ABSTRACT
Metaplastic breast cancer (MpBC) is a rare subset accounting for <1% of all breast cancers. However, MpBC is
a significant health challenge as it exhibits the most dismal prognosis of all breast cancers, even worse than
triple-negative breast cancer (TNBC), with a survival rate of 8 months or less in patients with metastatic disease.
Due to a lack of druggable targets, the main therapeutic option for metastatic MpBC remains systemic
chemotherapy, despite known resistance to most cytotoxic drugs. One common molecular alteration in MpBC is
hyperactivation of the phosphoinositide 3-kinase and protein kinase B (PI3K/AKT) pathway. Additionally, we
recently published that MpBC displays a gain-of-function oncogenic mutation in ribosomal protein L39 (RPL39),
which is responsible for treatment resistance, stem cell self-renewal, and lung metastasis. The mechanistic
function of RPL39 is mediated through inducible nitric oxide synthase (iNOS)-mediated nitric oxide production.
In addition, we demonstrated in a completed clinical trial that inhibiting this nitric oxide synthase (NOS) pathway
using pan-NOS inhibitor NG-methyl-L-arginine acetate (L-NMMA) may represent a highly effective therapeutic
option for TNBC patients. Therefore, we hypothesize that a combinatorial targeted approach of inhibiting
the two major oncogenic pathways implicated in MpBC, PI3K/AKT and NOS, would lead to significant
tumor regression. To test this hypothesis, this U01 application brings together research teams from Houston
Methodist Cancer Center (HMCC), The University of Texas MD Anderson Cancer Center, and the National
Cancer Institute (NCI). Specific Aim 1 seeks to define whether dual inhibition of PI3K/AKT using alpelisib and
NOS inhibition using L-NMMA combined with nab-paclitaxel will increase the objective response rate and survival
in metastatic MpBC patients. In Specific Aim 2, using blood and core biopsy tissues collected in the trial, we will
identify mechanisms of response to therapy to determine the efficacy of the targeted PI3K/AKT and NOS
pathway inhibitory approach. Furthermore, the cell-cell interactions among tumor cells, myeloid cells, lymphoid
cells, and stromal cells within the tumor microenvironment and their role in supporting cancer stem cell
populations and drug-resistant cell development during treatment will be evaluated. The impact of distinct cellular
localization patterns within the tumor ecosystem on the process of cancer stem cell maintenance and modulation,
as well as the development of drug resistance, will be analyzed at the single-cell level using spatial
transcriptomics, immunofluorescence, CyTOF imaging systems, and a multi-modal data analysis model. This
study thus proposes a mechanistic investigation of a combinatorial targeted approach against the two key
pathways in MpBC, develops unique crosstalk models, and identifies biomarkers of resistance and cell–cell
interactions using specimens derived from MpBC patients.
