Cyclophosphamide enhances anti-tumor effects of a fibroblast activation protein α-based DNA vaccine in tumor-bearing mice with murine breast carcinoma

Abstract

Cyclophosphamide (CY) is a DNA alkylating agent, which is widely used with other chemotherapy drugs in the treatment of various types of cancer. It can be used not only as a chemotherapeutic but also as an immunomodulatory agent to inhibit IL-10 expression and T regulatory cells (Tregs). Fibroblast activation protein α (FAPα) is expressed in cancer-associated fibroblasts in the tumor microenvironment. Immunotherapy based on FAPα, as a tumor stromal antigen, typically induces specific immune response targeting the tumor microenvironment. This study evaluated the efficacy of a previously unreported CY combination strategy to enhance the limited anti-tumor effect of a DNA vaccine targeting FAPα. The results suggested CY administration could promote the percentage of splenic CD8⁺T cells and decrease the proportion of CD4 ⁺ CD25 ⁺ Foxp3⁺Tregs in spleen. In tumor tissues, levels of immunosuppressive cytokines including IL-10 and CXCL-12 were also reduced. Meanwhile, the CY combination did not impair the FAPα-specific immunity induced by the DNA vaccine and further reduced tumor stromal factors. Most importantly, FAP-vaccinated mice also treated with CY chemotherapy showed a marked suppression of tumor growth (inhibition ratio =80%) and a prolongation of survival time. Thus, the combination of FAPα immunotherapy and chemotherapy with CY offers new insights into improving cancer therapies.

Keywords:

• Cyclophosphamide
• fibroblast activation protein α
• cancer combination therapy
• immunomodulation
• tumor immunology

Acknowledgements

The authors would like to thank Phuong Thi Sarkis for valuable suggestions and editorial help. We are grateful for the support from the Specialized Research Fund for the National Natural Science Foundation of China [no. 31300765, 81301803], Specialized Research Fund for the Doctoral Program of Higher Education [New Teachers] [grant no. 20120061120025], Jilin Province Science and Technology Development Program [no. 20130522006JH, 20160519018JH], National Science and Technology Major Project of the Ministry of Science and Technology of China [no. 2014ZX09304314–001, 2012ZX10001009–2], Fundamental Research Funds for the Central Universities [grant no. JCKY-QKJC03].

Disclosure statement

The authors declare that they have no conflicts of interest.

Additional information

Funding

We are grateful for the support from the Specialized Research Fund for the National Natural Science Foundation of China [no. 31300765, 81301803], Specialized Research Fund for the Doctoral Program of Higher Education [New Teachers] [grant no. 20120061120025], Jilin Province Science and Technology Development Program [no. 20130522006JH, 20160519018JH], National Science and Technology Major Project of the Ministry of Science and Technology of China [no. 2014ZX09304314–001, 2012ZX10001009–2], Fundamental Research Funds for the Central Universities [grant no. JCKY-QKJC03].