Selection of proteins
The proteins were selected based on their function in cancer development and progression. Five different proteins (Nf-kB p50 subunit, Nf-kB p65 subunit, MMP 9, Cyclin D1 and Bax) were selected based on its functional role in cancer pathways.
Nuclear factor-kappa B is a transcriptional factor belonging to
rel family that usually exist as dimeric form either as homodimer (p50/p50) or heteromer (p50/p65) in the cytoplasm. In case of tumour cells Nf-kB become active and undergo nuclear translocation where it will activate target genes. It is involved in many immune, inflammatory and apoptotic responses. p50 subunit binds to the DNA while the p65 subunit is responsible for the transcriptional activation (Nail
Besli et al., 2020).
Invasion and metastasis are mainly responsible for the cancer associated deaths. Several proteolytic enzymes take part in the degradation of tumour microenvironment such as extracellular matrix and basement membrane. MMPs are zinc dependent endopeptidase involved in ECM proteolytic process
(Egeblad et al., 2002).
Cancer can be due to the overexpression of proteins associated with cell cycle which can act either as positive or negative regulators. Cyclin proteins (Cyclin D, E, A and B) along with protein kinase group (CDK 4, 6 and 2) act as positive regulators and leads to acceleration of cell cycle
(Sumirtanudin et al., 2020).
Most of the cancer therapy aimed at induction of apoptosis which can be achieved either by intrinsic or extrinsic pathway. The extrinsic pathway is mostly associated in controlling the cell turnover and elimination of mutant cells while intrinsic pathway is involved in antineoplastic drug action. Bax protein is an important mediator in intrinsic pathway which will get activated by DNA fragmentation and in turn activates a cascade of reactions by releasing ‘cytochrome c’ from mitochondria that helps in activation of caspases and ultimately leads to cell death
(Kulsoom et al., 2018).
Ligand preparation
According to Lipinski rule of five
(Lipinski et al., 1997) the compound was filtered as given in Table 2. Drug likeness, ADME and toxicity predictions of curcumin were performed. The pharmacokinetic features of curcumin were satisfactory with human intestinal absorption value of 94.403394, MDCK cell permeability value about 99.9895, skin permeability value of -2. 33227, pure water solubility 10.8005 mg/L, Plasma protein binding 88.030378 and blood barrier penetration value 0.0913545. The toxicity studies showed that curcumin is a non-mutagen as well as non-carcinogen predicted by Ames test and carcinogenicity mice model test, respectively. Drug likeness predictions showed that curcumin has better drug like properties and fulfilling all the five rules.
Molecular docking
Molecular docking between curcumin and various receptors were performed to analyze the inhibitory action of curcumin. Best docking conformations were selected based on docking score and relative energy. The results on molecular docking are summarized in Table 3.The present study showed that curcumin has best binding properties to all receptors screened. Curcumin found to interact with p50 subunit of Nf-kB with a dock sore of 125.428 and binding energy 6.93 (Fig 1). They found to interact with LYS 241 and LEU22 (Fig 2).
Kumar and Bora. (2012) earlier reported similar interactions between curcumin and its derivatives to LYS 241 which was found to be a key residue involved in the binding of Nf-kB with DNA at the consensus sequences through hydrogen bonding. Curcumin also found to bind with p65 subunit of Nf-kB subunit with high affinity (Fig 3 and 4). Nf-kB is a nuclear factor that act on various signaling pathways, involved in cell proliferation and cell survival thereby involve in pathogenesis of cancer. So, inhibitors of Nf-kB likely to have benefits in the treatment of cancer. The present study revealed that curcumin has the ability to bind to both the subunits of Nf-kB with good binding affinity.
MMPs are mostly associated with functioning and migration of cancer cells. The result of present study indicates that curcumin can bind with MMP-9 with a dock score of 114.5 (Fig 5) and it was found that they interact with LEU 39 and ARG 51 with hydrogen bond distance of 1.47 and 1.48 A° (Fig 6).
Jerah et al., (2015) reported that curcumin can bind with MMP-3 with similar binding affinity as that of its known inhibitors and suggested that curcumin can act as a potential starting molecule for the design of anticancer drugs that target MMP enzymes.
The present study results suggested that curcumin can regulate cell cycle and apoptosis by binding with Cyclin D1 and Bax proteins. Curcumin found to interact with ARG26 of cyclin D1 with a hydrogen bond distance of about 1.07 A° (Fig 7 and 8). Curcumin interacts with Bax with a docking score of 98.6844 and binding energy 10.9384 (Fig 9 and 10). The present results also suggested that curcumin can act as a potential starting molecule for the design of anticancerous drug by interacting with multiple targets in the signaling pathways and apoptosis.
