G-Quadruplex Ligand RHPS4 Potentiates the Antitumor Activity of Camptothecins in Preclinical Models of Solid Tumors

Abstract

Purpose: The formation of G-quadruplex structures at telomeric DNA sequences blocks telomerase activity, offering an original strategy to design and develop new antitumor agents. The pentacyclic acridinium salt RHPS4 is one of the most effective and selective G4 ligands able to rapidly disrupt telomere architecture, resulting in apoptosis of cancer cells. Here, we studied the therapeutic index of RHPS4 and its integration with chemotherapeutics in preclinical model of solid tumors. Experimental Design: The antitumoral activity of RHPS4 was evaluated on human xenografts of different histotypes and compared with that of standard antineoplastic agents. Moreover, the effect of RHPS4/chemotherapeutics combinations on cell survival was studied and the most favorable combination was evaluated on tumor-bearing mice. Results: RHPS4 was active in vivo as single agent and showed a high therapeutic efficacy when compared with conventional drugs. Moreover, RHPS4 had antitumoral activity in human melanoma xenografts inherently resistant to chemotherapy and exhibited antimetastatic activity. RHPS4 also showed a strong synergistic interaction with camptothecins and this effect was strictly dependent on the drug sequence employed. Treatment of mice with irinotecan followed by RHPS4 was able to inhibit and delay tumor growth and to increase mice survival. Conclusions: Our data show that RHPS4 has a good pharmacodynamic profile and in combination therapy produces a strong antitumoral activity, identifying this drug as promising agent for clinical development.

PARP1 is activated at telomeres upon G4 stabilization: possible target for telomere-based therapy

“…For instance, G4 ligands are promising compounds because they limit the proliferation of cancer cells by both short-term (telomere uncapping) and long-term (telomerase inhibition) effects. RHPS4 is one of the most selective G4 ligands with anticancer activity both as a single agent and in combination with CPTs in pre-clinical models of solid tumors (Salvati et al, 2007;Leonetti et al, 2008). This agent, behind its classical telomerase-inhibitory properties, impairs fork progression and/or telomere processing, resulting in telomere dysfunction and activation of an ATR/ATM signaling pathway (Rizzo et al, 2009).…”

“…We recently showed that the combination of RHPS4 with CPT also has a strong synergistic interaction in vitro on colon cancer lines and produced marked antitumor activity on xenografts (Leonetti et al, 2008). Unfortunately, this combination failed to cure animals as no complete remissions were reported.…”

“…Finally, in the attempt to search for more effective anticancer therapy, we tested whether adding the TOPOI inhibitor could increase the therapeutic efficacy of the GPI/RHPS4 combination. This multi-component therapeutic strategy is based on previous data showing synergistic interaction between RHPS4 and CPT as well as CPT and PARP inhibitors (Tentori et al, 2006;Leonetti et al, 2008), and on data reported in this paper describing the activation of PARP at telomeres upon CPT treatment. The pre-treatment with GPI increased the tumor weight inhibition elicited by either RHPS4 or irinotecan (Figure 5a, left panel and Table 1).…”

“…The human colorectal adenocarcinoma cell lines HT29 and HCT116 and transformed BJ fibroblasts expressing hTERT and SV40 early region (BJ-EHLT) were obtained and maintained as previously reported Leonetti et al, 2008).…”

“…We revealed that this agent, by stabilizing G4 DNA at telomeres, impairs fork progression and/or telomere processing, resulting in telomere dysfunction and activation of an ATR-dependent ATM pathway (Rizzo et al, 2009). Interestingly, in view of clinical application, RHPS4 is active in vivo as a single agent with a good toxicological profile and potentiates the antitumoral efficacy of TOPOI inhibitors in preclinical models of solid tumors (Salvati et al, 2007;Leonetti et al, 2008).…”