High blood sugar levels but not diabetes mellitus significantly enhance oxaliplatin chemoresistance in patients with stage III colorectal cancer receiving adjuvant FOLFOX6 chemotherapy

Abstract

Background: The high prevalence of type 2 diabetes mellitus (DM) among patients with colorectal cancer (CRC) is becoming a serious public health concern worldwide. FOLFOX4 chemotherapy is one of the most widely used adjuvant therapies in patients with stage III colon cancer after surgical resection. However, chemotherapy resistance is associated with a poor prognosis. The prognostic impact of high blood sugar levels on oxaliplatin resistance in CRC patients is an unexplored topic.

Methods: In total, 157 patients with stage III CRC were classified according to their fasting blood sugar level (⩾126 or <126 mg/dl). Clinicopathological features and oxaliplatin chemoresistance/survival outcome of the two groups were compared. In vitro cell proliferation assay was performed through d-(+)-glucose administration.

Results: Multivariate analysis results revealed that high blood sugar level was a significantly independent prognostic factor of disease-free survival and overall survival (both p < 0.05), but not DM history. After metformin administration, enhanced proliferation of CRC cells (HT-29, HCT-116, SW480, and SW620) with d-(+)-glucose administration could be reversed and oxaliplatin chemosensitivity considerably increased (p < 0.05). Furthermore, phosphorylation of two glycolysis-related target proteins, SMAD3 and MYC, notably increased under high glucose concentration.

Conclusions: Hyperglycemia can affect clinical outcomes in stage III CRC patients receiving adjuvant chemotherapy, and the mechanism underlying oxaliplatin resistance is possibly associated with increased phosphorylation of SMAD3 and MYC and upregulation of EHMT2 expression.

Keywords: adjuvant chemotherapy; colorectal cancer; hyperglycemia; oxaliplatin resistance; prognosis.

Figure 1.

Effect of different metformin concentrations (0, 5, and 10 mM) on colon cancer cell proliferation under different glucose conditions using the CCK-8 assay. No metformin sample was normalized to 100% for all glucose concentrations as control. (A–D) Proliferation of HT-29, HCT-116, SW480, and SW620 cells decreased significantly after 24-h incubation with increasing metformin concentrations. Compared with 0 mM metformin, the proliferation rate of HT-29 and HCT-116 cells decreased significantly after metformin administration (1 and 5 mM; p value as shown).

Figure 2.

Assessment of the effects of oxaliplatin and metformin chemotoxicity on colon cancer cells using the CCK-8 assay. Compared with the proliferation rates of cells grown in 15 mM d-(+)-glucose without oxaliplatin and metformin treatment, those of the HT-29 (A), HCT-116 (B), SW480 (C), and SW620 (D) cells decreased significantly after oxaliplatin and metformin treatment.

Figure 3.

(A) Western blotting of proteins involved in the development of oxaliplatin resistance in SW620 cells. MYC and EHMT2 expression levels increased significantly at high glucose concentrations (15 mM glucose; lane 2), whereas SMAD3 expression level did not. Phosphorylation of SMAD3 and MYC also increased considerably at high glucose concentrations, but, after adding metformin, the increase in phosphorylation could be reversed (lanes 3 and 4). The upregulation of EHMT2 expression could also be reversed after metformin administration (lanes 3 and 4). (B) The proposed mechanism of the effect of high glucose concentrations on the oxaliplatin resistance of CRC. CRC, Colorectal cancer.

Figure 4.

Cumulative survival rates for the 157 UICC stage III CRC patients assessed using the Kaplan–Meier method, and differences in survival rates analyzed using a log-rank test. (A) Disease-free survival. With 2 years as the endpoint, the DFS of patients in the high blood glucose group (⩾126 mg/dl) was significantly poorer than that of patients in the low blood glucose group (<126 mg/dl; p = 0.012). (B) Overall survival. With 2 years as the endpoint, the OS of patients in the high blood glucose group (⩾126 mg/dl) was significantly poorer that of patients in the low blood glucose group (<126 mg/dl; p = 0.041). CRC, Colorectal cancer; DFS disease-free survival, OS, overall survival; UICC, Union for International Cancer Control.