A strategically designed homogeneous antibody-drug conjugate improves safety and therapeutic index in renal cell carcinoma

Renal cell carcinoma (RCC) is one of the leading causes of kidney cancer-related mortalities worldwide. Though the treatment method of RCC has advanced from nephrectomy to targeted therapy and immunotherapy, most patients suffer from therapeutic resistance, metastasis, and relapse. In recent days, antibody drug conjugates (ADCs) have emerged as a promising treatment modality by delivering cytotoxic payloads specifically to the cancer cells. However, previous efforts related to ADC have failed in the clinic because of severe toxicity. Here, we introduced a homogenous ADC (LT-025), which can target the kidney injury molecule (KIM) -1 receptor on RCC cells. We adopted the enzymatic conjugation involving microbial transglutaminase (MTGase) to attach the cytotoxic drug DM1 to the Fc region of the KIM-1 antibody. We demonstrated a site-specific conjugation of the drug-linker with a specific drug-to-antibody ratio (DAR) of 2. The ADC exhibited prolonged stability and superior antigen-binding capability, characterized using various bioanalytical methods. We proved that cellular internalization and cytotoxicity are dependent on the KIM-1 expression on RCC. The LT-025 displayed superior cytotoxicity to the metastatic RCC cells, then standard RCC treatment by sunitinib. The combination therapy of LT-025 and sunitinib showed increased therapeutic efficacy in vitro in RCC as well as in sunitinib-resistant RCC models. The LT-025 exhibited a safe and effective treatment in the syngeneic RCC mouse model. The combination therapy also showed an increased tumor growth inhibition in preclinical mouse model studies. A carefully designed KIM-1 targeting ADC can emerge as an effective treatment method for metastatic RCC.