Glucose Restriction Combined with Autophagy Inhibition and Chemotherapy in HCT 116 Spheroids Decreases Cell Clonogenicity and Viability Regulated by Tumor Suppressor Genes

Drug
resistance is a prevalent phenomenon that decreases the efficacy
of cancer treatments and contributes to cancer progression and metastasis.
Weakening drug-resistant cancer cells prior to chemotherapy is a potential
strategy to combat chemoresistance. One approach to damage resistant
cancer cells is modulation of nutritional intake. The combination
of nutrient restriction with targeted compound treatment results in
pronounced molecular changes. This study provides valuable information
about augmenting existing chemotherapeutic regimes with simultaneous
glucose restriction and autophagy inhibition in colorectal cancer
cells. In this study, we explore the chemical pathways that drive
the cellular response to nutrient restriction, autophagy inhibition,
and the chemotherapy irinotecan using global quantitative proteomics
and imaging mass spectrometry. We determined that significant pathways
were altered including autophagy and metabolism via glycolysis, gluconeogenesis,
and sucrose degradation. We also found that period circadian clock
2 (PER2), a tumor suppressor protein, was significantly up-regulated
only when glucose was restricted with autophagy inhibition and chemotherapy.
The upstream regulators of these differentially regulated pathways
were determined to have implications in cancer, showing an increase
in tumor suppressor proteins and a decrease in nuclear protein 1 (NUPR1)
an important protein in chemoresistance. We also evaluated the phenotypic
response of these cells and discovered autophagy inhibition and chemotherapy
treatment increased apoptosis and decreased cell clonogenicity and
viability. When glucose restriction was combined with autophagy inhibition
and chemotherapy, all of the phenotypic results were intensified.
In sum, our results indicate that glucose metabolism is of great importance
in the ability of cancer cells to survive chemotherapy. By weakening
cancer cells with glucose restriction and autophagy inhibition prior
to chemotherapy, cancer cells become more sensitive to therapy.