Combination therapy with a HIF-1alpha/c-MET peptide vaccine and carboplatin reprograms the tumor microenvironment to overcome platinum resistance in an intraperitoneal metastasis model of high-grade serous ovarian carcinoma

Ovarian cancer is the most lethal gynecologic malignancy, with most patients diagnosed atadvanced stages (III-IV). Although initially responsive to platinum-based chemotherapy, about60% of patients relapse within a few years due to acquired chemoresistance. Tumor hypoxiahas been implicated as a key driver of aggressive phenotypes and treatment resistance. Ourprevious study showed that a HIF-1alpha/c-MET-derived peptide vaccine combined with platinumcompounds elicited strong antitumor immunity in a mouse model of ovarian cancer. Here, weinvestigated whether type I immune activation could overcome platinum resistance in anaggressive intraperitoneal metastasis model in vivo. An intraperitoneal metastasis model was established in C57BL/6 mice using a murineplatinum-resistant ID8 ovarian cancer cell line. To evaluate antitumor effects, mice wereassigned to four groups: (1) control, (2) carboplatin, (3) HIF-1alpha/c-MET vaccine, and (4)combination of carboplatin and vaccine. The vaccine was administered subcutaneously threetimes at one-week intervals prior to tumor inoculation, and carboplatin was administered oneweek after tumor inoculation. Tumor progression and metastatic burden were monitored usingan in vivo imaging system (IVIS). Ascites formation was quantified by measuring abdominalcircumference. Immunohistochemistry (IHC) was used to assess HIF-1alpha and c-METexpression, intratumoral CD8⁺/ CD4⁺ T-cell ratios, and M1/M2 macrophage ratios in the peritoneum. Both monotherapies with either carboplatin or vaccine significantly inhibited intraperitonealmetastasis compared with the control. Furthermore, the combination therapy showedsignificantly better suppression of intraperitoneal metastasis than either monotherapy. Ascitesformation was markedly decreased in both monotherapy groups compared with the control,and it was further decreased in the combination group. IHC revealed that carboplatin aloneincreased HIF-1alpha and c-MET expression, suggesting activation of tumor-promoting signals,while the vaccine-alone or combined-suppressed expression of these markers. Bothtreatments enhanced intratumoral CD8⁺ T-cell infiltration and improved the CD8⁺/ CD4⁺ ratio(p < 0.0001) as well as the M1/M2 macrophage ratio (p < 0.0001), with the combination therapyshowing the significant effect. These results suggest that immunotherapy with a combination of HIF-1alpha/c-MET peptidevaccine with carboplatin reversed the tumor hypoxia induced by carboplatin alone andreprogramed the tumor microenvironment toward immune activation, offering a promisingimmunotherapeutic strategy to overcome platinum resistance and prevent recurrence in ovariancancer.