In vivo Antitumor, Pharmacological and Toxicological Study of Pyrim-ido[4',5':4,5]thieno(2,3-b)quinoline with 9-hydroxy-4-(3-diethylaminopropylamino) and 8-methoxy-4-(3-diethylaminopropylamino) Substitutions

BACKGROUND

We previously synthesized two DNA intercalative pyrim-ido[4',5':4,5]thieno(2,3-b) quinolines (PTQ), 9-hydroxy-4-(3-diethylaminopropylamino)pyrimido[4',5':4,5]thieno(2,3-b) quinolines (Hydroxy-DPTQ) and 8-methoxy-4-(3-diethylaminopropylamino) pyrimido[4',5':4,5]thieno(2,3-b) quinolines (Methoxy-DPTQ), and reported their cytotoxicity against cancer cell lines.

OBJECTIVE

In the present study, we sought to analyze the antitumor activity of Hydroxy-DPTQ and Methoxy-DPTQ on Ehrlich's ascites carcinoma in vivo models, along with other pharmacological activities and toxicity.

METHODS

Antitumor activity, In vivo antioxidant measurement, Anti-inflammatory activity Analgesic activity, Hematological study, Biochemical parameters, and Nephroprotective ac-tivity.

RESULTS

In this study, both the test molecules studied possess potent in vivo antitumor activi-ty without any hematological, biochemical or nephrotoxicity. Significant tumor regression was observed after treatment with both the test molecules, which is suggested by the decrease in the body weight of tumor bearing mice. Mean survival time of mice with tumor was increased from 16 days to 25 and 29 days after 40 and 80 mg/kg Hydroxy-DPTQ treatment, respectively, with a similar result for Methoxy-DPTQ. A dose dependent increase in lifespan upto 80-85% was also displayed by both Hydroxy-DPTQ and Methoxy-DPTQ. Reduction in the tumor volume of mice, upon treatment with molecules also confirmed their antitumor activity. These molecules also exhibited pharmacological activities such as antioxidant, anti-inflammatory and analgesic activities. Administration of Hydroxy-DPTQ and Methoxy-DPTQ not only reduced the level of lipid peroxidation in tumor bearing mice, but also restored the superoxide dismutase, glutathione and catalase levels to normal, substantiating the antioxidant property. Also, treatment of Hydroxy-DPTQ and Methoxy-DPTQ inhibited the pain to approximately 60-80% and 19-33%, respectively. Further, the treatment with Hydroxy-DPTQ and Methoxy-DPTQ reversed the abnormality in the RBC, WBC and haemoglobin levels, and gentamicin induced nephrotoxicity.

CONCLUSION

Hydroxy-DPTQ and Methoxy-DPTQ are good antitumor molecules with phar-macological properties.

The correlation between insulin and OCT-6 transcription factor in Schwann cells and sciatic nerve of diabetic rats

Insulin signal is one of the vital signaling cascade required for Schwann cells to myelinate the axons of peripheral nervous system (PNS). Myelin formation of peripheral nerve is a complex molecular event controlled by different neurotrophic and transcription factors. The altered or failure in this signaling progression is one of the reasons behind the demyelination of peripheral neurons in diabetic peripheral neuropathy (DPN). The Schwann cell in PNS includes POU domain transcription factor OCT-6 expression. This factor is considered as crucial for the initiation and enhancement of myelination during nerve regeneration. To know the importance of OCT-6 gene, here we studied the long term expression of OCT-6 nuclear protein in sciatic nerve of normal and diabetic neuropathic rats. Also for the first time we elucidated the role of insulin in controlling the expression of OCT-6 in hyperglycemic Schwann cells and sciatic nerve of diabetic neuropathic rats. The results shows that, there will be long term OCT-6 expression in sciatic nerve of adult rats and also their significant decrease is observed in the diabetic condition. But, addition of Insulin for primary Schwann cells and diabetic rats shows the increased OCT-6 expression in both invivo and invitro. Together these results indicate the failure of OCT-6 support in neuropathy and also the importance of insulin signaling cascade in the expression of OCT-6 transcription factor.

