Periodic Reporting for period 1 - TARGET (Targeting DNA repair pathways, sparking anti cancer immunity)
Periodo di rendicontazione: 2021-10-01 al 2023-03-31
This led to the unprecedented ‘pan cancer’ approval of immune therapeutic regimens based on tests to detect MMR deficiency and, in June 2020, to the approval of immune therapy for any solid tumor with high tumor mutational burden.
However, several aspects of this concept remain to be elucidated:
- What are the bases of the extraordinarily long-lasting responses of patients with MMRd tumors?
- Are there other DNA repair defects able to increase immune surveillance and response to immunotherapy?
- Can we pharmacologically inhibit DNA repair proteins to promote the production of tumor neoantigens allowing the immune system to detect cancer cells?
This unconventional, but possibly high gain approach, builds on the concept that the immune system can identify and selectively target tumor cells carrying DNA alterations and represent the final aim of this project.
By using a multidisciplinary approach and the exploitation of both patient-derived organoids and animal models (Fig. 2), we aim at systematically:
- assess whether and how inactivation of DNA repair pathways triggers anticancer immunity and restrict cancer;
- identify DNA repair pathways which, when disabled, reawaken the immune system;
- discover and develop inhibitors of DNA repair proteins able to induce significant increase of immunogenic neoantigens and tumor immunity;
- establish how DNA repair inhibitors and immune modulators can be combined in cancer treatments.
Since the majority of CRC patients are immune refractory, we are currently studying whether among these patients some of them could be eligible for immune based therapies. As a matter of fact, recent findings concerning immunohistochemical staining and molecular profiling of CRC tumors pinpointed the coexistence of MSS/MMRp and MSI/MMRd cancers cells in the same tumor lesion in almost 1% of CRC patients (Fig. 3). Intrigued by these findings, we generated a preclinical model of MMR heterogeneity, blending Mlh1+/+ and Mlh1-/- colorectal cancer murine cells at different ratio. Notably, tumor growth delay and tumor rejections occurred in Mlh1+/+ Mlh1-/- mixed tumors and increased when the percentages of Mlh1-/- cells was augmented in the mixed population. Overall, the observation that a MMRp tumor harboring a small fraction of MMRd cells can trigger an effective antitumor immune response might have implications for the rational design of clinical trials for tumors recalcitrant to immunotherapies
Tumors may evade immune control mainly owing to alterations in the antigen presenting machinery (APM). Several studies have reported that molecular defects in the major complex of histocompatibility I (MHC I) and in the protein Beta 2 Microglobulin (B2M) represent possible mechanisms of acquired resistance to immune checkpoint blockade in melanoma and lung tumors. We functionally evaluated the impact of B2M loss in immune evasion and resistance to immune checkpoint blockades in colorectal, pancreatic and breast cancer murine cell lines. Although the antigen presentation was compromised, the growth of MMRd murine cell lines was severely impaired by the administration of immune checkpoint blockades.
Although the APM was compromised, we provide evidence that patients bearing MMRd cancers other than colorectal may receive benefit from immune checkpoint blockades. The analysis of tumor microenvironment revealed that CD4+ T cells were pivotal in establishing an effective cancer immune response but only in the context of MMRd tumors. Overall, these data highlight the role of tumor associated effector CD4+ T cells in pre-clinical models and patients with impaired APM (Fig. 4).
Overall, we provide evidence that the inactivation of genes involved in DNA repair can be achieved pharmacologically with TMZ treatment, while offering potential clinical benefit to mCRC patients refractory to immune based treatments.