Background: Retinoblastoma is a sight and life-threatening embryonal tumor in children.
Though chemotherapy is the main mode of therapy, evolving resistance remains a major obstacle in
treatment success. The presence of cancer stem cells (CSC) is frequently reported to be responsible
for chemoresistance in multiple tumors.
Objective: Our study aims to identify the molecular factors that facilitate the chemoresistance
through cancer stem cells in retinoblastoma.
Methods: We developed etoposide and carboplatin resistant retinoblastoma (Y79) cell lines by
stepwise drug increment treatment, validated with MTT and TUNEL assays. Colony forming and
invasive ability were studied by soft-agar colony forming and transwell assays, respectively. Similar
analysis in non-responsive retinoblastoma tumors were carried out by histopathology. Finally, expression
of CSC/neuronal markers and ABC transporters were examined by quantitative PCR and
protein expression of neuronal stem cell markers was confirmed by Western blot.
Results: Larger colony size of resistant cells in soft-agar assay provided evidence for increased selfrenewability.
Histopathology in non-responsive tumors showed poorly differentiated cells predominantly.
Besides, both resistant cell lines and non-responsive tumors showed increased invasion with
higher expression of neuronal stem cell markers - SOX2, NANOG, OCT4 and ABC transporters -
ABCB1 and ABCC3. Increased self-renewal ability and invasion along with overexpression of
stemness markers in resistant cells and tumors provide evidence for stemness driving chemoresistance
and invasion in retinoblastoma.
Conclusion: We have demonstrated Neuronal stem cell/CSC markers that facilitate the maintenance
of cancer stem cells. Developing therapies targeting these factors will help in overcoming resistance
and improving retinoblastoma treatment.