compared to the monotherapies. In conclusion, we showed that the families of TLR9 agonists, dSLIM® and EnanDIM®, both enhance the limited anti-tumor effect of aPD-1 in pilot studies with tumor models.