Viral load

The most recent advance in treating HIV infections has been to simultaneously attack the virus on a second front using a protease inhibitor. Recall from Section 27.10 that proteases are enzymes that catalyze the hydrolysis of proteins at specific points. When HIV uses a cell s DNA to synthesize its own proteins, the initial product is a long polypeptide that contains several different proteins joined together. To be useful, the individual proteins must be separated from the aggregate by protease-catalyzed hydrolysis of peptide bonds. Protease inhibitors prevent this hydrolysis and, in combination with reverse transcriptase inhibitors, slow the reproduction of HIV. Dramatic reductions in the viral load in HIV-infected patients have been achieved with this approach. 

The Merck compound MK-0608 is a 2 -C-Me-7-deaza-adenosine analog, which has recently been reported to show a 5.7 log drop in viral load in HCV-infected chimpanzees after dosing QD at 2mg/kg (Olsen 2006). An efQcient and practical process for preparing kilogram quantities has been described (Bio et al. 2004). The 12-step synthesis provides an impressive 35% overall yield and starts from the inexpensive diacetone-D-glucose. The synthesis features a novel acyl migration in route to prepare the key crystalline furanose diol intermediate (Fig. 5). The conditions... 

Second, the INSTl, but not an RTl, may conceivably inhibit the virus production from the pool of resting CD4 T cells that are in a state of pre-integration latency (Murray et al. 2007). Upon activation, the preformed pro-viral DNA that is already located in the nucleus integrates into the genome of these cells, allowing them to contribute to the viral load. 

Pharmacokinetic studies demonstrated good oral bioavailability of maraviroc and a terminal half-life of 16-23 h following multiple dosing (Abel et al. 2003 Walker et al. 2005). Single doses of up to 900 mg and multiple doses of up to 300 mg BID for 28 days were well tolerated (Abel et al. 2003 Russell et al. 2003 Walker et al. 2005). In Phase 2a studies, treatment-naive HIV-1 patients with R5 virus who received maraviroc monotherapy at doses ranging from 25 mg QD to 300 mg BID for 10 days experienced a median viral load reduction of 1.64 log jg copies/mL and... 

The virological response, which is assessed by measuring HBV DNA levels in serum during and after therapy, is the best predictor of the outcome of antiviral treatment. It has been suggested that HBV viral load should be reduced to less than 2,000 lU/mL (de Franchis et al. 2003 Keeffe et al. 2006 Liaw et al. 2005 ... 

Shiratori Y, Nakata R, Shimizu N, Katada H, Hisamitsu S, Yasuda E, Matsumura M, Narita T, Kawada K, Omata M (2000) High viral eradication with a daily 12-week natural interferon-beta treatment regimen in chronic hepatitis C patients with low viral load. Dig Dis Sci 45 2414-2421 Sidwell RW, Huffman JH, Khare GP, Allen LB, Witkowski JT, Robins RK (1972) Broad-spectrum antiviral activity of Virazole l-beta-D-ribofuranosyl-l,2,4-triazole-3-carboxamide. Science 177 705-706... 

Despite these intense efforts to test different chemical modifications, there is so far little success in developing potent and safe antivirals. For hepatitis C virus (HCV), McHutchison et al. reported in vivo side effects of a 20-nucleotide PS-modified ohgonucleotide (ISIS-14803) (McHutchison et al. 2006). In a test group of 28 patients, only 3 patients responded to the treatment by a reduction in the HCV viral load. The researchers concluded that further studies are needed to evaluate this novel agent and its side effects. Previously, ISIS Pharmaceuticals reported a 3.8 log reduction in plasma virus in patients with chronic HCV infection, using ISIS-14803 (www.isispharm.com). 

Sacktor N, Skolasky RE, Tarwater PM, McArthur JC, Seines OA, Becker J, Cohen B, Visscher B, Miller EN (2003) Response to systemic HIV viral load suppression correlates with psychomotor speed performance. Neurology 61(4) 567-569... 

The reported risk factors for HIV-associated sensory neuropathy are varied and may have changed since the availability of HAART. In the pre-HAART era, age, nutritional deficiencies, alcohol exposure, higher HIV viral load, and low CD4 counts (Moyle and Sadler 1998 Childs et al. 1999), as well as mood, other neurologic disorders and functional abnormalities (Schifitto et al. 2002) were neuropathy risk factors. In the HAART era, the use of NRTI (Cherry et al. 2006 Pettersen et al. 2006) and exposure to protease inhibitor (PI) medication (Pettersen et al. 2006 Smyth et al. 2007) are considered additional risk factors. Although hepatitis C mono-infection has been associated with peripheral nerve disease, and there is... 

---