Table 3.

Important molecular roles and processes of resistance gene expression in mammalian cancer stem cells

Resistance Gene	Key Molecular Function	Mechanism of Gene Expression	References
ABC Transporters (e.g., ABCB1, ABCG2)	Efflux of chemotherapeutic drugs	Overexpression or altered expression due to genetic mutations, epigenetic modifications (e.g., DNA methylation, histone modifications), or transcriptional regulation by signaling pathways (e.g., Notch, Wnt)	[115, 265, 266]
DNA Repair Genes (e.g., BRCA1, BRCA2, ATM)	Repair of DNA damage caused by chemotherapy or radiation	Overexpression or enhanced activity due to genetic mutations, epigenetic modifications, or transcriptional regulation by signaling pathways (e.g., PI3K/AKT, NF-κB)	[114, 267, 268]
Anti-Apoptotic Genes (e.g., Bcl-2, Bcl-xL)	Inhibition of apoptosis	Overexpression or altered expression due to genetic mutations, epigenetic modifications, or transcriptional regulation by signaling pathways (e.g., PI3K/AKT, NF-κB)	[110, 138, 269]
Stem Cell Markers (e.g., CD44, CD133, ALDH1)	Maintenance of stem cell phenotype and self-renewal	Overexpression or altered expression due to genetic mutations, epigenetic modifications, or transcriptional regulation by signaling pathways (e.g., Notch, Wnt, Hedgehog)	[22, 107, 194, 270–273]
Epithelial–Mesenchymal Transition (EMT) Markers (e.g., vimentin, N-cadherin, Twist)	Acquisition of migratory and invasive properties	Overexpression or altered expression due to genetic mutations, epigenetic modifications, or transcriptional regulation by signaling pathways (e.g., TGF-β, Wnt, Notch)	[121, 274, 275]
Metabolic Enzymes (e.g., GLUT1, LDHA)	Altered metabolism to support survival and proliferation under stress conditions	Overexpression or altered expression due to genetic mutations, epigenetic modifications, or transcriptional regulation by signaling pathways (e.g., HIF-1α, MYC)	[110, 111, 276]