Imiquimod-gemcitabine nanoparticles harness immune cells to suppress breast cancer

Monotherapy with a single chemotherapeutic regimen has met with significant hurdles in terms of clinical efficacy. The complexity of cancer accentuates the need for an alternative approach with a combination of two or more therapeutic regimens to win the battle. However, it is still a challenge to develop a successful combination of drugs with high efficiency and low toxicity to control cancer growth. While gemcitabine monotherapy remains a choice of standard treatment for advanced breast cancer, the approach has not prolonged the median survival time of metastatic breast cancer patients. Here, we report a hyaluronic acid (HA)-based drug combination of gemcitabine (GEM) with imiquimod (IMQ) to stimulate immune cells for anticancer activity. Treatment of the drug combination (IMQ-HA-GEM) showed enhanced anticancer activity against 4T1 breast tumor cells in vitro. Our study with a microfluidics-based 3D, compartmentalized cancer model showed that infiltration of THP-1 monocytes occurred particularly at the site of cancer cells treated with IMQ-HA-GEM. Moreover, IMQ-HA-GEM significantly suppressed the volume of 4T1 breast tumor of mice in vivo. Flow cytometry study displayed a significantly higher activation of CD11b⁺ immune cells in the blood of mice treated with IMQ-HA-GEM, whereas immunohistochemistry study revealed greater prevalence of CD68⁺ tumor-associated macrophages in the tumor. Histological examination of isolated tumors of mice treated with IMQ-HA-GEM further confirmed the efficacy of drug combination on cancer cells. This study supports the conclusion that imiquimod potentiates the effect of gemcitabine by activating immune cells to suppress tumors in the form of combination nanoparticles.