Table III:

In vitro studies of drug resistance in 3D-breast cancer tumor models

Cell line model	Drugs Tested	Conclusion	Ref
MCF-7	Doxorubicin (3μM,18 h) Verapamil (Pgp inhibitor, 100μM) YC-1 (5μM, 24h)	MCF-7 3D-spheroids resistant to doxorubicin associated with elevated Pgp expression via activation of HIF-1α	[205]
MDA-MB-231	Paclitaxel (1–10nM) Doxorubicin (0–10nM)	Hypoxic spheroids resistant to paclitaxel and doxorubicin show progression	[207]
BT-549	Paclitaxel Doxorubicin	Dense spheroid formation simulates hypoxia, anti-apoptotic features and drug resistance	[138]
BT-474
T-47D
MCF-7
DA-MB-231
HCC-1954
MCF10A-ERBB2 MTEC-Neu SK-BR3	Lapatinib (1μM) Trametinib (MEK inhibitor)	HIF-1 blocks lapatinib mediated effects in ERBB2 cells and maintain downstream ERK signaling via inhibition of DUSP2. Trametinib treatment reverses hypoxia- mediated lapatinib resistance	[206]
MDA-MB-157 3D	Doxorubicin (100*10⁻⁹M) 5-Fluorouracil TH-302 (Hypoxia-activated prodrug)	Combination treatment (TH-302 and doxorubicin) targets drug resistant spheroids	[211]
MDA-MB-231 RAW 264.7	Paclitaxel (10ng/mL) Tyrphostin AG 1478(EGFR inhibitor)	Macrophages in heterotypic spheroids increase resistance to paclitaxel	[186]
BT-474		HER2+ BT-474 spheroids resistant to trastuzumab with increased breast cancer cells	[210]
MCF-7	Doxorubicin	Hypoxic cancer stem cells illicit high drug resistance to doxorubicin compared to normoxic cancer stem cells	[182]
MCF-7 MDA-MB-231	Paclitaxel Gemcitabine Adriamycin	Survival rates of breast cancer stem cells high in MCF-7 spheroid cells with drug treatment	[209]
MDA-MB-231	Doxycycline (5μg/μL) Doxorubicin (1μM)	AMPK mediates hypoxia induced drug resistance in MDA-MB-231 cells via Notch1 signaling	[208]
MCF-7	Tamoxifen Fulvestrant	Hypoxia induces switch in SNAT2/SLC38A2 regulation which leads to resistance to anti-hormone therapy	[212]

P-glycoprotein (Pgp), Hypoxia inducible factor 1 alpha (HIF-1α), Erb-B2 receptor tyrosine kinase 2 (ERBB2), Extracellular signal regulated kinase (ERK), Dual specificity phosphatase 2 (DUSP2), Mitogen activated protein kinase (MEK), Epidermal growth factor receptor (EGFR), Human epidermal growth factor receptor 2 (HER2), 5’-Adenosine monophosphate activated protein kinase (AMPK), Sodium-coupled neutral amino acid transporter 2 (SNAT2), Solute carrier family 38 member 2 (SLC38A2).