Dual-payload antibody-drug conjugate for chemo-immunotherapy of triple-negative breast cancers

SUMMARY Triple-negative breast cancers (TNBCs) are highly aggressive and often relapse post standard cytotoxic chemotherapies. The immunotherapies such as immune checkpoint blockers (ICBs) that target PD-1, PD-L1 or CTLA-4 represent a major breakthrough in cancer treatment, but 75-90% of TNBC patients failed to respond due

to primary and acquired resistance. The Sacituzumab-SN38 and Pembrolizumab-chemotherapy have been developed and applied to treat refractory metastatic TNBC, showing the great potential of combined and targeted therapies, but novel effective treatment strategies for TNBC are urgently needed. We recently detected

transmembrane CD276 (B7-H3) associated with angiogenesis, metastasis and immune tolerance in most TNBC patients, and developed a humanized anti-CD276 monoclonal antibody (mAb) capable of targeting CD276+ TNBC and upregulating tumoral immunity. Furthermore, we established innovative platforms for concurrent

conjugation of highly cytotoxic emtansine and immunoregulating toll-like receptor (TLR) agonist in one antibody- drug conjugate (ADC). Our preliminary evaluations showed that the CD276-targeted dual-payload ADC (276- DualADC) effectively killed multiple TNBC subtypes, significantly enhanced immune functions and overcame

ICB resistance to PD-1 mAb, and reduced tumor burden by 90-100% and metastasis in three animal models. These results indicate 276-DualADC is a promising therapeutic to treat TNBCs. Our goal is to develop and examine the effectiveness of combining humanized CD276 mAb-directed Hu276-DualADC, which targeting

delivers a potent chemotherapy and immunotherapy TLR 7/8 agonist, and PD-1-targeting ADC to eliminate heterogenous and metastatic TNBC cells in vivo. It is hypothesized that this novel combinatory strategy, named as Hu276/PD-1-DualADC, synergizes multiple chemo- and immuno-mediated anti-cancer mechanisms, i.e.,

direct cancer cell killing, tumoral immunity, tumoral cytokine, and immune checkpoint blockade, to enhance TNBC treatment efficacy. Three aims were proposed to test the hypothesis. Aim 1 will produce large-scale Hu276-DualADC carrying mertansine and imidazoquinoline, and characterize its affinity, TNBC-specificity,

biodistribution and toxicity. Optimal treatment strategy will be determined in maximal tolerated dose and pharmacokinetics studies. Finally, anti-TNBC efficacy will be evaluated in primary xenograft models and distant metastatic models. Aim 2 will assess the synergistic effects of HuCD276/PD-1-DualADC in three

immunocompetent models. The underlying mechanisms (proliferation, apoptosis, immune cell infiltration and activation, tumoral cytokine, and ICB restoration) will also be delineated. Aim 3 will fully evaluate the long-term therapeutic efficacy in metastatic syngeneic TNBC xenograft models post surgical resection and patient-derived

xenograft (PDX) models. Pre-IND toxicology will also be investigated to collect preclinical data for future clinical trial launching. Successful completion of this project will provide a new strategy to treat aggressive TNBCs.