Combined Approach Improves Anti-tumor Antibody Therapy in Melanoma

Researchers from Columbia University demonstrate that, in mouse-modeled melanoma, the therapeutic efficacy of unmodified anti-tumor antibodies is increased by combined immune checkpoint blockades and MEK inhibition.

Melanoma, a cancer developing from pigment-containing cells melanocytes, light micrograph, photo under microscope
Melanoma, a cancer developing from pigment-containing cells melanocytes, light micrograph, photo under microscope
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Melanoma is a highly prevalent human skin disease worldwide and, surprisingly, as much as 30% of all melanoma cases are a result of factors other than exposure to the sun or other ultraviolet light. The causes of such cases are still unknown to researchers, but some suggest causes may be hereditary. In the United States, one in five people will be diagnosed with melanoma by the age of 70.

Doctors have observed relative success in patient outcomes when treating melanoma and other cancers with specific anti-tumor antibodies. However, researchers warn that anti-tumor antibody therapies alone often result in toxicity and the emergence of drug-resistant tumors; and in advanced-stage tumors, infrequent and short-term clinical remissions have been observed—even with concurrent chemotherapy.

Researchers from Columbia University in New York, United States, conducted a study, published as the cover paper of Oncotarget’s Volume 12, Issue #2, designed to observe the effects in mice with melanoma tumors after treatment with unmodified anti-tumor antibodies enhanced with currently available targeted therapies, immune checkpoint blockades, and MEK inhibitors. They also tested the in vitro effects of MEK inhibitors on two mouse model melanoma cell lines.

Materials & Methods

This study consisted of seven-week-old female mice (purchased from The Jackson Laboratory), B16 mouse melanoma tumor cells (obtained from the Columbia University Skin Disease Resource-Based Center), and Yale University mouse melanoma (YUMM) mutant cells. Cell lines were cultured and the experiments were conducted according to Columbia University institute of comparative medicine policies and an IACUC approved protocol. 

Unmodified anti-tyrosinase-related protein-1 mouse monoclonal antibodies (anti-TYRP1 or TA99), T regulatory (Treg) depleting antibodies, immune checkpoint blockades, and MEK inhibitors were tested in vivo in mice with melanoma tumors and in vitro in B16 and YUMM mouse melanoma cell lines. Monoclonal antibodies used for in vivo treatment were purchased from BioXCell and the MEK inhibitor trametinib was purchased from Chemietek.

The researchers in this study used flow cytometry analysis, western blot analysis, quantitative RT-PCR, cell viability assays, and quantification and statistical analysis to determine their study results.

Antibodies & Immune Checkpoint Blockade

All mice were first injected with B16 or YUMM melanoma tumor cells and their tumor parameters were measured over the course of the study. Researchers note that the initial accumulation of Treg cells activates adaptive, tumor specific immunity and interferes with the therapeutic efficacy of anti-tumor antibodies. Therefore, PC61 (Treg depleting antibodies), were used in combination with TA99 (anti-tumor antibodies), in hopes of removing immune suppressive regulatory signaling.

“Administration of TA99 in combination with antibody-mediated depletion of Treg cells resulted in a significant reduction in subcutaneous B16 melanoma growth.”

After successfully testing TA99 with PC61, mice outside of the control group were treated with either anti-CTLA4 or anti-PD1—immune checkpoint blockade (ICB) therapies. The researchers observed a significant reduction in tumor volume when compared with the control or single treatment groups. To further investigate the efficacy of ICB therapies, the researchers tested the triplet combination of TA99, anti-CTLA4, and anti-PD1.

“Furthermore, as predicted from the current clinical data on anti-CTLA4 and anti-PD1 therapeutics [32, 33], we found that this combination resulted in a significant reduction of B16 tumors, which when combined with TA99 mAb therapy in a triple combination, resulted in eradication of solid subcutaneous tumors.”

MEK Inhibition

The researchers also tested the in vitro effects of MEK inhibitors on B16 cell viability. They tested MEKi selumetinib and trametinib and found that MEKi trametinib induced increased pigmentation in B16 mouse melanoma cells. Researchers then treated B16 and YUMM cells with trametinib and TA99, which resulted in significantly reduced tumor growth.

Based on their observations that the therapeutic effects of the anti-tumor antibodies TA99 could be enhanced by both ICB and MEKi targeted therapy, they tested the triple combination in a BRAF mutant YUMM1.7 cell line.

“This combination treatment with TA99, trametinib and ICB (with anti-PD1 or anti-CTLA4) mAb resulted in a significant reduction of tumor size compared to the control groups (Figure 6B).”

“In addition, we found that the MEK inhibitor (trametinib)-induced increased expression of melanosomal antigens further enhanced the anti-melanoma response to combination therapy with anti-tumor antibodies and immune checkpoint blockade in mouse models of melanoma.”

“Moreover, we found an improved therapeutic effect when YUMM tumor-bearing mice were treated with TA99 combined with MEKi and immune checkpoint blockade (anti-PD1 and anti-CTLA4).”

Conclusion

“Our findings suggest that MEKi induced an increased expression of tumor-associated antigens, which in combination with anti-tumor antibodies, generated a robust adaptive anti-tumor response that was sustained by immune checkpoint inhibition therapy.” 

The researchers in this study demonstrated that increasing the expression of melanoma derived antigens with MEK inhibitors, in combination with anti-tumor antibodies, improved therapeutic response rates to immune checkpoint blockades in the B16 and YUMM melanoma mouse models. They also found that in the B16 and YUMM mouse models of melanoma and TA99, the therapeutic effects of unmodified anti-tumor antibodies can be enhanced by ICB (anti-PD1 and anti-CTLA4 monoclonal antibodies).

“Together, our findings indicate that the combination therapy with TA99 and the elimination of the regulatory signals resulting from the activation of anti-tumor immune responses could be an effective therapeutic strategy for the management of malignant melanoma.”

“[…] these results invite further clinical investigation of unmodified anti-tumor antibodies in combination with ICB and targeted therapies, and may represent promising and innovative therapeutic interventions for the successful management of patients with advanced melanoma and other cancers.”

Click here to read the full scientific study, published in Oncotarget.

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