HER2-mediated delivery of cytotoxic agents in solid tumors

PROJECT SUMMARY ERBB2/HER2 is a receptor tyrosine kinase (RTK) that is amplified/overexpressed in 15-20% of breast and gastroesophageal cancers, for which anti-HER2 therapy is now standard of care.

HER2 can be hyperactivated by overexpression and by mutations driving oncogenesis through receptor phosphorylation, internalization, and increased turnover.

Hyperactivating HER2 mutations, possessed by thousands of patients with non-breast/non- gastric solid tumors, do not respond to classical anti-HER2 kinase therapy. Anti-HER2 antibody-drug conjugates (ADCs) offer a new treatment avenue for non-breast/non-gastric HER2-altered tumors.

ADCs bind to HER2 on the cell surface, get internalized, and release their cytotoxic payloads in the endolysosomes to induce cell death.

Two ?basket? trials at our institution testing the antitumor activity of the anti-HER2 ADCs, trastuzumab emtansine (T-DM1), and trastuzumab deruxtecan (T-DXd) in n found clinical responses in lung, colorectal, salivary duct, biliary tract, ovarian, and endometrial cancers. Moreover, we showed that HER2 mutant lung tumors are responsive to T-DM1 regardless of HER2 protein levels.

Here, we plan to use several cell line-based and patient-derived preclinical models (organoids, xenografts) bearing different HER2 protein levels, mutations, and activation/phosphorylation statuses to study how the variation in receptor expression/phosphorylation modulates endocytosis and anti-HER2 ADC activity.

We show that irreversible pan-HER inhibitors, such as neratinib, enhance ubiquitination, internalization, and consequent degradation of HER2.

Neratinib also increases HER2-ADC complex internalization in vitro, leading to complete tumor regression in patient-derived xenograft models (lung and colon cancer) bearing amplification or mutations of ERBB2.

We plan to identify determinants of sensitivity to DM1 or DXd payloads by integrating genomic, transcriptomic, and proteomic data acquired from sensitive and resistant models.

Finally, we will use these data to prioritize biomarkers of response to T-DM1 and T-DXd identified by genomic and proteomic analysis of the tumor samples, and imaging tumors bearing different HER2 alterations from the 124 patients enrolled in our basket trials.

Tumor biopsies and cell-free DNA samples collected before and during treatment, and at disease progression will be analyzed by targeted exome sequencing, whole exome sequencing, and droplet digital PCR.

These data will characterize changes in ERBB2 status during treatment and whether other genomic alterations modulate response to therapy during tumor evolution. FRET and other imaging-based techniques will quantify the level of HER2 dimerization with other RTKs.

Tumor biopsies, analyzed by global and targeted mass spectrometry, will identify a specific proteomic signature of response to the ADCs.

Clinical on-breast/non-gastric solid tumors, response to ADCs will also be correlated with HER2 levels by 89Zr-trastuzumab PET/CT.

Our studies will provide fundamental insights into the mechanism of action of anti-HER2 ADCs and will open new therapeutic horizons for patients without effective, targeted therapy options.