: Generally, heterocyclic compounds are included in a large class of pharmacologically active compounds. The indole scaffold in this category is widely distributed in nature and present in many active compounds, especially anti-cancer agents. Due to its unique physicochemical and biological properties, the indole platform has been considered a favorable scaffold in anti-cancer drug design and development. Various indole compounds (synthetic, semisynthetic, and natural) show remarkable anti-proliferative activity. According to the recent literature, this review describes the role of indole scaffolds as anti-cancer agents. Indole was reported to induce anti-tumor activity through multiple mechanisms, for example, Epidermal Growth Factor Receptors (EGFR), histone deacetylase (HDAC), kinase, DNA-topoisomerases, and tubulin inhibition. The current review focuses on some indole compounds with amazing effects against different types of cancers as there are too many FDA-approved drugs, for example, osimertinib, alectinib, and anlotinib in NSCLC treatment, panobinostat in multiple myeloma, midostaurin in acute myeloid leukemia treatment, etc. Moreover, several compounds are still in clinical trials to treat different cancer types. Additionally, there are some oxindole derivatives with potent inhibition against different types of tumors, such as ovarian cancer, colorectal cancer, and prostate cancer. Different series of oxindoles are promising and recommended for further studies due to their remarkable inhibition of tumor cells. Accordingly, the collection of data on a pharmacologically significant motif might aid researchers in further employing indoles in developing novel anti-cancer drugs with potentially fewer side effects and higher potency against this rapidly spreading disease.

A series of 3-benzylideneindolin-2-one compounds was designed and synthesized based on combretastatin A-4 and compound IC261, a dual casein kinase (CK1)/tubulin polymerization inhibitor, taking into consideration the pharmacophore required for EGFR-tyrosine kinase inhibition. The new molecular entities provoked significant growth inhibition against PC-3, MCF-7 and COLO-205 at a 10 μM dose. Compounds 6-chloro-3-(2,4,6-trimethoxybenzylidene) indolin-2-one, 4b, and 5-methoxy-3-(2,4,6-trimethoxybenzylidene)indolin-2-one, 4e, showed potent activity against the colon cancer COLO-205 cell line with an IC₅₀ value of 0.2 and 0.3 μM. A mechanistic study demonstrated 4b’s efficacy in inhibiting microtubule assembly (IC₅₀ = 1.66 ± 0.08 μM) with potential binding to the colchicine binding site (docking study). With an IC₅₀ of 1.92 ± 0.09 μg/mL, 4b inhibited CK1 almost as well as IC261. Additionally, 4b and 4e were effective inhibitors of EGFR-TK with IC₅₀s of 0.19 μg/mL and 0.40 μg/mL compared to Gifitinib (IC₅₀ = 0.05 μg/mL). Apoptosis was induced in COLO-205 cells treated with 4b, with apoptotic markers dysregulated. Caspase 3 levels were elevated to more than three-fold, while Cytochrome C levels were doubled. The cell cycle was arrested in the pre-G1 phase with extensive cellular accumulation in the pre-G1 phase, confirming apoptosis induction. Levels of cell cycle regulating proteins BAX and Bcl-2 were also defective. The binding interaction patterns of these compounds at the colchicine binding site of tubulin and the Gifitinib binding site of EGFR were verified by molecular docking, which adequately matched the reported experimental result. Hence, 4b and 4e are considered promising potent multitarget agents against colon cancer that require optimization.