Pharmacology: Tyrosine Kinase Inhibitor - Assignment Example

Pharmacology of the the assignment was due Pharmacology 1. Introduction Tyrosine Kinase Inhibitor (TKI) is an effective drug used in the treatment of many malignancies. The first drug used as TKI was Imatinib (Hartmann et al., 2009). TKI binds to the catalytic site of tyrosine kinase by the mechanism of competitive ATP (Adenosine Triphosphate) inhibition (Hartmann et al., 2009). Tyrosine kinases are the enzymes that catalyze the movement of ɣ phosphate group to the target protein from the ATP molecules. Tyrosine kinase molecules act as the membrane surface protein for the transduction of signals to the cytoplasm. Binding of the specific ligand to the tyrosine kinases result in autophosphorylation of cytoplasmic domains and thereby activates the enzyme. Activated tyrosine kinase in turn activates the signalling pathways such as protein kinase C pathway, Scaffolding proteins, Ras/Raf mitogen – activated protein kinase pathway, and phosphoinositol 3’ – kinase/Akt pathway (Arora and Scholar, 2005). These activated pathways alter the DNA synthesis along with cell growth, differentiation, and others. Almost all the TKI have side effects. The common side effects of TKI are anaemia, neutropenia, oedema, thrombopenia, hypothyroidism, diarrhoea, and vomiting (Hartmann et al., 2009). At the same time, TKI molecules are now approved for clinical trials in human. TKI application for cancer treatment in dogs and cats was approved earlier, with TKI drugs such as Palladia (Toceranid), Gleevec (imatinid) and Kinavet (mastinib) (London, 2009). 2. Non-clinical evaluation a) Safety pharmacology tests and studies: Before conducting the safety pharmacology tests, the regulatory guidelines for testing the undesirable pharmacodynamics effects on physiological functions should be focused. This is because, in the early phase pharmacology studies, all risk factors can be found out and eliminated. TKI are found to have adverse cardiovascular effects. So, when testing TKI in dogs and cats, telemetry has to be used for the continuous monitoring of systemic arterial pressure and chronotropic effects. The pharmacodynamic effects of TKI can be determined in the organs using tumor specimens. Surrogate marker can be used as an alternative approach. These tissues act as human models and TKI effect on these tissues reveals the potential effects of TKI molecules. (Kufe et al., 2003). These pharmacological screening methods enable the scientists to find out the adverse effects of TKI, and facilitate them to come up with ways on how the programme should be modified for human safety. The effect of the drug in organ function, and importantly the relevance of its potential in humans must be evaluated (Pugsley, Authier and Curtis, 2008). b) Safety studies: Animal models, invivo and invitro preparations can be used for the analysis. Invitro systems are used for supportive studies and invivo studies are used to determine the dose- response relationship of the adverse effects. The safety pharmacology studies are not necessary for the treatment of end- stage cancer patients. (ICH: S7A, 2000). Table 1: Invivo and Invitro test parameters: Invivo studies Invitro studies Dose- response relationship of adverse effects They are the supportive studies. Time of onset and duration of response of adverse effect Tests: herb potassium channel test, ventricular wedge preparation model, cultured cardiac myocytes. Highest concentration of test dose Interpretation of the results to limit the dose levels Tests required: Irwin test, respiratory plethysmography test. Animals: generally dogs and rats (consious and infused state) and larger animals. (ICH: S7A, 2000) c) Acute toxicity studies The acute toxicity of the drug can be minimized by the use of targeted therapy. For the patients with chronic myeloid leukaemia, the toxicity level of the drugs has to be analysed using the guidelines for anti-cancer therapy and thereby primary a safety end point has to be achieved. Tolerance is the first safety end point in any clinical study. (Cortes at al., 2012) this test is rarely needed if repeat-dose studies were performed. d) Repeat dose toxicity: TKI drugs show repeated dose toxicity in rats and dogs. (Mao et al., 2012). Similarly in rats, the PF-04254644 drug was administered for a 6 – day investigative repeat-dose study (Aguirre et al., 2010). The increase in heart rate was observed from day 1 and the rate increased gradually till last day of dosage. It was observed that tachycardia occurred in the rats and it was not to the level of toxicity. So, the maximum dosage level for the rodents and non- rodents should be determined. The repeated dose and toxicity levels, along with the number of animals used in the study must be determined. Table 2: Analysis for Repeat-dose toxicity tests: For genotoxic drugs - One rodent is sufficient for repeated- dose toxicity test (ICH S9) The results of the repeated-dose tests for a period of 3 months are required for Phase III studies (ICH S9) In rodents, the chronic toxicity testing is performed for a 6 months duration For non-rodents, a 9 months study is performed for toxicity testing. Determination of best route of administration Dose range - a total dose of 100 microgram can be administered and maximum 5 administrations are permitted. This trial can be extended to 1species through the specific route of administration with a 1000x magnification of the clinical dose (ICH S9). A standard 2 week repeated – dose study can be performed in rodents and non-rodents with specified dose (ICH S9). (ICH S4 and M3, 1998). Phases of Study a) Phase I study Phase I study is designed to