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Background: Treatment resistance of glioblastoma multiforme to chemo- and radiotherapy remains a challenge yet to overcome. In particular, the O6-methylguanine-DNA-methyltransferase (MGMT) promoter unmethylated patients have only little benefit from chemotherapy treatment using temozolomide since MGMT counteracts its therapeutic efficacy. Therefore, new treatment options in radiotherapy need to be developed to inhibit MGMT and increase radiotherapy response. Methods: Lomeguatrib, a highly specific MGMT inhibitor, was used to inactivate MGMT protein in vitro. Radiosensitivity of established human glioblastoma multiforme cell lines in combination with lomeguatrib was investigated using the clonogenic survival assay. Inhibition of MGMT was analyzed using Western Blot. Cell cycle distribution and apoptosis were investigated to determine the effects of lomeguatrib alone as well as in combination with ionizing radiation. Results: Lomeguatrib significantly decreased MGMT protein and reduced radiation-induced G2/M arrest. A radiosensitizing effect of lomeguatrib was observed when administered at 1 µM and increased radioresistance at 20 µM. Conclusion: Low concentrations of lomeguatrib elicit radiosensitization, while high concentrations mediate a radioprotective effect.

Tetrahydrolipstatin (orlistat), an inhibitor of lipases and fatty acid synthase, is used orally for long-term treatment of obesity. Although the drug possesses striking antitumor activities in vitro against human cancer cells and in vitro and in vivo against animal tumors, it also induces precancerous lesions in rat colon. Therefore, we tested the in vitro effect of orlistat on the expression of O-6-methylguanine-DNA methyltransferase (MGMT), a DNA repair enzyme that plays an essential role in the control of mutagenesis and carcinogenesis. Western blot analysis demonstrated that 2-day continuous exposure to 40 mu M orlistat did not affect MGMT levels in a human melanoma cell line, but downregulated the repair protein by 30-70% in human peripheral blood mononuclear cells, in two leukemia and two colon cancer cell lines. On the other hand, orlistat did not alter noticeably MGMT mRNA expression. Differently from lomeguatrib (a false substrate, strong inhibitor of MGMT) orlistat did not reduce substantially MGMT function after 2-h exposure of target cells to the agent, suggesting that this drug is not a competitive inhibitor of the repair protein. Combined treatment with orlistat and lomeguatrib showed additive reduction of MGMT levels. More importantly, orlistat-mediated downregulation of MGMT protein expression was markedly amplified when the drug was combined with a DNA methylating agent endowed with carcinogenic properties such as temozolomide. In conclusion, even if orlistat is scarcely absorbed by oral route, it is possible that this drug could reduce local MGMT-mediated protection against DNA damage provoked by DNA methylating compounds on gastrointestinal tract epithelial cells, thus favoring chemical carcinogenesis.

Background: The DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) reverses the O6-methylguanine (O6-meG) lesion induced by dacarbazine. Depletion of MGMT can be achieved using O6-meG pseudosubstrates. Herein, we report the first phase I experience of the novel O6-meG pseudosubstrate lomeguatrib, combined with dacarbazine. Methods: This is a phase I dose-escalation study to determine the maximum tolerated dose and recommended phase II dose (RP2D) of lomeguatrib combined with a single dose of dacarbazine on a 21-day schedule. Results: The vast majority of the 41 patients enrolled had metastatic melanoma (36/41) and most had no previous chemotherapy (30/41). The most frequent non-hematological adverse events (AEs) were nausea (52%), and fatigue (42%). The most frequent AEs of grade 3–4 severity were neutropaenia (42%), leukopaenia (17%), and thrombocytopaenia (12%). Only 1 patient had a partial response and 10 patients had stable disease. Conclusion: The RP2D of lomeguatrib was 40 mg orally twice daily for 10 days combined with 400 mg m−2 of dacarbazine IV on day 2. Oral administration of lomeguatrib substantially increases the haematological toxicity of dacarbazine consistent with experience with other O6-meG pseudosubstrates.

