Downregulation of the unfolded protein response by metformin may confer antineoplastic effects in colorectal cancer

Abstract

In 2020, there were 1.93 million cases of colorectal cancer (CRC) diagnosed and 935 thousand CRC-related deaths (1–3). Approximately 50 percent of patients are diagnosed with stage III or IV disease, limiting the efficacy of available treatments (4). Type 2 diabetes mellitus (T2D) is a risk factor for CRC development and progression. Nonetheless, metformin-treated diabetic CRC patients tend to have better clinical outcomes than diabetic CRC patients not exposed to metformin. Thus, we sought to investigate the molecular underpinnings of metformin’s protective effects to determine whether its mechanism could be exploited to improve patient outcomes.

We performed a targeted transcriptomic analysis of primary CRC tissue samples (N = 272). Next, a supervised learning algorithm was used to pinpoint features discriminating between metformin-treated and diet-controlled diabetic CRC samples, as well as those discriminating between non-diabetic samples based on their five-year survival status; these features were used to generate corresponding classification models. Finally, we analyzed the differential gene expression patterns in diabetic treatment groups and non-diabetic survival categories to identify expression profiles suggesting that a gene and/or pathway may be linked to metformin’s antineoplastic effects.

Our results show downregulation of TMEM132 in metformin-treated samples (p = 0.053) and non-diabetics with good clinical outcomes (p = 0.053) relative to diet-controlled and non-diabetics with poor survival, respectively; SCNN1A was upregulated in metformin-treated samples (p = 0.044) and non-diabetics with good clinical outcomes (p = 0.011) relative to diet-controlled samples and those with poor clinical outcomes, respectively; FN1 was downregulated in metformin-treated samples relative to diet-controlled samples (p = 0.121). These findings suggest a role for the unfolded protein response (UPR) in mediating metformin-related CRC protective effects, by enhancing apoptosis. We also show that sFas, an antiapoptotic protein, is downregulated in metformin-treated samples relative to diet-controlled samples (p = 0.005). Therefore, metformin may synergistically enhance apoptosis through the regulation of Fas alternative splicing, inhibiting CRC development and progression. Taken together, we outline two key cellular processes that may be implicated in metformin’s antineoplastic action and provide justification for further investigation of these pathways to determine if they may be targets for novel CRC therapies.