Insulin-induced upregulation of lipoprotein lipase in Schwann cells during diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is one of the major complications associated with diabetes. It is characterized by the degeneration of the myelin sheath around axons, referred to as demyelination. Such demyelinations are often caused by reduced lipid component of the myelin sheath. Since, lipoprotein lipase (LPL) provides the lipid for myelin sheath by hydrolysing the triglyceride rich lipoproteins, and also helps in the uptake of lipids by the Schwann cells (SCs) for its utilization, LPL is considered as the important factor in the regeneration of myelin sheath during diabetic neuropathy. Earlier reports from our laboratory have provided the insights of insulin and its receptor in SCs during diabetic neuropathy. In order to evaluate the long term effect of insulin on lipid metabolism during diabetic neuropathy, in this study, we analyzed the expression of LPL in SCs under normal, high glucose and insulin treated conditions. A decrease in the expression of LPL was observed in SCs of high glucose condition and it was reversed upon insulin treatment. Histochemical observations of sciatic nerve of insulin treated neuropathy subjects showed the improved nerve morphology, signifying the importance of insulin in restoring the pathophysiology of diabetic neuropathy.

Altered expression of IRS2 and GRB2 in demyelination of peripheral neurons: Implications in diabetic neuropathy

Demyelination of the peripheral nerves and dysfunction of Schwann cells (SCs) are the chronic complications involved in the development of peripheral neuropathy among diabetic patients. Insulin signaling plays an important role in restoring the myelin proteins in diabetic peripheral neuropathy (DPN). Since insulin levels are altered in diabetes, it becomes of great interest to appreciate the role and regulation of docking and adaptor protein, how these proteins respond to variations in the levels of insulin as experienced in juvenile diabetes. Tyrosine phosphorylation of receptor protein kinases provides a docking site for the activation of adaptor proteins which are the key regulators of insulin signaling pathway. In this report, we studied the long term effect of insulin as a neurotrophic factor and identified the isoform of receptor substrate involved in the propagation of insulin signal in SCs. We also studied the ability of insulin to regulate the expression of different receptor substrates like insulin receptor substrate-1 (IRS1), insulin receptor substrate-2 (IRS2) and growth factor receptor-bound protein-2 (GRB2) that propagate the insulin signaling and also their variation in hyperglycemic SCs and sciatic nerve of the diabetic rats. Results confirmed that IRS2 is the key receptor substrate involved in insulin signal transduction. But, a radical increase in the phosphorylation of IRS2 at serine 731 prevents the recruitment of GRB2 adaptor protein which may fail further to connect the Ras and other pathways required to the cell for its survival and to maintain integrity. These findings prove that SCs and sciatic nerve express IRS proteins that are altered by diabetes and thereby insulin signaling downstream is impaired and that contribute to the pathogenesis of DPN.

Insulin influenced expression of myelin proteins in diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is one of the downstream complications of diabetes. This complication is caused by the deficiency of insulin action and subsequent hyperglycemia, but the details of their pathogenesis remain unclear. Hence, it is of critical importance to understand how such hormonal variation affects the expression of myelin proteins such as myelin basic protein (MBP) and myelin associated glycoprotein (MAG) in the peripheral nerve. An earlier report from our lab has demonstrated the expression of insulin receptors (IR) in Schwann cells (SCs) of sciatic nerve. To assess the neurotrophic role of insulin in diabetic neuropathy, we studied the expression of these myelin proteins under control, DPN and insulin treated DPN subjects at developmental stages. Further, the expression of these myelin proteins was correlated with the expression of insulin receptor. Expression of myelin proteins was significantly reduced in the diabetic model compared to normal, and upregulated in insulin treated diabetic rats. Similarly, an in vitro study was also carried out in SCs grown at high glucose and insulin treated conditions. The expression pattern of myelin proteins in SCs was comparable to that of in vivo samples. In addition, quantitative study of myelin genes by real time PCR has also showed the significant expression pattern change in the insulin treated and non-treated DPN subjects. Taken together, these results corroborate the critical importance of insulin as a neurotrophic factor in demyelinized neurons in diabetic neuropathy.

