Evaluating the Combination of Radioimmunotherapy and Immunotherapy in a Melanoma Mouse Model

Abstract

Immunotherapy has changed the oncology landscape during the last decade and become standard of care for several cancers. The combinations of immunotherapy with other treatment modalities are also being investigated. One of the challenges to investigate such combinations is to identify suitable mouse models for the pre-clinical experiments. In the past, we and other researchers showed that murine B16-F10 melanoma in C57Bl6 mice is refractory to treatment with immune checkpoint inhibitors. In this work we studied the suitability of an alternative syngeneic model, Cloudman S91 murine melanoma in DBA/2 mouse (DBA/2NCrl), to study the combination of immunotherapy targeting PD-1 and radioimmunotherapy targeting melanin. DBA/2 male and female mice were injected subcutaneously with 3–6 million Cloudman S91 cells. When the tumors reached ~150 mm3 volume, the animals were treated intraperitoneally with PBS (sham), h8C3 unlabeled (cold) antibody to melanin, immunotherapy with anti-PD-1 antibody, radioimmunotherapy with 213Bismuth (213Bi)-labeled h8C3 antibody, or several combinations of immunotherapy and radioimmunotherapy. Treatments with immunotherapy alone produced very modest effect on the tumor size, while combination therapy resulted in significant slowing down of the tumor growth, increased animal survival, and no decrease in animal body weight. We conclude that Cloudman S91 murine melanoma in DBA/2 mouse is a suitable model to evaluate combination of immunotherapy of melanoma with tangentially targeted treatments.

Mechanistic Insights into Synergy between Melanin-Targeting Radioimmunotherapy and Immunotherapy in Experimental Melanoma

“…We observed that RIT alone, using either 177 Lu or 225 Ac, did not control tumor growth (Table 1, Figures 2 and 4). This contrasts with our previous studies, where we assessed the cytotoxic effect of the shorter-lived alpha emitter, 213 Bi [12,13]. In those works, we found that both the S91 Cloudman model and the more rapidly dividing B16F10 model were highly susceptible to RIT with 213 Bi.…”

“…In this study, we utilized male DBA/2 mice bearing Cloudman S91 tumors, a syngeneic melanoma model [ 20 ], to assess the combination of immunotherapy with long-lived alpha- and beta-emitting RIT. We and others have confirmed the utility of this model in evaluating the effectiveness of immunotherapy alone or in combination with other treatments and have demonstrated anti-PD-1 provides modest tumor control and improved survival [ 13 , 21 , 22 ]. Additionally, we have shown that the combination of anti-PD-1 therapy with RIT using 213 Bi-labeled h8C3, a humanized mAb targeting melanin, slows down tumor growth by 1.5 fold times and improves survival in this model [ 13 ].…”

“…With the success of ICB therapy in the clinical setting of advanced melanoma, we set out to test its effectiveness in combination with our anti-melanin targeted cytotoxic approach of RIT. In our most recent study, we treated Cloudman S91 murine melanoma in the immune-intact DBA/2 (DBA/2NCrl) mouse model with a combination of 213 Bi-labeled h8C3 mAb and anti-PD-1 ICB [ 13 ]. We were able to demonstrate that while ICB or RIT alone only had a modest effect on survival and tumor growth, repeat RIT dosing and the combination of RIT and ICB proved more effective at significantly increasing animal survival and at slowing down tumor growth, while also being well tolerated by the study animals.…”

Mouse Tumor Models for Advanced Cancer Immunotherapy

“…Syngeneic tumor models are also used to investigate the antitumor activity of ICIs, including anti-cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) [39] and anti-programmed death (PD)-1 anti-PD-L1 antibodies [31,40]. For example, using the syngeneic model of immunocompetent B6 mice transplanted with E.G7 hematopoietic cell line or its analogue with PD-L1 deficiency it has been shown that the PD-L1 pathway blockade contributed to the rejection of tumor cells in mice transplanted with both wild-type (WT) E.G7 cells or PD-L1 deficient E.G7 cells in the same degree.…”

“…Thus, the expression of PD-L1 on the cells of TME (either tumor infiltrating leukocytes or stromal cells) may contribute more significantly than the expression of PD-L1 on tumor cells [41]. One of the significant drawbacks of using syngeneic models to evaluate the effectiveness of ICIs is that the rapid Syngeneic tumor models are also used to investigate the antitumor activity of ICIs, including anti-cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) [39] and anti-programmed death (PD)-1 anti-PD-L1 antibodies [31,40]. For example, using the syngeneic model of immunocompetent B6 mice transplanted with E.G7 hematopoietic cell line or its analogue with PD-L1 deficiency it has been shown that the PD-L1 pathway blockade contributed to the rejection of tumor cells in mice transplanted with both wild-type (WT) E.G7 cells or PD-L1 deficient E.G7 cells in the same degree.…”