A comprehensive review of alkaloids in cancer therapy: focusing on molecular mechanisms and synergistic potential of piperine in colorectal cancer.

Alkaloids exhibit a wide range of anticancer activities, including the induction of apoptosis, regulation of autophagy, arrest of the cell cycle, inhibition of angiogenesis, and disruption of oncogenic signaling pathways. Among these compounds, piperine, a piperidine alkaloid derived from black pepper, demonstrates multifaceted activity against colorectal cancer (CRC). Preclinical studies indicate that piperine induces apoptosis through mitochondrial and reactive oxygen species (ROS)-mediated mechanisms, arrests the cell cycle at the G0/G1 and S phases, and suppresses oncogenic signaling pathways, such as Wnt/β-catenin, STAT3/Snail-EMT, and PI3K/Akt/mTOR pathways. Furthermore, it modulates inflammatory and oxidative stress responses by inhibiting NF-κB and activating Nrf2/Keap1 signaling while reducing angiogenesis via Src/EGFR-IL-8 regulation. These multi-targeted actions result in decreased proliferation, migration, invasion, and metastasis of CRC cells. In addition to its intrinsic anticancer properties, piperine serves as a potent natural bio-enhancer. Combination studies revealed synergistic effects with chemotherapeutics (celecoxib, apatinib), radiotherapy, and nutraceuticals (curcumin, resveratrol, and cannabinoids), significantly enhancing therapeutic efficacy and overcoming drug resistance. However, its pharmacokinetic limitations-poor aqueous solubility, rapid metabolism, and low oral bioavailability-pose challenges to its clinical application. Pharmacokinetic analyses reveal high lipophilicity, extensive distribution, and rapid elimination, necessitating innovative strategies to improve systemic stability. Recent advancements include nano-formulations (liposomal, polymeric, and lipid-polymer hybrids) and structural analogs, which increase solubility, stability, bioavailability, and targeted delivery, thereby increasing anticancer efficacy. A comparative evaluation with other alkaloids indicates that while piperine exhibits moderate direct cytotoxicity relative to agents such as camptothecin or berberine, its unique value lies in its broad pathway modulation ability and synergistic potential as an adjuvant. Collectively, mechanistic insights, pharmacologic evaluations, and combinational strategies establish piperine as a promising multifunctional agent for CRC prevention and therapy. Nonetheless, standardized preclinical methodologies, detailed pharmacokinetic profiling, and well-structured early-phase clinical trials are critical to validate its translational potential and facilitate its integration into colorectal cancer management.