investigate the safety and tolerability of the drug, and to identify the pharmacokinetics and pharmacodynamics of the drug. For the TKI molecules, four types of studies can be performed for the determination of dose concentration. They are: a single dose study, 7-day single dose investigative study, 7- day repeat-dose toleration study, and 6–day repeat–dose investigative study. These studies can be performed in rats and dogs. The parameters such as administration route, patient’s intrinsic and extrinsic factors such as food intake, organ dysfunction, concomitant medications, absorption, distribution, metabolism, and excretion of the drug must be monitored (Fitzpatrick, 2006). Table 3: Parameters to Assess in Phase I: Maximum tolerated dose Dose limiting toxicity Dosage calculation Toxicokinetic studies Repeat dose toxicity Preliminary antitumor activity of TKI Monitoring of adverse effects of TKI (ICH: S9, 2009). b) Phase 2 In phase II, the therapeutic efficiency of the drug is monitored in patients. The study should be designed in such a way that all the parameters are compared with the baseline values. The safety and efficacy of the drug, the dose regimen, and the dose response relationship are determined in this phase. Dose- response studies are continued into the phase 3. (Fitzpatrick, 2006). c) Phase 3 The pre-clinical safety pharmacology models are improved after every result from Phase I and Phase II. Some drugs may cross the phase I and II trials with no adverse effects on humans. However, they may show the liability of some adverse effects in the later stage of Phase III. The best example of such TKI is Sunitinib, which showed adverse cardiovascular effects when they are about to be approved for the treatment of renal cell carcinoma (Pugsley, Authier and Curtis, 2008). In the Phase III studies, the dose- response relationships, the use of the drug in wider population, application in different stages of diseases, and the effect of combination with another drug can be focused. Phase III studies should fulfil the required instructions of US FDA for domestic as well as worldwide use of the drug. The drugs must be checked for immunotoxicity, when the tyrosine kinase is inhibited in the body (Zhu et al., 2007). For the analysis of immunotoxicity and carcinogenicity, rats are used as the experimental element. The mice are exposed to a margin of exposure methodology ( MOE) for the analysis of carcinogenicity test and estimation of human risk. Similarly the genotoxicity studies were conducted to assess the oncogenic potenital of the TKI molecule. Generally, mutation test for the molecule is done in bacteria (Ames test), followed by invitro test for chromosomal damage analysis and finally an invivo test in rodent hematopoietic cells using ICH S2A guide lines for genotoxicity analysis. Reproductive toxicology studies must be completed before marketing. Carcinogenicicty studies for the analysis of the tumorigenic potential of hte TKI molecule in animals are assessed and used for predicting the harmfulness in humans. (Brock, Hastings and McGown, 2013). Immuno- modulating effects such as variation in the thymic and spleen weight and reduced lymphocyte counts of T, and B cells must be monitored (Fitzpatrick, 2006). References Aguirre, S. A. et al. (2010) Cardiovascular effects in Rats following exposure to a Receptor Tyrosine Kinase Inhibitor. Toxicologic Pathology. 38 (3). p.416 -428. Arora, A and Scholar, E. M. (2005) Role of Tyrosine Kinase Inhibitors in Cancer Therapy. The Journal of Pharmacology and Experimental Therapeutics. 315 (3). p.971 – 979. Brock, W.J., Hastings, K.L. and McGown, K.M. (2013) Non-clinical Safety Assessment: A guide to International Pharmaceutical Regulations, John Wiley and Sons Cortes, J. et al. (2010) Phase 2 study of Subcutaneous Omacetaxine Mepesuccinate after TKI failure in patients with Chronic – Phase CML with T3151 mutation. Blood. 120 (13). p.2573 – 80. Fitzpatrick, S. (2006) Clinical Trial Design. London: Institute of Clinical research. Hartmann, J. T. et al. (2009) Tyrosine Kinase Inhibitors – a Review on Pharmacology, Metabolism and Side effects. Current Drug Metabolism. 10 (5). p.470 -481. ICH S4 and M3. (1998) Duration of Chronic Toxicity testing in animals (Rodent and non Rodent Toxicity Testing, S4. [Online] Available from http://www.ich.org/fileadmin/Public_Web_Site/ICH_Products/Guidelines/Safety/S4/Step4/S4_Guideline.pdf(accessed on November 26, 2014) ICH: S7A. (2000) Safety Pharmacology Studies for Human Pharmaceuticals, S7A, [Online] Available from http://www.ich.org/fileadmin/Public_Web_Site/ICH_Products/Guidelines/Safety/S7A/Step4/S7A_Guideline.pdf(accessed on November 26, 2014) ICH: S9. (2009) Non-clinical Evaluation for Anticancer Pharmaceuticals, S9. [Online] Available from http://www.ich.org/fileadmin/Public_Web_Site/ICH_Products/Guidelines/Safety/S9/Step4/S9_Step4_Guideline.pdf(accessed on November 26, 2014) Kufe, D.W. et al. (2003) Holland- Freis Cancer Medicine Review. Decker Publishing London, C. A. (2009) Tyrosine Kinase Inhibitors in Veterinary Medicine. Topics in Companion Animal Medicine. 24 (3). p.106 -112. Mao, Y. et al. (2012) Evaluation of Subchronic Toxicity of SIM010603, a Potent Inhibitor of Receptor Tyrosine Kinase, after 28-day repeated Oral Administration in SD Rats and Beagle Dogs. Food and Chemical Toxicology. 50 (5). p.1256- 1270. Pugsley, M. K., Authier, S and Curtis, M. J. (2008) Principles of Safety Pharmacology. British Journal of Pharmacology. 154 (7). p.1382- 1399. Zhu, Y. et al. (2007). Immunotoxicity Assessment for the Novel Spleen Tyrosine Kinase Inhibitor R406. Toxicology and Applied Pharmacology. 221 (3). p.268 – 277. Read More