Precise sequential combination of cisplatin and cyclophosphamide induces higher anti-tumor and immunomodulatory...

Cisplatin (CIS) and cyclophosphamide (CTX) are commonly used in clinical oncology, often in combination to improve therapeutic outcomes. However, most preclinical studies have examined these agents individually, overlooking the potential synergistic and immunomodulatory effects of combined treatment. This study aimed to compare the antitumor and immune-modulating effects of single versus combined CTX and CIS chemotherapy, and to determine the treatment sequence that achieves maximum efficacy with minimal toxicity.

Adult female mice (n = 5/group) were inoculated intraperitoneal (i.p.) with 0.5 × 10⁶ fresh viable Ehrlich ascites carcinoma (EAC) cells. Twenty-four hours' post-inoculation, animals received a single administration of phosphate-buffered saline (PBS), CIS, CTX, or various combinatorial CIS-CTX regimens. Antitumor activity and alterations in myeloid cell subsets, including dendritic cells (DCs), monocytes, and neutrophils, were evaluated in peripheral blood and spleen by flow cytometry.

EAC-bearing mice showed changes in splenic and circulating immune cell populations based on CD11c and CD11b expression profiles, suggesting tumor-associated immunomodulatory alterations. CIS and CTX monotherapy partially restored myeloid cell populations. Notably, sequential regimens, particularly CIS followed by escalating doses of CTX-led to substantial increases in both mature neutrophils and plasmacytoid DCs (pDCs), while reducing CD11b⁺ myeloid cell population associated with immunosuppressive phenotypes. These changes suggest enhanced myelopoiesis and innate immune activation in treated mice.

A regimen consisting of high-dose CTX combined with low-dose CIS demonstrated robust anti-tumor activity while limiting leukopenia and systemic toxicity. This protocol may represent an optimal therapeutic strategy, balancing efficacy with safety.