Therapeutic Targeting of the Pentose Phosphate Pathway in Colorectal Cancer Using 6-Aminonicotinamide and 5-Fluorouracil.

Abstract

Colorectal cancer (CRC) is a significant global health concern with rising incidence and mortality rates. 5-Fluorouracil (5-FU) is the standard chemotherapy for CRC but is often constrained by resistance and toxicity, highlighting the need for more efficient treatments. The pentose phosphate pathway (PPP), a glucose metabolic shunt, is significantly upregulated in CRC to support nucleotide synthesis and redox balance. Therefore, we hypothesized that targeting the PPP decreases CRC cell growth, reduces tumor progression, and improves 5-FU therapy. Consequently, we investigated the anti-tumor activities, cell death mechanism, and mode of action of the PPP inhibitor, 6-aminonicotinamide (6-AN), and 5-FU alone or in combination against CRC. We used human CRC cell lines with different p53 and 5-FU resistance statuses and a CRC xenograft model. Our findings show that 6-AN reduced the viability of human CRC cells independently of their p53 and 5-FU resistance profile, with its effect further enhanced in combination with 5-FU. The 6-AN/5-FU combination treatment synergized by reducing the total dehydrogenase activity of the PPP, inducing oxidative stress, and promoting senescence in CRC cells. Furthermore, 6-AN treatment significantly decreased tumor growth in a CRC xenograft mouse model. However, combining 6-AN with 5-FU did not reduce tumor volume significantly, highlighting the complexities of translating in vitro findings to animal models. These results suggest that interfering with the PPP activity suppresses CRC cell growth and may reduce 5-FU resistance. This study underscores targeting cancer metabolism as a novel therapeutic strategy to minimize drug resistance and to improve CRC therapeutic outcomes.