Antitumour potential of BPT: a dual inhibitor of cdk4 and tubulin polymerization

Abstract

The marine natural product fascaplysin (1) is a potent Cdk4 (cyclin-dependent kinase 4)-specific inhibitor, but is toxic to all cell types possibly because of its DNA-intercalating properties. Through the design and synthesis of numerous fascaplysin analogues, we intended to identify inhibitors of cancer cell growth with good therapeutic window with respect to normal cells. Among various non-planar tryptoline analogues prepared, N-(biphenyl-2-yl) tryptoline (BPT, 6) was identified as a potent inhibitor of cancer cell growth and free from DNA-binding properties owing to its non-planar structure. This compound was tested in over 60 protein kinase assays. It displayed inhibition of Cdk4-cyclin D1 enzyme in vitro far more potently than many other kinases including Cdk family members. Although it blocks growth of cancer cells deficient in the mitotic-spindle checkpoint at the G0/G1 phase of the cell cycle, the block occurs primarily at the G2/M phase. BPT inhibits tubulin polymerization in vitro and acts as an enhancer of tubulin depolymerization of paclitaxel-stabilized tubulin in live cells. Western blot analyses indicated that, in p53-positive cells, BPT upregulates the expression of p53, p21 and p27 proteins, whereas it downregulates the expression of cyclin B1 and Cdk1. BPT selectively kills SV40-transformed mouse embryonic hepatic cells and human fibroblasts rather than untransformed cells. BPT inhibited the growth of several human cancer cells with an IC50 <1 μM. The pharmacokinetic study in BALB/c mice indicated good plasma exposure after intravenous administration. It was found to be efficacious at 1/10th the maximum-tolerated dose (1000 mg/kg) against human tumours derived from HCT-116 (colon) and NCI-H460 (lung) cells in SCID (severe-combined immunodeficient) mice models. BPT is a relatively better anticancer agent than fascaplysin with an unusual ability to block two overlapping yet crucial phases of the cell cycle, mitosis and G0/G1. Its ability to effectively halt tumour growth in human tumour-bearing mice would suggest that BPT has the potential to be a candidate for further clinical development.

Downregulated CDK10 expression in gastric cancer: Association with tumor progression and poor prognosis

“…Therefore, our study emphasizes the critical role of CDK10 as a prognostic biomarker for gastric cancer with great therapeutic promise. Although multiple CDK proteins, particularly those with great therapeutic promise, have been evaluated for prognosis and cancer therapy (19)(20)(21), studies on CDK10 have so far only focused on several cancer types. Our current analysis in gastric cancer documents that a connection exists between negative CDK10 expression with severe tumor progression phenotype, including advanced tumor stage, lymph node and distant metastasis, and poor tumor differentiation.…”

Current advances of tubulin inhibitors as dual acting small molecules for cancer therapy

“…These dual inhibitors, in many cases, through their multiple MOAs, have been observed to cause substantially enhanced apoptosis of cancer cells and strongly overcome cancer cell resistance compared with their single inhibitor counterparts . Additionally, numerous tubulin/kinase dual inhibitors have been observed to demonstrate substantially lower toxicities to normal cells with significantly higher maximum tolerated dose (MTD), overcoming one of the major limitations of single‐tubulin inhibitor–based therapeutic agents . In the event of dual inhibition, it is difficult to understand which MOA is responsible for the underlying cell toxicity and cell cycle arrest, given that both kinase and tubulin inhibitors are responsible for either phenotype .…”

“…The marine natural product fascaplysin is known to be one of the most potent cyclin‐dependent kinase 4 (CDK4) specific inhibitors . However, fascaplysin exhibits high toxicities due to its DNA intercalating properties .…”

“…[143][144][145][146][147][148][149] Additionally, numerous tubulin/kinase dual inhibitors have been observed to demonstrate substantially lower toxicities to normal cells with significantly higher maximum tolerated dose (MTD), overcoming one of the major limitations of single-tubulin inhibitor-based therapeutic agents. 147,150,151 In the event of dual inhibition, it is difficult to understand which MOA is responsible for the underlying cell toxicity and cell cycle arrest, given that both kinase and tubulin inhibitors are responsible for either phenotype. 140,142,144,145,147 In recent years, cell cycle arrest analysis at G 0 /G 1 phase and at G 2 /M phase as well as image analysis of cellular phenotypes has provided insight into a drug candidate's dual MOAs.…”

“…150,170 However, fascaplysin exhibits high toxicities due to its DNA intercalating properties. 150,171 As of recent, Mahale et al 150 identified a nonplanar tryptoline analogue, BPT (66), as potent CDK4 D1 enzyme specific inhibitor and did not demonstrate DNA binding properties, primarily due to its planar structure. BPT has shown cytotoxicity across p53-positive, p53-negative, pRb-positive, and pRb-negative cell lines with IC 50 < 1 µM, suggesting that antitumor efficacy is independent of tumor suppressor proteins, namely p53 and pRb.…”