Large, Anionic Liposomes Enable Targeted Intraperitoneal Delivery of a TLR 7/8 Agonist To Repolarize Ovarian Tumors’ Microenvironment

Abstract

Ovarian cancer is the most lethal gynecological malignancy in the United States. Current standard of treatment includes surgical debulking and chemotherapy, such as cisplatin and paclitaxel. However, the patients’ response rate for chemotherapy in ovarian cancer is not optimal, and they often develop chemoresistance and suffer from side effects. Current clinical trials make extensive use of immune checkpoint blockade (ICB) as a novel cancer immunotherapeutic strategy against ovarian tumors. However, the response rates for ICB antibodies remain limited to 10–20% of treated ovarian cancer patients despite the success of this approach in melanoma, renal, head and neck, and nonsmall cell lung cancers. This lack of efficacy is often attributed to the “cold” immune status of ovarian tumors, as these tumors often have a low number of tumor-infiltrating lymphocytes (TILs) but a high number of suppressive immune cells, including tumor-associated macrophages (TAMs), myeloid-derived suppressor cells (MDSCs), or regulatory T cells (Tregs). Repolarizing TAMs could be a promising strategy to reshape the tumor immune microenvironment and promote antitumor activity when combined with ICBs. Toll-like receptor (TLR) 7 and 8 agonists, such as imiquimod and resiquimod, are potent immunostimulatory molecules with potential to repolarize macrophages. However, these small molecules have poor pharmacokinetic profiles and can induce severe side effects when administered systemically. Previously, our group demonstrated that various large, anionic nanomaterials (silica, PLGA, and polystyrene) specifically target TAMs when administered intraperitoneally (IP) to ovarian tumor-bearing mice. In the present study, we demonstrate that large, anionic liposomes administered IP also efficiently localize to TAMs and can be used to target the delivery of resiquimod. Resiquimod delivered in this targeted fashion promoted activation of M1 macrophages and T cell infiltration, while reducing the percentage of Tregs in the tumor microenvironment. Finally, liposome-formulated resiquimod significantly enhanced the efficacy of PD1 blockade against syngeneic ovarian tumors. We anticipate that further optimization of our liposomal delivery strategy can generate a clinically relevant strategy for more effective and safer immunotherapy for ovarian cancer patients.

Targeting toll-like receptor 7/8 for immunotherapy: recent advances and prospectives

“…Repolarizing TAMs could be a promising strategy to reshape the tumor immune microenvironment and promote antitumor activity when combined with immune checkpoint blockades (ICBs) [ 154 ]. TLR7 and 8 agonists, such as IMQ and resiquimod, are potent immunostimulatory molecules with the potential to repolarize macrophages [ 139 ]. Combination strategies such as ICB and adoptive cell therapy, innate immune modifiers and cancer vaccines, as well as combination therapies with other therapeutic modalities can maximize the benefits of cancer immunotherapy [ 155 ].…”

“…Combination strategies such as ICB and adoptive cell therapy, innate immune modifiers and cancer vaccines, as well as combination therapies with other therapeutic modalities can maximize the benefits of cancer immunotherapy [ 155 ]. According to the action mechanism, TLR8 agonists are effective not only as monotherapy but also as combinations with other drugs, including immune checkpoint inhibitors, such as PD-1, PD-L1 monoclonal antibodies (mAbs) and chemotherapy drugs, to further expand the indications and enhance the efficacy [ 139 , 152 , 156 ].…”

Nanomedicine Strategies for Heating “Cold” Ovarian Cancer (OC): Next Evolution in Immunotherapy of OC

“…Recently, TLR agonist-based nanomedicines have been developed and demonstrated excellent efficacy for reversing cold TIM of OC. [98,99] For instance, Kang et al developed an anionic liposome-loaded large-size (≈400 nm) resiquimod (RSQ) to enhance OC targeting and reduce systemic toxicity of RSQ for OC immunotherapy. [99] RSQ is a TLR agonist with the immunostimulatory ability to repolarize macrophages from M2 to M1 and induce Th1 responses through nuclear factor kappa-B activation.…”

“…[98,99] For instance, Kang et al developed an anionic liposome-loaded large-size (≈400 nm) resiquimod (RSQ) to enhance OC targeting and reduce systemic toxicity of RSQ for OC immunotherapy. [99] RSQ is a TLR agonist with the immunostimulatory ability to repolarize macrophages from M2 to M1 and induce Th1 responses through nuclear factor kappa-B activation. The RSQ-loaded liposomes efficiently accumulated in TAMs of OC with up to 80% uptake due to the positive charge on the cell membrane surface of TAMs [67] and successfully repolarized TAMs to a proimmunogenic M1 state.…”

“…Recently, TLR agonist‐based nanomedicines have been developed and demonstrated excellent efficacy for reversing cold TIM of OC. [ 98 , 99 ] For instance, Kang et al. developed an anionic liposome‐loaded large‐size (≈400 nm) resiquimod (RSQ) to enhance OC targeting and reduce systemic toxicity of RSQ for OC immunotherapy.…”