Transcriptional-mediated effects of radiation on the expression of immune susceptibility markers in melanoma

BACKGROUND AND PURPOSE

We recently reported a time-sensitive, cooperative, anti-tumor effect elicited by radiation (RT) and intra-tumoral-immunocytokine injection in vivo. We hypothesized that RT triggers transcriptional-mediated changes in tumor expression of immune susceptibility markers at delayed time points, which may explain these previously observed time-dependent effects.

MATERIALS AND METHODS

We examined the time course of changes in expression of immune susceptibility markers following in vitro or in vivo RT in B78 murine melanoma and A375 human melanoma using flow cytometry, immunoblotting, and qPCR.

RESULTS

Flow cytometry and immunoblot revealed time-dependent increases in expression of death receptors and T cell co-stimulatory/co-inhibitory ligands following RT in murine and human melanoma. Using high-throughput qPCR, we observed comparable time courses of RT-induced transcriptional upregulation for multiple immune susceptibility markers. We confirmed analogous changes in B78 tumors irradiated in vivo. We observed upregulated expression of DNA damage response markers days prior to changes in immune markers, whereas phosphorylation of the STAT1 transcription factor occurred concurrently with changes following RT.

CONCLUSION

This study highlights time-dependent, transcription-mediated changes in tumor immune susceptibility marker expression following RT. These findings may help in the design of strategies to optimize sequencing of RT and immunotherapy in translational and clinical studies.

Abstract 4011: Effective in situ immunization via local radiation therapy (RT) and tumor-specific immunocytokine (IC): Suppression from distant tumor is blocked by RT or Treg-depleting CTLA-4 antibody

PURPOSE: Use “off the shelf” reagents to eradicate an established tumor and induce a tumor specific T cell response that destroys distant tumor.

PROCEDURES: We have identified a cooperative interaction between local tumor RT, intratumoral (IT) injection of IC hu14.18-IL2 (anti-GD2 hu14.18 mAb linked to IL2), and checkpoint blockade with anti-CTLA4 mAb. C57Bl/6 mice were implanted with 2×106 B78 (GD2+) melanoma in one flank (1-tumor model). In the 2-tumor model, mice received 2×106 B78 3 weeks (w) later in the opposite flank. After 5w the primary (1st) tumor was ∼200mm3, and ∼500mm3 after 7w. The 2nd tumor was ∼ 50mm3 at 5w. At 5w or 7w, mice received single fraction RT (12Gy) to the 1st tumor and 6 days later received 5-daily 50μg injections of IC (IT-IC). When used, anti-CTLA4 was given i.p. on days 3, 6 and 9 after RT.

NEW UNPUBLISHED DATA: For mice bearing a single 200mm3 tumor, RT+ IT-IC results in complete response (CR) in 71% of mice and a tumor-specific memory T cell response. Mice with a single 500mm3 tumor showed slowing of tumor growth, but only 27% CR after radiation + IT-IC. Adding anti-CTLA-4 to RT + IT-IC improved tumor response (73% CR) and survival compared to doublet combinations of these 3 modalities. In contrast, in the 2-tumor model, providing RT + IT-IC to the 1st ∼200mm3 tumor, but not to the distant ∼50mm3 tumor, did not enhance 1st tumor shrinkage compared to RT alone and had no effect on the 2nd 50mm3 tumor. The presence of the 2nd B78 tumor resulted in systemic immune suppression that prevented the local RT and IT-IC from eliminating the 1st tumor. This was tumor specific, as local RT + IT-IC to the 1st ∼200mm3 B78 tumor was still effective in treating the 1st tumor if the 2nd (∼50 mm3 tumor) was the syngeneic but unrelated Panc02 tumor. Delivering RT to both the 1st + 2nd B78 tumors eliminated the inhibitory effect of the 2nd tumor, enabling IT-IC to the 200mm3 tumor to cause eradication of that tumor in 64% of mice. Preliminary PCR analyses of FoxP3 in the 1st tumor showed Tregs are depleted by 1st tumor RT only in mice with 1 tumor and not in mice with 2 tumors. In this 2 tumor model we combined RT + IT-IC of the 1st tumor with anti-CTLA-4. The IgG2b anti-CTLA-4 (which doesn't substantially deplete Tregs) had minimal effect on 1st tumor response to RT + IT-IC. In contrast the IgG2a anti-CTLA-4 (that depletes Tregs) rendered 60% of mice disease-free (durable CR of both the treated 200mm3 and the untreated 50mm3 tumors). Preliminary data, using DEREG mice that enable diphtheria toxin to deplete Tregs, show Treg depletion in the 2 tumor model also enables eradication of both 1st and 2nd tumors in 60% of mice after RT + IT-IC to only the 1st tumor.

CONCLUSIONS: Local RT+ IT-IC can result in long-term tumor eradication of macroscopic tumors via adaptive immunity to the “in situ vaccine”, provided that Treg-associated immune suppression from distant tumor is eliminated by RT or Treg-depletion.

Citation Format: Zachary S. Morris, Emily Guy, David Francis, Monica M. Gressett, Eric A. Armstrong, Shyhmin Huang, Lauryn R. Werner, Stephen D. Gillies, Alan Korman, Jacquelyn A. Hank, Alexander L. Rakhmilevich, Paul M. Harari, Paul M. Sondel. Effective in situ immunization via local radiation therapy (RT) and tumor-specific immunocytokine (IC): Suppression from distant tumor is blocked by RT or Treg-depleting CTLA-4 antibody. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4011.

In Situ Tumor Vaccination by Combining Local Radiation and Tumor-Specific Antibody or Immunocytokine Treatments

Interest in combining radiotherapy and immune checkpoint therapy is growing rapidly. In this study, we explored a novel combination of this type to augment antitumor immune responses in preclinical murine models of melanoma, neuroblastoma, and head and neck squamous cell carcinoma. Cooperative effects were observed with local radiotherapy and intratumoral injection of tumor-specific antibodies, arising in part from enhanced antibody-dependent cell-mediated cytotoxicity (ADCC). We could improve this response by combining radiation with intratumoral injection of an IL2-linked tumor-specific antibody (termed here an immunocytokine), resulting in complete regression of established tumors in most animals associated with a tumor-specific memory T-cell response. Given the T-cell response elicited by combined local radiation and intratumoral immunocytokine, we tested the potential benefit of adding this treatment to immune checkpoint blockade. In mice bearing large primary tumors or disseminated metastases, the triple-combination of intratumoral immunocytokine, radiation, and systemic anti-CTLA-4 improved primary tumor response and animal survival compared with combinations of any two of these three interventions. Taken together, our results show how combining radiation and intratumoral immunocytokine in murine tumor models can eradicate large tumors and metastases, eliciting an in situ vaccination effect that can be leveraged further by T-cell checkpoint blockade, with immediate implications for clinical evaluation. Cancer Res; 76(13); 3929-41. ©2016 AACR.