Oxaliplatin Pt(IV) prodrugs conjugated to gadolinium-texaphyrin as potential antitumor agents.

Described here is the development of gadolinium(III) texaphyrin-platinum(IV) conjugates capable of overcoming platinum resistance by 1) localizing to solid tumors, 2) promoting enhanced cancer cell uptake, and 3) reactivating p53 in platinum-resistant models. Side by side comparative studies of these Pt(IV) conjugates to clinically approved platinum(II) agents and previously reported platinum(II)-texaphyrin conjugates demonstrate that the present Pt(IV) conjugates are more stable against hydrolysis and nucleophilic attack. Moreover, they display high potent antiproliferative activity in vitro against human and mouse cell cancer lines. Relative to the current platinum clinical standard of care (SOC), a lead Gd(III) texaphyrin-Pt(IV) prodrug conjugate emerging from this development effort was found to be more efficacious in subcutaneous (s.c.) mouse models involving both cell-derived xenografts and platinum-resistant patient-derived xenografts. Comparative pathology studies in mice treated with equimolar doses of the lead Gd texaphyrin-Pt(IV) conjugate or the US Food and Drug Administration (FDA)-approved agent oxaliplatin revealed that the conjugate was better tolerated. Specifically, the lead could be dosed at more than three times (i.e., 70 mg/kg per dose) the tolerable dose of oxaliplatin (i.e., 4 to 6 mg/kg per dose depending on the animal model) with little to no observable adverse effects. A combination of tumor localization, redox cycling, and reversible protein binding is invoked to explain the relatively increased tolerability and enhanced anticancer activity seen in vivo. On the basis of the present studies, we conclude that metallotexaphyrin-Pt conjugates may have substantial clinical potential as antitumor agents.

Paclitaxel gelatin nanoparticles for intravesical bladder cancer therapy.

PURPOSE: We have noted that inadequate drug delivery to tumor cells is a major cause of failed intravesical therapy for nonmuscle invading bladder cancer, partly due to the dilution of drug concentration by urine production during treatment. To address this problem we developed gelatin nanoparticles of paclitaxel designed to yield constant drug concentrations. The hypothesis that a constant, therapeutic concentration in urine, bladder tissue and tumors can be attained was evaluated in dogs. MATERIALS AND METHODS: We studied drug release from paclitaxel gelatin nanoparticles in culture medium in vitro. In vivo studies were performed in tumor-free dogs and in pet dogs with naturally occurring transitional cell carcinoma, in which the pharmacokinetics of paclitaxel gelatin nanoparticles were determined in plasma, urine and tumors. RESULTS: Paclitaxel release from paclitaxel gelatin nanoparticles in vitro and in vivo was rate limited by the drug solubility in aqueous medium. This property yielded constant drug concentrations independent of changes in urine volume during the 2-hour treatment. Intravesical paclitaxel gelatin nanoparticles showed low systemic absorption, and favorable bladder tissue/tumor targeting and retention properties with pharmacologically active concentrations retained in tumors for at least 1 week. CONCLUSIONS: Constant drug release from paclitaxel gelatin nanoparticles may overcome the problem of drug dilution by newly produced urine and the sustained drug levels in tumors may decrease treatment frequency.

Low dose suramin as a chemosensitizer of bladder cancer to mitomycin C.

PURPOSE: We have reported that acidic and basic fibroblast growth factors expressed in solid tumors induce broad-spectrum chemoresistance and their nonspecific inhibitor suramin (Sigma Chemical Co., St. Louis, Missouri) at nontoxic concentrations enhances the activity of chemotherapeutic agents. In the current study we evaluated whether low dose suramin enhances tumor sensitivity to mitomycin C (MMC) (Bristol-Myer Squibb Co., Wallingford, Connecticut). MATERIALS AND METHODS: Three-dimensional histocultures of RT4 (American Type Culture Collection, Rockville, Maryland) xenograft tumors and tumors from patients with bladder cancer were treated with MMC with or without 20 microM suramin. For in vivo studies mice bearing RT4 tumors received physiological saline, MMC (3 mg/kg), suramin (10 mg/kg) or MMC/suramin combination every 3 or 4 days. Two MMC schedules were studied, namely subtherapeutic (3 treatments) and therapeutic (6 treatments) schedules. RESULTS: Suramin enhanced MMC activity in xenograft and patient tumor histocultures by greater than 2-fold. The chemosensitization effect was observed in all patient tumors (2 superficial and 9 muscle invading lesions). In animals tumors in the control and suramin groups increased to approximately 3 to 5 times the initial size. The subtherapeutic MMC schedule retarded tumor growth but did not produce tumor shrinkage, whereas the therapeutic MMC schedule reduced tumor size by 27%. The addition of suramin enhanced MMC activity. Respective tumor sizes were 40% and 63% of the sizes after subtherapeutic and therapeutic MMC alone (p <0.01). The combination groups showed body weight losses similar to those of MMC alone. CONCLUSIONS: Low dose suramin enhanced the in vitro and in vivo activity of subtherapeutic and therapeutic MMC without enhancing host toxicity, thus, providing proof of concept for evaluating low dose suramin as a chemosensitizer with MMC in bladder cancer.