Phase 1b study defining the optimal dosing combinations of the mTOR inhibitor AP23573 and Paclitaxel (PTX)

3509

Background: AP23573 is a novel mTOR inhibitor with demonstrated anti-tumor activity in clinical trials. In vitro, AP23573 exhibits at least additive anti-proliferative activity in combination with a variety of agents including taxanes. This trial studied the combination of AP23573 and paclitaxel (PTX) in patients with advanced solid tumors. Methods: This was a modified, sequential (3+3) dose finding study with starting doses of 25 mg AP23573 i.v. and 80 mg/m2 PTX i.v. as Dose Level 1 (DL1) on days 1, 8 and 15 of a 28 day cycle. Doses of either drug were adjusted in successive cohorts. Blood samples and skin biopsies were collected for pharmacokinetic (PK) and pharmacodynamic (PD) studies. Dose limiting toxicity definitions included neutrophils <500/μL; thrombocytopenia = Grade 3 (CTC), any non- hematologic toxicities = Grade 2; missing 2 consecutive doses due to any toxicity. For PK and PD analysis, AP23573 and PTX were administered one day apart at the start of Cycle 1, reversing the sequence at Day 8. Results: Enrollment is complete and 29 patients with a variety of tumors (sarcoma, pancreatic, H&N, melanoma, thymoma) have been treated. Grade 3 thrombocytopenia and Grade 2 mouth sores were seen at DL1 as well as missed doses due to moderate (Grade 2) neutropenia. Adverse events include mouth sores and fatigue which were mild and reversible. Available PK data for AP23573 and PTX suggest no interaction. PD analysis in peripheral blood mononuclear cells demonstrates no interference by PTX on mTOR inhibition by AP23573. PD data in skin biopsies are forthcoming. Both 12.5 mg AP23573/80mg/m2 PTX and 37.5mg AP23573/60mg/m2 PTX are maximal dose combinations that appear to be well tolerated. Activity has been observed at multiple AP23573 mg/PTX mg/m2 dose levels (25/60, 12.5/80, 25/80). Five patients have been on study for >4 cycles, including 2 patients with partial responses (H&N and pancreatic). Conclusions: Combined therapy with AP23573 and PTX is safe. It is notable that evidence of anti-tumor activity was observed at modest doses of each drug when in combination. Combinations of these agents at both doses cited would be recommended for evaluation in trials examining efficacy in specific tumors.

No significant financial relationships to disclose.

Structural characterization and functional effects of a circulating heparan sulfate in a patient with hepatocellular carcinoma

A circulating anticoagulant was isolated from the plasma of a 42-year-old man with cirrhosis and hepatocellular carcinoma who had an unusual coagulation test profile. The patient developed a fatal coagulopathy, unresponsive to protamine therapy or plasma exchange following liver biopsy. However, at presentation, routine hemostasis assays were normal. The patient had mucocutaneous bleeding but the sole laboratory abnormality was a prolonged thrombin time (TT = 99 s, normal 25-35 s). Protamine titration indicated activity equivalent to a heparin concentration of 6-7 U/ml. Antithrombin III (AT III) antigen and activity were markedly elevated. The anticoagulant activity, purified from plasma by DEAE chromatography, was identified as a glycosaminoglycan (GAG). GAG anti-thrombin activity was completely abolished by heparin lyase III. Based on the degree of sulfation and HPLC pattern, the GAG was classified as heparan sulfate. Low levels (4 microM) of purified GAG markedly prolonged the TT (>120 s) but not the activated partial thromboplastin time (PTT) (31.4 s). In a Factor Xa assay, the GAG exhibited a potency equivalent to 0.06 U of low molecular weight heparin per nmol of uronic acid. Patients with endogenous circulating glycosaminoglycans can present with unusual laboratory coagulation test profiles. These reflect complex dysfunction of hemostasis, leading to difficulty in providing diagnosis and effective care.

Coccidioides immitis presenting as a hyphal form in a ventriculoperitoneal shunt

We report a case of meningitis in a 31-year-old man caused by Coccidioides immitis, where the organism was observed growing in the cerebrospinal fluid exclusively as hyphae. This unusual morphology was seen in fluid obtained from a ventriculoperitoneal shunt. Only C immitis was cultured. Its identity was confirmed by both DNA probes and standard culture techniques. To our knowledge this is the second report of C immitis taking a hyphal form in cerebrospinal fluid. Coccidioides immitis should be considered in the differential diagnosis when hyphal forms are seen in body fluids. The diagnosis can be hastened by using DNA probes, which enhance patient therapy and worker safety.

Mutations in the SH3 domain of the src oncogene which decrease association of phosphatidylinositol 3'-kinase activity with pp60v-src and alter cellular morphology

To analyze the signaling pathways utilized in malignant transformation by pp60v-src, we have isolated and characterized src mutants which possess normal levels of protein tyrosine kinase activity but which cause only a partially transformed phenotype. Our hypothesis is that such mutants are partially defective for transformation because they are defective in their ability to activate specific components of the cellular signaling machinery while still activating others. In this communication, we report on the molecular and biochemical characterization of one such mutant, CU12 (D. D. Anderson, R. P. Beckmann, E. H. Harms, K. Nakamura, and M. J. Weber, J. Virol. 37:455-458, 1981). Cells infected with this mutant are capable of anchorage-independent growth, but rather than exhibiting the rounded and refractile morphology characteristic of wild-type-infected cells, they display an extremely elongated, fusiform morphology. The morphological properties of this mutant src could be accounted for entirely by a single mutation in the SH3 domain (lysine 106 to glutamate). Other mutations were constructed in this region by in vitro mutagenesis, both in a v-src and in an activated c-src background, and several of them also induced a fusiform morphology. All of the mutations inducing fusiform morphology also resulted in decreased association of pp60src with phosphatidylinositol 3'-kinase activity. In addition, association of pp60src with some tyrosine-phosphorylated proteins was altered. We propose that the SH3 domain participates (along with the SH2 domain) in the interaction of pp60src with cellular signaling proteins, and we speculate that the association with phosphatidylinositol 3'-kinase plays an important role in the regulation of cellular morphology.

Acid-fastness of fungi in blastomycosis and histoplasmosis

In 60% of the infections caused by Blastomyces dermatitidis and in 47% of the infections caused by Histoplasma capsulatum, some of the organisms are acid-fast in tissue sections. Treatment with 1N hydrochloric acid at 60 degrees C abolishes the acid-fastness of H capsulatum, which indicates that the acid-fastness may be related to mycolic acid. Organisms of B dermatitidis, however, remain acid-fast in 83% of the sections treated with acid. The presence of acid-fastness in small cells can aid in the differentiation of B dermatitidis and H capsulatum from Cryptococcus neoformans and Candida albicans, Persistent acid-fastness of organisms after treatment with heated acid helps identify B dermatitidis in tissue sections, especially when the strain is small or in other ways atypical.