A Phase Ib Expansion Cohort Evaluating Aurora A Kinase Inhibitor Alisertib and Dual TORC1/2 Inhibitor Sapanisertib in Patients with Advanced Solid Tumors

BACKGROUND

This study further evaluated the safety and efficacy of the combination of alisertib and sapanisertib in an expansion cohort of patients, including a subset of patients with refractory pancreatic adenocarcinoma, with further evaluation of the pharmacodynamic characteristics of combination therapy.

METHODS

Twenty patients with refractory solid tumors and 11 patients with pancreatic adenocarcinoma were treated at the recommended phase 2 dose of alisertib and sapanisertib. Adverse events and disease response were assessed. Patients in the expansion cohort were treated with a 7-day lead-in of either alisertib or sapanisertib prior to combination therapy, with tumor tissue biopsy and serial functional imaging performed for correlative analysis.

RESULTS

Toxicity across treatment groups was overall similar to prior studies. One partial response to treatment was observed in a patient with ER positive breast cancer, and a patient with pancreatic cancer experienced prolonged stable disease. In an additional cohort of pancreatic cancer patients, treatment response was modest. Correlative analysis revealed variability in markers of apoptosis and immune cell infiltrate according to lead-in therapy and response.

CONCLUSIONS

Dual targeting of Aurora A kinase and mTOR resulted in marginal clinical benefit in a population of patients with refractory solid tumors, including pancreatic adenocarcinoma, though individual patients experienced significant response to therapy. Correlatives indicate apoptotic response and tumor immune cell infiltrate may affect clinical outcomes.

Overcoming doxorubicin resistance in triple-negative breast cancer using the class I-targeting HDAC inhibitor bocodepsin/OKI-179 to promote apoptosis

BACKGROUND

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype with a poor prognosis. Doxorubicin is part of standard curative therapy for TNBC, but chemotherapy resistance remains an important clinical challenge. Bocodepsin (OKI-179) is a small molecule class I histone deacetylase (HDAC) inhibitor that promotes apoptosis in TNBC preclinical models. The purpose of this study was to investigate the combination of bocodepsin and doxorubicin in preclinical TNBC models and evaluate the impact on terminal cell fate, including apoptosis and senescence.

METHODS

TNBC cell lines were treated with doxorubicin and CellTiter-Glo was used to assess proliferation and determine doxorubicin sensitivity. Select cell lines were treated with OKI-005 (in vitro version of bocodepsin) and doxorubicin and assessed for proliferation, apoptosis as measured by Annexin V/PI, and cell cycle by flow cytometry. Immunoblotting was used to assess changes in mediators of apoptosis, cell cycle arrest, and senescence. Senescence was measured by the senescence-associated β-galactosidase assay. An MDA-MB-231 xenograft in vivo model was treated with bocodepsin, doxorubicin, or the combination and assessed for inhibition of tumor growth. shRNA knockdown of p53 was performed in the CAL-51 cell line and proliferation, apoptosis and senescence were assessed in response to combination treatment.

RESULTS

OKI-005 and doxorubicin resulted in synergistic antiproliferative activity in TNBC cells lines regardless of p53 mutation status. The combination led to increased apoptosis and decreased senescence. In vivo, the combination resulted in increased tumor growth inhibition compared to either single agent. shRNA knock-down of p53 led to increased doxorubicin-induced senescence that was decreased with the addition of OKI-005 in vitro.

CONCLUSION

The addition of bocodepsin to doxorubicin resulted in synergistic antiproliferative activity in vitro, improved tumor growth inhibition in vivo, and promotion of apoptosis which makes this a promising combination to overcome doxorubicin resistance in TNBC. Bocodepsin is currently in clinical development and has a favorable toxicity profile compared to other HDAC inhibitors supporting the feasibility of evaluating this combination in patients with TNBC.

Abstract 136: Doxorubicin-induced senescence as a mechanism of resistance in TNBC cell lines

Background: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer which lacks HER2 overexpression, as well estrogen and progesterone receptor expression. TNBC constitutes 10-15% of all breast cancers but has a worse prognosis due to limited treatment options and high rates of metastatic recurrence. Doxorubicin (dox) remains one of the most active chemotherapy agents for the treatment of TNBC, although de novo and acquired resistance to chemotherapy remains a major challenge. The purpose of this work was to characterize dox resistant cell phenotypes and investigate treatment-induced senescence in p53-mutated (Mut) and wildtype (WT) TNBC cell lines.

Methods: A panel of 12 TNBC cell lines (p53 WT and p53 Mut) were exposed to dox (0-5 uM) for 72 hours and cellular proliferation was determined using the Cell Titer Glo assay. A subset of sensitive and resistant cell lines were treated with dox (0.1, 0.25 uM) or vehicle control and apoptosis was determined by flow cytometry (Annexin-V) at 24 and 48 hrs. Cells were treated with dox or control for 24 hrs and western blotting was performed for mediators of apoptosis. Senescence was analyzed by ß-galactosidase staining following treatment with dox for 3-14 days. shRNA knockdown (KD) of p53 was performed in the CAL-51 (p53 WT cell line) and cells were subject to investigations above.

Results: Doxorubicin treatment resulted in decreased cellular proliferation and increased apoptosis as assessed by Annexin-V expression in a subset of p53 WT and p53 Mut cell lines. Treatment with dox resulted in an increase in the pro-apoptotic proteins BID and p21, as well as a decrease in VAMP in sensitive cell lines. In a subset of cell lines resistant to dox treatment, we observed an increase in cells demonstrating phenotypic features of senescence and ß -galactosidase staining. We observed a decrease in p16 with dox treatment in the CAL-51 (p53 WT cell line) compared to an increase following treatment in p53 Mut cell lines. KD of p53 resulted in an increase in senescent cells following treatment with low dose dox.

Conclusions: Treatment with doxorubicin resulted in different terminal cell phenotypes in TNBC cell lines with apoptosis observed in p53 WT and Mut cell lines. Senescence was observed in resistant cells and KD of p53 increased dox-induced senescence, confirming a role for p53 in mediating terminal cell fate. Efforts are ongoing to understand the role of mutant p53 in mediating terminal cell fate in response to dox and rational combinations to overcome dox-induced senescence may be clinically active in metastatic TNBC.

Citation Format: Stephen G. Smoots, Anna R. Schreiber, Betelehem Yacob, Adrian Dominguez, Cecilia Levandowski, Todd M. Pitts, Jennifer R. Diamond. Doxorubicin-induced senescence as a mechanism of resistance in TNBC cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 136.