Acute myeloid leukemia (AML) is a highly lethal disease, especially in old patients. Chemoresistance and the absence of host immune responses against autochthonous malignancy play a major role in the poor prognosis of AML. The triazene compounds Dacarbazine and Temozolomide are monofunctional alkylators that donate methyl groups to many sites in DNA, including the O(6)-position of guanine producing O(6)-methylguanine (O(6)-MeG). If not repaired, O(6)-MeG frequently mispairs with thymine during DNA duplication. O(6)-MeG:T mismatches can be recognized by the mismatch repair (MMR) system which activates a cascade of molecular events leading to cell cycle arrest and cell death. If MMR is defective, cells continue to divide and GC → AT transition mutations occur. In preclinical models, such mutations can lead to the appearance of abnormal proteins containing non-self peptides ("chemical xenogenization" CX) that can be recognized by host cell-mediated immunity. Repair of O(6)-MeG is achieved by the DNA repair protein, O(6)-methylguanine-DNA methyltransferase (MGMT), which removes the methyl adduct in an autoinactivating stoichiometric reaction. High MGMT levels attenuate the pharmacodynamic effects of triazenes. In the last few years, triazenes, alone or with MGMT inhibitors, have been tested in AML. In view of their potential activity as CX inducers, triazenes could offer the additional advantage of host anti-leukemia immune responses. The present paper describes several studies of leukemia treatment with triazenes and a case of acute refractory leukemia with massive skin infiltration by malignant cells. Treatment with Temozolomide and Lomeguatrib, a potent MGMT inhibitor, produced a huge, although transient, blastolysis and complete disappearance of all skin lesions.

The DNA repair protein, O(6)-alkylguanine-DNA alkyltransferase (MGMT) can confer resistance to the cancer chemotherapeutic effects of the class of DNA damaging drugs generally referred to as the O(6)-alkylating agents. Inactivation of MGMT is thus a practical approach to improving the efficacy of such agents. An account is given of the collaboration between groups at Trinity College, Dublin and the Paterson Institute, Manchester which led to the development of the MGMT inactivating drug, Patrin (PaTrin-2, Lomeguatrib). The development of a simpler method of synthesis of O(6)-arylmethylguanines opened up the way to make a series of O(6)-heteroalkylmethyl analogues of the archetypal MGMT pseudosubstrate, O(6)-methylguanine. Of these, the furfuryl and thenyl compounds were the most active against recombinant Human MGMT in an in vitro assay. The 4-bromothenyl derivative was chosen for clinical trial as the most active compound. The MGMT active site tolerates O(6)-substituted guanines where the side chain can be quite large, but does not tolerate those with an aromatic or heteroaromatic ring with an 'ortho' substituent.

3597 Background: MGMT is implicated in tumor resistance to O6-alkylating agents, since the protein repairs DNA damage before replication results in cell death. Lomeguatrib (LM) is an orally bioavai...

8016 Background: TheDNA repair enzyme O6-Alkylguanine Alkyltransferase (AGT) directly reverses the O6-methylguanine (O6-MeG) base lesion induced by treatment with DTIC. Depletion of AGT using O6-MeG analogs enhances the cytotoxicity of DTIC in preclinical models and in early phase trials of O6-Benzylguanine. Lomeguatrib (Patrin, PN) is an orally bioavailable highly potent O6-MeG analog that is well tolerated as a single agent. We report the first phase I experience of PN combined with DTIC in patients who have failed prior systemic therapy. Methods: This open-label phase I study was performed to determine the toxicity profile and maximum tolerated dose (MTD) of PN given orally for 5 or 10 days (d) combined with a single dose of DTIC administered IV on d 2, repeated on a 21 d schedule. Of 30 pts enrolled 25 (83%) had metastatic melanoma, and all had ECOG PS ≤2. Dose escalation started at 40 mg of PN once daily for 5 d and 500 mg/m2 of DTIC. 6 pts failed prior chemotherapy, 16 failed prior immunotherapy, and 3 failed both. 5 pts had no prior systemic therapy. Results: Adverse events observed in more than 50% of pts included gr 1–2 nausea and vomiting and gr 1–2 fatigue. Hematologic toxicity was prominent with gr 3–4 neutropenia (13/30, 43%) and gr 3–4 thrombocytopenia (4/30, 13%) even at doses of DTIC 50% of usual clinical doses. Prolonged neutropenia accounted for all dose-limiting toxicities (DLT) observed so far. The MTD has not been reached, however hematologic toxicities requiring dose modifications of DTIC have been frequent (42% of all cycles administered). 16 pts (53%) had stable disease as their best response with a median time to progression of 53 days (95% C.I. 40–86 days). Conclusions: Oral administration of PN substantially alters the toxicity and tolerance of DTIC inducing prolonged hematologic toxicity at doses 2 of DTIC. [Table: see text]