HA15 (Zhengzhou University)

Nirmatrelvir, the active compound of the drug Paxlovid, inhibits the Main protease of SARS-CoV-2 (M^Pro, 3CL^Pro, NSP5). Its therapeutic application reduces but does not abolish the progression of COVID-19 in humans. Here we report a strong synergy of Nirmatrelvir with inhibitors of the ER chaperone GRP78 (HSPA5, BiP). Combining Nirmatrelvir with the GRP78-antagonizing drug candidate HA15 strongly inhibits the replication of SARS-CoV-2, to a far greater extent than either drug alone, as observed by diminished cytopathic effect, levels of detectable virus RNA, TCID₅₀ titers, and reduced accumulation of the non-structural proteins, as well as Spike and N proteins. The original SARS-CoV-2 strain as well as an Omicron variant were similarly susceptible towards the drug combination. Other GRP78 inhibitors or siRNAs targeting GRP78 also fortified the antiviral effect of Nirmatrelvir. In a hamster model of COVID-19, the combination of Nirmatrelvir with HA15 alleviated pneumonia-induced pulmonary atelectasis more effectively than the single drugs. In conclusion, inhibition of the virus Main protease and cellular GRP78 cooperatively diminishes virus replication and may improve COVID-19 therapy.

While significant upregulation of GRP78 has been documented in lung cancer patients, its association with resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) remains underexamined. Our study aimed to elucidate the functional importance of GRP78 in acquired resistance to EGFR-TKIs in non-small cell lung cancer (NSCLC) and to evaluate its potential as a therapeutic target.

Immunoblot analysis or flow cytometry was employed to assess several markers for endoplasmic reticulum (ER) stress and apoptosis. Ru(II) complex I and HA15, two known GRP78 inhibitors, were used to evaluate the functional role of GRP78. A Xenograft assay was performed to evaluate the in vivo anti-cancer effects of the GRP78 inhibitors.

We validated a significant increase in GRP78 protein levels in HCC827-GR, H1993-GR, and H1993-ER cells. The EGFR-TKI-resistant cells overexpressing GRP78 exhibited significantly higher cell proliferation rates than did their parental counterparts. Notably, GRP78 inhibition resulted in a more profound anti-proliferative and apoptotic response via heightened ER stress and subsequent reactive oxygen species (ROS) production in EGFR-TKI-resistant cell lines compared with their parental cells. In xenograft models implanted with HCC827-GR, both Ru(II) complex I and HA15 significantly suppressed tumor growth and reduced tumor weight. Additionally, we confirmed that GRP78 plays a critical role in the proliferation of H1975, an EGFR-TKI-resistant T790M-mutant cell line, relative to other NSCLC cell lines.

Our findings strongly support targeting of GRP78 as a promising therapeutic strategy for NSCLC patients with acquired resistance to EGFR-TKIs.