patritumab (U3-1287)

In diverse CSPC patient populations, ERBB3 OE was associated with high AR signaling despite low intraprostatic androgen. Mechanistic studies demonstrated a direct link between HER3 and enzalutamide resistance. ERBB3 OE as a biomarker could thus stratify patients for intensification of therapy in castration-sensitive disease, including targeting HER3 directly to improve sensitivity to AR-targeted therapies.

Background: HER3-DXd is an antibody drug conjugate (ADC) comprised of a fully human anti-HER3 IgG1 monoclonal antibody (patritumab), attached to a topoisomerase 1 inhibitor via a tetrapeptide-based cleavable linker that has shown promising efficacy in pts with HER3-expressing MBC (Krop, 2022). HER3-DXd had an acceptable safety profile, and the data further confirm the clinical activity in MBC in heavy pre-tx MBC across the broad range of HER3 expression levels. Parts B and Z are ongoing and data from this report support the potential entry of HER3-DXd into the therapeutic paradigm in MBC. Clinical trial information: NCT04699630.

HER3-DXd, a novel antibody-drug conjugate (ADC) composed of a human anti-HER3 IgG1 monoclonal antibody (patritumab) covalently linked to a topoisomerase I inhibitor payload (DXd), is currently being studied in clinical trials for breast cancer and NSCLC...NSCLC cell lines harboring EGFR activating mutations, ROS1 fusions, or ALK fusions were used to evaluate the effect of osimertinib, lorlatinib, or ceritinib on cell surface HER3 expression and payload release (osimertinib only). HER3-DXd was rapidly transferred to early endosomes after binding to HER3... HER3 expression was dynamically changed by HER3-DXd dosing regimen and by RTKi treatment, resulting in a substantial impact on payload release. These findings support our strategy of clinical studies using HER3-DXd after drugs that increase HER3 expression including EGFR TKI and indicate that HER3 dynamics may play a key role in achieving optimal efficacy of HER3-DXd.

Patients are randomized 1:1 to receive either HER3-DXd 5.6 mg/kg every 3 weeks or 4 cycles of PBC containing pemetrexed (can be continued as maintenance) with cisplatin or carboplatin. Patients are stratified by prior third-generation EGFR TKI treatment (osimertinib vs other), line of prior third-generation EGFR TKI use (first vs second line), region (Asia vs rest of world), and presence of stable brain metastases (yes vs no)...Other secondary endpoints include investigator-assessed progression-free survival, objective response rate, duration of response, clinical benefit rate, disease control rate, time to response (all assessed by investigator and BICR per RECIST 1.1), safety, and patient-reported outcomes. Enrollment began May 2022 and is ongoing, with sites in Asia, Australia, Europe, and North America.

Background: HER3, a member of the ERBB family of receptor tyrosine kinases that activates multiple oncogenic signaling pathways, is overexpressed in 50-70% of breast cancers (BC). The combination of HER3-DXd plus ATR inhibitors has therapeutic potential for overcoming tamoxifen resistance in HER3+/ER+ BC.

We established HER3-and/or MET-KO SW1116 cell lines, and HER3/MET-double KO resulted in the inhibition of in vitro cell proliferation and in vivo tumor growth in nude mice by SW1116 cells. Furthermore, the combination of patritumab, an anti-HER3 fully human mAb, and PHA665752, a MET inhibitor, markedly inhibited in vitro cell proliferation, 3D-colony formation, and in vivo tumor growth in nude mice by SW1116 cells The dual targeting of HER3/MET has potential as CRC therapy.

IR-induced activation of nuclear AKT occurs inside the nucleus that is mainly dependent on HER3 expression in NSCLC. These findings suggest that targeting HER3 in combination with radiotherapy may provide a logical treatment option for investigation in selected NSCLC patients.

Pts are randomized 1:1 to receive either HER3-DXd 5.6 mg/kg every 3 weeks or 4 cycles of PBC containing pemetrexed (can be continued as maintenance) with cisplatin or carboplatin. Pts are stratified by prior 3rd-gen EGFR TKI treatment (osimertinib vs other), line of prior 3rd-gen EGFR TKI use (first vs second line), region (Asia vs rest of world), and presence of stable brain metastases (yes vs no)...Enrollment began May 2022 and is ongoing, with sites in the US, Canada, EU, Asia, and Australia. This trial in progress was previously presented at ESMO 2022.

Pts are randomized 1:1 to receive either HER3-DXd 5.6 mg/kg every 3 weeks or 4 cycles of PBC containing pemetrexed (can be continued as maintenance) with cisplatin or carboplatin. Pts are stratified by prior 3rd-gen EGFR TKI treatment (osimertinib vs other), line of prior 3rd-gen EGFR TKI use (first vs second line), region (Asia vs rest of world), and presence of stable brain metastases (yes vs no)...Other secondary endpoints include investigator-assessed PFS, objective response rate, duration of response, clinical benefit rate, disease control rate, time to response (all per BICR per RECIST v1.1), safety, and patient-reported outcomes. Enrollment into the trial is starting in Q2 2022.

The primary objective of cohort 4 is to evaluate the PK of this formulation during the first treatment cycle. Secondary objectives include the evaluation of PK, safety, tolerability, immunogenicity, and efficacy.

Two breast cancer patient-derived xenograft (PDX) models were treated with patritumab (anti-HER3 antibody), polyclonal activated autologous T cells (PATCs) or a combination of patritumab and PATCs (P-PATCs) in order to test immunological modulation by the regulation of HER3 signals... These data suggest that HER3 expression in breast cancer associated with “cold” TIME and the regulation of its signal converts “cold” TIME to “hot”. Thus, inhibition of HER3 signal might be of interesting concept for both regulation of oncologic signal and immunological modulation in HER3-expressing breast cancer. Further HER3 related immune modulation exploration in breast cancer treatment strategy needs to be clarified in the future.