Boehringer Ingelheim's novel dual mTORC1/2 inhibitor BI 860585 has shown promising results in a Phase I clinical trial for patients with advanced breast cancer, according to data presented at the American Society of Clinical Oncology (ASCO) Annual Meeting.
The open-label, dose-escalation study evaluated BI 860585 both as a single agent and in combination with either exemestane or paclitaxel in patients with advanced solid tumors, with a particular focus on hormone receptor-positive (HR+) breast cancer.
Safety Profile and Dosing
The trial established that BI 860585 has a manageable safety profile at the recommended Phase II dose of 150mg daily. Common treatment-related adverse events included fatigue, nausea, hyperglycemia, and decreased appetite, consistent with the known class effects of mTOR inhibitors. Dose-limiting toxicities were primarily gastrointestinal and metabolic in nature.
"The dual inhibition of both mTORC1 and mTORC2 represents a potential advantage over first-generation mTOR inhibitors like everolimus, which only target mTORC1," explained the study's principal investigator. "This approach may help overcome resistance mechanisms that have limited the efficacy of current therapies."
Efficacy Signals
While the primary objective of the study was to determine safety and tolerability, investigators also observed encouraging preliminary efficacy signals. Several patients with HR+ breast cancer who had progressed on prior endocrine therapy achieved disease stabilization when treated with the combination of BI 860585 and exemestane.
Pharmacodynamic analyses demonstrated dose-dependent inhibition of both mTORC1 and mTORC2 signaling pathways, confirming the dual-targeting mechanism of action. Biomarker studies showed decreased phosphorylation of downstream targets including 4E-BP1, S6K, and AKT.
Addressing Resistance Mechanisms
The PI3K/AKT/mTOR pathway is frequently dysregulated in breast cancer, particularly in patients who develop resistance to endocrine therapy. First-generation mTORC1 inhibitors like everolimus have shown clinical benefit but are limited by feedback activation of AKT via mTORC2.
"By inhibiting both mTORC1 and mTORC2, BI 860585 has the potential to provide more complete pathway blockade and potentially superior efficacy compared to existing options," said a senior oncologist involved in the trial. "This could be particularly valuable for patients who have developed resistance to standard therapies."
Combination Strategies
The study explored two combination strategies: BI 860585 plus exemestane for HR+ breast cancer patients, and BI 860585 plus weekly paclitaxel for patients with various advanced solid tumors.
The exemestane combination showed particular promise in the HR+ breast cancer cohort, with several patients experiencing prolonged stable disease despite having progressed on prior endocrine therapies. This suggests potential for overcoming endocrine resistance, a significant clinical challenge in breast cancer treatment.
The paclitaxel combination demonstrated preliminary activity across multiple tumor types, though further evaluation is needed to determine which patient populations might benefit most from this approach.
Future Directions
Based on these encouraging Phase I results, researchers are planning additional studies to further evaluate BI 860585, particularly in HR+ breast cancer patients who have developed resistance to standard therapies.
"These findings support the continued development of BI 860585 as a potential new treatment option for advanced breast cancer," the lead investigator concluded. "The next step will be to conduct larger, randomized trials to confirm these preliminary signals and better define the patient populations most likely to benefit."
The researchers also noted that biomarker analyses are ongoing to identify potential predictive markers of response, which could enable more personalized treatment approaches in future studies.