A Novel Anticancer Agent, 8-Methoxypyrimido[4',5':4,5]thieno(2,3-b) Quinoline-4(3H)-One Induces Neuro 2a Neuroblastoma Cell Death through p53-Dependent, Caspase-Dependent and -Independent Apoptotic Pathways

Neuroblastoma is the most common cancer in infants and fourth most common cancer in children. Despite recent advances in cancer treatments, the prognosis of stage-IV neuroblastoma patients continues to be dismal which warrant new pharmacotherapy. A novel tetracyclic condensed quinoline compound, 8-methoxypyrimido [4',5':4,5]thieno(2,3-b) quinoline-4(3H)-one (MPTQ) is a structural analogue of an anticancer drug ellipticine and has been reported to posses anticancer property. Study on MPTQ on neuroblastoma cells is very limited and mechanisms related to its cytotoxicity on neuroblastoma cells are completely unknown. Here, we evaluated the anticancer property of MPTQ on mouse neuro 2a and human SH-SY5Y neuroblastoma cells and investigated the mechanisms underlying MPTQ-mediated neuro 2a cell death. MPTQ-mediated neuro 2a and SH-SY5Y cell deaths were found to be dose and time dependent. Moreover, MPTQ induced cell death reached approximately 99.8% and 90% in neuro 2a and SH-SY5Y cells respectively. Nuclear oligonucleosomal DNA fragmentation and Terminal dUTP Nick End Labelling assays indicated MPTQ-mediated neuro 2a cell death involved apoptosis. MPTQ-mediated apoptosis is associated with increased phosphorylation of p53 at Ser15 and Ser20 which correlates with the hyperphosphorylation of Ataxia-Telangiectasia mutated protein (ATM). Immunocytochemical analysis demonstrated the increased level of Bax protein in MPTQ treated neuro 2a cells. MPTQ-mediated apoptosis is also associated with increased activation of caspase-9, -3 and -7 but not caspase-2 and -8. Furthermore, increased level of caspase-3 and cleaved Poly (ADP Ribose) polymerase were observed in the nucleus of MPTQ treated neuro 2a cells, suggesting the involvement of caspase-dependent intrinsic but not extrinsic apoptotic pathway. Increased nuclear translocation of apoptosis inducing factor suggests additional involvement of caspase-independent apoptosis pathway in MPTQ treated neuro 2a cells. Collectively, MPTQ-induced neuro 2a cell death is mediated by ATM and p53 activation, and Bax-mediated activation of caspase-dependent and caspase-independent mitochondrial apoptosis pathways.

Intercalative pyrimido[4',5':4,5]thieno(2,3-b)quinolines induce apoptosis in leukemic cells: a comparative study of methoxy and morpholino substitution

DNA intercalating molecules are promising anticancer agents. Polycyclic aromatic molecules such as ellipticine intercalate into double-stranded DNA and affect major physiological functions. In the present study, we have characterized two molecules with the same chemical backbone but different side chains, namely 8-methoxy pyrimido[4',5':4,5]thieno (2,3-b)quinoline-4(3H)-one (MPTQ) and 4-morpholino pyrimido[4',5':4,5]thieno(2,3-b)quinoline (morpho-PTQ) at the 8th and 4th position, respectively. Although both MPTQ and morpho-PTQ show similar biophysical properties with high DNA affinity, here we show that they differ in their biological activities. We find that MPTQ is many fold more potent than morpho-PTQ and is cytotoxic against different leukemic cell lines. IC(50) value of methoxy PTQ was estimated between 2-15 µM among the leukemic cells studied, while it was more than 200 µM when morpho-PTQ was used. Cell cycle analysis shows an increase in sub-G1 phase, without any particular cell cycle arrest. Annexin V staining in conjunction with comet assay and DNA fragmentation suggest that MPTQ induces cytotoxicity by activating apoptosis. Thus the observed low IC(50) value of MPTQ makes it a promising cancer chemotherapeutic agent.