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Research Articles: Therapeutics, Targets, and Development

P276-00, a novel cyclin-dependent inhibitor induces G₁-G₂ arrest, shows antitumor activity on cisplatin-resistant cells and significant in vivo efficacy in tumor models

Departments of ¹ Pharmacology and ² Medicinal Chemistry, Nicholas Piramal Research Centre, Nicholas Piramal India Ltd., Mumbai, India and ³ Oncotest GmbH, Freiburg, Germany

Requests for reprints: Kalpana S. Joshi, Department of Pharmacology, Nicholas Piramal Research Center, Nicholas Piramal India Ltd., 1-Nirlon Complex, Goregaon (East), Mumbai 400 063, India. Phone: 91-22-3081-8421; Fax: 91-22-3081-8411. E-mail: kjoshi{at}nicholaspiramal.co.in

Abstract

P276-00, a flavone that inhibits cyclin-dependent kinases, has been identified by us recently as a novel antineoplastic agent. In this study, we have selected a panel of human tumor cell lines and xenografts to allow determination of selectivity and efficacy of P276-00. When tested against a panel of 16 cisplatin-sensitive and cisplatin-resistant cell lines, the antiproliferative potential of P276-00 was found to be 30-fold higher than cisplatin. Studies to show tumor sensitivity using clonogenic assay in 22 human xenografts indicated that P276-00 was 26-fold more potent than cisplatin, and further, it was also found to be active against cisplatin-resistant tumors of central nervous system, melanoma, prostate, and renal cancers. Further, we studied the effects of P276-00 on cell cycle progression by flow cytometry using asynchronous and synchronous population of tumor and normal cells. Asynchronous population of human prostate carcinoma (PC-3) and human promyelocytic leukemia (HL-60) cells when exposed to P276-00 showed arrest of slow-growing PC-3 cells in G₂-M with no significant apoptosis observed up to 72 h. Unlike PC-3, significant apoptosis was seen in fast-growing HL-60 cells at 6 h. However, synchronized human non–small cell lung carcinoma (H-460) and human normal lung fibroblast (WI-38) cells showed arrest of cells in G₁. H-460 cells undergo apoptosis, which increases with longer exposure to the compound and also after exposure to P276-00 for 48 h followed by recovery. In contrast, the normal cells (WI-38) remain arrested in G₁ with no significant apoptosis up to 72 h of exposure and also after 48 h of P276-00 treatment followed by recovery, confirming our previous results that P276-00 was less effective against normal cells compared with cancer cells. After promising in vitro results, P276-00 was checked for in vivo efficacy in murine tumor and human xenograft models. Growth inhibition of murine colon cancer (CA-51) was significant when P276-00 was administered i.p. at 50 mg/kg daily for 20 treatments. However, in murine lung carcinoma model (Lewis lung), an increased dose of 60 mg/kg (30 mg/kg twice daily) administered every alternate day i.p. for seven treatments showed significant inhibition in the growth. Further studies were undertaken to establish the efficacy profile of P276-00 in human tumor xenograft models. In the two xenograft models studied, P276-00 showed potent in vivo antitumor potential. Compound P276-00 at a dose of 35 mg/kg administered daily via the i.p. route for 10 days showed significant (P < 0.05) inhibition in the growth of human colon carcinoma HCT-116 xenograft. Furthermore, P276-00 at a dose of 50 mg/kg once daily and 30 mg/kg twice daily administered via i.p. route for 20 treatments significantly (P < 0.05) inhibited growth of human non–small cell lung carcinoma H-460 xenograft. Thus, the in vitro cellular potency, together with in vivo antitumor activity, confirms the potential of P276-00, a cyclin-dependent kinase inhibitor as an anticancer molecule. [Mol Cancer Ther 2007;6(3):926–34]

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received 10/ 4/06; revised 12/ 5/06; accepted 2/ 1/07.